Experimental Study On The Effect Of Sintering Temperature On The Fits Of Zirconia Crowns Made With Three Different Materials

ObjectiveTo study the effects of sintering temperature on the fits of three zirconia crowns using silicone copy crown clearance method, and provide theoretical basis for clinical and laboratory application.MethodsA standard model of left maxillary central incisor was prepared. In the standard model, the incisal preparation was2.0mm, the polymerization degree was10°, the width of shoulder was lmm, and the shape of shoulder was90°concave. Then an ultra-anhydrite-generation model was irrigated with silicon rubber material. Sirona inLab CAD/CAM system was used to design and cut30zirconia crowns using VITA In-Ceram YZ、UPCERA HT and KND. The zirconia crowns were divided into six groups according to sintering temperature. The crowns were placed into sintering furnace named’in Fire’, and sintered at six different temperatures of1330℃,1380℃,1430℃,1480℃,1530℃,1580℃, respectively. Then all-ceramic crowns were located on the ultra-anhydrite-generation model, and lightweight silicone rubber was used to fill the space between zirconia crown and ultra-anhydrite-generation model. After that, OLYMPUS BX53upright fluorescence microscope was used to measure the film thickness of silicone rubber. Finally the data obtained were analyzed using SPSS16.0package.Results1.The marginal and internal fits of the zirconia crowns became better with sintering temperature increased from1330℃to1580℃. The marginal and internal gaps of VITA zirconia crowns got its minimum (57.34±4.11um-76.09±10.75um) when the sintering temperature reached1530℃; The marginal gaps of UPCERA zirconia crowns presented declining trend with temperature increased, while the central gaps reached its minimum at1480℃(89.83±12.81μm), and the incisor gaps reached its minimum at1530℃(99.48±30.83μm); The marginal fits of KND became stable at1430℃, differences among the marginal gaps when the sintering temperature higher than1430℃had no statistically significant (P＞0.05), while the central fits tended to stable at1480℃. The incisal gaps showed a declining trend with temperature increased, and differences among incisal gaps at each sintering temperature had no statistically significant (P＞0.05).2.The marginal, middle and incisal fits of the zirconia crowns made with three different materials at the same sintering temperatures were compared, respectively. Differences among three marginal fits had statistically significant (P＜0.05). UPCERA marginal gap had maximum value, and was different compared with VITA and KND (P＜0.05), while the marginal gaps of VITA and KND had no significant difference (P＞0.05). Central and incisal gaps had no statistically difference (P＞0.05) except at1330℃. However, UPCERA had larger gaps.3.The marginal and internal fits of9control points at stable sintering temperature (1480℃,1530℃,1580℃) were compared. When sintering temperature resched1480℃, KND got the best fit. It mainly showed in buccal, lingual, mesial of the margin, and in buccal and mesial of the middle. Marginal fits difference between VITA and KND had no statistically significant (P＞0.05) at1530℃, but both were small than UPCERA (P＜0.05). VITA had minimum middle buccal gaps, and was different compared with KND and UPCERA (P＜0.05). When sintering temperature reaching1580℃, differences had no statistically significant (P＞0.05) except at marginal mesial, middle mesial and lingual (P＜0.05).Conclusion1.VITA, UPCERA, KND Zirconia crowns were sintered at temperatures of1330℃,1380℃,1430℃,1480℃,1530℃, and1580℃. The marginal and internal fits became better with sintering temperature increase.2. VITA zirconia all-ceramic crowns got the best fits at1530℃.3.The marginal and internal fits of UPCERA zirconia crown can reach a stable state at1480℃～1530℃.4. The fits of KND zirconia crown became stable at1480℃.5. At the same sintering temperature, the fits of VITA and KND crowns were better than UPCERA, and difference between VITA and KND had no statistically significant.6. Under stable state, KND showed good suitability at1480℃, VITA presented a better fit at1530℃, while there were no significant differences at1580℃.