REWIEV OF THE KNOWN APPLICATIONS SLM TECHNIQUES IN DENTISTRY 1

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1 Acta Sci. Pol., Medicina Veterinaria 13 (1-4) 2014, 5-14 ISSN (print) ISSN (on-line) REWIEV OF THE KNOWN APPLICATIONS SLM TECHNIQUES IN DENTISTRY 1 Małgorzata Cykowska 1, Edward Chlebus 1, Bogdan Dybała 1, Maciej Dobrzyński 2, Justyna Bazan 2, Olga Parulska 2, Maria Szymonowicz 2, Zbigniew Rybak 2, Karolina Goździewska-Harłajczuk 3 1 Wrocław University of Technology 2 Wrocław Medical University 3 Wrocław University of Environmental and Life Sciences Abstract. Laser technology of micro-metallurgy of powders (Selective Laser Melting, SLM) is applied to manufacture three-dimensional metal objects of any shape. These objects are manufactured by melting powder of metal layer by layer with a high-power laser. Each melted layer has a contour marked with a cross-section by a 3D model of the manufactured object. Wide application of SLM technologies allows construction of implants used in dentistry, plates for osteosynthesis micro-screws, clasps, wires, nails and bone screws. It is possible to adjust the implant shape individually to the patient s anatomy, and even to form a functional structure and surface (trabecular, sandwich or filled with pores of any shape, etc.) on the surface of the implant or inside of him. Such structure enables an effective growth of the bone tissue into the implant inside. Key words: SLM technique, dental implants, individual implants, computer tomography, functional structures INTRODUCTION Already since the beginning of the 1980s the geometry, shape and the way of dental implants production have been perfected [Estetyka w implantologii]. Implant optimalisations have been made to replace tooth losses, to recreate the appearance of organs, places with tissue losses [Janeczek and Sender-Janeczek 2008, Polkowska et al. 2009]. Thus, dental implants of losses are used for aesthetic purposes but also health purposes Copyright by Uniwersytet Przyrodniczy we Wrocławiu Corresponding author Adres do korespondencji: Karolina Goździewska-Harłajczuk, Department of Animal Physiology and Biostructure, Wrocław University of Environmental and Life Sciences, ul. Kożuchowska 1/3, Wrocław, k.gozdziewska.wroc@gmail.com

2 6 M. Cykowska et al. to prevent a bone tissue increase (in case of atrophy of the bone tissue around the formed loss). Due to the complicated shape and precision of connecting of dental implants elements, they belong to the implants hardest in production [Chen et al. 2012]. It is difficult to obtain an individualised shape of prosthesis or implant for a patient using traditional techniques (e.g. turning, milling, cutting) [An et al. 2005, Chen et al. 2012]. That is the reason why application of generative technologies has been started for the purpose to manufacture implants with a complicated shape. Due to the progress in technology researchers have started wondering over projecting and manufacturing implants customised for the patient. To make such an implant with SLM, at the beginning the place where the implant is to be grafted should be scanned with imagining technique (a computer tomography or magnetic resonance). Next, such images presenting cross-sections of the examined part of the patient s body should be transformed into a three dimensional image (reverse engineering). The next stage is a design of an implant model, whose mechanical resistance should be calculated with numeric simulations. Only at this stage it is possible to manufacture an implant model with laser technique of micro-metallurgy of powders (Fig. 1). Patient s CT scan Desing Dental implant Production of models implants FEA Fig. 1. Stages of customised tooth implant formation with application of computer tomography, numeric analysis and laser technique of micro-metallurgy of powders Rys. 1. Etapy wytwarzania niestandardowego implantu zęba z zastosowaniem tomografii komputerowej, analizy numerycznej i techniki laserowej mikrometalurgii proszków Source: Chen et al. [2012] Źródło: Chen i in. [2012] Acta Sci. Pol.

