The purposes of this study were (i) to examine the relationship between the number of natural teeth and the number of functional tooth units in Japanese adults, (ii) to evaluate how functional tooth units relate to subjective masticatory ability and (iii) to determine the minimum number of natural teeth and functional tooth units needed to maintain adequate self-assessed chewing function. A self-administered questionnaire was given and dental examination was conducted for 2164 residents aged 40 to 75 years. Counts were made on the number of functional tooth units of natural teeth (n-functional tooth units), the sum of natural teeth and artificial teeth on implant-supported and fixed prostheses (nif-functional tooth units) and the sum of natural teeth and artificial teeth on implant-supported, fixed and removable prostheses (total-functional tooth units). The average number of natural teeth, n-functional tooth units and nif-functional tooth units decreased with age, but these were often replaced by functional tooth units from artificial teeth on removable prostheses. Total-functional tooth units in 50-59 year old people were slightly lower compared with those in other age groups. Subjects who reported that they could chew every food item on an average had 23.4 total natural teeth, 12.6 posterior natural teeth, 7.6 n-functional tooth units, 8.6 nif-functional tooth units and 10.4 total-functional tooth units, and subjects without chewing difficulties had fewer functional tooth units from removable prostheses. Maintaining 20 and more natural teeth and at least eight nif-functional tooth units is important in reducing the likelihood of self-assessed chewing difficulties.

The purposes of this study were (1) to examine differences in dental status among various age groups, particularly, focusing on whether subjects retained 20 or more natural teeth, and (2) to investigate the relationship among dental status, the number and categories of functional tooth units (FTUs), and masticatory ability. A dental examination and self-administered questionnaire were conducted in a total of 2,164 residents aged 40 to 75 years who dwelt in Japan. The percentage of subjects with 20 and more natural teeth and their number of posterior teeth decreased with age. There was not much difference in the mean number of FTUs in subjects with and without 20 or more natural teeth, but those with 20 natural teeth had fewer numbers of FTUs than those with more than 20 natural teeth. The categories of the FTUs were extremely different. Subjects with 20 or more natural teeth had FTUs consisting mostly of natural to natural teeth. Subjects with 19 or fewer natural teeth had many FTUs consisting of removable prosthetic teeth. The subjective chewing ability test was significantly correlated with the number of natural teeth. Subjects could chew the higher number of test foods as the number of natural teeth increased. Not only the number of natural teeth but the categories of FTUs appear to be key factors of chewing ability. It is important to keep as many natural teeth as possible so that the person's categories of FTUs are mainly composed of natural to natural teeth to maintain better oral function.

Patients' reported number of remaining teeth, the data for which were collected via the questionnaire, provided reasonably valid data on the actual number of teeth within a population group.

The objective of this study was to analyze the relationships between subjective oral health symptoms and clinical oral health conditions on the perceived oral health of 1799 Japanese middle-aged adults. A self-administered questionnaire together with dental examinations was administered. A structural equation modeling analysis with Bayesian estimation was used to examine the factors influencing perceived oral health as a latent variable with 4 other latent variables: subjective oral health symptoms, clinical tooth conditions, clinical periodontal conditions, and other clinical oral conditions. For perceived oral health as the endogenous variable, only subjective oral health symptoms and clinical tooth conditions showed significant relationship. Clinical periodontal conditions and other clinical oral conditions did not show significant effects on the perceived oral health.

Smoking has a positive association with missing teeth and periodontitis. However, smoking cessation is beneficial for oral health. The odds of having more than eight missing teeth, or of having periodontitis, in those who had never smoked was similar to that of individuals who reported that they had stopped smoking for 11 years or more.

The results suggest that the level of education has an independent impact on dentition status in a group of Japanese adults, even after taking into account oral health-related factors. Therefore, providing appropriate oral health information from an early age within a compulsory school education program appears necessary to enhance health literacy and lessen the inequalities in dental health by educational level.

Smoking had a positive association with the number of missing teeth and smoking cessation is beneficial for maintaining teeth. The odds of having more than eight missing teeth in those who had never smoked was equal to that of individuals who reported that they had stopped smoking for 21 years or more.

BackgroundSeveral studies have shown that parity is associated with oral health problems such as tooth loss and dental caries. In Japan, however, no studies have examined the association. The purpose of this study was to determine whether parity is related to dentition status, including the number of teeth present, dental caries and filled teeth, and the posterior occlusion, in a Japanese population by comparing women with men.MethodsA total of 1,211 subjects, who participated both in the Japan Public Health Center-Based (JPHC) Study Cohort I in 1990 and the dental survey in 2005, were used for the study. Information on parity or number of children was collected from a self-completed questionnaire administered in 1990 for the JPHC Study Cohort I, and health behaviors and clinical dentition status were obtained from the dental survey in 2005. The association between parity or number of children and dentition status was analyzed, by both unadjusted-for and adjusted-for socio-demographic and health behavioral factors, using a generalized linear regression model.ResultsParity is significantly related to the number of teeth present and n-FTUs (Functional Tooth Units of natural teeth), regardless of socio-demographic and health behavioral factors, in female subjects. The values of these variables had a significantly decreasing trend with the rise of parity: numbers of teeth present (p for trend = 0.046) and n-FTUs (p for trend = 0.026). No relationships between the number of children and dentition status were found in male subjects.ConclusionHigher-parity women are more likely to lose teeth, especially posterior occluding relations. These results suggest that measures to narrow the discrepancy by parity should be taken for promoting women’s oral health. Delivery of appropriate information and messages to pregnant women as well as enlightenment of oral health professionals about dental management of pregnant women may be an effective strategy.