THE APPLIED ANATOMY OF THE PTERYGOMANDIBULAR SPACE. B. C. W. BAgKnR AND P. L. DAVIES Department of Anatomy, University of Sydney.

Transcription

1 British Journal of Oral Surgery (I972), xo, THE APPLIED ANATOMY OF THE PTERYGOMANDIBULAR SPACE B. C. W. BAgKnR AND P. L. DAVIES Department of Anatomy, University of Sydney. THE pterygomandibular space is the site of injection for nerve block of the inferior alveolar and lingual nerves. The occasional failure of this injection to achieve fully the required effects may be attributable, in some instances, to inadequate recall of the disposition of structures within the space. The purpose of this communication is to review the anatomy 0fthe pterygomandibular space, with emphasis FIG. I The puncture point for block anaesthesia of the inferior alveolar nerve is lateral to the pterygomandibular fold in the pterygotemporal depression. (By permission of Prof. M. Jolly.) on structures pierced by or related to the injecting needle (Fig. i). The anatomy of a region can be comprehended best by viewing the area in three dimensions and, accordingly, photographs of dissections of this space, performed by the authors from various aspects, are included. BOUNDARIES OF THE PTERYGOMANDIBULAR SPACE The pterygomandibular space is a cleft between the pterygoid musculature and the ramus of the mandible. Anteriorly the space is continuous with a superior recess between the lateral pterygoid muscle and temporalis. The medial surface of the ramus has certain notable features (Fig. 3). The lingula, which is variably developed, guards the mandibular foramen near the 43

2 44 BRITISH JOURNAL OF ORAL SURGERY centre of the ramus. The sulcus colli is a deep channel leading into the foramen but as it is traced up and back towards the neck of the condyle it becomes progressively shallower. Bone is prominent in front of the sulcus forming the crista retrornandibular vein s tylomc!ndibu~nembr ane styloid process parotid gland~ ~ ~ rnedial pterygoid jl interpterygoid fascia _~ temperopterygoid fascia rnasseter ---- temporalis tendons- \ ---- pterygomandibular raph buccal fat p a d ~ ~ buccinator - - ~ FIG. 2 Diagram of the pterygomandibular space in transverse section illustrating the fascial sheets which'bolmd the area. (After Dempster (1966).) 0! SUBMAXILLARY FIG. 3 The medial surface of the mandible. Surface features are highlighted in this diagram and labelled in conformity with modern physical anthropological terminology. (By permission of S. L. Larnach and N. W. G. Macintosh.) FOSSA endocondyloidea, and above the lingula this merges with the crista endocoronoidea to form an eminence, the toms triangularis. ' Superiorly, the triangular space is roofed by the inferior head of the lateral pterygoid muscle. Medially lies the lower part of the medial pterygoid as it

3 THE APPLIED ANATOMY OF THE PTERYGOMANDIBULAR SPACE 45 inclines infcrolatcrally and slightly posteriorly to insert into the ramus below the mylohyoid groove. The medial wall of the space is completed by intcrpterygoid fascia (Fig. 2)--a sheet of fibrous tissue wl~ch is of significance in limiting the spread of anaesthetic solution deposited in the pterygomandibular space. This interpterygoid fascia extends from the base of the skull, lying on the medial surface of lateral pterygoid muscle and lateral to the medial pterygoid muscle. Posteriorly it spans the interval between the diverging margins of the two ptcrygoid muscles (Fig. I3). It is attached to the mandible above the upper border of medial ptcrygoid insertion and to the lingula and the margin of the mandibular foramcn. The line of attachment continues backwards and upwards in a curve to the posterior border of the mandibular ramus, extending to the neck of the condyle. Here it blends with the stylomandibular membrane (Fig. 2). A fascial pouch is thus formed in which lies the inferior alveolar neurovascular bundle and the lingual nerve (Fig. 4). The portion of the intcrptcrygoid fascia extending from the region of the spine of the sphenoid and the petrotympanic fissure to the lingula is considerably thickened and is termed the sphenomandibular ligament. The dissection from the posterior aspect illustrates how the postcro-superior part of the interptcrygoid pouch is pierced adjacent to the condylar neck by the auriculotemporal nerve, the maxillary artery and vein from above downwards (Fig. I3). The anterior part of the interptcrygoid fascia is usually flimsy, but it may be reflected to form a septum between the pterygoids and the fascia on the deep surface of the temporal muscle. When well developed, this so-called temporoptcrygoid fascia would constitute the anterior boundary of the ptcrygomandibular space and would materially aid in confining injected anaesthetic solution within the pouch (Fig. 2). In a proportion of cases, the tcmporoptcrygoid fascia is located further posteriorly and hence divides the ptcrygomandibular space into an anterior and a posterior compartment. Anteriorly, the entrance into the pterygomandibular space is an interval between deep tendon of tcmporalis externally and medial ptcrygoid internally. The deep tendon of temporalis, passing from skull base to its tendinous insertion along the temporal crest (crista pharyngea) bulges inwards and this narrows the entrance considerably (Fig. 12). Draped across the entrancc and in front of the above muscles is buccinator. It is not uncommon to find that buccinator is more aponeurotic than muscular as it curves around behind the third molar tooth cn route to the hamulus and to enter into formation of the ptcrygomandibular raphe with superior constrictor (Barker, I969). In addition, the temporobuccinator band may be well developed as it spreads over the postcrolatcral surface of buccinator to become continuous with fibro-clastic tissue clothing the temporal tendons (Fig. i2). The entrance to the ptcrygomandibular space may therefore be guarded by fibrous tissue of varying density and this may offer slight resistance to an injecting needle. The tendinous anterior border of the medial pterygoid muscle, which extends from its attachment to the lower border of the palatine tubercle to the internal surface of the mandible, bears a changing relationship to the pterygomandibular fold. Since the raphe is attached superiorly to the hamulus of the medial pterygoid plate, it is clear that the medial pterygoid muscle lies wholly lateral to the raphe at the level of the maxillary tuberosity. But as the raphe passes down to be attached to mandible behind the third molar tooth, it necessarily follows that the anterior border of the muscle comes to lie more nearly behind the raphe in its lower extent.

4 46 BRITISH JOURNAL OF ORAL SURGERY CONTENTS OF THE PTERYGOMANDIBULAR SPACE (Figs. 4, 5, 6, 7, 8, 9, IO, II) The maxillary artery enters the space through the interpterygoid fascia and it initially lies in close relation to the neck of the condyle. It winds its way upwards towards the pterygomaxillary fissure passing either superficial or deep to lateral pterygoid and several branches arise during its progress through the upper ~Xq IAV IAA /AN IF /N FIG. 4 Fm. 5 Fig. 4.--Transverse histological section of the structures lying in the region of the sulcus colli immediately above the lingula. Note that the interpterygoid fascia in this specimen gains attachment to the mandible behind the lingual nerve. The inferior alveolar nerve, artery and vein(s) classically lie in this order from before backwards. H. & E. x 8. (By permission of P. L. Shields.) Fig. 5.--Dissection of structures following transverse section at the level of the atlas. The needle, which has been inserted according to the 'direct thrust' technique is seen to contact bone forming the posterior wall of the sulcus colli. KEY TO FIGS. 4 TO 14 A = atlas; ATN = auriculotemporal nerve; BM = buccinator muscle; BN = buccal nerve; BP = buccal pad; CTN = chorda tympani nerve; IAA = inferior alveolar artery; IAN = inferior alveolar nerve; IAV = inferior alveolar vein; ICA = internal carotid artery; IF = interpterygoid fascia; IJV = internal jugular vein; LN -- lingual nerve; LPM = lateral pterygoid muscle; LPP = lateral pterygoid plate; MA = maxillary artery; NIC = mandibular condyle; MHN -~ mylohyoid nerve; MM = masseter muscle; MN = masseteric nerve; = medial pterygoid muscle; MPP = medial pterygoid plate; MV = maxillary vein; N to = nerve to medial pterygoid muscle; ON = optic nerve; PG = parotid gland; RV = retromandibular vein; SC = sulcus coui; SG--submandibular gland; SML = sphenomandibular ligament; SS = spine of sphenoid; ST = sympathetic trunk; T = tongue; TBB = temporobuccinator band; TM (DT) = temporalis muscle deep tendon; TM (ST) = temporalis muscle superficial tendon.

