Design

This cross-sectional analysis of baseline data collected for the BRIGHT trial took place over two academic years: 2017-2018 and 2018-2019.10 Ethical approval was granted by East of Scotland Research Ethics Service (ref: 17/ES/0096).

Participants and recruitmentSchool recruitment

Secondary school eligibility criteria: located in Scotland, England or South Wales; state-funded; at least 60 pupils per year group; and above national average percentage of pupils eligible for FSMs.11,12,13

Participant recruitment

Eligibility of pupils at participating schools : aged 11-13 years old (Year 7 or 8 England and Wales; S1 or S2 Scotland); own mobile telephone; and whose parents had not opted them out of the trial. The overall target sample size was 5,040 pupils from 42 schools.8

Information about the study was distributed to children and their parents. Opt-out consent was obtained from parents and written consent from eligible pupils. If parents/carers did not return an opt-out form within the two-week window, it was assumed they were happy for their child to decide themselves if they would like to participate. Parents/carers could withdraw their child at any point over the trial. Children of parents who had not returned an opt-out form were then invited to participate and could decide whether or not to take part.

Sociodemographic characteristics of participants

Data were obtained from schools on date of birth, year group, sex, current FSM eligibility, school attendance and home postcode of participating pupils. Home postcode was used to obtain participants' Index of Multiple Deprivation (IMD) decile within each devolved nation.14

Clinical assessment

Dental assessments were conducted under standard conditions by a trained and calibrated dentist. Further details are in the protocol.8

Caries assessment

The International Caries Detection and Assessment System15 (ICDAS) was used to measure permanent teeth where:

Caries prevalence for obvious decay experience (D4-6MFT): at least one treated or untreated carious lesion, measured using the permanent tooth index ‘DMFT' (Decayed, Missing, and Filled Teeth). (Decayed = carious lesions extending into dentine - ICDAS levels 4-6; missing = teeth extracted due to caries; filled = restoration but not an obvious pit or fissure sealant, that is, restoration code was between 3 and 7 and caries code was 0, 1, 2 or 3)

Caries prevalence for all carious lesions (D1-6MFT): at least one treated or untreated carious lesion of any severity (ICDAS levels 1-6)

The number of teeth with any treated or untreated carious lesions (defined using D1-6MFT)

The number of teeth with any treated or untreated carious lesions extending into dentine (defined using D4-6MFT).

Plaque and gingivitis assessment

Plaque levels were assessed using Turesky's modification of the Quigley-Hein Plaque Index.16,17 Participants' whole mouth plaque index score was calculated by summing the surface codes (0 = no plaque to 5 = plaque covering two-thirds or more of the crown of the tooth) and dividing total score by number of surfaces (maximum 4 x 14 = 56 surfaces) examined.

Gingival inflammation was assessed using a modification of Gingival Index of Löe.18 The mean number of bleeding gingival sites per participant was calculated by summing the number of bleeding sites of each of the eight index teeth and dividing by the number of scorable sites (maximum 16, excluding missing teeth).

Self-reported oral health and behaviours

Participants completed a questionnaire which contained measures of HRQoL and OHRQoL and questions (using CDHS 20131,19 questions) about oral health behaviours, including toothbrushing frequency, toothpaste availability, diet and use of dental services and other fluoride use.

HRQoL was assessed using the Child Health Utility 9D20 (CHU9D) nine dimensions (5-point Likert scales).

OHRQoL was assessed using CARIES-QC (Caries Impacts and Experiences Questionnaire for Children):21 12 items (3-point Likert scale) measuring the symptomatic, functional and emotional impacts of caries on children with higher scores indicating increased impact of caries.

Participants reported the frequency of cariogenic foods/drinks consumed (cakes or biscuits, sweets or chocolate, cola or squash, fruit juices and smoothies, and energy drinks [for example, Powerade, Lucozade]). These were scored 0 = ‘never' to 5 = ‘four or more times a day'. A cariogenic score was calculated by summing these, dividing by the total possible score N, where N = 5 * the number of completed items and multiplying by 100.

Data analysis

The recruitment of schools and pupils and the collection of baseline data is depicted in a flow diagram (Fig. 1). Data are summarised descriptively. Mixed-effect logistic regression analyses were used to investigate the associations between obvious decay experience and age, sex, school attendance, FSM eligibility, IMD (standardised to account for the different scaling between countries), twice-daily toothbrushing, CARIES-QC, CHU9D and cariogenic scores. Mixed-effect bivariate analyses were undertaken initially, adjusting for school as a random effect, then all variables found to be associated with obvious decay experience (p <0.05) were included in a multivariate mixed-effect logistic regression analysis to account for possible confounding. Mixed-effect linear regression was used to consider the effect of twice-daily toothbrushing on plaque and bleeding scores, adjusting for site as a random effect.

Fig. 1

CONSORT (Consolidated Standards of Reporting Trials) flow diagram illustrating the flow of schools and pupils through the trial (a = approximate numbers, based on data available on the number of state-funded secondary schools in Scotland,22 England [South and West Yorkshire]23and Wales [Cardiff, Vale of Glamorgan, Rhondda Cynon Taf and Merthyr Tydfil local authorities]24 in 2016. b = approximate numbers, based on data available on the percentage of pupils eligible for FSMs in state-funded secondary schools in Scotland,22 England23 [South and West Yorkshire] and target local authorities in Wales25 in 2016)