Abstract
The bond strength by three point bending strength of two metal substrates (commercially pure titanium or grade II, and Ti-6Al-4V alloy or grade V) combined to three distinct low-fusing ceramic systems (LFC) and the nature of porcelain-metal fracture by scanning electron microscopy (SEM) were evaluated. The results were compared to a combination of palladium-silver (Pd-Ag) alloy and conventional porcelain (Duceram VMK68). Sixty metal strips measuring 25x3x0.5mm were made - 30 of titanium grade II and 30 of titanium grade V, with application of the following types of porcelain: Vita Titankeramik, Triceram or Duceratin (10 specimens for each porcelain). The porcelains were bonded to the strips with dimensions limited to 8x3x1mm. The control group consisted of ten specimens Pd-Ag alloy/Duceram VMK68 porcelain. Statistical analyses were made by one-way analysis of variance (ANOVA) and Tukey test at 5% significance level. Results showed that the bond strength in control group (48.0MPa ± 4.0) was significantly higher than the Ti grade II (26.7MPa ± 4.1) and Ti grade V (25.2MPa ± 2.2) combinations. When Duceratin porcelain was applied in both substrates, Ti grade II and Ti grade V, the results were significantly lower than in Ti grade II/Vitatitankeramik. SEM analysis indicated a predominance of adhesive fractures for the groups Ti grade II and Ti grade V, and cohesive fracture for control group Pd-Ag/Duceram. Control group showed the best bond strength compared to the groups that employed LFC. Among LFC, the worst results were obtained when Duceratin porcelain was used in both substrates. SEM confirmed the results of three point bending strength.
Highlights
The search for alloys to be employed in dental prosthesis, whether for better physical and mechanical properties or for economic factors, found attractive elements in titanium and its alloys
Significant differences were found in relation to bond strength between the control group (48.0MPa + 4.0) and the titanium combinations Ti grade II/ceramics (26.7MPa + 4.1) and Ti grade V/ceramics (25.2MPa + 2.2)
Greater quantities of residual porcelain islands adhering to the metal surface of the substrate were differentiated in the control group, suggesting the occurrence cohesive type fractures in the ceramic body - observations that attest to a better mechanical performance of this combination
Summary
The search for alloys to be employed in dental prosthesis, whether for better physical and mechanical properties or for economic factors, found attractive elements in titanium and its alloys. Metal exposure to temperatures that exceed 800oC leads to the absorption of oxygen and nitrogen, providing the formation of a thick superficial layer of oxide that may attain a thickness up to 1mm and harms the bonding of ceramic to substrate[1,11,15] In compliance with these criteria, low fusion ceramics were developed showing fusion temperatures close to 760oC (Togaya et al[25]). It displays color stability20.6, bending strength and chemical solubility[7] similar to conventional porcelains and a thermal expansion coefficient close to or slightly lower than titanium, reducing the stresses at the interface and permitting satisfactory bonding of the elements[25]
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