Immediately Loading a 3D-Printed Denture Following Implant Surgery
Fiber-composite reinforcement material offers alternative to metal bars
Daniel Domingue, DDS | Cory Glenn, DDS
Immediately loading lower-arch acrylic dentures onto implants is a common practice in dental offices that has demonstrated high success rates.1-3 However, the fracturing of these prostheses is also a very common occurrence.4 Intraoral welding is a well-documented technique5 that provides an immediate and strong fixed solution for patients who need full-arch fixed temporary teeth on the day of implant surgery. This procedure has been well-documented in the literature as a predictable solution for both the maxilla and mandible;6 however, it is not approved by the U.S. Food and Drug Administration (FDA) to be used in the United States. Even if this procedure was FDA-approved, acquiring an intraoral welding unit and the training to perform this technique can be costly regarding time and financial resources.
Therefore, in the United States, an acceptable lower-cost solution is needed to meet the demand for providing rigid fixed prosthetics on the day of surgery that reduces the number of complications postoperatively (eg, peri-implant bone loss, pain, failure due to mobility of temporary restorations from prosthesis fracture, etc).7,8
As patient awareness of the possibilities of immediately loaded full-arch converted dentures increases with marketing and advertising from various media outlets, the techniques used by oral surgeons to provide this service to the population should be predictable and reliable, increasing the success rates of strong osseointegrated implant retained temporary prostheses, eliminating minor complications, and preventing implant failure from overloaded implants.
One solution involves immediately loading a 3-dimensionally printed, digitally designed, resin denture that has been strengthened by a metal-free, fiber-composite material consisting of an epoxy resin matrix reinforced with multidirectional glass fibers (Trilor® Arch, Bioloren). If this concept, which is demonstrated in the following case report, is widely accepted and adopted, it could help to eliminate the risk of fracture, ensure patient satisfaction during the healing process, and reduce the overall cost of the denture. The immediate loading of the reinforced denture on four implants was no more or less difficult to accomplish when compared with conventional non-reinforced techniques that are used today.9
A patient who began experiencing tremors related to the rapid progression of Alzheimer's disease, which made it difficult to retain his lower denture, presented to the office seeking an implant-retained solution so that he could maintain a healthy diet while in treatment. A cone-beam computed tomography (CBCT) scan (PreXion3D CBCT, PreXion) of the upper and lower jaws was obtained, and the patient's existing dentures were scanned separately. The DICOM files obtained from the scans were then imported into planning software (Blue Sky Plan®, Blue Sky Bio) where all of the digital planning occurred. After the inferior alveolar nerves were initially mapped, four 3.5 x 11.5 mm implants (BIO Max NP, Blue Sky Bio) were virtually placed. These implants were planned and spaced appropriately to increase the anterior-posterior spread in the remaining available bone congruent to the final prosthetic outcome (Figure 1). The lower jaw was then segmented within the software to convert the DICOM file into one with surface geometry (ie, STL or OBJ). After the lower jaw was segmented, a guide was designed to achieve the desired bone reduction (Figure 2), which was then used to set up the design for the pilot drill guide congruent with implant depth, angulation, and proximal spacing (Figure 3). These guides were exported as STL files and fabricated with an in-office 3D printer (CEL Robox® 3D Printer, Robox) out of co-polyester filament material (nGen, colorFabb).
To design the temporary immediate load prosthetics, the scan of the patient's existing denture was imported into the planning software and turned into a digital replica in the form of an STL file. Although it would have been possible to just convert the patient's existing denture into a transitional prosthesis, the end result would have been weak and prone to breaking. Therefore, it was desirable to find a way to 3D print the digital replica denture and then convert it into a much stronger prosthesis that could be immediately loaded. The goal was to do this by reinforcing the denture with a preformed bar made from a metal-free, fiber-composite material consisting of an epoxy resin matrix reinforced with multidirectional glass fibers (Trilor® Arch, Bioloren), which has a high flexural strength (540 MPa) and physiologic modulus of elasticity (26 MPa).
Fabrication of the Prosthesis
The initial challenge was to figure out where the available space was within the denture to place the preformed arch bar. To accomplish this, the STL file of the denture was exported and then opened using free 3D modeling software (Meshmixer, Autodesk). Using the "hollow" function, the entire denture was hollowed out, leaving a wall thickness of 0.5 mm. Once hollowed, the outer shell was deleted, which resulted in the denture being uniformly (Figure 4) reduced by 0.5 mm in all dimensions. This remaining object represented all of the available space into which the preformed bar could be positioned without impinging on the 0.5-mm exterior surface of the denture. Next, the preformed bar was scanned using a desktop 3D dental scanner (AutoScan-DS-EX, Shining 3D), and this digital object was imported and positioned within the denture in a way that maximized the space available (Figure 5). Once the bar was virtually positioned into the greatest bulk of the denture, it could be further cut down to shape. The goal was to create a bar template that could be 3D printed and laid over the preformed bar to allow it to be precisely cut to fit within the denture using only chairside burs (Figure 6). In addition, it was necessary to 3D print a new denture that had this shape hollowed out of it so that the trimmed bar material could be picked up inside of it.