5 THE APPLIED ANATOMY OF THE PTERYGOMANDIBULAR SPACE 47 part of the pterygomandibular space. The branches which may pass through the space comprise the middle meningeal artery, ascending deep to the lateral pterygoid muscle; the posterior deep temporal artery passing up between the sigmoid fascia and the lateral pterygoid muscle, which it supplies; the inferior alveolar artery descending to the mandibular foramen where it comes into posterior relation with the inferior alveolar nerve; a lingual branch which may be given off from either the maxillary artery or the inferior alveolar branch to accompany the lingual nerve and, in addition, various small muscular branches. The pterygoid plexus of veins surrounds the inferior head of the lateral pterygoid muscle and is confluent posteriorly with a plexus surrounding the MN LPM BN IAN LN BM LPM IAN LN SG FIG. 6 FIG. 7 Fig. 6.--Dissection of structures following coronal section through the region of the pterygopalatille fossa and the coronoid process. Note the close relation of the lingual nerve to the inserted needle. Fig. 7.--D eeper dissection of the specimen shownin Figure 6, exposing the pterygomandibular space from an anterior and lateral approach. capsule of the temporomandibular joint. A large vein may drain the plexus and join the inferior alveolar vein or veins in close proximity to the ramus below the inferior border of the lateral pterygoid muscle. The resultant maxillary vein passes backwards, inferior to the maxillary artery, and after receiving other tributaries it perforates the interpterygoid fascia and joins the superficial temporal vein in the parotid gland to form the retromandibular vein. This large vein descends in close proximity to the posterior border of the ramus in lateral relation to the external carotid and it is frequently only partly infolded within the parotid gland. The lingual and inferior alveolar nerves separate from each other on the deep surface of the lateral pterygoid muscle and emerge into the space on the lateral surface of medial pterygoid. The lingual nerve, having joined with the chorda

6 4 8 BRITISH JOURNAL OF ORAL SURGERY tympani, runs forwards and downwards in front of the lingula to become flattened between the medial pterygoid and internal surface of ramus en route to the floor of the mouth. The inferior alveolar nerve lies posterior to the lingual nerve and diverges laterally to approach the mandibular foramen where it is situated between the sphenomandibular ligament and bone. Nerve, artery and vein(s) lie anteroposteriorly in this location. The mylohyoid nerve leaves the inferior alveolar ON TM PPF MA MM LPM AT N MA IAN LN BN LN T FIG. 8 FIG. 9 Fig. 8.--Superficial dissection of the infratemporal fossa from a lateral approach. Removal of the ramus of the mandible above the mandibular foramen reveals the pterygomandibular space bounded above by lateral pterygoid muscle. The lingual nerve and inferior alveolar neurovascular bundle are seen to lie on the medial pterygoid muscle while in the space. Fig. 9.--Deeper dissection of the infratemporal fossa from a lateral approach. Lateral pterygoid muscle has been removed and the mandibular nerve trunk is revealed. In this specimen the maxillary artery passed deep to lateral pterygoid muscle. nerve approximately 5 mm above the foramen, pierces the sphenomandibular ligament and descends to gain the mylohyoid groove. The auriculotemporal nerve lies above the pterygomandibular space deep to lateral pterygoid muscle, but the close relation which it establishes with the neck of the condyle as it passes posteriorly into the parotid gland has clinical significance when an injecting needle is advanced at a high level. The presence of the buccal nerve in the upper and anterior part of the pterygomandibular space is brief as it passes between the two heads of the lateral pterygoid muscle towards the deep portion of temporalis. It descends either in the substance of that muscle or is enveloped in its fascia. The buccal nerve subsequently emerges from beneath the temporobuccinator band to pass forwards on the buccinator muscle. Certain structures related to the pterygomandibular space should be recalled. The facial nerve descends from the stylomastoid foramen within the parotid gland,

