Our study was nested on the third version of the Chilean National Health Survey (ENS 2016–2017). In the ENS 2016–2017, the sample size was calculated with a 20% relative error to estimate a national prevalence of over 3%. One participant per household was randomly selected using a computational Kish algorithm. The sample was representative of the Chilean population, including men and women who lived in rural or urban areas from all country regions. In this respect, a complex, stratified, multistage cluster sampling technique was used. The survey had a response rate of 67.0% from the eligible participants, whereas the rejection rate was 9.8%.
The health problems measured in the total sample of the ENS 2016–2017 and showed the highest prevalence (over 30%) achieved national and regional representativeness, having an estimation of relative error lower than 30%. After conducting questionnaires and an intraoral examination, oral health was measured, following the WHO STEPwise approach to chronic disease surveillance [15]. Our study included 5473 participants who were 15 years or over, residents in each household selected randomly, and had undergone a complete intraoral examination. The exclusion criteria were pregnancy and the risk of violence against interviewers.
Dental status was assessed using the standard diagnostic criteria of the World Health Organization [16]. These assessments were conducted by nurses trained by nine dentists associated with the Ministry of Health of Chile (MINSAL). Also, MINSAL provided the nurses with a handbook for conducting dental assessments called “The Nurse Manual.” This handbook is available in the national repository of population-based surveys (http://epi.minsal.cl/encuestas-poblacionales/). The following three aspects were measured in each subject overall and per dental arch during the examination: 1- The wearing of a removable prosthesis, 2- The number of remaining teeth, and 3- The loss of anterior teeth. According to the pilot study of the ENS 2003, the nurses' sensitivity to detect tooth loss was 70% [17], and the inter-examiner concordance was significant (kappa = 0.75, value-p < 0.001) [18]. As to the ENS 2016–2017, the inter-examiner concordance relating to the assessment of anterior tooth loss was almost perfect and significant (kappa = 0.85 ± 0.11, value-p < 0.01) [19].
The nurses wore gloves, surgical masks, head flashlights, tongue depressors, and flat mouth mirrors. Clinical examination was carried out while the participant was sitting in a straight back chair, in front of the light from the head flashlight. To determine the number of remaining teeth, a nurse asked to brush their teeth previously and remove their prosthesis; then, they counted the participants' teeth in each dental arch. To assess anterior tooth loss, the nurses had to register the results by selecting one of the two response alternatives, "Yes" or "No," where "Yes" meant that at least one of the six anterior teeth in a dental arch was missing. This data was collected using an electronic tablet and then submitted and validated according to the ENS 2016–2017 protocols. Participants suffering from severe tooth pain, dental trauma, suppuration, facial swelling, or post-extraction bleeding were referred to outpatient dental emergency care.
To measure HRQoL, we used the EQ-5D system developed by the EuroQoL [20]. The EQ-5D is a non-disease-specific instrument consisting of five dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. The possible responses to each dimension were: G1, no problems; G2, some problems; and G3, problematic.
To assess OHRQoL, a general question (GQ/ENS) and five specific questions (SQ/ENS) included in the two previous versions of the Chilean National Health Survey (ENS 2003 and ENS 2009–2010) were asked to each respondent. The GQ/ENS was phrased as "How would you rate your oral health?" and participants were given five response alternatives: "Excellent," "Good," "Neutral," "Poor," and "Very Poor." Also, the SQ/ENS included the following questions: 1- Do my teeth or prosthesis feel uncomfortable when speaking? 2- Do my teeth or prosthesis cause me pain and suffering? 3- Do my teeth or prosthesis feel uncomfortable when eating? 4- Do my teeth or prosthesis interfere with my daily activities (e.g., work, study, housework)? and 5- Do my teeth or prosthesis interfere with my social relationships? For these five questions, the available responses were categorized as follows: "Never," "Rarely," "Sometimes," "Very often," and "Always."
We performed the statistical analysis based on the collected data from the ENS 2016–2017, available at http://epi.minsal.cl/encuestas-poblacionales/. Variables were estimated using the complex sampling module in SPSS 24.0 (Mac OS X) (SPSS Inc., Chicago, IL, USA). Using the Taylor linearization method, the means, and proportions with respective standard errors (se) and confidence intervals of 95% were calculated. The dependent variables were HRQoL, measured through the EQ-5D, and the OHRQoL, measured through the GQ/ENS and the SQ/ENS. The statistical models considered independent variables of the total number of remaining teeth (continuous variable) and the anterior tooth loss per jaw (dichotomous variable). One-way ANOVA was performed to identify differences in the number of teeth with the EQ-5D, GQ/ENS, and SQ/ENS. We used multinomial logistic regressions with stepwise selection to examine the odds ratio (OR) for EQ5-D, GQ/ENS, and SQ/ENS according to anterior tooth loss. For confounding control, age, sex (men/women), geographical area (urban/rural) and educational level (low/medium/high) were considered as adjustment variables.