Objective : To compare the clinical effects of polymer ceramic onlay and all ceramic crown in short crown molars Methods : 45 cases of polymer ceramic onlay and 45 cases of Zirconium dioxide all ceramic crowns which repaired the short crowm molars after root canal therapy were compared clinically from the aspects of beauty of restoration, fracture and dislodgement, marginal adaptation and the preservation of abutment teeth. Results : One polymer ceramic onlay had fall out form the teeth after half year, while the all ceramic crowns have been 8 cases after 6~12 months. There were significant differences in fracture and dislodgement between the two groups (χ2=4.44, P < 0.05). Conclusion Polymer ceramic onlay has good clinical effects in the restoration of short crown molars.

Objective : To compare and analyze the effects of thermal etching on the shear strength of zirconia substrates and decorative ceramics. Methods: A total of 20 specimens made with zirconia ceramics were randomly divided into an observation group and a control group with 10 cases in each group. The control group was treated with sandblasting, while the observation group was treated with sandblasting and thermal etching. The surface characteristics were examined by scanning electron microscope (SEM) and phase analysis of X-ray diffraction (XRD), and the shear strength was tested using a universal testing machine. The characteristics of surface destruction were examined by SEM. Results : SEM showed that the peak structure was observed in both groups. The observation group exhibited deep fissures, and the control group exhibited small fissures. The diffraction peaks of the two groups are similar. The T (101) peak is the main peak, and both groups exhibit an M (111) peak. However, the peak intensity is relatively small. The relative levels of monoclinic zirconia were 15.16% in the observation group and 16.22% in the control group. The shear bond strength of the observation group was 24.74 ± 3.02 MPa, which was significantly higher than that of the control group at 21.09 ± 2.58 MPa. The difference was statistically significant (t=2.599, P=0.021). In the control group, the porcelain residue on the zirconia surface was minimal at low magnification, and the zirconia substrate was obviously exposed. The zirconia surface was similar to cristae obliqua at high magnification, and the porcelain exhibited a scattered distribution. In the observation group, a large amount of residual veneer porcelain remained on the zirconia surface at low magnification, but considerable porcelain was observed at high magnification. Conclusion Thermal etching and sandblasting treatment can improve the shear strength of zirconia substrate.