Effect of Die Spacer Thickness on the Fracture Resistance of CAD/CAM Lithium Disilicate Veneers on Maxillary First Premolars.
Objective
The purpose of this study was to compare the fracture resistance of ceramic veneers with digital die spacer settings at 20 µm, 40 µm, and 100 µm.


Materials and Methods
Eighteen sound maxillary first premolars were divided into three groups (n=6) according to their digital die spacer settings: group A=20 µm, group B=40 µm, group C=100 µm. Each tooth was prepared to a depth of 0.5 mm to receive lithium disilicate veneers (IPS e.max CAD, Ivoclar Vivadent). All groups were thermocycled (2500 cycles at 5-55°C) and subjected to fracture resistance test using a universal testing machine until failure. Failure modes were examined using a stereomicroscope.


Results
The values (N) for group A=1181.34±301.33, group B=1014.29±291.12, and group C=841.89±244.59. One-way ANOVA showed no statistical difference among the three groups (p=0.145). However, chi-square test showed that a significant difference was present in the modes of failure (p=0.009). Tukey's post hoc test indicated that the failure modes of group A were statistically different from those of group C, showing 83.3% adhesive failure for group A compared to 0% adhesive failures in group C. A p-value of ≤0.05 was considered as statistically significant.


Conclusion
Digital die spacer thickness did not influence the mean fracture resistance values of CAD/CAM lithium disilicate veneers. However, the way the failure occurred differed significantly at various die spacer thicknesses.
['Farag|Sherine Mohamed|SM|0000-0003-4899-2494', 'Ghoneim|Mona Mohamed|MM|', 'Afifi|Rania Reda|RR|']
die spacer fracture resistance CAD/CAM cement space cement thickness lithium disilicate CAD veneers