Using Digital Smile Design to Yield Predictable Results

Digital dentistry is preferably integrated into treatment plans, as it often increases precision and efficiency while achieving a highly esthetic, predictable result.^7-11 There are several options for hardware, software, and restorative materials within the confines of digital dentistry. Yttria-stabilized tetragonal zirconia is a common material used for various dental applications that research has deemed acceptable and predictable, particularly for fixed dental prostheses and crowns.^11-21 It has been shown that better fit can be achieved with CAD/CAM zirconia compared to conventional metal-ceramic fabrication.²² In addition, zirconia restorations have favorable properties, as they cause less antagonistic wear to opposing dentition than other restorative materials.^23,24 Various studies have shown more favorable crown margins with CAD/CAM zirconia crowns milled from 5-axial milling units as opposed to 4-axial milling units.^20,25

When treating complex patients, it is useful to evaluate the entire orofacial complex; use the evaluation to identify specific treatment objectives and  plans; and communicate that information to the entire interdisciplinary team, including the ceramist. A communicative relationship between clinician and ceramist is vital to successful outcomes. The purpose of this article is to illustrate how a symbiotic relationship between prosthodontist and ceramist, in conjunction with digital dentistry, can yield predictable, superior outcomes.

A 48-year-old female reported for dental treatment with the chief complaints of undesirable crown shade and contours on her central incisors, dislike of the shade and contours of her lower posterior crowns, and missing teeth. A thorough clinical examination revealed occlusal instability with signs of attrition, tooth migration, lack of anterior guidance, and a disrupted occlusal plane. A medical and dental health history was completed, as well as extraoral and intraoral examinations. Impressions of both arches, a facebow record, interocclusal records, a full mouth series of x-rays, a panoramic x-ray, a localized cone-beam computed tomography scan, and photographs were all obtained for treatment planning (Figure 1 through Figure 5). Diagnostic casts were mounted on a SAM 3 Articulator (Great Lakes Orthodontics; greatlakesortho.com) and evaluated. The photographs were used to aid in treatment planning, including digital smile design.

Digital smile design was first completed in a 2-dimensional software program, using the face as a guide for designing the smile (Figure 6). Results from the 2D digital smile design suggested that the patient might benefit esthetically from minor anterior crown lengthening in order to improve the width-to-length ratio of the anterior teeth. The 2D digital smile design was then transferred to a wax-up in order to improve the tooth proportions and assess treatment options (Figure 7).

Treatment plan options were presented to the patient. She declined any surgical procedures including anterior crown lengthening and ridge augmentation with implant placement for Tooth No. 5. She opted to receive bleaching for the lower arch; crowns on all maxillary teeth, including two maxillary bridges; and lower posterior crowns to improve the interocclusal relationship and provide proper centric occlusion with anterior guidance. A secondary analysis of the smile using 2D digital smile design was completed, and that information transferred to a new diagnostic wax-up without the anterior crown lengthening (Figure 8).

The maxillary teeth were prepared and provisionalized using the new diagnostic wax-up as a mold for the provisionals (Integrity, Dentsply Sirona; dentsplysirona.com). During the following appointment, the lower teeth were prepped and provisionalized. The patient was then kept in the provisionals for 8 weeks. Keeping the patient in provisionals for an extended period allows for the opportunity to refine the occlusion while ensuring the patient functions appropriately without a restricted envelope of function. It also allows time to evaluate esthetics and phonetics, including incisal exposure with the lips at rest (Figure 9). The patient's anterior guidance and envelope of function were evaluated and monitored.

Once the occlusion was deemed stable and the patient was happy with the esthetics, she reported for final impressions. Photographs, impressions, a facebow record, and interocclusal records were taken of the upper and lower provisionals.¹⁷ Records of the provisionals are crucial to replicate the stable position and desired esthetics to the ceramist for final restoration fabrication. Interocclusal records between the tooth preparations and provisionals were then obtained in order to cross-mount the provisional models with the tooth preparation models. The maxillary posterior provisionals were first removed and a stiff polyvinyl siloxane record was made of the maxillary posterior tooth preparations against the lower provisionals. The anterior provisionals remained on and served as a “stop” to create a tripod with the joints and the anterior teeth in order to hold the patient's joint in its repeatable and stable centric relation position—the same position in which the patient's provisionals had been equilibrated. Next, the lower provisionals were removed, and an interocclusal record was taken of the upper preparations against the lower preparations. The upper and lower provisionals were then removed, and final polyvinyl siloxane (Aquasil, Dentsply Sirona) impressions were taken (Figure 10 and Figure 11). Shade records were obtained by taking photographs of the prepared maxillary teeth and unprepared lower anterior teeth with a shade guide,  both with and without a polarizer (Figure 12).

