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Applied Anatomy II: Mandibular Arch

Buccal ner

alveolar nerve

alveolar artery

oid muscle

https://t.me/med1917

Bucinator

muscle

Lingual nerve

Lingual vein and artery

Submandibular gland duct

Inferior

alveolar vein

Inferior

Figure3.4 Sagittal section of the floor of the mouth through the third molar. Source: Redrawn with changes from Andreasen

etal. (1997).

Inferior

Mylohyoid nerve

Mylohy

alveolar process (Figure3.4), in 10% it may lie over the lingual alveolar crest at the third molar and in one in 300 cases it may run above the soft retromolar tissue (Annex 3).

The lingual nerve passes very near the surface here, underneath the mucosa of the floor of the mouth and over the mylohyoid muscle (Figure3.4), separating off the bone toward the medial zone and running deeper as it progresses forward (Annex 3). This is a good area to block the lingual nerve.

Here it distributes branches to the submandibular ganglion, a peripheral parasympathetic ganglion that receives fibers from the chorda tympani. Its course subsequently deepens, crossing medially beneath the submandibular or Wharton’s duct. It then rises medially (internally), entering the tongue where its branches communicate with the hypoglossal nerve (CN XII). It terminates at the sublingual gland, where it gives off its terminal branches.

Innervation

The lingual nerve supplies:

● The fibromucosa (alveolar mucosa and gums), bone, and

periosteum of the lingual zone of the lower arch on the same side to the midline.

● The fibromucosa of the floor of the mouth on the same

side to the midline.

● The anterior two- thirds of the tongue to the midline.

The lingual nerve supplies some proprioception to the muscles of the tongue (Barker and Davies1972) and some gustatory perception to the anterior tongue (Malamed2004; Jastak etal.1995).

Remarks

At the lingula, the lingual nerve is multifascicular, with one to eight (mean = three) fascicles, although in 30% of cases it has only one, making it vulnerable to irreversible damage in the event of trauma caused by needle impact during the mandibular block procedure (Pogrel etal.2003). Moreover, in the retromolar and third molar zones it may adopt a ribbon- like shape with a diameter of 0.5 mm in less than 10% of cases according to some authors (Kiesselbach and Chamberlain 1984). Since, as noted, it courses adjacent to the lingual alveolar process (Annex 3), it is vulnerable there also (given that the diameter of a 25 G needle is

0.5

mm).

Inferior Alveolar Nerve

Course

The inferior alveolar nerve, the largest of the three branches of the posterior division of the mandibular nerve, arises around 4–5

mm under the foramen ovale, descends along the pterygomandibular space between the internal surface of the lateral (external) pterygoid muscle and the interpterygoid aponeurosis, and courses obliquely (posteriorlyanteriorly, interiorly- exteriorly) from there parallel to but following a more posterior and external course than the lingual nerve. In this downward length it gives off the mylohyoid nerve (Figure3.2).

In its descent it converges with the internal surface of the ramus of the mandible as far as the mandibular foramen (Sicher1946; Barker and Davies 1972), through which it passes with the inferior alveolar artery (branch of the

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35 Mandibular Nerve (V3)

incisive canal

loop

foramen

canal

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maxillary artery) and associated veins (tributaries of the pterygoid plexus; Archer and Zubrow 1954; Khoury etal.2010), which are usually located behind the inferior alveolar nerve (Murphy and Grundy 1969; Roda and Blanton1994). In this area, where its diameter is 2–3

mm (Annex 3), it gives an accessory branch for the wisdom tooth in 10–40% of cases just before or after entering the mandibular canal (Sicher1946; Barker and Davies1972).

The inferior alveolar nerve runs across the body of the mandible through the mandibular canal, usually under the mandibular molar apexes, close to the mental foramen (normally located near the second premolar apex) where, around half the time, it courses further, forming a 2–3 mm long anterior loop (Annex 4) that takes an abrupt posterior and vestibular turn, rising until it abuts with the mental foramen. At this point it distributes two branches (Figure3.5).

