284 Forensic dentistryGusta fson’s legac y is considerable for t he forensic odontolog ist. But, rat her
than pursuing his collective mix of six dental changes, most researchers have
elaborated on the scientific bases of one or another of these processes. We
revisit some of these topics below.13.4.2 Root Transparency
Beginning with Bodecker,^93 followed by Gustafson^118 and others, several
researchers have described the age-progressive increase in root transparency.
The procedure is destructive in that the tooth has to be extracted, sectioned,
and polished before measurement. Root transparency develops due to pro-
gressive sclerosing of the tubules, first at the root apex, then advancing coro-
na l ly.^119 De Jonge reported that the average width of dentinal tubules is about
3.2 μ in young individuals, narrowing to about 1.5 μ at fifty, and down to 1.2 μ
at seventy years of age.^120 Opaqueness of young dentin is due to differences
in the refractive indexes between the crystalline and the intratubular organic
components. Aging causes the refractive indexes to converge, making the
dentin transparent to transmitted light.^121 Whittaker and Bakri^122 note that
there are diverse opinions as to the cause of the dentin changes; factors caus-
ing deposition of sclerotic dentin seem to be toxins from diseased periodontal
tissues, absence of functional stimuli, and the diminished diameters of the
dentinal tubules due to increased mineralization of the intratubular matrix,
especially at the root apex. Changes may be seen as early as the later teens,
though typically starting in adulthood.^123
Whittaker and Bakri^122 showed that staining with methylene blue in a
partial vacuum significantly enhanced contrast of the sclerotic and nonscle-
rotic root areas. They also suggest that the rate of sclerosis differs among
populations (possibly due to dietary differences), and that the rate may not
be linear throughout adulthood (possibly slowing in older adults). Sognnaes
et al. describe a method of quantifying the sclerotic portion of dentin using
intact teeth.^124
Drusini et al.^125 reported a correlation of 0.84 between the proportion of
transparent dentin and chronological age, which is fairly low. These authors
found that at least 55% of their age estimates deviated by more than five years.
13.4.3 Cementum Annulations
Wildlife biologists have noted that in mammals living in temperate and polar
regions (where climate, activity, and food availability vary seasonally), layers
of cementum are laid down on tooth roots as alternating light and dark bands,
with one layer corresponding to (approximately) one year of life.126,127 Stott
et al. showed that humans also possess these layers (now termed cementum
annulations) and suggested they would be useful for age estimation (adjusting