Comparative evaluation of resistance failure in nonprecious metal-ceramic restoration at the incisal edge with varying thickness under different application of load: an in vitro study

To determine the resistance failure value of nonprecious metal-ceramic restorations at the incisal edge with varying thickness under different application of load. An Ivorian central incisor was prepared to receive metal-ceramic crown, which was further duplicated, invested, casted and 72 metal dies were fabricated in Co-Cr alloy. Metal dies were relieved with die spacer, lubricated and wax patterns were prepared for metal copings, which were further invested and casted and 72 metal copings were fabricated. The ceramic materials were used for the study viz. Vita/VMK, IPSd SIGN, and superporcelain. Ceramic built-up was carried out according to manufacturer instructions. Incisal ceramic built-up was carried out with increasing thickness from 2.00 to 2.5 and 3.00 mm. A total of 72 samples, prepared for the study, were divided into two groups, i.e. group I (36 samples) and group II (36 samples), as per the direction of application of load. The samples were mounted on acrylic block (6 samples/block). A total 12 acrylic blocks were prepared. All the samples were tested using universal testing machine (MTS/USA). The load was applied with crosshead speed of 5 mm/min. Fracture resistance was found to be highest for the 2.00 mm and lowest for 3.00 mm incisal ceramic thickness samples regardless of the ceramic material in both groups. There was a gradual decrease in fracture resistance as the incisal ceramic thickness increased from 2.00 to 3.00 mm in all samples. Fracture resistance was marginally higher for incisal ceramic build-up of 3 mm thickness on group II metal copings than on group I copings. Fracture resistance was highest for IPSd SIGN followed by that of Vita/VMK-95 and superporcelain. A 3.00 mm incisal ceramic thickness offered greater fracture resistance in comparison to lower values of incisal thickness; IPSd SIGN offered greatest fracture resistance followed by that of Vita/VMK-95 and superporcelain.