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Infratemporal and pterygopalatine fossae and temporomandibular joint
Infratemporal Fossa
The infratemporal fossa lies deep to the ramus of the mandible. It communicates with the temporal fossa superiorly deep to the zygomatic arch; the orbit anteriorly through the inferior orbital fissure; the pterygopalatine fossa medially through the pterygomaxillary fissure; the middle fossa through the foramina ovale and spinosum. It contains lateral and medial pterygoid, the mandibular division of the trigeminal nerve, the chorda tympani (facial nerve), the otic ganglion, the maxillary artery and the pterygoid venous plexus.
The infratemporal fossa has a roof and anterior, lateral and medial walls, and is open to the neck posteroinferiorly, which means that it has no anatomical floor. Approximately 80% of the roof is formed by the infratemporal surface of the greater wing of the sphenoid. The remainder is formed by the infratemporal surface of the temporal bone, ending at the articular eminence of the temporomandibular joint and the spine of the sphenoid on the deep medial aspect. The roof contains the foramina ovale and spinosum. The anterior wall is formed by the posterior surface of the maxilla, ending inferiorly at the maxillary tuberosity. The inferior orbital fissure forms the upper limit of the anterior wall, meeting the pterygomaxillary fissure at right-angles. The medial wall is formed anteriorly by the lateral pterygoid plate of the pterygoid process of the sphenoid, and more posteromedially by the pharynx and tensor and levator veli palatini. It contains the pterygomaxillary fissure, across which structures pass between the infratemporal and pterygopalatine fossae ( Fig. 38.1 ). The lateral wall is formed by the medial surface of the ramus of the mandible.
Lateral pterygoid provides a key to understanding the relationships of structures within the infratemporal fossa. This muscle lies in the roof of the fossa and runs anteroposteriorly in a more or less horizontal plane from the region of the pterygoid plates to the mandibular condyle. Branches of the mandibular nerve and the main origin of medial pterygoid are deep relations and the maxillary artery is superficial. The buccal branch of the mandibular nerve passes between the two heads of lateral pterygoid. Medial pterygoid and the lingual and inferior alveolar nerves emerge below its inferior border, and the deep temporal nerves and vessels emerge from its upper border. The pterygoid venous plexus lies around and within lateral pterygoid and is important in the spread of infection.
There is a lack of consensus in the surgical literature with regard to both the boundaries and contents of the infratemporal fossa. Thus, the fossa is sometimes defined as the anatomical space beneath the floor of the middle fossa, incorporating the remainder of the subcranial temporal bone as part of the roof, with the exception of the glenoid fossa of the temporomandibular joint. In this description, the fossa is limited posteriorly by the prevertebral fascia and includes the internal carotid artery, the internal jugular vein, the lower cranial nerves, the cervical sympathetic trunk, and the styloid process with its attached muscles and ligaments. Alternatively, the ‘extended’ infratemporal fossa is said to consist of the parapharyngeal and masticator spaces ( Fig. 38.2 ) ( , , , ).
Bones
The sphenoid bone, the paired maxillae and temporal bones, the palatine bones and the mandible collectively provide the skeletal framework to the infratemporal and pterygopalatine regions. The mandible and the two temporal bones articulate at the right and left temporomandibular joints. The disarticulated maxilla and palatine bone are described in Chapter 36 , the temporal bone is described in Chapter 42 , and the sphenoid and mandible are described here.
Sphenoid
The sphenoid lies in the base of the skull between the frontal, temporal and occipital bones. It has a central body, paired greater and lesser wings that spread laterally from the body, and two pterygoid processes that descend from the junction of the body and greater wings ( Fig. 38.3 ).
Body
The body of the sphenoid is cuboidal. It contains two air sinuses separated by a septum. Its cerebral (superior) surface articulates anteriorly with the cribriform plate of the ethmoid bone via the smooth jugum sphenoidale, which is related to the overlying gyri recti and olfactory tracts. The jugum is bounded behind by the anterior border of the sulcus chiasmaticus leading laterally to the optic canals. The tuberculum sellae is posterior; behind it is the deeply concave sella turcica that houses the hypophysis cerebri within the hypophysial fossa. The anterior edge of the sella turcica is completed laterally by two middle clinoid processes. Posteriorly, the sella turcica is bounded by a square dorsum sellae with superior angles that bear variable posterior clinoid processes. The diaphragma sella and the tentorium cerebelli are attached to the clinoid processes. On each side, below the dorsum sellae, a small petrosal process articulates with the apex of the petrous part of the temporal bone. The body of the sphenoid slopes directly into the basilar part of the occipital bone posterior to the dorsum sellae and together these bones form the clivus. In the growing child, this is the site of the spheno-occipital synchondrosis: premature closure of this joint gives rise to the skull appearances seen in achondroplasia.
The lateral surfaces of the body are united with the greater wings and the medial pterygoid plates. A broad carotid sulcus accommodates both the internal carotid artery and the cranial nerves associated with the cavernous sinus above the root of each wing. The sulcus is deepest posteriorly and is overhung medially by the petrosal part of the temporal bone. Its sharp lateral margin, the lingula, continues back over the posterior opening of the pterygoid canal.
A median triangular bilaminar sphenoidal crest on the anterior surface of the body of the sphenoid makes a small contribution to the nasal septum. The anterior border of the crest articulates with the perpendicular plate of the ethmoid bone, and a sphenoidal sinus opens on either side of it. In the articulated state, the sphenoidal sinuses are closed anteroinferiorly by the sphenoidal conchae that are almost inevitably destroyed when disarticulating a dried skull. Each half of the anterior surface of the body of the sphenoid possesses a superolateral depressed area joined to the ethmoidal labyrinth that completes the posterior ethmoidal sinuses; a lateral margin that articulates with the orbital plate of the ethmoid above and the orbital process of the palatine bone below; and an inferomedial, smooth, triangular area that forms the posterior nasal roof. The orifice of a sphenoidal sinus lies near the superior angle of this triangular area.
The inferior surface of the body of the sphenoid bears a median triangular sphenoidal rostrum, embraced above by the diverging lower margins of the sphenoidal crest. The narrow anterior end of the rostrum fits into a fissure between the anterior parts of the alae of the vomer, and the posterior ends of the sphenoidal conchae flank the rostrum, articulating with its alae. A thin vaginal process projects medially from the base of the medial pterygoid plate on each side of the posterior part of the rostrum, behind the apex of the sphenoidal concha.
