Release of metal in vivo from stressed and nonstressed maxillofacial fracture plates and screws

Objectives. To analyze the release of metal into the adjacent tissues from stressed and nonstressed titanium and stainless steel miniplates and screws . Study design. Two miniplates were inserted into the cranial vaults of 12 be agle dogs while they were under general endotracheal anesthesia. One minipl ate was shaped to fit the curvature of the skull (control). Another minipla te, made of the same material, was bent in a curve until the midpoint was r aised 3 mm above the ends. Screws were inserted and tightened until the pla te conformed to the skull curvature, creating stresses in the system. Four animals (2 each, having titanium or stainless steel plates and screws) were killed after 4, 12, and 24 weeks. Metallosis of adjacent soft tissues was assessed qualitatively. Miniplates and screws were removed, and adjacent so ft tissue and bone was excised. Titanium, iron, chromium, nickel, and alumi num levels were assayed by ultraviolet/visible light and atomic absorption spectrophotometry. Nonparametric statistical methods were used for data ana lysis. Results. There was no clear relationship between pigmentation of soft tissu e adjacent to the miniplates and screws and the concentrations of metal pre sent. The data did not demonstrate any consistent differences in the concen trations of metallic elements next to stressed and nonstressed (control) mi niplates and screws of either material. Conclusion. Stresses arising through poor contouring of miniplates do not a ppear to influence the extent of release of metal into the adjacent tissues .