Deterioration of the Provox silicone tracheoesophageal voice prosthesis: microbial aspects and structural changes. - Van Weissenbruch,R.; Albers,F.W.; Bouckaert,S.; Nelis,H.J.; Criel,G.; Remon,J.P.; Sulter,A.M. (Acta Otolaryngol, 1997)