QUALITY CONTROL OF DENTAL BRIDGES AND REMOVABLE PROSTHESES MANUFACTURED USING PHENIX SYSTEMS EQUIPMENT

Transcription

1 QUALITY CONTROL OF DENTAL BRIDGES AND REMOVABLE PROSTHESES MANUFACTURED USING PHENIX SYSTEMS EQUIPMENT Maria Averyanova PHENIX SYSTEMS, Parc Européen d'entreprises, Rue Richard Wagner, Riom, France ABSTRACT Currently, the mass parts production all over the world becomes more and more individual. It is required to be able to manufacture personalized complex shape parts with necessary microstructural, mechanical, thermo-physical, chemical and other properties in a quicker and a cheaper way. Selective Laser Sintering /Melting, a process of Additive manufacturing technologies, is applied to answer on this request. This paper discusses the manufacturing of dental fixed and removable prostheses directly from Co-Cr alloy powder using PHENIX SYSTEMS process. The quality control from the powder properties analyses up to the final laser sintered parts characterization has been performed. The applied Co-Cr alloy, developed by the company SINT-TECH, is CE certified and the physico-chemical properties of the sintered parts are matched to the dental standards NF IN ISO and NF IN ISO KEYWORDS Selective laser sintering/melting, dental bridges, removable prosthesis, Co-Cr alloy

2 Quality control of dental bridges and removable prostheses manufactured using Phenix Systems equipment 1. INTRODUCTION The world globalization results in a demand for highly individualized products that should be cost-effective, rapidly manufactured and fulfill to the required properties [1-2]. One of the most commonly used Additive Manufacturing processes, Selective Laser Sintering /Selective Laser Melting (SLS/SLM) is the technology that makes possible the fabrication of high-added value complex geometry parts that fulfill the client requirements. Now their advantages are about to be recognized and are predicted to revolutionize traditional way of manufacturing in many different industrial areas. The trend is that the SLS/SLM technology becomes more and more mature. The laser material interaction, the significance and the impact of powder properties, process parameters, scanning strategy, part design and orientation on the building platform are better studied and understood [3-4]. The quality and the working stability of lasers, optics and other essential module of the SLS/SLM equipment have been increased considerably. An important progress has been done in order to perform the online process monitoring. For example, the online atmosphere quality control is performed. The user has no direct contact with powder. It s an important advantage, because the risk of powder oxidation, as well as, of environment pollution decreases dramatically. Consequently, more and more industries apply or start applying the SLS/SLM for parts production. The main fields are mechanical, tires industry, luxury, watchmaking, biomedical, in particular, dental application (Fig.1). (a) (b)

3 (c) (d) Fig.1: Examples of parts manufactured using Phenix Systems for (a) jewelry, (b) watchmaking, (c) nuclear and (d) dental application Many thousands of personalized dental parts per month could be manufactured directly from their CAD data. Using the SLS/SLM technology, manufacturing of multiple personal removable and fixed dental parts for different customers is possible in a single production. This enables a mass customization. It should be mentioned that successful application of the SLS/SLM technology for dental framework manufacturing using Phenix Systems machine over a period of 14 months has been demonstrated in [5]. In order to be applied for a dental or for other medical application, complete analyses of powder properties, as well as of SLS/SLM manufactured parts properties should be performed. The quality control of manufacturing process should be realized. The results obtained have to correspond to existing dental standards. The objective of the paper is to demonstrate that, applying quality control methodology, the initial powder properties, as well as, final fixed and removable dental parts properties manufactured using PHENIX SYSTEMS process meet the dental standards NF IN ISO and NF IN ISO EXPERIMENTAL SET-UP Since 2005, the Phenix Systems machines have been working for dental metal frameworks manufacturing. Thousands of dental cups, bridges, crowns etc. are produced every day in dental production centers and laboratories that are presented on international markets. Now the new generation of equipment is available. PXS Dental (equipped with a 50W fiber laser) and PXM Dental (equipped with a 300W fiber laser) systems are applied for fixed and removable prosthesis manufacturing in Co-Cr powder (Fig.2).

