الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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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™ 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. Results: The highest mean value of maximum load (Fracture resistance) was found in group A (vonlay) (1522.64 ± 352.52) followed by group C (total onlay) (1301.34 ± 177.12) followed by group B (partial onlay) (879.63 ±158.92), the least mean value of maximum load (Fracture resistance) was found in group D (Intact tooth) (717.33 ± 198.59). Conclusions: Within the limitations of this study, all fracture resistance loads obtained in this study were far beyond the maximum masticatory forces.