Risk-based, 6-monthly and 24-monthly dental check-ups for adults: the INTERVAL three-arm RCT

Jan E. Clarkson (Lead / Corresponding author), Nigel B. Pitts, Beatriz Goulao, Dwayne Boyers, Craig R. Ramsay, Ruth Floate, Hazel J. Braid, Patrick A. Fee, Fiona S. Ord, Helen V. Worthington, Marjon van der Pol, Linda Young, Ruth Freeman, Jill Gouick, Gerald M. Humphris, Fiona E. Mitchell, Alison M. McDonald, John D. T. Norrie, Kirsty Sim, Gail DouglasDavid Ricketts

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)
203 Downloads (Pure)


Background: Traditionally, patients are encouraged to attend dental recall appointments at regular 6-month intervals, irrespective of their risk of developing dental disease. Stakeholders lack evidence of the relative effectiveness and cost-effectiveness of different recall strategies and the optimal recall interval for maintenance of oral health.

Objectives: To test effectiveness and assess the cost-benefit of different dental recall intervals over a 4-year period.

Design: Multicentre, parallel-group, randomised controlled trial with blinded clinical outcome assessment at 4 years and a within-trial cost-benefit analysis. NHS and participant perspective costs were combined with benefits estimated from a general population discrete choice experiment. A two-stratum trial design was used, with participants randomised to the 24-month interval if the recruiting dentist considered them clinically suitable. Participants ineligible for 24-month recall were randomised to a risk-based or 6-month recall interval.

Setting: UK primary care dental practices.

Participants: Adult, dentate, NHS patients who had visited their dentist in the previous 2 years.

Interventions: Participants were randomised to attend for a dental check-up at one of three dental recall intervals: 6-month, risk-based or 24-month recall.

Main outcomes: Clinical - gingival bleeding on probing; patient - oral health-related quality of life; economic - three analysis frameworks: (1) incremental cost per quality-adjusted life-year gained, (2) incremental net (societal) benefit and (3) incremental net (dental health) benefit.

Results: A total of 2372 participants were recruited from 51 dental practices; 648 participants were eligible for the 24-month recall stratum and 1724 participants were ineligible. There was no evidence of a significant difference in the mean percentage of sites with gingival bleeding between intervention arms in any comparison. For the eligible for 24-month recall stratum: the 24-month (n = 138) versus 6-month group (n = 135) had an adjusted mean difference of -0.91 (95% confidence interval -5.02 to 3.20); the risk-based (n = 143) versus 6-month group had an adjusted mean difference of -0.98 (95% confidence interval -5.05 to 3.09); the 24-month versus risk-based group had an adjusted mean difference of 0.07 (95% confidence interval -3.99 to 4.12). For the overall sample, the risk-based (n = 749) versus 6-month (n = 737) adjusted mean difference was 0.78 (95% confidence interval -1.17 to 2.72). There was no evidence of a difference in oral health-related quality of life between intervention arms in any comparison. For the economic evaluation, under framework 1 (cost per quality-adjusted life-year) the results were highly uncertain, and it was not possible to identify the optimal recall strategy. Under framework 2 (net societal benefit), 6-month recalls were the most efficient strategy with a probability of positive net benefit ranging from 78% to 100% across the eligible and combined strata, with findings driven by the high value placed on more frequent recall services in the discrete choice experiment. Under framework 3 (net dental health benefit), 24-month recalls were the most likely strategy to deliver positive net (dental health) benefit among those eligible for 24-month recall, with a probability of positive net benefit ranging from 65% to 99%. For the combined group, the optimal strategy was less clear. Risk-based recalls were more likely to be the most efficient recall strategy in scenarios where the costing perspective was widened to include participant-incurred costs, and in the Scottish subgroup.

Limitations: Information regarding factors considered by dentists to inform the risk-based interval and the interaction with patients to determine risk and agree the interval were not collected.

Conclusions: Over a 4-year period, we found no evidence of a difference in oral health for participants allocated to a 6-month or a risk-based recall interval, nor between a 24-month, 6-month or risk-based recall interval for participants eligible for a 24-month recall. However, people greatly value and are willing to pay for frequent dental check-ups; therefore, the most efficient recall strategy depends on the scope of the cost and benefit valuation that decision-makers wish to consider.

Future work: Assessment of the impact of risk assessment tools in informing risk-based interval decision-making and techniques for communicating a variable recall interval to patients.

Trial registration: Current Controlled Trials ISRCTN95933794.

Original languageEnglish
Pages (from-to)1-138
Number of pages138
JournalHealth Technology Assessment
Issue number60
Publication statusPublished - Nov 2020

ASJC Scopus subject areas

  • Health Policy


Dive into the research topics of 'Risk-based, 6-monthly and 24-monthly dental check-ups for adults: the INTERVAL three-arm RCT'. Together they form a unique fingerprint.
  • No photo of David Ricketts

    Ricketts, David

    • Dentistry - Professor of Evidence Based Operative Dentistry & Evidence Based Operative Dentistry

    Person: Academic

Cite this