Article Text

Theory-derived intervention to improve oral health of older adults: study protocol for a randomised controlled trial
  1. Xiaoli Gao1,2,
  2. Mun Loke Wong1,
  3. Ashish Chetan Kalhan1,
  4. Joshua Jiaming Xie1,
  5. Hamzah Siti Hajar1,
  6. Alvin Boon Keng Yeo1,
  7. Patrick Finbarr Allen1
  1. 1Faculty of Dentistry, National University of Singapore, Singapore
  2. 2Saw Swee Hock School of Public Health, National University of Singapore, Singapore
  1. Correspondence to Dr Xiaoli Gao; dengx{at}


Introduction Changing health behaviours is an important and difficult task. Despite growing interest in behavioural theories and models, there is a paucity of research examining their validity in explaining oral health behaviours, and there is a need for interventional studies to assess their effectiveness in improving oral health. This study aims to test the explanatory power of the dominant psychological theories, develop theory-derived intervention and evaluate its effectiveness in improving oral health of older adults.

Methods and analysis 440 community dwelling older adults will be recruited. To be eligible for this trial, one needs to be 55–79 years old, having at least 8 natural teeth, and with no life-threatening disease, impaired cognitive function, or radiotherapy in the head and neck region. At the initial visit, each participant will be required to complete a detailed questionnaire which collects information on sociodemographic background, oral health behaviours and domains of three psychological theories and models: (1) health belief model, (2) theory of planned behaviour and (3) social cognitive theory. The theory or model that best explains the health behaviours will be selected for designing the oral health intervention. The effectiveness of the theory-derived intervention will be evaluated in a randomised controlled trial. Participants will be randomly assigned to two groups, receiving theory-derived intervention and conventional health education, respectively. At baseline and at 12 and 24 months post intervention, each participant will complete a short questionnaire and undergo an oral examination (dental check-up). The effectiveness of the interventions will be evaluated using behavioural outcomes (diet, toothbrushing, interdental cleaning) and clinical outcomes (oral hygiene, dental caries and periodontal conditions).

Ethics and dissemination This study has been approved by the Institutional Review Board of National University of Singapore (Ref: NUS-IRB-2020-417). Findings will be presented in international conferences and peer-reviewed journals.

Trial registration number NCT04946292.


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Strengths and limitations of this study

  • This study adopts a randomised controlled trial design and is likely to generate robust evidence on theory-derived intervention for improving oral health of older adults.

  • Recruitment of participants from different socioeconomic strata of a multiethnic community will contribute to the generalisability of the study findings.

  • Effectiveness of the intervention will be evaluated using both self-reported, behavioural outcomes and objective, clinical outcomes.

  • Dental examiners will be blinded to the group allocation to reduce potential bias.

  • There may be potential Hawthorne effect as participants may modify some of the behaviours simply because they are being observed.


The world’s population is ageing rapidly, and this trend is expected to accelerate based on the recent United Nations report.1 The number of people aged 65 years and over is projected to increase from 0.7 billion (9%) in 2019 to 1.5 billion (16%) in 2050.1 In Singapore, the proportion of residents aged 65 years and over increased from 8.8% in 2009 to 14.4% in 2019,2 and is projected to surge to 47% in 2050.1

As pointed out by WHO, older adults should not be stereotyped as frail and dependent.3 Although some suffer from multiple health issues and compromised daily functions, many maintain good physical and mental capacities and are fully engaged in the society.3 This highly varied health status among older adults is largely determined by their experiences, exposure, living conditions and health behaviours during their life course. Promoting healthy lifestyles is therefore regarded as the gateway to healthy ageing.3

Oral diseases, such as dental caries and periodontal diseases, are among the most prevalent conditions, affecting 3.5 billion people across the world.4 Prevalence of oral diseases increases with age, and almost all older adults have been affected some forms of oral diseases.4 These oral conditions are chronic and significantly compromise one’s daily functions and quality of life.5 6 Treatment of these diseases and their complications imposes heavy economic burden on individuals, families and the healthcare systems.4 Chronic oral diseases are largely determined by one’s lifestyles and are preventable if one can adopt healthy behaviours.7 A sizeable body of evidence supports that, if older adults adopt healthy lifestyles, their health outcomes are improved and disease risk or complications are reduced.1 8 This in turn contributes to better quality of life and extended lifespan.8 9

Changing lifestyles is, however, a difficult task. Although health professionals make tremendous efforts to educate the public, the outcomes are often disappointing. Conventional health education focuses on disseminating information and giving normative advice.10 In the dental context, educational efforts have been largely directed to promoting healthy diet, good oral hygiene practices and regular dental attendance.7 Research evidence, however, has shown that although oral health knowledge is often improved after health education, such knowledge gain seldom translates into sustained changes in health behaviours.11 12

