Expression of inflammatory mediator and histological changes of 3D oral Mucosal model in response to yttria-stabilized nanozirconia

Abstract

Monolithic zirconia developed from nano-sized zirconia powders has superior translucency and mechanical properties than the commercially available zirconia for dental restorations. However, nanotoxicity is a concern, which may manifest as gingival inflammation clinically. Hence, this study aimed to assess the biocompatibility of yttriastabilized nanozirconia (3-YZP) on the 3-dimensional oral mucosal models (3DOMM). Firstly, human gingival fibroblast (HGF) and immortalised human oral keratinocyte cell line (OKF6/TERT-2) were cultured on 3-YZP and IC separately for 24 hours. The morphology of these cells was then viewed through electron microscope scanning. The 3D-OMMs were constructed using HGF and OKF6/TERT-2, co-cultured on an acellular dermal matrix and grown for 5 days. The models were lifted for seven days at the air-liquid interface afterwards, while the growth media were changed every 2 days. On day 12, the tissue models were exposed to 3-YZP (test) and inCoris TZI (IC) (reference material). The growth media were collected at 24 and 48 hours of exposure to materials. The media were centrifuged to obtain the supernatant and assessed for cytokine released (IL-1β). The 3D-OMMs were fixed with 10% formalin for the histopathological assessments. The 3-YZP and IC supported the cellular attachment of fibroblasts, and keratinocytes were noted. Compared to the unexposed 3D-OMM, supernatants of 3-YZP and IC expressed higher concentrations of IL-1β. However, the concentration of the IL-1β was not statistically different between the two materials, assessed with ANOVA (0.77, 95% CI (-3.5 to 5.07), P = 0.892). Histologically, stratification of epithelial cells was formed without evidence of cytotoxic damage to any models. The epithelial thickness measured was the same for all model tissues (Welch’s F (2,14.0) = 0.68, P = 0.523). In conclusion, the excellent biocompatibility of nanozirconia, as evidenced by the multiple endpoint analyses of the 3D-OMM, may indicate the potential of its clinical application as a restorative material