Optical Properties of Clear Aligner Materials: A Systematic Review

Abstract

Background: The aesthetic appeal of clear aligners is fundamentally dependent on their optical properties,
including transparency, transmittance, color stability, and absorbance. Understanding how different aligner
materials and manufacturing processes affect these properties is essential for clinical decision-making and
patient satisfaction.
Objectives: To systematically review and synthesize the available evidence on optical properties of clear
aligner materials, evaluate changes following intraoral aging, and compare different material types and
manufacturing processes.
Data Sources: Electronic searches were conducted in PubMed, Scopus, Web of Science, and Cochrane
Library databases from inception to January 2026. Additional hand-searching of reference lists and grey
literature was performed.
Data Selection: Studies evaluating optical properties (transparency, transmittance, absorbance, color
stability) of clear aligner materials using spectrophotometry or colorimetry were included. Both in vitro and
in vivo studies were eligible.
Data Extraction: Two independent reviewers extracted data on study characteristics, material composition,
measurement methods, aging protocols, optical outcomes, and effect sizes. Risk of bias was assessed using
appropriate tools.
Data Synthesis: Twenty-four studies met inclusion criteria. Spectrophotometric analysis revealed significant
variations in transmittance (90.5-96.2% at 400nm) and absorbance (0.02-0.04) among materials. PETG-based
materials demonstrated superior optical stability (mean transmittance reduction: 1.24%, Cohen's d = 0.32)
compared to polyurethane-based materials (mean reduction: 3.68%, Cohen's d = 0.78) after 14-day aging.
Color stability varied significantly with exposure to staining agents, with coffee and black tea causing the
greatest discoloration (ΔE > 3.3). Three-dimensionally printed aligners exhibited greater color changes than
thermoformed counterparts (mean difference: 1.2 ΔE units, p < 0.01).
Conclusions: Material composition significantly influences optical properties of clear aligners. PETG-based
and copolyester materials demonstrate superior transparency and color stability compared to polyurethane-
based materials. Clinicians should consider material optical properties when selecting aligner systems and
provide evidence-based dietary guidance to patients to maintain aesthetic integrity throughout treatment.