‘Periodontal health and disease in an older population: A 10- year longitudinal study’

Objectives: To investigate alveolar bone loss (ABL), which is an indicator of periodontitis, and to identify risk factors for ABL in an older population between 2008 and 2018. Methods: This longitudinal study used data from a questionnaire survey and a clinical examination administered on two occasions ten years apart to 273 individuals who were 65 years and 75 years in 2008. Results: The mean number of teeth decreased significantly over the ten- year study period, while the proportion of individuals with calculus and moderate ABL visible on radiographs increased. For both ages, the number of teeth decreased by a mean of 2 teeth. The proportions of participants reporting poor general health, daily medication, xerostomia, living singly, visiting dental care irregularly and being in need of extra support in their homes all increased over the observation period. Conclusions: Despite an increased progression of moderate alveolar bone loss, a fairly good dentition and chewing capacity was retained in this older population. However, the individual's age and fragility are important indicators that need to be considered when planning oral health care and the availability of dental care.

proportion of individuals who retain their natural teeth into old age is increasing, while the proportion of edentulous individuals is decreasing. 7,8 The prevalence of moderate periodontal disease ranges between 22% and 33%, and the more severe form affects between 6% and 9% of Swedes. 6,7 Mean number of teeth among older people (> 65 years of age) is somewhere between 20.0 and 22.5. 7,9 The prevalence of periodontal disease differs among countries, races and ethnic groups, [10][11][12] and periodontitis is, together with dental caries, the most common reason for tooth loss in adults. [13][14][15][16] A study by Elter et al 17 identified risk factors for periodontitis in adults using longitudinal data, confirming a multifactorial aetiology.
A longitudinal population-based study of periodontal disease by Thomson et al found that most attachment loss in older people manifests as an increase in gingival recession rather than probing depth, and the 5-year incidence estimate for attachment loss was higher among those with diabetes and those who had lost at least one tooth since baseline. Smoking was not a significant predictor in that age group. 18 Smoking is a known risk factor for the development and progression of periodontitis. 19,20 Irregular use, or no use of dental health services, single status and low socioeconomic status have been shown to be associated with tooth loss and periodontitis. [21][22][23][24] Maintaining good oral health requires adequate oral hygiene to prevent oral health problems. This could be especially challenging for older people living on their own if they are dependent on others for help with, for example, their personal hygiene. Since the older population is increasing, and to be able to plan for future dental resources, it is vital to investigate the occurrence and influence of poor oral health in older people. The aim of this study was to investigate ABL and its possible risk factors in an older population followed between 2008 and 2018.

| Study design and participants
In 2008, a random sample of 360 individuals in each of the age groups 65 and 75 years was selected from the Dalarna population registry. In 2018, according to the Dalarna population registry, 420 of the 720 individuals who participated in the 2008 study were eligible and thus invited to participate in the 2018 study ( Figure 1). Those not eligible had either died or moved out of the Region or to other countries.
All individuals were mailed an invitation to participate together with information about the study and a questionnaire. Written informed consent was obtained from all participants. Further details are given elsewhere. 7

| Measures
The clinical examination, including 2-6 bitewing radiographs, was conducted by each participant's regular dental practitioner. The dental practitioners used their ordinary X-ray equipment, X-ray holders and clinical examination procedures. Individuals without regular dental contact were offered a referral to a dental practitioner of their choice.
A standardized examination protocol with comprehensive written information was used. All documents and radiographs were coded, and personal identification details were deleted before data processing. Two calibrated reviewers, one of whom was a periodontist and one a registered dental hygienist, reviewed all radiographs.

| Questionnaire
The questionnaire focussed on sociodemographic characteristics (such as education, marital status and financial resources for dental care), self-perceived general health and medication, oral hygiene and dental care habits, and tobacco use. Clinical belonging (private or public dental care) was also requested.

| Statistical analysis
Marital status was dichotomized into 'cohabiting' and 'living as a single'. A common interval for visiting dental care in Sweden is every two years. Dental care was dichotomized into 'regular' (at least every two years) and 'irregular'. Financial resources were dichotomized into 'fewer dental visits due to limited financial resources' and 'no changes in dental visits'. Daily medication was dichotomized into 'no daily medication' and 'daily medication'. Smoking was registered as never smoked and 'current/former smoker'. Perceived general health and chewing ability were dichotomized into 'good' and 'bad'.
Living condition was dichotomized into "independent" and "dependent" (in need of help from others). Xerostomia during the past six months was divided into 'never', 'sometimes' and ' daily/almost daily'. Education was dichotomized into 'high' (university or college of higher learning) and 'low' (up to secondary school).
Data were analysed using version 26.0 of IBM SPSS (SPSS Inc,).
Mean values, standard deviations (SDs), frequencies, distributions and 95% confidence intervals (CIs) were calculated. McNemar's test was used on paired nominal data and a P-value ≤ .05 was considered to indicate statistical significance. A paired-samples t test was used when calculating mean values, and binary logistic regression was used to analyse factors that could have an influence on ABL.
Cohen's kappa value for inter-individual agreement between the two reviewers who performed the classification of ABL was 0.73.

