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Purpose: The current study aimed to compare modified Polyether-ether-ketone's fracture resistance and failure mode versus lithium disilicate glass–ceramic endocrowns. Materials and methods: A total of 16 butt-joint endocrown specimens on mandibular second molar teeth were fabricated and divided into two equivalent groups; Pressable modified Polyether-ether-ketone (PEEK) (BioHPP®) and Pressable lithium disilicate glass ceramic (IPS e.max® Press). A computer-aided design/computer-aided manufacturing system was used to digitally create and milled wax patterns. Final restorations were cemented each to its corresponding prepared tooth. Thermomechanical cycling loading representing one year of clinical service was done in a chewing simulator. Fracture resistance was evaluated utilizing a universal testing machine. The failure mode was evaluated by inspecting fractured surfaces using a Stereomicroscope and further examined by a Scanning Electron Microscope (SEM) amongst both groups. Results: A statistically significant variation in fracture resistance was recorded with a mean load of (2762.96 ± 216.15 N) for modified PEEK and (2175.91 ± 267.72 N) for lithium disilicate glass–ceramic endocrowns. Conclusion: Modified PEEK endocrowns have higher fracture resistance than lithium disilicate glass–ceramic endocrowns. Moreover, the likeliness of catastrophic fracture in molars receiving endodontic treatment restored by modified PEEK is less than teeth restored with lithium disilicate glass ceramics. [ABSTRACT FROM AUTHOR]

Objective: The use of vertical margin design in all-ceramic restoration has generated inquiries regarding its clinical efficacy under diverse dynamic oral conditions. This research aims to assess the marginal fit and fracture resistance of monolithic zirconia crowns featuring vertical margin design as opposed to those with conventional horizontal margin design., Materials and Methods: Two metal dies were employed to generate replicated resin dies mimicking mandibular first molar preparation. The metal dies were precision-engineered with two margin designs: vertical margin design presenting a shoulderless configuration (Featheredge) and horizontal margin design (Radial Shoulder). Forty zirconia crowns were produced on the replicated resin dies using two varieties of monolithic zirconia, with twenty crowns in each category: pre-shaded and multilayered zirconia. Both sets were further subdivided into two groups based on the finish line configuration utilized (n = 10). The vertical marginal gap of the zirconia crowns was gauged before and after thermocycling (5-55oC/5000 cycles), followed by loading the crowns until fracture occurred. Statistical analysis was performed using one-way analysis of variance (ANOVA), accompanied by Bonferroni's post hoc test and independent t-test for pairwise comparisons., Results: The Shoulder subgroup of BruxZir exhibited the highest mean marginal gap value (120.06 ± 10.15 µ), while the Featheredge subgroup of BruxZir displayed the lowest value (49.72 ± 6.53 µ). Among the BruxZir group, the Featheredge subgroup showcased the highest mean fracture resistance value (4251.57 ± 279.90 N), whereas the Shoulder subgroup recorded the lowest value (1721.60 ± 225.16 N)., Conclusion: Monolithic zirconia crowns with vertical margin design (Featheredge) demonstrated statistically enhanced performance compared to conventional horizontal margin design, as evidenced by lower marginal gap values and increased fracture resistance tolerance., (© 2025 The Author(s). Clinical and Experimental Dental Research published by John Wiley & Sons Ltd.)