Effect of post-rinsing time on the mechanical strength and cytotoxicity of a 3D printed orthodontic splint material

ObjectiveSince the post-rinsing time is inconsistently recommended, this study aims to investigate the effect of post-rinsing time on the flexural strength and cytotoxicity of an stereolithographically (SLA) printed orthodontic splint material.MethodsSLA-printed specimens were ultrasonically rinsed with isopropanol (IPA) for 5 min, 12 min, 20 min, 30 min, 1 h, and 12 h, respectively. Surface characterization was conducted by scanning electron microscopy and roughness measurements. Flexural strength was evaluated using a three-point bending test. Cytotoxicity was determined by direct contact test and extract test. For both tests, cell viability (live/dead staining) and cell metabolic activity (CCK-8 assay) were evaluated. Additionally, water sorption and water solubility were tested to analyze the mass loss from immersion.ResultsNo apparent surface alterations could be detected on the samples post-rinsed for less than 1 h. In contrast, when the post-rinsing time was prolonged to 12 h, surface fissures could be observed. Flexural strength linearly decreased with increasing post-rinsing time. All post-processed specimens did not show an obvious cytotoxic effect.SignificanceThe removal of cytotoxic methacrylate monomers by post-rinsing with IPA could be achieved in 5 min. Extending post-rinsing time could not improve the cytocompatibility of the SLA-printed orthodontic splint material, and may result in a decrease in flexural strength.     

Effect of the volume fraction of zirconia suspensions on the microstructure and physical properties of products produced by additive manufacturing

Objective

The objectives of the present study were: (1) to analyze the dispersion and optical properties of suspensions with various volume fractions of zirconia, and (2) to assess the influence of zirconia volume fraction on the microstructure and physical properties of products produced by the additive manufacturing and sintering process.

Fracture toughness of conventional,milled and 3D printed denture bases

ObjectivesThe aim of this study was to determine and compare fracture toughness (K_IC) and work of fracture (WOF) of a conventional (C) denture base, using the notchless triangular prism (NTP) specimen K_IC test, with CAD/CAM (milled, M) and 3D-printed (P) materials at 7 d and 90 d.MethodsLucitone 199 (C), Lucitone 199 CAD (M) and Lucitone Digital Print (P) (Dentsply, USA) were used to fabricate NTP specimens. Samples were stored in 37 °C water for 7 d (20/group) and 90 d (20/group) and conditioned in 23 °C water for 1 h prior to testing. For testing, samples were secured in custom-made jigs and loaded in tension until crack arrest/failure. The maximum-recorded load was used to calculate KIC. The results were analyzed by two-way ANOVA, Scheffé multiple mean comparisons (α = 0.05), independent t-tests and Weibull. WOF (in KJ/m²) was calculated by dividing the area under the load-displacement graphs by twice the corresponding crack-arrested cross sectional area of the fractured surfaces.ResultsThe results have shown that: 1) the tested materials had significantly different K_IC (P > C > M; p < 0.005) and WOF at both 7d and 90d; 2) ageing in 37 ºC water for 90 d resulted in a significant decrease of K_IC in the C and M groups (p < 0.001) and of WOF in all groups.SignificanceThe tested P denture base exhibited significantly higher K_IC and WOF, suggesting that it could be more resistant to crack propagation than the C and M materials tested. Water storage for 90 d significantly decreased K_IC of C and M materials and WOF of all.     

