Abstract :
The increasing use of nickel containing devices in orthodontics and the growing prevalence
of nickel allergy in the population significantly increases the interest in biocompatibility
studies of these devices. The decisive factor determining the biocompatibility of
orthodontic wires is their corrosion behaviour. Therefore seven nickel titanium levelling
arches, one titanium molybdenum, a cobalt chromium and three stainless steel wires were
analysed with respect to their corrosion behaviour under realistic conditions. Potentiostatic
tests to determine rupture potentials in artificial saliva and static immersion tests in
artificial saliva (AS) or lactic acid (LA), as well as immersion tests with mechanical, thermal
and combined mechanical and thermal stresses were performed. Subsequently, the
surfaces of the wires were investigated employing scanning electron microscopy (SEM)
with energy dispersive X-ray analysis (EDX) and the nickel release into the corrosion media
of the specimens was measured with inductively coupled plasma mass spectrometry
(ICP-MS). The results yield information not only about the relative corrosion tendency of
the wires under in vitro conditions but also give a quantitative estimation about the nickel
ion release of the orthodontic wires during in vivo treatment. Generally, the maximum
release of nickel ions was two orders of magnitude below the daily dietary intake level.
Mechanical and thermal loading increases nickel release in the immersion tests by a factor
of 10 to 30. Two NiTi wires (Dentaurum Tensic, Forestadent Titanol Low Force) examined
showed lower rupture potentials and a higher tendency towards corrosion in the
immersion tests than the others due to their surface composition. However these
differences are levelled off by long-term mechanical and thermal loading.
C
2005 Springer Science + Business Media, Inc.
