Compatibility of Metallic Materials Used for Dentures Related to Different Cleaning Regimens

Objectives: To clean dentures, different products are commercially available, but consumers also use aggressive remedies. Aim of this study was to assess material integrity and surface compatibility of various metallic denture materials after different, representative cleaning regimens, i.e. to compare surface morphology, composition and mechanical properties of the materials before and after cleaning treatments.
Methods: Orthodontic metal wires from stainless steel, a CoCr-based casting alloy and three different solders varying in metal composition were investigated. Eight specimens per material were tested. A cyclic test procedure contained soaking and combined soaking and brushing was performed. The following cleansing products, remedies and references were investigated: tablet cleanser, bleach solution containing sodium hypochlorite, vinegar, soap, mouthwash, toothpaste, isopropyl, and water. Test parameters were adapted according to realistic assumptions for application and manufactures instructions. The experiments simulated a period of 2 years. Scanning electron microscopy (SEM), including element detection (EDX), profilometry and nanoindentation were applied for material characterisation.

Results: Compatibility of cleaning substances can differ enormously between the tested metal components. Different kinds of surface incompatibilities (pitting corrosion, layer formation) were observed. Stainless steel has shown highest resistance against chemical and mechanical impacts by the cleaning test regimens. CoCr-alloy was damaged by bleach. Layer formations were observed on silver-based solders for bleach and cleansing tablet; this was not observed for solders with gold-content of 48%.
Conclusions: The use of bleach can lead to dramatic surface damage and its use should not be recommended. Besides the negative aspect of material degradation (mechanical behaviour, aesthetic appearance), surface alterations caused by inappropriate or too intensive cleaning of dentures could enhance the potential of bacterial adhesion and the associated possible oral infections. The obtained knowledge can be used to derive recommendations for application of cleansing products or regimens.