Virtual techniques for designing and fabricating a retainer

Recent advances in additive manufacturing of patient-specific devices for dental and maxillofacial rehabilitation

OBJECTIVES

Customization and the production of patient-specific devices, tailoring the unique anatomy of each patient's jaw and facial structures, are the new frontiers in dentistry and maxillofacial surgery. As a technological advancement, additive manufacturing has been applied to produce customized objects based on 3D computerized models. Therefore, this paper presents advances in additive manufacturing strategies for patient-specific devices in diverse dental specialties.

METHODS

This paper overviews current 3D printing techniques to fabricate dental and maxillofacial devices. Then, the most recent literature (2018-2023) available in scientific databases reporting advances in 3D-printed patient-specific devices for dental and maxillofacial applications is critically discussed, focusing on the major outcomes, material-related details, and potential clinical advantages.

RESULTS

The recent application of 3D-printed customized devices in oral prosthodontics, implantology and maxillofacial surgery, periodontics, orthodontics, and endodontics are presented. Moreover, the potential application of 4D printing as an advanced manufacturing technology and the challenges and future perspectives for additive manufacturing in the dental and maxillofacial area are reported.

SIGNIFICANCE

Additive manufacturing techniques have been designed to benefit several areas of dentistry, and the technologies, materials, and devices continue to be optimized. Image-based and accurately printed patient-specific devices to replace, repair, and regenerate dental and maxillofacial structures hold significant potential to maximize the standard of care in dentistry.

An In Vivo Study to Compare the Clinical Effectiveness of Clear Retainer Made on a Conventional and a Digitally Fabricated Model Over a Six-Month Period After Debonding

Background With the advent of 3D printing, many more possibilities have arisen for treatment planning. 3D rapid prototyping has enabled us to see a whole other dimension that has helped us to give the best possible care for our patients. With more and more advancements being made in this subject, it becomes necessary to check the reliability of the equipment and its effectiveness in the management of the problem at hand. This original study was conducted with the aim of checking the accuracy, dimensional stability, and reliability of orthodontic retainers made on a conventional and digitally fabricated model over a six-month period after debonding. Material and methods The patients were selected from those who have completed fixed orthodontic mechanotherapy from the Department of Orthodontics and Dentofacial Orthopaedics, Sri Guru Ram Das Institute of Dental Sciences and Research, Sri Amritsar. Fifty patients received a clear retainer, which was fabricated for the upper and lower arch after removing the brackets. Patients were included in this study irrespective of their age groups. The manual method used a vacuum-forming machine to fabricate six retainers on stone models. In the digital method, new impressions were taken after three months, and digital models were obtained through 3D scanning and printing, followed by clear retainer fabrication. The data were gathered through a systematic process involving manual and digital methods for clear retainer fabrication and subsequent evaluation. The data obtained was computed for statistical evaluation and comparison. Results Mean and standard deviations of conventional (manual) and digital variables in the two groups were calculated. An ANOVA test was used to evaluate statistically significant differences for mesiodistal width and buccolingual width, and a post hoc Tuckey test was applied for multiple comparisons. The results indicated that most mesiodistal and buccolingual width measurements showed non-significant variations and exhibited a good correlation. Extraction space opening, assessed through an independent t-test for both the maxilla and mandible, also yielded non-significant and comparable results. Additionally, intra-operator and inter-operator measurements using a digital caliper demonstrated high agreement. Intra-class correlation (ICC) values exceeded 0.75, and inter-operator ICC results reflected a high level of agreement ranging from 0.8 to 0.99. Conclusion The primary objective of this study was to establish a correlation between the accuracy, dependability, and clinical efficacy of orthodontic retainers produced using both conventional and digitally created models. This investigation spanned a duration of six months following the removal of orthodontic brackets. The results showed that most of the statistically significant values were due to the inherent potential of the 3D printer for polymerization shrinkage, which, being a stereolithographic 3D printer, had a potential for a slight dimensional shift in the transverse dimension. However, the mean difference between all the models printed was slight and clinically insignificant.