1) The internal branch or mandibular incisive nerve pro-

ceeds in more 85% of cases from a forward10–15

mm long mandibular incisive canal, coursing

running,

adjacent to the buccal surface of the mandible (Annex

4) and through the trabecular or medullary bone under the apexes of the anterior teeth (Mardinger etal.2000; Pires etal.2012; Apostolakis and Brown2013; Huang et al. 2013) to supply the mandibular first premolar, canine, and incisors on that side. In the few cases where there is no mandibular incisive canal, the mandibular incisive nerve forms a plexus in the trabecular or spongy bone to substitute for it, but in neither case does it cross the midline (Olivier1927; Sicher1946), site of the intermandibular cartilage in the embryo.

Mandibular

Figure3.5 Termination of the mandibular canal at the

mandibular incisive canal, mental foramen, and anterior loop.

Mental

Mandibular

2) The external branch or mental nerve initially runs

upward and backward after exiting the mental foramen to then turn forward and form the labial plexus in the soft tissue mucosa, which does cross the midline (Figure19.9, Chapter19). It subsequently anastomoses with fibers from the other side, passing in some cases through foramina of the body of the mandible and at times innervating the pulp of the contralateral incisors (Starkie and Stewart1931; Rood1977).

Innervation

The inferior alveolar nerve supplies:

● The molar and premolar pulp and periodontal ligament,

and via the mandibular incisive nerve, canines and incisors.

● Interdental papillae as well as molar and premolar (and

via the mandibular incisive nerve, also canine and incisor) fibromucosa, bone, and periosteum.

● Buccal, via the mental nerve; fibromucosa (alveolar

mucosa and attached gums), bone, and periosteum of the entire zone between the premolars and the lower central incisor, although this may vary depending on the area covered by the buccal nerve (Sutton 1974), with extremes ranging from the entire molar zone (10% of cases) to the canines and incisors only (1%) (Hendy and Robinson1994).

● Tip of the chin and its skin, lower lip, likewise via the

mental nerve.

Remarks

When the mouth is closed the inferior alveolar nerve is folded and lies very medially (internally) in the pterygomandibular space, separated from the ramus of the mandible. When the mouth is wide open, the nerve stretches and is positioned posteriorly, coursing adjacent to the internal surface of the ramus (Sicher1950) near the sulcus colli (Bremer1952; Via1953).

The inferior alveolar nerve comprises several fascicles whose composition tends to change along its course (Rood 1978a). Its myelinated fibers exhibit a node of Ranvier every 0.5–1.8 mm (Rood1977,1978b) and given that to anesthetize a nerve of these characteristics at least three such nodes must be blocked (Blair and Erlanger

1939), around 6 mm of the inferior alveolar nerve must be bathed in the anesthetic (Rood1977,1978b). The myelin sheathes around the axons of this nerve bear Schmidt– Lantermann clefts. These oblique inclusions communicate the axon with the exterior and afford the nerve greater elasticity when the mouth is wide open, facilitating application of the anesthetic through the clefts (Heasman and Beynon1987).

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Applied Anatomy II: Mandibular Arch

Mandibular

foramen

ondylar

Mandibular

groove

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Since at the lingula the inferior alveolar nerve is multifascicular, with three to 14 fascicles (mean=7), it is less likely to be injured by needle trauma during mandibular block as it is highly unlikely that all the fascicles would be injured (Pogrel etal.2003).

Mylohyoid Nerve

Course

Motor fibers predominate in this mixed nerve. The mylohyoid nerve branches from the inferior alveolar nerve around 15

mm (range 4–23 mm) before entering the mandibular foramen (Wilson etal.1984; Bennett and Townsend2001; Stein etal.2007) (Figure3.2). It runs against the ramus of the mandible in the mylohyoid groove, an osseous groove located beneath the mandibular foramen, crosses the sphenomandibular ligament and the medial (internal) pterygoid muscle insertion to then enter the floor of the mouth or submandibular region (Archer and Zubrow 1954; Roberts and Harris 1973; Madeira et al. 1978). It passes under the mylohyoid muscle (Figure3.4), coursing along and adjacent to the internal surface of the body of the mandible, just below the mylohyoid line, which in 15% of cases may form a canal for the mylohyoid nerve as the ligaments and periosteum that cover it ossify (Arensburgh and Nathan1979).

