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

May 31, 2026 updated by: Emilia Rusu, George Emil Palade University of Medicine, Pharmacy, Sciences and Technology of Targu Mures

Colorimetric Stability of Finishing Clear Aligners According to Marginal Termination Design (Supragingival Versus Juxtagingival) After 14 Days of Intraoral Wear During Orthodontic Treatment: A Prospective 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.

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

  • BACKGROUND AND RATIONALE
  • Two trimming-line (edge) designs are commonly used during the finishing (refinement) stage of clear aligner therapy. The supragingival design uses a straight edge positioned approximately 2 mm apical to the free gingival margin, covering approximately 2 mm of gingival tissue. The juxtagingival festooned design follows the natural scalloped contour of the free gingival margin, without covering gingival tissue. Color stability of the aligner during wear is relevant to esthetics and patient acceptance. Whether marginal termination design influences the colorimetric stability of the aligner during wear has not been investigated.
  • STUDY DESIGN
  • This is a prospective, within-person (split-mouth) interventional study. Each participant receives both designs simultaneously: the supragingival design on one dental arch and the juxtagingival festooned design on the contralateral arch. The split-mouth design controls for inter-individual variation in oral hygiene, diet, and salivary composition. The aligner material (CA Pro tri-layer, SCHEU-DENTAL GmbH, Iserlohn, Germany; CE-marked thermoplastic) is identical for both designs; only the marginal termination geometry differs.
  • ALLOCATION RULE (NON-RANDOMIZED)
  • Allocation follows a pre-specified hierarchical rule documented prior to enrollment. Primary criterion: the dental arch with the greater magnitude of planned dental intrusion (mm, from the digital treatment setup) receives the supragingival design. Tiebreaker (equal or zero planned intrusion on both arches): a pre-specified systematic alternating sequence in enrollment order. Planned intrusion magnitude per arch is recorded as a covariate.
  • TARGET TEETH AND MEASUREMENT
  • Colorimetric measurements of the aligner are performed extraorally at six target-tooth positions per participant: three maxillary (1.4, 1.1, 2.3) and three mandibular (4.3, 3.1, 3.4). Measurements are obtained with a dental spectrophotometer (VITA Easyshade V) operated in Custom Color mode, which simultaneously displays the CIE L, a, and b color coordinates. To ensure reproducibility, the aligner is measured under standardized optical conditions using a standardized optical substrate and a fixed positioning reference (methodological details reported separately). Each target position is measured in triplicate at each visit.
  • VISITS
  • Measurements are obtained at T0 (day 0, at placement of the finishing aligner) and T1 (day 14 ± 2 of wear), yielding 36 L, a, b measurements per participant (6 positions × 3 repetitions × 2 visits).
  • OUTCOME
  • The primary outcome is the colorimetric change (ΔE00, CIEDE2000) of the aligner between T0 and T1, computed per dental arch from the measured L, a, b coordinates, compared between the supragingival-design arch and the juxtagingival-design arch. The CIELAB ΔEab value is reported descriptively for comparability with prior literature.
  • STUDY CONTEXT
  • The study is conducted during the finishing (refinement) stage, when only small residual tooth movements remain, so that observed color changes can be attributed to wear and marginal termination design rather than to substantial tooth movement.
  • RELATIONSHIP TO COMPANION STUDY
  • A subset of participants may be concurrently enrolled in the companion study PATHO-ALIGN (ClinicalTrials.gov NCT07533058), a split-mouth study of finishing-aligner marginal termination design and subgingival periodontal microbiota conducted by the same investigator at the same sites. Co-enrolled participants wear the same finishing clear aligners with the same arch-level marginal-design allocation in both studies; the present study adds only a non-invasive, extraoral colorimetric assessment of the aligners and does not interfere with the companion study. The two studies have distinct outcomes.
  • STATISTICAL ANALYSIS
  • Primary confirmatory analysis: The confirmatory endpoint is the arch-level aligner color change (ΔE00) between T0 and T1. The supragingival-design arch and the juxtagingival-design arch are compared within participants using a paired test (two-sided, alpha = 0.05). Normality of the paired differences is assessed (Shapiro-Wilk); a paired t-test is used if the assumption holds, otherwise the Wilcoxon signed-rank test. A single confirmatory comparison is pre-specified, controlling the type I error rate without multiplicity correction.
  • Adjusted analysis: A linear mixed-effects model is fitted to arch-level ΔE00, with marginal termination design (supragingival vs juxtagingival), dental arch (maxillary vs mandibular), planned intrusion magnitude per arch, and self-reported daily wear time as fixed effects, and a participant-level random intercept to account for the paired (split-mouth) structure. Including dental arch as a covariate separates a potential arch-level effect from the design effect.
  • Secondary analyses (descriptive): Component color changes (ΔL, Δa, Δb) per arch between T0 and T1; overall aligner color change across all target positions (ΔE00 and ΔEab); and the proportion of arch-level changes exceeding the Paravina (2015) perceptibility (ΔE00 = 0.8) and acceptability (ΔE00 = 1.8) thresholds.
  • Measurement reliability: Intra-position reproducibility across the three repeated measurements is quantified using the intraclass correlation coefficient (ICC).
  • Missing data and quality control: Repeated measurements failing pre-specified inter-repetition agreement criteria are excluded, and the mean of the remaining repetitions is used; analyses use available per-protocol data.
  • SAMPLE SIZE JUSTIFICATION
  • Sample size was determined for a paired within-subject (split-mouth) comparison of arch-level aligner color change (ΔE00). In the absence of prior data specific to marginal termination design effects on aligner color, parameters were selected conservatively: a minimum meaningful between-arch difference of ΔE00 = 0.8 (50:50% perceptibility threshold; Paravina 2015), an assumed standard deviation of paired differences of approximately 0.9 (derived from an assumed arch-level standard deviation with an intra-subject correlation rho = 0.4), and a two-sided alpha = 0.05 (paired test). Under these assumptions, 50 participants provide power exceeding 90% to detect the specified difference and remain adequately powered (approximately 85%) for smaller between-arch differences (ΔE00 ≈ 0.4). The enrolled sample (50 participants; 100 aligners, two per participant) also serves to estimate within-subject colorimetric variability to refine power assumptions for subsequent confirmatory studies.

