Impact of preparation designs and computer-aided design/computer-aided manufacturing materials on the fracture resistance of dental posterior indirect adhesive restorations
Creators: name: Alzahrani, Khulood K.
Publisher: name: University of Iowa
Year: 2026
Subjects: CAD/CAM
Dental materials
Digital Dentistry
Indirect Adhesive Dental Restorations
Restorative Dentistry
Biomechanics

description: This study evaluated two Posterior Indirect Adhesive Restorations (PIARs) preparation designs restored with different Computer-aided design and Computer-aided manufacturing (CAD/CAM) materials on the tooth-restoration fracture resistance as compared with sound tooth structure. The tested null hypotheses were: there will be no difference in the fracture resistance between the control group and the different PIAR designs, and there will be no difference in the fracture resistance between the control group and the different CAD/CAM materials. Seventy-five crack-free, sound human molars (n=15/group) were randomly divided into five groups: C (Control, sound tooth), A-Hyb (Design-A preparation with rounded-shoulder finish line) restored with hybrid nano ceramic block, A-LiSi (Design-A prep with rounded-shoulder finish line) restored with lithium disilicate block, B-Hyb (Design-B preparation with butt-joint finish line) restored with hybrid nano ceramic block, B-LiSi (Design-B prep with butt-joint finish line) restored with lithium disilicate block. The cementation process involved selective enamel etch, followed by application a self-adhesive primer and self-adhesive resin cement. The specimens were thermo-cycled (10,000 cycles, simulating approximately 1 year of aging), followed by mechanical cycling (500,000 cycles at 50 N, positioned 90° with the occlusal surface at a frequency of 1 Hz, simulating approximately 2 years of aging). The fracture resistance of the tooth-restoration system was assessed through a compressive test using a Zwick universal machine. The specimens were subjected to compressive load at a 90° angulation using a 5 mm stainless-steel conical-shaped piston in a compression test apparatus until fracture. Statistical analysis was conducted using two-way ANOVA to compare the means among the five groups, and Tukey post hoc tests to compare the mean pairwise if a significant difference was found at α = 0.05. Further statistical analysis was undertaken through linear regression analysis, aimed at explaining the relationships between material types, preparation designs, and the fracture pattern. The control group data was integrated as a reference level within the regression framework enabling the interpretation of coefficients, providing insight into how each variable’s alteration influences the fracture resistance relative to control. All tests were done with the type-1 error rate of α = 0.05. The results revealed that no statistically significant differences were observed among groups considering preparation design (p = 0.972) or materials (p = 0.278) and they were not statistically significant differences in relation to the sound tooth (p &gt; 0.05). The regression analysis showed a significant correlation in the value of the fracture resistance (Fmax) between the cracked group and the other fracture pattern gropes. Specimens with the lowest Fmax values demonstrated crack type of fracture; while type IV had the highest mean Fmax value. In conclusion, PIARs fabricated with CAD/CAM materials achieved comparable fracture resistance to those of sound teeth when applied with precision and adherence to clinical and manufacturing guidelines regardless of the preparation design and the material selection. There were no differences in fracture resistance regardless of the material type and the preparation design.