Lourenço SH*1, Coelho R2 and Vieira MT2
Received: October 11, 2018; Published: October 24, 2018
*Corresponding author: Lourenço SH, Instituto Pedro Nunes, CEMMPRE - Centre for Mechanical Engineering, Materials and Processes, Universidade de Coimbra, Portugal
Micro Powder Injection Molding (μPIM) has being the elected process for large series production of near net shape metal/ceramic parts with complex geometries and high series. The present study demonstrates the feasibility of Yttrium-Stabilized Zirconia dental implants and abutments production by μPIM giving rise to cheap devices. Coatings of nanocrystalline ZrxOy contributes to an asset due the improvement of osseointegration.
Nowadays the teeth loss is increasingly a reality which can affect people either physical and psychologically. A high number of patients have one or more missing tooth and it is estimated that one in four Americans over the age of 74 have lost all their natural teeth. Many options exist to replace missing teeth, but dental implants have become one of the most functional biomaterials to replace one (or more) missing tooth over the last decades. The most used materials in dental implants are titanium and its alloys (historically) and zirconia (more recently) , because of their excellent biocompatibility with the hard tissues. Ceramic implants, partially stabilized zirconia implants, are gradually becoming an excellent option for implantologists arousing the interest of the biggest dental implant companies worldwide, due to factors such as biocompatibility , non-release of metal ions (contrary to titanium implants). Besides, the white colour feature that prevents the development of greyish gums over time  and their excellent mechanical properties distinguish this biomaterial of the other ones . Some companies are already producing/selling this type of implants. However, the most of them, the implant and the abutment are one-piece. Moreover, the manufacturing process is subtractive, becoming this kind of implants extremely expensive.
The high cost associated to implant production becomes a huge hindrance for dental implants rehabilitation, being only available to people with high purchasing power. Thus, μPIM is a very promising a near net shape technique, due to its advantages for complex geometry, precision and production in great series of implants with high performance, without finishing process . The μPIM process have five processing steps, as follow: raw material selection, mixing powder with binder for feedstock, injection moulding of feedstock into the mould with the desired shape (implant and abutment), debinding to remove the binder and sintering to give the required properties . In order to select the Yttria Stabilized zirconia powder for feedstocks production is necessary evaluate the 4S's (shape, particle size, particle size distribution and structure). Furthermore, it is necessary to know the melting and degradation temperatures of binder, to define the processing conditions for mixing and injection, as well as the binder removal cycle.
In feedstocks preparation is important to avoid a critical powder volume concentration (CPVC) in order to achieve optimal mixing torque to produce homogeneous feedstocks and consequently defect-free implants . After, homogeneous mixing, feedstocks were granulated to the injection moulding. Finally, the extracted implant and abutment from moulds denominated green parts are submitted to debinding and sintering in order attain the final form. The debinding and sintering thermal cycles, were carried out in a high temperature oven under controlled atmosphere of argon and hydrogen, to avoid the changing of stoichiometry of zirconia. The debinding cycle was based on binder thermal analysis (TGA= thermal gravimetric analyses) and the sintering conditions were carried out according to the selected powder.
Physical vapour deposition, like sputtering, allows the deposition ofthin films, with a controlled structure, which allows the deposition of nanocrystalline coatings [8,9]. The surface of implant is very important. Different research works show for titanium- based implants that surface roughness and nanocristallinity could be essential to osseointegration and bone-implant contact and promotes fast osteoblastic differentiation and even reduces the recovery time of the patients [10,11]. The application of zirconia (ZrO2) coatings in implants is the strategy used to improve osseointegration and biocompatibility [12,13]. However, there are no references about studies of different stoichiometry of zirconia to be applied in medical dentistry. In this context, to contribute for the advancement of the knowledge in this specific area of the interface coating/biologic material, was studied coatings with different O/ Zr ratios (ZrXOY) including the ratio 2  are studied. Recent researches show that mesenchymal stem cells isolated from the dental pulp (DPSCs) were successfully used, associated with the presence of a nanostructured coating to promote osseointegration .
The μPIM technique is suitable to produce ceramic two-piece dental implants (implant and abutment). The surface of sintered dental implant is suitable for improving osteointegration with combination of nanostructured coatings. The μPIM process is an excellent strategy for manufacturing low-cost Yttria-Stabilized Zirconia Dental Implants with excellent biological and mechanical characteristics.
This article results in the project BePIM III through the program PT2020, COMPETE2020.