Introduction to Teeth - Dental Biotribology - page 13

It seemed that Wright [ 78 ] published the first paper in Wear about dental wear in
the tribological, or engineering, journal in 1969. Through a radiotracer and a
machine to simulate oral brushing, he studied the wear behavior of dental tissues
under hard and soft abrasives with different sizes of particles and their interrelation-
ship with brush fiber geometry and dentifrice concentration. A critical particle size
effect was observed in relationship to the abrasive wear of dental tissue.
The first review paper on the wear of dental enamel was published by Powers
et al. [ 79 ] in Wear in 1973. Four factors influencing the wear damage were listed:
physiological, pathological, toothbrush use, and dentifrice use. Normal masticatory
function is a physiological process termed “dental attrition” (two-body contact). For
ancient or primitive humans, attrition was often severe due to the abrasive nature of
the food, but this became considerably less for the modern populations due to the
soft diet. Xerostomia and bruxism were the most frequently reported pathologic
causes of wear. Such wear forms may be particularly destructive to individual teeth
or the entire dentition for some patients. Toothbrush and dentifrice use are neces-
sary to maintain a healthy oral environment. Tooth abrasion is unavoidable but can
be limited by avoiding heavy pressure and certain conditions, such as excessive use
of dentifrice. In Powers et al.'s paper, the wear behavior of fluorapatite single crys-
tals and human enamel were investigated in a single pass under different normal
loads, and the authors concluded that fluorapatite was a satisfactory model for pre-
dicting the surface of human teeth.
Changes in the fluoride concentration of human teeth and the effect of tooth wear
on the distribution of fluoride in the enamel surface were studied by Weatherell
et al. [ 80 , 81 ]. They indicated that there were higher fluoride concentrations in the
enamel surface near the biting edge and lower toward the cervical margin for young
teeth, while the inverse was apparent for aged teeth. Wear effects seemed to be con-
sidered a major reason. Bruxism may be considered as the frequent clenching and
grinding of the teeth at times and for purposes other than for the mastication of food.
According to the investigations by Graf and Zander, excessive tooth wear is caused
by bruxism in most cases [ 82 ]. The progress of tooth wear and the change in struc-
ture morphology on individual teeth of bruxist subjects, compared with nonbruxers,
was reported by Xhongda [ 83 ]. Not surprisingly, the main conclusion was that the
tooth wear progressed faster in bruxers than in nonbruxers. In 1985, Carlsson et al.
reported that the continuing wear process was slow after long-term treatment with
occlusal splints through a follow-up study of 18 patients with moderate to several
dental wear by bruxism [ 84 ]. Severe loss of teeth tissue may be observed for brux-
ists, as shown in Fig. 1.8 . The teeth have flattened incisal edges, as the enamel and
the dentin wear at the same rate [ 10 ].
A series of investigations on the loss of hard tissue from the teeth surface were
performed, and an overview on tooth surface loss by abrasion, attrition, and particu-
larly by erosion was published by Eccles et al. [ 42 , 85 , 86 ]. In combination with
some clinical observations, Eccles indicated that abrasion is the result of tooth-
brushing using either a particularly abrasive toothpaste or a normal toothpaste with
heavy pressure; attrition is a physical process where tooth surface is removed
through the movement of teeth against one another, possibly with an abrasive