Equine Dental Restraint and Sedation: Keeping Your Patient Safe and Happy!

Transcription

1 Equine Dental Restraint and Sedation: Keeping Your Patient Safe and Happy! Bruce P. Whittle, DVM Honey Creek Veterinary Hospital Trenton, Missouri General Restraint Considerations Unfortunately, in veterinary medicine, we do not always get to choose the best conditions in which to work. However, the need for equine dentistry does not usually constitute an emergency. Consideration should be made to ensure safety for the patient, the clinician and any bystanders. A non-slip surface is preferred to avoid falling of either the clinician or patient. Because lavage of the oral cavity is necessary for performance of a thorough examination, the work area can become wet, a recipe for disaster with unsatisfactory footing. Each clinician has his or her preferences regarding method of patient restraint for dentistry. The simplest is a free-standing horse that is sedated with its head supported on a portable head stand. Often, an assistant or owner has been asked to serve as a head stand by holding the horse s head on their shoulder but this can be very dangerous for the holder! A heavy oral speculum in a horse s mouth becomes a dangerous weapon if the horse swings its head. Many veterinarians work on horses in a stall doorway with either a headstand or the head suspended in a dental halter hung from the stall front. Another option is stationary or portable horse stocks with the horse s head supported by either a head stand or a dental halter suspended from a bar extending forward from the top of the stocks. If this option is chosen, it is important that the overhead bar extends far enough forward that the suspension point is in in front of the horse s muzzle. Otherwise, the horse s neck will flex, making oral access more difficult. When supporting a horse s head, it is important to not allow the poll to become overextended because this has been associated with sudden collapse. A dental stool of some type for the clinician can be very helpful to allow a lower positioning of the horse s head. This option should not be used unless there is a barrier such as the front gate of horse stocks between the patient and the clinician. One of the most often overlooked considerations during an equine dentistry procedure is lighting. Dim lighting that can be found in the shade under a large tree or, even better, a shed or barn allows better visualization inside the oral cavity. If you must work in direct sunlight, make sure the sun is behind you to avoid glare. Even with a very bright light source, examination of the equine oral cavity in bright sunlight is sub-optimal. Sedation for Equine Dentistry Sedation for equine dentistry is very important because it helps relax the patient, allowing for a thorough oral examination. Sedation also helps provide better safety for both patient and clinician, though care must be taken to provide good footing so a mildly ataxic patient does not fall. No single pharmacologic agent will provide all of the ideal characteristics. A combination of sedative and analgesic agents will provide reliable sedation with adequate analgesia while minimizing ataxia. The use of combinations allows smaller dosages of each agent, thus minimizing potential side effects. The major classes of drugs used in these combinations include alpha-2 agonists, opioids, pheno-thiazine tranquilizers and benzodiazepines.

2 Alpha-2 agonists Sedation for equine dentistry is similar to that for any other standing procedure of the head. Sedation cocktails vary among dental clinicians. The basis for any sedation protocol is typically an α2 agonist because they offer both sedation and analgesia. At lower doses the effects are dose-dependent but once the dosage hits a plateau effect on analgesia, additional drug only prolongs the duration of effect. However, increased doses increase the chance of adverse effects. The α2-agonist drugs licensed in the United States for use in horses include xylazine, romifidine and detomidine. These are usually used in combination with other agents such as an opioid, benzodiazepine or tranquilizer to allow lower dosages of each drug, thereby decreasing the adverse side effects. An understanding of the pharmacology of the drugs we use helps us to be better clinicians. For this reason, periodically reviewing this information is an important part of our continuing clinical education. Alphaadrenoreceptors are present in the central nervous system and in most peripheral tissues and are divided into two subclasses, α1 and α2. The α2-adrenoreceptors are further divided into numerous subtypes that regulate various physiologic effects including alpha-2a, alpha- 2B and alpha-2c. Clinically, the affinity of a drug for the α2- versus the α1-adrenoreceptor as well as for the various α2-adrenoreceptor subtypes is related to its potency and side effects. The more selective a drug is for the α2- adrenoreceptor site, the more potent it is. Because all of the available alpha-2 agonist drugs also activate the alpha-1 receptors to some extent, some undesirable effects can be observed. Dexmedetomidine, a drug that is licensed for dogs in the United States, but has been studied in the horse, has the highest affinity for the α2-adrenoreceptor versus the α1-adrenoreceptor (1620/1) thus is the most potent. Of the equine licensed α2-agonists, romifidine (340/1) has the highest affinity, detomidine is intermediate (260/1) and xylazine has the lowest affinity (160/1). Alpha-2 agonists act pre-synaptically at adrenoreceptors in the locus ceruleus of the brainstem to block the release of norepinephrine. Because norepinephrine is excitatory, the net effect of its blockade is sedation. Sedative and analgesic effects are mediated primarily through alpha-2a receptors. The analgesic effects are a result of inhibition pre-synaptically that reduces release of neurotransmitters and postsynaptically in the dorsal horn of the spinal cord blocking ascending nociceptive transmission. Xylazine was discovered in Germany in It was first studied for its antihypertensive effects in humans but due to its severe side effects, its use in humans was abandoned. It was discovered to have sedative effects in animals. Xylazine has a shorter duration of action than the other α2 agonists. It is contraindicated in late-term pregnant mares because its use can cause uterine contractions. Ataxia is another common undesirable effect. Detomidine was introduced in veterinary medicine in the mid 1980 s. It became a favored sedative agent among equine veterinarians, especially in combination with butorphanol. Detomidine has a dosage dependent duration of effective sedation for 30 to 60 minutes. Its major disadvantage is ataxia. It can be used successfully in a constant rate intravenous infusion for longer procedures to allow for a steadier state of sedation. Romifidine is the most recently introduced sedative labeled for use in horses in the United States and was approved by the FDA in It has the advantage of creating less ataxia. It also has a longer duration of action than either xylazine or detomidine. This can be a potential disadvantage in shorter procedures because of the longer lasting inhibition of gastrointestinal motility. One additional advantage of romifidine is that its lower concentration makes it easier to dose smaller patients such as miniature horses. Dexmedetomidine is not currently labeled for use in horses in the United States.

3 However, it is labeled for small animals and has been studied for use in horses and is labeled for horses in other countries. It has the advantage of having a higher affinity for the α2- adrenoreceptor than the other available α2- agonists. Dexmedetomidine has a shorter duration of cardiovascular effects but does provide an equal or better level of analgesia than detomidine. When newer alpha-2 agonists become available, they will likely have more specificity for the α2-adrenoreceptor resulting in fewer side effects. Some clinicians reverse all of their equine sedation events with an alpha-2 antagonist. Tolazoline is the only antagonist labeled for use in horses in the United States. Yohimbine and atipamezole are antagonists that are licensed for use in dogs. Both tolazoline and yohimbine have been associated with sudden death in horses. Personally, I reserve the alpha-2 antagonists for emergency situations and prefer to allow my patients to recover with no further intervention. Opioids Opioids are commonly used in conjunction with the alpha-2 agonists. Opioid receptors are found in similar pre-synaptic locations as the alpha-2 receptors and act synergistically with the alpha-2 agonists. Opioid receptors are divided into mu, kappa and delta. Opioid drugs are classified according to their interaction with the various receptors as well as whether they are agonists, antagonists or mixed agonist-antagonists. Opioid drugs are also classified by their potency compared to morphine. Butorphanol is the most commonly used opioid in equine medicine. It is considered a mixed agonist-antagonist acting as an antagonist at the mu receptor and an agonist at the kappa receptor. Butorphanol is approximately 4 times more potent than morphine. It provides some analgesia and is useful in equine dentistry because it tends to keep the tongue less active. Butorphanol is a controlled substance so does come with the disadvantage of increased record keeping. Some horses tend to push forward with butorphanol so care should be used if there is not a barrier in front of the horse. Buprenorphine is another opioid that has been used in horses, although it is not labeled for use in horses in the United States. It is classified as a partial mu agonist. Buprenorphine is times more potent than morphine. It has the advantage of not causing respiratory depression at clinical doses. Tranquilizers Tranquilizers are drugs that reduce anxiety and induce calmness. Acepromazine is the most commonly used tranquilizer in horses. It is a controversial drug in equine medicine due to its association with penile paralysis in male horses. This is an extremely rare complication but a serious one when it occurs. However, acepromazine can be an extremely useful drug, especially in anxious horses. It does take 15 to 20 minutes to take maximal effect after intravenous injection. I will often perform a general physical examination on an equine dentistry patient I know to be more anxious then give it an injection of acepromazine. I then sedate and work on the next horse before sedating and working on the first horse. This allows the acepromazine time to take maximum effect. Because the duration of activity of acepromazine can be 1-2 hours, this strategy can be helpful. Acepromazine also tends to quiet the activity of the tongue. I do avoid its use in stallions. When I administer it to a gelding, I make sure the horse can fully retract its penis before allowing the owner to transport the horse or before I leave the farm. Benzodiazepines Benzodiazepines are sometimes used as an adjunct to sedatives in horses. Benzodiazepines are a class of drugs with a similar chemical structure that enhance the activity of the neurotransmitter GABA (gamma amino butyric acid) at the GABA receptor, resulting in sedative hypnotic and muscle relaxant effects. The most commonly used benzodiazepines in equine medicine are

4 diazepam and midazolam. Both drugs are controlled substances, requiring increased record keeping. Though short-acting, both drugs can help relax the tongue to facilitate periodontal probing or short procedures such as diastema burring on the lingual side of the mandibular cheek teeth. Local / Regional Anesthetic Techniques for Equine Dentistry The local anesthetics are perhaps one of the most underused classes of pharmaceuticals in veterinary medicine. Local anesthetic techniques can be a valuable part of a multimodal pain protocol. While alpha-2 agonists and opioids provide some analgesia, they do not block the pain response in some horses with severe periodontal disease or during extractions. Pre-emptive local or regional anesthesia can be very beneficial in these cases. The major local anesthetics available for use in veterinary medicine are lidocaine, mepivicaine and bupivacaine. The local anesthetics exert their mechanism of action by decreasing the permeability of the nerve cell membranes to the sodium ion, thus preventing the cells from becoming depolarized in preparation for nerve transmission. They vary in their onset of action and duration of analgesia. (Table 1) Local anesthetics work poorly near sites of infection due to the more acidic environment so tend to work best when administered further proximally on the nerve as a regional block. A more acidic environment increases the proportion of the ionized versus the non-ionized base. Because the non-ionized base penetrates cell membranes more readily, the less acidic the local environment, the more local anesthetic can penetrate the nerve cells. The dissociation constant (pka) of mepivicaine Table 1. Characteristics of Local Anesthetics Name Onset Duration favors a higher concentration of non-ionized base at the same local ph than either lidocaine or bupivacaine. Lidocaine can be more locally irritating than the other local anesthetics. There are 4 main regional anesthetic injection sites in the horse that affect the oral cavity. They each block a site of either the maxillary or mandibular branch of the trigeminal nerve (Cranial Nerve-V). These 4 sites are 1) the maxillary nerve at or near the maxillary foramen, 2) the infraorbital nerve within the infraorbital canal, 3) the inferior alveolar nerve block of the mandibular branch and 4) the mental nerve block that desensitizes the inferior alveolar nerve within the inferior alveolar canal. In addition to these 4 sites, local infiltration can be used to block specific sites such as the palatal side of maxillary cheek teeth and the wolf teeth. Local anesthetics can also be injected within the periodontal ligament space with the use of special dental injection syringes that allow injection under increased pressures. Preparation for these regional nerve blocks is similar to preparation for any other nerve block. Some clinicians clip and perform a surgical scrub whereas others do only a minimal prep. The maxillary nerve block near the maxillary foramen deserves a more thorough preparation due to the number of vessels and other nerves in the vicinity as well as the proximity to the globe. An iatrogenic infection in this location is certainly undesirable. Likewise, thorough preparation prior to the inferior alveolar nerve block is desirable due to the depth of needle penetration. Maxillary Nerve Block (MAX) Extra- Periorbital Fat Body Insertion Technique Maxillary nerve blockade at the maxillary foramen can be achieved in a few ways. The major difference is the depth of needle insertion. The older technique used full depth insertion to the bone and risked puncture of a venous sinus or laceration of Lidocaine 5 min. 1 2 hours Mepivicaine 5 min. 2 3 hours Bupivicaine min. 6 8 hours

