Roughness and wettability of aligner materials

The characterisation of surface roughness and energy of contemporary thermoplastic materials used in manufacturing of orthodontic aligners.

In vitro, laboratory study.

Four commercially available thermoplastic materials were selected (CA-medium/CAM, Essix-copopyester/COP, Duran/DUR and Erkodur/ERK). Five disks from each, as received, material were tested and subjected to: (1) reflected light microscopy; (2) optical profilometry for the estimation of Sa, Sz, Sq, Sdr, Sc, Sv surface roughness parameters (n = 5); and (3) contact angle measurements with a Zisman series of liquids for the estimation of critical surface tension (γ_C), total work of adhesion (W^A), as well as the work of adhesion due to polar (W^P) and dispersion (W^D) components employing the Zisman method (n = 5/liquid). Thermoformed disks were prepared against a dental stone model and the roughness parameters were calculated again Statistical analysis was performed by one-way ANOVA/ Tukey multiple comparison test and t-test (a = 0.05).

Microscopic and profilometric analyses revealed a smooth surface texture in the as-received materials, but a very rough texture after thermoforming, with insignificant differences within each state. Significant differences in the as-received state were found in the surface energy parameters; CAM showed the lowest γ_C and the highest W^A, W^P, W^D, whereas ERK with the highest γ_C demonstrated lower W^A. COP and DUR were ranked in an intermediate group regarding γ_C, with a statistically significant difference in W^A between them, mainly attributed to the lower W^P of the former.

Given the differences in surface energy parameters and the lack of roughness differences within the as received or thermoformed groups, it may be concluded that variations in the plaque retaining capacity are anticipated, determined by γ_C, W^A and the W^P, W^D components.