Effect of orthodontic bracket bonding on the surface roughness of e.max glass ceramics: an in vitro study

Orthodontic treatment is now commonly used in adult patients, mandating bonding brackets to existing ceramic crowns. The bonding and debonding of orthodontic brackets might alter the surface roughness of glass ceramics, promoting plaque accumulation and compromising gingival health. The objective of this study was to investigate the effect of different bracket bonding and polishing techniques on the surface roughness (Ra) of e.max samples. Fifty e.max samples were cut and fired, after which orthodontic brackets were bonded to the samples after phosphoric acid (PhA), hydrofluoric acid (HFA), roughening, roughening and PhA, and roughening and HFA treatment. After removal of the bracket and excess bond, surfaces were polished using either Sof-Lex discs or a ceramic polishing kit. Surface roughness was measured after firing, after debonding, and after polishing. Differences between groups at each step were compared with one-way ANOVA and t-tests. There was a significant increase in surface roughness after bracket removal using all five bonding techniques, especially after use of mechanical roughening techniques (one-way ANOVA p < 0.0001). Although surface roughness was still significantly higher than baseline after polishing with all surface treatments and for both polishing approaches, Ra values were all < 0.3 μm, which is clinically acceptable. Sof-Lex discs were more effective when used with PhA and HFA, ceramic polishing was more effective when used with roughening, and the polishing system had no effect with roughening or acid etching. Physical surface preparation has a greater effect on surface roughness than chemical preparation and, in general, polishing returns the surface to a clinically acceptable state.