Surgical anatomy of periodontium and related structures

Periodontium consists of gingiva, periodontal ligament, cementum and alveolar bone. These structures surround and support the teeth and function as a unit to keep the teeth in position. The components of periodontium are supported and surrounded by various anatomical structures. Periodontitis and other pathologies associated with tooth and its supporting structures are commonly treated by surgical intervention. That is why, a sophisticated knowledge of the anatomy of the periodontium and related structures is mandatory to perform any surgical intervention in this region.  In the following discussion, we shall discuss in detail the anatomy of various structures associated with teeth and periodontium.

Maxilla

The two maxillae on each side of the face, house the maxillary teeth, contain maxillary sinus and makes the floor of the orbit. Each maxillary bone consists of a body and four processes. The body of maxilla makes the largest part of the bone and is pyramidal in shape. The interior part of the body is hollowed out by the…………………..

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Maxillary teeth are supplied by the maxillary division of the trigeminal (5th cranial) nerve, which arises as the sensory root from the pons, enters the trigeminal ganglion and divides into three branches viz. ophthalmic, maxillary and mandibular. The mandibular nerve leaves the cranial cavity foramen ovale, maxillary nerve leaves the cranial cavity via foramen rotundum and passes into the pterygopalatine fossa. In this fossa, the maxillary nerve is associated with the pterygopalatine ganglion (secretomotor) from which several other branches are given off before the nerve enters the orbit. These branches include posterior superior alveolar nerves (which enter maxilla via post alveolar foramina), greater palatine nerve, lesser palatine nerve, nasal nerves, lateral and medial posterior superior nasal and nasopalatine nerves. Then it enters the orbit via the inferior orbital fissure becoming the infraorbital nerve. Before the nerve comes out from infraorbital foramen, it gives off a number of branches collectively known as anterior superior alveolar nerve and middle superior alveolar nerve.

The palatine process of maxilla makes the anterior two-thirds of the palate (hard palate). The posterior one-third (soft palate) is a muscular structure with a fibrous foundation. The palatine processes of both the maxillae meet at………………

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The free gingival graft and connective tissue graft are commonly done periodontal surgical procedures for root coverage and for increasing the width of attached gingiva. The palate is most commonly used site for harvesting the graft. While harvesting the graft if the incision is made too palatal, the greater palatine neurovascular bundle may get damaged. If the greater palatine artery is cut, excessive bleeding results, which should be immediately controlled by placing a suture noose.

Maxillary sinus (Antrum of Highmore):

Maxillary sinuses are the largest of all the paranasal sinuses. These open in the middle nasal meatus of the nasal cavity. Each sinus is pyramidal in shape and contains three cavities. These are smaller in size (8 X 4 mm) at birth, but gradually enlarge variably and greatly by pneumatization until they reach the adult size by the eruption of the permanent teeth. The process of pneumatization occurs by resorption of the internal walls (except the medial wall) at a rate that slightly exceeds the growth of the maxilla. In younger age, the rate of pneumatization is proportional to the growth of the maxilla but with advancing age, the rate of pneumatization exceeds the rate of growth of the maxilla. The extension of the maxillary sinus in the alveolar process is not only between the roots of adjacent teeth but also between the roots of the individual tooth. The blood supply of the maxillary sinus is derived from the following branches of the maxillary artery: the posterior superior alveolar artery, the infraorbital artery, and the descending palatine artery 1-5.

Clinically, the floor of the maxillary sinus is a limiting factor for implant placement. If there is an insufficient bone for implant placement, direct or indirect sinus lift procedure is done so that implant with sufficient length can be placed.

The membranous lining of the maxillary sinus cavity is known as a Schneiderian membrane. The perforation of this membrane is…………..

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Maxillary sinus may also possess maxillary sinus septa or Underwood’s septa which are fin-shaped projections of bone. These were first described in 1910 by Arthur S. Underwood. These play an important role while planning for dental implant therapy. These must be identified if present, because while doing the sinus lift procedure, the presence of these septa may completely change the treatment plan.

Mandible

The mandible is the only mobile bone of the facial skeleton. It has a horizontal horseshoe-like body with a flat ramus, projecting upward at each end (Figure 55.1 a, b). The rami are divided into two processes: posterior condylar process and anterior coronoid process. It is formed by intramembranous ossification. The complete structure of the mandible is formed by two hemi-mandibles joined at the midline by a vertical symphysis. Initially developed separately, these hemi-mandibles fuse to form a single bone by the age of 2 years.

