الفهرس 
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Abstract
This in vitro study aimed to evaluate the fracture resistance of Vita suprinity and Lava ultimate partial coverage restorations with different preparation designs.
A two caries-free maxillary human premolars extracted for orthodontic reasons were collected from orthodontic department, Faculty of Dentistry, Ain-Shams University. The two natural teeth were embedded parallel to their long axis in self cure acrylic֘1.0 mm apical to the cemento-enamel junction using a custom made rubber mold, each natural tooth was prepared according to the type of cavity design D1 (MOD cavity according to specific guidelines and 2.0mm anatomical reduction of the buccal and palatal cusps), D2 (receiving additional to the MOD cavity and cusps reduction a shoulder finish line 1.0mm above CEJ).
After cavity preparation, the two natural teeth were duplicated by using silicone duplicating material, then each mould were poured fourteen times using Epoxy Resin.
Teeth were divided into 4 groups (n=7) according to type of restoration materials and cavity preparation, group LU-D1 (Lava Ultimate restore D1 cavity preparation). group VS-D1 (Vita Suprinity restore D1 cavity preparation). group LU-D2 (Lava Ultimate restore D2 cavity preparation). group VS-D2 (Vita Suprinity restore D2 cavity preparation).
3D scanner was used to obtain digital impressions for preparation samples, Exo-Cad SW 2018 (valletta 2.2) used to design restorations, then CORITEC 350i PRO+ milling machine was used to mill the samples.
The finished onlays were luted to epoxy resin specimens using self-adhesive resin cement (All Bond Universal, BISCO Inc, Schaumburg, USA). Specimens exposed to thermocycling 5000 cycles. The fracture resistance of specimens were evaluated in a universal testing machine. The results were analyzed by 2-way ANOVA and pairwise t-test with benferroni correction.
The results of two-way ANOVA test showed that there was a significant interaction between ceramic material and preparation design (p=0.005). Lava Ultimate samples had a significantly higher value of fracture resistance than Vita Suprinity samples in D1 (p<0.001), but Vita Suprinity samples had a higher value of fracture resistance than Lava Ultimate samples in D2, yet the difference was not significant (p=0.853).