Providing effective pain control is one of the

Transcription

1 Is the mandibular nerve block passé? Stanley F. Malamed, DDS Providing effective pain control is one of the most important aspects of dental care. Patients rate a dentist who does not hurt and one who can give painless injections as the second and first most important criteria in evaluating dentists. 1 The ability to provide consistently profound anesthesia for dental procedures in the mandible remains elusive. This inability is even more of a problem when infected teeth, primarily mandibular molars, are involved. On the other hand, although anesthesia of maxillary teeth occasionally is difficult to achieve, it rarely is an insurmountable problem. One reason is that the cortical plate of bone overlying maxillary teeth normally is thin, thus allowing for better diffusion of the local anesthetic when it is administered by means of supraperiosteal injection. The posterior superior alveolar, middle superior alveolar, anterior superior alveolar and anterior middle superior alveolar 2 nerve blocks are alternatives to infiltration. The substantially higher failure rate for mandibular anesthesia compared with that for maxillary anesthesia is related to a number of factors including, but not limited to, the thickness of the cortical plate of bone of the body of the adult mandible, which precludes the use of simple infiltration techniques; the thickness of soft tissue through which the needle must penetrate to access the inferior alveolar nerve (IAN), which leads to the inability to locate the IAN consistently 3 ; and the possibility of accessory innervation. Use of the mandibular infiltration technique can be successful if the patient has a full primary dentition. 4,5 Once mixed dentition develops, it is thought that the mandibular cortical plate of bone has thickened to such a degree that the infiltration anesthetic technique might not be effective, which can lead to a recommendation that mandibular nerve block techniques be used. 6 The thickness of the soft tissue through which the needle must pass to gain access to the IAN is 20 to 25 millimeters in the typical adult. Because dental needles have a bevel, they tend to deflect as they are advanced ABSTRACT Background. Providing effective pain control is a critical part of dental treatment, yet achieving consistently reliable anesthesia in the mandible has proved elusive. The traditional inferior alveolar nerve block (IANB) has a high failure rate; for example, the failure rate in lateral incisors is 81 percent. As a consequence, new approaches and techniques have been developed. The purpose of this supplement to The Journal of the American Dental Association is to determine whether the mandibular nerve block has become passé. Conclusions. The high failure rate of the IANB can be frustrating for dentists and lead to discomfort for the patient during treatment. The reasons for this high failure rate include thickness of the cortical plate of bone in adults, thickness of the soft tissue at the injection site leading to increased needle deflection, the difficulty of locating the inferior alveolar nerve and the possibility of accessory innervation. Although the IANB can be unreliable, it is used commonly to provide mandibular anesthesia. Clinical Implications. Pain control is an essential part of dental treatment. Alternative injection techniques and devices that can help increase the success rate of mandibular anesthesia are available. Key Words. Inferior alveolar nerve; inferior alveolar nerve block; mandibular block; Gow-Gates mandibular nerve block; Akinosi-Vazirani nerve block; articaine hydrochloride; periodontal ligament injection; intraosseous anesthetic injection. JADA 2011;142(9 suppl):3s-7s. Dr. Malamed is a dentist anesthesiologist and a professor of anesthesia and medicine, Herman Ostrow School of Dentistry of USC, 925 W. 34th St., Los Angeles, Calif , malamed@usc.edu. Dr. Malamed also is the guest editor of this supplement. Address reprint requests to Dr. Malamed. JADA 142(9 suppl) September S

2 Figure 1. Distribution of anesthesia after inferior alveolar nerve block. Reprinted with permission of Elsevier from Malamed. 3 All rights reserved. through soft tissues. Thinner needles (for exam - ple, 30 gauge) deflect considerably more than do thicker needles (for example, 25 or 27 gauge), which leads to greater inaccuracy during administration of an injection. 7 There is an absence of consistent landmarks to help dentists locate the proper site for needle penetration. Numerous approaches to performing the IAN block (IANB) have been described The failure rates for the IANB, which commonly but inaccurately is referred to as the mandibular nerve block, are high. For example, the failure rate in lateral incisors is 81 percent. 11 The higher failure rate in the incisor region might be caused by collateral innervation from the contralateral side. 12 Not only is locating the IAN difficult, but the results of studies in which investigators used ultrasonography 13 and radiography 14,15 to locate the inferior alveolar neurovascular bundle or mandibular foramen indicated that accurately injecting the needle did not guarantee successful pain control. 16 The central core theory best explains this problem. 