Determination of optimum adhesive thickness using varying degrees of force application with light-cured adhesive and its effect on the shear bond strength of orthodontic brackets: An in vitro study

The thickness of the adhesive layer under a bracket may be an important factor that affects the final tooth position and bond strength. With increasing use of preadjusted brackets, it is important to ensure that a consistently even layer of composite is placed under each bracket to take full advantage of bracket design and to avoid the need for compensatory bends to be placed in the archwire. Therefore, the present study is aimed at determining the optimum adhesive thickness by varying the force of application and observing the effect on the shear bond strength of orthodontic brackets.Sixty premolars extracted for orthodontic purposes were divided into three groups of 20 samples each. Adhesive thickness was measured by varying the force of application while bonding brackets with light-cured adhesive and tested on a universal testing machine to evaluate the shear bond strength.The study showed that adhesive thickness is inversely proportional to applied force. In addition, the shear bond strength has a tendency to increase with a decrease in adhesive thickness up to a certain extent and then decrease.Adhesive thickness between bracket base and tooth surface decreases with an increase in the amount of force application from 1 to 3 oz. Mean shear bond strength increases when adhesive thickness decreases from 0.99 to 0.83 mm, and then it has a tendency to decrease when adhesive thickness decreases to 0.72 mm. Optimum adhesive thickness should be considered to be 0.83 mm, which is the thickness required to achieve sufficient bond strength to prevent chances of bond failure.