Comparison in Terms of Accuracy between DLP and LCD Printing Technology for Dental Model Printing

An Evaluation of the Performance of Low-Cost Resin Printers in Orthodontics

BACKGROUND/OBJECTIVES

This study evaluated the trueness and precision of three low-cost 3D printers compared to a professional-grade printer in fabricating orthodontic models.

METHODS

Two upper dental models, one crowded and one non-crowded, were designed using Blenderfordental and Autolign. The models were printed with Anycubic M3 Premium, Anycubic Photon D2, Phrozen Sonic Mini 8K, and Ackuretta Sol at 45° and 90° using Elegoo orthodontic and Ackuretta Curo resins. A total of 384 models were produced: 256 crowded (128 at 90° and 128 at 45°) and 128 non-crowded (all at 45°). Chitubox Dental Slicer and ALPHA AI slicer were used for slicing. Post-processing involved cleaning with Ackuretta Cleani and curing in Ackuretta Curie. The models were scanned with Smartoptics Vinyl Open Air. Trueness was assessed using RMS deviation analysis in CloudCompare and linear measurements.

RESULTS

One-way ANOVA showed significant differences in trueness among the printers at 45° (p < 0.001) and 90° (p < 0.001). The Ackuretta Sol (LCD) exhibited the highest trueness, with the lowest mean RMS values at 45° (0.095 ± 0.008 mm) and 90° (0.115 ± 0.010 mm). The Anycubic M3 Premium (LCD) had the lowest trueness, with RMS values at 45° (0.136 ± 0.015 mm) and 90° (0.149 ± 0.012 mm). The 45° build angle resulted in significantly better trueness than 90° (p < 0.001). In linear measurements, deviations exceeding 0.25 mm were observed only in the R1 distance, except for the Ackuretta SOL, which remained below this threshold.

CONCLUSIONS

The professional-grade printer demonstrated the best performance overall. Printing at a 45° build angle resulted in improved accuracy. Despite differences among devices, all printers produced results within clinically acceptable limits for orthodontic use.

Effects of postcuring times on the trueness of 3D -printed dental inlays made with permanent resins

OBJECTIVE

The aim of this study was to evaluate the trueness of 3D-printed dental inlays fabricated using different permanent dental resins and subjected to distinct postcuring times.

MATERIALS AND METHODS

A total of 180 inlay specimens were fabricated and divided into nine groups of 20 specimens each. The inlays were first designed using 3D design software (Ansys SpaceClaim) and then transferred to a 3D printer. Using LCD technology, 60 inlays were fabricated from Senertek P-CrownV3 Ceramic (Senertek) resin, another 60 inlays from VarseoSmile Crown Plus (Bego) resin and the final 60 inlays from Saremco Print Crowntec (Crowntec) resin. Each of these three groups was divided into three equally sized subgroups (n = 20) cured with 2,000, 4,000 and 6,000 flashes, respectively, using the Otoflash G171 device (NK Optik, Germany). Then, the specimens were scanned and digitised using an intraoral digital scanner, and their trueness was evaluated by superimposing the digital measurements on the reference design and calculating their root mean squares (RMSs) and total overlap ratios (TORs). MANOVA was used to compare the measurements, and Tukey's test was utilised for the post hoc analysis.

RESULTS

Significant differences in trueness were observed among the inlays fabricated with different resin types (p < 0.001). The Crowntec resin had the lowest RMS (0.08 ± 0.018 mm) and the highest TOR (94.59 ± 2.49%), indicating the best trueness, while Senertek had the highest RMS (0.114 ± 0.017 mm) and the lowest TOR (80.15 ± 5.95%), reflecting the lowest trueness. The postcuring time also significantly affected the trueness of the inlays. The 6,000-flashes group had the lowest RMS (0.095 ± 0.02 mm), and the 4000-flashes group had the highest TOR (89.81 ± 0.5%). The interaction between the resin type and the postcuring time was significant for the TOR (p = 0.01), suggesting that trueness improvements are material dependent.

CONCLUSION

Both the resin type and the postcuring time significantly influenced the trueness of the 3D-printed dental inlay restorations. The Crowntec resin consistently exhibited superior trueness, and the Senertek resin demonstrated the lowest trueness. The optimal postcuring time varied by material, but 4,000 flashes generally provided favourable trueness outcomes. These findings highlight the importance of selecting an appropriate resin and optimising the postcuring parameters to enhance the trueness of dental inlays, potentially improving their clinical fit and longevity.

CLINICAL RELEVANCE

Appropriate resin selection and adherence to optimised postcuring protocols are essential for achieving clinically true 3D-printed restorations, ultimately improving their adaptations in dental applications.

Three-Dimensional Printing in Prosthodontics, Restorative, and Surgical Dentistry

In dentistry, several types of 3D resin printers are commonly used, each with its advantages and applications. 3D printing traces back to the 1980s. Each type of 3D resin printer has its strengths and limitations, and the choice of printer depends on factors such as desired resolution, printing speed, material compatibility, and budget. In dental practice, a combination of different types of resin printers may be used to meet the diverse needs of patients and clinicians. In summary, 3D-printing is likely to become a mainstay of every dental office with significant applications in prosthodontics, enhancing patient care pathways.

The influence of 3-dimensional printing layer thickness on model accuracy and the perceived fit of thermoformed retainers

INTRODUCTION

This study aimed to investigate the accuracy of dental model printing using 2 different layer height settings and how these settings affect the fabrication of thermoformed retainers.

METHODS

Subjects were recruited from the Department of Orthodontics at Case Western Reserve University and scanned according to specific selection criteria. A total of 30 stereolithography files were produced and used as reference files. The stereolithography files were printed at the recommended layer height of 100 μm and 170 μm with a Sprint Ray Pro 95 3-dimensional (3D) printer (Sprint Ray, Los Angeles, Calif). All printed models were scanned using the same iTero intraoral scanner (Align Technology, San Jose, Calif) as was used for the initial intraoral scan as well. The accuracy of the printed models was based on the evaluation of root mean square values resulting from 3D superimpositions. Afterward, vacuum-formed retainers were fabricated. The vacuum-formed retainers were evaluated by the patient and an American Board of Orthodontics-certified orthodontist.

RESULTS

No difference was observed in the maxillary arch (P = 0.85) and the mandibular arch accuracy (P = 0.08) by assessing the root mean square values. No difference was observed in the doctor retainer score of the maxillary retainers (P = 0.37) and the mandibular retainers (P = 0.77). There was no difference in the patient retainer score of the maxillary (P = 0.08) and the mandibular retainers (P = 0.22) when comparing retainers. Conversely, less printing time was observed when printing the models with 170 μm compared with 100 μm (P <0.001).

CONCLUSIONS

The accuracy of a dental model printed with a Sprint Ray Pro 95 3D printer was not affected by the 100 or 170 μm layer height. Orthodontists and patients did not detect a statistically significant difference in retainer fit.

