Influence of Different Thicknesses of Monolithic Crowns Made from Different Resin-Bonded Glass Ceramic on Their Load-bearing Capacity (An in vitro Comparative Study)

Abstract

Objective: To investigate the load-bearing capacity of the full-coverage crowns made from lithium disilicate glass-ceramic LDGC (IPS e.max®, Ivoclar Vivadent) and 10% zirconia reinforced lithium silicate glass ceramic ZLS (Dentsply DeTrey) with different thicknesses. Methods: Forty resin dies with supporting bases were duplicated from two prepared typodont teeth for all-ceramic crowns as a maxillary first molar. Forty crowns corresponding to each die were prepared and then they were divided into four groups: Group I (n 10) made from ZLS with a restoration thickness of (1.0 mm occlusally and 1.0 mm radially) and Group II (n 10) made from LDGC with a restoration thickness of (1.0 mm occlusally and 1.0 mm radially), and Group III (n 10) made from ZLS (1.5 mm occlusally and 1.5mm radially) and Group IV (n 10) made from LDGC (1.5 mm occlusally and 1.5 radially). All crowns were fabricated by chair side CEREC CAD/CAM and crystallized with Speed fire Dentsply Furness. The virolink resin cement (VariolinkII, Ivoclar Vivadent) was used to bond the crowns to the corresponding dies.  All samples were thermo-cycled (10000 cycles between 5c and 55c) and tested for fracture resistance using a Universal testing machine at 0.5 mm/minute speed until failure. ANOVA and Tukey HSD test were used to compare the fracture resistance between groups. Results: The result demonstrates that the fracture resistance means and SD of ZLS with different thicknesses ranged from 572 N ± 122.002 to 1171±217.432 N, and those of LDGC with different thicknesses ranged from 625 N ±151.676 N to 845 N ±388.222 N. Conclusions: The fracture resistance increased with increasing crown thickness using different glass-ceramic materials.