Evolution of Artificial Teeth
A complete digital denture workflow is now a reality
Robert Kreyer, CDT, and Charles Goodacre, DDS, MSD
In the last 100 years, various materials and manufacturing processes have been used to make artificial teeth for complete dentures. The technique for setting and arranging artificial denture teeth has basically remained the same until recently due to advances in digital denture technology.
Arrangement of artificial teeth in complete denture prosthetics has shifted from porcelain denture teeth with vulcanization, to acrylic and porcelain teeth with polymerization processes, and now to digitalization with a click of the mouse. With this new evolution, the technical designer can create an esthetic and functional occlusion within negative, or restorative edentulous, space.
The traditional immediate denture process requires technicians to conduct model surgery on mounted master casts. They then grind and set manufactured denture teeth one by one in their proper esthetic and functional positions (Figure 1 through Figure 4). This technical process is labor intensive, requiring significant grinding or sculpting of denture teeth to fit in established negative or restorative spaces. If denture teeth are adjusted too much, resulting in a very thin tooth, issues with potential bonding could lead to delamination of tooth to base. This delamination or de-bonding of artificial tooth to base has been a common problem when converting a mucosal-supported denture to an implant-supported prosthesis.
In complete denture prosthetics, we have now evolved to the digitalization of artificial teeth arrangement. Digital denture diagnostics is now possible, allowing technicians and clinicians to analyze restorative space for immediate dentures transitioning to implant overdentures or hybrid prosthetics.
The following immediate digital denture prostheses used a digital workflow for design and manufacturing. A true digital denture process has 3 components. The first part is CAD, which allows the user to scan impressions or master casts, and then virtually design an esthetic and functional occlusion within the restorative edentulous space. The second component is CAM, which enables the user to utilize robotics for milling or printing the definitive denture. The third part of a digital denture workflow is computer-aided engineering (CAE), which involves the software that enables CAD to connect with CAM.
Prosthodontic Patient Presentation
A patient presented with all 32 teeth needing to be extracted (Figure 5). The immediate digital denture process began with scanning the master casts (Figure 6 through Figure 8). The maxillary and mandibular dentate master casts were scanned independently of each other, and STL files were created and saved. On duplicate dentate master casts, model surgery was completed by removing existing clinical crowns and adjusting the ridge according to the clinician’s needs and instructions (Figure 9 and Figure 10). These duplicated, now edentulous casts were then scanned to communicate the amount of trimming of ridge for transitional immediate denture design. This step of cast duplication can be eliminated if desired, and a digital denture designer can perform this virtually.
The scans of dentate casts and duplicated trimmed casts were merged, and the overlay virtual design of an esthetic and functional occlusion digital denture was seen in different colors and transparencies (Figure 11 through Figure 13). In the sagittal views seen in Figure 12 and Figure 13, the proposed design of artificial teeth had been morphed from the broken-down anterior dentate state to an esthetic and functional position. The digitized edentulous restorative space (Figure 14) allowed a virtual analysis of inter-residual ridge space.
This evolutionary digital process for artificial teeth arrangement that reestablishes the natural tooth position and contour is called morphing and scaling of virtual teeth from a digital mold. The virtual placement of digital teeth had been morphed and scaled into desired esthetic and functional positions according to the restorative edentulous space. To verify the position of teeth in relation to the residual ridge, a ridge crest analysis was performed (Figure 15 and Figure 16). The green dotted line represents ridge crest of the edentulous arch. In Figure 15, an inferior occlusal view illustrates the mandibular ridge crest to virtual-morphed placement of artificial teeth. The ridge relationship is visible as well, which helps determine posterior occlusal schemes for a functional occlusion. In Figure 17, a superior occlusal view illustrates the maxillary artificial teeth in relation to the green dotted ridge crest line.
A completed digital artificial teeth arrangement is seen in Figure 17 through Figure 19, achieving an esthetic and functional occlusion. For this immediate digital denture case, prosthodontist Gary Laine, DDS, of Palo Alto, California requested a monoplane, or flat on flat, occlusion.
From sagittal views, Figure 17 and Figure 18 show the morphed artificial occlusal scheme. The esthetic and functional occlusion was virtually created in Figure 19 with this evolutionary digital process of arranging artificial teeth.
