Nanomechanics and morphology of salivary pellicle
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Acquired salivary pellicle is a thin protein-rich film formed by the adsorption of saliva onto teeth. It plays important roles in lubrication during mastication and protecting the teeth from chemical attack. Pellicle can become colonized by bacteria to form dental plaque which can lead to dental caries if the bacteria are acidogenic. Abrasive polishing with a dentrifice is used periodically to remove the pellicle from teeth. Pellicle can interact with dietary polyphenolic compounds (tannins) to create extrinsic stains on the tooth surface. The staining can modify the pellicle’s mechanical properties and change its morphology resulting in a “squeaky” feeling when the tongue is rubbed over the teeth. Atomic force microscopy imaging and nanoscale mechanical measurements show that unstained pellicle has a dense undulating morphology and is a surprisingly stiff, viscoelastic solid. In contrast, tannin-stained pellicle has fewer but larger surface undulations and exhibits substantial viscous creep.
I. INTRODUCTION
The oral cavity is a complex chemo-mechanical environment where abrupt changes in pH and temperature are combined with repetitive mechanical loading during mastication to give extremely hostile conditions. Yet, remarkably, dental enamel can survive for 70 years or more in these conditions. One reason for this is the presence of a thin protein-rich layer, called the acquired salivary pellicle, on the enamel’s surface. Pellicle is believed to act as a lubricant during mastication and as a diffusion barrier that impedes chemical attack of the enamel.1 Pellicle forms by adsorption of salivary proteins and carbohydrates onto the enamel surface. Over time it can become colonized by bacteria and develop into dental plaque, which can be very detrimental to the teeth if the bacteria are acidogenic. To reduce the risk of colonization by bacteria the pellicle layer is partially or fully removed by abrasive cleaning with a dentrifice and toothbrush several times each day. In the oral cavity, the acquired salivary pellicle begins growing on clean surfaces (natural teeth and restorations) within minutes of exposure to saliva. Over time it thickens,2 to about 1 m and takes on an undulating a)
Present address: Hysitron, Inc., Minneapolis, MN 55344. Address all correspondence to this author. e-mail: [email protected] This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http:// www.mrs.org/publications/jmr/policy.html. DOI: 10.1557/JMR.2006.0248 b)
1996 J. Mater. Res., Vol. 21, No. 8, Aug 2006 http://journals.cambridge.org Downloaded: 01 Apr 2015
morphology that can be examined with atomic force microscopy (AFM).3 Chemical reactions involving food or drink with the acquired salivary pellicle can lead to extrinsic stains on teeth.4 Typically, a yellow-brown to dark red discoloration of the pellicle5 is caused by polyphenolic compounds, commonly called tannins, which are found in tea, red wine,
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