7 THE APPLIED ANATOMY OF THE PTERYGOMANDIBULAR SPACE 49 and becoming superficial, divides into its numerous branches behind the retromandibular vein about the level of the neck of the condyle. The internal jugular vein, internal carotid artery and cranial nerves 9, Io, I I and I2 together with the the sympathetic trunk all lie posteromedial to the pterygomandibular space and deep to styloid process. LPP MA ATN CTN IAV IAN/MHN SML Lt~ FIG. I0 FIG. II Fig. Io.--A medial approach to the pterygomandibular space. The tongue, pharynx, and structures related to its side wall have been removed to reveal medial pterygoid muscle. The parotid gland is wrapped around the posterior border of the ramus and a deep process of the gland overlaps the medial pterygoid muscle. Fig. n.--removal of medial pterygoid muscle from the specimen shown in Figure IO allows the demonstration of structures in the pterygomandibular space from a medial aspect. The maxillary artery is again deep to lateral pterygoid muscle and a root of the auriculotemporal nerve is seen to loop beneath the artery. The inferior alveolar vein is of substantial size. (By permission of the Australian Dental Journal.) (Barker, 1971). INTRAORAL SURFACE LANDMARKS When the mouth is widely opened, the pterygomandibular fold is usually clearly discernible for the underlying buccinator muscle and raphe is stretched between bony attachments. The buccal pad may also be seen, although this formation varies considerably in its degree of prominence and the margins are not always well defined. The buccal pad referred to here is not the body of fat wedged between masseter and buccinator which passes back between buccinator and temporalis, but rather the thick submucous layer of fibrous tissue which separates buccinator from the oral mucosa lateral to and behind the molar teeth (Fig. 5). This pad has been described by Lindsay (vide Nevin, I952). When well developed, the superior and inferior margins of the pad converge to a blunt apex which closely approaches the pterygomandibular fold and which lies near the level of the maxillary molars when the mandible is depressed. Palpable landmarks are the external oblique crest and its continuation upwards as the anterior border of the ramus, the retromolar fossa (fossa precoronoidea), deep tendon of temporalis and the pterygotemporal depression. With D

8 50 BRITISH JOURNAL OF ORAL SURGERY the ball of the index finger in the sulcus extramolaris alongside the third molar tooth, the anterior border of the ramus lies laterally, and the fossa precoronoidea receives the tip of the palpating finger. When the finger is rolled medially the deep temporal tendon may be palpated as it passes down to insert along the temporal crest as far as the apex of the retromolar triangle. Palpation of the anterior border of the ramus will detect the vertical concavity above the occlusal plane of the mandibular molars, but this so called 'coronoid notch' may be encroached upon by the insertion of the superficial temporal tendon. The entrance to the pterygomandibular space may be clarified by palpation of the pterygotemporal depression with a blunt instrument. Gentle backward pressure lateral to the pterygomandibular fold will disclose the site between deep tendon of temporalis and medial pterygoid where the mucosa may be invaginated with little resistance. ANATOMICAL CONSIDERATION OF INFERIOR ALVEOLAR AND LINGUAL NERVE BLOCK TECHNIQUES Two intra-oral techniques are in common use for depositing anaesthetic solution in the neighbourhood of the inferior alveolar nerve. In both techniques the penetration of the needle to the sulcus colli is implicit, since the nerve lies in the same coronal plane as the sulcus when the mandible is depressed fully. In the direct thrust technique, the needle is intended to pass unhindered through the pterygomandibular space along an oblique path into the floor of the sulcus colli (Fig. 5). Its accuracy depends to a large extent upon the selection of an appropriate puncture point and upon the correct angulation of the needle relative to the mandibular ramus. In the technique recommended by Sicher and DuBrul (I97O), the needle is initially passed behind the deep tendon of temporalis to contact bone, then angled to slide along the inner surface of the ramus until it is felt to cross the crista endocondyloidea into the sulcus coui. The technique recommended by Jorgensen and Hayden (1967) differs little from that of Sicher and DuBrul in that periosteal contact is made first 'anterior to the lingula' and the needle is slid 'gently along the periosteum and over the