Greater wings
The greater wings of the sphenoid curve broadly superolaterally from the body. Posteriorly, each is triangular, fitting the angle between the petrous and squamous parts of the temporal bone at a sphenosquamosal suture. The cerebral surface contributes to the anterior part of the middle cranial fossa. Deeply concave, its undulating surface is adapted to the anterior gyri of the temporal lobe of the cerebral hemisphere. The foramen rotundum lies anteromedially and transmits the maxillary nerve. The foramen ovale, posterolateral to the foramen rotundum, transmits the mandibular nerve, accessory meningeal artery and sometimes the lesser petrosal nerve, although the latter nerve may have its own canaliculus innominatus medial to the foramen spinosum. When present, a small emissary sphenoidal foramen (foramen of Vesalius) transmits a small vein from the cavernous sinus, and can lie medial to the foramen ovale (on one or both sides). The foramen spinosum lies behind the foramen ovale and transmits the middle meningeal artery and meningeal branch of the mandibular nerve.
The lateral surface is vertically convex and divided by a transverse infratemporal crest into temporal (upper) and infratemporal (lower) surfaces. Temporalis is attached to the temporal surface. The infratemporal surface is directed downwards and, with the infratemporal crest, is the site of attachment of the upper fibres of lateral pterygoid. It contains the foramen ovale and foramen spinosum. The small downward-projecting spine of the sphenoid lies posterior to the foramen spinosum; the sphenomandibular ligament is attached to its tip. The medial side of the spine bears a faint anteroinferior groove for the chorda tympani nerve and appears in the lateral wall of the sulcus for the pharyngotympanic tube. A ridge passes downwards to the front of the lateral pterygoid plate, medial to the anterior end of the infratemporal crest, and forms a posterior boundary of the pterygomaxillary fissure.
The quadrilateral orbital surface of the greater wing faces anteromedially and forms the posterior part of the lateral wall of the orbit. It has a serrated upper edge that articulates with the orbital plate of the frontal bone, and a serrated lateral margin that articulates with the zygomatic bone. Its smooth inferior border is the posterolateral edge of the inferior orbital fissure, and its sharp medial margin forms the inferolateral edge of the superior orbital fissure, on which a small tubercle gives partial attachment to the common anular ocular tendon. Below the medial end of the superior orbital fissure, a grooved area forms the posterior wall of the pterygopalatine fossa that is pierced by the foramen rotundum.
The irregular margin of the greater wing, from the body of the sphenoid to the spine, is an anterior limit of the medial half of the foramen lacerum. It contains the posterior aperture of the pterygoid canal and its lateral half articulates with the petrous part of the temporal bone at a sphenopetrosal synchondrosis. The sulcus tubae inferior to the synchondrosis contains the cartilaginous pharyngotympanic (auditory) tube. Anterior to the spine of the sphenoid the concave squamosal margin is serrated, bevelled internally below and externally above, for articulation with the squamous part of the temporal bone. The tip of the greater wing, bevelled internally, articulates with the sphenoidal angle of the parietal bone at the pterion. Medial to this, a triangular rough area articulates with the frontal bone; its medial angle is continuous with the inferior boundary of the superior orbital fissure, and its anterior angle joins the zygomatic bone by a serrated articulation. Fractures of the zygomatic bone preferentially pass through this articulation with the greater wing because it is a line of weakness in the lateral orbit.
Lesser wings
The lesser wings of the sphenoid are triangular pointed plates that protrude laterally from the anterosuperior regions of the body. The superior surface of each wing is smooth and related to the frontal lobe of the cerebral hemisphere. The inferior surface is a posterior part of the orbital roof and upper boundary of the superior orbital fissure and overhangs the middle cranial fossa. The posterior border projects into the lateral fissure of the cerebral hemisphere. The medial end of the lesser wing forms the anterior clinoid process: the anterior and middle clinoid processes are sometimes united to form a caroticoclinoid foramen. The lesser wing is connected to the body by a thin, flat anterior root and a thick, triangular posterior root (the optic strut), between which lies the optic canal. The optic strut extends from the base of the anterior clinoid process to the body and separates the optic canal from the superior orbital fissure. The optic canal is bounded by the body of the sphenoid medially, the lesser wing superiorly, and the optic strut inferiorly and laterally.
Superior orbital fissure
The superior orbital fissure connects the cranial cavity with the orbit. It is bounded medially by the body of the sphenoid; above by the lesser wing of the sphenoid; below by the medial margin of the orbital surface of the greater wing; and laterally, between the greater and lesser wings, by the frontal bone. The contents of the superior orbital fissure are described in Chapter 44 (see Fig. 44.4 ).
Pterygoid processes
The pterygoid processes descend perpendicularly from the junctions of the greater wings and body. Each consists of a medial and lateral plate with upper parts that are fused anteriorly. The plates are separated below by the angular pterygoid fissure: the margins of the fissure articulate with the pyramidal process of the palatine bone and diverge behind. Medial pterygoid lies in the cuneiform pterygoid fossa between the plates. Above is the small, oval, shallow scaphoid fossa, formed by division of the upper posterior border of the medial plate. Part of tensor veli palatini is attached to the fossa. The anterior surface of the root of the pterygoid process is broad and triangular: it forms the posterior wall of the pterygopalatine fossa and is pierced by the anterior opening of the pterygoid canal.
Lateral pterygoid plate
The lateral pterygoid plate is broad, thin and everted. The lateral surface forms part of the medial wall of the infratemporal fossa and the lower part of lateral pterygoid is attached to it. The medial surface is the lateral wall of the pterygoid fossa and most of the deep head of medial pterygoid is attached to it. The upper part of its anterior border is a posterior boundary of the pterygomaxillary fissure, and the lower part articulates with the palatine bone. The posterior border is free.
