age estimation from oral and dental structures 271Mandibular m2 is less developed, with the individual cusp tips mineral-
ized and some enamel bridging across the cusps, but the overall occlusal
table is incomplete. Root growth progresses throughout the first year of
life, completing for the incisors at about 1½ years of age, but not until about
3¼ years for the canines.
Problems with the use of formation stages are (1) there are few distin-
guishable grades and (2) there are “gaps” between one stage and the next.
And yet, it is evident that crown-root mineralization is a continuous, seam-
less process. Liversidge et al.^56 suggest that finer age discrimination can be
obtained by measuring tooth length and estimating age at death from pre-
dictive equations that they developed from regressing tooth length on age.
Liversidge and coworkers provide predictive equations for the deciduous
(and some permanent) teeth. Their data show that, between birth and about
five years of age, tooth length increases on the order of 0.6 to 0.9 mm per
year. They studied the eighteenth- and nineteenth-century internments of
known age from Christ Church, London. The method shows promise of pro-
viding finer age estimation^57 than when using ordinally spaced morphologi-
cal grades. Liversidge and Molleson^58 showed that the method can be applied
to radiographs of the teeth, so extracted elements are unnecessary.
13.3.2 Permanent Tooth Formation
While tooth mineralization is a seamless developmental process, it can
be partitioned into visually distinguishable stages or grades.^59 These arti-
ficial ordinal grades allow the researcher to visually identify the extent of
crown-root development based on morphological features (so measure-
ment and concerns about magnification are irrelevant). Several researchers
have devised ordinal schemes for gauging tooth formation. Some are more
elaborate than others.28,60,61 The competing issues are that (1) there should be
as many grades as possible so the extent of tooth formation can be gauged
precisely, but (2) stages that are too close together create ambiguities and
misclassifi cations between them. Currently, the two most popular grading
schemes are those of Moorrees et al.,^28 with thirteen grades for single-rooted
teeth and fourteen for multirooted teeth (Figure 13.3), and Demirjian’s
method,^62 which uses just eight grades (Figure 13.4).
An important convention when using these schemes is that the exam-
iner should score the highest grade that has been attained (Moorrees, per-
sonal communication), because this improves repeatability. If a tooth’s
morphology places it between two grades, one should pick the higher grade
actually achieved, not the “closer” grade, nor should one try to interpolate
between grades.