The Effect of Different Cement Space Thickness on Fracture Strength of CAD/ CAM all Ceramic Crown Restorations
Objectives: The purpose of this in vitro study was to evaluate the effect of variable cement space thickness on the fracture strength of CAD/CAM all ceramic crown restorations.
Materials and method: 16 sound human maxillary first permanent premolar teeth of comparable size and shape extracted for orthodontic purposes were collected and selected to be used in this in vitro study. All the dimensions of each crown were tested with using one-way ANOVA in order to reduce the confounding variables. The teeth samples were divided into two main groups according to the different cement space parameter setting (n=8). Group A: 0 cement space around the margin and additional cement space of 100 Mm starting 1mm above the finish lines of the teeth. Group B: 0mm cement space around the margin and additional cement space of 120 Mm starting 1mm above the finish lines of the teeth. Standardized tooth preparation for full contour monolithic ceramic crown restorations for all samples was done with the following preparation features: Deep chamfer finishing line of 1 mm thickness, axial reduction 1-1.5mm, occlso-axial height 4mm, anatomical occlusal reduction and total convergence angle 6 degree. The teeth were then scanned using 3 shape intra-oral digital scanner. Sirona In-Lab MC X5 milling device was used to fabricate the all ceramic crowns. Then the crowns are cemented with dual cure self-adhesive resin cement Rely X™ U200, and then tested with computer controlled Universal testing machine (Laryee, Beijing, China) and the mode of fracture also has been noted.
Results: The study revealed that the mean of fracture resistance of all ceramic crowns in Group A and Group B were (1688.75N), (1936.25 N) respectively. Student’s t-test was then applied to see whether the difference between two groups statistically significant or non, this test reveal, that, there is statistically a significant difference between two groups at p>0.05.
Conclusions: increasing cement space parameter setting significantly improve the fracture strength of all ceramic restoration.