The effect of crowding on the accuracy of 3-dimensional printing

INTRODUCTION

The purpose of this study was to evaluate the accuracy of 3-dimensional (3D) printed aligners compared to conventional vacuum-formed thermoplastic aligners with varying levels of dental crowding.

METHODS

Digital intraoral scans of 10 cases were assigned to their respective groups (n = 10, each, 30 total) as follows: no crowding (control), moderate crowding, and severe crowding. Digital images of these models were created in standard tessellation language (STL) file format using 3Shape software and randomly 3D printed. The STL files of each case were also sent to a dental laboratory to fabricate vacuum-formed samples, the current technology used for manufacturing aligners. The intaglio surfaces of fabricated aligners in both groups were scanned using cone beam computed tomography to create STL files, which were then compared to the original STL files of the cases using Geomagic Control X software. Absolute deviations from the original file and root mean square values were recorded. A Kruskal-Wallis test was conducted to analyze the difference in average deviation, and a t-test was repeated for the RMS measure. The significance level was set at 0.05.

RESULTS

The crowding did not affect the trueness of aligners manufactured using 3D printing or conventional vacuum-forming techniques (P = 0.79). 3D-printed aligners showed less deviation than the vacuum-formed samples (0.1125 mm vs 0.1312 mm; P <0.01). Aligners manufactured with the vacuum-forming technique had significantly higher variation than those with the 3D printing process (P = 0.04).

CONCLUSIONS

3D aligners printed directly from an STL file exhibited better precision and trueness than those fabricated using the conventional vacuum-forming technique. Since accuracy is defined as a combination of precision and trueness, it is concluded that direct printing from an STL file can be used to manufacture aligners.

3D Technology Used for Precision in Orthodontics

One of the most crucial technologies used by orthodontists to assess and document the dimensions of craniofacial features is imaging. Orthodontists frequently employ two-dimensional (2D) imaging methods, although 2D imaging cannot localize or determine the depth of structures. Early in the 1990s, three-dimensional (3D) imaging was invented, and it has since become a crucial part of dentistry, especially in orthodontics. One of the newest and most important breakthroughs in dentistry is 3D technology. Clinicians have been able to significantly improve patient care while also shortening the time spent on treatment planning due to these technologies, which include intra-oral scanning, 3D imaging, computed-axial tomography (CAT) scan, cone-beam computed tomography (CBCT), computer-aided design/computer-aided manufacturing (CAD/CAM), and 3D software. 3D models of maxillary and mandibular arches can take the place of conventional plaster casts and their limits for planning treatments, appliance production, and estimated treatment results as part of this continuous progress. Digital orthodontics procedures have become more popular in the recent past. The development of "personalized" orthodontic appliances makes use of technology. These technologies' overall improvement can increase clinicians' productivity and efficiency by simplifying traditional methods that are seen to be particularly laborious. The objectives of this review are to provide an overall description of the 3D technology nowadays and to assess its orthodontic applications.

The Impact of Adding Chitosan Nanoparticles on Biofilm Formation, Cytotoxicity, and Certain Physical and Mechanical Aspects of Directly Printed Orthodontic Clear Aligners

Aligner treatment is associated with bacterial colonization, leading to enamel demineralization. Chitosan nanoparticles have been demonstrated to have antibacterial properties. This in vitro study aims to determine the effect of adding chitosan nanoparticles to directly 3D-printed clear aligner resin with regard to antibiofilm activity, cytotoxicity, degree of conversion, accuracy, deflection force, and tensile strength. Different concentrations (2%, 3%, and 5% w/w) of chitosan nanoparticles were mixed with the clear resin, and the samples were then 3D printed. Additionally, the thermoforming technique for aligner manufacturing was utilized. The obtained specimens were evaluated for antibiofilm activity against Streptococcus mutans bacteria and cytotoxicity against L929 and 3T3 cell lines. Additionally, Fourier transform infrared spectroscopy via attenuated total reflection analysis was used to assess the degree of conversion. Geomagic Control X software was utilized to analyze the accuracy. In addition, the deflection force and tensile strength were evaluated. The results indicated a notable reduction in bacterial colonies when the resin was incorporated with 3 and 5% chitosan nanoparticles. No significant changes in the cytotoxicity or accuracy were detected. In conclusion, integrating biocompatible chitosan nanoparticles into the resin can add an antibiofilm element to an aligner without compromising the material's certain biological, mechanical, and physical qualities at specific concentrations.

