Strength and Reliability of Fabricate Zirconia by Additive Manufacturing

Zirconia's distinctive intrinsic qualities have drawn the interest of the dentistry community in medical settings. The technology of additive manufacturing (AM), which produces very little waste, has been utilized to create complex and highly accurate materials. Despite AM has a number of potential bene�ts for e�ciently producing functional, complicated shape zirconia components, there is still a paucity of industrial importance in implementations. Objective: To evaluate the strength and reliability of zirconia manufactured using the AM technology. Methods: A 3D printer was used to create zirconia bars in both horizontal and vertical orientations. The samples' geometrical correctness, density, layer thickness, and ductility were all measured using short bars. In tests for tensile properties, long bars were utilized. Using a caliper, the lengths of three short bars were measured, and the average values were calculated. They were contrasted with the theoretical parameters using a one-sample t-test. Results: It was discovered that varied construction orientations affect dimensional correctness, translucency, and dynamic qualities. Vertical-printed zirconia is denser and translucent than horizontally-printed zirconia. Conclusions: Nonetheless, zirconia that has been printed horizontally has remarkable precision and mechanical qualities. Stress and poor adhesion between the layers of materials should be �xed.

chipping for porcelain fused to zirconia restorations [5]. The term "net shaping forming" is frequently used to describe additive manufacturing, creating the idea that it will automatically generate items with "precisely the same" structure as the suggested conceptual layout. This is false with in majority of instances, especially when drying, debinding, and sintering are involved both before and after printing, such as is the situation with the present ceramics stereolithography process used to produce zirconia dental prosthesis [6]. Additive manufacturing (AM) offers various bene ts and has established itself as a legitimate method of producing metals and polymers for use in dentistry [7]. Three-dimensional (3D) printing, also known as AM, which Strength and Reliability of Fabricate Zirconia by Additive Manufacturing

I N T R O D U C T I O N
Zirconia's distinctive intrinsic qualities have drawn the interest of the dentistry community in medical settings. The technology of additive manufacturing (AM), which produces very little waste, has been utilized to create complex and highly accurate materials. Despite AM has a number of potential bene ts for e ciently producing functional, complicated shape zirconia components, there is still a paucity of industrial importance in implementations. Objective: To evaluate the strength and reliability of zirconia manufactured using the AM technology. Methods: A 3D printer was used to create zirconia bars in both horizontal and vertical orientations. The samples' geometrical correctness, density, layer thickness, and ductility were all measured using short bars. In tests for tensile properties, long bars were utilized. Using a caliper, the lengths of three short bars were measured, and the average values were calculated. They were contrasted with the theoretical parameters using a one-sample t-test. Results: It was discovered that varied construction orientations affect dimensional correctness, translucency, and dynamic qualities. Vertical-printed zirconia is denser and translucent than horizontally-printed zirconia. Conclusions: Nonetheless, zirconia that has been printed horizontally has remarkable precision and mechanical qualities. Stress and poor adhesion between the layers of materials should be xed. thick and 4mm wide. The short bars were printed (V), lying on three 4 mm2 faces and for (H), the long and short bars lying on four 36 mm2 faces and four 22 mm2 faces respectively. The specimen dimensions' correctness, densities, layer thickness, and exural strength were all measured using short bars. In tests for toughness, long bars were employed. They went through a binder burning p r o c e d u r e to p r o d u c e d e n s e p a r t s a f te r b e i n g ultrasonically cleaned with ethanol.

