An In Vitro Investigation of a Novel, Two-Piece Zirconia Dental Implant System

Implant treatment is currently overriding other prosthetic solutions especially in the case of replacing anterior teeth in the aesthetic zone. Zirconia ceramics exhibit promising aesthetic, periointegration and antibacterial properties that may overcome critical drawbacks associated with titanium based dental implants. They also possess distinctive mechanical properties due to the unique transformation toughening mechanism. However, the effects of low-temperature degradation (LTD) or ageing on the durability of the material is of a major concern. Additionally, the currently available one-piece and two-piece zirconia dental implant designs exhibit sub-standard performance. This study aimed to investigate ageing, mechanical properties and biofunctional characteristics of a new implant system with a novel biomechanical design. The proposed design utilises a relatively low-strength glass fibre composite abutment bonded with resin cement to an injection-moulded, soft tissue level, acid-etched zirconia implant. Hydrothermal treatment was used to simulate in vivo ageing. A battery of complimentary crystallographic and imaging studies was used to characterise hydrothermally- and stress-induced phase transformation. Additionally, the effect of ageing on basic mechanical properties of standard samples was investigated at the macro-, micro- and nano-scales. Dynamic fatigue was performed in order to determine durability and reliability of various components and interfaces of the design under simulated clinical conditions. The acid-etched zirconia surface (MDS) was compared to a high-performance, mechanically and chemically modified titanium surface in terms of; surface topography, biocompatibility and cell biofunctional response. The results of this study indicated that hydrothermal ageing resulted in phase transformation that was localised to the surface of the material without any involvement of the bulk. No evidence of extensive cracking was detected as a result of the used ageing conditions. The aged samples exhibited static mechanical properties that were not significantly different from the control group apart from marginal decreases in surface hardness. The implant samples restored with two different crown materials did not exhibit any premature failures. The engineered weak connection seemed to favour retrievable failures especially when low strength crown material was used to restore the implants. The studied MDS zirconia surface exhibited moderate surface roughness and high biocompatibility when tested with human osteoblast-like cells and human gingival fibroblasts. Cell attachment and bone formation capacity of cells were similar or marginally higher in cells cultured on MDS surface when compared to titanium (SLActive-like) counterpart. Within the limitations of this study, it can be concluded that the studied zirconia material was not drastically affected by hydrothermal ageing and thereby, in vivo LTD may be not of a concern whilst using such material. The current implant design may withstand long-term functional forces in the anterior region of the oral cavity. The MDS surface may reduce the time required for bone and soft tissue healing which is essential for clinical cases require immediate provisionalisation and/or early loading. Soft tissue remodelling may be of a less concern owing to the high soft tissue attachment (periointegration) capacity of the studied MDS zirconia surface.