3D-Printed anterior repositioning splint versus stabilization splint for patients with anterior disc displacement with reduction: A randomized cross-over clinical trial

AIM

The aim of this study was to compare the improvement of pain between a digitally constructed stabilization splint (SS) and anterior repositioning splint (ARS) for patients with anterior disc displacement with reduction (DDWR).

SETTINGS AND DESIGN

The trial was a cross-over randomized control trial.

MATERIALS AND METHODS

Twenty patients were diagnosed using magnetic resonance imaging to have anterior disc displacement were included in the following trial. All included patients met the inclusion criteria and they were all suffering from pain and were classified as anterior DDWR. They were randomized using the sealed envelopes into two groups. Group A patients received ARS for 3 months and then SS for another 3 months after a 14-day wash out period, while in group B patients received SS for 3 months and then ARS for another 3 months after a wash out period of 14 days. All included patients received a primary impression followed by a centric relation record and a protrusive record for the fabrication of the splints. All splints were designed and then printed. Pain was evaluated using the Visual Analog Scale (VAS), an easy subjective proportion of pain intensity using a scale from 0 to 10, where 0 indicates no pain and 10 indicates high intensity.

STATISTICAL ANALYSIS USED

An independent t-test was performed for both groups at each fixed time interval.

RESULTS

There was a statistically significant difference within absolute change in pain reduction for both groups over the 3-month follow-up period. During the 1st week, Group B showed a greater pain reduction compared to Group A (0.43 vs. 0.32, respectively; P = 0.0001). However, at the 2nd week, 1 month, 2 months, and 3 months, Group A demonstrated greater pain reduction than Group B, with the values of (0.87, 1.5, 1.54, and 1.82) for Group A and (0.81, 1.19, 1.43, and 1.78) for Group B, respectively (P = 0.0001).

CONCLUSION

Within the limitations of this study, both splints are considered reliable treatment options for patients with anterior disc displacement. The ARS initially demonstrated a greater improvement in pain compared to the SS. However, after the 3-month follow-up period, no significant difference was observed between the two splints.

Students' perceptions of knowledge reinforcement on indirect prosthetic dental material choices by a translational approach

PURPOSE/OBJECTIVES

The aim of this study is to evaluate students' perceptions of the reinforcement of knowledge via innovative, case-based, hands-on learning regarding indirect prosthetic material choice.

METHODS

Six different clinical cases that represented common prosthetics were used in this simulation training. In each case, clinical pictures were associated with three-dimensional (3D)-printed replicates of final restorations and PolyJet polychromatic models with the goal of enabling students to deliberate and exchange ideas in small groups. After a debriefing session regarding the therapeutic potentialities of the first three cases alongside teachers, a lecture concerning prosthetic material choices was provided, and a zirconia crown was stained by each student to enable them to obtain a better understanding of the dental technician profession. Finally, the latter three cases were studied and analyzed in the same manner. The students' perceived reinforcement of knowledge was recorded before and 1 month after the hands-on simulation training experience, and their satisfaction was evaluated immediately thereafter on Likert scales. Students' perceived reinforcement of knowledge was subjected to statistical evaluation.

RESULTS

A high level of overall satisfaction was observed (4.60). All of the items pertaining to students' satisfaction received scores >3. One month after this hands-on approach, students' confidence in their ability to choose a material on the basis of its mechanical, optical, and luting properties increased significantly (from 2.58 to 3.64; from 2.83 to 3.64; and from 2.72 to 3.58, respectively) (p < 0.05).

CONCLUSIONS

This innovative, hands-on approach had a significant positive effect on students' perceived reinforcement of knowledge.

Impact of Autoclaving on the Dimensional Stability of 3D-Printed Guides for Orthodontic Mini-Implant Insertion - An In Vitro Study

OBJECTIVES

This study aimed to assess the effect of the printing process itself and steam autoclaving on the geometrical stability of 3D-printed guides for mini-implant insertion.

MATERIAL AND METHODS

Fifty guides (n = 10 per group) were printed with five printer/resin combinations (PRCs) from the same STL file using either digital light processing (DLP/EG, DLP/Next, DLP/Opti), desktop stereolithography (SLA/DSG) or liquid crystal display stereolithography printers (LCD/Amber). Half were sterilized by steam autoclaving with Cycle 1 (121°C, 1 bar, 20.5 min), half with Cycle 2 (134°C, 2 bars, 5.5 min). Before (T0) and after sterilization (T1) the guides were scanned with a structured light 3D scanner, and selected guides also with micro-CT for validation. Linear measurements were performed in three axes on STL, and on T0 and T1 scans. Linear mixed-effects models were used, followed by post-hoc tests in case of significance.

RESULTS

Measurements at T0 and T1 differed significantly from STL in both x- and y-axis (4 and 3 PRCs, respectively) (p < 0.05); in z-axis only DLP/Next showed significant differences between T0 and STL (p < 0.001). The comparison between T0 and T1 revealed significant differences in x-axis for DLP/Next and DLP/Opti after Cycle 1 and Cycle 2, respectively (p < 0.05), while in the y-axis no intra-group difference was recorded. In the z-axis all PRCs except for SLA/DSG exhibited significant shrinkage (for Cycles 1 or 2). Differences between the two cycles at T1 were registered only in z-axis (DLP/Next and LCD/Amber).

CONCLUSIONS

Compared with the original, all PRCs except for SLA/DSG presented significant changes in their dimensional stability owing to the printing process itself and/or the sterilization. If these changes are of clinical significance, they remain to be verified.

CLINICAL RELEVANCE

With the utilized design, the guides fabricated with SLA provided lower dimensional changes as compared to the ones produced by the other printing techniques.

Effect of different 3D-printing systems on the flexural strength of provisional fixed dental prostheses: a systematic review and network meta-analysis of in vitro studies

OBJECTIVES

The aim of this systematic review and network meta-analysis was to compare the flexural strength of provisional fixed dental prostheses (PFDPs) fabricated using different 3D printing technologies, including digital light processing (DLP), stereolithography (SLA), liquid crystal display (LCD), selective laser sintering (SLS), Digital Light Synthesis (DLS), and fused deposition modeling (FDM).

MATERIALS AND METHODS

A comprehensive literature search was conducted in databases including PubMed, Web of Science, Scopus, and Open Grey up to September 2024. Studies evaluating the flexural strength of PFDPs fabricated by 3D printing systems were included. A network meta-analysis was performed, using standardized mean differences (SMDs) and 95% confidence intervals (CIs) to assess the effects of each system on flexural strength.

RESULTS

A total of 11 in vitro studies were included, with 9 studies contributing to the network meta-analysis. SLS (77.70%) and SLA (63.82%) systems ranked the highest in terms of flexural strength, while DLP ranked the lowest (23.40%). Significant differences were observed between SLS and multiple other systems, including DLP (-14.58, CI: -22.67 to -6.48), LCD (-14.65, CI: -25.54 to -3.59), FDM (-12.87, CI: -23.30 to -2.52), SLA (-11.41, CI: -18.74 to -4.01), and DLS (-10.89, CI: -21.23 to -0.67). Direct comparisons were limited, with DLP vs. SLA having the most data. Other comparisons were predominantly indirect.

