Objective: to evaluate the internal fit of all ceramic restoration fabricated by two CAD/CAM milling systems using cone beam CT (CBCT).
Materials and methods: A total number of 20 all ceramic restorations were manufactured in this study, and were equally divided into two main groups (n=10) according to the type of CAD/CAM system used in the manufacturing process. Group I (Cerec in-lab system) and group II (Everest system) using the e.max CAD blocks specified for each milling system. specially designed stainless steel die was manufactured with specified dimensions. The die was scanned, the all ceramic restoration was designed and milled according to the different CAD/CAM milling systems used, and then crystallization procedure was carried. Duplication of the metal die into epoxy resin dies was performed and the final all ceramic restorations were the placed over the epoxy resin dies and examined for internal gap measurement using cone beam computed tomography (CBCT). Numerical data were explored for normality using Kolmogorov-Smirnov test of normality. Normally distributed (parametric data), were presented as mean, standard deviation and were compared between groups using independent t test. Non-parametric data were compared between groups using Mann Whiney U test. Gingival, axial and occlusal segments were compared using Friedman test and Wilcoxon signed rank test. The significance level was set at p < 0.05. Statistical analysis was performed with SPSS 18.0 for windows.
Results: Comparison between groups using the mean of the 3 successive sections in bucco-lingual section revealed that a higher mean value was recorded in Cerec for each of the gingival, axial and occlusal segments, with no statistically significant difference between groups (p=0.138, p=0.06, p=0.276 respectively), while in mesio distal section a higher mean value was recorded in Cerec in the gingival and axial segments, with no significant difference between groups (p=0.296, p=0.568 respectively). In the occlusal section, a higher mean value was recorded in Kavo Everest, with no statistically significant difference between groups (p=0.734). Comparison of gingival, axial and occlusal segments within the same group in bucco-lingual section revealed that in Kavo Everest group, a significantly higher mean value was recorded in occlusal segment in comparison to the gingival and axial segments (p=0.001). In cerec group, a significantly higher mean value was recorded in occlusal segment in comparison to the gingival and axial segments (p=0.00), while in mesio distal section , in Kavo Everest group, a significantly higher mean value was recorded in occlusal segment in comparison to the gingival and axial segments (p=0.00). In Cerec group, a significantly higher mean value was recorded in occlusal segment in comparison to the gingival and axial segments (p=0.00).
Conclusion: The technique of CAD/CAM milling system has affected the internal fit of CAD/CAM all-ceramic restorations.