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The release of mercury vapor from class I amalgam restorations prepared in human molar teeth was studied during chewing simulations in an artificial mouth of a bi-axial servo-hydraulic mechanical test system. So that the total mercury released from the restoration over a fixed time could be determined, a closed chamber surrounded the envelope of chewing motion. In addition, the influence of sampling frequency on mercury release was corrected by the use of different sampling frequencies over a fixed time interval of mercury release measurement and extrapolation to zero sampling time. Thus, a combination of a closed environment and an extrapolation method to determine the mercury release under continuous sampling was used to determine the mercury released under normal breathing conditions. The measured mercury release rate data were used to calculate the potential daily mercury dose in a patient due to a single amalgam restoration, following the method previously outlined by Berglund. The mercury release from both a conventional and a high-copper amalgam was evaluated at different age intervals after the restoration was placed in the teeth. The results show that while the age of the amalgam and the amalgam type influence the extent of mercury release during the initial non-steady-state conditions, the steady-state value of mercury daily dose due to a single amalgam filling is 0.03 micrograms/day, which is well below the calculated threshold-limiting value (TLV) of 82.29 micrograms/day considered dangerous for occupational exposure in the United States.

The purpose of this study was to compare the levels of Lactobacilli (LB) and Streptococcus mutans (SM) colony forming units (CFU) in the saliva of subjects before and after orthodontic appliance placement.This was a controlled, prospective two-group, two-measurement, clinical trial performed on 64 study patients, 12-15 years old. Subjects in the experimental group were sampled for LB and SM in stimulated saliva collected on the same day but prior to band and bracket placement. The subjects in the control group were sampled on their first screening appointment two months prior to band and bracket placement. The second samples of LB and SM were taken from the experimental and control groups after two months. Saliva was transferred to a selective agar carrier and incubated for 48 hours at 37°C / 99 °F. LB and SM colonies forming units were compared with standard densities.The experimental group wearing orthodontic appliances had significantly higher mean LB CFU counts than the control group at the 2 month follow- up (3.25 vs. 2.57, p =0.0036). The two groups, however, did not show any difference in mean SM CFU counts at the 2 month follow-up (3.0 vs. 3.1, p = 0.66). The results of this study showed that a higher number of CFUs of LB were associated with the group wearing orthodontic appliances after two months and may play a role in the increased levels of plaque seen in many orthodontic patients.

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