Intraoral Aging of 3D Printed Orthodontic Aligners

The Effect of Intraoral Aging on 3D-Printed Aligners: A Randomized Split-Mouth Study

This study aims to bridge the gap in literature by conducting a combined evaluation of the mechanical, chemical, optical, and morphological changes of 3D-printed clear aligners manufactured from TC-85 and TA-28 resins that occur after clinical use. By analyzing aligners retrieved after two weeks of intraoral use, this research will offer critical insights into the material stability and aging behavior of the two types of 3D-printed clear aligners.

Study Overview

• Status: Completed
• Conditions: Orthodontic Aligners
• Intervention / Treatment: Device: TC-85 directly 3D-printed aligner; Device: TA-28 directly 3D-printed aligner

Detailed Description

Background: Direct 3D-printing of clear aligners is emerging as a promising alternative to conventional thermoformed systems, offering enhanced precision, digital workflow efficiency, and improved material control. Among the photopolymer resins used for 3D-printed aligners, Tera Harz TC-85 and Tera Harz TA-28 have emerged as leading materials due to their reported shape-memory behavior, dimensional stability, and mechanical performance. However, despite increasing clinical adoption, limited evidence exists regarding how these two materials respond to intraoral aging, where fluctuating pH, temperature changes, salivary enzymes, and occlusal forces may alter their mechanical, optical, chemical, and surface characteristics. Understanding these changes is essential for determining the clinical reliability and long-term performance of each resin.Therefore, a demanding evaluation of post-aging changes in 3D-printed aligners is essential to determine their suitability for sustained orthodontic force delivery and to guide material selection in clinical practice. Assessing how key properties such as mechanical behavior, dimensional accuracy, surface topography, and optical characteristics evolve after intraoral exposure will provide valuable insight into material durability and clinical reliability.

• Study Type: Interventional
• Enrollment (Actual): 12
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Egypt
  • Alexandria Governorate
    • Alexandria, Alexandria Governorate, Egypt, 21526
      • Department of Orthodontics, Faculty of Dentistry, Alexandria University

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 35 years (Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

Description

Inclusion Criteria:

• Patients aged 18-35 years.
• Mild to moderate crowding.
• Good oral hygiene and healthy periodontium.
• Permanent dentition with no active caries.

Exclusion Criteria:

• Patients with systemic diseases affecting saliva or oral mucosa.
• Smoking or alcohol consumption.
• History of parafunctional habits.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Double

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: TC-85 maxillary / TA-28 mandibular; Participants received a directly 3D-printed TC-85 aligner in the maxillary arch and a directly 3D-printed TA-28 aligner in the mandibular arch. Both aligners were worn simultaneously for 2 weeks (22 hours/day).	Device: TC-85 directly 3D-printed aligner; Aligner directly 3D-printed from Tera Harz TC-85 shape-memory resin [add printer, layer thickness and post-curing protocol]. Worn 22 hours/day for 2 weeks in the maxillary or mandibular arch, according to a computer-generated randomization sequence.
Experimental: TA-28 maxillary / TC-85 mandibular; Participants received a directly 3D-printed TA-28 aligner in the maxillary arch and a directly 3D-printed TC-85 aligner in the mandibular arch. Both aligners were worn simultaneously for 2 weeks (22 hours/day).	Device: TA-28 directly 3D-printed aligner; Aligner directly 3D-printed from Tera Harz TA-28 shape-memory resin [same printer, layer thickness and post-curing protocol as above]. Worn 22 hours/day for 2 weeks in the maxillary or mandibular arch, according to a computer-generated randomization sequence.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in indentation hardness (HIT), measured by instrumented nanoindentation	Indentation hardness (HIT, GPa) of directly 3D-printed TC-85 and TA-28 aligners, measured by instrumented nanoindentation using a Nano Indenter XP (MTS Systems Corporation, USA) with a Berkovich diamond indenter. Tests were displacement-controlled to a maximum depth of 2000 nm at a constant strain rate of 0.05 s-¹, with 25 indentations per specimen spaced 30 μm apart. Testing followed ISO 14577-1:2015 and data were analyzed by the Oliver and Pharr method. Retrieved aligners are compared with unused aligners printed from the same digital design.	Baseline (unused aligner) and after 2 weeks of intraoral use

