A comparison between RMGIC and composite with acid-etch preparation or hypochlorite on the adhesion of a premolar metal bracket by testing SBS and ARI: In vitro study.

Objective: A bonding material can be acceptable in orthodontics when Shear Bond Strength (SBS) is higher than 5.9Mpa. The aim of our study was to compare the bonding of a metal orthodontic bracket "in vitro" under different types of healthy enamel surface preparations and with two bonding products: the composite and the Resin Modified Glass Ionomer Cement (RMGIC).

Methods: Premolars preserved in 1% thymol water were bonded on their vestibular and palatal/lingual surfaces with different techniques of bonding and surface preparation: Group 1: Etching+Bonding+Composite, Group 2: Etching+Fuji Ortho LC, Group 3: V-prep+Fuji Ortho LC, Group 4: V-prep+Fuji Ortho LC+Thermocycling. The SBS was measured in Newton on the universal testing machine and the sample was observed under an optical microscope with 10-fold magnification to note the adhesive remnant index score (ARI), before and after thermocycling.

Results: 120 premolars were used in this study. RMGIC bonding was significantly increased when the surface was prepared at V-prep (P<0.001). In these conditions, RMGIC bonding on the buccal surface was similar to that of the composite and superior on the palatal/lingual surface (P=1). After 2 years of aging using a thermocycling machine for simulation, RMGIC bonding significantly decreased (P<0.001). The ARI score was significantly lower for the RMGIC group than the composite group (P<0.001).

Conclusions: RMGIC bonding with V-prep preparation is recommended for palatal/lingual surfaces and for hard-to-dry surfaces. For vestibular surfaces, studies are still needed to recommend bonding with RMGIC instead of composite.