The first step was to split the STL file of the mandibular denture in half along the horizontal plane, creating an upper and lower part into which the trimmed preformed bar could be sandwiched. Next, the trimmed bar template must be subtracted from both the upper and lower parts to create the space for the final material to fit into. This was accomplished by using the free 3D modeling software to perform a Boolean subtraction (Figure 7).
Once the software portion of the prosthetic design was completed, the upper and lower halves of the denture needed to be created. Traditionally, it would be necessary to mill or cast a prosthesis to realize sufficient strength; however, in this case, only low-cost 3D printing was used. A 3D-printed fixed prosthesis would normally be far too weak, but with the reinforcement of a high-tech fiber composite material, it becomes an incredibly strong prosthesis. The upper half was printed (Moonray S 3D Printer, SprintRay) in a white shade crown and bridge material (C&B Micro Filled Hybrid, NextDent), the lower half was printed in a pink base material (Nextdent™ Base, NextDent), and the bar template was printed to be used to transfer the shape over to the final preformed arch bar material (Figure 8). Because the entire upper portion was printed with tooth-colored material, it was necessary to apply pink gingiva by hand around the necks of the teeth. This was done by syringing on additional pink base resin and light curing.
After the patient was intravenously sedated, a surgical incision was made with a No. 15C scalpel blade, splitting the keratinized gingiva to the retromolar pad area on both sides of the arch (Figure 9). A full-thickness flap was elevated buccally and lingually, releasing the soft tissue enough to allow the bone reduction guide to fully seat on the bone without soft-tissue impingement (Figure 10). Using an electric surgical handpiece with a cutting bur (Lindemann Side Cutting Bur-HP, Salvin Dental Specialties), 4 mm of mandibular bone was removed and the ridge was smoothed to level the horizontal plane of occlusion. The sequential surgical guides were then placed on the reduced mandible and checked for a precise fit before a series of twist drills (ie, starter pilot 2.0 mm, 2.6 mm, 3.4 mm, 3.6 mm implant guide) were used at a speed of 2,000 rpm with copious saline irrigation to create four osteotomies. The sequential drills were used to widen the osteotomies before four 3.5 x 11.5 mm implants (BIO Max NP, Blue Sky Bio) were placed and torqued to initial stability (ie, 35 Ncm) through the implant guide (Figure 11). Next, 3-mm multiunit abutments were placed on the implants and torqued to 30 Ncm to allow for the temporary titanium multiunit coping abutments to be seated. These were then tied together using floss and a modeling resin material (primopattern LC Universal Modeling Resin, primotec USA) (Figure 12) to ensure stability. An open tray final impression was taken (Aquasil® Ultra Smart Wetting® Impression Material, Dentsply Sirona) and brought into the laboratory to pour a model with the multiunit implant analogs (Figure 13). In the patient's mouth, cover caps were placed on the multiunit abutments, the exposed bone was covered with platelet-rich fibrin (PRF), and the soft tissue was loosely sutured to closely approximate the gingiva around the layers of PRF that kept it from gaining primary closure (Figure 14).
To guide the adjustments made on the temporary 3D-printed bar template, the laboratory used a No. 2 pencil to mark the top of the titanium sleeves (Figure 15), then lined them up and pressed them against the bar template, which left marks that indicated areas of adjustments. The bar template was then placed over the 3.5 mm preformed arch bar, the details were transferred, and the final bar was trimmed to the correct size to fit passively over the temporary titanium multiunit implant abutments and into the 3D-printed denture. Once the final bar was passively fit into the denture, four holes were made through the denture that were congruent with the bar (Figure 16). Because of time constraints imposed by the patient, the implant surgery was performed on a Friday, and he returned the following week to fixate the lower denture. Titanium sleeves were transferred from the model into the patient's mouth, and then, the preformed arch bar and denture were checked for passivity (Figure 17) before being picked up in a hard denture reline material (Rebase II, Tokuyama) once the bite was confirmed. The prosthesis was smoothed and highly polished before final delivery. A final panoramic x-ray image was taken to confirm the fit of the abutments (Figure 18). Although the intention was to provide the final restoration within 3 months, due to the severity of the patient's medical condition, he missed several appointments and was unable to return for 12 months. With the added strength of the fiber-composite reinforcement material, his temporary denture remained stable for the entire 12-month period.
This technique of placing a preformed arch bar within a 3D-printed denture and over endosteal dental implants exceeded expectations. In this case, the design process, printing, shipping, and performance of the surgery were completed in 3 days; however, with increased access to 3D-printed denture techniques and future developments in software, this time could be further reduced to a predictable 1-day turnaround for an immediately loaded full-arch case.
Other future techniques could possibly include use of the preformed arch bar in the final prosthesis or delivery of the final, permanent fixed denture on the day of surgery. More procedures need to be performed on patients, and the results need to be documented to assess the long-term success rates regarding fracture when compared with traditional dentures and other fixed dentures, both with and without metal-reinforced substructures. As the materials used in 3D printing increase in strength and stability and future techniques are developed to improve upon this design and accomplish immediate fixation of the prosthesis inside the mouth instead of inside the laboratory, this could eventually become a routine and predictable procedure to provide an unbreakable temporary or permanent denture on the day of surgery.
About the Author
Daniel Domingue, DDS
American Academy of Implant Dentistry
American Board of Oral Implantology
International Congress of Oral Implantologists
Cory Glenn, DDS
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