Medial pterygoid plate
The medial pterygoid plate is narrower and longer than the lateral. Its lower end is continued into an unciform projection, the pterygoid hamulus, which curves laterally. The pterygomandibular raphe is attached to the hamulus, and the tendon of tensor veli palatini winds around the hamulus. The lateral surface forms the medial wall of the pterygoid fossa and the medial surface provides a lateral boundary for the posterior nasal aperture. The medial plate is prolonged above on the inferior aspect of the body of the sphenoid as a thin vaginal process that articulates anteriorly with the sphenoidal process of the palatine bone and medially with the ala of the vomer. The plate articulates with the posterior border of the perpendicular plate of the palatine bone in the lower part of its anterior margin. Inferiorly, it bears a furrow that is converted anteriorly into the palatovaginal canal by the sphenoidal process of the palatine bone. The palatovaginal canal transmits pharyngeal branches of the maxillary artery and pterygopalatine ganglion. The pharyngobasilar fascia is attached to the whole of the posterior margin of the medial plate, and the superior pharyngeal constrictor is attached to its lower end. The small pterygoid tubercle is found at the upper end of the plate, just below the posterior opening of the pterygoid canal. The processus tubarius, which supports the cartilaginous pharyngeal end of the pharyngotympanic tube, projects back near the midpoint of the margin of the medial pterygoid plate.
Though adjacent, the medial and lateral pterygoid plates have distinct roles. The lateral plate is the province of the infratemporal fossa and masticator space, forming part of the medial boundary of the infratemporal fossa and providing attachment for the lateral and medial pterygoids. The medial plate is functionally related to the pharynx, providing attachment for the pharyngobasilar fascia, superior constrictor and pterygomandibular raphe.
Midface fractures
Midface fractures at Le Fort I, II and III levels invariably involve the pterygoid plates at different levels; displacement of the outlines of these bones radiographically confirms the diagnosis. Mid-face fractures and current classification of these injuries are described and discussed in Chapter 36 .
Sphenoidal conchae
The sphenoidal conchae are two thin, curved small plates, attached anteroinferiorly to the body of the sphenoid bone. The superior concave surface of each forms the anterior wall and part of the floor of a sphenoidal sinus. In situ , each has vertical quadrilateral anterior and horizontal triangular posterior parts. The anterior part consists of a superolateral depressed area that completes the posterior ethmoidal sinuses and joins below with the orbital process of a palatine bone, and a smooth and triangular inferomedial area that forms part of the nasal roof and is perforated above by a round opening connecting the sphenoidal sinus and spheno-ethmoidal recess.
Anterior parts of the two bones meet in the midline and protrude as the sphenoidal crest. The horizontal part appears in the nasal roof and completes the sphenopalatine foramen. Its medial edge articulates with the rostrum of the sphenoid and the ala of the vomer. Its apex, directed posteriorly, is superomedial to the vaginal process of the medial pterygoid plate and joins the posterior part of the ala. A small conchal part sometimes appears in the medial wall of the orbit, lying between the orbital plate of the ethmoid anteriorly, the orbital process of the palatine bone inferiorly and the frontal bone superiorly.
Ossification
Until postmenstrual weeks 25–32, the sphenoid body has a presphenoidal part, anterior to the tuberculum sellae and continuous with the lesser wings, and a postsphenoidal part, consisting of the sella turcica and dorsum sellae, that is integral with the greater wings and pterygoid processes. Much of the bone is preformed in cartilage. There are six ossification centres for the presphenoidal parts and eight centres for the postsphenoidal parts.
Presphenoidal part
At about postfertilization weeks 8–9 (postmenstrual week 10–11), a centre appears in each wing, lateral to the optic canal; two bilateral centres appear in the presphenoidal body a little later. Each sphenoidal concha has a centre that appears superoposteriorly in the nasal capsule during postmenstrual weeks 17–20. As it enlarges, it partly surrounds a posterosuperior expansion of the nasal cavity that becomes the sphenoidal sinus. The posterior conchal wall is absorbed and the sinus invades the presphenoidal component. The concha fuses with the ethmoidal labyrinth in the fourth year and with the sphenoid and palatine bones before puberty; its anterior deficiency persists as an opening for the sphenoidal sinus.
Postsphenoidal part
The first centres appear in the greater wings at about postmenstrual week 11, one in the basal cartilage of each wing below the foramen rotundum. These centres only contribute to the root of the greater wing (near the foramen rotundum and pterygoid canal). The remainder of the greater wing and the lateral pterygoid plate are ossified in mesenchyme. Two centres flanking the sella turcica appear between postmenstrual weeks 13 and 16 and soon fuse. The medial pterygoid plates are also ossified in ‘membrane’, a centre in each probably appearing in about postmenstrual weeks 9 or 10. The hamulus is chondrified during postmenstrual weeks 9–12 and begins to ossify at once. The medial and lateral pterygoid plates join at about postmenstrual weeks 21–24. A centre for each lingula appears during postmenstrual weeks 13–16 and soon joins the body. The neonatal optic canal is relatively large and has a keyhole or ‘figure of eight’ shape rather than the circular profile seen in the adult ( ).
Postnatal details
Presphenoidal and postsphenoidal parts fuse at about postmenstrual weeks 29–32; an unciform cartilage persists after birth in the lower parts of this junction. At birth, the bone is tripartite and consists of a central part (body and lesser wings) and two lateral parts that each consist of a greater wing and pterygoid process. During the first year, the greater wings and body unite around the pterygoid canals, and the lesser wings extend medially above the anterior part of the body, meeting to form the smooth, elevated jugum sphenoidale. By the twenty-fifth year, the sphenoid and occipital bones are completely fused. An occasional vascular foramen, often erroneously termed the craniopharyngeal canal, is occasionally seen in the anterior part of the hypophysial fossa.
Although the sphenoidal sinus can be identified between postmenstrual weeks 13 and 16 as an evagination of the posterior part of the nasal capsule, by full-term birth (notionally postmenstrual week 40) it represents an outgrowth of the spheno-ethmoidal recess. Pneumatization of the body of the sphenoid has been identified from 4 postnatal months and a distinct cell is visible by 2 years. Pneumatization spreads first into the presphenoid and later invades the postsphenoid part. The sinus reaches full size in adolescence, but often enlarges further by absorption of its walls as age advances.
Certain parts of the sphenoid are connected by ligaments that may occasionally ossify, e.g. the pterygospinous ligament between the sphenoidal spine and the upper part of the lateral pterygoid plate; the interclinoid ligament between the anterior and posterior clinoid processes; and the caroticoclinoid ligament between the anterior and middle clinoid processes.
Premature synostosis of the junction between pre- and postsphenoidal parts, or of the spheno-occipital suture, produces a characteristic appearance, obvious in profile, of an abnormal depression of the nasal bridge.
