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The University of Southampton

Research project: Delivery of fluoride and antimicrobial agents into dental plaque biofilms

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Tooth enamel is composed largely of impure calcium hydroxyapatite, Ca10(PO4)6(OH)2, which, like all mineralised tissue, is sensitive to pH variations inside the mouth. If the fluid surrounding the tooth drops below a "critical pH" of 5.5 enamel dissolution (or demineralisation) (Dawes 2003) occurs where the enamel will start to lose minerals.

If the exposure to acid is short the saliva will raise the pH naturally so the enamel loss can be repaired through remineralisation (Stoodley, Wefel et al. 2008). However, if the exposure to acid is prolonged the remineralisation rate may not repair the loss from demineralisation, and this will increase the probability of developing two different pathologies:  dental erosion, which is the irreversible loss of dental hard tissue caused by the prolonged exposure of the enamel to the acids from foods such as fruit juice or commercial soft drinks (Al-Malik, Holt et al. 2001) and, dental decay, in which the dissolution is through acid production by bacteria living inside the dental plaque biofilm. Acidogenic bacteria (i.e. Streptococcus mutans and Lactobacillus) produce lactic acid from fermentable dietary carbohydrates, and therefore create acid microenvironments, which leads to the formation of localized micro cavities (Featherstone 1999).

Routine daily oral hygiene and periodical visits to the dentist can almost completely prevent plaque mediated dental diseases or tooth erosion, especially when this is combined with a reduced frequency of sugar consumption. However, as it is difficult to alter established eating patterns and to maintain a high degree of oral hygiene, alternative preventive measures are being studied and developed. These include the addition of fluoride or antimicrobial agents (i.e. chlorexidine) to toothpastes, mouthwashes and varnishes in order to enhance remineralisation or kill biofilm bacteria. Dental plaque biofilms are a diverse and dynamic community of microorganisms embedded in a strong extracellular polymeric matrix. This complicated structure enhances their resistance to antiplaque agents by limiting the transport of dentifrices inside the biofilm. But, if the anticaries agent is able to enter inside the biofilm plaque, the biofilm itself could act as a reservoir, and thus provide a therapeutic effect by enhancing the remineralisation of the enamel.

Recently, a device (Sonicare® AirFloss) which uses a high-velocity burst of air and water droplets to clean between teeth has been developed by Philips. It is thought that this innovative product could also deliver cleaning agents inside the biofilm either by incorporating fluoride or germicide agents inside microdroplets or simply by fluid dynamic action.

The aim of the present project is to enhance mass transfer of fluoride or antimicrobial agents inside the biofilm by using a micro water drop oral device. The objective is to combine both the delivery of fluoride or antimicrobial agents inside the biofilm with the mechanical removal of dental plaque by fluid shear.

This project is funded by Philips Oral Healthcare and a Faculty of Engineering and the Environment (FEE) Tizard PhD scholarship award.

Related research groups

national Centre for Advanced Tribology at Southampton (nCATS)
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