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Direct Inkjet Printing of Dental Prostheses Made of Zirconia


Abstract and Figures

CAD/CAM milling systems provide a rapid and individual method for the manufacturing of zirconia dental restorations. However, the disadvantages of these systems include limited accuracy, possible introduction of microscopic cracks, and a waste of material due to the principle of the 'subtractive process'. The hypothesis of this study was that these issues can be overcome by a novel generative manufacturing technique, direct inkjet printing. A tailored zirconia-based ceramic suspension with 27 vol% solid content was synthesized. The suspension was printed on a conventional, but modified, drop-on-demand inkjet printer. A cleaning unit and a drying device allowed for the build-up of dense components of the size of a posterior crown. A characteristic strength of 763 MPa and a mean fracture toughness of 6.7 MPam(0.5) were determined on 3D-printed and subsequently sintered specimens. The novel technique has great potential to produce, cost-efficiently, all-ceramic dental restorations at high accuracy and with a minimum of materials consumption.
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Biomaterials & Bioengineering
DOI: 10.1177/0022034509339988
Received May 7, 2008; Last revision February 25, 2009;
Accepted March 9, 2009
J. Ebert1, E. Özkol1, A. Zeichner1,
K. Uibel1,2, Ö. Weiss3, U. Koops3,4,
R. Telle1, and H. Fischer5*
1Department of Ceramics and Refractory Materials, RWTH
Aachen University, Mauerstrasse 5, 52064 Aachen,
Germany; 2ESK, Max-Schaidhauff-Strasse 25, 87437
Kempten, Germany; 3Heraeus Kulzer, Quarzstrasse 8, 63450
Hanau, Germany; 4W.C. Heraeus, Heraeusstrasse 12-14,
63450 Hanau, Germany; and 5Dental Materials and
Biomaterials Research, University Hospital Aachen,
Pauwelsstrasse 30, D-52074 Aachen, Germany; *corre-
sponding author,
J Dent Res 88(7):673-676, 2009
CAD/CAM milling systems provide a rapid and
individual method for the manufacturing of zirco-
nia dental restorations. However, the disadvan-
tages of these systems include limited accuracy,
possible introduction of microscopic cracks, and a
waste of material due to the principle of the ‘sub-
tractive process’. The hypothesis of this study was
that these issues can be overcome by a novel gen-
erative manufacturing technique, direct inkjet
printing. A tailored zirconia-based ceramic suspen-
sion with 27 vol% solid content was synthesized.
The suspension was printed on a conventional, but
modified, drop-on-demand inkjet printer. A clean-
ing unit and a drying device allowed for the
build-up of dense components of the size of a pos-
terior crown. A characteristic strength of 763 MPa
and a mean fracture toughness of 6.7 MPam0.5
were determined on 3D-printed and subsequently
sintered specimens. The novel technique has great
potential to produce, cost-efficiently, all-ceramic
dental restorations at high accuracy and with a
minimum of materials consumption.
KEY WORDS: rapid prototyping, direct inkjet
printing, zirconia, microstructure, mechanical
Direct Inkjet Printing of Dental
Prostheses Made of Zirconia
The introduction of CAD/CAM milling systems in the dental field enabled
zirconia ceramics to be used as a standard material for dental prosthetic
restorations (Luthardt et al., 1999; McLaren and Terry, 2002). In the mean-
time, more than 20 milling systems have been introduced into the market.
Among CAD/CAM milling systems, two types can be differentiated. For
‘hard machining’, a restoration is milled out of a sintered monoblock, whereas
a white monoblock is milled for ‘soft machining’, with subsequent sintering.
The disadvantage of both systems is the considerable amount of waste of raw
material, because the unused portions of the monoblocks must be discarded
after milling, and recycling of the excess ceramic material is not feasible.
Advantages of restorations produced by ‘hard machining’ are accurate shape
and precise dimensions (Bindl and Mörmann, 2007). However, the tooling of
sintered high-strength ceramics is costly and time-consuming. The tools are
exposed to heavy abrasion and therefore withstand only short running cycles.
Moreover, there is a considerable risk of microscopic cracks that can be intro-
duced into the ceramic surface due to the tooling process of the brittle material
(Wang et al., 2008). Surface damage does not occur during ‘soft machining’,
because the shaping is performed prior to sintering. Furthermore, the mill-
ing of white monoblocks results in shorter machining times and longer ser-
vice life cycles of the tools. However, the accuracy of contour and shape of
‘soft-machined’ restorations is more critical compared with that of the ‘hard-
machined’ components because of the shrinkage during subsequent sintering,
which must be considered and controlled. Additionally, quality assurance of
the white monoblocks is difficult relative to storage and shipping, and with
respect to the sintering process, which is performed not in an (controlled)
industrial, but in a dental laboratory environment.
