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Am J Orthod Dentofacial Orthop. 2019 Feb;155(2):165-172. doi: 10.1016/j.ajodo.2018.07.016.

Effectiveness of part-time vs full-time wear protocols of Twin-block appliance on dental and skeletal changes: A randomized controlled trial.

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Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom.
Department of Orthodontics and Dentofacial Orthopedics, School of Dental Medicine, Medical Faculty, University of Bern, Bern, Switzerland.
Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom. Electronic address:



The aim of this 2-arm parallel study was to compare the dentoalveolar and skeletal changes achieved with Twin-block appliance therapy prescribed on either a part- or full-time basis for 12 months.


Sixty-two 10- to 14-year-old patients were randomly allocated to either full-time (FT, 22 hours daily) or part-time (PT, 12 hours daily) wear of a modified Twin-block appliance. Participants were recruited from the Institute of Dentistry, Barts and the London School of Medicine and Dentistry, London, United Kingdom, and recalled at 6- to 8-week intervals. Electronic randomization was undertaken, with group allocation concealed using opaque, sealed envelopes. The outcome assessor was blinded; however, it was not feasible to blind either operator or patients. Study models and cephalograms were taken at baseline and after 12 months of treatment.


Data from 55 of the 62 participants were analyzed. Overjets were reduced by 7 mm (SD, 2.92) in the PT group and 6.5 mm (SD, 2.62) in the FT group, with no statistical difference between the groups (P = 0.587; 95% CI, -1.01, 1.78). Similarly, no clinical or statistical differences were noted for skeletal changes: ANB angle (PT, -1.51°; FT, -1.25°; P = 0.828; 95% CI, -0.68, 0.849), pogonion-sella vertical (PT, 3.25 mm; FT, 3.35 mm) or A-sella vertical (PT, 1.28 mm; FT, 1.06 mm). Mean wear durations were 8.78 hours a day in the PT group and 12.38 hours in the FT group.


There was no difference in either dental or skeletal changes achieved with PT or FT wear of a Twin-block appliance over 12 months. Less onerous PT wear regimens may therefore be a viable alternative to FT wear of removable functional appliances.




The protocol was not published before trial commencement.

[Indexed for MEDLINE]

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