Biomedical Engineering Reference
In-Depth Information
There has been a worldwide increase in the consumption of soft drinks, fruit
juices, and sport drinks [1, 4, 9]. Exposure of teeth to an acidic oral environment is
becoming commonplace. The mouth environment of a person with a particularly
acidic diet could be acidic with a pH of 3 [4]. The pH values of acidic drinks range
from 1 to 6. Enamel is composed of 92-96 % mineral substances, 1-2 % organic
materials, and 3-4 % water by weight [10]. Most of the mineral substances are
hydroxyapatite. Hence, demineralization caused by the dissolution of hydroxyapa-
tite will occur on the surface of enamel in an acidic oral environment. Mineral loss
of the tooth surface only due to a chemical process of acidic dissolution is widely
called “erosion” in the dental literature, and its meaning is completely different
from that in engineering fi elds [1, 11, 12]. Tooth wear caused by acidic erosion
observed clinically is the combination of the direct substance loss of tooth surface
by demineralization and abrasion of the demineralized surface by surrounding oral
soft tissues, food mastication, and toothbrushing [13]. The tooth wear rate of
patients with clinically evident palatal erosion (median: 6
m/month) was reported
to be ten times of that of people without any evidence of abnormal wear (median:
0.6
μ
m/month) [14].
It has been widely accepted that once acidity in the mouth increases, tooth lesions
will occur whether or not the tooth surface is subjected to friction action [15, 16].
A vast amount of literature is available concerning dental erosion due to its high
prevalence clinically. From the available information, it emerges that these studies
mainly focused on the direct loss of tooth tissues caused by surface demineraliza-
tion in soft drinks or juices without friction or sliding, and the erosive lesions of
human teeth were reported to increase with the acidity of the solution regardless of
whether or not a static or cyclic load was applied to the tooth surface [17-19].
However, research work on the friction and wear behavior of human teeth in acidic
medium is still very limited. Most people usually drink beverages when eating.
Sometimes people even chew acidic foods directly such as fi brous fruits. The
surfaces of teeth, therefore, are usually subjected to simultaneous chemical and
physical actions in the mouth. The wear rate of enamel in an acidic environment was
reported to be higher compared to that under alternating chemical and mechanical
actions [8, 13, 20]. Therefore, studying the interplay of erosion and attrition in tooth
wear is really necessary to reveal the wear mechanism of teeth.
Generally, avoiding erosive foods will adequately prevent tooth wear caused by
erosion. However, it appears that the consumptions of acidic drinks will increase in
the future rather than diminish. This implies that the prevalence of tooth erosion by
acid attack is increasing. Therefore, studies on the repair mechanism and methods
of tooth lesions due to acid attack have been increasingly recognized to be neces-
sary in clinically dealing with tooth erosion [21, 22]. Erosive substance loss of
enamel is a dynamic process with demineralization and remineralization [14].
Remineralization is the process of restoring mineral ions into the hydroxyapatite
latticework structure [
23
]. It has been widely accepted that saliva is a source of
inorganic ions necessary for remineralization because it supplies calcium and phos-
phate ions to build blocks [
24
]. In the mouth, therefore, remineralization is an indis-
pensable phenomenon during the natural healing process of enamel decay. It was
μ
