Here is the design of a clinical trial:

Official Title: Developing and Evaluating a Theory-derived Intervention to Improve Oral Health of Community-dwelling Elderly

Included conditions:
- Periodontal Diseases
- Dental Caries

Study Armgroups:
- {'label': 'Theory-derived intervention', 'type': 'EXPERIMENTAL', 'description': 'Questionnaire will be used including the scales for three dominant theoretical models, Health Belief Model (HBM), Theory of planned behaviour (TPB) and Social Cognitive Theory (SCT). The theoretical model that best explains the health behaviours of the selected participants will be selected for designing oral health intervention.The theory-derived intervention will address the constructs/domains of the selected model(s) in the context of the three target behaviours (diet, toothbrushing and dental flossing).', 'interventionNames': ['Behavioral: Theory-derived intervention']}
- {'label': 'Conventional health education', 'type': 'ACTIVE_COMPARATOR', 'description': 'Participants will be randomly assigned to the control group, stratified by gender and education level. Allocation concealment will be ensured by using sealed opaque envelopes.', 'interventionNames': ['Behavioral: Conventional health education']}

Interventions:
- {'type': 'BEHAVIORAL', 'name': 'Theory-derived intervention', 'description': 'The intervention will be delivered through multimedia materials and group activities, as appropriate. Participants will spend approximately 30-45 minutes for the intervention. Intervention materials and activities will be carefully designed to address all the constructs/ domains of the selected theoretical model(s). The effectiveness of the interventions will be evaluated using behavioural outcomes (diet, brushing, flossing) and clinical outcomes (oral hygiene, caries and periodontal conditions).', 'armGroupLabels': ['Theory-derived intervention']}
- {'type': 'BEHAVIORAL', 'name': 'Conventional health education', 'description': 'The conventional health education will be delivered through an oral health talk and oral health booklet. Topics covered are: (i) common oral diseases and its consequences; (ii) common dental problems among older adults; (iii) importance of oral health measures (healthy diet, toothbrushing and dental flossing); and (iv) proper techniques for toothbrushing and dental flossing.', 'armGroupLabels': ['Conventional health education']}

Primary Outcomes:
- {'measure': 'Increment of coronal caries', 'description': 'Number of new surfaces with coronal caries', 'timeFrame': 'From baseline to 2 years post-intervention'}
- {'measure': 'Increment of root caries', 'description': 'Number of new surfaces with root caries', 'timeFrame': 'From baseline to 2 years post-intervention'}

Please estimate the sample size based on the assumption: 
Based on a significance level of 5% and a power of 80%, with an estimated 25% attrition rate.
Sample size calculation
        The sample size needed for this study was calculated by using the software G*Power V.3.1.9.2 (Franz Faul, University of Kiel, Germany). The sample size calculation was based on the primary outcomes, namely increment of coronal caries (ÎDFS â coronal) and increment of root caries (ÎDFS â root), and independent t-tests for comparing means of two independent groups. A caries incidence study among the elderly reported that the mean (SD) 5âyears 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.