| Orthodontic fixed appliances have been used extensively due to their high efficiency and accuracy. But as some appliances such as brackets adhere to the surface of teeth, which can change the ecological environment in certain parts of the mouth, the plaque around them may lose the ecological balance, and this can lead to some complications such as enamel decalcification and gingival swelling. So the ability to adsorb plaque and their influence upon the plaque around constitute the important factors to cause ecological imbalance. The aim of the research paper was to make a comparison of metal and ceramic brackets in their impacts upon adhesion of plaque by means of laboratory research and clinical research so as to direct clinical application.Laboratory research: two types of brackets made from metal and ceramic were used in the experiment. Twelve groups of saliva-coated brackets and 12 non-coated brackets of each type, with a group consisting of 4 brackets, were immersed in a streptococcus mutans solution at a density of 10s cell per ml. Then each sample was immersed in broth at 37 癈 for 24, 48 and 72 hours respectively to measure the adherence of streptococcus mutans to these samples by plate cultivation counts.The results are as follows:1. In the case of the saliva-coated groups , during 48 hours, the affinity of streptococcus mutans to the metal brackets was lower than that to the ceramic brackets; within 72 hours there was no significant difference in the affinity of streptococcus mutans to the two type of brackets.2. As for the non-coated groups, the affinity of streptococcus mutans to the metal brackets was lower than that to the ceramic brackets.3. For the saliva-coated groups, the affinity of streptococcus mutans to the metal and ceramic brackets after 24 storage time was higher than the initial affinity. For the non-coated groups, there was , however , no significant difference among initial,24hour, 48hour, and 72hour storage times.4. Within 24 hours, saliva caused decreased affinity of streptococcus mutans to the metal and ceramic brackets. From 48-hour storage time to 72-hour storage time, saliva caused increased affinity of streptococcus mutans to the metal and ceramic brackets. Clinical research: Fourteen patients with malocclusion were randomly selected. One week before the placement of the brackets, the patients were treated with periodontal scaling. Before the placement of brackets, supragingival and subgingival plaques of lower incisors were assessed by Gram staining bacterial smear. The observed value was served as the baseline vecords. Then the metal and ceramic brackets adhere respectively to the left and right lower incisors. After the placement of the brackets, the microorganism of the plaque was assessed 2 weeks, 4 weeks, 6 weeks and 8 weeks later. The data concerned were statistically analyzed by SAS package.The results are as follows:1. In every period of time, there was no difference in the bacteria formation of supragingival and subgingival plaques around metal and ceramic brackets.2. After the placement of the brackets, as far as the subgingival plaque was concerned, Gram-Positive bacteria decreased significantly, but Gram-Negative bacteria increased remarkably, and Gram-positive bacillus increased most significantly.3. Gram-Positive bacteria dominated the supragingival before or after the placement of the brackets. But before the placement, Gram-Positive bacillus took the dominant place. From six to eight weeks after the placement, Gram-Positive coccus did.From the above results, it was found that the initial affinity of streptococcus mutans to the metal brackets was lower than that to the ceramic brackets, and the two types of the brackets could lead to increased pathogenicity of the surrounding plaque, however, with no significant difference between them.
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