In this study, the fatigue properties of additively manufactured titanium clasps were compared with those of commercially pure titanium (CPTi) and Ti-6Al-4V (Ti64), manufactured using laser powder-bed fusion. Methods: Fourteen specimens of each material were tested under the cyclic condition at 1 Hz with applied maximum strokes ranging from 0.2 to 0.5 mm, using a small stroke fatigue testing machine. A numerical approach using finite element analysis (FEA) was also developed to predict the fatigue life of the clasps. Results: The results showed that although no significant differences were observed between the two materials when a stroke larger than 0.35 mm was applied, CPTi had a better fatigue life under a stroke smaller than 0.33 mm. The distributions of the maximum principal stress in the FEA and the fractured position in the experiment were in good agreement. Conclusions: Using a design of the clasp of the present study, the advantage of the CPTi clasp in its fatigue life under a stroke smaller than 0.33 mm was revealed experimentally. Furthermore, the numerical approach using FEA employing calibrated parameters for the Smith-Watson-Topper method are presented. Under the limitations of the aforementioned clasp design, the establishment of a numerical method enabled us to predict the fatigue life and ensure the quality of the design phase before manufacturing.

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In this study, ultra-high-resolution micro-computed tomography (micro-CT) was used to classify the root canal morphology of the distobuccal root of the maxillary first molar and investigate the incidence of accessory root canals, as well as to identify some aspects of their association with root canal re-infection during and after molar-infected root canal treatment. The specimens used were 100 maxillary first molars from Japanese individuals held in the collection of the Department of Anatomy of Tokyo Dental College. They were scanned by micro-CT, after which three-dimensional reconstruction was conducted, the pulp cavity and accessory root canals were observed, the root canal morphology was classified, and the incidences of the different types of accessory root canals were calculated. The distobuccal root of the maxillary first molar was a single root in all teeth from Japanese individuals. The main root canal was classified as Type I in 98.0% of cases, the incidence of lateral branches was 27.0%, and their incidence on the apical side was higher than that previously reported. These results suggest that, despite the simplicity of the root canal, the existence of accessory root canals should be borne in mind during root canal treatment.

(5) The influence of bite force on the internal structure through implant (6) anatomy 2 AbstructApplying proper quantity of stress through the teeth is considered essential for maintaining the homeostasis of jaw.The aim of this study is to clarify the effects of the pressure applied via endosseous implants on internal structures of the jaw. A mandible with dental implants for 15 years was analyzed by micro-CT to prepare a finite element model of the mandible including implants and surrounding internal microstructures. Based on this model, mechanical analysis was conducted by the three-dimensional finite element method. The results of the three-dimensional finite element analysis showed that the stress distribution was seen in the trabecular bone around the implants. It became clear that the pressure is transmitted to mandibular internal structures via implants, and stress is dispersed along internal trabecular alignment.

Recent years have seen attempts to perform access cavity preparation in a minimally invasive manner from the standpoint of preserving the tooth substance. However, age-related changes in pulp cavity morphology are unavoidable and may sometimes hinder the operator. Few studies appear to have addressed these changes in detail. The aim of this study was to identify age-related differences in the side walls of the pulp chamber for access cavity preparation using ultra-high-resolution micro-computed tomography (micro-CT). Specimens were human extracted maxillary first molars showing no caries, attrition, or abrasion, classified by age at extraction into adult (age 21-40 years, n=20), middle-aged (age 41-60 years, n=20), and senior (age ≥61 years, n=22) teeth. Specimens were scanned by micro-CT, with the resulting data used to create 3-dimensional (3D) reconstructions for examination of pulp cavity morphology. We also measured dentin thickness using reference lines and measurement lines, and compared the differences between age groups. The observations and measurements of dentin thickness made using these 3D reconstructions showed that in senior teeth, narrowing of the pulp cavity between the mesial and distal side walls was evident from the midline to the pulp chamber floor compared with adult teeth. Narrowing of the pulp cavity was also evident from immediately below the midline of the distobuccal wall to the pulp chamber floor. The dentin thickness of each side wall was measured, and the results showed that senior teeth were significantly thicker than adult teeth in the mesial, distal and distopalatal side walls. These results suggest that when preparing access cavity in senior patients, it is necessary to remove the distobuccal side wall in addition to the mesial and distal side walls for identification of canal orifice in maxillary first molar.