UK (Mixed) 2009.
| Methods | Location: United Kingdom Number of centres: 13 centres Recruitment period: March 1997 to August 1999 Funding source: Medical Research Council (G9410454) Trial design: randomised parallel group trial |
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| Participants | Inclusion criteria: children in the mixed dentition with overjet greater than 7 mm, and willingness of the patient and a parent to participate in the study. Participants had to be in the mixed dentition with at least the permanent incisors and first molars erupted, but there was no age criterion Exclusion criteria: craniofacial syndromes Age at baseline: the average age was 9.7 (SD 0.98) years for the treatment group and 9.8 (SD 0.94) years for the control group. Number randomised: 174 Number evaluated: 127 |
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| Interventions | Gp A: Twin Block early treatment: randomised 89, completed 67 Gp B: Twin Block delayed treatment: randomised 85, completed 73 |
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| Outcomes | (i) Overjet (ii) Skeletal discrepancy measured by Pancherz analysis (iii) Dental alignment measured with the PAR index (iv) Sociopsychological effects of treatment |
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| Notes | Duration of intervention: 15 months Sample size calculation: "This showed that the mean duration of treatment for patients who had later treatment after early treatment was 25 months (SD 11). It was decided that a meaningful difference between the treatment duration for children who did, or did not, receive early treatment was 6 months. To give a study a power of 80% and an alpha of 0.05, the sample size needed to be 60 in each group." |
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| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| Random sequence generation (selection bias) | Low risk | "The randomization was made at the start of the study with pre‐prepared random number tables with a block stratification on centre and sex." |
| Allocation concealment (selection bias) | Low risk | Randomisation carried out using a central telephone line and minimisation software |
| Blinding of outcome assessment (detection bias) All outcomes | Low risk | Assessor blinded to outcomes. "The cephalograms and the study casts were scored with the examiner unaware of the patient's group." |
| Incomplete outcome data (attrition bias) All outcomes | Low risk | Clear information on withdrawals, but rates different in each group. 22/89 (25%) in the Twin Block group and 12/85 (14%) in the control group Reasons for exclusion specified (unpublished data) Control group: 4 refused to consent for phase 2 treatment, 1 withdrew due to illness, 3 had multiple DNAs with no final records, 1 moved away/lost contact, 2 had Twin Blocks fitted in phase 1 in error, 1 had sore mouth and required treatment in phase 1 Treatment group: 2 moved away/lost contact, 9 had multiple DNA with no follow‐up records, 4 did not start as eligibility criteria was not met, 5 refused to continue, 1 had poor oral health, 1 removed from study due to health problems |
| Selective reporting (reporting bias) | Low risk | All variables reported |
| Other bias | Low risk | Groups appear similar at baseline |