So-called generative manufacturing techniques exhibit the potential to over-
come the described deficiencies. With these techniques, a three-dimensional
component can be built up layer by layer. While the generative manufacturing
of metallic- and polymer-based materials is state-of-the-art and commercially
available, generative production with ceramic materials, worldwide, is still in
development (Tay et al., 2003). For ceramic materials, 5 generative manufac-
turing techniques are of special interest: (i) stereo-lithography (Doreau et al.,
2000); (ii) 3D-P, i.e., printing of a polymeric or inorganic binder into a ceramic
powder bed (Uhland et al., 1999); (iii) selective laser sintering (Bourell et al.,
1992); (iv) selective laser melting (Hollander et al., 2003); and (v) direct inkjet
printing (Zhao et al., 2002). Only porous structures, however, can be created
by the first 4 technologies (i-iv) mentioned above. In contrast, direct inkjet
printing of a ceramic suspension provides the possibility of generating dense
green bodies at a high resolution and complex shape (Ebert et al., 2008; Özkol
et al., 2009). Besides, only thin walls of some 100 µm of thickness and a height
of 1 mm at most, or small pillar-shaped arrays of less than 100 µm of diameter
674 Ebert et al. J Dent Res 88(7) 2009
and a few 100 µm of height have been generated up to now
(Zhao et al., 2002; Noguera et al., 2005; Lewis et al., 2006).
The objective of the present study was to develop a tailored
direct inkjet printing process that can be used to build up dental
prosthetic restorations made of high-strength zirconia ceramics.
A tailored additive system was developed that allows for the
printing of a suspension with a high solid content of zirconia
powder, with the use of direct inkjet printing technology with
conventional drop-on-demand inkjet print heads (Uibel et al.,
2006). A well-balanced drying device was developed for the
creation of three-dimensional structures of the size of dental
prosthetic restorations at high accuracy with respect to its
dimensions. Additionally, a tailored cleaning unit, based on a
modified ultrasonic bath, was integrated into the printer, which
allows for long printing periods without nozzle clogging. With
our study, we tested the hypothesis that it is possible to over-
come the major issues of CAD/CAM milling sytems—limited
accuracy, possible introduction of microscopic cracks, and a
waste of raw material—by the direct inkjet printing technique.
Synthesis of the Ceramic Suspension
The ceramic suspension consisted of approximately 27 vol% of
zirconia powder, 55% distilled water, a boehmite sol, and dis-
persants (Uibel et al., 2006). The boehmite sol was used to
prevent agglomeration of the ceramic particles and to increase
the green body strength. We synthesized the boehmite sol by
adjusting distilled water to a pH value of 2.0. Boehmite (Disperal
P2, Sasol, Hamburg, Germany) was added at a temperature of
80°C. A 3 mol% quantity of yttria partially stabilized zirconia
powder (TZ-3YS-E, Tosoh, Tokyo, Japan) was added to the sol.
The mean ceramic particle size was 90 nm, and the specific
surface area was 7 m2/g. The bulk density of the powder was
6.05 g/cm3. The pH value of the ceramic ink was recorded by
potentiometry (In-Lab 417, Mettler Toledo, Gießen, Germany).
The viscosity of the slurry was determined with the use of a
rotational rheometer (Viscolab LC 10, Physica, Stuttgart,
Set-up of the Printing Station and Printing Procedure
The ceramic suspension was injected into an empty standard HP
cartridge (HP 51645a, 42 mL, Hewlett Packard, Palo Alto, CA,
USA) by means of a syringe. The printing device, based on a
modified drop-on-demand deskjet printer (HP DeskJet 930c,
Hewlett Packard), consisted of the following units. The original
printing carriage held the cartridge, driven by the original servo-
motor. The cleaning system was comprised of an ultrasonic bath
(Carrera 2309, 50 W/50 Hz, Lutter & Partner, München, Germany)
and stripping rollers. The printhead was automatically soaked and
cleaned in the ultrasonic bath after each printing cycle, when the
cartridge returned to the starting position in the x-direction. A mix-
ture of water and ethanol was used as cleaning fluid. To prevent
jams or error messages such as ‘printer out of paper’ after the sub-
stitution of paper feed by a z-axis, we developed a paper-simulating
unit. As in commercial two-dimensional printers, printing occurred
line by line in the x-direction, and the maximum line width
(y-direction) was determined as the maximum width for the printed
component. A z-drive (Servo motor, Isel Elektronik, Eichenzell,
Germany) was implemented to allow for the printing of specific
Figure 1. Weibull plot with strength distribution of fired zirconia
specimens (N = 21) that were built up by the direct inkjet printing
Figure 2. Fracture surface of a flexural strength test specimen. (a) The
cross-section of the printed and sintered sample appears quite homoge-
neous and dense. No layering structure can be detected. Only one row
of process-related defects, due to nozzle clogging during printing, can
be seen at the right side of the specimen. One additional large single
process-related defect is located close to the bottom of the sample. (b)
Detailed view of the micrograph showing the large single defect and the
lower part of the string of defects at the side. The different perspective
in the detail view additionally shows the lower surface of the specimen,
which reveals that the string of defects (resulting from one single clogged
nozzle) was located over the complete length of the specimen.
