Accuracy of digital light processing printing of 3-dimensional dental models

Effect of print orientation on the dimensional accuracy and cost-effectiveness of rapid-prototyped dental models using a PolyJet photopolymerization printer: An in vitro study

OBJECTIVES

The purpose of this study was to evaluate the accuracy and cost-effectiveness of the dental models 3D printed in vertical and horizontal orientation as compared to the conventional plaster and digital models.

METHODS

This study involved scanning 50 plaster models using Maestro 3D Desktop Scanner (AGE Solutions, Pisa, Italy). The STL file obtained from the scanner was processed and three-dimensionally (3D) printed in the horizontal and vertical orientation using a PolyJet 3D printer (Objet 30 prime, Stratasys Ltd., Eden Prairie, Minnesota, United States). The accuracy of the rapid-prototyped (3D printed) models was measured from the pre-determined landmarks and was compared among the groups. In addition, determining the cost-effectiveness of the 3D printed models in different orientations was based on the amount of material (resin) utilized during the 3D printing process. ANOVA was used to determine the accuracy of the models.

RESULTS

There were statistically insignificant differences (P>0.05) among rapid-prototyped models (≤0.06mm) compared to plaster models and digital models for the linear measurements made in all three planes of space. The dental models printed in the horizontal orientation were found to be more cost-effective than those printed in a vertical orientation in terms of the amount of material (resin) utilized and printing time during the 3D printing process.

CONCLUSIONS

The accuracy of rapid-prototyped models 3D printed in the horizontal and vertical orientations was comparable to the plaster models and digital models for clinical applications. Horizontally printed models were more cost-effective than vertically printed models.

Effect of printing technology, layer height, and orientation on assessment of 3D-printed models

BACKGROUND

Three-dimensional (3D) printing technologies have become popular in orthodontics. The aim of this study is to determine the effect of printing technology, orientation, and layer height on the accuracy of 3D-printed dental models.

METHODS

The maxillary arch of a post-treatment patient was scanned and printed at different orientations (0°, 90°) and layer thicknesses (25 µm, 50 µm, 100 µm, and 175 µm) using two different printing technologies (digital light processing and stereolithography). The 120 models were digitally scanned, and their average deviation from the initial model was analyzed using 3D algorithm. A multivariable linear regression analysis was used to estimate the effect of all variables on the average deviation from the initial model for the common layer thicknesses (50/100 µm). Finally, one-way ANOVA and Tukey posthoc test was used to compare the stereolithography (SLA) 25 µm and digital light processing (DLP) 175 µm groups with the groups that showed the least average deviation in the former analysis.

RESULTS

The multivariable linear regression analysis showed that the DLP 50 µm (mean ± SD: -0.022 ± 0.012 mm) and 100 µm (mean ± SD: -0.02 ± 0.009 mm) horizontally printed models showed the least average deviation from the initial model. Finally, the DLP 175 µm horizontally printed models (mean ± SD: 0.015 ± 0.005 mm) and the SLA 25 µm horizontally (mean ± SD: 0.011 ± 0.005 mm) printed models were more accurate.

CONCLUSIONS

All the models showed dimensional accuracy within the reported clinically acceptable limits. The highest accuracy was observed with DLP printer, 175 µm layer thickness, and horizontal orientation followed by SLA printer, 25 µm layer thickness, and horizontal orientation.

Dimensional Accuracy of Different Three-Dimensional Printing Models as a Function of Varying the Printing Parameters

Even in digital workflows, models are required for fitting during the fabrication of dental prostheses. This study examined the influence of different parameters on the dimensional accuracy of three-dimensionally printed models. A stereolithographic data record was generated from a master model (SOLL). With digital light processing (DLP) and stereolithography (SLA) printing systems, 126 models were produced in several printing runs-SolFlex350 (S) (DLP, n = 24), CaraPrint 4.0 (C) (DLP, n = 48) and Form2 (F) (SLA, n = 54)-and their accuracy was compared with plaster and milled polyurethane models. In addition to the positioning on the build platform, a distinction was made between parallel and across arrangement of the models to the printer's front, solid and hollow models, and printing with and without support structures. For accuracy assessment, five measurement sections were defined on the model (A-E) and measured using a calibrated digital calliper and digital scans in combination with the GOM Inspect Professional software 2021. The mean deviation between the measurement methods for all distances was 79 µm. The mean deviation of the models from the digital SOLL model were 207.1 µm for the S series, 25.1 µm for the C series and 141.8 µm for the F series. While positioning did not have an influence, there were clinically relevant differences mainly regarding the choice of printer, but also individually in alignment, model structure and support structures.

