# Effect of cigarette smoke on surface roughness and bacterial adhesion of orthodontic aligners: an in vitro investigation

## TL;DR

Cigarette smoke increases surface roughness and bacterial adhesion on orthodontic aligners, suggesting a need for better oral hygiene for smokers.

## Contribution

This study is the first to demonstrate that cigarette smoke exposure increases surface roughness and bacterial adherence on orthodontic aligners in vitro.

## Key findings

- Cigarette smoke exposure significantly increased surface roughness (Ra and Rz) of aligners.
- Aligners exposed to cigarette smoke showed higher bacterial adherence and lower pH levels.
- Growth group samples had the highest microbial counts compared to other groups.

## Abstract

This study aims to evaluate the impact of cigarette smoke on Invisalign® aligners in surface roughness, bacterial adherence rates, pH changes and multispecies biofilm formation after exposure.

Seventy-two flat samples of growth (G1), sterility (G2), saliva (G3), and smoke (G4) groups were exposed to artificial saliva, and G4 underwent 21 cycles of smoke. Linear roughness (Ra) and average depth (Rz) were assessed before and after saliva (G3.1) and smoke (G4.1) exposure. Independent and paired t-tests compared measurements over 5 days of evaluation [biofilm, microorganisms (CFU/mL), pH, and volumetric surface roughness (Sa)], measurements were taken before (T0) and after (T1) exposure to saliva and cigarette smoke.

Increased roughness post-exposure to cigarette smoke Ra (p = 0.003) and Rz (p = 0.014) in G4.1 at T1 (p = 0.046), and higher roughness over time (Ra: 0.139 ± 0.007; Rz: 0.741 ± 0.026), unlike G3.1 (Ra: 0.122 ± 0.002; Rz: 0.616 ± 0.021). G1 had the highest CFU (8.57 × 108), significantly higher than the G4.2 (5.33 × 108) and G3.2 (2 × 108). From 24 to 96 h, pH in G4.2 (5.75) and G1 (4.45) showed slight decreases, G2 (6.76) and G3.2 (6.35) increased. G1 had the highest Sa (48.97 ± 14.19), compared to G2 (4.27 ± 1.14), G3 (7.60 ± 4.28), and G4 (13.98 ± 8.18).

Cigarette smoke exposure elevated surface roughness and enhanced bacterial adherence on aligners. Clinical Relevance: Reinforce smoking cessation and strict oral hygiene protocols for aligner-wearing patients. In vivo studies are warranted to confirm these findings.