CONCLUSIONS

SLS and SLA systems exhibited superior flexural strength compared to other systems. However, the limited number of direct comparisons and reliance on indirect evidence suggest that further research is necessary to confirm these findings.

Transforming orthodontic retention: potential of 3D printing and biocompatible material characteristics

This review article delves into the cutting-edge realm of 3D printing and its impact on the fabrication of customised orthodontic retainers, which is an essential utility in the prevention of relapse post orthodontic treatment. This review evaluates the use of biocompatible materials and provides insight into future perspectives and improvements in this field. It highlights the potential of data collecting method and 3D printing to improve orthodontic retainers' fabrication and emphasises the importance of using biocompatible materials for patient safety and efficacy. It also explains cytotoxic qualities of retainer fabrication materials, which are vital for safeguarding the oral health of the patient. The evaluation procedure enables the early diagnosis and correction of any potential difficulties, such as maladjustment or inappropriate fit, allowing for a more effective treatment. It illustrates the breakthroughs and innovations in the field of orthodontics, the advantages of 3D printing over conventional methods, as well as the advantages and disadvantages of various fabrication method. Incorporating 3D printing and review into the production of orthodontic retainers enhances the overall effectiveness and efficiency of patient treatment.

Accuracy of occlusal splints printed in different orientations by liquid crystal display technology: an in vitro study

OBJECTIVES

To evaluate the accuracy of occlusal splints printed in different orientations by liquid crystal display technology.

METHODS

An occlusal splint was digitally designed, and additively manufactured using an LCD printer (Phrozen Sonic 4k, Phrozen) at three orientations relative to the printer building plate: 0, 45, and 70 degrees (n=10). The 3D-printed occlusal splints were digitised using a desktop scanner, resulting in experimental meshes. The meshes were analysed in a metrology software program, comparing the experimental ones with the initially designed occlusal splint (trueness) and each other within the same group (precision). The discrepancies were shown in a colour map and the root mean square indicated the magnitude of the total discrepancy between the meshes. Kruskal-Wallis test was used (α=0.05) followed by post-hoc Dunn's test.

RESULTS

There was no statistical difference in trueness among the groups (P=0.086); however, splints printed at 70 degrees showed better precision compared to those printed at 0 (P<0.001) and 45 degrees (P<0.001). The splints printed at 0 and 45 degrees exhibited a similar discrepancy pattern, with highest values concentrated in the posterior segment-positive on the buccal surface and negative on the lingual surface of molars. In contrast, splints printed at 70 degrees had highest discrepancy values in both anterior and posterior segments, with an inverted pattern on molars.

CONCLUSION

The accuracy of occlusal splints was affected by the different orientation in terms of precision, with 70 degrees resulted in highest precision compared to 0 and 45 degrees. No difference was found in terms of trueness. Higher discrepancies were found located in molars and incisal edge of anterior teeth.

CLINICAL SIGNIFICANCE

3D-printing using LCD technology stands out for its affordability and good resolution, however the optimal printing angle remains unclear. Vertical positioning allows more objects to fit on the printer building plate, while horizontal positioning reduces print time. According to literature, for DLP printers, a 0-degree angle provides good accuracy for occlusal splints, whereas a 90-degree angle results in lower accuracy. This study found that for LCD printers, 0, 45, and 70 degrees had similar trueness, with 70 degrees offering the highest precision. Thus, vertical positioning at 70 degrees can be a safe choice for the accuracy of occlusal splints printed on LCD technology.

Hollow Fiber Microreactor Combined with Digital Twin to Optimize the Antimicrobial Evaluation Process

In order to reproduce pharmacokinetics (PK) profiles seen in vivo, the Hollow Fiber Infection Model (HFIM) is a useful in vitro module in the evaluation of antimicrobial resistance. In order to reduce the consumption of culture medium and drugs, we developed a hollow fiber microreactor applicable to the HFIM by integrating the HFIM function. Next, we constructed a novel control method by using the "digital twin" of the microreactor to achieve precise concentration control. By integrating functions of the HFIM, the extra-capillary space volume was reduced to less than 1/10 of conventional HFIM. The control method with the digital twin can keep drug concentration in the extra-capillary space within an error of 10% under simulated drug destruction. The control method with the digital twin can also stabilize the drug concentration both in the intra-capillary space and the extra-capillary space within 15 min.

Advances in materials and technologies for digital light processing 3D printing

Digital light processing (DLP) is a projection-based vat photopolymerization 3D printing technique that attracts increasing attention due to its high resolution and accuracy. The projection-based layer-by-layer deposition in DLP uses precise light control to cure photopolymer resin quickly, providing a smooth surface finish due to the uniform layer curing process. Additionally, the extensive material selection in DLP 3D printing, notably including existing photopolymerizable materials, presents a significant advantage compared with other 3D printing techniques with limited material choices. Studies in DLP can be categorized into two main domains: material-level and system-level innovation. Regarding material-level innovations, the development of photocurable resins with tailored rheological, photocuring, mechanical, and functional properties is crucial for expanding the application prospects of DLP technology. In this review, we comprehensively review the state-of-the-art advancements in DLP 3D printing, focusing on material innovations centered on functional materials, particularly various smart materials for 4D printing, in addition to piezoelectric ceramics and their composites with their applications in DLP. Additionally, we discuss the development of recyclable DLP resins to promote sustainable manufacturing practices. The state-of-the-art system-level innovations are also delineated, including recent progress in multi-materials DLP, grayscale DLP, AI-assisted DLP, and other related developments. We also highlight the current challenges and propose potential directions for future development. Exciting areas such as the creation of photocurable materials with stimuli-responsive functionality, ceramic DLP, recyclable DLP, and AI-enhanced DLP are still in their nascent stages. By exploring concepts like AI-assisted DLP recycling technology, the integration of these aspects can unlock significant opportunities for applications driven by DLP technology. Through this review, we aim to stimulate further interest and encourage active collaborations in advancing DLP resin materials and systems, fostering innovations in this dynamic field.

Incorporating an artificially synthesized fluoride complex into urethane-acrylate-based 3D printing resin: Effects on mechanical properties, cytotoxicity, antimicrobial actions, and its long-term fluoride-releasing properties

OBJECTIVES

To synthesize a 3D printing resin with antibacterial and long-term fluoride-releasing properties.

METHODS

(4,4-Bis-4-[2‑hydroxy-3-(2-methacryloyloxy)propoxy]-phenyl-pentanol-amine)-N,N-diacetic acid zirconium (IV) fluoride complex was synthesized from 4,4-bis-(4-hydroxyphenyl)-pentanoic acid and monitored using proton nuclear magnetic resonance spectroscopy. The synthesized complex was incorporated into a urethane-acrylate-based (UA) resin at 5 wt% and 10 wt% (5F-UA and 10F-UA groups, respectively). The UA resin without the synthesized complex was considered as the control group. All groups were 3D printed using a DLP printer, followed by 10 min of washing and 20 min of curing. Surface characteristics were observed using scanning electron microscopy. The mechanical properties were assessed by measuring its flexural strength and Vickers hardness. The antibacterial property was investigated with direct and indirect contact tests and a WST-8 metabolic activity assay. The suspension was fully mixed and diluted for counting the number of colony-forming units. The cell viability test was performed using a cell proliferation assay. The amount of fluoride released was measured daily for 28 days using ion chromatography. One-way analysis of variance was performed for statistical analyses using SPSS software.

