Mechanics of shape distortion of DLP 3D printed structures during UV post-curing

Comparison of accuracy in internal, marginal, and external regions of ceramic copings fabricated via milling, DLP printing, and heat-pressing methods

OBJECTIVE

The present study aimed to evaluate the accuracy of ceramic copings fabricated by milling, DLP printing, and heat-pressing methods.

METHODS

A central maxillary incisor coping was designed after scanning a typodont model. Thirty specimens were fabricated using milling (MCC), DLP printing (PCC), and heat-pressing methods (HCC) (n = 10 per group). All the specimens were scanned with a lab scanner. The scanned data were segmented into external, internal, and marginal regions and analyzed using 3D measurement software. The accuracy of each group was evaluated and Root mean square (RMS) deviations were calculated. For statistical analysis of the measurements, the Kolmogorov-Smirnov test was conducted to assess the normality and homogeneity of variance among the three groups and the results. As equal variances were not observed (p < 0.05), a nonparametric Kruskal-Wallis test was conducted, followed by post-hoc analysis using the Bonferroni-adjusted Mann - Whitney U test (α = 0.016).

RESULTS

The MCC group recorded RMS values of 14.29 ± 1.80 µm and 15.80 ± 2.36 µm in the internal and marginal regions, respectively, with lower deviation (p < 0.001). The PCC group showed the highest RMS in the internal region at 39.43 ± 4.59 µm (p = 0.684). The HCC group's RMS value was highest in the external region at 55.53 ± 5.71 µm (p < 0.001). Statistical analyses indicated significant differences in RMS values in external and internal regions but not in the marginal region (p = 0.143). All the RMS values remained within the clinically acceptable range.

CONCLUSION

This study confirmed that different fabrication techniques significantly influence the dimensional accuracy of ceramic copings. The MCC group showed lower RMS values whereas the PCC and HCC groups exhibited higher RMS values. However, all RMS values remained within the clinically acceptable range.

CLINICAL SIGNIFICANCE

This study assessed the trueness and precision of ceramic copings made by different fabrication methods. The MCC group exhibited the greatest precision in both the internal and marginal regions. In contrast, the PCC group, while requiring additional research and validation in marginal areas, displayed enhanced accuracy and reproducibility in the external region compared to the HCC group.

Sericin from Bombyx Mori as a By-product for DLP 3D Printing in Pharmaceutical and Biomedical Applications

Sericin, a silk-derived protein, has emerged as a potential material for Digital Light Processing (DLP) printing, particularly in uses requiring biocompatibility and sustainability. Sericin is a candidate for developing durable and precise 3D-printed structures due to its natural origin and intrinsic properties like film-forming ability and cross-linking potential. Its biocompatibility makes it suitable for medical applications, such as targeted delivery of anticancer drugs or creation of therapeutic supports directly on affected skin, orthodontic and cosmetic biomaterials, disease modulation, wound healing, antioxidant and antimicrobial applications, and regenerative medicine. Additionally, sericin can strengthen and stabilize printed structures while maintaining environmental integrity, aligning with the growing demand for eco-friendly materials in advanced manufacturing. However, formulating sericin-based resins for DLP printing presents challenges, including optimizing cross-linking and curing processes for obtaining desired properties of material. Overcoming these challenges could unlock the full potential of sericin in diverse fields, such as tissue engineering, where biocompatibility and precise structural integrity are critical. This review investigates the potential of sericin-based resins for 3D printing, emphasizing the protein's compatibility with photopolymerizable systems and its capacity to improve the overall performance of DLP-printed materials. Further research is essential to refine sericin-based formulations, enabling their broader application in 3D printing technologies. By examining the unique characteristics of sericin, including its origins and material properties, this review underscores the protein's potential to drive innovation in sustainable manufacturing. Ultimately, sericin offers a viable alternative to synthetic resins and holds promise for advancing both biomedical and environmental applications through innovative 3D printing technologies.

Impact of 3D resin and base designs on the accuracy of additively manufactured casts using a stereolithography technology

STATEMENT OF PROBLEM

Three-dimensional (3D) printed casts can be fabricated using a wide range of 3D polymer resins and designed with varying casts´ base configurations. Nevertheless, the influence of different base designs, in conjunction with various 3D printing resins, on the final dimensional accuracy of casts manufactured through SLA-LCD 3D printing technology remains unclear.

PURPOSE

This study assessed the impact of 3D printing resins and base designs on the dimensional accuracy of diagnostic casts fabricated using a SLA-LCD vat-polymerization 3D printer. Two resins (NextDent Model 2.0 and Aqua Gray 4K) and 5 different base configurations were evaluated for their effect on trueness and precision.

MATERIAL AND METHODS

A digital maxillary cast was modified into three base designs: solid (Group S), honeycomb (Group HC), and hollow (Group H). Honeycomb and hollow designs had subgroups with 1-mm (HC1, H1) and 2-mm (HC2, H2) wall thicknesses, resulting in 50 specimens (n=10 per subgroup). Eleven embedded precision cubes were used for accuracy assessment. A Sonic Mini 4K vat-polymerization printer was used for cast printing, and dimensional deviations were captured using a coordinate measuring device. Trueness was defined by the average dimensional discrepancy, and precision was indicated by the standard deviation. Statistical analysis included Kruskal-Wallis and Mann-Whitney U tests (α=.05).

RESULTS

NextDent resin showed trueness falling between 44.8 5 µm and 64.5 µm and precision values varying between 33.5 5 µm and 48.9 µm, while Aqua Gray 4K resin ranged from 24.1 5 µm to 81.1 µm for trueness and 19.8 5 µm to 65.9 µm for precision. Significant differences (P<.001) were observed in all axes (x-, y-, z-axes) and 3D deviations, influenced by resin and base design.

CONCLUSIONS

Resin type and base design significantly affect the dimensional accuracy of 3D printed casts. Aqua Gray 4K with a 2-mm hollow base provided the highest accuracy, particularly when matched with the printer manufacturer. All casts met clinical standards.

Influence of the print orientation and cast thickness on the accuracy of DLP master casts for fixed dental prostheses

BACKGROUND

This study aimed to evaluate the influence of different print orientations and external shell thickness on the accuracy of master casts printed with direct light processing (DLP) technology for fixed dental prostheses.

METHODS

Seventy-two maxillary hollow master casts were printed with a DLP printer from a standard tessellation language (STL) reference file with dental preparations for a single crown and a 3-unit fixed partial denture. Study groups consisted of six groups (n = 12) according to the print orientation (0, 10, and 20 degrees) and the external shell thickness of the cast (2 mm and 4 mm). Each specimen was digitized with a laboratory scanner. Discrepancies between the reference STL and the experimental STL of the printed cast were measured by using the root mean square (RMS) error. Data were statistically analyzed using one-way ANOVA and Tukey's HDS test to evaluate the trueness, and precision was assessed using the Levene test (α = 0.05).

RESULTS

No significant differences were found in the overall trueness and precision between the groups analyzed for the print orientation and the shell thickness. The 2-mm external shell thickness demonstrated the best trueness on selected points.

CONCLUSIONS

The print orientation in the range of 0 to 20 degrees and the cast thickness did not influence the overall accuracy of DLP-printed master casts for fixed prostheses with clinically acceptable range values. Trueness was affected by the external shell thickness on selected points.

Are There Clinical Differences Between 3D-Printed and Milled Complete Dentures? A Systematic Review and Meta-analysis

Limited studies assess clinical key factors in the success of digitally fabricated complete dentures between additive and subtractive methods. This study aimed to compare 2 determinants of clinical success-retention and patient satisfaction- in complete dentures fabricated using additive and subtractive approaches. PubMed, Scopus, Web of Science, Embase, Cochrane Library, and Google Scholar were searched up to August 2024. Records were screened by title, abstract, and full text against the eligibility criteria. The standardized mean difference (SMD) was calculated using the data extracted from each included study. A random effects model pooled the effect sizes, and heterogeneity was assessed with Cochran's Q test, I-squared, and Tau-squared indices; publication bias was evaluated using Begg's funnel plot and the Egger test, while sensitivity analyses checked result robustness. The risk of bias was assessed using the Cochrane RoB 2 and ROBINS-I tools. Of the initial 1098 records, a total of 4 articles were deemed eligible. Although mean denture retention was higher in the additive compared to the subtractive method, the difference was not statistically significant (SMD = 0.165 N, 95% CI = [-0.176, 0.506], P = .343, I² = 58.72%). Similarly, mean satisfaction was lower in the additive compared to the subtractive method, but this difference was not statistically significant (SMD = -0.595, 95% CI = [-1.579, 0.389], P = .236, I² = 85.94%). Considering the high heterogeneity and the small number of studies, it can be cautiously concluded that there is no significant difference between complete dentures fabricated by 3D printing and milling approaches.