The unsatisfactory outcomes of conventional health education has cast doubts on the traditional knowledge-attitude-practice model.13 Alternatively, psychological theories and models have been proposed to explain and predict health behaviours. Health Belief Model (HBM), Theory of Planned Behavior (TPB) and Social Cognitive Theory (SCT) models13 14 are among the most influential ones that attract much scholarly attention. These theories and models aim to understand the cognitive factors and psychological mechanisms behind one’s behaviours, and therein may inform the development of effective interventions.13 14 Despite the growing interest in theories and models for health promotion, there is a paucity of research examining their validity in explaining oral health behaviours, and there is a need for scientific evidence on the effectiveness of theory-based interventions.14

To address these knowledge gaps, this study will be conducted among community dwelling older adults. The objectives are (1) to test the explanatory power of the dominant psychological theories and models, (2) to develop theory-derived intervention for oral health, and (3) to evaluate the effectiveness of the theory-derived intervention in improving oral health. The hypothesis is that theory-derived intervention is more effective than conventional health education in improving oral health behaviours and preventing oral diseases among older adults.

Methods and analysis

This study protocol (version 1, 3 May 2022) describes the design of a multicentre, two-arm parallel-group randomised controlled trial (RCT) (1:1 ratio) conducted at active ageing centres and senior activity centres in Singapore. The study protocol conforms with the Standard Protocol Items: Recommendations for Interventional Trials,15 while the RCT will conform to the Consolidated Standards of Reporting Trials statement for reporting RCTs.16 The study was registered at in June 2021 (NCT04946292). The planned start and end dates are 31 March 2022 and 28 February 2025.

Sample size calculation

The sample size needed for this study was calculated by using the software G*Power V. (Franz Faul, University of Kiel, Germany). The sample size calculation was based on the primary outcomes, namely increment of coronal caries (ΔDFS – coronal) and increment of root caries (ΔDFS – root), and independent t-tests for comparing means of two independent groups. A caries incidence study among the elderly reported that the mean (SD) 5 years caries incidence were 2.65 (3.14) for coronal caries and 2.21 (2.83) for root caries.17 The 2-year incidence of coronal caries and root caries were therefore estimated to be 1.06 (1.26) and 0.88 (1.13), respectively, in the control group. The effect of an intervention is considered clinically significant if it reduces the caries incidence by 40%. Based on a significance level of 5% and a power of 80%, 140 subjects per group are needed for coronal caries and 165 subjects are needed for root caries outcome measures. To take both outcome measures into account, the higher number (ie, n=165) will be adopted. Allowing for a 25% attrition rate, 220 elderly persons will need to be recruited into each group, giving a total sample size of 440.

Study participants

A total of 440 participants fulfilling the below criteria will be recruited in the study.

Inclusion criteria

  • Aged 55–79 years.

  • Living in the community (alone or with family members), instead of residing in a nursing home.

  • Having at least eight natural teeth.

Exclusion criteria

  • Having life-threatening disease(s) (eg, advanced cancer, acute stroke).

  • Impaired cognitive function (eg, Alzheimer’s syndrome).

  • Radiotherapy in the head and neck region.

  • Planning to emigrate during the study period.

Recruitment procedure

The study participants will be recruited from the community with the assistance of a social service organisation. Advertisement posters, with an embedded QR code, will be displayed at these designated centres to enrol the participants. Participant may also approach the staff of the participating centres for assistance in enrolment. If the participant meets the eligibility criteria, the study details will be explained in his/her preferred language, using an information sheet. If the participant is willing to take part in the study, a written informed consent (online supplemental appendix 1) will be obtained by a trained research staff.

Testing of theoretical models

Each study participant will be required to complete a detailed questionnaire at the initial visit through an interview. Information on sociodemographic background (ethnicity, gender, age, education level, past occupation and type of housing) and oral health behaviours (diet, toothbrushing, and interdental cleaning) will be collected. The questionnaire will also include the scales for three dominant psychological theories and models:

  1. HBM, which suggests that health-promoting behaviours are triggered by the presence of six domains: perceived susceptibility, perceived severity, perceived barriers, perceived benefit, cue to action and perceived self-efficacy.18

  2. TPB which was developed on the basis of the Theory of Reasoned Action and states that intention towards behaviour, subjective norms, and perceived behavioural control, together shape an individual’s behavioural intentions and behaviours.19

  3. SCT which states that behaviour is a function of individuals’ expectations of the consequences of the action (outcome expectations), their abilities to execute the action (self-efficacy), and their beliefs that the action will achieve a desired outcome (response efficacy).20

The explanatory power of each theory and model will be analysed by structural equation modelling and hierarchical multiple regression, controlled for potential confounders. Model fit indices (χ2/df, RMSEA, and CFI) and R2 (% of variance explained) will be used to evaluate and compare the validity of the theories and models.