RESULTS

The amount of fluoride released increased with the concentration of fluoride complex in the resin. The fluoride ions were constantly released at a low concentration from the 3D printed specimens (5F-UA: around 0.13 ppm daily; 10F-UA: around 0.22 ppm daily). The antibacterial efficacy was acceptable in both the 5F-UA and 10F-UA groups, and higher in the latter. No cytotoxicity of the resin was detected. The mechanical properties were significantly influenced by the addition of the fluoride-releasing complex.

CONCLUSIONS

The present 3D printing UA resin incorporating a fluoride complex effectively inhibited the growth of S. mutans and demonstrated the ability to slowly release fluoride over an extended period of time.

CLINICAL SIGNIFICANCE

This study provided informative composition of a fluoride-releasing UA-based 3D printing resin, ideal for dental applications such as crowns, bridges, removable partial dentures, and orthodontic appliances, which can benefit from sustained fluoride release and antimicrobial properties. Further modifications to the resin composition can be easily achieved to enhance the resin qualities.

Accuracy of immediately placed implants using surgical guides from different 3-dimensional printers: An in vitro study

AIM

The aim of this study was to evaluate the accuracy of 3-dimensional (3D)-printed surgical guides for fully guided immediate implants from different manufacturers.

METHODS

Eighteen 3D printed fully guided surgical guides (split into 3 groups [n = 6] according to their manufacturer: Company, Desktop, or Lab), were used to place 72 implants (n = 24) in identical maxillary models. After placement, the mean global, angular, mesiodistal, buccopalatal, and vertical deviation at the platform and apex of the placed implants, relative to their preoperatively planned positions, was calculated.

RESULTS

Significant differences in global apex deviation, angular deviation, mesiodistal apex deviation, and vertical platform and apex deviation were found between the Lab and Desktop groups (p ≤ 0.007). Significant differences in mesiodistal platform and apex deviation and buccopalatal apex deviation were also found between the Company and Desktop groups (p ≤ 0.005). Finally, significant differences in buccopalatal apex deviation, and vertical platform and apex deviation were found between the Company and Lab groups (p ≤ 0.003). Mean differences between guide groups across all parameters never exceeded 0.5 mm or 1°.

CONCLUSIONS

The choice of 3D printer has a significant effect on the accuracy of fully guided immediate implants. However, the clinical relevance of these differences may be considered limited.

Effects of post-curing light intensity on the trueness, compressive strength, and resin polymerization characteristics of 3D-printed 3-unit fixed dental prostheses

PURPOSE

To investigate the effect of different post-curing light intensities on the trueness, compressive strength, and resin polymerization of 3D-printed 3-unit fixed dental prostheses (FPD).

MATERIALS AND METHODS

A total of 60 specimens were prepared to support a 3-unit FDP with a deep chamfer marginal design, utilizing computer-aided design and computer-aided manufacturing (CAD-CAM) technology. Light-polymerizing FDP resin with varying light intensities (105, 210, 420, and 840 mW/cm2) was employed for 10 min. Subsequently, trueness assessment, fracture load testing, scanning electron microscopy (SEM) surface examination, and Fourier-Transform Infrared (FTIR) analysis were conducted. A one-way analysis of variance (ANOVA) was performed to ascertain the differences between the experimental groups (p < 0.05).

RESULTS

The group exposed to 210 mW/cm2 showed the highest trueness (57.6 ± 2.1 µm), while the 840 mW/cm2 group had the highest deviation (79.3 ± 2.7 µm) (p < 0.001). Significant differences in fracture resistance were found between groups (p < 0.001), with mean fracture strengths of 1149.77 ± 67.81 N, 1264.92 ± 39.06 N, 1331.34 ± 53.62 N, and 1439.93 ± 34.58 N for light intensities of 105, 210, 420, and 840 mW/cm2, respectively (p < 0.001). The resin polymerization analysis shows a peak intensity surge at 3579 cm-1 for O-H and C-H stretching vibrations, except in samples exposed to 105 mw/cm2 light, with the lowest peak at 2890 cm-1. The performance of resin polymerization is most significant under the condition of 840 mW/cm2.

CONCLUSION

The light intensity of 210 mW/cm2 exhibited the highest trueness, while the 840 mW/cm2 group showed the highest deviation. However, the light intensity of 840 mW/cm2 demonstrated the highest compressive strength. Furthermore, polymerization occurred at all post-treatment light intensities except 105 mW/cm2. These findings indicate that while low-intensity usage offers greater trueness, high-intensity usage provides better compressive strength and polymerization. Therefore, 210 mW/cm2 could be the recommended solution for post-curing.

Effect of 3D printing technology and print orientation on the trueness of additively manufactured definitive casts with different tooth preparations

OBJECTIVES

To evaluate the fabrication trueness of additively manufactured maxillary definitive casts with various tooth preparations fabricated with different 3-dimensional (3D) printers and print orientations.

METHODS

A maxillary typodont with tooth preparations for a posterior 3-unit fixed partial denture, lateral incisor crown, central incisor and canine veneers, first premolar and second molar inlays, and a first molar crown was digitized with an industrial scanner. This scan file was used to fabricate definitive casts with a digital light processing (DLP) or stereolithography (SLA) 3D printer in different orientations (0-degree, 30-degree, 45-degree, and 90-degree) (n = 7). All casts were digitized with the same scanner, and the deviations within each preparation site were evaluated. Generalized linear model analysis was used for statistical analysis (α = 0.05).

RESULTS

The interaction between the 3D printer and the print orientation affected measured deviations within all preparations (P ≤ 0.001) except for the lateral incisor crown and canine veneer (P ≥ 0.094), which were affected only by the main factors (P < 0.001). DLP-90 mostly led to the highest and DLP-0 mostly resulted in the lowest deviations within posterior tooth preparations (P ≤ 0.014). DLP-30 led to the lowest deviations within the first premolar inlay and DLP-45 led to the lowest deviations within the central incisor veneer preparation (P ≤ 0.045).

CONCLUSIONS

Posterior preparations of tested casts had the highest trueness with DLP-0 or DLP-30, while central incisor veneer preparations had the highest trueness with DLP-45. DLP-90 led to the lowest trueness for most of the tooth preparations.

CLINICAL SIGNIFICANCE

Definitive casts with tooth preparations fabricated with the tested DLP 3D printer and the print orientation adjusted on tooth preparation may enable well-fitting restorations. However, 90-degree print orientation should be avoided with this 3D printer, as it led to the lowest fabrication trueness.

