Influence of crown-to-abutment height ratio on fracture resistance of full-coverage anterior restorations.

Abstract

Purpose: To assess the effect of crown-to-abutment (C/A) height ratio on fracture resistance (FR) of full-coverage anterior restorations.

Materials and methods: In this in vitro study, 66 human maxillary central incisors were assigned to six groups according to their abutment height (n = 11): control (sound tooth), V4 (prepared vital tooth with 4 mm height), V4e (4 mm abutment with 4 mm height gain through elective endodontic treatment, fiber post, and core build-up), V6 (prepared vital tooth with 6 mm height), V6e (6 mm abutment with 2 mm height gain through elective endodontic treatment, fiber post, and core build-up), and V8 (prepared vital tooth with 8 mm height). Zirconia crowns with 10 mm height were fabricated for all teeth and cemented. After thermomechanical loading, the FR and fracture mode were assessed. Data were analyzed by independent t test, analysis of variance (ANOVA) with James-Howell test for pairwise comparisons, and Fisher's exact test (α = 0.05).

Results: Among the experimental groups, V8 showed a significantly lower FR than other groups (p < 0.05). The FR of V6 was significantly lower than V4 (p < 0.001). V4 had a significantly higher FR than V4e (p < 0.001). However, the difference in FR was not significant between V6 and V6e (p = 0.408). V6e had the highest frequency of unfavorable fractures, and V4 had the highest frequency of favorable fractures.

Conclusion: In the same restorative space, the minimum tested abutment height resulted in the highest FR in full-coverage anterior restorations, eliminating the need for invasive procedures to increase the abutment height.