Effects Of The Fracture Strength Of Maxillary Incisors Restored With IPS-Empress Ⅱ Restorations By Different Method Of Preparation In Vitro

Objective: In vitro study was to explore the fracture strength of maxillary incisors restored with IPS-EmpressⅡrestorations; making use of a new and conservative method, applying three different method of preparation,and then finding the best treatment plan according the result of the test. In this study, the incisal edge of all maxillary incisors has some defect.Methods: Eighteen, caries-free human maxillary central incisors were used as abutments and were randomly divided into three groups of 6 samples each, respectively 2mm group,3mm group and 4mm group according to the different distance to incisal edge, namely the ratio of the area of the preparation and the area of the defect was 1:1,1.5:1,2:1.The depth of the preparation was overall 0.5mm in each group , so that it remained mainly within the enamel .After preparation , making impression with silicone rubber .Testing the fractured force using the electronic universal testing machine after finishing restorations and being cemented according to the directions.Statistical data analysis performed using the SPSS13.0 software.Groups were compared using the one-way ANOVA.Result: Among the different groups significant difference was found. There were statistical significant(p<0.05).The fracture strength of 2mm group,3mm group and 4mm group is 263.9±23.2N,240.3±9.1N,501.0±22.6N respectively. The fracture strength of each group was larger than the average occlusal force of the up anterior teeth; Significant difference was found between 4mm group and 2mm group,namely there were statistical significant(p<0.05).And the same result was found between 4mm group and 3mm group; there were statistical significant(p<0.05),but there were not any statistical significant (p>0.05)between 2mm group and 3mm group.Conclusions: All mean values obtained were larger than the average occlusal force of the up anterior teeth; and within the limits of clinical acceptance, and hinting that the strength of the new technology could satisfy the need of the mastication. And supposing the result of the test has some association with the area of cementation of the restorations, and that the ratio of the area of defection and cementation was 1:2 was better.