Introduction to Teeth - Dental Biotribology - page 21

Based on Payne and other people's work, Brown developed a scoring system for
fallow deer [ 128 ]. The linear regression of age on total molar scores gives the pre-
dicted age, together with the 95 % prediction interval associated with any particular
score. He believed that the data can be used to make an assessment of the age of an
animal of unknown age. The scoring system was based on wear patterns. A score
was given to wear location on individual molars. An age prediction equation was
summarized based on abundant data:

( )

2

Predictedage = 0 0035 . × score . (1.1)

However, the scoring system and the age prediction equation could not quantita-
tively reflect tooth wear. They could only provide the age prediction by means of the
state of wear. Before considering methods of age determination by means of tooth
changes, it is necessary to consider tooth growth, structure, and function and to
understand the use of these characteristics in age determination. Without an insight-
ful view of the structure of tooth and mechanisms of tooth wear, simply using sta-
tistical methods to correlate wear patterns is very challenging. The application and
development of scanning electron microscopy and other surface analysis instru-
ments provided powerful tools to study the microstructure of animal teeth.
Tooth tribology first appeared in Spinage's paper in 1973, which was only a few
years after “tribology” was introduced in 1966 by the British Committee for the
Science of Wear, Lubrication, and Friction [ 119 ]. Studies developed from age deter-
mination to study the structure of teeth. Every and Kuhne suggest that attrition results
from two processes: abrasion and thegosis, or sharpening [ 129 ]. Abrasion begins
from the contact of the tooth with food. The food forms a loose, abrasive medium.
The enzymes and acids released during mastication have an insignificant effect upon
the erosion of sheep's' teeth, mechanical wear being the most important factor.
Severinghaus [ 130 ] provided a detailed study to correlate tooth development and
wear with the age of white-tailed deer. It was found that the height of molars reached
a maximum value within 100 weeks and then decreased with age. Walker [ 131 ]
studied a few groups of monkeys and found that wear striations on primate teeth
were potentially the result from (1) movement of the jaw while the teeth are indirect
contact with each other, (2) movement of the jaw while food or some other sub-
stance is interposed between the teeth, and (3) food or other materials being pulled
or pushed across the teeth by movements of the hand and head. The study could be
used to determine the diet and habitat of different groups of monkeys. Skogland
[ 132 ] conducted an interesting study and concluded that food limitations induced
the overgrazing of winter food supplies, causing rapid tooth wear. As a consequence,
the body condition of females with a lower food availability starts to deteriorate.
Associated effects are reduced neonatal growth rates, leading to a smaller adult
body size. Food-limited reindeer expand their winter diet to include less profitable
items, which increase the rate of tooth wear and reduce lifetime reproduction, lead-
ing to a smaller adult body size. This food-limitation syndrome should provide
important lessons and insight for the understanding of the life history of other
mammals.