Aging and post-polymerization effects on conversion degree and properties of additive splint materials

The study objective was to analyze dimensional change, flexural strength, surface hardness, wear profile, and conversion degree of different additive splint materials under various post-polymerization conditions of time and artificial aging. Two additive manufacturing systems (Cara Print 4.0, Dima Print Ortho, Kulzer; SprintRay Pro, SprintRay Splint, SprintRay), and a thermally activated resin control (Clássico) were evaluated in artificial aging (deionized water or saliva; 28 or 84 days at 37°C), with recommended or doubled post-polymerization cycles. Dimensional change (surface metrology), flexural strength (ISO 20795-1:2013), fractography (SEM), Knoop hardness, two-body wear profilometry (150,000 cycles; 3mmØ; 20N; 2.1Hz), and conversion degree (FTIR spectroscopy) were assessed. Two-way ANOVA and post-hoc Tukey tests were used for parametric data, and Kruskal-Wallis and post-hoc Dunn tests, for non-parametric data (α = 0.05). Results indicated no statistically significant differences in dimensional change or flexural strength among the materials. Recommended post-polymerization cycles resulted in lower hardness for additive resins than the thermally activated control. Doubling post-polymerization time significantly increased flexural strength and hardness of Dima Print Ortho, but decreased flexural strength of SprintRay Splint, and did not affect wear resistance. Dima Print Ortho demonstrated the highest wear resistance. Artificial aging did not affect flexural strength, surface wear, or dimensional change, but negatively impacted the hardness of all materials except Dima Print Ortho. The conversion degree was unaffected by post-polymerization time, and no significant differences were found among the materials. Overall, additive materials exhibited mechanical and dimensional properties comparable to thermally activated resin, with doubling post-polymerization time positively influencing the properties.

Influence of print orientation on the accuracy (trueness and precision) of diagnostic casts manufactured with a daylight polymer printer

STATEMENT OF PROBLEM

Print orientation may affect the manufacturing accuracy of vat-polymerized diagnostic casts. However, its influence should be analyzed based on the manufacturing trinomial (technology, printer, and material) and printing protocol used to manufacture the casts.

PURPOSE

The purpose of this in vitro study was to measure the influence of different print orientations on the manufacturing accuracy of vat-polymerized polymer diagnostic casts.

MATERIAL AND METHODS

A standard tessellation language (STL) reference file containing a maxillary virtual cast was used to manufacture all specimens using a vat-polymerization daylight polymer printer (Photon mono SE. LCD 2K) and a model resin (Phrozen Aqua Gray 4K). All specimens were manufactured using the same printing parameters, except for print orientation. Five groups were created depending on the print orientation: 0, 22.5, 45, 67.5, and 90 degrees (n=10). Each specimen was digitized using a desktop scanner. The discrepancy between the reference file and each of the digitized printed casts was measured using the Euclidean measurements and root mean square (RMS) error (Geomagic Wrap v.2017). Independent (unpaired) sample t tests and multiple pairwise comparisons using the Bonferroni test were used to analyze the trueness of the Euclidean distances and RMS data. Precision was assessed using the Levene test (α=.05).

RESULTS

In terms of Euclidean measurements, significant differences in trueness and precision values were found among the groups tested (P<.001). The 22.5- and 45-degree groups resulted in the best trueness values, and the 67.5-degree group had the lowest trueness value. The 0- and 90-degree groups led to the best precision values, while the 22.5-, 45-, and 67.5-degree groups showed the lowest precision values. Analyzing the RMS error calculations, significant differences in trueness and precision values were found among the groups tested (P<.001). The 22.5-degree group had the best trueness value, and the 90-degree group resulted in the lowest trueness value among the groups. The 67.5-degree group led to the best precision value, and the 90-degree group to the lowest precision value among the groups.

CONCLUSIONS

Print orientation influenced the accuracy of diagnostic casts fabricated by using the selected printer and material. However, all specimens had clinically acceptable manufacturing accuracy ranging between 92 μm and 131 μm.

Comparison of shock absorption capacities of three types of mouthguards: A comparative in vitro study

BACKGROUND/AIM

3D printing processes can be used to manufacture custom-made mouthguards for sports activities. Few studies have compared the impact performance of industrial-created mouthguards with that of custom-made mouthguards manufactured by thermoforming or 3D printing. The objective of this in vitro study was to compare the shock absorption capacities of custom-made mouthguards manufactured by 3D printing with industrial mouthguards and thermoformed ethylene vinyl acetate (EVA) mouthguards.

MATERIALS AND METHODS

For each type of mouthguard, eight samples were produced. 3D-printed mouthguards were manufactured using digital light processing technology. Each mouthguard was subjected to an impact performance test defined by the standard AFNOR XP S72-427, which evaluate maximum deceleration and force transmitted during impact. The thickness of each mouthguard before and after a series of five impacts was measured at the impacted inter-incisal area.

RESULTS

The mean maximum decelerations during impact ranged from 129 to 189 g for industrial mouthguards, 287 to 425 g for thermoformed EVA mouthguards, and 277 to 302 g for 3D-printed mouthguards. The mean reduction in mouthguard thickness at the impact zone after five tests was 1.2 mm for industrial mouthguards, 0.6 mm for 3D-printed mouthguards, and 2.2 mm for thermoformed EVA mouthguards.

CONCLUSIONS

Custom-made 3D printed mouthguards showed slightly better shock absorption ability than thermoformed mouthguards with respect to the indicator proposed in XP S72-427. They seemed to combine the practical advantages of thermoformed mouthguards in sports with better shock absorption capacity and lower cost. Furthermore, they had the least thickness variation during the test, and their shock absorption capacity was the least affected by repeated mechanical tests. Other types of 3D-printing resin materials that will become available must continue to be tested for shock absorption to provide the best protection to users at low cost.

Effects of Post-Processing Parameters on 3D-Printed Dental Appliances: A Review

In recent years, additive manufacturing (AM) has been recognized as a transformative force in the dental industry, with the ability to address escalating demand, expedite production timelines, and reduce labor-intensive processes. Despite the proliferation of three-dimensional printing technologies in dentistry, the absence of well-established post-processing protocols has posed formidable challenges. This comprehensive review paper underscores the critical importance of precision in post-processing techniques for ensuring the acquisition of vital properties, encompassing mechanical strength, biocompatibility, dimensional accuracy, durability, stability, and aesthetic refinement in 3D-printed dental devices. Given that digital light processing (DLP) is the predominant 3D printing technology in dentistry, the main post-processing techniques and effects discussed in this review primarily apply to DLP printing. The four sequential stages of post-processing support removal, washing, secondary polymerization, and surface treatments are systematically navigated, with each phase requiring meticulous evaluation and parameter determination to attain optimal outcomes. From the careful selection of support removal tools to the consideration of solvent choice, washing methodology, and post-curing parameters, this review provides a comprehensive guide for practitioners and researchers. Additionally, the customization of post-processing approaches to suit the distinct characteristics of different resin materials is highlighted. A comprehensive understanding of post-processing techniques is offered, setting the stage for informed decision-making and guiding future research endeavors in the realm of dental additive manufacturing.

