Study of fracture and fatigue resistance of monolithic zirconia dental crowns fabricated through a novel material jetting technique

Study of fracture and fatigue resistance of monolithic zirconia dental crowns fabricated through a novel material jetting technique | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Study of fracture and fatigue resistance of monolithic zirconia dental crowns fabricated through a novel material jetting technique Jizhe Lyu, Yin Zhou, Xunning Cao, Jianguo Tan, Xiaoqiang Liu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6766588/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Additive manufacturing is becoming a promising method for dental applications. The advanced customized jetting technique, one of Material jetting (MJ), is a newly introduced additive manufacturing technique that can produce high-accuracy zirconia restorations. However, the fracture and fatigue resistance of monolithic zirconia crown fabricated with MJ is still unknown. One hundred and twenty monolithic zirconia crowns were fabricated using subtractive manufacturing (SM), stereolithography (SLA), and MJ techniques. The crowns were subjected to cyclic loading for 1.2 × 10 4 , 1.2 × 10 5 , and 1.2 × 10 6 cycles, simulating clinical use over several 2 weeks, 6 months, and 5 years, respectively (n = 10 per group). After cyclic loading, the crowns underwent static loading tests. Both the initial fracture load and the complete fracture load were recorded. Fractographic analysis was conducted via scanning electron microscopy on fractured parts from each group. The initial fracture load for the SM group was significantly higher than that of the SLA and MJ groups ( P < 0.05). The 3 groups demonstrated similar complete fracture load before fatigue loading. After 1.2 × 10 4 and 1.2 × 10 5 cycles, MJ crowns exhibited the highest complete fracture load. After 1.2 × 10 6 cycles, SLA crowns showed the lowest complete fracture load values. Fractography analysis revealed minimal defects in the SM group, while the SLA and MJ groups exhibited varying degrees of pores, inclusions, and delamination. This study indicated that MJ can fabricate zirconia crowns with reliable mechanical properties in 5 years of in vitro simulation. Zirconia Dental Restorations Fracture Resistance Fatigue Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Zirconia, particularly 3 mol% yttria-stabilized tetragonal polycrystalline zirconia (3Y-TZP), has emerged as the most popular all-ceramic restorative material due to its exceptional mechanical properties [ 1 ]. Zirconia dental restorations are predominantly designed using computer-aided design (CAD) and fabricated through computer-aided manufacturing (CAM). This manufacturing process can be divided into subtractive and additive methods. Subtractive manufacturing (SM) remains the most widely adopted approach, offering time and cost efficiency while delivering a certain quality level compared with traditional workflows. However, this method has important limitations, including material waste [ 2 ], limited precision of intricate details, and increased risk of microcracks during the milling process [ 3 ]. By contrast, additive manufacturing (AM), also known as three-dimensional (3D) printing, provides superior geometric freedom and significantly reduces waste [ 4 ]. These advantages position AM as a promising alternative for fabricating dental restorations. Several technologies can be utilized in AM for producing zirconia restorations. The American Society for Testing and Materials Committee has classified AM into 7 categories: VAT photopolymerization [including stereolithography (SLA) and digital light processing (DLP)], material jetting (MJ), material extrusion (also known as fused deposition modeling), binder jetting, powder bed fusion, sheet lamination, and direct energy deposition [ 5 ]. VAT photopolymerization, further divided into SLA and DLP based on different light-curing methods, is the most extensively researched and applied method for dental restoration. Studies have shown that 3Y-TZP fabricated using LCM can achieve a relative density of 99% of theoretical density and flexural strengths of 894.1 ± 160.1 MPa, meeting clinical requirements [ 6 , 7 ]. However, previous studies have reported that zirconia produced via photopolymerization exhibits mechanical properties and printing accuracy still fall short compared with SM zirconia [ 8 – 11 ]. Material jetting is another AM technique in which material droplets are selectively deposited to form an object [ 12 ]. The advanced customized jetting (ACJ) technique, a specific MJ variation, offers a resolution of 16.000 × 17.625 µm with a layer thickness of 10.5 µm, enabling the fabrication of more precise and dense restorations. In the MJ process, zirconia nanoparticles suspended in liquid are ejected from nozzles and deposited on a heated print platform (160–250°C). As the liquid evaporates upon contact with the platform, zirconia particles are deposited layer by layer to form the green body [ 13 ]. Previous studies showed dental monolithic crowns fabricated using MJ have demonstrated greater dimensional accuracy and smaller marginal gaps than those produced via SM [ 14 ]. Zhong et al. [ 15 ] reported that zirconia fabricated using MJ achieved an average relative density of 99.5% and a flexural strength of 699 ± 104 MPa. Willems et al. [ 13 ] reported MJ zirconia reaching 99.7% relative density and biaxial bending strength of up to 1004 ± 138 MPa. These findings demonstrate the excellent printing accuracy and mechanical properties of MJ, highlighting its potential for dental applications. Fracture remains one of the primary modes of failure for ceramic restorations. While studies have demonstrated the reliable physicochemical properties of MJ-fabricated zirconia in standard specimen tests [ 13 , 15 , 16 ], the stress conditions experienced by restorations during mastication are far more complex. Assessing the fracture resistance of 3D-printed zirconia restorations is critical for evaluating their mechanical properties in clinical applications. In addition, restorations in the oral cavity are subjected to repeated low-intensity loads. The structural integrity of ceramic components may be compromised through progressive damage during repeated low-load cycling, and could lead to premature material failure. Fatigue induced by dynamic loading accelerates crack propagation in restorations, which makes fatigue testing essential for predicting long-term performance [ 17 , 18 ]. Despite the excellent printing dimensional accuracy and potential of MJ in dental restorations, limited research has been conducted on the mechanical properties of MJ zirconia, with most studies focusing on standard specimens [ 13 , 15 , 16 ]. It remains uncertain whether MJ-fabricated zirconia restorations can withstand the long-term chewing forces experienced in clinical settings. Therefore, this study compared the fracture and fatigue resistance of monolithic zirconia complete crowns fabricated using SM, SLA, and MJ. The null hypothesis was that neither the manufacturing method nor fatigue loading would affect the fracture and fatigue resistance of complete crowns made of zirconia. 2. Materials and Methods 2.1 Sample preparation A standardized typodont right mandibular first molar (A5SAN 500, Nissin Dental Products Inc.,Osaka, Japan) was prepared for a complete crown, with an occlusal reduction of 1.0–1.5 mm and a margin design of 0.7 mm chamfer. The tooth preparation was digitized using an intraoral scanner (IOS, TRIOS 3; 3Shape A/S, Copenhagen, Denmark), and 120 identical tooth preparation abutments were fabricated using resin-based ceramics (Hyramic, Upcera, Shenzhen, China) using a milling system (DGA+, VHF technologies GmbH, Ammerbuch, Germany). The elastic modulus of the resin-based ceramic (15 GPa) is similar to that of human dentin to simulate clinical situation. The fabricated tooth preparation abutment was rescanned, and a complete crown was designed using a software program (DentalCAD 3.0 Galway, exocad GmbH, Darmstadt, Germany) with the cement gap set to 30 µm. Then the crown was exported as standard tessellation language (STL) files and fabricated using three techniques: SM, SLA, and MJ. Forty complete crowns for each technique and a total of 120 crowns were fabricated. For additive manufacturing crowns, the printing direction were set at 180° with the occlusal surface facing the print platform. For SM-fabricated crowns, a 5-axis milling machine (DWX 51D, Roland DG Corp., Shizuoka, Japan) was used to mill a partially sintered 3Y-TZP zirconia block (ST, Upcera, Shenzhen, China), which then was sintered at 1 530°C for 2 hours following the manufacturer’s instructions. For SLA-fabricated crowns, an occlusal full-supporting structure was used to obtain higher fabrication quality. Full supporting bases were designed for each crown using a software program (Materialise Magics, Materialise, Leuven, Belgium). A uniform approximately 100 µm gap between the restoration and the base was set, and the supporting base could be easily removed after printing to avoid defects introduced during the manually removal of supporting pillars. During the printing process, an SLA printer (J2 S100P Ceramics, Junjing, Guangdong, China) and a 3Y-TZP slurry containing a 20 wt% photosensitive resin mixture and 80 wt% zirconia powder were used. The slurry was cured under a 355 nm wavelength laser beam light source. The scan speed was set at 5000 mm/s, and the print layer thickness was 40 µm. After printing, the green body was cleaned in an ultrasonic bath to remove the extra slurry and then subjected to debinding and sintering at 1 470°C for 3 hours to produce the dense part. For MJ-fabricated crowns, an inkjet printer (PGJ180, Thales, Hangzhou, China) was used to produce the green part. The inkjet printer was equipped with 24 print heads, 12 of which print zirconia ink, while the other 12 print support materials. Five hundred and twelve nozzles contained in the 24 print heads working simultaneously, enabling the selective deposition of the ink onto the print platform. The zirconia ink (Zrcoop, Thales, Hangzhou, China) consisted of approximately 45 wt% zirconia powder stabilized with 3 mol% yttrium oxide, combined with glycol ethers and a dispersing agent. The ink was ejected from the nozzles and selectively deposited onto the print platform. The temperature of the printing platform was controlled between 160°C and 250°C by a passing lamp. Upon contact with the platform, the solvent in the ink evaporated, leaving only the zirconia particles deposited onto the surface. After one layer of printing was completed, a roller planed the layer and controlled its thickness to 10.5 µm. After the printing process, the printed green body was washed in distilled water to remove the support material, followed by debinding and sintering in air at 1 450°C for 4 hours to achieve the final density. No glazing or polishing was conducted on the fabricated crowns in the 3 groups. 