Inexpensive 3D printers for in-office solutions

Dr Fernanda Zegarra

Wed. 8. May 2024

save

The use of 3D printers is rapidly gaining interest across the world. 3D printing is threatening to replace traditional subtractive CAD/CAM methods in dentistry owing to its ability to print complex geometries, provide minimal residual stresses, eliminate tool wear and material waste, and fabricate multiple objects in a single print. These innovative machines, in combination with artificial intelligence technology, are allowing users to print virtually anything in great detail quickly and efficiently.¹

First developed in the 1980s, 3D printing has come a long way towards clinical applications in the dental field. Within the past ten years, it has become possible for clinicians to acquire printers and perform chairside CAD/CAM dentistry on their day-to-day cases.¹ Dentists are now using 3D printers to create working models, restorations, orthodontic appliances, surgical guides and maxillofacial prostheses with great accuracy and in a time-efficient manner.^1, 2

Costs of 3D printers have plummeted recently owing to the expiry of patents previously protecting the underlying technology.² As a result, we are seeing steady growth in the number of clinicians turning to 3D printing and learning how to provide patients with high-quality work without breaking the bank. This article will describe a workflow for 3D-printing and staining in-office immediate temporary restorations using an inexpensive off-the-shelf 3D printer.

Background

3D printing is an additive manufacturing method that converts a digital model into a solid 3D object. Typically, the 3D model is represented in an STL file, which stores a tessellated representation of the object as a triangular mesh.² The 3D-printing process begins by converting the triangular mesh into a series of 2D images generated by slicing the 3D model along parallel planes. The 2D images are converted to G-code, a programming language that communicates the path a printer must follow in order to reproduce the image. By printing the series of 2D images one on top of the other, a 3D object can be built from the original model.³

Different processes exist to produce 3D prints, but they can all be described as modifications to the original 3D-printing technique, stereolithography (SLA). SLA directs a UV laser along the outline of the 2D image in order to photopolymerise the resin. Once the layer has been polymerised, the build platform is raised and separated from the bottom of the tank, allowing fresh resin to flow underneath. This process repeats until the print is completed.^2, 3 Each printing technique has benefits and limitations. Typical metrics to compare printing techniques are printing speed, print quality (resolution), cost and limitations on printing materials and colours.²

The technique described in this article uses the liquid crystal display (LCD) printing process. This process uses an array of UV LEDs as a light source and passes the light through an LCD screen to project each layer’s image on to the resin. By using an LCD screen to form the image, the entire image can be projected at once, which significantly reduces the printing time compared with the single laser used in traditional SLA printing. LCD printers are high-speed and low-cost and produce accurate and precise prints with great resolution.^4, 5

Fig. 1

Fig. 2

Fig. 3

Patient scanning, support design and slicing

The process of printing an immediate temporary restoration starts with an intra-oral scan to generate a 3D digital image of the patient’s teeth and surrounding tissue. The 3D model is stored in an STL file, which can be imported into 3D modelling software to begin the design work.

In this case, the system utilised to perform the scanning was the TRIOS 5 (3Shape). Two sets of scans were taken and sent to the laboratory. First, the upper and lower jaws were scanned and a digital bite registration was recorded prior to the surgery. Then, after the implants had been placed, Neodent scan bodies (Straumann) were attached, and another digital scan was taken (Fig. 1). All of the digital models produced were sent through the 3Shape interface to Chameleon Digital Dental Lab in North Carolina in the US for the design of a maxillary FP-3 restoration.

Once the finished design had been received and approved, the STL model of the hybrid bridge was transferred to CHITUBOX 2.0 for support placement and horizontal slicing of the completed design. First, the 3D model was oriented at a 45° angle with the incisal/occlusal surface of the teeth facing the build platform to avoid any distortion on the surface of the print that will be in contact with soft tissue. The support configuration suggested for the Ferguson Mini Plate (Digital Educators) was imported into CHITUBOX, using a 1.5 mm z-axis elevation and a 75% support density as the design parameters (Fig. 2). The recommended resin profiles for the Rodin Sculpture ceramic nano-hybrid resin in Shade A1 (Pac-Dent) were then imported into CHITUBOX (Fig. 3).⁶ Finally, the design was horizontally sliced to generate 2D images of the layers to construct the 3D print.

