Effect of accelerated aging on long-term accuracy of full arches manufactured using various 3-dimensional printers

Introduction

It is possible to produce prostheses faster and more easily with the introduction of digital dentistry based on computer-aided design (CAD)/computed-aided manufacturing (CAM) systems than by conventional methods; this has facilitated the mass production of various types of prosthesis (1-3). The continuous development of intraoral scanners has resulted in a transition from impression and gypsum-based indirect impression techniques to chairside digital impression techniques based on dental CAD/CAM systems. The quick and easy generation of digital impressions is a key technology for providing convenience to both patients and dentists. The CAD/CAM system consists of an intraoral scanner, which acquires the image of an object, CAD software for designing the prosthesis using the scanned image, and a milling machine for manufacturing the prosthesis. The performance of the dental CAD/CAM system is evaluated by the accuracy of the image acquired by the oral scanner and the internal/ marginal fit between the abutment and prosthesis (4, 5). High accuracy and fit can reduce clinical impression errors and increase success ratesfor customized prostheses (6, 7).

Clear aligners are plastic forms of dental braces used for the adjustment of teeth with high esthetic appeal. This treatment was revolutionized by the development of CAD/CAM technology (8), which enables a patient's impression image to be acquired using a digital scanner and a full arch machined by a 3-dimensional (3D) printer (9, 10). Some 3D printers, such as the stereo-lithography apparatus (SLA), digital light processing (DLP), Polyjet^TM (POL), and fused deposition modeling (FDM) printers, are commonly used for the preparation of full arches.

Although many 3D printers have been introduced to the field of dentistry, digital dental prostheses have mainly been used to address the model fit of dental prosthesis made using CAM-based milling machines (11, 12). The feasibility of 3D printing impressions or model digitization in dental practice has already been verified in many studies (13-16). However, 3D printed products are susceptible to deformation during long-term storage because of their weak interlayer bonding and the nature of polymer-based 3D printing materials, and prior research on the long-term stability of 3D printed productsis insufficient (17, 18).

Therefore, in this study, we evaluated the long-term accuracy of full arches fabricated using four 3D printers, including the SLA, DLP, POL, and FDM printers. Long-term accuracy was estimated by calculating the absolute trueness and precision values of distances between the 4 cusp tips of scanned images of the full arch before and after an accelerated aging treatment.

Materials and Methods

1. Full arch machining and 3D printers

The test object for a full arch was a model of a lower jaw with a dentition of 14 teeth (ANA-4V CER, Frasaco GmbH, Tettnang, Germany; Figure 1(A)). The original image of the full arch was obtained using a laboratory scanner (R1000, 3shape A/S, Copenhagen, Denmark) and used to produce full-arch replicas using 3D printers and measure reference values.

Figure 1.

(A) Real image and (B) STL format images of the full arch model;A(13-23 cusp tip),B(13 cusp tip-16 mesiobuccal cusp tip),C(23 cusp tip-26 mesiobuccal cusp tip), D(13 cusp tip-26 mesiobuccal cusp tip), E(23 cusp tip-16 mesiobuccal cusp tip), F(16 mesiobuccal cusp tip-26 mesiobuccal cusp tip).

Four 3D printers were used to produce full-arch replicas: SLA (Digital Wax029D, DWS Systems, Thiene VI, Italy;), DLP (3Dent, Envisiontec Co., Michigan, USA), POL (EDEN260V, Stratasys Co., Rehovot, Israel), and FDM (Vis-mini, Vision Tech Korea Co., Daejeon, Korea) printer. The printing materials which are recommended by each manufacturer were used in this study (Invicta 917 for SLA, MED 690 for Polyjet, Orthotough for DLP, and PLA for FDM). Five full-arch replicas per experimental group were produced and scanned using the laboratory scanner. Figure 2 shows the full-arch replicas produced by the four 3D printers.

Figure 2.

Real images of 3D printed full arches prepared by (A) SLA, (B) DLP, (C) POL and (D) FDM type 3D printers.

Results

1. Accuracy of 3D printed full arches before accelerated aging treatment

Figures 3 and 4 show boxplots of the absolute mean trueness and precision values for distances A, B, C, D, E, and F before accelerated aging treatment. The POL group showed the highest accuracy among all experimental groups (trueness value of distance D: 72.00 ± 49.70 μm, precision value of distance B: 56.00 ± 33.62 μm). There were no significant differences in absolute mean precision values between all experimental groups (p>0.05). However, some absolute mean trueness values for FDM (distance D) and DLP groups(distances E and F) were significantly higher than those for the other experimental groups at each distance (p<0.05).

Figure 3.