Evaluation of industrial and consumer 3-D resin printer fabrication of microdevices for quality management of genetic resources in aquatic species

Aquatic germplasm repositories can play a pivotal role in securing the genetic diversity of natural populations and agriculturally important aquatic species. However, existing technologies for repository development and operation face challenges in terms of accuracy, precision, efficiency, and cost-effectiveness, especially for microdevices used in gamete quality evaluation. Quality management is critical throughout genetic resource protection processes from sample collection to final usage. In this study, we examined the potential of using three-dimensional (3-D) stereolithography resin printing to address these challenges and evaluated the overall capabilities and limitations of a representative industrial 3-D resin printer with a price of US$18,000, a consumer-level printer with a price Collapse

Key Words

• 3-D resin printing
• Aquaculture industry
• Aquatic species
• Genetic resources
• Germplasm repository
• Photolithography
• Soft lithography

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MESH Headings Collapse

Grants

• R24 OD028443 NIH HHS
• R24 OD034058 NIH HHS

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Affiliation(s)

Seyedmajid Hosseini Department of Electrical & Computer Engineering, Louisiana State University, Baton Rouge, LA, USA
Jack C. Koch Aquatic Germplasm and Genetic Resources Center, School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, LA, USA
Yue Liu Aquatic Germplasm and Genetic Resources Center, School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, LA, USA
Ignatius Semmes Department of Biological & Agricultural Engineering, Louisiana State University and Louisiana State University Agricultural Center, Baton Rouge, LA, USA
Isabelina Nahmens Department of Mechanical & Industrial Engineering, Louisiana State University, Baton Rouge, LA, USA
W. Todd Monroe Department of Biological & Agricultural Engineering, Louisiana State University and Louisiana State University Agricultural Center, Baton Rouge, LA, USA
Jian Xu Department of Electrical & Computer Engineering, Louisiana State University, Baton Rouge, LA, USA
Terrence R. Tiersch Aquatic Germplasm and Genetic Resources Center, School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, LA, USA

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Impact of postpolymerization devices and locations on the color, translucency, and mechanical properties of 3D printed interim resin materials

STATEMENT OF PROBLEM

How postpolymerization conditions affect the color and mechanical properties of 3-dimensional (3D)-printed prostheses is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the color, microhardness, and flexural strength of 3D printed interim resin materials and to assess the effect of postpolymerization devices, polymerizing locations, and thermocycling on those properties.

MATERIAL AND METHODS

A total of 270 disk-shaped specimens and 180 bar-shaped specimens were designed and 3D printed with interim resin material (NextDent C&B). The specimens were postpolymerized in 1 of 3 devices (Group ND; NextDent, Group CR; Carima, and Group FL; Formlabs). Each group was divided into 3 circular zones of the polymerizing plate (central, medial, and lateral). Half of the specimens were subjected to 10 000 thermocycles. Color measurement, Vickers microhardness test, and 3-point flexural strength test were performed. Data were statistically analyzed by using the Kruskal-Wallis and Mann-Whitney tests (α=.05).

RESULTS

The L∗a∗b∗ color coordinates exhibited significant differences among the 3 zones (P<.05). The color and translucency differences according to CIELab and CIEDE among the zones exceeded the clinically perceptible levels in group CR. ΔE and ΔTP between with and without thermocycling were significantly different among the devices (P<.05). Microhardness and flexural strength were significantly different among the zones for those affected by thermocycling (P<.05).

CONCLUSIONS

Different locations in postpolymerization devices influenced the color, translucency, and mechanical properties of 3D printed interim resin materials. Thermocycling induced color and translucency changes and the mechanical weakening of postpolymerized resins, and the impact differed according to the device type.

Influence of base designs on the manufacturing accuracy of vat-polymerized diagnostic casts using two different technologies

STATEMENT OF PROBLEM

Diagnostic casts can incorporate different base designs and be manufactured using different vat-polymerization technologies. However, the influence of the interrelation between the base design and the 3D printing technology on the casts' final accuracy remains unclear.

PURPOSE

The purpose of this in vitro study was to assess the influence of different base designs of 3D printed casts on the accuracy of 2 vat-polymerization technologies.

MATERIAL AND METHODS

A digital maxillary cast was obtained and used to generate 3 different base designs: solid (S group), honeycombed (HC group), and hollow (H group). The HC and H groups were subdivided based on the wall thickness of the cast design, resulting in 2 subgroups with thicknesses of 1 mm (HC1 and H1) and 2 mm (HC2 and H2) (N=100, n=10). Eleven reference cubes were added to each specimen for subsequent measurements. Specimens were manufactured by using 2 vat-polymerization 3D printers: Nextdent 5100 (ND group) and Sonic Mini 4K (SM4K group) and a resin material suitable for both 3D printers (Nextdent Model 2.0). A coordinate measuring machine quantified the linear and 3-dimensional discrepancies between the digital cast and each reference specimen. Trueness was defined as the average absolute dimensional discrepancy between the virtual cast and the specimens produced through additive manufacturing (AM), while precision was delineated as the standard deviation in dimensional discrepancies between the digital cast and the AM specimens. The data were analyzed using the Kruskal-Wallis and Mann-Whitney U pairwise comparison tests (α=.05).

RESULTS

For the NextDent group the trueness ranged from 21.83 µm to 28.35 µm, and the precision ranged from 17.82 µm to 37.70 µm. For the Phrozen group, the trueness ranged from 45.15 µm to 64.51 µm, and the precision ranged from 33.51 µm to 48.92 µm. The Kruskal-Wallis test showed significant differences on the x-, y-, and z-axes and in the 3D discrepancy (all P<.001). On the x-axis, the Mann-Whitney U test showed significant differences for the Phrozen group between the H-2 and H-1 groups (P=.001), H-2 and S groups (P<.001), and HC-2 and S groups (P=.012). On the y-axis, significant differences were found in the Phrozen group between the H-2 and H-1 groups (P=.001), the H-2 and S, H-1 and HC-1, and HC-1 and S groups (P<.001), the H-1 and HC-2 groups (P=.007), and the HC-2 and S groups (P=.009). The NextDent group exhibited significant differences, particularly among the HC-1 and H-2 groups (P=.004), H-1 (P=.020), and HC-2 (P=.001) groups; and on the z-axis significant differences were found in the Phrozen group between the H-2 and H-1 and S groups and the HC-2 group and H-1 and S groups (both P<.001). In the NextDent group, significant differences were found between the H-2 and HC-2 (P=.047) and HC-1 (P=.028) groups. For the 3D discrepancy analysis, significant differences were found in the Phrozen group between the H-2 and H-1 and S groups (P<.001), the H-1 and HC-2 groups (P=.001), the S and HC-1 and HC-2 groups (P<.001), and the H-1 and HC-1 groups (P=.002). In the NextDent group, significant differences were observed between the H-2 and HC-1 groups (P=.012).

CONCLUSIONS

The accuracy of digital casts depends on the manufacturing trinomial and base design of the casts. The honeycomb and hollow based designs provided the highest accuracy in the NextDent and Phrozen groups respectively for the material polymer tested. All specimens fell in the clinically acceptable range.

An organotypic model of oral mucosa cells for the biological assessment of 3D printed resins for interim restorations

STATEMENT OF PROBLEM

Three-dimensionally (3D) printed resins have become popular as a new class of materials for making interim restorations. However, little is known about how the fabrication parameters can influence biological compatibility with oral tissues.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of the postpolymerization time on the cytotoxicity of resins for printing interim restorations by using a 3D organotypic model of the oral mucosa.

MATERIAL AND METHODS

Cylindrical specimens were prepared with conventional acrylic resin (AR), computer-aided design and computer-aided manufacture (CAD-CAM) resin (CC), composite resin (CR), and 2 resins for 3D printing (3DP) marketed as being biocompatible. The 3DPs were submitted to postpolymerization in an ultraviolet (UV) light chamber for 1, 10, or 20 minutes (90 W, 405 nm). Standard specimens of the materials were incubated for 1, 3, and 7 days in close contact with an organotypic model of keratinocytes (NOK-Si) in coculture with gingival fibroblasts (HGF) in a 3D collagen matrix, or directly with 3D HGF cultures. Then, the viability (Live/Dead n=2) and metabolism (Alamar Blue n=6) of the cells were assessed. Spectral scanning of the culture medium was performed to detect released components (n=6) and assessed statistically with ANOVA and the Tukey post hoc test (α=.05).

RESULTS

Severe reduction of metabolism (>70%) and viability of keratinocytes occurred for 3DP resin postpolymerized for 1 minute in all periods of analysis in a time-dependent manner. The decrease in cell metabolism and viability was moderate for the 3D culture of HGFs in both experimental models, correlated with the intense presence of resin components in the culture medium. The resins postpolymerized for 10 and 20 minutes promoted a mild-moderate cytotoxic effect in the period of 1 day, similar to AR. However, recovery of cell viability occurred at the 7-day incubation period. The 3DP resins submitted to postpolymerization for 20 minutes showed a pattern similar to that of CR and CC at the end of the experiment.

CONCLUSIONS

The cytotoxic potential of the tested 3DP resins on oral mucosa cells was influenced by postprinting processing, which seemed to have been related with the quantity of residual components leached.

The three-dimensional stability and accuracy of 3D printing surgical templates: An In Vitro study

OBJECTIVE

To evaluate the three-dimensional (3D) stability and accuracy of additively manufactured surgical templates fabricated using two different 3D printers and materials.

