The understanding of the facial anatomy with its associated osseous and neurovascular structures is essential to the implant surgeon. During treatment planning and implant surgery, certain critical landmarks and boundaries must be respected. The anatomy of the maxilla and mandible is complex, and the implant surgeon should also keep in mind that many variations exist between individuals. The aim of this module is to review the basic anatomy of the facial region and to provide an overview of the important structures involved in implant dentistry in the average adult patient.

After completing this module you should be able to describe the osseous structures of the maxilla, describe the osseous structures of the mandible, list the vascular structures of the maxilla and mandible; and list the neural structures of the maxilla and mandible.

The maxilla serves several functions: it houses the maxillary teeth with the alveolar process, forms the roof of the oral cavity, contributes to the floor and the lateral walls of the nasal cavity, houses the maxillary sinus, and contributes to the inferior rim and floor of the orbit. The maxilla consists of two paired osseous structures, the maxillary bone and the palatine bone. Each paired bone is joined at the midline, and together they form the middle third of the face.

The body of the maxilla is shaped like a pyramid and features four processes: The frontal processes form the anteromedial part of the orbit. The palatine processes deviate horizontally and fuse at the intermaxillary suture. The palatine processes form the greater part of both the roof of the oral cavity and the floor of the nasal cavity.

Zygomatic processes are on the lateral aspects, and they are the buttressing maxillary contribution to the zygomatic arch. Each zygomatic process is an apex of the pyramid. The alveolar processes contain the roots of the teeth and form the upper dental arch. The protuberances in the outer surface of the alveolar process are referred to as alveolar yokes or root eminences.

The anterior nasal spine forms the most anterior part of the maxilla and can be used for local bone harvesting, whereas the maxillary tuberosity is the most posterior part of the maxilla. It too can be used for local bone harvesting.

The infraorbital foramen is found 6 to 9 millimeters below the infraorbital rim in the apical extension of the premolar region. Its location is 24 to 29 millimeters lateral to the midline, or in the medial third of the orbit. It forms the opening of the infraorbital canal and transmits its neurovascular structures to the face.

The canine fossa is the concavity distal to the canine. It extends to the premolar roots and upward to the infraorbital foramen. It is the site of injection for local anesthesia.

The maxillae contain pneumatized or air-filled structures known as the maxillary sinuses. The maxillary sinus varies in size but generally extends anteriorly to the facial surface, laterally to the zygomatic process, posteriorly to the infratemporal wall, superiorly to the orbital floor, and inferiorly to the alveolar process.

Running across the roof of the sinus is the infraorbital canal, which extends into the sinus like a ridge. Occasionally the roots of the maxillary molars are in close proximity to, or even protrude into, the sinus.

The maxillary hiatus is the opening from the maxillary sinus into the nasal cavity. Its aperture is elliptical in shape, 7 to 11 millimeters long and 2 to 6 millimeters wide.

Sinus septa are barriers of cortical bone that divide the sinus into two or more compartments and were first described by Underwood in 1910. They are typically knife-edged projections that extend from the lateral to the medial sinus wall. The prevalence of sinus septa has been reported to be 10% to 48%. A higher incidence of septa has been found in the first and second molar region.

The incisive foramen is a funnel-shaped opening in the maxilla immediately behind the central incisors. The diameter of the incisive foramen is usually less than 6 millimeters; when it exceeds 10 millimeters, a pathological condition may be present, as shown in this clinical image of a nasopalatine canal cyst. The incisive foramen is also called the nasopalatine foramen or the anterior palatine foramen.

The incisive canal carries the nasopalatine nerve and descending nasopalatine artery. It runs inferiorly and anteriorly from the floor of the nasal cavity to the incisive foramen. At the level of the nasal floor, a two-canal, Y-shaped morphology is common, occurring in 65% of patients, but up to four openings have been described in 11% of patients.

The paired palatine bones consist of horizontal, rectangular plates that together form the posterior third of the hard palate. The greater and lesser palatine foramina are located at the posterior lateral area. In most patients, the greater palatine foramen is related to the maxillary third molar.

Osseous Structure of the Maxilla, Key Learning Points: The maxilla consists of two paired osseous structures, the maxillary bone and the palatine bone. The infraorbital foramen is located 6 to 9 mm below the infraorbital rim in the apical extension of the premolar region. The incisive foramen is an opening in the maxillary bone behind the central incisors. The maxillary sinus varies in size. Sinus septa divide the sinus into two or more compartments and are present in up to half of patients, with a higher incidence in the first and second molar region.

The mandible contains the mandibular teeth with the alveolar process and forms the lower third of the facial area. It is a U-shaped bone and is the only mobile bone of the facial skeleton. The mandible is composed of two hemimandibles joined at the midline by a vertical symphysis. The hemimandibles fuse to form a single bone by the age of 2 years. The mandible consists of two parts: a horizontal body that includes the alveolar process and a vertical ramus. Two processes top the ramus: an anterior sharp coronoid process and a posterior rounded condylar process.

