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Inside Dental Technology

June 2013, Volume 4, Issue 6
Published by AEGIS Communications


Embracing Digital Dentistry

Esthetics with minimal tooth preparation achieved through a digital approach

Edwin Chung, RDT, MDC Sebastian Ercus, DMD Ed McLaren, DDS, MDC

In both the dental laboratory and clinical environments, computer-assisted technology along with new materials are leading to a paradigm shift in what many practitioners and technicians 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 laboratories. In the not-too-distant future it is likely every laboratory and dental office will use computer software to simulate procedures for better communication among dental team members and the patient, use a digital scanner instead of physical impressions, and use CAD/CAM technology to digitally design and manufacture the restorations. Computer assisted surgery, too, will be common, such that, for example, implants will be placed with 100% accuracy, exactly where indicated by reverse engineering the treatment plan and in perfect relationship with the tissues surrounding the implant site and the final restoration. In both the dental laboratory and clinical environments, computer-assisted machines and an understanding of new materials available today have already led to a paradigm shift in what many practitioners and technicians regard as standard of care for patients.1,2

Case Presentation

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).

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 be able to perform a complete occlusal equilibrium 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.)

Transitional Restoration

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).

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 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 was taken, the position of the Nikon® SB 200 Wireless Speedlight flashes on the R2 Dual Point Flash Bracket (Photomed USA, www.photomed.net) were 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 post-operatively is shown in Figure 10.

Dental Laboratory Procedure

The following is the laboratory procedure used after intraoral digital impressions were taken and laboratory computer-assisted design (CAD) protocol had been followed, as was done in the case described above.

After milled iTero model and dies were received, they were 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) was created with a hard laboratory putty polysiloxane material (Coltène® Lab-Putty, Coltène Whaledent, Inc., www.coltene.com). The matrix would be used for accuracy checks of refractory dies that would be produced later.

On the palatal aspect, the tissue of the cast was 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 provided 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) was 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 was 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 would 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 were then duplicated using a PVS silicone laboratory duplicating material (Double Take, Pearson Dental, www.pearsondental.com). Because the pin of the iTero was not included in the duplication, the original dies could 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 corresponded to the selected compatible veneering porcelain (VITA VM®13) was then poured into the newly created mold. Before degassing of the refractory dies, the margins were 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 had been degassed, an accuracy check was 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 was 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 layered overtop the gingival-to-incisal portions of the veneer, after which the enamel layer was placed (VM13 Effect Opal and Window).

A postoperative case photograph of the final restorations is seen in Figure 9, while Figure 22 shows the final restorations on the cast.

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.

Conclusion

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.

References

1. Mclaren EA, Culp L, White S. The evolution of digital dentistry and the digital dental team . Dent Today. 2008;27(9):112-117.

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.

About the authors

Edwin Chung, RDT, MDC
Krest Lab
Toronto, Ontario
Post-Graduate Student
Esthetic Program
UCLA Center for Esthetic Dentistry
Los Angeles, California

Sebastian Ercus, DMD
Post-Graduate Student
Esthetic Program
UCLA Center for Esthetic Dentistry
Los Angeles, California

Ed McLaren, DDS, MDC
Professor, Founder, and Director
UCLA Post Graduate Esthetics
Founder and Director
UCLA Master Dental
Ceramist Program
UCLA School of Dentistry
Los Angeles, California


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Image Gallery

Full-face social smile, pre-treatment.

Fig 1.

Close-up front view, pre-treatment.

Fig 2.

Occlusal view, upper arch, pre-treatment.

Fig 3.

Occlusal view, lower arch, pre-treatment.

Fig 4.

Insertion of the nanohybrid composite transitional mock0up, or BFEP, using a cure-through matrix stabilized by a clear custom tray.

Fig 5.

Transitional BFEP restoration.

Fig 6.

Wax-up proposal on which the carrying matrix for the nano-hybrid composite was fabricated.

Fig 7.

Digitally generated alveolar models.

Fig 8.

Postoperative photograph of final restorations.

Fig 9.

Patient's full-face smile 3 weeks postoperative.

Fig 10.

Putty matrix made from milled iTero cast with original iTero dies. Putty matrix will be used later for accuracy checks of refractory dies.

Fig 11.

Modification to iTero cast creating taper for proper lingual stops.

Fig 12.

A separating medium is applied to modified areas of the cast.

Fig 13.

Wax is filled into the modified areas of the cast.

Fig 14.

Die with spacer, falling short of the margin.

Fig 15.

Modified dies with die spacer and lingual wax additions are duplicated with PVs silicone duplicating material.

Fig 16.

Duplicated refractory die (left) compared to original.

Fig 17.

Lingual view of properly fitted refractory dies in iTero cast.

Fig 18.

Putty matrix is used to check accuracy of refractory die seating.

Fig 19.

Transparent dentin is thinly layed on the gingival and middle thirds of the teeth. Opacious dentin is thinly layed toward incisal structures to avoid a visible line between natural tooth structure and the incisal of the veneer.

Fig 20.

Enamel porcelains are layered overtop internal dentin porcelains.

Fig 21.

Final restorations on the cast.

Fig 22.