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.

Optimization of three-dimensional printing parameters for orthodontic applications

OBJECTIVES

To determine the impact of build orientation, increased layer thickness, and dental crowding on the trueness of three-dimensional (3D)-printed models, and to evaluate how these parameters affect the fit of thermoformed appliances.

MATERIALS AND METHODS

Ninety-six dental models were printed horizontally and vertically on the building platform using different 3D-printing technologies: (1) a stereolithography (SLA) printer with layer thicknesses of 160 μm and 300 μm and (2) a digital light processing (DLP) printer with layer thicknesses of 100 μm and 200 μm. Each printed model was digitalized and superimposed on the corresponding source file using 3D rendering software, and deviations were quantified by the root mean square values. Subsequently, a total of 32 thermoformed appliances were fabricated on top of the most accurate 3D-printed models, and their fit was evaluated by digital superimposition and inspection by three blinded orthodontists. Paired t-tests were used to analyze the data.

RESULTS

Significant differences (P < .05) between printing technologies used were identified for models printed horizontally, with the SLA system achieving better trueness, especially in crowded dentitions. No significant differences between technology were found when models were printed vertically. The highest values of deviation were recorded in appliances fabricated on top of DLP-printed models. The results of the qualitative evaluation indicated that appliances fabricated on top of SLA models outperformed the DLP-modeled appliances.

CONCLUSIONS

Three-dimensional printing with increased layer height seems to produce accurate working models for orthodontic applications.

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.

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.

Spatial Trueness Evaluation of 3D-Printed Dental Model Made of Photopolymer Resin: Use of Special Structurized Dental Model

(1) Background: Various 3D printers are available for dental practice; however, a comprehensive accuracy evaluation method to effectively guide practitioners is lacking. This in vitro study aimed to propose an optimized method to evaluate the spatial trueness of a 3D-printed dental model made of photopolymer resin based on a special structurized dental model, and provide the preliminary evaluation results of six 3D printers. (2) Methods: A structurized dental model comprising several geometrical configurations was designed based on dental crown and arch measurement data reported in previous studies. Ninety-six feature sizes can be directly measured on this original model with minimized manual measurement errors. Six types of photo-curing 3D printers, including Objet30 Pro using the Polyjet technique, Projet 3510 HD Plus using the Multijet technique, Perfactory DDP and DLP 800d using the DLP technique, Form2 and Form3 using the SLA technique, and each printer's respective 3D-printable dental model materials, were used to fabricate one set of physical models each. Regarding the feature sizes of the simulated dental crowns and dental arches, linear measurements were recorded. The scanned digital models were compared with the design data, and 3D form errors (including overall 3D deviation; flatness, parallelism, and perpendicularity errors) were measured. (3) Results: The lowest overall 3D deviation, flatness, parallelism, and perpendicularity errors were noted for the models printed using the Objet30 Pro (overall value: 45 μm), Form3 (0.061 ± 0.019 mm), Objet30 Pro (0.138 ± 0.068°), and Projet 3510 HD Plus (0.095 ± 0.070°), respectively. In color difference maps, different deformation patterns were observed in the printed models. The feature size proved most accurate for the Objet30 Pro fabricated models (occlusal plane error: 0.02 ± 0.36%, occlusogingival direction error: -0.06 ± 0.09%). (4) Conclusions: The authors investigated a novel evaluation approach for the spatial trueness of a 3D-printed dental model made of photopolymer resin based on a structurized dental model. This method can objectively and comprehensively evaluate the spatial trueness of 3D-printed dental models and has a good repeatability and generalizability.

Effect of Model Body Type and Print Angle on the Accuracy of 3D-Printed Orthodontic Models