5 several nerves. Dr. Carsten Staszyk, a German veterinary anatomist used magnetic resonance imaging to confirm that injection into the extraperiorbital fat body that lies just medial to the medial fascia of the masseter muscle resulted in diffusion to the maxillary nerve without the risks of injuring sensitive structures. A few venous sinuses are present near the bone of the skull, the puncture of which can result in proptosis due to hematoma formation behind the globe. There are a couple methods for determining the site of needle insertion in the skin. The facial crest courses fairly straight, caudally to a point ventral to the orbit then deviates caudo-dorsally. From the point where it deviates, the needle is inserted perpendicular to the skin on a line extending caudally from the straight portion of the facial crest approximately cm caudal to the deviation. The other technique to determine the injection site involves a line drawn perpendicular to the top of the skull that divides the orbit 2/3 medial and 1/3 lateral. The injection site will be located ventral to the zygomatic bone. (Figure 1) The injection site is typically in a palpable depression in this location. The needle, a 3-1/2 inch x 22 gauge spinal needle is inserted approximately 1 cm past the medial fascia of the masseter muscle. Failure to inject deep enough will only result in local infiltration in the masseter muscle and diffusion to the maxillary nerve will not occur. The typical injection volume is 5 8 ml. The caudal maxillary nerve block should desensitize all of the ipsilateral maxillary teeth but will usually not desensitize the palatal side of the teeth. Figure 1. Anatomic landmarks for the maxillary nerve block Inf rao rbi tal Nerve Block (IFO) The maxillary branch of the trigeminal nerve can also be blocked at the infraorbital foramen. The infraorbital nerve block should desensitize the ipsilateral incisors and canine tooth as well as the wolf tooth and variably the first couple cheek teeth. The local anesthetic must be injected into the infraorbital canal because the nerve fibers that innervate the teeth branch off before the main nerve exits the foramen. Care must be taken when performing this block because many horses react violently and quickly if the needle contacts the nerve. Some clinicians inject the anesthetic solution as they advance the needle slowly. A special type of epidural needle called a Tuohy needle may work better as the bevel is offset so that it pushes the soft tissue out of the way better, possibly avoiding nerve puncture. The infraorbital foramen is covered by the levator labii superioris muscle. The foramen can be located by drawing an imaginary line between the nasoincisive notch and the rostral end of the facial crest. (Figure 2) The foramen will be located approximately 1 cm caudal to this line on a perpendicular line that bisects the original line. A simpler method to find the foramen is for the operator to take his or her hand that corresponds with the side of the horse s face being blocked (eg. left hand used to locate left infraorbital foramen) and

6 placing the middle finger in the nasoincisive notch and the thumb on the cranial end of the facial crest. The index finger should then be dropped in place and will usually be right over the foramen. The muscle will usually have to be pushed dorsally to be able to readily palpate the foramen. A 22 gauge, 2-inch needle (spinal or hypodermic) is inserted slightly cranial to the foramen, parallel to the bone. Some clinicians will place of bleb of local anesthetic at the site of injection but this can make palpation of the foramen prior to the actual nerve block more difficult. If the needle is advanced slowly into the foramen and local anesthetic is slowly injected as the needle is advanced into the infraorbital canal, reaction of the horse can be minimized. However, the clinician should be prepared for a sudden reaction by the horse. This regional nerve block should not be attempted in an unsedated horse. Once the needle is inserted within the canal, the remainder of the local anesthetic, usually 5 10 ml total is slowly injected. The idea is to flood the canal with local anesthetic as far caudally as possible. Because the canal is a confined space, care must be taken to not inject under too much pressure as this may damage the nerve. Many experienced clinicians tend to avoid this block and instead perform the higher order maxillary nerve block near the maxillary foramen at the caudal end of the infraorbital canal. Inferior Alveolar Nerve Block (IFA) The inferior alveolar nerve block targets the mandibular branch of the trigeminal nerve. This block should desensitize the ipsilateral mandibular teeth. It is perhaps the most difficult dental nerve block to perform due to the depth of needle insertion. The nerve is blocked where it enters the inferior alveolar foramen on the medial aspect of the mandibular ramus. A 6 or 8 inch spinal needle is typically required for the average light horse. The needle can be inserted from either the ventral or caudal aspects of the mandible, although the ventral aspect seems to be most common. The landmark for the site of the inferior alveolar foramen is the intersection of a line representing the occlusal surface of the mandibular cheek teeth extended caudally and a perpendicular line that that extends to the caudal rim of the orbit. (Figure 3) Alternate landmarks are the intersection of the same line extending caudally from the occlusal surface of the mandibular cheek teeth with a line extending from the depression in the dorsal surface of the zygomatic arch to the bump on the ventral aspect of the ramus of the mandible. The medial aspect of the mandible has a concave nature so the bevel of the needle has to skate off the bone to the level of the foramen. Because of the concern for self-trauma of the tongue in the case of desensitization of the nearby lingual nerve, clinicians are advised to use shorter duration local anesthetics to allow the block to wear off more quickly postoperatively and thus decrease the chance of this complication. Horses should be monitored for several hours after this nerve block is performed to help ensure they are not chewing on their tongues. As previously discussed, surgical site preparation is preferred before performing this block. If the needle tip placement is accurate, ml of local anesthetic should be sufficient. Higher volumes are more likely to result in complications. Figure 2. Landmark for the location of the infraorbital nerve block.

7 Figure 3. Location of landmarks for inferior alveolar nerve block. Figure 4. Location of landmarks for the mental nerve block. Mental Nerve Block (MEN) The mental nerve block desensitizes the mandibular branch of the trigeminal nerve at the middle mental foramen. This block usually desensitizes the ipsilateral mandibular canine tooth and incisors. Like the infraorbital nerve block, horses often react violently if the nerve is contacted during insertion of the needle into the canal. Additionally, it is important to infuse the local anesthetic agent into the canal because the nerve roots that innervate the teeth branch off within the canal before the nerve exits the foramen. (Figure 4) The levator labii inferioris muscle lies over the foramen, making it difficult to palpate directly. However, the foramen usually lies at the level of the caudal aspect of the mandibular symphysis, making its location easier to find. (Figure 5) Similarly to the infraorbital nerve block, some clinicians infuse a bleb of local anesthetic at the needle insertion site but this may obscure the landmarks. Once the needle is inserted, local anesthetic can be slowly injected as the needle, a 22 gauge, 2-inch hypodermic or spinal needle, is advanced into the canal. The remainder of the local anesthetic, usually 5 ml total is then injected slowly to avoid pressure necrosis of the nerve in the confined space of the canal. Figure 5. Location of the middle mental foramen in relation to the mandibular symphysis Local Anesthesia for Wolf Tooth Extraction While the maxillary nerve block at the level of the maxillary foramen will desensitize the alveolus and gingiva of the maxillary wolf tooth, most clinicians use a simpler local technique. Local anesthetic can be injected submucosally above the mucogingival line dorsal to the wolf tooth on the vestibular side and in an adjacent palatal fold slightly caudal to the wolf tooth. Care must be taken during the palatal injection to aspirate the syringe prior to

8 injecting the local anesthetic to make sure the needle is not inserted into the greater palatine artery. I like to use a 25 gauge by 5/8 inch needle and inject 0.75 ml of lidocaine or bupivacaine per site. Mandibular wolf teeth are very uncommon. During extraction of these teeth, nerve blockade is best achieved by use of the inferior alveolar nerve block because locally infused local anesthetics diffuse poorly in the denser mandibular bone. Palatal Nerve Block Many clinicians have noted that, during extraction of maxillary cheek teeth, the maxillary nerve block fails to desensitize the palatal gingiva and mucosa. This indicates there is likely additional innervation to the palatal side of the tooth. Local anesthetic can be injected palatally in a manner similar to that described for desensitization of the palatal mucosa for wolf tooth extraction. Summary Safety is the major consideration in the restraint of equine dental patients. A clinician should select a drug protocol that will provide the needed restraint while minimizing the potential side effects. Use of local or regional nerve blocks will provide pain control that will facilitate painful procedures such as periodontal therapies or dental extractions. As veterinarians, we have the capability to provide equine dentistry services in a safer, more pain free manner than non-veterinarians. Recommended Reading Staszyk C, Bienert A, Bäumer W, et al. Simulation of local anaesthetic nerve block of the infraorbitalnerve within the pterygopalatine fossa: Anatomical landmarks defined by computed tomography. Res in Vet Sci 2008; 85:

9 Equine Dental Treatments: Floating, Deciduous Tooth Management, the Canine and Wolf Teeth Bruce P. Whittle, DVM Honey Creek Veterinary Hospital Trenton, Missouri Equine Dental Treatments: Introduction Equine teeth are fairly unique among the domestic species that are presented for dental problems. Equid teeth are classified as radicular hypsodont, which means they erupt for a significant period of the horse s life. This type of teeth forms true roots at some point after eruption. Within a couple years of eruption, the tooth ceases to grow in length and will experience a net loss in length with continued eruption and wear. Because of the continued eruption and consequent wear, there is the possibility of wear abnormalities developing. However, the continued eruption can also be used to good advantage when treating some conditions of the equine mouth because the constant remodeling of the periodontal ligament allows for improvement of periodontal disease. The continually renewed chewing surface allows some malocclusions to be corrected with proper odontoplasty. Equine dentistry is the discipline of veterinary medicine that includes the evaluation, diagnosis, prevention and treatment of diseases, disorders and conditions of the oral cavity, maxillofacial area and the adjacent and associated structures as well as the evaluation of the contribution of oral conditions to the overall health of the individual patient. Teeth floating is a subset of the discipline of equine dentistry and refers to the reduction of sharp enamel points on the vestibular-occlusal aspect of the maxillary cheek teeth and the lingual-occlusal aspect of the mandibular cheek teeth. Odontoplasty is another term that simply means removal of dental hard tissue. Odontoplasty There is much controversy over the indications for and the degree of reduction of enamel points during teeth floating. Studies have examined the effects of teeth floating on nutrient digestibility and behavior of horses and have not found a significant correlation. The primary rationale for teeth floating is to reduce sharp enamel points that are causing soft tissue trauma of the cheeks and tongue. This underscores the necessity of a thorough oral examination prior to any dental interventions to determine what, if any, pathologic processes are occurring within the oral cavity. Odontoplasty instrumentation There is a large variety of instruments available for odontoplasty procedures. One only has to go to an equine veterinary trade show to see the multitude of instruments for sale. However, a clinician should remember that there is no single instrument that will do everything. Odontoplasty instruments only have one purpose - removal of dental hard tissue. Much of the decision as to which instrument to use is based upon operator preference. Instruments may be powered by muscle power, electricity or compressed air. Electrical powered instruments may be either AC (corded) or DC (battery) powered. The grinding surface may be made of solid milled carbide, carbide chips or diamonds. The grinding surface may consist of a right-angle disc, an in-line rotary bur or a flat oscillating blade. Some powered instruments have water-

10 cooling or vacuum capabilities to help minimize tooth dust and prevent the teeth from overheating. Hand floats can be used to perform acceptable odontoplasty, though they are more tiring for the operator. They come in different configurations to allow for access to different areas of the mouth. A clinician will often need at least a couple hand floats to address areas of the mouth that cannot be adequately smoothed with power instruments, particularly the mesial aspects of teeth distal to a missing tooth or the distal aspects of the mandibular 11 s. Some horse owners think power instruments are harmful. However, with knowledge of dental anatomy and discretion, power instruments can be used safely with less stress on the operator. Before purchasing any equipment, a clinician should try a variety of instruments. Many companies offer a trial period for a veterinarian to try equipment. Wet labs are another good place to try out a variety of instruments. Odontoplasty / Floating Theory The question of how much tooth material to remove during a floating procedure is up for debate, but the current thinking among many clinicians is to remove the enamel points sufficiently to prevent further soft tissue trauma while preserving the occlusal surface. During the odontoplasty process, the clinician should be cognizant of the proximity of the pulp system of the tooth and should minimally disrupt the normal rough occlusal surface. The first step in odontoplasty is to remove the sharp enamel points at a 45 o angle to the long axis of the cheek tooth. That edge of the tooth is then contoured into a smooth radius. In the absence of malocclusions, the end result should be minimal tooth reduction of the occlusal surface while smoothing the edge of the teeth sufficiently to prevent laceration of the adjacent soft tissues (cheek and tongue). Because the cingula on the lingual aspect of the mandibular cheek teeth are much less pronounced that those on the vestibular aspect of the maxillary cheek teeth, less tooth removal will be required for appropriate odontoplasty of the mandibular cheek teeth as compared to the maxillary cheek teeth. Treatment of Class 1 malocclusions is a separate issue. Class 1 malocclusions are defined as either wear abnormalities or maleruptions of incisors or cheek teeth. By nature of the malocclusions, treatment usually involves disruption of the occlusal surface. Some individuals have suggested specific floating limits of 3 4 mm as hard and fast rules to avoid iatrogenic damage to the dental pulps. Unfortunately, the only way to determine the depth of the pulp horns in an individual tooth would be some type of advanced imaging such as computed tomography (CT) an impractical tool for routine cases. There are two key points in the reduction of Class 1 malocclusions. First, the malocclusion did not develop in 5 minutes and does not need to be corrected in 5 minutes. It is acceptable and actually desirable to reduce the malocclusion in a staged manner as necessary to preserve the integrity of the pulp system of the tooth. Second, knowledge of the three-dimensional anatomy of the tooth and the resulting appearance of the occlusal surface with wear will help guide treatment decisions. Research into the subocclusal secondary dentin depth (distance from the occlusal surface to the nearest pulp horn) in normal teeth showed depths of 1.8 to 35 mm. Because 1.8 mm is less than the touted floating limits, tooth removal should proceed in small increments with frequent examination of the occlusal surface. A pulp remnant will turn from dark brown to tan to pink to bleeding. If the dark brown color is lost in any of the pulp horns, odontoplasty should be discontinued. A dental explorer should also be used to evaluate the dentin overlying a pulp horn. Odontoplasty should cease if any sticking of the dental explorer is noted. Further treatment is probably safe after 3 to 4 months, but we have no way of determining the effectiveness of the odontoblasts at depositing adequate subocclusal secondary dentin to prevent iatrogenic pulp exposure. A clinician should

11 always use caution along with knowledge of dental anatomy and physiology to determine how much tooth material can be removed. One of the more common class 1 malocclusions is the hook. Because a hook usually only involves less than 1/3 of the occlusal length of a tooth, complete reduction is sometimes possible during one treatment session as long as the tooth material is removed in small increments. The area of reduction should be frequently water cooled and evaluated with a mirror to evaluate the secondary dentin so treatment can be stopped before a clinician violates a pulp horn. A ramp or step often require multiple treatments to correct since these malocclusions involve most of the occlusal surface of the tooth and the vital pulp horns are possibly not as deep. However, odontoplasty should proceed in the same manner as with hooks, removal of small amounts of dental material followed by rinsing and cooling of the tooth and evaluation of the occlusal surface with an intraoral mirror to evaluate the pulp remnants. Mass malocclusions such as wave complexes that involve multiple teeth should not arbitrarily be leveled. In doing so, numerous teeth will be taken out of occlusion to the point that a horse may not be able to masticate feed materials. Judicious odontoplasty of high teeth should be considered in this type of case if there is extreme wear of the opposing teeth. The goal is not to flatten the arcades in a mesial-distal dimension, but to selectively reduce tall teeth to prevent the rapid destruction of the opposing, weak tooth. Adjacent teeth should be left in occlusion and the major goal should be to smooth the sharp enamel points on the edges of the teeth to prevent soft tissue trauma. Abnormal transverse ridges are another Class 1 malocclusion. Transverse ridges are a normal feature of the cheek teeth but sometimes they become tall enough that they interfere with the rostro-caudal movement of the mandible. In these cases, the tops of the ridges are reduced to the point that free movement of the mandible is restored. Deciduous tooth management A knowledge of the eruption pattern and times of eruption and exfoliation of the deciduous and permanent dentitions of the horse is important for determining when or if a deciduous tooth should be extracted. Horses usually erupt 24 deciduous teeth in their first 6 8 months of life. At approximately one year of age, the first permanent teeth erupt. From one to about five years of age, the horse should exfoliate the 24 deciduous teeth and erupt up to 44 permanent teeth. Because of all of this activity in the mouth in the first 5 years of life, it is prudent to perform a semi-annual oral examination within this time period in order to detect any problems as early as possible. Maleruptions of teeth are not uncommon and are often the result of a deciduous tooth failing to shed, causing the permanent tooth to erupt in an abnormal position. Because of differences in the relationship of the permanent tooth to its deciduous precursor between cheek teeth and incisors, maleruptions will be different for each type of tooth. When considering the cheek teeth, only the first 3 cheek teeth in each arcade have both a deciduous and permanent component. The last 3 cheek teeth are molars and only have a permanent component. The permanent premolar develops immediately beneath its deciduous precursor. Therefore the permanent premolar can either erupt correctly into the cheek teeth row or can erupt lingually or vestibularly. The most common cheek tooth to malerupt is the 08 because it has to erupt in between two permanent cheek teeth that are already in position. A common reason the permanent 08 malerupts is the premature extraction of the deciduous 08, allowing the permanent 07 and 09 in that cheek teeth row to drift together and close the space the 08 is supposed to erupt into. If the 08 becomes impacted in its eruption path, it is possible to use orthodontic appliances to separate the 07 and 09 to allow proper eruption. If on the other hand, the 08 malerupts toward the

12 tongue or toward the cheek, it often causes soft tissue trauma, is more likely to experience periodontal disease and may need to be extracted. For this reason, deciduous premolar teeth (caps) should not be extracted until the permanent tooth is ready to erupt into position. This can be ascertained by visualization of the permanent tooth beneath the deciduous tooth, bleeding at the interface between the permanent tooth and the deciduous tooth and instability of the cap when tested with extraction forceps. The occlusal surface of the premolars of young horses should be closely examined for cap fragments because it is not uncommon for the thin deciduous tooth to fracture and part of it can be retained, stuck to the permanent tooth. Extraction of premolar teeth should be based upon an oral examination and not based upon the age of the horse because eruption times can vary significantly from horse to horse. Permanent incisor teeth erupt different than permanent cheek teeth because the permanent incisor tooth bud forms beneath but slightly lingual to the deciduous precursor. Therefore, if the deciduous tooth fails to exfoliate, the permanent incisor will often erupt lingual to the deciduous tooth. In extreme cases, a horse will present with 2 rows of incisors, the front row usually being the retained deciduous teeth and the back row being the malerupted permanent incisors. Occasionally, persistent deciduous teeth must be extracted in a staged manner over time to maintain occlusal contact of maxillary and mandibular incisors. The more common situation is where one or two analogous deciduous incisors fail to exfoliate and their permanent components erupt caudally. If detected early, extraction of the persistent deciduous tooth will allow the permanent tooth to drift into its normal position. Often, these problems are not detected until all of the permanent teeth have erupted and the chance of being able to attain a normal incisor occlusion is not very good. It is very frustrating, as a clinician, to see an 8 year old horse that has a poor incisor occlusion due to a problem that could have been corrected if it had been diagnosed as a 3 or 4 year old. Another common incisor malocclusion problem occurs when the permanent incisor becomes partially impacted on the adjacent deciduous incisor. This may occur because the permanent tooth is wider than the deciduous tooth it is replacing. Most of the time, when the deciduous teeth exfoliate, the malocclusion will resolve as long as the permanent tooth does not begin to erupt lingually. Although controversial, many clinicians will remove a thin segment of the overriding deciduous tooth to allow the permanent tooth an open eruption pathway. Care must be taken to not invade the pulp of the deciduous tooth. An indirect pulp exposure is possible in this situation due to opening of dentinal tubules so the risk versus benefit should be determined first. Deciduous teeth in this situation will usually be shed within 3 6 months. As long as the clinician removes only enough tooth material from the mesial edge of the deciduous tooth to clear the eruption pathway, the risk should be minimal. Canine Teeth The canine teeth of the horse are usually the forgotten teeth. Very little exists in the equine dentistry literature regarding the canine teeth. The canine teeth may be absent in the mare or may be present as vestigial teeth that are barely erupted, unerupted or even as full sized teeth similar in size to the canine teeth of male horses. Equid canine teeth are hypsodont teeth as characterized by the gross anatomy of their unerupted crown. They do have a single pulp horn whose subocclusal depth is as variable as that in the cheek teeth. Because the canine tooth does not occlude with another tooth, it retains the dome of enamel over its crown unless it experiences abrasion from an external object. If this enamel barrier is violated through odontoplasty, the dentinal tubules are opened resulting in a potential indirect pulp exposure. The lingual surface of the canine teeth, particularly the mandibular