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in indentation elastic modulus (EIT), measured by instrumented nanoindentation	Indentation elastic modulus (EIT, GPa) of directly 3D-printed TC-85 and TA-28 aligners, measured by instrumented nanoindentation using a Nano Indenter XP (MTS Systems Corporation, USA) with a Berkovich diamond indenter. Tests were displacement-controlled to a maximum depth of 2000 nm at a constant strain rate of 0.05 s-¹, with 25 indentations per specimen spaced 30 μm apart. A Poisson's ratio of 0.4 was assumed. Testing followed ISO 14577-1:2015 and data were analyzed by the Oliver and Pharr method. Retrieved aligners are compared with unused aligners printed from the same digital design.	Baseline (unused aligner) and after 2 weeks of intraoral use
Change in color (ΔE₀₀, CIEDE2000), measured by UV-visible spectrophotometry	Color of directly 3D-printed TC-85 and TA-28 aligners measured with a UV-visible spectrophotometer (V-770, JASCO Corporation, Tokyo, Japan). Each aligner was sectioned along the right central incisor-canine region, and the labial surface was positioned in a standardized manner facing the incident-light window. CIE Lab* coordinates were recorded according to ISO 11664-4:2019, and the color change between unused and retrieved aligners was calculated as ΔE₀₀ using the CIEDE2000 equation (parametric factors set to 1). Values are interpreted against 0.8 (50:50% perceptibility) and 1.8 (50:50% acceptability).	Baseline (unused aligner) and after 2 weeks of intraoral use
Change in light transmittance and absorbance (400-700 nm), measured by UV-visible spectrophotometry	Light transmittance and absorbance of TC-85 and TA-28 aligners recorded across the visible range (400-700 nm) with a UV-visible spectrophotometer (V-770, JASCO Corporation, Tokyo, Japan) using Spectra Manager II software, after calibration according to the manufacturer's instructions. Values at 400 and 700 nm were extracted from each spectrum and compared between materials and between unused and retrieved aligners.	Baseline (unused aligner) and after 2 weeks of intraoral use
Change in aligner thickness (μm), measured by confocal laser scanning microscopy	Thickness of TC-85 and TA-28 aligners measured by confocal laser scanning microscopy (Leica DMi8, Leica Microsystems, Wetzlar, Germany) with a 10× objective and 1.5× digital zoom under standardized imaging conditions. Standardized 4 × 4 mm specimens were taken from the labial surface of the left central incisor region. Z-stack images were reconstructed in 3D using Leica LAS AF software (version 1.1.0.12420), and thickness was calculated as the perpendicular distance between the upper and lower specimen surfaces. Each specimen was measured twice and the mean was used.	Baseline (unused aligner) and after 2 weeks of intraoral use
Change in surface roughness (Sa, Sq, Sp, Sv), measured by confocal laser scanning microscopy	Surface roughness of the inner surface of directly 3D-printed TC-85 and TA-28 aligners, assessed on the same 4 × 4 mm specimens used for thickness measurement, imaged by confocal laser scanning microscopy (Leica DMi8, Leica Microsystems, Wetzlar, Germany). Height maps generated from the z-stacks with Leica LAS AF software were analyzed in ImageJ (National Institutes of Health, USA) with the SurfCharJ-1q plugin to calculate Sa (arithmetical mean height), Sq (root mean square height), Sp (maximum peak height) and Sv (maximum valley depth), in µm. Analysis was repeated twice per specimen and the mean was used. Identical acquisition and analysis settings were applied to all specimens.	Baseline (unused aligner) and after 2 weeks of intraoral use
Change in degree of conversion (DC), measured by ATR-FTIR spectroscopy	Degree of conversion (%) of TC-85 and TA-28 aligners, calculated from attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectra as the reduction of the aliphatic C=C band near 1638 cm-¹ relative to, referenced to the corresponding unset resin. Retrieved aligners are compared with unused aligners.	Baseline (unused aligner) and after 2 weeks of intraoral use
Change in chemical structure, assessed by ATR-FTIR spectral analysis	Qualitative comparison of ATR-FTIR spectra of unused and retrieved TC-85 and TA-28 aligners, focusing on the O-H/N-H stretching bands (3400-3200 cm-¹), aliphatic C-H bands (about 2920 and 2850 cm-¹), the carbonyl (C=O) band (about 1700 cm-¹) and the C-O/C-O-C region (1200-1000 cm-¹).	Baseline (unused aligner) and after 2 weeks of intraoral use

Collaborators and Investigators

• Sponsor: Alexandria University
• Investigators: Principal Investigator: Azza Gamal Wafa, PHD, Alexandria University

Study record dates

Study Major Dates

• Study Start (Actual): February 1, 2026
• Primary Completion (Actual): April 1, 2026
• Study Completion (Actual): September 1, 2026

Study Registration Dates

• First Submitted: October 31, 2026
• First Submitted That Met QC Criteria: November 5, 2026
• First Posted (Actual): November 9, 2026

Study Record Updates

• Last Update Posted (Actual): November 9, 2026
• Last Update Submitted That Met QC Criteria: November 5, 2026
• Last Verified: January 1, 2026

More Information

Terms related to this study

• Keywords: Orthodontic aligners; Printing, three-dimensional; Degree of conversion; Elastic modulus; Hardness; Intraoral aging; Polymerization
• Other Study ID Numbers: 1223

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED

IPD Plan Description

Individual participant data will not be shared publicly because of participant confidentiality and privacy considerations. The study involves a relatively small sample, and sharing individual-level data may pose a risk of participant identification. De-identified aggregate results will be reported in the published manuscripts. Data may be made available from the corresponding author upon reasonable request, subject to institutional ethical approval and applicable data-protection requirements.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No