MATERIALS AND METHODS

Forty surgical templates were designed and printed using two different 3D printers: the resin group (n = 20) used a digital light processing (DLP) 3D printer with photopolymer resin, and the metal group (n = 20) employed a selective laser melting (SLM) 3D printer with titanium alloy. All surgical templates were scanned immediately after production and re-digitalized after one month of storage. Similarly, the implant simulations were performed twice. Three-dimensional congruency between the original design and the manufactured surgical templates was quantified using the root mean square (RMS), and the definitive and planned implant positions were determined and compared.

RESULTS

At the postproduction stage, the metal templates exhibited higher accuracy than the resin templates (p < 0.001), and these differences persisted after one month of storage (p < 0.001). The resin templates demonstrated a significant decrease in three-dimensional stability after one month of storage (p < 0.001), whereas the metal templates were not affected (p > 0.05). No significant differences in implant accuracy were found between the two groups. However, the resin templates showed a significant increase in apical and angular deviations after one month of storage (p < 0.001), whereas the metal templates were not affected (p > 0.05).

CONCLUSION

Printed metal templates showed higher fabrication accuracy than printed resin templates. The three-dimensional stability and implant accuracy of printed metal templates remained unaffected by one month of storage.

CLINICAL SIGNIFICANCE

With superior three-dimensional stability and acceptable implant accuracy, printed metal templates can be considered a viable alternative technique for guided surgery.

Effects of solvent type and UV post-cure time on 3D-printed restorative polymers

OBJECTIVES

This study evaluated the impact of different solvents and UV post-curing times on properties of 3D printing resins for provisional restorations.

METHODS

The post-processing methods were tested using two solvents (isopropyl alcohol or absolute ethanol) and three UV times (5, 10, or 30 min). The resins tested were Resilab 3D Temp, Printax Temp, and Prizma Bioprov. Microhardness (kgf/mm2), fracture toughness (KIC, MPa√m), surface roughness (Ra, µm), gloss (gloss units), and degree of CC conversion (%DC) were measured (n = 8). All response variables were collected from the same specimen. The specimens were 3D printed using an SLA/LCD printer (150° angulation, 50 µm layer thickness). Light exposure times were adjusted for each material, and the post-processing methods were applied using an all-in-one machine immediately after printing. Data were analyzed using Three-Way ANOVA (α = 0.05).

RESULTS

Microhardness was affected by UV post-cure time and 3D resin. Resilab showed higher microhardness with isopropyl alcohol and 30-min UV time, while Printax had higher microhardness with absolute ethanol. KIC was influenced by solvent type, UV time, and 3D resin, with varying effects on different resins. Roughness was affected by 3D resin and UV time, but no significant differences were seen for Resilab or Prizma. Gloss was influenced by 3D resin, and for Prizma, it was lower with specific solvent/UV time combinations. DC was influenced by 3D resin, with each resin behaving differently.

SIGNIFICANCE

Tailoring the combination of 3D resin, solvent washing type, and UV post-curing time is important to achieve optimal mechanical and aesthetic outcomes for restorations.

Comparison of surface roughness of additively manufactured implant-supported interim crowns fabricated with different print orientations

PURPOSE

To assess the influence of print orientation on the surface roughness of implant-supported interim crowns manufactured by using digital light processing (DLP) 3D printing procedures.

MATERIALS AND METHODS

An implant-supported maxillary right premolar full-contour crown was obtained. The interim restoration design was used to fabricate 30 specimens with 3 print orientations (0, 45, and 90 degrees) using an interim resin material (GC Temp PRINT) and a DLP printer (Asiga MAX UV) (n = 10). The specimens were manufactured, and each was cemented to an implant abutment with autopolymerizing composite resin cement (Multilink Hybrid Abutment). Surface roughness was assessed on the buccal surface of the premolar specimen by using an optical measurement system (InfiniteFocusG5 plus). The data were analyzed with a Shapiro-Wilk test, resulting in a normal distribution. One-way ANOVA and the Tukey HSD tests were selected (α = 0.05).

RESULTS

Statistically significant discrepancies were found in the surface roughness mean values among the groups tested (p < 0.001). The lowest mean ± standard deviation surface roughness was found with the 90-degree group (1.2 ± 0.36 μm), followed by the 0-degree orientation (2.23 ± 0.18 μm) and the 45-degree group (3.18 ± 0.31 μm).

CONCLUSIONS

Print orientation parameter significantly impacted the surface roughness of the implant-supported interim crowns manufactured by using the additive procedures tested.

Effects of postpolymerization time and temperature on the flexural properties and hardness profile of three-dimensional printed provisional resin

Background/purpose

Three-dimensional (3D) printing technique was widely used for provisional restorations in clinical use. However, the effects of post-polymerization temperature and time on the flexural properties and hardness profile were not fully elucidated yet. The purpose of this study is to investigate the effects of post-polymerization temperature and time on the flexural properties and hardness profile of the provisional restoration.

Materials and methods

3D-printing provisional resin was printed and post-polymerized at various temperatures (room temperature, 40 °C, 60 °C and 80 °C) and periods (0, 15, 30, 60, 90 and 120 min of photopolymerization). Afterwards, the flexural strength, flexural modulus, surface hardness, and internal hardness at different depth were evaluated.

Results

The group post-polymerized without concurrent heating had significantly shallow depth of cure comparing to the heating counterparts. The surface hardness of the groups post-polymerized at different temperatures did not show any difference. All groups with post-polymerization temperature at 40 °C, 60 °C and 80 °C and post-polymerization time ranged between 15 and 90 min, had curing depth between 3 and 4 mm. Group post-polymerized without concurrent heating has significantly shallow depth of cure comparing to the heating counterparts.

Conclusion

Post-polymerization at an elevated temperature, preferably 60 °C, is suggested. The wall thickness of the 3D-printing provisional prosthesis thinner than 3-4 mm is recommended.

Polyurethane Acrylate Oligomer (PUA) Microspheres Prepared Using the Pickering Method for Reinforcing the Mechanical and Thermal Properties of 3D Printing Resin

Some photosensitive resins have poor mechanical properties after 3D printing. To overcome these limitations, a polyurethane acrylate oligomer (PUA) microsphere was prepared using the Pickering emulsion template method and ultraviolet (UV) curing technology in this paper. The prepared PUA microspheres were added to PUA-1,6-hexanediol diacrylate (HDDA) photosensitive resin system for digital light processing (DLP) 3D printing technology. The preparation process of PUA microspheres was discussed based on micromorphology, and it was found that the oil-water ratio of the Pickering emulsion and the emulsification speed had a certain effect on the microsphere size. As the oil-water ratio and the emulsification speed increased, the microsphere particle size decreased to a certain extent. Adding a suitable proportion of PUA microspheres to the photosensitive resin can improve the mechanical properties and thermal stability. When the modified photosensitive resin microsphere content was 0.5%, the tensile strength, elongation at break, bending strength, and initial thermal decomposition temperature were increased by 79.14%, 47.26%, 26.69%, and 10.65%, respectively, compared with the unmodified photosensitive resin. This study provides a new way to improve the mechanical properties of photosensitive resin 3D printing. The resin materials studied in this work have potential application value in the fields of ceramic 3D printing and dental temporary replacement materials.

Simple Non-Equilibrium Atmospheric Plasma Post-Treatment Strategy for Surface Coating of Digital Light Processed 3D-Printed Vanillin-Based Schiff-Base Thermosets

A simple non-equilibrium atmospheric plasma post-treatment strategy was developed for the surface coating of three-dimensional (3D) structures produced by digital light processing 3D printing. The influence of non-equilibrium atmospheric plasma on the chemical and physical properties of vanillin-derived Schiff-base thermosets and the dip-coating process was investigated and compared to the influence of traditional post-treatment with UV-light. As a comparison, thermosets without post-treatment were also subjected to the coating procedure. The results document that UV post-treatment can induce the completion of the curing of the printed thermosets if complete curing is not reached during printing. Conversely, the plasma post-treatment does not contribute to the curing of the thermoset but causes some opening of the imine bonds and the regeneration of aldehyde functions. As a consequence, no great differences are observed between the not post-treated and plasma post-treated samples in terms of mechanical, thermal, and solvent-resistant properties. In contrast to the UV post-treatment, the plasma post-treatment of the thermosets induces a noticeable increase of the thermoset hydrophilicity ascribed to the reformation of amines on the thermoset surface. The successful coating process and the greatest uniformity of the lignosulfonate coating on the surface of plasma post-treated samples are considered to be due to the presence of these amines and aldehydes. The investigation of the UV shielding properties and antioxidant activities documents the increase of both properties with the increasing amount and uniformity of the formed coating. Interestingly, evident antioxidant properties are also shown by the noncoated thermosets, which are deduced to their chemical structures.

