Asian Journal of Paleopathology Vol.2, 9–20, 2018
Received: September 27, 2017
Accepted: January 28, 2018
DOI: 10.32247/ajp2018.2.2

Original Article
Effects of ritual tooth extraction on development of mandibular torus in Jomon people of Japan

Shota Kataoka, Masanori Iwasaki, Toru Takahashi, Miho Tsuruta, Satoko Kakuta, Inho Soh,
Toshihiro Ansai

Abstract
　A mandibular torus is an intraoral bony outgrowth that occurs on the lingual surface of the mandible, which may be the result of para-functional disease. Although various causes have been proposed, unified consensus has yet to be obtained. The aim of this study was to examine how occlusal changes caused from loss of the upper canine by ritual tooth extraction (Rt-Ext) had effects on mandibular torus development in skulls dating from the end/last of the Jomon period in Japan. Gender, Rt-Ext, remaining teeth, mandibular torus size and position, and attrition were evaluated, and relationships among those factors were determined using a Bayesian network method. Evidence of Rt-Ext was seen in 68.1% of the examined specimens and a mandibular torus occurred in 59.4%. The results of Bayesian network analyses suggested that Rt-Ext had effects on “posterior mandibular torus size” and “attrition”, while “posterior mandibular torus size” had an effect on “anterior mandibular torus size”. We considered that those effects were related to occlusal interference of lateral movements of the jaw in molar areas by decreased anterior guidance following Rt-Ext of the upper canine. In addition, posterior mandibular torus size was affected by gender. Differences in occlusal force and gender-related activities were also considered to be contributing factors.

Key words
Mandibular torus, ritual tooth extraction, Jomon, parafunction-related factors, Bayesian network