The assortment of low-cost 3D printers for "in-practice" use, e.g., for clear aligner therapies, is ever increasing. To address concerns about the accuracy of orthodontic models produced on such printers when cost-efficient modes of 3D printing are employed, this study examined the effect of print model body type and print angulation on accuracy. Six printing-configuration groups were included: two model types (solid or hollow shell) combined with three print angles (0°, 70°, or 90°) with 10 models/group; all models were printed with 100 µm layer thickness using a digital light processing-based three-dimensional printer. Eleven selected structures and distances were measured on the printed models with a digital microscope and compared to the same measures on a digitized master model. The clinically acceptable range was set at ±0.25 mm difference from the master model for single tooth measurements (intra-tooth) and ±0.5 mm for cross-arch measurements (inter-tooth). For individual measurements across all models, 98% fell within clinical acceptability. For mean measurements within each model group, only canine height for the shell-0° model had a mean difference (-0.26 mm ± 0.03) outside the clinically acceptable range for intra-tooth measurements. Standard deviations for all intra-tooth measurements were within 0.07 mm. While none of the mean inter-tooth measurements exceeded the acceptability range, the standard deviations were larger (0.04 to 0.30 mm). The accuracy of the orthodontic models for clear aligner therapies was not impacted beyond the clinically acceptable range when altering model body type and print angulation to improve efficiency of 3D printing. These findings suggest greater flexibility of the practitioner to alter print settings to address time and cost efficiency in various clinical scenarios and still maintain clinically acceptable model accuracy.

Application of 4D printing in dentistry: A narrative review

4D printing is an innovative digital manufacturing technology that originated by adding a fourth dimension, i.e., time, to pre-existing 3D technology or additive manufacturing (AM). AM is a fast-growing technology used in many fields, which develops accurate 3D objects based on models designed by computers. Dentistry is one such field in which 3D technology is used for manufacturing objects in periodontics (scaffolds, local drug-delivering agents, augmentation of ridges), implants, prosthodontics (partial and complete dentures, obturators), oral surgery for reconstructing jaw, and orthodontics. Dynamism is a vital property needed for the survival of materials used in the oral cavity since the oral cavity is constantly subjected to various insults. 4D printing technology has overcome the disadvantages of 3D printing technology, i.e., it cannot create dynamic objects. Therefore, constant knowledge of 4D technology is required. 3D printing technology has shortcomings, which are discussed in this review. This review summaries various printing technologies, materials used, stimuli, and potential applications of 4D technology in dentistry.

Experimental study on dimensional variations of 3D printed dental models based on printing orientation

This research investigates the trueness and precision of 3D printing technology in dental applications, specifically focusing on dimensional variations observed in models printed at different angles. The methodology involved importing a dental model into slicing software, adjusting its orientation, and implementing support structures for stability. Subsequently, the model underwent 3D printing five times for each orientation using appropriate equipment and underwent post-processing steps, including cleaning, washing, and UV-light post-curing. The printed models were then scanned using a specialized desktop scanner for further analysis. Accuracy assessment was carried out using dedicated software, employing an algorithm for precise alignment by comparing the scanned files. Color deviation maps were utilized to visually represent variations, aiming to evaluate how positioning during printing influences the trueness and precision of 3D-printed dental models. Trueness and precision analyses involved the Shapiro-Wilk test for normality and a one-way ANOVA to compare means of three independent groups, with statistical analyses conducted using IBM SPSS Statistics software. The color maps derived from 3D comparisons revealed positive and negative deviations, represented by distinct colors. Comparative results indicated that models positioned at 0° exhibited the least dimensional deviation, whereas those at 90° showed the highest. Regarding precision, models printed at 0° demonstrated the highest reproducibility, while those at 15° exhibited the lowest. Based on the desired level of precision, it is recommended that printed models be produced at an inclination angle of 0°.

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.

Three-dimensional (3D) printing in dental practice: Applications, areas of interest, and level of evidence

OBJECTIVES

The aim of this review to overview three-dimensional (3D) printing technologies available for different dental disciplines, considering the applicability of such technologies and materials development.

MATERIALS AND METHODS

Source Arksey and O'Malley's five stages framework using PubMed, EMBASE, and Scopus (Elsevier) databases managed this review. Papers focusing on 3D printing in dentistry and written in English were screened. Scientific productivity by the number of publications, areas of interest, and the focus of the investigations in each dental discipline were extracted.

RESULTS

Nine hundred thirty-four studies using 3D printing in dentistry were assessed. Limited clinical trials were observed, especially in Restorative, endodontics, and pediatric dentistry. Laboratory or animal studies are not reliable for clinical success, suggesting that clinical trials are a good approach to validate the new methods' outcomes and ensure that the benefits outweigh the risk. The most common application for 3D printing technologies is to facilitate conventional dental procedures.

CONCLUSIONS

The constantly improving quality of 3D printing applications has contributed to increasing the popularity of these technologies in dentistry; however, long-term clinical studies are necessary to assist in defining standards and endorsing the safe application of 3D printing in dental practice.

CLINICAL RELEVANCE

The recent progress in 3D materials has improved dental practice capabilities over the last decade. Understanding the current status of 3D printing in dentistry is essential to facilitate translating its applications from laboratory to the clinical setting.

