REWIEV OF THE KNOWN APPLICATIONS SLM TECHNIQUES IN

REWIEV OF THE KNOWN APPLICATIONS SLM TECHNIQUES IN

Acta Sci. Pol., Medicina Veterinaria 13 (1-4) 2014, 5-14
ISSN 1644–0676 (print) ISSN 2083–8670 (on-line)
REWIEV OF THE KNOWN APPLICATIONS SLM
TECHNIQUES IN DENTISTRY 1
Małgorzata Cykowska1, Edward Chlebus1, Bogdan Dybała1,
Maciej Dobrzyński2, Justyna Bazan2, Olga Parulska2,
Maria Szymonowicz2, Zbigniew Rybak2,
Karolina Goździewska-Harłajczuk3
Wrocław University of Technology
Wrocław Medical University
3
Wrocław University of Environmental and Life Sciences
1
2
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, 51-631 Wrocław, e-mail: [email protected]
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]
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Rewiev of the known applications SLM...
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
Compact bone
Kość zbita
Spongy bone
Kość gąbczasta
Ti-6Al-7Nb
Ti-6Al-4V
Young’s
module [GPa]
Moduł Younga
Resistance to
stretching
Rm [MPa]
Odporność na
rozciąganie Rm
Plasticity limit
Rp0.2 [MPa]
Granica
plastyczności
Rp0,2 [MPa]
Resistance to
squeezing [MPa]
Odporność na
ucisk
17–20
107–109
50–150
159–193
0,4–1
1–2
10–20
7–10
101–110
113–114
900–1024
950
800–921
880
–
970
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
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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/cm3 [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/cm3, while density of Ti-6Al-7Nb is 4.52 g/cm3. 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 TiO2 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, 15–40 μm, enables only connecting fibrous tissue with
the implant surface [Hulbert et al. 1972, Zimna 2007]. A bit bigger size of pores, which
is 40–100 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 500–600 μm [Klawitter et al. 1976, Ozgur et al.
1999, Zimna 2007, Gilbert et al. 2011]. Pores with the size of 250–300 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.
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Rewiev of the known applications SLM...
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]
dP
Define arasity
er
Us
Converting to
CAD using
Mimics ©
Desing and
Manufacturing
of Functionally
Porous Dental
Implants
g
ssin
roce s ©
ic
prep
RM g Mag
usin
Prep
Impla aration
fo
nt In
serti r
on
CT
I or
MR ning
n
a
c
S
De
nta
(ne l Imp
tfab lan
tD
b
Inv , Auto esign
ent
d
or) esk
ing
us ler
ng mb
i
c
i
e
sil Ass
RM uild
B
Ce
ra
in min
st c
al C
la ro
tio w
n n
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
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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]
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Rewiev of the known applications SLM...
laser
scanning system
lens
wiper
laser beam
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
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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.
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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: 18.12.2015
For citation – Do cytowania: Cykowska M., Chlebus E., Dybała B., Dobrzyński M.,
Bazan J., Parulska O., Szymonowicz M., Rybak Z., Goździewska-Harłajczuk K., 2014.
Rewiev of the known applications SLM techniques in dentistry, Acta Sci. Pol. Med. Vet.
13 (1-4), 5–14.
Acta Sci. Pol.