13 canines, is often concave resulting in a sharp rim of enamel at the periphery. This can be carefully smoothed without destroying the integrity of the tooth. Previously, it was recommended to reduce the canine teeth to the level of the 3 rd incisors or even crown amputate them to the level of the gingiva. This risks a direct pulp exposure. When it comes to the equid canine teeth, the saying, less is more certainly applies. Tartar accumulation on the mandibular canines is relatively common. It can be removed with a curette, a specialized instrument designed for scraping the surface of a tooth. Ideally the tooth surface could then be polished with a low speed handpiece to leave a very smooth surface to prevent the attachment of plaque forming bacteria. Periodontal disease can also be present around the canine teeth so the gingival sulcus should be examined with a periodontal probe. Equine odontoclastic tooth resorption and hypercementosis is a condition that often begins with the canine teeth. It typically affects horses in their early teens and older and should be considered as a differential in horses with periodontal lesions of the canine teeth. Radiography is helpful in the diagnosis of this condition. Although treatment of EOTRH is beyond the scope of this paper, extraction of affected teeth is considered the treatment of choice at this time. Wolf Teeth The wolf teeth are the 1 st premolars, also known as the 05 s according to the modified Triadan tooth numbering system. An individual horse can have from zero to four wolf teeth, usually positioned mesial to the first cheek teeth (06 s). Wolf teeth have been given a bad reputation over the years, but not all wolf teeth cause problems. As with any aspect of dentistry, a treatment decision should not be made without a thorough oral examination. Wolf teeth come in many shapes and sizes and can be positioned in various locations in relation to the 06 s. Maxillary wolf teeth are more likely to be present than mandibular wolf teeth, but all positions should be checked in all horses to ensure a potential problem is not missed. Wolf teeth are often thought of as being a small, vestigial tooth, but some wolf teeth are molarized and look like a smaller version of a cheek tooth. If a wolf tooth is smooth and there are no signs of soft tissue damage, extraction may be unnecessary. If a wolf tooth is sharp and is causing lacerations of the cheek or tongue, extraction is usually recommended. In young horses about to enter training, many clinicians will err on the side of caution and extract the wolf teeth that are present so they will not contribute to mouth pain that could complicate a training program. On the other hand, in horses that will not have a bit placed in their mouth, extraction of the wolf teeth is unnecessary unless the teeth are exceptionally sharp or abnormally positioned. Extraction of the wolf teeth should be based upon a conscious decision and not be just another cookbook procedure. A special type of wolf tooth is the unerupted wolf tooth, also known as a blind wolf tooth. These teeth, as the name suggests, are found underneath the gingiva with no part of the tooth erupted. The teeth are often present in a horizontal position and can be found anywhere in the bars of the mouth. These teeth are often painful to the horse. Careful palpation of the bars is necessary to detect some of these abnormally positioned teeth. Extraction of a wolf tooth should be based upon an examination of the mouth and a reasonable certainty that the tooth is going to cause soft tissue trauma. Wolf tooth extraction is a surgical procedure because it first involves separation of the gingiva surrounding the tooth. The presence of the greater palatine artery palatal to maxillary wolf teeth necessitates care to avoid its accidental laceration. Pain control should be considered in any surgical procedure, including the extraction of the wolf teeth. Although a regional nerve block such as infraorbital nerve block or maxillary

14 nerve block would likely be successful, the regional nerve blocks clinically do not desensitize the gingiva on the palatal side of the tooth. A simpler method is to deposit local anesthetic locally above the mucogingival line on the vestibular side of the tooth and deposit an additional bleb of local anesthetic in the palate slightly palatal and distal to the wolf tooth. Because the local anesthetics require at least 3 5 minutes to achieve desensitization of the area, nerve blocks can be applied prior to odontoplasty procedures then the teeth can be extracted after sufficient time has passed. There are numerous methods of extracting wolf teeth. A successful extraction of any tooth is characterized by complete extraction of the entire tooth with minimal disruption to the bony alveolus. The use of various sizes of elevators and luxators will achieve these goals better than other methods. While the Burgess style of wolf tooth extractors seems to be safer because the sharpened surface surrounds the tooth and thus makes slippage of the instrument less likely, they result in greater disruption of the gingiva and alveolus. Proper use of elevators takes patience and care but results in the least tissue trauma. The periodontal ligament fatigues more quickly if elevator pressure is applied to the tooth for a sufficient amount of time to compress the periodontal blood supply of the opposing edge of the tooth. When enough of the periodontal ligament loses its blood supply, the tooth can easily be retrieved from the alveolus. The exception to this is in horses older than 2 3 years of age in which the root of the tooth has ankylosed in the alveolus. In these cases, fracture of the root tip is likely. If a root tip is fractured during the extraction process, it should be removed if practical. However, if the clinician fears that attempts at extraction are likely to cause more trauma, the root tip can be left but it must be noted on the dental chart that the root tip was intentionally left. Additionally, the owner should be informed that the remaining tooth portions can later erupt into the oral cavity and may need to be removed at that point. In summary, the decision to extract a wolf tooth should be based upon an oral examination to determine the likelihood of it causing soft tissue trauma. The use of the horse should also be considered. Proper technique, including the use of dental elevators to systematically fatigue the periodontal ligament, results in the best surgical outcomes. Local anesthesia can be helpful for keeping the patient more comfortable during the procedure and afterward. Recommended Reading Caldwell LA. Caps, canines and wolf teeth in the horse: The quick guide to embryology, eruption, exfoliation, extraction, reduction and other things you need to know. Proceedings AAEP Annual Convention Pp Easley J. Evolution of odontoplasty the dental float. Proceedings AAEP Focus on Dentistry Pp

15 Equine Oral Anatomy: What a Veterinarian Needs to Know! Figure 1. Modified Triadan numbering system Bruce P. Whittle, DVM Honey Creek Veterinary Hospital Trenton, Missouri brucewhittle@gmail.com Introduction The equine oral cavity is exquisitely designed to allow for adequate function within a range of normal variations and often despite fairly significant abnormalities. From the histologic structure of the teeth to the threedimensional arrangement of the teeth within the oral cavity to the oral soft tissues, each feature has a specific purpose. The astute clinician will strive to understand these features to better care for the horse s oral cavity. Definitions Apical the end of the tooth toward the roots Occlusal the chewing end of the tooth (also called coronal when discussing the tooth not yet in wear) Mesial the region of the tooth toward the midline of the dental arch Distal the region of the tooth furthest from the midline of the dental arch Proximal Space the space between two adjacent teeth (also interproximal)

16 Lingual that portion of a tooth facing the tongue (although lingual is the preferred term, palatal can be used to refer to this same surface of the maxillary teeth.) Vestibular that portion of the tooth facing the cheek (although vestibular is the preferred term, the term buccal is often used to refer to the same surface.) Modified Triadan system - The preferred composite numbering system for the teeth of a horse in which the four dental arcades are numbered 100 (upper right), 200 (upper left), 300 (lower left) and 400 (lower right) and the teeth are numbered from 1 to 11 starting with the central incisor and proceeding to the 3rd molar. For example, lower right 2nd premolar is numbered 406. Deciduous teeth are numbered similarly but the dental arcades are numbered 500 (upper right), 600 (upper left), 700 (lower left) and 800 (lower right) (Figure 1). nutrition, responding to insults and directing reparative responses. The pulp comprises a large percentage of the volume of a tooth and is surrounded only by a thin shell of mineralized tissues in the young horse. The number of pulp horns per tooth remains constant though their height and diameter decreases with age due to the deposition of secondary dentin. Horses retain an open apex for a longer period of time than many species thus allowing a better blood flow to the pulp for a longer period of time. This may help facilitate repair mechanisms in the event of insult to the pulp. The pulp can be divided into three regions: the root canals, the common pulp chamber and the pulp horns. (Figure 2) The common pulp chamber is only present in multirooted teeth (cheek teeth) and serves as a connection for multiple pulp horns and root canals. Structural Dental Anatomy: The Building Blocks Just like any architectural marvel, teeth are composed of multiple building blocks that are arranged in an ordered fashion that confers strength and durability to perform specific functions. The building blocks of the teeth, considered from the most interior to the exterior of the tooth are the pulp, dentin, enamel and cementum. With brachydont teeth (humans, dogs and cats), only enamel is normally exposed in the oral cavity. However, in the teeth of horses, all three of the mineralized dental tissues become exposed on the occlusal surface during masticatory wear. The pulp is composed of blood vessels, nerves, immune cells, connective tissue and undifferentiated stem cells. I like to consider the pulp the heart and brain of the tooth because it is the connection of the tooth to the head through the nervous and circulatory systems and it is responsible for providing Figure 2. Divisions of the pulp system (red) of an equine maxillary cheek tooth in a young horse. Maxillary cheek teeth typically have 3 roots, two on the vestibular aspect (mesiovestibular and distovestibular) and one on the lingual aspect. Mandibular cheek teeth usually have 2 roots, one mesial and one distal. The root canals enter the tooth through each

17 tooth root before communicating at the common pulp chamber. The individual pulp horns divide from the common pulp chamber before traversing toward the occlusal end of the tooth. All teeth have at least one pulp horn. (Figure 3) The average horse has at least 142 pulp horns and may have as many as 150 pulp horns if it has a full complement of teeth. When performing odontoplasty on a horse, there are thus at least 142 opportunities to damage a pulp horn! The clinician who has a good understanding of dental anatomy will be much less likely to harm the horse in the course of his or her treatments. Recent studies (White 2010, Marshall 2012) have measured the depth of vital pulp horns below the occlusal surface, referred to as the subocclusal secondary dentin depth (SO2D). The hypothesis was that pulp horns might be closer to the surface in teeth that were not in occlusion with the opposing tooth due to wear abnormalities or absence of the opposing tooth. What was found was that the SO2D depth varied greatly and was not predictable. Individual pulp horns in normally occluding teeth were found to range in depth from 2.64 mm to mm with a mean depth of mm. Teeth that were elongated due abnormal wear had SO2D depths that varied from 1.87 to mm with a mean depth of mm. These findings demonstrate that we cannot reliably predict the SO2D. While not foolproof, a clinician can use knowledge of the appearance of the occlusal surface, specifically the pulp remnant, to stage tooth reduction of elongated teeth in 0.5 to 1.0 mm increments to avoid damaging a pulp horn. Figure 3. Pulp horn numbering diagram The pulp horns are the most vulnerable portion of the pulp system to iatrogenic damage since they are present in the supragingival part of the tooth. One cannot know with certainty how deep below the occlusal surface an individual pulp horn is. Unfortunately, due to the overlap of mineralized structures in a cheek tooth, radiography is not very helpful in this determination. In order to precisely characterize the pulp horn structure, advanced imaging such as computed tomography would be necessary. Since this is not practical in the majority of cases, a clinician must use his or her knowledge of dental structural anatomy to predict how much tooth material can be safely removed during an odontoplasty procedure. Fig. 4. Arrangement of pulp, odontoblast cell bodies, and processes, dentin, and enamel. The dentin immediately surrounds the pulp and is constantly being deposited by odontoblasts throughout the life of the tooth.