Boxplots of absolute mean trueness (comparison of test model datasets to the reference model datasets) value of distance A, B, C, D, E, and F of reference model before accelerated aging treatment.* Different alphabetical letters mean that there is a significant statistical difference between data.

Figure 4.

Boxplots of absolute mean precision (comparison of test model datasets within a single 3D printer) value of distance A, B, C, D, E, and F of reference model before accelerated aging treatment.* Different alphabetical letters mean that there is a significant statistical difference between data.

2. Accuracy of 3D printed full arches after accelerated aging treatment

Figures 5 and 6 show boxplots of absolute mean trueness and precision values for distances A, B, C, D, E, and F for full arches after accelerated aging treatment. The SLA group showed the highest accuracy (trueness value of distance B: 80.00 ± 38.73 μm, precision value of distance B: 48.00 ± 38.99 μm) among all experimental groups. For the FDM group, several absolute mean trueness (distances A, B, C, D, E, and F) and precision values (distances E and F) were significantly higher than those for the other experimental groups at each distance (p<0.05).

Figure 5.

Boxplots of absolute mean trueness (comparison of test model datasets to the reference model datasets) value of distance A, B, C, D, E, and F of reference model after accelerated aging treatment.* Different alphabetical letters mean that there is a significant statistical difference between data.

Figure 6.

Boxplots of absolute mean precision (comparison of test model datasets within a single 3D printer) value of distance A, B, C, D, E, and F of reference model after accelerated aging treatment.* Different alphabetical letters mean that there is a significant statistical difference between data.

Discussion

In this study, the accelerated aging treatment were performed to simulate the long-term storage condition within a short period. Four types of 3D printers such as SLA, DLP, POL, and FDM methods, which are commonly used for producing the full arches in the field of dentistry now, were selected to evaluate the effect of the long-term storage on the accuracy of 3D printed full arches. 3D printing systems have promoted the generalization and popularization of the invisible aligner as an alternative to traditional dental braces. Many studies have analyzed the accuracy of full arch digitization and 3D printing in dentistry (24-26). However, sufficient research relating to the long-term stability of 3D printedfull arches fabricated using different 3D printers has not been conducted. In the present study, we estimated the volumetric stability of 3D printed full arches after the long-term storage by analyzing the accuracy the full arches produced by the four types of 3D printers before and after accelerated aging treatment.

Many factors such as the type of 3D printing mechanism, 3D printing materials, the design of scanned full arches, and laboratory conditions (Temperature and humidity during the fabrication of 3D printed full arches) can affect the long-term stability of 3D printed full arches. Among them, different 3D printing material was expected to affect the accuracy of 3D printed full arches due to its physical nature. However, it was impossible to find the same 3D printing material used in four different 3D printers. Therefore, we could not consider the effect of 3D printing materials on the long-term stability of 3D printed full arches.

Before treatment, it was found that the POL group (trueness value of distance D: 72.00 ± 49.70 μm, precision value of distance B: 56.00 ± 33.62 μm) showed the highest accuracy among all experimental groups. Polyjet^TM type printer using solid support materials during light curing, has the best linear accuracy compared to DLP or SLA type printers, which use liquid materials (27, 28). Conversely, the DLP printer resulted in the lowest linear accuracy among the 4 printers, which was attributed to the working mechanism of the DLP system. Generally, 3D printers that use photo-curable liquid resin materials are thought to produce high surface quality; however, DLP printers require a wider range of light irradiation than SLA printers (29), and the brightness of light seems to be lowered or distorted for output sizes as large as our full arch model.

After accelerated aging treatment, the volumetric stability of FDM products was remarkably reduced compared to that of the other types of 3D printers. Furthermore, it was confirmed that the linear accuracy of FDM arches had a range of 934.00-2824.00 μm after treatment. The reduced accuracy for the FDM printer seems to result from the storage environments during long-term storage, which affects the stacked thermoplastic filament resin. In addition, the output performance of printers is largely influenced by the minimum layer thickness. The minimum layer thicknesses for the 3D printers used in this study were reported to be 10, 25, 16, and 50 μm for the SLA, DLP, POL, and FDM printers, respectively; therefore, the FDM printer was predicted to be the least accurate (30).

On the condition of the accelerated aging time which simulates the long-term storage, the full arches produced by all 3D printers, except for the FDM printer, were considered clinically acceptable in terms of long-term accuracy (31). However, we recommended that 3D printed full arches are prepared immediately before every invisible aligning treatment, because irregular deformation of 3D printed prostheses caused by long-term storage could affect their corrective force (32).