J Dent Res 88(7) 2009 Inkjet Printing of Zirconia Prostheses 675
cross-sections, layer on layer, to build up the three-dimensional
components. We used special software (CEC TestPoint, Capital
Equipment Corp., Billerica, MA, USA) to control the vertical
motion. A step size, i.e., a resolution in the z-direction of $z = 5
µm, was achieved. The drying unit consisted of 3 components: 2
narrow-spot spotlights (1000 W, PAR 64 can, Showtec, Köln,
Germany), magnifying glasses to focus the light, and a fan
(Minebea Co. Ltd., NMB 2408NL-04W-B40, Ayutthaya, Thailand)
to decrease the humidity in the printed area. The temperature in the
printing zone was approximately 90°C. Graphite plates (Ringsdorff
Werke, Bad Godesberg, Germany) of 4 mm thickness were used as
substrates. The three-dimensional components were printed page-
by-page from Microsoft Word files that contained the black-colored
cross-sections. Each cross-section represented a slice with a thick-
ness of 5 µm of the respective section in the z-direction (height) of
the component.
Heat Treatment and Characterization
of the Printed Components
The printed 3D components were first dried in a chamber dryer
(T 5022, Heraeus Kulzer, Hanau, Germany) at 80°C for 12 hrs.
The organic additives were then removed in a ceramic furnace at
550°C, and the parts were subsequently fired at 1450°C for 2.5
hrs. The density of the as-fired specimens was determined
according to the principle of Archimedes. SEM micrographs (Leo
440i, Carl Zeiss, Jena, Germany) were taken from the cross-
sections of cut specimens to analyze the microstructure. Printed
and subsequently sintered specimens (1.5 x 3.0 x 30.0 mm3, n =
21) were ground on a precision surface grinding machine (PS
R300, G&N, Erlangen, Germany) to determine the Weibull
parameters, i.e., characteristic strength S0 and Weibull modulus m
(Munz and Fett, 1999). The grid size of the final diamond charged
grinding wheel was 46 µm. Additionally, printed and sintered
specimens (3.0 x 6.0 x 30.0 mm3, n = 4) were ground to determine
the fracture toughness KIc. These KIc-specimens were notched by
means of a diamond-charged cut-off wheel (thickness: approx.
200 Mm). The notches (depth: 20% of specimen thickness) were
sharpened by the razor-blade method (Kübler, 1997) (SEVNB,
i.e., single-edge V-notched beam). Note that SEVNB specimens
were used only for fracture toughness measurements, and speci-
mens for strength measurements had inherent flaws without any
pre-cracking. The specimens were mechanically tested in a uni-
versal testing machine (model 1186H0425, Instron, Darmstadt,
Germany) in four-point bending mode. The inner and outer roller
spans were 12 and 24 mm, respectively. The stressing rate was set
at 100 MPa-1 to avoid subcritical crack growth during testing.
The pH value of the suspension was set at 8.5. The relative den-
sity of the fired specimens was 96.9%. An isotropic shrinkage of
20 vol% was determined. SEM micrographs of the printed and
sintered specimens (cross-section) revealed a rather homoge-
neous microstructure, with some submicron-sized pores. The
characteristic strength of the ground bars was S0 = 763 MPa,
with a 90% confidence interval of [678;859]. The Weibull
modulus was m = 3.5 [2.4;4.4] (Fig. 1). The fracture toughness
of the SEVNB specimens was KIc = 6.7 ± 1.6 MPam0.5. The
SEM analysis of the fracture surfaces of the flexural strength
specimens revealed homogeneous cross-sections. Only single
larger defects were detected on a few specimens (Fig. 2). These
process-related defects were a result of single clogged nozzles
that were either dried up or blocked by agglomerates during the
printing process (Fig. 3). It was possible for crack-free compo-
nents to be built up on the centimeter scale after optimization of
the drying and cleaning process. Based on a CAD file, three-
dimensional components of the size of a crown, with its charac-
teristic occlusal surface topography, were built up (Fig. 4).
