The Effect Of Different Cement Space On The Fitness Of CAD/CAM Zirconia Crown

Objective:The purpose of this study is to evaluate the effects of different spacer thickness and the distance from the spacer to the finish line on the marginal adaptation as well as the internal adaptation of the CAD/CAM upcera zirconia monolithic crown.Methods:The mandibular first premolar in the standard model was made.Fifty-four working models were created from the silicone impression.The working models were randomly divided into 9 groups.Fifty-four digital optical models were obtained by digital scanning instrument.The spacer thickness is set to 20μm,30μm and 40μm,and the distance from the spacer to the finish line is set to 0.5 mm,1.0 mm and 1.5mm respectively.54 all-ceramic crowns were obtained by CNC milling machine.All-ceramic crowns were bonded with glass ionomer cement.The section of the specimen was scanned by stereomicroscope after embedding and hard tissue sectioning,and the data were analyzed statistically.Results:The marginal fitness and internal fitness of all-ceramic crowns were measured with the software of Las X.The spacer thickness and the distance from the spacer to the finish line were analyzed with one-way ANOVA.The results showed that:1.The spacer thickness and the distance from spacer to the finish line had significant effects on the marginal gap(P<0.05),the interaction of the spacer thickness and the distance from spacer to the finish line had a significant effect on the marginal discrepancy(P<0.05).2.The spacer thickness and the distance from spacer to the finish line had significant effects on the axial spaces(P<0.05),the interaction of the spacer thickness and the distance from spacer to the finish line had significant effect on the axial spaces(P<0.05).3.The spacer thickness and the distance from spacer to the finish line had significant effects on the occlusional space(P<0.05),however,the interaction of the spacer thickness and the distance from spacer to the finish line had no significant effect on the occlusional space(P>0.05)Conclusions:Different CAD/CAM systems,different porcelain materials,different adhesives and other factors will affect the fitness of CAD/CAM zirconia all-ceramic crowns.In this experiment,simulate the clinical procedure as much as possible,strict control of variables,reduce the error caused by other factors,and reached the following conclusions:1.When the space thickness is set at 30μm,the marginal fitness of CAD/CAM zirconia all-ceramic crown is the best.2.When the space thickness is set to 20μm and 30μm,the axial fitness and occlusal fitness of CAD/CAM zirconia all-ceramic crowns are the best.3.When the distance from spacer to the finish line is set to 1.0 mm,the marginal fitness and internal fitness of CAD/CAM zirconia all-ceramic crowns are the best.4.It is suggested that the space thickness should be set to 30μm and the distance from spacer to the finish line should be set to 1.0mm to achieve the best fit.