Evaluation of mechanical properties and porcelain bonded strength of nickel-chromium dental alloy fabricated by laser rapid forming.

The aim was to evaluate the mechanical properties and porcelain bonded strength of nickel-chromium (Ni-Cr) dental alloy fabricated by laser rapid forming (LRF). The tensile properties and porcelain bonded strengths of LRF Ni-Cr dental alloy were evaluated by tensile tests (five specimens per group) and three-point bending tests (ten specimens per group). The same tests for the cast Ni-Cr dental alloy were used as for the control. The microstructure and the bonding interface of the metal substrate to porcelain were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The tensile strength of LRF Ni-Cr dental alloy (840 MPa) was superior to that of the cast Ni-Cr alloy (670 MPa), but the ductility had decreased. The porcelain bonded strength of LRF Ni-Cr dental alloy was 44.7 MPa, which was also superior to that of the cast Ni-Cr dental alloy (41.6 MPa). According to analysis by Student's t-test, the porcelain bonded strengths of the Ni-Cr dental alloy presented statistically significant differences between the groups of LRF and cast alloy (P < 0.05), but the porcelain bonded strengths were all above the acceptable value required by the International Organization for Standardization (ISO) standard 9693 (25 MPa). The coefficient of thermal expansion (CTE, mean value of five specimens) of LRF Ni-Cr dental alloy (14 x 10(-6) degrees C(-1)) was higher than that (13.7 x 10(-6) degrees C(-1)) of the cast Ni-Cr dental alloy. Both LRF and cast Ni-Cr dental alloy had positive Deltaalpha, not exceeding the maximum difference (1 x 10(-6) degrees C(-1)) in CTE. SEM and EDS results showed that all the specimens measured for porcelain bonded strength and prepared from the LRF and cast Ni-Cr alloy exhibited a mixed mode of cohesive and adhesive failure. Evaluation of the mechanical properties and porcelain bonded strengths of LRF Ni-Cr alloy revealed that both superior tensile and porcelain bonded properties can be obtained. With improvement of the technique, it is hoped that the LRF Ni-Cr dental alloy could be a good alternative to the conventional cast Ni-Cr dental alloy in the future.