In contrast to results of studies published previously (Zhao
et al., 2002; Noguera et al., 2005; Lewis et al., 2006), not only
thin structures of some 100-µm thickness, but also components
of high shape accuracy can be produced by direct inkjet print-
ing. It was demonstrated that it is possible, by this technology,
Figure 3. Single nozzle blocked by agglomerated particles.
Figure 4. SEM micrograph showing the 3D-printed occlusal surface of
a dental crown.
676 Ebert et al. J Dent Res 88(7) 2009
to build up dense three-dimensional components of the size and
shape of a dental crown out of high-strength zirconia ceramics.
Although the microstructures of the printed and fired samples
were not completely free of process-related defects, the obtained
density was at 96.9% of the theoretical density—high enough to
provide mechanical properties (S0 = 763 MPa, KIc = 6.7 ± 1.6
MPam0.5) that can be compared with those of conventionally
produced 3Y-TZP via cold isostatic pressing (NN, 2006).
The strong scattering of the strength (m = 3.5) is attributed to
the clogging of single nozzles during printing, which was dem-
onstrated on some single specimens and was responsible for the
decreased strength of those samples. However, strengths of up
to 1200 MPa were achieved on those specimens that contained
no large defects due to clogged nozzles during printing. The
strengths of those specimens without process-related large
defects were determined by the inherent microscopic flaw dis-
tribution of the zirconia material itself.
It is remarkable that the developed ceramic suspension, with
27 vol% of solid content, was printable through original HP
inkjet nozzles (diameter: approx. 28 µm), although the system
had been developed originally for inks with a solid content of
less than 5 vol%. The successful printing arose from the nano-
scaled ceramic powder and the tailored additive system, which
has been described in more detail elsewhere (Özkol et al.,
2009). Moreover, the build-up of crack-free three-dimensional
parts of the size presented was obtained due to the well-designed
drying and cleaning system.
Regarding adjusted drying, pre-heating of the substrate ensured
the avoidance of temperature gradients leading to internal stresses
and bending of layers during drying. Concerning the cleaning
system, an ethanol content of < 10 wt% in aqueous solution was
determined as sufficient in terms of nozzle cleaning, without
intense evaporation and the formation of bubbles on the printed
surface during drying that would lead to later delamination.
In the next step of development, an advanced 3D printer will
be used. The most important new feature will be the control of
each single nozzle of the print heads by special software,
whereby, in case of sudden nozzle-clogging during printing, the
cartridge can be immediately moved to the cleaning unit, where
the clogged nozzle will be re-opened, and the printing process
can proceed. Moreover, this advanced printer will consist of
more than one cartridge, to print support material in parallel. This
will allow for the manufacture of not only a three-dimensional
occlusal surface of a restoration, but also complete crowns and
bridges with hollow spaces. It should be noted that shrinkage
due to drying or sintering can be a critical issue in individually
made dental ceramic prostheses. Isotropic shrinkage was deter-
mined on rectangular dense specimens. This may differ when
cap structures with various wall thicknesses are to be printed.
Therefore, the optimization of the drying process and a tailored
multiple-stage sintering process, as well as an advanced design
and scale of the three-dimensional data, are additional steps for
further development.
This work was supported by Heraeus Kulzer, Hanau, Germany.
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
... zirconia-based ceramic suspension as the source material [85]. The obtained 3D-printed dental crowns possessed high mean fracture toughness (KIc = 6.7 MPam 0.5 ) and characteristic strength of the ground bars (σ0 = 763 MPa) with a 90% confidence interval of [678;859]. ...
... Despite providing a rapid technique for the fabrication of zirconia dental restorations, CAD/CAM milling systems present a few disadvantages, such as material waste, processing defects, such as microscopic fractures, and inadequate accuracy [98]. Ebert et al. employed direct inkjet 3D printing to fabricate all-ceramic dental restorations using zirconia-based ceramic suspension as the source material [85]. The obtained 3D-printed dental crowns possessed high mean fracture toughness (K Ic = 6.7 MPam 0.5 ) and characteristic strength of the ground bars (σ 0 = 763 MPa) with a 90% confidence interval of [678;859]. ...
