Influence of amalgam on the growth of mutans streptococcus: an in vivo study.

Objective: To study the antibacterial activity of dental amalgam against mutans streptococcus.

Methods: Study volunteers included 14 patients, 21 to 35 years old, with aged amalgam fillings, with no antibiotic use during the previous 3 months, and 16 patients, 22 to 24 years of age, without aged amalgams, but with unfilled caries. Plaque samples were collected once from the subjects with aged amalgams. Subjects with fresh amalgams had plaque samples collected at 1 day, 1 week, 2 weeks, 4 weeks, and 8 weeks after amalgam restoration. As controls, plaque samples were collected from unrestored occlusal enamel surfaces on the same side, or on the opposite side of the same occlusion. Frequency of mutans streptococci from aged amalgams and fresh amalgams and the colony-forming units (CFU) were tested.

Results: The difference of CFU of mutans streptococci in the plaque samples between the amalgam restorations, the aged amalgams, and the controls was not significant within 8 weeks after amalgam filling. The difference of CFU of mutans streptococci in plaque samples from the amalgam restorations between all the timepoints was significant except between the fourth week and eighth week. For the control group, however, the difference in values between the first day and the timepoints afterward were significant, except between the first day and the first week. The difference between the first week and later timepoints was significant, but not between the second week and later, or between the fourth week and later. At the eighth week, the difference between the aged-amalgam and controls was not significant.

Conclusion: Amalgam had some inhibitory effect on the in vivo growth of mutans streptococci.