17,18 Nerve fibers on the periphery of the nerve bundle (mantle fibers) supply the molars, whereas the more centrally located nerve fibers (core fibers) innervate incisors. Therefore, local anesthetic solution deposited close to the IAN but not in the optimal place may diffuse and block the outermost fibers but not those located more centrally, which can lead to incomplete mandibular anesthesia. This difficulty in providing consistently reliable anesthesia in the mandible can be frustrating for most dentists. The term mandibular slump accurately describes the problem faced by dentists when, for no apparent reason, they endure periods of almost absolute failure when performing an IANB. Patients whose dentists were able to provide mandibular anesthesia to them easily now have to undergo multiple IANBs. The problem soon may become psychological, leading to dentists doubting their abilities. Considering that one-half of all dental treatment is in the mandible, the inability of dentists to use the IANB to provide consistently reliable pain control is a problem that needs to be solved. This inconsistency has led to the development of alternatives to the traditional IANB. Among these techniques are the Gow-Gates mandibular nerve block, 19 Akinosi-Vazirani (closed-mouth) mandibular nerve block, 20 periodontal ligament (PDL) injection 21 and intraosseous (IO) anesthetic injection. 22 Recently, use of the mandibular infiltration technique in adult patients has received considerable attention. 12 Although all techniques have some advantage over the traditional IANB, none is without faults and contraindications. This supplement to The Journal of the American Dental Association will look critically at the traditional IANB. It also will include reviews of alternative mandibular nerve block techniques and seek to answer the question regarding whether the mandibular nerve block is passé. INFERIOR ALVEOLAR NERVE BLOCK The IANB is the most frequently used and possibly the most important injection technique in dentistry other than infiltration. It also can be difficult to perform and has the highest percentage of clinical failures even when it is administered properly. 11,23 The technique commonly used in dentistry is the Halsted approach, named for William Stewart Halsted, MD, who, in 1884, administered the first documented injection of a local anesthetic (cocaine with epinephrine) in a patient for a surgical procedure. 24 The injection was the IANB. Nerves blocked when the IANB is successful are the inferior alveolar, incisive, mental and, commonly, lingual. The distribution of anesthesia (Figure 1) includes the mandibular teeth to the midline, body of the mandible, inferior portion of the ramus, buccal mucoperiosteum, mucous membrane anterior to the mental foramen (mental nerve), anterior two-thirds of the tongue and floor of the oral cavity (lingual nerve), and the lingual soft tissues and periosteum (lingual nerve). Indications for performing an IANB include procedures on multiple teeth in one mandibular quadrant, procedures on the buccal periodontium anterior to the first molar and procedures on the lingual periodontium. Contraindications to performing an IANB include infection or acute inflammation at the needle penetration site (rare), as well as patients who are more likely to ABBREVIATION KEY. IAN: Inferior alveolar nerve. IANB: Inferior alveolar nerve block. IO: Intra - osseous. PDL: Periodontal ligament. 4S JADA 142(9 suppl) September 2011

3 Figure 2. Height of the inferior alveolar nerve block is established by visualizing a line (arrow) through the coronoid notch to the posterior border of the pterygomandibular raphe. Adapted with permission of Elsevier from Malamed. 3 All rights reserved. bite their still-numb lip or tongue after treatment is concluded. An advantage of performing an IANB is that one injection provides anesthesia to a wide area, which is useful when providing treatment throughout a quadrant. There are several disadvantages to performing an IANB. One is the wide area of anesthesia; the IANB is not indicated for localized procedures. Other disadvantages are that there is a substantial rate of inadequate anesthesia (as high as 81 percent); intraoral landmarks are not consistently reliable; there is a positive aspiration rate of 10 to 15 percent, which is the highest for all intraoral injection techniques 25 ; lingual and lower lip anesthesia can occur, which is uncomfortable for many patients and can be dangerous because it can lead to self-inflicted soft-tissue trauma in certain people 26 ; partial anesthesia is possible where a bifid IAN and bifid mandibular canals are present 27 ; and crossinnervation can occur in the lower anterior region, which may lead to incomplete anesthesia. For the IANB technique, a long dental needle (approximately 32 mm) is recommended for use in adult patients; a 25-gauge needle is preferred, but a 27-gauge needle is acceptable. Short needles and 30-gauge needles should not be used because of the slight possibility of needle breakage. 