Background and aim: reduction of dental plaque pH is an effective factor in the incidence of dental caries. One of the common methods for assessment of the cariogenic potential of food products is the study of plaque pH changes in the oral environment. The present study was performed due to the importance of dental plaque and its known complications and also the increase in consumption of industrial fruit juices which are encouraged nowadays as healthy drinks and also the positive effect of pomegranate juice on the amount of dental plaque which has been mentioned in the reports.

Materials and methods: This clinical trial was performed with crossover design. Complete prophylaxis was performed during the first session. Then, the participants were asked to refrain from oral hygiene methods for 48 hours and not to eat or drink for at least 2 hours before the experiment. The baseline plaque pH was measured, and afterwards 10 cc of fruit juice was kept in mouth for 2 minutes and then swallowed. Afterwards, plaque pH was measured at time intervals of 2, 5, 7, 10 and 30 minutes. After one week of wash out period, the participants were again evaluated by the same method and with the other type of fruit juice. The measurement of plaque pH was performed with microtouch method by use of Metrohm electrode. The data were analyzed by repeated measures ANOVA.

Results: pH in pomegranate juice group before fruit juice intake equaled 6.73± 0.24 and reached 5.57±0.34 at the fifth minute and finally reached 6.19±0.32 at the 30^th minute (p˂0.01). Also, in orange juice group, pH before intake equaled 6.16±6.8 and reached 5.62±0.17 at the seventh minute and 6.15±0.2 at the 30^th minute (p˂0.01). The maximum fall in pH for both fruit juices occurred at the fifth and seventh minutes. pH after consumption of both fruit juices began to increase from the tenth minute. These two fruit juices were not significantly different regarding plaque pH at the zero minute and at the time of maximum pH fall and at the 30^th minute. (p˂0.08)

Conclusion: The results showed that plaque pH after consumption of both fruit juices falls below the critical level for seven minutes and this decline is similar for both fruit juices.