In vivo aging-induced surface roughness alterations of Invisalign^® and 3D-printed aligners

<jats:sec><jats:title>Objective:</jats:title><jats:p> To assess the surface roughness of in-house 3D-printed orthodontic aligners compared to Invisalign<jats:sup>®</jats:sup> appliances, both retrieved as well as in the ‘as-received’ control status. </jats:p></jats:sec><jats:sec><jats:title>Design:</jats:title><jats:p> An in vitro study following intra-oral material aging. </jats:p></jats:sec><jats:sec><jats:title>Setting and participants:</jats:title><jats:p> Twelve clinically used Invisalign<jats:sup>®</jats:sup> appliances and the same number of 3D-printed aligners were obtained from a respective number of patients, without involvement of attachments. A similar number of ‘as-received’ aligners of each material were used as control (CON) groups. </jats:p></jats:sec><jats:sec><jats:title>Method:</jats:title><jats:p> Four groups of materials were examined: A = Invisalign<jats:sup>®</jats:sup> CON; B = Invisalign<jats:sup>®</jats:sup> used; C = 3D-printed CON; and D = 3D-printed used. Optical profilometry was employed to examine the following surface roughness parameters: amplitude parameters Sa, Sq and Sz and functional parameters Sc and Sv. Descriptive statistics and quantile regression modeling were conducted, and the level of statistical significance was set at α = 0.05. </jats:p></jats:sec><jats:sec><jats:title>Results:</jats:title><jats:p> Intra-oral exposure of 3D-printed aligners was significantly associated with increase in all tested parameters ( P < 0.001 at all occasions). Significant differences were detected in the retrieved 3D-printed aligners compared to Invisalign<jats:sup>®</jats:sup> retrieved, with the exception of Sz. The respective effect sizes (median differences) were as follows: Sa: 169 nm, 95% confidence interval [CI] = 89–248, P < 0.001; Sq: 315 nm, 95% CI = 152–477, P < 0.001; Sc: 233 nm<jats:sup>3</jats:sup>/nm<jats:sup>2</jats:sup>, 95% CI = 131–335, P < 0.001; and Sv: 43 nm<jats:sup>3</jats:sup>/nm<jats:sup>2</jats:sup>, 95% CI = 17–68, P = 0.002. </jats:p></jats:sec><jats:sec><jats:title>Conclusion:</jats:title><jats:p> Within the limitations of this report, we concluded that surface roughness differences existed between 3D-printed aligners and Invisalign<jats:sup>®</jats:sup> in the retrieved status, as well as between the control and retrieved 3D-printed groups. </jats:p></jats:sec>