2.2 Experiment The intaglio surface of all complete crowns was airborne-particle abraded with 50 µm aluminum oxide particles (Cobra, Rengert, Germany) at 0.25 MPa for 20 seconds. Following this, all crowns and corresponding abutments were cleaned using ethanol ultrasonic cleaning and air-dried. Then the crowns were cemented to the abutments using resin cement (RelyX U200, 3M, Minnesota, USA), with excess cement carefully removed. The cement was fully cured using an LED light for 40 seconds to ensure complete polymerization. After cementation, the specimens were stored in deionized water at 37°C for 24 hours. Ten crowns of each manufacturing method underwent static loading tests using a universal testing machine (Instron 5969; Instron Corp., Massachusetts, USA) to assess immediate fracture resistance. The loading was applied vertically to the central fossa of the crown using a 4 mm diameter tungsten carbide indenter at a speed of 1 mm/min. When the applied force reached a certain threshold, an initial crack would form at the central fossa, although the crown would not completely fracture (Fig. 1 a). The load force at this point was recorded as the initial crack load. After the formation of the initial crack, the stress-strain curve continued to rise until the crown experienced catastrophic failure (Fig. 1 b). The load at the drop point was recorded as the crown’s complete fracture load. The representative load-displacement curve was shown in Fig. 2 . Thirty complete crowns of each group underwent fatigue loading tests using a universal testing machine (E1000; Instron Corp., Massachusetts, USA). A 4 mm diameter tungsten carbide ball was applied to the central fossa of the crown for vertical cyclic loading (30–300 N, 20 Hz) [ 19 ]. (Fig. 3 ) The crowns were subjected to 1.2 × 10 4 , 1.2 × 10 5 , and 1.2 × 10 6 cycles, simulating clinical use over several weeks, months, and 5 years, respectively (n = 10/group) [ 19 , 20 ]. After fatigue loading, the crowns were further subjected to static loading tests using the mechanical testing machine (Instron 5969; Instron Corp., Massachusetts, USA) at a speed of 1 mm/min, the position of the indenter was consistent for both cyclic loading and static test. The initial fracture load value as well as the complete fracture load value was recorded. Representative fractured samples from each group were ethanol ultrasonic cleaned and then sputter-coated (Model 681, Gatan, Pleasanton, USA) for 60 seconds with a gold/platinum alloy. The specimens were observed using a scanning electron microscope (SEM, S-4800, Hitachi, Tokyo, Japan) with an acceleration voltage of 5 kV. 2.3 Statistical analysis All statistical analyses were performed using a software program (IBM SPSS Statistics, v 27.0; IBM Corp., NY, USA). Before statistical analysis, the normality of the results was tested using the Shapiro-Wilk test. Data of initial fracture load and complete fracture load met the normal distribution (P > .05), and 2-way analysis of variance was conducted, followed by post hoc least significant difference (LSD) tests for further comparison. 3. Experimental Results All ceramic crowns remained intact under fatigue loading. A software program (G*Power v.3.1.9.6; Heinrich Heine University, Nordrhein-Westfalen, Germany) was used to calculate the actual post-hoc power (1-β), which was 0.91. Table 1 shows the effects of different manufacturing methods and fatigue loading on the initial fracture load. The initial fracture load for the SM group was significantly higher than that for the SLA and MJ groups (P < 0.05). No statistically significant differences were found between the SLA and MJ groups in terms of initial crack load. Fatigue loading cycles significantly influenced the initial fracture load of the SM group. Complete crowns subjected to 1.2 × 10 5 and 1.2 × 10 6 cycles (2599.3 ± 279.6 N and 2402.2 ± 400.0 N, respectively) exhibited lower fracture loads than those of the non-fatigued group and the group subjected to 1.2 × 10 4 cycles (2898.8 ± 283.8 N and 2944.0 ± 394.8 N, respectively). By contrast, the number of fatigue cycles did not affect the fracture load for the MJ and SLA groups. Table 1 Mean ± standard deviation values of fracture force of the initial crack (N) for subtractive manufacturing, stereolithography, and material jetting before and after dynamic fatigue loading Fatigue cycle 0 1.2 × 10 4 1.2 × 10 5 1.2 × 10 6 F P SM 2898.8 ± 283.8 A,ab 2944.0 ± 394.8 A,a 2599.3 ± 279.6 A,bc 2402.2 ± 400.0 A,c 4.925 0.003 SLA 2076.4 ± 399.1 B,a 1779.1 ± 288.0 B,a 1672.4 ± 422.5 B,a 1826.6 ± 415.0 B,a 2.277 0.084 MJ 1916.1 ± 502.4 B,a 1917.1 ± 242.4 B,a 1564.4 ± 249.2 B,a 1839.8 ± 302.5 B,a 2.176 0.095 F value 18.604 31.504 25.169 8.398 P < 0.001 < 0.001 < 0.001 < 0.001 Uppercase letters indicate statistically significant differences within a column ( P < 0.05). Lowercase letters indicate statistically significant differences within a row ( P < 0.05). SM: subtractive manufacturing, SLA: stereolithography, MJ: material jetting. Table 2 presents the complete fracture load results for different manufacturing methods and fatigue loading cycles. Before fatigue loading, no significant differences in complete fracture load were observed among the SM, SLA, and MJ groups. After 1.2 × 10 4 and 1.2 × 10 5 loading cycles, the MJ group exhibited higher complete fracture load values, whereas no significant differences were found between the SM and SLA groups. After 1.2 × 10 6 cycles, the SLA group exhibited the lowest complete fracture load among the three groups. Table 2 Mean ± standard deviation values of fracture force of complete crack (N) for subtractive manufacturing, stereolithography, and material jetting before and after dynamic fatigue loading Fatigue cycle 0 1.2 × 10 4 1.2 × 10 5 1.2 × 10 6 F P SM 3623.4 ± 482.3 A,a 3415.6 ± 642.9 A,a 3325.7 ± 524.2 A,a 3688.2 ± 575.2 A,a 0.648 0.586 SLA 3370.4 ± 314.2 A,a 3239.6 ± 383.6 A,a 3315.1 ± 500.1 A,a 3046.9 ± 318.3 B,a MJ 3558.5 ± 550.7 A,a 4399.8 ± 470.7 B,a 3962.2 ± 852.4 B,a 4084.7 ± 342.3 A,a F 0.598 14.545 5.109 10.204 P 0.552 < 0.001 0.008 < 0.001 Uppercase letters indicate statistically significant differences within a column ( P < 0.05). Lowercase letters indicate statistically significant differences within a row ( P < 0.05). SM: subtractive manufacturing, SLA: stereolithography, MJ: material jetting. Figure 4 – 6 shows the fractured surfaces in 3 groups examined by scanning electron microscopy. Key fracture surface features, including compression curls, arrest lines, wake hackles, and fracture mirrors, indicated by white arrows, facilitated the identification of fracture origins. SM crowns exhibited cone cracks below the contact points (Fig. 4 ). No critical defects were identified in the representative SM crowns. The SLA group demonstrated distinct defects, including porosities, agglomerates, and delamination (Fig. 5 ). The fracture surface of an SLA crown revealed a staircase-like morphology, and the crack propagated through interlayer connections. The phenomenon was more pronounced after 1.2 × 10 6 cycles (Fig. 5 j-l). MJ crowns demonstrated evenly distributed sphere pores on the fracture surface, marked by blue arrows (Fig. 6 ). Small porosities near the surface under contact areas may acted as critical defects leading to failure. Surrounding arrest lines and hackles indicate the direction of crack propagation. 4. Discussion This study investigated the fracture loads and fatigue resistance of monolithic zirconia crowns fabricated with SM, SLA, and MJ. The 3 groups showed significant differences in the initial fracture load and complete fracture load after fatigue cycling; therefore, the null hypothesis was partially rejected. The initial fracture load reflects the force at which cracks begin to form in the crowns under stress, which is related to the crown’s resistance to deformation under compressive and tensile forces. The result revealed that the SM group showed significantly higher initial fracture load than that for the SLA and MJ groups. Previous studies have reported that the flexural strength of additively manufactured zirconia ranges from 306 to 1044 MPa, varying across studies, whereas the flexural strength of SM zirconia generally falls within the range of 1000 to 1500 MPa [ 21 – 23 ]. This higher flexural strength was likely responsible for the higher fracture load observed in SM crowns. After simulating 5 years of clinical service, the SM group exhibited a statistically significant decrease in initial crack load. This phenomenon may be attributed to subcritical surface microcrack propagation under cyclic loading stress, which compromised crown strength as confirmed by SEM observations (Fig. 4 l) [ 24 ]. Zirconia's phase transformation toughening mechanism typically inhibits crack advancement. In SM zirconia, diamond bur processing might induce tetragonal to monoclinic phase transitions, potentially diminishing this toughening effect. Notably, both SLA and MJ groups maintained initial crack loads despite fatigue cycling. This could be explained by wear patterns developing at the identical occlusal contact position during both dynamic and static loading [ 19 , 25 ]. Such localized wear might optimize stress distribution during static testing, thereby compensating for potential strength degradation. When the initial fracture load was reached, a crack formed at the central fossa of the crown (Fig. 1 a). Following this, the stress-strain curve slightly declined and then continued to increase until a complete fracture occurred, at which point the stress-strain curve sharply dropped (Fig. 2 ). The load at this stage is referred to as the complete fracture load. The 3 groups demonstrated similar complete fracture load values. Similar findings were reported in Zandinejad et al. [ 26 ], who found no significant difference in fracture load between crowns fabricated using the SM and SLA methods once bonded to the abutment. The initial fracture load reflects the failure