Anatomical Overview

When performing any surgical procedure, it is important to be aware of the anatomy to guide one’s incisions and avoid damage to or impingement on nerves, vessels, or other vital structures. Often, a cone beam computed tomography (CBCT) image becomes necessary to determine the location of the anatomical features to reduce the risk of surgical complications as there is variability amongst patients.⁴⁹ Important landmarks in maxillary and mandibular arches are described in brief below.

Maxilla

The nasopalatine foramen contains the nasopalatine nerve and descending palatine vessels. It is located anteriorly along the midline of the palate.⁴⁹ Larger canal dimensions may affect the amount of available bone to place implants in these sites. To circumvent this issue, the canal contents may be removed and grafted to enable implant placement.^49,50 The greater palatine artery is located opposite the 2nd and 3rd molar area on the palate and has the potential of causing intra operative hemorrhage if damaged intra-surgically.⁴⁹ It is important to take note of these features especially in edentulous sites, as their locations will appear closer to the crest.

The maxillary sinus is a prominent feature in the posterior maxilla. When posterior teeth are extracted pneumatization ensues, limiting the vertical dimension of the bone available for implant placement.⁵¹ In such cases, sinus membrane elevation and augmentation procedures may become necessary. The amount of native alveolar bone available below the sinus floor, will determine staging of implant and approach to sinus augmentation. Shorter implants (implant length 6 mm) have also been proven to be successful in sites with decreased height of bone and have comparable survival rates when compared to longer implants.⁵² This may be a feasible alternative, eliminating the need for additional surgical procedures.

Mandible

In the mandible, the inferior alveolar canal, which houses the inferior alveolar nerve as well as an artery, vein and lymphatic vessels, is located in the posterior regions.⁴⁹ The canal is located about 3.5-5.4 mm from the apices of the mandibular molars.⁴⁹ As the inferior alveolar nerve approaches the premolar region, it divides into the mental nerve, which emerges from the mental foramen usually between the first and second premolar region, and the incisive nerves more anteriorly. A branch of the inferior alveolar nerve may form an intraosseous loop, which extends beyond the mental foramen.^53, This anatomical variation, called the anterior loop of the mandibular canal has a prevalence ranging from 27-100% in the literature.^54,55 Cone Beam CT studies have shown that the anterior loop is located at a mean of 3.1mm anterior to the mental foramen and the majority are less than 4mm in length.^54,56 A 2 mm zone of safety between the implant and these structures can avoid nerve damage.²²

The lingual nerve is a branch of the mandibular nerve and is located, on average, at a vertical distance of 9.6, 13, 14.8 mm from the second molar, first molar, and second premolar, respectively.⁵⁷ Vertical incisions should be avoided in this area and care should be taken when elevating a flap to avoid injury to the nerve.

Another important anatomical feature of the mandible to note is the lingual concavity. The depth of this undercut is on average 2.4 mm and located about 11.7 mm from the CEJ of the second premolar.⁵⁸ Perforation is likely to occur during osteotomy preparation if not identified and may result in damage to surrounding vital structures. Hemorrhage resulting from lingual cortex perforation and injury to sublingual vessels can cause life threatening sublingual hematomas and airway obstruction. 3D imaging to visualize the individual shape of the mandible can help reduce these complications.⁵⁹

Figure 5.

A. Nasoplalatine foramen in #9 edentulous site.

B. Posterior maxillary site showing limited bone due to sinus pneumatization.

Figure 5.

C. Mapping the Inferior Alveolar Canal in CBCT Scan.

D. Lingual concavity in #30 implant site.