3D-printing inherently MRI-visible accessories in aiding MRI-guided biopsies

BACKGROUND

3D printers have gained prominence in rapid prototyping and viable in creating dimensionally accurate objects that are both safe within a Magnetic Resonance Imaging (MRI) environment and visible in MRI scans. A challenge when making MRI-visible objects using 3D printing is that hard plastics are invisible in standard MRI scans, while fluids are not. So typically, a hollow object will be printed and filled with a liquid that will be visible in MRI scans. This poses an engineering challenge however since objects created using traditional Fused Deposition Modeling (FDM) 3D-printing techniques are prone to leakage. Digital Light Processing (DLP) is a relatively modern and affordable 3D-printing technique using UV-hardened resin, capable of creating objects that are inherently liquid-tight. When printing hollow parts using DLP printers, one typically requires adding drainage holes for uncured liquid resin to escape during the printing process. If this is not done liquid resin will remain inside the object, which in our application is the desired outcome.

PURPOSE

We devised a method to produce an inherently MRI-visible accessory using DLP technology with low dimensional tolerance to facilitate MRI-guided breast biopsies.

METHODS

By hollowing out the object without adding drainage holes and tuning printing parameters such as z-lift distance to retain as much uncured liquid resin inside as possible through surface tension, objects that are inherently visible in MRI scans can be created without further post-processing treatment.

RESULTS

Objects created through our method are simple and inexpensive to recreate, have minimal manufacturing steps, and are shown to be dimensionally exact and inherently MRI visible to be directly used in various applications without further treatment.

CONCLUSION

Our proposed method of manufacturing objects that are inherently both MRI safe, and MRI visible. The proposed process is simple and does not require additional materials and tools beyond a DLP 3D-printer. With only an inexpensive DLP 3D-printer kit and basic cleaning and sanitation materials found in the hospital, we have demonstrated the viability of our process by successfully creating an object containing fine structures with low spatial tolerances used for MRI-guided breast biopsies.

Comparing the accuracy of 3 different liquid crystal display printers for dental model printing

INTRODUCTION

This study aimed to evaluate the accuracy in terms of trueness and precision of 3 different liquid crystal display (LCD) printers with different cost levels.

METHODS

Three LCD 3-dimensional (3D) printers were categorized into tiers 1-3 on the basis of cost level. The printers' accuracies were assessed in terms of trueness and precision. For this research, 10 standard tessellation language (STL) reference files were used. For trueness, each STL file was printed once with each 3D printer. For precision, 1 randomly chosen STL file was printed 10 times with each 3D printer. After that, a model scanner was used to scan the models, and STL comparisons were performed using reverse engineering software. For the measurements regarding trueness and precision, the Friedman test was used.

RESULTS

There were significant differences among the 3 printers (P <0.05). The trueness and precision error were lower in models printed with a tier-1 printer than in the remaining 3D printers (P <0.05). The tier-2 and -3 printers presented very similar performance.

CONCLUSIONS

LCD 3D printers can be accurately used in orthodontics for model printing depending on the specific orthodontic use. The cost of a printer is relevant to the results only for the higher expense of the 3D printer in this study.

Dimensional accuracy and surface characteristics of complete-arch cast manufactured by six 3D printers

Objective

This in vitro study aimed to quantitatively and qualitatively evaluate and compare the horizontal and vertical accuracies of complete-arch casts produced by six 3D printers with different printing principles and resolutions using a low-viscosity resin material.

Methods

A reference cast was designed by CAD software. The 3D printers used were DLPa (Asiga MAX), DLPk (cara Print 4.0), LCD2o (Ondemand 2 K Printer), LCD2p (Photon Mono X), LCD4s (SONIC 4 K), and SLA (ZENITH U). Ten casts were printed for each 3D printer using a low-viscosity resin. The accuracy of each printed cast was evaluated using shell-to-shell deviations, 12 linear, one angular, and five height deviations, with a reference cast as the control. The surface features of the casts were examined using field-emission scanning electron microscopy (FE-SEM) and digital cameras.

Results

The evaluation of shell-to-shell deviation revealed that DLPa and SLA printers exhibited low trueness values, whereas LCD printers displayed high trueness values. Among the LCD printers, LCD4s and LCD2o exhibited the lowest and highest trueness values, respectively. DLPa printers showed lower trueness values for intercanine and intermolar distances, whereas LCD printers generally demonstrated high trueness values. However, LCD4s exhibited similar trueness values to those of SLA and DLPk. The height deviation was smallest in the anterior area, whereas the largest height deviation occurred in the canine teeth. The surface characteristics indicated that the SLA casts had greater light reflection and blunt canine tips. The FE-SEM observations highlighted that the LCD and DLP printers exhibited varying layer characteristics, with some presenting rough and uneven borders in the anterior lingual area.

Significance

The accuracy of 3D printed casts varied among the 3D printer groups: DLPa and SLA were accurate for shell-to-shell deviation, with DLPa being the most accurate for linear and angular deviations. Regardless of the XY resolution, the DLP printers outperformed the LCD printers. Among the LCD group of 3D printers, higher-resolution LCD4s demonstrated increased accuracy. The SLA exhibited soft layer borders in the FE-SEM owing to its laser spot characteristics and prominent light reflection in the digital camera images.

The impact of base design and restoration type on the resin consumption, trueness, and dimensional stability of dental casts additively manufactured from liquid crystal display 3D printers

PURPOSE

To evaluate the effects of two base types and three restoration designs on the resin consumption and trueness of the 3D-printed dental casts. Additionally, the study explored the dimensional stability of these 3D-printed dental casts after 1 year of storage.

MATERIALS AND METHODS

Various types of reference dental casts were specifically designed to represent three types of dental restoration fabrications, including full-arch (FA), long-span (LS), and single-unit (SU) prostheses. The reference casts were digitized with a dental laboratory scanner and used to create flat and hollow base designs (N = 18) for the 3D-printed study casts. The 3D-printed study casts were digitized and evaluated against their corresponding references immediately after 3D printing and again after 1 year of storage, with the trueness quantified using the root mean square error (RMSE) at both time points. Volumes of resin used were recorded to measure resin consumption, and the weights of the 3D-printed study casts were also measured. The data were analyzed using two-way ANOVA and a Tukey post hoc test, α = 0.05.

RESULTS

Volumetric analysis showed the flat-base design had significantly higher resin consumption with weights for the FA group at 42.51 ± 0.16 g, the LS group at 31.64 ± 0.07 g, and the SU group at 27.67 ± 0.31 g, as opposed to 26.22 ± 1.01 g, 22.86 ± 0.93 g, and 20.10 ± 0.19 g for the hollow designs respectively (p < 0.001). Trueness, assessed through two-way ANOVA, revealed that the flat-base design had lower RMSE values indicating better trueness in the LS (54 ± 6 µm) and SU (59 ± 7 µm) groups compared to the hollow-base design (LS: 73 ± 5, SU: 99 ± 11 µm, both p < 0.001), with no significant difference in the FA group (flat-base: 50 ± 3, hollow: 47 ± 5 µm, p = 0.398). After 1 year, the flat-base design demonstrated superior dimensional stability in the LS (flat base: 56 ± 6 µm, hollow base: 149 ±45 µm, p < 0.001) and SU groups (flat base: 95 ± 8 µm, hollow base: 183 ±27 µm, p < 0.001), with the FA group showing no significant difference in the base design (flat base: 47 ± 9, hollow base: 62 ± 12 µm, p = 0.428).

