الفهرس 
Title : Fracture Resistance and Mode of Failure of Premolar Restored with Lithium Disilicate Vonlay Partial Coverage Restorations versus Lithium Disilicate Onlay Partial Coverage Restorations (In-vitro study)
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Abstract
Aim: The purpose of this in-vitro study was to compare the fracture resistance and failure modes of ceramic partial coverage premolar restorations made of a lithium-disilicate ceramic with different preparation designs. Methods: Sixteen human maxillary premolars were used in this study. Teeth were chosen to be free from any caries, defects, or cracks. To facilitate standardization of tooth position during preparation and during test procedure, teeth were mounted in epoxy resin blocks. Teeth were randomly divided into four groups (4 each) according to designs of preparation as follows: group A: (n= 4) upper premolars restored with lithium disilicate vonlay partial coverage. group B: (n= 4) upper premolars restored with lithium disilicate partial onlay partial coverage. group C: (n= 4) upper premolars restored with lithium disilicate total onlay partial coverage. group D: (n= 4) intact teeth. Restorations were fabricated by IPS e.max press material, and were cemented on epoxy dies using RelyX{u2122} ultimate resin cement. All samples were pre-loading in a cyclic manner equivalent to the average masticatory cycle. Afterward, samples were loaded until fracture using a universal test machine. . Data were analyzed for each group using one-way analysis of variance (ANOVA); P values which were 0.05 or less were considered statistically significant. the fracture mode of all samples was examined using stereomicroscope