To compare the fracture strength between Monolithic Lithium Disilicate pressed crowns and the Bi-layered zirconia based pressed crowns.
The samples were prepared by utilizing the shape of mandibular right first molar tooth, with the following preparation criteria: 6-degree axial taper, 1.5-mm shoulder finish line placed 0.5 mm occlusal to the cemento-enamel junction, 1.5-mm axial reduction, 2-mm occlusal reduction, and 5-mm occluso-gingival height. A master metal die used for all groups. Full contour wax up to form mandibular right first molar tooth done and preserved to be used for all groups. Group “A” (Zirconia Based ) the abutment were scanned, zirconia coping milled and the veneering porcelain pressed according to the manufacture recommendations. Group “B” (Monolithic) a full contour wax up exactly the same as group “A” were done on the master die then the crowns pressed according to the manufacture recommendations. The samples were then loaded by a controlled load profile utilizing the Texture Analyzer Machine for 100,000 cycles under wet condition. At the end of cyclic loading, each specimen was loaded statically until fracture to determine the ultimate strength of the porcelain and fracture mode.
Result: The mean fracture load was 1360.6 N for the monolithic crowns group, 1014.2 N for the zirconia based crowns group. Non of the monolithic lithium disilicate crowns failed during cyclic loading, However zirconia based crowns shows crack line during cyclic loading with no chipping or bulk fracture.
Based on the present study, Monolithic Lithium Disilicate fully anatomical pressed crowns shows more fracture resistance after fatigue load than zirconia based pressed crowns.
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