Sample collection Locally available and/or produced beverages and bottled drinking water samples were collected from different markets and super shops of Dhaka, Bangladesh. The collected samples were broadly classified into four categories: (a) soft drinks (13 brands), (b) energy drinks (4 brands), (c) fruit juices (12 brands; all were mango juices), and (d) bottled drinking water (8 brands). For each brand, three samples from different production batches were collected.
Chemical analyses All the chemicals used were reagent grades. Each test was repeated three times (i.e., samples from three batches and three tests for each sample) and the average results were used for further analysis. All the tests were carried out at room temperature. The pH of each sample drink was measured immediately upon opening. A calibrated bench-top pH meter (Hanna HI2211) was used to measure pH of the samples. A HACH Model 44600 Conductivity/TDS Meter was used to measure the TDS of the samples. The TDS of each sample drink was measured immediately upon opening. For carbonated samples, however, the samples were allowed to sit till some of the gas escaped. The TA of each sample was measured by titrating 25 mL of each sample with 0.1 M NaOH, using phenolphthalein as the indicator. For the samples with an intense color (e.g., black cola), the samples were diluted for accuracy to determine the titration endpoint. The calcium (Ca2+) concentrations in the samples were determined using complexometric titration method. Ethylenediaminetetraacetic acid (EDTA) solution was prepared by dissolving 1.4612 g of reagent grade EDTA (Sigma Aldrich) in 500 mL of water to prepare a 0.01 M solution. A pH 11 buffer solution was prepared to maintain an alkaline environment which would help any magnesium precipitate; else the EDTA would simultaneously complex with the magnesium ions. Then, 25 mL of the samples were titrated with the EDTA solution, using Calcon as the indicator. The phosphate content of the beverage samples were measured using a spectrophotometer (Hach UV/vis spectro-photometer, DR4000). Now, 10 mL samples of the beverages were taken into cuvettes, diluted appropriately so as to reduce color effect or reduce the phosphate (PO4 3− ) concentration below the maximum threshold of the equipment. Using the preset program for determining total phosphate as orthophosphate, the procedure was carried out. Dental samples were analyzed via scanning electron microscopy (acceleration voltage = 3.0 kV; JSM-7600F SEM). SEM images were taken before and after dissolution of dental samples in beverages (Fanta, Speed, and Fruitika) for 10 days.
Dental erosion potential characterization Acidity and dissolution The dental erosion potential of soft drinks and food items can be characterized using pH and TA. Beverages with pH values below 6.7 and 5.2–5.5 can potentially cause erosive wear to root dentin and enamel, respectively. Soft drinks, including carbonated beverages, fruit juices, and energy drinks, are considered highly acidic; therefore, continuous consumption of such drinks can lead to dental erosion. High acidity or a low pH implies the presence of high concentration of hydrogen ions (H+ ) that will be available to cause the replacement of minerals (e.g., calcium) from tooth structure. On the other hand, TA indicates the amount of alkali required to neutralize the acid. Therefore, TA is also known as buffering capacity. The greater the buffering capacity (i.e., TA) of the drink, the longer it will take for the saliva to neutralize the acid. TA works as a better indicator of dental erosion than pH. pH gives an indication of the equilibrium concentration of hydrogen (H+ ) ions but does not provide a measure of the free hydrogen ions that can cause demineralization.
Calcium and phosphate Calcium (Ca2+) and phosphate (PO4 3−) contents of beverages are important factors influencing erosive potential. Different research groups demonstrated that the enamel loss is lower for the people who consume the calcium-fortified drinks than for the people drinking conventional orange drinks. Scientists have suggested that fortifying dentally erosive drinks with calcium and phosphate reduces the erosive potential of the drink on tooth surface. Added calcium and phosphate saturate the drink with respect to hydoxyapatite mineral [Ca5(PO4)3OH] of the enamel. High levels of calcium in the solution blocks the release of calcium ions (Ca2+) from the enamel surface. However, a high concentration of calcium in beverages may cause an unpleasant metallic taste.
Degree of saturation The degree of saturation is the driving force for the dissolution process. This parameter is a potential indicator to show how far the mineral composition is from equilibrium. A high degree of saturation inhibits demineralization of the enamel and dentin. The loss of minerals and re-mineralization of enamel is a constant process. The equilibrium between the tooth enamel and the fluid surrounding the tooth surface is influenced by the degree of saturation. A critical pH value of a beverage controls the dissolution of minerals from tooth. However, this critical pH is not a fixed value, and it depends on the concentration of other ions such as calcium and phosphate. The pH of saliva is higher than the critical pH for tooth, and is supersaturated with respect to the enamel. Due to its mineral content of calcium, phosphate, and fluoride, saliva can possess a reparative effect on early enamel erosion which is characterized by surface softening and slight subsurface mineral loss. The degree of saturation could be calculated with respect to hydroxyapatite by determining the pH, calcium, and phosphate contents of the beverages.