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Everyday Dentistry with CAD/CAM and Lithium Disilicate by Marshall Hanson, DDS

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My first in-depth introduction to in-office CAD/CAM technology was at a two-day event in Arizona at the Scottsdale Center for Dentistry. By the second day of lectures and hands-on demonstrations, I was convinced of the value of the technology and of its clinical advantages to both my patients and me. My biggest hesitation, however, was that the restorations would not be as aesthetically pleasing as what I was currently getting from my lab. I remember even asking the equipment representative if I could return it for a full refund if I found that it wasn't meeting the aesthetic demands of my patients and those that I had for myself. With the advent of Ivoclar's e.max paired with CAD/CAM, I have since been overwhelmingly surprised and more than satisfied with the results that are achievable. Routinely, precise marginal adaptation, high strength and excellent aesthetics, rivaling even some of the best labs I have worked with, can be the everyday result of the everyday dentistry that we do in our offices for our patients. Under this premise, I wish to share this example of a common posterior procedure - restoring a molar, with the help of CAD/CAM and lithium disilicate. And then, as a side note, show some of the predictable aesthetics achievable with this technology and material as it relates to a few anterior cases.

Initial Condition of the Tooth

Upon clinical examination, the patient's lower right first molar (#30) was found to have some large failing amalgam fillings, with evidence of recurrent decay. Sub-enamel shadows were clearly visible surrounding the grossly open margins (Fig. 1).

Diagnosis and Treatment Planning

Mentally envisioning the preparation design that would be required to remove the failing filling material and the defective tooth structure, and seeing that it would involve two functional cusps, plans were made to restore the tooth with an indirect partial coverage restoration using lithium disilicate and in-office CAD/CAM technology. The material would offer strength to withstand posterior biting forces and provide the aesthetics to help the restoration blend in with the surrounding dentition.

CAD/CAM technology would offer not only the convenience of sameday treatment and immediate bonding, but also provide very predictable marginal adaptation and further contribute to the overall integrity and predicted longevity of the restoration.

Operative Step-wise Process

1. Anesthesia. The patient was anesthetized.

2. Assess bite. While the anesthetic was given time to take effect, the bite was checked with carbon paper in maximum intercuspation and in excursions to identify any deflective contacts or cuspal interferences with the intent to remove them with a fine diamond bur prior to the pre-op digital scan.

3. Pre-op scan. An Isolite was placed for moisture control, and the quadrant was dusted with reflective powder (Perfect Powder) to capture the occlusal morphology as a "blueprint" for the new restoration. The digital scan was accomplished with Sirona's CEREC Bluecam in correlation mode. Once the digital model was rendered, the powder was removed. The anesthesia was checked and confirmed with the patient to be profound. The tooth was then ready for preparation.

4. Remove decay. Under a single-tooth rubber dam, the defective amalgam was removed with a carbide fissure bur. Recurrent decay was then removed with a large round bur on a slow-speed handpiece. Depth of decay was significant on the buccal and occlusal aspects. The tooth preparation was then microetched (Danville) to clean the surface.

5. Placement of glass ionomer. Deep dentin was conditioned and glass ionomer (Fuji 9, GC America) was placed according to manufacture guidelines. Glass ionomer is an excellent dentin replacement, providing a predictable seal with low risk for sensitivity.

6. Refinement of tooth preparation. Refinement of the preparation was then accomplished with a short round-end tapered diamond bur. The bur was held perpendicular to the occlusal surface, parallel with the line of draw, and held static in that orientation as the bur traversed clockwise along the internal walls of the prep, refining the cavosurface margin. An electric handpiece was used for this step, turned all the way down to two. No water is needed at this speed, and any undercut in the preparation to the restoration's path of insertion can be easily visualized by the light powder created by the bur, and carefully removed. This step is key to predictably getting a milled restoration that fits seamlessly upon try-in. Once the margins and preparation design are refined, it is ready for a final scan (Fig. 2).


7. Ingot selection. Selecting an ingot involves some mental artistry. One must consider multiple factors, namely: the thickness of the ceramic, the underlying tooth color, the transparency of the ingot, deeper base color in contrast to surface characterization effects, and the desired shade of the final result. An A1 hightranslucency block (A1 HT e.max, Ivoclar Vivadent) was selected based on the aforementioned considerations.

8. Final scan. I have found that with partial-coverage restorations often fewer high quality final images, compared to multiple images, yield a better fit at try-in. If there is enough surrounding anatomy to pair up with the pre-scan, one high quality image is preferred. Once the desired image (Fig. 3) was obtained, the tooth was again micro-etched to remove the powder and any other contaminants in preparation for bonding.

