A Comparative Study of Shear Bond Strength of Direct Bonding System with and without a Liquid Primer: An In Vitro Study

BACKGROUND: A primer in dental bonding agents enhances the bond between the adhesive and the tooth by way of deriding the tooth surface of moisture and creating a hydrophobic surface for the adhesive to bond and by facilitating the flow of the adhesive into the etched tooth surface. In the orthodontic context, however, there have been debatable results in the published literature as to how significantly the use of primer affects the bond strength between the bracket and the tooth surface. AIMS: This study aimed to evaluate and compare the shear bond strength of two commercially available direct bonding systems with and without using liquid primer and to record their adhesive remnant index scores. SETTINGS AND DESIGN: A total of 100 natural human teeth, extracted for orthodontic therapies, had been selected as specimens for the study. They were equally divided into four categories. Two commercially available products were used to bond metallic orthodontic brackets to the teeth, both with the use of and without the use of a primer to test the shear bond strengths of the four types of adhesive-tooth complexes created. Shear bond strength was measured using universal testing machine, and Student’s t-test was applied for the comparison of the results. MATERIALS AND METHODS: A total of 100 extracted human premolar teeth were divided into two groups: Group I and Group II, each of which contained two subgroups (with one subgroup pretreated with a primer and the other, not pretreated with the primer). All the teeth were divided equally among the subgroups and were mounted on color-coded acrylic blocks to aid in identification. Group I was bonded with Transbond XT Light Cure Adhesive (3M Unitek Orthodontic Products, Monrovia, California) and Group II was bonded using Phase II two-paste system (Reliance Orthodontic Products, Itasca, Illinois). The shear bond strength of Transbond XT Light Cure Adhesive used with Transbond XT primer and Phase II orthodontic two-paste system used with liquid primer was compared with that of those used without a liquid primer, respectively. The shear bond strength was evaluated using universal testing machine and the adhesive remnant scores were evaluated subsequently. The Student’s t-test was applied for comparison of the two groups. STATISTICAL ANALYSIS: Descriptive statistics, such as mean, standard deviation, and a standard error, were calculated for Transbond XT used with and without primer and for Phase II two-paste system used with and without a liquid resin. The Student’s t-test was applied for comparison of the two groups. RESULTS: In Group I, the mean bond strength of Transbond XT without primer (12.5272MPa, 95% CI: 11.76–13.68) was compared to that of Transbond XT with XT primer (13.2028MPa, 95% CI: 12.39–14.06). In Group II, the mean shear bond strength of Phase II two-paste system without primer (10.66MPa, 95% CI: 10.13–11.18) was compared to that of Phase II two-paste system with primer (10.66MPa, 95% CI: 10.13–11.18), and the values were statistically insignificant. CONCLUSION: The shear bond strength of the brackets bonded with Transbond XT and Phase II without using the liquid primer was sufficient enough to withstand the masticatory forces, which implies the elimination of liquid primer during bonding. CLINICAL SIGNIFICANCE: The development of the acid-etch technique and Bisphenol A-glycidyl methacrylate-based liquid resin has changed the practice of orthodontics over the years more than any other single principle formulated. Despite its wide popularity, the cytotoxicity, which stems from the use of liquid primer, needs attention.