Biomedical Engineering Reference
In-Depth Information
Chapter 4
Effect of the Oral Environment
on the Tribological Behavior of Human Teeth
4.1
Introduction
Tooth wear is a complex multifactorial phenomenon involving chemical, physical,
and mechanical processes [1]. The oral environment plays an extremely important
role in the tribological behavior of both human teeth and artifi cial teeth.
Saliva is the most important component of the chemistry of human mouth. All
solid substrata as well as mucosa membranes exposed to the oral environment are
covered by a layer of absorbed salivary proteins, the acquired pellicle [2], whose
formation starts within seconds on any solid surface exposed to the oral environ-
ment. The physiological role of saliva in the oral cavity is manifold. An important
function of saliva is to form a boundary lubrication system and serve as a lubricant
between hard (enamel) and soft (mucosal) tissues [3] to help decrease the wear of
teeth and reduce the friction of oral mucosa and tongue surfaces to prevent those
lesions, and make swallowing easier, which is of crucial importance to maintain
functions such as mastication, deglutition, and the faculty of speech. In general,
saliva has a pH of 7 (neutral); however, corrosive agents such as acids can be intro-
duced into the mouth [4]. Therefore, another role of saliva is thought to involve both
the protection of tooth surfaces against acid attack because it is a buffer to acids
produced in plaque and the provision of a matrix for remineralization [5, 6] because
it supplies calcium and phosphate ions to remineralize enamel.
Apart from the saliva, the tribological behavior of human teeth is also closely
associated with food particles and occlusal load. Mass [7] carried out compression
tests to investigate the microscopic wear features on the occlusal surfaces of teeth
caused by food particles. The results showed that large particles produced fewer,
larger wear features than the small particles, and the total wear area increased with
particle size. Interestingly, wear seemed to be independent of load. But Eisenburger
and Addy found that load signifi cantly infl uenced enamel wear by attrition both in
acidic and neutral conditions [8]. Although such studies have taken the effects of
food particles and normal load on tooth wear into account, they focused simply on
the wear loss, rather than investigating the wear mechanism in detail.