Full-text available
Revolutionary fabrication technologies such as three-dimensional (3D) printing to develop dental structures are expected to replace traditional methods due to their ability to establish constructs with the required mechanical properties and detailed structures. Three-dimensional printing, as an additive manufacturing approach, has the potential to rapidly fabricate complex dental prostheses by employing a bottom-up strategy in a layer-by-layer fashion. This new technology allows dentists to extend their degree of freedom in selecting, creating, and performing the required treatments. Three-dimensional printing has been narrowly employed in the fabrication of various kinds of prostheses and implants. There is still an on-demand production procedure that offers a reasonable method with superior efficiency to engineer multifaceted dental constructs. This review article aims to cover the most recent applications of 3D printing techniques in the manufacturing of dental prosthetics. More specifically, after describing various 3D printing techniques and their advantages/disadvantages, the applications of 3D printing in dental prostheses are elaborated in various examples in the literature. Different 3D printing techniques have the capability to use different materials, including thermoplastic polymers, ceramics, and metals with distinctive suitability for dental applications, which are discussed in this article. The relevant limitations and challenges that currently limit the efficacy of 3D printing in this field are also reviewed. This review article has employed five major scientific databases, including Google Scholar, PubMed, ScienceDirect, Web of Science, and Scopus, with appropriate keywords to find the most relevant literature in the subject of dental prostheses 3D printing.
... Ceramics are high-strength and high-temperature-resistant materials that are widely used in automobiles, electronics, energy components, various machinery parts, jewelry, and bio industries [1][2][3][4]. Especially in the medical field, ceramics are replacing parts of the body, such as artificial bones and teeth, due to their high biocompatibility [5]. However, ceramics have a higher strength than metals, making them difficult to machine in general. ...
Full-text available
Ceramics are high-strength and high-temperature resistant materials that are used in various functional parts. However, due to the high strength and brittleness properties, there are many difficulties in the fabrication of complex shapes. Therefore, there are many studies related to the fabrication of ceramic parts using 3D printing technology optimized for complex shapes. Among them, studies using photo-polymerization (PP) 3D printing technology with excellent dimensional accuracy and surface quality have received the most widespread attention. To secure the physical properties of sintered ceramic, the content and distribution of materials are important. This study suggests a novel 3D printing process based on a high-viscosity composite resin that maximizes the content of zirconia ceramics. For reliable printing, the developed 3D printers that can adjust the process environment were used. To minimize warpage and delamination, the divided micro square pattern images were irradiated in two separate intervals of 1.6 s each while maintaining the internal chamber temperature at 40 °C. This contributed to improved stability and density of the sintered structures. Ultimately, the ceramic parts with a Vickers hardness of 12.2 GPa and a relative density of over 95% were able to be fabricated based on a high-viscosity resin with 25,000 cps.
... 31,32 AM of zirconia, especially vat photopolymerization or stereolithography (SLA), has been investigated for dental applications with promising outcomes. [32][33][34][35][36][37][38][39] Additively manufactured zirconia has been reported to have similar strength and accuracy as subtractive manufactured zirconia. 37,38,[40][41][42][43][44][45][46] However data on the bonding of porcelain to AM zirconia are sparse. ...
ABSTRACT Statement of problem. Delamination of veneering ceramic is one of the most common challenges relating to veneered zirconia restorations. Additive manufacturing (AM) is a fast-expanding technology that has gained widespread acceptance in dentistry and is increasingly being used to produce dental restorations. However, information about bonding of porcelain to AM zirconia is lacking. Purpose. The purpose of this in vitro study was to investigate the shear bond strength (SBS) of porcelain to milled and additively manufactured zirconia, and the effect of surface treatment on bond strength. Material and methods. A Ø12×5-mm disk was designed virtually to fabricate all specimens, which were divided into 2 groups according to the manufacturing technique: additively manufactured or milled zirconia. The effect of airborne-particle abrasion and a zirconia liner before porcelain application was investigated in both groups. Veneering porcelain was fired into an alumina ring mold on the zirconia surface. SBS was measured by using a universal testing machine at a crosshead speed of 1 mm/min before and after aging (n=10). SBS data were analyzed with 3-way ANOVA (a=.05) Results. A significant difference was found between milled and AM zirconia. The SBS of porcelain to milled zirconia was significantly higher (1.38 MPa) than to AM zirconia (0.68 MPa) (P<.001). The surface treatment of zirconia had no significant effect on porcelain SBS in either group (P=.254), whereas thermocycling significantly reduced the SBS of porcelain to zirconia in both milled and AM groups (P=.001). Conclusions. Porcelain bonding to milled zirconia was better than to AM zirconia. Pretreating the zirconia substrate before porcelain application did not improve the porcelain bond.
... To improve the behavior of and solve the problems associated with zirconia suspensions that contain a high fraction of solid particles, studies are being conducted to achieve low viscosity while maintaining a high particle content by subjecting the particles to surface treatment using a silane coupling agent [27][28][29][30][31][32][33]. In general, a large number of hydroxyl groups are present on the surface of ceramic particles; and, as a result, these particles have hydrophilic properties, and they tend to aggregate [34]. ...
