Zirconia Ceramic Porcelain - Free VM 9 Trial Kit!

September 2017
Volume 8, Issue 9

Peer-Reviewed

The Best of Both Worlds

Combine artistry and technology to make a masterpiece

Tommy Zhu, CDT, TE

A high level of clinical and technical knowledge is vital to the success of any case in the dental field, regardless which methods and techniques dentists and technicians use. Both professions must utilize developing technology in their workflow, while understanding that skill and the human touch are just as important.

This case demonstrates how clinical and technical knowledge combined with the latest technology can result in successfully meeting a patient’s demand for restoring the esthetics and function of his maxillary anterior teeth. A senior male patient presented to his prosthodontist for replacement of his six maxillary crowns and bridge due to esthetic reasons (Figure 1). Since he lived 12 hours away from the office, he planned to immediately replace the six maxillary anterior teeth and schedule to replace the remaining maxillary posterior teeth in the near future.

Planning

The prosthodontist supplied the laboratory with images of the patient’s condition. Upon analysis of the photographs of the original restorative work (Figure 2), it is possible to discern why this patient wanted to replace them. First, there were gaps in the interproximal areas between teeth Nos. 7 and 8, 8 and 9, and 9 and 10. Second, the three-unit bridge on teeth Nos. 9, 10, and 11 was poorly made. The bridge was not fully seated, and, as a result, the margin was clearly exposed on teeth Nos. 9 and 11. The crown of tooth No. 10 was not fully seated to the tissue. Third, crown No. 9 was longer and wider than tooth No. 8. Last, the shade of the six maxillary anterior crowns did not match each other, and the shape of the teeth was too rounded for this senior male patient.

The patient’s dentist, Frank LaMar, DDS, formulated a treatment plan that included removal of the patient’s existing PFM bridge and crowns and the placement of four implants in the areas of teeth Nos. 6, 8, 9, and 11. The dentist’s treatment plan called for a six-unit titanium-based layered zirconia bridge with pink porcelain in the interproximal areas. The patient and Dr. LaMar chose a 1M1 tooth shade for the bridge, even though the tooth shade was much brighter than his mandibular teeth. Matching the tooth shade of the six-unit bridge to the patient’s remaining maxillary posterior teeth was not a concern since he planned to have those teeth restored in the near future.

Design

The oral surgeon extracted teeth Nos. 6, 8, 9, and 11 and placed the four implants. An impression was taken and sent to the laboratory for fabrication of the six-unit bridge (Figure 3). Both of the models were poured, soft tissue model made, and the model mounted to the articulator. Using CAD technology, the four implant abutments were custom designed. During the design stage, the design team kept in mind that this restoration was going to be a one-piece six-unit bridge (Figure 4). Therefore, they needed to ensure that there was no undercut or the framework could not be fully seated on the abutments. After carefully designing the abutments, the project was outsourced for milling.

Due to limitations of the CAD/CAM design software, the milled custom implant abutments required some minor adjustments by hand. The margin area of each abutment was brought within 0.8 mm to 1 mm below the soft tissue to ensure that the metal band would not show in the mouth (Figure 5). An indication line was cut on the face of each abutment to guide the dentist on which direction the abutment was facing. Most importantly, all abutments were anodized a yellow color to prevent the original gray color of the titanium abutments from lowering the final restoration’s value (Figure 6). All abutments were then checked carefully and steam cleaned prior to designing and milling the zirconia framework.

When designing the framework, function was the first priority, rather than focusing primarily on esthetics (Figure 7). If technicians ignore function, the case risks a higher chance of failure. Once the design team was technically pleased with the length, form, shape, size, and width of the design, the facial was cut back about 1.3 mm and the length lowered about 0.5 mm for future porcelain application. Finally, since the restoration was a long six-unit bridge, a stabilizer was added to prevent the framework from rocking.

Before and After Sintering

Once the bridge was milled, it was cut from the puck with a bur (Figure 8). Then, the sprue area was ground out and readied to be fine finished in the green or soft stage. The fit, contact, and occlusion of the bridge could not be checked at this point because it was 20% larger than the final size. However, the technician could reshape the line angles, thin the margins, separate each tooth, restore the contour height, and cutback the incisal edges—but not before marking the bridge to provide guidance during the fine finish stage (Figure 9). Once the fine finish was done, the bridge was then ready for colorization (Figure 10).

