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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. Funding: This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme [project numbers 06/35/05 (Phase I) and 06/35/99 (Phase II)] and will be published in full in Health Technology Assessment; Vol. 24, No. 60. See the NIHR Journals Library website for further project information.

Background: Periodontal disease is preventable but remains the most common oral disease worldwide, with major health and economic implications. Stakeholders lack reliable evidence of the relative clinical effectiveness and cost-effectiveness of different types of oral hygiene advice (OHA) and the optimal frequency of periodontal instrumentation (PI). Objectives: To test clinical effectiveness and assess the economic value of the following strategies: personalised OHA versus routine OHA, 12-monthly PI (scale and polish) compared with 6-monthly PI, and no PI compared with 6-monthly PI. Design: Multicentre, pragmatic split-plot, randomised open trial with a cluster factorial design and blinded outcome evaluation with 3 years’ follow-up and a within-trial cost–benefit analysis. NHS and participant costs were combined with benefits [willingness to pay (WTP)] estimated from a discrete choice experiment (DCE). Setting: UK dental practices. Participants: Adult dentate NHS patients, regular attenders, with Basic Periodontal Examination (BPE) scores of 0, 1, 2 or 3. Intervention: Practices were randomised to provide routine or personalised OHA. Within each practice, participants were randomised to the following groups: no PI, 12-monthly PI or 6-monthly PI (current practice). Main outcome measures: Clinical – gingival inflammation/bleeding on probing at the gingival margin (3 years). Patient – oral hygiene self-efficacy (3 years). Economic – net benefits (mean WTP minus mean costs). Results: A total of 63 dental practices and 1877 participants were recruited. The mean number of teeth and percentage of bleeding sites was 24 and 33%, respectively. Two-thirds of participants had BPE scores of ≤ 2. Under intention-to-treat analysis, there was no evidence of a difference in gingival inflammation/bleeding between the 6-monthly PI group and the no-PI group [difference 0.87%, 95% confidence interval (CI) –1.6% to 3.3%; p = 0.481] or between the 6-monthly PI group and the 12-monthly PI group (difference 0.11%, 95% CI –2.3% to 2.5%; p = 0.929). There was also no evidence of a difference between personalised and routine OHA (difference –2.5%, 95% CI –8.3% to 3.3%; p = 0.393). There was no evidence of a difference in self-efficacy between the 6-monthly PI group and the no-PI group (difference –0.028, 95% CI –0.119 to 0.063; p = 0.543) and no evidence of a clinically important difference between the 6-monthly PI group and the 12-monthly PI group (difference –0.097, 95% CI –0.188 to –0.006; p = 0.037). Compared with standard care, no PI with personalised OHA had the greatest cost savings: NHS perspective –£15 (95% CI –£34 to £4) and participant perspective –£64 (95% CI –£112 to –£16). The DCE shows that the general population value these services greatly. Personalised OHA with 6-monthly PI had the greatest incremental net benefit [£48 (95% CI £22 to £74)]. Sensitivity analyses did not change conclusions. Limitations: Being a pragmatic trial, we did not deny PIs to the no-PI group; there was clear separation in the mean number of PIs between groups. Conclusions: There was no additional benefit from scheduling 6-monthly or 12-monthly PIs over not providing this treatment unless desired or recommended, and no difference between OHA delivery for gingival inflammation/bleeding and patient-centred outcomes. However, participants valued, and were willing to pay for, both interventions, with greater financial value placed on PI than on OHA. Future work: Assess the clinical effectiveness and cost-effectiveness of providing multifaceted periodontal care packages in primary dental care for those with periodontitis. Trial registration: Current Controlled Trials ISRCTN56465715. Funding: This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 22, No. 38. See the NIHR Journals Library website for further project information.