Most studies of dental microevolution have used the standard
methodologies employed in dental anthropology: buccolingual/mesiodistal
lengths and the frequencies of non-metric dental traits. In this work we
use the occlusal polygon method which is based on a polygon created by
linking the four molar cusp apices using digital analysis. This method
has been used to identify different evolutionary trends in Neandertal
and modern humans; our objective was to assess the existence of changes
in the occlusal polygon area, and thus the general morphology of first
upper molars, between two Portuguese samples from the Late Neolithic
(4130 ± 90 BP) and the early 20th century. This method allows us to
evaluate both tooth size and relative cusp position in the occlusal
plane. Contrary to the accentuated tooth size reduction commonly found
from the past 10000 years using buccolingual/mesiodistal measurements,
no statistically significant change of the total occlusal area of the
crown was observed between these samples. Nevertheless, we report an
increase of 7.45% in the size of the occlusal polygon and hence 9.38% in
its relative area, from 27.30% of the total crown area to 30.30% over
this time span. This result implies that microevolutionary changes among
Portuguese populations led to changes in the positions of the cusps
relative to one another in the first upper molar, whereas the location
of their apices have moved away from the centre of the crown to a more
peripheral position. This apparent increasing trend contrasts with the
one reported in studies of both Neandertals and modern humans.