Innervation

● The motor part of the nerve supplies the mylohyoid mus-

cle and the anterior belly of the digastric muscle.

● The sensory fibers innervate the skin at the tip of the

chin (Roberts and Harris1973) and the dental pulp of molars, premolars, canines, and incisors (Novitzky1938; Sicher1946; Carter and Keen1971; Frommer etal.1972; Madeira et al. 1978; Chapnick 1980; Bennett and Townsend 2001), as well as the contralateral incisors (Madeira etal.1978).

Coronoid

process

Mental

Figure3.6 Predominant anatomical features on the external

surface of the mandible.

Coronoid process

Temporal crest

Coronoid nocht

Retromolar fossa

Retromolar trigone

Figure3.7 Predominant anatomical features on the internal

surface of the mandible.

Oblique line

Myloyoid line

Myloyoid

nocht

Condyle

C neck

Angle of mandibl

nocht

Condyle

Sulcus coll

Lingula

Mandibular foramen

Angle of mandible

Note: Exceptionally, the mylohyoid nerve may proceed from the inferior end of the lingual nerve (Jablonski etal.1985).

Body ofthe Mandible

The mandible is the largest, strongest, and lowest facial bone. It is horseshoe- shaped, with a horizontally curved body (body of the mandible) flanked posteriorly by two ascending branches (rami of the mandible). The body of the mandible, also known as the horizontal ramus of the mandible, features several characteristics of interest here (Figures3.6 and3.7).

Cortical Bone Thickness

The teeth are housed in the alveolar part, on the upper border of the body of the mandible. The mandible or lower jaw is denser than the maxillary bone and, as shown in Table3.2, at the apex the cortical, as well as the spongy or medullary bone, is thicker, particularly in the posterior vestibule, due in part to the more lingual position of the molars (Denio et al. 1992). For that reason, mandibular block is required in pulpal anesthesia of the molars.

Buccal infiltration techniques can be used in the anterior mandible, which is less dense than the posterior bone. In contrast, the cortical bone is even thicker in the lingual region.

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Table3.2 Mean vestibular andlingual height (mm) ofcortical

igone

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andmedullary bone over apexes ofmandibular teeth.

Buccal Lingual

Tooth Cortical Medullary Cortical Medullary

Incisors 1–2 2–3 3–4 2–3 Canines 1–2 3–5 2–3 4–5 Premolars 0–5 0.5–5 3.5 1–3 Molars 2–5 2–6 3–4 1–2

Source: From data published by Arens etal. (1984), Denio etal. (1992) and Gowgiel (1992).

Retromolar Zone (Trigone andFossa)

This zone has significant practical implications in light of the presence of accessory innervation, primarily in the dental pulp of the mandibular molars very likely due to: (i) the high frequency (45%, ranging from 12% to 92%) of mandibles with accessory foramina (Löfgren1957; Carter and Keen1971; Haveman and Tebo1976), the largest diameter foramina in the mandible (Haveman and Tebo1976), and the presence, confirmed by anatomic dissections and histological studies, of many nerve fibers (Schejtman etal.1967; Sutton1974; Singh1981); and (ii) the existence of dual (bifid) mandibular canals, here denominated retromolar canals (Table3.3), detected with modern cone beam computed tomographic techniques in 15% of cases. The retromolar zone consists in two structures, the retromolar trigone and fossa (Figure3.8).

   37

emporal crest

Alveolar crest

Retromolar

fossa

Oblique line

Figure3.8 Retromolar trigone and fossa.

Retromolar tr

raphe or ligament, the reference point for direct or conventional mandibular block.

