Inside Dental Technology
September 2011, Volume 2, Issue 8
Published by AEGIS Communications
Enhancing Success with CAD/CAM Supra-structure Services
There are several important steps that laboratories should follow to optimize these fabrication services.
By Kristi Gregory, CDT
The implant bar-supported restoration has provided excellent clinical viability as a restorative option. The conventional casting technique for creating bars is limited in its fitting accuracy, especially over wide spans. Implant-supported prostheses require a higher level of accuracy. The solution for these problems and others is the use of stress-free passive fit bars milled from one piece in a homogenous material quality. This is only possible with CAD/CAM-fabricated bars. In this article, we will discuss steps that the laboratory can take to ensure success with CAD/CAM fabrication services using the COMPARTIS® ISUS model.
Know your Implant Systems and Protocols
Whether working with conventional internal hex systems (eg, XiVE®, DENTSPLY Tulsa Dental, www.store.tulsadental.com) or advanced tissue-care connection systems (eg, ANKYLOS®, DENTSPLY Tulsa Dental), there are specific protocols required to restore them (Figure 1). Implant manufacturers offer extensive training on these protocols. Familiarity with these systems will also facilitate productive discussions with surgeons and restoring dentists who will value the input. Planning the case using CT-scan based systems such as SimPlant® (Materialise Dental, www.materialise.com) can also enhance predictability from the start of the treatment process (Figure 2). COMPARTISISUS supports more than 250 implant platforms.
Ensure Good Impressions
Implant restorations demand a higher level of accuracy than conventional restorations, where periodontal mobility can allow for some variance. The master impression—whether closed or open tray—for any implant prosthesis must be accurate and provide all of the required information for successful restoration completion. For the best accuracy and enhanced model pouring capability, we recommend VPS materials (Aquasil Ultra, DENTSPLY Caulk, www.caulk.com; Elite Implant, Zhermack USA, www.en.zhermack.com; or Genie VPS®, Sultan Healthcare, www.sultanhealthcare.com) (Figure 3). Accurate, defect-free model work from such impressions also enhances downstream processes. VPS materials may also be used to create soft tissue moulage (Figure 4). A good addition silicone (eg, Gingifast Rigid, Zhermack USA) will allow for easy trimming, precision, and margin stability. In combination, a good model and the set-up information will enable the technician to visualize and plan the bar design needed.
Insist on an Implant Verification Jig
The inter-implant accuracy of a splinted prosthesis is crucial to the long-term clinical success of the case. The validation of an accurate master cast is ensured by the clinical confirmation provided by creating and using a verification jig (Figure 5). Verification jigs may be created using VLC materials (Triad® Gel, DENTSPLY Trubyte, prosthetics.dentsply.com) or acrylics (Duralay™, Reliance Dental, www.reliancedental.net). The verification jig fabricated by the laboratory is returned to the practitioner for intraoral try-in and to check for accuracy of the master model. Should the stent be passive fitting, the laboratory then proceeds with fabrication of the CAD/CAM framework (Figure 6). If the stent does not fit passively, then the practitioner will need to section the resin stent and re-lute it intraorally and pick this up in an impression for the laboratory in order to correct the master model.
QA the Model Work
CAD/CAM laboratory services such as COMPARTIS ISUS will guarantee the fit of the bar, hybrid, or bridge to the high-quality model. ADA Type III model stones (eg, LabStone, DENTSPLY Prosthetics, Elite Model Fast, Zhermack USA) are recommended. When sending a model to a CAD/CAM service, ensure the model is disinfected thoroughly, for the safety of all our colleagues. The model must be removable from the articulator and from mounting plates so that it will fit in the scanner. Analogs sent with the model need to be new or undamaged. They must fit stably, without rotation, and be free of debris and clean for accurate scanning.
Plan the Ideal Set-Up and Design
A trial denture or diagnostic set-up with soft tissue moulage is required with the work order so that the bar or bridge can be accurately placed over the ridge and does not infringe on tooth placement (Figure 7). This is especially necessary when some subgingival abutment collars are present, and allows for precise scanning of the model. Clearly indicate the implant positions and the design requirements on the work order. This enables precise scanning, including the scan flags specific to your system (Figure 8).
Communicate with Partners
The more specific the instructions on the work order, the easier it is for any service to design a unique bar, bridge, or hybrid to specifications. Review the viewer files you receive from COMPARTIS ISUS, and make sure that the design meets all your needs, taking full advantage of the isometric and view rotation capabilities (Figure 9). Modify the virtual design as needed to satisfaction (Figure 10). A variety of attachments and retentive elements may be designed in. Alternatively, a design can be copy milled for you. Technical support will work with you to design and deliver the right substructure for your patient.
Enhance Quality in the Laboratory
The ISUS process produces supra-structures accurate to about 20 µm. You should need no adjustment nor further finishing prior to processing the restoration over the ISUS supra-structure. An intraoral try-in can verify this and be a confidence-building measure for the dentist and patient as well (Figure 11). Integrate any attachments needed, and you can begin processing over the structure—either with acrylic or with porcelain—to achieve an excellent finished restoration (Figure 12).
Implant restoration procedures based on clinically sound fundamentals are essential in all aspects of the process. Attention to detail, as outlined in the steps in this article, increases the predictability of the restorative process. Continuing the verification and communication between the partners in the restorative team enhances confidence and results in better patient outcomes. The improvements afforded by CAD/CAM technology such as COMPARTIS ISUS in eliminating technique dependency and variability are tremendous. The technology allows us to be more productive through improved efficiency and precision.
We are grateful to Dr. David Little and Dr. Timothy Wright, and Troy Apparicio CDT, for their courtesy in sharing clinical images.
The manufacturer provided the preceding material. The statements and opinions contained therein are solely those of the manufacturer and not of the editors, publisher, or the Editorial Board of Inside Dental Technology.
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About the Author
Kristi Gregory, CDT, is a technical specialist with DENTSPLY and has more than 20 years of experience in the dental laboratory field.