Effect of cigarette smoke on the optical properties of clear orthodontic aligners: an in-vitro study

Abstract

Aim:

This study assessed the optical properties of aligner surfaces post-cigarette smoke exposure.

Design:

In-vitro experimental study.

Setting:

Laboratory analysis of clear aligners subjected to cigarette smoke exposure at Federal University of Rio de Janeiro, Brazil.

Methods:

A total of 20 plastic pieces from the labial surfaces of upper central incisors of Invisalign^® clear aligners were randomly divided into a control group (CG) and an experimental group (EG). The specimens were divided equally (n = 10): CG, stored in artificial saliva at 37°C ± 1°C for 14 days; and the EG, exposed to cigarette smoke using a sealed acrylic device with 10 cigarettes per cycle for 20 cycles. A spectrophotometer was used to evaluate changes in colour and light transmittance based on CIELab* colour parameters. Measurements were taken before (T0) and after (T1) exposure. The total colour difference (∆E) and National Bureau of Standards (NBS) were calculated. T-tests were used for comparisons at a significance level of 0.05.

Results:

Statistically significant colour changes (P < 0.05) were observed at T1 in the EG (luminosity [L*] = 77.20 ± 3.33; difference along green-red axis [a*] = −1.57 ± 0.02; and difference along blue-yellow axis [b*] = 6.74 ± 0.55) compared to the CG. The mean ∆E* value at T1 was significantly higher in the EG (14.27 ± 2.72) compared to the CG (2.39 ± 0.56; P = 0.002). Light transmittance decreased significantly after cigarette smoke exposure (CG = 68.396 ± 8.683; EG = 59.538 ± 5.089; P = 0.012).

Conclusions:

Cigarette smoke exposure significantly altered the optical properties of clear orthodontic aligners, affecting both colour and light transmittance.

Plain language summary

How does smoking compromise the invisible appearance of clear aligners?

Why was the study done? Clear aligners are a widely used option for orthodontic treatment because they are nearly invisible. Meanwhile, adults also smoke cigarettes, which can stain dental materials. This study aimed to find out whether smoking changes the invisible appearance of clear aligners.

What did the researchers do? Twenty pieces of clear aligner material (Invisalign^®) were analysed in a laboratory. Half were kept in artificial saliva to mimic normal mouth conditions (control group), while the other half were exposed to cigarette smoke in a sealed acrylic device (experimental group). They measured changes in colour and light transmission before and after exposure for comparisons.

What did the researchers find? Aligners exposed to cigarette smoke became significantly darker and more yellowish compared to the control group. The smoked aligners also let through less light, meaning they became less clear. These changes were large enough to be noticeable and would likely affect the appearance of the aligners when worn.

What do the findings mean? Smoking can cause clear aligners to become visibly stained and less transparent, which reduce their aesthetic appeal. Dentists should inform patients who smoke about the high risk of staining and discuss possible solutions, like more frequent replacement or quitting smoking to maintain the aligners’ appearance.