Coffee Staining and Simulated Brushing Induced Color Changes and Surface Roughness of 3D-Printed Orthodontic Retainer Material

This in vitro study evaluated the influence of combined coffee staining and simulated brushing-induced color changes and surface roughness on 3D-printed orthodontic retainers. Specimens measuring 10 × 10 × 0.75 mm³ were obtained either by conventional vacuum forming or 3D printing at four print angulations (0°, 15°, 30°, and 45°) (n = 10). The prepared specimens were immersed in a coffee beverage and then mechanically brushed using a simulating device. The specimen's color difference (ΔE) and surface roughness (Ra) were quantified using a spectrophotometer and a non-contact profilometer, respectively. The highest and lowest mean ΔE values were recorded for the 3D-printed-45° (4.68 ± 2.07) and conventional (2.18 ± 0.87) groups, respectively. The overall mean comparison of ΔE between the conventional and 3D-printed groups was statistically significant (p < 0.01). After simulated brushing, all groups showed a statistically significant increase in the Ra values (p < 0.01). The highest Ra was in the 3D-printed-45° (1.009 ± 0.13 µm) and conventional (0.743 ± 0.12 µm) groups, respectively. The overall ΔE of 3D-printed orthodontic retainers was not comparable to conventional VFRs. Among the different angulations used to print the retainers, 15° angulations were the most efficient in terms of color changes and surface roughness and were comparable to conventional VFRs.

Direct 3D-Printed Orthodontic Retainers. A Systematic Review

Three-dimensional (3D) printing technology has shed light on many fields in medicine and dentistry, including orthodontics. Direct 3D-printed prosthetics, implants or surgical devices are well-documented. The fabrication of orthodontic retainers using CAD technology and additive manufacturing is an emerging trend but the available data are scarce. The research approach of the present review included keywords in Medline, Scopus, Cochrane Library and Google Scholar up to December 2022. The searching process concluded with five studies eligible for our project. Three of them investigated directly 3D-printed clear retainers in vitro. The other two studies investigated directly 3D-printed fixed retainers. Among them, one study was in vitro and the second was a prospective clinical trial. Directly 3D-printed retainers can be evolved over time as a good alternative to all the conventional materials for retention. Devices that are 3D-printed are more time and cost efficient, offer more comfortable procedures for both practitioners and patients and the materials used in additive manufacturing can solve aesthetic problems, periodontal issues or problems with the interference of these materials with magnetic resonance imaging (MRI). More well-designed prospective clinical trials are necessary for more evaluable results.

Clinically Relevant Properties of 3D Printable Materials for Intraoral Use in Orthodontics: A Critical Review of the Literature

The review aimed at analyzing the evidence available on 3D printable materials and techniques used for the fabrication of orthodontic appliances, focusing on materials properties that are clinically relevant. MEDLINE/PubMed, Scopus, and Cochrane Library databases were searched. Starting from an initial retrieval of 669 citations, 47 articles were finally included in the qualitative review. Several articles presented proof-of-concept clinical cases describing the digital workflow to manufacture a variety of appliances. Clinical studies other than these case reports are not available. The fabrication of aligners is the most investigated application of 3D printing in orthodontics, and, among materials, Dental LT Clear Resin (Formlabs) has been tested in several studies, although Tera Harz TC-85 (Graphy) is currently the only material specifically marketed for direct printing of aligners. Tests of the mechanical properties of aligners materials lacked homogeneity in the protocols, while biocompatibility tests failed to assess the influence of intraoral conditions on eluents release. The aesthetic properties of 3D-printed appliances are largely unexplored. The evidence on 3D-printed metallic appliances is also limited. The scientific evidence on 3D printable orthodontic materials and techniques should be strengthened by defining international standards for laboratory testing and by starting the necessary clinical trials.