Figure 55.1 Various anatomical landmarks on the lateral (a) and medial (b) surface of the mandible

anatomy of mandible

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Body of the mandible:

The anterior inferior aspect of the lateral surface of the mandible body affords attachment to quadratus labii inferioris and triangularis; the platysma is attached below it. Buccinator muscle attachment is present at the superior portion of the mandible.

The medial surface of the bony has 2 paired protuberances termed, the superior and inferior mental spines, just lateral to the symphysis. The superior mental spines give attachment to……………….

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Know more…………..

Autogenous bone graft harvesting from oral cavity:

Although various types of bone grafts such as autogenous bone grafts, allografts, xenografts, and alloplasts have been used for regenerative procedures, autogenous bone is still considered as gold standard 7. The choice of a bone graft harvesting site depends on factors like quantity, quality and the form of the bone required. Typical intraoral donor sites for alveolar ridge augmentation are the ascending ramus, mandibular body, symphysis and maxillary tuberosity, out of which ascending ramus is the most preferable site for intra-oral bone graft harvesting 8. This part of the ramus can provide a bone graft of dimensions approximately 2 to 4.5 mm thick, 1.5 cm in height and 3 cm in length 9. Presently, modulated ultrasonic frequency technology (Piezosurgery) is commonly used for harvesting autogenous bone graft from ramus.

 

Ramus of the mandible:

The ramus of the mandible extends in the posterosuperior direction from the body of each hemi-mandible. The angle of the mandible is the intersection point formed by the inferior rim of the body and the posterior rim of the ascending ramus. As already stated, the ramus divides into two processes superiorly: anterior coronoid process and posterior condylar process. The coronoid process provides attachment to temporalis muscle. Condylar process articulates with the glenoid fossa of the temporal bone forming the temporomandibular joint. The lateral surface of the ramus provides attachment to masseter muscle.

The medial surface of the mandible has the mandibular foramen (foramen mandibulae) which leads into the mandibular canal. The mandibular canal runs in the body of the mandible and opens as the mental foramen on the lateral surface of the body, in the space between the first and second premolars. The inferior alveolar nerve and blood vessels run through the mandibular canal. The nerve emerging out of the mental foramen is termed as mental nerve, which divides into three branches. One nerve runs forwards and downwards to supply the skin of the chin. Other two nerves run forwards and upwards to supply the mucous membrane and skin of the lower lip and mucous membrane of the labial alveolar surface. It should be remembered that……………….

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The neurovascular bundle traversing the mandibular canal is an important anatomical limiting factor during dental implant placement. There should be a safety margin of around 2 mm from the implant and inferior alveolar canal. However, in cases with deficient alveolar bone; a surgical procedure such as nerve lateralization is done to place implant below the level of the mandibular canal. Injury to the inferior alveolar nerve results in partial or complete paresthesia of the lip and area of the mouth which is supplied by the nerve. Nortje et al. (1977) 10 on the basis of panoramic radiographs have demonstrated that the vertical mandibular canal position can be divided into four categories,

  1. High mandibular canal (within 2 mm of the apices of the first and second molars),
  2. Intermediate mandibular canal,
  3. Low mandibular canal, and
  4. Other variations – these include duplication or division of the canal, apparent partial or complete absence of the canal or lack of symmetry.

The medial edge of the foramen has a projection named lingula of the mandible (lingula mandibulae) which is the attachment site for sphenomandibular ligament. Posterior to lingula, is present a mylohyoid groove which runs downwards and forwards.  It lodges the mylohyoid nerve and vessels. Lingual nerve, which is the branch of the posterior division of the mandibular nerve, descends along the ramus of the mandible medial to and in front of inferior alveolar nerve. The nerve lies close to the mucosa in the third molar region. The lingual nerve provides senses to the front two-thirds of the tongue, as well as to the underside that surrounds it. It can easily get damaged during the delivery of local anesthesia and oral surgery procedures.

Maxillary and mandibular tori

The torus is a localized bony protuberance that originates from the cortical plate. When present in maxilla it is called as torus palatines and when present in mandible it is called as torus mandibularis. It is a non-pathological benign growth. Various etiologies have been proposed for their growth including masticatory hyperfunction, genetic factors (common in females), environmental factors and multifactorial etiology. Tori are usually reduced when planning for dentures. However, these also provide an undercut for denture retention. When planning for dental implants, large mandibular torus may create a false impression of the amount of the available bone height as well as can cause difficulty in identifying the borders of mandibular canal.

Lymphatic drainage areas of the face and neck

The spread of infection and inflammation most commonly follows the route of lymphatic drainage. Infection in various different parts of the oral cavity may involve different spaces according to their lymphatic drainage. Table 55.1 describes lymphatic drainage of various parts of the oral cavity.

