Effects of frequency and duration of acid exposure on demineralization/remineralization behaviour of human enamel in vitro.

An in vitro oscillating system, employing human enamel and realistic time intervals and temperature (approximately 35 degrees C) and measuring mineral loss/gain on a volume basis, was used to investigate the effects of both frequency and duration of exposure to low pH (< 5) on the demineralization and remineralization behaviour of human enamel. Sections of human teeth were cycled through one of three different regimens: (1) 3 x 20-min acid challenges; (2) 6 x 10-min acid challenges and (3) 6 x 20 min acid challenges, over single 24-hour periods. The acid challenge periods of 3 x 20, 6 x 10 and 6 x 20 min produced no significant differences in net mineral lost, i.e., the volume of mineral lost per volume of enamel exposed was similar irrespective of frequency or duration of acid exposure (approximately 0.5% vol/vol). Increased frequency of acid exposure did, however, tend to alter the total demineralization/total remineralization amounts, resulting in significantly greater amounts of mineral loss and gain. The data suggest that the remineralization capacity of enamel is considerable and that factors such as inhibition of remineralization may be important in determination of net mineral loss from the tooth.