Advances in orthodontic clear aligner materials

Rapid technological improvements in biomaterials, computer-aided design (CAD) and manufacturing (CAM) have endorsed clear aligner therapy (CAT) as a mainstay of orthodontic treatment, and the materials employed for aligner fabrication play an all-important role in determining the clinical performance of clear aligners. This narrative review has attempted to comprehensively encompass the entire gamut of materials currently used for the fabrication of clear aligners and elucidate their characteristics that are crucial in determining their performance in an oral environment. Historical developments and current protocols in aligner fabrication, features of contemporary bioactive materials, and emerging trends related to CAT are discussed. Advances in aligner material chemistry and engineering possess the potential to bring about radical transformations in the therapeutic applications of CAT; in the absence of which, clear aligners would continue to underperform clinically, due to their inherent biomechanical constraints. Finally, while innovations in aligner materials such as shape memory polymers, direct three-dimensional (3D) printed clear aligners and bioactive materials combined with clear aligner materials are essential to further advance the applications of CAT; increased awareness of environmental responsibilities among aligner manufacturers, aligner prescribing clinicians and aligner users is essential for better alignment of our climate change goals towards a sustainable planet.

Accuracy of additive manufacturing in stomatology

With the rapid development of the three-dimensional (3D) printing technology in recent decades, precise and personalized manufacturing has been achieved gradually, bringing benefit to biomedical application, especially stomatology clinical practice. So far, 3D printing has been widely applied to prosthodontics, orthodontics, and maxillofacial surgery procedures, realizing accurate, efficient operation processes and promising treatment outcomes. Although the printing accuracy has improved, further exploration is still needed. Herein, we summarized the various additive manufacturing techniques and their applications in dentistry while highlighting the importance of accuracy (precision and trueness).

The Application of a 3-Dimensional Printing Technique in Refining the Orthodontic Trans-Palatal Arch

The aim of this article was to describe the process of designing and manufacturing 3D TPAs and to discuss some clinical cases in which 3D TPAs were used. Digital models were acquired by scanning the casts, scanning the PVS impressions or scanning the dentitions directly. The scanning data in a common STL format was used for the computer design that follows. Then, the design instructions were sent to a 3D printer for fabrication. Finally, manual polishing should be performed. Seven clinical cases in which 3D TPAs were used to assist orthodontic treatment were presented and discussed. The presented clinical cases demonstrated that the 3D TPA was a simple, convenient appliance for the patient and the doctor, and thus, might be more cleansable. The 3D TPA could be designed in different types based on the clinical needs of each case. The application of 3D TPA could be expanded, but clinical trials are necessary to verify the advantages reported here.

Three-Dimensional-Printed Customized Orthodontic and Pedodontic Appliances: A Critical Review of a New Era for Treatment

Three-dimensional (3D) designing and manufacturing technology is a direct derivative of digital technology. Three-dimensional volume and surface acquisition, CAD software, and 3D manufacturing are major changes included in daily practice in many orthodontic and pedodontic offices. Customized appliances can be designed using dental CAD software or general-purpose CAD software in the office or a laboratory. Materials that can be used are resins, alloys, or zirconia. Methods: The search strategy of this critical review included keywords in combination with MeSH terms in Medline, Scopus, and Cochrane Library up to June 2022 in the English language without any limit to the publication period. Results: According to our search, 12 articles were selected for our study. All the articles were in vitro prospective studies. Conclusions: The results suggested that almost all the known appliances can be designed and printed in a tailor-made fashion in contrast to the traditional one-size-fits-all approach. Customized appliances should be manufactured according to the patient’s needs, and this is justified by the certainty that this approach will be beneficial for the patient’s treatment. There is a need for more research on all direct 3D-printed appliances.

Comparison of 3-dimensional printing technologies on the precision, trueness, and accuracy of printed retainers

INTRODUCTION

This study aimed to evaluate the differences in the precision, trueness, and accuracy of 3-dimensional (3D) printed clear orthodontic retainers fabricated using printer systems with different printing technologies.