Retromolar Fossa

This depression, the insertion of the buccinator muscle, is lodged in the lateral (external)-

most part of the retromolar trigone. It is bounded medially (internally) by the alveolar crest.

Mandibular Canal

Retromolar Trigone

The retromolar trigone is a triangular depression located behind the wisdom teeth. It has no muscular insertions (Sicher1946) and is bounded laterally (externally) by the alveolar crest and medially (internally) by the temporal crest in the ramus of the mandible (Löfgren1957). Its internal surface is the attachment of the pterygomandibular

Table3.3 Percentage ofretromolar (bifid) canals discovered withcone beam computerized tomography.

Reference No. of patients No. of hemimandibles No. of retromolar canals Percentage (%)

Naitoh etal. (2009) 122 244 29 12.0 Kuribayashi etal. (2010) 252 301 5 1.7 Naitoh etal. (2010) 28 56 3 5.4 Orhan etal. (2011) 242 484 78 16.1 Correr etal. (2013) 75 150 80 53.3 Kang etal. (2014) 1933 — 104 5.4

After entering the mandibular foramen the inferior alveolar vascular-

nerve package passes through this canal, also formerly known as the inferior dental canal, across the entire body of the mandible to the mental foramen (Figure3.9). The nerve lies in the center of the canal while the veins (Figure3.4) normally run along its ceiling and the artery courses lingually to the nerve (Pogrel etal.2009) or

Rounded mean 15%

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Applied Anatomy II: Mandibular Arch

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Figure3.9 Position of mandibular canal relative to the

posterior mandibular teeth.

Table3.4 Diameter ofmandibular canal.

Reference Diameter (mm)

DuBrul (1988) 4 Gowgiel (1992) 3 Ikeda etal. (1996) 3.4 Kilic etal. (2010) 2.5 Kuribayashi etal. (2010) 3.3 (2–4.6) OliveiraKang etal. (2014) 2.8 (1.5–4.3) Yu etal. (2015) 2.8 Koivisto etal. (2016) 3 Mean 3.1 Rounded mean 2–4 mm

Santos etal. (2012) 2–4

± 0.5 ± 0.8

± 0.5 (2.1–3.7)

superolingually (Lee etal. 2015). The canal is 2–4 mm in diameter (Table3.4), around 60 mm long (Liu etal.2009), and consists of a thin layer of condensed trabecular or spongy bone (Gowgiel 1992; Denio et al. 1992; Kilic etal.2010). Nonetheless, in around 25% of cases, the mandibular canal is not clearly defined (Table3.5).

The mandibular canal passes under the apexes of the posterior teeth 95% of the time and over them in less than 5%, coursing vestibularly in 60% of cases (Littner

Table3.5 Percentage ofpoorly defined mandibular canals.

Reference Number Method Percentage (%)

Olivier (1927) 50 Dissection 40 Carter and Keen (1971) 92 XHeasman (1988) 80 XDenio etal. (1992) 22 Dissection 28

Rounded mean 25

rays 11 rays 25

etal.1986). It sometimes passes lingually to the first molars and exactly at the apex in less than 5% of cases (Littner etal.1986; Denio etal.1992).

The canal runs downward, gradually separating off the third, second, and first molar apexes. It turns slightly upward near the premolars (Littner et al. 1986; Denio etal.1992), coursing adjacent to the lingual surface of the cortical bone and then shooting abruptly upward and toward the vestibule and often backward toward the mental foramen (Gowgiel1992). Half of the time the backward bend forms the so- called (2–3 mm long) anterior loop, forward of the mental foramen (Annex 3) (Figure3.5).

In the anterior area, forward of the anterior loop and the mental foramen, the mandibular canal disappears, forming in over 85% of cases a mandibular incisive canal around 2 mm in diameter and 10–15 mm long (Annex 4), which tends to course adjacent to the vestibular cortical bone (Starkie and Stewart1931; Gowgiel1992; Annex 4), favoring infiltration-

mediated pulpal anesthesia in the

incisor–canine area.

