21.1 Introduction

The alveolar ridge is defined as the bony ridge of the maxilla and mandible that harbors the tooth roots. It may also be described as the upper and lower gum, or gingiva. Along the maxilla, it is bounded anteriorly by the maxillary buccal vestibule and posteriorly by the hard palate to the pterygopalatine arch. The inferior alveolar ridge is bounded anteriorly by the mandibular buccal vestibule and posteriorly by the free mucosa of the floor of mouth; it extends along the ramus, ending at the retromolar trigone. The gingiva comprises the primary mucosa that lines the alveolar ridge. This is a nonkeratinized mucosa that forms the characteristic lining mucosa of a part of the oral cavity. Given that the mucosa in this region is in close proximity to the bone with minimal soft tissue, bony invasion can be common. As will be discussed in this chapter, in-depth knowledge of dental anatomy can aid decision-making when considering surgery in this region, help understand patterns of tumor spread, and help preserve dental and palate function. Disease in this region is commonly identified by oral dentists or oral surgeons, who also assist in comprehensive care of these patients including in reconstruction with obturators or dental implants.

21.2 Epidemiology

The oral cavity is the most common site of squamous cell carcinoma of the head and neck, particularly human papillomavirus (HPV) negative disease. Within the oral cavity, alveolar ridge cancers comprise about 7-12% of oral cavity cancers. ^{1 , 2}

Median age of diagnosis of alveolar ridge carcinoma is 66 years of age. ³ With regard to patient’s gender, unlike other lesions of the oral cavity or oropharynx, there is a similar rate of presentation between men and women, with about 53-58% of patients being women. ^{3 – 5} Smoking and alcohol use are major risk factors for oral cavity cancer with higher risk associated heavy smoking and alcohol use. It is believed that inhaled carcinogens tend to mix into the saliva and come in contact with dependent regions of the oral cavity such as the floor of mouth or lateral tongue. In contrast, chewed carcinogens (chewing tobacco, betel nut) come in direct contact with the mucosa and may increase the risk of buccal or gingival cancers. ⁶ In addition, some risk factors that are specific to the alveolar ridge are a diet with low vegetable intake, poor oral hygiene, and periodontal disease which may contribute to chronic inflammation and cell turnover. ⁷

With regard to oral hygiene, there is also some evidence that the oral microbiome may play a role in carcinogenesis in patients with oral cavity. A study in Taiwan found that patients with periodontitis have increased risk (1.79 adjusted hazard ratio) of developing oral cancer. ⁸ This may be a result of direct effects of bacterial toxins which impact cell growth, stimulate chronic inflammation, or affect the host microenvironment and immune system. Porphyromonas gingivalis is a known contributor to periodontal disease, resulting in microbial imbalance and chronic inflammation. In addition, P. gingivalis also inhibits apoptosis and has been shown to suppress the tumor suppressor p53. ⁹ Similar to other oral cavity cancers, tumors of the alveolar ridge are generally not associated with HPV.

Epidemiology of alveolar ridge cancer is similar to that of other oral cavity sites. The incidence in the past 30 years has overall decreased in the United States. ¹⁰ However, there is global variation in incidence. India has the highest incidence of oral cavity cancer, about 15-20%. Other risk factors, such as betel nut chewing, play an important role in the risk for oral cavity cancer in Asia, and as such, incidence of oral cavity cancer is actually rising in many Asian countries. ⁷ Betel nut chewing may be a more significant risk factor for oral cavity cancer than alcohol or tobacco use (adjusted odds ratio [OR] 6.9). ¹¹

21.3 Clinical Presentation

Clinical presentation of alveolar ridge lesions can vary significantly based on the location as well as patient factors (▶ Fig. 20.8). Early lesions are often asymptomatic and can be detected by routine oral examination. ¹ As lesions progress, the patient may experience pain (about 30-40%) that can manifest as dental pain, burning pain, gingival pain, or ear pain. ¹² Additional presenting complaints include bleeding (from ulceration), loose teeth, problems with denture fit, numbness of the teeth or lips, and trismus (secondary to pterygoid involvement).

