The participants of this study were Japanese adults aged 20 to 89 years. The smoking rate, prevalence of diabetes, and proportion of participants with BMI >25 were all lower than the mean values for the Japanese population as a whole. This suggests that the participants had good awareness of health issues.
The mean PPD was 2.3 mm to 2.9 mm, depending on the age group, and was lowest among participants in age 20–35 group and highest in those in the oldest age group, although the difference was only 0.6 mm. The periodontal pockets 4 mm in depth were present in 79.1% of participants in age 20–35 group (the lowest rate) and in 97.2% of those in the over age 75 groups. Pockets 6 mm in depth were present in 20.8% of participants in age 20–35 group, and the prevalence increased with advancing age, reaching 63.6% of those in the over age 75 group. The 2011 Survey of Dental Diseases12 included an assessment of the community periodontal index (CPI) by partial inspection, which found that the prevalence of pockets of depth 4 mm ranged from 13.5% among individuals in their 20s to 50.8% among those in their 70s. The corresponding prevalence of pockets 6 mm in depth was 1.1% to 16.5%. These figures were clearly lower than those found in the present study. The difference between our results and those of the Survey of Dental Diseases may have stemmed from the use of partial inspection to assess the CPI, possibly causing some pockets to be overlooked. Baelum et al.15 found that Community Periodontal Index of Treatment Needsdata for ten teeth overestimated the prevalence and severity of attachment loss among younger people and underestimated it for those over 35 years of age. The fact that all teeth were covered by our study was thus a major advantage.
The proportion of tooth surfaces exhibiting pockets was lower in younger age groups and higher in older ones. This indicated that even if pockets were apparent in younger people, they were restricted to a small area of the teeth.
The mean CAL was 1.8 mm to 3.6 mm, with a greater difference due to age than that apparent for PPD. Similarly, to PPD, the percentage of tooth surfaces with attachment loss was lower in younger than in older patients.
The percentile plots for all subjects of sites with CAL 3 mm showed that the line was almost straight. On the other hand, in the same figure of CAL 5 mm, the slope of the 10% to 20% subset showed a substantially higher percentage of affected sites. This means that, a small proportion of subjects show higher susceptibility to periodontitis.
A recently reported epidemiological survey on periodontal disease carried out in the United States from 2009 to 2010 16) found that 47.2% of adults aged 30 years or over had periodontitis. The prevalence of CAL 3 mm was 85.9% and of CAL 5 mm, 43.4%. In all of these categories, the prevalence increased with advancing age. The results of that study suggested that the severity of periodontitis is associated with male sex, Mexican-American ethnicity, educational level, poverty, and smoking. An epidemiological survey of a rural area of Thailand, however, found that the mean proportion of tooth surfaces with attachment loss of 4 mm was 23.9% in their 30s and 63.9% in their 60s, while the mean proportion with pockets 4 mm in depth was 11.6% to 20.5% 17. A study by Corraini et al.4 carried out in an isolated population in Brazil from 2005 to 2006 found that CAL of 3 mm was present in 100% of participants, and attachment loss of 5 mm was evident in 100% of those aged 50 years or more. In adults, the extent of tooth surfaces with attachment loss of 5 mm was also high (2.0% to 43.6%). The data from Takahagi City included a higher prevalence and extent of attachment loss than that reported by Eke et al. and was also lower than the results of the South American and Southeast Asian studies. These differences may be related to factors including ethnicity, educational level, and oral hygiene.
Inter-operator variation must also be considered. In the studies performed in other countries, measurements were carried out by multiple investigators; but in the Takahagi City survey, all measurements were made by a single periodontist. This was a major advantage in terms of the reproducibility of measurements.
