Effect of different initial finishes and Parylene coating thickness on the surface properties of coated PMMA

Statement of the problem. The colonization of microorganisms on acrylic resin dentures may result in denture-induced stomatitis. No efficient coating has yet been proposed to address this issue. Purpose. The purpose of this in vitro study was to assess the effect of various initial surface finishes and different Parylene coating thicknesses on the surface roughness (Ra) and surface free energy (SFE) of Parylene coated polymethyl methacrylate (PMMA). Material and methods. One hundred and sixty PMMA specimens were produced and divided into 8 groups as follows: group A: uncoated, 1000 grit finish; group Ap1: 10 mu m Parylene coated, 1000 grit finish; group B: uncoated, 1200 grit finish; group Bp: 10 mu m Parylene coated, 1200 grit finish; group C: uncoated, 2400 grit finish; group Cp: 10 mu m Parylene coated, 2400 grit finish; group Ap2: 20 mu m Parylene coated, 1000 grit finish; group Ap3: 30 mu m Parylene coated, 1000 grit finish. The Ra of all specimens was measured with a noncontact profilometer. To calculate the SFE, the Owens-Wendt approach was applied after measuring the contact angles with a goniometer. The topography of the specimens was observed by scanning electron microscope. Results. Groups Ap1 and Bp presented significantly lower Ra values compared with their respective uncoated groups A and B (P<.001). No statistical difference was found between the Ra values of groups C and Cp, between A and Ap3, and between Ap2 and Ap3. The SFE values of the coated groups were significantly higher than the SFE values of the uncoated groups with the same initial finish (P<.001). Conclusions. Coating with a 10-mu m layer of Parylene C resulted in lower Ra values for the rougher groups and increased SFE values. Increasing the coating thickness resulted in an increase of the Ra.