Zirconia CAD/CAM bridge in three pieces

The patient, a 50-year-old female, presented with a large diastema, irregular teeth size and dull color. Furthermore, the shape of the teeth on the right versus left sides was different-as is apparent in the pre-op photo (Fig. A). The teeth on her left side were longer than those on the right.
To fill in the gap left by missing tooth Nos. 4, 5, 7, 10, 12 and 13 she had worn a partial for years. However, she had no occlusion and was especially unhappy with the large diastema between her centrals. In addition, I noted that No. 8 was in a good position but No. 9 was too long, with both Nos. 8 and 9 being too large in size. 

The patient and clinician wanted a metal-free restoration and chose zirconia for the frame design. To be certain of the predictable outcome, I used the 3D Milling Center in Seattle for the CAD/CAM frame design for tooth Nos. 3-8, 9-14 and 22-27 in three separate pieces. Especially with this case, the parallelism with the path of insertion was very important to ensure proper fit and no rocking in the mouth. We also checked tissue design for the framework.
3D Milling designed full contour cut-back for proper frame design incisally, facially and lingually-especially in the joint between the teeth. This measure helped protect against fracturing from extreme bite forces. Too much porcelain could easily lead to fracture in a case like this one-the reason for the cut-back procedure.

Case Study

In Figure A pre-operatively, we have a clear view of the patient’s problems: large diastema between centrals, discoloration, size discrepancy and right side teeth are longer than left side.

01 In the clinician’s image (Fig. B), the prep design and marginal integrity are captured. Tooth Nos. 9, 11 and 14 were not prepared.

02 The CAD/CAM design required detailed work (Figs. C, D), but the results were excellent.

03 3D Milling Center Digital Design in Seattle then milled the frame design for the laboratory (Fig. E). They also have the capability to fabricate all kinds of restorations, from press to zirconia and titanium.

3Shape Scanner owners (Fig. F) can scan their frame design and send it to 3D Milling Center to have their restoration completed and sent back in a timely manner, a definite convenience for lab owners.  

04 After sandblasting, cleaning and touching up the zirconia bridge, it had this appearance (Fig. G). Frame modifier from GC Initial Porcelain was then applied.

05 The restoration for tooth Nos. 22-27 was finished, with a slight amount of pink porcelain provided to match with existing gum tissue (Fig. H). With back light the restoration had this appearance (Fig. I).

06 The base shade color I chose was A-1. GC Initial Low Fusing Porcelain for the dentin and enamel colors was my choice for porcelain (Fig. J).

07 To create contouring, I applied a second build-up of enamel overlay (Fig. K).

08 To prepare texture for lobe angulation, I drew black lines on the model and red lines to note where to grind to create depth (Fig. L).

09 The 12 units of maxillary restorations were prepared as two separate bridges and placed on the model with fluorescent lighting (Fig. M).

10 As a mirrored image, the completed restorations are beautifully displayed for a translucency check (Fig. N).

11 Pre-operatively, the patient’s side smile view reveals an unappealing emergence profile (Fig. O). The restorations on the model in the same positioning (Fig. P) are much prettier as an alternative.

Conclusion

Before choosing a Milling Center, and sending your CAD/CAM design to them for milling, first look into their quality or work and the way they handle fit questions. If they don’t have a systematic way of dealing with cases like the one we have discussed here, or show hesitation in the best way to move forward, chances are they will not provide you with the best possible fit for the patient.

When we receive the cases back from a milling center, we look for a slightly thicker fit rather than thinly made. Our opinion is that the marginal integrity and communication we receive from the milling center must be understood from the get-go so that we are sure we will get back what we request. 

About the author

An accomplished dental technician with more than 20 years of experience, Luke S. Kahng, CDT, is the founder and owner of LSK121 Oral Prosthetics, a dental laboratory in Naperville, Ill. He has published more than 60 articles in dental journals, and his lectures have taken him across the United States and internationally. He is the creator of the Chair Side Shade Selection Guide to facilitate effective communication regarding color between doctors, patients and technicians.