Effect of investment type and mold temperature on casting accuracy and titanium-ceramic bond

Abstract

This study evaluated the casting accuracy of crown margins and metal-ceramic shear bond strength (SBS) of pure titanium injected into casting molds made using 2 investment types at 3 mold temperatures. Sixty crown (30-degree beveled finish line) and 60 cylinder (5 mm diameter x 8 mm high) patterns were divided into 6 groups (n=10), and cast using a phosphate-bonded investment (P) and a magnesium oxide-bonded investment (U), at 400°C (groups P400 and U400), 550°C (groups P550 and U550) and 700°C (groups P700 and U700) mold temperatures. Crown margins were recorded in impression material, the degree of marginal rounding was measured and margin length deficiencies (µm) were calculated. Titanium-ceramic specimens were prepared using Triceram ceramic (2 mm high) and SBS was tested. Failure modes were assessed by optical microscopy. Data were subjected to two-way ANOVA and Tukey's HSD test (α=0.05). For casting accuracy, expressed by marginal deficiency (µm), investment U provided more accurate results (64 ± 11) than P (81 ± 23) (p<0.001). The increase in temperature resulted in different effects for the tested investments (p<0.001), as it provided better casting accuracy for U700 (55 ± 7) and worse for P700 (109 ± 18). Casting accuracy at 700°C (82 ± 31) was significantly different from 400°C (69 ± 9) and 550°C (68 ± 9) (p<0.05). For SBS, there was no significant differences among the groups for factors investment (p=0.062) and temperature (p=0.224), or for their interaction (p=0.149). Investment U provided better casting accuracy than investment P. The SBS was similar for all combinations of investments and temperatures.

Bonding of Dental Ceramics to Titanium: Processing and Conditioning Aspects

“…In addition, cpTi experiences a phase transformation at 882°C from a close-packed hexagonal α structure to a body-centered cubic β structure above this temperature. This is associated with changes at the titanium-porcelain interface [50]. Moreover, a major cause of porcelain bonding failures in titaniumporcelain systems is the high affinity of titanium for oxygen.…”

Effects of surface treatment methods on shear bond strength of ceramic to cast, milled and laser-sintered titanium frameworks

“…Therefore, using an arc melting pressure and a high-speed centrifugal CST machine with an argon atmosphere are recommended to improve the castability of Ti (9). Also, stable oxides like magnesia, alumina, and zirconia, refractory materials of investment, are used to control the thickness of the surface TiO 2 layer, which weakens the Ti-ceramic bond (10,11). Because of CST difficulties of Ti, milling (ML), spark erosion, laser welding, and selective laser melting (SLM) emerged as alternative techniques for the fabrication of more predictable Ti frameworks than CST (6,(12)(13)(14).…”