In an earlier study, common soft drinks were evaluated for erosivity using the same method as in the present study. It was demonstrated that the gravimetric method was appropriate to detect differences in erosivity [13]. Soft drinks, which had shown high erosivity, were included in the present trial. This was done with the purpose to find a possibility to reduce the erosivity of such drinks and consequently to reduce tooth erosion. It was not the aim of the study to generate data that can directly be transferred to the in-vivo-situation, but they should allow a ranking for erosivity of common soft drinks in relation to the non-erosive tap water. To realize this aim, the tooth specimens were subjected to highly erosive conditions.
Calcium hydrogen phosphate dihydrate (DCPD, Brushit, Ca[PO3(OH)]·2H2O) was chosen as an agent because it is soluble at low pH-values of 4 and under and provides calcium- and phosphate-ions which are able constrain the solubility of hydroxyapatite (Ca10 (PO4)6OH2), the anorganic component of dental hard tissue. Concentrations of 100 or 200 mg/150 ml calcium phosphate were chosen to ensure effectiveness and safety for consumers. According to the Scientific committee of the European Food Safety Authority (EFSA) a group acceptable daily intake (ADI) for phosphates expressed as phosphorus is 40 mg/kg body weight per day: This ADI is regarded as protective for the human population. [14]
That means that for DCPD the ADI is 222 mg/kg bodyweight. In the present study, already 100 mg/150 ml resulted in a considerably reduced erosivity of the soft drinks. If assuming that 1,500 ml soft drink consumption/day can be seen as an upper limit when no abuse is present, this would result in a daily intake of 1,000 mg DCPD/per day. The ADI for DCPD for an adult with 75 kg bodyweight would be 16,650 mg (75 × 222 mg).
In comparison to the data from our earlier study [13], the erosivity of Cola was reduced by 97% for enamel (from 7.45 mg to 0.25 mg) and by 92% (from 6.45 mg to 0.55 mg) for dentine when 100 mg DCPD/150 ml were added. The respective values for orange juice were 90% (enamel, from 23.85 mg to 2,35 mg) and 37% (dentine, from 19.40 mg to 12.30 mg), for Red Bull 95% (enamel, from 16.05 mg to 0.80 mg) and 38% (dentine, from 16.85 mg to 10.55 mg), and for Bonaqua Fruits 100% (enamel, from 17,95 mg to -0.60 mg) and 93% (dentine, from 16.60 mg to 1.20 mg). For Cola and Bonaqua Fruits, non-erosivity on enamel and dentine could be reached by the addition of 100 mg/150 DCPD when compared to tap water. For Red Bull, this could be reached when 200 mg DCPD/150 ml were added. Even with this addition, orange juice remained erosive on dentine, but not on enamel. However, the erosivity on dentine was reduced by 73% (from 19.4 mg to 5.30 mg) in this case.
DCPD may not be the only calcium phosphate which is able to reduce erosivity when added to soft drinks. Barbosa et al. could abolish the erosivity of Coca-Cola on bovine enamel by adding 5 mM calcium glycerophosphate (CaGP). This corresponds to 157,60 mg CaGP/150 ml and to 23,24 mg phosphorus/150 ml. In the present study, the addition of 100 mg DCPD including 18 mg phosphorus/150 ml resulted in a non-erosivity for Coca Cola. This seems to show a slight advantage for DCPD. However, the method to detect erosivity was different and therefore the results may not be comparable [15].
Jensdottir et al. added 8 g calcium tri-phosphate to 1 l pure orange juice. As a result, the critical pH for demineralization was reduced from 5.27 to 4.24. The 8 g calcium tri-phosphate corresponds to 315.6 mg phosphorus/150 ml. Coming back to the assumed 1,500 ml soft drink consumption per day, the resulting 3,156 mg phosphorus still seem tolerable.
Another research group tested metallic ions as additives to soft drinks to prevent erosions. [16, 17] They found that ferrous sulfate (human teeth, in situ) as well as combinations of copper, magnesium, manganese, or zinc (bovine tooth powder, in vitro) also show some potential to reduce the erosvity on enamel and dentine. A 7–27% reduction of the dissolution capacity on enamel of two soft drinks was found. [16, 17]
To stop the problem of erosion, several authors looked into application of agents with remineralizing potential after substance loss had already occurred. [18, 19] [20] Bertoldi et al. applied casein phosphopeptide-amorphous calcium phosphate for seven days to eroded extracted teeth and detected partial remineralization. However, the agent was applied for seven days and no further exposure to the erosive agents took place during this time, which is not what happens in real life with its continuous and intermittent exposure to the acidic beverages. [19] Lechner et al. studied remineralization after erosion by beverages with a 90 min exposure to a paste containing calcium and phosphate ions. The results were also an indicator for possible remineralization, however, it might not be practicable on a routine basis, i.e. to alternate drinking and remineralization with every intake of an erosive agent. [20] In summary the attempts to rebuilt enamel or dentine after erosion are inconclusive and it is not clear whether they are of clinical relevance. From a preventive viewpoint, it would be preferable to add a substance to the beverages which avoids erosion in the first place. Therefore, the aim of the present study was to determine whether an addition of calcium phosphate to the erosive beverages would lead to less loss of hard tissue.
To analyze the erosivity, specimens from bovine teeth were used in the present study. The reason, why bovine teeth were used instead of human once, was discussed earlier [13]. It has been shown for erosion studies, that bovine teeth are an equivalent substitute to human teeth [21]. The specimens of the present study had the same diameter of 5 mm and thickness of 1 mm and therefore the same surface (55.0 mm²) resulting in the same exposure to the tested liquids. This makes the results comparable to the results from the earlier study [13].
This study wanted to examine, whether an addition of calcium phosphate to erosive drinks would prohibit erosion in teeth. This could be confirmed under the conditions of this experiment.