Daizo Okada

The relationship between bite force and oral sensation during biting in molars

BACKGROUND In prosthodontic treatment, the occlusal form should be designed such that bite force is applied at the position that has higher load-bearing capacity and is comfortable for the patient. The purpose of this study was to clarify the differences in bite force and occlusal sensation with different loading positions on the occlusal surface. METHODS Twelve healthy subjects were recruited for this study. Bite force and occlusal sensation were measured at five loading points on the upper and lower left first molars. Occlusal sensation was evaluated using a Visual Analogue Scale (VAS). RESULTS Bite forces on the lingual side of the upper first molar and the buccal side of the lower first molar were significantly higher and VAS scores were significantly lower, i.e. the subjects felt less discomfort during biting on the buccal side of the upper first molar and the lingual side of the lower first molar compared to the other side of each molar. CONCLUSIONS Loading on the occlusal surfaces of the functional cusps of the upper and lower first molars produces more load-bearing capacity and is more comfortable than loading on the non-functional cusps.

Photoelastic stress analysis of endodontically treated teeth restored with different post systems: normal and alveolar bone resorption cases

The present study examined the influence of different post materials and their lengths on the mechanical stress of endodontically treated incisor roots in two alveolar bone conditions. Two-dimensional photoelastic models were fabricated to simulate the endodontically treated maxillary central incisors restored with three kinds of posts materials (low Youngs modulus glass fiber post, high Youngs modulus glass fiber post, and prefabricated stainless steel post) and two post lengths (8 and 4 mm). Completed models were placed in a transmission polariscope and loaded with a static force of 150 N at 45° to the tooth axis. Photoelastic photographs and the magnitudes of fringe order revealed stress distribution in the root, and suggest that the glass fiber post with a low Youngs modulus and long length can reduce the stress concentration both in normal and alveolar bone resorption conditions.