CONCLUSIONS

The hollow-base design group showed lower resin consumption than the flat-base design group. However, the flat-base designs exhibited superior trueness and less distortion after 1 year of storage. These findings indicate that despite the higher material usage, flat-base designs provide better initial accuracy and maintain their dimensional stability over time for most groups.

Dimensional Stability of Additively Manufactured Dentate Maxillary Diagnostic Casts in Biobased Model Resin

This study aimed to evaluate the dimensional stability of maxillary diagnostic casts fabricated from a biobased model resin, which consists of 50% renewable raw materials for sustainable production, a model resin, and stone, over one month. A master maxillary stone cast was digitized with a laboratory scanner to generate a reference file. This master cast was also scanned with an intraoral scanner to additively manufacture casts with a biobased model resin (BAM) and a model resin (AM). Polyvinylsiloxane impressions of the master cast were also made and poured in type III stone (CV) (n = 8). The same laboratory scanner was used to digitize each model one day (T0), 1 week (T1), 2 weeks (T2), 3 weeks (T3), and 4 weeks (T4) after fabrication. Deviations from the reference file were calculated with an analysis software and analyzed with generalized linear model analysis (α = 0.05). The interaction between the material and the time point affected measured deviations (p < 0.001). Regardless of the time point, CV had the lowest and AM had the highest deviations (p < 0.001). BAM mostly had lower deviations at T0 and mostly had higher deviations at T4 (p ≤ 0.011). AM had the highest deviations at T4 and then at T3, whereas it had the lowest deviations at T0 (p ≤ 0.002). The measured deviations of CV increased after each time point (p < 0.001). BAM casts had deviations within the previously reported clinically acceptable thresholds over one month and had acceptable dimensional stability. Therefore, tested biobased resin may be a viable alternative for the sustainable manufacturing of maxillary diagnostic casts that are to be used clinically.

Quality assurance of 3D-printed patient specific anatomical models: a systematic review

BACKGROUND

The responsible use of 3D-printing in medicine includes a context-based quality assurance. Considerable literature has been published in this field, yet the quality of assessment varies widely. The limited discriminatory power of some assessment methods challenges the comparison of results. The total error for patient specific anatomical models comprises relevant partial errors of the production process: segmentation error (SegE), digital editing error (DEE), printing error (PrE). The present review provides an overview to improve the general understanding of the process specific errors, quantitative analysis, and standardized terminology.

METHODS

This review focuses on literature on quality assurance of patient-specific anatomical models in terms of geometric accuracy published before December 4th, 2022 (n = 139). In an attempt to organize the literature, the publications are assigned to comparable categories and the absolute values of the maximum mean deviation (AMMD) per publication are determined therein.

RESULTS

The three major examined types of original structures are teeth or jaw (n = 52), skull bones without jaw (n = 17) and heart with coronary arteries (n = 16). VPP (vat photopolymerization) is the most frequently employed basic 3D-printing technology (n = 112 experiments). The median values of AMMD (AMMD: The metric AMMD is defined as the largest linear deviation, based on an average value from at least two individual measurements.) are 0.8 mm for the SegE, 0.26 mm for the PrE and 0.825 mm for the total error. No average values are found for the DEE.

CONCLUSION

The total error is not significantly higher than the partial errors which may compensate each other. Consequently SegE, DEE and PrE should be analyzed individually to describe the result quality as their sum according to rules of error propagation. Current methods for quality assurance of the segmentation are often either realistic and accurate or resource efficient. Future research should focus on implementing models for cost effective evaluations with high accuracy and realism. Our system of categorization may be enhancing the understanding of the overall process and a valuable contribution to the structural design and reporting of future experiments. It can be used to educate specialists for risk assessment and process validation within the additive manufacturing industry.

Trueness of five different 3D printing systems including budget- and professional-grade printers: An In vitro study

Problem

Several types of 3D printers with different techniques and prices are available on the market. However, results in the literature are inconsistent, and there is no comprehensive agreement on the accuracy of 3D printers of different price categories for dental applications.

Aim

This study aimed to investigate the accuracy of five different 3D printing systems, including a comparison of budget- and higher-end 3D printing systems, according to a standardized production and evaluation protocol.

Material and methods

A maxillary reference model with prepared teeth was created using 16 half-ball markers with a diameter of 1 mm to facilitate measurements. A reference file was fabricated using five different 3D printers. The printed models were scanned and superimposed onto the original standard tesselation language (.stl) file, and digital measurements were performed to assess the 3-dimensional and linear deviations between the reference and test models.

Results

After examining the entire surface of the models, we found that 3D printers using Fused filament fabrication (FFF) technology -120.2 (20.3) μm create models with high trueness but high distortion. Distortions along the z-axis were found to be the highest with the stereolithography (SLA)-type 3D printer at -153.7 (38.7) μm. For the 4-unit FPD, we found 201.9 (41.8) μm deviation with the digital light processing (DLP) printer. The largest deviation (-265.1 (55.4) μm) between the second molars was observed for the DLP printer. Between the incisor and the second molar, the best results were produced by the FFF printer with -30.5 (76.7) μm.

Conclusion

Budget-friendly 3D printers are comparable to professional-grade printers in terms of precision. In general, the cost of a printing system is not a reliable indicator of its level of accuracy.

Comparing CBCT to model scanner for dental model scanning. An in vitro imaging accuracy study

OBJECTIVE

The aim of this study is to compare the accuracy of cone beam computed tomography (CBCT) for dental model scanning to the accuracy of model scanners.

METHODS

Subjects from private practice were collected and scanned according to specific selection criteria. A total of 10 STL files were produced and used as reference files. They were printed with a three-dimensional (3D) printer and then scanned with CBCT and model scanner. For trueness evaluation, all models were scanned once with both equipments. Each file derived from each scan was compared with the corresponding reference model file. For the precision measurements, the physical model from the first master reference model file was scanned 10 times with each equipment and compared with the reference STL file. A reverse engineering software was used for all 3D best-fit comparisons.

RESULTS

With regard to the measurement of trueness of each method, the calculated mean root mean square (RMS) value was 0.06±0.01mm for the CBCT, and 0.15±0.02mm for the model scanner. There was a significant difference between the two methods (P<0.01). For the evaluation of precision of each scanner, the mean RMS value was 0.0056±0.001mm for the CBCT, and 0.153±0.002mm for model scanner. There was a significant difference between the two methods (P<0.01).

CONCLUSIONS

Cone Beam Computed Tomography seems to be an accurate method for scanning dental models. CBCT performs better than model scanners to scan dental models in terms of trueness and precision.