Stylohamular plane
A plane exists between the pharyngeal side wall and the infratemporal fossa/masticator space. It is readily identified by palpating the tip of the styloid process and with gentle blunt finger dissection passing anteriorly and medially to the pterygoid hamulus at the lower border of the medial pterygoid plate. Termed the ‘stylohamular plane’ ( ), it defines the medial and superior boundaries of the infratemporal fossa and is the medial boundary for tumours confined to the infratemporal fossa. With resections using the stylohamular plane as a guide, the internal carotid artery, internal jugular vein and the vagus nerve should not be at risk because they are deep to the styloid apparatus ( Fig. 38.4 ).
Mandible
The mandible is the largest, strongest and lowest bone in the face. It has a horizontally curved body that is convex forwards, and two broad rami that ascend posteriorly ( Fig. 38.5 ). The body of the mandible supports the mandibular teeth within the alveolar process. The rami bear the coronoid and condylar processes. Each condyle articulates with the adjacent temporal bone at the temporomandibular joint.
Body
The body has external and internal surfaces separated by upper and lower borders. Anteriorly, the upper external surface shows an inconstant faint median ridge indicating the site of the fused symphysis menti. Inferiorly, this ridge divides to enclose a triangular mental protuberance; its base is centrally depressed but raised on each side as a mental tubercle. The mental protuberance and mental tubercles constitute the chin. The mental foramen, from which the mental neurovascular bundle emerges, lies midway between the upper and lower borders of the body, below either the interval between the premolar teeth, or the second premolar tooth. The posterior border of the foramen is smooth and accommodates the nerve as it emerges posterolaterally. A faint external oblique line ascends backwards from each mental tubercle and sweeps below the mental foramen, becoming more marked as it continues into the anterior border of the ramus.
The lower border of the body, the base, extends posterolaterally from the mandibular symphysis into the lower border of the ramus behind the third molar tooth. The anterior belly of digastric is attached to a rough digastric fossa near the midline on each side. Behind the fossa, the base of the body is thick and rounded, with a slight anteroposterior convexity that changes to a gentle concavity as the ramus is approached, giving the base an overall sinuous profile.
The upper border, the alveolar part, contains 16 alveoli for the roots of the lower teeth. It consists of buccal and lingual plates of bone joined by interdental and inter-radicular septa. Near the second and third molar teeth, the external oblique line is superimposed on the buccal plate. As is the case in the maxilla, the form and depth of the mandibular tooth sockets is related to the morphology of the roots of the mandibular teeth. The sockets of the incisor, canine and premolar teeth usually contain a single root, while those for the three molar teeth each contain two or three roots. The third molar is variable in its position and root presentation: it may be impacted vertically, horizontally, mesially or distally, and its roots may be bulbous, hooked, divergent or convergent, and occasionally embrace the mandibular (inferior dental) canal. The internal surface of the mandible is divided by an oblique mylohyoid line that gives attachment to mylohyoid and, above its posterior end, to the superior pharyngeal constrictor, some retromolar fascicles of buccinator, and the pterygomandibular raphe behind the third molar. The mylohyoid line extends from a point approximately 1 cm from the upper border behind the third molar as far forwards as the mental symphysis; it is sharp and distinct near the molars but faint further forwards. The mylohyoid groove extends downwards and forwards from the ramus below the posterior part of the mylohyoid line and contains the mylohyoid neurovascular bundle. The area below the line is a slightly concave submandibular fossa and is related to the submandibular gland. The area above the line widens anteriorly into a triangular sublingual fossa and is related to the sublingual gland; the bone is covered by mucosa above the sublingual fossa as far back as the third molar. In an edentulous subject, it may be necessary to reduce any ridge-like prominence of the mylohyoid line so that dentures can fit without traumatizing the overlying oral mucosa.
Above the anterior ends of the mylohyoid lines, the posterior symphysial aspect bears a small elevation that is often divided into upper and lower parts, the mental spines (genial tubercles). The spines are sometimes fused to form a single eminence, or they may be absent, in which case their position is indicated merely by an irregularity of the surface. Genioglossus is attached to the upper part, and geniohyoid is attached to the lower part. Midline lingual (genial) foramina, above and/or below the genial tubercles, and lateral lingual foramina in the premolar region are present in most mandibles and are of importance in the vascular supply to the symphysis. A rounded elevation of compact bone, the torus mandibularis, sometimes develops above the mylohyoid line; it is most prominent in the premolar region, is usually bilateral and only of clinical significance if repeatedly traumatized.
Ramus
The mandibular ramus is quadrilateral. It has two surfaces (lateral and medial), four borders (superior, inferior, anterior and posterior) and two processes (coronoid and condylar). The lateral surface is relatively featureless and bears the (external) oblique ridge in its lower part. On the medial surface, the mandibular foramen lies midway between the anterior and posterior borders of the ramus, about level with the occlusal surfaces of the teeth. The inferior alveolar neurovascular bundle passes through the foramen to gain access to the mandibular canal. The foramen is overlapped anteromedially by a thin, sharp, triangular spine, the lingula, to which the sphenomandibular ligament is attached, and which is the landmark for an inferior alveolar local anaesthetic block injection. There is often a small prominence on the lateral surface of the ramus level with the lingula that forms a guide during surgical exposure of the lateral surface for osteotomies of the vertical ramus. Below and behind the foramen, the mylohyoid groove runs obliquely downwards and forwards.
The inferior border is continuous with the mandibular base and meets the posterior border at the angle, which is typically everted in males but frequently inverted in females. The thin superior border bounds the mandibular incisure (sigmoid or mandibular notch, incisura semilunaris), which is surmounted in front by the somewhat triangular, flat coronoid process and behind by the condylar process. The thick, rounded posterior border extends from the condyle to the angle, and is gently convex backwards above and concave below. The anterior border is thin above, where it is continuous with the edge of the coronoid process, and thicker below, where it is continuous with the external oblique line. The temporal crest is a ridge that descends on the medial side of the coronoid process from its tip to the bone just behind the third molar tooth. The triangular depression between the temporal crest and the anterior border of the ramus is the retromolar fossa (retromolar trigone).
The ramus and its processes provide attachment for the four primary muscles of mastication: masseter to the lateral surface; medial pterygoid to the medial surface; temporalis to the coronoid process and anterior ramus; the inferior head of lateral pterygoid to the condyle. The thickness of the ramus decreases markedly behind the external oblique line laterally, the temporal crest medially, and above the lingual, and there may be fusion of the lateral and medial cortical plates. This is of importance in mandibular ramus osteotomies and also influences the frequency of fractures of the mandibular angle.
