Bond strength of attachments feature for Clear Aligner: evaluation of different simplified adhesive approaches

Aim: to evaluate the influence of three different variables (enamel surface pretreatment, pre-etching with H3PO4, and different adhesive systems) on the shear bond strength of composite orthodontic attachments and surface morphology of aprimsatic enamel. Materials and methods: 48 extracted maxillary central incisors were collected and randomly divided into 8 groups as follows: G1=no etching and iBond (Kulzer), G2=no etching and Scotchbond Universal (3M), G3=etching for 40 s and iBond, G4=etching for 40 s and Scotchbond, G5=sandblasting, no etching and iBond, G6=sandblasting, no etching and Scotchbond, G7= sandblasting, etching for 40 s and iBond, G8=sandblasting, etching for 40 s and Scotchbond. Then, a round-shaped composite attachment was applied on the prepared vestibular surface of each sample. Shear bond strength (SBS) testing was performed with a universal testing machine. For SEM observation, 8 human molars were collected and analyzed after pretreatment with/without etching. Results: Statistical analyses showed that there is a statistically significant difference for the variable pretreatment (p < 0.01) and etching (p = 0.015), while no significant differences were detected for tested adhesives. SEM images showed visible differences in enamel surface roughness. Conclusions: The use of sandblasting over sound enamel is necessary to enhance the bond strength of composite attachments for Clear Aligners. The pre-etching procedure had been demonstrated to yield greater SBS values, independently of the universal adhesive employed. iBond seems to be more performant than SBU without pre-etching procedure, probably due to its higher acidity degree.