June 2013, Volume 34, Issue 6
Published by AEGIS Communications
Esthetics with Minimal Tooth Preparation Achieved Through a Digital Approach
In both the clinical and dental laboratory environments, computer-assisted technology along with new materials are leading to a paradigm shift in what many practitioners regard as standard of care for patients. The case described uses digital solutions for smile design, patient communication, minimal tooth preparation, scanning, digitally generated models, and a nanohybrid transitional mock-up (bonded functional esthetic prototype [BFEP]). It also highlights a novel technique for digitally generated alveolar models duplicated in refractory dies layered with feldspathic porcelain for the optimum esthetic outcome.
Today, digital approaches play a significant part in the daily routine of many dental practices. In the not-too-distant future it is likely every office will use computer software to simulate procedures for better communication with patients, a digital scanner instead of physical impressions, and new restorations will be digitally designed and manufactured. Computer-assisted surgery, too, will be common, such that, for example, implants will be placed with 100% accuracy, exactly where indicated by backward planning and in perfect relationship with the tissues surrounding it and the final restoration. In both the clinical and dental laboratory environments, computer-assisted machines and an understanding of new materials available today have already led to a paradigm shift in what many practitioners regard as standard of care for patients.1,2
At the UCLA Center for Esthetic Dentistry, a woman presented with the following chief complaints: not showing teeth while smiling, discolored dentition, and missing tooth structure off the incisal edge of her upper anterior teeth (Figure 1 and Figure 2).
Diagnostic Findings and Treatment Plan
The authors first performed a thorough work-up, including diagnostic photographs, facial and dentofacial esthetics diagnoses, a periodontal examination, radiographs, and occlusal study—both clinically and on mounted casts. Upon completing the work-up their recommendation was to use a bonded functional esthetic prototype (BFEP) during a transitional stage that would enable them not only to assess the patient’s acceptance of the proposed new smile design but also to be able to perform a complete occlusal equilibration and follow the stability of the new selectively bonded prototype over a period of weeks or even months.
With the patient having no temporomandibular joint disorder, and considering the patient’s wear patterns that were identified clinically and on the mounted casts, along with her posterior interferences in functional movements, the authors concluded that an occlusal cause was the reason for the attrition (Figure 3 and Figure 4). Attrition patterns matched perfectly with the opposing dentition. (It should be noted that differential diagnosis between an interference bruxer and a delta bruxer is not the subject of this presentation.)
Teeth Nos. 5 through 12 were prepared for insertion of the nanohybrid composite (REVEAL™ Composite, BISCO, Inc., www.bisco.com) transitional mock-up—ie, BFEP—using a cure-through matrix (Tescera Clear Matrix PVS, BISCO, Inc.) stabilized by a clear Triad® custom tray (DENTSPLY Prosthetics, www.prosthetics.dentsply.com) (Figure 5). A selective bonding approach was taken. As such, the etching pattern did not extend all the way to the gingival margin (1.5 mm coronally off the gingival margin), and the bonding material would more easily flake away at the time of mock-up removal.
The high accuracy of the matrix used would ensure a very good adaptation at the gingival margin of the BFEP, and any further adjustments needed could be done with a very fine grit needlepoint diamond bur.
The nanohybrid composite material was inserted into the matrix, ensuring no air bubbles were present. Placing the PVS matrix in the mouth with the Triad custom tray provides high stability with no risk of over-pressing the matrix and subsequently changing the final desired outcome before curing. An initial cure (15 to 20 sec/tooth area) should be done through the clear tray. After this step, the tray was removed and a 20 sec/tooth curing through the PVS matrix was performed, followed by its removal.
The patient wore the transitional mock-up for 4 weeks and was able to test it both functionally and esthetically in various situations. She was very pleased with the esthetics and had no cohesive breakage of the prototype after a month of function. The bonded prototype thus created (Figure 6) offered the patient a chance to “test drive” the proposed final restoration over a period of weeks to ascertain the acceptability of the esthetics as well as the function of the planned final product.
Permanent Restoration Fabrication
Since in this case, the material of choice was feldspathic porcelain (VM®13, Vident, www.vident.com) on a refractory die, the wax-up proposal (Figure 7) was designed on a duplicated model. The alveolar models were digitally generated (Figure 8) using iTero® (Align Technology, Inc., www.itero.com). The models were replicated in refractory material following the technique developed at UCLA CED by Dr. McLaren and Ceramist Edwin Chung, which is described later in this case presentation.
As a general rule of feldspathic porcelain buildup, a 0.3-mm space is needed for a shade change for a better control and filtering of the direct light.3 The mock-up was removed in a controlled manner with a 0.4-mm-deep depth gauge bur, which did not penetrate the mock-up. The enamel was polished, and sharp angles that would make the porcelain fracture during both the manufacturing process and cementation procedure were corrected.
A shade information image was taken with a Nikon® D90 12.3 megapixel digital single-lens reflex camera (Nikon, www.nikonusa.com) of the VITA Linearguide 3D-Master® (Vident, www.vident.com) tooth shades. When this particular image is taken, the position of the Nikon® SB 200 Wireless Speedlight flashes on the R2 Dual Point Flash Bracket (Photomed USA, www.photomed.net) are 3 inches lateral and 2 inches posterior of the lens, offering repetitive and consistent results.4
Intraoral scanning was performed with the iTero scanner for laboratory milling (ie, Align/Cadent milling center) of the alveolar models, which were duplicated in refractory material at the UCLA CED laboratory. The progression from initial presentation through transitional mock-up, to final restoration can be seen in Figure 2, Figure 6, and Figure 9. The patient’s full-face smile 3 weeks postoperatively is shown in Figure 10.
