Immediate Dentures Based on Digital Impressions and Digital Workflow
CAD/CAM tools help the restorative team meet the patient’s desires
Germen Versteeg
Immediate dentures are always a difficult treatment because they involve the dental team transitioning a patient from his or her own dentition to a denture that inevitably feels foreign. Thus, the restorative team needs to make the denture look and feel as good as possible based on the patient's natural dentition. The use of CAD/CAM processes can prove beneficial in achieving these goals.
Scanning the patient's oral environment with an intraoral impression scanner creates a direct copy of the soft tissue. Unlike analog methods, it does not involve manipulating or putting pressure on the tissue. This helps the dental team fabricate a denture that has an extremely close fit and, subsequently, offers less chance of creating sore spots that occur so often with immediate dentures.
Additionally, patients receiving immediate dentures are often nervous about this treatment, so anything that can be done to increase their comfort is important. Many patients find digital scanning to be more comfortable than conventional impression taking, and some also are more confident in the treatment process knowing that state-of-the-art technology is being used.
Finally, digital design and fabrication offer various benefits in terms of precision, case planning, and more when creating an immediate denture that will leave the patient feeling comfortable and satisfied.
Case Study
A female patient presented having suffered from periodontitis for several years. Periodontic treatments did not produce satisfactory results (Figure 1 and Figure 2), so the restorative team explained to her the possible advantages of a removable full denture. The patient's expectations were very important. Her chief concern was that people would realize she was wearing a denture, so she wanted the denture to resemble her present teeth set-up as closely as possible (Figure 3). She also expressed a fear of conventional impression taking and a preference for a digital process. After consulting with the restorative team, the patient accepted a treatment plan for a full denture.
Treatment Plan
Because of the patient's anxiety about the treatment, the team planned for the full extraction of the maxillary and mandibular teeth in one session with immediate placement of the dentures.
Digital impressions and bite registration of the maxillary and mandibular arches were taken using an intraoral scanner (TRIOS 3, 3Shape, 3shape.com) (Figure 4 through Figure 6). To match the characteristic set-up of the patient's own teeth, portrait images of her face in a smile position were also taken (Figure 7). The restorative team used this photo as an extra reference in 3Shape Smile Design software.
Due to the small intermaxillary space between the patient's maxillary and mandibular arches, the team chose to use a digital full-arch workflow (SR Vivodent, Ivoclar Vivadent; ivoclarvivadent.com) (Figure 8 through Figure 13). The patient's facial characteristics were matched with photos and the wax rim using 3Shape RealView. This helped to verify the design in relation to the patient's smile and achieve optimal esthetics (Figure 12).
A photograph of the patient was imported into the software so that the team could refer to the full face showing the patient's natural dentition. It was also possible to overlay the intraoral scan including the patient's own teeth over the design, so the team was able to view the scan of the virtually extracted teeth (the first step in the design phase) as well as a scan with the natural teeth. Another benefit of working digitally was that the team could overlay the intraoral scan of the patient's teeth on the proposed design so all could view both in the same space. This process provides the ability to mill the teeth in the same shape as the natural teeth, following up with some minor adjustments according to the patient's wishes.
The author appreciated the simplicity of digital denture design and fabrication over a conventional workflow. The restorative team believed using a full arch bonded to a milled base (IvoBase CAD, Ivoclar Vivadent) provided the immediate denture with greater strength when compared with a conventional denture or a milled denture using stock teeth (Figure 14 through Figure 17). Intraoral scans were combined with patient photos in 3Shape Smile Design to design the full denture. The images were overlaid in the 3D design to match the existing set-up and tooth forms as closely as possible.
Upon finishing the design, the team milled the base and arch in an oversized milling protocol, leaving the whole surface rough milled. Only the connection between the arch and the base was fine milled, so the fit was perfect. The connection of the arch and the base was sandblasted. Then PMMA was used for bonding both together and for cold polymerization. After 15 minutes of polymerization, the team put the disc with the bonded arch back into the machine for fine milling. Both milling processes together took approximately 2 hours for each arch. After milling, it was necessary only to separate the denture from the disc, smooth the support, and polish and shine. The arch's esthetics were due to the surface reflection of the light as well as the thicker and thinner areas that give a different color and light absorption. No extra colorization was added. The bonded base and arch together were characterized with SR Nexco composite (Ivoclar Vivadent), as the team felt it provided the best esthetics. They also performed some extra visual lengthening of the front teeth because of the patient's small inter-maxillary space.
One week after delivery, the team checked in on the patient, who reported that she was acclimating to the denture. The fit and retention on the maxillary and mandibular arches were perfect, and the patient was very happy and satisfied with the esthetics. Her biggest compliment was that no one had noticed that she was wearing a denture (Figure 18 and Figure 19). The patient was able to eat nearly her normal diet after 1 week. The immediate denture was replaced by a final denture 6 months later.
Discussion
Scanning soft tissue using an intraoral scanner has been the subject of considerable discussion in the industry. The main benefits in a case like this are patient comfort and live bite registration. As the figures from this case show, the restorative team did not have any problems scanning the patient's soft tissue. The teeth in the patient's mouth provided perfect reference points for the scans. In addition, the rugae for the maxilla and the lingual ridge of the mandible were strong reference points.
Static occlusion with plaster models is always different from the intraoral dynamic occlusion. Moreover, with digital processes, bite-registration material is not needed between the maxilla and mandible, which minimizes the chance of error in the bite registration.
In previous cases, the author milled bases using stock teeth. With recent updates to materials and software, laboratories are now able to use teeth blanks and mill the full arch separately. Milling full-arch dentures offers several advantages, including strength, turnaround time, esthetics, and better occlusion.
A full arch bonded in a milled base provides more strength for the denture because the strength of both materials bonded together forms a full block of PMMA. Milling also offers benefits in terms of efficiency, which are evident when comparing the time it takes bonding separate teeth into the milled base to the time spent finishing the denture and making the stock teeth free of bonding material. Esthetically, technicians are now able to morph the teeth in every way, so it is possible to exactly replicate the patient's natural teeth with the denture teeth. Better occlusion can be achieved by using the software and the digital articulator to perform a full re-occlusion and reproduce all lateral and proximal movement. These movements then can be adapted to the design of the teeth. (With stocked teeth, there is always a little fault in the margin because it is possible to bond teeth in the wrong position.) With the new oversized milling workflow, the occlusion is finely milled after the bonding of the full arch and base. As a result, the occlusion pattern is always the same as the design.
About the Author
Germen Versteeg
Founder
DTL Mediaan and Mediaan Clinic
Heerhugowaard, Netherlands
