Beverage parameters

Dental erosion may be caused by extrinsic and intrinsic factors. A major extrinsic cause of dental erosion is thought to be the consumption of acidic beverages (Dugmore and Rock, 2004). The consumption of acidic beverages has risen over the last years. In the USA a 300% increase in soft drink consumption in a period of 20 years has been reported (Cavadini et al., 2000), an increase that probably has not been reduced as the consumption of soft drinks has not reduced since then.

Recently, a summary of the outcomes of the Workshop on Methodology in Ero-sion Research has been published (Shellis et al., 2011). Different aspects to which erosion models should comply are suggested such as the use of bovine or human enamel, the use of standardised polishing procedures and storage of samples, the use of an erosive agent resembling an acidic beverage, the use of a clinically rele-vant pH of the applied erosive agent, agitation during exposure, temperature and duration of erosive challenge. In the studies described in chapter 2 and 3 we al-ready complied partly with the workshop suggestions although these studies were performed far before the outcomes of the workshop were published. For example, we used in these studies bovine enamel as a substrate. The use of bovine enamel is considered acceptable because of its relatively close resemblance to its human counterpart (Zero, 1996). It should be noted, however, that morphological diffe-rences exist between bovine and human enamel, such as a higher porosity of bo-vine enamel (Featherstone and Mellberg, 1981). Fortunately, Meurman and Frank (1991) did not observe any difference in the progression of erosion or the surface ultrastructure of erosive lesions between bovine and human enamel, making bo-vine enamel a sound alternative to human enamel, thereby surpassing the inherent ethical and other problems that arise when using human material. Furthermore, it should be noted that in our studies with bovine enamel, a comparison between the measurement methods and beverages was performed and not an extrapola-tion of the results to the clinical situaextrapola-tion.

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General discussion & future perspectives

A major limitation of the studies described in chapters 2 and 3 was the absence of saliva during the erosive challenge. The presence of saliva allows for dilution and buffering of the acids. Moreover, the presence of a salivary pellicle can reduce acid diffusion to the enamel (O’Sullivan and Curzon, 2000; Hannig and Balz, 1999). This limitation raises questions with respect to the external validity of the performed experiments. It can be expected that in the clinical situation the loss of enamel will probably be less than the extent of hard tissue loss that was reported in chapters 2 and 3 as usually saliva is present in the mouth of an individual. A possible solution for this caveat could be the use of (artificial) saliva prior to applying the erosive challenge.

In chapter 3 of this thesis we have described that the pH of a beverage is more closely related to the loss of enamel after exposure to an acidic beverage than any of the other studied parameters (calcium and phosphorus concentration, sa-turation (DSHA), titratable acidity (TA) to pH 5.5, fluoride concentration, viscosity of the beverage and the interaction terms between pH and calcium concentration and titratable acidity and pH). The results of the experiments reported in chapter 3 confirm the results of other studies, viz. that the pH of an acidic beverage is the main indication for their erosive potential (Grobler and van der Horst, 1982; Larsen and Nyvad, 1999; Larsen and Richards, 2001).

In a number of studies it has been suggested to modify acidic beverages chemi-cally to reduce the erosive potential (Grenby, 1996, Hughes et al., 1999; Jensdottir et al., 2005). Modifications of drinks by addition of calcium have been shown to reduce its erosive potential (Barbour et al., 2011). A drawback of the addition of calcium is the relatively high concentration (5 - 10 mmol/l) that is needed to reduce the erosive potential (Barbour et al., 2011). The addition of high concentrations of calcium is accompanied by an unpleasant metallic taste (Jensdottir et al., 2005).

Moreover, the effect of the addition of calcium on reducing the erosive potential of a beverage was shown to be higher in drinks with pH values above 4.0 (Jensdot-tir et al., 2005). As such, the modification of very acidic beverages requires high concentrations of calcium with a negative effect on its taste. In literature, it is also suggested that the addition of phosphate to a beverage might reduce its erosive potential (McDonald and Stookey, 1973; Attin et al., 2003). However, in contrast to the latter studies, Hemingway et al (2006) and Barbour et al (2011) failed to show a relationship between erosive potential and phosphorus concentration. Further-more, it has been suggested that calcium / phosphate ratios may influence the ero-sive potential of an agent independent of saturation levels (Barbour et al., 2003).

Our volume of data did not allow for assessing this potential relationship, therefore we were not able to evaluate an interaction between phosphate, calcium and pH or between calcium and phosphate. Further research should take this interaction into account.

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Chapter 8

In a recent published longitudinal study assessing factors associated to erosive wear, no positive significant association was found between erosive wear and consump-tion of acidic beverages (El Aidi et al., 2011). A comparable result was also reported in some other studies (Bartlett et al., 1998; van Rijkom et al., 2002; Milosevic et al., 2004). In contrast with the above-mentioned results, numerous other studies have reported an association between erosive wear and the consumption of acidic be-verages (e.g. O’Sulllivan and Curzon, 2000; Lussi and Schaffner, 2000; Dugmore and Rock, 2004; Bardolia et al., 2010). The difference between the longitudinal study by Bardolia et al. (2010), where a positive association was found between beverage consumption and erosion, and the study by El Aidi et al (2011) could be explained by the much higher average consumption of beverages in the study by Bardolia et al (2010). This somewhat contradictory information illustrates that soft-drinks and acidic beverages are only one factor in the development of erosion and not the explanation whether erosion will occur or not. In other words, in the susceptibility of individuals to dental erosion a variety of individual biological and behavioural factors are involved, as was also mentioned in chapter 1. Therefore, it should be suggested that the biological factors and behavioural factors play an important role, next to the beverage parameters, in explaining and preventing the susceptibility of a particular subject to dental erosion. Especially behavioural factors such as drinking habits may play an important role whether dental erosion will occur in individuals, as well as to which extent. Unusual eating and drinking methods, as well as swal-lowing habits that increase the direct contact time of acidic foods and beverages with the teeth, are factors that will increase the risk of dental erosion. In addition, the manner that dietary acids are introduced in the mouth (gulping, sipping, use of a straw) will affect the clearance pattern by saliva and which teeth are in contact with the erosive product (Zero and Lussi, 2006). The use of the measurement of erosive potential (chapter 3) has its value, but the results obtained should be interpreted with caution and should be considered as a limited source of information about the erosive potential of soft drinks and beverages. In vivo these in vitro obtained results will be modified by behavioural and biological factors. Therefore, for future research it is recommended to test the erosive potential of drinks in vivo. To facilitate such research, special dentures for edentulous volunteers containing enamel samples could be designed. In this way it will become possible to expose enamel samples to the acidic beverages in vivo without causing unwanted or unexpected damage to the natural dentition of the volunteer similarly to studies assessing the result of the effect of exposure of enamel to a dry oral environment. A model used by Jansma et al (1988) to investigate xerostomia-related dental caries could be modified for use in erosion research. By inclusion of biological factors such as saliva and salivary pel-licle in the above mentioned model it becomes interesting to know which individual components of saliva and salivary pellicle influence the development of erosion.

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General discussion & future perspectives