lingular notch and into the sulcus.' In view of the fact that the inferior alveolar nerve inclines medially away from the ramus immediately above the level of the apex of the lingula it is apparent that deposition of solution as close as possible to this site of divergence is indicated in both techniques. While the deposition of solution in the sulcus at a level a little above the apex of the lingula may still effect anaesthesia of the inferior dental nerve by diffusion to it, it is clear that the higher the location of the needle, the greater is the distance between nerve and injection site. Delivery of the solution below the line of attachment of the sphenomandibular ligament and the interpterygoid fascia would make difficult the infiltration of the anaesthetic upwards and, indeed, injection may well occur into the substance of the medial pterygoid muscle. Since the lingular apex represents the most suitable level for needle insertion it is necessary to evaluate the intra-oral landmarks which are commonly used to determine the position of this feature and thus the site of the puncture point in a vertical plane. Three landmarks are employed: the occlusal plane, the concavity of the anterior border of the ramus (the so-called 'coronoid notch') and the apex of the

9 THE APPLIED ANATOMY OF THE PTERYGOMANDIBULAR SPACE 51 buccal pad. It appears however that none of these features bears a constant relationship to the lingular apex. Bremer's (1952) metrical observations on 4o0 mandibles, presumably Scandinavian, showed considerable variability in the position of the lingula relative to the occlusal plane. In per cent of mandibles the lingular apex was situated from o to I mm above the occlusal plane; in 47"7 per cent from I to 5 mm; in 27 per cent from 5 to 9 mm; in 5.2 per cent from 9 to I I mm and in 4.8 per cent from I I to 19 mm above the occlusal plane. In one mandible the lingular apex was 3 mm below the occlusal plane. Bremer used the second molar rather than the third in assessing the occlusal plane in the majority of mandibles. Using the foregoing figures as a guide, a needle placed 5 mm above the occlusal plane and parallel to it would lie above the lingula in 63 per cent of mandibles and below it in 37 per cent. A needle placed I I mm above the plane would lie above the lingula in 95 per cent of mandibles, but at this level the needle would lie at least 5 mm above the lingula in 63 per cent of mandibles. Bremer has indicated that the distance of the lingular apex above the occlusal plane tends to vary with the height of the ramus, and that in children the lingula lies much closer to the occlusal plane. He also measured 88 mandibles in order to assess the relationship of the lingular apex to the level of the deepest point of the concavity of the anterior border of the ramus. In 35 mandibles the concavity coincided with the level of the lingular apex; in 35 it was above the apex; in 17 it was I mm below the apex and in one mandible k was 4 mm below the apex. Bremer concluded that the concavity may be considered a relatively reliable indicator of the level for needle insertion. It should be noted, however, that the concavity in the mouth may be concealed to a varying degree by the insertion of the superficial temporal tendon, and the clinical assessment of the level by palpation may often be a few millimetres inferior to the deepest part of the bony concavity, and thus be slightly inferior to the lingular apex. A well defined apex of the buccal pad is not always present. When the mandible is depressed maximally the apex of the pad is displaced only slightly below the occlusal plane of the maxillary molars and may therefore lie as much as 15 to 2o mm above the mandibular occlusal plane. Using Bremer's data as a guide, it is apparent that a needle inserted at the apex of the pad may lie from Io to 15 mm above the lingula and the possibility of involving the maxillary vessels is greatly increased. It seems that no small element of chance is involved in the accurate prediction of the site of the lingular apex using the landmarks generally recommended. With regard to the site of the puncture point in a transverse plane, it is clear that the pterygomandibular space should be entered between the deep tendon of temporalis and the medial pterygoid muscle. In the technique of Sicher and Dubrul, as well as that of Jorgensen and Hayden, where the ramus is contacted anterior to the lingula in the region of the torus triangularis, puncture is effected close to the medial border of the inwardly projecting deep tendon of the temporal muscle. The needle is angled to pass behind the tendon and when bone is encountered, the syringe is redirected to allow the progress of the needle along the internal surface of the ramus. In the direct thrust technique, where the needle is passed directly into the depths of the sulcus colli, a more,medial puncture point into the pterygotemporal depression is required, and the barrel of the syringe is held over the opposite premolar teeth. While it is apparent that insertion of the

