This prospective, single-center, single-blinded, 2-arm parallel clinical trial was conducted with a 1:1 allocation ratio in accordance with the Consolidated Standards of Reporting Trials statement reporting guidelines ( Fig 1 ). Ethical approval was obtained from the University’s Institutional Ethical Committee (Manav Rachna International Institute of Research and Studies/Manav Rachna Dental College/Faculty of Dental Surgery/Institutional Ethical Committee/2023/05).

Consort flowchart.

Participants aged between 18 and 30 years presenting at the Department of Orthodontics outpatient clinic were screened for eligibility. Inclusion criteria comprised patients diagnosed with Class I or Class II malocclusion, exhibiting mild crowding of <5 mm, with a decayed, missing, and filled teeth score of ≤2, and a Simplified Oral Hygiene Index score of ≤3. Patients were excluded if they reported habits of smoking or chewing betel quid or tobacco in any form, demonstrated signs of bruxism, or exhibited poor oral hygiene.

Digital Scanning and Treatment Planning-Intraoral scanning (TRIOS Core intraoral scanner; 3Shape, Copenhagen, Denmark) of both arches was done to obtain digital models. Treatment planning was done, digitally, using Maestro 3D software (AGE Solutions, Pontedera [Pisa], Italy).

The digital model was transferred to the Direct Aligner Designer software (Graphy Inc, Seoul, South Korea) to design the aligners. The dentulous area was demarcated, and a digital analog of the aligner was obtained. Auxiliaries that would allow the resin material to flow during the 3D printing of the aligner and would hold the aligner were designed using the same software.

The digital aligner design was imported into UNIZ Dental software (Beijing, China) to optimize positioning for 3D printing. The final aligners were fabricated using the UNIZ UBEE printer with Graphy TeraHarz TC85, a photopolymerizable resin, at a uniform thickness of 0.7 mm. Postprinting, the aligners were centrifuged at 500 rpm using the Tera Harz Spinner to eliminate excess resin, followed by postcuring in a 97% nitrogen atmosphere using the Tera Harz Cure 2 unit (Graphy Inc) to ensure biocompatibility and be ready for clinical use.

For each aligner stage, 3D digital models with a standardized base height of 20 mm were fabricated using a Phrozen Sonic Mega 14K 3D printer (Phrozen, Taiwan) with 3D Accuprint resin (D-Tech, Mumbai, India). Thermoforming of aligners was conducted with 0.762-mm PET-G sheets (Taglus Premium, Laxmi Dental Export Pvt Ltd, Mumbai, India) heated to 220-230°C and pressed at 4.5-5.0 bar using a Ministar pressure thermoforming unit (Scheu Dental GmbH, Germany). Daily wear of 20-22 hours, for 14 consecutive days, was recommended for the patients from both groups. Aligner removal was allowed only while brushing, eating, and drinking beverages such as tea, coffee, or wine. Patients were also asked to clean the aligners per the recommended guidelines.

Randomization and allocation concealment: Selected participants were randomly allocated to each group using computer randomization software ( https://www.random.org/ ). The participants were blinded to the type of aligner they were given. Opaque sealed envelopes were used for allocation concealment.

Both aligners were assessed for optical properties (absorbance, transmittance) and color stability at 2 time points: baseline (T1) and after 14 days of intraoral aligner wear (T2)

Absorbance (in absorbance unit) was measured across a wavelength range of 400-700 nm at 10 nm intervals (UV-Vis spectrophotometer, Shimadzu UV-3600i Plus, Shimadzu, Kyoto, Japan).

Transmittance (in %) was calculated with the following formula: T = 10 ^−A (T denotes transmittance, whereas A denotes absorbance)

Color Assessment was done using the VITA Easyshade V spectrophotometer (VITA Zahnfabrik, Sackingen, Germany). A composite resin right central incisor (Shofu Inc, Kyoto, Japan) in A2 shade was fabricated to simulate the intraoral dental hard tissue for color measurement. L∗a∗b∗ color scheme of the Commission Internationale de l’Eclairage (CIE L∗a∗b∗) was used in which L∗ indicates lightness (0, black ; 100, white ), a∗ indicates red/green coordinate, and b∗ indicates yellow/blue coordinate.

Color difference (ΔE) between T1 and T2 was calculated using the formula: ΔE = √ [(L ₁ − L ₂ ) + (a ₁ − a ₂ ) + (b ₁ − b ₂ )

The values were converted to National Bureau of Standards (NBS) units using NBS = ΔE × 0.92. This established a clinical standard for the observed color changes ( Table I ).

A total of 40 patients (mean age, 22.3 ± 5.2 years) were screened for eligibility. Of these, 16 patients were excluded for not meeting the inclusion criteria, leaving 26 patients (9 males and 17 females) who were subsequently allocated to receive either 3D-printed aligners (group 1) or thermoformed aligners (group 2). One patient from each group discontinued treatment and was excluded from the final analysis.

Sample size calculations were conducted using G∗Power software (version 3.0; Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany) based on data from Lombardo et al. With mean values of 0.265 and 0.280 for groups 1 and 2, respectively, and a standard deviation of 0.036, a sample size of 12 per group was determined to achieve 80% power (β = 0.20) at an α of 0.05, assuming equal group sizes.

At T1, 3D-printed aligners exhibited significantly higher absorbance values compared with thermoformed aligners in both maxillary and mandibular arches ( P <0.001) ( Figs 2 , A and B and 3 , A ; Tables II and III ).

Box plot showing the ( A ) absorbance values, ( B ) transmittance, and ( C ) color change of maxillary and mandibular aligners in group 1 (G1) and group 2 (G2) at T1 and T2. The upper limit of the line represents the maximum value, the lower limit the minimum value, the box the interquartile range, and the line the median value.

Scatter and line plot for ( A ) absorbance and ( B ) transmittance values of maxillary and mandibular aligners in group 1 (G1) and group 2 (G2) at T1 and T2.

Table III

Intergroup comparison of the optical properties (absorbance and transmittance) of groups 1 and 2 at the 2 time intervals

Properties	Timeline	Aligners	Group	Mean	SD	SE	P value	t	Mean difference	SE difference	95% CI
Absorbance	T1	Maxillary	1	1.504	0.756	0.218	0.007 ∗	2.959	0.676	0.229	0.202-1.150
			2	0.828	0.236	0.068
		Mandibular	1	1.516	0.516	0.149	<0.001 ∗	4.758	0.751	0.158	0.424-1.079
			2	0.765	0.181	0.052
	T2	Maxillary	1	1.978	1.036	0.299	0.007 ∗	3.003	0.912	0.304	0.282-1.541
			2	1.066	0.179	0.052
		Mandibular	1	1.889	0.705	0.203	<0.001 ∗	4.177	0.899	0.215	0.453-1.345
			2	0.990	0.242	0.070
Transmittance	T1	Maxillary	1	5.500	3.276	0.946	0.003 ∗	−3.343	−11.696	3.498	−18.951 to −4.441
			2	17.196	11.667	3.368
		Mandibular	1	4.369	2.239	0.646	<0.001 ∗	−6.042	−14.437	2.389	−19.393 to −9.482
			2	18.806	7.969	2.300
	T2	Maxillary	1	5.057	5.613	1.620	0.036 ∗	−2.232	−4.186	1.876	−8.076 to −0.296
			2	9.243	3.272	0.945
		Mandibular	1	2.779	2.051	0.592	<0.001 ∗	5.156	−8.857	1.718	−12.420 to −5.295
			2	11.637	5.586	1.613

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