Antilingula
The term ‘antilingula’ has been used to describe an inconstant bony prominence on the lateral aspect of the ramus. This localized bulge, initially thought to be the result of the entrance of the inferior alveolar neurovascular bundle into the medial ramus, has been used as a guide to the position of the mandibular foramen in mandibular osteotomies. However, there is little correlation between the position of the antilingula and the mandibular foramen. It has been suggested that the prominence (when present) on the lateral ramus could reflect the insertion of fibres of masseter ( , , ).
Mandibular canal
The mandibular foramen leads into the mandibular canal, which runs downwards and forwards within the ramus, gently curving inferiorly within the body under the roots of the molar teeth, with which it communicates by small openings, and ascending in the premolar region to the mental foramen. The canal is not always easy to define on plain X-rays, especially anterior to the mental foramen. Its walls may be formed either by a thin layer of cortical bone or, more frequently, by trabecular bone. Although the buccal–lingual and superior–inferior positions of the canal vary considerably between mandibles, in general, the mandibular canal is situated nearer the lingual cortical plate in the posterior two-thirds of the bone, and closer to the labial cortical plate in the anterior third. Bilateral symmetry (location of the canal in each half of the mandible) is reported to be common. Near the mental foramen, the inferior alveolar nerve branches into the mental nerve, which ultimately leaves the mandible via the mental foramen, and the incisive nerve, which remains within the bone and supplies the anterior teeth. The mental nerve may extend anteriorly for 2–3 mm within the mandible before curving back to the mental foramen (the ‘anterior loop’ of the mental nerve). Appreciation of the three-dimensional course of the mandibular canal during its passage through the mandible from the mandibular to the mental foramina is essential if damage to the inferior alveolar nerve is to be avoided in third molar surgery, mandibular osteotomies, dental implant surgery and harvesting of mandibular bone grafts.
The availability of computed tomography (CT), cone beam CT (CBCT) imaging and computer-assisted intraoperative navigation permits the assessment of the course of the mandibular canal throughout its length both prior to and during any surgical procedure that could place the inferior alveolar nerve and/or the mental nerve at risk ( ).
Coronoid process
The coronoid process projects upwards and slightly forwards as a triangular plate of bone. Its posterior border bounds the mandibular incisure and its anterior border continues into that of the ramus.
Coronoid hyperplasia
Elongation of the coronoid process may be found bilaterally or unilaterally, resulting in progressive, painless restriction of mandibular opening, as a result of the impingement of the coronoid process on the medial aspect of the zygomatic arch(es) or on the posterior maxilla. This rare condition is more common in patients with ankylosis (fusion) of the temporomandibular joint as a reactive response to attempted muscle function against resistance and more common in males. It usually presents in the middle of the third decade, although it has been reported in neonates. The aetiology is unknown. Treatment involves the resection of the coronoid process(es) ( ).
Condylar process
The mandibular condyle varies considerably in both size and shape. It consists of a core of cancellous bone covered by a thin outer layer of compact bone; the intra-articular aspect is covered by layers of fibrocartilage. When viewed from above, the condyle is roughly ovoid in outline, its anteroposterior dimension (approximately 1 cm) being roughly half its mediolateral dimension. The long axis of the condyle is at right-angles to that of the mandibular ramus but, as a result of the flare of the ramus, the lateral pole of the condyle is slightly anterior to the medial: if the long axes of the two condyles are extended, they meet at an obtuse angle, varying from 145° to 160°, at the anterior border of the foramen magnum. The slender neck of the condyle expands transversely upwards and joins the ramus to the articular head. The pterygoid fovea, a small depression on the anterior surface of the neck below the articular surface, receives part of the attachment of the inferior head of lateral pterygoid. The condyle is one of the most common sites for mandibular fractures.
Condylar hyper- and hypoplasia
Hyperplasia of the mandibular condyle is a rare unilateral condition that results in facial asymmetry and an altered occlusion (bite). The condition may present at any age; if it develops prior to puberty, growth may not cease at the end of the growth period. Reports vary as to male : female ratio. Although condylar hyperplasia is said to be self-limiting, removal of the growth site in the condyle may be necessary to arrest the condition. Correction of the asymmetry of the jaw is usually performed; however, self-correction of the asymmetry has been reported. A variety of classification systems have been suggested ( , , , ).
Condylar hypoplasia is also uncommon. It is often associated with more extensive craniofacial anomalies, particularly hemifacial microsomia, where many of the first arch structures fail to develop fully and with failure of the development of the whole temporomandibular articulation. The condition has been subclassified by and a modified version by : currently the OMENS classification is widely used to assess both bone and soft tissue defects ( ).
Accessory foramina
Accessory mandibular foramina are usually unnamed and infrequently described, and yet they are numerous. They may transmit auxiliary nerves to the teeth (from facial, mylohyoid, buccal, transverse cervical cutaneous, lingual and other nerves), and their occurrence is significant in dental anaesthetic blocking techniques. The innervation of the teeth is discussed in Chapter 37 . The accessory lingual foramina in the mandibular symphysis are particularly relevant in dental implant surgery and osteotomies, e.g. genioplasty, at this site.
Ossification
The mandible forms in dense fibromembranous tissue lateral to the inferior alveolar nerve and its incisive branch, and also in the lower parts of Meckel’s cartilage (first branchial arch). Each half is ossified from a centre that appears near the mental foramen between postfertilization days 42 and 50. From this site, ossification spreads medially and posterocranially to form the body and ramus, first below, and then around, the inferior alveolar nerve and its incisive branch. Ossification then spreads upwards, initially forming a trough, and later crypts, for the developing teeth. From postmenstrual week 10, Meckel’s cartilage below the incisor rudiments is surrounded and invaded by bone. The mandibular condyle and coronoid process do not develop from the primary (Meckel’s) cartilage but from secondary cartilages that appear later ( Fig. 38.6 ). A conical mass, the condylar cartilage, extends from the mandibular head downwards and forwards in the ramus, and contributes to its growth in height. Although it is largely replaced by bone by midfetal life, its proximal end persists as proliferating cartilage under the fibrous articular lining until about the third decade. Another secondary cartilage, which soon ossifies, appears along the anterior coronoid border, and disappears before birth. One or two cartilaginous nodules also occur at the symphysis menti. These may ossify as variable mental ossicles in symphysial fibrous tissue between postmenstrual weeks 25 and 28; they unite with adjacent bone before the end of the first postnatal year.
