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A clinical investigation of force delivery systems for orthodontic space closure

Eastman Dental Hospital, London, UK

Claire Nightingale, 74 Antrim Mansions, Antrim Road, London NW3 4XL, UK. E-mail: claire{at}nightingales.org.uk

Objective: To investigate the force retention, and rates of space closure achieved by elastomeric chain and nickel titanium coil springs.

Design: Randomized clinical trial.

Setting: Eastman Dental Hospital, London and Queen Mary’s University Hospital, Roehampton, 1998–2000.

Subjects, materials and methods: Twenty-two orthodontic patients, wearing the pre-adjusted edgewise appliance undergoing space closure in opposing quadrants, using sliding mechanics on 0.019 x 0.025-inch posted stainless steel archwires. Medium-spaced elastomeric chain [Durachain, OrthoCare (UK) Ltd., Bradford, UK] and 9-mm nickel titanium coil springs [OrthoCare (UK) Ltd.] were placed in opposing quadrants for 15 patients. Elastomeric chain only was used in a further seven patients. The initial forces on placement and residual forces at the subsequent visit were measured with a dial push–pull gauge [Orthocare (UK) Ltd]. Study models of eight patients were taken before and after space closure, from which measurements were made to establish mean space closure.

Main outcome measures: The forces were measured in grammes and space closure in millimetres.

Results: Fifty-nine per cent (31/53) of the elastomeric sample maintained at least 50 per cent of the initial force over a time period of 1–15 weeks. No sample lost all its force, and the mean loss was 47 per cent (range: 0–76 per cent). Nickel titanium coil springs lost force rapidly over 6 weeks, following that force levels plateaued. Forty-six per cent (12/26) maintained at least 50 per cent of their initial force over a time period of 1–22 weeks, and mean force loss was 48 per cent (range: 12–68 per cent). The rate of mean weekly space closure for elastomeric chain was 0.21 mm and for nickel titanium coil springs 0.26 mm. There was no relationship between the initial force applied and rate of space closure. None of the sample failed during the study period giving a 100 per cent response rate.

Conclusions: In clinical use, the force retention of elastomeric chain was better than previously concluded. High initial forces resulted in high force decay. Nickel titanium coil springs and elastomeric chain closed spaces at a similar rate.

Key words: Elastomeric chain, force decay, in vivo study, nickel titanium coil springs, space closure

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