Trueness and surface characteristics of 3-dimensional printed casts made with different technologies

STATEMENT OF PROBLEM

Three-dimensional (3D) printers should be capable of fabricating products with high accuracy for potential use in a wide range of dental applications. The trueness and surface characteristics of 3D-printed casts made with different technologies remain unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the trueness and surface characteristics of 4 types of dental casts printed using 6 different 3D printers.

MATERIAL AND METHODS

Four dental casts prepared for intracoronal and extracoronal restorations were printed using 6 different 3D printers-2 printers of each printing technology (FDM: Creator, Lugo; DLP: D2, ND5100; SLA: Form 2, Form 3). The printed casts were scanned to obtain standard tessellation language (STL) data sets that were superimposed onto the reference to evaluate their trueness (n=15). Trueness was measured based on overall deviations for each cast and for sectional deviations within the cavities. For qualitative evaluation, the surface characteristics of the 3D-printed casts were analyzed by using a digital camera, stereomicroscope, and scanning electron microscope. Statistical analyses were conducted using the Kruskal-Wallis test, followed by multiple Mann-Whitney U tests for pairwise comparisons among groups (α=.05).

RESULTS

The overall median trueness values were lowest with the Form 3 (27.9 μm), followed by the ND5100 (30.0 μm), Lugo (37.1 μm), D2 (41.4 μm), Form 2 (46.9 μm), and Creator (83.3 μm) (P<.05). Sectional deviations within the cavity were generally greater than overall deviation. Macroscopic and microscopic images showed that the reproduced casts had the smoothest surface with the SLA, followed by the DLP and FDM printers. Horizontal layers were more discernible with the FDM printer.

CONCLUSIONS

The trueness of the 3D-printed casts was influenced by the type of tooth preparation and was printer dependent. Among the tested 3D printers, the Form 3 produced the most accurate casts, while the Creator produced the least accurate casts.

In-house three-dimensional printing within the digital orthodontic workflow

Intraoral scanning techniques, and the associated software, have revolutionized model acquisition, analysis, and virtual planning in orthodontics. Three-dimensional printing is the final aspect of this digital workflow, converting these virtual models and simulations of the tooth and occlusal movements into physical reality. This article provides an insight into how in-house three-dimensional printing is now a feasible and transformative reality for many orthodontic settings and how this empowers orthodontists to optimize their patient care.

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.

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

Background: The aim of this study is to evaluate the accuracy of a Liquid Crystal Display (LCD) 3D printer compared to a Direct Light Processing (DLP) 3D printer for dental model printing. Methods: Two different printers in terms of 3D printing technology were used in this study. One was a DLP 3D printer and one an LCD 3D printer. The accuracy of the printers was evaluated in terms of trueness and precision. Ten STL reference files were used for this study. For trueness, each STL file was printed once with each 3D printer. For precision, one randomly chosen STL file was printed 10 times with each 3D printer. Afterward, the models were scanned with a model scanner, and reverse engineering software was used for the STL comparisons. Results: In terms of trueness, the comparison between the LCD 3D printer and DLP 3D printer was statistically significant, with a p-value = 0.004. For precision, the comparison between the LCD 3D printer and the DLP 3D printer was statistically significant, with a p-value = 0.011. Conclusions: The DLP 3D printer is more accurate in terms of dental model printing than the LCD 3D printer. However, both DLP and LCD printers can accurately be used to print dental models for the fabrication of orthodontic appliances.

Three-Dimensional Printing Technology in Orthodontics for Dental Models: A Systematic Review

Background: Three-dimensional printing technology is an additive manufacturing technology that is used to reconstruct 3D objects. In the last decade, it has been rapidly involved in dentistry and in orthodontics. This article aims to review the literature and present the accuracy of different 3D printer types and any factors that could affect the 3D printing of dental models in the orthodontic field. Methods: The search strategy of this systematic review included keywords in combination with MeSH terms in Medline, Scopus, and Cochrane Library until June 2022 and only in English. Results: Eleven articles were selected for our study. All the articles were in vitro prospective studies, and they presented a low risk of bias. The results suggested that the accuracy of a printed dental cast can be affected by the different types of 3D technologies, the dental cast’s base design, and the printing materials. The accuracy appears to not be affected by the layer height and the position of the model on the building template. Conclusions: According to this systematic review, all different types of 3D technology can produce clinically accepted results for orthodontic purposes. There is a need for more studies to clarify the accuracy and added value of 3D printing technology in orthodontics.

