Purpose: The purpose of this study was to investigate the dynamic retentive force of a mandibular unilateral distal-extension partial denture framework with a back-action clasp that was designed in a buccally tilted cast on a dental surveyor. The retention mechanism of this framework was analyzed in comparison with other typical unilateral and bilateral frameworks for the mandibular Kennedy class II case. Materials and Methods: Experimental gold alloy frameworks of three designs were repositioned to the master cast, and lifted upward to the vertical direction to the occlusal plane. The load required to dislodge each framework was recorded. The retentive force of each framework was determined by the maximum load in a dislodgment cycle. The bending strength of a plain clasp pattern of the same length as the clasp arm used in each framework was also measured by cantilever beam test. Results: The mean retentive force of the unilateral framework with a back-action clasp of relalively low bending strength was significantly higher (P < 0.01) than that of the unilateral framework with two Akers clasps of relatively high bending strength, and 70 to 80% of the bilateral framework with two Akers clasps on the edentulous side and a double Akers clasp on the contralateral side. The unilateral framework with a back-action clasp showed the greatest early load resistance in the dislodgment cycle among the three designs. Conclusion: The reasonable retention mechanism was demonstrated by the unilateral framework with a back-action clasp.

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Oral cancers of tobacco and betel chewers represents a unique in-vivo model to understand the genotoxic effect of tobacco and betel carcinogens on oncogenes and tumor suppressor genes. Coordinated interactions of p53 and MDM2 play an important role in regulation of critical growth control gene following exposure to DNA damaging agents. The purpose of this study is to determine if the tumor suppressor function of p53 is inactivated by mutation or other alternative mechanisms in carcinogen-induced oral squamous cell carcinoma (SCC), and to investigate the clinicopathological significance of p53 and MDM2 expression. The p53 mutation in oral SCC of tobacco and betel chewers (n=40) was detected by polymerase chain reaction - single strand conformation polymorphism (PCR-SSCP) analysis and immunohistochemistry (IHC) was done to investigate p53 and MDM2 proteins overexpression. The incidence of p53 mutation was relatively low (17.5%), but there was a high prevalence of MDM2 overexpression (72.5%). In the total of 40 cases, IHC phenotype showed p53 positive immunostaining with MDM2 positive immunostaining (p53+/MDM2+) 62.5%, p53 negative immunostaining with MDM2 negative immunostaining (p53-/MDM2-) 15%, p53 positive immunostaining with MDM2 negative immunostaining (p53+/MDM2-) 12.5%, and p53 negative immunostaining with MDM2 positive immunostaining (p53-/MDM2+) 10%. A significant correlation was found between MDM2 and p53 overexpression (p=0.0289). Moreover, p53+/MDM2+ phenotype was significantly associated with poorly differentiated tumors (p=0.0007). These results conclude that other factors than p53 mutation is likely to be the targets of tobacco/betel carcinogens and MDM2 may play an important role in tobacco/betel chewing-related oral SCCs. Overexpression of MDM2 protein may constitute an alternative mechanism for p53 inactivation.

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This study aimed to investigate the effects of different sensory-evaluated food textures on masticatory movements, and to identify meaningful factors that correspond to different food textures. Masticatory movements of three healthy subjects were evaluated with a jaw movement tracking device using five different test foods: almond, hard and light rice crackers, apple, and chewing gum. The movements of the incisor point, working and non-working condyle and the entire mandible at the occlusal phase in the horizontal plane were analyzed. For harder foods, the incisor entered the intercuspal position from a rear and lateral, the working condyle showed anterior and noticeable medial movements as the entire mandible translated posteriorly and medially. For soft foods, the incisor movements were nearly coincidental with the lateral border movements, and the mandible rotated towards the inner side near the working condyle. Although the overall paths of the mandibular movements are individually different, it appeared that jaw movement at the final closure is particular to the food texture. From the standpoint of mandibular movements, it is suggested that masticatory movements during the occlusal phase in the horizontal plane is useful for revealing the relationship between mandibular movements and food textures that were evaluated with onomatopoetic words.

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The purpose of this study was to investigate the effect of different mandibular positions on the body equilibrium by measuring the gait rhythm. Twelve young healthy subjects volunteered to participate in this study. Subjects were instructed to walk for a 18m distance with the mandible guided at six different positions by occlusal splints. The gait was recorded at fast, ordinary and slow walking speeds under occluded condition. Gait cycle, coefficient of variation for gait cycle and gait velocity were calculated during the 10m-walk. One-way ANOVA with repeated measures demonstrated significant differences among the six mandibular positions for the gait cycle at all gait speeds, for the coefficient of variation at fast speed and ordinary speed and for the gait velocity at fast speed (P<0.05). Regarding these variables, multiple comparison tests were also performed between the mandibular position without instruction for occlusion and other five mandibular positions. Gait cycle, coefficient of variation and gait velocity changed significantly in 5mm opening position from the intercuspal position, and in 5 mm left and 5mm right position from the 3mm opening position at fast speed (P<0.05). The result of this study suggests that the change of mandibular position could affect the gait stability.

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