Mental Foramen

The mandibular canal terminates at the mental foramen before becoming the mandibular incisive canal. The mental foramen is round or oval, normally with a diameter of 2–4 mm and in 70% of cases opening toward the rear (Annex 5).

In 95% of cases, its horizontal position relative to the mandibular teeth is above the zone of the second premolar apex (Figure3.10). The zone of the second premolar apex is defined here to start slightly anterior to the second premolar, between the first and second premolar, and end slightly posterior to the second premolar, between the second premolar and the mesial root of the first molar. Vertically, it is positioned 10–15

mm above the lower ridge of the mandi-

ble (Annex 5).

In 5% of cases, the mental foramen has accessory foramina, 25% of which are multiple (Annex 5). These accessory foramina are smaller than the main foramen and there is usually only one, although cases of up to three or four have been reported (Martani and Stefanini 1964; Kadanoff

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Figure3.10 The most likely (95%) positions of the mental

https://t.me/med1917

foramen relative to the apex of the second mandibular premolar.

et al. 1970; Gershenson et al. 1986; Askar et al. 2018). Mandibles lacking the mental foramen have exceptionally been observed (Annex 5).

   39

Ramus ofthe Mandible

The ramus of the mandible was formerly also known as the ascending ramus of the mandible (Figures3.6 and3.7).

Divergent Angle

The divergent angle of the ramus of the mandible is formed by the line defining its axis (the most prominent anterior and posterior points of its margins) and the median (or midparallel to 27°, or very open (Simon and Kömives1938) (Figure3.11).

In around 90% of cases the angle ranges from 0° to 18°, providing access to the sulcus colli from the antagonist mandibular premolars in direct or conventional mandibular block. In the 10% of cases with a very open angle (18–27°), the syringe must rest on a very posterior area, around the contralateral mandibular molars, to reach the sulcus colli when performing a mandibular block (Simon and Kömives1938).

Ramus Width

sagittal) plane. It varies from 0° or nearly

Figure3.11 Divergent angle of the ramus of the mandible.

Source: Simon and Kömives (1938).

Lingula

The lingula, formerly also known as the Spix spine, lies on the inner part of the ramus of the mandible forward of (Hayward et al. 1977) and 5–9 mm above (Bremer 1952; Harvey1970) the mandibular foramen (Figure3.12). The lingula gives attachment to the wide, thin sphenomandibular ligament that runs from the lingula upward and backward along the internal surface of the medial (internal) pterygoid muscle to the spine of the sphenoid (Angelman1945).

The height of the lingula relative to the occlusal plane varies. In nearly 100% of adults it lies on average around 5 mm above the plane (Table 3.7) (Bremer 1952). The height varies with age in children and is usually below the plane in the youngest (Via1953; Benham1976). The factor that conditions the vertical position of the lingula is the eruption of the permanent teeth: as the permanent dentition erupts, the lingula will gradually move above the occlusal plane (Table3.8).

The width helps determine the depth of the insertion of the needle to reach the sulcus colli, where the inferior alveolar nerve lies when the mouth is wide open for a direct mandibular block. This anterior- posterior width ranges from 20 to 40 mm (Table3.6) with a mean of around 30 mm.

Mandibular Foramen

This is the foramen through which the inferior alveolar nerve and its vascular bundle enter the mandibular canal. It lies on the internal surface of the ramus of the mandible,

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Applied Anatomy II: Mandibular Arch

ular

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Table3.6 Anterior–posterior width ofthe ramus ofthe

mandible.

Value Sample

Range

Reference

Simon and Kömives (1938)

Nevin and Putterbaugh (1949)

Bremer (1952) 33 24–43 100 — Harvey (1970) 30 24–43 316 UK

Kay (1974) 34 18–50 451 — Hayward etal.

(1977) Menke and

Gowgiel (1979)

Nicholson (1985) 30 22–37 80 India Hetson etal.

(1988) Ashkenazi etal.

