Effect of in vivo aging on the surface and electrochemical properties of magnetic attachments used in facial prostheses: A retrieval analysis study

Statement of problem: Reasons associated with the failure of facial prosthesis are of major concern and may be associated with deterioration of both elastomeric materials and magnetic attachments. However, the extent of deterioration of these components is unclear. Purpose: The purpose of this in vitro study was to evaluate selected retrieved facial prostheses and provide information regarding the electrochemical characterization of the recovered magnetic attachments. Material and methods: Five facial prostheses (RP1, RP2, RP3, RP4, RP5) fabricated at the University of Texas, M.D. Anderson Cancer Center were retrieved following clinical use. The intaglio and external surfaces of the prostheses along with the incorporated magnetic attachments were photographed. The areas with the detected failures on the retrieved prostheses, as well as the recovered magnetic attachments, were evaluated under a reflected light stereomicroscope at ×16 nominal magnification and photographed with a digital camera. Five magnetic attachments recovered from the prostheses (retrieved group RT) were evaluated for degradation of their corrosion resistance after electrochemical testing in artificial sweat solution and were compared with 5 unused magnetic attachments (control group, CT). To identify the elemental composition of the intact magnet surface, 1 specimen from the control group was investigated by X-ray energy dispersive spectroscopy (EDS). Means and standard deviations of the open circuit potential (E_OCP), the zero-circuit potential (E_corr), and I_corr were calculated and statistically analyzed by a t test (α=.05 for all tests). Results: The main reasons of failure were discoloration, degradation and rupture of the silicone elastomer, marginal misfit, and delamination of the polyurethane sheet. Additional findings were tarnish and discoloration of the magnetic attachments accompanied by considerable smear build-up. EDS results verified the Ni plating of tested magnets. Electrochemical testing revealed that retrieved magnets showed significantly lower OCP (P<.001) and E_corr (P<.001) but similar I_corr (P=0.083) while the pseudopassivity region of unused magnets vanished in the retrieved group, denoting a degradation of electrochemical properties after clinical use. Conclusions: In vivo aging exerts extended degradation on the elastomer part of facial prostheses as well as deterioration of their surface integrity and electrochemical properties.