Basic and clinical research for root fracture

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New indexes, Complexity and Radial SD using periapical radiolucency were evaluated to make a differential diagnosis between apical periodontitis and vertical root fracture on a radiograph. New indexes could be useful for the diagnosis of vertical root fractures. Training on how to analyze dental radiographs is very important for the differential diagnosis between vertical root fracture and periapical inflammation. Whereas clinical experience had no significant effect on the correct diagnosis, the specialty of dentists showed a significant difference. An incomplete vertical fracture was detected after removing cementium under a dental poreating microscope.Coronal leakage inhabitation using a resin-coating technique after endodontic treatment was evaluated. The dye penetration was influenced by post space preparation, resin coating, and temporization.The relationship between occlusal force and tooth displacement in function was evaluated. The direction of the tooth displacement and that of the occlusal force of the upper first molar almost coinceded and they were along ahte palate-apical direction. In the lower first molar, the direction of occlusal force was in the apical direction, and the tooth displacement path was along the lingual direction. The influence of alveolar bone level on the fracture resistance of root restored with post and core was evaluated. With normal bone model, cast post and core showed the highest fracture resistance. In the resorbed bone model, there was no significant difference in fracture resistance between cast post and core and fiber post with composite resin.The remaining tooth structure played an important role in the root fracture and preparation of a post hole with a large taper easily caused root fracture.