9. Digital design and mill. CEREC 3.4 software was used for the digital designing of this restoration in correlation mode (Fig. 4). When the final scan image is paired up properly with the pre-op scan, getting a milled restoration that requires little to no occlusal adjustments becomes very predictable. The design was wirelessly sent to the MCXL milling unit to be milled of an A1 HT e.max block. The milling process required about eight minutes.

10. Try-in. The milled restoration was then taken back to the mouth and tried in to confirm the fit and the occlusion (Fig. 5). The sprue was removed with a fine diamond bur and the surface subsequently polished with a gray Dialite wheel. A fissure bur was used with an extremely light touch to define the occlusal grooves and give a place for the stain and glaze to follow.

11. Stain and glaze. The restoration was cleaned. In order to add depth to the restoration, staining and glazing was performed. A thin layer of clear "paint-on" glaze was applied to "wet" the surface. A sunset yellow stain was applied next to the pit and fissure areas. A brown mahogany was then added in a very small "spot" at the central pit. An endo file was then used to drag the color through the occlusal grooves with one sweep per groove from the central pit laterally. A fine amount of white was applied with a paint brush to highlight cusp tips, creating depth.

12. Firing parameters. The restoration was supported with a putty-fix (Ivoclar Vivadent) and placed on a firing tray into the porcelain oven. With the paint-on stain and glaze, a 26-minute firing cycle is required. Once the cycle is complete, the restoration is set aside and allowed to cool for five minutes.

13. Ceramic preparation. After cooling, the restoration was cleaned and prepared for bonding. A Pic-n-Stick was used to hold the restoration from the occlusal aspect while it was internally etched with 4% HF acid for 20 seconds, rinsed and dried. The internal aspect was then treated with a silane coupler, Monobond Plus (Ivoclar Vivadent), for 60 seconds and air dried.

14. Tooth bonding. Moisture isolation for this tooth was accomplished with an Isolite. The tooth was rinsed and dried. Phosphoric acid was applied selectively to the enamel for 15-30 seconds, rinsed and dried. The tooth was then re-wet with a chlorohexidine scrub for 20 seconds and then all excess moisture was blotted away with small cotton pellets. Multilink's A and B bond was then applied to the tooth and air dried but not cured.

15. Cementation. Multilink Automix was then applied to the intaglio surface of the restoration and into the tooth, lining the preparation. The restoration was seated, expressing excess cement at the margins. The excess cement was removed with a rubber tip instrument. The proximal contacts were flossed and the restoration was light cured.

16. Cleaning and finishing. After light curing, a jiffy cup (Ultradent) was used to remove any excess surface cement. Any flash was removed from near the margins and the tooth was inspected for a polished finish (Fig. 6). Occlusion was confirmed again, and the patient was dismissed.

Conclusion

Utilizing advancing technology and its partnered materials helps us to maximize the care and results we can predictably provide for our patients on an everyday basis. Getting predictable, lasting results with partial coverage posterior restorations promotes more conservative treatment, and often even better aesthetics, when compared to full-coverage crowns as an alternative treatment option for restoring large portions of posterior teeth. To routinely get natural-looking indirect restorations that are conservative of healthy tooth structure, strong and well-fitting solutions to many of my patient's most common everyday treatment needs, and to accomplish it all efficiently in the same visit - that is something worth smiling about (Figs. 7 and 8).

Not only can this material and technology be a solution to treatment needs in the posterior, it can also be applied predictably to even the most aesthetically demanding of anterior restorations (Figs. 9-13). As an example, the enamel-like properties of high translucency lithium disilicate, paired with the predictability afforded through in-office CAD/CAM, made achieving accreditation through the American Academy of Cosmetic Dentistry much more controllable and doable for me, as all of my indirect porcelain cases were done in-office with CEREC and e.max. In other words, a very high level of aesthetic dentistry is possible with these materials, and the technology available is making it easier for the everyday dentist to reach and provide to our patients.

Author's Bio
Dr. Marshall Hanson is an accredited Member of the American Academy of Cosmetic Dentistry. He graduated with honors from the University of the Pacific Arthur A. Dugoni School of Dentistry (UOP) in 2007, and has owned a private practice in Chandler, Arizona, since 2008.

Due to his love for teaching and learning, while at UOP Dr. Hanson founded Clinic Survival Courses, a series of presentations designed by and for students to facilitate achieving predictable and successful clinical outcomes. He endeavors to maintain education and teaching a continually growing part of his future dental career.

Dr. Hanson thoroughly enjoys the art and science of clinical dentistry, and became the first doctor to achieve accreditation status within the AACD using CEREC.

For more information visit www.marshallhansondentistry.com or email mhanson07@gmail.com
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April 2024
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