The Feasibility Experimental Research Of Porcelain-fused-to-Ti2448Coping Fabricated With CAD/CAM Technology

As the CAD/CAM technology rapid development, the CAD/CAM technology has become a kind of important processing technology of dental prosthetic restoration and been widely applying in the oral cavity field. At present the CAD/CAM technology can processing not only all-ceramic materials but also some metal materials, such as titanium and its alloys. Ti-24Nb-4Zr-7.9Sn alloy (wt.%, Ti2448) is a new β-type titanium alloy which has been developed by Chinese researchers. It belongs to the third-generation titanium alloy. It has excellent mechanical properties, biocompatibility and good corrosion resistance. Especially, the alloy has relatively lower Young’s modulus (forging33GPa, casting42GPa) than other titanium alloys. So Ti2448alloy has good application prospects in the dental field. Whether Ti2448alloy could be used for cutting material has not been reported in the literature.The objective of this study was to know the feasibility that porcelain-fused-to-Ti2448 coping is fabricated by the CAD/CAM technology. This study was designed to measure the fit of Ti2448copings machine-milled by Wieland CAD/CAM system, and evaluate the bond strength between milled Ti2448alloys and low-fusing porcelain. The effect of thermal and mechanical cycling on the bond strength was evaluated.Method:1. Ti2448and cp Ti copings were fabricated by Wieland CAD/CAM system. The margin and internal fit of the copings were measured under Stereoscopic Microscope.2. Ti2448and cp Ti specimens were milled. The thermal expansion coefficient (CTE) of Ti2448was evaluated. The bond strength of Duceratin kiss porcelain fused to Ti2448alloy was analyzed with the three-point bending test according to ISO9693standard.The debonding surface and metal-porcelain interface were analyzed by SEM/EDS, cp Ti as control group.3. Ceramic-Ti2448and ceramic-cp Ti specimens were first thermocycled for3000cycles between5℃and55℃in water, and then mechanically loaded20,000or40,000cycles under50N load, immersion in water at37℃, The bond strength was measured.Results:1. Ti2448copings have the characteristics of structural integrity, smooth surface, no crack, continuous smooth marginal. The vertical marginal discrepancy of the Ti2448and cp Ti copings was27.38±3.00μm,21.62±1.65μm respectively (P<0.01), which was within the clinically required maximum gap of120μm.2. The CTE of Ti2448alloy was9.52×10-6·℃-1, The bond strength of Ti2448and Duceratin kiss porcelain was43.90±1.52MPa which was higher than the bond strength of cp Ti (30.52±2.34MPa)(P<0.01),and above the lowest limit value in the ISO9693standard (25MPa)(P<0.01).3. Thermal-cycling for3000times and mechanical-cycling for40,000times decreased the bond strength (MPa) values significantly for ceramic-Ti2448(44.86±1.75) and ceramic-cp Ti combinations (29.21±2.21) when compared to the non-aged groups (39.61±2.06,21.04±2.87, for Ti2448and cp-Ti, respectively)(P<0.01). Conclusion:Porcelain-fused-to-Ti2448copings fabricated by CAD/CAM technology meet clinical requirements. Thermal-cycling for3000times and mechanical-cycling for40,000times decreased the bond strength values significantly for ceramic-Ti2448combination.