Fit, Form and Function; the Clinical Realities of Chairside CAD CAM Dentistry
While it is easy to talk about the clear advantages of chairside CAD CAM dentistry; the convenience factors for the patient (one visit) and the economic benefits for the surgery (reduced overhead), they should only be considered as a restorative option after the fundamentals of sound restorative care have been met; fit, form and function. The introduction of the E4D Dentist™ (D4D Technologies, Richardson, TX USA) system and resulting line extensions of E4D Studio™ and E4D Labworks™ has set new standards in ease of use and functionality for the fabrication of glass ceramic restorations and common communication avenues. The E4D Systems have been able to capture a significant share of the chairside and now laboratory markets for the fabrication of indirect restorations that meet the demands of the profession and the expectations of the patients without compromise. (figure 1 & 2)
Figure 1: Proper preparation for all ceramic (IPS e.max CAD) restoration
Figure 2: Final IPS e.max CAD all ceramic restoration fabricated with E4D Dentist™
Figure 3: Screenshot of parameter settings available on DentaLogic Software
Figure 4: Measurements of internal and marginal fit of E4D restorations.
Fit
Early generation of chairside CAD CAM systems suffered from statements such as "an island of ceramic swimming in a sea of cement." While it is certainly true that the materials, as well as the cements, have improved and enamel, dentin and ceramic bonding systems have minimized much of the concern of the tooth-to-restorative interface, so too has the efficacy and accuracy of the chairside CAD CAM systems. While the professional standard of 100 microns or less for marginal clinical acceptance has been recorded for many of the accepted dental materials and fabrication processes , continuing development of the E4D Dentist™ System has provided an optimal method for clinicians to assure themselves of the best fit possible with axial and occlusal space references and a margin ramp slider (figure 3) which along with detailed mill and simulation mill are able to provide marginal fits within the clinically acceptable range and well within the 100 micron limit. (figure 4). Other chairside or digital impression systems which require powdering, spraying or dusting of the surface for contrast during an optical impression certainly can also achieve these requirements, however the variable of powder thickness, and compensation for such, always has to be considered. The fit of the restorations is a combination of proper preparation guidelines related to the material selected as well as the limits of the milling process. Knowledge of proper preparation design per restorative material and fabrication system is key to fit and clinical success as is clear access to margins with soft tissue control (e.g. cord, laser, chemical) for optical impression systems.
Figure 5: When only top-down scanning is completed, areas below the height of contour are not captured and instead interpolated in the final virtual model
Figure 6: Multiple unit cases benefit from full 3-D capture showing neighboring contours and soft tissue alignment
Figure 7: With multiple captures the E4D System is able to reproduce a true 3-D image
Figure 8: Scanned patient-approved provisionals used for template of final design using E4D Clone™ feature.
Form
The E4D Dentist Systems capture information from all sides of the preparation and neighboring teeth, little if any data is interpolated to make the virtual model. This in contrast to systems that record only from the top down or at restricted angles and simply drape anything below the height of contour or areas not captured (figure 5). While information such as the bell-shaped contours of the neighboring dentition may not be important during the restoration of single unit posterior teeth or partial coverage restorations, its importance becomes clearly evident when restoring multiple full coverage anterior or posterior restorations or constructing a "smile design" (figure 6). Here, not only is the full contours of the neighboring teeth important but so can the contour of the soft tissue and the interproximal data for contact refinement and embrasure consistency (figure 7). The E4D System can capture the full 3-D environment and accurately portray it in the virtual model ready for design.
