Perspectives of CAD/CAM technology: Removable restorations - Part 1

28. November, 2016
From left to right:
- Exploded view of the digitally designed lower jaw full denture with Locator fixation
- Position of the intersecting plane
- The sectional view of the full denture shows the virtual adaptation of the prefabricated denture teeth to the antagonist and the created exemption of the denture tooth and base to the adhesive cap according to the Locator.

The combination of different, already existing CAD functionalities will, in future, also allow more complex partial prosthetic restorations to be fabricated using computer-aided technology. Gaps in the manufacturing side must be closed and individual modules adapted to provide a continuous workflow according to dental technology logic. However, the basic functions already exist, including the newly developed algorithms for full-denture prosthetics.

In the “Removable restorations 2.0” series Dipl.-Ing. Ineke Knill and Dipl.-Ing. Falko Noack (both AG R&D Department) explain which complex types of restorations are fundamentally suitable for digital fabrication in future using the Ceramill system, and outline the possible approaches and process stages using fictitious cases.

CASE 1 - FULL-LOWER DENTURE WITH LOCATOR FIXATION

INITIAL SITUATION AND PLANNED RESTORATION:

Edentulous lower jaw, 4 implants with Locator fitted for better retention of the denture. Upper jaw: Fixed occlusal antagonist situation

SOFTWARE MODULE:

Virtual articulator
Implant module
Full-denture prosthetics module

TEETH USED:

Prefabricated denture teeth

TEETH ADAPTATION:

Basally and occlusally

SCAN

Digitalisation of the functional model using a dental 3D scanner – this must not only record the topography of the model surface but also the position of the upper and lower jaw in the articulator. This allows both the relationship of the jaws to one another and also to the condyles to be recorded and transferred to the CAD software.

MODEL ANALYSIS

Here, adaptation of conventional (present analysis with digital full-dentures) model analysis is required. While when planning a full denture, upper and lower jaws must be assessed statically and functionally as denture-bearing areas, this only applies to the lower jaw in this case. The challenge here is to perform a model analysis, which not only takes into account the requirements of the setting-up areas for tissue-borne dentures but also includes the antagonist situation.

TOOTH SET-UP

The teeth are set up using prefabricated denture teeth. The existing library and denture tooth blanks can be used. As the options for positioning the teeth require a greater degree of freedom and customisation for taking into consideration the specific, existing initial situation of the antagonist, the prescribed occlusion concept stored in the library is no longer used.

IMPLANT POSITIONING

A new feature is the combination of different CAD modules – via the implant module the existing workflow can be used for positioning and selection of implants with suitable, stored geometry for the matrix (adhesive cap). The set up denture teeth must not only be adapted basally in any areas they penetrate the alveolar ridge, but also allow similar reduction in the matrix area. The set-up must also allow penetration of the denture teeth and antagonists, this penetration should be trimmed digitally and the adaptation transferred to the actual tooth to ensure functional occlusal relationship to the antagonists. Adaptations of the denture tooth are implemented by a CNC milling machine and use of denture tooth blanks.

DENTURE BASE

Gingiva sections are automatically generated in the full-denture prosthetics software in the form of denture bases. The user can customise the suggested gingiva design using virtual freeform tools. A suitable socket is cut from the base for each tooth to enable connection of the denture teeth and denture bases. The fitting surface of the base, which does not lie fully on the mucosa, must also have recesses without undercuts in the area of the adhesive cap. This denture base is also subsequently fabricated on the CNC milling machine.

FINAL STEPS

The adapted denture teeth are removed from the blank frame, cleaned, inserted into the sockets in the denture bases and bonded with the bases. The adhesive caps must also be inserted in the recesses provided. At this stage, the wax denture is converted to the finished acrylic denture conventionally after try-in at the dental practice. In future, users will have the option of milling the bases from a gingiva-coloured blank. A reliably functioning bonding concept must be available for connecting the acrylic bases with the denture teeth.

Categories: Software