Exostosis

Exostosis is a benign, non-neoplastic, localized overgrowth of bone arising from the cortical surface of the alveolar process of the maxilla or mandible.[1][2] These protuberances are developmental anomalies rather than true pathologic conditions and are composed predominantly of dense cortical bone with limited trabecular involvement.[2] The etiology is multifactorial, reflecting a complex interplay of genetic predisposition and environmental factors—particularly functional and parafunctional occlusal loading (e.g., bruxism)—consistent with the functional matrix hypothesis and Wolff's law of bone remodeling.[2] Radiographically, exostoses present as well-defined, cortically continuous radiopaque projections from the alveolar bone surface. No treatment is required unless the exostosis interferes with prosthetic rehabilitation, oral hygiene, or causes chronic mucosal trauma.[2][3]

The term exostosis (plural: exostoses) refers to localized bony overgrowths of the alveolar process, distinct from torus palatinus (midpalatal suture) and torus mandibularis (lingual mandible above the mylohyoid line).[2] Exostoses are subclassified by location:

• Buccal exostosis — alveolar buccal cortex, most commonly in the maxillary premolar–molar region[4]
• Palatal exostosis — palatal alveolar process, distinct from torus palatinus[2]

Some older literature uses "torus" and "exostosis" interchangeably, which contributes to inconsistent prevalence data.[2] The term "torus maxillaris" has been applied to palatal alveolar exostoses in some studies.[2] Exostoses are not classified as neoplasms and are not included in the WHO Classification of Head and Neck Tumours; they are recognized as benign anatomic variations.[5] The distinction from peripheral osteoma—a true benign neoplasm—remains clinically important, though histopathologic differentiation can be unreliable.[6]

Exostoses are common findings in adult populations, though reported prevalence varies widely depending on the population studied, examination method (clinical vs. dry skull), and inconsistent terminology.[2]

• Prevalence: Buccal exostoses range from approximately 1% to 56% across populations; palatal exostoses from approximately 2% to 41%. Buccal exostoses are generally considered the least common of the oral bony protuberances, after torus palatinus, torus mandibularis, and palatal exostoses.[2]
• Age: Growth typically begins in puberty but may not become clinically apparent until the mid-30s. Peak frequencies are observed in the 35–65-year age range, with a decline in older age groups correlating with increasing tooth loss.[2]
• Sex: Males generally have a higher frequency of oral exostoses than females.[2]
• Location: Buccal exostoses favor the maxillary premolar and molar regions. Palatal exostoses occur along the palatal alveolar process bilaterally.[4]
• Population variation: Frequencies vary substantially across ethnic and geographic groups, with some of the highest reported rates in circumpolar and northern-latitude populations.[2]

Exostoses are frequently identified as incidental findings on CBCT examinations obtained for other indications.[3]

Presentation

Exostoses present as firm, sessile, bony-hard swellings on the buccal or palatal alveolar process, covered by normal-appearing but thin, poorly vascularized mucosa.[2] They may be nodular, flat, or pedunculated and range from small, barely palpable elevations to large lobulated masses.[2] Growth is characteristically slow and continuous but may cease with loss of adjacent teeth.[2]

Symptoms

The majority of exostoses are asymptomatic and discovered incidentally during routine oral examination or radiographic imaging.[1][3] When symptoms occur, they typically relate to:

• Chronic mucosal trauma and ulceration from mastication or prosthetic appliances
• Interference with denture fabrication and seating
• Difficulty maintaining oral hygiene around the protuberance
• Rarely, speech alteration when palatal exostoses are large[7]

Complications

• Oral ulceration with bone sequestration (OUBS): Exostoses, particularly buccal, are a recognized predisposing site for this condition, in which chronic mucosal trauma leads to ulceration and superficial bone sequestration.[8]
• Post-graft exostosis: Buccal exostosis has been reported as an uncommon complication following free gingival graft procedures, attributed to periosteal trauma.[1][9]

Red flags

A rapidly enlarging, painful, or destructive bony mass should not be attributed to exostosis and warrants further investigation to exclude osteoma, osteosarcoma, or other bone-forming neoplasms.[1][10]

Location and distribution

Exostoses arise from the external cortical surface of the alveolar process. Buccal exostoses characteristically involve the maxillary premolar–molar region and are commonly bilateral.[2][4] Palatal exostoses occur along the palatal alveolar ridge, distinct from the midline location of torus palatinus.[2] Mandibular buccal exostoses are less common. On panoramic radiographs, buccal exostoses may be superimposed over the roots of the premolars and molars, creating a localized radiopacity that can be mistaken for an intraosseous lesion.[11]

Periphery and shape

• The periphery is characteristically well-defined and corticated, with the base of the exostosis in direct, uninterrupted continuity with the parent alveolar cortex.[1][2]
• Shape varies from broad-based (sessile) to nodular or lobulated; pedunculated forms occur occasionally.[2]
• No perilesional radiolucent halo or capsule is present, distinguishing exostoses from encapsulated neoplasms.