 Table 55.1 Lymphatic drainage of various head and neck areas

[table “133” not found /]

Potential anatomical spaces around oral cavity

There are several potential anatomical spaces present around the oral cavity which can be easily distended by inflammatory fluid and infection. Although fascias, muscle attachments and bones separate the orofacial region into different compartments, the infection may still spread beyond the dentoalveolar tissue to involve distant spaces 11, 12. To understand various potential spaces in the head and neck region, knowledge of fascia which covers and invests various structures is important.

Fascia is a layer of fibrous tissue that surrounds muscles, vessels, and nerves. In head and neck region, deep cervical fascia has three divisions which separate various structures into three compartments; the investing (superficial), middle and deep layers. The investing or superficial layer is present just below the subcutaneous tissue and platysma. Superiorly it is attached to the lower border of the mandible and inferiorly to the sternum and clavicle 13. The middle layer of fascia encircles central organs which include the larynx, trachea, pharynx and strap muscles. It forms the anterior part of the carotid sheath. Inferiorly, this layer extends into the mediastinum to attach to the pericardium 13. The deep fascia divides into two layers: alar and prevertebral fascia. Posteriorly, alar fascia covers the carotid sheath and retropharyngeal space which extends from the base of the skull to the level of the sixth cervical vertebra. As the name indicates the prevertebral fascia makes the potential prevertebral space anteriorly.

Classification of potential spaces in orofacial region

The potential spaces in the orofacial region can be classified depending on the site/space involved:

  • Spaces related to the mandible
    • Submandibular
    • Sublingual
    • Submental spaces
    • Submasseteric space
    • Masticator space
    • Pterygomandibular space
    • Buccal space
  • Spaces related to the maxilla:
    • Canine fossa abscess
    • Infratemporal spaces
    • Buccal space
  • Deep fascial spaces of the neck
    • Lateral pharyngeal
    • Retropharyngeal
    • Danger space
    • Prevertebral space

Description of the individual spaces

Spaces related to the mandible:

Submandibular space:

The submandibular space is located superficially on the surface of the mylohyoid muscle between the anterior and posterior bellies of the digastric muscle (Figure 55.2, 55.3). Mylohyoid muscle separates the submandibular space from the sublingual space. This muscle also determines the direction of the spread of dental infections. The apex of the first molar is above the mylohyoid line and apices of second and third molars below and the mylohyoid line. So, infection in 2nd and 3rd molars spread into submandibular space, whereas infection in 1st molar spreads into sublingual space. The infection further spreads to lateral pharyngeal space from submandibular space.

Figure 55.2 Diagrammatic representation of various potential spaces in the orofacial region

Potential facial spaces

Figure 55.3 The potential spaces for the spread of infection in orofacial region

Potential facial spaces

Sublingual space:

This is a potential space contained between soft tissue beneath the tongue and above the origin of the mylohyoid muscle. This space contains……………..

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Submental spaces:

This potential space is present between mylohyoid muscle superiorly and the investing layer of deep cervical fascia covered by platysma inferiorly (Figure 55.2). Laterally, the area is bounded by the anterior bellies of the digastric muscle.  This space also contains submental lymph nodes. Clinically, submental space abscess appears as a firm swelling beneath the chin. This space gets involved due to the infection in lower anterior teeth.

Submasseteric space:

Masseter muscle is divided into three parts, namely superficial, middle and deep (Figure 55.2, 55.3). The superficial part is inserted at the lower third of the ramus; the middle part being the smallest part is inserted at the thin line curving posteriorly and superiorly over the middle third of the ramus and the deep part is inserted at the lateral aspect of the coronoid process and the upper third of the ramus of the mandible. The submasseteric space is present beneath the masseter muscle on the lateral aspect of the mandible with the ascending ramus of the mandible on the medial aspect. The most important clinical feature of involvement of this space is, acute tenderness on palpation of the masseter muscle extra-orally and significant trismus.

Masticator space:

This is a potential deep facial space which is bounded superficially by the superficial layer of the deep cervical fascia (Figure 55.3). This space contains…………

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Pterygomandibular space:

This potential space is present between the medial surface of the mandible and the medial pterygoid muscle. The medial pterygoid muscle originates from the medial surface of the lateral pterygoid plate, the pyramidal process of the palatine bone and maxillary tuberosity. The muscle is inserted into the medial surface of ramus and angle of the mandible. The important nerves and vessels that traverse this space are lingual nerve, mandibular nerve, and the inferior alveolar artery. This space communicates posteriorly with the lateral pharyngeal space. This space is usually involved following the involvement of submandibular or buccal spaces. Clinically, the patient has limited mouth opening. Intraoral swelling may be present in the area of the tonsils. In severe swelling, the airway may get obstructed.

