Bone Exostosis

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  • Nodular swellings of normal bone in the oral cavity
  • Also known as tori (torus = singular)
  • Common sites:
    • Hard palate (torus palatinus)
    • Lingual premolar region of the mandible (torus mandibularis)
    • Buccal alveolar bone of maxilla or mandible
Commonly affected area in numb chin syndrome

Clinical Features

Commonly affected area in numb chin syndrome

Clinical Features

Commonly affected area in numb chin syndrome

Clinical Features

Epidemiology

  • Incidence varies between different races[1]
    • More common in Inuit, Native American and Asian populations
  • Torus palatinus
    • More common than mandibular tori
    • Incidence - 9-66%
    • ♀ > ♂
  • Torus mandibularis
    • Incidence - 0.5-63.4%
    • ♂ > ♀

Clinical Features

  • Firm swellings with normal overlying mucosa
    • Whilst mucosa is normal it is usually thin and can have a blanched appearance (sometimes can ulcerate)
  • Small-sized lesions → <3mm elevation and <10mm diameter
  • Medium-sized lesions → 3-5mm elevation and 10-15mm diameter
  • Large-sized lesions → >5mm elevation and >15mm diameter
  • Usually only affects one site in an individual
  • Torus palatinus
    • Occurs in the midline of the palate (usually in the mid-third)
    • Usually symmetrical but if large can also become an irregular rounded mass
  • Torus mandibularis
    • Found on the lingual surface of the mandible
    • Usually adjacent to premolars and above the mylohyoid attachment
    • If very large can interfere with tongue movement
    • Common presentations:
      • Bilateral solitary > bilateral multiple > unilateral solitary > unilateral multiple
  • Other sites
    • Multiple bone exposes can also affect the buccal aspect of maxilla or mandible

Aetiology and Pathogenesis

Aetiology

  • Largely unknown
  • Some suggestions:
    • Hereditary (autosomal dominant inheritance has been described in some)
    • Masticatory hyperfunction

Pathogenesis

  • Also largely unknown
  • In palatal tori, there is suggestion of continued activity of the embryonic osteoblasts which pile up at the palatal suture after the median palatal suture junction is completed

Investigations

Imaging

  • Radiographically tori appear as radiopaque masses
  • Dense bone ∴ they can obliterate details of the teeth and maxillary sinus in plain film radiographs
  • In large tori - the spongy layer in the middle appears less dense than the cortical bone

Histology

  • Torus palatinus
    • Cross-sectional analysis of tori palatine demonstrate three layers:
      1. Nasal compact layer - same thickness irrespective of size of tori ∴ confirming that development occurs by downward growth (nasal floor always remains flat)
      2. Middle spongy layer - may not be seen in smaller tori
      3. Oral compact layer
  • Torus mandibularis
    • Seen as lamellar periosteal outgrowth of the mandible

Management

  • No active treatment needed
  • Patient reassurance
  • Removal is sometimes needed if they interfere with function or to facilitate dental prosthesis
  • Tori have been described as a source of autogenous bone graft in implant placement[2][3][4]

Prognosis and Complications

  • Benign
  • Recurrent ulceration can occur due to thin overlying mucosa
  • Large lesions can interfere with function and dental prosthesis

Follow-up

  • None needed

References