Evaluating the conversion degree of interim restorative materials produced by different 3-dimensional printer technologies

STATEMENT OF PROBLEM

Three-dimensional (3D) printers are a relatively new technology, but the degree of conversion (DC) of the resin specimens produced by using this method is currently unknown. However, the DC of resin interim restorative materials is critical for their biocompatibility and physical properties.

PURPOSE

The purpose of this in vitro study was to evaluate the DC of interim restorative materials produced by using different 3D printer technologies and compare them with conventionally manufactured polymethyl methacrylate.

MATERIAL AND METHODS

Stereolithography, digital light processing, and liquid crystal display 3D printers were used as experimental groups, and a conventional (C) method was used as the control. Five different 3D printers (DWS Systems, Formlabs [FL], Asiga, Mega, and Vega) were included. The 3D printed specimens were designed in a rectangular prism geometry (10×4×2.5 mm) by using a computer-aided design software program (Materialise 3-matic) and printed with a layer thickness of 50 µm in the horizontal direction (n=15). Fourier transform infrared spectroscopy (FT-IR) spectra were measured in 3 steps: the liquid state of the resins, after washing with 99% isopropanol, and after final polymerization. For the C method, FT-IR spectra were assessed in 2 steps: immediately after mixing the liquid and powder and after polymerization. Statistical analysis of the data was performed with 1-way ANOVA followed by the post hoc Tukey honestly significant difference (HSD) test (α=.05).

RESULTS

There was no statistically significant difference in DC values between the 3D printed groups (P>.05). There was a statistically significant difference only between FL and the C in terms of DC (P=.042).

CONCLUSIONS

Three-dimensionally printed interim resin materials found comparable results with those of the C group. The DC was not affected by different 3D printing technologies.

Light scattering in a three-phase photosensitive system via Monte Carlo approach

Digital light processing (DLP)-based additive manufacturing has emerged as a powerful technique for fabricating structures from filled resin systems, in which the light scattering behavior is critical to the dimensional fidelity of the cured part. Recently created low density filled resins that incorporate hollow microspheres introduce a third optically active phase, producing yet more complex scattering and cure behaviours that existing empirical relationships cannot predict. This study simulates light scattering in these systems via Mie theory and a novel Monte Carlo model, providing insight into the relationship between filler volume fraction and cured dimensions, and proposes an inversion parameter for predicting film dimensions. Cured resin geometry dimensions such as cured depth (CD) and cured width (CW) are predicted using the developed model for 10, 30, and 50 vol% hollow glass microsphere filled resin systems. In contrast to standard two-phase models, our three-phase model predicts a positive relationship between cured depths and half-widths and the filler volume fraction, consistent with experimental data. By elucidating the intricacies of light scattering in three-phase systems, this work provides valuable insights for advancing DLP-based additive manufacturing and designing filled resin formulations to achieve the desired cured dimensions.

Rapid Micromolding of Sub-100 µm Microfluidic Channels Using an 8K Stereolithographic Resin 3D Printer

Engineering microfluidic devices relies on the ability to manufacture sub-100 micrometer fluidic channels. Conventional lithographic methods provide high resolution but require costly exposure tools and outsourcing of masks, which extends the turnaround time to several days. The desire to accelerate design/test cycles has motivated the rapid prototyping of microfluidic channels; however, many of these methods (e.g., laser cutters, craft cutters, fused deposition modeling) have feature sizes of several hundred microns or more. In this paper, we describe a 1-day process for fabricating sub-100 µm channels, leveraging a low-cost (USD 600) 8K digital light projection (DLP) 3D resin printer. The soft lithography process includes mold printing, post-treatment, and casting polydimethylsiloxane (PDMS) elastomer. The process can produce microchannels with 44 µm lateral resolution and 25 µm height, posts as small as 400 µm, aspect ratio up to 7, structures with varying z-height, integrated reservoirs for fluidic connections, and a built-in tray for casting. We discuss strategies to obtain reliable structures, prevent mold warpage, facilitate curing and removal of PDMS during molding, and recycle the solvents used in the process. To our knowledge, this is the first low-cost 3D printer that prints extruded structures that can mold sub-100 µm channels, providing a balance between resolution, turnaround time, and cost (~USD 5 for a 2 × 5 × 0.5 cm3 chip) that will be attractive for many microfluidics labs.

Sputtering Plasma Effect on Zinc Oxide Thin Films Produced on Photopolymer Substrates

This work presents a post-cured treatment alternative for photopolymer substrates considering the plasma produced via the sputtering process. The sputtering plasma effect was discussed, analyzing the properties of zinc/zinc oxide (Zn/ZnO) thin films deposited on photopolymer substrates, with and without ultraviolet (UV) treatment as a post-treatment process, after manufacturing. The polymer substrates were produced from a standard Industrial Blend resin and manufactured using stereolithography (SLA) technology. After that, the UV treatment followed the manufacturer's instructions. The influence of the sputtering plasma as an extra treatment during the deposition of the films was analyzed. Characterization was performed to determine the microstructural and adhesion properties of the films. The results showed the effect of plasma as a post-cured treatment alternative: fractures were found in thin films deposited on polymers with previous UV treatment. In the same way, the films showed a repetitive printing pattern due to the phenomenon of polymer shrinkage caused by the sputtering plasma. The plasma treatment also showed an effect on the thicknesses and roughness values of the films. Finally, according to VDI-3198 standards, coatings with acceptable adhesion failures were found. The results provide attractive properties of Zn/ZnO coatings on polymeric substrates produced by additive manufacturing.

Design and Validation of Additively Manufactured Injection Molds

The injection molding process is only economical with large batch sizes due to expensive tools that cannot be used variably. Additively manufactured tools made of plastic could reduce manufacturing costs and represent an alternative to conventionally manufactured tools for prototype applications as well as enabling small series with the injection molding process. The aim of this article was to examine additively manufactured injection molding tools; to determine their potential in terms of service life, surface quality, and production time; and to link them with the production costs so that the profitability can be assessed. Therefore, a reference component and an injection mold have been designed. To test the capabilities of different 3D printing techniques and materials, three molds have been produced by fused filament fabrication (FFF), one by PolyJet process, one by digital light processing, and for a direct comparison to conventional methods, one mold has been milled from aluminum. All molds have been tested in two series. First, they were used under the same conditions over a period of 100 injection molding cycles. Based on the knowledge obtained and an additional profitability analysis, three forms could be identified as promising. Two of these forms could be further investigated in a second series of tests. Based on all experiments, the technical feasibility of additively manufactured injection molds for small batch production could be confirmed. It could be evaluated that each manufacturing process and every material has some advantages and disadvantages. On the one hand, temperature-resistant thermoplastics can be processed with FFF, which can withstand service lives of more than 150 cycles without any signs of wear and are therefore suitable for small series. On the other hand, the PolyJet process achieves good surface qualities and short production times, which means that it can be used for prototype applications.

Accuracy of a dynamic navigation system for dental implantation with two different workflows and intraoral markers compared to static-guided implant surgery: An in-vitro study

PURPOSE

To investigate the accuracy of a miniaturized dynamic navigation system with intraoral markers and two different workflows for dental implantation and to compare with static computer-assisted implant surgery (sCAIS) surgery.

MATERIALS AND METHODS

Two operators performed a total of 270 implant insertions in polyurethane mandibular models under simulated clinical conditions. Implants were placed after CBCT-based virtual planning in three different groups: two workflows utilizing dynamic computer-assisted implant surgery (dCAIS; DG1: marker in CBCT; DG2: 3D-printed marker) and the others with sCAIS (TG: template guided). Postoperative surface scans were matched to the planning data and allowed an evaluation of the angular and spatial deviation between the planned and the actually achieved implant position. Descriptive statistics were followed by a Mixed Model Analysis to determine the influence of the operator, the method, and operating area on different accuracy parameters and the random effect of the model number.

RESULTS

The mean angular deviation ranged from 2.26° (DG1) to 2.96° (TG). The mean 3D deviation at the implant's tip ranged from 1.08 mm (TG) to 1.51 mm (DG2) and at the implant's base from 0.69 mm (TG) to 1.49 mm (DG2). The operator showed no significant influence on the accuracy. The method showed significant influence on singular parameters and the operating area on all spatial accuracy parameters.

CONCLUSIONS

Dynamic navigation systems with intraoral markers enable accurate implant positioning, which is comparable to the static-guided implant surgery. 3D-printed markers provide less accurate results compared to prefabricated markers, attached before CBCT scan.

