Matched cohort, 1,140 children, 12 schools

Dentistry research poster example

A school varnish programme is usually reported by how many children were seen, which goes up whether or not anyone ends up with fewer holes. This board reports what changed instead: new decayed surfaces per child at 24 months in six programme schools against six matched comparison schools, counted by examiners who did not know which was which.

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TU
School fluoride varnish and new caries at 24 months: 1,140 children in 12 schools
S. Tarrant ¹, B. Ngata ¹, V. Duhamel ², K. Ranasinghe ¹ ²
1 School of Dentistry, Thornbury University · 2 Regional Oral Health Service, Northern District
ABSTRACT
Fluoride varnish applied at school reaches children who do not reach a dental chair, and the programmes that do it are usually reported by how many children were seen rather than by what changed. This cohort followed 1,140 children in 12 schools for 24 months. Six schools ran a twice yearly varnish programme and six did not, and examiners who did not know which school was which recorded new decayed surfaces at the start and at 24 months. Children in programme schools developed a mean of 0.9 new decayed surfaces against 1.6 in comparison schools, which is 44 per cent fewer.
INTRODUCTION
Varnish is cheap, quick and does not need a chair, a drill or a parent present, which is why school programmes keep being funded and keep being evaluated badly. The usual evaluation counts applications. That number goes up whether or not any child ends up with fewer holes, and it says nothing about the children who were absent on the day.
METHODS
Design. Prospective cohort in 12 primary schools, six running a twice yearly varnish programme and six matched comparison schools with no programme, followed for 24 months.
Matching. Schools were paired on enrolment size, the share of children with a health care card and water fluoridation status, so every programme school has a comparison school on the same water supply.
Programme. Five per cent sodium fluoride varnish applied by a dental therapist twice a year in school time, with written consent from a parent and a record of every child absent on the day.
Measure. New decayed surfaces counted at baseline and at 24 months by two examiners who were not told which schools ran the programme and who scored a 10 per cent duplicate sample.
Analysis. Mean new decayed surfaces per child compared between arms with the school treated as the unit of clustering, and reported for each year group as well as overall.
ProgrammeComparison00.40.81.21.6
Figure 1. Mean new decayed surfaces per child over 24 months, by arm.
Source: 1,140 children, 12 schools, blinded examination.
RESULTS
Children in the six programme schools developed a mean of 0.9 new decayed surfaces over 24 months against 1.6 in the six comparison schools, a difference of 0.7 surfaces a child and 44 per cent fewer. By year group the means were 0.7 against 1.3 in year 1, 0.9 against 1.6 in year 3 and 1.1 against 1.9 in year 5, with 380 children in each year group split evenly between the arms. The direction is the same in every pair of schools and in every year group, and the absolute gap grows with age because decay accumulates in both arms rather than because the programme works better in older children. Attendance on varnish days was 86 per cent at the first round and 81 per cent at the fourth, so roughly one child in six missed any given application. Examiner agreement on the duplicate sample was 0.91 on the presence of a new decayed surface and 0.84 on the count. Consent was returned for 94 per cent of children in the programme schools, and the six comparison schools ran no varnish at any point across the 24 months.
00.511.52Year 1Year 3Year 5
Figure 2. Mean new decayed surfaces per child by year group and arm, 380 children per year group.
Source: baseline and 24 month examination, 12 schools.
44%
fewer new decayed surfaces
0.9 against 1.6 surfaces a child over 24 months
DISCUSSION
A difference of 0.7 surfaces a child over two years is the kind of number that reads as small on a board and matters in a clinic, because it is roughly one filling avoided for every one and a half children. Three things about this design deserve to be said out loud rather than left to the method block. Schools were not randomised, so a school that agreed to run a programme may differ from one that did not in ways the matching did not catch, including how many of its families already attend a dentist.
CONCLUSIONS
Over 24 months children in schools running a twice yearly varnish programme developed 44 per cent fewer new decayed surfaces than children in matched comparison schools, 0.9 against 1.6 per child. The finding held in all three year groups. It rests on matched schools rather than randomised ones, and on a programme that reached about five children in six on any given day.
Schools were matched, not randomised, so selection is not ruled out
One child in six missed any given varnish application
Children knew their school ran the programme; examiners did not
Two years of follow up says nothing about permanent teeth later
REFERENCES
1.Okonjo, A. and Tarrant, S. (2024) School based fluoride varnish: what the application count hides. Journal of Community Oral Health, 27(1), 33 to 58.
2.Bellweather, R. (2025) Examiner blinding in school caries surveys. Dental Measurement Reports, 10(2), 112 to 130.
3.Duhamel, V. (2026) Attendance and dose in twice yearly varnish programmes. Thornbury Dentistry Working Paper 2026-02.