Some patients may also present after transformation of premalignant lesions. Oral leukoplakia is a descriptive diagnosis, referring to a white “patch” or “plaque.” Among these lesions, dysplasia or carcinoma occurs in up to 17-25% of lesions. ^{13 , 14} Some studies have suggested that leukoplakia lesions that arise in the floor of mouth, ventrolateral tongue or retromolar trigone, and soft palate have higher rates of transformation to malignancy, which were correlated with loss of heterozygosity in these subsites. ¹⁵

Tumors of the alveolar ridge may present at any stage (T1-T4), with or without clinically evident nodal disease. One study reviewing 155 cases of lower alveolar ridge carcinoma showed that most tumors were diagnosed as T2 lesions (45%). ³ Furthermore, most patients (82%) had clinically N0 neck at the time of presentation. In the upper alveolar ridge, the rates of clinically positive nodes are slightly higher—4% in T1 lesions, 10-15% in T2/3 lesions, and 25% in T4 lesions. ⁴

21.4 Diagnosis and Evaluation

Evaluation should focus on assessment of factors that will determine definitive treatment. These factors include pathology, extent of tumor including involvement of adjacent structures, bony invasion, native bony stock, dental status, nodal disease burden, and distant metastasis. This assessment will help to determine the first steps in surgical treatment including marginal versus segmental mandibulectomy, extent of bony resection for maxillary lesions, need for neck dissection, and potential need for reconstruction. Clinical evaluation should assess tumor size, extension to other subsites (floor of mouth, lip, oral tongue, palate), nerve involvement (V2 or V3 numbness, tongue weakness), fixation to the bone (which may be suggestive of invasion), and dental status (will be discussed below).

Diagnosis is made from clinical biopsy of suspicious lesions. In the oral cavity, alveolar ridge lesions are generally accessible and amenable to biopsy in the clinic, unless significant trismus is present. Biopsies should be performed using punch technique rather than shave technique to allow for assessment of depth of invasion. Evaluation of bony or periosteal invasion may not be possible from in-office biopsy, but may be enough to secure a diagnosis of malignancy to guide further treatment.

Recently the American Joint Committee on Cancer (AJCC) 8th edition staging manual included changes to T staging for oral cavity tumors to include depth of invasion. These changes were made to reflect the correlation between depth of invasion and aggressive biologic tumor behavior.

Imaging: Computed tomography (CT) with contrast is the mainstay of imaging for cancers involving the alveolar ridge, and offers the best sensitivity and specificity for bony invasion compared to panorex or bone scan. ¹⁶ However, evaluation can still be challenging due to irregularities of the dental socket and artifact from dental amalgam; ¹⁷ therefore, clinical evaluation remains important. ¹⁸ If there is question of soft tissue invasion into the intrinsic tongue musculature, magnetic resonance imaging (MRI) can provide additional insight. Both of these modalities can also identify cervical lymph adenopathy. In addition, chest imaging should be performed for staging to rule out distant metastases or second primary, particularly in patients with a history of smoking.

Bony invasion: Evaluation of bony invasion is critical for surgical decision-making. In histologic studies, the routes of bony invasion are shown to come from direct extension from the primary tumor. ¹⁹ Notably, tumors of the alveolar ridge are more likely to have bony invasion compared to other oral cavity tumors, and this generally occurs at the occlusal ridge. ^{19 , 20} Two patterns of invasion have been observed: erosive and infiltrative. The erosive pattern shows a broad tumor front that pushes into the bone, with a well-defined border. The infiltrative pattern shows a more irregular tumor front with finger-like extensions into the bone. In a study of 68 patients, 60% of patients had erosive pattern of bony invasion. Patients with infiltrative pattern of bony invasion were more likely to have positive bony margins, and had a significantly worse 3-year overall survival. ²¹

Routes of bony invasion can also be impacted by the existing bony stock. The most common site of bony invasion is along the occlusal ridge. ²² Entry into the bone occurs in this region as it lacks a thick cortical bony barrier. In dentulous patients, this may track along the dental sockets. In edentulous patients, the occlusal ridge is at a lower height and more easily accessed (▶ Fig. 21.1). In addition, invasion in the lingual and buccal cortical plates may also occur due to thinner bone stock. Nerve foramina represent another area where a defect in the cortical bone allows tumors to directly access medullary bone, and patients with nerve involvement are likely to have bony involvement, especially in edentulous patients. ²³ In patients with history of irradiation, cortical bony invasion is more common, and tends to be less predictable, occurring in multiple foci (▶ Fig. 21.2).

