Marginal Biofilm Distribution and Periodontal Response to Supragingival and Juxtagingival Aligner Designs (BIOFILM-ALIGN)

Experimental: Supragingival Trimming-Line Design

Dental arch fitted with a clear aligner trimmed with a supragingival straight-cut margin. The aligner edge extends approximately 2 mm onto the marginal gingiva, in direct contact with the gingival surface but without entering the gingival sulcus. Assigned to the arch with the greater planned intrusion; when planned intrusion is equal or absent on both arches, assignment follows a pre-specified alternating sequence in enrollment order.

Dispositivo: Supragingival aligner trimming-line

Clear aligner trimmed with a supragingival straight-cut margin extending approximately 2 mm onto the marginal gingiva, in direct contact with the gingiva but not entering the sulcus. Fabricated from CA Pro tri-layer thermoplastic material (SCHEU-DENTAL GmbH, Iserlohn, Germany; CE-marked) by Orto Performance Orthodontic Laboratory, Cluj-Napoca, Romania. The intervention under study is the trimming-line design, not the aligner material; material and thickness are identical to the comparator.

Comparador activo: Juxtagingival Festooned Trimming-Line Design

Contralateral dental arch, within the same participant, fitted with a clear aligner trimmed with a juxtagingival festooned margin that follows the scalloped contour of the gingival margin and terminates at the free gingival margin, without covering the gingiva and without entering the sulcus. Assigned to the arch with the lesser or no planned intrusion.

Dispositivo: Juxtagingival festooned aligner trimming-line

Clear aligner trimmed with a juxtagingival festooned margin following the scalloped gingival contour, terminating at the free gingival margin without covering the gingiva or entering the sulcus. Fabricated from CA Pro tri-layer thermoplastic material (SCHEU-DENTAL GmbH, Iserlohn, Germany; CE-marked) by Orto Performance Orthodontic Laboratory, Cluj-Napoca, Romania. The intervention under study is the trimming-line design, not the aligner material; material and thickness are identical to the comparator.

Bleeding on probing at 6 months (percentage of sites per arch)

Percentage of sites with bleeding on probing within each dental arch. Bleeding on probing is recorded as present or absent within approximately 10 to 15 seconds after gentle probing at six sites per tooth (mesiobuccal, mid-buccal, distobuccal, mesiolingual, mid-lingual, distolingual) using a calibrated periodontal probe. The percentage is calculated as the number of bleeding sites divided by the total number of scorable sites in the arch, multiplied by 100. The two arches within each participant are compared by trimming-line design. The primary endpoint is the within-person, between-arch difference at 6 months (T2), with baseline (T0) as the reference. The 3-month (T1) assessment is analyzed as a secondary, intermediate time point and does not contribute to the primary comparison.

Bleeding on probing at 3 months (intermediate, percentage of sites per arch)

Percentage of sites with bleeding on probing within each dental arch at the 3-month assessment, recorded and computed identically to the primary outcome (six sites per tooth, present or absent within approximately 10 to 15 seconds of gentle probing), compared between arches by trimming-line design. This intermediate time point describes the trajectory of periodontal response and is not the primary comparison.

Mean probing depth (per arch)

Arithmetic mean of probing depth values (mm) within each dental arch, measured at six sites per tooth using a calibrated periodontal probe, calculated separately for each arch and compared by trimming-line design.

Maximum probing depth (per arch)

The greatest single probing depth value (mm) recorded within each dental arch, calculated separately for each arch and compared by trimming-line design.

Turesky-Quigley-Hein plaque index (per arch)

Mean plaque score on the Turesky-Quigley-Hein ordinal scale (0 to 5), recorded on the vestibular surfaces of teeth after application of a two-tone plaque-disclosing agent (Rondell, Directa AB, Sweden), calculated separately for each dental arch and compared by trimming-line design.

Marginal Gingival Plaque Presence (MGPP%)

Percentage of tooth-associated gingival units showing disclosed plaque on the vestibular aspect of the free gingival margin (within 0 to 2 mm of the gingival crest), scored as present or absent per unit from standardized intraoral photographs by two independent blinded examiners, calculated per arch.

Vestibular Interdental Papilla Plaque Presence (VIPPP%)

Percentage of interdental papillary units showing disclosed plaque on the visible vestibular aspect of the interdental papilla, scored as present or absent per unit from standardized intraoral photographs by two independent blinded examiners, calculated per arch.

Marginal Demarcation Pattern (MDP)

Categorical classification of the predominant pattern of disclosed marginal plaque distribution on the buccal gingiva, scored per arch from standardized intraoral photographs by two independent examiners blinded to allocation. The categories are morphological, not ordinal severity levels: 0 = absent (no disclosed plaque pattern on the marginal gingiva); 1 = diffuse (disclosed plaque scattered over the gingiva without a defined coronal outline); 2 = papillary (disclosed plaque confined to the interdental papillae); 3 = linear/band (a continuous, clearly demarcated horizontal band of disclosed plaque spanning the buccal aspect of two or more adjacent teeth, including the papilla between them). The numeric codes denote distinct categories and not increasing severity; the predominant pattern is recorded for each arch. Inter-examiner agreement is assessed using the Cohen kappa coefficient for nominal categories.