Fracture strength of single crowns made with different all ceramic systems

OBJECTIVES. TO evaluate fracture strength of all-ceramic single crowns compared with metal-ceramic rehabilitation. Materials and methods. 32 premolars were endodontically treated, randomly divided into 4 groups and restored with fiber posts (FRC Postee, Ivoclar Vivadent) luted with dual curing composite resin cement (Multilink Automix, Ivoclar Vivadent). A composite build-up was realized using an adhesive bonding system (Adhese, Ivoclar Vivadent) and dual curing composite (MultiCore HB, Ivoclar Vivadent). All teeth were prepared in the same way: 2 mm of occlusal reduction; 1.5 mm of axial reduction; round shoulder of 1.0-mm depth with 8° convergence coronal to cement-enamel junction. Group I teeth were restored with all-ceramic crowns fabricated in zirconia core and pressable veneering ceramic (ZirCAD/ZirPress, Ivoclar Vivadent). Groups Il teeth were restored in the same way as in group I but with margin of pressable ceramic. Group III teeth were all made in lithium disilicate glass ceramic material (IPS E.max Press, Ivoclar Vivadent). Group IV teeth, as control group, were realized with a conventional framework in metal alloy (IPS D.sign 91, Ivoclar Vivadent) and pressable veneering ceramic (PoM, Ivoclar Vivadent). All crowns were luted with a self adhesive, dualcuring composite cement (Multilink Sprint, Ivoclar Vivadent). Thermal cycling and mechanical loading (TCML) were made to simulate a 5-year period of oral function [parameters: 6000 thermal cycles (5 C/55 C), 1,2x10 6 mastication cycles at 50 N using an artificial oral environment]. After TCML all crowns were loaded in axial direction under an angle of 135° up to failure in a universal testing machine (v = 1 mm/min, Zwick 1445). Statistical analysis was performed using the Turkey-Kramer and t'test at α=0,05 significance level. RESULTS. The mean values of fracture strength were 654 ± 98 N for Group I, 688 ± 181 N for Group II, 551 ± 126 N for Group III and 501 ± 110 N for Group IV. CONCLUSIONS. Fracture strength showed no difference between teeth restored with all-ceramic and metal-ceramic single crowns. All-ceramic restorations showed higher marginal adaptation compared to the control group. Lithium disilicate with resin luting agent can act as biomimetic material, optimizing the distribution of occlusal stress at the cervical margin.