Full-text available
To prepare a photocurable ceramic suspension for use in commercialized additive manufacturing equipment, the effects of the rheological properties of zirconia particles added to a binder, and the presence or absence of a silane coupling agent on the particles was evaluated. To this end, three experimental groups (ZSs, ZMs, ZLs) and three control groups (ZS, ZM, ZL) were designed depending on the size of the underlying zirconia particles. The test-group zirconia suspensions were prepared through silanization, which was not applied to the control-group suspensions. Depending on the particle size, viscosity differences between the test and control groups were 16,842, 18,623, and 12,303 mPa·s, respectively. Compared to the other groups, the viscosity of the ZLs group suspension decreased by 70.98–88.04%. This confirmed that the viscosity of the suspensions was affected by the particle size and the presence of silane coating. The dispersion stability of the zirconia suspensions was evaluated over 20 days. A sedimentation test confirmed that the sedimentation rate of the ZLs group was slower than those of the other groups. This study aimed to optimize the suspension manufacturing method to effectively be utilized in further commercializing zirconia three-dimensional (3D) printing and could also help to develop various medical applications.
Slurries with high solid content and low viscosity are highly necessary to lower the sintering shrinkage and avoid possible defects for ceramic components fabricated by vat photopolymerization technique. However, the viscosity of slurry dramatically arises with the increase of solid content, which severely affects the printing process and the quality of preformance. To solve this issue, a novel combined strategy of powder surface modification and selection of dispersant was proposed to significantly increase the solid load without too much increase in viscosity. The surface of Al2O3 particles was modified by Silane A174 to improve its wettability with resins, and then the use of KOS 110 formed steric hindrance between particles achieving good dispersion. The synergistic effect of the modifier and dispersant was realized. Al2O3 slurry with a high solid loading up to 65 vol% and low viscosity of 20.0 Pa·s at 30 s−1 was prepared for stereolithography-based DLP 3D printing, which had among the highest performance in photosensitive Al2O3 slurries.
Purpose: The purpose of this study was to analyze the fibroblast growth and proliferation on 3D-printed zirconia in presence and absence of porosities. Material and methods: Total of 40 bars (8×4×3) were included in this study. Thirty 3D-printed and 10 milled zirconia samples were prepared. The 3D-printed samples had different porosities i.e., 0% (PZ0), 20% (PZ20) and 40% (PZ40) with 10 specimens in each group. Milled zirconia samples were used as the control (MZ). Rat gingival fibroblasts were cultured for 48 hours and the proliferation of fibroblasts on each sample in each group (n = 10) was determined by MTT assays. The differences among the 4 groups were compared by one-way ANOVA. To test the significance of the observed differences between 2 groups, an unpaired Student's t-test was applied. The significance level was set at p < 0.05. Qualitative analysis for the cell culture was performed using scanning electron microscopy (SEM). Results: One way ANOVA showed the numbers of the fibroblasts among the 4 groups had a statistical difference. Post Hoc Bonferroni test revealed that there was no significant difference between PZ0 and MZ, however all other groups and among groups were significantly different. Conclusions: Fibroblasts had a better affinity towards the MZ and PZ0 in a short period of cell culture time. This article is protected by copyright. All rights reserved.
Objective: The background and clinical understanding of the properties of currently available indirect restorative systems and fabrication methods is, along with manufacturer and evidence-based literature, an important starting point to guide the clinical selection of materials for tooth and/or implant supported reconstructions. Therefore, this review explores most indirect restorative systems available in the market, especially all-ceramic, along with aspects of manufacturing process, clinical survival rates, and esthetic outcomes. Overview: Progressive incorporation of new technologies in the dental field and advancements in materials science have enabled the development/improvement of indirect restorative systems and treatment concepts in oral rehabilitation, resulting in reliable and predictable workflows and successful esthetic and functional outcomes. Indirect restorative systems have evolved from metal ceramics and polymers to glass ceramics, polycrystalline ceramics, and resin-matrix ceramics, aiming to improve not only biological and mechanical properties, but especially the optical properties and esthetic quality of the reconstructions, in attempt to mimic natural teeth. Conclusions: Based on several clinical research, materials, and patient-related parameters, a decision tree for the selection of indirect restorative materials was suggested to guide clinicians in the rehabilitation process. Clinical significance: The pace of materials development is faster than that of clinical research aimed to support their use. Since no single material provides an ideal solution to every case, professionals must continuously seek information from well designed, long-term clinical trials in order to incorporate or not new materials and technological advancements.
