Salivary Streptococcus mutans levels in patients with conventional and self-ligating brackets

The objective of this study was to investigate the effect of bracket type (conventional and self-ligating) on the levels of Streptococcus mutans and total bacterial counts in whole saliva of orthodontic patients. Thirty-two male and female patients were selected using the following inclusion criteria: adolescents (mean age 13.6 years, range 11-17 years), fixed appliances in both arches, non-smoker, and no reported oral habits. Demographic and oral hygiene characteristics were determined for each subject. The patients were subdivided into two groups with random allocation of bracket type (conventional or self-ligating). An initial saliva sample was obtained before the initiation of treatment (T1) and a second sample 2-3 months following appliance bonding (T2). Salivary S. mutans and total bacteria were enumerated and analysed after growth in culture. The demographic and clinical characteristics of the samples were analysed with a t- or chi-square test, where applicable, to assess the random allocation of bracket group to participants. The results of S. mutans and total facultative bacterial counts were log transformed and statistically analysed with analysis of covariance with bracket (conventional versus self-ligating) as the categorical variable and initial total bacterial counts or initial S. mutans levels serving as the covariate. No difference was found in the demographics and oral hygiene indices between the two groups, verifying the random assignment of brackets to the population sample. The levels of S. mutans in whole saliva of orthodontically treated patients do not seem to be significantly different between conventional and self-ligating brackets. The pre-treatment levels of S. mutans are significant predictors of the levels of S. mutans after placement of orthodontic appliances, while this was not the case for total bacterial counts.