Pathophysiology

Authors: Mette Hørberg, consultant in oral and maxillofacial surgery, Frederik Gulmark Hansen, med.stud., Magnus Balslev Avnstorp MD and Jytte Buhl, consultant in oral and maxillofacial surgery

Mandibular bone defects can be secondary to trauma, tumour resection, both benign and malignant, or other pathological, developmental, or congenital disorders.

Most common causes of mandibular bone defects

Oral squamous cell carcinoma: 

Squamous cell carcinoma is a carcinoma with squamous differentiation arising from the mucosal epithelium. Squamous cell carcinomas account for more than 90% of cancers in the oral cavity(1).

Squamous cell carcinoma arises from dysplastic surface epithelium, invading the basement membrane and the subepithelial connective tissue(1). Squamous cell carcinoma is caused by multiple factors (carcinogen) and both intrinsic and extrinsic factors may be needed to trigger such a malignancy. Extrinsic factors include, tobacco, alcohol, syphilis and sunlight. Intrinsic factors include systemic or generalized states such as immunodeficiency. Many oral squamous cell carcinomas arise from a precancerous lesion, such as dysplasia, which often appears as a white lesion – leukoplakia(2).

Osteosarcoma:

Osteosarcoma constitutes a group of malignant bone tumours of mesenchymal origin whose neoplastic cells produce bone. Conventional osteosarcoma is an aggressive high-grade tumour, periosteal osteosarcoma is of intermediate grade, and low-grade central and parosteal osteosarcomas are low-grade subtypes(1).

The majority of osteosarcomas originate intramedullary, but juxtacortical and extra skeletal types are also described in the literature(2). 

Osteosarcoma is rare, with an overall annual incidence of approximately four cases per 100,000 people. Most cases are high-grade tumours affecting the metaphysis of long bones. The fourth most common site of origin is the jaw bones, accounting for about 6% of cases(1); 2-8% of all maxillofacial osteosarcomas are low-grade or intermediate grade tumours(1). The incidence is highest in younger adults and primary treatment is surgery(2).

Osteoradionecrosis: 

Osteoradionecrosis is caused by damage to osseous cells due to radiation therapy. When the osseous cells lose their normal function, bone turnover is suppressed by inhibiting osteoclasts and angiogenesis. Osteoradionecrosis arises secondary to local trauma such as a dental extraction in previously irradiated bone but may also appear spontaneously. By eliminating dental foci of infection before initiating radiation therapy bone necrosis might be avoided(2).