(2011) Ashkenazi etal.

(2011) Sittitavornwong

etal. (2017)

(mm) Number Origin

30 20–44 750 Multi- ethnic

18–44 — United States

—

31 — 34 —

30 — 107 Multi- ethnic

31 24–38 35 Europe and

30 23–37 317 —

30 — 21 Israel

32 —

32 27–38 28 United States

31.3 21.3–41.8 Mean 30 20–40 mm Rounded means

332 India 46 Multi- ethnic

Africa United States

(Bedouin)

38 Israel

(Bedouin)

Lingula

level

Occlusal plane

Mandib foramen

Figure3.12 Position of the lingula and mandibular foramen

relative to the mandibular occlusal plane.

Table3.7 Height oflingula relative toocclusal plane inadults

Bremer (1952)

Height (mm)

−3 0.25 2.5 1–5 63 91 6–10 31 6.5 11–20 5 0.1

Table3.8 Position oflingula over occlusal plane by age

Age (years) Number

n=399 (%)

Over occlusal

plane (%) Cause

Kay (1974) n=963 (%)

located anterior- posteriorly (from the oblique line to the posterior border) backward of mid- width (Via 1953; Benham1976; Hayward etal.1977; Menke and Gowgiel1979; Hetson etal.1988). In dry skulls it exhibits a wide, 8–10 mm (range 6–12

mm) diameter (Hayward etal.1977), although dimensions of around only 5 mm appear on (admittedly deformed) panoramic X- rays (Liu etal.2009).

As noted, the mandibular foramen lies backward of and under the lingula (Figure 3.12) and in around 75% of cases, and under the occlusal plane and above it in only 5% (Table3.9).

Sulcus colli

The sulcus colli or groove of the mandibular neck (Sicher1946) is a depression located in the distal third of

2.5–5 6 50 Stabilization primary teeth 5–9 11 80 Eruption first permanent

molar

9–11 24 100 Eruption first and second

premolars

>12 13 100 Eruption second

permanent molar

Source: From Benham (1976).

the internal surface of the ramus of the mandible (at times just barely visible) that descends obliquely forward toward the internal condylar neck to the mandibular foramen (Figure3.7).

While not included in anatomical terminology (FCAT1998), this anatomical structure is important for clinicians because in a wide open mouth the inferior alveolar nerve, which is targeted by the needle in direct or

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Pterygomandibular Space 41

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Table3.9 Position ofmandibular foramen relative toocclusal

plane.

Position relative to

occlusal plane

Below

Flush

Above

Reference Number Population

Lotric (1956) 200 Yugoslavia 82 13 5 Harvey (1970) 210 India 84 9 7 Harvey (1970) 158 Britan 70 24 6 Nicholson

(1985) Mwaniki and

Hassanali (1992) Palma etal.

(2020)

80 India 75 23 2

79 Kenia 65 31 5

82 Brazil 84 1 15

Means 76.7 16.7 6.7

Round means 75 20 5

(%)

conventional mandibular block, stretches and tends to run inside this groove (Bremer1952; Via1953).

Coronoid Notch

The coronoid notch is a depression where the mandible meets the anterior border of the ramus of the mandible located below the coronoid process and between the most anterior and lateral (external) parts of the ramus, a continuation of the oblique line, and the medial (internal)- most part of the temporal crest (Figure3.7).

Although this structure is not found in the anatomical

terminology (FCAT 1998) either, it has practical

significance because in this depression clinicians rest their finger or mirror to guide the needle and stretch the mucosa to access the pterygotemporal depression, the site for needle penetration in a direct or conventional mandibular block.

Accessory Foramina

The accessory foramina, 0.2–1.5 mm diameter holes on the surface of the mandible, provide passage to nutritional vessels and nerves (Shiller and Wiswell 1954; Carter and Keen1971; Barker and Davies1972; Sutton1974; Haveman and Tebo1976; Chapnick1980). Eight to 36 foramina per mandible are located in both the ramus of the mandible and its body, predominantly (80–85% of cases) on the internal surface (Sutton1974; Haveman and Tebo1976), where the largest lie (Carter and Keen 1971; Haveman and Tebo1976; Chapnick1980) (Table3.10). The practical significance of these foramina is that they may favor accessory innervation of the dental pulp.