Conclusion

We evaluated the long-term accuracy of full arches produced by four 3D printers (SLA, DLP, POL, and FDM) before and after accelerated aging treatment. The POL and SLA groups showed the highest accuracy and precision before and after treatment, respectively. In addition, all absolute mean trueness values for the FDM group showed a significant change after treatment. All trueness relative errors for the FDM group were also greater than 0.04 after treatment, which was high compared to the other groups. Therefore, within the limitation of this study, the full arches produced by SLA, DLP, and POL type 3D printers were considered clinically acceptable after long-term storage. Also, immediate preparation and clinical application of 3D printed prostheses should be recommended unless otherwise specified.

Acknowledgments

This paper was supported by Wonkwang University in 2018.

References

• Miyazaki, T, Hotta, Y, Kunii, J, Kuriyama, S, Tamaki, Y, A review of dental CAD/CAM: current status and future perspectives from 20 years of experience, Dent Mater J., (2009), 28(1), p44-56. [https://doi.org/10.4012/dmj.28.44]
• Miyazaki, T, Hotta, Y, CAD/CAM systems available for the fabrication of crown and bridge restorations, Austral Dent J., (2011), 56(Suppl 1), p97-106. [https://doi.org/10.1111/j.1834-7819.2010.01300.x]
• Alghazzawi, TF, Advancements in CAD/CAM technology: Options for practical implementation, J Prosthodont Res., (2016), 60(2), p72-84. [https://doi.org/10.1016/j.jpor.2016.01.003]
• Rossini, G, Parrini, S, Castroflorio, T, Deregibus, A, Debernardi, CL, Diagnostic accuracy and measurement sensitivity of digital models for orthodontic purposes: A systematic review, Am J Orthod Dentofacial Orthop., (2016), 149(2), p161-70. [https://doi.org/10.1016/j.ajodo.2015.06.029]
• Ahlholm, P, Sipila, K, Vallittu, P, Jakonen, M, Kotiranta, U, Digital versus conventional impressions in fixed prosthodontics: A Review, J Prosthodont., (2018), 27(1), p35-41. [https://doi.org/10.1111/jopr.12527]
• Goracci, C, Franchi, L, Vichi, A, Ferrari, M, Accuracy, reliability, and efficiency of intraoral scanners for full-arch impressions: a systematic review of the clinical evidence, Europ J Orthodont., (2016), 38(4), p422-8. [https://doi.org/10.1093/ejo/cjv077]
• Lee, SJ, Betensky, RA, Gianneschi, GE, Gallucci, GO, Accuracy of digital versus conventional implant impressions, Clinic Oral Implant Res., (2015), 26(6), p715-9. [https://doi.org/10.1111/clr.12375]
• Wong, BH, Invisalign A to Z, Am J Orthod Dentofacial Orthop., (2002), 121(5), p540-1.
• Martorelli, M, Gerbino, S, Giudice, M, Ausiello, P, A comparison between customized clear and removable orthodontic appliances manufactured using RP and CNC techniques, Dent Mater., (2013), 29(2), pe1-10. [https://doi.org/10.1016/j.dental.2012.10.011]
• Shalish, M, Cooper-Kazaz, R, Ivgi, I, Canetti, L, Tsur, B, Bachar, E, et al. , Adult patients' adjustability to orthodontic appliances. Part I: a comparison between Labial, Lingual, and Invisalign, Europ J Orthodont., (2012), 34(6), p724-30.
• de Franca, DG, Morais, MH, das Neves, FD, Barbosa, GA, Influence of CAD/CAM on the fit accuracy of implant-supported zirconia and cobalt-chromium fixed dental prostheses, J Prosthet Dent., (2015), 113(1), p22-8.
• Tomita, S, Shin-Ya, A, Gomi, H, Matsuda, T, Katagiri, S, Suzuki, H, et al. , Machining accuracy of CAD/CAM ceramic crowns fabricated with repeated machining using the same diamond bur, Dent Mater J., (2005), 24(1), p123-33. [https://doi.org/10.4012/dmj.24.123]
• Quimby, ML, Vig, KW, Rashid, RG, Firestone, AR, The accuracy and reliability of measurements made on computer-based digital models, Angl Orthodont., (2004), 74(3), p298-303.
• Stevens, DR, Flores-Mir, C, Nebbe, B, Raboud, DW, Heo, G, Major, PW, Validity, reliability, and reproducibility of plaster vs digital study models: comparison of peer assessment rating and Bolton analysis and their constituent measurements, Am J Orthod Dentofacial Orthop., (2006), 129(6), p794-803. [https://doi.org/10.1016/j.ajodo.2004.08.023]
