Is it really necessary for patients to wear aligners for 22 hours a day to achieve effective orthodontic correction?
Aligner therapy has become increasingly popular in recent years. However, compliance with the recommended 22-hour daily wear remains a clinical challenge. Discomfort during initial wear, speech difficulties, and waning motivation often lead to reduced adherence. In patients seeking correction of very mild crowding, such as relapse cases, it is clinically relevant to question whether shorter daily wear times might still be effective without compromising outcomes.
A recent randomized clinical trial published in the European Journal of Orthodontics explored whether a reduced 12-hour daily wear protocol could deliver comparable outcomes in adults with mild malocclusions.
Study Overview
This single-centre randomized clinical trial included 50 adult patients aged between 18 and 60 years with Angle Class I malocclusion and very mild crowding, defined as a maximum Little Irregularity Index of 2 mm. All participants had complete permanent dentition and good periodontal health.
Patients were randomly assigned to two groups. One group followed the conventional 22-hour daily wear protocol, while the other wore aligners for 12 hours per day. Both groups changed aligners every 14 days and were evaluated after completing the first 10 aligners, corresponding to approximately 140 days of treatment.
All patients were treated with Invisalign aligners made of SmartTrack material, using a standardized initial setup focused exclusively on dental alignment. During this phase of treatment, no interproximal reduction, elastics, dental ramps, expansion, or distalization were planned.
Digital intraoral scans were obtained before treatment (T1) and after the tenth aligner (T2). Outcomes were assessed using digital models by a blinded examiner.
Advance your career by studying for a
world-leading postgraduate diploma
Study at the cutting-edge of dental research with curricula taught by global experts and
an online schedule that suits you.
Findings
The primary outcome measure was the change in maxillary and mandibular Little Irregularity Index. Secondary outcomes included intercanine, interpremolar, and intermolar widths, as well as overjet and overbite.
Both groups showed statistically significant improvements in maxillary and mandibular alignment over the study period.
Importantly, maxillary alignment outcomes were similar between the 12-hour and 22-hour wear groups. This suggests that, for mild upper arch crowding, reduced daily wear may still allow effective alignment during the early stages of treatment.
However, a key difference emerged in the mandible. Correction of mandibular anterior crowding was significantly greater in the 22-hour wear group compared with the 12-hour wear group.
In contrast, no statistically significant differences were observed between the groups in arch widths, overjet, or overbite at the end of the observation period.
No relevant adverse effects were reported during the study, apart from mild, transient discomfort during initial aligner wear.
Clinical Interpretation
The findings suggest that in carefully selected adult patients with very mild crowding, particularly in the maxillary arch, a 12-hour daily wear protocol may achieve clinically acceptable alignment over the short term.
However, reduced wear time appears to be less efficient for mandibular alignment, reinforcing the importance of full-time wear when lower incisor irregularity is a primary treatment objective.
For clinicians, this highlights the importance of case selection when considering alternative wear protocols. While reduced wear schedules may be appropriate in certain limited scenarios, conventional full-time wear remains the most predictable approach when more comprehensive tooth movement is required.
Study Limitation
Aligner wear time in the study was self-reported using patient logs rather than objectively measured with microsensors, which may have introduced reporting bias.
About Dr. Jamal
Dr. Jamal Giri is an orthodontist and associate professor at B.P. Koirala Institute of Health Sciences in Nepal. He obtained his orthodontic training from the Institute of Medicine, Tribhuvan University, Nepal, in 2014.
Currently pursuing a PhD at the University of Adelaide, Dr. Jamal’s research focuses on the genetic and environmental factors influencing malocclusion development. He also holds a postgraduate certificate in clinical education from the University of Edinburgh and a master’s in medical education from the University of Nottingham.
Dr. Jamal teaches on the Diploma in Orthodontics and Dentofacial Orthopaedics at the London Dental Institute.
Read More
Fialho T, Angheben CZ, Ohira ET, Cotrin P, Garib D, Prado E, Freitas KM, De Freitas MR. Evaluation of the effectiveness of orthodontic treatment with Invisalign in different wear time protocols: Randomized Clinical Trial. European Journal of Orthodontics. 2025 Dec;47(6):cjaf089.
Get Our Research Round-Ups in Your Inbox
Each month, we publish bite-sized summaries of critical research to keep you updated with the latest advancements in dental science.
Subscribe below to stay ahead in your practice and enhance your knowledge with concise and informative summaries, delivered straight to your inbox.
