Influence of Microorganisms and Acidic Beverages on Enamel in Vitro

Objectives: In the present in-vitro study a possible mutual influence of acidic beverages and microbial metabolites on erosive changes of enamel was to be examined. Methods: Only fully retained wisdom teeth from young patients (20-23 years of age) were used for this study. The dental crowns were cut into 5 slices, fixed in 12-well plates so that an enamel area of about 20mm2 was exposed. The dental slices were either incubated with various acidic beverages (Coca Cola, Fanta Citrell, Jim Beam Black, Bacardi Breezer Orange) for up to 48h at 37oC, or with Schaedler broth freshly inoculated with S. mutans 10449 or S. oralis H1. Then enamel samples were incubated either first with acidic beverages (24h) and then with one of the streptococci (24h) (n=6) or vice versa. The control samples were incubated in saline for 48h. After the incubation the amounts of released calcium were determined using a colorimetric assay (Randox, Krefeld) and expressed in mg/dl/20mm2. The samples were also visually analyzed in a SEM (Zeiss, DSM 962). Results: The incubation of the enamel slices with acidic beverages or with streptococci led to a time- and substrate-dependent release of calcium. After the dental samples were incubated for 24h with the respective test solutions, the following amounts of calcium were released (mean value ±SD mg/dl/20mm2): Coca Cola: 10.3±1.29; Fanta Citrell: 19.96±1.79; Jim Beam Black: 32.0±4.7; Bacardi Breezer Orange: 35.9±7.2; S. oralis H1: 0.43±0.49; S. mutans 10449: 1.23±0.97. The incubation of the dental slices first with acidic beverages and a subsequent bacterial colonization caused a significantly greater calcium release, e.g. after incubation with Jim Beam Black: S. oralis H1 4.1±1.3; S. mutans 10449 3.9±0.38. Conclusion: This study indicates that microbial metabolic activities can be especially harmful for the respective tooth surfaces if erosive changes caused by acidic beverages are already present.