Internal architecture

• The internal density is characteristically uniformly radiopaque, matching or approaching cortical bone density.[2][12]
• Larger exostoses may contain a limited amount of trabecular bone centrally, but the dominant pattern is dense cortical bone.[2]
• No ground-glass pattern, mixed radiolucent–radiopaque areas, or internal calcification foci are present, which helps distinguish exostoses from fibro-osseous lesions.[12][13]

Effects on teeth and adjacent structures

• Exostoses do not cause root resorption, tooth displacement, or widening of the periodontal ligament space.[4]
• The lamina dura and periodontal ligament space of adjacent teeth remain intact.
• On panoramic radiographs, superimposition of a buccal exostosis over tooth roots may simulate periapical pathology or an intraosseous radiopaque lesion; occlusal radiographs or cross-sectional imaging readily clarifies the surface origin.[1][11]

Extent and cortical involvement

• Exostoses are entirely exophytic; they expand outward from the cortical surface without cortical destruction, erosion, or periosteal reaction.[2]
• The underlying alveolar bone architecture is preserved.
• Cross-sectional imaging confirms the surface location and demonstrates the smooth, continuous cortical contour of the protuberance merging with the parent bone, which is the most reliable feature for confirming the diagnosis.[3][14]

Growth pattern

• Growth is slow and self-limiting, consistent with a reactive or developmental process rather than neoplasia.[2]
• Serial imaging, when available, shows no aggressive features such as rapid enlargement, cortical breakthrough, or soft-tissue extension.

Variants

• Multiple exostoses: Bilateral or multifocal buccal and palatal exostoses may coexist with torus palatinus and torus mandibularis in the same patient.[2]
• Post-surgical exostosis: Localized buccal exostosis developing at the site of a prior free gingival graft is a recognized variant; imaging shows a focal cortical protuberance at the graft site.[9]

Exostoses are usually diagnosed clinically and radiographically without biopsy. The principal diagnostic challenge is distinguishing exostosis from other surface or periosteal radiopaque lesions of the jaws, particularly when the finding is incidental on panoramic radiography and the surface origin is not immediately apparent.

The highest-risk diagnostic pitfall is misidentifying a peripheral osteoma or, rarely, a surface osteosarcoma as a benign exostosis. Any solitary, enlarging, or symptomatic bony mass—especially at a non-alveolar site or in a patient with a history of familial adenomatous polyposis—warrants cross-sectional imaging and consideration of biopsy.[7][10][16]

Microscopic findings

Exostoses are composed of mature, vital lamellar bone with a thick cortical shell and variable amounts of central trabecular (cancellous) bone.[2][19] The bone is well-organized with Haversian systems and resting (cement) lines indicating incremental appositional growth.[9] Osteocytes are present within lacunae, and moderate signs of bone remodeling (osteoid seams, occasional osteoclasts) may be observed.[9][19] The overlying connective tissue is typically thin, with keratinized epithelium of normal thickness and no inflammation.[9]

Distinction from tori and osteoma

One histomorphometric study identified an asymmetric bone remodeling pattern in tori—osteoid deposition on the free surface side and osteoclastic resorption on the opposite side of Haversian canals—proposed as a distinguishing feature from exostoses.[19] However, routine histopathologic examination cannot reliably differentiate exostoses from peripheral osteomas; the distinction remains primarily clinical and radiographic.[6]

Radiologic–pathologic correlation

The uniformly dense radiopacity on imaging corresponds to the predominance of compact lamellar bone. Larger exostoses with a slightly less dense center on cross-sectional imaging correlate with a greater proportion of central trabecular bone.[2]

Indications for treatment

Most exostoses require no treatment.[3] Surgical removal is indicated when the exostosis:

• Interferes with fabrication or seating of removable prostheses
• Causes chronic mucosal trauma or recurrent ulceration
• Impairs oral hygiene maintenance
• Produces patient discomfort or cosmetic concern
• Is needed as a source of autogenous bone graft material[3][20]

Surgical technique

Removal is performed under local anesthesia via an intraoral approach. A full-thickness mucoperiosteal flap is raised to expose the exostosis, which is then reduced with a high-speed rotary handpiece, osteotomes, or piezoelectric instruments.[21] The thin, poorly vascularized overlying mucosa requires careful flap management to ensure adequate soft-tissue closure.[2]

Autogenous graft harvest

Surgically excised exostoses and tori represent a convenient source of autogenous intramembranous bone for periodontal and implant-related grafting procedures, providing osteogenic, osteoinductive, and osteoconductive properties.[3][20]

Recurrence and prognosis

Exostoses are benign with no malignant potential. Recurrence after surgical removal is uncommon but has been documented for tori, with reports of regrowth up to 11–14 years postoperatively.[21][22] Persistence of the original functional stimulus (e.g., bruxism, heavy occlusal loading) may contribute to recurrence.[2] No long-term surveillance is required after removal unless symptoms recur.