Objective: To investigate the vertical changes in incisors and molars that occur following molar distalisation with clear aligners.
Methods: A total of 30 patients receiving clear aligner treatment (Invisalign, Align Technology, San Jose, CA, USA) were included in the study. Patients’ digital models were exported from the ClinCheck software (Align Technology) and measured using Geomagic Studio 2014 (Raindrop Geomagic, Research Triangle Park, NC, USA). Various indices regarding characteristics of vertical changes following molar distalisation with clear aligners were measured and compared, including the predicted and achieved molar distalisation, intrusion and change in vertical overlap. A simple linear regression was conducted to examine the impact of distalisation on molar intrusion.
Results: The characteristics of spatial changes in molar distalisation with clear aligners were measured, particularly in the vertical dimension. The actual vertical overlap deepened after clear aligner treatment (central incisors 0.43 ± 2.14 mm, lateral incisors 0.79 ± 1.91 mm). Molar intrusion occured (first molar 0.51 ± 0.77 mm, second molar 0.97 ± 0.87 mm), and the difference between the actual and expected molar intrusion was statistically significant. A significant positive correlation was identified between molar distalisation and molar intrusion (P 0.05).In addition, by comparing the different positions of the dental arch, the intrusive effect of molar distalisation was found to be progressively greater from the anterior to the posterior teeth (P 0.05). With the use of temporary anchorage devices, the deepening of vertical overlap and the effects of posterior open bite effects were significantly greater (P 0.05).
Conclusions: Molar intrusion is a common occurrence during molar distalisation with clear aligners. It may result in open bite in the molar region and increased vertical overlap in the incisors. The intrusive effect of molar distalisation increases gradually from the anterior to the posterior teeth. Temporary anchorage device–assisted molar distalisation with clear aligners exacerbates open bite in the molar region. Aligner overtreatment of incisor intrusion is recommended if the vertical dimension should be reduced, whereas additional molar extrusion is implemented if the vertical dimension should be maintained or increased for molar distalisation with clear aligners.