After the final restorations were delivered, a complete occlusal equilibration was carried out, and a processed clear acrylic nightguard was manufactured. At the time of delivery the nightguard was finely fitted on the upper arch by using red fit checker spray, and the occlusion was adjusted to achieve simultaneous contact points with no functional interferences in lateral movements.
Dental Laboratory Procedure
The following is the laboratory procedure used after intraoral digital impressions are taken and laboratory computer-assisted design (CAD) protocol has been followed, as was done in the case described above.
After milled iTero model and dies are received, they are fitted and checked for any voids or irregularities that may be misrepresentative of a patient’s situation. A putty matrix of the patient’s incisal edge position (Figure 11) is created with a hard laboratory putty polysiloxane material (Coltène® Lab-Putty, Coltène Whaledent, Inc., www.coltene.com). The matrix will be used for accuracy checks of refractory dies that will be produced later.
On the palatal aspect, the tissue of the cast is modified by creating tapered retention notches (approximately 30 to 45 degrees) toward the cast’s apical stop for dies (Figure 12). Making tapered retention notches in the cast provides the ability to wax-in a positive retention taper on the master die.
Wax-releasing agent (DVA Very Special Separator, Dental Ventures of America, Inc., www.dentalventures.com) is first applied onto the newly created cast modification followed by dental inlay wax (Finesse® All-Ceramic, DENTSPLY Prosthetics) (Figure 13 and Figure 14). Using a sharp waxing instrument, the wax is then flushed with the unprepared palatal tissues of the cast to provide an additional visual check of proper seating after duplication.
Since these newly modified “master” iTero-milled dies will be duplicated in refractory material, the necessary die spacer for cement must be applied on the preparation area, falling short of the margin (Figure 15). Modified dies are then duplicated using a PVS silicone laboratory duplicating material (Double Take, Pearson Dental, www.pearsondental.com). Because the pin of the iTero is not included in the duplication, the original dies can be removed from the duplicate mold without tearing or breakage (Figure 16).
Refractory material (G-Cera® Orbit Vest Orbitvest, GC America Inc., www.gcamerica.com) that corresponds to the selected compatible veneering porcelain (Vita VM13) is then poured into the newly created mold. Before degassing of the refractory dies, the margins are marked with a heat-resistant pencil material. As with any refractory veneer technique, the quality of dies should be checked for any surface porosities, voids, or chips (Figure 17). After the dies have been degassed, an accuracy check is made with the previously created putty or stone matrix of the iTero dies in cast. Figure 18 through Figure 21 depict the dies in cast, putty matrix verification, and porcelain build-up.
The next step is the porcelain build-up. As indicated previously, because the authors did not penetrate the mock-up during the preparation appointment, very little tooth structure needed to be replaced. Minimally prepped veneers utilize more translucent porcelain to take advantage of the existing colors in the underlying tooth. As a result, the only opacious porcelain (VM13 Base Dentin) was used at the incisal tooth and ceramic junction. This helped blend the veneer to avoid a visible difference between the ceramic and natural tooth. A thin layer of transparent dentin (VM13 Dentin) was layed overtop the gingival-to-incisal portions of the veneer, after which the enamel layer was placed (VM13 Effect Opal and Window).
In the contemporary dental office patients can now enjoy the comfort of a digital impression as clinicians are able to offer them the service of noninvasive or minimally invasive procedures. Meanwhile, clinicians have the ability to communicate more effectively online with their dental laboratory. The physical can became virtual and vice versa, leaving the dental ceramist with many choices regarding material selection and processing techniques.
ABOUT THE AUTHORS
Sebastian Ercus, DMD
Post-Graduate Student, Esthetic Program, UCLA Center for Esthetic Dentistry,
Los Angeles, California; Owner, Dental Specialty Center Brussels, Ixelles, Belgium
Edwin Chung, RDT, MDC
Post-Graduate Student, Esthetic Program, UCLA Center for Esthetic Dentistry,
Los Angeles, California; Master Ceramist, Krest Lab, Toronto, Ontario, Canada
Ed McLaren, DDS, MDC
Professor, Founder, and Director, UCLA Post Graduate Esthetics; Director, UCLA Center for Esthetic Dentistry; Founder and Director, UCLA Master Dental Ceramist Program, UCLA School of Dentistry, Los Angeles, California
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2. Fasbinder DJ. Digital dentistry: innovation for restorative treatment. Compend Contin Educ Dent. 2010;31 spec no 4:2-11.
3. McLaren EA. The skeleton buildup technique: a systematic approach to the three-dimensional control of shade and shape. Pract Periodontics Aesthet Dent. 1998;10(5):587-597.
4. McLaren EA, Schoenbaum T. Digital photography enhances diagnostics, communication, and documentation. Compend Contin Educ Dent. 2011;32 spec no 4:36-38.
For more information, read Digital Photography Enhances Diagnostics, Communication, and Documentation at dentalaegis.com/go/cced413