3 Rewiev of the known applications SLM... 7 Computer tomography and magnetic resonance Computer tomography (CT) and magnetic resonance imaging (MRI) are used to obtain images of cross-sections of an examined patient. However, in case when we want to design a custom-made implant, these devices depict the place where the implant is to be grafted. The obtained two-dimensional images of the scanned fragment of bone allow their transformation into a three-dimensional image with special software. Three-dimensional images obtained in this way will allow a design of a dental implant custom-made for a patient [Gilbert et al. 2011]. Apart from the implant geometry ideally suited to the dental defect, imagining techniques allow shortening of the design costs of the custom-made implant. Such modelled implant will ideally complete the bone defect and simultaneously it will ideally adhere to the bone. Numeric analysis A modelled implant can also be tested numerically before its production to check its mechanical resistance. The numeric analysis can be performed thanks to finished elements method. In this way it is checked if the designed implant will resist burden, strengths of occlusion or mastification [Geng et al. 2001]. If it turns out that the implant does not have proper mechanical resistance (Table 1), such implant should be redesigned. It would be best for the implant to reflect the mechanical properties of the bone tissue which it is to replace to avoid overstiffening as in the case when an implant a higher resistance than the bone (Table 1). During designing and numeric simulations, the material the implant will be made from should be taken into account. After obtaining the proper resistance and geometry of the implant, such implant can be manufactured with SLM technique. Table 1. Selected mechanical properties of bone tissue and titanium Tabela 1. Wybrane właściwości mechaniczne tkanki kostnej i tytanu Young s module [GPa] Moduł Younga Resistance to stretching R m [MPa] Odporność na rozciąganie R m Plasticity limit R p0.2 [MPa] Granica plastyczności R p0,2 [MPa] Resistance to squeezing [MPa] Odporność na ucisk Compact bone Kość zbita Spongy bone Kość gąbczasta 0, Ti-6Al-7Nb Ti-6Al-4V Source: Będziński et al. [2005], Świeczko-Żurek [2009], Titanium TI-6AL-4V (Grade 5) Źródło: Będziński i in. [2005], Świeczko-Żurek [2009], Titanium TI-6AL-4V (Grade 5) Medicina Veterinaria 13 (1-4) 2014

4 8 M. Cykowska et al. Titanium and its alloys More and more often titanium and its alloys are used to manufacture dental implants [Chen 2011]. The choice is justified by high corrosion resistance of titanium in the human organism (pitting, intercrystalline and stress corrosion), high biocompatibility, very good mechanical properties, low density 4.5 g/cm 3 [Gronkiewicz et al. 2009, Chen 2011]. To the advantages of its application in medicine belong also: lack of allergic reactions to titanium and its alloys and lack of toxicity. Ti-6Al-4V and Ti-6Al-7Nb (Table 1) are titanium alloys most often used in medicine [Chen 2011]. Moreover, alloy elements which change the density of the titanium alloy are added to titanium, thus density of Ti-6Al-4V is 4.42 g/cm 3, while density of Ti-6Al-7Nb is 4.52 g/cm 3. Adding heavy elements to pure titanium increases its density but after adding aluminium, the density of titanium alloy decreases [Biel 2006]. Moreover, a very important property of titanium is acquiring of a passive layer on the surface of the grafted implant which, thanks to TiO 2 layer enables osteointegration [An et al. 2005, Geng et al. 2008]. It contributes to quicker regeneration of the bone tissue around an implant which influences graft fixing in the bone tissue and allows earlier burdening of implants, e.g. during mastification. Functional structures The porosity of implant should be also taken into account during modelling so that bone cells have possibility of migration and next growing into the implant structure [An et al. 2005]. According to scientists the best implant porosity which allows osteointegration is 100 μm. A smaller size of pores, μm, enables only connecting fibrous tissue with the implant surface [Hulbert et al. 1972, Zimna 2007]. A bit bigger size of pores, which is μm influences growing of connective tissue in the implant structure. According to the authors of the publication bone tissue may undergo infiltration only when pores are bigger from 100 μm, but not bigger than μm [Klawitter et al. 1976, Ozgur et al. 1999, Zimna 2007, Gilbert et al. 2011]. Pores with the size of μm suit the sizes of Haversian canals, that is, the basic structural unit of bone tissue called osteon [Klawitter et al. 1976, Ozgur et al. 1999, Zimna 2007]. Porosity in implants is obtained already at the very manufacturing through laser technology of powder micrometallurgy [Cykowska 2013, Pawlak and Cykowska 2013]. Such implant is covered or filled with functional structure and due to this the mass of the element and its stiffness decreases (Fig. 2) [Cykowska 2012]. In such a way it is possible to replace a bone fragment with a functional structure which with its geometry and stiffness will resemble the structure of a bone tissue [Cykowska and Pawlak 2012]. Application of functional structures which define the porosity of implant will influence obtaining Young s modulus similar to the bone tissue. Filling the implant with such porous structure will influence the osteointegration process [Wohlers 2009]. The bone tissue can grow into the inner part of such structure and in this way a bone tissue will be rebuilt in the implanted place. Generative technologies (Fig. 3) and most often laser technology of micrometallurgy of powders (SLM) has been started to manufacture such functional structures characterised with a very complicated geometry and shape. Acta Sci. Pol.