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.

Error propagation from intraoral scanning to additive manufacturing of complete-arch dentate models: an in vitro study

OBJECTIVES

. To evaluate deviation propagation from data acquisition with an intraoral scanner to additive manufacturing of complete-arch dentate models.

METHODS

. A reference (Ref) mandibular dentate model having 5 precision spheres was scanned with a coordinate measurement machine equipped with a laser scanning head (ALTERA; Nikon) producing a Ni reference data set (n=1). Digital impressions were taken of the Ref model with intraoral scanner (IOS) (Trios4; 3Shape) with Insane (T4_Imo) and Classic (T4_Cmo) scanning modes (each n=10). T4_Imo scans were used as a second reference data set and to produce test models with two additive manufacturing (AM) devices (each n=10): MAX UV385 (Asiga) and NextDent 5100 (3DSystems). As for the control group, dual viscosity vinyl polysiloxane impressions were taken of the Ref model and poured with Type IV dental stone (n=10). All AM and stone models were scanned with a laboratory scanner (E4; 3Shape). Trueness and precision of linear (intermolar and intercanine width, arch length) and surface deviations were measured between reference (Ni, T4_Imo), test (T4_Cmo, AM), and control (stone) groups using best-fit alignments (Geomagic Control X; 3D Systems). The normality of data and differences between the groups were analyzed using Shapiro-Wilk, Levene's, Mann-Whitney U, Welch's t-test statistical analysis (p<0.05).

RESULTS

. The accuracy of the IOS impression was not significantly affected by the scanning mode (p>0.05). Stone models showed significantly better trueness than IOS impressions (p<0.05). AM models had higher trueness than IOS Imo digital impressions (p<0.05). The precision of AM models was comparable (linear, p>0.05) or lower (surface, p<0.05) than of IOS Imo digital impressions. Trueness was insignificantly different among the stone and AM models (p>0.05). Higher trueness was achieved by Max UV385 than with Nextdent 5100 (p<0.05). The majority of linear and all surface deviations of IOS impressions and AM models were below 200 μm.

CONCLUSIONS

. Within the limitations of this in vitro study, digital IOS impressions and AM models using the aforementioned equipment have acceptable accuracy for orthodontic and prosthodontic applications when complete-arch dentate records are used.

CLINICAL SIGNIFICANCE

. IOS and AM devices can have a significant influence on error propagation when applying digital workflow with complete-arch dentate models.

Effect of Different CAD/CAM Milling and 3D Printing Digital Fabrication Techniques on the Accuracy of PMMA Working Models and Vertical Marginal Fit of PMMA Provisional Dental Prosthesis: An In Vitro Study

Background: Minimal evidence exists on the efficacy of different digital manufacturing techniques in the fabrication of precise dental working models and provisional prosthesis. Aim of study: The objective was to evaluate the effect of two digital fabrication techniques (CAD/CAM milling and 3D printing) on the accuracy of PMMA working models and marginal fit of PMMA provisional prosthesis. Materials and methods: Two abutment teeth of modified typodont were prepared. A reference stone model was fabricated, and an optical impression was performed to obtain a CAD reference model. Four CAM milled working models and four printed working models were fabricated. CAD software was used to design the provisional prostheses. Group A tested four milled provisional prosthesis, and group B tested four 3D printed prosthesis. The 3D accuracy of working models was assessed by superimposition of the control reference working model on the CAD test working model. A stereo-optical microscope was used to assess vertical marginal fit of the provisional dental prosthesis. Student’s t and Mann–Whitney U tests were utilized to compare the two groups. Results: Results showed no statistically significant difference between the two tested groups. Conclusion: The two digital working model fabrication techniques recorded comparable accuracy. Similarly, 3D printed provisional prosthesis showed comparable marginal fit to the CAD/CAM milled ones.

Smart 3D Printed Hydrogel Skin Wound Bandages: A Review

Wounds are a major health concern affecting the lives of millions of people. Some wounds may pass a threshold diameter to become unrecoverable by themselves. These wounds become chronic and may even lead to mortality. Recently, 3D printing technology, in association with biocompatible hydrogels, has emerged as a promising platform for developing smart wound dressings, overcoming several challenges. 3D printed wound dressings can be loaded with a variety of items, such as antibiotics, antibacterial nanoparticles, and other drugs that can accelerate wound healing rate. 3D printing is computerized, allowing each level of the printed part to be fully controlled in situ to produce the dressings desired. In this review, recent developments in hydrogel-based wound dressings made using 3D printing are covered. The most common biosensors integrated with 3D printed hydrogels for wound dressing applications are comprehensively discussed. Fundamental challenges for 3D printing and future prospects are highlighted. Additionally, some related nanomaterial-based hydrogels are recommended for future consideration.