Additive fabrication or layer-by-layer synthesis technologies is one of the most dynamically developing areas of digital production. Modern additive technologies can be used to fabricate zirconia-based restorations. The first part of this article will present the fabrication of zirconia restorations using additive technologies such as stereolithography, digital light processing, selective laser sintering, selective laser melting and inkjet printing, as well as the advantages and disadvantages of the mentioned technologies.
Additive manufacturing (AM) technologies build physical three‐dimensional (3D) geometries by a consecutive layer‐by‐layer addition of material. AM technologies can also produce 3D structures that can actively change their properties under environmental influences. When using subtractive or additive fabricating methods or computer‐aided design (CAD) and computer‐aided manufacturing procedures, the manufacturing workflow of a dental device starts with its virtual design, normally obtained using a dental or non‐dental CAD software program. In dentistry, vat‐polymerization, material jetting technologies, and material extrusion have been frequently used to process polymers and fabricate dental devices, such as dental casts, custom trays, silicone indexes, positioning guides for custom abutments, tooth preparation guides, interim dental restorations, removable prostheses, occlusal devices, and surgical guides. Powder bed fusion technologies are the most frequent metal AM technology used to manufacture cobalt–chromium and titanium frameworks in restorative dentistry.
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A printing-unit for Direct Inkjet Printing of ceramic suspensions was developed by modifying a commercial printer. An aqueous suspension of submicrometer-sized 3Y-TZP powder was prepared. The viscosity and sur-face tension of the suspension was adjusted to provide compatibility with the printing unit. Three-dimensional 3Y-TZP components in millimetre scale were produced by direct inkjet printing. The printed structures had up to 97 % of the theoretical density, a flexural strength of up to 1200 MPa and a fracture toughness of up to 8.9 MPa 0.5 .
Ceramic materials are widely used as components in a great variety of applications. They are attractive due to their good high temperature strength, high wear resistance, good corrosion restistance and other special physical properties. Their major drawback is their brittleness and the large scatter of mechanical properties. This book describes failure phenomena in ceramic materials under mechanical loading, methods for determining the material properties, and the principles that one should apply when selecting a material. The fracture-mechanical and statistical principles and their use in describing the scatter of strength and lifetime are also covered. Special chapters are devoted to creep behaviour, multiaxial failure criteria and thermal shock behaviour.
Direct jet printing can assemble ceramic powder into a three dimensional shape by firing droplets of ink through a nozzle to build a multiple layered structure. As with stereolithography and selective laser sintering, the surface texture is expected to witness the layered assembly. The ability to create vertical walls by direct ink-jet printing was explored using a test piece based on a maze. The structure and topography are discussed in terms of droplet spreading and drying.
Solid Freeform Fabrication has been used to describe collectively a growing number of toolless manufacturing techniques. One of these processes is Selective Laser Sintering, in which a part is generated in layers from powder using a computer-controlled laser/scanning apparatus and power feed system. An overview of the basic principles of SLS machine operation is given. Two binding mechanisms are described for powder which becomes thermally activated by the scanning laser beam: viscous flow and melting of a low-melting-point phase in mixed powders of differing chemistries. The production of parts from metals and ceramics/glasses is described, including post processing to improve structural integrity and/or induce a transformation. Attendant issues such as material spheroidization under the laser beam, interparticle wetting, atmosphere effects and dimensional stability are also described.
Different investigations have been carried out to optimize an ink-jet printing technique, devoted to the fabrication of 3D fine scale ceramic parts, by adjustment of the fluid properties of the ceramic suspensions and by controlling the ejection and impact phenomena. A 10vol.% PZT loaded suspension characterized by a Newtonian behavior corresponding to a viscosity of 10mPas and to a ratio Re/We1/2 of 5.98 has been selected. The ejection and impact phenomena strongly depend on the driving parameters of the printing head, in particular the formation of the droplet, with satellite or not, as well as its velocity and volume are function of the pulse amplitude. Moreover, the conditions of ejection (droplet velocity and volume) control the characteristics of the deposit (definition, spreading and thickness uniformity). Green PZT pillar array corresponding to the skeleton of 1–3 ceramic polymer composite for imaging probes has been achieved by ink-jet printing with a definition equal to 90μm.
Direct jet printing can assemble ceramic powder into a three dimensional shape by firing droplets of ink through a nozzle to build a multiple layered structure. As with stereolithography and selective laser sintering, the surface texture is expected to witness the layered assembly. The ability to create vertical walls by direct ink-jet printing was explored using a test piece based on a maze. The structure and topography are discussed in terms of droplet spreading and drying.