5 Rewiev of the known applications SLM... 9 Fig. 2. Examples of functional structures constructed with SLM Rys. 2. Przykłady struktur funkcjonalnych wytworzonych metodą SLM Source: Pawlak and Cykowska [2013], Łyczkowska et al. [2014] Źródło: Pawlak i Cykowska [2013], Łyczkowska i in. [2014] MRI or CT Scanning Converting to CAD using Mimics Dental Implant Design (netfabb, Autodesk Inventor) User DefinedParasity RM preprocessing using Magics Preparation for Implant Insertion Desing and Manufacturing of Functionally Porous Dental Implants Ceraminc Crown installation RM silicing using Build Assembler Rapid Menufacturing Via EBM Fig. 3. Designing and manufacturing of dental implants with a complicated shape Rys. 3. Projektowanie i produkcja implantów zębowych o złożonych kształtach Source: Gilbert et al. [2011] Źródło: Gilbert i in. [2011] Laser technology of micro-metallurgy powders Layer technologies have already been known for 30 years [Borsuk-Nastaj and Młynarski 2012]. At the very beginning they were used in production of unique tools and in the aviation and car industry to manufacture precise and complicated elements [Costa Santos et al. 2006]. In the later period this technology found application in medicine and especially in prosthetics and implantology. SLM technology is used in dentistry for prosthetic re- Medicina Veterinaria 13 (1-4) 2014

6 10 M. Cykowska et al. storations of lost teeth [Geng et al. 2008, Borsuk-Nastaj and Młynarski 2012]. Endosteal implants, implant connectors as well as crowns and bridges with a complicated shape adjusted to the patient s loss are also produced (Fig. 4) [Jemt and Lekholm 1998]. An advantage of producing implants dental prostheses with this technology is obtaining any complex geometry which is customised for a patient [Kruth et al. 2005, Borsuk-Nastaj and Młynarski 2012]. Laser technology of micro-metallurgy of powders SLM consists of local melting of metal powder layer by layer with a focused beam of laser which is computer directed with a help of mirrors (Fig. 5) [Abe et al. 2001]. LaserNd: YAG may be applied in this technology. The focused laser beam during this process has large power, often 100 W [Abe et al. 2001]. Objects in this technology are built layer by layer till obtaining a three-dimensional uniform structure [Chlebus 2000]. Object produced with SLM are characterised with large precision and internal uniformity without systolic cavities. Material manufactured with SLM has almost the same mechanical properties as moulded. Moreover, in manufacturing an object with the help of layers reflecting a transverse cross-section of the model we are not much limited by the complexity of geometrical shape [Shellabear 2004, Borsuk-Nastaj and Młynarski 2006]. It influences the possibility of manufacturing very complicated objects with a complex internal structure which are not possible to obtain with traditional technologies [Chlebus and Kurzynowski 2006]. Additionally, an object just after being manufactured acquires a passive coat which influences the increase of surface resistance to corrosion [Borsuk-Nastaj and Młynarski 2012]. To manufacture an object with SLM technology, it has to be earlier designed in a computer with programmes CAD. Objects manufactured with technology of laser micro-metallurgy of powders may be in a later period of time connected with objects from other materials, e.g. from ceramics porcelain (to map teeth surface Fig. 6) and they may also be covered with coats, e.g. from hydroxyapatite (to improve osteointegration after implant grafting in the bone to permanently connect the implant with the bone tissue) [Kruth et al. 2005, Geng et al. 2008]. Fig. 4. Model 3D of a teeth implant (a), draft of an implant (b) and model of an implant manufactured with SLM technology Rys. 4. Model 3D implantu zębowego (a), projekt implantu (b) i model implantu wytworzonego w technologii SLM Source: Kruth et al. [2005] Źródło: Kruth i in. [2005] Acta Sci. Pol.

