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Most restorative dentists are familiar with the "conventional" (also known as traditional or analog) technique of denture fabrication with the multiple steps and visits required: preliminary impressions, preliminary casts, custom trays, border molding, final impressions, master casts, maxillomandibular records, try-ins, and final delivery. If post-delivery adjustment visits are included, this technique requires a minimum of six visits over an extended period of time. Designing and manufacturing dentures digitally has streamlined the fabrication process and dentures can now be delivered conceivably in as little as one visit (Ivory Digital Denture, Ivory Digital Dentures; ivorydigitaldenture.com). Once impressions are made, all the necessary scanning, design, and printing of the final dentures are done while the patient waits in the office. This requires the purchase of a scanner and 3D printer and may present a financial barrier to some, but it highlights the progress that has been made over the past several years.
Digital Denture Options Abound
The very first commercially available digital denture system in the United States was offered by Dentca, followed by Avadent. There were several variations made available over time, starting with 3-dimensional printing then eventually milling of the various components. Over the following years, numerous companies have developed their own systems for digital denture fabrication, including, but not limited to: 3Shape, Amann Girrbach, Blue Sky Bio, Dental Wings, exocad, Ivoclar Vivadent, Kulzer, and Merz.
Space limitations in this article do not permit a complete and thorough explanation of each and every service that is offered. Various options involve digitizing different parts of the process, from scanning to design to the try-in and fabrication of the final prosthetic. Full and partial outsourcing options are available, along with complete in-house solutions. Milling and/or 3D printing can be utilized. The final prosthetic can be fabricated completely digitally including the teeth, completely conventionally (following digital design and try-in), or partially digitally with a milled or printed base and traditional denture teeth. This article will serve as an introduction, overview and update of the numerous digital options available today for complete dentures.
Once collaborations began, additional options became available. For example, Avadent now receives their milling disks from Dentsply Sirona and can provide almost any brand of denture tooth the practitioner desires. The denture base is milled to accommodate the shape of the denture tooth. Each individual denture tooth is then bonded into place (Figure 1). However, this can be a tedious, time-consuming process. As an alternative, Avadent's proprietary eXtreme-Cross-Linked (XCL) technology provides a milled, monolithic, one-piece denture (Figure 2 and Figure 3). Dentca provides design services and will either 3D print the denture base and teeth and deliver the finished denture (Figure 4) or send the STL file to the dentist to print on-site, provided that the printer and materials are compatible with Dentca's software (Figure 5 and Figure 6). Because the denture teeth are 3D printed, they tend to be monolithic and can present some esthetic challenges. Ivoclar Vivadent has provided yet another alternative. The milling process is done in multiple stages. First, the denture base is milled with precise cavities for the denture teeth. Next, the dental arch is milled as one piece, occlusally oversized but basally exact (Figure 7). The dental arch is then quickly and easily cemented to the denture base. The disk is then returned to the mill for final finishing and excess adhesive removal.1
The advantages of CAD/CAM complete dentures have been very well documented. It reduces the amount of chair time and number of patient visits,2 provides better fit,3 has superior mechanical and physical properties,4 and costs less overall5 than conventionally fabricated dentures. In addition, digitally fabricated dentures have been shown to result in higher patient satisfaction.6-8
The theme for all digital dentures is similar. Computer software aids the design, then the denture base and teeth are either milled or 3D printed. With the increasing popularity and decreasing costs of 3D printers and milling machines, much of complete denture fabrication is now done without the use of injection molding or conventional flasking.
One Denture Made Three Ways
A healthy 71-year-old woman presented to the office with maxillary and mandibular complete dentures with a chief complaint of a loose mandibular denture. After examination it was determined that her maxillary complete denture was serviceable, comfortable, intact, retentive and stable. Her mandibular denture however was ill-fitting, with underextended posterior borders due to an enlarged maxillary tuberosity. Since the two-implant mandibular overdenture has long been accepted as the standard of care for the edentulous mandible,9,10 it was determined this would be the patient's treatment plan.