point of the crown due to the brittle, elastic failure nature of cramics. However, the second drop of complete fracture may be linked to the failure of the entire construct (ceramic-cement-abutment complex) [ 17 ]. The cement and abutment teeth supporting structures may be compensate for the lower flexural strength in MJ and SLA groups. The internal fit of restorations also plays a critical role in determining the strength of the complex [ 27 ]. Studies have shown crowns with a thicker cement gap tend to exhibit higher stress concentrations at the central fossa and lower fracture loads, as the lower elastic modulus of the cement allows for greater deformation of the crown [ 27 , 28 ]. Previous studies showed that MJ-fabricated crowns exhibit better marginal adaptation than SM-fabricated crowns, which might be the reason of high complete fracture load in this study [ 14 ]. For SLA-fabricated crowns, the occlusal full-supporting structure approach used in this study demonstrated better printing accuracy compared with the traditional pillar supports method [ 29 ]. The comparable dimensional accuracy of the MJ and SLA may explain why their complete fracture load is comparable to that of the SM group. The fatigue loading did not affect the complete fracture load of complete crowns across the 3 manufacturing techniques, simulating longer durations of mastication with an increased number of loading cycles might yield more significant results. Fractographic and microstructural analyses of the fractured crown fragments using SEM provided detailed insights into the loading failures of the tested crowns. In the SM group, both the non-fatigue and fatigue cycling groups exhibited cone cracks under the contact area due to local stress concentrations (Fig. 4 ). No critical defects were identified in the representative SM crowns, which exhibited consistent uniform transgranular or intergranular fracture characteristics with minimal flaws. The SLA group demonstrated distinct defects, including porosities, agglomerates, and delaminations. The fracture surface of SLA crowns revealed irregular pores near the surfaces (Fig. 5 f,i) and staircase-like morphology (Fig. 5 a,l). The crack propagation initiated perpendicular to the occlusal surface, twisting along delaminated regions and extending through interlayer connections. Flat fracture surfaces in interlayer regions suggested insufficient interlayer bonding strength. Porosities and delamination s were the primary defects affecting the strength of SLA-manufactured zirconia in this study. The presence of these defects is strongly associated with a reduction in mechanical strength [ 2 , 10 , 31 , 30 ]. Lu et al. [ 9 ] reported that defects significantly reduce the flexural strength of zirconia produced using photopolymerization techniques. Similarly, Saâdaoui et al. [ 10 ] used XCT analysis to identify porosities in SLA-fabricated zirconia ranging from 7 to 20 µm in diameter, with a maximum size of 54 µm, consistent with the findings in this study. Pores represent the most prevalent failure origin in restorations, acting not merely as structural defects but also as critical stress concentrators [ 31 ]. In polycrystalline materials, these voids induce equatorial cracks extending approximately half a grain depth into the matrix, effectively creating sharp flaws that significantly compromise material strength [ 32 ]. Macroporosities located within tensile stress zones and adjacent to contact interfaces act as critical stress concentrators, ultimately evolving into dominant flaws that dictate structural failure. Delamination and insufficient interlayer bonding strength also significantly impact the mechanical properties of SLA-fabricated zirconia [ 33 ]. Fracture propagation along interlayer boundaries is well-documented in the literature [ 2 , 7 , 13 ]. The bonding strength between layers depends on UV light intensity and curing time, where both under-curing and over-curing of the photopolymer can result in delamination [ 34 , 35 ]. Incomplete removal of organic materials during the debinding phase further exacerbates delamination issues [ 35 ]. Pores are the main defects found in the MJ group. Evenly distributed circular pores are visible on the fracture surface marked by blue arrows (Fig. 6 ) The circular porosities typically measure 4–7 µm in diameter. The high-magnification image in Fig. 6 c and 6 i highlights such porosity, showing zirconia grains within the void with a rounded shape and relatively uniform size. A high-magnification image (2500×) in Fig. 6 l also reveals the fracture origin in a porous region beneath the surface. Compared with SLA crowns, the diameters of these porosities were smaller in MJ group, and their shapes were more spherical. These findings are consistent with those of Willems et al. [ 13 ]. This difference may be partially attributed to the different printing principles employed in the MJ process. In MJ, zirconia particles suspended in a solvent are jetted onto a heated printing platform. The solvent evaporates upon contact with the platform, leaving behind the solid phase of the ink to form the green body, this process results in a green body with a lower organic content, which makes it easier to remove during the debinding stage. Furthermore, MJ uses nanoscale liquid ink droplets, and its printing layer thickness is smaller than that of SLA (10.5 µm vs. 40 µm), which results in smaller defect sizes. Previous research has shown that spherical defects tend to have a lesser impact on mechanical properties than other defect shapes, while delamination significantly affects strength [ 34 ]. In this study, no significant delamination was observed in MJ crowns, but porosities near the surface acted as stress concentrators and limited the strength of these restorations. The origins of porosities in MJ technology are multifaceted. The boiling of liquid solvents in the ink can lead to the formation of spherical porosities [ 36 , 37 ]. In addition, the impact of droplets can create defects if the previously deposited layer has not completely solidified. The binder in the ink slows down solvent evaporation, and because the printing platform’s temperature is controlled by a passing heating lamp, temperature gradients may arise, leaving earlier layers incompletely solidified. Blockages or partial blockages in nozzles can also cause droplets to deposit in unintended locations, creating defects. Air entrapment during printing is another potential contributor to porosity formation. To enhance the mechanical strength of MJ-fabricated samples and reduce defects, improvements are needed in the heating methods for uniform temperature control, ink composition to enhance wettability, and optimization of the debinding processes. Occlusal forces typically range from 450 to 520 N, with forces reaching up to 790 N in patients with bruxism [ 38 ]. In this study, although the initial fracture load of additively manufactured zirconia crowns was lower than that of SM-fabricated crowns, it remained above the maximum clinical occlusal force even after a simulated 5 years of usage. This indicates that the mechanical properties of additively manufactured zirconia are reliable for clinical application. However, this study had certain limitations. Only 2 AM methods were investigated, and variation in printing systems, parameter settings, and slurry formulations could significantly affect the final results. Therefore, these findings may not be generalizable to all AM techniques. In addition, this study simulated a maximum of 5 years of intraoral mastication, and longer simulations might reveal more pronounced differences in performance. Nevertheless, the results in this study demonstrate that AM can produce restorations with clinically acceptable mechanical properties, challenges such as high porosity, numerous defects, delamination, and insufficient interlayer bonding remain. Further advancements are needed to optimize these processes and achieve superior mechanical performance for future applications in the dental field. 5. Conclusions This study evaluated the fracture and fatigue resistance of monolithic zirconia crowns produced using a novel material jetting (MJ) technique. Within the limitation of this study, the following conclusions are drawn: The initial fracture load of monolithic crowns fabricated by SM was significantly higher than that of SLA and MJ. However, SM, SLA, and MJ demonstrated comparable complete fracture load values. Five years of in vitro chewing simulation reduced the initial fracture load of SM, but did not affect the complete fracture load of monolithic zirconia crowns fabricated by SM, SLA, and MJ. MJ can fabricate zirconia crowns with reliable mechanical properties in 5 years of in vitro simulation. Defects and weak bonding strength between successive printing layers were the main issues for crowns fabricated by AM methods. Declarations Author Contribution All authors contributed to the study conception and design. Jizhe Lyu, Yin Zhou and Xunning Cao performed Material preparation, data collection and analysis. The first draft of the manuscript was written by Jizhe Lyu and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Five authors contributed to this research and their contributions to the paper are listed below：Jizhe Lyu: Methodology, Software, Investigation, Data curation, Writing - Original Draft, and Visualization. Yin Zhou: Formal analysis, Resources, Supervision. Xunning Cao: Validation, Formal analysis, and Visualization. Jianguo Tan: Conceptualization, Supervision, and Project administration. Xiaoqiang Liu: Conceptualization, Writing - Review & Editing, Supervision, Project administration, and Funding acquisition. References Grech J, Antunes E (2019) Zirconia in dental prosthetics: a literature review. 