OBJECTIVES: The purpose of this study was to compare the marginal fit of two CAD/CAM monolithic zirconia crowns with two finish line designs after thermo-mechanical aging. MATERIALS AND METHODS: A total of 20 zirconia crowns were divided into two groups Bruxzir and Prettau zirconia (n=10). Each type of zirconia
crowns was divided into two groups according to the finish line design chisel (CH) and deep chamfer (DC) groups (n=5) After cementation of crowns to their corresponding
dies, the vertical marginal gap was measured then the all crowns of both groups were subjected to thermo-mechanical aging then the vertical marginal gap was measured again. RESULTS: Statistical analysis showed that. The thermo-mechanical aging significantly increased the vertical marginal gap where DC non-aged Bruxzir recording the lowest mean value (31.41±5.9) and the CH aged Bruxzir recorded the highest mean value (95.28±9.2) as indicated by three-way ANOVA test (F= 23.0741,
p=<0.0001<0.05). CONCLUSIONS: Thermo-mechanical aging significantly increased
the vertical Marginal gap and the deep chamfer finish line preparation is preferred
for construction of monolithic zirconia crowns.