Fig. 4

Fig. 5

Fig. 6

Fig. 7

3D printing

The 3D printer of choice was the Phrozen Sonic Mini 4K (Phrozen). This printer uses a high-resolution 4K LCD screen. The Phrozen build platform was exchanged for a Ferguson Mini Plate and a Ferguson Pro Vat Warmer (Digital Educators). This decreases the printing time by decreasing the size of the build platform, and by warming up the resin in the vat to make it less viscous and decrease the lifting time (Fig. 4).⁷

To prepare for printing, the vat was filled with Rodin Sculpture Shade A1, the Ferguson Mini Plate was installed and the vat warmer was set to 35 °C.⁶ Once the correct temperature had been reached, the printing was started. By using the Ferguson Mini Plate, the printing time was reduced from 2 hours to 1 hour and 8 minutes.

Fig. 8

Fig. 9

Fig. 10

Removal and processing of the print

Once the print had been completed, it was sprayed with compressed air until all of the remaining liquid resin was removed from the surface (Figs. 5 & 6). A small amount of 97% isopropyl alcohol was then sprayed on to the prosthesis to continue the cleaning process (Figs. 7 & 8). The amount of alcohol must be controlled to avoid degrading the structure of the print. The cleaning process was completed with one final application of compressed air. The supports were then manually removed and any trace of the attachment points on the tooth surface were removed with slow-speed acrylic burs (Figs. 9 & 10).

Characterisation and flash polymerisation

For the characterisation process, all polishing and staining were done on the unpolymerised print in order to avoid microfracturing. Anatomy and details were added with acrylic burs by slightly deepening the gingival margin and the interproximal contacts of the teeth and texturing the vestibular surfaces of the incisors and canines (Fig. 11). The Rodin Palette Naturalizing Kit was then used to stain the print. For the first layer, a mix of red and Rodin Glaze was added to the surface of the soft tissue (Fig. 12) and was polymerised with 400 flashes (no nitrogen) using the Otoflash G171 polymerisation unit (NK-Optik; Fig. 13). A thin layer of Rodin Denture Base was added, and a mix of colours were applied in different areas following organic patterns (Figs. 14–16). This process was completed in sections until the characterisation of the soft tissue was completed. Each layer of stain was polymerised using 400 flashes without nitrogen. Next, Shades A and C were applied to the gingival third of the artificial teeth, and violet and white were applied to the incisal edges and canines. The shades were blended and mixed by feathering from the middle third downwards with a wisp flat brush (Figs. 17–20) and polymerised using 400 flashes in the Otoflash.

Fig. 11

Fig. 12

Fig. 13

Fig. 14

Fig. 15

Fig. 16

Fig. 17

Fig. 18

It is important to maintain a count of the number of flashes the print is exposed to, since Rodin Sculpture is fully polymerised at 4,500 flashes.⁸ The prosthesis was exposed to 3,800 flashes during the characterisation process, so a final polymerisation stage using 700 flashes was required. The final polymerisation was performed in a nitrogen gas environment in order to remove the oxygen inhibition layer. This is achieved by flushing the polymerisation chamber intermittently with nitrogen for 30 seconds. After 30 seconds, the light activates and the polymerisation chamber continues to be flushed with nitrogen for 60 seconds (Fig. 21). Doing this prevents oxygen from interfering with the polymerisation process of the outermost layer of the print, which improves its biocompatibility.⁵ Also, studies have indicated that post-polymerising in a nitrogen gas atmosphere could improve the polymerised 3D-printing material for temporary restorations by enhancing the mechanical properties and surface smoothness.⁵ The finished print was then washed with soap and water to remove any excess material, at which point it was ready to be delivered to the patient (Figs. 22-26).

Fig. 19

Fig. 20

Fig. 21

Conclusion

We have seen that 3D printing is a fast, efficient and cost-effective process that can make clinicians’ work easier by providing a means to generate high-quality models, restorations, appliances, guides and prostheses in-house and without the need for a return visit. I have demonstrated a process to create an immediate temporary restoration using cost-effective, off-the-shelf equipment.

It is an excellent time to get started with 3D printing in dental practices owing to the low cost and high accessibility of 3D-printing equipment. For those getting started, learning to use the equipment and materials is quite achievable owing to the documentation and training provided by laboratories and equipment manufacturers, as well as the support from communities like the Dental 3D printing group Facebook group and www.digitaleducators.com, who provide parameter data and free advice for both experts and novice users.

Fig. 22

Fig. 23

Fig. 24

Fig. 25

Fig. 26

Acknowledgements

I would like to provide thanks to Dr Moemen Metwally of Van Horne Dental in Toronto in Canada for the laboratory equipment and images of his surgical case used in this study, to Dr Richard Ferguson of Dental Educators in the US for his guidance and providing the resin profiles and support configurations for printing on the Ferguson Mini Plate and to Andrew Priddy of C2C in the US for all of his advice and his introduction to the processing and staining of 3D prints.

Editorial note:

This article was published in 3D printing—international magazine of dental printing technology vol. 3, issue 2/2023. A complete list of references can be found here.