Age changes in the mandible
At birth, the two halves of the mandible are united by a fibrous symphysis menti ( Fig. 38.7B ). The anterior ends of both rudiments are covered by cartilage, separated only by a symphysis. Until fusion occurs, new cells are added to each cartilage from symphysial fibrous tissue, and ossification on its mandibular side proceeds towards the midline. When the latter process overtakes the former and ossification extends into median fibrous tissue, the symphysis fuses. At this stage, the body is a mere shell, which encloses the imperfectly separated sockets of deciduous teeth. The mandibular canal is near the lower border, and the mental foramen opens below the first deciduous molar and is directed forwards. The condyle is almost in line with the occlusal plane of the mandible and the coronoid projects above the condyle. During the first three postnatal years, the two halves join at their symphysis from below upwards, although separation near the alveolar margin may persist into the second year. The body elongates, especially behind the mental foramen, providing space for three additional teeth. During the first and second years, as a chin develops, the mental foramen alters direction; it no longer faces forwards but now faces backwards, as in the adult mandible, and accommodates the changing direction of the emerging mental nerve.
In general terms, increase in height of the body of the mandible is achieved primarily by formation of alveolar bone associated with the developing and erupting teeth, although some bone is also deposited on the lower border. Increase in length of the mandible is accomplished by deposition of bone on the posterior surface of the ramus and concomitant compensatory resorption on the anterior surface (accompanied by deposition of bone on the posterior surface of the coronoid process and resorption on the anterior surface of the condylar process); a part of the ramus is therefore modelled into an addition to the mandibular body. Increase in width of the mandible is produced by deposition of bone on the outer surface of the mandible and resorption on the inner surface. An increase in the comparative size of the ramus compared with the body of the mandible occurs during postnatal growth and tooth eruption.
The role of the condylar cartilages in mandibular growth remains controversial. One view suggests that continued proliferation of this cartilage is primarily responsible for the increase in both the mandibular length and the height of the ramus. Alternatively, there is persuasive experimental evidence that proliferation of the condylar cartilage is an adaptive response to function, rather than being genetically determined. Condylar growth and remodelling have been shown to be influenced significantly by local factors – notably, movement and loading of the temporomandibular joint – and to be relatively immune to systemic influences such as vitamin C and D deficiency. Considering the changes that occur in the dentition throughout life, continuous adaptation of the temporomandibular articulation is required in order to maintain functional occlusal alignment between the upper and lower arches of teeth; this adaptation is thought to be largely the result of ongoing condylar remodelling.
In adults, alveolar and subalveolar regions are about equal in depth, and the mental foramen appears midway between the upper and lower borders. If teeth are lost, alveolar bone is resorbed, and both the mental foramen and the mandibular canal come to lie closer to the superior border ( Fig. 38.7A ). The mental foramen is placed higher than the mandibular canal posterior to it, and so resorption of the alveolus in edentulous patients exposes the nerve at the foramen, i.e. prior to the nerve in the mandibular canal ( , , ).
Bone resorption in the mandible
The pattern of bone resorption (atrophy) of the mandible following the loss of teeth is said to be in a centrifugal (‘down and out’) direction, compared to a centripetal direction in the maxilla. These differences produce a progressive increase in the incongruity of the alveolar processes of the jaws. Bone loss is not limited to the alveolar part; it can involve the base (basal bone) to varying degrees. Progressive remodelling of the mandible and maxilla accompany the bone loss; it is not limited to the body of the mandible but also involves the coronoid process and the mandibular condyle, and reduction in both the height and width of the ramus. This bone loss has implications in denture construction, dental implant surgery and mandibular fractures ( Figs 38.8 – 38.9 ) ( , , , , ).
Blood supply of the mandible
The blood supply to the body of the mandible is derived from its principal nutrient artery, the inferior alveolar artery, and from the vessels supplying genioglossus, geniohyoid and the anterior belly of digastric (all muscles attached to the lingual aspect of the body of the mandible between the mental foramina). The blood supply to these muscles is from the sublingual branch of the lingual artery and the submental branch of the facial artery. Branches of these vessels may perforate the lingual cortical plate through lateral lingual foramina in the premolar region and genial foramina in the midline (when these foramina are present) ( Fig. 38.10 ). Anastomoses are common. A branch of the submental artery may anastomose with the mental artery, permitting retrograde vascular supply to the body and symphysis (relevant in mandibular fractures). The vascular supply to the mandibular symphysis is of importance in dental implant surgery. The ramus, including the mandibular angle, is supplied by the inferior alveolar artery and from the vessels supplying masseter and medial pterygoid. Vessels supplying temporalis supply the coronoid process. The vascular supply to the mandibular condyle, temporomandibular joint and the individual masticatory muscles is described below ( , , , , ).
Endosseous blood supply to the mandible via lingual foramina
The endosseous supply of the mandibular symphysis via the lingual foramina, and the rich vascular supply to the anterior floor of the mouth are of particular importance in dental implant surgery and osteotomies, e.g. genioplasty, at this site.
Foramina at the level of, or above, the genial tubercle (superior genial foramen) and below the genial tubercle (inferior genial foramen) are almost always found ( , ). Lateral lingual foramina are usually identified, with an average distance above the lower border of the mandible of 5 mm ( ). The superior genial foramen may contain a branch of the lingual artery and nerve. The inferior foramen may contain a branch of the sublingual or submental arteries and a branch of the mylohyoid nerve. The lateral foramen may contain a branch of the submental artery ( , ). Although the relative contributions from the individual vessels vary, anastomoses between these perforating vessels and the inferior alveolar artery, within the mandible, are common. The soft tissues in the anterior floor of the mouth adjacent to the mandible are supplied by contributions from the sublingual, submental and mylohyoid arteries; there are considerable anastomoses between them ( , , , ). Brisk, potentially life-threatening haemorrhage has been reported with dental implant placement in the mandibular symphysis, usually associated with perforation of the lingual cortical plate of the mandible ( , , , ) ( Fig. 38.11 ) and death has resulted from genioplasty, secondary to haemorrhage in the anterior floor of the mouth (personal communication). The precise source of the haemorrhage can be difficult to detect and may arise from both within the mandible and the soft tissues in the floor of the mouth, from any of the above-named vessels. The anastomoses between the vessels may result in haemorrhage on both sides of mylohyoid and thus into the sublingual and the submental/submandibular spaces bilaterally. As the lateral and midline lingual foramina are closer to the lower border of the mandible, caution with longer implants has been recommended in this region.