10 52 BRITISH JOURNAL OF ORAL SURGERY needle medial to the pterygomandibular fold will result in piercing of the superior constrictor and then the medial pterygoid if the syringe is directed towards the sulcus colli, it is by no means certain that a puncture point lateral to the raphe will always avoid penetrating the anterior portion of medial pterygoid. This is a consequence of the fact that the fold crosses the anterior border of medial pterygoid muscle diagonally, and the higher the insertion of the needle the greater the possibility of encountering the muscle. Provided the anterior part of the muscle is avoided by a broad angle of approach and a puncture point which is not too close to the hamulus, it would present no further obstacle to passage of the needle. This presupposes that the path of the needle follows the plane of the lower border of the mandible. Downward inclination of the advancing needle may well result in injection into the medial pterygoid muscle as it inserts into mandible below the lingula and this may be the cause of failure to anaesthetise the inferior dental nerve in a proportion of cases. Entrance to the pterygomandibular space from the mouth necessarily involves piercing mucosa, buccinator, temporobuccinator band, fat and the temporopterygold fascia and these layers may resist penetration to a varying degree. The lingual nerve lies wedged between the medial pterygoid and ramus and may also be pierced some IO mm beyond the puncture point (Figs. 5 & 6). A well directed needle should pass between the ramus and the sphenomandibular ligament into the sulcus colli, and if it is a little above the the lingular apex the likelihood of piercing the inferior alveolar nerve is lessened. Vulnerable, however, are the inferior alveolar vessels, particularly the large and thin-walled veins. Nerve, artery and vein lie in that relation anteroposteriorly, and the advancing needle may impale a vein against bone in the depths of the sulcus colli. The advisability of withdrawing the needle slightly after contacting bone and then aspirating would appear to be sound clinical practice. Using the direct thrust technique, bone should be initially encountered before injecting the anaesthetic fluid. Indeed, if bone is not felt at a depth of insertion of 2o to 25 ram, the needle should be withdrawn and the barrel of the syringe laid more obliquely over the opposite first molar teeth before reinsertion. Passage of the needle beyond the posterior border of the ramus may result in complications such as nerve block of the facial nerve within the parotid gland or injection into the large retromandibular vein which is closely applied to the posterior border (Fig. 14). A needle would have to be very aberrantly directed to involve the more medially placed carotid sheath and adjacent nerves, but as pointed out by Murphy and Grundy (1969) these structures do lie within the range of a 47 mm needle and Dodd (1956) has reported an instance of probable sympathetic trunk involvement following attempted inferior dental nerve block. Some clinicians intentionally deliver a 'high' block of the inferior alveolar nerve and deposit solution below the insertion of lateral pterygoid into the condylar neck. The inferior alveolar nerve is in medial relation to this site, but the anatomy of the part should not prevent diffusion of the solution to the nerve in the majority of instances. But untoward sequelae may supervene following this approach. The maxillary vein may lie less than IO mm above the lingula and the maxillary artery lies immediately above it ill relation to the neck of the condyle. Either vessel may be encountered, and instances ofischaemia of the upper face may be the result of direct impingement of the needle on the maxillary artery and its surrounding sympathetic plexus with reflex contraction. The auriculotemporal nerve crosses