The maxillary provisional model was mounted on a SAM 3 Articulator on a mounting plate to a magnetic Axiosplit. The lower provisionals were then mounted to the upper provisionals using hand articulation. The maxillary prepared arch was then mounted by relating the model to the mandibular provisional model using the interocclusal record previously obtained (Figure 13). The lower prepared arch was then related to the upper prepared arch by using the interocclusal record also previously obtained (Figure 14 and Figure 15). The mounted models of both the provisionals and the preparations could then be cross-checked by comparing the mountings to photographs of the patient, specifically checking the maxillary anterior teeth of both the provisionals and preparations against the interpupillary line. A laboratory prescription was sent to the ceramist requesting zirconia restorations with a facial cutback and porcelain layering for crowns No. 6 through 11, with the remaining posterior crowns to be monolithic.

The ceramist and clinician chose Zirkonzahn Prettau Anterior zirconia (Zirkonzahn; zirkonzahn.com) for the restorations, with porcelain application (VITA VM9; vitanorthamerica.com) for the facial cutback of the maxillary anterior six. The models, single dies, and bite registration were all scanned utilizing the Zirkonzahn S600 Arti scanner. The model .STL (stereolithography) files were imported into Zirkonzahn Modellier software to begin computer-aided design of the restorations. With the Zirkonzahn system, there are 10 different anatomy choices (Heroes Library) to choose from based on age, wear, and facial shape. In this case, a youthful female library (Aida) was utilized. The restorations were designed, modified, and aligned, and fine adjustments were made to the occlusion, contacts, and anatomy for proper function (Figure 16). The anterior restorations were then facially cut back in preparation for porcelain layering after milling (Figure 17). Once design was complete, the restorations were virtually placed in a Prettau Anterior puck and calculated. They were then milled in the Zirkonzahn M4 milling unit (Figure 18).

As referenced earlier, a high-translucency zirconia was milled in order to obtain the necessary translucency throughout the restoration. After milling, the frameworks were painted with B1 shading liquid and blue and violet incisal shading liquids (Anterior Aquarell, Zirkonzahn) to create a polychromatic look throughout the copings (Figure 19). The restorations were then sintered in a programmable oven (Zyrcomat 6000 MS, VITA) according to the program recommended by the manufacturer. After sintering, the frameworks were returned to the model, at which time fit and function were checked with minimal adjustments.

The restorations were layered by first applying VITA Akzent Plus stains, which contributed to chroma saturation. A firing cycle to freeze the stain was required at this point, and was accomplished using a fast glaze cycle at 895°C (Vacumat 600, VITA). Next, a thin layer of highly fluorescing porcelain (Effect Liner, VITA) was applied to the facial cutback aspect and fired at 945°C in order to create a stronger bond between the veneering porcelain and the framework. After the Effect Liner firing cycle, the first buildup of porcelain was applied. Since the restorations were only facially layered and minimal room was available, a more chroma-dense material was needed. Base dentin (VITA VM9) in shade 1M2 was layered around the gingival third, then base dentin 1M1 was layered in the middle third, 0M3 base dentin was applied on the line angles, and finally, 1M2 was layered in the middle incisal third. The same process was repeated in a thinner layer of Transpa Dentin (VITA VM9) to full contour. The restorations were then cut back for application of incisal characterization and enamels. A blue modifier (Effect Enamel 10, VITA VM9) was placed on the distal and mesial incisal edges of the anteriors, then a blue/gray modifier (Effect Enamel 9, VITA VM9) was placed on the incisal edge. After that, a small amount of mamelon material (MM1, VITA VM9) was placed over the more chromatic middle incisal half to create depth and contrast. Finally, a mixture of two-thirds enamel (ENL, VITA VM9) and one-third blue/gray modifier (Effect Enamel 9, VITA VM9) was layered in a thin veneer over the facial two-thirds of the restorations. Once the buildups were complete, they were fired at 910°C with a 30-second hold time.

The second and final buildup were accom-plished using a cervical enamel (Effect Enamel 5, VITA VM9) at the gingival third, a white opal (Effect Opal 2, VITA VM9) at the height of contour and the line angles, a neutral translucent (Effect Enamel 2, VITA VM9) in the middle third, and finally, Effect Opal 2 on the incisal edge. The restorations were fired again at 910°C with a 30-second hold time.

The restorations were then glazed at a lower temperature of 895°C to preserve the anatomy and create an eggshell satin finish to mimic the patient's natural dentition. At this point, a diamond polishing paste was utilized to finish the natural look. The restoration was then returned to the dental practice.

Upon arrival at the clinician's office, the restorations were first evaluated on the articulator (Figure 20), and then checked intraorally. The restorations were individually checked for marginal adaptation, and then checked together for interproximal contacts, occlusal contacts, phonetics, esthetics, and anterior guidance (Figure 21 and Figure 22). Crowns were then luted (RelyX Unicem, 3M; 3m.com), and occlusion was checked. The patient was monitored with routine checks for occlusion and hygiene. Final radiographs and photographs were taken, and before-and-after facial photographs presented to the patient (Figure 23 through Figure 26), who was very pleased with the end result.

As shown in this case, superior outcomes can be achieved when the dentist and technician collaborate and communicate effectively, allowing the use of mutually preferred technology with which both can be comfortable and confident.

Stephanie Zeller, DDS, MS
Prosthodontist
Spear Aesthetics
Seattle, WA

Bobby Williams, CDT
Synergy Ceramics
Plano, TX