Dietary influences on oral pH
The potential impact of diet is not simply resolved by avoiding the most acidic foods. The pH value gives some information but both the duration and type of the erosive challenge also needs to be noted.
To better understand the potential erosive effects, the concept of titratable acidity can be a helpful tool. This is a measure of the amount of alkali (for example the number of milliliters of 0.1M sodium hydroxide) which needs to be added to an acid to neutralize acid and reach a pH = 7.0. It indicates the amount of available acid, both bound and free hydrogen ions,33 and thus the erosive potential of a substance.
This measure takes into account the ability of the food or liquid to act as a buffer. Cola drinks, which have a pH of 2.5, have a relatively low titratable acidity at 0.7. Grapefruit juice is less acidic with a pH of 3.2, but has much more titratable acid with a relative value of 9.3. This shows how the erosion potential for fruit juices can be higher than for carbonated drinks.
To support this, a study comparing the erosive potential of cola drinks and orange juices found the mean pH of cola drinks to be more than one unit lower than the mean pH of the orange juices. However, despite having a higher pH, the orange juices' titratable acidity values (to reach pH 5.5) were nearly five fold higher on average than in the cola drinks.35
The study also demonstrated how erosive potential can vary over time. The initial erosive potential for the colas was more than ten fold higher (p<0.001) than in the orange juice, but the erosive potential changed more quickly in the cola drinks, so that after three minutes, the erosive potential in the cola drinks slowed more than 40 fold, compared to only a three-fold slowing in the orange juice.35
The researchers also established the protective buffering effects of salivary proteins increased with increased erosive potential within the first minutes of exposure to the drinks. Importantly, the proteins halved the erosive potential of cola drinks with a low pH, while only limited effect was found with orange juices that had higher pH values and seemingly lower erosive potential.35
Another study looked at the buffering capacities of soft drinks, and concluded that fruit juices and carbonated fruit-based drinks with their increased buffering capacities may induce a prolonged drop in oral pH.36 The researchers ranked buffering capacities, with fruit juices having most buffering ability, followed by fruit-based carbonated drinks and flavored mineral waters, followed by non-fruit based carbonated drinks, then sparkling mineral waters, and finally still mineral water. 36
Of course, food and drink acidity can be beneficial for prolonging shelf life as a lower pH deters microbial growth: a pH below 4.6 will inhibit most food borne bacteria.37
Attempts have been made to investigate the relationship of various foods and drinks to erosion in a large study examining diet and eating habits of 2,385 adolescents in the UK in 2004. This appeared to show a relationship between dental erosion and acidic foods.39 Apples and tinned fruit were on the borderline of having an association with dental erosion, whereas pickles and sauces had the greatest association with tooth wear. It did not identify an association with oranges, although there was with grapefruit; and other studies, as described above, have demonstrated erosion with fruit juices.35
On average adolescent males drank more sodas than females, with a mean consumption of 8.6 cans a week, two more a week than girls, putting boys at greater risk of erosion.39 This was manifest as greater dentinal exposure and/or more eroded teeth.
As demonstrated by the relationship between increased consumption of sodas and a higher incidence of erosion, it is important to think about how the food or drink is consumed. Frequent snacking or sipping a drink repeatedly exposes teeth to enhanced risk of erosive challenge, as the protective salivary proteins and pellicle may not have time to replenish.35 Soft drink intake, even in relatively short duration can reduce enamel microhardness, so this may be a critical factor for people who tend to sip soft drinks throughout the day.35
Young children who use a drinking cup or an infant bottle to drink juice, and use it like a soother or pacifier, increase the risk of erosive challenge.20 Other eating, drinking and swallowing habits can be implicated, for example, swishing a drink round the mouth for a long time before swallowing increases exposure time.40