Clinical Evaluation and Laboratory Wear- Testing Methods - Dental Biotribology - page 36

detrimental oral habits [ 8 , 12 ], which generally include chewing tobacco; biting on
hard objects such as pens, pencils, or pipe stems; opening hairpins with teeth; and
biting fi ngernails. In addition, occupational habits may result in the wear of teeth
and restorations. For instance, tailors or seamstresses sever thread with their teeth,
shoemakers and upholsterers hold nails between their teeth, glassblowers and
musicians play wind instruments, and so on.
It was pointed out in Chapter 1 that in normal use, the benefi ts of toothbrushing
far outweigh the potential harm; however, wear can occur as a result of overzealous
toothbrushing and the improper use of dental fl oss and toothpicks. Scaling and
cleaning have been shown to result in minor wear of teeth. Dental treatments usu-
ally involve such processes as cutting, fi nishing, and polishing; and they cause the
wear of teeth and restorations to some extent [ 7 ]. The actual wear situation in the
mouth may vary considerably because of different substrates, opposing wear sur-
faces, lubrication systems involved, and third-party abrasives [ 13 ]. The mouth pro-
vides an extremely complex tribological system. Therefore, the wear of teeth and
restorations is multifactorial in the mouth and dependent on physical and chemical
conditions [ 14 ]. It has long been recognized that it is diffi cult to ascribe many indi-
vidual cases to any one category [ 9 ].

2.2.2 Wear Location

Wear of teeth and restorations occurs mainly at sites of occlusal surfaces and incisal
surfaces during mastication, thegosis, and bruxism. Masticatory wear also can occur
on the lingual and buccal aspects of teeth, as coarse food is forced against these
surfaces by the tongue, lips, and cheeks during mastication. Prophylactic wear,
which is caused by toothbrushing, scaling, cleaning, etc., can occur on the buccal,
lingual, occlusal, and approximal aspects of teeth. It was reported that the occlusal
surface showed the greatest wear, and the cervical, lingual, and buccal showed the
least, respectively [ 15 ]. Notable is that the approximal wear at sites of proximal
contacts is often forgotten [ 16 ]. Regarding the tooth position, the fi rst molar showed
the greatest degree of wear, while the canine and premolar showed the least, respec-
tively. As for the tooth location, mandibular occlusal surfaces showed greater wear
than maxillary occlusal surfaces in all age groups [ 17 ].
A vast amount of literature is available concerning the occlusal wear of dental
materials. Most studies made a distinction between occlusal contact area (OCA) and
contact-free occlusal area (CFOA) wear [ 18 ]. The occlusal contact area is the region
where opposing materials contact directly (including tooth-tooth, tooth-restoration,
and restoration-restoration). It usually represents the region where two-body wear
can occur. Contact-free occlusal area is the region where only three-body wear
occurs, caused by food particles, toothpaste, and other physical objects. In addition,
for dental implants, fretting can occur at the interface between the implant and alve-
olar bone during occlusal movements [ 19 , 20 ]. Fretting has been regarded as one of
the causes of dental implant failure, which can result in implants' loosening.