Dental prosthesis design procedures. Understanding 4D CAD/CAM
Posted on 20th June 2018 at 22:16
By: Sébastien Felenc and Maxime Jaisson.
Three-dimensional imaging has invaded our workspaces and transformed dental prosthesis design procedures. The fourth dimension adds the time factor to the display of dental anomalies, allowing models to be animated according to the precise movement of a patient’s dental arch.
Dynamic recording of jaw motion has many applications. This is no longer an articulator stimulation, but a genuine digital avatar of the patient. In this document, we present the various clinical and laboratory applications of this new technology.
This technology developed by Modjaw, involves recording jaw movements directly on the patient, based on a protocol selected by the practitioner. This animated 3D arch recording (STL file recording patient spatial movements in real-time) allows the practitioner to replay a video of the recorded movements with 3D management features. In concrete terms, you can see and analyse what is happening with the patient’s dental arches.
Overall, what are the therapeutic benefits?
By adopting the patient’s envelope of function (envelop created by the set of points originated by mandibular movements), which is in turn governed by the posterior occlusion determinants, the resulting prostheses are more functionally relevant. Occlusion management becomes more readily accessible and can integrate the CAD/CAM workflow, both in the surgery and the laboratory. Treatments are more rapidly implemented and margins of error are greatly reduced. Fewer occlusion corrections are required. Patient comfort is increased. Overall, dental professionals produce better quality prostheses while saving time. The implementation of 4D promises all of this.
This topic is part of the history of our profession.
Numerous researchers and authors have studied jaw dynamics and chewing, using a diverse range of more or less easy-to-use devices. Many publications on these topics are available. The Replicator article by Lundeen and Gibbs is one of the best-known® .
In fact, the term 4th dimension was first mentioned by François Duret in his work on the Access Articulator® and the concept of neuromuscular compatibility was developed with Jean-Pierre Toubol in 1989 .
The reason why this work remained at the scientific research stage, without really impacting prosthesis production, is that the technology was not fully mature at the time.
The obstacles have now been lifted and CAD/CAM has matured. It has fully permeated prosthesis design and production. Functional integration is now a reality and it may directly influence the anatomy of dental prostheses in routine digital workflows.
The last link in the digital chain
Up until recently, the digital loop was incomplete , requiring plaster and physical articulator assembly steps before switching over to the virtual replica. The loop has now been closed, the last link has arrived and it is now a simple matter of precisely transferring the spatial position of the jaw relative to the intercondylar axis to a virtual articulator. We shall see below, however, that articulator use has evolved: it is no longer used to simulate paths considered to be healthy (directly recorded and reproduced from actual movements), but rather to anticipate a therapeutic jaw position.
Using 4D throughout the treatment Preoperative phase
The initial diagnosis is greatly improved by the analysis of interincisal point and mandibular condyle trajectories. The ability to manipulate the patient while recording movements provides a degree of precision that was previously impossible to achieve so easily. And while graphs continue to be used, they are directly correlated to the 3D motion vision; their purpose is to facilitate understanding and analysis. In concrete terms, it becomes easier to view articular projections and, more importantly, to record the spatial position of the jaw upon disc displacement and/or realignment. The demonstration of interference on closing, the search for a reproducible centric relationship, along with all components of therapeutic occlusion, are rendered achievable and simplified.Capturing the mandibular dynamics integrates the initial diagnostic protocol, along with medical photographyand imaging. The articulator-based assembly of the initial models is rendered obsolete as this process is now performed virtually. 4D helps the practitioner in his/her differential diagnosis between pathogenic occlusion and occlusion deemed to be adequate. The practitioner can then select an initial treatment aimed at restoring articular and functional health, before reassessing the patient when moving on to the following steps. Initial and post-treatment records can then be compared objectively.
At the start of treatment
If a cap splint (of any type) is indicated, its design is greatly facilitated. Following 4D analysis - hence after postmanipulation video analysis of the 3D models the practitioner can define a spatial position of the jaw and export a clearly defined intermaxillary relationship. Subsequent steps are performed in the laboratory, with a 3D design phase based on cap splint prescription and production (machined or printed).
Any extended prosthetic processing starts with the modelling of therapeutic objectives. Wax-up remains widely used, in particular because computer-assisted anatomies are relatively unnatural and difficult to manipulate. This step, however, is being improved and 3D modelling is gaining ground. Henceforth, 4D-derived data will allow for initial
anatomical proposals to be greatly improved. Firstly in terms of intermaxillary relationship management when increasing the occlusion vertical dimension.