With the patient's consent, it was agreed that the restoration team would fabricate three complete mandibular overdentures using three different methods. This exercise illustrates some of the numerous options available today for complete denture fabrication.
Using the Massad technique,11 a conventional impression was made using a mandibular Dentca tray. Compared to conventional techniques, the Massad technique has been shown to require no additional adjustments after 1 year12 and to exhibit no difference in retention in the final denture.13 An alginate impression was made of the existing maxillary denture, and the impressions were poured in Denstone Golden Type III Model Stone (Kulzer; kulzer.com) (Figure 8). A baseplate and occlusal rim were fabricated, and maxillomandibular records were obtained. After an anterior and posterior tooth try-in, the conventionally processed mandibular overdenture was fabricated.
This particular method has truly withstood the test of time. It has been in use for numerous decades and continues to be used successfully today. Although more time consuming for both the patient and practitioner, it has been proven to provide a satisfactory result.
The same master and counter casts that were made for the conventional fabrication were scanned using a 3Shape desktop D2000 scanner (Figure 9) (3shape.com). The same baseplate and wax occlusion rim fabricated from the prior method were also used, and maxillomandibular records were obtained and scanned. The 3Shape denture module software was then used to design the mandibular overdenture (Figure 10). Although it required an additional cost, the 3Shape denture software allowed the selection from several denture tooth libraries. It also allowed latitude in the process, allowing the practitioner to design the entire denture, including border extensions and occlusal scheme.
Upon completion of the design, the STL file was sent to the milling machine (vhf R5, vhf camfacture AG; vhf.de) and the denture base and teeth were milled from Ivoclar Vivadent acrylic disks (Figure 11 and Figure 12). A variety of brands and materials can be used to mill the denture teeth and denture base.
The mandibular impression taken for the conventional setup was sent to Dentca along with an occlusal record and the maxillary counter cast (Figure 13). A design proposal for the mandibular overdenture was sent back via email for approval (Figure 14), as modifications of the proposed design can be requested at this stage. Once the design was approved, a 3D printed try-in of the proposed denture was returned and tried in the mouth (Figure 15 and Figure 16). After approval of the try-in, the final denture was fabricated (Figure 17).
Dentca offers a unique process with the first try-in included. However, it does not ordinarily allow the practitioner access to change the STL design files. Modifications cannot be made by the practitioner; they must be communicated via email and then made by Dentca.
Another approach, a bit closer to the conventional method, is to just have the denture bases milled, then complete the remaining steps using the conventional methods of wax rims and setting denture teeth.14 This allows for the benefit of the superior accuracy of the fit of the milled dentures bases, but the dentist maintains more control in the manipulation of the artificial tooth set-up.
The patient in this case report received three separate mandibular overdentures, each of which was clinically acceptable. At the time of writing, she showed a slight preference for the milled denture. She reports that they all fit well and are very secure, but she likes the way that one looks the best. It is difficult to make any conclusions from just one patient's experience, but her statement reminds us just how important esthetics can be to the individual.
Many have asked "When will we be able to scan the edentulous arch, and do away with impression material and border molding altogether?" A recent systematic review has shown that intraoral scanning of edentulous arches is possible, but still remains a challenge.15 Although that may be the case, some reports show it is being attempted successfully, with acceptable clinical results.16,17 Intraoral retraction devices have been suggested to minimize soft tissue movement and enable the maximum amount of capture of the soft tissue.18 Two-dimensional photographs have also been used to produce 3D images.19
The digital denture realm continues to advance at a fast pace. Several fabrication options and numerous software modules exist giving the provider a wide range of choices. With the advancements of 3D printing and milling, it is conceivable that very soon an actual physical impressions may no longer be needed and the fabrication of complete dentures will truly be an entirely digital process.
The author would like to thank Dmitriy Solomonyuk, the extremely talented laboratory technician who helped with the denture design and milling, and Anthony Ceccacci, DDS, for allowing the use of his magnificent laboratory facilities.
1. Print communication Digital Denture Brochure PC-691466, www.ivoclardigital.com
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