Date of Graduation

1999

Document Type

Thesis

Degree Type

MS

College

School of Dentistry

Department

Orthodontics

Committee Chair

Elizabeth Kao

Committee Member

John Thomas

Committee Member

Peter Ngan

Abstract

Different orthodontic appliances possesses distinct surface characteristics that enhance bacterial colonization therefore, increasing the risk for caries. The objectives in this study were to evaluate three bracket types by first, to optimize two bacterial indicators strain concentrations and incubation times, and, second, to determine the differences in adherence to these brackets, in vitro. 54 metallic(M), polycarbonate(PC) and ceramic(C) brackets, respectively were used with Streptococcus mutans (ATCC 25175) and Lactobacilli casei (ATCC 393) as the bacteria. The indicator strains were incubated for 48-72hrs at 37C /CO2 then colony forming units(CFU’s) per ml. were counted in triplicates and measured by JSM-6400 S.E.M. Statistically significant differences between bacterial adherence (CFU’s) were determined using ANOVA methods. Statistical differences were not detected (p< .1894 Appendix D. 12 & 14) when the challenge load of Lc was increased in 100 fold concentration: 102 CFU to 104 to 106. There were significant differences of adherence p< 0.001 (Appendix D. 1) for the different concentration levels for Sm. There were no differences (p< .4106 Appendix D. 12 & 16 & p< 0.3550 Appendix 12 & 15) when the incubation time was either 30, 60, or 120 minutes for SM or LC. Greatest adherence occurred (p< 0.0090 Appendix 1 & 4) with the metallic bracket, which had 3-5x fold increase in adherence CFU’s of SM. There were no significant differences p< 0.1931 (Appendix 12 & 15) found for the adherence of

Lc among the three different bracket types. These observations were iii corroborated by S.E.M. at various magnifications. Of 4 variables and 3 brackets evaluated, the metallic composition influenced adherence the most and may be a significant factor in promotion of dental caries. (This study was supported by the West Virginia University Health Associates)

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