| RE SULTS
At baseline, 419 individuals answered a questionnaire and were clinically examined, and 273 (65.2%) of these were re-examined after 10 years. Characteristics among those lost to follow-up are displayed in Table 1. Those lost to follow-up had more missing teeth and alveolar bone loss (ABL) at baseline. Calculus visible on bitewing radiographs were more prevalent among those lost to follow-up,  Table).

F I G U R E 1 Recruitment of participants
Sociodemographic characteristics are presented in Table 3. Some 13% of participants reported an education level of college or higher learning (not shown in Table). Individuals living in nursing homes increased over this period of ten years, as well as those in need of home care (P < .001). Proportionately more participants reported single living, daily medication, irregular dental visits, worse general health and xerostomia in 2018. Most reported good chewing ability.
In 2008, current smoking was reported by 7% of the participants and former smoking by 36%; the corresponding figures in 2018 were 6% and 40%, respectively. The majority of the participants visited private dental clinics and 2% reported no permanent belonging to any dental clinic.

| D ISCUSS I ON
The principal findings of this longitudinal study were that the prevalence of moderate ABL and calculus visible on radiographs increased and approximately two teeth were lost during this period of ten years. Smoking was found to be the strongest risk factor for ABL.
The loss of participants from a cohort over time can lead to nonrepresentativeness of the study sample in longitudinal epidemiological studies. In this study, those remaining after ten years were periodontally healthier, had a higher mean number of teeth, and were more likely to visit dental care regularly and the proportion of smokers was lower than among those lost to follow-up. Previous studies have shown that nonrespondents are generally less healthy than participants in health investigations. 25 Participants lost to follow-up in the present study had more advanced ABL than those re-examined after ten years. The current study's findings should, therefore, be regarded as an underestimation of the periodontal disease progression in this cohort and generalizations from the present study may, therefore, be made with a certain degree of caution.
Some variables had very small numbers in response categories, making it hard to draw definitive conclusions. As a large number of professionals performed the clinical examinations, detailed written information and illustrations were provided for the different clinical variables to be recorded to ensure the best conformity. The classification of ABL was performed by one of the authors (KE, registered dental hygienist) and a periodontist, strengthening the clinical measures.
As a consequence of changes in health-related behaviours, such as reduced smoking and improved knowledge of the importance of TA B L E 4 Univariate, unadjusted and multiple adjusted analysis of the association between alveolar bone loss (moderate and advanced) and socioeconomic and sociobehavioural variables presented as odds ratio (95% CI in brackets (n = 248)

| Strengths and limitations
As there were many individuals performing the dental examination, and no calibration was possible, and to ensure the best conformity, detailed written information and illustrations were provided for the clinical variables to be recorded. The categorization of ABL was performed by one of the authors (KE, registered dental hygienist) and one periodontist, which strengthens the analysis of the clinical measures. It is reasonable to expect that the nonrespondents did not have better general or oral health than the respondents, as other studies have shown that nonrespondents are generally less healthy than participants in health investigations. 25 Those lost to follow-up were more periodontally unhealthy, more likely to be smokers and irregular dental visitors making it hard to generalize the study findings.

| CON CLUS ION
Despite an increasing progression of moderate alveolar bone loss, a fairly good dentition and chewing capacity was retained in this older population. However, age and fragility are important indicators to be considered when planning oral health care and availability of dental care.

ACK N OWLED G EM ENTS
The authors thank Jan Ifver for his biostatistical consultation and expertize, and all the dental teams at the public and private dental clinics for helping with the data collection. This study was funded by the Research Foundation for the Public Dental Service, Dalarna, Sweden, and the Center for Clinical Research, Falun, Sweden. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.

CO N FLI C T O F I NTE R E S T
The authors declare no conflicts of interest with respect to the authorship or publication of this article.

AUTH O R CO NTR I B UTI O N S
All authors have made major contributions to data analysis and interpretation as well as writing the manuscript and revising it critically, and have given final approval of the version to be published. KE planned and performed the data collection.

DATA AVA I L A B I L I T Y S TAT E M E N T
Data available on request due to privacy/ethical restrictions.