28 The target for the deposition of the local anesthetic is the IAN as it passes down from the foramen ovale toward but before it enters the mandibular foramen. The site of needle penetration is the mucous membrane on the medial (lingual) side of the mandibular ramus at the intersection of two lines: one horizontal, representing the height of needle insertion, and one vertical, representing the anteroposterior plane of injection. The patient should be in a supine position or semisupine, if necessary, with his or her mouth opened wide to allow for greater visibility of and access to the injection site. Figure 3. Locating insertion point three-quarters of the anteroposterior distance from the coronoid notch to the pterygomandibular raphe. Figure 4. Posterior border of the mandibular ramus can be seen intraorally by using the pterygomandibular raphe as it bends up toward the maxilla. Reprinted with permission of Elsevier from Malamed. 3 All rights reserved. When locating the needle penetration site, consider the height of the injection, the anteroposterior placement of the needle and the depth of penetration. To determine the height of the injection, place your index finger or thumb in the coronoid notch. An imaginary line extends posteriorly from the fingertip in the coronoid notch to the deepest part of the pterygomandibular raphe (Figure 2). This imaginary line should be parallel to the occlusal plane of the mandibular molars. In most patients, this line lies 6 to 10 mm above the occlusal plane. The needle insertion point lies three-quarters of the anteroposterior distance from the coronoid notch to the deepest part of the pterygomandibular raphe (Figure 3). The posterior border of the mandibular ramus can be seen intraorally by using the pterygomandibular raphe as a guide as it bends up toward the maxilla (Figure 4). An alternative method of approximating the width of the ramus is to place your thumb on the coronoid notch and your index finger extraorally on the posterior border of the ramus and estimate the distance between these two points. After properly preparing the tissue for needle penetration, place the barrel of the syringe in the corner of the mouth on the contralateral side, usually over the premolars (Figure 5). Needle penetration occurs at the intersection of two points. The first point is along the horizontal line from the coronoid notch to the deepest part of the pterygomandibular raphe as it ascends toward the palate as described above (Figure 4). The second point is on a vertical line through the first point about three-quarters of the distance from the anterior border of the ramus. The intersection of these two points determines the anteroposterior site of the injection (Figure 3). Advance the needle slowly until you contact bone. The average depth of penetration at which you will contact the bone is 20 to 25 mm, approximately two-thirds to three-quarters of the length of a long dental JADA 142(9 suppl) September S

4 Figure 5. A. The syringe barrel is in the corner of the mouth, usually over the premolars. B. Placement of the needle and syringe for an inferior alveolar nerve block. Reprinted with permission of Elsevier from Malamed. 3 All rights reserved. Figure 6. A. The needle positioned too far anteriorly on the ramus. B. The syringe barrel repositioned forward over the lateral incisor or canine. Reprinted with permission of Elsevier from Malamed. 3 All rights reserved. Figure 7. A. The needle inserted too far and not making contact with the bone. B. The syringe barrel repositioned over the molars. Reprinted with permission of Elsevier from Malamed. 3 All rights reserved. needle. When you contact the bone, withdraw the needle approximately 1 mm to prevent subperiosteal injection. Then perform an aspiration test and, if aspiration is negative, slowly deposit 1.5 milliliters of anesthetic across a minimum of 60 seconds. Because of the high incidence of positive aspiration and the natural tendency to deposit solution too rapidly, I recommend a sequence of slow injection, reaspiration, slow injection. Withdraw the syringe, and when approximately one-half its length remains within the tissue, perform the aspiration test again. If aspiration is negative, deposit 0.2 ml of the remaining solution to anesthetize the lingual nerve. In most patients, this deliberate injection for lingual nerve anesthesia is not necessary because local anesthetic from the IANB anesthetizes the lingual nerve. After removing and recapping the needle, return the patient to the upright or semiupright position. The depth of penetration to contact the bone can help determine the approximate location of 6S JADA 142(9 suppl) September 2011 the needle tip in relation to the IAN. As I stated above, the average depth of penetration to contact with the bone is 20 to 25 mm, approximately twothirds to three-quarters of the length of the long dental needle. If bone is contacted prematurely (less than onehalf the length of a long dental needle in the average-sized adult), the needle tip is located too far anteriorly (laterally) on the ramus. To correct this problem, withdraw the needle slightly but do not remove it from the tissue. Move the syringe barrel toward the front of the mouth, over the canine or lateral incisor on the contralateral side. The needle tip now is located more posteriorly in the mandibular sulcus (Figure 6). Advance the needle until a more appropriate depth of insertion is obtained. If bone is not contacted, the needle tip usually is located too far posteriorly (medially). To correct this prob - lem, withdraw the needle slightly, leaving approximately one-fourth of its length in the tissue, and reposition the syringe barrel