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

A 10 microm film of a chlorine-substituted poly(para-xylylene) was evaluated as a protective coating for commercial chain modules. Segments of modules were either non-coated or coated using five modes: 0%, 100%, and 200% elongation during coating and shipping; and 100% and 200% elongation only during coating. Prior to hydration, coating coverage was examined via light and electron microscopy. When hydrated, the presence or absence of the coating did not appreciably change the total weight gain (1.5%). However, when the modules were post-coating elongated to either 100% or 200%, neither the non-coated nor the coated modules sorbed water. Hydration did not significantly change the mechanical properties of the modules. As expected, most of the mechanical properties of the coated modules were greater than the properties for the uncoated modules. With regard to the coated modules only the properties of those modules having 0% elongation during coating and shipping were, 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 recovered approximately 74% and 62% of the peak loading, respectively. Using the load-time data from these curves, Maxwell-Weichert models accurately predicted the decay profiles of both the non-coated and coated modules. Because the water sorption and the mechanical properties of these coated modules were favorable, they should be further characterized for staining. Copyright 2000 Kluwer Academic Publishers