The present study included healthy patients older than 18 who were recruited from among adults seeking routine dental care at the school teaching hospital at Rabat Morocco. Eligible patients were volunteer adults with no history of other health conditions.
Adults treated for any other health condition or seeking the dental hospital for dental emergency needs were excluded.
The recruitment phase of the study was conducted between March and May 2012. Data in the present study were recorded from questionnaires, anthropometric measurements and oral examination.
Definition of variables
Eligible adults were interviewed during their dental attendance. All interviews were conducted using a structured questionnaire designed for the present study, which included information on demographic data (age and gender), general health, education level, monthly family income and oral health behaviour.
Data were collected ensuring the privacy and confidentiality by face-to-face interviews and document review.
The monthly family income was measured relative to the Moroccan minimum wage during the period of data gathering. Three-point scales were used (low, moderate and high).
Educational level was divided into three categories: low (none or primary), average (secondary) and high (university education).
Oral health behaviours included information on frequency of tooth brushing and when the patients started tooth brushing. Frequency of tooth brushing was divided into brushing twice a day, more than twice a day and once or less a day. Brushing motion was also recorded as appropriate or inappropriate.
The nature of dental attendance was noted according to a two-category system (planned visit, acute visit).
The interviewer measured the weight (kg) and height (m) at the time of interview and computed BMI. BMI was computed as weight divided by squared height (kg/m2).
Body weight and height were taken with participants in bare feet and light clothing, and measured to the nearest 0.1 kg and 0.1 cm, respectively. Body weight was measured using a portable digital scale and body height using a stadiometer.
Dental caries was recorded with tooth as the unit of measurement. The dental examination used international criteria standardized by the World Health Organization for oral health surveys . The numbers of decayed (DT), filled (FT) and missing (MT) teeth were calculated. Dental caries diagnosis was based on visual-tactile criteria using a sterile mirror and a blunt dental probe. The examination was performed in a fully equipped dental clinic using plane mirror and sharp probe after the teeth had been dried with air. In this paper, the term “caries” includes caries with cavitation.
Periodontal and oral hygiene status were assessed using the Community Periodontal Index (CPI), the Calculus Surface Index (CSI), the Gingival Index (GI) and the Simplified Debris Index (SDI).
Anthropometric measurements and oral examination were conducted by one examiner after calibration. Intra-examiner reliability was assessed by re-examining 10 volunteers after one week (Cohen’s kappa coefficient = 0.92).
Data analysis was conducted using SPSS 13.0 (SPSS Inc., Chicago, IL, USA) and Stata 13 (StataCorp LP, College Station, TX, USA) software.
The data were presented as the mean ± standard deviation (SD) for continuous variable with a normal distribution, and as median with interquartile range (IQR) for variables with skewed distribution. For categorical variables, data were presented as proportion.
To evaluate the association between untreated dental caries and recorded variables, a Poisson regression analysis was first applied to estimate the Prevalence ratio (PR) of untreated dental caries through levels of various explanatory factors. The high prevalence of dental caries in the study group meant that odds ratios were poor indicators of relative frequency, so prevalence ratios were determined using Poisson regression modelling . Prevalence ratio (PR) and related 95% confidence intervals (95% CI) were estimated in both univariate and multivariate regression analysis. The multiple regression model included the variables with p < 0.25. The adjusted rate ratios were considered statistically significant when p-values were 0.05 or less. The dependent variable used was the number of untreated decayed teeth (DT). The severity of dental caries at tooth level was defined as the increased amount of untreated dental decay. This means that we evaluated each subject’s likelihood to have more or less dental decay according to studied factors.
Three BMI categories were first used for analysis. Underweight subjects were defined as BMI < 18.5, normal weight as BMI of 18.5–24.99, and overweight and obese as BMI ≥ 25. Overweight and obese were combined during regression analysis due to the low proportion of obese subjects when analysing BMI as a categorical variable.
To avoid potentially arbitrary categorization, restricted cubic splines evaluated the likelihood of dental decay in each subjects according to the factors evaluated [13, 14]. Non-linearity was tested using the likelihood ratio, comparing the model with only the linear term to the model with both linear and cubic spline terms. We specified three knot positions at the 10th, 50th and 90th percentiles of BMI, that is, at BMI values of 17.75, 21.19 and 28.64, respectively. The reference level was set to the median value of BMI 23.23.
Poisson regression was used to compute prevalence ratios for the number of untreated dental caries, according to BMI. We controlled for age, income, frequency of tooth brushing, tooth brushing motion, age at beginning of tooth brushing, education level, simplified debris index, gingival index and reason for dental attendance.