ABSTRACT
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.
Subject(s)
Dental Porcelain , Dental Restoration Wear , Dental Polishing , Humans , Materials Testing , Printing, Three-Dimensional , Surface Properties , ZirconiumABSTRACT
The development of new ophthalmic drug delivery systems capable of increasing the residence time of drugs in the eye and improve its bioavailability relatively to eyedrops has been object of intense research in recent years. Several studies have shown that drug-loaded therapeutic soft contact lenses (SCLs) constitute a promising approach, with several potential advantages as compared with collyria. The main objective of this work is to study the effect of repetitive load and friction cycles caused by the eye blinking, on the drug release from hydrogels used in SCLs which, as far as we know, was never investigated before. Two poly-2-hydroxyethylmethacrylate-based hydrogels, pHEMA-T and pHEMA-UV, were used as model materials. Levofloxaxin was chosen as model drug. The hydrogels were fully characterized in what concerns structural and physicochemical properties. pHEMA-UV revealed some superficial porosity and a lower short-range order than pHEMA-T. We observe that the load and friction cycles enhanced the drug release from pHEMA-UV hydrogels. The application of a simple mathematical model, which takes into account the drug dilution caused by the tear flow, showed that the enhancement of the drug release caused by blinking on this hydrogel may be relevant in in vivo conditions. Conversely, the more sustained drug release from pHEMA-T is not affected by load and friction cycles. The conclusion is that, depending on the physicochemical and microstructural characteristics of the hydrogels, blinking is a factor that may affect the amount of drug delivered to the eye by SCLs and should thus be considered.
