other acids over a similar pH range. No erosion occurred after pH 3á2 with phosphoric acid under these condi- tions.
Sodium hydroxide alone produced negligible enamel and dentine loss. Trisodium citrate alone resulted in about 1 lm dentine loss after 10 min and 2 lm enamel loss after 30 min.
Discussion
United Kingdom's soft drinks consumption has grown by 56% in the past 10 years to just under 10 000 million L in 1996. This represents about 0á5 L per person per day, but in reality in the under 20-year-olds this is nearer 1 L per day (Zenith International Ltd, 1997). Further, soft drinks represent nearly one-fourth of all drinks consumed in the UK including tap water. Citric and phosphoric acids are the two main dietary acids present in these soft drinks. The concentration of the beverage acids vary in each product, but are in the order of 0á3% (w/v) citric acid for orange juice with a pH around 3á2 and relative titratable acidity of about 4á8; and for cola beverages about 0á1% (w/v) phos- phoric acid with pH around 2á5 and relative titratable acidity of about 0á7. Hence, this investigation aimed to determine dentine and enamel loss because of 0á3% (w/v) citric acid as compared with 0á1% (w/v) phos- phoric acid over a range of pH values. These acid concentrations were employed to gain a pragmatic clinical comparison, rather than an explanatory chem- ical comparison of erosion using identical molarites. Further, the amount of tissue loss attributed to citric acid chelation, as opposed to that of dissolution was ascertained by comparing a strong mineral acid, hydro- chloric acid, with citric acid a weak acid, at similar pH and molarity.
Examining the position of the phosphoric acid curves in relation to the citric acid curves in Fig. 2, it can be seen that over the common pH range CANaOH was more erosive than PA at any given pH, particularly with regard to enamel. This is of relevance clinically, as it suggests cola type drinks will be less erosive than citric acid based ones at the concentra- tions evaluated. Certainly, observational studies for differences in erosion of dentine by commercial beverages supports this contention (Absi et al., 1992). Further, fruit drinks tend to have greater buffering capacity than the cola drinks, potentially increasing erosion rates further. If the pH of the acidic