Dimensional changes of the gingival tissues induced by clear aligners and fixed orthodontic appliances

Objective: The aim of this study was to evaluate gingival tissue adaption induced by orthodontic tooth movement, in terms of clinical crown height (i.e., attachment loss), and thickness of the keratinized gingiva at the margin level. Methods: Pre- and post-treatment intraoral models/scans of 100 orthodontically treated patients (50 treated with clear aligners and 50 treated with fixed appliance) were acquired. Models were digitally scanned. Each couple of pre- and post-treatment scans were superimposed using the Compare© software (Medit, Seoul, South Korea) taking the same reference landmarks in all cases, that were the palatal rugae for the upper arch, and the labial median frenulum for the lower arch. Only teeth that had undergone vestibulo-palatal (or vice versa) movement, greater than 1 mm were included in the analyses. The change from pre-treatment to post-treatment, in the clinical crown height and thickness of the keratinized gingiva at the margin level were digitally measured and compared between the two groups. Statistical analysis included paired t-tests, and unpaired t-tests with significance set at p<0.05. Results: There was a statistically significant change in clinical crown height and gingival thickness in both groups. However, a clinically relevant attachment loss was found only within the fixed appliance group. Whereas, regarding the change in gingival thickness, there was no clinically relevant changes between the two groups. Conclusions: Orthodontic tooth movement with fixed appliance is associated to a clinically relevant attachment loss. Clear aligners seem to be associated with a more discrete attachment loss than the one observed with fixed appliances. Clinical relevance: Orthodontists should pay attention and monitoring the clinical crown height (i.e., attachment loss) during orthodontic movement, mostly when using fixed appliances.