The influence of the tooth to denture base discrepancy on cervical dental caries

Abstract

Coinciding with the progress of human civilization, the incidence of dental caries has increased because of oral pollution, while human dentition shows a tendency towards reduction. Especially, since the historic ages the rate of reduction of facial bones and teeth has become inconsistant and because of rapid changes in human food and eating behavior, the discrepancy between them has become greater and greater as these periods have progressed. Thus through this phenomenon, the erupting time of teeth is prolonged, and the self cleansing action through mastication is decreased. This is considered to be one of the major factors causing an increase in the incidence of dental caries.
From this point of view, I and my colleague have conducted many kinds of investigations incorporating evidence from the present era and evidence from Japanese skeletal remains. But because of variation in the kinds of dental caries, and the different effects caused by oral pollution and the tooth to denture base discrepancy, conclusive proof of significant correlations between the incidence of dental caries and the discrepancy has not been obtained yet. Because of this, this paper considers cervical dental caries as opposed to other dental caries because it has the simplest symptoms and seems to be the most closely related to the tooth to denture base discrepancy, and tries to draw general conclusions about the effect of the tooth to denture base discrepancy on cervical dental caries.
In accordance with this thesis, the following four investigations have been conducted: 1. Observation of the decalcification of cervical enamel in the extracted teeth of young people. One hundred and seventy extracted teeth, which were extracted in the process of orthodontic treatment for young people with a large tooth to denture base discrepancy, were examined. The decalcification of cervical enamels and its rate, position, and degree were examined. Decalcification was observed in 96.5% of the extracted teeth belonging to those with a large tooth to denture base discrepancy, and the possibility that the decalcification is the expression of primitive dental caries was considered. 2. The measurement of-the tooth to denture base discrepancy in clinical cases in which there was much cervical dental caries. Eighteen clinical cases with much cervical dental caries were considered. The prevalence, the tooth-to-tooth distribution of cervical dental caries and the types of occlusion were examined. In ten cases in which the measurement of the tooth to denture base discrepancy was possible, the total discrepancy was measured with Tweed's method, and the results were compared with the data obtained from general population and discussed. In 83.3% of the cases there was crowding, bimaxillary protrusion, and maxillary protrusion, such that a deep relationship to the tooth to denture base discrepancy is indicated. Significant differences (p<0.001) in the statistical means of total discrepancy between the examined group and general population were seen 3. The relationship between the incidence of cervical dental caries and the tooth to denture base discrepancy in the general population was considered. Because there were so few clinical cases in the clinical investigation, tudy models, roentgenographic cephalograms, and panoramic radiograms of 905 young adults with an average age of 23 years and 7 months were used in discussing the relationship between the incidence of cervical dental caries and the tooth to denture base discrepancy. Below 0.001 level of significance, a definite correlation between the incidence of cervical dental caries and the tooth to denture base discrepancy was seen.