7 Rewiev of the known applications SLM laser scanning system laser beam lens wiper built up model build platform unmelted powder Fig. 5. Scheme of an appliance used to manufacture implants with technology of laser micro metallurgy of powders Rys. 5. Schemat urządzenia stosowanego do produkcji implantów w technologii laserowej mikrometalurgii proszków Fig. 6. Exemplary tooth implants manufactured with SLM technology Rys. 6. Przykładowe implanty zębów wytworzone w technologii SLM Source Źródło: Dental Lab Product 2014 CONCLUSIONS On the basis of the performed review, it was proved that implants manufactured with laser technology of micro-metallurgy of powders are most often applied in bone implants. Also in dentistry implants are used which are manufactured with SLM technology, are custom-made for a patient, have any complicated shape. Implants with a complicated internal geometry enable migration of cells to the internal part of an implant. It influences a quicker process of rebuilding of bone tissue in the place of defect. Moreover, porosity of implants manufactured with laser technology Medicina Veterinaria 13 (1-4) 2014

8 12 M. Cykowska et al. of micro-metallurgy influences a better osteointegration which enables quicker putting porcelain or ceramic tooth crown and it accelerates the process of regaining the ability to chew and improves aesthetical appearance. REFERENCES Abe F., Osakada K., Shiomi M., Uemaksu K., Matsumoto M., The manufacturing of hard tools from metallic powders by selective laser melting. Journal of Material Processing Technology 111, An Y.B., Oh N.H., Chun Y.W., Kim Y.H., Kim D.K., Park J.S., Kwon J-J., Choi K.O., Eom T.G., Byun T.H., Kim J.Y. Reucroft P.J., Kim K.J., Lee W.H., Mechanical properties of environmental-electro-discharge-sintered porous Ti implants. Materials Letters 59, Będziński R., Kędzior K., Kiwerski J., Morecki A., Skalski K., Wall A., Biomechanika i inżynieria rehabilitacyjna, Tom 5. Akademicka Oficyna Wydawnicza Exit. Biel M., Mikrostruktura i właściwości biomateriałów tytanowych po obróbce powierzchni. Kraków. Borsuk-Nastaj B., Młynarski M., Selective laser melting (SLM) technique in fixed prosthetic restorations. Protetyka Stomatologiczna, LXII, 3, Chen X., Xie L., Chen J., Du R., Deng F., Design and fabrication of custom-made dental implants. Journal of Mechanical Science and Technology 26, Chen L., Finite Element Analysis of the Stress on the Implant-Bone Interface of Dental Implants with Different Structures, Transactions of Nonferrous Metals Society of China 01/21(7), Chlebus E., Techniki komputerowe CAx w inżynierii produkcji. Wydawnictwo Naukowo- -Techniczne. Warszawa. Chlebus E., Kurzynowski T., Przegląd technik RapidPrototyping do budowy metalowych modeli prototypowych. Górnictwo Odkrywkowe, 48, Costa Santos E., Shiomi M., Osakada K., Laoui T., Rapid manufacturing of metal components by laser forming. International Journal of Machine and Manufacture 46, Cykowska M., Zastosowanie struktur fukcjonalnych. Nowe trendy w naukach inżynieryjnych 3. T. 3. Creative time. Kraków, Cykowska M., Badanie doświadczalne właściwości mechanicznych struktur funkcjonalnych. Interdyscyplinarność badań naukowych Oficyna Wydawnicza Politechniki Wrocławskiej Cykowska M., Pawlak A., Rodzaje, budowa i sposób wytwarzania struktur funkcjonalnych. Młodzi naukowcy dla polskiej nauki. Wpływ młodych naukowców na osiągnięcia polskiej nauki - Nowe trendy w naukach inżynieryjnych, III edycja, Cz. 7, Nauki inżynieryjne. T. 4 / Marcin Kuczera. Creative time. Kraków, Dental Lab Product, Innovations advancing productivity, proficiency, and profitability , 4. Dentistry today, Sun dental labs Estetyka w implantologii. ksiazek/stomatologia%20estetyczna/sto-est%20ii.pdf. Geng J.-P., Tan B.C., Liu G.-R., Application of finite element analysis in implant dentistry: A review of the literature. The Journal of Prosthetic Dentistry, Geng J., Yan W., Xu W., Application of the Finite Element Method in Implant Dentistry. Springer. Acta Sci. Pol.

