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The correlation between spiral CT and physical measurement was high except in sites of very thin mucosa. Spiral CT can be considered an alternative method for the measurement of oral mucosal thickness. Because of the higher radiation exposure, caution should be exercised and radiation dosage versus clinical benefit assessment is required.

Objectives: The aims of this study were (1) to assess the validity of limited cone beam CT (CBCT) in detecting the distribution of bifid mandibular canals in the retromolar region by comparing its findings with those of panoramic radiography and spiral CT imaging, and (2) to confirm the contents of such canals depicted on limited CBCT images by using gross anatomical and histological methods. Methods: Bilateral bifid mandibular canals of a Japanese cadaver were investigated. The canals depicted on panoramic radiography, spiral CT and limited CBCT images were compared. Cross-sectional limited CBCT images of these canals were compared with gross anatomical sections of the mandible and their contents were confirmed histologically. Results: The spiral CT and limited CBCT images showed the bilateral bifid mandibular canals in the retromolar region whereas the panoramic radiographs indicated the presence of only the left bifid mandibular canal. The canal distribution was more distinct in the limited CBCT images than in the spiral CT images and the cross-sectional limited CBCT images were consistent with the gross anatomical sections. Histologically, the canals contained several nerve bundles and arteries among which the largest nerve and artery were of a similar size. Conclusion: Limited CBCT is valuable for assessing the distribution of bifid mandibular canals. It is clinically significant to accurately localize a bifid mandibular canal of the retromolar region because it contains a nerve bundle and artery.

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Using Hiranuma's classification, we carefully examined anatomical variations in the first compartments of 246 human wrist joints from 124 cadavers. Morphological examinations were conducted to determine the number of accessory tendons and the existence of dissepiments for the extensor pollicis brevis (EPB) and abductor pollicis longus (APL) tendons. Anatomical variations of EPBs and APLs were grouped together by type, and appearance ratios were calculated based on Hiranuma's classification. Of the 246 wrist joints, 156 were categorized as normal type (63.4%), 57 as complete dissepiment type (23.2%), 22 as incomplete dissepiment type (8.9%), and 11 as EPB-lacking type (4.5%). Accessory tendons were identified in both the EPB and the APL tendons of most cadavers, and the incidence of dissepiment in tendon sheaths was approximately 33%. Sixty-six of the 193 wrist joints (34.2%) showed equal numbers of right and left accessory tendons. However, the number of EPB accessory tendons was higher than in previous studies, and in all cases some kind of dissepiment was observed in the APL and EPB. The number of EPB and APL accessory tendons showed no clear differences by gender, age, or right and left specificity.