Introduction to Teeth - Dental Biotribology - page 20

to extinct species [ 113 - 117 ]. Interestingly enough, at the early period of such
research, few studies attempted to link human tooth wear with results from
animals.
At the beginning, two groups of scientists were interested in investigating tooth
wear. One was zoologists, for a better understanding of age determination of ani-
mals via the measurements of teeth and evaluation of tooth wear. The other group
was paleontologists. They wanted to know the food that dinosaurs ate and how their
living environment influenced their diet [ 118 ]. It may be this dual animal interest
that caused the correlation between human tooth wear and animal tooth wear not to
be established at an early stage. However, once attention was turned to human tooth
wear, there was a considerable body of literature already in existence from the
results based on mammals.
Many groups recognized that through wear patterns, the age of a particular ani-
mal could be determined. Knowledge of the ages of individuals is essential to
understand the rate of growth, onset of sexual maturity, fertility peak, senescent
decline and life span, as well as social behavior of animals [ 119 ]. However, extreme
precision in age determination was often more of an academic than a practical inter-
est. Many studies were conducted to summarize wear patterns of known-age ani-
mals and attempted to correlate the trends to unknown-age animals [ 120 ]. Others
did not support the theory and believed that by using wear patterns, age determina-
tion was not reliable [ 121 ]. Instead, cementum layers were used to determine the
ages of coyotes and other species [ 122 , 123 ]. However, Lowe felt that similar to
growth rings in trees, interpreting or counting cementum layers was not convincing
[ 120 ]. It was influenced greatly by environmental factors. The overall agreement of
cementum layers to real ages of red deer was only around 50 %, and the method of
analyzing the wear of teeth had a better correlation to match the real age of animals
[ 120 ]. Debate over whether or not to use cementum layers or tooth wear to deter-
mine the ages of animals had been a hot topic. For various animal groups, conclu-
sions seemed to vary. Linhart et al. and others tried to find a relationship between
tooth wear classes and cementum layers [ 121 ].
Methods of age determination were then divided into two categories: methods
separating age groupings, and methods of determining chronological age of the
groups, such as eruption and replacement of teeth, attrition of the permanent teeth,
cementum line counts, and other methods [ 123 - 125 ]. Wear models have suggested
that in the absence of known-age specimens, age may be determined by the use of
models that approximate to the rates of growth or wear of the teeth. This is a step
forward, which takes wear mechanisms and the structure of animal teeth into
account.
Payne studied sheep and goats [ 126 ] using two parameters, crown height index
( h / d ) (crown height-to-width ratio) and anterior fold index (width to length ratio).
Coding systems were developed to record wear states in the mandibular cheek teeth
of sheep and goats, which could provide useful information about the nutritional
status and stocking rate [ 127 ]. However, the wear state symbols based on the pattern
of exposed dentin have proved to be well suited for field and laboratory use but not
in publication and computer coding at that time.