[Effects of repeated firing on microleakage of selective laser melting ceramic crowns].

PURPOSE: To investigate the effects of repeated firing on microleakage of selective laser melting ceramic crowns. METHODS: Fifty molars were randomly divided into 2 groups (25 teeth in each group). Teeth in group A received a chamfer finish line preparation, whereas teeth in group B received a shoulder finish line. After SLM metal crowns were fabricated, all the crowns received initial oxidation step, opaque firing, dentin firing and glaze firing, then crowns in each group were randomly divided into 5 sub-groups according to different time of clinical firings. Glass ionomer was applied for bonding. After 5000 thermocycles ranging from 5degrees centigrade to 55degrees centigrade, all the specimens was evaluated by dye penetration and then microleakage was examined under light microscopy. The data were analyzed with SPSS 20.0 software package. RESULTS: Microleakage between all specimens of group A were not statistically significant (P>0.05) whereas that of group B were statistically significant (P<0.05); After the fifth time of clinical firing, microleakage of specimens in group B(B5) were significantly higher than that of group A(A5). CONCLUSIONS: Repeated firings had no significant influence on marginal microleakage of SLM ceramic crowns whereas the crowns of chamfer finish lines result in better clinical performance after repeated firings.

[Comparative study of microleakage by using different finished lines in selective laser melting metal crowns].

PURPOSE: To evaluate microleakage of SLM Co -Cr alloy metal crown with two types finished line (chamfer and shoulder), compared with conventional fabrication of Co -Cr alloy metal crowns. METHODS: Thirty healthy non-carious human molars were selected and randomly assigned to 3 groups, 10 in each. Teeth in group A and C received a chamfer finish line preparation, whereas teeth in group C received a shoulder finish line. Conventional Co -Cr alloy metal crowns were fabricated for group A when SLM metal crowns were made for group B and group C. Glass ionomer was applied for bonding. After 5000 thermocycles ranging from 5degrees centigrade to 55degrees centigrade,all the specimens were evaluated by dye penetration and then microleakage was examined under light microscope. The data were analyzed statistically with SPSS 20.0 software package. RESULTS: Microleakage in group A was significantly higher than the other two groups, group B and group C showed no significant difference in microleakage while microleakage in group B was higher than that in group C. CONCLUSIONS: Microleakage of SLM metal crowns was significantly less than that of conventional Co-Cr alloy metal crowns; chamfer finish line designs was recommended for SLM metal crowns in consideration of reducing microleakage and protecting tooth.

[Effect of different surface treatments on the shear bond of zirconia substructure and veneering ceramic].

PURPOSE: To investigate the effect of different surface treatments on the shear bond strength of zirconia substructure and veneering ceramic. METHODS: Kavo zirconia specimens were divided into 4 groups (each group contains 8 specimens) according to different surface treatments: Group A was pigmented by dipping presintered blocks in the coloring solution VITA LL5, and not treated with abrasion after firing; Group B was pigmented with the same solution and then dealt with abrasion; Group C was not treated by any methods and Group D was only dealt with abrasion. All the veneering ceramics were fired on the zirconia substructure by slip-casting technique and the shear bond strength of zirconia substructure and veneering ceramic were tested. The data was analyzed statistically with SPSS 10.0 software package. RESULTS: The shear bond strength of the abrasive-treated groups (group B and group D) was significantly higher than the other two groups, but no significant difference was found between pigmented-treated groups (group A and group C) and non-pigmented-treated groups (group B and group D). CONCLUSIONS: Abrasion can increase the shear bond between Kavo zirconia substructure and veneering ceramics while pigmentation has no significant effect on the bonding strength.

[Clinical analysis of laser welding on porcelain bonded metal surface].

PURPOSE: To evaluate the clinical effect of laser-welded crowns and bridges. METHODS: Two hundred defective crowns and bridges were welded by using Heraplus laser welding machine, and then restored by porcelain. RESULTS: After being welded ,those defective crowns and bridges of different materials fit well and their marginal areas were also satisfactory. During the follow up period of one year, no fractured porcelain and crack were found at welding spots. CONCLUSIONS: The technology of laser welding has no direct effect on welding spots between metal and porcelain and could be used to deal with the usual problems of the crowns and bridges.