Clear Aligner Therapy and Marginal Edge Design: Clinical and Laboratory Evidence on Periodontal and Biological Outcomes—A Scoping Review

<b>Background:</b> Clear aligner (CA) therapy has been increasingly adopted as an alternative to fixed orthodontic appliances. However, evidence regarding its periodontal effects, including gingival inflammation, biofilm composition, and the potential role of aligner marginal edge design, remains insufficiently mapped. The objective of this scoping review was to map and synthesize available clinical and laboratory evidence on periodontal and biological outcomes associated with CA therapy, with particular attention to the potential influence of aligner marginal edge design. <b>Methods:</b> This scoping review followed PRISMA-ScR and the Population-Concept-Context (PCC) framework. PubMed, Scopus, and Web of Science were searched from 1 January 2015 to 24 October 2025. A total of 1587 records were identified; after deduplication, 770 unique records were screened by title and abstract, followed by full-text assessment of potentially eligible articles. Twenty-five primary studies published between 2020 and 2025 met eligibility criteria and were included in the review. <b>Results:</b> The final synthesis comprised clinical investigations, laboratory studies, and case reports. Clinical periodontal indices and inflammatory biomarkers were assessed using heterogeneous protocols and timepoints. Only three studies specifically addressed aligner marginal edge design; one directly compared margin configurations, reporting differences in local gingival response, with substantial diversity in study design precluding quantitative synthesis. <b>Conclusions:</b> Available evidence on periodontal outcomes during CA therapy is methodologically heterogeneous. Investigations of aligner marginal edge design remain scarce. Standardized assessment protocols and targeted clinical studies are needed to establish the periodontal relevance of trimline configurations.