Effect of H3PO4 concentration on bond strength

Effect of lactic Acid etching on bonding effectiveness of orthodontic bracket after water storage

Objective. To determine the effect of lactic acid at various concentrations on the shear bond strength of orthodontic brackets bonded with the resin adhesive system before and after water storage. Materials and Methods. Hundred extracted human premolars were divided into 5 treatment groups and etched for 30 seconds with one of the following agents: lactic acid solution with (A) 10%, (B) 20%, (C) 30%, and (D) 50%; group E, 37% phosphoric acid (control). Metal brackets were bonded using a Transbond XT. Bonding effectiveness was assessed by shear bond strength after 24 hours and 6 months of water storage at 37°C. The data were analyzed with 2-way analysis of variance and Tukey's Honestly Significant Difference (HSD) test (α = .001). Results. Lactic acid concentration and water storage resulted in significant differences for brackets bond strength (P < .001). 20% lactic acid had significantly higher mean bond strength values (SD) for all conditions: 24 hours [12.2 (.7) MPa] and 6 months [10.1 (.6) MPa] of water storage. 37% phosphoric acid had intermediate bond strength values for all conditions: 24 hours [8.2 (.6) MPa] and 6 months [6.2 (.6) MPa] of water storage. Also, there were differences in bond strength between storage time, with a reduction in values from 24 hours and 6 months for all experimental groups (P < .001). Conclusion. Lactic acid could be used in place of phosphoric acid as an enamel etchant for bonding of orthodontic brackets.

Acid-etch interval and shear bond strength of Er,Cr:YSGG laser-prepared enamel and dentin

The formation of a superficial layer of tiny flakes has been observed on teeth prepared by Erbium lasers. It has been suggested that removing this layer (mechanically or chemically) may increase the bond strength of the resin composite. The purpose of this study is to evaluate the effect of various etching times on bond strength of resin composite to enamel and dentin prepared by Er,Cr:YSGG laser. Sixty previously flattened human molars were irradiated for 10 s by an Er,Cr:YSGG laser. Enamel (E) specimens were etched with 37% H(3)PO(4) for 20, 40 or 60 s and dentin (D) specimens were etched for 15 or 30 s. All specimens were prepared for a standard shear bond strength (SBS) test (1 mm/min). Data were analyzed [ANOVA, Tukey post-hoc, a < 0.05)] and the failure mode was studied under SEM. Mean SBS+/-sd (MPa) for each group was 16.97 +/- 7.77 (E20s), 21.34 +/- 3.55 (E40s), 14.08 +/- 4.77 (E60s), 13.62 +/- 7.28 (D15s) and 13.15 +/- 6.25 (D30s). SBS for E40s was significantly higher than E60s (p = 0.023). No difference was noted between the dentin groups. SEM evaluation showed predominantly cohesive failure. Within the limits of this study, etching time significantly influenced the SBS of composite resin to laser-prepared enamel. SEM showed subsurface cracks, fissures, and deformities leading to predominantly cohesive failure in both enamel and dentin.