more posteriorly over the mandibular molars (Figure 7). Advance the needle again 20 to 25 mm until the bone is contacted. The subjective signs and symptoms of anesthesia include tingling or numbness of the lower lip, which indicates anesthesia of the mental nerve, a terminal branch of the IAN. These signs and symptoms are good indicators that the IAN is anesthetized, although they are not reliable indicators of the depth of anesthesia. Tingling or numbness of the tongue indicates anesthesia of the lingual nerve, a branch of the posterior division of the mandibular nerve. Softtissue anesthesia usually occurs as a result of IANB but may be present in the absence of anesthesia of the IAN. Use of an electric pulp tester that elicits no response to maximal output on two consecutive tests conducted at least two minutes apart is a reliable test of successful pulpal anesthesia in nonpulpitic teeth A common cause of absent or incomplete anesthesia after an IANB is performed is depositing the anesthetic too low (below the mandibular foramen). To correct this problem, reinsert the needle approximately 5 to 10 mm above the previous injection site. Another cause is that the anesthetic may be deposited too far anteriorly (laterally) on the ramus. This problem can be diagnosed by means of a lack of anesthesia

5 except at the injection site and by evaluating the minimum depth of needle penetration before contact with bone (for example, a long needle usually is less than one-half of the way into the tissue). To correct this problem, redirect the needle tip posteriorly. Lastly, there may be accessory innervation to the mandibular teeth. The primary symptom is isolated areas of incomplete pulpal anesthesia in the incisors and molars, most commonly the mesial portion of the mandibular first molar. The PDL anesthetic injection technique or the IO anesthetic injection technique may be used to correct this problem. CONCLUSIONS Failure rates are high for profound pulpal anesthesia after a traditional IANB is performed in nonpulpally involved teeth. This problem has led to the development of alternative techniques, including the Gow-Gates mandibular nerve block, Akinosi-Vazirani closed-mouth mandibular nerve block, PDL anesthetic injection and IO anesthetic injection. The introduction of articaine hydrochloride (in 1985 in Canada and in 2000 in the United States) has spurred interest in the use of this local anesthetic by means of infiltration in the adult mandible. The articles in this supplement to The Journal of the American Dental Association review these alternative mandibular anesthetic techniques. Dr. Haas 32 reviews the Gow-Gates mandibular nerve block and the Akinosi-Vazirani closedmouth mandibular nerve block. Dr. Moore and colleagues 33 present alternative techniques for providing local anesthesia in the mandible: the PDL anesthetic injection and the IO anesthetic injection. Dr. Meechan 34 describes the use of the infiltration anesthetic technique to anesthetize mandibular teeth in adults and explores its mechanism of action. So, is the mandibular nerve block passé? Maybe not yet, but there are a number of alternative anesthetic techniques available that can help dentists provide treatment comfortably in the mandibular arch. Disclosure. Dr. Malamed is a consultant to Septodont, Lancaster, Pa., and OnPharma, Los Gatos, Calif. 1. de St Georges J. How dentists are judged by patients. Dent Today 2004;23(8):96, Friedman MJ, Hochman MN. The AMSA injection: a new concept for local anesthesia of maxillary teeth using a computercontrolled injection system. Quintessence Int 1998;29(5): Malamed SF. Techniques of mandibular anesthesia. In: Handbook of Local Anesthesia. 5th ed. St. Louis: Elsevier Mosby; 2004: Oulis CJ, Vadiakis GP, Vasilopoulou A. The effectiveness of mandibular infiltration compared to mandibular block anesthesia in treating primary molars in children. Pediatr Dent 1996;18(4): Sharaf AA. Evaluation of mandibular infiltration versus block anesthesia in pediatric dentistry. ASDC J Dent Child 1997;64(4): Malamed SF. Local anesthetic considerations in dental specialties. In: Handbook of Local Anesthesia. 5th ed. St. Louis: Elsevier Mosby; 2004: Robison SF, Mayhew RB, Cowan RD, Hawley RJ. 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Needle breakage: incidence and prevention. Dent Clin North Am 2010;54(4): Robertson D, Nusstein J, Reader A, Beck M, McCartney M. The anesthetic efficacy of articaine in buccal infiltration of mandibular posterior teeth. JADA 2007;138(8): Dreven LJ, Reader A, Beck M, Meyers WJ, Weaver J. An evaluation of an electric pulp tester as a measure of analgesia in human vital teeth. J Endod 1987;13(5): Certosimo AJ, Archer RD. A clinical evaluation of the electric pulp tester as an indicator of local anesthesia. Oper Dent 1996;21(1): Haas DA. Alternative mandibular nerve block techniques: a review of the Gow-Gates and Akinosi-Vazirani closed-mouth mandibular nerve block techniques. JADA 2011;142(9 suppl):8s-12s. 33. Moore PA, Cuddy MA, Cooke MR, Sokolowski CJ. Periodontal ligament and intraosseous anesthetic injection techniques: alternatives to mandibular nerve blocks. JADA 2011;142(9 suppl):13s-18s. 34. Meechan JG. The use of the mandibular infiltration anesthetic technique in adults. JADA 2011;142(9 suppl):19s-24s. JADA 142(9 suppl) September S