Additive Manufactured Strain Sensor Using Stereolithography Method with Photopolymer Material

As a result of the developments in additive manufacturing (AM) technology, 3D printing is transforming from a method used only in rapid prototyping to a technique used to produce large-scale equipment. This study presents the fabrication and experimental studies of a 3D-printed strain sensor that can be used directly in soft applications. Photopolymer-based conductive and flexible ultraviolet (UV) resin materials are used in the fabrication of the sensor. A Stereolithography (SLA)-based printer is preferred for 3D fabrication. The bottom base of the sensor, which consists of two parts, is produced from flexible UV resin, while the channels that should be conductive are produced from conductive UV resin. In total, a strain sensor with a thickness of 2 mm was produced. Experimental studies were carried out under loading and unloading conditions to observe the hysteresis effect of the sensor. The results showed a close linear relationship between the strain sensor and the measured resistance value. In addition, tensile test specimens were produced to observe the behavior of conductive and non-conductive materials. The tensile strength values obtained from the test results will provide information about the sensor placement. In addition, the flexible structure of the strain sensor will ensure its usability in many soft applications.

Degree of conversion of 3D printing resins used for splints and orthodontic appliances under different postpolymerization conditions

OBJECTIVES

To measure the degree of conversion (DC) of different 3D printing resins used for splints or orthodontic appliances under different postpolymerization conditions.

MATERIALS AND METHODS

Five 3D-printed photopolymer resins were studied. Each resin was analyzed in liquid form (n = 15), and then cylindrical specimens (n = 135) were additively manufactured and postcured with Form Cure (Formlabs) at different times (10, 60, and 90 min) and temperatures (20 °C, 60 °C, and 80 °C). The DC of each specimen was measured with Fourier transform infrared spectroscopy (FTIR). The data were statistically analyzed using a 3-way ANOVA followed by Tukey's post hoc test.

RESULTS

The time and temperature of postpolymerization significantly influenced the DC of each resin: when time and/or temperature increased, the DC increased. For all resins tested, the lowest DC was obtained with a postcuring protocol at 10 min and 20 °C, and the highest DC was obtained at 90 min and 80 °C. However, at 80 °C, the samples showed a yellowish color.

CONCLUSIONS

With the Form Cure device, the time and temperature of postcuring could have an impact on the DC of the 3D printing resins studied. The DC of the 3D printing resins could be optimized by adjusting the postpolymerization protocol.

CLINICAL RELEVANCE

Regardless of the resin used, when using the Form Cure device, postcuring at 60 min and 60 °C would be the minimal time and temperature conditions for achieving proper polymerization. Beyond that, it would be preferable to increase the postcuring time to boost the DC.

Ink Material Selection and Optical Design Considerations in DLP 3D Printing

Digital light processing (DLP) 3D printing has become a powerful manufacturing tool for the fast fabrication of complex functional structures. The rapid progress in DLP printing has been linked to research on optical design factors and ink selection. This critical review highlights the main challenges in the DLP printing of photopolymerizable inks. The kinetics equations of photopolymerization reaction in a DLP printer are solved, and the dependence of curing depth on the process optical parameters and ink chemical properties are explained. Developments in DLP platform design and ink selection are summarized, and the roles of monomer structure and molecular weight on DLP printing resolution are shown by experimental data. A detailed guideline is presented to help engineers and scientists to select inks and optical parameters for fabricating functional structures for multi-material and 4D printing applications.

Predicting the Printability of Poly(Lactide) Acid Filaments in Fused Deposition Modeling (FDM) Technology: Rheological Measurements and Experimental Evidence

In this work, the authors aimed to identify a potential correlation between the printability and crucial rheological characteristics of materials involved in fused deposition modeling (FDM) technology. In this regard, three different poly(lactide) acid (PLA)-based filaments (two commercially available (here called V-PLA and R-PLA) and one processed in a lab-scale extruder (here called L-PLA)) have been considered. Dynamic rheological testing, in terms of frequency sweep at five different temperatures (130, 150, 170, 190, and 210 °C), was performed. Rheological properties expressed in terms of viscoelastic moduli and complex viscosity curves vs. frequency, characteristic relaxation times, activation energy (Ea), zero shear viscosity (η0) and shear thinning index (n) were derived for each material. A characteristic relaxation time of around 0.243 s was found for V-PLA, a similar value (0.295 s) was calculated for R-PLA filaments, and a lower value of about an order of magnitude was calculated for L-PLA filament (~0.0303 s). The activation energy and shear thinning index resulted to be very comparable for all the filaments. On the contrary, V-PLA and R-PLA possessed a zero-shear viscosity (~104 Pa*s at 170 °C) much higher than L-PLA (~103 Pa*s). All the filaments were processed in a 3D printer, by attesting the effect of nozzle temperature (180, 190, and 210 °C, respectively) on printing process, and macroscopic shaping defects in printed objects. Final considerations allowed us to conclude that polymer relaxation time, zero-shear viscosity, and melt viscosity (affected by printing temperature) were critical parameters affecting the printing quality.

On the Evolution of Additive Manufacturing (3D/4D Printing) Technologies: Materials, Applications, and Challenges

The scientific community is and has constantly been working to innovate and improve the available technologies in our use. In that effort, three-dimensional (3D) printing was developed that can construct 3D objects from a digital file. Three-dimensional printing, also known as additive manufacturing (AM), has seen tremendous growth over the last three decades, and in the last five years, its application has widened significantly. Three-dimensional printing technology has the potential to fill the gaps left by the limitations of the current manufacturing technologies, and it has further become exciting with the addition of a time dimension giving rise to the concept of four-dimensional (4D) printing, which essentially means that the structures created by 4D printing undergo a transformation over time under the influence of internal or external stimuli. The created objects are able to adapt to changing environmental variables such as moisture, temperature, light, pH value, etc. Since their introduction, 3D and 4D printing technologies have extensively been used in the healthcare, aerospace, construction, and fashion industries. Although 3D printing has a highly promising future, there are still a number of challenges that must be solved before the technology can advance. In this paper, we reviewed the recent advances in 3D and 4D printing technologies, the available and potential materials for use, and their current and potential future applications. The current and potential role of 3D printing in the imperative fight against COVID-19 is also discussed. Moreover, the major challenges and developments in overcoming those challenges are addressed. This document provides a cutting-edge review of the materials, applications, and challenges in 3D and 4D printing technologies.

Accuracy of 3D printed models and implant-analog positions according to the implant-analog-holder offset, inner structure, and printing layer thickness: an in-vitro study

PURPOSE

This study aimed to determine how the implant-analog-holder (IAH) offset, inner structure, and printing layer thickness influence the overall accuracy and local implant-analog positional changes of 3D printed dental models.

METHODS

Specimens in 12 experimental groups (8 specimens per group) with different IAH offsets, inner structures, and printing layer thicknesses were printed in three dimensions using an LCD printer (Phrozen Shuffle) and digitized by a laboratory scanner (Identica T500). The trueness and precision of the printed model as well as the angular distortion, depth deviation, and linear distortion of the implant analog were evaluated using three-way ANOVA.

RESULTS

The positional accuracy was significantly higher for IAH offsets of 0.04 mm and 0.06 mm than for one of 0.08 mm, for a hollow than a solid inner structure, and for a printing layer thickness of 100 µm than for one of 50 µm (all P<.001).

CONCLUSIONS

The accuracies of the 3D printed models and the implant-analog positions were significantly affected by the IAH offset, inner structure, and printing layer thickness.

CLINICAL SIGNIFICANCE

Given the observation of this study, premeditating the IAH offset of 0.06 mm, hollow inner structure, and printing layer thickness of 100 µm before printing can help clinicians reach the optimum overall printing accuracy and minimum the local positional changes of the implant-analogs.

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 < .001], storage condition [F(1, 220) = 4.11, P = .044], and storage time F(2, 440) = 10.37, P < .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 < .001) with no significant differences between Type IV stone and LCD 3D-printer groups (P = .577). DLP 3D-printer groups had higher RMS values than both SLA 3D-printer groups and CLIP 3D-printer groups (P < .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 = .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 <.001, than the ones at the immediate post-manufacturing stage. However, the RMS values after 1-month and 3-month storage were not significantly different from each other (P = .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. This article is protected by copyright. All rights reserved.