METHODS

Retainers (n = 15) were 3D printed using 4 different printers: stereolithography (SLA), digital light processing (DLP), continuous DLP, and polyjet photopolymer (PPP) printers. Printed retainers were transformed into a digital image through a cone-beam computed tomography scan and compared with the original image using 3D superimposition analysis software. At previously chosen landmarks (R6, L6, R3, L3, R1, and L1), intaglio surfaces of the retainers were compared to that of the reference model. The intercanine and the intermolar width measurements were also assessed. A discrepancy of up to 0.25 mm between the printed retainer and the reference retainer intaglio surfaces indicated accuracy and clinical acceptability. Precision and trueness were also determined. Root mean square and percent of points within the tolerance level were calculated for precision and trueness for each retainer. Statistical significance was set at P <0.05.

RESULTS

Interrater correlation coefficient indicated good agreement. Statistically significant differences were found between printer types among the 6 landmarks and the arch width measurements. When evaluating tolerance level and root mean square, statistically significant differences in median precision and trueness among each printer type were found.

CONCLUSION

Retainers fabricated by SLA, DLP, continuous DLP, and PPP technologies were shown to be clinically acceptable and accurate compared to the standard reference file. Based on both high precision and trueness, SLA and PPP printers yielded the most accurate retainers.

Application of Three-Dimensional Digital Technology in Orthodontics: The State of the Art

Three-dimensional technologies are one of the most recent and relevant advancements in the field of Dentistry. These systems, including intraoral scans, 3D imaging exams (CAT scan, CBCT and MRI), CAD/CAM 3D printing devices and 3D computer software, have enabled clinicians to greatly improve patient care along with reducing treatment planning time. The present descriptive study aims to explore possible applications of 3D technologies during the diagnosis, treatment plan, case monitoring and result assessment in orthodontics. The overall upgrade provided by these technologies can improve the clinicians’ workflow and effectiveness by simplifying conventional techniques considered to be especially arduous.

Effect of print angulation on the accuracy and precision of 3D-printed orthodontic retainers

INTRODUCTION

The study aimed to (1) compare the accuracy and precision of 3-dimensional (3D) printed retainers at various angulations and (2) evaluate the effect of angulation on printing time and the amount of resin consumed.

METHODS

Using a stereolithography 3D printer, 60 clear retainers were printed at 5 angulations (n = 12, each): 15°, 30°, 45°, 60°, and 90°. Samples for each group were randomly printed in a batch of 6 retainers at all print angulations as print 1 and print 2 cycles. Digital images of the original and printed samples were superimposed. Discrepancies on 8 landmarks were measured by 2 independent examiners, and 0.25 mm was set as the clinically acceptable threshold to determine the accuracy of the retainers.

RESULTS

Deviations ranged from 0.074 mm to 0.225 mm from the reference retainer at the cusp tips and incisal edges at all angulations, falling within the threshold of clinical acceptance. However, smooth surface measurements with deviations up to 0.480 mm were deemed clinically not acceptable. Three-dimensional printing at 15° was estimated to be the most time-efficient, whereas 3D printing at 45° was shown to be the most cost-effective setting.

CONCLUSIONS

Three-dimensional printed retainers, using a stereolithography printer, were found to be accurate within 0.25 mm at all print angulations at the cusp tips and incisal edges compared with the digital reference file. Smooth facial surfaces did not meet clinical acceptability. Print angulations were shown to affect the cost and amount of resin used.

Orthodontic retention: what's on the horizon?

Orthodontic retention remains one of the great challenges in orthodontics. In this article, we discuss what is on the horizon to help address this challenge, including biological approaches to reduce relapse, treating patients without using retainers, technological developments, personalised medicine and the impact of COVID-19 on approaches to orthodontic retention.

