Inside Dental Technology
The New Face of Esthetic and Reconstructive Dentistry: Digital Design and Fabrication
Using the digital tools available to apply a technician’s knowledge of reconstructive treatment
Full-mouth reconstruction in a patient with deteriorating dentition needs to involve a multidisciplinary approach. A team comprising orthodontic, oral surgery, periodontic, and restorative specialities has to work in harmony to create a more ideal dentition for the patient. Team members will consider esthetic display; ideal functional shape, form, and position; and interactive dynamics in the development of the treatment plan. The orthodontist handles tooth movement to a more ideal restorative position and gingival esthetic display. The periodontist may also be called upon to develop more tissue volume for pontic areas or to perform an osseous recontouring. The oral surgeon may conduct bone grafting for implant placement. Setting the stage for ideal reconstruction is the treating prosthodontist or general dentist supervising these procedures. The dental technician typically designs a diagnostic wax-up from which prototype restorations are fabricated to test the design and provisionalize the patient while final restorations are fabricated. The technician and prosthodontist consult about materials choices to determine abutment design and appropriate preparation.
Typically, a combination of materials is needed to restore both natural teeth and implant-supported prosthetics. The need to idealize esthetics and preserve natural tooth structure favors the use of bonded ceramic, such as lithium disilicate (IPS e.max, Ivoclar Vivadent, ivoclarvivadent.com), in the anterior regions on existing natural teeth. Color also dictates the use of hybrid zirconia abutments on implants in the esthetic zone. In the posterior areas, strength to withstand increased occlusal forces becomes a primary consideration. Lithium disilicate restorations may still be used, but thickness is increased to provide more strength.1 Monolithic, or minimally layered zirconia, is also employed in areas requiring increased strength. Gold crowns may be used in this region as well if the patient does not object to the color. Although porcelain-fused-to-metal historically has been used in this type of restoration, the minimal strength of the layering ceramic leaves the potential for chipping. For this reason, mostly monolithic zirconia with strategic layering in visible, nonload-bearing areas has become the material of choice for posterior bridge applications, as well as other high-stress areas.
Laboratory fabrication of restorations traditionally has been accomplished by technicians who wax up a diagnostic prototype and then fabricate provisional restorations. The provisional is delivered to the patient to be adjusted and photographed. The impressions of the provisional are used as a guide for final restorative fabrication. The technician then uses the provisional as a reference and tries to reproduce position and shape in the various materials via waxing or building up powdered ceramic with a brush. Silicone guides made from the temporaries help orient the shape, form, and position of the restorations. Although this traditional system of fabrication has worked well for years, it is time consuming and has the risk for creating inaccuracies.
Digital Coming of Age
With the development of advanced CAD software such as 3Shape, the digital world is now coming of age in reconstructive dentistry. The software is now focused on full-contour laboratory-designed and -fabricated restorations. The newer generations of digital design software have the tools to enable use for a broad spectrum of esthetic and reconstructive cases. These tools are capable of replicating natural tooth shapes, and digital articulators are available to analyze occlusal interactions of the entire dentition. Photos of the patient’s face can be overlaid on the digital design to evaluate the facial orientation of the restorations as well as the final appearance of the case. With proper training, technicians can now produce final shape, form, and function in extensive, complex cases, which result in needing very little hand finishing to idealize the outcome.
This is not to say that the software can create the cases without the technician’s expertise, but rather to note that this technology is a useful tool with which the technician can apply knowledge of esthetics and function to restorative applications with greater efficiency than before. Using these digital tools to help produce multidisciplinary treatment is the new frontier of high-quality dentistry.
A male patient presented with the need for a full-mouth reconstruction (Figure 1) with implant involvement. The patient was missing teeth in the lower anterior as well as molar and bicuspid regions of the upper and lower arches. Existing dentition was treatment planned for lithium disilicate restorations for all but the second molars, which were to be gold. The edentulous areas were prepared for implant placement. Titanium was selected as an abutment material for maximum strength in the posterior areas, while a screw-retained zirconia bridge was chosen for the lower anterior bridge. The case was prepared and impressed. Provisional restorations were fabricated, photographed, and analyzed, and laboratory instructions for fabrication were completed. The model work was completed in the laboratory prior to scanning the models into the 3Shape dental designer software system. A full-contour upper and lower design was completed (Figure 2) in the smile designer phase prior to designing the implant abutments. Abutments were designed based on the tooth position and shape achieved in the initial design (Figure 3). Then, the case was advanced to the “Sculpt” phase for final occlusal adjustments. Cusp-to-fossa relationships were established, and overbite and over-jet relationships were developed. The articulator (Figure 4) function was activated, and excursive movements were checked. Facial photos (Figure 5) were overlaid, and the design was modified to idealize facial orientation. The contact slicing function was activated while the facial photo overlay was in place to assure a vertical midline contact between the centrals. Minimum thickness criteria was enforced. The zirconia restorations were designed full contour first; then the visible, nonfunctional areas were selected for a minimal cutback of 0.3 mm to allow room for layering ceramic. Once the design process was completed, the CAM output files were created to export to the milling machine. All gold and lithium disilicate restorations were milled in wax (Figure 6 and Figure 7). for later casting and pressing operations. The zirconia restorations were milled from precolored disks (Wieland Zenostar, www.zenostar.de), then additional color staining was done prior to the centering operations. After the IPS e.max restorations were pressed, the gold cast and polished, and the sintered zirconia fit back to the master model (Figure 8 and Figure 9), the case was hand finished using traditional ceramic layering staining and glazing procedures appropriate for the various materials selected for this case (Figure 10).
1. Guess PC, Zavanelli R, Silva N, Thompson VP. Mouth motion fatigue and durability study. Accessed July 25, 2014. http://www.ivoclarvivadent.us/emaxchangeseverything/durability-study/summary.php.
About the author
Matt Roberts, CDT, is the founder of CMR Dental Laboratory in Idaho Falls, Idaho.Graham Meng, DDS, MS, is in private practice in Missoula, Montana
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