The purpose of this study was to conduct static load-bearing tests on 4-unit Y-TZP all-ceramic fixed partial denture (FPD) frameworks with different cross-sectional areas and forms to evaluate the influence of connector design on fracture load. Each of the central, mesial and distal connectors was prepared with one of 2 different cross-sectional areas and one of 3 different forms (one circular and two oval forms) to give a total of 18 designs. Five frameworks were then prepared for each design, making a total of 90. Each framework was cemented to the test model with glass ionomer cement. Fracture load was measured with a universal testing machine at a cross-head speed of 1.0 mm/min. A three-way ANOVA revealed significant differences in fracture load depending on cross-sectional area, central connector cross-sectional form, or mesial/distal connector cross-sectional form (p<0.01). No interaction was observed, however, between any two connector design elements. The results of a Tukey analysis revealed a significant difference between the two connector cross-sectional areas investigated, with an increase in connector cross-sectional area resulting in an increase in fracture load. Fracture load decreased as the height of the mesial or distal connector decreased. Fracture load was significantly higher in frameworks in which the height of the central connector was greater than that of the distal or mesial connector. In conclusion, these results suggest that sufficient height needs to be maintained in the mesial/distal connector to secure a high fracture load in zirconia 4-unit all-ceramic FPDs. Moreover, even when this is not possible, a high fracture load may still be obtained by making the height of the central connector as great as possible. Furthermore, extending the connector cross-sectional area is effective in increasing fracture load.

The wear performances of bovine tooth enamel (BTE) against translucent tetragonal zirconia polycrystals (TZP) compared to that of feldspar porcelain and the influence of surface treatments of translucent TZP were investigated by the two-body wear test. Translucent TZP and feldspar porcelain were used as hemisphere abrader specimens with a radius of curvature of 5 mm; flat BTE surfaces were used as substrate specimens. The cross-sectional area of the worn surfaces of the substrates and the wear volume of the antagonist abraders were measured. Surface roughness, hardness and coefficient of friction as well as SEM observations and EPMA analyses were also performed to investigate the underlying mechanism of wear. The results suggested that BTE is less susceptible to wear when translucent TZP is used as the antagonist in contrast to the use of feldspar porcelain, and that surface treatment of the TZP abraders significantly influenced the wear of BTE substrates.

顎 運 動 に 関 す る 研 究 は，1984 年 に Lundeen と Gibbs 1) が，咀嚼運動や咬合接触点を再現するために 顎運動測定器を開発し，研究報告されてきた．日本で も種々の顎運動測定器を用いて運動解析した多くの研 究が報告されている 2-5) が，それらは数値化するにと どまり，顎運動を様々な角度からビジュアル化して 3 次元表示することはできなかった．現在では，口腔内 スキャナや CAD/CAM スキャナから読み取ったスタ Purpose: The purpose of this study was to reproduce three-dimensional chewing movements and the change of occlusal contact points by software. Materials and Methods:The study model was converted into the software as STL data from a CAD scanner. In addition, we recorded XML data of the mandibular border movement, opening and closing movements, and chewing movements using a six-degree-of-freedom jaw tracking device (ARCUS digma2, KaVo, Biberach, Germany). The XML data was converted to STL data, and we reproduced the three-dimensional chewing movements and occlusal contact points by the software. Discussion: Using the functional analysis program, it is possible to reproduce the border movements, opening and closing movements, and chewing movements in three dimensions. We could also observe the change of occlusal contact points in the chewing movements. We suggest that occlusal interference could be found or the temporo-mandibular joint could be examined in the future by using the software to analyze three-dimensional jaw movements. Conclusions:We succeeded in observing three-dimensional jaw movements from every angle by the software. In addition, the changes of occlusal contact points in chewing movements were reproduced.