Intraoral bacterial growth on tetracycline-impregnated dentin

Previous studies have shown that tetracyclines react with enamel and dentin in vitro to form slightly soluble compounds with a pronounced and long-lasting antimicrobial capacity. The purpose of the present project was to study the effect of doxycycline-impregnation of dentin on the growth of oral microorganisms in vivo. Slabs of native human dentin were immersed in aqueous solutions of doxycycline HCl, 10 mg/ml, for 10 min, and were subsequently ligated to orthodontic brackets placed bucally on maxillary molars in seven individuals. Untreated native dentin specimens were similarly placed on contralateral teeth. Test and control specimens were removed from the oral cavity after 2 h, 24 or 120 h, respectively. The individual specimens were then placed in 0.5-ml saline and agitated mechanically for 30 s. The resulting bacterial suspensions were plated onto blood agar and various selective growth media. Based on CFU-counts obtained after incubation of the plates, doxycycline-treated dentin specimens showed a significantly lower number of viable microorganisms after 2 h and 24 h in the oral cavity than did the control specimens. The bacterial growth was also less pronounced in the test specimens after 120 h. The effect of doxycycline was similar for all the cultivable bacteria. No significant difference in yeast growth was seen between test and control specimens.