11 THE APPLIED ANATOMY OF THE PTERYGOMANDIBULAR SPACE 53 the posterior opening of the pterygomandibular space above the maxillary artery, and while the maxillary vessels would appear to act as a barrier to infiltration of a solution upwards (see illustration in Berns & Sadove (I962)) in most cases, ternporal anaesthesia is not unknown. I TM(ST) TM (DT) /MV TBB BM FIG. I2 FIG. I4 /MHN FIG. I3 Fig. I2.--Dissection of structures bounding the entrance to the pterygomandibular space from an anterior and superior approach. Note the large deep tendon of temporalis muscle which bulges medially and narrows the cleft between it and medial pterygoid muscle. Fig. I3--Dissection of structures entering and leaving the pterygomandibular space from the posterior aspect. The interpterygoid fascia spans the gap between the pterygoid muscles, but its posterior extent is deficient to allow the passage of auriculotemporal nerve and the maxillary artery and vein. Fig. r4.--dissection of the pterygomandibular space from a lateral approach. The large retromandibular vein lies in close proximity to the posterior border of the ramus, and a needle which fails to encounter bone may pass into it. Another variation of the inferior alveolar block technique has been advocated by Gottlieb (cited by Bremer (I952)), whereby solution is deposited on the periosteum posterior to the deep temporal tendon and anterior to the lingula apex. Murphy and Grundy (I969) have stated that their anatomical evidence suggests such an approach to be effective and safe. The dissections of the present authors have shown the site in question to be free of major blood vessels. Two small

12 54 BRITISH JOURNAL OF ORAL SURGERY branches of the inferior alveolar artery may bc present--one that passes forwards and down over the internal surface of the mandible to accompany the lingual nerve, and another that enters the fleshy fibres of the temporal muscle inserted behind its deep tendon. The success of this technique, however, may largely depend on the presence or otherwise of a well developed interpterygoid fascial scptum across the anterior part of the ptcrygomandibular space (tcmporopterygoid fascia). If dense, and the solution is deposited in front of the septum, infiltration posteriorly to the inferior alveolar nerve trunk may be prevented and anaesthesia of the lingual nerve only would supervene. This factor could explain an illustration in Berns and Sadove (1962) where a radiopaque solution deposited I cm in front of the mandibular foramen appeared to spread upwards and forwards from the site of delivery. Provided the needle pierces the fascia there is no further anatomical barrier to prevent infiltration backwards to the nerve trunk. It does seem, however, that advancement of the needle along the periostcum to the crista endocondyloidca at the level of the lingual notch is preferable. Provided the crest is recognised, the close proximity of the inferior alveolar nerve renders further penetration unnecessary. The buccal nerve is not accessible to anaesthetic solution delivered into the pterygomandibular space at the customary level. This nerve exits from bctween the heads of the lateral pterygoid, pierces the fascia of the deep temporal tendon some 2 to 3 cm above the usual site of puncture and descends within the fascia infcrolatcrally across the anterior surface of the deep tendon. It emerges from beneath the temporobuccinator band on to the lateral surface of the buccinator muscle adjacent to the retromolar triangle, and this site is generally used for buccal nerve block. EFFECTS OF LINGUAL AND INFERIOR ALVEOLAR NERVE BLOCK The lingual nerves carry general sensory fibres to the mucous membrane of the anterior two-thirds of the tongue, of the floor of the mouth, and of the internal surface of the mandibular alveolar process. They carry taste fibres from the anterior two-thirds of the tongue and relay parasympathetic fibres to the submandibular, sublingual and lingual salivary glands. In addition the lingual nerves are believed to transmit proprioceptive sense from tlie tongue musculature. The effects to be expected following lingual nerve block are, on the side of injection, complete loss of sensation of the mucous membrane in the regions outlined, inhibition of secretory activity of the salivary glands mentioned and some impairment of volitional tongue control. The