18 Because of the intimacy of the dentin and pulp, they are often referred to as the dentin-pulp complex. (Figure 4) Dentin is approximately 70% mineralized. Histologically, there are four types of dentin: primary dentin, regular secondary dentin, irregular secondary dentin and tertiary dentin. Understanding the structure, timing and location of deposition of the different types can help a clinician make diagnostic and treatment decisions based upon the appearance of the dentin on the occlusal surface of the tooth. Primary dentin is deposited during the early development of a tooth, ceasing at approximately the time of eruption of the tooth. At that time, the odontoblasts begin producing secondary dentin that is slightly different histologically but is a continuation of the primary dentinal structure. Regular secondary dentin has a tubular structure similar to primary dentin and is deposited in a centripetal manner around the periphery of the pulp. Irregular secondary dentin is produced at the occlusal end of the pulp horn. It lacks the regular tubular structure so serves a protective role to avoid allowing the entrance of bacteria into the most vulnerable portion of the pulp horn. Clinically, the difference in appearance of regular and irregular secondary dentin is most easily observed on the incisors. (Figure 5) exposed tubular structure. The irregular secondary dentin has a cream colored appearance because it does not retain plant pigments. Tertiary dentin is deposited in response to noxious insults to the teeth. When a tooth is fractured, overheated during odontoplasty or pulp horns are directly or indirectly exposed during dental treatments, the odontoblasts attempt to wall off the area of damage with tertiary dentin. When this process does not proceed rapidly enough, pulpitis develops and the tooth can become infected. The next layer outward is enamel. Enamel is produced by ameloblasts. Unlike the other dental components, enamel has no capacity for repair because the ameloblasts die off as soon as tooth development is completed. Enamel is 96-98% mineralized and is the hardest and most brittle substance in the body. Enamel is deposited as one of two types, Type 1 and Type 2. Type 1 enamel has a regular arrangement of parallel prisms and is very resistant to wear. The enamel in maxillary cheek teeth is primarily Type 1. Type 2 enamel has an irregular three-dimensional structure that is more resistant to shearing forces. The enamel in the incisors is predominantly Type 2. Mandibular cheek teeth are composed of a mixture of Type 1 and Type 2 enamel. Enamel surrounds the dentin as a peripheral ribbon and forms the infundibular walls in the maxillary cheek teeth and all incisors. (Figure 6) Figure 5. Appearance of dentin and enamel on the incisor occlusal surface The pulp remnant, aka star, is composed of both of these substances. The regular secondary dentin is usually dark brown due to the uptake of dark plant pigments into its Figure 6. Peripheral and infundibular enamel in a maxillary cheek tooth

19 Figure 7. Peripheral enamel folding in a mandibular cheek tooth. Note the high degree of infolding. Mandibular cheek teeth do not have infundibula so the enamel ribbon is much more highly folded in order to distribute the enamel more evenly across the surface of the tooth. (Figure 7) The presence of infundibula in the maxillary cheek teeth and incisors serves to distribute enamel more evenly across the surface of those teeth. Once wear proceeds beyond the level of the apical end of the infundibulum, the tooth will wear quickly because the center of the tooth is composed only of dentin at that point. Because enamel is so brittle, it must be protected by adjacent cementum and dentin in a layering system similar to that found in safety glass in vehicles. (Figure 8) Figure 8. Cross-sectional diagram showing the relationship of dental components The final dental component is cementum. It is produced by cementoblasts, is approximately 60% mineralized and is histologically similar to bone. Cementoblasts are active throughout the life of a tooth. Cementum is produced in a thicker layer immediately subgingival so that the cementum covering the erupted portion of the crown is thicker, except for in the interproximal spaces. Because of its histologic similarity to bone, it serves as an anchoring point for the periodontal ligament to attach the tooth within the alveolus. In addition to being found on the periphery of a tooth, external to enamel, cementum is also found filling the infundibula, internal to the infundibular enamel. The Periodontium Equid teeth are classified as hypsodont, meaning they continue to erupt throughout the life of the tooth. They are further classified as radicular hypsodont teeth because they form true roots at the end of development then cease to grow in length. From that time forward, the subgingival portion of the radicular hypsodont tooth gets shorter as the tooth is erupted into the oral cavity with continuing wear of the occlusal surface. Aradicular hypsodont teeth, found in rabbits and rodents, do continue to grow and erupt throughout the life of the tooth but do not form true roots. The other major classification of teeth is brachydont. This type of teeth is found in humans, dogs and cats. Brachydont teeth cease to grow and erupt once they have erupted into their final position in the oral cavity. The hypsodont nature of equid teeth gives them a continually renewed chewing surface as they are worn down through mastication of fibrous forages. In addition, because the periodontal ligament is continually detaching and re-attaching to allow eruption of the tooth, periodontal disease can improve to some extent with proper care. The periodontium consists of the alveolar bone, periodontal ligament, cementum and gingiva. (Figure 9) The alveolar bone is shaped to fit the tooth. It is protected by the attached gingiva. The gingiva has a free edge that sits against the tooth to form a small crevice. The gingiva is attached to the tooth

20 Figure 9. Anatomy of the Periodontium slightly apical to this point. The crevice is called the gingival sulcus and contains gingival crevicular fluid. This fluid contains immune cells that help prevent the ingress of bacteria into deeper tissues. When examining the oral cavity with a periodontal probe, it is the depth of the gingival sulcus that is being evaluated. The cementum that surrounds the tooth serves as the attachment surface for the opposite end of the periodontal ligament. The periodontal ligament itself is a fascinating structure. It provides support and compressive stiffness for the attachment of the tooth. Periodontal ligament fibers are present in numerous planes to oppose forces acting upon a tooth from different directions. This allows the tooth to withstand the vertical or diagonal vector forces that act upon it during the process of mastication. When extracting a tooth, it is the periodontal ligament that must be detached to allow extrusion of the tooth from the bony alveolus. This can occur by cutting the periodontal ligament fibers with a sharp luxator or by levering the tooth against the opposite alveolar wall to disrupt the blood supply. When the blood supply has been disrupted circumferentially around the tooth, the periodontal ligament will fatigue and release the tooth. Functional Dental Anatomy The teeth have a three-dimensional arrangement within the skull that allows for function of various batteries of teeth with different mandible movements. Their arrangement also allows for satisfactory function despite fairly significant malocclusions. The arrangement of the teeth, tongue, palate and cheeks plays a role in mastication and the transport of a food bolus to the pharynx for swallowing. The astute clinician realizes that the equine oral cavity is not a cavern but a space in which all of the dental hard tissues and oral soft tissues are in close contact. Horses exhibit anisognathism, a condition characterized by unequal jaw widths with the maxillary cheek teeth arcades being more widely separated than the mandibular cheek teeth arcades. The mandibular cheek teeth arcades thus have to travel laterally to contact the ipsilateral maxillary cheek teeth arcade. Masticatory movements are actually more complicated than this and will be described in detail. Maxillary cheek teeth are approximately 40% wider than mandibular cheek teeth. This feature makes the individual maxillary cheek teeth in the center of the row relatively square as compared to the rectangular shape of the mandibular cheek teeth. The cheek teeth on the ends of each arcade, the 06 s and 11 s tend to be shaped like a boat hull on the respective mesial and distal surfaces. (Figure 10) Figure 10. Anisognathism, width of maxillary versus mandibular cheek teeth and teeth shapes.

21 Figure 11. Cingula (yellow arrows) and relationship to vestibular pulp horns (red arcs) Maxillary cheek teeth have prominent vertical folds on their vestibular surfaces termed cingula. (Figure 11) These outfoldings at the occlusal surface are the location where sharp enamel points develop. Care must be taken when reducing these sharp enamel points to not invade the adjacent vestibular pulp horns that can be in close proximity. While mandibular cheek teeth technically have cingula, they are much less prominent than those on the maxillary cheek teeth. Transverse ridges are another normal feature of cheek teeth. Each cheek tooth possesses 1 3 ridges that course in a linguovestibular direction. (Figure 12) The ridges on the maxillary cheek teeth tend to interdigitate with the valley between two ridges on the opposing mandibular cheek tooth. While the purpose of these ridges in not known, they may play a role in guiding the lateromedial movement of the mandible during mastication and may further increase the surface area of the teeth for grinding. The teeth should be positioned tightly against one another so that there is no gap in the interproximal spaces. The order of eruption of the teeth, both deciduous and permanent, is very important in facilitating this. The incisors erupt in succession from central to corner thus are able to maintain the tight interproximal spaces unless they malerupt. The permanent cheek teeth erupt in a staggered manner. (Figure 13) The last permanent cheek tooth to erupt is the 4 th premolar or Triadan 08. It has to erupt between two permanent cheek teeth and acts as a keystone to wedge the teeth in each arcade together into a single grinding unit. However, it is also one of the most commonly malerupted teeth since sometimes its eruption pathway is blocked by the 07 and 09 drifting together if the deciduous 08 is shed or extracted too early. Figure 12. Prominent transverse ridges are present on the maxillary (yellow arrows) and mandibular (red arrows) arcades of this skull specimen. Photo courtesy of Dr. Dennis Rach. Figure 13. Timing and pattern of eruption of cheek teeth Because there is no gingival tissue in between the teeth, if a gap does develop due to positioning of the teeth or orthodontic forces acting on the teeth, periodontal disease is extremely likely. The interproximal spaces are not necessarily perpendicular to the line of cheek teeth. Individual interproximal spaces