A printability study of multichannel nerve guidance conduits using projection-based three-dimensional printing

Multichannel nerve guidance conduits (NGCs) replicating the native architecture of peripheral nerves have emerged as promising alternatives to autologous nerve grafts. However, manufacturing multichannel NGCs is challenging in terms of desired structural stability and resolution. In this study, we systematically investigated the effects of photopolymer properties, inner diameter dimensions, printing parameters, and different conditions on multichannel NGCs printability using projection-based three-dimensional printing. Low viscosity and rapid photocuring properties were essential requirements. A standard model was generated to evaluate multichannel NGC printed quality. The results showed that printing deviations decreased with increased mechanical strength and inner diameter. Subsequently, gelatin methacrylate (GelMA) NGCs was selected as a representative. It was found that printing conditions, including printing temperature, peeling, and shrinkage affected final NGC accuracy and quality. PC-12 cells cultured with the GelMA NGCs displayed non-toxic and promoted cell migration. Our research provides an effective, time-saving, and high-resolution technology for manufacturing multichannel NGCs with high fidelity, which may be used as reference templates for biomedical applications.

Microfluidic technology and its application in the point-of-care testing field

Since the outbreak of the coronavirus disease 2019 (COVID-19), countries around the world have suffered heavy losses of life and property. The global pandemic poses a challenge to the global public health system, and public health organizations around the world are actively looking for ways to quickly and efficiently screen for viruses. Point-of-care testing (POCT), as a fast, portable, and instant detection method, is of great significance in infectious disease detection, disease screening, pre-disease prevention, postoperative treatment, and other fields. Microfluidic technology is a comprehensive technology that involves various interdisciplinary disciplines. It is also known as a lab-on-a-chip (LOC), and can concentrate biological and chemical experiments in traditional laboratories on a chip of several square centimeters with high integration. Therefore, microfluidic devices have become the primary implementation platform of POCT technology. POCT devices based on microfluidic technology combine the advantages of both POCT and microfluids, and are expected to shine in the biomedical field. This review introduces microfluidic technology and its applications in combination with other technologies.

Accuracy of Additively Manufactured Dental Casts Compared with That of Virtual Scan Data Obtained with an Intraoral Scanner: An In Vitro Study

The study aimed to evaluate the time-related accuracy of additively manufactured dental casts and to compare it with scan data obtained with an intraoral scanner in vitro. Twenty-eight markers were attached to a set of dentiforms as reference model, and the distances between the markers were measured using a digital caliper. An intraoral scanner was used to obtain the virtual scan data of the reference model with a total of 30 scans per arch. The distances between markers were measured using a three-dimensional inspection software for all scans (group IOS). Scan data were additively manufactured using a 3D printer, and the distances between markers were measured as in the reference model immediately after post-polymerization (group PPIA), 1 day (group PP1D), 7 days (group PP7D), and 30 days after post-polymerization (group PP30D). The linear deviation in group IOS was 199.74 ± 11.14 μm, PPIA was 242.88 ± 49 μm, PP1D was 259.9 ± 42.59 μm, PP7D was 289.82 ± 39.74 μm, and PP30D was 315.8 ± 33.28 μm, in comparison with the reference model, with significant differences among all groups (all p < 0.05). When additively manufacturing casts from scan data to verify the quality of dental prostheses designed virtually, the prostheses should be adapted to casts manufactured within one week.

Compressive and Flexural Strength of 3D-Printed and Conventional Resins Designated for Interim Fixed Dental Prostheses: An In Vitro Comparison

A provisionalization sequence is essential for obtaining a predictable final prosthetic outcome. An assessment of the mechanical behavior of interim prosthetic materials could orient clinicians towards selecting an appropriate material for each clinical case. The aim of this study was to comparatively evaluate the mechanical behavior—with compressive and three-point flexural tests—of certain 3D-printed and conventional resins used to obtain interim fixed dental prostheses. Four interim resin materials were investigated: two 3D-printed resins and two conventional resins (an auto-polymerized resin and a pressure/heat-cured acrylic resin). Cylindrically shaped samples (25 × 25 mm/diameter × height) were obtained for the compression tests and bar-shaped samples (80 × 20 × 5 mm/length × width × thickness) were produced for the flexural tests, observing the producers’ recommendations. The resulting 40 resin samples were subjected to mechanical tests using a universal testing machine. Additionally, a fractographic analysis of failed samples in bending was performed. The results showed that the additive manufactured samples exhibited higher elastic moduli (2.4 ± 0.02 GPa and 2.6 ± 0.18 GPa) than the conventional samples (1.3 ± 0.19 GPa and 1.3 ± 0.38 GPa), as well as a higher average bending strength (141 ± 17 MPa and 143 ± 15 MPa) when compared to the conventional samples (88 ± 10 MPa and 76 ± 7 MPa); the results also suggested that the materials were more homogenous when produced via additive manufacturing.

Photopolymerization of Ceramic Resins by Stereolithography Process: A Review

Stereolithography is known as one of the best Additive Manufacturing technologies in terms of geometrical and dimensional precision for polymeric materials. In recent years, a lot of studies have shown that the creation of ceramic resins, through a particular combination of monomeric components and ceramic powders, allows to obtain complex shape geometries thanks to the photopolymerization process. This review highlights the characteristics and properties of ceramic resins, peculiarities of the ceramic stereolithography processes, up to the relationship between the composition of the ceramic resin and the complexity of the post-processing phases. The comparison of different studies allows outlining the most common steps for the production of ceramic resins, as well as the physical and chemical compatibility of the different compounds that must be studied for the good feasibility of the process.

Additive Manufacturing Technologies: Current Status and Future Perspectives

A review of the main additive manufacturing technologies including vat-polymerization, material extrusion, material jetting, binder jetting, powder-based fusion, sheet lamination, and direct energy deposition is provided. Additionally, the dental applications of polymer, metal, and ceramic printing technologies are discussed.

Overview of 3D-Printed Silica Glass

Not satisfied with the current stage of the extensive research on 3D printing technology for polymers and metals, researchers are searching for more innovative 3D printing technologies for glass fabrication in what has become the latest trend of interest. The traditional glass manufacturing process requires complex high-temperature melting and casting processes, which presents a great challenge to the fabrication of arbitrarily complex glass devices. The emergence of 3D printing technology provides a good solution. This paper reviews the recent advances in glass 3D printing, describes the history and development of related technologies, and lists popular applications of 3D printing for glass preparation. This review compares the advantages and disadvantages of various processing methods, summarizes the problems encountered in the process of technology application, and proposes the corresponding solutions to select the most appropriate preparation method in practical applications. The application of additive manufacturing in glass fabrication is in its infancy but has great potential. Based on this view, the methods for glass preparation with 3D printing technology are expected to achieve both high-speed and high-precision fabrication.

A low-cost and high-performance 3D micromixer over a wide working range and its application for high-sensitivity biomarker detection

Homogenous mixing in microfluidic devices is often required for efficient chemical and biological reactions.Passive micromixing without external energy input has attracted much research interest. We have developed a high-performance 3D...

Effect of post-curing time on the color stability and related properties of a tooth-colored 3D-printed resin material

This study investigated the effect of post-curing time on the color stability and related properties, such as degree of conversion (DC), surface roughness, water contact angle, water sorption (W_sp), and water solubility (W_sl) of 3D-printed resin for dental restorations. The 3D-printed specimens were divided into four groups according to the post-curing time (0, 5, 10, and 20 min). Color changes (ΔE₀₀) of the specimens immersed in aging media were measured using a spectrophotometer at different aging times. The DC of the resin was measured using a FTIR. The surface roughness (Ra) of the resin immersed in coffee was measured at different aging times. Water contact angle was evaluated using the sessile drop method, and W_sp and W_sl were tested according to the ISO 4049:2019. The ΔE₀₀ values of the specimens immersed in coffee and red wine decreased with increasing post-curing time. As the post-curing time increased up to 10 min, the DC increased and water contact angle decreased. The Ra value of the group without post-curing (0 min) increased gradually for 30 days, except between 7 and 15 days. However, when the post-curing time increased to greater than 10 min, no apparent change in Ra value was detected. The W_sp and W_sl of the group without post-curing were significantly lower and larger than that of the other groups, respectively. The longer the post-curing time of the tooth-colored 3D-printed resin, the better the color stability. The post-curing time of the 3D-printed resin affected the DC, surface roughness after aging in the staining media, water contact angle, water sorption, and water solubility.

Accuracy of Additively Manufactured and Milled Interim 3-Unit Fixed Dental Prostheses

PURPOSE

To investigate the accuracy of additive manufacturing (AM) by means of internal fit of fixed dental prostheses (FDPs) fabricated with two AM technologies using different resins and printing modes (validated vs non-validated) compared to milling and direct manual methods.

