Methods: The sample was 150 children (9-12 years of age, 77 males, 73 females) from Lisbon, Portugal who participated in a randomized trial designed to test the safety of amalgam. The children had > 1 carious lesion on a permanent tooth and no previous exposure to amalgam. Routine dental treatment was provided with one group receiving amalgam and the other receiving resin composite restorations on posterior teeth. Each child had bacterial cultures, from right lower quadrant at the gumline and right cheek, prior to randomization, 3 months later (after dental treatment) and annual intervals for 7 years follow-up. Cultures were diluted an plated on Blood Agar (BA), or media supplemented with tetracycline, erythromycin or ampicillin and Brain Heart Infusion agar with 100 mM mercury chloride. Cultures were incubated in 5% CO2 , 36.5 0C for 2-3 days and counted.
Results: The groups' demographic variables were similar at baseline. Of the original 150 children, 112 children remained in the study for at least 5 years and 80 children remained for the all 7 years. No statistically significant differences between treatment groups and level of growth on antibiotic or mercury plates were found from baseline throughout the 7-year follow-up ( p-values > 0.05). Associations were observed between presence of mercury and erythromycin resistant bacteria (odds-ratio 2.76, 95% CI 1.22, 6.23) or ampicillin resistant bacteria (odds-ratio 3.06, 95% CI 2.40, 3.92).
Conclusion: This study provides no evidence that treatment of children with amalgam for posterior restorations influenced the level of antibiotic/mercury resistant oral bacteria.
Supported by grant NIDCR grant U01 DE-1189,contract N01 DE-72623.