Comparative Evaluation of Fracture Toughness and Marginal Adaptation of PEEK and Cast Metal Crowns for Restoring Posterior Teeth with Endocrown and Richmond Crown: An In Vitro Study

Purpose: The purpose of this study was to evaluate and compare the fracture toughness and marginal adaptation of polyether ether ketone (PEEK) and cast metal crowns for restoring posterior teeth using the endocrown and Richmond crown techniques. Materials and methods: Forty-two extracted permanent first molars were divided into three groups (<i>n</i> = 14 each): group E (endocrown), group R (Richmond crown), and the control group. Groups E and R were subdivided based on materials (PEEK and cast metal) used into PEEK endocrown (EP), cast metal endocrown (ECM), PEEK Richmond crown (RP), and cast metal Richmond crown (RCM). Standardized endocrown and Richmond crown preparations were done, and samples were randomly divided into subgroups. Restorations were fabricated, and marginal gap evaluation was conducted using two-dimensional (2D) cross-sectional analysis. After cementation, specimens were subjected to compressive stress until failure using a universal testing machine. Failure loads and modes were recorded. Statistical analysis was performed using one-way analysis of variance (ANOVA) and Tukey Honestly Significant Difference (HSD) test (<i>p</i> < 0.05). Results: One-way ANOVA revealed significant differences in fracture toughness, with the RCM subgroup showing the highest mean fracture toughness (3530.06 N) compared to RP (2879.89 N), EP (2249.56 N), and ECM (2919.69 N). The EP subgroup exhibited favorable fractures in 71% of samples. No significant variations in mean marginal gap were observed among groups, with all mean values within clinical acceptability. Conclusion: PEEK and cast metal crowns achieved satisfactory marginal adaptation within clinically acceptable limits, ensuring effective sealing against microleakage. Richmond crowns demonstrated superior fracture toughness but were prone to catastrophic failures. Conversely, the endocrown technique exhibited high fracture toughness with a safer, more predictable failure mode. PEEK-based restorations, particularly EPs, showed promising results in terms of fracture toughness, marginal adaptation, and favorable failure patterns. How to cite this article: Singh C, Singla S, Singh S, <i>et al.</i> Comparative Evaluation of Fracture Toughness and Marginal Adaptation of PEEK and Cast Metal Crowns for Restoring Posterior Teeth with Endocrown and Richmond Crown: An <i>In Vitro</i> Study. Int J Prosthodont Restor Dent 2024;14(4):234–241.