Mutational Signatures in Mandibular Ameloblastoma Correlate with Smoking.

Ameloblastoma is a rare tumor of odontogenic epithelium, the low incidence rate of which precludes statistical determination of its molecular characterizations. Despite recent genomic and transcriptomic profiling, the etiology of ameloblastomas remains poorly understood. Risk factors of ameloblastoma development are also largely unknown. Whole exome sequencing was performed on 11 mandibular ameloblastoma samples. We identified 2 convergent mutational signatures in ameloblastoma: 1) a signature found in multiple types of lung cancers with probable etiology of tobacco carcinogens (COSMIC signature 4) and 2) a signature present in gingivobuccal oral squamous cell carcinoma and correlated with tobacco-chewing habits (COSMIC signature 29). These mutational signatures highlight tobacco usage or related mutagens as one possible risk factor of ameloblastoma, since the association of BRAF mutations and smoking was demonstrated in multiple studies. In addition to BRAF hotspot mutations (V600E), we observed clear inter- and intratumor heterogeneities. Interestingly, prior to BRAF mutation, important genes regulating odontogenesis mutated (e.g., corepressor BCOR), possibly playing important roles in tumorigenesis. Furthermore, recurrent mutations in the CDC73 gene, the germline mutations of which predispose patients to the development of jaw tumors, were found in 2 patients, which may lead to recurrence if not targeted by therapeutic drugs. Our unbiased profiling of coding regions of ameloblastoma genomes provides insights to the possible etiology of mandibular ameloblastoma and highlights potential disease risk factors for screening and prevention, especially for Asian patients. Because of the limited sample size and incomplete habitual, dietary, and occupational data, a causal link between tobacco usage and ameloblastoma still requires further investigations.

The spatial location of the mandibular canal in Chinese: a CT study.

The inferior alveolar nerve (IAN) is vulnerable to injury from mandible fractures and surgical procedures so anatomical variations of IAN are important. Postoperative sensory alteration of the lip and chin region is high after mandibular orthognathic surgery. The incidence of IAN paresthesia following sagittal split ramus osteotomy (SSRO) ranges from 54% to 86% at 4-8 days, 41 to 75% at 1 month, 33 to 66% at 3 months, 17 to 58% at 6 months and 15 to 33% at 1 year postoperatively. This study determined the anatomical position of the mandibular canal in relation to cortical bone and molar teeth in Chinese using archived CT records. The mandibular canal was the farthest from the buccal cortex at the second molar region (mean 6.79mm; minimum distance 4.80mm). The anatomical location of the mandibular canal in local Chinese compares with studies on Asian cadavers. The mandible body was thickest in the region of the second molar (11.9mm). The vertical buccal cut for SSRO should be in the region of the mandibular second molar where the bone is thickest and the mandibular canal is furthest from the buccal cortex. The safe depth for the vertical buccal cut is 4.8mm (minimum horizontal distance).

Clinical characteristics of trigeminal nerve injury referrals to a university centre.

The aim of this retrospective study was to determine the aetiology and characteristics of trigeminal nerve injuries referred to a university centre with nerve injury care. Fifty-nine patients with 73 injured trigeminal nerves were referred in 10 months. The most common aetiologies were odontectomy (third molar surgery) (52.1% of nerves), local anaesthetic (LA) injections (12.3%), orthognathic surgery (12.3%) and implant surgery (11.0%). The inferior alveolar nerve (IAN) was most commonly injured nerve (64.4%), followed by the lingual nerve (LN) (28.8%). About a quarter of IAN injuries (27.3%) and half of LN injuries (57.1%) from odontectomy had severe sensory impairment. There were twice as many LN than IAN injuries from local anaesthetic injections, but all had mild or no sensory impairment. Nerve injuries from implant surgery occurred only in IAN injuries; none had severe sensory impairment. Neuropathic pain occurred in 14.9% of IAN injuries and only in those with mild or no sensory impairment. Nerve surgery was offered to 45.8% of patients; a third underwent surgery.

Osteo-odonto-keratoprosthesis surgery: a combined ocular-oral procedure for ocular blindness.

The aim of this retrospective study was to describe the oral procedures used in osteo-odonto-keratoprosthesis (OOKP) surgery, and the demographics and oral findings of candidate patients in Singapore. The OOKP procedure utilizes an autologous tooth-bone complex to mount a poly-methylmethacrylate optical cylinder, as an artificial cornea, stabilized by an overlying autologous buccal mucosal graft. Consecutive patients referred over 3 years for dental evaluation prior to OOKP surgery were included. A total of 21 patients underwent oral clinical and radiographic evaluation. The aetiology of blindness included Stevens-Johnson's syndrome (11 cases), chemical burns (9 cases) and multiple failed corneal grafts (1 case). Evaluation revealed that 12 patients were suitable for OOKP surgery, 8 were at risk of complication or failure and 1 had no usable teeth. Fourteen patients have undergone unilateral OOKP Stage 1 surgery successfully. Complications included fracture of a tooth from its lingual bone necessitating the harvesting of a second tooth (1 case), oronasal perforation (1 case), exposure of adjacent roots (5 teeth), lower lip paresthesia (2 cases) and submucosal scar band formation in the buccal mucosal graft donor site (10 cases). Thirteen patients have completed Stage 2 surgery, with attainment of their best possible visual potential following OOKP surgery.