Block by block

What each block on the board is for, in the order a reader walks it.

Title band and four authors
The title carries the intervention, the outcome, the follow up and the sample. Four authors sit over two affiliations with the presenting author marked.
Abstract
Why a varnish programme is usually evaluated badly, what this cohort did instead, and the headline: 0.9 new decayed surfaces per child in programme schools against 1.6 in comparison schools, present in all three year groups.
Background
Varnish is cheap and needs no chair, a drill or a parent present, which is why the programmes keep being funded and keep being counted rather than measured. A programme is worth its cost only if new decay falls.
Methods as a labelled protocol
Five labelled entries: the cohort design, how schools were paired on enrolment, health care card share and water fluoridation, the varnish protocol and consent, the blinded examination, and the analysis with the school as the unit of clustering.
Figure 1, the headline comparison
Two bars, programme and comparison, at 0.9 and 1.6 new decayed surfaces per child. Two categories put the legend in the gap between them rather than over a tick label.
Results in full
The overall difference, the three year group means, the direction in every pair of schools, attendance on varnish days, examiner agreement, the consent rate and the baseline, which was 1.4 surfaces per child in both arms.
Figure 2, by year group
Horizontal bars for years 1, 3 and 5 with both arms, 380 children per year group. Horizontal bars carry the year labels without rotating them and keep the two series legend clear of the axis.
Discussion, conclusions and limits
The three things this design cannot rule out, a conclusion that repeats the number with its denominator, four checked limits rather than four boasts, and three numbered references.

What makes this board work

The outcome is a count, not an activity

New decayed surfaces per child, 0.9 against 1.6, is the number on the board. The application count that most varnish programmes report appears only as attendance, which is where it belongs: a measure of delivery rather than of effect.

Blinding is stated where it matters

The methods block says the two examiners were not told which schools ran the programme and scored a 10 per cent duplicate sample, with agreement of 0.91. A cohort poster that does not say who measured the outcome invites the first question from the floor.

The design is criticised on the board

Schools were matched, not randomised, and the discussion says so before a reviewer can. It also names the two consequences: families who already attend a dentist, and children who received one application in two years sitting in the same arm as children who received four.

Questions people ask

What goes on a dental research poster?

The clinical or public health question, the population and how it was selected, the intervention and its protocol, who examined the teeth and whether they were blinded, the outcome per child with its denominator, and the limits. Attendance and consent rates belong on the board because they bound the result.

Why blind the examiners in a caries study?

Because counting a new decayed surface involves judgement, and an examiner who knows a child is in the programme arm can shade that judgement without meaning to. This study used two examiners who were not told which schools ran the programme, plus a duplicate sample to report agreement.

Matched schools or randomised schools?

Randomised is stronger and often impossible when a programme is already running. Matching on enrolment size, health care card share and water fluoridation narrows the gap but cannot close it, so a matched cohort poster should say what the matching could not fix rather than implying a trial.

How do I show three subgroups without a table?

This layout has no table block, so the three year group means sit in the results block and appear again as a two series horizontal bar chart. Only three of the forty poster designs carry a table block, so check the design before planning a table.

How big should the text be on an A0 poster?

Large enough to read from about a metre and a half, which in practice means a body size that fills its block without shrinking. The layout sets the type scale per block, so the honest way to keep text readable is to write to the block rather than to paste a paragraph and let it shrink.

Can the four checked points be limitations?

Yes, and on this board they are. The list block takes exactly four items on this design, so the three limitations in the brief became four short caveats rather than four claims, which is a better use of the last block on a cohort poster.

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