Marginal Biofilm Distribution and Periodontal Response to Supragingival and Juxtagingival Aligner Designs

* This prospective, longitudinal, within-person (split-mouth) clinical study evaluates the influence of two clear aligner trimming-line designs on marginal soft-tissue biofilm distribution and periodontal tissue response over a six-month period. * Two trimming-line designs are compared. The supragingival design has a straight, horizontal edge that extends approximately 2 mm onto the marginal gingiva, resting in direct contact with the gingival surface but not entering the gingival sulcus. The juxtagingival design follows the scalloped contour of the gingival margin and terminates at the free gingival margin, without covering the gingiva and without entering the sulcus. * Each participant receives both designs simultaneously, one per dental arch, and therefore serves as their own control. The assignment of each design to an arch is determined by the treating clinician according to the orthodontic treatment indications and is not randomized. * The primary outcome is the percentage of sites with bleeding on probing per arch at six months. Secondary outcomes are bleeding on probing at three months, mean probing depth, maximum probing depth, and the Turesky-Quigley-Hein plaque index, with three exploratory photographic soft-tissue variables describing marginal gingival plaque presence, vestibular interdental papilla plaque presence, and the marginal demarcation pattern. Clinical and photographic assessments are performed at baseline (before aligner delivery), at three months, and at six months. * All aligners are fabricated from a tri-layer clear aligner material (CA Pro, SCHEU-DENTAL GmbH, Iserlohn, Germany) by a single orthodontic laboratory.

Inclusion Criteria: * Permanent dentition * Adult patients * Mild to moderate crowding not requiring extractions for orthodontic purposes Exclusion Criteria: * Mouth breathing (may influence the status of the marginal periodontium) * Periodontal involvement (gingivitis or periodontitis) * Presence of fixed prosthetic restorations with incorrect marginal adaptation * Deficient oral hygiene