Polyols and remineralisation of enamel subsurface lesions
Introduction
Sugar-free chewing gums containing polyols have been demonstrated to reduce caries experience when compared with no gum chewing in randomised clinical trials [1], [2], [3], [4]. The anticariogenic effect of chewing the sugar-free gum has been attributed to the stimulation of saliva [4], [5]. Recently the anticariogenic efficacy of sugar-free gum has been enhanced by the addition of the salivary biomimetic casein phosphopeptide amorphous calcium phosphate (CPP-ACP) which significantly increases the buffering and remineralisation capacity of saliva by providing bioavailable calcium and phosphate ions stabilised by the CPP [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]. In a randomised controlled clinical trial a sugar-free chewing containing CPP-ACP with a sorbitol-mannitol (polyol) blend was significantly better than a control chewing gum containing only the polyols in slowing the progression of dental caries and enhancing regression of early lesions in children [10]. Enhanced remineralisation of enamel demineralised lesions and an increase in salivary calcium levels by sugar-free chewing gum containing CPP-ACP have been demonstrated in a number of other clinical studies [6], [7], [8], [9], [11], [13], [14], [15], [17], [18].
Sugar-free chewing gum with or without CPP-ACP may be formulated using different combinations of sugar alcohols (polyols) such as xylitol, sorbitol, mannitol and maltitol [5]. The polyols act as both binding and sweetening agents in sugar-free gums and are all considered non-cariogenic as they are poorly fermented by oral bacteria [5], [19]. The most common polyols used in sugar-free gums are xylitol and sorbitol although more recently blends of polyols are being used to provide certain taste characteristics [2], [5], [9], [20].
Makinen and Soderling [21] have suggested that sorbitol and xylitol at very high concentrations in a saturated calcium sulphate solution form Ca2+-polyol complexes through the formation of cis-cis-triol coordination complexes. Based on these findings the authors proposed that these polyols may influence calcium bioavailability in saliva and thereby may directly promote remineralisation of enamel subsurface lesions. Similarly, in an in vitro enamel lesion remineralisation study Miake et al. [22] suggested that a remineralisation solution containing 20% w/w xylitol produced less remineralisation in the outer layers of the lesion but greater remineralisation in the deeper layers compared with the solution without xylitol. The authors proposed that xylitol could influence remineralisation of deeper layers of demineralised enamel by facilitating Ca2+ movement into the lesion.
These results taken together suggest that the use of different polyols may effect the amount or pattern of remineralisation of enamel subsurface lesions by saliva or saliva/CPP-ACP. However, data from clinical studies suggested that chewing sugar-free gum containing CPP-ACP with either xylitol or sorbitol resulted in comparable remineralisation of enamel subsurface lesions [13], suggesting that, at physiologically relevant salivary concentrations of the polyols, no measurable difference in remineralisation could be detected. These inconsistent findings suggest further research is required to clarify the direct effect of polyols on enamel subsurface remineralisation. To date, no study has directly compared the remineralisation efficacy of saliva or saliva/CPP-ACP in the presence of the four commonly used polyols (xylitol, mannitol, sorbitol or maltitol) at physiologically relevant concentrations released by normal use of commercially available sugar-free chewing gum containing high levels of the polyols. Therefore, the hypothesis to be tested in this current in vitro study was that artificial saliva (AS), or AS/CPP-ACP, with and without xylitol, sorbitol, maltitol or mannitol at physiologically relevant concentrations were statistically equivalent with respect to their ability to remineralise enamel subsurface lesions.
Section snippets
Enamel subsurface lesion preparation
Extracted human third molars were obtained from the Melbourne Dental School, The University of Melbourne after informed patient consent. The study was approved by the University of Melbourne’s Human Research Ethics Committee (number 1136929). The teeth were first washed thoroughly in distilled deionised water (DDW) then sterilised with 4.1 kGy of gamma radiation. After sterilisation, any soft tissues were removed from the teeth and sound relatively planar buccal and lingual surfaces free of
Results
The effect of the four polyols (xylitol, sorbitol, maltitol and mannitol) on remineralisation of enamel subsurface lesions by AS is shown in Table 1. There was no significant difference in size (ΔZd and Ld) of the demineralised lesions before remineralisation and there was no significant difference in the level of mineral gain (ΔZd−ΔZr) between any of the polyol/AS solutions compared with the AS alone (Table 1). Furthermore, all the polyols were equivalent with respect to the level of
Discussion
This controlled in vitro study showed that polyols at the maximum physiologically relevant concentration (12.6% w/v) related to that released into saliva by chewing sugar-free gum did not promote remineralisation of enamel subsurface lesions by artificial saliva or by artificial saliva containing the salivary biomimetic CPP-ACP. The polyols studied were xylitol, sorbitol, maltitol and mannitol; the common polyols used in commercially available sugar-free chewing gums. Hence the results of the
Conclusions
In conclusion, this controlled in vitro investigation suggested that polyols (xylitol, sorbitol, maltitol and mannitol) at physiologically relevant concentrations released into saliva upon gum chewing do not promote remineralisation of enamel subsurface lesions by forming Ca2+-polyol complexes and facilitating calcium uptake into the lesion.
Clinical significance statement
The results of this study suggest that polyols do not promote remineralisation of enamel subsurface lesions by forming Ca2+-polyol complexes under physiologically relevant conditions.
Declaration of interests
The authors declare that they have no conflict of interest.
Acknowledgement
This work was supported by the Australian Government, Department of Industry, Innovation and Science.
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