The aim of this in vitro study was to investigate the change of erosive properties of apple and orange juice after dilution with tap water. Apple juice, orange juice and citric acid were assessed for pH and titratable acidity at different aqueous dilutions (100% – pure liquid, 60% – 3 : 2 mixing ratio, and 40% – 2 : 3 mixing ratio respectively). Thus, 72 bovine enamel specimens were distributed to 9 groups (n = 8 specimens per group), followed by 25 minutes of erosion by superfusion with the described test liquids according to group allocation. Erosive substance loss (µm) was determined profilometrically. The different substance losses within a dilution series were tested using the Wilcoxon rank sum test. The significance level was set to p <= 0.05.

Erosive substance loss [µm] for 100% concentrations (median ± interquartile range) was highest for apple juice (5.7 ± 0.8), followed by citric acid (4.6 ± 0.4) and orange juice (1.5 ± 0.5). The dilution of apple juice (60%: 4.2 ± 0.7; 40%: 3.1 ± 0.5) and citric acid (60%: 3.7 ± 0.9; 40%: 2.8 ± 0.7) with tap water lead to a significant (p < 0.05) reduction of erosive potential in comparison to 100% concentrations. This effect was not consistent for orange juice, where significantly more substance loss was found for pure juice (100%) than for 60% diluted juice (60%: 1.1 ± 0.3, p < 0.05), but no significant difference was found between 100% and 40% (40%: 0.9 ± 0.6, p > 0.05), and 60% and 40%, respectively.

In conclusion, dilution of apple juice with tap water led to a significant reduction of its erosive potential. For orange juice, the effect of dilution on the erosive substance loss was only limited.

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