Comparison of Patient-Reported Comfort Between Two Clear Aligner Trimming-Line Designs: A Split-Mouth Study

* The trimming-line design of clear aligners (supragingival versus juxtagingival) is a routine clinical decision whose influence on patient-reported comfort has not been established; available evidence on aligner comfort derives almost exclusively from comparisons with fixed appliances. * This observational, cross-sectional study compares two clear aligner trimming-line designs with respect to patient-reported comfort: a supragingival design, whose edge rests on the marginal gingiva, and a juxtagingival design, whose edge follows the gingival contour without covering it. Because the two designs sit differently against the gingival soft tissue, they may be experienced differently during wear. * Participants are patients already wearing one trimming-line design on one dental arch and the other on the contralateral arch; each participant thus serves as their own control. After a minimum of four weeks of wear, participants complete a 20-item questionnaire once, rating the frequency of defined oral experiences for the maxillary and mandibular arch separately on a three-point ordinal scale (0 = none, 1 = occasional, 2 = frequent). * The questionnaire is anonymous; the design worn on each arch is identified from which of two identical forms a participant completes. Responses for the two designs are compared within each participant. The study evaluates whether trimming-line design is associated with differences in patient-reported comfort.

Inclusion Criteria: * Adolescent or adult patient (aged 15 years or older) * Active orthodontic treatment with clear aligners, including finishing (refinement) aligners * Wearing two clear aligners with different trimming-line designs, one per dental arch: a supragingival design on one arch and a juxtagingival design on the contralateral arch * At least 4 weeks of wear of the two designs at the time of questionnaire completion * Good treatment compliance * Willing and able to complete the online questionnaire and provide the required consent Exclusion Criteria: * Mixed orthodontic treatment (aligners combined with fixed appliances) * Pre-existing neurological, cognitive, or speech disorders * Systemic conditions affecting the oral cavity (e.g., xerostomia, mucosal disorders)