4 Evaluation of knowledge value based on the knowledge maturity model (a) (b) Fig.2: The general view of Phenix Systems machine: (a) PXS and (b) PXM During the SLS/SLM process, a powder is deposited by a roller onto a base plate of the building unit of the machine. This is one of the peculiarities of PHENIX SYSTEMS equipment that makes possible to create powder layers from different materials. It means that ceramics or metals with different particle size (down to D50 3µm), size distribution and different morphology can be applied. Once a homogeneous powder bed is created, the laser sinters/melts the necessary section of a powder according to its CAD data (Fig.3). A new powder layer is put and the process is repeated. Fig.3: The view of powder laser interaction during the dental frameworks manufacturing using Phenix Systems machine

5 3. PHENIX SYSTEMS PARTS MANUFACTURING METHODOLOGY In order to be able to answer on the industrial demand, an appropriate methodology of parts manufacturing using Phenix Systems facilities should be found. First of all, a complete parts specification is required. Then, the most suitable powder material (ceramic or metal) is chosen and analyzed. Sometimes, the physical, chemical powder properties should be adopted according to the Phenix manufacturing process features, as well as to the final parts characteristics. After that, the optimum process parameters window is searched. Once the parameters are found, their validation is performed. The production process repeatability in time is analyzed. The eventual post-treatments are analyzed and preconized for the users. This methodology is applied to all parts manufactured using Phenix Systems equipment. At the present paper, Phenix Systems manufacturing methodology is applied for the customized dental frameworks fabrication. 4. STEPS OF CO-CR DENTAL PROSTESES MANUFACTURING In order to realize the quality control of the dental fixed and removable prostheses manufactured using Phenix Systems equipment, the production cycle should be analyzed. The main reasons of errors that could prevent a successful dental manufacturing are also discussed. The dental prosthesis production cycle using SLS/SLM technology concerns the following steps: Patient dental imprint realization and 3D scanning of patient dental jaw Import of scan data to a specially established dental software for a design purpose CAM dental software Powder preparation SLS/SLM physical manufacturing Post treatment: finishing (surface preparation and polishing), post heat treatment and dental supports remove Ceramic coating Step 1: Patient dental imprint realization and its 3D scanning Currently, major part of dental frameworks is still being manufactured manually based on the investment casting manufacturing process.

6 Evaluation of knowledge value based on the knowledge maturity model Step 2: Import of scan data to specially established dental software 3D scan of dental jaw is used for a dental prosthesis design realized by a specially elaborated CAD software. Step 3: Dental software Phenix Systems company realizes itself their own CAD/CAM software. For the dental application Phenix Dental CAM software has been created (Fig.4). Fig.4: View of Phenix Dental software Using Phenix Dental, an appropriate parameters setting (optimum scanning strategy and optimum machine process parameters) according to the type of dental element (single crown, bridge etc.) is chosen. The design of supports is done. In order to guarantee the surface parts quality, a special attention should be paid to the parts orientation. It should be noted that the part orientation and positioning on the building platform, as well as the supports part modeling (choice of the supports type, supports orientation, supports process parameters) is one of crucial point of the SLS/SLM parts manufacturing. For example, if the supports orientation is not well designed, the final parts quality will be bad (high roughness). The supports should be mechanically strong and, at the same time, the removal of the supports should be easy and fast. It takes about 15 min to remove the supports from dental removable prosthesis manufactured by Phenix Systems machine.