The mental protuberance is a triangular thickening of the bone in the anterior inferior midline region. The thickened inferior rim of the mental protuberance extends laterally from the midline and forms two rounded protrusions called mental tubercles. Posterior to the mental tubercles, the external oblique line extends to join the anterior edge of the coronoid process.

The mental foramen is located in adults at the vertical midpoint of the inferior border and the alveolar crest in the region of the second premolar. In children, it is located in the lower third of the mandible. In edentulous patients, the foramen is located in the upper third of the mandible or even on the crest of the ridge due to resorption of the alveolar process.

Its anteroposterior position may vary by 6 to 10 millimeters. In the Caucasian population the mental foramen is most often inferior to the second premolar or between the two premolars. However, in the Asian and black populations the mental foramen is most often inferior to the second premolar or between the second premolar and the first molar. Accessory mental foramina are rare but when present are most often located posterior and inferior to the mental foramen.

The mental spines or genial tubercles are two paired protuberances located on the inner surface of the mandible lateral to the symphysis. The digastric fossa is a concavity just lateral to the inferior mental spines on the inferior border of the mandible. Lingual foramina may be present and have been the subject of several reports on critical hemorrhages in the floor of the mouth after surgical procedures. A study using cone beam computed tomography reported that lingual foramina are most frequently present at the midline (as seen in 96% of patients) followed by the first premolar area.

The mylohyoid ridge extends obliquely in a posterosuperior direction from the midline and serves as an attachment site for the mylohyoid muscle. Above and below the mylohyoid ridge are the sublingual fossa and the submandibular fossa, two concavities against which the sublingual and submandibular glands abut.

A study has shown that in 80% of patients the depth of the submandibular fossa is greater than 2 millimeters. This increases the risk of perforation of the lingual cortical plate and injuries to the terminal branches of the sublingual artery during implant placement. It has been shown that submental and sublingual arteries may course intimately to the lingual cortical plate from the floor of the mouth. It should be emphasized that the edentulous mandible is shorter and therefore perforation may occur even deeper in the floor of the mouth.

The ramus extends vertically in a posterosuperior direction to the body on each hemimandible. Two processes top the ramus: an anterior sharp coronoid process and a posterior roller-shaped condylar process. On the medial or inner surface of the ramus is an aperture called the mandibular foramen. Just medial to the mandibular foramen is a projection of bone called the lingula.

The mandible has a large core of trabecular bone with a 2- to 4-millimeter rim of cortical bone. The mandibular canal begins at the mandibular foramen and courses inferiorly and anteriorly toward the mental foramen. In adults, the mandibular canal is in close proximity to the roots of the third molars. Within the mandibular body, the canal courses along the inferior border and typically runs inferior to the level of the mental foramen.

The mandibular canal ends in the mental foramen in an extension known as the anterior loop. The length of the anterior loop has been reported as 5 to 9 millimeters in several studies.

When placing implants mesial to the mental foramen, the anterior loop length as well as the position of the mandibular incisive canal should be considered. The mandibular incisive canal extends from the anterior loop towards the midline and may be engaged during placement of interforaminal implants, resulting in stretching or damage to the main inferior alveolar nerve.

Osseous Structure of the Mandible, Key Learning Points: The mandible is composed of two hemimandibles and consists of the horizontal body and the vertical ramus. The position of the mental foramen varies depending on the patient's age, race, and degree of edentulism. When placing implants in the anterior mandible, the mental foramina, their anterior loops, and the mandibular incisive canals must be considered. Concavities on the medial surface of the mandible such as the submandibular and sublingual fossae and the lingual foramina should also be considered in order to avoid vascular damage during surgery.

The face is supplied with blood from various arteries. The entire blood supply is derived from either the internal or external carotid arteries, and terminal branches of these arteries anastomose frequently. The three branches of the external carotid artery are responsible for the blood supply of the maxillary and mandibular region: the lingual artery, the facial artery, and the maxillary artery. The vascular supply arises in a posterior to an anterior direction, with an avascular zone on the central area of the alveolar crest.

The lingual artery arises from the external carotid artery just above the tip of the greater horn of the hyoid bone. It travels through the submandibular region into the tongue and divides further into the dorsal lingual branches and a sublingual branch.

The lingual artery communicates with the facial artery through the lingual foramina. Perforation on the lingual aspect of the mandible during surgery can therefore lead to a critical hemorrhage in the floor of the mouth due to injury to the lingual artery.

The facial artery runs anteriorly and enters the submandibular region near the medial aspect of the body of the mandible and the external surface of the mylohyoid muscle, by the submandibular gland. The artery takes a lateral course, curls over the inferior border of the mandible, and ascends to supply the anterior portion of the face with its terminal branches, the superior and inferior labial arteries and the angular artery. The facial artery anastomoses with branches of the ophthalmic artery, which originates from the internal carotid artery.

The maxillary artery is responsible for the blood supply of the mandible via the inferior alveolar artery and the mental artery. Additionally, it supplies the maxilla via the posterior superior alveolar artery, the infraorbital artery, and the buccal artery. The palate obtains its blood supply from the descending palatine artery, which divides into the greater and lesser palatine arteries.