Vat Photopolymerization 3D Printing in Dentistry: A Comprehensive Review of Actual Popular Technologies

In this comprehensive review, the current state of the art and recent advances in 3D printing in dentistry are explored. This article provides an overview of the fundamental principles of 3D printing with a focus on vat photopolymerization (VP), the most commonly used technological principle in dental practice, which includes SLA, DLP, and LCD (or mSLA) technologies. The advantages, disadvantages, and shortcomings of these technologies are also discussed. This article delves into the key stages of the dental 3D printing process, from computer-aided design (CAD) to postprocessing, emphasizing the importance of postrinsing and postcuring to ensure the biocompatibility of custom-made medical devices. Legal considerations and regulatory obligations related to the production of custom medical devices through 3D printing are also addressed. This article serves as a valuable resource for dental practitioners, researchers, and health care professionals interested in applying this innovative technology in clinical practice.

The flexural strength of 3D-printed provisional restorations fabricated with different resins: a systematic review and meta-analysis

BACKGROUND

Three-dimensional (3D) printing technology has revolutionized dentistry, particularly in fabricating provisional restorations. This systematic review and meta-analysis aimed to thoroughly evaluate the flexural strength of provisional restorations produced using 3D printing while considering the impact of different resin materials.

METHODS

A systematic search was conducted across major databases (ScienceDirect, PubMed, Web of Sciences, Google Scholar, and Scopus) to identify relevant studies published to date. The inclusion criteria included studies evaluating the flexural strength of 3D-printed provisional restorations using different resins. Data extraction and quality assessment were performed using the CONSORT scale, and a meta-analysis was conducted using RevMan 5.4 to pool results.

RESULTS

Of the 1914 initially identified research articles, only 13, published between January 2016 and November 2023, were included after screening. Notably, Digital Light Processing (DLP) has emerged as the predominant 3D printing technique, while stereolithography (SLA), Fused Deposition Modeling (FDM), and mono-liquid crystal displays (LCD) have also been recognized. Various printed resins have been utilized in different techniques, including acrylic, composite resins, and methacrylate oligomer-based materials. Regarding flexural strength, polymerization played a pivotal role for resins used in 3D or conventional/milled resins, revealing significant variations in the study. For instance, SLA-3D and DLP Acrylate photopolymers displayed distinct strengths, along with DLP bisacrylic, milled PMMA, and conventional PMMA. The subsequent meta-analysis indicated a significant difference in flexure strength, with a pooled Mean Difference (MD) of - 1.25 (95% CI - 16.98 - 14.47; P < 0.00001) and a high I2 value of 99%, highlighting substantial heterogeneity among the studies.

CONCLUSIONS

This study provides a comprehensive overview of the flexural strength of 3D-printed provisional restorations fabricated using different resins. However, further research is recommended to explore additional factors influencing flexural strength and refine the recommendations for enhancing the performance of 3D-printed provisional restorations in clinical applications.

Materials and Applications of 3D Printing Technology in Dentistry: An Overview

PURPOSE

This narrative review aims to provide an overview of the mechanisms of 3D printing, the dental materials relevant to each mechanism, and the possible applications of these materials within different areas of dentistry.

METHODS

Subtopics within 3D printing technology in dentistry were identified and divided among five reviewers. Electronic searches of the Medline (PubMed) database were performed with the following search keywords: 3D printing, digital light processing, stereolithography, digital dentistry, dental materials, and a combination of the keywords. For this review, only studies or review papers investigating 3D printing technology for dental or medical applications were included. Due to the nature of this review, no formal evidence-based quality assessment was performed, and the search was limited to the English language without further restrictions.

RESULTS

A total of 64 articles were included. The significant applications, applied materials, limitations, and future directions of 3D printing technology were reviewed. Subtopics include the chronological evolution of 3D printing technology, the mechanisms of 3D printing technologies along with different printable materials with unique biomechanical properties, and the wide range of applications for 3D printing in dentistry.

CONCLUSIONS

This review article gives an overview of the history and evolution of 3D printing technology, as well as its associated advantages and disadvantages. Current 3D printing technologies include stereolithography, digital light processing, fused deposition modeling, selective laser sintering/melting, photopolymer jetting, powder binder, and 3D laser bioprinting. The main categories of 3D printing materials are polymers, metals, and ceramics. Despite limitations in printing accuracy and quality, 3D printing technology is now able to offer us a wide variety of potential applications in different fields of dentistry, including prosthodontics, implantology, oral and maxillofacial, orthodontics, endodontics, and periodontics. Understanding the existing spectrum of 3D printing applications in dentistry will serve to further expand its use in the dental field. Three-dimensional printing technology has brought about a paradigm shift in the delivery of clinical care in medicine and dentistry. The clinical use of 3D printing has created versatile applications which streamline our digital workflow. Technological advancements have also paved the way for the integration of new dental materials into dentistry.

Fabrication of 3D-printed molds for polydimethylsiloxane-based microfluidic devices using a liquid crystal display-based vat photopolymerization process: printing quality, drug response and 3D invasion cell culture assays

Microfluidic platforms enable more precise control of biological stimuli and environment dimensionality than conventional macroscale cell-based assays; however, long fabrication times and high-cost specialized equipment limit the widespread adoption of microfluidic technologies. Recent improvements in vat photopolymerization three-dimensional (3D) printing technologies such as liquid crystal display (LCD) printing offer rapid prototyping and a cost-effective solution to microfluidic fabrication. Limited information is available about how 3D printing parameters and resin cytocompatibility impact the performance of 3D-printed molds for the fabrication of polydimethylsiloxane (PDMS)-based microfluidic platforms for cellular studies. Using a low-cost, commercially available LCD-based 3D printer, we assessed the cytocompatibility of several resins, optimized fabrication parameters, and characterized the minimum feature size. We evaluated the response to both cytotoxic chemotherapy and targeted kinase therapies in microfluidic devices fabricated using our 3D-printed molds and demonstrated the establishment of flow-based concentration gradients. Furthermore, we monitored real-time cancer cell and fibroblast migration in a 3D matrix environment that was dependent on environmental signals. These results demonstrate how vat photopolymerization LCD-based fabrication can accelerate the prototyping of microfluidic platforms with increased accessibility and resolution for PDMS-based cell culture assays.

Factors influencing the dimensional accuracy of additively manufactured dental models: A systematic review of in vitro studies

OBJECTIVES

This study aims to systematically review the literature and evaluate the effect of post-printing factors such as aging, heat, appliance fabrication and storage on the dimensional accuracy of full-arch dental models manufactured by additive manufacturing (AM) technology for the intended use of working model purposes.

MATERIALS AND METHODS

Three online databases, Medline (Ovid), Scopus and Web of Science were screened and last searched in March 2023. In-vitro studies and publications involving any distortions and shrinkage to the additively manufactured (AMed) model after printing and post-processing were included. However, literature reviews, abstracts, publications in a language different from English, or publications not testing a dental model with an arch or dentition were excluded. The references cited in the studies included were also checked via Google Scholar to identify relevant published studies potentially missed.

RESULTS

The systematic search identified and screened 769 different studies after the removal of duplicates. After applying inclusion and exclusion criteria, a total of 30 relevant titles and abstracts were found, yielding six final selections after full-text screening. Four out of the six studies evaluated the effect of both storage and aging on the dimensional accuracy of AMed dental models. The other two studies assessed the dimensional accuracy after the fabrication of thermoformed and vacuum-formed appliances on the AMed dental model.

