In vitro quantitative microhardness assessment of enamel with early salivary pellicles after exposure to an eroding cola drink

To assess the erosive effect of a cola drink on enamel incorporating early salivary pellicles, 72 groups of human enamel slabs were immersed in fresh cola, with groups differing in that slabs were (1) incubated in whole or in clarified saliva, (2) under three regimes of frequency intake (1, 5 and 10 times/day); (3) immersed with or without agitation, and (4) the pellicle was incubated for 20 min, 6 or 24 h. Quantitative assessments were done over an 8-day interval using surface microhardness testing. Results for primary enamel showed a sharp decrease from baseline (344.2+/-32.4 Vickers Units; mean +/-SD) to day 1 (268.9+/-36.8), and reached 155.2+/-68.6 on day 8. Results for permanent enamel were 350.8+/-42.2, 315.9+/-39.2, and 149.8+/-85.2. Microhardness was affected by agitation, level of intake and type of saliva, but not by the pellicle incubation interval nor the type of enamel. The joint effect of static baths and higher immersion frequency was the most important factor in decreasing hardness.