Date of Award
Summer 2014
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Dentistry
First Advisor
Bradley, Thomas G.
Second Advisor
Berzins, David
Third Advisor
Liu, Dawei
Abstract
Introduction: More patients are seeking esthetic alternatives for their orthodontic treatment options, which has led to increased use of ceramic brackets in recent years. These brackets were marketed before independent scientific research was completed. Many of the early ceramic brackets used a silane coupling agent to allow for a chemical bond between the bracket and the adhesive resin. Early reports from clinicians of increased bond strengths and iatrogenic tooth damage after bracket removal were common. Manufacturers have made changes to their base designs, relying more on mechanical retention for bond strength. The goal of this study was to test the shear bond strength of two newer generations of mechanically retained ceramic brackets and compare them to a traditional stainless steel bracket. Materials and Methods: Two types of ceramic brackets, Clarity Advanced (3M Unitek, Monrovia, CA), and Avex CX (Opal Orthodontics, South Jordan, UT) and one type of metal bracket, Victory Series MBT (3M, Unitek, Monrovia, CA) were used in this study. Exemption from IRB Application was granted by the Marquette University Institutional Review Board (IRB) on 7-12-13. The shear bond strength of the three groups of brackets were examined after bonding to extracted premolars. Brackets were debonded with a universal testing machine (Instron Corporation, Canton, MA) in a motion parallel to the bracket/tooth interface. Each tooth and bracket was viewed under an optical stereomicroscope at 10x magnification and given an adhesive remnant index (ARI) score. The one way ANOVA and Tukey's post hoc tests were used to determine significant differences in bond strengths, and the Kruskal-Wallis and Mann-Whitney post hoc tests were used to analyze the difference in ARI scores. Results: Statistically significant (p<0.01) differences were found between the shear bond strengths of the Victory Series and Clarity Advanced groups, with the Victory Series having a mean strength of 199.4 N and the Clarity Advanced having an average of 136.0 N. Significant (p<0.0001) differences in ARI scores were found between the Victory Series and both ceramic groups, with an average score of 1 for the Victory Series and an average score of 2 for both ceramic groups. The two ceramic brackets were not statistically different from each other in bond strength or ARI score. Conclusions: The shear bond strengths of the new generations of ceramic brackets are lower than those of the metal bracket tested, which suggests a safer bond to enamel. Further research on clinical debonding characteristics and behavior intra-orally are needed to support the in vitro results found in this study.