Zirconia is a pure white material, so technicians must colorize it prior to sintering. The technique performed in this case included using a dentin stain in shade 1M1 on the inside and outside of each of the copings and in the sprue area. Any area not stained would show as pure white after sintering. The cervical portion of each tooth required extra dentin stain, as it is the darkest area of the tooth. The middle third area required half the amount of dentin stain, and the incisal third called for the least amount of dentin stain (Figure 11). Translucency stains in blue, gray, and violet stains were chosen and applied cautiously, as these stains can be quite intense. Because the 1M1 shade chosen by the patient has a very high value, the technician needed to use much less of the translucency stain than normal for an A2 shade. The more translucency stain used, the more it brings down the value. The blue stain was applied on all the line angles, the lingual ridge, and the cingulum of each tooth (Figure 12), followed by a gray stain to create a halo effect. Last, a violet stain was applied between the blue and the gray to create the illusion of depth so that the overall translucency didn’t appear too uniform. Once the staining was complete, the framework was placed under a heat lamp for approximately 40 minutes or until the stain dried completely.

After sintering, the bridge was removed from the stabilizer. Zirconia is very sensitive to temperature, so if adjustments must be made, a handpiece that incorporates water spray as a coolant is required to be used at all times. Each abutment was carefully fitted to the bridge (Figure 13) by using a spray fit checker and making adjustments with a high-speed handpiece. Next, all the abutments were screwed to the analog in order to check for undercut (Figure 14). When the path of insertion was confirmed, the soft tissue was relieved to about 0.5 mm for a better seal of the crown to the tissue (Figure 15). Finally, the technician checked the contacts, the occlusion, and, most importantly, the function of the zirconia frame, making sure every step was done perfectly before moving on to porcelain application.

Porcelain Layering

Next, all models, abutments, and the frame were steam cleaned before the application of wash bake to the frame (Figure 16). The wash bake was chosen in order to create a better bond between the frame and the porcelain, as well as to prevent future tearing. The wash bake must be fired 100 degrees higher than the first normal bake. Once the wash bake was applied and fired, the shading began. Since the patient wanted a bright 1M1 shade, the author stayed away from using intense mamelon effects. Some ceramists focus too much of their time on hue and chroma, but value is the most important aspect of replicating nature. If the hue or chroma is inaccurate, it is less noticeable than an inaccurate value. When layering this case, care was taken not to lower the value and to keep it simple. First, a small amount of 1M2 dentin ceramic was used to layer the cervical area of each tooth, the connectors, and the contact area. Then, 1M1 dentin ceramic was used to finish the overall build-up (Figure 17). The cutback of the dentin is extremely important because it will determine the final amount and level of translucency. After the dentin cutback, blue, white, gray, and clear transpa effects were layered. Light yellow mamelon effects were added from the middle to the incisal third of each tooth, and the work was finished using two different shades of pink porcelain for the interproximal areas (Figure 18).

This technique requires that the technician use the vast majority of labor hours (80%) on layering, 15% on contouring, and approximately 5% on glazing and polishing. The overall shape of the bridge was primarily created by layering alone (Figure 19). After firing and cooling the bridge, the contact, occlusion, and function were checked on the model again. When checking for function, make sure the lower teeth can move freely in all directions and are not locked up. There must be canine guidance in order to protect the maxillary incisors from chipping or cracking. Many professionals believe that the chipping of the crown is due to the material, which is partly why full contour zirconia is currently so popular. However, if the function is correct, there should not be any chipping, regardless of whether it is a full contour, facially layered, or fully layered restoration. Once the author checked the function, then the focus could be turned to esthetics. As for the contouring of the anterior teeth, the line angles, long axis, and height of contour were the keys for creating a natural appearance. Once those steps were completed, the facial texture was ground into the surface of the teeth and articulating paper was used to check it (Figure 20). Finally, a disc was used to open up the interproximal area for the patient’s oral hygiene.

Rather than add an external stain (which would be brushed away over the years), the technician opted to use internal stain before the last porcelain layer, adding a thin translucency to protect the stain from wearing away in the future (Figure 20). During glazing, he did not use glazing paste because it tends to “melt down” the facial texture. The bridge was then polished by hand in order to bring out the shine (Figure 21).

After seating the bridge, the restoring dentist attached a filter to the camera and took photos to check for internal effects (Figures 22 and 23) and then showed them to the patient. The patient now appears more confident when smiling, looks much younger compared to the pre-op photo, and is extremely happy with the end result (Figure 24). He loves the function, shape, and the bright white 1M1 shade of his new layered zirconia bridge.

As this case demonstrates, artistry and technology are both equally important in creating successful outcomes. Technology like computer-aided design and resources such as external milling centers help dental technologists with most of the preliminary work, saving tremendous amounts of labor time. This allows technicians to focus more on the detailed work of restoring function and esthetics. While each case is different, every case needs the human touch for the best results.

About the Author

Tommy Zhu, CDT, TE
Chief Certified Ceramist
Hybridge Implants
Rochester, NY

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