Load-bearing capacity of CAD/CAM 3D-printed zirconia,CAD/CAM milled zirconia,and heat-pressed lithium disilicate ultra-thin occlusal veneers on molars

ObjectivesThe load-bearing capacity of ultra-thin occlusal veneers made of 3D-printed zirconia were compared to the ones obtained by fabricating these reconstructions by CAD/CAM milling zirconia or heat-pressing lithium-disilicate.MethodsOn 60 extracted human molars, the occlusal enamel was removed and extended into dentin. Occlusal veneers of 0.5 mm thickness were digitally designed. The specimens were divided into 3 groups (n = 20 each) differing in the restorative material and the fabrication technique of the occlusal veneer. (1) 3DP: 3D-printed zirconia (Lithoz); (2): CAM: milled zirconia (Ceramill Zolid FX); (3) HPR: heat-pressed lithium disilicate (IPS e.max Press). After conditioning procedures, the restorations were adhesively bonded onto the conditioned tooth. Thereafter, all specimens were aged in a chewing simulator by exposure to cyclic fatigue and temperature variations. Subsequently the specimens were statically loaded and the load which was necessary to decrease the maximum load by 20% and initiate a crack (F_initial) and the load which was needed to fracture the specimen (F_max) were measured. Differences between the groups were compared applying the Kruskal-Wallis (KW) test and the Wilcoxon-Mann-Whitney-Test (WMW: p < 0.05).ResultsThe median F_initial values for the groups 3DP, CAM and HPR were 1’650 N, 1’250 N and 500 N. The differences between all three groups were statistically significant (KW: p < 0.0001). The median F_max values amounted to 2’026 N for the group 3DP, 1’500 N for the group CAM and 1’555 N for the group HPR. Significant differences were found between 3DP and CAM (WMW: p = 0.0238).SignificanceRegarding their load-bearing capacity, 3D-printed or milled zirconia as well as heat-pressed lithium disilicate can be recommended as restorative material for ultra-thin occlusal veneers to prosthetically compensate for occlusal tooth wear. Despite statistically significant differences between the restoration materials, all load-bearing capacities exceeded the clinically expected normal bite forces.     

The 3D-printed miniplate-jig system: a new,rapid, precise,and user-friendly approach to miniplate fixation of free-tissue mandibular reconstructions

Patient-specific, additively manufactured (printed) titanium reconstruction plates have been widely used to improve accuracy and efficiency of fibular flap reconstruction of the mandible. Miniplates possess some potential advantages over single-piece reconstruction plates, however multiple-miniplate fixation can be more technically demanding and may lengthen the duration of surgery. Furthermore, incremental angulation errors in screw placement for each miniplate could compromise overall dimensional accuracy of the neomandibular reconstruction. This preliminary article reports the first clinical use of a new patient-specific, printed titanium miniplate-jig system in a patient undergoing hemimandibulectomy for osteoradionecrosis of the mandible with fibular flap reconstruction. Our initial experience with the new device and technique demonstrates a quick, user friendly, and precise method for the placement and fixation of multiple miniplates in fibular-flap reconstruction of the mandible.     

Comparison of various 3D printed and milled PAEK materials: Effect of printing direction and artificial aging on Martens parameters

ObjectivesThe aim of this study was to investigate the effect of artificial aging on the Martens parameters of different 3D printed and milled polyaryletherketon (PAEK) materials.MethodsIn total 120 specimens of 4 different polyetheretherketon (PEEK) materials (Essentium PEEK, KetaSpire PEEK MS-NT1, VICTREX PEEK 450 G and VESTAKEEP i4 G) were additively manufactured via fused layer manufacturing (FLM) in either horizontal or vertical directions (n = 15 per group). 75 specimens were milled out of prefabricated PAEK blanks from the materials breCAM.BioHPP, Dentokeep, JUVORA Dental Disc 2 and Ultaire AKP ( = 15 per group). Martens hardness (HM), indentation hardness (H_IT) and indentation modulus (E_IT) were determined initially and longitudinally after thermocycling (5−55 °C, 10,000x) and autoclaving (134 °C, 2 bar). In each case, the surface topography of the specimens was examined for modifications using a light microscope.Data were analysed with Kolmogorov-Smirnov test, univariate ANOVA followed by post-hoc Scheffé test with partial eta squared (η_p²), Kruskal–Wallis-, Mann–Whitney-U-, Friedman- and Wilcoxon-Test. A value of p < 0.05 was considered as significant.ResultsMilled specimens showed higher Martens parameters than printed ones (p < 0.001). Artificial aging had a negative effect on the measured parameters (p < 0.001). Horizontally printed specimens presented higher Martens parameters than vertically printed ones, regardless of material and aging process (p < 0.001). Essentium PEEK and breCAM.BioHPP showed the highest and VICTREX PEEK 450G as well as Ultaire AKP the lowest values of all investigated PAEK materials initially, after thermocycling and after autoclaving (p < 0.001). Microscopic examinations showed that artificial aging did not cause any major modifications of the materials.SignificanceAdditively manufactured PEEK materials showed lower Martens parameters than milled ones, whereas horizontally printed specimens presented higher values than vertically printed ones. Artificial aging had a negative effect on the Martens parameters, but not on the surface topography.     