Development of theory-derived intervention

The theory or model that best explains the health behaviours will be selected for designing oral health interventions. If no single model reaches adequate explanatory power (χ2/df<3 and R2>0.3) or the best model differs across behaviours, two models with the best fit will be simultaneously considered. The theory-derived intervention will then be developed by an expert panel, consisting of a behavioural scientist, a health psychologist, a public health researcher and a dental specialist. Intervention materials and activities will be carefully designed to address all the constructs/domains of the selected theory or model. Relevant medical and dental literature will be referred to in the design of the intervention. The needs, interests and health literary of the target group (ie, older adults of varied social and educational backgrounds) will be taken into full consideration. The intervention will be tested in a small group of 15–20 older adults to ensure its relevance, practicality and acceptability.

Randomisation and interventions

Participants will be randomised into two interventional groups (1:1 allocation ratio), stratified by gender and educational level. Randomisation will be performed by a researcher who is not involved in data collection. Allocation sequence will be computer generated, and will be concealed until interventions are assigned.

The two study groups will receive either of the following interventions:

Conventional health education

The conventional health education will be delivered through oral health pamphlets. Topics covered will include: (1) common oral diseases (dental caries, periodontal diseases) and their consequences; (2) common dental problems among older adults; (3) importance of oral health self-care measures (healthy diet, toothbrushing/denture brushing and interdental cleaning); and (4) proper techniques for toothbrushing and interdental cleaning.

Theory-derived intervention

The intervention will be delivered through multimedia materials (printed materials, PowerPoint slides, short videos, tooth models) and group activities (quiz, discussion, demonstration, practice and feedback), as appropriate. Participants will spend approximately 30–45 min for the intervention. Intervention materials and activities will be carefully designed to address all the constructs/domains of the selected theory or model. Three rounds of short messages will be sent to participants’ mobile phones to provide continuous support and facilitate behavioural changes.

Data collection procedure

The study flow is described in figure 1. At baseline and at 12 and 24 months post intervention, each participant will undergo a dental examination and complete an interviewer-administered questionnaire.

Figure 1

Flow chart of randomised controlled trial.

A detailed questionnaire (online supplemental file 1) will be completed at baseline, and a short questionnaire (online supplemental file 2) will be completed at each follow-up visits. The detailed questionnaire collects information on participants’ sociodemographic background, oral health awareness and behaviours, and constructs of the theoretical models. The short questionnaire includes oral health behaviours at each follow-up time point, and participants’ dental visits and the treatments received since last visit. Trained research assistants, well versed in local languages, will administer the questionnaires and address any queries of the participants.

Dental examinations will be carried out by trained, qualified and calibrated dental professionals who will be blinded to the group allocation. The findings of the dental examination will be conveyed to the participants after each visit using a simple oral health report. Duplicate examination will be performed on a randomly selected sample of 10% of the study participants, to evaluate the interexaminer reliability. The dental examination will include the following indices: (1) Decayed, Missing, Filled Surfaces/Teeth21; (2) Root Caries Index22; (3) Community Periodontics Indication of Treatment Needs23; and (4) Plaque Index.24 Participants will be examined in supine position in a portable dental chair. The detection of dental caries will be based on visual and tactile examinations. No radiographs will be taken. Periodontal condition will be examined by using a lightweight CPI probe with a 0.5-mm ball tip, a black band between 3.5 and 5.5 mm, and rings at 8.5 and 11.5 mm from the ball tip. As for oral hygiene status, plaque scores of four surfaces (buccal, lingual, mesial and distal) of six indexed teeth (#16, #12, #24, #36, #32, #44) will be recorded.

Study outcomes

Behavioural outcomes

  1. Change in dietary behaviours: dietary behaviours will be categorised into: (i) favourable (frequency of snack intake, sweet/desert intake and/or sugary drinks<2 times/day) and (ii) unfavourable (frequency of snack intake, sweet/desert intake and/or sugary drinks≥2 times/day).

  2. Change in toothbrushing behaviours: toothbrushing behaviours will be categorised as: (i) favourable (frequency of brushing≥2 times/day and brushing time≥2 min) and (ii) unfavourable (frequency of brushing<2 times/day and brushing time<2 min).

  3. Change in interdental cleaning behaviours: frequency of interdental cleaning (with≥once/day considered as favourable and <once/day considered unfavourable).