The true test of a virtually designed esthetic and functional occlusion is how the digital dentures appear in the oral environment during speaking and smiling (Figure 20 through Figure 22). From scanning the dentate master cast to morphing or scaling artificial teeth into their natural position as in Figure 12 and Figure 13, the milled monolithic digital denture provided the edentulous patient with an esthetic and functional prosthesis.
This evolutionary process for virtually designing an esthetic and functional occlusion in a monolithic milled denture utilized the first true digital molds called Signature TeethTM (AvaDent Digital Denture Solutions, avadent.com).
Brief History of Signature Teeth
One of the most significant advancements in denture tooth fabrication for many years has been the introduction of Signature Teeth by Global Dental Science, developer of AvaDent™ Digital Dentures. Signature Teeth are computer generated and computer manufactured to produce a better outcome for the patient. It is now possible to actually customize teeth as needed to meet the specific needs and desires of each patient.
The history of this innovation extends multiple decades when this article’s coauthor Charles Goodacre, DDS, MSD, began teaching tooth morphology in 1975 at Indiana University. To prepare for this responsibility, he read textbooks and articles discussing the morphology of human teeth, beginning with G. V. Black’s 1897 book called Descriptive Anatomy of the Human Teeth. Goodacre’s resources described the characteristics considered to be typical of each secondary tooth. In addition, many publications presented average dimensions for each tooth.
Based on the provided dimensions, the average dimensional data from all the sources were combined, thereby creating what might be described as an average of the averages, or grand mean, for each tooth. Satoshi Sakamoto, an expert dental laboratory technician, created a set of 32 life-sized teeth that had dimensions replicating the grand mean and also exhibiting all the morphologic characteristics that had been determined to be typical for each tooth. Global Dental Science scanned these teeth, creating 3-dimensional replicas of each tooth that became the digital library foundation for the Signature Teeth.
Signature Teeth feature many advantages and have begun a new era in denture teeth fabrication. Available in multiple shades, they can be fabricated using a single-layer or multiple-layer technique. They have natural incisal/occlusal embrasures and proximal contact locations that enhance their esthetics. In addition, they can be used in the fabrication of monolithic dentures, for which the teeth and base are 1 unit, thereby augmenting strength compared with the use of traditional denture teeth. The teeth are milled together as a monolithic complete arch of natural-looking teeth that are integral with the base of the denture.
Signature teeth can be digitally adapted to meet both esthetic and functional requirements. The style of Signature Teeth is changed by stretching (orthotropic scaling) and morphing. For example, the various shape parameters available to morph anterior teeth include taper, slant, roundness of the mesioincisal, distoincisal, and gingiva; convexity of the mesial, distal, and incisal edges; and the overall aspect (height to width) of the tooth crown. Once the desired style of the Signature Teeth is designed, the size (isotropic scaling) of the Signature Teeth can be altered to create teeth that match the patient’s arch form and general anatomy. Sizing and stretching of the Signature Teeth is also used to close interproximal spaces that would be present with conventional denture teeth in anatomic setups.
The versatility of Signature Teeth opens the door to a new era in denture teeth that will reduce the need for dental laboratories to stock a large number of teeth and enhance the options available for customization of complete dentures and implant prostheses.
The technical process for arranging artificial teeth with immediate or complete dentures has evolved dramatically since 2013. Virtual artificial teeth are now available that allow technical morphing or scaling of a mold into any desired negative space.
This morphing and scaling ability of a digital designer creating an esthetic and functional occlusion will eliminate the arbitrary grinding and sculpting of manufactured artificial denture teeth. This innovative process of arranging denture teeth has many advantages. With a true digital denture, a file is created and saved that allows milling of a duplicate monolithic denture if needed. The duplicated digital teeth will be in the same position as the definitive digital denture due to using a digital file—compared with using new impressions, relationship records, manual tooth arrangement, and conventional processing for a duplicate denture. Complete denture diagnostic techniques have evolved with the aid of digital technology processes for a digital denture workflow. These evolutionary prosthetic processes will significantly reduce labor and material manufacturing costs.