Effect of Different Enamel Conditioning on the Bond Strength of a Resin Modified Glass Ionomer Cement and Ceramic Brackets

The introduction of direct bonding of brackets was a major development in the quality of care provided to the orthodontic patient. Resin composites have been the standard material for direct bonding in Orthodontics for many years. However, they are sensitive to moisture contamination and do not release fluoride. Caries formation during treatment remains a concern to the orthodontists. An adhesive system that provides sufficient retention to orthodontic accessories and that prevents caries development would be ideal. Recent reports have suggested that resin modified glass ionomer cements may have these properties. The use of ceramic brackets has increased in the past years due to a higher demand for a more esthetic orthodontic appliance. This investigation was designed to evaluate the effect of different enamel conditioning procedures on the shear bond strength and on the bond failure pattern of a resin modified GIC used to bond mechanically retained ceramic brackets. One hundred and five human premolars extracted for orthodontic reasons were randomly assigned to one of the seven treatment groups. The tooth samples were stored in distilled water at room temperature until ready for bonding. After bracket placement the specimens were stored in distilled water at room temperature for 24 hours. The shear force necessary to debond the brackets was recorded using an lnstron Universal Testing Machine at a cross head speed of 0.05 mm/min. The characteristics of bond failure were evaluated under a stereo microscope and Adhesive Remnant Index (ARI) was assigned according to the amount of adhesive remaining on the tooth and the bracket Based on the results of the investigation the following conclusions were drawn: 1. There was a significant difference in the mean shear bond strength values obtained with different enamel treatments. Moisture contamination significantly decreased the: SBS of GIC on those groups that had enamel conditioned with polyacrylic acid. 2. When the manufacturers recommendations for enamel preparation were followed (l0% polyacrylic acid for 20 seconds, rinse, apply wet cotton pellet) the mean bond strength obtained was the lowest and the most variable among the groups tested. 3. Overall enamel etching with 35% phosphoric acid for 15 seconds resulted in higher and more consistent SBS values than those observed in the groups that had tooth surface conditioned with polyacrylic acid. 4. There was a statistically significant difference in the failure sites among the seven different enamel treatment groups. All brackets bonded with composite resin had 100% of the adhesive remaining on the enamel (adhesive failure at the brackets-adhesive interface). The GIC groups showed a more variable pattern with most of the failures of cohesive nature (within the adhesive). 5. All different treatment groups produced SBS values that are considered clinically acceptable. Therefore, resin modified glass ionomer cement may be considered an alternative to composite resin for direct bonding of mechanically retained ceramic brackets. Moisture contamination decreased SBS. but seamed not to preclude the use of GIC as an adhesive material