Tissue spaces
The contents of the infratemporal fossa are contained within a well-defined space that is bounded by and incorporates the masticatory muscles and is termed the masticator space ( ). It contains temporalis, masseter, medial and lateral pterygoid, the ramus and coronoid process of the mandible, the mandibular nerve and otic ganglion, the maxillary artery and the pterygoid venous plexus, and part of the buccal fat pad anterolaterally. The masticator space is closed posteriorly by the attachment of the deep cervical fascia, medial pterygoid and masseter (pterygomasseteric sling), and anteriorly, lateral to the ramus, by the firm attachment of masseter (the submasseteric space is a ‘potential’ space). Above the level of the zygomatic arch, the temporal fascia provides both the superior and lateral limits, by its attachments to the superior temporal line and the zygomatic arch, respectively. Below the zygomatic arch, the investing layer of deep cervical fascia (superficial layer of deep cervical fascia) splits into two laminae to enclose masseter, the lower part of temporalis and medial pterygoid, further defining the boundaries of the masticator space. The superficial (lateral) lamina covers masseter and is attached to the zygomatic arch, and the deep (medial) lamina runs on the deep surface of medial pterygoid, attaching to the skull base medial to the foramen ovale ( ). This fascial covering of the masticatory muscles is considered to be distinct from the parotid fascia (capsule). The superficial temporal space lies between the temporal fascia laterally and temporalis medially. The deep temporal space, like the submasseteric space, is a ‘potential’ space between temporalis laterally and the temporal fossa of the skull medially. Both spaces are in communication with the remainder of the masticator space inferiorly. There is a view that the upper limit of the masticator space should be at the level of the zygomatic arch, on the grounds that since both temporal spaces communicate with the remainder of the masticator space, a single masticator space incorporates the temporal fascia, muscles and temporal spaces. Medial to the ramus of the mandible, the pterygomandibular space (part of the masticator space) communicates freely with the pterygopalatine fossa, offering little resistance to the spread of infection or tumours. Posteriorly penetrating maxillary tumours directly involve the masticator space/infratemporal fossa and the pterygopalatine fossa. Resection of the masticator space has been termed a ‘compartment’ resection of the mandible ( , ) ( Fig. 38.12 ).
Temporomandibular Joint
The temporomandibular joint (TMJ) is a synovial joint between the glenoid fossa (mandibular fossa) of the temporal bone and the mandibular condyle. It is unusual in that its articular surfaces are lined by fibrocartilage, rather than by hyaline cartilage: fibrocartilage is less susceptible to degeneration and has a greater repair capacity. The joint cavity is divided into upper and lower compartments (‘spaces’) by a fibrocartilaginous articular disc.
The anterior limit of the glenoid fossa is the articular eminence. This transverse ridge of dense bone, tilted down at an angle of approximately 25° to the occlusal plane, forms most of the articular surface of the mandibular fossa. It is strongly convex in the sagittal plane with a slight concavity in the coronal plane and extends out laterally to the zygomatic arch as the articular tubercle. The articular eminence may contain air cells from the mastoid in around 5% of cases on CT scan ( ), which may be clinically relevant when the eminence is surgically reduced or screws are placed for fixation. The roof of the glenoid fossa is thin and often translucent when held to the light, confirmation that this is not a major load-bearing area of the joint ( ). The posterior wall is formed by the tympanic plate, which also forms the anterior wall of the external acoustic meatus.
The anterior articular area of the fossa (articular fossa) is formed entirely from the squamous portion of the temporal bone and lined by articular tissue that extends anteriorly beyond the articular summit on to the preglenoid plane. The squamotympanic fissure marks the junction with the posterior non-articular (tympanic) area. The tegmen tympani, a bony plate of the petrous temporal, intervenes in the medial aspect of the fissure, where the squamotympanic fissure becomes the petrotympanic fissure. The postglenoid tubercle at the root of the zygomatic arch, just anterior to the squamotympanic fissure, separates the squamotympanic fissure laterally from the tympanic plate.
The condylar head, tilted forwards on the neck at an angle of approximately 30° (physiological anteversion), articulates with the fossa on its anterior and superior surfaces. Like the eminence, both its slope and shape are variable and influenced by age, function and dentition. In the coronal plane, its shape varies from that of a gable (particularly marked in those whose diet is hard) to roughly horizontal (in the edentulous).
It is probably impossible to measure the pressure developed on the articular surfaces of the human jaw joint when biting: direct measurement of loads across the joint in animals has demonstrated significant intermittent loading during mastication. However, there is irrefutable theoretical evidence based on Newtonian mechanics that the jaw joint is a weight-bearing joint. With a vertical bite force of 500 N on the left first molar, the right condyle must support a load of well over 300 N ( ). The non-working condyle is more loaded than the condyle on the working side, which may help explain why patients with a fractured condyle choose to bite on the side of the fracture.
Fibrous capsule
The lower part of the joint is surrounded by tight fibres that attach the condyle of the mandible to the disc (collateral ligament). The upper part of the joint is surrounded by loose fibres that attach the disc to the temporal bone ( Fig. 38.13 ). Thus, the articular disc is attached separately to the temporal bone and to the mandibular condyle, forming what could be considered two joint capsules. These attachments stabilize the disc but allow rotation over the condyle. Longer fibres joining the condyle directly to the temporal bone may be regarded as reinforcing. The capsule is attached superiorly to the anterior edge of the preglenoid plane, posteriorly to the lips of the squamotympanic fissure, between these to the edges of the articular fossa, and inferiorly to the periphery of the neck of the mandible.
Ligaments
The ligaments of the temporomandibular joint are the temporomandibular (lateral), sphenomandibular and stylomandibular ligaments.
Temporomandibular (lateral) ligament
The broad temporomandibular ligament reinforces the joint capsule laterally and is attached superiorly to the articular tubercle on the root of the zygomatic process of the temporal bone (see Fig. 38.13 ). It extends downwards and backwards at an angle of approximately 45° to the horizontal, and is attached to the lateral surface and posterior border of the neck of the condyle, deep to the parotid gland. A short, almost horizontal band of collagen connects the articular tubercle anteriorly to the lateral pole of the condyle posteriorly and may function to prevent posterior displacement of the resting condyle and initiate translation of the condyle on mouth opening.
