Force and amount of resin composite paste used in direct and indirect bonding

Objective: To investigate the relationship between the forces applied by the operator and the amount of adhesive used in the direct and indirect bonding methods. Materials and Methods: A system for measuring the force applied by operator was used to test specimens prepared by 12 orthodontic specialists. To determine the proper amount of adhesive, metal brackets were bonded to transparent resin teeth using composite resin paste and different forces (100, 200, and 300 g); the area of the composite resin paste was then measured using image-analysis software. The mean forces applied in direct and indirect bonding were compared by Student's t-test. Results: Various values for force were obtained for the direct bonding (53-940 g) and indirect bonding (150-870 g) techniques. Although in all cases the area of composite resin paste after the application of constant force was greater than the area of the metal brackets, an insufficient amount of composite resin paste on the bracket base was observed with forces of 100 and 200 g. Conclusions: A force of greater than 200 g might be preferable for obtaining a thin composite resin layer and for achieving sufficient spreading of the composite resin paste.