Post-fatigue fracture resistance of premolar teeth restored with endocrowns: An in vitro investigation

Objectives: To evaluate the post-fatigue load-to-failure and failure modes of endodontically treated premolar teeth restored with endocrowns fabricated from different CAD/CAM materials. Materials and methods: A total of 60 extracted human, single-rooted premolar teeth were endodontically treated and sectioned horizontally 2 mm above the cementoenamel junction. Sectioned teeth were restored using two reconstruction designs: endocrowns (C-endo) or post-crowns (C-post) (n = 30 p/g). In each group, reconstructions were fabricated from 3 different CAD/CAM substrates (n = 10 p/g); a resin-based composite (Cera), a lithium disilicate glass ceramic (LiSi) and a monolithic, translucent zirconia (Zir). Additional 10 intact teeth were used as control. Restored teeth were subjected to dynamic fatigue test (10- 50 N, 600,000 cycles) and thermocycling (5 - 55 degrees C, 1500 cycles). Load-to-failure and failure mode was determined following application of a static, 45 degrees oblique compressive load on each specimen. One-way and Two-way analysis of variance (ANOVA), Tukey's post hoc and chi-square tests were used to determine statistically significant interactions among experimental and control groups. Results: All specimens survived the mechanical and thermal fatigue tests. A statistically significant interaction between reconstruction design and material type was observed (p < 0.001). C-post Zir and C-endo Cera groups exhibited significantly higher post-fatigue load-to-failure when compared to other materials of the same reconstruction design (p <= 0.001). The highest frequency of catastrophic failures was observed with Zir reconstructions in both designs. Intact teeth exhibited significantly higher load-to-failure when compared to all groups (p <= 0.042) except C(post)Zir (p = 0.345). Conclusion: Single piece, CAD/CAM resin composite endocrowns can present a reliable option for restoring endodontically treated premolar teeth. Clinical Significance: Endocrowns can be as effective as post-crowns provided appropriate preparation; material selection; and bonding protocols are utilized. Clinicians need to be cautious when prescribing zirconia endocrowns to restore premolar teeth owing to the low fracture resistance and high risk of catastrophic failures.