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J Eur Ceram Soc 41:5292–306. https://doi.org/10.1016/j.jeurceramsoc.2021.04.018 Lyu J, Yang X, Li Y, Tan J, Liu X (2024) Dimensional accuracy and clinical adaptation of monolithic zirconia crowns fabricated with the nanoparticle jetting technique. J Prosthet Dent 132:985.e1–7. https://doi.org/10.1016/j.prosdent.2023.04.008 Zhong S, Shi Q, Deng Y, Sun Y, Politis C, Yang S (2022) High-performance zirconia ceramic additively manufactured via nanoparticle jetting. Ceram Int 48:33485–98. https://doi.org/10.1016/j.ceramint.2022.07.294 Baysal N, Tuğba Kalyoncuoğlu Ü, Ayyıldız S (2022) Mechanical properties and bond strength of additively manufactured and milled dental zirconia: a pilot study. J Prosthodont 31:629–34. https://doi.org/10.1111/jopr.13472 Özcan M, Jonasch M (2018) Effect of cyclic fatigue tests on aging and their translational implications for survival of all-ceramic tooth-borne single crowns and fixed dental prostheses: cyclic fatigue of all-ceramic restorations. J Prosthodont 27:364–75. https://doi.org/10.1111/jopr.12566 Eroğlu Z, Gurbulak AG (2013) Fatigue behavior of zirconia-ceramic, galvano-ceramic, and porcelain-fused-to-metal fixed partial dentures. J Prosthodont 22:516–22. https://doi.org/10.1111/jopr.12059 Zhai Z, Qian C, Jiao T, Sun J (2023) In vitro fracture and fatigue resistance of monolithic zirconia crowns fabricated by stereolithography. J Prosthet Dent https://doi.org/10.1016/j.prosdent.2023.02.017. Access on 23 Mar 2023 Epub ahead of print. Rosentritt M, Behr M, Gebhard R, Handel G (2006) Influence of stress simulation parameters on the fracture strength of all-ceramic fixed-partial dentures. Dent Mater 22:176–82. https://doi.org/10.1016/j.dental.2005.04.024 Zhang Y, Lawn BR (2018) Novel zirconia materials in dentistry. J Dent Res 97: 140–7. https://doi.org/10.1177/0022034517737483 Branco AC, Colaço R, Figueiredo-Pina CG, Serro AP (2023) Recent advances on 3D-printed zirconia-based dental materials: a review. Materials 16:1860. https://doi.org/10.3390/ma16051860 Alghauli MA, Alqutaibi AY, Wille S, Kern M (2024) The physical-mechanical properties of 3D-printed versus conventional milled zirconia for dental clinical applications: A systematic review with meta-analysis. J Mech Behav Biomed Mater 156:106601. https://doi.org/10.1016/j.jmbbm.2024.106601 Kelly JR, Cesar PF, Scherrer SS, Della Bona A, van Noort R, Tholey M, Vichi A, Lohbauer U (2017) ADM guidance-ceramics: Fatigue principles and testing. Dent Mater 33:1192-1204. https://doi.org/10.1016/j.dental.2017.09.006 Schmitter M, Mueller D, Rues S (2012) Chipping behaviour of all-ceramic crowns with zirconia framework and CAD/CAM manufactured veneer. J Dent 40:154–62. https://doi.org/10.1016/j.jdent.2011.12.007 Zandinejad A, Das O, Barmak AB, Kuttolamadom M, Revilla-León M (2022) The flexural strength and flexural modulus of stereolithography additively manufactured zirconia with different porosities. J Prosthodont 31:434–40. https://doi.org/10.1111/jopr.13430 Rezende CEE, Borges AFS, Gonzaga CC, Duan Y, Rubo JH, Griggs JA (2017) Effect of cement space on stress distribution in Y-TZP based crowns. Dent Mater 33:144–51. https://doi.org/10.1016/j.dental.2016.11.006 May LG, Kelly JR, Bottino MA, Hill T (2012) Effects of cement thickness and bonding on the failure loads of CAD/CAM ceramic crowns: multi-physics FEA modeling and monotonic testing. Dent Mater 28:e99–e109. https://doi.org/10.1016/j.dental.2012.04.033 Li R, Xu T, Wang Y, Sun Y (2023) Accuracy of zirconia crowns manufactured by stereolithography with an occlusal full-supporting structure: an in vitro study. J Prosthet Dent 130:902–7. https://doi.org/10.1016/j.prosdent.2022.01.015 Uçar Y, Aysan Meriç İ, Ekren O (2019) Layered manufacturing of dental ceramics: fracture mechanics, microstructure, and elemental composition of lithography‐sintered ceramic. J Prosthodont 28(1):e310-8. https://doi.org/10.1111/jopr.12748 Rice RW (1984) Pores as fracture origins in ceramics. J Mater Sci 19:895–914. https://doi.org/10.1007/BF00540460 Lu CS, Danzer R, Fischer FD (2004) Scaling of fracture strength in ZnO: effects of pore/grain-size interaction and porosity. J Eur Ceram Soc 24: 3643–51. https://doi.org/10.1016/j.jeurceramsoc.2003.12.001 Xing H, Zou B, Li S, Fu X (2017) Study on surface quality, precision and mechanical properties of 3D printed ZrO2 ceramic components by laser scanning stereolithography. Ceram Int 43:16340–7. https://doi.org/10.1016/j.ceramint.2017.09.007 Zhang K, Meng Q, Cai N, Qu Z, He R (2021) Effects of solid loading on stereolithographic additive manufactured ZrO2 ceramic: A quantitative defect study by X-ray computed tomography. Ceram Int 47:24353–9. https://doi.org/10.1016/j.ceramint.2021.05.149 Jang KJ, Kang JH, Fisher JG, Park SW (2019) Effect of the volume fraction of zirconia suspensions on the microstructure and physical properties of products produced by additive manufacturing. Dent Mater 35:e97–e106. https://doi.org/10.1016/j.dental.2019.02.001 Song JH, Nur HM (2004) Defects and prevention in ceramic components fabricated by inkjet printing. J Mater Process Technol 155–156:1286–92. https://doi.org/10.1016/j.jmatprotec.2004.04.292 Özkol E, Ebert J, Uibel K, Wätjen AM, Telle R (2009) Development of high solid content aqueous 3Y-TZP suspensions for direct inkjet printing using a thermal inkjet printer. J Eu Ceram Soc 29:403–9. https://doi.org/10.1016/j.jeurceramsoc.2008.06.020 Nishigawa K, Bando E, Nakano M (2001) Quantitative study of bite force during sleep associated bruxism. J Oral Rehabil 28:485–91. https://doi.org/10.1046/j.1365-2842.2001.00692.x Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6766588","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":466766887,"identity":"218ce78d-97ff-4bab-bd39-0164d997bc3b","order_by":0,"name":"Jizhe Lyu","email":"","orcid":"","institution":"Peking University School and Hospital of Stomatology","correspondingAuthor":false,"prefix":"","firstName":"Jizhe","middleName":"","lastName":"Lyu","suffix":""},{"id":466766888,"identity":"7952df1b-d03d-4c02-9335-746eeabb2fa1","order_by":1,"name":"Yin Zhou","email":"","orcid":"","institution":"Peking University School and Hospital of Stomatology","correspondingAuthor":false,"prefix":"","firstName":"Yin","middleName":"","lastName":"Zhou","suffix":""},{"id":466766889,"identity":"996cf74c-bbc9-482f-9af9-dbf8fc91f091","order_by":2,"name":"Xunning Cao","email":"","orcid":"","institution":"Peking University School and Hospital of Stomatology","correspondingAuthor":false,"prefix":"","firstName":"Xunning","middleName":"","lastName":"Cao","suffix":""},{"id":466766890,"identity":"bff6cb4f-e188-41cd-ada0-eacd34c5c211","order_by":3,"name":"Jianguo Tan","email":"","orcid":"","institution":"Peking University School and Hospital of Stomatology","correspondingAuthor":false,"prefix":"","firstName":"Jianguo","middleName":"","lastName":"Tan","suffix":""},{"id":466766891,"identity":"7d439133-f5f4-46bb-b423-f71ca4529fc6","order_by":4,"name":"Xiaoqiang Liu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/0lEQVRIiWNgGAWjYBACPmYgkQDEbCDexwYwxSCBTwsbshbGmURpQeYw8zYwEKGFncdM4kGNjWwf+9nDr2138EUbHGA+eJuHwS4Pt8N4jA0SjqUZt/HkpVnnnmHL3XCALdmahyG5GI8WwwcJbIcT2xhyzIxz20BaeMykeRgOJDbg1mJwIOEfUAv/GzNjS7AW/m+EtBg+SGwDapHIMX7MCLGFjYAWtmKDxD6gXyTemDH2Av0y8zCbseUcg2ScWvj5D2+T/PHNRnZ+f47xh587juX2HW9+eONNhR1OLTDACFTABoyOY8DYAfENCKiHamH+wMBQQ1jpKBgFo2AUjDgAANCuUODLe452AAAAAElFTkSuQmCC","orcid":"","institution":"Peking University School and Hospital of Stomatology","correspondingAuthor":true,"prefix":"","firstName":"Xiaoqiang","middleName":"","lastName":"Liu","suffix":""}],"badges":[],"createdAt":"2025-05-28 09:38:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6766588/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6766588/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":84199131,"identity":"45a2e709-e0b7-489e-9990-4e7b51aa2494","added_by":"auto","created_at":"2025-06-09 08:13:42","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":20656,"visible":true,"origin":"","legend":"\u003cp\u003eInitial crack formation and complete fracture of monolithic zirconia complete crown\u003c/p\u003e\n\u003cp\u003ea: Initial crack; b: Complete crack\u003c/p\u003e","description":"","filename":"fig1.tif.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6766588/v1/8cb7dad4c4b5ce85e3d367ff.jpg"},{"id":84199881,"identity":"899302a7-407e-4659-9020-fa913fe68d2e","added_by":"auto","created_at":"2025-06-09 08:21:43","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":214943,"visible":true,"origin":"","legend":"\u003cp\u003ePresentative load-displacement curves\u003c/p\u003e\n\u003cp\u003eThe left triangle represents initial crack load and the right triangle represents complete crack load\u003c/p\u003e","description":"","filename":"fig2.tif.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6766588/v1/c3e78b8844167ff81496de35.jpg"},{"id":84199130,"identity":"480ae49c-64e8-420d-9c12-170d55089091","added_by":"auto","created_at":"2025-06-09 08:13:42","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":22521,"visible":true,"origin":"","legend":"\u003cp\u003eA 4 mm diameter tungsten ball was positioned on the cental fossa of the crown\u003c/p\u003e\n\u003cp\u003ea: 4 mm tungsten carbide ball; b: Occlusal contact configuration between the ball and the crown.\u003c/p\u003e","description":"","filename":"fig3a.tif.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6766588/v1/9137da4d35bb30bac544fb5b.jpg"},{"id":84199143,"identity":"52dd8a91-aab1-4271-a350-1fc256f4d378","added_by":"auto","created_at":"2025-06-09 08:13:43","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1519425,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron microscope images of fractured crowns fabricated by subtractive manufacturing before and after dynamic fatigue loading\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;a-c: Before dynamic loading; d-f: After 1.2 × 10\u003csup\u003e4\u003c/sup\u003e cycles; g-i: After 1.2 × 10\u003csup\u003e5\u003c/sup\u003e cycles; j-l: After 1.2 × 10\u003csup\u003e6\u003c/sup\u003e cycles. a,d,g,j: Lower\u0026nbsp;magnification views, b,c,e,f,h,i,k,l: higher magnification views. The fracture origin is indicated by yellow arrows, the direction of crack propagation is indicated by black arrows, key fracture surface features are indicated by white arrows, and fine cracks below the surface are indicated by blue arrows.\u003c/p\u003e","description":"","filename":"Fig4.tiff.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6766588/v1/497ae3db0b41f5ef23af89ca.jpg"},{"id":84199162,"identity":"810252fd-335d-4a74-9999-132ca7d0acaf","added_by":"auto","created_at":"2025-06-09 08:13:44","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1473868,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron microscope images of fractured crowns fabricated by stereolithography before and after dynamic fatigue loading\u003c/p\u003e\n\u003cp\u003ea-c: Before dynamic loading; d-f: After 1.2 × 10\u003csup\u003e4\u003c/sup\u003e cycles; g-i: After 1.2 × 10\u003csup\u003e5\u003c/sup\u003e cycles; j-l: After 1.2 × 10\u003csup\u003e6\u003c/sup\u003e cycles. a,d,g,k: Lower\u0026nbsp;magnification views, b,c,e,f,h,i,j,l: higher magnification views. The fracture origin is indicated by yellow arrows, the direction of crack propagation is indicated by black arrows, key fracture surface features are indicated by white arrows. Blue arrows indicate pores and green arrows indicate the staircase morphology.