Temporal Changes in Maxillary Alveolar Profile Angle and Inclination of Incisor in Japan

Abstract

The alveolar profile angle has been measured on skulls of prehistoric and historic populations of Japan by several authors. However, there is still a veil on the trend of the change of this angle specially in the modern times.
The present study approaches this problem by using a X-ray lateral cephalometric technique with the skeletal materials of at least 40 individuals from each period (a total of 470 individuals from 7 periods: Jomon, Yayoi, Kofun, Medieval, Edo, Modern I, and Modern II). Temporal changes of alveolar profile angle and correlations of this angle with other measurements were examined using cephalograms of these skeletal materials. This angle had high within-group correlations with facial height and the inclination of the upper central incisor to the Frankfurt horizontal. An individual having a large profile angle had an up-right position of the upper incisor. The angle being the largest in Jomon people was gradually reduced in the Medieval to Edo period before increasing again up to the present time. Although the inclination of the incisor showed a parallel relationship with the alveolar profile angle up to the Edo period, it did not show a clear increase in modern times. It was concluded that these two angles had a close association in an individual level of a single population. The cause of these changes in craniofacial morphology, especially in Medieval and Edo periods, might not be simple, but this characteristic should be considered along with other physical characteristics such as stature, alveolar prognathism, tooth size, and dental disorders which were previously reported as showing similar trends of temporal changes in Japan. The present study basically support previous studies, but it showed that samples after World War II represented a catch up of this angle, and that some highly correlated items in cranial measurements with this angle such as facial height and incisor inclination were found in almost all the samples in 7 periods.