Influence of Finishing Clear Aligner Marginal Termination Design on Subgingival Periodontal Microbiota During Orthodontic Treatment: A Split-Mouth Study.

The goal of this clinical trial is to learn whether the edge design of a finishing orthodontic clear aligner at the gumline affects the bacteria living in the groove between the tooth and the gum (the gingival sulcus) in patients undergoing the finishing phase of orthodontic treatment. The main question it aims to answer is: \- Does a supragingival aligner edge design - which covers approximately 2 mm of gum tissue - lead to higher levels of disease-associated bacteria in the gingival sulcus compared to a juxtagingival edge design that follows the gumline exactly, after 4 and 8 weeks of aligner wear? Researchers will compare the supragingival trimming-line design to the juxtagingival festooned design to see if covering gum tissue with the aligner edge creates conditions that favor the growth of anaerobic bacteria associated with gum disease. Participants will: * Wear finishing clear aligners with both designs simultaneously - one design on the upper jaw and one on the lower jaw - for 8 weeks * Provide fluid samples from the gum groove at 3 visits: at the start of treatment (baseline), at 4 weeks, and at 8 weeks. Two aligner edge designs are compared: a supragingival design, which has a straight horizontal edge positioned approximately 2 mm over the gumline, covering approximately 2 mm of gum tissue with direct contact but without entering the gum groove itself, and a juxtagingival design, which follows the natural scalloped shape of the gumline exactly, terminating at the free gingival margin without covering gum tissue and without entering the groove. The biological rationale for comparing these two designs is the following: the supragingival design, by covering 2 mm of gum tissue, creates a partially enclosed space at the entrance of the gum groove, potentially reducing the clearance of saliva and limiting oxygen access to that area. These conditions may favor the growth of anaerobic bacteria associated with gum disease. The juxtagingival design, by following the gum contour exactly at its edge, leaves the gum groove entrance more accessible to saliva and oxygen, potentially maintaining a less favorable environment for those bacteria. Each participant receives both designs at the same time - one on the upper jaw and one on the lower jaw - and serves as their own comparison group. This within-person (split-mouth) approach eliminates differences between individuals in general health, oral hygiene habits, and saliva composition, making the comparison between the two designs more precise. Samples are analyzed using the PeriodontScreen Real-TM real-time PCR kit (Sacace Biotechnologies Srl, Como, Italy; CE-marked in vitro diagnostic device), which detects and quantifies seven bacteria known to cause gum disease: Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, Porphyromonas endodontalis, Fusobacterium nucleatum, and Prevotella intermedia. The main measurement is the number of these seven bacteria that exceed the clinically significant concentration threshold defined by the kit at each jaw arch and time point. A score of 0 means none of the seven bacteria exceed the threshold; a score of 7 means all seven do. The study hypothesis is that the supragingival trimming-line design - by covering gingival tissue and partially enclosing the sulcus entrance - creates microenvironmental conditions that favor anaerobic periodontal pathogen colonization, resulting in higher pathogen burden scores compared to the juxtagingival design after 4 and 8 weeks of finishing aligner wear. The study is conducted during the finishing phase of orthodontic treatment, when planned tooth movements are minimal (no more than 0.5 mm per tooth), so that any differences in bacterial levels can be attributed to aligner edge design rather than to tooth movement forces.

\- BACKGROUND AND RATIONALE Clear aligner therapy is widely used in orthodontics. Two trimming-line designs are commonly employed during the finishing phase. The supragingival design uses a straight horizontal cut positioned approximately 2 mm apical to the free gingival margin: the aligner edge covers approximately 2 mm of gingival tissue with direct contact but does not penetrate the gingival sulcus. The juxtagingival festooned design uses a scalloped cut that follows the natural contour of the free gingival margin exactly, terminating at the gingival margin without covering gingival tissue and without entering the sulcus. The two designs differ fundamentally in their relationship with the gingival margin. The supragingival design creates a semi-enclosed microenvironment at the sulcus entrance: by covering 2 mm of gingival tissue, the aligner limits access of saliva and atmospheric oxygen to the sulcus entrance region. Reduced salivary clearance and decreased oxygen tension are established conditions that favor anaerobic bacterial growth in the periodontal environment. Whether 2 mm of gingival tissue coverage by the aligner edge is sufficient to produce a measurable change in sulcular oxygen tension or salivary clearance has not been directly demonstrated and constitutes the biological hypothesis under investigation. The juxtagingival design, following the gingival contour at its margin, leaves the sulcus entrance more accessible to saliva and oxygen, potentially maintaining less favorable conditions for anaerobic colonization. These microenvironmental differences have not been investigated in published studies. No prior study has examined whether trimming-line geometry affects subgingival periodontal microbiota composition in patients undergoing aligner therapy. * STUDY DESIGN This is a prospective, longitudinal, within-person (split-mouth) interventional study. Each participant receives both trimming-line designs simultaneously: supragingival on one dental arch and juxtagingival festooned on the contralateral arch. The split-mouth design controls for inter-individual variation in systemic health, oral hygiene, salivary composition, and baseline microbiological status. The aligner material (CA Pro tri-layer, SCHEU-DENTAL GmbH, Iserlohn, Germany; CE-marked thermoplastic) is identical for both designs; only trimming-line geometry differs. * ALLOCATION RULE (NON-RANDOMIZED) Allocation follows a pre-specified hierarchical rule documented prior to enrollment: 1. Primary criterion: The dental arch with the greater magnitude of planned dental intrusion (mm, from the digital treatment setup prior to fabrication) receives the supragingival design, consistent with its clinical indication for vertical force transmission. 2. Tiebreaker (equal or zero planned intrusion on both arches): A pre-specified systematic alternating sequence in enrollment order. The first participant meeting this criterion receives supragingival on the maxillary arch; the sec Покажи пълното описание...

Inclusion Criteria: * Permanent dentition (excluding third molars) * Age 15 years or older at enrollment * Currently undergoing the finishing phase of orthodontic treatment with clear aligners * Residual planned tooth movements no greater than 0.5 mm per tooth per aligner stage * Absence of active periodontal disease at baseline: probing depth 3 mm or less at all sites, and no bleeding on probing at index sampling sites * Written informed consent; for participants aged 15-17 years, written consent from parent or legal guardian is also required Exclusion Criteria: * Systemic conditions known to affect periodontal tissues (e.g., uncontrolled diabetes mellitus, immunosuppressive therapy) * Antibiotic therapy within the 3 months preceding enrollment * Active gingivitis (modified gingival index 2 or greater) or periodontitis at baseline * Habitual mouth breathing (self-reported or clinically assessed) * Poorly adapted fixed prosthetic restorations adjacent to planned index sampling sites * Visible plaque at more than 50% of tooth surfaces at baseline * Self-reported aligner compliance below 22 hours per day during the study period * Pregnancy or breastfeeding