Recently, fixed dental prostheses (FDPs) with a hybrid structure of CAD/CAM porcelain crowns adhered to a CAD/CAM zirconia framework (PAZ) have been developed. The aim of this report was to describe the clinical application of a newly developed implant-supported FDP fabrication system, which uses PAZ, and to evaluate the outcome after a maximum application period of 36 months. Implants were placed in three patients with edentulous areas in either the maxilla or mandible. After the implant fixtures had successfully integrated with bone, gold-platinum alloy or zirconia custom abutments were first fabricated. Zirconia framework wax-up was performed on the custom abutments, and the CAD/CAM zirconia framework was prepared using the CAD/CAM system. Next, wax-up was performed on working models for porcelain crown fabrication, and CAD/CAM porcelain crowns were fabricated. The CAD/CAM zirconia frameworks and CAD/CAM porcelain crowns were bonded using adhesive resin cement, and the PAZ was cemented. Cementation of the implant superstructure improved the esthetics and masticatory efficiency in all patients. No undesirable outcomes, such as superstructure chipping, stomatognathic dysfunction, or periimplant bone resorption, were observed in any of the patients. PAZ may be a potential solution for ceramic-related clinical problems such as chipping and fracture and associated complicated repair procedures in implant-supported FDPs.

Within the limitations of this study, Ce-TZP/A was found to provide sufficient stability as a framework material in all regions. Special attention, however, must be paid to designing framework that provides sufficient support for the veneer. Furthermore, studies with longer observation periods and more patients are needed.

Abstract.[Purpose] The purpose of the present study was to prepare an experimental model for estimating the shear force for a person sitting in a comfortable posture while leaning against a backrest, and then to verify its validity.[Subjects] The subjects were 16 healthy adult men without leg and trunk diseases (age: 21.6 ± 0.8 years; height: 172.5 ± 5.3 [cm]; and body weight: 63.4 ± 6.4 [kg]).[Methods] Using the model, the shear force applied to the gluteal region in a sitting posture was estimated, and at the same time, the shear force was measured using a force plate. The model's validity was assessed by comparing the estimated and measured values in terms of correlation coefficients.[Results] The average estimated shear force was 36.6 ± 11.8 [N], and the average reaction force in the posterior direction as part of the anteroposterior components of the floor reaction force (shear force in the anterior direction) was 35.9 ± 15.8 [N]. No significant difference existed (p=0.797), and the correlation coefficient was 0.897 (p<0.0001), thus exhibiting a strong positive correlation. [Conclusion] This result shows that the validity of the present experimental model is high, and the model is useful in clinical settings because shear force in a comfortable sitting posture can be relatively easily estimated without a special device.

ABSTRACT:The purpose of this study was to verify the initial mechanism of shear force in comfortable sitting position on chair. With 10 healthy men as subjects, we measured the displacement width of sitting pressure distribution with trunk backward inclining and the time difference from contact with the backrest until the beginning of the shift of the sitting pressure center position under two conditions of "with" and "without" backrest using a pressure distribution meter. The results show that the sitting pressure center position gradually moves backwards with trunk backward inclining, and in the case of "with" backrest turned forward just after the inclining (0.2 ± 0.1 sec). The displacement width was a shift forward from the base sitting position of 0.5 ± 1.2 cm "with" backrest and a shift backward of 2.0 ± 1.1 cm "without" backrest, showing a significant difference between them (p<0.01). These results suggest the intervention of backrest is indispensable in the initiation of shear force.

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