Mechanical behavior of endocrowns fabricated with different CAD-CAM ceramic systems.

STATEMENT OF PROBLEM: The mechanical behavior of ceramic endocrowns is unclear. PURPOSE: The purpose of this in vitro and 3-dimensional finite element analysis (3D-FEA) study was to evaluate the mechanical behavior of endodontically treated teeth restored with ceramic endocrowns made by using different computer-aided design and computer-aided manufacturing (CAD-CAM) systems. MATERIAL AND METHODS: Sixty mandibular human molars were endodontically treated, prepared for endocrowns, and divided into 4 groups (n=15) according to the following various ceramic systems: leucite-based glass-ceramic (LC group), lithium disilicate-based glass-ceramic (LD group), glass-ceramic based on zirconia-reinforced lithium silicate (LSZ group), and monolithic zirconia (ZR group). After adhesive bonding, the specimens were subjected to thermomechanical loading and then to fracture resistance testing in a universal testing machine. The failure mode of the specimens was qualitatively evaluated. Three-dimensional FEA was performed to evaluate the stress distribution in each group. Data were analyzed by using a 1-way ANOVA and the Tukey HSD test (α=.05). RESULTS: Statistically significant differences among the groups were observed (P<.05). The outcomes of the LC, LD, and LSZ groups were similar (1178 N, 1935 N, and 1859 N) but different from those of the ZR group (6333 N). The LC and LD groups had a higher ratio of restorable failures, while LSZ and ZR had more nonrestorable failures. Fractographic analysis indicated a regular failure pattern in the ZR group and irregular failure patterns in the other groups. Three-dimensional FEA revealed similar values and stress pattern distributions among the groups. CONCLUSIONS: The mechanical performance of monolithic zirconia was better than that of the other ceramic endocrowns considered in this research; however, monolithic zirconia presented a higher rate of catastrophic tooth structure failure.

Effect of Intracoronal Depth of Teeth Restored with Endocrowns on Fracture Resistance: In Vitro and 3-dimensional Finite Element Analysis.

INTRODUCTION: Endodontically treated teeth have an increased risk of biomechanical failure because of significant loss of tooth structure. The biomechanical behavior of endodontically treated teeth restored was evaluated using different extensions of endocrowns inside the pulp chamber by in vitro and 3-dimensional finite element analysis (FEA). METHODS: Thirty mandibular human molars were endodontically treated. Standardized endocrown preparations were performed, and the teeth were randomly divided into 3 groups (n = 10) according to different endocrown extensions inside the pulp chamber: G-5 mm, a 5-mm extension; G-3 mm, a 3-mm extension; and G-1 mm, a 1-mm extension. After adhesive cementation, all specimens were subjected to thermocycling and dynamic loading. The survival specimens were subjected to fracture resistance testing at a crosshead speed of 1 mm/min in a universal testing machine. All fractured specimens were subjected to fractography. Data were analyzed by 1-way analysis of variance and the Tukey post hoc test (P < .05). Stress distribution patterns in each group were analyzed using FEA. Qualitative analyses were performed according to the von Mises criterion. RESULTS: After dynamic loading, a survival rate of 100% was observed in all groups. For static loading, statistically significant differences among the groups were observed (P < .05) (G-5 mm = 2008.61 N, G-3 mm = 1795.41 N, and G-1 mm = 1268.12 N). Fractography showed a higher frequency of compression curls for G-5 mm and G-3 mm than for G-1 mm. FEA explained the results of fracture strength testing and fractography. CONCLUSIONS: Greater extension of endocrowns inside the pulp chamber provided better mechanical performance.

Evaluation of resistance to displacement of metal posts with different lengths.

AIMS AND OBJECTIVES: to evaluate the resistance to displacement of metal intraradicular retainers of different lengths by means of the shear test. MATERIAL AND METHODS: Thirty-six maxillary central incisors were cross-sectioned at 16 mm from the root apex, endodontically treated and randomly divided into three groups that were treated as follows: G1 (control) preparation of 2/3 (10.6 mm) of the total root length; G2: preparation of 1/2 (8 mm) of the total root length and G3: preparation of 1/3 (5.3 mm) of the total root length. After canal preparation, a matrix was made of the coronal and radicular portions using Duralay to obtain metal intraradicular retainers. These retainers were cemented with zinc phosphate cement and subjected to the compression shear test in a Universal Test Machine (EMIC DL 2000) at a crosshead speed of 0.5 mm/minute. The results were subjected to statistical analysis by analysis of variance (ANOVA) and Newman- Keuls, which showed statistically significant difference (P < 0.01). RESULTS: The means in Newtons and their respective standard deviations were: G1 = 972.05 (±81.36); G2 = 921.15 (±112.25); G3 = 686.66 (±113.02). CONCLUSION: It could be concluded that metal retainers of 2/3 and 1/2 the length of the root portion showed higher resistance to displacement values when compared with the group that had been prepared for 1/3 of the root length.