The posterior superior alveolar artery and the infraorbital artery anastomose in the area of the maxillary sinus. Within the lateral bony wall of the sinus there exists an intraosseous anastomosis between these two vessels. This anastomosis is located 16 to 19 millimeters from the alveolar crest. In 7% of patients, the diameter of the intraosseous vessel can be significant, between 2 and 3 millimeters.

In addition, an extraosseous anastomosis within the facial soft tissue is present in about 40% of patients, and this anastomosis must be considered when periosteal releasing incisions are performed.

The veins mostly follow their corresponding arteries. The most important veins are the facial vein, retromandibular vein, the pterygoid plexus of veins, and external and internal jugular veins. Of clinical importance is the spreading of infections from the canine fossa along the angular vein and the ophthalmic vein into the cavernous sinus of the brain. The pterygoid plexus also communicates with the cavernous sinus, and infections can ascend into the brain.

Vascular Structures, Key Learning Points: The lingual, facial, and maxillary arteries provide the blood supply to the maxillary and mandibular region. The lingual artery can be injured by perforation on the lingual aspect of the mandible, causing a life-threatening hemorrhage in the floor of the mouth. Within the lateral bony wall of the maxillary sinus there is an intraosseous anastomosis between the posterior superior alveolar artery and the infraorbital artery. Infections can spread from the canine fossa along the angular and ophthalmic veins or the pterygoid plexus into the cavernous sinus of the brain.

The facial cutaneous sensory supply is derived from the trigeminal nerve, the largest of the cranial nerves. Within the skull the nerve divides into three branches: the ophthalmic nerve, a sensory nerve associated with the orbit and its contents; the maxillary nerve, a sensory nerve associated with the nasomaxillary complex; and the mandibular nerve, a sensory and motor nerve associated with the mandible and the muscles of mastication.

The maxillary nerve divides in the pterygopalatine fossa into three branches. The nasopalatine nerve descends through the incisive canal into the mucosa of the anterior palate. Other important branches of the nasopalatine nerve, the greater and lesser palatine nerves, also provide sensory fibers to the palate. The zygomatic nerve leaves the fossa through the inferior orbital fissure to enter the orbit. The infraorbital nerve branches into the anterior, middle, and posterior superior alveolar nerves, which form the dental plexus.

The infraorbital nerve surfaces onto the face through the infraorbital foramen and immediately divides into three main terminal groups of branches: the inferior palpebral branches, the lateral nasal branches, and the superior labial branches. An injury to the infraorbital nerve may result in sustained sensory perception due to overlapping distribution of branches. In addition, Hwang and colleagues have described non-overlapping nerve branches, in which injury could result in loss of sensation.

The mandibular nerve is the largest of the three branches from the trigeminal nerve. It consists of a large sensory component and a smaller motor component. The nerve exits the cranium through the foramen ovale to enter the infratemporal region. Several of its branches are important to the practice of dentistry.

The long buccal nerve passes forward and lateral. Its buccal branch is sensory to the mucosa and skin of the cheek and the buccal gingiva of the mandibular molar region. The lingual nerve appears under the inferior border of the lateral pterygoid muscle and runs toward the lingual aspect of the third molar into the floor of the mouth. The inferior alveolar nerve enters the mandibular foramen into the mandibular canal. At the mental foramen the inferior alveolar nerve splits into the incisive nerve, which continues within the mandibular incisive canal, and the mental nerve. The mental nerve sends branches to supply the skin in the chin area, the buccal gingiva, and the mucous membranes of the anterior mandible.

Neural Structures, Key Learning Points: The trigeminal nerve is the largest cranial nerve. The trigeminal nerve has three main branches: the ophthalmic nerve, the maxillary nerve, and the mandibular nerve. The infraorbital and the inferior alveolar nerves are prone to sensory disturbances if anatomical boundaries are not respected.

Anatomy with Relevance to Implant Surgery, Module Summary: The infraorbital foramen is located 6 to 9 mm below the infraorbital rim in the medial third of the orbit. Sinus septa have a higher incidence in the first and second molar region. The mental foramen in adults is located at the midpoint of the inferior border and the alveolar crest in the region of the second premolar, with variation of 6-10 mm in the anterior-posterior position. When placing implants in the anterior mandible, the mental foramina and their anterior loops and the mandibular incisive canals must be considered. Concavities on the medial surface of the mandible such as the submandibular and sublingual fossae together with the lingual foramina should also be considered in order to avoid vascular damage.

The maxillary artery is responsible for the blood supply of the mandible and maxilla. Within the lateral bony wall of the maxillary sinus, there are intraosseous and extraosseous anastomoses between the posterior superior alveolar artery and the infraorbital artery. Infections can spread along the veins into the brain, particularly from the canine fossa and the pterygoid plexus. The trigeminal nerve is the largest cranial nerve and has three main branches: the ophthalmic nerve, the maxillary nerve, and the mandibular nerve. The infraorbital and inferior alveolar nerves are prone to sensory disturbances if anatomical boundaries are not respected.