The effects of additive manufacturing technologies and finish line designs on the trueness and dimensional stability of 3D-printed dies

Purpose

To evaluate the effects of 5 manufacturing technologies and 2 finish line designs on the trueness and dimensional stability of 3D-printed definitive dies at finish line regions under different storage conditions and time.

Material and methods

Preparation of light chamfer and round shoulder finish lines were adopted individually on two mandibular first molar typodont teeth and digitalized as standard tessellation language (STL) files. A total of 240 samples (192 AM definitive dies and 48 definitive conventional stone dies) in 20 groups (n = 12) were manufactured based on 2 finishing line designs (chamfer and shoulder), 5 manufacturing technologies (4 additively manufactured technologies and conventional stone die), and 2 storage conditions (light exposure and dark). The 4 additively manufactured (AM) technologies include a DLP 3D-printer, an economic LED 3D-printer, a CLIP 3D-printer, and an SLA 3D-printer. All the study samples were distributed into two storage conditions. Subsequently, samples were digitalized to STL files at 3 different time points (within 36 hours, 1-month, and 3-months). A surface matching software was used to superimpose the sample STL files onto the corresponding original STL files with the best-fit alignment function. The trueness of each printed and stone definitive dies and their dimensional stabilities were measured by the root mean square (RMS, in mm). A linear mixed-effects model was used to test the effects of the finish line design, manufacturing technology, storage condition, and storage time on RMS values (α = 0.05).

Results

While finish line designs had no significant effects [F(1, 220) = 0.85, p < 0.358], the manufacturing technologies [F(3, 220) = 33.02, p < 0.001], storage condition [F(1, 220) = 4.11, p = 0.044], and storage time F(2, 440) = 10.37, p < 0.001] affected the trueness and dimensional stability of 3D-printed dies at finish line regions. No significant interactions were found among the 4 factors. For the manufacturing technologies, Type IV stone groups and LCD 3D-printer groups had significantly higher RMS values than the other 3 printers (p < 0.001) with no significant differences between Type IV stone and LCD 3D-printer groups (p = 0.577). DLP 3D-printer groups had higher RMS values than both SLA 3D-printer groups and CLIP 3D-printer groups (p < 0.001). There were no significant differences between SLA 3D-printer groups and CLIP 3D-printer groups, p = 0.671. For the effects of storage conditions, RMS values were significantly higher in the groups stored with the direct light exposure than the ones stored in the dark, p = 0.044. In terms of the effects of storage time, the RMS values were significantly higher after 1-month storage, p = 0.002; and 3-month storage, p < 0.001, than the ones at the immediate postmanufacturing stage. However, the RMS values after 1-month and 3-month storage were not significantly different from each other (p = 0.169).

Conclusions

Manufacturing technologies, storage conditions, and storage time significantly affected the trueness and dimensional stability of 3D-printed dies at finish line regions, while finish line designs had no significant effects. Among the AM technologies tested, all have produced either comparable or truer 3D-printed dies than the Type IV dental stone dies, and the CLIP and SLA 3D-printers produced the best outcomes. 3D-printed dies showed significant distortion after 1-month and 3-months storage, especially under light exposure storage conditions. These findings may negate the clinical need to preserve 3D-printed dies, and digital data should be preserved instead.     