M E T H O D S
is different from subtractive manufacturing in that it produces less waste, has been applied to create complex and highly precise materials [8]. Zirconia is one of the dental ceramics that is growing in popularity and application in dentistry because of its exceptional qualities [1,2,9]. It provides the opportunity to construct the structure and morphology of ceramic components without geometrical restrictions in a material-saving way since it is the only method for ceramic AM that is now commercially available [10]. Thus, it is advantageous to use AM techniques to considerably lower production waste and associated manufacturing costs [11]. Although AM has a number of potential bene ts for e ciently producing functional, complicated shape zirconia components, there is still a paucity of industrial interest in actual applications. The purpose of this study was to evaluate the strength and reliability of fabricate zirconia manufactured using the AM principle.
Zirconia powder (Guangdong Orient Zirconic Ind. Sci. Tech. Co., China) and alumina powder (AztroGrit, USA) were combined in a 4:1 weight (wt) ratio. After that, ultrasonography was used to dilute the combination in ethanol. Afterwards, zirconia balls were used to ball-mill the blending in a planetary ball mill for six hours. After that, the mixture was dried for 12 hours in a 60 °C oven. Lastly, a 100-mesh screen was used to sift the dry powder. Four ingredients made up the blended solution that was utilized to make the enameled suspension: acrylamide, N, N' methylenebisacrylamide, glycerin, and deionized water. With a volume concentration of 30 vol%, the powder was then mixed to the mixture. Polyvinyl pyrrolidone K-15 was chosen as 1.2 wt% of the powder, and it was utilized as the dispersion to create the ceramic suspension. After that, zirconia balls were used to ball-mill the ceramic suspension for 12 hours. A vacuum mixer was then used to de-gas the suspension for 30 minutes. Under ultrasound, 2-hydroxy-2methyl-1-phenyl-1-acetone was added to the ceramic suspension as an initiator in order to create a UV-curable ceramic suspension. The mass fraction of the photo initiator used in this investigation was set to 1 weight percent of the premixed solution. The Magics programme was used to produce the structural framework and slice the sections after the UG application was used to make the 3D model. The stereolithographic machine was then equipped with the nal data, which had an x-y resolution, laser beam diameter, and layer thickness of 0.1 mm, 0.06 mm, and 0.07 mm. two distinct patterns of zirconia tiny bars (22 mm long) and long bars (36 mm long) i.e., vertically (V) and horizontally (H) was obtained by stereolithography using the ceramic suspension mentioned above ( Figure 1). Both were 3mm R E S U L T S One-way ANOVA was utilized to perform the study, and post hoc was employed to compare the groups for group H. The As-V and Polished-V-samples were compared using independent-samples t-tests. The sets for group H were compared using LSD post hoc, and one-way ANOVA was utilized to conduct the study. The As-V and Polished-Vsamples were compared using independent-samples ttests. The obtained products were sent to the Scanning Electron Microscopy Lab. at Centre for Nanotechnology and Advanced Materials Research, UET, Lahore is fully operational and scanning electron microscopy was used to investigate the fracture surfaces of the short bars following 3-point bend tests. The structural dependability of the AM zirconia fabricate was characterized with Weibull-modulus and Weibull-characteristic strength. Utilizing the methodology covered by Xiang et al., the fracture toughness was evaluated and the comparison was analyzed through LSD post hoc test and one-way ANOVA [11]. The data were normal and the variance was homogeneous. Statistical software (SPSS Statistics for Windows, version 26.0) was used to conduct all statistical analyses. o f t h e Z -a x i s l a ye r s r e p r e s e n te d by t h e s e t wo measurements. This speci es that a minor stack height is associated with precise dimension. V H The exural strength between the Polished-V and As-V samples i.e., (226.44 45.10 MPa) and (205.73 32.00 MPa) almost resemble each other. Despite the samples in the Vgroup having denser samples than those in H-group, an opposite tendency in exural strength discovered. The samples that were printed vertically had parallel layers to the force applied, which is one explanation for this. This shows that the binding inside a single layer is stronger than t h e b o n d i n g b e t we e n t h e l a ye r s . T h e s a m p l e s manufactured vertically before and after polishing had identical exural strengths. This behavior further con rms that there is insu cient adhesion between neighboring layers and that the effect of surface characteristics on exural strength is not readily apparent. Layers are securely sintered into a complete body as evidenced by structural characteristics that have a minor ripple-like appearance. It needs to be recognized that imperfections including pores, agglomerations, and surface faults are unavoidable. These imperfections raise the possibility of a partial loss of AM zirconia's strength. Because of this, zirconia requires polishing, re ning, and tinting in order to increase both its exural strength and dependability as well as its visual and aesthetic qualities. The porosity in HC, the agglomerations, and the surface faults in V are representative aws of AM zirconia, respectively. Any kind of sample might have one of these three categories of defects. The size of the data dispersion increases with decreasing Weibull modulus. In contrast to As-V, which has values of 219.6 MPa and 8, As-H has a greater Weibull characteristic strength and modulus of 920.22 MPa and 6.50 (Figure 3). This strength typically ts better when de ning the strength of ceramic. The data of As-H appear to be more dispersed due to the lower Weibull modulus. With the exception of the thickness of H-samples and length of the V-samples, which are spread fairly uniformly in the bar graphs shown in Figure 2 in which the majority of data is lower in comparison with theoretical value (almost all points are above the theoretical values). This demonstrates that more shrinkage than anticipated happens in the XY direction during the sintering process. The wide uctuations in size demonstrate the unreliability of the ndings for huge diameters. The sole mean value that exceeds the predicted value is the length of V, demonstrating that the shrinkage in the Z axis direction is less severe than expected. Low shrinkage is thought to be a factor in potential deformation and the development of aws between subsequent layers. When the printing dimensions are huge, this tendency is ampli ed (22 mm). The width of H is equal to the theoretical value thanks to a balance struck between the excessive shrinking and layerby-layer delamination. This suggests that printing accuracy may not match clinical standards, particularly when the stacking height is composed of various thicknesses. Yet, these ndings offer a benchmark for raising printing precision.  The indentation method is widely used to evaluate toughness since it is rapid and simple. In the same test circumstances, this approach may be used to study the difference in fracture toughness of other substances, although the computed results do not truly represent zirconia's fracture resistance. According to ISO 23146, the SEVNB technique is advised for use for testing ceramic durability. The SEVNB technique is not appropriate for zirconia because it is challenging to generate a precise notch-tip radius in yttria tetragonal polycrystalline zirconia; thus, the samples used in this investigation were precisely cut into a V shape. The KIc value for the H, V, and C groups, which are 12.63 (1.38), 9.29 (1.0), and 14.72 (0.97) MPam1/2, differ noticeably from one another. The H-group can inhibit fracture propagation better than the V-group, as evidenced by the fact that its KIc values are substantially higher.
AM zirconia be polished. In the current study, there was no statistically signi cant difference between the As-H sample and the AM zirconia exural strength, however both H-samples' strengths were decreases in comparison to the Polished-H sample. The H-group has considerably higher KIc values for fracture toughness than the V-group, representing that the H-group is enhanced and able to prevent crack propagation. The V-notch and force line are parallel to the layers in the V-group of samples but perpendicular to the layers in the H-group of samples, which may be why specimens with different orientations exhibit varying exural strengths. Similar ndings were also discovered by Xiang et al.,[11]. Khanlar et al., analyzed the many AM techniques that may be used to create zirconia, including SLA, direct light processing, direct inkjet printing, and lithography-based (LCM) processes [2]. Only in the SLA among various AM processes was create zirconia found to be strong and reliable. These ndings concur with the present research's ndings of Ferrage et al.,and Lüchtenborg et al.,as well [17,18]. The early lab investigations demonstrate several AM processing methods for zirconia for a variety of clinical uses, mostly in implant and restorative dentistry [19,20]. Although each method has signi cant bene ts, AM of zirconia for dental applications seems to most frequently use vat polymerization [21]. Although in-vitro investigations indicate that this new technique has similar mechanical qualities and precision to milling and its potential is highly promising, more advancements are required in a number of areas, including printer improvement, material research, and optimizing the printing settings.