Study Type

Interventional

Enrollment (Estimated)

50

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Locations

  • Romania
    • Sibiu County
      • Sibiu, Sibiu County, Romania, 550118
        • Aorys Clinic
        • Contact:
        • Principal Investigator:
          • EMILIA (PRODEA) RUSU, DDS, Specialist Orthodontist

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Child
  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Description

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

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Basic Science
  • Allocation: Non-Randomized
  • Interventional Model: Crossover Assignment
  • Masking: Single

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: Supragingival Trimming-Line Design
Finishing clear aligner with a straight trimming-line positioned approximately 2 mm apical to the free gingival margin, covering approximately 2 mm of gingival tissue. Assigned to the arch with greater planned intrusion; if equal or zero on both arches, assigned by pre-specified systematic alternation in enrollment order.
Device: Tri-layer thermoplastic finishing clear aligner
Finishing clear aligner fabricated from CA Pro tri-layer thermoplastic (SCHEU-DENTAL GmbH, Iserlohn, Germany; CE-marked), fabricated by SC APARAT DENTAR SRL, Sibiu, Romania. Each participant receives aligners with both trimming-line designs simultaneously - supragingival on one arch and juxtagingival festooned on the contralateral arch. Material and thickness are identical for both designs; only trimming-line geometry differs. (Cross-referenced to both arms.)
Active Comparator: Juxtagingival Festooned Trimming-Line Design
Finishing clear aligner with a festooned trimming-line following the natural scalloped contour of the free gingival margin, terminating at the gingival margin without covering gingival tissue. Assigned to the contralateral arch.
Device: Tri-layer thermoplastic finishing clear aligner
Finishing clear aligner fabricated from CA Pro tri-layer thermoplastic (SCHEU-DENTAL GmbH, Iserlohn, Germany; CE-marked), fabricated by SC APARAT DENTAR SRL, Sibiu, Romania. Each participant receives aligners with both trimming-line designs simultaneously - supragingival on one arch and juxtagingival festooned on the contralateral arch. Material and thickness are identical for both designs; only trimming-line geometry differs. (Cross-referenced to both arms.)

