Effect of soldering on metal-porcelain band strength in repaired porcelain-fused-to-metal castings

Statement of problem. Chemical bending plays a major role in the adherence between metal and porcelain. The formation of an oxide layer on solder material has not been described in the literature. It is unknown whether the application of solder negatively affects the bond strength between porcelain and metal. Purpose. This in vitro study assessed the effect of solder on the bond strength between metal and porcelain. Material and methods. Forty 20 x 6 x 0.5 mm patterns were divided into test (20) and control (20) groups. Test samples were perforated and repaired with solder, and 2 layers of opaque and dentin porcelain subsequently were applied on all samples. The samples were subjected to a 3-point flexural test on a screw-driven mechanical testing machine at a crosshead speed of 0.5 mm/min. Failure type (adhesive vs cohesive) was quantified by digitizing photographs of test and control samples. Three samples in each group also were examined with an SEM coupled with an x-ray energy-dispersive spectroscopy apparatus (SEM/EDS). Means and standard deviations of loads at failure, sample thickness, and surface area covered with porcelain were calculated, and data were analyzed with Student t test (P less than or equal to .05). Results. The mean fracture load for test samples was significantly greater than for control samples (P=.0038). Test samples also were significantly thicker (mean thickness difference 0.14 mm) (P=.0001). When the data were controlled for thickness by using a multiple linear regression analysis, no significant difference was found (P=.68). Test samples had a greater surface area covered with opaque porcelain (P=.0006) as determined by visual inspection. Conclusion. In this study, soldered and nonsoldered samples did not show any significant difference in porcelain-to-metal bond strength. Visual analysis revealed a significant difference in the amount of porcelain remaining on the fracture surface of the test and control samples; a complete quantitative elemental analysis with SEM/EDS is in progress.