Erosion is defined as chemical wear as the result of
extrinsic or intrinsic acid or chelators acting on plaque-free
tooth surfaces [102]. Erosion starts by softening of the
surface and is followed by continuous layer-by-layer disso-
lution leading to permanent loss of tooth volume with soft-
ened layer at the surface of the remaining tissue. There are
extrinsic and intrinsic causes of erosion. Extrinsic factors are
not only mainly acidic food and beverages but also medi-
cines and oral hygiene products [120]. Intrinsic erosion is
caused by gastric juices, possibly caused by, for example,
reflux disease, eating disorders, chronic alcoholism and
pregnancy. However, different biological, chemical and
behavioural factors modify the effect of acidic agents on
enamel [121]. In a hitherto unpublished study, the authors
demonstrated that saliva, from patients without erosion,
exhibited a protective effect compared to saliva from indi-
viduals with severe erosion. This may be one reason why
some individuals exhibit less erosion than others even if
they are exposed to exactly the same acid challenge in the
diet. Erosive tooth wear is not caused solely by acid
challenge and chelating agents themselves. In vitro studies
show that a few micrometres of tissue is lost due to the
influence of an erosive challenge (once the surface is soft-
ened, it might be easily abraded by oral soft tissues), tooth-
brushing with dentifrices or coarse food stuff [120, 122].
Potential routes for deep acid penetration into the dentin are
afforded by the dentin tubules where clearance and salivary
buffering are less effective. The collagen layer is largely
unaffected by dietary erosion and forms a mat of fibrils as
the mineralized matrix dissolves, although abrasive influen-
ces will probably result in change. The relevance and clin-
ical implications of this layer have yet to be fully understood
in the erosion/abrasion wear of dentin [123, 124].