\u003c/p\u003e","description":"","filename":"Fig5.tiff.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6766588/v1/5f51d78e5bc71aed7c04cfda.jpg"},{"id":84199138,"identity":"519ebee6-eeef-4e24-a62f-500fce5a15af","added_by":"auto","created_at":"2025-06-09 08:13:43","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1905056,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron microscope images of fractured crowns fabricated by material jetting before and after dynamic fatigue loading\u003c/p\u003e\n\u003cp\u003ea-c: Before dynamic loading; d-f: After 1.2 × 10\u003csup\u003e4\u003c/sup\u003e cycles; g-i: After 1.2 × 10\u003csup\u003e5\u003c/sup\u003e cycles; j-l: After 1.2 × 10\u003csup\u003e6\u003c/sup\u003e cycles. a,e,g,j: Lower\u0026nbsp;magnification views, b,c,d,f,h,i,k,l: higher magnification views. The fracture origin is indicated by yellow arrows, the direction of crack propagation is indicated by black arrows, key fracture surface features are indicated by white arrows. Blue arrows indicate pores.\u003c/p\u003e","description":"","filename":"Fig6.tiff.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6766588/v1/2d2eac67b929b94e2764bd4f.jpg"},{"id":84202024,"identity":"530c13a4-1b98-4cb4-8e97-942d5971cfd9","added_by":"auto","created_at":"2025-06-09 08:37:44","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5699870,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6766588/v1/04ec3b7f-7a89-48b7-bc1b-aa44f9daebf4.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Study of fracture and fatigue resistance of monolithic zirconia dental crowns fabricated through a novel material jetting technique","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eZirconia, particularly 3 mol% yttria-stabilized tetragonal polycrystalline zirconia (3Y-TZP), has emerged as the most popular all-ceramic restorative material due to its exceptional mechanical properties [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Zirconia dental restorations are predominantly designed using computer-aided design (CAD) and fabricated through computer-aided manufacturing (CAM). This manufacturing process can be divided into subtractive and additive methods. Subtractive manufacturing (SM) remains the most widely adopted approach, offering time and cost efficiency while delivering a certain quality level compared with traditional workflows. However, this method has important limitations, including material waste [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], limited precision of intricate details, and increased risk of microcracks during the milling process [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. By contrast, additive manufacturing (AM), also known as three-dimensional (3D) printing, provides superior geometric freedom and significantly reduces waste [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. These advantages position AM as a promising alternative for fabricating dental restorations.\u003c/p\u003e \u003cp\u003eSeveral technologies can be utilized in AM for producing zirconia restorations. The American Society for Testing and Materials Committee has classified AM into 7 categories: VAT photopolymerization [including stereolithography (SLA) and digital light processing (DLP)], material jetting (MJ), material extrusion (also known as fused deposition modeling), binder jetting, powder bed fusion, sheet lamination, and direct energy deposition [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. VAT photopolymerization, further divided into SLA and DLP based on different light-curing methods, is the most extensively researched and applied method for dental restoration. Studies have shown that 3Y-TZP fabricated using LCM can achieve a relative density of 99% of theoretical density and flexural strengths of 894.1\u0026thinsp;\u0026plusmn;\u0026thinsp;160.1 MPa, meeting clinical requirements [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, previous studies have reported that zirconia produced via photopolymerization exhibits mechanical properties and printing accuracy still fall short compared with SM zirconia [\u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMaterial jetting is another AM technique in which material droplets are selectively deposited to form an object [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. The advanced customized jetting (ACJ) technique, a specific MJ variation, offers a resolution of 16.000 \u0026times; 17.625 \u0026micro;m with a layer thickness of 10.5 \u0026micro;m, enabling the fabrication of more precise and dense restorations. In the MJ process, zirconia nanoparticles suspended in liquid are ejected from nozzles and deposited on a heated print platform (160\u0026ndash;250\u0026deg;C). As the liquid evaporates upon contact with the platform, zirconia particles are deposited layer by layer to form the green body [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Previous studies showed dental monolithic crowns fabricated using MJ have demonstrated greater dimensional accuracy and smaller marginal gaps than those produced via SM [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Zhong et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] reported that zirconia fabricated using MJ achieved an average relative density of 99.5% and a flexural strength of 699\u0026thinsp;\u0026plusmn;\u0026thinsp;104 MPa. Willems et al. [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] reported MJ zirconia reaching 99.7% relative density and biaxial bending strength of up to 1004\u0026thinsp;\u0026plusmn;\u0026thinsp;138 MPa. These findings demonstrate the excellent printing accuracy and mechanical properties of MJ, highlighting its potential for dental applications.\u003c/p\u003e \u003cp\u003eFracture remains one of the primary modes of failure for ceramic restorations. While studies have demonstrated the reliable physicochemical properties of MJ-fabricated zirconia in standard specimen tests [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], the stress conditions experienced by restorations during mastication are far more complex. Assessing the fracture resistance of 3D-printed zirconia restorations is critical for evaluating their mechanical properties in clinical applications. In addition, restorations in the oral cavity are subjected to repeated low-intensity loads. The structural integrity of ceramic components may be compromised through progressive damage during repeated low-load cycling, and could lead to premature material failure. Fatigue induced by dynamic loading accelerates crack propagation in restorations, which makes fatigue testing essential for predicting long-term performance [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Despite the excellent printing dimensional accuracy and potential of MJ in dental restorations, limited research has been conducted on the mechanical properties of MJ zirconia, with most studies focusing on standard specimens [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. It remains uncertain whether MJ-fabricated zirconia restorations can withstand the long-term chewing forces experienced in clinical settings.\u003c/p\u003e \u003cp\u003eTherefore, this study compared the fracture and fatigue resistance of monolithic zirconia complete crowns fabricated using SM, SLA, and MJ. The null hypothesis was that neither the manufacturing method nor fatigue loading would affect the fracture and fatigue resistance of complete crowns made of zirconia.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Sample preparation\u003c/h2\u003e \u003cp\u003eA standardized typodont right mandibular first molar (A5SAN 500, Nissin Dental Products Inc.,Osaka, Japan) was prepared for a complete crown, with an occlusal reduction of 1.0\u0026ndash;1.5 mm and a margin design of 0.7 mm chamfer. The tooth preparation was digitized using an intraoral scanner (IOS, TRIOS 3; 3Shape A/S, Copenhagen, Denmark), and 120 identical tooth preparation abutments were fabricated using resin-based ceramics (Hyramic, Upcera, Shenzhen, China) using a milling system (DGA+, VHF technologies GmbH, Ammerbuch, Germany). The elastic modulus of the resin-based ceramic (15 GPa) is similar to that of human dentin to simulate clinical situation. The fabricated tooth preparation abutment was rescanned, and a complete crown was designed using a software program (DentalCAD 3.0 Galway, exocad GmbH, Darmstadt, Germany) with the cement gap set to 30 \u0026micro;m. Then the crown was exported as standard tessellation language (STL) files and fabricated using three techniques: SM, SLA, and MJ. Forty complete crowns for each technique and a total of 120 crowns were fabricated. For additive manufacturing crowns, the printing direction were set at 180\u0026deg; with the occlusal surface facing the print platform.\u003c/p\u003e \u003cp\u003eFor SM-fabricated crowns, a 5-axis milling machine (DWX 51D, Roland DG Corp., Shizuoka, Japan) was used to mill a partially sintered 3Y-TZP zirconia block (ST, Upcera, Shenzhen, China), which then was sintered at 1 530\u0026deg;C for 2 hours following the manufacturer\u0026rsquo;s instructions.\u003c/p\u003e \u003cp\u003eFor SLA-fabricated crowns, an occlusal full-supporting structure was used to obtain higher fabrication quality. Full supporting bases were designed for each crown using a software program (Materialise Magics, Materialise, Leuven, Belgium). A uniform approximately 100 \u0026micro;m gap between the restoration and the base was set, and the supporting base could be easily removed after printing to avoid defects introduced during the manually removal of supporting pillars. During the printing process, an SLA printer (J2 S100P Ceramics, Junjing, Guangdong, China) and a 3Y-TZP slurry containing a 20 wt% photosensitive resin mixture and 80 wt% zirconia powder were used. The slurry was cured under a 355 nm wavelength laser beam light source. The scan speed was set at 5000 mm/s, and the print layer thickness was 40 \u0026micro;m. After printing, the green body was cleaned in an ultrasonic bath to remove the extra slurry and then subjected to debinding and sintering at 1 470\u0026deg;C for 3 hours to produce the dense part.