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Aligner Color Change (ΔE00) After 14 Days of Wear
Time Frame: Day 0 and day 14
Mean color change (ΔE00, CIEDE2000) of the finishing aligner between day 0 and day 14, per dental arch, computed from CIE L*, a*, b* coordinates averaged over three target positions measured in triplicate. The supragingival-design arch and the juxtagingival-design arch are compared within each participant (paired split-mouth).
Day 0 and day 14

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Component Color Changes (ΔL*, Δa*, Δb*)
Time Frame: Day 0 and day 14
Mean changes in the individual CIE coordinates per arch between day 0 and day 14, characterizing the direction of color change (lightness; red-green; yellow-blue axes).
Day 0 and day 14
Overall Aligner Color Change (ΔE00 and ΔE*ab, pooled)
Time Frame: Day 0 and day 14
Color change of the finishing aligner across all target positions regardless of marginal termination design, reported as ΔE00 (CIEDE2000) and, for comparability with prior literature, ΔE*ab (CIELAB), characterizing overall colorimetric stability during wear.
Day 0 and day 14

Other Outcome Measures

Outcome Measure
Measure Description
Time Frame
Proportion of Measurements Exceeding Perceptibility / Acceptability Thresholds
Time Frame: Day 0 and day 14
Proportion of arch-level color changes exceeding the 50:50% perceptibility (ΔE00 = 0.8) and acceptability (ΔE00 = 1.8) thresholds (Paravina 2015). Interpreted descriptively; these thresholds were established for permanent restorations compared with adjacent teeth and are used here only as a reference standard, not as a clinical failure criterion for a temporary 14-day aligner.
Day 0 and day 14

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

George Emil Palade University of Medicine, Pharmacy, Sciences and Technology of Targu Mures

Collaborators

SC APARAT DENTAR SRL, Sibiu, Romania
Aorys Clinic, Sibiu, Romania

Investigators

  • Study Chair: LUMINITA LAZAR, PhD, Professor, George Emil Palade University of Medicine, Pharmacy, Science, and Technology of Targu Mures, 38 Gheorghe Marinescu Street, 540139 Targu Mures, Romania
  • Principal Investigator: EMILIA (PRODEA) RUSU, DDS, Specialist Orthodontist, George Emil Palade University of Medicine, Pharmacy, Science, and Technology of Targu Mures, 38 Gheorghe Marinescu Street, 540139 Targu Mures, Romania

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Helpful Links

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

June 15, 2026

Primary Completion (Estimated)

August 15, 2026

Study Completion (Estimated)

August 15, 2026

Study Registration Dates

First Submitted

May 31, 2026

First Submitted That Met QC Criteria

May 31, 2026

First Posted (Actual)

June 5, 2026

Study Record Updates

Last Update Posted (Actual)

June 5, 2026

Last Update Submitted That Met QC Criteria

May 31, 2026

Last Verified

May 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • SPECTRO-ALIGN-ORTHO

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

IPD Plan Description

De-identified individual participant data (participant codes, arch-level color change values ΔE00 and ΔE*ab, component changes ΔL*/Δa*/Δb* and baseline covariates) will be made available as a CSV or Excel file upon reasonable request to the corresponding author following publication of study results.

IPD Sharing Time Frame

Beginning 6 months after publication of primary study results.

IPD Sharing Access Criteria

Upon reasonable request to the corresponding author (PI); requests reviewed within 30 days.

IPD Sharing Supporting Information Type

  • STUDY_PROTOCOL
  • SAP

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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