Clinical outcomes (* Primary outcomes)

  1. * Coronal caries increment: number of new surfaces with coronal caries.

  2. * Root caries increment: number of new surfaces with root caries.

  3. Change in oral hygiene status (plaque score).

  4. Change in periodontal conditions: number of sites with deep periodontal pockets, shallow periodontal pockets and gingival bleeding only.

Data management

Personal information about participants will be kept separate from the main dataset and will not be shared. All personal data will be stored securely in order to protect confidentiality before, during and after the trial, and the study data will be accessible only to the authorised study team members. Data entry and coding of the deidentified data will be conducted by a trained staff to achieve satisfactory data quality. Written informed consent will be obtained by a trained research staff from the study team and the documents will be stored securely along with other study related data.

Data monitoring and auditing

The study will not have a formal data monitoring committee as adverse events of interventions are not expected. Annual auditing of the trial conduct will be undertaken by the Institutional Review Board of National University of Singapore where the study team will be required to submit annual progress reports of the trial and report any untoward incident, if encountered. This auditing process will be independent of the investigators and study sponsors.

Statistical analysis

Data will be analysed on an intention-to-treat basis. χ2 tests will be used for comparing proportions. Independent samples t-test or its non-parametric equivalent will be adopted for comparing means. Analysis of covariance (ANCOVA) and multiple regressions will be performed to evaluate the effects of various factors on the outcomes. A detailed statistical analysis plan will be made publicly available before unblinding the data and any analyses are performed.

Ethics and dissemination

This study has been approved by the Institutional Review Board of National University of Singapore (Ref: NUS-IRB-2020-417). All protocol related amendments will be reported to the ethics body (Institutional Review Board of NUS) and also updated on the trial registry ( Results will be presented in peer-reviewed journals and at international conferences. Authorship eligibility will be based on the recommendations from the International Committee of Medical Journal Editors.

Patient and public involvement

Patients or the public were not involved in the design, or conduct, or reporting, or dissemination plans of our research.


There has been growing scholarly interest in the potential of psychological theories and models in guiding health interventions. In the dental arena, some attempts have been made to incorporate these concepts into oral health promotion and optimisation of patient care.13 14 These efforts, however, appeared to be scattered, and scientific evidence is scarce.14

To the best of our knowledge, this is the first study which systemically test the dominant theories and model and, based on that, develop and evaluate theory-derived interventions for oral health. This study is likely to generate much needed evidence, pave the way for translation of these theories and models into practice, and contribute to addressing oral health challenges in the increasingly ageing population.

To control the participation burden and reduce the number of visits, short-term behavioural changes (eg, 1, 3 or 6 months post intervention) will not be observed. This trial will focus on sustainable behavioural changes and clinical outcomes throughout the 12 and 24 months periods. It is anticipated that there will be a considerable number of participants who drop out during the 24-month trial. To reduce bias, efforts will be made to follow up the participants and control the attrition rate to below 20%. Such attrition rate has also been accounted for in the sample size calculation. It is anticipated that some participants may visit dentist during the study period. The visits are however likely to be treatment driven (eg, extraction and restoration), with little preventive measures. Therefore, the effect of possible dental visits on the outcomes is supposed to be minimal. Nevertheless, information on the dental visits and treatments received will be collected and included in the data analysis.

The target behaviours are dietary intake, toothbrushing and flossing. Since diet and personal hygiene are common risk factors that are related to both oral health and systemic conditions, the intervention is relevant for advancing general health of the elderly population. Meanwhile, oral health is an integral part of general health. An intervention that improves oral health of older adults is likely to improve their nutritional status, daily functional and quality of life as a whole. Although the findings may not be directly generalisable to countries with different social and cultural contexts, some useful implications can be expected.

Ethics statements

Patient consent for publication


We acknowledge the supports of active ageing centers and senior activity centers. A final list of centers will be included in future publications.


Supplementary materials


  • Contributors XG conceived this study, coordinated the study design and prepared the proposal, which served as the first draft for this manuscript. MLW and PFA contributed to the study design and the preparation of the proposal. ACK contributed to the refinement and pretesting of the questionnaire and the preparation of the manuscript. JJX, HSH and ABKY contributed to the refinement of questionnaire and the preparation of the manuscript. All authors have read the manuscript, critically revised it, and approved the version submitted for publication.

  • Funding This trial is funded by the NUS Startup grant (Grant No.: R-221-000-140-133) sponsored by the Ministry of Education, Singapore.

  • Disclaimer The study sponsor and funders have no roles in study design; collection, management, analysis, and interpretation of data; writing of the report; and the decision to submit the report for publication.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.