Long-term corrosion of a Ga-containing restorative material.
OBJECTIVE
The aim was to simulate and characterize the long-term corrosion of a Ga-containing alloy (Galloy, SDI).


METHODS
To induce corrosion, cylindrical specimens, 8 x 4 mm, of the material were subject to potentiostatic polarization at -0.1 V (SCE) in a phosphated buffered saline (PBS) solution at 20 degrees C for d. The current-time transients during polarization were recorded and the corresponding anodic charge, Q, was calculated. Parallel potentiostatic corrosion tests in a Cl-free PBS solution were also conducted to demonstrate the significance of the Cl- ion in corrosion. In addition, potentiodynamic anodic polarization tests were performed to characterize the overall corrosion behavior of the alloy in both electrolytes. The external and internal corroded layers, formed during potentiostatic corrosion in PBS, were measured by optical microscopy. SEM and EDXA were used to characterize the morphology and composition of the potentiostatically polarized surfaces.


RESULTS
Galloy was passive in Cl-free PBS. The Cl- ion in PBS destroyed passivity and initiated a "dissolution-precipitation" type reaction during potentiostatic corrosion. The latter led to circumferential internal corrosion and growth of a layer of external corrosion products. The thickness of the internal and external corrosion layers was 0.77 +/- 0.07 and 0.86 +/- 0.37 mm, respectively. The Q value (89.3 +/- 13.7 C/cm2) in PBS was about two orders of magnitude higher than that (0.66 +/- 0.24 C/cm2) in Cl-free PBS. The corrosion products contained Sn, Ga, In, Cu, O and Cl.


CONCLUSIONS
Massive internal and external corrosion in a Cl-containing medium as in saliva, accumulation of corrosion products at the cavity wall, and the consequent stress build-up contribute to post-operative pain, tooth straining, marginal breakdown and fractured teeth reported with the clinical use of Galloy.
Sarkar
N K
NK
School of Dentistry, Louisiana State University, 1100 Florida Ave., New Orleans, LA 70119, USA. nsarka@lsud.lsumc.edu
Moiseyeva
R
R
Berzins
D W
DW
Osborne
J W
JW
D002021:Buffers; D011232:Chemical Precipitation; D002712:Chlorides / Q000737:chemistry; D003300:Copper / Q000737:chemistry; D003343:Corrosion; D003722:Dental Alloys / Q000737:chemistry*; D003793:Dental Restoration, Permanent; D004563:Electrochemistry; D004577:Electron Probe Microanalysis; D005708:Gallium / Q000737:chemistry*; D006801:Humans; D007204:Indium / Q000737:chemistry; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D010100:Oxygen / Q000737:chemistry; D010710:Phosphates; D012965:Sodium Chloride; D012995:Solubility; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014001:Tin / Q000737:chemistry
D002021:Buffers; D002712:Chlorides; D003722:Dental Alloys; C100747:Galloy; D010710:Phosphates; D007204:Indium; D012965:Sodium Chloride; D014001:Tin; D003300:Copper; D005708:Gallium; D010100:Oxygen