Tribocorrosion Studies of Dental Materials, and the Clinical Implications

The questions this study seeks to answer are i) whether nicotine leads to greater tribocorrosion in titanium alloy, thus invoking a non-biological implant centered failure mechanism in dental implants, and ii) whether a processing technique such as thermal oxidation can reduce the corrosion and increase the longevity of dental implants in smokers. The methods used to evaluate these questions are electrochemical impedance spectroscopy, potentiodynamic testing, white light interferometry, and scanning electron microscopy. A tribocorrosion apparatus simulating the oral environment was used under both free potential and potentiostatic mode to study the effect of nicotine on titanium alloy. Using Faraday’s law the potentiostatic mode allows us to calculate weight loss due to corrosion, and wear separately as well as classify the material breakdown on a spectrum of both. For the tribocorrosive studies of nicotine, different doses, 0, 1, 5, and 20 mg in artificial saliva were used to mimic smoking habits in patients, as well as an acidic and resting oral pH to mimic the effects of food. For the thermal oxidation studies, different temperatures 200, 400, and 700 °C were used as well as both acidic and neutral pH to mimic food, and different annealing times of 1, 3, and 6 hours. The major findings for the thermal oxidation study were: (1) temperature dependence of corrosion properties that at first improve with temperature and then reverse as higher temperatures display inhomogeneity and cracking, (2) time independence of the effect of thermal oxidation on the corrosion properties, and (3) reduction in the effect of acidic medium on the corrosion properties. The major findings for the tribocorrosion study of nicotine were: (1) a dose dependence of nicotine with a protective effect at low doses and a detrimental one at high doses, (2) a pH reversal of the protection of nicotine due to its effect on polarization resistance, (3) synergism between wear and corrosion, and (4) a three-body mechanism of degradation. Overall, the results of this study indicate that thermal oxidation is an effective prophylaxis for implant centered failure and that smoking habits in patients determine failure risks.