Study design, setting, and population
Data was collected through a household survey conducted between December 2018 and January 2019 in Ife Central Local Government Area of Osun State, a semi-urban community in South-West Nigeria. Adolescents were eligible for the study if they were 10 to 19-years old and living in the study setting. Adolescents who were mentally challenged, critically ill and who were otherwise unable to respond independently to the survey were excluded from participation. Written individual consent, and assent and/or parental consent were obtained per national guidelines (See Ethical Considerations). Recruitment of participants continued until study sample size was reached.
Sample size and sampling technique
The minimum sample size was calculated with the formula proposed by Araoye . With a caries prevalence of 13.9% among 12-year-olds in the study setting , a margin of error of 5%, and a confidence level of 95%, the minimum sample size was 1323 adolescents. Adolescents were recruited using a multi-stage sampling technique. First, 70 of the 700 enumeration areas in Ife Central Local Government Area were sampled with a simple random technique. Next, every other household in the selected enumeration areas was identified as an eligible household. Finally, in each household, one adolescent who met the inclusion criteria was recruited for study participation. The next eligible household was substituted whenever a household declined to participate.
Data on socioeconomic status were collected with an adapted version of the index developed by Olusanya et al. , which had been used in a previous study in the same setting . This index is a multiple-item index combining the mother’s level of education with the father’s occupation. For this study, data were collected on the educational levels and professions of respondents’ parents. The social class of the adolescent was determined by adding the score of the mother’s level of education to that of the father’s occupation. Each adolescent was allocated into social classes I–V (class I: upper class; class II: upper middle class; class III: middle class; class IV: lower middle class; and class V: lower class). When an adolescent had lost a parent, the socioeconomic status was determined using the status of the living parent. When an adolescent had lost both parents, the socioeconomic status was determined using the status of the caregiver/guardian.
Respondents were also asked to indicate the frequency of tooth brushing using the following alternatives—irregularly or never, once a week, a few (2–3) times a week; once a day, and more than once a day. Respondents who chose the options ‘irregularly or never, once a week, a few (2–3) times a week; once a day’ were classified as not having undertaken preventive dental care .
Use of dental floss
Respondents were also asked to indicate how often dental floss was used for to clean the teeth using the following alternatives—‘Not at all, occasionally, a few (2–3) times a week, once in a day, more than one time in a day’. Respondents, who chose the options ‘Not at all, occasionally, a few (2–3) times a week’, were classified as not having undertaken preventive dental care .
Consumption of refined carbohydrate in-between-meals
Respondents were also asked to indicate the frequency of consuming sugar-containing snacks or drinks between main meals using the following alternatives—‘About 3 times a day or more, about twice a day, about once a day, occasionally; not every day, rarely or never eat between meals.’ Respondents who chose the options ‘About 3 times a day or more, about twice a day, about once a day’, were classified as not having undertaken preventive dental care .
Dental service utilization
Respondents were also asked to indicate the time of the last check-up using the following alternatives—‘within the last 6 months, more than 6 months to one year ago, more than 1 to 2 years ago, more than 2 to 5 years ago, more than 5 years, never, do not remember.’ Attending a dental check-up within the last year was defined as preventive care use. Respondents who chose the options ‘more than 1 to 2 years ago, more than 2 to 5 years ago, more than 5 years, never, do not remember’ were classified as not having undertaken preventive dental care .
The Patient Health Questionnaire (PHQ-9) is a nine-item questionnaire with scores for each of the nine DSM-IV criteria, from "0" (not at all) to "3" (nearly every day). The PHQ-9 can be used to monitor the severity of depression and response to treatment. It has 61% sensitivity and 94% specificity in adults . Possible scores range from 0 to 27. Scores 0–4 indicate no depression, 5–9: mild depression, 10–14: moderate depression, 15–19: moderately severe depression, and 20–27: severe depression . It has good concurrent validity with Beck’s depression inventory (0.61) and has a one-month test–retest reliability of 0.89 among young Nigerian adults .
Each participant was examined sitting, under natural light, with sterile dental mirrors by trained dentists. The teeth were examined wet. Plaque index  was used to determine oral hygiene status. The plaque index score was based on six numerical determinations representing the amount of debris found on the surfaces of index permanent teeth 12, 16, 24, 32, 36, and 44. The mesial, distal, buccal, and lingual gingival areas of the index teeth are scored from 0 (no plaques) to 3 (abundance of soft matter within the gingival pocket and/or on the tooth and gingival margin). The mean score for each tooth is obtained, and the mean score for the individual is determined by adding the indices for each tooth and dividing by the number of teeth examined.
The presence and severity of gingivitis was evaluated with the gingival index, described by Löe and Silness . Changes in the gingiva in relation to the appropriate six index teeth (16, 12, 24, 36, 32 and 44) in the permanent dentition were assessed. Four areas of each index tooth were scored, and the scores were summed and divided by four to give the gingival index for each tooth. The gingival index of each participant was obtained by adding the values of all index teeth and dividing by six. Gingivitis was classified as mild, moderate, or severe, with values of 0.1–1, 1.1–2, and 2.1–3, respectively. Gingivitis was dichotomized into normal gingiva/mild gingivitis and moderate/severe gingivitis .
Descriptive analyses were conducted to determine the proportion of adolescents with the study variables. Bivariate analyses were conducted to determine the associations between the explanatory variables (depressive symptoms), confounders and the outcome variable (gingivitis) using chi square and t tests. Univariate logistic regression models were constructed to determine the association between moderate/severe gingivitis and the explanatory and confounding variables. Two multivariable models were constructed: one including individual, behavioral and clinical factors, and the other including these factors in addition to depressive symptoms. Using separate multivariable models, we also assessed modification by depressive symptoms of the associations between the presence of mild to severe gingivitis and variables significantly associated with it in bivariate analyses. The estimated coefficients, expressed as adjusted odds ratios (AOR) and their 95% confidence intervals, were calculated. The statistical analyses were conducted using SPSS for Windows version 23.0 (IBM Corp., Armonk, N.Y., USA). Statistical significance was inferred at P ≤ 0.05.
Ethical approval was obtained from the Ethics and Research Committee of the Institute of Public Health, Obafemi Awolowo University, Ile-Ife, Nigeria. Approval for conduct of the study was obtained from the Local Government Authority prior to commencement. The study was conducted in line with guidance from the Federal Ministry of Health . Efforts were made to minimize risks and loss of confidentiality by ensuring anonymized data collection was conducted privately and collected with an electronic data platform. Study participants’ discomfort with the personal nature of questions was limited by ensuring field workers were trained on how to ask sensitive questions and to clarify non-verbal cues observed during the interviews. No compensation was paid for study participation.