OBJECTIVETo evaluate the dynamic changes of Streptococcus mutans concentration of plaque during fixed appliance treatment and the effects of two materials of ligation on Streptococcus mutans concentration.

METHODSTwenty-eight patients undergoing fixed appliance treatment were observed. Ligature wire and elastomeric rings were applied on one side of arches, stochastically. The dynamic changes on the quantity and percentage of Streptococcus mutans were observed before and after fixed appliance bonding.

RESULTSStatistically significant increase of the quantity and percentage of Streptococcus mutans was found after fixed appliance bonding, and the percentage of Streptococcus mutans in the plaque around the brackets ligated with elastomeric rings was more than that of ligature wire at the beginning of fixed appliance bonding, statistically.

CONCLUSIONSThe finding suggested that the caries-associated capability of the plaque increased after bonding and there was greater caries-associated capability of the plague on the teeth when elastomeric rings was used than that of the plague when ligature wire was used at treatment beginning. The ligature wire is recommended in the fixed appliance treatment.