Optimized 3D printed zirconia-reinforced leucite with antibacterial coating for dental applications.

OBJECTIVES: This study aims to produce by robocasting leucite/zirconia pieces with suitable mechanical and tribological performance, convenient aesthetics, and antibacterial properties to be used in dental crown replacement. METHODS: Leucite pastes reinforced with 12.5%, 25%, and 37.5% wt. ZrO2 nanoparticles were prepared and used to print samples that after sintering were characterized in terms of density, shrinkage, morphology, porosity, mechanical and tribological properties and translucency. A coating of silver diamine fluoride (SDF) and potassium iodide (KI) was applied over the most promising material. The material's antibacterial activity and cytotoxicity were assessed. RESULTS: It was found that the increase of ZrO2 reinforcement up to 25% enhanced both microhardness and fracture toughness of the sintered composite. However, for a superior content of ZrO2, the increase of the porosity negatively affected the mechanical behaviour of the composite. Moreover, the composite with 25% ZrO2 exhibited neglectable wear in chewing simulator tests and induced the lowest wear on the antagonist dental cusps. Although this composite exhibited lower translucency than human teeth, it was three times higher than the ZrO2 glazed material. Coating this composite material with SDF+KI conferred antibacterial properties without inducing cytotoxicity. SIGNIFICANCE: Robocasting of leucite reinforced with 25% ZrO2 led to best results. The obtained material revealed superior optical properties and tribomechanical behaviour compared to glazed ZrO2 (that is a common option in dental practice). Moreover, the application of SDF+KI coating impaired S. aureus proliferation, which anticipates its potential benefit for preventing pathogenic bacterial complications associated with prosthetic crown placement.

Tribological performance of the pair human teeth vs 3D printed zirconia: An in vitro chewing simulation study.

This study aims to evaluate the tribological performance of the pair human teeth/robocasted zirconia, with a special focus on the enamel wear mechanisms. Zirconia pieces produced by robocasting (RC) and unidirectional compression (UC) were compared in terms of crystalline structure, density, porosity, hardness and toughness. Chewing simulation tests were performed against human dental cusps. The cusps wear was quantified and the wear mechanisms identified. Although most of the properties of UC and RC samples are similar, differences were observed for surface roughness and porosity. Although the samples did not suffer wear, the antagonist cusps worn in a similar way. In conclusion, robocasting seems a promising technique to produce customized zirconia dental pieces, namely in what concerns the overall tribological behaviour.

Suitability of 3D printed pieces of nanocrystalline zirconia for dental applications.

OBJECTIVES: The main goal of this work is to evaluate the suitability of nanostructured zirconia pieces obtained by robocasting additive manufacturing (AM), for dental applications. METHODS: The density, crystalline structure, morphology/porosity, surface roughness, hardness, toughness, wettability and biocompatibility of the produced samples were compared with those of samples obtained by conventional subtractive manufacturing (SM) of a similar commercial zirconia material. Chewing simulation studies were carried out against dental human cusps in artificial saliva. The wear of the material was quantified and the wear mechanisms investigated, as well as the influence of glaze coating. RESULTS: AM samples, that revealed to be biocompatible, are slightly less dense and more porous than SM samples, showing lower hardness, toughness and wettability than SM samples. After chewing tests, no wear was found both on AM and SM samples. However, the dental wear was significantly lower when AM samples were used as counterbody. Concerning the glazed samples, both coated surfaces and dental cusps suffered wear, being the cusps' wear higher than that found for unglazed samples. More, cusps tested against AM coated samples suffered less wear comparatively to those opposed to SM coated samples. SIGNIFICANCE: Overall, the results presented in this paper show that AM processed nanostructured zirconia can be used in dental restorations, with important advantages from the point of view of processing and tribological performance. Moreover, the option for glaze finishing should be carefully considered both in SM and AM processed specimens.

Comparative study of the wear of the pair human teeth/Vita Enamic® vs commonly used dental ceramics through chewing simulation.

Ceramic based prosthetic materials have been used in dental restorations due to their excellent aesthetic and biocompatibility. However, due to concerns related to their mechanical properties and abrasive action against natural teeth, a proper selection of these materials is crucial to preserve the occlusal interactions and prevent abnormal dental wear. The aim of this work is to compare the wear performance of Vita Enamic®, a polymer infiltrated ceramic (PIC), with that of other three commercial ceramic based dental materials - Zirconia, Leucite and Zirconia Veneered - when tested against natural teeth. The crystalline structure, wettability, topography and hardness of the prosthetic materials were characterized before wear testing. Chewing simulator experiments (360,000 cycles, load 49 N) against dental human cusps were carried out using artificial saliva as lubricant. The wear of both teeth and prosthetic materials was quantified and the involved wear mechanisms were analyzed by scanning electron microscopy. The results showed that Zirconia presented the most suitable tribological behavior, since it led to the lowest wear on both occlusal surfaces. The prosthetic material presenting the highest wear was Vita Enamic®. Regarding the cusps' wear, the highest values were found for both Leucite and Zirconia Veneered. Polishing wear was the main wear mechanism in Zirconia system (prosthetic material and opposing enamel), while in the remaining ones was fragile fracture associated with abrasive wear. No direct relation could be established between wettability, initial roughness and hardness of the prosthetic materials and the wear of the tribological systems. Contrarily, microstructure and toughness revealed to be critical parameters.