Often, through the use of diagnostic wax-ups and patient-approved provisionalization it is preferred to simply duplicate the ideal or the patient-approved provisional case (figure 8). Laboratories often do this using silicone stents and waxing to the physical confines of the stents to reproduce exactly what the final case should copy. With the introduction of the 1.9 version of DentaLogic™ Software, and the cloning feature – E4D Clone™, the E4D system can simply scan a model of the patient-approved provisionals or the diagnostic wax-up and replicate it exactly in the final design. Even after replication, with the DentaLogic software of the E4D Systems, the technician or designer has full control of the design elements and can even overlay a virtual stent (the diagnostic or provisional scan) (figure 9) from which to work within – assuring the patient and the clinician final restorations meeting the form (and function) of the originals with no surprises (figure 10).
We can even take this one step further – utilizing E4D Clone™ and an existing library tooth in a hybrid process. Take for example a patient arrives with a broken lingual cusp or missing some part of an existing restoration, while the portion still intact is complete and has accepted occlusion. Rather than mock up and restore the missing piece of restoration or tooth structure in the mouth or on the model with composite and then scan for the ideal, we can utilize a process that will keep the intact portion and simply "fill-in" the missing portion with a selected library tooth. This identifying and then merging of data to form the ideal while keeping the existing occlusion intact provides immediate time savings to the clinician and retains important occlusal information (figures 11,12,13,14).
The ability to accurately replicated full tooth form or even partial tooth form adds an incredible array of possibilities to the surgery for fractured dentition, ideal diagnostic.
Figure 9: Overlay of Clone over cut-back designs of the final restorations
Figure 10: Final restorations (IPS Empress CAD) in place
Figure 11: Initial scan of preoperative condition
Figure 12: Combination of existing and proposed
Function
While the most popular systems currently in use utilize a static bite and not yet accommodate true motion, the E4D Dentist System has adjusted its user interface to more accurately portray daily clinical relevance. Initial reports when having contact designed in the positive measurements (and what seems to make initial sense) reported heavy contacts when placed and adjusted in the mouth. Not the same for proximal contacts, which are ideally set at approximately +50 microns. After evaluation and examination of the clinical cases it was found that a default setting of -80 microns provided a majority of success from clinicians. Obviously each clinician may have his/her preferences and they can be set as defaults. The new addition to the software to be able to "see" negative contact numbers makes sense when we consider the fact that articulation paper is used sometimes as thick as 200 microns to seat restorations and the practical fact that many technicians provide the restorations back just out of contact allowing for the natural adjustment of the masticatory function (figure 15).
The constant implementation of the fundamentals of restorative care – fit, form and function combined with ease of use, consistency and improved esthetics offered by today's materials and CAD CAM systems provides a tremendous advantage to the surgery, the laboratory and to the patient. Chairside CAD CAM dentistry or lab-fabricated CAD CAM dentistry can indeed exceed the requirements of the profession and the patients.
Clinical photos courtesy of mckinneydentist.com and Lida Swann, DDS.
Dr. Gary Severance is a 1987 graduate of the University of Minnesota School of Dentistry. Currently he is Vice President of Marketing and Clinical Affairs of D4D Technologies – the company responsible for the development, manufacturing, education and support of E4D Dentist™, E4D Studio™ and E4D Labworks™.
Lee Culp, CDT is the Vice President of Dental Technologies at D4D Technologies, owner of Mosaic Studios and the Director of Technology and Innovation at the Dawson Academy. He maintains an active teaching schedule at these, and other postgraduate teaching centers focusing on reconstructive and esthetic dentistry.
D4D Technologies is located in Richardson, Texas (USA) and is partnered with Henry Schein, Ivoclar Vivadent and 3M ESPE to provide the latest in digital dentistry products, support and service.
Figure 13: Together, the hybrid of Clone and Library complete the design proposal
Figure 14: The final restoration design combining existing and proposed components
Figure 15: Occlusal contacts demonstrating "close" to contact areas graphically
1 Marginal fit of leucite-glass pressable ceramic restorations and ceramic-pressed-to-metal restorations E. Goldin, N. Boyd III, G. Goldstein, E. Hittelman, V. Thompson The Journal of Prosthetic Dentistry, Volume 93, Issue 2, Pages 143-147
