Digital manufacturing techniques and the in vitro biocompatibility of acrylic-based occlusal device materials.

OBJECTIVES: Material chemistry and workflow variables associated with the fabrication of dental devices may affect the biocompatibility of the dental devices. The purpose of this study was to compare digital and conventional workflow procedures in the manufacturing of acrylic-based occlusal devices by assessing the cytotoxic potential of leakage products. METHODS: Specimens were manufactured by 3D printing (stereolithography and digital light processing), milling, and autopolymerization. Print specimens were also subjected to different post-curing methods. To assess biocompatibility, a human tongue epithelial cell line was exposed to material-based extracts. Cell viability was measured by MTT assay while Western blot assessed the expression level of selected cytoprotective proteins. RESULTS: Extracts from the Splint 2.0 material printed with DLP technology and post-cured with the Asiga Flash showed the clearest loss of cell viability. The milled and autopolymerized materials also showed a significant reduction in cell viability. However, by storing the autopolymerized material in dH2O for 12 h, no significant viability loss was observed. Increased levels of cytoprotective proteins were seen in cells exposed to extracts from the print materials and the autopolymerized material. Similarly to the effect on viability loss, storing the autopolymerized material in dH2O for 12 h reduced this effect. CONCLUSIONS/CLINICAL RELEVANCE: Based on the biocompatibility assessments, clinical outcomes of acrylic-based occlusal device materials may be affected by the choice of manufacturing technique and workflow procedures.

Pre-cementation procedures' effect on dental zirconias with different yttria content.

OBJECTVE: Several pre-cementation procedures have been advocated to enhance adhesion between zirconia and resin-based cement. There is, however, limited documentation on how these pre-treatments affect the strength of zirconia crowns as most tests are performed on discs or bars. The aim was to assess the effect of pre-cementation procedures on fracture mode, fracture strength and cement retention on zirconia. METHODS: Two dental zirconia materials with different yttria content were assessed (<4 and>5 mol%). Both discs (n = 45) and crown-shaped specimens (n = 30) of the two materials were pretreated with either air-abrasion or hot-etching with KHF2 and compared with untreated controls with regards to surface roughness, crystallography, wettability, cement adhesion and fracture strength. RESULTS AND SIGNIFICANCE: Air-abrasion improves adhesion and strength of zirconia with moderate yttria content (<4 mol%). Acid etching with heated KHF2 showed the best effect on strength and cement retention on zirconia with higher yttria content (>5 mol%). Application of KHF2 was, however, complicated on crown-shaped specimens. Pre-treatment and cementation protocols should be optimized for different dental zirconias to improve both strength and retention.

Ion release from three different dental alloys - effect of dynamic loading and toxicity of released elements.

Objective: The aims of this in vitro study were to assess if dynamic loading increases the metal ion release of selected dental alloys and to evaluate the cytotoxicity of the released metal ions. Materials and methods: One Pd-Ag alloy (Aurolite 2B) and two Co-Cr alloys (Wirobond 280 and d.Sign 30) were investigated. Two different corrosion immersion tests were used: a standardized static test (ISO 22674: 2016) and an experimental dynamic test. Both tests involved immersion of the specimens in a lactic acidic solution (pH = 2.3). Inductively coupled plasma mass spectrometry was used to identify and quantify released elements. A human monocyte cell-line (THP-1) was exposed to serially diluted solutions containing the selected metal ions. Cell viability was measured using the methyl-thiazolyl-tetrazolium assay. Results: According to the threshold defined in ISO 22674, only low concentrations of released elements were observed for both corrosion tests. No increase in metal ion release from the dynamic test compared with the static test was observed. Of the released elements, only Zn(II) and Co(II) showed a cytotoxic effect on THP-1 cells at 250 µM and higher concentrations. No increased viability loss was observed when adding other released elements to the exposure mixture. Conclusions: The tested alloys showed low levels of metal ion release from both static and dynamic corrosion testing. Dynamic loading did not increase the metal ion release compared to the static corrosion test. Concentrations of 250 µM and above of Zn(II) and Co(II) showed a cytotoxic effect on THP-1 cells.