22 may be at an angle other than 90 degrees, a feature that must be taken into account when a clinician is placing a molar spreader in the interproximal space during tooth extraction or using a diastema bur to widen a portion of the interproximal space to prevent feed stasis. (Figure 14) Also, the maxillary cheek teeth arcades are usually curved toward the distal end of the cheek tooth row so that the vestibular aspects of the last one or two molars are difficult to access with odontoplasty instruments. tooth and allows the cheek teeth to function when the incisors are not in occlusion. Rarely, the table angles on one side of the mouth can become increased (shear mouth) due to pathology of the temporomandibular joint resulting in an abnormal chewing pattern. The incisor table surface is on a different plane that that of the cheek teeth. (Figure 16) A line drawn along the incisor table surface that is extended caudally should transect the temporo-mandibular joint (TMJ). Because the TMJ serves as the pivot point for the mandible, this relationship makes sense. The incisors function to nip grass so that it can be processed further caudally in the oral cavity. Figure 14. Non-parallel nature of the cheek teeth interproximal spaces (blue lines) and curvature of the vestibular aspect of the maxillary cheek teeth arcades (red line) Figure 16. Relationship of incisor table surface and TMJ compared to occlusal table surface of cheek teeth. Figure 15. Cheek teeth occlusal table angles. The cheek teeth table surfaces are angled approximately degrees from vestibular to lingual. (Figure 15) The angle is not consistent throughout an arcade. The angle provides for a wider chewing surface on each The TMJ is a unique joint in that it allows two separate motions, pivoting and translation. Pivoting is simply a hinge-type motion that occurs when the incisors are used for nipping. Translation is a complex motion in which the TMJ opposite the side of chewing somewhat subluxates to allow the mandibular and maxillary arcade on the contralateral side as the TMJ to come into contact. The TMJ is a diarthrodial joint that has a fibrocartilaginous meniscus. Despite the types of movement effected by the TMJ, disease of the joint is relatively uncommon. Mastication in the horse is a complex process. The mandibles start in the central position in which the interproximal spaces between the maxillary and mandibular 01 s

23 line up. However, in many horses, there is a slight offset between these maxillary and mandibular interproximal spaces in the resting position, so this must be considered. In the neutral position, while the mandibular and maxillary incisors are in occlusal contact, there is a space between the maxillary and mandibular cheek teeth on each side. (Figure 17) The mandible then drops ventrally and moves slightly laterally toward the side that chewing will occur. Opening of the mouth is predominantly a passive movement although contraction of the digastricus muscles assists. In the closing stroke of the mandible, the mandible closes in a lateral direction until the ipsilateral mandibular and maxillary arcades excursion than horses on a more fibrous diet. This may predispose horses fed a concentrate diet to less effective wear across the entire tooth surface, causing sharp enamel points or malocclusions. Figure 17. Incisor and cheek teeth relationship in centric incisor occlusion. come into contact. The final phase of mastication is the power stroke. During the power stroke, the mandible slides axially in a powerful movement in which feedstuffs are ground between the maxillary and mandibular cheek teeth. (Figure 18) This movement is facilitated by numerous muscles but predominantly the masseter muscles and medial and lateral pterygoid muscles. Once the masticatory movements are completed on one side, they may then transfer to the contralateral side in a figure-8 fashion or may continue in a circular motion on the ipsilateral side. Most horses tend to chew predominantly on one side or the other. The types of feedstuffs can affect the movement of the mandibles. Horses that are fed pelleted feeds have a shorter lateral Figure 18. Diagrammatic representation of one chewing cycle. The final parts of the masticatory puzzle are the adjacent soft tissues. The very mobile lips of a horse are important for bringing feed materials into the oral cavity for processing. The cheeks serve as barriers that help keep the feed materials in between the chewing surfaces of the cheek teeth. Although our common view of the oral cavity represents a cave, the tongue is actually in contact with the palate when the mouth is closed. The palate has a series of staggered rugae on its surface that, together with the tongue, act as an auger system to move

24 masticated feed materials distally in the oral cavity where they are swallowed and enter the esophagus. (Figure 19) Recommended Reading Dixon PM, du Toit N, Staszyk C. A fresh look at the anatomy and physiology of equine mastication. Vet Clin North Am Equine Pract 2013;29: Marshall R, Shaw D, Dixon P. A study of subocclusal secondary dentine thickness in overgrown equine cheek teeth. Vet J 2012; 193: Staszyk C, Suske A, Pöschke A. Equine dental and periodontal anatomy: A tutorial review. Equine Vet Educ. 2015;27: Figure 19. Staggered palatal folds indicated by yellow and red arrows. Summary Equine teeth are composed of various dental materials that, when arranged in a specific order, allow for durability and function. The precise arrangement allows for a continually renewed grinding surface. Although skeletal asymmetry and malocclusion of teeth are fairly common, because of the way the teeth are arranged three-dimensionally, satisfactory function is still possible. A clinician should be aware of the structure and ongoing change surrounding the pulp system to avoid damaging this vital structure. A clinician should consider the functional anatomy of the horse s mouth when making treatment decisions. The goal is not to sculpt the mouth into some preconceived ideal because every horse is different. By understanding how the teeth inter-relate and interact, better decisions can be made to improve the function of the masticatory apparatus. White C, Dixon PM. A study of the thickness of cheek teeth subocclusal secondary dentine in horses of different ages. Equine Vet J 2010; 42: Whittle BP. How to improve your equine dentistry practice by better understanding oral anatomy. Proceedings AAEP 2016: 62:32 43.

25 Equine Oral Disease: What Could Possibly Go Wrong?? Bruce P. Whittle, DVM Honey Creek Veterinary Hospital Trenton, Missouri Equine dentistry involves much more than just dealing with sharp points on the teeth. Numerous pathologies can be present in the oral cavity affecting the teeth, bone and adjacent soft tissues. Disease processes such as periodontal disease and pulp disease are very painful. Failure to diagnose these painful conditions will prevent a clinician from improving the health of the horse. A clinician should do a thorough examination of the entire oral cavity to detect any pathology of either the dental hard tissues or the soft tissues. Oral Hard Tissue Pathology The oral hard tissues include the teeth and the bone. A clinician should consider the various pathologic processes that can affect the different tissues. Table 1 summarizes the major pathologic processes that affect the oral hard tissues. Table 1: Oral Hard Tissue Pathology 1) Class 1 malocclusions - dental elongations or maleruptions 2) Class 2 and 3 malocclusions - bone growth disparities of maxilla versus mandibula 3) Class 4 malocclusion wry bite (asymmetry) 4) Supernumerary teeth - extra teeth 5) Oligodontia fewer than normal teeth 6) Infundibular cavities 7) Dental fractures 8) Bone fractures of the maxilla or mandibles 9) Dental dysplasia 10) Neoplasia 11) EOTRH Class 1 Malocclusions: dental elongations Class 1 malocclusions are defined as either wear abnormalities or maleruptions of incisors or cheek teeth. Dental elongations are the most common oral pathology that a clinician is presented with. They are the result of abnormal wear of opposing teeth. These may include hooks, ramps, waves, steps and abnormal transverse ridges of the cheek teeth and diagonal bites, ventral curvature, dorsal curvature and steps of the incisors. When one of the pair of opposing teeth is elongated, it is usually the healthy tooth of the pair. The tooth that is wearing excessively is usually the tooth that has some type of pathology, including enamel hypoplasia or infundibular cavities. Determining the cause of the abnormal wear can help in the formulation of a treatment plan. A hook is an elongation of a tooth at either end of a cheek teeth arcade in which its vertical dimension is greater than the horizontal dimension. Hooks form due to improper alignment of the cheek teeth arcades due to one of several factors: a supernumerary tooth in one of the cheek teeth rows, one of the rows is inherently longer than its opposing row, one of the cheek teeth rows is missing a tooth or the horse is fed from an elevated feeder that encourages mastication in a head position that results in retraction of the mandible and thus malalignment of the cheek teeth arcades. Although hooks can occur on the teeth on either end of a cheek teeth row, they are most common on the maxillary 06 s and the mandibular 11 s. Careful examination of the cheek teeth rows will allow a clinician to determine the cause of the hook(s). If the hooks were the result of feeding the horse from an elevated feeder, once corrected, feeding the horse at ground level may prevent recurrence of the hooks. A ramp is an elongation of a cheek tooth at the end of a cheek teeth row that is lower in the vertical dimension than it is in the horizontal dimension. A ramp forms for many of the same reason as hooks, there is likely some pathology of the opposing tooth that causes it to wear more quickly than it should. Ramps are most common on the mandibular 06 s and the mandibular 11 s.

26 A wave is a malocclusion characterized by dental elongation in an undulating pattern as viewed from the side, affecting multiple teeth in a cheek teeth row. Waves are more common in older horses and are often associated with the loss of the infundibula of the maxillary 09, allowing the mandibular 09 to elongate since it will wear more slowly against the maxillary 09 that now has no central enamel. Instead of just being a focal elongation within a cheek teeth row that involves only one tooth (a step), the wave involves unequal wear of the adjacent teeth also. Each cheek tooth normally has two to three transverse ridges on the occlusal surface. The alternating ridges and troughs along the cheek teeth row may help to guide the cheek teeth in a medial-lateral direction during mastication, but their function is unclear. When the transverse ridges are greater than 3 4 mm higher than the adjacent tranverse grooves, they are considered abnormal transverse ridges. If tall enough, these abnormal transverse ridges may interfere with the rostro-caudal movement of the mandible in relation to the maxilla. However, since the cheek teeth are not in contact when the incisors are in centric occlusion, the abnormal transverse ridges would have to be fairly significant to cause interlock resulting in restriction of mandibular movement. The incisors may also be affected by Class 1 malocclusions characterized by differential wear resulting in tooth elongation. A diagonal bite is characterized by a sloping of the incisor table surfaces from side to side. A diagonal bite is classified by the location of the tallest mandibular incisor teeth. For example, a diagonal 4 (abbreviated DGL-4) is characterized by a slant of the incisor table surfaces that is highest at 403 and lowest at 303. Diagonal bites can be a result of either a missing incisor or asymmetry of the bones of the head resulting in a twisting of the maxillae and/or mandibles. A diagonal incisor bite will often prevent contact of the cheek teeth during mastication on the side opposite the high mandibular incisors in cases where the diagonal formed due to a missing incisor. In cases of diagonal incisor bite due to skull asymmetry, the cheek teeth usually erupt differentially so that they can make occlusal contact despite the incisor malocclusion. A ventral curvature of the incisor tables, commonly known as a smile bite is relatively common. It is nearly universal in donkeys. A ventral curvature probably develops when the deciduous incisors 501 and 601 exfoliate before 701 and 801. This allows 101 and 201 to erupt into position. When the 701 and 801 deciduous teeth exfoliate, 101 and 201 can continue to erupt until they contact 301 and 401. Because the incisors slide side to side during mastication, the elongations of 101 and 201 tend to wear more on , causing a ventral curvature of the arcades. Because 403 and 303 are left relatively longer, they tend to wear and more than normal. The end result is an incisor malocclusion that resembles a permanent smile. A dorsal curvature of the incisor tables is just the opposite of the ventral curvature. Teeth 301 and 401 will be the high incisors along with 103 and 403 and the resulting malocclusion resembles a permanent frown. Cheek teeth contact can be minimized with either a ventral or dorsal incisor curvature because the incisors will still be in contact further lateral than normal, preventing the cheek teeth from coming into contact. An incisor step is characterized by an individual tooth whose occlusal surface is higher than that of the rest of the incisor teeth in that arcade. Because the incisors slide side to side during mastication, a true step is rarely seen because the wear will usually involve multiple teeth. A step is often the result of a missing opposing tooth or an opposing tooth that wears excessively due to abnormal enamel. An incisor step can interfere with occlusal contact of the cheek teeth during the power stroke phase of mastication when the incisors are coming back into centric occlusion. Malerupted teeth, another type of Class 1 malocclusion, are teeth that erupt in an abnormal plane, often due to failure of their deciduous precursor to shed at the appropriate time. They can also be a result of the developing tooth bud becoming malpositioned prior to eruption of the tooth. Malerupted teeth can present as teeth that are rotated on their long

