Effects of surface texture and etching time on roughness and bond strength to ground enamel

The aim of this study was to assess the influence of surface texture and etching technique on surface roughness (Ra) and bond strength (BS) to enamel and to determine if a correlation exists between them.

Fifty enamel blocks were either roughened with 600-grit SiC paper or polished with diamond pastes. After establishing ten test groups (n=5), the initial Ra measurements, rough (R) and smooth (S) enamel surfaces were etched according to the following protocols: Group 1(R)/Group 2(S)- 35% phosphoric acid gel (H3PO4) for 15 seconds; Group 3(R)/Group 4(S)- 35% H3PO4 for 60 seconds; Group 5(R)/Group 6(S)- Clearfil SE Bond primer for 20 seconds; Group 7(R)/Group 8(S)- self-etching primer (SEP) for 60 seconds; Group 9(R)/Group 10(S)- 35% H3PO4 for 15 seconds + SEP for 20 seconds. After treatments, a new Ra measurement was performed and enamel surfaces were bonded with either Single Bond (Group 1 to Group 4) or Clearfil SE Bond (Group 5 to Group 10). Afterwards, specimens were prepared for the microtensile test. Ra values were analyzed using repeated-measures analysis of variance (ANOVA) and the BS values were analyzed using a two-way ANOVA and Tukey test (5%). Correlation between BS and Ra values was assessed using the Pearson's test.

The application of SEP produced the lowest Ra values. No significant difference was detected between the BS values of polished and rough surfaces. No correlation was observed between Ra and BS values. Even though etching enamel with the SEP resulted in a surface with less roughness, similar BS values were observed for both self-etching and etch-and-rinse techniques.

Within the limits of this study increasing the etching time or combining both etching techniques failed to improve the BS using SEP or etch-and-rinse systems.

Based on the findings of this study, there is no clinical justification for increasing the etching time or for combining the use of a SEP following the use of a 35% H3PO4 etchant to achieve a greater BS to ground enamel.