Evaluation of accuracy of 3-dimensional printed dental models in reproducing intermaxillary relational measurements: Based on inter-operator differences

Objective

Although, digital models have recently been used in orthodontic clinics, physical models are still needed for a multitude of reasons. The purpose of this study was to assess whether the printed models can replace the plaster models by evaluating their accuracy in reproducing intermaxillary relationships and by appraising the clinicians’ ability to measure the printed models.

Methods

Twenty sets of patients’ plaster models with well-established occlusal relationships were selected. Models were scanned using an intraoral scanner (Trios 3, 3Shape Dental System) by a single operator. Printed models were made with ZMD-1000B light-curing resin using the stereolithography method 3-dimensional printer. Validity, reliability, and reproducibility were evaluated using measurements obtained by three operators.

Results

In evaluation of validity, all items showed no significant differences between measurements taken from plaster and printed models. In evaluation for reliability, significant differences were found in the distance between the gingival zeniths of #23–#33 (DZL_3) for the plaster models and at #17–#43 (DZCM_1) for the printed models. In evaluation for reproducibility, the plaster models showed significant differences between operators at midline, and printed models showed significant differences at 7 measurements including #17–#47 (DZR_7).

Conclusions

The validity and reliability of intermaxillary relationships as determined by the printed model were clinically acceptable, but the evaluation of reproducibility revealed significant inter-operator differences. To use printed models as substitutes for plaster models, additional studies on their accuracies in measuring intermaxillary relationship are required.

Properties of CAD/CAM 3D Printing Dental Materials and Their Clinical Applications in Orthodontics: Where Are We Now?

In the last years, both medicine and dentistry have come across a revolution represented by the introduction of more and more digital technologies for both diagnostic and therapeutic purposes. Additive manufacturing is a relatively new technology consisting of a computer-aided design and computer-aided manufacturing (CAD/CAM) workflow, which allows the substitution of many materials with digital data. This process requires three fundamental steps represented by the digitalization of an item through a scanner, the editing of the data acquired using a software, and the manufacturing technology to transform the digital data into a final product, respectively. This narrative review aims to discuss the recent introduction in dentistry of the abovementioned digital workflow. The main advantages and disadvantages of the process will be discussed, along with a brief description of the possible applications on orthodontics.

Evaluating the Three-Dimensional Printing Accuracy of Partial-Arch Models According to Outer Wall Thickness: An In Vitro Study

The printing accuracy of three-dimensional (3D) dental models using photopolymer resin affects dental diagnostic procedures and prostheses. The accuracy of research into the outer wall thickness and printing direction data for partial-arch model printing has been insufficient. This study analyzed the effects of wall thickness and printing direction accuracy. Anterior and posterior partial-arch models were designed with different outer wall thicknesses. After 3D printing, a trueness analysis was performed. Those with full-arch models were the control group. The full-arch model had an error value of 73.60 ± 2.61 µm (mean ± standard deviation). The error values for the partial-arch models with 1-, 2-, and 3-mm thick outer walls were 54.80 ± 5.34, 47.58 ± 7.59, and 42.25 ± 9.19 μm, respectively, and that for the fully filled model was 38.20 ± 4.63 μm. The printing accuracies differed significantly between 0 degrees and 60 degrees, at 49.54 ± 8.16 and 40.66 ± 6.80 μm, respectively (F = 153.121, p < 0.001). In conclusion, the trueness of the partial-arch model was better than that of the full-arch model, and models with thick outer walls at 60 degrees were highly accurate.

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.

Accurate Bracket Placement with an Indirect Bonding Method Using Digitally Designed Transfer Models Printed in Different Orientations-An In Vitro Study

