Effect of surface treatment on bond strength of low-fusing porcelain to commercially pure titanium

Statement of problem

Due to the pronounced oxidative nature of titanium at high temperatures, an excessively thick layer of TiO₂ may form on the surface. This oxide layer could adversely affect titanium-porcelain bonding.

Purpose

The purpose of this study was to investigate the effect of bonding agent and surface treatment using airborne-particle abrasion and hydrochloric acid on the bond strength between a low-fusing porcelain and commercially pure cast titanium.

Material and methods

A casting unit was used to cast 60 specimens of commercially pure titanium (25.0 × 3.0 × 0.5 mm). The specimens were equally divided into 3 groups. The first group received no surface treatment and served as the control, the second group was subjected to airborne-particle abrasion, and the third group was treated with hydrochloric acid. The specimens in each group were further divided into 2 subgroups of 10 each. Ten specimens were treated with bonding agent (Noritake), and 10 specimens were not treated with bonding agent. Low-fusing porcelain (Noritake) was fired onto the surface of the specimens. A universal testing machine was used to perform the 3-point bending test. The titanium-ceramic interfaces were subjected to scanning electron microscopic analysis. The bond failure data (MPa) were analyzed with a 2-way analysis of variance and Tukey multiple range tests (α=.05). Four specimens from each group were selected for scanning electron microscopic examination.

Results

The debonding test showed that surface treatment with airborne-particle abrasion followed by application of a bonding agent resulted in the strongest (35.60 ± 8.15 MPa) titanium-ceramic bond (P<.001), followed by airborne-particle abrasion alone (25.6 ± 5.4 MPa) and bonding agent alone (24.7 ± 6.3 MPa). Hydrochloric acid surface treatment provided no beneficial effect to the titanium-ceramic bond strength compared to untreated specimens (P=.975). The photomicrographs of the titanium surface after debonding demonstrated residual porcelain retained on the metal surface for all groups.

Conclusions

Surface treatment using either airborne-particle abrasion or bonding agent alone enhanced the bond strength of cast commercially pure titanium to low-fusing porcelain. The combination of airborne-particle abrasion and bonding agent provided the greatest improvement in titanium-ceramic bond strength. Titanium surface treatment with hydrochloric acid, with or without bonding agent, produced values that were not statistically different than the control.