Physical and mechanical characteristics of a chlorine-substituted poly(para-xylylene) coating on orthodontic chain modules

A 10 mu m film of a chlorine-substituted poly(para-xylylene) was evaluated as a protective coating for commercial chain modules. Segments of modules w ere either non-coated or coated using five modes: 0%, 100%, and 200% elonga tion during coating and shipping; and 100% and 200% elongation only during coating. Prior to hydration, coating coverage was examined via light and el ectron microscopy. When hydrated, the presence or absence of the coating di d not appreciably change the total weight gain (1.5%). However, when the mo dules were post-coating elongated to either 100% or 200%, neither the non-c oated nor the coated modules sorbed water. Hydration did not significantly change the mechanical properties of the modules. As expected, most of the m echanical properties of the coated modules were greater than the properties for the uncoated modules. With regard to the coated modules only the prope rties of those modules having 0% elongation during coating and shipping wer e, in general, significantly different from the other coated modules. Post- coating elongation reduced the stiffness of the coated modules more than 79 %. In regard to stress relaxation, the non-coated and coated modules recove red approximately 74% and 62% of the peak loading, respectively. Using the load-time data from these curves, Maxwell-Weichert models accurately predic ted the decay profiles of both the non-coated and coated modules. Because t he water sorption and the mechanical properties of these coated modules wer e favorable, they should be further characterized for staining. (C) 2000 Kl uwer Academic Publishers.