Objective: A digital workflow opens up new possibilities for the indirect bonding (IDB) of brackets. We tested if the printing orientation for bracket transfer models on the build platform of a 3D printer influences the accuracy of the following IDB method. We also evaluated the clinical acceptability of the IDB method combining digitally planned and printed transfer models with the conventional fabrication of pressure-molded transfer trays. Materials and Methods: In total, 27 digitally planned bracket transfer models were printed with both 15° and 75° angulation from horizontal plane on the build platform of a digital light processing (DLP) printer. Brackets were temporarily bonded to the transfer models and pressure-molded trays were produced on them. IDB was then performed using the trays on the respective plaster models. The plaster models were scanned with an optical scanner. Digitally planned pre-bonding and scanned post-bonding bracket positions were superimposed with a software and resulted in three linear and three angular deviations per bracket. Results: No statistically significant differences of the transfer accuracy of printed transfer models angulated 15° or 75° on the 3D printer build platform were found. About 97% of the linear and 82% of the angular deviations were within the clinically acceptable range of ±0.2 mm and ±1°, respectively. The highest inaccuracies in the linear dimension occurred in the vertical towards the gingival direction and in the angular dimension in palatal crown torque. Conclusion: For the IDB method used, the printing orientation on the build platform did not have a significant impact on the transfer accuracy.

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.

Effect of rinsing time on the accuracy of interim crowns fabricated by digital light processing: An in vitro study

PURPOSE

This study was to evaluate the effect of rinsing time on the accuracy of interim crowns fabricated by digital light processing.

MATERIALS AND METHODS

The maxillary right first molar master die was duplicated using a silicone material, while a study die was produced using epoxy resin. Scans of the epoxy resin die were used in combination with CAD software to design a maxillary right first molar interim crown. Based on this design, 24 interim crowns were fabricated with digital light processing. This study examined the trueness and precision of products that were processed with one of the three different postprocessing rinsing times (1 min, 5 min, and 10 min). Trueness was measured by superimposing reference data with scanned data from external, intaglio, and marginal surfaces. Precision was measured by superimposing the scan data within the group. The trueness and precision data were analyzed using Kruskal-Wallis, nonparametric, and post-hoc tests, and were compared using a Mann-Whitney U test with Bonferroni correction (α=.05).

RESULTS

The trueness of the external and intaglio surfaces of crowns varied significantly among the different rinsing times (P =.004, P =.003), but there was no statistically significant difference in terms of trueness measurements of the marginal surfaces (P =.605). In terms of precision, statistically significant differences were found among the external, intaglio, and marginal surfaces (P =.001).

CONCLUSION

Interim crowns rinsed for 10 minutes showed high accuracy.

Dimensional Accuracy Evaluation of Temporary Dental Restorations with Different 3D Printing Systems

With the advent of 3D printing technologies in dentistry, the optimization of printing conditions has been of great interest, so this study analyzed the accuracy of 3D-printed temporary restorations of different sizes produced by digital light processing (DLP) and liquid crystal display (LCD) printers. Temporary restorations of 2-unit, 3-unit, 5-unit, 6-unit, and full-arch cases were designed and printed from a DLP printer using NextDent C&B or an LCD printer using Mazic D Temp (n = 10 each). The restorations were scanned, and each restoration standard tessellation language (STL) file was superimposed on the reference STL file, by the alignment functions, to evaluate the trueness through whole/point deviation. In the whole-deviation analysis, the root-mean-square (RMS) values were significantly higher in the 6-unit and full-arch cases for the DLP printer and in the 5-unit, 6-unit, and full-arch cases for the LCD printer. The significant difference between DLP and LCD printers was found in the 5-unit and full-arch cases, where the DLP printer exhibited lower RMS values. Color mapping demonstrated less shrinkage in the DLP printer. In the point deviation analysis, a significant difference in direction was exhibited in all the restorations from the DLP printer but only in some cases from the LCD printer. Within the limitations of this study, 3D printing was most accurate with less deviation and shrinkage when a DLP printer was used for short-unit restorations.

Evaluation of the dimensional accuracy of thermoformed appliances taken from 3D printed models with varied shell thicknesses: An in vitro study

OBJECTIVE

Clinicians make numerous decisions when 3D printing models for fabrication of thermoformed appliances, including printing solid or hollow models. While hollow models can reduce resin use, models intended for thermoformed appliance fabrication must be printed with sufficient thickness to withstand thermoforming. The aim of the study was to determine for hollow 3D printed orthodontic models if there is an effect of shell thickness on the dimensional accuracy of retainers thermoformed upon them as compared with solid models and, if so, to identify the minimum shell thickness that ensures dimensional accuracy of the thermoformed retainer under the conditions investigated.

MATERIAL AND METHODS

Thermoformed appliances were fabricated on 3D printed models of six shell thicknesses: 1.0mm, 1.5mm, 2.0mm, 2.5mm, 3.0mm, and solid (n=10/group). The models were scanned before and after thermoforming. Thermoformed appliances were captured by two methods: scanning a polyvinylsiloxane casting of the appliance and scanning the appliance interior surface (intaglio surface). Each model-appliance pair was compared using superimposition software. A generalized linear model and post-hoc Tukey contrasts (α=0.05) were applied to compare each thickness.

