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

To assess the surface roughness of in-house 3D-printed orthodontic aligners compared with Invisalign^® appliances, both retrieved as well as in the 'as-received' control status.

An in vitro study following intra-oral material aging.

Twelve clinically used Invisalign^® appliances and the same number of 3D-printed aligners, without involvement of attachments, were obtained from a respective number of patients. A similar number of 'as-received' aligners, of each material, were used as control (CON) groups.

Four groups of materials were examined: A = Invisalign^® CON; B = Invisalign^® 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.

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 with Invisalign^® 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 nm³/nm², 95% CI = 131-335, P < 0.001; and Sv: 43 nm³/nm², 95% CI = 17-68, P = 0.002.

Within the limitations of this study, we concluded that surface roughness differences existed between 3D-printed aligners and Invisalign^® in the retrieved status, as well as between the control and retrieved 3D-printed groups.