The study sample is a subset of the participants of the Mexican Study of Nutritional and Psychosocial Markers of Frailty (the Coyoacan cohort), a prospective cohort study aiming to evaluate the nutritional and psychosocial determinants of frailty among Mexican community-dwelling elderly, conducted by the Department of Geriatrics of the National Institute of Medical Sciences and Nutrition “Salvador Zubirán” (INCMNSZ) of Mexico in collaboration with the National Institute of Public Health (INSP), the Department of Dental Public Health, the Graduate Studies and Research Division of the Dental School at the National Autonomous University of Mexico (UNAM), the Department of Health of the Government of the Federal District of Mexico, and the National Institute of Geriatrics of the Mexican Ministry of Health.
Population
The study population consisted of 33 347 persons who lived independently in the District of Coyoacán, one of the 16 districts of Mexico City. They all received support from the Food Support, Medical Care, and Free Drugs Program, a local government program that serves 95% of elderly aged 70 and older. This district was selected because it was easily accessible and was home to citizens from a wide range of socioeconomic strata.
The sample was chosen by a random sampling procedure, stratified by age and gender, and we ensured a sample size that could reliably estimate a prevalence rate of frailty of at least 14% among participants with α = 5% and β = 20% (n = 1294).
Baseline data were collected during 2008 and 2009 in two stages. During the first stage, an interview was conducted using a standard questionnaire; during the second stage, a clinical (medical and dental) evaluation was carried out. The interview and clinical evaluation were carried out in the participant’s home. The study protocol was approved by the Ethical Committee of the INCMNSZ. Each participant signed an informed consent and was free to refuse a specific part of the examination.
Variables
Frailty was defined according to the construct derived from the Cardiovascular Health Study [26] and validated in other studies [32, 36]. Frail persons were identified as having three or more of the five following components: unintentional weight loss, poor endurance and energy, low physical activity, slowness, and weakness. These components were defined as follows:
➢ Weight loss: self-reported weight loss of 5 kg or more in the last 6 months was considered positive for this item.
➢ Poor endurance and energy: Self-report of exhaustion was assessed by two questions from the Center for Epidemiologic Studies-Depression scale (CES-D) [37]: “I felt that everything I did was an effort” and “I could not get going”. Participants were asked: “How often, in the last week, did you feel this way?” and the answer was quoted as follows: 0 = rarely or none of the time; 1 = some or a little of the time; 2 = a moderate amount of the time; or 3 = most of the time. Participants answering “2” (a moderate amount of the time) or “3” (most of the time) to either of these two questions were considered as frail for this criterion.
➢ Low physical activity: The Physical Activity Scale for the Elderly questionnaire (PASE) [38] was used to assess physical activity. Participants who scored in the lowest quintile adjusted for gender were categorized as frail for the low physical activity criterion.
➢ Slowness: A response “yes” or “can’t do” to any of the following questions was used to estimate slowness: Because of a health problem, “do you have difficulty walking one block?” or “do you have difficulty with climbing several flights of stairs without resting?”
➢ Weakness: participants who answered “yes” to the question Because of a health problem, “do you have difficulty with lifting or carrying objects weighting over 5 kg, like a heavy bag of groceries?” were categorized as frail for this criterion.
Oral health variables
Number of teeth. (0–32 teeth): Number of natural teeth present in the mouth.
Dental condition (edentulism/partial edentulism/completely dentate): Edentulism is defined as the absence of all natural teeth; partial edentulism is defined as having one to 24 natural teeth; completely dentate is defined as having ≥25 teeth [39].
Utilization of removable partial dentures (RPD) or complete dentures (CD) (Yes/No): Determined during the clinical examination. Participants were asked to show their RPD or CD to the examiner; both those who were using dentures at the time of the evaluation and those who showed but did not use them were classified as denture users.
Functionality of Removable Partial Dentures or Complete Dentures (Functional/Nonfunctional): Evaluation of the stability, retention, occlusion, extension, and integrity of the dental prosthesis, as proposed by Ettinger [40]. Dentures failing in one or more of the above criteria were considered nonfunctional. Prostheses were also considered nonfunctional when the subjects expressed that they did not wear their removable prostheses regularly.
