The Effects of Bonding Temperature and Humidity on Bond Strengths to Enamel

Abstract

This study was a continuation of a group of studies and finite element modeling stress analyses that were undertaken to investigate variables in in vitro testing protocols. Previous studies indicated that the type of testing modality and the cement thickness may affect bond strengths. This study evaluated the effect of varying environmental conditions on bond strengths. Hypothesis: The relative bond strengths of two cements will be the same under torsional loading regardless of bonding temperature and humidity if the cement thickness is constant. The purpose of this study was to evaluate the effects of bonding temperature and humidity on the bond strengths to enamel. A resin-modified glass ionomer (Photac-fil) and a resin composite (System 1 +) were utilized in the study. 204 bovine incisors were randomly divided into 12 groups. Stainless steel brackets were flattened with a force of approximately 200Nper bracket. They were then bonded to the flattened labial surfaces of the incisors per manufacturers directions under varying environmental conditions. Three temperatures (65°F, 85°F, and 98°F) and two relative humidities (37% and 85%) were used. Specimens were stored at 100% humidity and 37°C for 2 ½ weeks prior to debond testing under torsion using the MTS Bionix machine. The remaining adhesive was determined using the Adhesive Remnant Index. The results indicated that humidity had a consistent, significant effect on the bond strength of the glass ionomer. High humidity resulted in significantly higher bond strengths than low humidity. Humidity had an effect on bond strength of composite only at high temperature where bond strengths at high humidity were significantly less than at low humidity. Temperature had no effect on bond strengths of glass ionomer and only appeared to affect composite at high temperature as the bond strength of composite at 98°F was significantly greater than at 65° or 85°. The bond strength of the glass ionomer was significantly greater than that of composite at the high humidity, but there was no significant difference between them at low humidity. There was a mild positive correlation (R=.60) between ARI and bond strength. The ARI for composite at high temperature and high humidity was significantly lower than at high temperature low humidity. Conclusion: The relative bond strengths of two cements are different under torsional loading and are influenced by temperature or humidity when cement thickness is held constant.