Impact of endodontic access design on the fracture resistance of zirconia mandibular molar crowns.

PURPOSE: This in vitro study aimed to evaluate and compare the fracture resistance of zirconia mandibular molar crowns with the traditional trapezoidal (TT) shaped access and three novel conservative access designs. The designs tested were the TT, conservative trapezoidal (CT), ultraconservative circular (UC), and two conservative single accesses (TC).

MATERIALS AND

METHODS

A mandibular right first molar typodont tooth was prepared for a full coverage zirconia crown. The preparation was scanned, and a total of 56 monolithic zirconia crowns were milled. Resin dies were printed for each restoration. Crowns were cemented with dual curing resin cement to the printed dies. The specimens were artificially aged with 10,000 thermal cycles between 5°C and 55°C with a dwell time of 30 s and were loaded to failure using a universal testing machine. Furthermore, scanning electron microscope (SEM) images were taken to evaluate the fracture patterns of the specimens. The fracture load was analyzed using the Shapiro-Wilks normality test, followed by a one-way ANOVA with a post hoc Tukey test.

RESULTS

The fracture resistance of mandibular molar zirconia crowns significantly varied according to the endodontic access cavity design. Crowns with UC access had the highest fracture resistance (2722 ± 113 N, p < 0.001), followed by the CT (2469 ± 126 N) and the TT access (1915 ± 71 N). The two-conservative single access design had the lowest value (1064 + 129 N).

CONCLUSIONS

All endodontic access designs for mandibular molar zirconia crowns appeared to withstand the average occlusal forces. Crowns with UC access demonstrated the highest fracture resistance among different endodontic access designs. Two conservative single accesses in the same crowns significantly diminished the fracture resistance.