CONCLUSIONS

AMed models can be utilised as working models on the condition that specific printing parameters are followed and additional model design features are employed. No definitive conclusions can be drawn on standardised methods to assess the dimensional accuracy of AMed dental models after storage, aging and appliance fabrication. In addition, there is no consensus on specific storage periods for an AMed model. Majority of study designs removed the palatal region to create a horseshoe shaped model, making the results less applicable to a working model scenario requiring the palate for retention purposes. The parameters investigated on AMed models include storage, aging, and appliance fabrication through thermoforming and vacuum-forming. Printing densities of solid models and wall thickness of hollow models were shown to influence the accuracy of AMed models. Dimensional accuracy of AMed models have been shown to be affected during appliance fabrication through thermoforming and vacuum-forming in certain conditions.

SIGNIFICANCE

There is a clear need of standardisation when manufacturing AMed dental models for working model purposes. The current methods investigated in this study lack established protocols to accurately manufacture the AMed models, and effectively store and utilise an AMed dental model for fabrication of orthodontic and prosthodontic appliances.

Accuracy of models of partially edentulous arches obtained by three-dimensional printing: An in vitro study

Aim

The aim of this study was to evaluate the accuracy of models of partially edentulous arches obtained by three-dimensional (3D) printing.

Settings and Design

This was an in vitro study.

Materials and Methods

Fifteen partially edentulous models were evaluated, using two methods of measuring dimensions: virtual, using the Standard Tessellation Language files of the models and software (control group), and physical, through printing the models and digital caliper (test group). For both methods, measurements were made regarding the dimensions of the teeth (width and length - buccal/lingual or palatal/occlusal) and distances between the teeth.

Statistical Analysis Used

For the variable of linear measurements (width and length) and distances between teeth of the same hemiarch, the Wilcoxon test was used, while for the variable between opposite hemiarches, the paired t-test was used.

Results

In the evaluation of the linear measurements, a significant difference was observed only when the width of the molar tooth was analyzed (P = 0.014). When the buccal length was measured, all teeth had linear measurements provided by the virtual method that was lower than the physical (P = 0.000), as well as the lingual/palatal length in incisors (P = 0.003) and molars (P = 0.009) and in total (P = 0.001). As for the analyses between teeth, no difference was identified between the measurements provided by the virtual method compared to the physical one.

Conclusions

The 3D printer used to print partially edentulous models provided linear distortions in the teeth but without changes in the distances between teeth of the same hemiarch and between teeth of opposite hemiarches.

Three-Dimensional Printing of Large Objects with High Resolution by Dynamic Projection Scanning Lithography

Due to the development of printing materials, light-cured 3D printing is playing an increasingly important role in industrial and consumer markets for prototype manufacturing and conceptual design due to its advantages in high-precision and high-surface finish. Despite its widespread use, it is still difficult to achieve the 3D printing requirements of large volume, high resolution, and high speed. Currently, traditional light-cured 3D printing technologies based on stereolithography, such as regular DLP and SLA, can no longer meet the requirements of the processing size and processing rate. This paper introduces a dynamic projection of 3D printing technology utilizing a digital micro-mirror device (DMD). By projecting the ultraviolet light pattern in the form of "animation", the printing resin is continuously cured in the exposure process to form the required three-dimensional structure. To print large-size objects, the three-dimensional model is sliced into high-resolution sectional images, and each layer of the sectional image is further divided into sub-regional images. These images are dynamically exposed to the light-curing material and are synchronized with the scanning motion of the projection lens to form a static exposure pattern in the construction area. Combined with the digital super-resolution, this system can achieve the layering and fine printing of large-size objects up to 400 × 400 × 200 mm, with a minimum feature size of 45 μm. This technology can achieve large-size, high-precision structural printing in industrial fields such as automobiles and aviation, promoting structural design, performance verification, product pre-production, and final part processing. Its printing speed and material bending characteristics are superior to existing DLP light-curing 3D printing methods.

Comparative Analysis of Fused Deposition Modeling and Digital Light Processing Techniques for Dimensional Accuracy in Clear Aligner Manufacturing

BACKGROUND This study aimed to compare fused deposition modeling (FDM) and digital light processing (DLP) techniques in terms of dimensional accuracy for printing dental models used for the manufacture of clear dental aligners. MATERIAL AND METHODS Based on the intraoral scan of an adult patient, a sequence of 10 aligner models was created using BlueSkyPlan4. The test models (n=30) were fabricated with 2 desktop 3D printers: (DLP) and (FDM) printers. Two groups of samples were created (digitized using a desktop optical scanner). To calculate trueness (n=20) and precision (n=10), printed models were compared to the source files (REF). REF, DLP, and FDM files were superimposed and converted to point clouds. The cloud-to-cloud distances were calculated using CloudCompare software. Using the same algorithm, distortions of models were measured. Data were analyzed using one-way ANOVA and Tukey's post hoc test. RESULTS Significant differences were found between the trueness and precision of DLP and FDM groups. The average calculated trueness of DLP and FDM was 0.096 mm (0.021) (P<0.001) and 0.063 mm (0.024) (P<0.001), respectively. The average calculated precision of DLP and FDM was 0.027 mm (0.003) (P<0.001) and 0.036 mm (0.003) (P<0.001), respectively. A widening (0.158 mmfor DLP and 0.093 mmfor FDM, P=0.05) and twisting (0.03 mmfor DLP and 0.043 mmfor FDM, P=0.05) of the printed models was observed. CONCLUSIONS Both printers had sufficient precision for aligner models manufacturing. FDM showed a higher trueness and this device can be applied as an alternative to DLP. Polymerization shrinkage is a significant factor in decreasing the trueness of DLP printers.

Recent Advances on 3D-Printed Zirconia-Based Dental Materials: A Review

Zirconia-based materials are widely used in dentistry due to their biocompatibility and suitable mechanical and tribological behavior. Although commonly processed by subtractive manufacturing (SM), alternative techniques are being explored to reduce material waste, energy consumption and production time. 3D printing has received increasing interest for this purpose. This systematic review intends to gather information on the state of the art of additive manufacturing (AM) of zirconia-based materials for dental applications. As far as the authors know, this is the first time that a comparative analysis of these materials' properties has been performed. It was performed following the PRISMA guidelines and using PubMed, Scopus and Web of Science databases to select studies that met the defined criteria without restrictions on publication year. Stereolithography (SLA) and digital light processing (DLP) were the techniques most focused on in the literature and the ones that led to most promising outcomes. However, other techniques, such as robocasting (RC) and material jetting (MJ), have also led to good results. In all cases, the main concerns are centered on dimensional accuracy, resolution, and insufficient mechanical strength of the pieces. Despite the struggles inherent to the different 3D printing techniques, the commitment to adapt materials, procedures and workflows to these digital technologies is remarkable. Overall, the research on this topic can be seen as a disruptive technological progress with a wide range of application possibilities.