Accuracy of additively manufactured zirconia four-unit fixed dental prostheses fabricated by stereolithography,digital light processing and material jetting compared with subtractive manufacturing

ObjectiveTo evaluate the manufacturing accuracy of zirconia four-unit fixed dental prostheses (FDPs) fabricated by three different additive manufacturing technologies compared with subtractive manufacturing.MethodsA total of 79 zirconia FDPs were produced by three different manufacturing technologies, representing additive (one stereolithography [aSLA] and one material jetting [aMJ] device, two digital light processing [aDLP1/aDLP2] devices) and subtractive manufacturing (two devices [s1/s2]), the latter serving as references. After printing, additively manufactured FDPs were debound and finally sintered. Subsequently, samples were circumferentially digitized and acquired surface areas were split in three Regions Of Interest (ROIs: inner/outer shell, margin). Design and acquired data were compared for accuracy using an inspection software. Statistical evaluation was performed using the root mean square error (RMSE) and nonparametric Kruskal-Wallis method with post hoc Wilcoxon-Mann-Whitney U tests. Bonferroni correction was applied in case of multiple testing.ResultsRegardless the ROI, significant differences were observed between manufacturing technologies (P < 0.001). Subtractive manufacturing was the most accurate with no significant difference regarding the material/device (s1/s2, P > 0.054). Likewise, no statistical difference regarding accurary was found when comparing s2 with aMJ and aSLA in most ROIs (P > 0.085). In general, mean surface deviation was< 50 µm for s1/s2 and aMJ and< 100 µm for aSLA and aDLP2. aDLP1 showed surface deviations> 100 µm and was the least accurate compared to the other additive/subtractive technologies.SignificanceAdditive manufacturing represents a promising set of technologies for the manufacturing of zirconia FDPs, but not yet as accurate as subtractive manufacturing. Methodological impact on accuracy within and in between different additive technologies needs to be further investigated.     

Rinsing postprocessing procedure of a 3D-printed orthodontic appliance material: Impact of alternative post-rinsing solutions on the roughness,flexural strength and cytotoxicity

ObjectiveThe present study evaluated the effect of different rinsing postprocessing solutions on surface characteristics, flexural strength, and cytotoxicity of an additive manufactured polymer for orthodontic appliances. These solutions have been deemed an alternative to the standard isopropanol which is a flammable liquid, known to have toxic effects.MethodsTested specimens were manufactured using direct light processing of an orthodontic appliance polymer (FREEPRINT® splint 2.0, Detax) and post-processed with different post-rinsing solutions, including isopropanol (IPA), ethanol (EtOH), EASY 3D Cleaner (EYC), Yellow Magic7 (YM7), and RESINAWAY (RAY), respectively. All groups were post-cured following the manufacturer’s instructions. Surface topography and roughness (Ra and Rv) were evaluated. In addition, flexural strength was measured by a three-point bending test. An extract test was performed to evaluate cytotoxicity. The data were analyzed by the Kruskal-Wallis test with Dunn's multiple comparisons test (p < 0.05).ResultsVarious post-rinsing solutions did not significantly affect the roughness values (Ra and Rv). Specimens post-processed with EtOH (98.1 ± 12.4 MPa) and EYC (101.1 ± 6.3 MPa) exhibited significantly lower flexural strength compared to the groups of IPA (110.7 ± 5.3 MPa), RAY (112.1 ± 5.6 MPa) and YM7 (117.3 ± 5.9 MPa), respectively. Finally, there were no cytotoxic effects of parts cleaned with different post-rinsing solutions.SignificanceConsidering the use of 3D-printed orthodontic appliance materials, different rinsing postprocessing procedures did not affect surface characteristics. However, the flexural strength was significantly influenced, which could be attributed to the chemical ingredients of the post-rinsing solutions. Various post-rinsing treatments had no alternation concerning cytocompatibility.