D I S C U S S I O N
By adjusting the production parameters, AM has been demonstrated to produce both completely sintered (solid) and partially sintered (more porous) objects. In order to simulate the mechanical characteristics of dentin and enamel and make it possible to create reinforced composite dental restorations, adding pores can alter the material's mechanical properties. Li et al., evaluated the internal and marginal adaptation of zirconia ceramic dental crowns along with the mechanical and physical characteristics of SLA additively generated zirconia crowns [10]. Flexural strengths of 812-128 MPa and a Weibull modulus of 7.44 made the SLA-manufactured zirconia crowns in this experiment strong enough to be used to construct dental crowns. Similar to this, Li et al., investigated and contrasted the e cacy of milled and SLA produced zirconia crowns with chamfer, rounded shoulder, and knife-edge nishing lines [12]. Utilizing 3D deviation evaluation, fabrication reliability was measured, and margin quality was evaluated using optics. Three digital abutment models with knife-edge nishing lines, rounded shoulders, and chamfers of 0.5 mm depth were created. Numerous threshold values could be found in literature for the roughness of surface which obstructs bacterial adherence [13][14][15]. Because of this, the Ra values of threevarieties of AM zirconia, together with H-coatings with or without manual aws and surface of V, are still too high even when compared to the roughness value that is considered to be the most acceptable (Ra 0.59 m) (the minimum Ra is 0.70 m). As a result, if these fabrics were to be utilized in dental restoration, the chance of secondary c a r i e s a n d p e r i o d o n t i u m i n a m m a t i o n w o u l d simultaneously increase. The opposing enamel is also worn down by a rough surface [15,16]. To prevent the growth of microorganisms and antagonist wear, it is crucial that the

C O N C L U S I O N S
It was discovered that varied construction orientation affects dimensional correctness, translucency, and mechanical qualities. Vertically printed zirconia is denser and translucent than horizontally printed zirconia. Furthermore, zirconia that has been printed horizontally has remarkable precision and mechanical qualities. Tension and a lack of strong adhesion between the materials' successive layers are the main issues that need to be xed.AM zirconia having considerable promise for use in dental applications and can be employed in single-unit dental prostheses, but more research is required to demonstrate their dependability under conditions that more closely resemble real-world clinical settings.

C o n  i c t s o f I n t e r e s t
The authors declare no con ict of interest S o u r c e o f F u n d i n g The author(s) received no nancial support for the research, authorship and/or publication of this article