Does the Exposure to Cigarette Smoke Influence the Colour Stability and Mechanical Properties of Different Orthodontic Elastic Ligatures? – in Vitro Study

Objective > The aim of this study was to evaluate the colour stability and mechanical resistance of orthodontic elastic ligature exposed to cigarette smoke. Methods > Four commercial brands were used: Aditek (R) (GA), Eurodonto (R) (GE), Morelli (R) (GM) and Orthometric (R) (GO). Eight elastic ligature rings (for mechanical analysis) and eight 5 x 5 mm fragments of the material (for colour stability analysis) were separated from each commercial brand for the control group (C) (n = 64) and experimental group (E) (n = 64). The control group was not exposed to cigarette smoke. Colourimetric status (CIEL*a*b* System) and light transmittance (% transmitted light) were evaluated using Vita Easyshade Compact and CM2600 spectrophotometers, respectively. The mechanical resistance was evaluated using a universal testing machine (EMIC DL), performing tensile testing (speed 5 mm/min). The analyses occurred at the following times: T0, before exposure to the smoke; T1, after the 1st exposure; and T2, after the 2nd exposure to cigarette smoke. Comparison between the groups and evaluation of the time effect were performed with the ANOVA/Tukey (a = 0.05) and ANOVA-MR tests with Bonferroni correction (a=0.016). Results > Significant differences were only observed for colour stability in the GA-E (NBS T2: 15.94 +/- 1.88) and GM-E (NBS T2: 16.11 +/- 4.54) groups (P < 0.05); transmittance in the GA-E group (T2T0: -9.07 +/- 5.01) (P < 0.016) and mechanical resistance in the GA-C group (T2-T0: -0.95 +/- 0.61 N) (P < 0.016). Conclusion > The orthodontic elastic ligatures were sensitive to the cigarette smoke exposure regarding to loss of mechanical strength properties and change in colour stability.