The foramina on the external surface tend to cluster around incisors and canines (Sutton1974). Their practical implications stem not only from their role in the passage of accessory innervation (Starkie and Stewart 1931; Sutton 1974), but also in favoring the diffusion of anesthetic solutions, rendering local buccal infiltration effective in that region.

Pterygomandibular Space

The pterygomandibular space (formerly known as the pterygomaxillary space) is a narrow groove between the medial (internal) pterygoid muscle and the internal surface

Table3.10 Percentage ofdry mandibles withforamina onthe internal surface.

Reference Number Condylar

Carter and Keen (1971) 62 20 Ye s 33 — — Barker (1972) 122 40 Yes — — — Haveman and Tebo (1976) 150 100 100 92 — — Bilecenoglu and Tuncer (2006) 80 — — 25 — — Shiller and Wiswell (1954) 126 — — — 63 90 Zivanovic (1970) 335 — — — — 100 Sutton (1974) 300 — — — 80 85 Chapnick (1980) 122 — — — 69 —

Yes, foramina present but % of mandibles bearing them not specified; — , no data.

Ramus of mandible Body of mandible

Mandibular

neck (%)

t.me/Dr_Mouayyad_AlbtousH

foramen (%)

Retromolar

fossa (%)

Mylohyoid line

under premolar (%)

Genial

spine (%)

Applied Anatomy II: Mandibular Arch

Lateral pterygoid muscle

Superior pharyngeal

https://t.me/med1917

Mandibular nerve

Foramen ovale

Otic ganglion

Tensor veli

palatine nerve

Tensor veli palatini

muscle

Interpterygoid fascia

constrictor muscle

Medial pterygoid

nerve

Medial pterygoid

muscle

Figure3.13 Sagittal/frontal section of pterygomandibular space. Source: Redrawn with changes from Rouviere (1976).

Temporal muscle

Deep temporal nerve

Buccal nerve

Zygomatic process

Coronoid process

Maxillary artery

Inferior alveolar artery

Inferior alveolar nerve

Mandibular foramen

Masseter muscle

Ramus of mandible

of the ramus of the mandible. It lies in the lower infratemporal fossa (formerly the zygomatic fossa) (Galbreath and Eklund

1970) (Figures3.13 and3.14).

Anatomic Boundaries ofthe Pterygomandibular Space

● External/lateral. This boundary, formed by the internal

surface of the ramus of the mandible, features, from back to front, the sulcus colli, the mandibular foramen, and the lingula (forward of and above the mandibular foramen) (Sicher 1946; Barker and Davies 1972; Shaw and Fierst1988).

● Internal/medial. In the medial to external direction this

boundary consists o: the tensor veli palatini, the interpterygoid fascia or aponeurosis (a layer of fibrous tissue that prevents the diffusion of the anesthetic solution to the most medial/internal part of the pterygomandibular space) (Barker and Davies1972; Watson1973), and the medial (internal) pterygoid muscle under the interpterygoid fascia in the lower pterygomandibular space (Sicher 1946; Murphy and Grundy 1969; Shaw and Fierst1988). The interpterygoid fascia is partially thickened, especially this part which is attached to the spine of the sphenoid, on the skull base and the lingual of the mandible; this segment is named the sphenomandibular

ligament (Barker and Davies 1972; Lipski et al. 2013; Khoury etal.2011).

● Anterior/ventral (Murphy and Grundy1969; Galbreath

and Eklund1970).

○ The structures at the two ends of these boundaries are

as follows (Figure3.14).

■ In the lateral (external)- most region, the space is

bounded by the temporal crest that gives attachment to the deep tendon of the temporal muscle.