\u003c/p\u003e \u003cp\u003eFor MJ-fabricated crowns, an inkjet printer (PGJ180, Thales, Hangzhou, China) was used to produce the green part. The inkjet printer was equipped with 24 print heads, 12 of which print zirconia ink, while the other 12 print support materials. Five hundred and twelve nozzles contained in the 24 print heads working simultaneously, enabling the selective deposition of the ink onto the print platform. The zirconia ink (Zrcoop, Thales, Hangzhou, China) consisted of approximately 45 wt% zirconia powder stabilized with 3 mol% yttrium oxide, combined with glycol ethers and a dispersing agent. The ink was ejected from the nozzles and selectively deposited onto the print platform. The temperature of the printing platform was controlled between 160\u0026deg;C and 250\u0026deg;C by a passing lamp. Upon contact with the platform, the solvent in the ink evaporated, leaving only the zirconia particles deposited onto the surface. After one layer of printing was completed, a roller planed the layer and controlled its thickness to 10.5 \u0026micro;m. After the printing process, the printed green body was washed in distilled water to remove the support material, followed by debinding and sintering in air at 1 450\u0026deg;C for 4 hours to achieve the final density. No glazing or polishing was conducted on the fabricated crowns in the 3 groups.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Experiment\u003c/h2\u003e \u003cp\u003eThe intaglio surface of all complete crowns was airborne-particle abraded with 50 \u0026micro;m aluminum oxide particles (Cobra, Rengert, Germany) at 0.25 MPa for 20 seconds. Following this, all crowns and corresponding abutments were cleaned using ethanol ultrasonic cleaning and air-dried. Then the crowns were cemented to the abutments using resin cement (RelyX U200, 3M, Minnesota, USA), with excess cement carefully removed. The cement was fully cured using an LED light for 40 seconds to ensure complete polymerization. After cementation, the specimens were stored in deionized water at 37\u0026deg;C for 24 hours.\u003c/p\u003e \u003cp\u003eTen crowns of each manufacturing method underwent static loading tests using a universal testing machine (Instron 5969; Instron Corp., Massachusetts, USA) to assess immediate fracture resistance. The loading was applied vertically to the central fossa of the crown using a 4 mm diameter tungsten carbide indenter at a speed of 1 mm/min. When the applied force reached a certain threshold, an initial crack would form at the central fossa, although the crown would not completely fracture (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). The load force at this point was recorded as the initial crack load. After the formation of the initial crack, the stress-strain curve continued to rise until the crown experienced catastrophic failure (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The load at the drop point was recorded as the crown\u0026rsquo;s complete fracture load. The representative load-displacement curve was shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThirty complete crowns of each group underwent fatigue loading tests using a universal testing machine (E1000; Instron Corp., Massachusetts, USA). A 4 mm diameter tungsten carbide ball was applied to the central fossa of the crown for vertical cyclic loading (30\u0026ndash;300 N, 20 Hz) [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) The crowns were subjected to 1.2 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e, 1.2 \u0026times; 10\u003csup\u003e5\u003c/sup\u003e, and 1.2 \u0026times; 10\u003csup\u003e6\u003c/sup\u003e cycles, simulating clinical use over several weeks, months, and 5 years, respectively (n\u0026thinsp;=\u0026thinsp;10/group) [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. After fatigue loading, the crowns were further subjected to static loading tests using the mechanical testing machine (Instron 5969; Instron Corp., Massachusetts, USA) at a speed of 1 mm/min, the position of the indenter was consistent for both cyclic loading and static test. The initial fracture load value as well as the complete fracture load value was recorded.\u003c/p\u003e \u003cp\u003eRepresentative fractured samples from each group were ethanol ultrasonic cleaned and then sputter-coated (Model 681, Gatan, Pleasanton, USA) for 60 seconds with a gold/platinum alloy. The specimens were observed using a scanning electron microscope (SEM, S-4800, Hitachi, Tokyo, Japan) with an acceleration voltage of 5 kV.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Statistical analysis\u003c/h2\u003e \u003cp\u003eAll statistical analyses were performed using a software program (IBM SPSS Statistics, v 27.0; IBM Corp., NY, USA). Before statistical analysis, the normality of the results was tested using the Shapiro-Wilk test. Data of initial fracture load and complete fracture load met the normal distribution (P\u0026thinsp;\u0026gt;\u0026thinsp;.05), and 2-way analysis of variance was conducted, followed by \u003cem\u003epost hoc\u003c/em\u003e least significant difference (LSD) tests for further comparison.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Experimental Results","content":"\u003cp\u003eAll ceramic crowns remained intact under fatigue loading. A software program (G*Power v.3.1.9.6; Heinrich Heine University, Nordrhein-Westfalen, Germany) was used to calculate the actual post-hoc power (1-β), which was 0.91. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the effects of different manufacturing methods and fatigue loading on the initial fracture load. The initial fracture load for the SM group was significantly higher than that for the SLA and MJ groups (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). No statistically significant differences were found between the SLA and MJ groups in terms of initial crack load. Fatigue loading cycles significantly influenced the initial fracture load of the SM group. Complete crowns subjected to 1.2 \u0026times; 10\u003csup\u003e5\u003c/sup\u003e and 1.2 \u0026times; 10\u003csup\u003e6\u003c/sup\u003e cycles (2599.3\u0026thinsp;\u0026plusmn;\u0026thinsp;279.6 N and 2402.2\u0026thinsp;\u0026plusmn;\u0026thinsp;400.0 N, respectively) exhibited lower fracture loads than those of the non-fatigued group and the group subjected to 1.2 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e cycles (2898.8\u0026thinsp;\u0026plusmn;\u0026thinsp;283.8 N and 2944.0\u0026thinsp;\u0026plusmn;\u0026thinsp;394.8 N, respectively). By contrast, the number of fatigue cycles did not affect the fracture load for the MJ and SLA groups.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation values of fracture force of the initial crack (N) for subtractive manufacturing, stereolithography, and material jetting before and after dynamic fatigue loading\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFatigue cycle\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.2 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.2 \u0026times; 10\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.2 \u0026times; 10\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2898.8\u0026thinsp;\u0026plusmn;\u0026thinsp;283.8\u003csup\u003eA,ab\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2944.0\u0026thinsp;\u0026plusmn;\u0026thinsp;394.8\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2599.3\u0026thinsp;\u0026plusmn;\u0026thinsp;279.6\u003csup\u003eA,bc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2402.2\u0026thinsp;\u0026plusmn;\u0026thinsp;400.0\u003csup\u003eA,c\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.925\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.003\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSLA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2076.4\u0026thinsp;\u0026plusmn;\u0026thinsp;399.1\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1779.1\u0026thinsp;\u0026plusmn;\u0026thinsp;288.0\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1672.4\u0026thinsp;\u0026plusmn;\u0026thinsp;422.5\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1826.6\u0026thinsp;\u0026plusmn;\u0026thinsp;415.0\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.277\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.084\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMJ\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1916.1\u0026thinsp;\u0026plusmn;\u0026thinsp;502.4\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1917.1\u0026thinsp;\u0026plusmn;\u0026thinsp;242.4\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1564.4\u0026thinsp;\u0026plusmn;\u0026thinsp;249.2\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1839.8\u0026thinsp;\u0026plusmn;\u0026thinsp;302.5\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.176\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.095\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eF value\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18.604\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31.504\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e25.169\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8.398\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"7\"\u003eUppercase letters indicate statistically significant differences within a column (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Lowercase letters indicate statistically significant differences within a row (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). SM: subtractive manufacturing, SLA: stereolithography, MJ: material jetting.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents the complete fracture load results for different manufacturing methods and fatigue loading cycles. Before fatigue loading, no significant differences in complete fracture load were observed among the SM, SLA, and MJ groups. After 1.2 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e and 1.2 \u0026times; 10\u003csup\u003e5\u003c/sup\u003e loading cycles, the MJ group exhibited higher complete fracture load values, whereas no significant differences were found between the SM and SLA groups. After 1.2 \u0026times; 10\u003csup\u003e6\u003c/sup\u003e cycles, the SLA group exhibited the lowest complete fracture load among the three groups.