Influence of rubbing during etching on surface roughness and interfacial characteristics of intact enamel

Rubbing phosphoric acid during etching has been shown to improve surface roughness in prepared enamel. This study aimed to compare intact enamel's surface roughness and resin tag lengths after etching with and without rubbing. Extracted sound third molars were used for testing, mesially for conventional and distally for dynamic (rubbing) etchant application. All surfaces were etched for 20 s with 37% phosphoric acid etchant and rinsed with water for 10 s. Optical profilometry and high-vacuum scanning electron microscopy (HV-SEM) were used for enamel surface assessment and evaluation of the infiltrating capacity of a bonding resin into enamel. Statistical analyses were done by a paired t-test. The obtained results demonstrated that rubbing the acid agent during etching showed no statistically significant increase in enamel surface roughness. In both groups, texture aspect ratio (Str) values were close to 1 (standard Str = 0.86, rubbing Str = 0.90), indicating that both surfaces can be considered isotropic. HV-SEM images showed a more typical etching pattern after rubbing, but with insignificant differences in the height of the resin tags. It can be concluded that rubbing during the etching of intact enamel results in a similar surface roughness and resin-enamel interface compared with the conventional etching technique. This stands in contrast to the reported improvement achieved on prepared enamel.