■ The medial (internal)- most boundary is the ptery-

gomandibular raphe or ligament, a fibrous band

that joins the posterior and most aponeurotic part of the buccinator muscle to the anterior-

most part of the superior pharyngeal constrictor muscle (buccino- pharyngeal aponeurosis) and lies forward of the medial (internal) pterygoid muscle. This ligament runs from the internal flange of the pterygoid process to the posterior-

most part of the

mylohyoid line.

The pterygotemporal depression, elliptical and elongated in shape that is pierced by the needle and hence of critical significance in direct or conventional mandibular block, lies between these two extremes (Figure16.7, Chapter16).

○ From the external- most to the internal- most part of the

pterygotemporal depression (Angelman1945) lie the

t.me/Dr_Mouayyad_AlbtousH

Pterygomandibular Space 43

Superficia

https://t.me/med1917

Facial nerve

(VII cranialnerve)

External carotid a.

Retromandibular v.

Parotid gland

Inferior alveolar v.

Inferior alveolar a.

Inferior alveolar n.

Lingula

Masseterm.

Ramus of mandible

Temporal crest

Deep tendon of the

temporal m.

Coronoid notch

ltendonof

the temporal m.

Buccal n.

Internal jugular v.

Vagus n. (X cranial nerve)

Internal carotid a.

Interpterygoid fascia

Sphenomandibular ligament

Medial pterygoid m.

Lingual n.

Lingual a.

Superior pharingeal constrictor m.

Pterygomandibular ligament/raphe

Temporopterygoid fascia

Pterygotemporal depression

Buccinator m.

Oral mucosa

Figure3.14 Schematic representation in cross- section of the pterygomandibular space at a medium height. a., artery; m., muscle;

n., nerve; v., vein. Source: Based on data from Sicher (1946), Murphy and Grundy (1969) and Barker and Davies (1972).

oral mucosa, the most aponeurotic part of the buccinator muscle, small adipose bodies, and the temporopterygoid fascia. That aponeurosis, like the interpterygoid aponeurosis or fascia of which it is a continuation, prevents the diffusion of the local anesthetic solution to the anterior and outer pterygomandibular space (Barker and Davies1972; Watson1973).

● Posterior/dorsal (Berns and Sadove 1962; Murphy and

Grundy1969; Galbreath and Eklund1970; Petersen1971; Shaw and Fierst1988). Here the boundary is the posterior border of the ramus of the mandible and the distalmost part of the parotid gland with its capsule (Angelman

1945). The facial nerve (CN VII) (Petersen1971) and the retromandibular vein (Murphy and Grundy1969) lie in the parotid (Figure3.14).

Behind and medially (internally) to the pterygomandibular space lies the parapharyngeal space, which houses the external and the (more posterior and medial) internal (common) carotid artery, the (more medial) jugular vein and the (more posterior) vagus nerve (CN X), and their fascia (Murphy and Grundy 1969; Petersen 1971). The internal carotid artery, internal

jugular vein, and vagus nerve run inside the carotid sheath (Kafalias etal.1987).

● Superior/cranial (Sicher 1946; Galbreath and

Eklund 1970; Coleman and Smith 1982; Shaw and Fierst1988). A frontal cross- section of the pterygomandibular space reveals its triangular shape, with the widest base at the top (Sicher1946; Petersen1971). It houses the condylar neck and the inferior surface of the lateral (external) pterygoid muscle, through whose bellies/fascicles/heads the buccal nerve runs (Figure3.13), and the descending loop of the maxillary artery (internal maxillary artery), where present (Lacouture etal.1983).

● Inferior/caudal (Sicher1946; Bremer 1952; Galbreath

and Eklund1970). The vertex and narrowest part of the triangle mentioned in the preceding bullet point lie at the bottom, where the following are found: the medial (internal) pterygoid muscle at its insertion into the internal surface of the ramus of the mandible (Figure3.13) and the lingual nerve exit to the floor of the mouth and submandibular (submaxillary) space (Via1953).

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