27 axis, tipped on their long axis or erupted adjacent to their proper position. The 4 th premolars (Triadan 08 position), are one of the more commonly malerupted teeth because the permanent tooth has to erupt between two permanent teeth (Triadan 07 and 09). If the eruption path is blocked due to the 07 and 09 drifting together prior to eruption of the 08, the 08 will either cease eruption once it becomes stuck or will erupt lingually or vestibularly. Lingually tilted teeth are especially problematic because of the limited space the tongue has to occupy in the already narrow space between the left and right mandibles. The 08 maleruption may be predisposed by prematurely extracting the deciduous 08 caps, allowing the 07 and 09 to drift together. The permanent 3 rd incisors (Triadan 03) are also fairly commonly malerupted due to failure of the deciduous 3 rd incisors to exfoliate at the appropriate time. Individual incisors can also malerupt due to trauma to the developing permanent tooth bud. Cheek teeth or incisors that malerupt in a rotated manner will be associated with a greater incidence of periodontal disease due to the presence of abnormal spaces between teeth that can trap food material. Classes 2 and 3 Malocclusions A Class 2 malocclusion is a skeletal malocclusion in which the maxillae are longer in relation to the mandibles. The mandibles can either be too short or the maxillae can be too long. If the maxillary and mandibular central incisors are still in partial occlusion, but the maxillary central incisors are forward with the head in a downward, grazing, position, the malocclusion is considered an overjet. If, however, the maxillary and mandibular central incisors have no occlusion, the malocclusion is considered an overbite. An extreme case of overbite is one in which the incisive bone that the maxillary incisors are embedded in actually rotates downward this is referred to as a parrot mouth. A Class 3 malocclusion is the skeletal malocclusion that is the opposite of a class 2 malocclusion. In a Class 3 malocclusion, the maxillae are shorter in relation to the mandibles. When there is still some occlusion between the maxillary and mandibular central incisors with the head in a downward position, it is called an underjet. If there is no contact between the maxillary and mandibular central incisors, the malocclusion is termed an underbite. Some common names for underbite are monkey mouth or sow mouth. Class 4 Malocclusion A Class 4 Malocclusion is a malocclusion characterized by skeletal asymmetry of the skull. A common name is wry bite. Class 4 malocclusion is often associated with a diagonal incisor bite. The maxillary cheek teeth arcade on the side opposite the high mandibular incisor is often higher (the distance from the gingival line to the occlusal surface) than the other side. In addition, the palatal rugae will be asymmetrical from left to right, with the rugae on one side being more arched and the other side appearing flatter. Sometimes the skeletal asymmetry is subtle enough that it is missed on the preliminary external examination of the head but is discovered due to asymmetrically arched palatal rugae. Supernumerary Teeth Supernumerary teeth exist where there are additional teeth beyond the number normally present in the dental formulae of horses. The most common location of supernumerary teeth is the distal end of the maxillary cheek teeth rows. Supernumerary incisors are also possible and can be present in any incisor tooth position. Supernumerary teeth are often elongated because they do not have an opposing tooth to cause them to wear properly. Oligodontia Oligodontia is a term referring to the presence of fewer teeth than expected according to the equine dental formulae. Incisor oligodontia is relatively common and is likely due to destruction of a permanent incisor tooth

28 bud during its formation in a young horse. Incisor oligodontia can be associated with a diagonal incisor bite if the missing tooth is in the 03 position. Infundibular Cavities In dentistry, a cavity is defined as a defect in the dental hard tissue. An infundibular cavity refers to decreased cementum in the infundibulum of a maxillary cheek tooth. Infundibular cavities are staged according to which dental material(s) is affected using the modified Honma Classification System. (Table 2) The word caries refers to a cavity as the result of an infectious etiology. Caries are much less common in horses than in humans due to the low concentration of soluble sugars in the typical equid diet. However, caries in horses have been associated with feeding of a high concentrate ration or haylage, probably due to erosion of the dental hard tissues by dietary acids. Infundibular cavities are most commonly associated with the maxillary 09 s, the oldest permanent teeth in the horse s mouth. This fact dispels the commonly held belief that this condition in the cheek teeth is due to premature extraction of the deciduous cap because the first molars do not have a deciduous precursor. Table 2. Staging of infundibular cavities Stage 1: The cavity only involves the cementum Stage 2: The cavity penetrates through the cementum and into the enamel Stage 3: The cavity penetrates through the cementum and enamel and into the dentin Stage 4: The cavity affects the integrity of the entire tooth Stage 5: The cavity results in tooth loss Dental Fractures Dental fractures can occur in any of the horse s teeth. Teeth tend to fracture longitudinally most of the time. Uncomplicated fractures do not involve the pulp system of the tooth whereas complicated fractures do involve the pulp. Dental fractures are further classified based on whether they involve the exposed crown, reserve crown or root. Radiography is often necessary to determine the extent of the fracture. Bone Fractures Involving the Mouth Bone fractures involving the mouth can affect the maxillae, mandibles or incisive bone. The maxillary incisors are imbedded within the incisive bone so fracture in this area will usually affect these teeth. These fractures are usually a result of a kick to the mouth or the horse biting a horizontal surface then being spooked and pulling back. Incisor fractures in young horses without a complete adult incisor dentition are especially problematic because of damage to the still developing permanent tooth buds. Mandibular fractures are usually the result of trauma but can be predisposed by bone neoplasia. If the mandibular fracture is unilateral and non-displaced, the fracture will often heal well without surgical support unless a tooth is present in the fracture line. Teeth involved in mandibular fractures often have to be extracted at some point in order for the fracture to heal. If bone fractures involving the oral cavity have to be surgically repaired, care must be taken to not damage the reserve crown or tooth roots. Dental Dysplasia Dental dysplasia refers to the abnormal development of a tooth. Dental dysplasia can take several different forms including fusion in which multiple tooth buds form together into a single, abnormal tooth unit or gemination where a tooth bud splits during development, resulting in incomplete formation of two teeth. Additionally, dysplasia can present as a grossly malformed tooth. Dental dysplasia affects the incisors more commonly than the cheek teeth. Dysplastic teeth may need to be extracted if they do not occlude properly with their opposing tooth or if they result in periodontal disease.

29 Hard Tissue Neoplasia Hard tissue neoplasia can be divided into two types, those that affect dental tissues and those that affect bone. (Table 3) Diagnosis is rarely possible based upon gross characteristics and usually requires histopathology. Table 4: Oral Soft Tissue Pathology 1) Periodontal disease 2) Endodontic disease (pulp disease) 3) Oral soft tissue trauma 4) Oral foreign bodies 5) Oral soft tissue neoplasia Table 3. Oral hard tissue neoplasia Odontogenic origin neoplasia Ameloblastoma Ameloblastic odontoma Complex odontoma Compound odontoma Cementoma Osteogenic neoplasia Osteoma Osteosarcoma Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH) EOTRH is a disease of equine teeth that was first reported in Its etiology is unknown at this time although there are several hypotheses. EOTRH is a painful disease due to resorption of dental hard tissues resulting in exposure of the pulp system. It is associated with periodontal disease in many cases. Many cases also exhibit hypercementosis in which significant amounts of cementum are deposited on the apical end of the tooth, forming a large bulb in place of the normal tapered structure of the root. EOTRH most commonly affects the canine teeth and incisors but there have also been reports of cheek teeth involvement. Often, the first thing an owner notices is inability to nip a carrot or apple. Radiography is critical for evaluating the extent of involvement and developing the treatment plan which entails extraction of affected teeth. Oral Soft Tissue Pathology The possible pathologies that affect the oral soft tissues are summarized in Table 4. Periodontal Disease Periodontal disease refers to a continuum of pathology of the supporting structures of the teeth including the gingiva, periodontal ligament cementum and alveolar bone. Periodontal disease has been estimated and reported to affect 60% of horses. Periodontal disease is graded according to the degree of pathology. (Table 5) Although periodontal disease is not truly reversible, due to the hypsodont dentition of the horse the health of the soft tissue components affected can be improved although the lost alveolar bone will likely not improve. Table 5. Stages of Periodontal Disease Stage 0 (PD 0): normal Stage 1 (PD 1): gingivitis, no attachment loss Stage 2 (PD 2): early periodontal disease, <25% attachment loss Stage 3 (PD 3): moderate periodontal disease, <50% attachment loss Stage 4 (PD 4): advanced periodontal disease, >50% attachment loss Periodontal disease is progressive. Many times, malocclusions predispose to periodontal disease. For example, a transverse ridge opposing an interproximal space can act to wedge the opposing teeth apart, causing a disruption of periodontal anatomy allowing access of bacteria into deeper tissues. Malerupted teeth also cause disruption of the periodontal architecture. Most odontoplasty procedures indirectly serve to reduce conditions that favor periodontal disease. This in turn helps prolong the longevity