Dental status and bone height also impact surgical decision-making. If there is involvement of the periosteum, at least a marginal mandibulectomy should be performed. However, only dentate patients with healthy bone stock should be considered for possible marginal mandibulectomy procedures. In these patients, average height of the mandible is higher in the parasymphyseal region (38 mm) compared to the molar region?(26 mm). Therefore, invasion in the molar region requiring > 10 mm bony resection leaves insufficient height for a stable marginal mandibulectomy. ²⁰ As will be discussed in surgical approaches, rim or sagittal marginal mandibulectomy approaches may be considered.

In the edentulous patient, the duration of edentulous status impacts the height and strength of the mandibular bone stock, as atrophy occurs over time. Segmental mandibulectomy is recommended if any bony resection is required. Due to inadequate bone stock, the risk of pathologic fracture is high. However, if the bony resection is lateral, the mandible may be left “swinging” without bone or plated reconstruction. In this case, soft tissue coverage is important to prevent tethering or trismus. Midline mandibulectomy however necessitates rigid reconstruction, to prevent significant retrognathia and subsequent airway compromise, as the tongue musculature and tongue base attach to the mandible anteriorly.

Lastly, history of radiation is an important factor to consider. As discussed previously, the patients with history of radiation tend to have less predictable and multifocal regions of bony tumor invasion. In addition, previously radiated bone has decreased vascular supply within the marrow and is at risk of poor wound healing and higher risk of pathologic fracture. Therefore, segmental mandibulectomy is recommended if any bony resection is required.

21.5 Anatomic Considerations/Relevant Anatomy

An understanding of dental anatomy is helpful in documentation and treatment planning for alveolar ridge disease. Recall that numbering of teeth begins at the right third molar from #1 and is then numbered clockwise to #32. There are three molars on each side, in both the maxilla and mandible, although the third molar or wisdom tooth is not always erupted. Medial to the molars are the first and second premolars, followed by canine, lateral incisor, and central incisor. Each tooth has enamel which is the hardest surface layer, primarily composed of calcium phosphate. Underneath the enamel is dentin, which is more porous—thus symptoms of pain or sensitivity of teeth may be a sign of exposed dentin from enamel erosion. Within the dentin is the pulp containing vasculature and nerve fibers of the tooth root. The length of tooth roots is generally between 1.0 and 1.5 cm with canines having the longest roots. Knowledge of tooth roots can be helpful in planning osteotomy incisions or drilling bone for plating.

Additional landmarks in the maxilla that are of particular importance are the anterior and posterior ethmoidal arteries, skull base, and lacrimal fossa. The lacrimal fossa contains the lacrimal duct and opens in the medial orbit bounded by the anterior and posterior lacrimal crest. The nasolacrimal duct then travels along the anteriomedial wall of the maxillary sinus and empties in the inferior nasal meatus. The anterior ethmoidal foramen is located posterior to the lacrimal crest, while the posterior ethmoidal artery enters 36 mm from the lacrimal crest (and 12 mm from the anterior ethmoidal artery). The optic canal lies 6 mm behind the posterior ethmoidal artery. The frontoethmoidal suture line marks the superior boundary of any bony dissection to avoid injury to the cribiform plate. Recall that posterior to the maxilla is the pterygopalatine fossa, which contains the internal maxillary artery, pterygopalatine ganglion, and maxillary nerve (V2).

In the mandible, blood supply is primarily from the inferior alveolar artery (which takes off from internal maxillary artery), facial artery, and lingual artery. The innervation is supplied by the inferior alveolar nerve, which enters on the lingual surface of the mandibular ramus through the mandibular foramen and exits through the mental foramen at the second premolar. The lingual nerve runs medially within the floor of mouth in close proximity to the mandible and should be identified during intraoral dissection.