Ludwig’s angina:

The bilateral involvement of submandibular, sublingual and submental spaces results in a condition known as Ludwig’s angina. It occurs due to rapidly spreading cellulitis. The bilateral space involvement is associated with elevation and edema of the tongue, drooling of saliva, and airway obstruction.

Spaces related to the maxilla:

Canine fossa abscess:

It is a potential bilateral space present between the levator anguli oris muscle inferiorly and the levator labii superioris muscle superiorly on either side of the face in relation to the maxilla. The involvement of this space occurs due to odontogenic infection derived from canine. This space communicates with buccal space posteriorly. The components of this potential space are the angular artery, angular vein and infra-orbital nerve.

Infratemporal space:

The infratemporal space lies superior to the pterygomandibular space (Figure 55.3). It is located posterior to the maxilla, between the lateral pterygoid plate of the sphenoid bone medially and by the base of skull superiorly.  It is in continuity with the deep temporal space laterally. The most common reason for the involvement of this space is odontogenic infection derived from maxillary third molars. The infratemporal space contains pterygoid plexus and infection of this space may be life threatening because of the communication of the pterygoid plexus to the cavernous sinus via emissary veins. Clinically, the involvement of this space is evident as swelling of the face in the region of the sigmoid notch. Swelling is usually present in the area of the maxillary tuberosity with trismus.

Buccal space infections:

The space is anteriomedially bounded by the buccinator muscle and posteriomedially by the masseter, pterygomandibular raphe and anterior border of the ramus of the mandible (Figure 55.4). The superior boundary of the space is zygomatic arch and the inferior boundary is the lower border of the mandible. The lateral covering of the space is provided by superficial cervical fascia and skin. This space contains buccal fat pad, Stenson’s duct, terminal branches of the facial nerve, and the facial artery and veins. The odontogenic infection derived from maxillary bicuspid and molar teeth and even the mandibular equivalents may result in the involvement of this space. The infection is easily diagnosed as there is often marked cheek swelling, but trismus is not severe. The infection from buccal space may extend to involve temporal space or submandibular space with which this space communicates.

Figure 55.4 Diagrammatic representation of buccal space infection

Buccal space

Deep fascial spaces of the neck

Lateral pharyngeal space:

The lateral pharyngeal space occupies a critical area in the neck. The space is like an inverted cone with the base of the cone formed by the base of the skull and apex formed by the hyoid bone. Its medial wall is formed by superior constrictor muscle along with styloglossus and stylopharyngeus. The lateral wall is formed by fascia covering the medial pterygoid, angle of the mandible and submandibular salivary gland. Posteriorly, this space is limited by the parotid gland, prevertebral fascia and upper part of the carotid sheath (Figure 55.3). This space communicates with all other fascial spaces. The space is divided into anterior and posterior compartments by the styloid process. Clinically, most of the times, this space is involved via the spread of infection from other spaces. Systemic symptoms are frequently present and the patient complains of pain on swallowing. Trismus is also commonly present. The lateral pharyngeal wall and tonsils are pushed towards the opposite side of the mouth.  The uvula is deflected medially most of the times.

Retropharyngeal:

The retropharyngeal space lies between the visceral division of the middle layer of the deep cervical fascia around the pharyngeal constrictors and the alar division of the deep layer of deep cervical fascia posteriorly. It is located anterior to the danger space and prevertebral space and laterally adjacent to carotid space (Figure 55.2).

Danger space:

Danger space lies posterior to the retropharyngeal space. This potential space exists between the alar layer and prevertebral layer of the deep fascia. It is named so because it contains loose areolar tissue and offers little resistance to the spread of infection. It is extended superiorly from the base of the skull. Inferiorly till the diaphragm (Figure 55.2).

Prevertebral space:

This potential space lies between the prevertebral fascia and the vertebral bodies. It consists of dense areolar tissue.

Conclusion

A thorough knowledge of the anatomy of the orofacial region is absolutely essential to perform any surgical intervention in this area. Both maxilla and mandible have in proximity, various vital structures which must be handled carefully during surgical procedures. This region is one of the highly vascularized regions of the body, so excessive bleeding may be encountered if any blood vessel is severed. Hence, while performing any surgical intervention, important nerves and vessels should be preserved. However, if any emergency is encountered, one should be well equipped for its management.

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References:

References available in the hard copy of the website

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