Sphenomandibular ligament
The sphenomandibular ligament is medial to, and normally separate from, the capsule (see Fig. 38.13 ). It is a flat, thin band that descends from the spine of the sphenoid. It widens as it reaches the lingula of the mandibular foramen, having an average width at its insertion into the mandible of about 12 mm. Some fibres traverse the medial end of the petrotympanic fissure and attach to the anterior malleolar process: they represent a vestige of the dorsal end of Meckel’s cartilage.
With the jaw closed, there is approximately 5 mm slack within the ligament. It becomes taut when the jaw is about half open. Superiorly, lateral pterygoid, the auriculotemporal nerve and the maxillary artery and vein are lateral to the ligament, the nerve and vessels running between the ligament and the condylar neck. The chorda tympani nerve lies medially and occasionally grooves the spine of the sphenoid. Anteroinferiorly, the inferior alveolar nerve and vessels and a parotid lobule separate the ligament from the ramus of the mandible. The vessels and nerves to mylohyoid pierce the ligament adjacent to the lingula. Medial pterygoid is inferolateral. The sphenomandibular ligament is separated from the pharynx by fat and a pharyngeal vein.
Stylomandibular ligament
The stylomandibular ligament is a thickened band of deep cervical fascia that stretches from the apex and adjacent anterior aspect of the styloid process to the angle and posterior border of the mandible (see Fig. 38.13 ). Its position and orientation indicate that it cannot mechanically constrain any normal movements of the mandible and does not seem to warrant the status of a ligament of the joint.
Synovial membrane
The synovial membrane lines the inside of the capsule of the joint but does not cover the disc or the articular surfaces (condyle, fossa or articular eminence). The synovium is most abundant in the bilaminar zone of the articular disc, forming loose folds posteriorly when the condyle is positioned in the glenoid fossa. These folds disappear when the condyle is protruded and the synovium is stretched.
Synovial fluid and joint lubrication
The coefficient of friction between the articulating surfaces of the temporomandibular joint is almost zero ( ), reflecting the net result of a combination of adequate joint lubrication, the surface structure of the articulating surfaces and the articular disc. Joint lubrication depends on the synovial fluid, which also provides protection and nutrition to the articular surfaces and is the sole supplier of nutrients to the avascular disc. Surface active phospholipids (SAPLs) and hyaluronic acid are the key lubricants of the joint and act to protect the articular surfaces. Abnormalities of the joint lubrication system, e.g. changes resulting from uncontrolled oxidative stress, may play a role in the onset of some temporomandibular joint disorders such as anchored disc phenomenon ( ).
Articular surfaces
The anterior and superior surfaces of the mandibular condyle and the articular eminence and preglenoid plane of the squamous temporal bone are the principal articulating surfaces of the joint, as reflected in the thickness of the articular tissue covering these surfaces. The fibrocartilaginous covering of the condyle is composed of four distinct layers ( ). The most superficial layer consists of densely packed fibres of type I collagen arranged mostly parallel to the articular surface and aligned in an anteroposterior direction (this can be seen as striation on arthroscopy – ). This covers a thin cellular layer, the proliferative zone that is continuous with the cambial layer of the periosteum beyond the margins of the joint. The third layer, of hypertrophic cartilage, is rich in intercellular matrix and contains chondrocytes scattered throughout its depth and randomly orientated fibres of collagen type II. The fourth layer, immediately above the subchondral bone, is the zone of calcification. Although the number of chondrocytes within the hypertrophic zone decreases with age, undifferentiated mesenchymal cells have been identified in postmortem specimens of all ages ( ), indicating a persistent capacity for proliferation and repair in condylar cartilage and may explain why condylar remodelling occurs throughout life ( , ).
Articular disc
The articular disc divides the joint into a superior (discotemporal) space and an inferior (discomandibular) space, both filled with synovial fluid. The transversely oval disc is composed of avascular dense fibrous connective tissue with some chondrification in areas of maximum loading ( Fig. 38.14 ). It has a thick margin forming a peripheral anulus and a central depression in its lower surface that accommodates the articular surface of the mandibular condyle. The depression probably develops as a mechanical response to pressure from the condyle as it rotates inside the anulus. The disc is stabilized on the condyle in three ways. Its edges are fused with the part of the capsular ligament that surrounds the lower joint compartment tightly and is attached around the neck of the condyle; well-defined bands in the capsular ligament attach the disc to the medial and lateral poles of the condyle (collateral ligaments); the thick anulus prevents the disc sliding off the condyle (self-centring capability), provided that the condyle and disc are firmly lodged against the articular fossa (as is normally the case).
In sagittal section, the disc has three distinct parts, namely an anterior band, a thinner intermediate zone and a posterior band. The posterior band is the thickest. Its upper surface is concavo-convex where it fits against the convex articular eminence and the concavity of the articular fossa. Posteriorly, the disc is attached to a richly vascularized and innervated region, the bilaminar zone (posterior attachment), that splits into two laminae: unlike the rest of the disc, its normal function is to provide attachment rather than intra-articular support. The upper lamina is composed of fibroelastic tissue and is attached to the squamotympanic fissure. A condensation of elastic fibres in the medial portion of the upper lamina is visible as the posterior oblique protuberance on arthroscopy (see ). The lower lamina is composed of fibrous non-elastic tissue and is attached to the posterior aspect of the condyle. The intervening connective tissue between the upper and lower laminae contains a vascular plexus and is well innervated, but the central part of the disc itself is avascular and not innervated. With anterior movement of the disc–condyle complex, the volume of the posterior attachment increases as a result of the negative pressures generated, resulting in an influx of blood into the venous plexus: this pumping mechanism is important in the nutrition of the joint ( ).
Upper and lower joint compartments
The upper joint space contains approximately 1.2 ml of synovial fluid and the lower approximately 0.9 ml. Both spaces may be considerably distended with fluid for diagnostic purposes in temporomandibular joint arthrography, for therapeutic purposes in arthrocentesis, and to improve access and visibility in arthroscopy. Both joint spaces have an anterior and posterior recess or pouch, and are lined by synovium, which has a grey hue when viewed through an arthroscope (see ).
The anterior portion of the disc is attached to part of the upper head of lateral pterygoid and this muscle may aid in anterior translation of the disc during joint function. Hyperactivity of lateral pterygoid is thought to contribute to anterior disc displacement and possibly dislocation of the condyle, and for this reason injection of botulinum toxin is found to be helpful in the management of both of these conditions.
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