Effect of Finishing Clear Aligner Marginal Termination Design (Supragingival vs Juxtagingival) on Aligner Color Stability After 14 Days of Wear: A Split-Mouth Study

* The goal of this clinical study is to learn whether the gumline edge design of a finishing orthodontic clear aligner affects how much the aligner's color changes after 14 days of wear. * The main question is: does a supragingival edge design - a straight edge covering about 2 mm of gum tissue - lead to a different amount of color change in the aligner compared with a juxtagingival edge design that follows the gumline exactly, after 14 days of wear? * Each participant wears finishing clear aligners with both edge designs at the same time - one design on the upper jaw and the other on the lower jaw - and serves as their own comparison (split-mouth). This within-person approach removes differences between individuals in oral hygiene, diet, and saliva. * The aligner's color over six selected teeth (three upper, three lower) is measured with a dental spectrophotometer (VITA Easyshade V) at placement (day 0) and after 14 days. Each measurement is repeated three times under standardized optical conditions. The amount of color change is expressed as a color-difference value (ΔE). * The study hypothesis is that marginal termination design (supragingival versus juxtagingival) is associated with a difference in the 14-day colorimetric change (ΔE00) of the finishing aligner. * The study is carried out during the finishing (refinement) stage of orthodontic treatment, when only small residual tooth movements remain, so that color changes can be attributed to wear and edge design rather than to tooth movement.

Inclusion Criteria: * Adolescent and adult patients (age 15 years or older at enrollment) * Undergoing a finishing (refinement) stage of clear aligner therapy, with only small residual tooth movements remaining, including both patients completing active orthodontic treatment and patients with prior orthodontic treatment who require additional refinement (e.g., minor relapse or loss of retention) * Adherence to the prescribed oral hygiene instructions * Written informed consent; for participants aged 15-17 years, written consent from a parent or legal guardian Exclusion Criteria: * Deficient oral hygiene * Excessive consumption of intensely staining beverages (coffee, tea, red wine, colored carbonated drinks) * Systemic conditions or medications that may affect salivary secretion or tooth color * Non-compliance with the aligner / orthodontic appliance wear protocol