Ethics and study design
The Study of Periodontal Health in Almada-Seixal (SoPHiAS) is a population-based representative study, with a target population living in the municipalities of Almada and Seixal (Portugal) [22]. This study was approved by the Research Ethics Committee of the Regional Health Administration of Lisbon and Tagus Valley, IP (Portugal) (8696/CES/2018) and in accordance with the Declaration of Helsinki, as revised in 2013. Participants were informed about their periodontal status after examination. Patients diagnosed with periodontal disease were referred to the Egas Moniz Dental Clinic (EMDC) for treatment without additional costs [22]. The study followed the STrengthening the Reporting of OBservational studies in Epidemiology (STROBE) guidelines [23].
Sample size and measurement reproducibility
A fully detailed report on elderly sampling strategy and measurement reproducibility are mentioned in [22]. A total of 1064 participants, aged 18 to 95 years, gave their consent and were examined [22]. For the purpose of this study, a subset of 592 participants, 320 women and 272 men, with 65 years old or over were studied.
Periodontal examination and clinical variables
Each clinical examination was performed using proper lightening with the individuals seated on an adjustable stretcher in the FHU’s medical office. Periodontal examination was made as described in Botelho et al. [22]. Periodontitis case definitions were defined according to the new AAP/EFP consensus [24].
Questionnaires
Information on sociodemographic characteristics and behaviours was collected by a self-reported questionnaire. The questionnaire covered questions on the following items: 1) gender, age, marital status, educational level, occupation; 2) monthly family gross income; 3) smoking habits; 4) oral hygiene-related behaviours (tooth brushing frequency, interproximal cleaning); 5) attitudes and awareness towards oral health.
Participants completed the Portuguese versions of the Oral Health Impact Profile-14 (OHIP-14-PT) [25] to assess OHRQoL, Summated Xerostomia Inventory-5 (SXI-5-PT) [26] to quantify xerostomia and Perceived Stress Scale-10 (PSS-10-PT) to estimate recognised stress [27].
The OHIP-14 consists of 14 questions representing seven domains (functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability and handicap) of OHRQoL. Each question is scored by 0 (never,) 1 (hardly ever), 2 (occasionally), 3 (fairly often) and 4 (very often). Thus, a higher score indicates poorer OHRQoL. Each pair of questions represents one of seven domains of the OHIP-14. The sum of the scores of the 14 questions ranges from 0 to 56 and the sum of each domain ranges from 0 to 8 (Slade et al. 1997). Further, individuals were categorised as frequently affected individual with respect to OHRQoL (answering with 3 or 4 to at least one of the questions in the OHIP-14) or with less affected individuals (responding with 0, 1 or 2 on all the items) [13].
The SXI-5 is a 5-questions tool where each question is scored by 0 = never, 1 = occasionally 2 = frequently. The scores from the five questions are summed, with the result representing the degree of xerostomia the subject feels [26].
The PSS-10 is 10-items instrument indicated to assess self-perceived stress. Each of the items on the PSS-10 is rated on a 5-point Likert scale, and each question is scored 0 = never, 1 = almost ever, 2 = sometimes, 3 = fairly often and 4 = very often. The PSS-10 consists of two domains: six positively (items 1, 2, 3, 6, 9 and 10) and four negatively (items 4, 5, 7 and 8, that require reversion) worded items. Total scores range from 0 to 40, with higher scores indicating higher levels of perceived stress [28].
Assessment of confounders
Furthermore, the participants have also been categorised into three groups according to the extent of periodontitis: no disease, localized periodontitis and generalized periodontitis [24]. Concerning oral hygiene, patients were categorized for their interproximal hygiene (no = 0, occasionally = 1, and yes = 2) and for frequency of toothbrushing per day (less than one time per day = 0, one time per day = 1, and two or more times per day = 2). Also, patients were questioned to the use of dentures and registered as a dichotomous variable (no = 0, or yes =1).
Statistical methods
The total scores of OHIP-14, PSS-10 and SXI-5 were calculated and their correspondent descriptive measures (mean and standard deviation (SD)) were computed. For analysis purposes, these scores were considered as continuous variables. The data analyses were conducted for all participants and for sample subsets, according to gender and periodontitis extent. Mann-Whitney and Kruskal-Wallis tests were used to compare OHRQoL scores as a function of gender and periodontitis extent. For categorical variables, the analyses were performed using Chi-square test. Spearman’s rank correlation coefficient (rho) was used to analyse the correlation of OHIP-14 scores with PSS-10 and SXI-5 total scores, number of missing teeth and periodontal clinical variables. The effect size of correlations was analysed according to Cohen’s standard. Further, a multiple forward stepwise linear regression analysis was carried out in order to evaluate the impact of those variables on the OHIP-14 total score. Next, a multivariable forward stepwise logistic regression was applied using the dichotomised dependent OHIP-14 variable “frequently affected” vs “less affected” OHRQoL as in [13]. Odds ratio (OR) and correspondent 95% confidence level intervals (95% CI) were calculated. Data were analysed using IBM SPSS Statistics, v. 25, (NY, USA). A level of significance of 5% was considered in all inferential analyses.
