Intranuclear cell uptake and toxicity of titanium dioxide and zirconia particles as well as bacterial adhesion on dental titanium- and zirconia-implants

Abstract

ObjectivePrevious studies have shown that particles can be released from dental titanium (Ti)- and zirconia (ZrO2)-implants. Titanium dioxide (TiO2)- and ZrO2-particles were compared regarding their toxicity and intranuclear cell uptake as well as the adhesion of various anaerobic bacteria on Ti- and ZrO2-implants. MethodsCyto- and genotoxicity of TiO2-microparticles (TiO2-MPs) and TiO2-nanoparticles (TiO2-NPs) in periodontal ligament (PDL)-hTERT cells were determined with XTT test and DNA damage with comet assay. Particle sizes of TiO2- and ZrO2-particles were measured with scanning electron microscope. Intranuclear uptake in PDL-hTERT cells was determined with laser scanning confocal microscopy. Adhesions of relevant anaerobic mouth bacteria Porphyromonas gingivalis, Prevotella intermedia and Aggregatibacter actinomycetemcomitans on Ti- and ZrO2-implants were investigated by cultivation and counting bacterial colonies. ResultsParticle size measurements revealed that 99% of the TiO2-NPs had a size below 100 nm and 88% of the TiO2-MPs sizes were between 50 and 200 nm. Following EC50 values were found for particles (mg/l): 92 (TiO2-MPs) and 15 (TiO2-NPs). A significant increase in olive tail moment (OTM) was found for TiO2-NPs at a concentration of 1/10 EC50. TiO2- and ZrO2-NPs had a higher intranuclear cell uptake efficiency, compared to corresponding TiO2- and ZrO2-MPs. All investigated particles could be detected in cell nucleus. Adhesion of all investigated bacterial species was significantly higher on Ti-implants, compared to ZrO2-implants. ConclusionTi usually develops an oxide layer (TiO2). Particles released from Ti-implants should be TiO2-particles or Ti-particles coated with a TiO2-layer. Toxicity of released Ti-particles depends on their oxidation state and on their size (NP or MP). Particularly, NPs were more cyto- and genotoxic compared to the corresponding MPs. TiO2- and ZrO2-NPs showed a significant increase in the intranuclear cell uptake ratio at higher exposure concentration, compared to lower concentrations and consequently might lead to a higher potential of DNA damage. Adhesion of bacteria to ZrO2-implants is reduced, compared to Ti-implants. Therefore, ZrO2-implants might contribute to reduced biological complications (e.g. periimplantitis).