Biomechanical analysis of reinstating buccally flared maxillary 2nd molars using 3D printing anchorage supports: a 3D finite element study

The buccally flared maxillary 2nd molar has certain consequences on oral function and health. However, existing methods have some degree of disadvantages, such as invasion, complexity and side effects. The objectives of this study were to design anchorage systems to correct buccally flared maxillary 2nd molars and analyze their biomechanical effects by 3-dimensional (3D) finite element analysis. Finite element (FE) models of the 3D tanspalatal arches (TPAs) and 3D splints with different thicknesses and force points were constructed. The stress distribution on teeth, the hydrostatic pressure on periodontal ligaments and the initial displacement of teeth were analyzed. A total of 18 FE models were constructed and analyzed. The stress concentrated on a single anchorage tooth, and the hydrostatic pressure and initial displacement of the anchorage tooth were greater than those of the malposed 2nd molar in the 3D splint anchorage system. The stress spread on all anchorage teeth and the hydrostatic pressure and initial displacement of the anchorage tooth were less than those of the malposed 2nd molar in the 3D TPA anchorage system. Theoretically, the 3D TPA was better than the 3D splint as an anchorage to correct the buccally flared 2nd molar. A combination of 0.8 mm of thickness and mesial force point provided the optimal conditions for the 3D TPA. Further clinical studies should be conducted to verify the effects of 3D appliances.

Mechanical and geometric properties of thermoformed and 3D printed clear dental aligners

INTRODUCTION

The aim of this research was to compare compressive mechanical properties and geometric inaccuracies between conventionally manufactured thermoformed Duran clear dental aligners and 3D printed Dental Long Term (LT) resin-based clear aligners using 3D modeling and printing techniques.

METHODS

Impressions of the patient's dentition were scanned and using 3D modeling software, dental models were designed and 3D printed. These printed models then underwent vacuum thermoforming to thermoform a clear Duran thermoplastic sheet of 0.75-mm thickness into clear dental aligners of the same thickness of 0.75 mm. For the same dental model, aligners were also designed and 3D printed to 0.75-mm thickness creating biocompatible clear dental aligners using Dental LT resin utilizing a Formlabs 3D printing machine for direct usage by the patients. Five observers calculated teeth height for both types of aligners for evaluation of geometric deviations. Both types of aligners were subjected to compression loading of 1000 N to evaluate their load vs displacement behavior.

RESULTS

3D printed cured clear dental aligners were found to be geometrically more accurate with an average relative difference in tooth height of 2.55% in comparison with thermoformed aligners (4.41%). Low standard deviations (0.03-0.09 mm) were observed for tooth height measurements taken by all the observers for both types of aligners. 3D printed aligners could resist a maximum load of nearly 662 N for a low displacement of 2.93 mm; whereas, thermoformed aligners could resist a load on only 105 N for 2.93-mm displacement. Thermoformed aligners deformed plastically and irreversibly for large displacements; whereas, 3D printed aligners deformed elastically with reversibility for lower displacements.

CONCLUSIONS

3D printed and suitably cured Dental LT resin-based clear dental aligners are suggested to be more suitable for patient use as they are geometrically more accurate; this presents an opportunity to make processing time savings while ensuring an aligner is mechanically stronger and elastic in comparison with the conventionally produced thermoplastic-based thermoformed clear dental aligners.

Comparison of Overall Fit of Milled and Laser-Sintered CAD/CAM Crown Copings

Background and Aims

The aim of this study was to investigate the effect of computer-aided design/computer-aided manufacturing (CAD/CAM) procedures on the overall fit of metal copings.

Materials and Methods

A standardized die was made in die stone of an upper right molar prepared for a full crown. The die was digitalized by an Identica Blue Light Scanner, and the coping substructure was designed using CAD software. Ten milled specimens and ten laser-sintered specimens were manufactured by Renishaw plc based on the generated file by the software. All twenty copings were digitized by the Identica scanner, and the data were superimposed with the original premanufacturing data file of the prepared full crown. Using the Geometric Modelling Library (GML) package, the fit discrepancies were displayed as colour maps showing discrepancies in three dimensions. Each map was made up of thousands of data points carrying numerical error values allowing detailed analyses.

Results

The milled group displayed a mean of fit discrepancies of 42.20 μm (SD 3.04 μm), while the laser-sintered group showed a mean of 42.24 μm fit discrepancies (SD 2.94 μm). Thus, a small difference of 0.04 μm between the two groups was detected.

Conclusions

The evaluated manufacturing systems can be used in dental practice as a small and insignificant discrepancy of fit between the two manufacturing methods was detected.