9 Rewiev of the known applications SLM Gilbert C., Pauline S., Radovan K., Raed A., Khaldoun A., Digital Engineering of Bio Adaptable Dental Implants, Implant Dentistry A Rapidly Evolving Practice. Gronkiewicz K., Majewski S., Majewski P., Titanium-bone heat conduction and methods for measuring the temperature generated during the course of implant-prosthetic treatment. Implantoprotetyka X, 4, 37. Hulbert S., Morrison S., Klawitter J., Tissue Reaction to Three Ceramics of Porous and Non- Tissue Reaction to Three Ceramics of Porous and Non-Porous Structures, Journal of Biomedical Materials Research 6, Janeczek M., Sender-Janeczek A., Implantologia w stomatologii weterynaryjnej. Weterynaria w praktyce 4, Jemt J., Lekholm U., Measurments of Bone and Framework Deformations Induced by Misfit of Implant Superstructures, a Pilot Study. Clinical Oral Implants Research 9, Kruth J.P., Vanderbroucke B., Van Vaerenbergh J., Naert I., Digital Manufacturing of biocompatybile metal frameworks for complex dental prostheses by means of SLS/SLM, Proc. of second Int. Conf. on Advanced Research in Virtual and rapid Prototyping, Leira. 9, Klawitter J., Bagwell J., Weinstein A., Sauer B., Pruitt J., An Evaluation of Bone Growth into Porous High Density Polyethylene. Journal of Biomedical Materials Research 10, Łyczkowska E., Szymczyk P., Dybała B., Chlebus E., Chemical polishing of scaffolds made of Ti 6Al 7Nb alloy by additive manufacturing. Archives of Civil and Mechanical Engineering. Overton G., Photonics Applied: Laser Additive Manufacturing: How does additive manufacturing stack up against subtractive methods? volume-50/issue-02/features/laser-additive-manufacturing-how-does-additive-manufacturingstack-up-against-subtractive-methods.html, Laser Focus World 02. Ozgür Engin N., Cüneyt Tas A., Manufacture of Macroporous Calcium Hydroxyapatit Manufacture of Macroporous Calcium Hydroxyapatite Bioceramics. Journal of the European Ceramic Society 19, Pawlak A., Cykowska M., Możliwości wytwarzania struktur funkcjonalnych w technologii laserowej mikrometalurgii, na przykładzie struktury kratowej. Interdyscyplinarność badań naukowych Oficyna Wydawnicza Politechniki Wrocławskiej Polkowska I., Załęski P., Szyszkowska A., Tooth reconstruction using an implant mounted porcelain crown in a dog. Med. Wet. 65, Shellabear O.N., DMLS development history and state of the art, Proceedings of the Fourth Laser Assisted Net Shape Engineering, LANE, 1, Świeczko-Żurek B., Materiały biomedyczne. Katedra Inżynierii Materiałowej, Gdańsk. Titanium TI-6AL-4V (Grade 5), Annealed. ssnum=mtp641. ASM Aerospace Specification Metals Inc. Wohlers T., Wohlers Report State of Industry. Annual Worldwide Progress Report, Wohlers Associates, Inc., Colorado. Zimna A., Wpływ dodatków modyfikujących na właściwości hydroksyapatytowe wielofunkcyjnych tworzyw implantacyjnych przeznaczonych na nośniki leków. Akademia Górniczo- -Hutnicza. Rozprawa doktorska. Kraków. Medicina Veterinaria 13 (1-4) 2014

10 14 M. Cykowska et al. PRZEGLĄD ZNANYCH APLIKACJI TECHNOLOGII SLM W DENTYSTYCE Streszczenie. Technologia laserowej mikrometalurgii proszków (Selective Laser Melting, SLM) pozwala na wytwarzanie trójwymiarowych metalowych przedmiotów o dowolnych kształtach. Obiekty te powstają poprzez stopienie proszku warstwy metalicznej za pomocą lasera o dużej mocy. Każda warstwa zawiera kontur oznaczony w przekroju poprzecznym na modelu 3D wytwarzanego obiektu. Szerokie zastosowanie technologii SLM umożliwia konstrukcję implantów stosowanych w stomatologii, płytek do osteosyntezy mikrośrub, klamer, drutów, gwoździ i śrub do kości. Możliwe jest dostosowanie kształtu implantu indywidualnie do anatomii pacjenta, jak również utworzenie struktury funkcjonalnej (beleczkowatej, warstwowej lub wypełnionej porami o dowolnym kształcie itd.) na powierzchni implantu lub w jego wnętrzu. Taka struktura umożliwia skuteczny wzrost tkanki kostnej do wewnątrz implantu. Słowa kluczowe: technika SLM, implanty zębowe, implanty indywidualne, tomografia komputerowa, struktury funkcjonalne Accepted for print Zaakceptowano do druku: For citation Do cytowania: Cykowska M., Chlebus E., Dybała B., Dobrzyński M., Bazan J., Parulska O., Szymonowicz M., Rybak Z., Goździewska-Harłajczuk K., Rewiev of the known applications SLM techniques in dentistry, Acta Sci. Pol. Med. Vet. 13 (1-4), Acta Sci. Pol.