Background: The current research aimed to assess the outcome of dissimilar cement types on the strength of zirconium crowns fabricated by a computer-aided design and manufacturing (CAD/CAM) system at varying occlusal cement gap widths for primary molars. Methods: A total of 40 extracted mandibular deciduous 2^nd. molars were prepared and randomly allocated into two main sets and two subgroups, totaling 4 groups according to the cement type and occlusal gap width. After preparation, the deciduous molars were implanted in methyl methacrylate blocks. The restorations were made-up from zirconium (InCoris TZI C, Sirona Dental Systems, GmbH, Bensheim, Germany) using CAD/CAM system, with occlusal cement gap widths of 100 µm and 200 µm, and were then glass ionomer cement and adhesive resin cements were used to cement the crowns. Fracture strength was measured for all samples at a crossheading speed of 10 mm/min, and the values were verified in Newtons (N). statistical analysis of results were done through the Shapiro–Wilk normality test and independent t-tests. A significance level of p < 0.05 was used for all analyses. Results: Cement type and cement gap width had statistically insignificant effect on the zirconium fracture strength of (p > 0.05). The greatest fracture resistance was detected in the 100 µm cement gap and adhesive resin cement group (3847±984,74 N). Conclusions: Zirconia crowns fabricated using CAD/CAM technology demonstrated high fracture strength when placed on primary teeth. Different cement types and gap widths may be considered clinically acceptable alternatives in pediatric applications.

Fracture resistance, CAD/CAM, zirconia crown, cement gap, primary molar