[Changes in the enamel after in vitro debonding of brackets bonded with a modified glass ionomer cement]

The aim of this study was to assess the incidence on the enamel behavior of debonding two types of orthodontic brackets, bonded with two different adhesives. Ninety recently extracted human premolars were bonded with two types of brackets (30 Minitrim and 60 Discovery). Two bonding protocols were used. The first one consisted in bonding 30 Minitrim and 30 Discovery brackets on etched and dried enamel surfaces with No Mix orthodontic resin. The second one consisted in bonding 30 Discovery brackets on unetched and wet enamel surfaces with a modified glass ionomer cement, Fuji Ortho LC. Teeth were stored in hydrated ambiance at 37 degrees C for 7 days before debonding. A LLOYD (LR 30K) testing machine was used to evaluate the orthogonal tensile bond strength. The debonded base brackets were examined with a scanning electron microscope (JEOL JSM 6400) and qualitatively analyzed with an OXFORD-LINK-ISIS to assess the site of bond failure and the enamel detachments. An Enamel Detachment Index (EDI) was defined. The results showed that the types of orthodontics brackets and adhesives influenced the bond strength and the enamel detachment. The Discovery/No Mix couple presented higher bond strength (214.9 N) than observed with the Discovery/Fuji Ortho LC (98.5 N) or the Minitrim/No Mix (82.3 N) couples. The surfaces of enamel detachment were insignificant and not extended for all brackets. Nevertheless, the Discovery/No Mix couple presented 42% of an EDI score of 1, compared to the Discovery/Fuji Ortho LC and Minitrim/No Mix couples which presented, respectively, 8% an 20% of an EDI score of 1. The laser sculpted base (Discovery) bonded on unetched and wet enamel surfaces with the modified glass ionomer cement (Fuji Ortho LC) offers a good resistance to debonding forces and preserve enamel integrity.