7 Step 4: Powder preparation For more than 50 years cast Co-based alloy has been used as a dental and orthopedic implant material because of its adequate mechanical properties, wear and corrosion resistance, fatigue strength and biocompatibility [6]. Currently, all over the world different types of Co-based alloys are applied for dental manufacturing [7], [8]. Based on literature overview and according to the dental prosthesis requirements, it was decided to use Ni-free Co-Cr alloy developed by SINT-TECH company. It was shown previously that chemical, physical, technological and thermal powder properties have a significant effect on the SLM process and on final part characteristics [9]. It is well known that the initial powder chemical composition as well as its crystalline microstructure has a significant influence on final parts properties and microstructure. Following the NF IN ISO standards requirements, the powder chemical composition has been studied. The results obtained show that the chemical composition meets the standard requirements, the dangerous elements such as Be, Cd, Ni are absent. Finally, the Co-Cr powder applied for dental manufacturing is CE-marked powder. Step 5: SLS/SLM physical manufacturing The SLS/SLM is defined as a complex, non-equilibrium process characterized by several fast-occurring physical mechanisms such as sintering, melting, solidification, vaporization, heat conductivity, Marangoni forces, chemical reactions, phase transformation etc. The successful functional parts manufacturing depends on the process (laser power, scanning speed, layer thickness, scanning strategy etc.) and materials (particle size and size distribution, morphology, flowability etc.) parameters. An appropriate parameters window, that differs according to the type of materials, and depends on thermo-physical materials properties, should be found. The impact of process parameters combination is more important than the impact of individual parameters during laser powder material interaction. The analyses of the significance of these process parameters have resulted in a successful dental prostheses manufacturing using Phenix Systems equipment. Physico-chemical properties of the sintered parts (Fig.5) manufactured using this optimum parameters window are matched to the dental standards NF IN ISO and NF IN ISO 9693.

8 Evaluation of knowledge value based on the knowledge maturity model Fig.5: Dental bridges and removable prostheses manufactured using Phenix Systems equipment Step 6: Post-treatment The post processing concerns the post heat-treatment in order to release residual stresses, occurred during melting/solidification processes; the removal of the supports and the removal of the part from the building platform; the parts surface treatments (sandblasting, polishing). As a result, the physical appearance and surface quality of dental parts manufactured using SLS/SLM technology is similar to the traditionally manufactured (investment casting). 5. SOURCE OF ERRORS DURING DENTAL FRAMEWORK MANUFACTURING The sources of errors in Co-Cr partial denture frameworks manufacturing using traditional investment casting techniques have been analyzed and reported earlier in [10]. As for a traditional manufacturing, a high quality dental impression is required. 3D scanning should be realized in a proper way by a skillful technician. The design of dental parts is then realized using a CAD software. If the dental part design is not realized in a proper manner, the SLS/SLM manufacturing will not be successful. The risk related to the material or SLS/SLM process data errors is very low. The powder material is always the same and matches dental standards, the process parameters are constant. Besides, the user must follow the instructions recommended by the SLS/SLM equipment supplier. 6. CONCLUSION The quality control of dental bridges and removable prostheses manufactured using Phenix Systems equipment have been performed. An important number of analyses has been performed. As a result, the applied Co-Cr alloy powder,

9 developed by the company SINT-TECH, is CE certified and the physico-chemical properties of the sintered parts manufactured Phenix Systems equipment are matched to the dental standards NF IN ISO and NF IN ISO REFERENCES [1] Schleifenbaum, H. et al., Individualized production by means of high power Selective Laser Melting, CIRP Journal of manufacturing science and technology, 2010, pp [2] Lyons, B., Additive manufacturing in aerospace: examples and research outlook, The Bridges, pp.13-19, 2012 [3] Kruth, J. et al., Part and material properties in selective laser melting of metals, Proceedings of the 16th International Symposium on Electromachining. 16th International Symposium on Electromachining (ISEM XVI). Shanghai-china, 2010 [4] J. Jhabvala, Study of the consolidation process under Macro- et Microscopic thermal effects in SLS and SLM, PhD Thesis, EPFL, 2010 [5] Averyanova et al.,manufacture of Co-Cr dental crowns and bridges by selective laser melting technology, Virtual and Physical Prototyping, Vol. 6, N.3, pp , 2011 [6] Dobbs, H., Robertson, J., Heat treatment of cast Co-Cr-Mo for orthopaedic implant use, Journal of Materials Science, 1983, pp [7] Li et al., Combustion synthesis of CoCrMo orthopedic implant alloys: Microstructure and properties, Materials Research Innovation, 7, pp [8] Vandenbroucke, B. et al., Selective laser melting of biocompatible metals for rapid manufacturing of medical parts, Rapid Prototyping Journal, 2007, pp [9] Averyanova et al., Studying the influence of initial powder characteristics on the properties of final parts manufactured by the selective laser melting technology, Virtual and Physical Prototyping, Vol. 6, Issue 4, 2011, pp [10] Stern et al., Clinical evaluation of removable partial denture rest seat adaption, Journal of prosthetic dentistry, Vol. 53, N.5, 1985, pp