This is certainly the key aspect of advances in 4D technology. The practitioner analyses the video and precisely selects the therapeutic jaw spatial position. He/she exports an STL format file containing the patient’s maxilla and jaw in this new relationship and sends the file to the laboratory. The laboratory then imports this data into its CAD software to model the project. The precision gain is significant as approximations associated with wax imprints, followed by transfer to a mechanical or virtual articulator, are eliminated. The CAD can also be guided by the virtual occlusion planes selected and positioned according to concrete anatomical data and X-ray overlays.
4D can also be used to record mandibular (or maxillary) Functionally Generated Paths (FGPs)  used for the spatial modelling of a functionally generated surface (FGS) in STL format. This surface corresponds to the arch motion border  (QR-code 5). These 4D-guided virtual diagnostic models can be directly used for implant planning and can also be printed to produce a physical model. Virtual prosthesis planning, or virtual wax-ups, are gradually taking hold thanks to the time saved when creating them and to the increased precision offered by 4D technology .
During aesthetic anticipation
The mock-up test phase requires transitioning from 2D (photograph-based facial analysis) to 3D (smile modelling). Several techniques are available for this: the conventional and widespread manual wax model, or CAD/CAM modelling which allows for the creation of a cap splint for the mock-up, or printing of models to create a key. Many applications propose this function, 3
of which are noteworthy: 3-Shape, which was used in the case illustrated, Cerec by Sirona and Nemotec, which is directly derived from the DSD (Digital Smile Design) family.
In this case, the role of 4D is to allow the creation of appropriate palatal surfaces. While smile design and testing
techniques are very popular, the functional aspect of these restorations is frequently overlooked. 4D technology allows for the creation of relevant anterior guides thanks to the generation of virtual articulators and the use of FGP .
When creating machined single-piece prostheses
The additional information provided by 4D to the process of prosthesis creation- thanks to the simple and comprehensive programming of a virtual articulator, the FGP and the intermaxillary relationship management is extremely effective if the defined prostheses are machined. This is particularly true when single-piece reinforced glass ceramics are used. The case chosen to illustrate this situation is that of a patient presenting with temporomandibular joint (TMJ) disorders and postural problems. Ultimately,the prostheses are machined from a single piece of lithium disilicate, providing full access to the virtual prosthetic chain.
For the creation of total bimaxillary prostheses
The total adjoint prosthesis (TAP) requires precise occlusal management. For more than a century, the entire profession has been concerned with managing occlusal concepts and, specifically in this case, the creation of an ordinarily balanced occlusion. 4D technology allows the concept selected by the practitioner to be analysed and created. This is an additional degree of freedom. The all-digital prosthetic chain functions, as rapidly summarized in the case presented here.
Whether the case is simply treated, or subsequently monitored, 4D technology allows dynamic occlusions to be precisely analysed. The detection of prematurities and interferences is greatly facilitated, as illustrated above. However, the envelope of function analysis and resulting prosthesis matching are decisive here. The chosen example is that of a total implant-supported
maxillary bridge displaying recurrent fractures to anterior cosmetic elements. 4D analysis reveals a conflict between envelope of function and design.
There are multiple potential applications for a 4D analysis device in orthodontics. Whether for the initial diagnosis, to detect a centric relationship, to optimize compensation graphs, or even in preparing the way for orthognathic surgery. However, the greatest benefits of 4D analysis are most certainly to be found in optimizing chewing function, in particular through chewing functional angle balancing, promoting a new dental occlusion paradigm .
Where do we go from here?
4D technology has proven itself, the data collected are decisive and prosthetic implementation is already accessible, but the near future is even more promising. If joint and muscle health is deemed good, 3D anatomical design (CAD) will be performed directly on the patient’s initial 4D files. In disease situations, 4D can be used as a diagnostic and re-evaluation tool used to precisely guide the use of a virtual articulator to determine a therapeutic mandibular position and to design relevant dental anatomies.
In our opinion, this will represent the next major breakthrough in dental prosthesis workflow, for the great benefit of patients, bringing the dental surgery and prosthetic laboratory professions together.
About the Authors
Correspondence : email@example.com
Maxime Jaisson designed the solution and is Chairman of Modjaw.
1. Lundeen HC, Gibbs CH. Advances in occlusion, John Wright, Boston 1982.
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