• Wesemann, C, Muallah, J, Jonas, M, Accuracy and efficiency of full-arch digitalization and 3D printing: A comparison between desktop model scanners, an intraoral scanner, a CBCT model scan, and stereolithographic 3D printing, Quintessence Int., (2017), 48(1), p41-50.
• Sousa, MV, Vasconcelos, EC, Janson, G, Garib, D, Pinzan, A, Accuracy and reproducibility of 3-dimensional digital model measurements, Am J Orthod Dentofacial Orthop., (2012), 142(2), p269-73. [https://doi.org/10.1016/j.ajodo.2011.12.028]
• Wu, W, Geng, P, Li, G, Zhao, D, Zhang, H, Zhao, J, Influence of layer thickness and raster angle on the mechanical properties of 3D printed PEEK and a comparative mechanical study between PEEK and ABS, Mater., (2015), 8(9), p5834-46. [https://doi.org/10.3390/ma8095271]
• Dizon, JR, Espera Jr, AH, CHen, Q, Advincula, RC, Mechanical characterization of 3D printed polymers, Additive Manufactur, (2018), 20, p44-67. [https://doi.org/10.1016/j.addma.2017.12.002]
• International Organization for Standardization, ISO 11607-1:2006, Packaging for terminally sterilized medical devices - Part 1: Requirements for materials, sterile barrier systems and packaging systems, Geneva, ISO, (2006).
• International Organization for Standardization, ISO 11607-2:2018, Packaging for terminally sterilized medical devices - Part 2: Validation requirements for forming, sealing and assembly processes, Geneva, ISO, (2018).
• American Society for Testing and Materials, ASTM F1980-16A:2016, Standard guide for accelerated aging of sterile barrier systems for medical devices, West Conshohocken, ASTM, (2016).
• Patzelt, SB, Emmanouilidi, A, Stampf, S, Strub, JR, Att, W, Accuracy of full-arch scans using intraoral scanners, Clin Oral Investigat., (2014), 18(6), p1687-94. [https://doi.org/10.1007/s00784-013-1132-y]
• American Dental Association, ADA/ANSI 132:2015, Scanning accuracy of dental chairside and laboratory CAD/CAM system, Chicago, ADA, (2015).
• Nowak, R, Wesemann, C, Robben, J, Muallah, J, Bumann, A, An in-vitro study comparing the accuracy of full-arch casts digitized with desktop scanners, Quintessence Int., (2017), p667-76.
• Shaheen, E, Sun, Y, Jacobs, R, Politis, C, Three-dimensional printed final occlusal splint for orthognathic surgery: design and validation, Internat J Oral & Maxillofac Surg., (2017), 46(1), p67-71. [https://doi.org/10.1016/j.ijom.2016.10.002]
• Kim, BC, Lee, CE, Park, W, Kim, MK, Zhengguo, P, Yu, HS, et al. , Clinical experiences of digital model surgery and the rapid-prototyped wafer for maxillary orthognathic surgery, Oral Surg Oral Med Oral Pathol Oral Radiol Endod., (2011), 111(3), p278-85. [https://doi.org/10.1016/j.tripleo.2010.04.038]
• Monzon, M, Ortega, Z, Hernandez, A, Paz, R, Ortega, F, Anisotropy of photopolymer parts made by digital light processing, Mater., (2017), 10(1), p64.
• Kent, NJ, Joliver, L, O'neill, P, Brabazon, D, An evaluation of components manufactured from a range of materials, fabricated using Polyjet technology, Adv in Mater & Proc Technol., (2017), 3(3), p318-29. [https://doi.org/10.1080/2374068x.2017.1330856]
• Ge, LS, Dong, LT, Wang, D, Ge, Q, Gu, GY, A digital light processing 3D printer for fast and high-precision fabrication of soft pneumatic actuators, Sensor Actuat a-Phys., (2018), 273, p285-92. [https://doi.org/10.1016/j.sna.2018.02.041]
• Keating, AP, Knox, J, Bibb, R, Zhurov, AI, A comparison of plaster, digital and reconstructed study model accuracy, J Orthodont., (2008), 35(3), p191-201. [https://doi.org/10.1179/146531207225022626]
• Hazeveld, A, Huddleston Slater, JJ, Ren, Y, Accuracy and reproducibility of dental replica models reconstructed by different rapid prototyping techniques, Am J Orthod Dentofacial Orthop., (2014), 145(1), p108-15. [https://doi.org/10.1016/j.ajodo.2013.05.011]
• Zilberman, O, Huggare, JA, Parikakis, KA, Evaluation of the validity of tooth size and arch width measurements using conventional and three-dimensional virtual orthodontic models, Angl Orthodont., (2003), 73(3), p301-6.