Effect of different preparation designs and all ceramic materials on fracture strength of molar endocrowns.

OBJECTIVE

The aim was to compare the fracture strength of Molar endocrowns fabricated from different all-ceramic materials and various preparation designs.

MATERIALS AND

METHODS

Ninety extracted human molar teeth were root canal treated and randomly divided into three groups according to the all ceramic materials used for fabrication of the endocrowns (n = 30): (1) Lithium disilicate (IPS e.max Press); (2) Polymer infiltrated ceramic (Vita Enamic); (3) High translucency zirconia (Ceramill Zolid HT). Each group was subdivided into 3 subgroups (n = 10) according to the preparation design as 2 mm occlusal reduction, 4.5 mm occlusal reduction, and 4.5 mm occlusal reduction with 2 mm radicular extension. The endocrowns from each material were fabricated and surface treated according to the manufacturer's recommendations. After cementation with self-adhesive resin luting cement, the specimens were stored in a humid environment for 72 hours and subsequently subjected to 5000 thermal cycles. After, a compressive, static-axial load was applied using a universal testing machine until failure. Load-to-failure was recorded (N) and the specimens were examined under a stereomicroscope to determine the failure type. The data was statistically analyzed using One-way ANOVA and Tukey HSD tests at p < 0.05.

RESULTS

The Lithium Disilicate endocrowns recorded the higher mean fracture strength for 4.5 mm occlusal thickness and 2 mm radicular extension at 3770.28 N and 3877.40 correspondingly. The High translucency zirconia endocrowns at conventional 2 mm thickness showed the highest mean fracture load (3533.34 N). Even though polymer infiltrated ceramic endocrowns displayed comparatively lesser fracture load; they recorded the predominantly favorable fractures.

CONCLUSIONS

Increased occlusal thickness showed a significant improvement in fracture strength of lithium disilicate and polymer infiltrated ceramic molar endocrowns. Although the 2 mm radicular extension had the substantial enhancement of fracture strength in high translucency zirconia, it resulted in more unfavorable failure types.