We carefully read the letter from Dr Waese with great interest and are pleased to reply. The main content of this letter was that tooth movement had an effect on intraoral volume, which could lead to breathing obstruction.

Tongue volume and position are critical factors in tongue biomechanics. Whether the tongue adapts to fill an existing oral morphology or actively molds surrounding tissues has been controversial. Some scholars have claimed that tongue volume is correlated with dentition position, mandibular arch size, and posture. On the other hand, tongue volume is coordinated functionally with tongue position. Numerous clinical studies have shown that regional volumetric changes of the tongue occur during eating, chewing, ingesting, and drinking. In most extraction cases, tooth movement during orthodontic treatment usually reduces the intraoral volume; however, breathing obstruction was rarely found after orthodontic treatment. This suggests that the tongue can adapt to the oral morphology during orthodontic treatment.

Because the patient in our case report had a hypertrophic tongue, we offered her a choice of surgery to reduce her tongue size if she had breathing discomfort during the treatment. During the entire treatment and 1-year retention, she had no discomfort when breathing.

We recently recalled our patient, and she was still satisfied with the treatment results after 2 years of retention. We think that the width of the dental arch changes slowly during orthodontic treatment, and, correspondingly, the tongue volume decreased slowly and integrated functionally with the tongue position. We used a removable cast splint circumferential retainer, which controls tongue function and position similar to a tongue crib appliance. We believe that the tongue adapts to the oral morphology at this stage. However, we will continue to observe this patient in the long term. Thank you for your advice.