Tribocorrosion Behavior of Dental Alloys in Contact With Different pH

Objectives: The purpose of this study was to determine if the tribocorrosion behavior of the CoCr, NiCr and NiCrTi alloys can be affected by differences artificial saliva´s pH and the cast technique.
Methods: 15 samples of each alloy (13x2mm) were casted by flame and 15 by casting machine, five for each pH analyzed, ground (SIC 2200) and ultrasonically cleaned. The tribocorrosion experiments were performed using a ball-on-flat contact configuration and the open circuit potential was monitored during the test. To reproduce the oral environment, different pH values of artificial saliva were analyzed (3.0; 6.5; 9.0). The tests were performed for 750 cycles simulating the daily dental contact.
Results: The better tribocorrosion behavior were recorded in acid environment in both casting techniques: flame and machine, respectively (NiCr: -117mV and -138mV; NiCrTi: -285mV and -265mV; CoCr: -314mV and -192mV) verifying that only NiCr showed to be more resistant to corrosion in acidic medium when casted by flame. In basic and neutral media, CoCr alloy showed similar OCP values ​​for both casting techniques (pH 6.5: -372mV and -338mV; pH 9.0: -368mV and -272mV), being slightly higher values ​​for casting machine. The NiCrTi alloy casted by flame presented a higher corrosion behavior in basic and neutral medium (-222mV and -213mV, respectively) than when it was casted by machine (-298mV and -284mV).
Conclusions: As a general tendency, the samples casted by machine presented a different corrosion behavior than those casted by flame, and it seems that the pH values can influence on the tribocorrosion behavior of the tested alloys.