inferior alveolar nerve, with the exception of its mylohyoid branch, is wholly general sensory in nature. Apart from supplying dental pulps, it innervates periodontal tissues and gingival papillae, and its large mental branch supplies skin and mucosa of the lower lip and vestibule. Adequate time must be allowed for full diffusion of the anaesthetic solution through the thick nerve trunk to ensure profound anaesthesia of all these tissues. For some ill-defined reason, the incisors and occasionally the canines are not anaesthetised in a unilateral block. It has been postulated that there is crossing of incisive nerve fibres across the midline which would account for residual sensitivity, but the persistence of a median symphysis during the first year of life would make difficult such an overlapping. Indeed, the dental papillae of the incisor and canine tooth germs are sufficiently mature to lay down dentine by the third month

13 THE APPLIED ANATOMY OF THE PTERYGOMANDIBULAR SPACE 55 of life, and it seems likely that their nerve supply is established from their own side by this time. The hypothesis that the transverse cutaneous nerve of the neck participates in the supply of the anterior teeth appears to be unfounded when the embryology of the part is considered. The incisor teeth and the mandible form in first branchial arch territory and the nerve supply would logically be from the trigeminal complex. Clinicians have observed that injection at the inner surface of the mandible in the premolar canine region is occasionally successful in anaesthetising the incisors, and this has been ascribed to the blocking of the mylohyoid nerve deep to the mylohyoid muscle. Sicher (197o) states that the mylohyoid nerve is known to contain sensory fibres to the skin of the chin and sends a branch into the mandible in about IO per cent of cases. Fibres may therefore travel to the incisors by this indirect route in some instances. But the mylohyoid nerve is usually given off from the inferior alveolar nerve just above the mandibular foramen and would commonly be anaesthetised along with its parent trunk. Only in cases where the mylohyoid nerve originates at a high level and enters a bony canal would it be left unaffected and possibly responsible for residual midline sensitivity. The fourth hypothesis suggests that the fibres from the anterior teeth are centrally situated in the nerve trunk and are less accessible to infiltration of the solution, but this postulation has not been substantiated conclusively. The phenomenon awaits a satisfactory explanation. Anatomical considerations suggest that bilateral block of the inferior alveolar and lingual nerves should be avoided if possible, for patient discomfort may be extreme through loss of control ofthe tongue and the floor of the mouth. Paralysis of mylohyoid and anterior belly of both digastrics may occur with concomitant difficulty in swallowing. Anaesthesia of the lingual nerve on both sides leads to loss of sensation from the anterior two-thirds of the tongue and probably loss of proprioceptive afferents as well. SUMMARY Photographs of dissections of the pterygomandibular space, performed from various approaches, are presented with a view to clarifying the disposition of structures in the region. Tlie application of the anatomy of the region to generally recommended nerve block techniques is discussed. REFERENCES BARKER, B. C. W. (I97I). Australian Dental Journal, I6, 163. BARKER, B. C. W. (1969). Annals of the Australian College of Dental Surgeons, 2, 22. BERNS, J. M. & SADOVE, M. S. (1962). Journal of the American Dental Association, 65, 735. BKEMER, G. (1952). Oral Surgery, Oral Medicine & Oral Pathology, 5, 966. DEMPSTER, W. T. (1966). Selected Dissections of the Facial Regions for Advanced Dental Students, 5th Ed. (Revised by I-Iuelke, D. F.) Ann Arbor: Overbeck. DODD, A. E. (1956). Journal of the Dental Association of South Africa, II, 385. JORGENSEN, N. B. & HAYDEN, J. (1967). Premedication, Local and General Anaesthesia in Dentistry. Philadelphia: Lea and Febiger. LARNACI-I, S. L. & MACINTOSH, N. W. G. (1971). The Oceania Monographs No. z7, University of Sydney. MURPHY, T. R. & GRUNDY, E. M. (I969). Dental Practitioner and Dental Record, 20, 41. NEVlN, M. (1952). Problems in Dental Anaesthesia, p Brooklyn, N.Y., 1952: Dental Items of Interest Publishing Co., Inc. SICHER, H. & DuBRUL, E. L. (197o). Oral Anatomy, 5th Ed. St. Louis: Mosby.