Figure 1. Experimental set-up. (A) pH measurements (pH₀) and titration of soft drink with 1 M NaOH to a pH above 5.5 (N = 20). From these data, the titratable acidity was determined in µL 1 M NaOH. (B) Addition of 50 mg of pure hydroxyapatite (HAp) crystals to the drink (N = 20), under constant stirring, and pH recordings every 15 sec (pH₁–pH₁₂). After the initial recordings, the drink was left with constant stirring until the last pH recording was obtained after 30 min (pH₁₃). (C) Titratable acidity (from Fig. 1A) up to each pH value obtained over time in response to HAp dissolution in the drinks (from Fig. 1B). The amount (µL) of base (1 M NaOH) needed to obtain each pH value induced by HAp addition was used to calculate the amount of HAp crystals dissolved (mg) per sec per liter soft drink (N = 20). In (C), iEP denotes the initial erosive potential (i.e., during the first minutes of exposure), and eEP denotes the end erosive potential (i.e., after 30 min).