The purpose of this study was to evaluate the design of resin-bonded fixed partial dentures (RBFPDs) with zirconia frameworks. The abutment teeth were the upper central incisor and the canine. Three types of frameworks were fabricated as follows: 0.5-mm-and 0.8-mm-thick zirconia frameworks with grooves and holes (0.5ZrG, 0.8ZrG) and 0.5-mm-thick zirconia frameworks without grooves and holes (0.5Zr). The control group was designed as a 0.8-mm-thick metal framework with grooves and holes (0.8MG). Static loading was applied and the surface strain of the retainers was measured with strain gages. The magnitude of the principal strain of the 0.5ZrG framework was significantly lower than that of the 0.8MG and the 0.5Zr frameworks. This result suggests that the zirconia and retention form had a significant effect on decreasing the framework deformation, indicating that the RBFPDs that use a 0.5-mmthick zirconia framework are effective for replacing a single anterior missing tooth.

This study was aimed at evaluating the fracture resistance of structurally compromised roots restored with four different post and core systems. Thirty-two bovine roots were uniformly shaped to simulate human mandibular premolar roots. The roots were divided into four groups based on the type of restoration: cemented cast post and core (Group MC), resin composite build-up (Group CR), resin composite and prefabricated glass fiber post build-up (Group FRC), and thick-layer dual-cured resin composite-reinforced smalldiameter tapered cast post and core (Group CRM). After a static loading test, the failure mode and fracture resistance were recorded. Group CRM (719.38±196.73 N) exhibited a significantly high fracture resistance compared with the other groups (Group MC: 429.56±82.43 N; Group CR: 349.56±66.21 N; Group FRC: 398.94±112.71 N; p<0.05). In conclusion, Group CRM exhibited better mechanical properties for structurally compromised roots with no ferrules, although all types of restorations showed non-restorable fracture modes.

The purpose of this study was to evaluate the influence of flexural modulus of non-metal posts on the fracture strength and failure mode of composite resin cores. Thirty-two human premolars were divided into four groups: prefabricated glass fiber post with 1.0 mm diameter and composite resin core (Group PE1.0), that with 1.5 mm diameter and composite resin core (Group PE1.5), experimental post (flexural modulus; 4.25GPa) and composite resin core (Group EX), and preparation for abutment teeth only (Group NT). After a static loading test, the fracture strength and failure mode were recorded. Group NT (1670.81 N) showed higher fracture strength than Groups PE1.0 (866.44 N), PE1.5 (825.19 N) and EX (1075.63 N) (p<0.05). This study showed that the fracture strength of endodontically treated teeth restored with composite resin cores is not influenced by the flexural modulus of non-metal posts.

A hot spline forming process of an ultra high strength steel gear drum was developed to manufacture high tensile strength steel spur gears. Since the cross-sectional area of a side wall of a cup formed by cold deep drawing and ironing was uniform, the side wall formed put between the upper and lower electrodes was uniformly heated by the electrification in the axial direction. The uniformity of the temperature was improved by inserting a copper foil between the electrode and the side wall, and by decreasing the area of contact. Although the high strength steel cup was fractured by cold spline forming, a spur gear was successfully manufactured by the hot spline forming. The load for a hot spline forming of the high strength steel gear drum is similar to that for the cold forming of a mild steel gear drum, and the accuracy of teeth was improved. In addition, the formed gear drum was hardened by die quenching.