We attempted to compare the results of this study with those of an epidemiological survey of 319 residents of Ushiku City, Ibaraki Prefecture, that was carried out in the 1980s13)14). Only numerical data provided in those papers were analyzed. In the early study, the age of participants was between 20 to 79 years and they were classified into 6 age groups. For comparison, participants in the present study who were more than 79 years were excluded, and a total of 573 subjects were divided into 6 age groups in the same way as in the early study (Table 4). The mean number of missing teeth per participant among all the participants in the 1980s survey was 7.2 6.3. This number had declined to 6.1 4.6 missing teeth in our survey (data not shown). In the 1980s survey, the mean number of missing teeth recorded was around four teeth for participants in their 20s and a mean of 15 teeth for those over 60 years, whereas in this study, the numbers were 3.3 1.6 teeth for participants in their 20s and 9.3 6.3 teeth for those in their 70s (data not shown). This means that, participants in older age groups had significantly more teeth than in 1980s subjects. The mean proportion of tooth surfaces harboring plaque was 64% 17% in the 1980s survey and 58.2% 20.2% in the present study. In the 1980s survey, the mean proportion of BoP in their 20s was approximately 35%, when compared with approximately 60% to 65% for elderly participants. In the present study, the mean proportion of BoP in their 20s was 33.2% 13.2%, as compared with a range of 30.9% 17.1% to 33.4% 17.5% for those over 60 years, indicating a particularly marked change among elderly participants. The records from the 1980s survey indicated that treatment had involved mainly symptomatic therapy and treatment of acute symptoms. However, in the recent data from Takahagi City, 23% of participants were undergoing regular dental checkups, indicating a higher awareness of dentistry and oral hygiene among the general public. In the 1980s, survey participants in their 20s and 30s had the lowest scores; but in the recent study, participants in their 20s and 30s and also those in their 70s exhibited poor oral hygiene. The rates of interdental cleaner use and of regular dental checkups were lower among participants in their 20s and 30s, and this may have been reflected in their high plaque scores. As with the plaque scores, the proportion of tooth surfaces exhibiting BOP was also greatest among participants in their 20s and 30s and those in their 70s.
The mean PPD was between 2.2 0.5 mm and 2.8 0.7 mm in the 1980s survey, as compared with between 2.3 0.2 mm and 2.7 0.6 mm in the present study. When the data were compared with a 95% confidence interval, there were no significant differences in the mean PPD among the two data sets. Despite the higher number of remaining teeth when compared with the 1980s, there was no change in the mean PPD in all age groups. BOP actually decreased, suggesting that some participants had undergone periodontal treatment and this may have helped preserve a large number of teeth with attachment loss. Ushiku City, from where the 1980s data were obtained, had at that time a population of around 50,000; the population has grown to approximately 80,000 today. The difference in size of the two cities may have had some effect.
The mean CAL was between 1.2 0.6 and 3.7 1.5 mm in the 1980s survey, as compared with between 1.6 0.5 mm and 3.4 1.0 mm in the recent study. The differences between the 1980s data and recent data were statistically significant for participants in their 30s and 40s. For the 30s group, the prevalence of attachment loss of 5 mm was significantly higher in the recent study when compared by chi-squared test (p<0.05). The reason for this difference in mean CAL among relatively young age groups in recent data and data from the 1980s may lie in inter-operator variation in the measurement of CAL when the cement–enamel junction is below the gingival margin. In any case, the PPD for participants in their 20s and 30s was below the mean PPD, indicating the absence of root exposure in most cases, and within this range a high value of CAL does not necessarily indicate a pathological condition.
A lower prevalence of CAL of 5 mm in current participants compared with the 1980s data was seen only in their 60s. Interestingly, in the current data, mean plaque score was the lowest in the 40s and second-lowest in the 50s. It may be speculated that the inhabitants in these age groups generally started to be more aware of oral hygiene.
Studies have compared the prevalence of periodontal disease in the 1970s and 1980s with that in recent years in several different countries9–11,18. Although the parameters and diagnostic criteria used in these studies vary, oral hygiene and the prevalence of periodontal disease has improved in most countries in the 21st century compared with the 1970s and 1980s. Interestingly, however, the prevalence of severe periodontitis has not necessarily gone down. In a Swedish study, Hugoson et al. 9 classified participants into five categories according to the severity of periodontitis on clinical examination and radiographic findings. Between 1973 and 2003, the proportion of individuals with healthy gingival tissue who were categorized as Group 1 increased from 8% to 44%, and the prevalence of gingivitis and moderate periodontitis declined. However, there was no change between 1983 and 2003 in the proportion of individuals in Group 5, the most severe category, with periodontitis with significant bone resorption in at least two-thirds of tooth roots. Similarly, a Norwegian study by Skudutyte-Rysstad et al. 18 in patients over 35 years of age also found that although the number of participants with little or no bone loss decreased between 1973 and 2003, the proportion of participants in the most severe category (bone loss of over 20%) had hardly changed (from 6% to 7%). Periodontitis may thus be difficult to prevent by means of normal oral cleaning in highly susceptible individuals. In addition to the reasons described above, the tendency we observed for improvements in plaque score and gingival inflammation since the 1980s, although the frequency of attachment loss actually increased, may have been due to the presence of individuals who were highly susceptible to periodontitis.