Fixed retainers are effective in maintaining the alignment of the anterior teeth more than 90% of the time, but they can produce inadvertent tooth movement that in the most severe instances requires orthodontic retreatment managed with a periodontist. This is different from relapse into crowding when a fixed retainer is lost. These problems arise when the retainer breaks but remains bonded to some or all teeth, or when an intact retainer is distorted by function or was not passive when bonded. In both instances, torque of the affected teeth is the predominant outcome. A fixed retainer made with dead soft wire is the least likely to create torque problems but is the most likely to break. Highly flexible twist wires bonded to all the teeth appear to be the most likely to produce inadvertent tooth movement, but this also can occur with stiffer wires bonded only to the canines. Orthodontists, general dentists, and patients should be aware of possible problems with fixed retainers, especially those with all teeth bonded, because the patient might not notice partial debonding. Regular observations of patients wearing fixed retainers by orthodontists in the short term and family dentists in the long term are needed.

The aim of this study was to evaluate the effect of low-level light therapy using light-emitting diodes (LEDs) on the speed of tooth movements that were required for the leveling and aligning of the lower anterior segment during non-extraction orthodontic treatment. The sample was comprised of patients (n = 40) with lower anterior crowding who were treated with self-ligating orthodontic brackets and a standardized wire sequence. A test group of patients (n = 20) who were treated with extraoral infrared light therapy for 20 min daily with at least 80 % compliance was compared to a control group (n = 20). The date of the first arch wire placement was recorded as T1, and the date of the completion of the lower anterior segment decrowding was recorded as T2. A final impression was also taken at T2. The time between T1 and T2 was significantly reduced by 22 % in the test group compared to the control group (68.3 vs. 87.8 days, respectively, p < 0.043). The use of photobiomodulation for 20 min daily at a wavelength of 850 nm might reduce the time required to resolve lower anterior crowding. This trial and its protocol were not registered on a publicly accessible registry.

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