MATERIAL AND METHODS

Sixty 3-unit interim FDPs replacing the first mandibular molar were divided into 6 groups (n = 10): manual (Protemp 4), milled (Telio-CAD), and AM groups were subdivided based on AM technology (direct light processing (Rapidshape P30 [RS]) and stereolithography (FormLabs 2 [FL])) and the polymer type (P-Pro-C&B [St] and SHERAprint-cb [Sh]) (RS-St, RS-Sh, FL-St, FL-Sh). Validated (RS-Sh and RS-St) or non-validated (FL-St and FL-Sh) modes were adopted for AM. The specimens were scanned to 3D align (GOM inspect) according to the triple scan method. The internal space between the FDPs and preparation surfaces in four sites (marginal, axial, occlusal, and total) was measured using equidistant surface points (GOM Inspect). Statistical analysis was done using Kruskal Wallis and Dunn post-hoc tests. (α = .05).

RESULTS

One AM group (FL-Sh) and milling exhibited better adaptation compared to manual and RS-St at molar site (P<.05). FDPs with St resin (FL-St and RS-St) displayed bigger marginal space than milled, FL-Sh, and RS-Sh. The non-validated printing mode showed better mean space results (P<.05) with higher predictability and repeatability (P<.001).

CONCLUSIONS

The AM interim FDPs tested provided valid alternatives to the milled ones in regard to their accuracy results. The printing mode, resin, and the AM technology used significantly influenced the manufacturing accuracy of interim FDPs, particularly at the marginal area. The non-validated printing mode with lower-cost 3D printers is a promising solution for clinical applications. This article is protected by copyright. All rights reserved.

3D printing of glass by additive manufacturing techniques: a review

Additive manufacturing (AM), which is also known as three-dimensional (3D) printing, uses computer-aided design to build objects layer by layer. Here, we focus on the recent progress in the development of techniques for 3D printing of glass, an important optoelectronic material, including fused deposition modeling, selective laser sintering/melting, stereolithography (SLA) and direct ink writing. We compare these 3D printing methods and analyze their benefits and problems for the manufacturing of functional glass objects. In addition, we discuss the technological principles of 3D glass printing and applications of 3D printed glass objects. This review is finalized by a summary of the current achievements and perspectives for the future development of the 3D glass printing technique.

Utilization of Antibacterial Nanoparticles in Photocurable Additive Manufacturing of Advanced Composites for Improved Public Health

This paper presents the additive manufacturing and characterization of nanoparticle-reinforced photocurable resin-based nanocomposites with a potential antimicrobial function for improved public health applications. Two types of photocurable resins are reinforced by titanium dioxide (TiO₂) or zinc oxide (ZnO) nanoparticles with average diameters in the 10-30 nm range to provide antimicrobial properties. The developed nanocomposites can be additively manufactured using the digital light processing method with an outstanding surface quality and precise geometrical accuracy. Experimental characterizations are conducted to investigate key mechanical properties of the 3D printed nanocomposites, including Young's Modulus, tensile strength, and abrasion resistance. Specimens produced were observed to demonstrate the following characteristics during testing. Tensile strength increased by 42.2% at a maximum value of 29.53 MPa. The modulus of elasticity increased by 14.3%, and abrasion resistance increased by 15.8%. The proper dispersion of the nanoparticles within the cured resin is validated by scanning electron images. The wettability and water absorption testing results indicate that the developed nanocomposites have an outstanding water resistance capability. The pairing of digital light processing with these novel nanocomposites allows for the creation of complex composite geometries that are not capable through other manufacturing processes. Therefore, they have the potential for long-term usage to improve general public health with antimicrobial functionality. The pairing of an unmodified photocurable resin with a 1% ZnO concentration demonstrated the most promise for commercial applications.

Recent Advances in 3D Printing for Parenteral Applications

3D printing has emerged as an advanced manufacturing technology in the field of pharmaceutical sciences. Despite much focus on enteral applications, there has been a lack of research focused on potential benefits of 3D printing for parenteral applications such as wound dressings, biomedical devices, and regenerative medicines. 3D printing technologies, including fused deposition modeling, vat polymerization, and powder bed printing, allow for rapid prototyping of personalized medications, capable of producing dosage forms with flexible dimensions based on patient anatomy as well as dosage form properties such as porosity. Considerations such as printing properties and material selection play a key role in determining overall printability of the constructs. These parameters also impact drug release kinetics, and mechanical properties of final printed constructs, which play a role in modulating immune response upon insertion in the body. Despite challenges in sterilization of printed constructs, additional post-printing processing procedures, and lack of regulatory guidance, 3D printing will continue to evolve to meet the needs of developing effective, personalized medicines for parenteral applications.

Influence of the base design on the accuracy of additive manufac tured casts measured using a coordinate measuring machine

PURPOSE

To measure the accuracy of the additively manufactured casts with 3 base designs: solid, honeycomb-structure, and hollowed bases.

METHODS

A virtual cast was used to create different base designs: solid (S Group), honeycomb-structure (HC group), and hollowed (H group). Three standard tessellation language files were used to fabricate the specimens using a material jetting printer (J720 Dental; Stratasys) and a resin (VeroDent MED670; Stratasys) (n=15). A coordinate measuring machine was selected to measure the linear and 3D discrepancies between the virtual cast and each specimen. Shapiro-Wilk test revealed that all the data was not normally distributed (P<.05). Kruskal Wallis and Mann Whitney U tests were used (α=.05).

RESULTS

The S group obtained a median ±interquartile range 3D discrepancy of 53.00 ±73.25 µm, the HC group of 58.00 ±67.25 µm, and the H group of 34.00 ±45.00 µm. Significant differences were found in the x- (P<.001), y- (P<.001), and z-axes (P<.001), and 3D discrepancies among the groups (P<.001). Significant differences were found between the S and H groups (P=.002) and HC and H groups (P<.001) on the x-axis; S and H groups (P<.001) and HC and H groups (P<.001) on the y-axis; S and H groups (P<.001) and HC and H groups (P<.001) on the z-axis; and S and H groups (P<.001) and HC and H groups (P<.001) on the 3D discrepancy.

CONCLUSIONS

The base designs influenced on the accuracy of the casts but all the specimens obtained a clinically acceptable manufacturing range. The H group obtained the highest accuracy.

3D Printing of Electrically Responsive PVC Gel Actuators

Additive manufacturing of electrically responsive soft actuators is of great importance in designing and constructing novel soft robots and soft machines. However, there are very limited options for 3D-printable and electrically responsive soft materials. Herein, we report a strategy of 3D printing polyvinyl chloride (PVC) gel actuators that are electrically controllable. We print a jellyfish-like actuator from PVC ink, which can achieve 130° bending in less than 5 s. With the multi-material 3D printing technique, we have further printed a soft actuator with a stiffness gradient that can generate undulatory motion. As a proof-of-concept demonstration, we show that a 3D-printed PVC gel-based smart window can change its transparency upon the application of voltage. The 3D printing strategy developed in this article may expand the potential applications of electrically responsive soft materials in diverse engineering fields.

Evaluating the accuracy (trueness and precision) of interim crowns manufactured using digital light processing according to post-curing time: An in vitro study

PURPOSE

This study aimed to compare the accuracy (trueness and precision) of interim crowns fabricated using DLP (digital light processing) according to post-curing time.

MATERIALS AND METHODS

A virtual stone study die of the upper right first molar was created using a dental laboratory scanner. After designing interim crowns on the virtual study die and saving them as Standard Triangulated Language files, 30 interim crowns were fabricated using a DLP-type 3D printer. Additively manufactured interim crowns were post-cured using three different time conditions-10-minute post-curing interim crown (10-MPCI), 20-minute post-curing interim crown (20-MPCI), and 30-minute post-curing interim crown (30-MPCI) (n = 10 per group). The scan data of the external and intaglio surfaces were overlapped with reference crown data, and trueness was measured using the best-fit alignment method. In the external and intaglio surface groups (n = 45 per group), precision was measured using a combination formula exclusive to scan data (₁₀C₂). Significant differences in accuracy (trueness and precision) data were analyzed using the Kruskal-Wallis H test, and post hoc analysis was performed using the Mann-Whitney U test with Bonferroni correction (α=.05).

RESULTS

In the 10-MPCI, 20-MPCI, and 30-MPCI groups, there was a statistically significant difference in the accuracy of the external and intaglio surfaces (P <.05). On the external and intaglio surfaces, the root mean square (RMS) values of trueness and precision were the lowest in the 10-MPCI group.

CONCLUSION

Interim crowns with 10-minute post-curing showed high accuracy.