Aim and Background: Scientific approach is the utilization of the new generative manufacturing process termed Selective Laser Melting (SLM) for the creation of biocompatible three-dimensional (3-D) bone substitutes made of the titanium alloy TiAl6V4. The SLM technique enables direct transfer of virtual 3-D structures into solid metal materials with full serial characteristics and typically great freedom of geometric design. Material and Methods: Individual 3-D CAD data which are derived from computed tomography models of anatomic structures are subdivided into layers of defined thickness. The actual part is generated by a repeating process of applying TiAl6V4 powder in layers of 0.003–0.1 mm on the process chamber platform transferring the area and contour information of each layer into the material using a laser beam. The physical process is a complete remelting of the powder with a metallurgical bonding between the layers yielding densities of approximately 100%. This operation is repeated step by step until the generation of the 3-D part is completed. We cultured human primary osteoblast-like cells on different surfaces of SLMmanufactured TiAl6V4 parts to prove osteoblast compatibility. Proliferation, vitality, and alkaline phosphatase (AP) activity of osteoblast cultures are presented. Results: It has become possible to produce complex 3-D geometries with different surface properties within few hours. Compatibility of the tested TiAl6V4 material with human osteoblasts is demonstrated. The cultured cells attach and proliferate on SLM substrates and show AP activity. Conclusions: The presented results demonstrate the potential offered by the SLM process. On the basis of scanned information, the generation of complex anatomic structures is realizable. The presented promising advantages make this procedure interesting for the production of individual implants or bone substitutes.
Solid freeforming is a genus of manufacturing processes in which three-dimensional objects are assembled by point, line or planar addition of material. Confining surfaces, such as mould or die walls, are absent. The shape is built by adding rather than subtracting material. Solid freeforming has come to be computer controlled over the past two decades in parallel with the expansion of the data handling capacity of personal computers. It can be used for rapid prototyping but also offers mass production pathways in which individuation is possible. It is of particular interest for the creation, inter alia, of prosthetics that can be individually built from modified X-ray computed tomographic data. Some routes offer the additional capability to control, from the computer, not just the shape but also the composition throughout a component. Thus, three-dimensional functional gradients in multiphase ordered composites become possible. The concept of 'design' now embraces the integration of the spatial variation of composition, microstructure and hence of properties together with the shape parameters for multifunctional materials. This is a vast and expanding field in which the first textbooks are emerging. A review of this type must necessarily be focused. The emphasis here therefore is placed on ceramic processing. This review attempts to set out the taxonomy of solid freeforming in an historical context, disentangling the multiplicity of process names that have arisen over the past two decades. Special emphasis is placed on multilayer printing methods, because they have tended to be neglected in popular reviews, and upon applications in the medical arena, because they, among all possible applications, demand the individuation that solid freeforming can offer.
The Three-Dimensional Printing (3DP™) process has been modified to incorporate colloidal science for the fabrication of fine ceramic parts. Complex shaped alumina and silicon nitride components have been formed directly from 3-dimensional CAD files using submicron powders. Parts were built using a sequential layering process of the ceramic slurry followed by ink jet printing of a binder system. A well dispersed slurry and optimized printing parameters are required to form a uniform powder bed with a high green density. Liquid-powder bed interactions affect the geometry and internal structure of the component. The redispersion of the unprinted powder bed is critical in order to retrieve the printed components. The slurry and powder bed chemistry are the major factors controlling powder bed redispersion. The process is generic and can be readily adapted for new materials systems. Our research is currently focused on the fabrication of dielectric RF filters. Preliminary results have demonstrated the ability to successfully fabricate cylindrical RF resonators.
Many methods are currently used to measure the fracture toughness of ceramic materials. Procedures based on a widely accepted theory are often difficult to realise, unreliable, or expensive. The Single-Edge-Notched Beam (SENB) method was developed as a simple and inexpensive alternative, but the results can be influenced by the tip radius of the sawed notch. Recently a technique was introduced to taper a saw cut to a sharp tip radius using a razor blade sprinkled with diamond paste. This leads to V-notches, hence the name Single-Edge-V-Notched Beam (SEVNB). An aim of this study was to evaluate whether the method is user-friendly, reliable, and most importantly, how well its results compare with other methods. Fracture toughness values measured on alumina, silicon carbide, silicon nitride and a composite, all used in previous international fracture toughness round robin tests, compared well with values measured with the Single-Edge-Precracked Beam (SEPB), Surface Crack in Flexure (SCF) and Chevron Notch (CN) tests. Values measured on fine grained zirconia were in the range of values from the SCF method, but significantly lower than values from the CN method. The results exhibited only a small statistical spread. Therefore, the user-friendly SEVNB method is a potential standard test method and should be studied further.