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation values of fracture force of complete crack (N) for subtractive manufacturing, stereolithography, and material jetting before and after dynamic fatigue loading\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFatigue cycle\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.2 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.2 \u0026times; 10\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.2 \u0026times; 10\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3623.4\u0026thinsp;\u0026plusmn;\u0026thinsp;482.3\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3415.6\u0026thinsp;\u0026plusmn;\u0026thinsp;642.9\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3325.7\u0026thinsp;\u0026plusmn;\u0026thinsp;524.2\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3688.2\u0026thinsp;\u0026plusmn;\u0026thinsp;575.2\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e0.648\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e0.586\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSLA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3370.4\u0026thinsp;\u0026plusmn;\u0026thinsp;314.2\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3239.6\u0026thinsp;\u0026plusmn;\u0026thinsp;383.6\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3315.1\u0026thinsp;\u0026plusmn;\u0026thinsp;500.1\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3046.9\u0026thinsp;\u0026plusmn;\u0026thinsp;318.3\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMJ\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3558.5\u0026thinsp;\u0026plusmn;\u0026thinsp;550.7\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4399.8\u0026thinsp;\u0026plusmn;\u0026thinsp;470.7\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3962.2\u0026thinsp;\u0026plusmn;\u0026thinsp;852.4\u003csup\u003eB,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4084.7\u0026thinsp;\u0026plusmn;\u0026thinsp;342.3\u003csup\u003eA,a\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.598\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.545\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.109\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10.204\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.552\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"7\"\u003eUppercase letters indicate statistically significant differences within a column (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Lowercase letters indicate statistically significant differences within a row (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). SM: subtractive manufacturing, SLA: stereolithography, MJ: material jetting.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the fractured surfaces in 3 groups examined by scanning electron microscopy. Key fracture surface features, including compression curls, arrest lines, wake hackles, and fracture mirrors, indicated by white arrows, facilitated the identification of fracture origins. SM crowns exhibited cone cracks below the contact points (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). No critical defects were identified in the representative SM crowns. The SLA group demonstrated distinct defects, including porosities, agglomerates, and delamination (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe fracture surface of an SLA crown revealed a staircase-like morphology, and the crack propagated through interlayer connections. The phenomenon was more pronounced after 1.2 \u0026times; 10\u003csup\u003e6\u003c/sup\u003e cycles (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ej-l). MJ crowns demonstrated evenly distributed sphere pores on the fracture surface, marked by blue arrows (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Small porosities near the surface under contact areas may acted as critical defects leading to failure. Surrounding arrest lines and hackles indicate the direction of crack propagation.\u003c/p\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThis study investigated the fracture loads and fatigue resistance of monolithic zirconia crowns fabricated with SM, SLA, and MJ. The 3 groups showed significant differences in the initial fracture load and complete fracture load after fatigue cycling; therefore, the null hypothesis was partially rejected.\u003c/p\u003e \u003cp\u003eThe initial fracture load reflects the force at which cracks begin to form in the crowns under stress, which is related to the crown\u0026rsquo;s resistance to deformation under compressive and tensile forces. The result revealed that the SM group showed significantly higher initial fracture load than that for the SLA and MJ groups. Previous studies have reported that the flexural strength of additively manufactured zirconia ranges from 306 to 1044 MPa, varying across studies, whereas the flexural strength of SM zirconia generally falls within the range of 1000 to 1500 MPa [\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. This higher flexural strength was likely responsible for the higher fracture load observed in SM crowns. After simulating 5 years of clinical service, the SM group exhibited a statistically significant decrease in initial crack load. This phenomenon may be attributed to subcritical surface microcrack propagation under cyclic loading stress, which compromised crown strength as confirmed by SEM observations (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003el) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Zirconia's phase transformation toughening mechanism typically inhibits crack advancement. In SM zirconia, diamond bur processing might induce tetragonal to monoclinic phase transitions, potentially diminishing this toughening effect. Notably, both SLA and MJ groups maintained initial crack loads despite fatigue cycling. This could be explained by wear patterns developing at the identical occlusal contact position during both dynamic and static loading [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Such localized wear might optimize stress distribution during static testing, thereby compensating for potential strength degradation.\u003c/p\u003e \u003cp\u003eWhen the initial fracture load was reached, a crack formed at the central fossa of the crown (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). Following this, the stress-strain curve slightly declined and then continued to increase until a complete fracture occurred, at which point the stress-strain curve sharply dropped (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The load at this stage is referred to as the complete fracture load. The 3 groups demonstrated similar complete fracture load values. Similar findings were reported in Zandinejad et al. [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], who found no significant difference in fracture load between crowns fabricated using the SM and SLA methods once bonded to the abutment. The initial fracture load reflects the failure point of the crown due to the brittle, elastic failure nature of cramics. However, the second drop of complete fracture may be linked to the failure of the entire construct (ceramic-cement-abutment complex) [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. The cement and abutment teeth supporting structures may be compensate for the lower flexural strength in MJ and SLA groups. The internal fit of restorations also plays a critical role in determining the strength of the complex [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Studies have shown crowns with a thicker cement gap tend to exhibit higher stress concentrations at the central fossa and lower fracture loads, as the lower elastic modulus of the cement allows for greater deformation of the crown [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Previous studies showed that MJ-fabricated crowns exhibit better marginal adaptation than SM-fabricated crowns, which might be the reason of high complete fracture load in this study [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. For SLA-fabricated crowns, the occlusal full-supporting structure approach used in this study demonstrated better printing accuracy compared with the traditional pillar supports method [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The comparable dimensional accuracy of the MJ and SLA may explain why their complete fracture load is comparable to that of the SM group. The fatigue loading did not affect the complete fracture load of complete crowns across the 3 manufacturing techniques, simulating longer durations of mastication with an increased number of loading cycles might yield more significant results.\u003c/p\u003e \u003cp\u003eFractographic and microstructural analyses of the fractured crown fragments using SEM provided detailed insights into the loading failures of the tested crowns. In the SM group, both the non-fatigue and fatigue cycling groups exhibited cone cracks under the contact area due to local stress concentrations (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). No critical defects were identified in the representative SM crowns, which exhibited consistent uniform transgranular or intergranular fracture characteristics with minimal flaws.