Effect of heating palladium-silver alloys on ceramic bond strength.

STATEMENT OF PROBLEM: The effects of different heat treatments on the internal oxidation and metal-ceramic bond in Pd-Ag alloys with different trace elements require further documentation. PURPOSE: The purpose of this in vitro study was to determine whether heat treatment affects the metal-ceramic bond strength of 2 Pd-Ag alloys containing different trace elements. MATERIAL AND METHODS: Thirteen cast specimens (25×3×0.5 mm) from each of 2 Pd-Ag alloy groups (W-1 and Argelite 61+3) were allocated to heat treatments before porcelain application: heating under reduced atmospheric pressure of 0.0014 MPa and 0.0026 MPa and heating under normal atmospheric pressure. Bond strengths were evaluated using a 3-point bending test according to ISO9693. Results were analyzed using 2-way ANOVA and Tukey HSD test (α=.05). Visual observation was used to determine the failure types of the fractured specimens. Scanning electron microscopy and energy dispersive spectroscopy were used to study morphologies, elemental compositions, and distributions in the specimens. RESULTS: The W-1 group had a mean bond strength significantly higher than that of Argelite 61+3 (P<.001). Heating under reduced atmospheric pressures of 0.0014 MPa and 0.0026 MPa resulted in similar bond strengths (P=.331), and both pressures had significantly higher bond strengths than that of heating under normal atmospheric pressure (P=.002, P<.001). Heating under different air pressures resulted in Pd-Ag alloys that contained either Sn or In and Ga, with various degrees of internal oxidation and different quantities of metallic nodules. CONCLUSIONS: Heating under reduced atmospheric pressure effectively improved the bond strength of the ceramic-to-Pd-Ag alloys.

Evaluation of the effect of four surface conditioning methods on the shear bond strength of metal bracket to porcelain surface.

OBJECTIVE: This study evaluated the effect of superpulse CO2 laser irradiation and deglazing of porcelain surfaces on the shear bond strength (SBS) of metal orthodontic brackets, and compared it with two conventional etching techniques. METHODS: Forty-eight Feldspathic porcelain fused to metal specimens embedded in cylindrical acrylic resin tubes were fabricated, and all the specimens were divided into four groups. In Group 1, the specimens were roughened with a diamond bur and etched with hydrofluoric acid (HFA) gel for 4 min. In Group 2, the specimens were roughened with a bur and irradiated by a CO2 laser with a 2 W power setting for 20 sec. In Group 3, the specimens were only irradiated by a CO2 laser. In Group 4, the porcelain surface was sandblasted with 50 µm aluminum oxide. Before bonding, the bracket silane was applied on the porcelain surfaces. SBS was evaluated by a Universal testing machine (Zwickroll, Germany). The remaining adhesive after the bond failure was evaluated using an adhesive remnant index (ARI). Statistical analysis was conducted by analysis of variance (ANOVA), Tukey, and Kruskal-Wallis tests. RESULTS: ANOVA revealed significant differences in SBS among the four groups (p<0.001). Group 1 demonstrated significantly higher bond strength (13.13±2.47) when compared with the other groups. Group 2 showed higher bond strength (9.60±1.91) when compared with group 4 (6.40±1.67) (p=0.016). Group 1 displayed the highest ARI scores among the groups. CONCLUSIONS: Deglazing combined with HFA etching produced the highest bond strength, but CO2 laser irradiation provided adequate bond strength and allowed for elimination of the HFA step. Deglazing is not recommended as a preliminary step before CO2 laser conditioning.

Effects of sandblasting and laser irradiation on shear bond strength of low-fusing porcelain to titanium.

PURPOSE: To investigate the bond strength of low-fusing porcelain to commercially pure titanium (Ti) that was laser irradiated with different levels of energy and sandblasted. MATERIALS AND METHODS: A total of 30 titanium rods (10 mm in length and 12 mm in diameter) were prepared. The rods were divided into three groups (n = 10) according to surface treatments: SB: sandblasted; L1: Nd:YAG laser irradiated at 100 mJ, 10 Hz, and 1 W; L2: Nd:YAG laser irradiated at 200 mJ, 10 Hz, and 2 W. After surface treatment, low-fusing porcelain was applied onto the titanium specimens according to the manufacturer's instructions, and these specimens were stored in distilled water at 37°C for 24 h. The shear bond strength test was performed at a crosshead speed of 1 mm/min. In addition, Kruskal-Wallis and Mann-Whitney U-tests were used to compare the bond strength results (α = 0.05). SEM and EDS analysis were also performed for one specimen of each group after the shear bond strength test to evaluate the nature of the fracture surface. RESULTS: Group L2 produced the highest shear bond strength among the groups. There was a statistically significant difference in shear bond strength between groups L1 and L2 (p < 0.001). Nevertheless, no significant difference was found between groups SB and L1. EDS analysis revealed that laser treatment reduced presence of oxygen on the surface of Ti. In contrast to the sandblasted specimens, laser-irradiated specimens showed predominantly adhesive failure. CONCLUSION: Laser treatment may be an alternative method to sandblasting for enhancing the bond strength of low-fusing porcelain to commercially pure titanium.

Porcelain surface treatment by laser for bracket-porcelain bonding.

INTRODUCTION: The purposes of this study were to investigate the effect of laser irradiation on the adhesion of brackets bonded to feldspathic porcelain and to compare it with brackets bonded with conventional techniques. METHODS: One hundred porcelain-fused-to-metal specimens were divided into 10 groups of 10. The treatment groups were sandblasted (SB), sandblasted with silane (SB+S), orthophosphoric acid (OFA), orthophosphoric acid with silane (OFA+S), hydrofluoric acid (HFA), hydrofluoric acid with silane (HFA+S), laser etched (L), laser etched with silane (L+S), glazed (Control 1/C1), and deglazed (Control 2/C2). Five other specimens were irradiated by 2-, 3-, 5-, 10-, and 15-watt superpulse carbon dioxide (CO2) laser for 20 seconds and examined by scanning electron microscopy. Metal brackets were bonded with a self-cure composite material and the specimens were stored in water at 37 degrees C for 24 hours and then thermocycled in water baths between 5 degrees C and 55 degrees C 500 times. Bond strength was determined in megapascals (MPa) by shear test at 1 mm/minute crosshead speed. Bond failure modes were observed under stereomicroscope. For the statistical analysis, 1-way ANOVA and Tamhane post hoc test were used. RESULTS: Statistical analysis showed significant differences between the groups at the .05 level. The HFA+S group yielded the highest mean strength (15.07 +/- 1.44). This was followed by SB+S (13.81 +/- 2.00), HFA (10.78 +/- 0.62), OFA+S (10.73 +/- 1.12), L+S (8.25 +/- 0.90), L (6.26 +/- 0.58), C2 (2.45 +/- 0.54), OFA (2.36 +/- 0.41), SB (2.04 +/- 0.41), and C1 (1.64 +/- 0.33). The bond failure modes of HFA and silane groups, except L+S, were cohesive in porcelain. Control groups and other test groups showed adhesive failure. Only irradiation by 2 watts for 20 seconds provided a porous surface texture without cracks. CONCLUSIONS: Two-watt/20 second superpulse CO2 laser irradiation might be an alternative conditioning method for pretreating ceramic surfaces. Increased bond strength can be achieved by silanation after CO2 laser irradiation.