Bond Characteristics Between Porcelain And Ni-cr Alloy Fabricated By Laser Rapid Forming

Nickel–chromium (Ni–Cr) dental alloy has been widely used in the preparation of metal–porcelain crowns and fixed dentures. It offers the advantage of maintaining rigidity with less bulk due to higher elastic modulus than that of noble alloy. Even though the casting of Ni–Cr dental alloy is difficult, due to its high melting range and potential for oxidation during casting, it is still the conventional method for the preparation of the metal substrate, for economic considerations. LRF provides an innovative way for thepreparation of Ni–Cr dental alloy without dies and subsequent finishing. In this study, the experiments (including tensile strength, thermal expansion, and bond strength) were designed to investigate and evaluate the properties of Ni–Cr dental alloy prepared by LRF. Crucial factors affecting the characteristics of the LRF Ni–Cr dental alloy are also evaluted, 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.The aim was to evaluate the mechanical properties, the coefficient of thermal expansion of nickel–chromium (Ni–Cr) dental alloy fabricated by laser rapid forming (LRF). And evaluate the optimal treatment method for the LRF Ni–Cr dental alloy. First, using the different size of Al2O3 (50μm, 120μm, 250μm) to rough the LRF Ni-Cr alloy surface. Second, using the different solutions (Acetone, ethyl acetate, 10%HF, 50%NaOH, 95% C2H5OH) to clean the LRF Ni-Cr alloy surface. Final, using the different preoxidation temperatures (850℃, 900℃, 950℃,1000℃,1050℃) to modify the LRF Ni-Cr alloy surface. Meanwhile, the surface roughness, the free surface energy and the bond strength of LRF Ni-Cr was evaluated. The LRF Ni-Cr alloy specimens were treated using electro-spark deposition (ESD) technology. The corrosion behavior and bond strength of LRF Ni-Cr alloy was evaluated after treated by ESD.Results:1. The Vickers hardness (297.83~369.91 Hv) of LRF Ni-Cr alloy is higher than cast material (188.19~277.45 Hv). The tensile strength (840 MPa) of LRF Ni–Cr dental alloy was superior to that (670 MPa) of the cast materials, and the yield strength (618 MPa) is greater than that of the cast material(390 MPa). However, ductility (17%) is lower than casting Ni-Cr alloy(22%). The elastic modulus (156 GPa) of LRF Ni–Cr dental alloy was comparable to that of the cast Ni–Cr alloy (185 GPa).2. The mean CTE value of LRF Ni–Cr dental alloy is 14×10-6·℃-1. According to the manufacturer, the CTE of the porcelain used in this study was 13.2×10-6·℃-1. The difference between porcelain and LRF Ni-Cr was 0.8×10-6·℃-1. The LRF Ni-Cr had an ideal thermal compatibility with the porcelain.3. The bond strength of LRF Ni-Cr and porcelain was higher after using 120μm Al2O3 sandblasting, acetone ablutioning and preoxidation treatment at 950°C. Additionally, the porcelain bonded strengths of LRF Ni-Cr (44.98±2.85MPa) was all above the acceptable value required by the ISO 9693 specification (25 MPa).4. The corrosion behavior and bond strength (48.65±2.50MPa) were significantly changed after treated by ESD at Ti electrode, silicon oil media, 40mV voltage and 160μF capacitance.