\u003c/p\u003e \u003cp\u003eThe SLA group demonstrated distinct defects, including porosities, agglomerates, and delaminations. The fracture surface of SLA crowns revealed irregular pores near the surfaces (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef,i) and staircase-like morphology (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea,l). The crack propagation initiated perpendicular to the occlusal surface, twisting along delaminated regions and extending through interlayer connections. Flat fracture surfaces in interlayer regions suggested insufficient interlayer bonding strength. Porosities and delamination\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003es\u003c/span\u003e were the primary defects affecting the strength of SLA-manufactured zirconia in this study. The presence of these defects is strongly associated with a reduction in mechanical strength [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Lu et al. [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] reported that defects significantly reduce the flexural strength of zirconia produced using photopolymerization techniques. Similarly, Sa\u0026acirc;daoui et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] used XCT analysis to identify porosities in SLA-fabricated zirconia ranging from 7 to 20 \u0026micro;m in diameter, with a maximum size of 54 \u0026micro;m, consistent with the findings in this study. Pores represent the most prevalent failure origin in restorations, acting not merely as structural defects but also as critical stress concentrators [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. In polycrystalline materials, these voids induce equatorial cracks extending approximately half a grain depth into the matrix, effectively creating sharp flaws that significantly compromise material strength [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Macroporosities located within tensile stress zones and adjacent to contact interfaces act as critical stress concentrators, ultimately evolving into dominant flaws that dictate structural failure. Delamination and insufficient interlayer bonding strength also significantly impact the mechanical properties of SLA-fabricated zirconia [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Fracture propagation along interlayer boundaries is well-documented in the literature [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The bonding strength between layers depends on UV light intensity and curing time, where both under-curing and over-curing of the photopolymer can result in delamination [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Incomplete removal of organic materials during the debinding phase further exacerbates delamination issues [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePores are the main defects found in the MJ group. Evenly distributed circular pores are visible on the fracture surface marked by blue arrows (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) The circular porosities typically measure 4\u0026ndash;7 \u0026micro;m in diameter. The high-magnification image in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ei highlights such porosity, showing zirconia grains within the void with a rounded shape and relatively uniform size. A high-magnification image (2500\u0026times;) in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003el also reveals the fracture origin in a porous region beneath the surface. Compared with SLA crowns, the diameters of these porosities were smaller in MJ group, and their shapes were more spherical. These findings are consistent with those of Willems et al. [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. This difference may be partially attributed to the different printing principles employed in the MJ process. In MJ, zirconia particles suspended in a solvent are jetted onto a heated printing platform. The solvent evaporates upon contact with the platform, leaving behind the solid phase of the ink to form the green body, this process results in a green body with a lower organic content, which makes it easier to remove during the debinding stage. Furthermore, MJ uses nanoscale liquid ink droplets, and its printing layer thickness is smaller than that of SLA (10.5 \u0026micro;m vs. 40 \u0026micro;m), which results in smaller defect sizes. Previous research has shown that spherical defects tend to have a lesser impact on mechanical properties than other defect shapes, while delamination significantly affects strength [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. In this study, no significant delamination was observed in MJ crowns, but porosities near the surface acted as stress concentrators and limited the strength of these restorations. The origins of porosities in MJ technology are multifaceted. The boiling of liquid solvents in the ink can lead to the formation of spherical porosities [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. In addition, the impact of droplets can create defects if the previously deposited layer has not completely solidified. The binder in the ink slows down solvent evaporation, and because the printing platform\u0026rsquo;s temperature is controlled by a passing heating lamp, temperature gradients may arise, leaving earlier layers incompletely solidified. Blockages or partial blockages in nozzles can also cause droplets to deposit in unintended locations, creating defects. Air entrapment during printing is another potential contributor to porosity formation. To enhance the mechanical strength of MJ-fabricated samples and reduce defects, improvements are needed in the heating methods for uniform temperature control, ink composition to enhance wettability, and optimization of the debinding processes.\u003c/p\u003e \u003cp\u003eOcclusal forces typically range from 450 to 520 N, with forces reaching up to 790 N in patients with bruxism [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. In this study, although the initial fracture load of additively manufactured zirconia crowns was lower than that of SM-fabricated crowns, it remained above the maximum clinical occlusal force even after a simulated 5 years of usage. This indicates that the mechanical properties of additively manufactured zirconia are reliable for clinical application. However, this study had certain limitations. Only 2 AM methods were investigated, and variation in printing systems, parameter settings, and slurry formulations could significantly affect the final results. Therefore, these findings may not be generalizable to all AM techniques. In addition, this study simulated a maximum of 5 years of intraoral mastication, and longer simulations might reveal more pronounced differences in performance. Nevertheless, the results in this study demonstrate that AM can produce restorations with clinically acceptable mechanical properties, challenges such as high porosity, numerous defects, delamination, and insufficient interlayer bonding remain. Further advancements are needed to optimize these processes and achieve superior mechanical performance for future applications in the dental field.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThis study evaluated the fracture and fatigue resistance of monolithic zirconia crowns produced using a novel material jetting (MJ) technique. Within the limitation of this study, the following conclusions are drawn: The initial fracture load of monolithic crowns fabricated by SM was significantly higher than that of SLA and MJ. However, SM, SLA, and MJ demonstrated comparable complete fracture load values. Five years of in vitro chewing simulation reduced the initial fracture load of SM, but did not affect the complete fracture load of monolithic zirconia crowns fabricated by SM, SLA, and MJ. MJ can fabricate zirconia crowns with reliable mechanical properties in 5 years of in vitro simulation. Defects and weak bonding strength between successive printing layers were the main issues for crowns fabricated by AM methods.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors contributed to the study conception and design. Jizhe Lyu, Yin Zhou and Xunning Cao performed Material preparation, data collection and analysis. The first draft of the manuscript was written by Jizhe Lyu and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Five authors contributed to this research and their contributions to the paper are listed below：Jizhe Lyu: Methodology, Software, Investigation, Data curation, Writing - Original Draft, and Visualization. Yin Zhou: Formal analysis, Resources, Supervision. Xunning Cao: Validation, Formal analysis, and Visualization. Jianguo Tan: Conceptualization, Supervision, and Project administration. Xiaoqiang Liu: Conceptualization, Writing - Review \u0026amp; Editing, Supervision, Project administration, and Funding acquisition.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eGrech J, Antunes E (2019) Zirconia in dental prosthetics: a literature review. 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J Oral Rehabil 28:485\u0026ndash;91. https://doi.org/10.1046/j.1365-2842.2001.00692.x\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Zirconia, Dental Restorations, Fracture Resistance, Fatigue","lastPublishedDoi":"10.21203/rs.3.rs-6766588/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6766588/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAdditive manufacturing is becoming a promising method for dental applications. The advanced customized jetting technique, one of Material jetting (MJ), is a newly introduced additive manufacturing technique that can produce high-accuracy zirconia restorations. However, the fracture and fatigue resistance of monolithic zirconia crown fabricated with MJ is still unknown. One hundred and twenty monolithic zirconia crowns were fabricated using subtractive manufacturing (SM), stereolithography (SLA), and MJ techniques. The crowns were subjected to cyclic loading for 1.2 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e, 1.2 \u0026times; 10\u003csup\u003e5\u003c/sup\u003e, and 1.2 \u0026times; 10\u003csup\u003e6\u003c/sup\u003e cycles, simulating clinical use over several 2 weeks, 6 months, and 5 years, respectively (n\u0026thinsp;=\u0026thinsp;10 per group). After cyclic loading, the crowns underwent static loading tests. Both the initial fracture load and the complete fracture load were recorded. Fractographic analysis was conducted via scanning electron microscopy on fractured parts from each group. The initial fracture load for the SM group was significantly higher than that of the SLA and MJ groups (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The 3 groups demonstrated similar complete fracture load before fatigue loading. After 1.2 \u0026times; 10\u003csup\u003e4\u003c/sup\u003e and 1.2 \u0026times; 10\u003csup\u003e5\u003c/sup\u003e cycles, MJ crowns exhibited the highest complete fracture load. After 1.2 \u0026times; 10\u003csup\u003e6\u003c/sup\u003e cycles, SLA crowns showed the lowest complete fracture load values. Fractography analysis revealed minimal defects in the SM group, while the SLA and MJ groups exhibited varying degrees of pores, inclusions, and delamination. This study indicated that MJ can fabricate zirconia crowns with reliable mechanical properties in 5 years of in vitro simulation.\u003c/p\u003e","manuscriptTitle":"Study of fracture and fatigue resistance of monolithic zirconia dental crowns fabricated through a novel material jetting technique","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-09 08:13:37","doi":"10.21203/rs.3.rs-6766588/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"9f771c11-e032-4be2-b7e6-f6136b2c205f","owner":[],"postedDate":"June 9th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-14T06:57:16+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-09 08:13:37","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6766588","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6766588","identity":"rs-6766588","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}