Severe periodontitis (Yes/No): Periodontitis status was evaluated using a modified version of the Periodontal Screening and Recording Index (PSR) [41]; we measured the clinical attachment loss of periodontal ligament by probing six sites per tooth (distobuccal, midbuccal, mesiobuccal, mesiolingual, midlingual, and distolingual) on all teeth present in the mouth, recording the highest PSR score on each tooth. We classified each participant according to the following criteria: Severe periodontitis was defined as having at least one tooth with a PSR score of 3 (3.5–5.5 mm of attachment loss) and furcation involvement or gingival recession of ≥3.5mm, or at least one tooth with a PSR score of 4 (>5.5 mm of attachment loss); the absence of severe periodontitis was defined by all teeth having PSR scores of 0 thru 3 (0–5.5 mm of attachment loss) without furcation involvement or gingival recession.
The following variables were assessed during the interview: self-perception of oral health compared with other persons of the same age (Better/Equal/Worse), utilization of dental services during the last year (Yes/No), xerostomia (Yes/No), and self-reported chewing problems (Yes/No).
Covariates
The following socio-demographic and health variables were collected by interview: age, gender, education level (years), current and past smoking (Yes/No); cognitive impairment as evaluated by the Mini-Mental State Examination (MMSE) (≤18/19-30) [42]; urinary incontinence (Yes/No); falls three times or more in the previous 12 months (Yes/No); hospitalization in the previous 12 months (Yes/No), and the number of medications per day.
The presence or absence of six self-reported diseases was interrogated for their relationship with dental conditions and frailty: myocardial infarction, stroke, hypertension, diabetes, osteoporosis, and arthritis.
Interview
The interview was completed by 86.9% of the study sample (n = 1124); 24 persons could not be reached, 37 refused to participate, 18 were deceased, and the remaining 91 did not participate for other reasons. The interviews were performed by trained and standardized interviewers (Figure 2).
Clinical evaluation
The participants were visited by an interdisciplinary team, consisting of a physician, a nutritionist, and a dentist. The subjects underwent a comprehensive geriatric health evaluation including examination of functional status, pharmacological treatments, physical performance, nutritional status and oral condition.
The oral evaluation included determination of the number of teeth present in the mouth, dental condition, use and functionality of RPD and CD, and presence of severe periodontitis. The dentists who carried out this evaluation were students of the dental school at UNAM; they were previously standardized in periodontal evaluation (Kappa = 0.7) and evaluation of the functionality of RPD and CD (Kappa = 0.9). The clinical evaluation was performed with artificial light, a dental mirror (#5), and a periodontal probe (CP11.5B, Hu-Friedy®), which had been previously sterilized; infection control procedures were strictly followed.
The overall clinical evaluation was completed by 945 subjects, and 107 subjects refused the oral evaluation; 74.5% (838/1124) of participants completed both the interview and the oral clinical evaluation (Figure 2).
Analysis
Variables were described using frequencies and proportions or arithmetic means and standard deviations (SD) when appropriate. Univariate analyses testing oral health conditions (and covariates) with frailty status were carried out using chi-squared test for categorical data (self-rated oral health compared with others, xerostomia, dental condition, periodontitis, and utilization and functionality of RPD and/or CD), estimating the odds ratio when appropriate. Student’s t test for independent groups were also performed.
A binary logistic regression model was used, employing frailty status as the dependent variable and the dental variables (perception of oral health compared with others, utilization of dental services during the previous year, xerostomia, report of chewing problems, number of teeth, and severe periodontitis) as independent variables. We also included interactions between history of smoking and severe periodontitis, diabetes and hospitalization, diabetes and hypertension, diabetes and severe periodontitis, diabetes and number of teeth present, myocardial infarction and hypertension, myocardial infarction and hospitalization, and hypertension and hospitalization. Utilization and functionality of RPD and CD were excluded because of their collinearity with the number of teeth. Socio-demographic and medical covariables identified as statistically significant in the univariate analysis were also included. The final model was determined by performing a backward variable selection procedure.
A p-value of 0.05 was used as the threshold for statistical significance, and 95% confidence intervals (95% CI) were estimated when appropriate. SPSS software for Windows (SPSS Inc., Chicago, IL, version 19) was used to perform all statistical tests.