RESUMEN
Streptococcus mutans and Streptococcus sobrinus are major etiological agents in enamel demineralization around orthodontic appliances. This study was designed to examine the prevalence of these streptococci on orthodontic brackets in vivo using polymerase chain reaction. Four incisor brackets in the upper and lower arches were removed and collected from 80 patients at the time of debonding. The genomic DNA of adhered bacteria was extracted and each dextranase gene of S. mutans and S. sobrinus was amplified using the specific oligonucleotide primers. The results showed that the maxillary incisor brackets were colonized by both cariogenic streptococci to a somewhat higher degree than that taken from the mandible. The prevalence of S. mutans was 50.0% on the maxillary incisor brackets and 33.8% on the mandibular incisor brackets, and that of S. sobrinus was 17.5% and 15.0%, respectively. Both species were detected on the maxillary incisor brackets of 7 patients (8.8%) and the mandibular incisor brackets of 5 patients (6.3%). These results suggest that cariogenic streptococci can adhere to the incisor brackets and may be resident species on the incisor brackets.