Dr. Ingrid Grunert presents a case of a patient with teeth using full dentures – but is 3D printing accurate enough?
The world is changing – also from the point of view of dental prosthetics.
There is already talk of industry 4.0, which refers to a future project that will lead to a comprehensive digitization of industrial production processes.
This will affect not only large sectors of industry, but also the field of dental prosthetics where the trend towards more and more digitization and automation is clearly recognizable.
But let’s keep the young horses in check.
For a work remains a work.
Again and again, we see that we are still a long way from being able to manufacture many forms of craft in a fully digitized process.
Using an example of a non-invasive restoration with veneers on anterior teeth, the authors show how digital processes can be successfully combined with a manufacturing process that is essentially hand-crafted.
Entering the digital world
Do you make your full dentures digitally or do you prefer to make them the conventional way?
Digitally designed and milled denture bases have a significantly better fit than conventionally fabricated dentures. Even in challenging jaw arches.
There are several ways to enter the digital world of full dentures, depending on the individual desires and skills of the prosthodontist.
Complete digital dentures can either be milled or printed. Full denture printing is relatively new compared to milled dentures.
Full digital dentures have seen a real boom in recent years and have been ubiquitous at conferences and in industry.
This is surprising, as conventionally fabricated mucosal supported dentures have had a rather shadowy existence for decades in the field of prosthodontics.
Furthermore, there have been no significant changes or improvements to the conventional concepts.
However, due to new digital manufacturing capabilities by milling denture bases, great progress has been made in the treatment of edentulous patients. This is because the elimination of polymerization shrinkage results in a more uniform denture, thus offering improved retention over conventional dentures.
Denture arm
Several manufacturers have also presented innovative and accelerated methods for the fabrication of complete dentures, in which several work steps are combined in a single session (especially in taking the impression and determining the jaw relationship) in order to reduce the overall treatment time.
However, this does not necessarily lead to a simplification of the treatment of the edentulous patient, since even prosthodontists have to learn the new digital workflow.
We are now experiencing a new boom in full dentures with 3D printed prostheses.
At Lab Day of the Chicago Midwinter Meeting in 2020, the industry presented a manufacturing method for definitive complete dentures, primarily to save time, material and ultimately cost.
However, it remains to be seen whether this new technology will actually lead to a denture fit as good as that of milled bases, as the first studies are just beginning to be published.
What information is required to create functional dentures?
The following results must be properly recorded on the patient to produce functional and aesthetically pleasing digital dentures:
- Accurate upper and lower impressions with a representation of all areas that will subsequently be covered by dentures
- Determining the correct vertical occlusion dimension
- Identifying a central relationship
- Determination of the length of the incisal edge of the central incisors and the midline, paying particular attention to the parallelism of the anterior teeth with the midline
- Determination of the slope of the mafric plane (parallel to Camper’s plane).
There are several suppliers of CAD/CAM dentures including: Avadent, Baltic Dentures, Wieland Digital Dentures, Vita, Amann Girrbach and Dentca Digital Dentures.
Comparison of CAD/CAM systems
Manufacturers’ new treatment protocols have differences in the clinical treatment process compared to conventional full dentures, where each system combines different steps and also offers its own tools for this purpose.
Depending on the manufacturer, the number of sessions required to fabricate the full CAD/CAM denture varies from two to four sessions to in situ.
The Baltic Denture System requires the least number of clinical sessions required with only two sessions until the prosthesis is inserted.
The Wieland complete denture system is similar to the conventional procedure with four sessions until the dentures are placed.
With all systems except the Wieland complete denture system, only one impression is needed. After taking the impression, the ratio of the jaws is determined in the same session.
However, even experienced prosthodontists have to get used to the idea of combining multiple parts in a single session.
It is not easy to correctly adjust the esthetically and functionally important parameters, because the determination of the vertical dimension and the ratio of the mandible is done without wax valleys.
Stay in control
Since it is also much more difficult or even impossible to check the individual underpasses in the new ideas, it is a good idea in any case to schedule a test before milling the prosthetics to find and eliminate errors while we still have time. .
A reassembly to optimize occlusion is also necessary for digital prostheses. The different clinical processes of the four systems were demonstrated using a clinical case.
With all systems it was possible to fabricate adequate dentures.
To minimize changeover difficulties during the production of the complete denture, most manufacturers now offer the possibility to work in individual steps up to waxing in the usual way and thus benefit from a better adaptation to the CAD/CAM milling production of the bases.
Milled prostheses are more accurate
With milled denture bases, suction is significantly better due to more uniform support in the alveolar ridges.
Figure 13 illustrates the before and after results of a phln study, the precision fit of conventionally polymerized dentures was compared to the steps of four-step digital fabrication systems (Avadent, Baltic Dentures, Whole You Nexteeth, Wieland Digital Dentures).
Conventionally polymerized dentures showed the greatest difference with the primary model.
Avadent dentures had the smallest difference, followed by Wieland Digital Dentures, Whole You Nex-tooth and Baltic Dentures. However, all digitally fabricated systems had better accuracy than conventionally fabricated dentures, which have relatively high polymerization during fabrication.
The precision of the application also explains the often surprising suction result, although the new systems generally require less effort to take impressions compared to conventional production with functional anatomical impressions.
With the new systems, as mentioned above, only one impression is taken with thermoplastic trays and silicone silicone that can be scanned well, with the exception of the Wieland digital denture.
Complete dentures with the Wieland digital system
The clinical procedure is described based on a clinical case with very difficult maxillary diseases (Figures 1 and 2).
The Wieland digital denture follows the conventional execution for complete dentures with some modifications to save time.
After a first impression in alginate (Figure 3), during the first session we proceeded to determine the temporary determination of the vertical dimension and the central relationship with the Central Disc and to determine the occlusal plane using UTS CAD, a special occluder (Figures 4 -7).
The UTS CAD is attached to the Centric Tray adapter and is aligned parallel to the double pupil line and Camper plane.
In the laboratory, the first impressions are scanned and the central tray and individual impression trays (3DPlates) are fabricated (Figure 8).
These serve as the basis for the functional impressions and the recording instrument (CAD Gnathometer) and thus to determine the relationship of the jaws through the Gothic arch registration (Figures 9-20).
Perfect occlusion
One-piece prostheses can be tried in the third session (Figure 21).
An error in occlusion was detected during the test, so the jaw position was re-determined with central registration (Figures 22-24).
During the fourth session, he finished it in situ (Figures 25-26).
The application of the prostheses and the aesthetic appearance were satisfactory, the occlusion perfect.
Open questions
A few steps are still missing for fully digitized complete denture production.
It remains to be seen to what extent digital impressions will deliver useful results both at the top and bottom.
The weak point still seems to be the lower palate. Although early reports of mandibular data acquisition with the new scanners can already show acceptable results 171 . It is doubtful whether the determination of the central relationship can ever be accomplished digitally.
Furthermore, it has not yet been clarified whether the 3D printed prosthesis can provide clinically acceptable results for a complete denture.
Early in vitro studies show that 3D printing is still very imprecise. This is also confirmed by clinical cases.
Furthermore, it has not yet been clarified at which tilt angle the prostheses should be configured to achieve the best possible accuracy.
conclusion
CAD/CAM complete dentures with milled bases represent a major step forward in the treatment of the canine patient thanks to better precision.
Dentures with excellent suction effect can also be made in difficult jaw situations.
To avoid the need for familiarization with accelerated treatment pathways, it is recommended that non-edentulous patients with mucosa-supported dentures perform the clinical procedures up to and including hair removal in the usual manner.
Whether 30 printed dentures will equate to a milled denture remains to be seen.
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