To evaluate the effects of thermoforming systems on surface roughness and Knoop microhardness of thermoplastic materials used for in-house clear orthodontic aligners (COAs).

Four thermoplastic materials were evaluated: G1) Taglus®; G2) Essix ACE®; G3) Pro-Aligner X®; and, G4) Bio Art Cristal®. The materials were tested under three conditions: control (no thermoforming), temperature-controlled (Track-V® machine), and non-temperature-controlled (P7® machine). Surface roughness and Knoop microhardness were measured after processing. Statistical analysis was performed using generalized linear models (α = 0.05).

Compared with the control condition, non-temperature-controlled (NTC) thermoforming significantly increased surface roughness in all materials ( P < 0.05). Temperature-controlled (TC) thermoforming increased roughness in G1 and G3, with no significant change in G4. Knoop microhardness increased after NTC thermoforming in G1 and G4 ( P < 0.05), whereas TC thermoforming produced smaller microhardness changes in these materials. Under NTC conditions, G1 and G4 showed the highest hardness values. Under TC conditions, G1 exhibited greater microhardness compared with G2 and G3 ( P < 0.05).

Thermoforming modifies the mechanical properties of COA materials, and these changes depend on the thermoforming system employed. Non–temperature-controlled systems resulted in greater increases in roughness and microhardness, indicating that equipment-specific fabrication parameters should be considered to optimize in-house aligner performance.