Biomedical Engineering Reference
In-Depth Information
caused by toothbrushing. Traditionally, studies on toothbrushing were conducted
in vitro by using various wear simulators, while more recently, in situ methods have
frequently been used [
52
]. Although toothbrushes alone or combined with tooth-
paste have been proposed to cause tooth wear, abrasion of gingival tissues, and
gingival recession and also be involved in the etiology of dentin hypersensitivity
[
51
], the toothbrush alone appears to have no obvious effect on the wear of enamel
and very little on dentin [
56
]. Most, but not all, toothpastes have a low relative
enamel abrasivity value, are implicated to have a minimal effect on enamel, and in
normal use would not cause signifi cant wear of dentin in a lifetime of use [
51
].
However, it should be noted that dentin is considerably more susceptible than
enamel to abrasion caused by toothpaste abrasivity, and dentin loss appears to cor-
relate with toothpaste abrasivity [
55
]. The overuse or abuse of toothbrushing with
toothpaste would only be relevant to dentin, and not enamel wear unless toothpastes
with a high relative enamel abrasivity value were in use; as stated, those are unusual
[
51
]. Therefore, toothpaste with a lower abrasivity might be advisable for the daily
oral hygiene practice of patients with excessive tooth wear.
Wear of enamel and dentin can be dramatically increased if toothbrushing fol-
lows an erosive challenge [
51
], which may result in noncarious cervical lesions
[
57
]. Attin et al. suggested that for protection of dentin surfaces, at least 30 min
should elapse before toothbrushing after an erosive attack [
58
]. It is interesting to
note that a recent study by Hooper et al. showed that toothbrushing with fl uoride
toothpaste containing sodium hexametaphosphate before meals could provide sig-
nifi cant erosive protection in susceptible individuals [
59
].
3.7
Concluding Remarks
This chapter describes the in vitro friction and wear tests we performed on different
locations of human teeth to explore the effect of the tooth microstructure. We inves-
tigated the wear process and mechanism of enamel in detail. Moreover, we also
studied the effect of age on the tribological behavior of human teeth. Finally, we
reviewed pathological factors and toothbrushing. Based on the given test condi-
tions, the main conclusions can be summarized as follows:
1. Microhardness and tribological properties differ remarkably between layers in a
permanent tooth. A higher microhardness, lower friction coeffi cient, and better
wear resistance are observed in the enamel zone than in the dentin, which appears
both on the occlusal section and on the axial section. Furthermore, friction and
wear behaviors of an individual tooth depend strongly on microstructural orien-
tations. A tooth shows better wear resistance along the occlusal section than
along the axial section due to the orientation of the enamel rods and the dentinal
tubule.
2. The wear of human tooth enamel changes gradually from two-body wear into
three-body wear, with plastic delamination occurring on the enamel surface