RESULTS

Model thickness has a statistically significant effect on dimensional accuracy of thermoformed appliances. Appliances fabricated on 1.0mm and 1.5mm models displayed poor accuracy, with a statistically significantly lower percentage of data points within tolerance (±0.250mm) than appliances fabricated on models printed at 2.0mm thickness and greater.

CONCLUSIONS

3D printed model thickness affects the dimensional accuracy of a thermoformed retainer. To ensure minimal deformation and promote clinical utility of the thermoformed appliance, models should be printed with a minimum shell thickness of 2.0mm for the materials investigated.

Impact of Layer Thickness and Storage Time on the Properties of 3D-Printed Dental Dies

The purpose of this study was to evaluate the effect of printing layer thickness on the repeatability and surface roughness of 3D-printed dies and detect the effect of layer thickness and storage time on the dimensional stability of 3D-printed dies. One stereolithography (STL) file of an upper molar prepared for a full ceramic crown was used to print three groups of dies: 25 µm, 50 µm, and 100 µm. Repeatability was evaluated by linear and area measurements with a digital caliper and a digital metrology microscope. Dimensional stability was analyzed at 3 weeks, 6 months, and 1 year of storage time. Surface roughness parameters were measured with a 3D confocal laser scanning microscope. Statistics were completed using one-way analysis of variance and Tukey’s post hoc tests, p < 0.05. Printing time decreased as layer thickness increased. All groups showed high repeatability and comparable surface roughness while showing differences in their linear dimensions and surface areas. At the 3 week storage interval, dimensional changes were observed in all groups. Within this experimental study’s constraints, it can be concluded that changing the 3D-printing layer thickness does not affect the repeatability or the surface roughness of the product; meanwhile, changes to the layer thickness and storage time influence the dimensional stability of 3D-printed dies.

Dental 3D-Printing: Transferring Art from the Laboratories to the Clinics

The rise of three-dimensional (3D) printing technology has changed the face of dentistry over the past decade. 3D printing is a versatile technique that allows the fabrication of fully automated, tailor-made treatment plans, thereby delivering personalized dental devices and aids to the patients. It is highly efficient, reproducible, and provides fast and accurate results in an affordable manner. With persistent efforts among dentists for refining their practice, dental clinics are now acclimatizing from conventional treatment methods to a fully digital workflow to treat their patients. Apart from its clinical success, 3D printing techniques are now employed in developing haptic simulators, precise models for dental education, including patient awareness. In this narrative review, we discuss the evolution and current trends in 3D printing applications among various areas of dentistry. We aim to focus on the process of the digital workflow used in the clinical diagnosis of different dental conditions and how they are transferred from laboratories to clinics. A brief outlook on the most recent manufacturing methods of 3D printed objects and their current and future implications are also discussed.

Accuracy of 3-Dimensionally Printed Full-Arch Dental Models: A Systematic Review

The use of additive manufacturing in dentistry has exponentially increased with dental model construction being the most common use of the technology. Henceforth, identifying the accuracy of additively manufactured dental models is critical. The objective of this study was to systematically review the literature and evaluate the accuracy of full-arch dental models manufactured using different 3D printing technologies. Seven databases were searched, and 2209 articles initially identified of which twenty-eight studies fulfilling the inclusion criteria were analysed. A meta-analysis was not possible due to unclear reporting and heterogeneity of studies. Stereolithography (SLA) was the most investigated technology, followed by digital light processing (DLP). Accuracy of 3D printed models varied widely between <100 to >500 μm with the majority of models deemed of clinically acceptable accuracy. The smallest (3.3 μm) and largest (579 μm) mean errors were produced by SLA printers. For DLP, majority of investigated printers (n = 6/8) produced models with <100 μm accuracy. Manufacturing parameters, including layer thickness, base design, postprocessing and storage, significantly influenced the model’s accuracy. Majority of studies supported the use of 3D printed dental models. Nonetheless, models deemed clinically acceptable for orthodontic purposes may not necessarily be acceptable for the prosthodontic workflow or applications requiring high accuracy.

Introducing 3D printing in your orthodontic practice

Many orthodontists are aware of the potential applications of three-dimensional (3D) printing in orthodontics but are hesitant in introducing this technology into their clinical practice and workflow. Therefore, this article explains the hardware and software requirements, plus the workflow.