30 of the teeth. Periodontal probing is an important part of the oral examination to discover problems that could lead to tooth loss through periodontal disease. Endodontic (Pulp) Disease The pulp is the heart and brain of the tooth. Because of its importance, pathology of the pulp can result in the death of a tooth. The pulp can become diseased by one of 4 ways: anachoresis, indirect pulp exposure, direct pulp exposure or extension of periodontal disease to the apex of the tooth. Anachoresis is the result of bacterial invasion from the bloodstream localizing in the apex of the tooth. An indirect pulp exposure occurs either iatrogenically during odontoplasty or by a dental fracture in which the pulp is not directly exposed but the dentinal tubules that communicate with the pulp are opened to leave a pathway for the entrance of bacteria to the pulp. A direct pulp exposure occurs either iatrogenically during odontoplasty or by a dental fracture in which the pulp is directly exposed to the oral cavity. Periodontal disease that extends to the apex of the tooth can also result in bacterial access to the endodontic system. In the event of an indirect or direct pulp exposure, the odontoblasts can often deposit tertiary dentin rapidly enough to seal off the area of damage. Unfortunately, when the pulp becomes inflamed, it can take years for the damage to become clinically apparent. If the odontoblasts die, they will cease production of secondary (or tertiary) dentin. This can result in exposure of the pulp cavity with occlusal wear of the tooth. Earlier in the process, cessation of production of secondary dentin can be observed radiographically in equine incisors and canine teeth as a tooth with a larger pulp horn than that in its corresponding contralateral tooth. Unfortunately, there is too much overlap of structures in the cheek teeth for radiography to discern pulp pathology in these teeth. However, radiology can be helpful in the evaluation of the apical region of the cheek teeth in properly positioned views. Computed tomography is necessary to evaluate the endodontic system in the cheek teeth. Imaging should be used to evaluate the pulp system in the event that examination with a dental explorer reveals inconsistencies in a pulp remnant on the occlusal surface. Sinusitis, a condition characterized by inflammation and/or infection of the paranasal sinuses, can be primary or secondary in the horse. Secondary sinusitis is often related to a tooth root infection that extends into the adjacent sinus, although fractures or sinus cysts can also be causative. The alveoli of the 08 and 09 teeth usually sit within the rostral maxillary sinus and the alveoli of the 10 and 11 teeth usually sit within the caudal maxillary sinus. Extraction of the affected tooth causing the sinusitis is usually necessary. Secondary Soft Tissue Trauma Soft tissue trauma is often associated with laceration or ulceration of the cheek mucosa or the tongue by sharp enamel points of the teeth. The degree of soft tissue trauma does not always correlate with severity of enamel points. Some horses may be predisposed due to narrow intermandibular width or tight cheeks. Soft tissue trauma is the primary indication for teeth floating, odontoplasty of the sharp enamel points on the edges of the cheek teeth. Oral Foreign Bodies Oral foreign bodies can also cause trauma to the soft tissues of the mouth. Cases have been reported in which a stick or woody weed stem lodges between the maxillary cheek teeth against the palate causing pressure necrosis. Fibrous feed materials can become trapped in valved diastema between cheek teeth, promoting periodontal disease. Grass seeds (awns) can also cause trauma by sticking into the gingival sulcus or oral mucosa, resulting in inflammation. Gingivitis induced by grass seeds or coarse fiber seems to be most common in the late winter when horses are fed poor quality hay that is overly mature and contains a lot of stems and seed heads. Metallic foreign bodies can sometimes be found in oral soft tissues,

31 especially the tongue. Swelling of the tongue should prompt a clinician to obtain a dorsoventral radiograph of the head to look for metallic foreign bodies. Soft Tissue Neoplasia Neoplasia of the soft tissues of the mouth presents in many shapes and sizes. (Table 6) As with the diagnosis of most neoplasia, histopathology of a biopsy or excised mass is necessary for a specific diagnosis. Prognosis and treatment options vary with the type of neoplasia. Submission to a pathologist that reads a lot of oral histopathology specimens is important to get an accurate diagnosis. Most soft tissue neoplastic processes affecting the head carry a poor prognosis due to their locally invasive nature. Recommended Reading Dixon PM, Dacre I. A review of equine dental disorders. The Vet Journal 2005; 169: Dixon PM, et al. Equine dental pathology. In Easley J, Dixon P, Schumacher J. Equine Dentistry, 3 rd ed Pp Tremaine H, Casey M. A modern approach to equine dentistry 2. Identifying lesions. In Practice 2012; 34: Table 6. Soft Tissue Oral Neoplasia Squamous cell carcinoma Sarcoid Fibroma / fibrosarcoma Melanoma Ossifying fibroma Myxoma complex Hemangiosarcoma Salivary adenocarcinoma Lymphosarcoma / lymphoma Hemangiosarcoma Non-neoplastic masses epulis, papilloma, dental cysts Summary There is a wide range of pathological processes that can affect the horse s oral cavity and adjacent structures of the head. Focusing on the teeth and failing to evaluate the adjacent structures in the oral cavity can result in a failure to resolve pain. A clinician who understands the range of pathologies that can afflict the equid mouth will be more successful at minimizing pain and maximizing the function of the masticatory apparatus.

32 Equine Oral Examination: A Step-By-Step Approach Bruce P. Whittle, DVM Honey Creek Veterinary Hospital Trenton, Missouri brucewhittle@gmail.com Introduction The comprehensive oral examination of a horse is the first step in any equine dentistry procedure. Just as in any other medical discipline, successful treatment depends upon an accurate diagnosis. It is important to perform the examination in a systematic manner to avoid missing potential problems. The clinician should also realize this is an oral examination, not just a dental examination. There are many important soft tissue structures in the mouth that can either have pathology or can indicate pathology of the dental hard tissues. When Should a Horse Have an Oral Examination?? A horse should have an oral examination every time there is an opportunity. This does not always mean a sedated complete examination. When I am examining a horse for a medical problem, Coggins testing or a certificate of veterinary inspection, I will do a brief oral examination. I am sure to tell the owner it is NOT a thorough examination but I will often find something that supports recommending a sedated, thorough oral examination. Horses less than five years of age should have a thorough examination twice per year until all of the permanent teeth have erupted into their occlusal positions. Due to the eruption and exfoliation processes occurring during this time, malocclusions are relatively common and are better addressed early. Horses with a permanent dentition benefit from an annual thorough examination unless they have pathology that has been previously diagnosed that requires more frequent examination and treatment, often 2 3 times per year. Requirements for a Thorough Oral Examination It is important to perform the examination in a safe area with good footing for the patient and the clinician. An area out of direct sunlight allows better visualization of the oral cavity. If you must perform an examination in direct sunlight, make sure the sun is to your back so the horse s mouth is not backlit. A footing surface that does not become slick with water used to rinse the mouth is also important to help prevent the sedated, ataxic patient from slipping and falling. As with any veterinary procedures, there is a minimum amount of equipment required for a thorough oral examination: 1) Knowledge 2) Method of patient restraint 3) Full-mouth speculum 4) Oral lavage system 5) Bright light source speculum mounted or headlamp 6) Cheek retractor 7) Rigid dental mirror or oral endoscope 8) Periodontal probe, explorer and dental picks 9) Oral examination / treatment chart Before a clinician can perform an oral examination, he or she should have a thorough knowledge of the histologic and threedimensional anatomy of the teeth. Understanding how the structures of the oral cavity function together to acquire, process and transport feed material helps guide the

33 development of a treatment protocol to avoid causing harm. A clinician should try to determine the cause for any pathology to be able to address the cause instead of just the result. This requires a careful inspection of the opposing and adjacent teeth and soft tissues instead of just identifiying a hook, step, etc. Comprehension of how oral pathology develops allows a clinician to provide better care. Full-mouth specula come in several different types. The oldest design that is still in widespread use is the Macpherson style. It relies on a ratcheting tooth system with 5 to 7 teeth on each side of the speculum frame. This style can be more difficult to open but is the least expensive type available. They can be purchased in different sizes, but many clinicians have successfully used a Macpherson speculum in horses ranging from minis to Drafts. The incisor plates on Macpherson specula are usually interchangeable so that cow bars can be used in their place to work on horses with malaligned incisors such as those with a parrot mouth. The cow bars sit in the bars of the horse s mouth and should be padded to avoid causing soft tissue trauma. Another popular speculum has a somewhat similar design but has many more notches on the lower frame of the speculum that allows for a more infinite adjustment. Other specula have a larger frame then have the adjustment system on the front of the speculum. Several specula have a screw mechanism, placed either at the front of the speculum or on either side, for adjusting the opening of the incisor plates. Personal preference is definitely the key when it comes to a speculum. The best recommendation is to try before you buy. Participation in an equine dentistry wet lab where you can try several different models is especially valuable. A method to lavage the oral cavity to remove feed material is essential for being able to detect pathology. While many clinicians use a ml dosing syringe, I prefer a setup with a rubber tipped wand attached to a garden hose. (Figure 1) This gives a more focused spray with higher pressure that allows better cleaning between the teeth. It is easily assembled from parts obtained from a farm store. Figure 1. Homemade oral lavage system Bright light sources for equine dentistry come in different varieties. The two basic types are lights mounted to a headband worn by the clinician or lights mounted to the speculum. Again, personal preference applies. The advantages of a speculum-mounted light are that clients can easily see pathology because the light is fixed and you can take intraoral photographs more easily because the oral cavity is consistently illuminated. On the other hand, head mounted lights are often brighter and can be more easily focused on the site of interest within the mouth. It is more difficult to show pathology to a client when using a head mounted light. LED lights for either mounting type are becoming more popular because they run cooler and last longer with a battery supply than a halogen light. Some LED lights can cause a color shift for the operator that casts a bluish tint to the tissues. While not necessary (you can use your fingers), a cheek retractor can facilitate visualization of the vestibular pouch to examine the percentage of overlap of the maxillary and mandibular cheek teeth arcades as well as allow observation of the cheek teeth arcades as they are moved through a lateral excursion. A cheek retractor can be as simple as an L shaped piece of flat metal that is rigid enough to hold the cheek away from the teeth. An intraoral mirror or rigid oral endoscope is an essential instrument for every oral examination. The typical view a clinician is

34 afforded of the horse s oral cavity is through a relatively small opening on the cranial end of the oral cavity. Side views or right angle views of the cheek teeth are not possible without some type of mirror or scope. The instruments allow for visualization at a right angle to better observe the occlusal surfaces as well as the vestibular and lingual surfaces of the teeth adjacent to the cheeks or tongue. These visualization instruments are also valuable when performing treatments to better view pathologic diastema for debridement, ensuring molar spreaders are placed accurately in the interproximal space and visualizing the alveolus after extraction of a tooth for remaining roots or other tooth fragments. Mirrors with different head sizes and shapes as well as at differing angles in relation to the instrument shaft can be helpful for visualizing different areas of the mouth. A common complaint with mirror usage is fogging of the mirror. The general problem is using a cold mirror in the warm mouth of the horse. Fogging of a mirror can be minimized by submerging the mirror in a bucket with warm water containing chlorhexidine solution. Alternately, the mirror can be temporarily warmed on the horse s tongue. Others spray the mirror with alcohol but I do not like this option as well because alcohol dripping into a periodontal pocket would not be my idea of fun. A periodontal probe is a thin, blunttipped instrument with graduated markings used for evaluating the depth of the gingival sulcus. (Figure 2) The probe should not be dragged along the floor of the sulcus but rather moved in a series of little hops to avoid traumatizing the tissue. Figure 3. Periodontal probing of the gingival sulcus showing a probe with Williams markings. The normal gingival sulcus should be less than 3 5 mm. (Figure 3) You want to purchase a periodontal probe that has a thin tip that can easily enter the sulcus. Some of the probes on the market are too thick for use except as a dental pick. While it is ideal to probe the gingival sulcus around each tooth, a clinician should, at minimum, learn to recognize gingival anomalies and probe these areas. If the horse s tongue is particularly active, it can cause breakage of the fragile probe. Use of diazepam or midazolam can facilitate the periodontal examination but their effects are relatively short-lived so the examination should be quick and efficient. A dental explorer should have a sharp, springy tip. (Figure 4) Figure 2. Periodontal probes Figure 4. Dental explorer