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Ten Units in Five Hours with a Fast and Easy Milling Material by Bart McFarland, DMD, FDOCS, MICOI

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Our capabilities in same-day dentistry have steadily improved since the introduction of devices like the CEREC almost 30 years ago. Among the most welcome improvements have been the new varieties of milling material that have given dentists valuable new options for meeting patients' aesthetic expectations and functional needs. When we consider those functional needs, however, it's important to remember that strength and hardness are not the same thing. Some currently available milling materials are quite strong but also quite hard, which can cause damage and wear to dentition opposing the crown.

Now, a new milling material is available that gives chairside dentists a great alternative to traditional blocks that are hard on enamel. This material, 3M ESPE Lava Ultimate Restorative, is a resin nano-ceramic, a new class of milling material that is strong, aesthetic and gentle on opposing dentition. The elastic modulus of this block are comparable to dentin, and much lower than that of glass ceramic or PFM veneering porcelains. This makes the material better able to absorb chewing forces and reduces stress to restorations. While these attributes are attractive for almost any restoration, they are particularly useful for patients with a history of bruxism or for restoring crowns over implants.

An additional benefit of this new material for dentists with in-office CAD/CAM systems is the fact that restorations need no firing, and are fast and easy to mill. Because it's less brittle than glass ceramic or lithium disilicate, restorations made with the block have better edge quality. After milling is complete, polishing can be completed in just a few minutes. The material can be worked on just like real tooth structure, so occlusion can be easily adjusted with additive or subtractive techniques. If a hole must later be cut into the crown for access to an abutment and implant or for endodontic treatment, it can be resealed with composite and re-polished without the need for removal. The material is available in eight shades and two translucencies, which gives users plenty of options for either anterior or posterior restorations.

The case shown here will demonstrate the use of this material to efficiently create 10 units in a one-day treatment.

Case Presentation

The patient was a 72-year-old man from out of state who was in the area visiting his daughter. He had been treated with a same-day crown on a previous visit to our office, and wished to have his bottom anterior teeth similarly restored. As seen in the photos, the lower posterior teeth had been treated with gold crowns that were in good condition, but the premolars were extremely worn down by the patient's heavy bruxing (Fig. 1). PFMs had been placed on tooth numbers 22-27, but these were worn down as well, with the porcelain very noticeably worn away on numbers 22 and 23 (Fig. 2).

Because of the patient's bruxism and history of wearing through crowns, Lava Ultimate restorative was selected as the most appropriate crown material due to its shock absorbency and low wear to opposing occlusion. Shade A1 was selected as the best match to the opposing teeth.

Work began with numbers 20 and 21, which were prepped, designed in individual mode and sent to the CEREC milling units. Numbers 28 and 29 were prepped next and designed in individual mode (Figs. 3 and 4) while 20 and 21 were milling. After milling of 20 and 21 was completed, 28 and 29 were ready to be milled.

Next, 20 and 21 were placed in the mouth and the margins, contacts and occlusion were checked. After milling of numbers 28 and 29 was complete, the crowns were placed in the mouth and prepared to seat with numbers 20 and 21. While the premolar crowns were dry seated, the lower anterior teeth were imaged in biocopy mode after some line angle contouring. The PFMs on numbers 22-27 were then removed, after which those teeth were cleaned and prepped as well. The preps were imaged and designed, beginning with numbers 22 and 23; after these were sent to mill, work moved to numbers 26 and 27 (Fig. 5). The last teeth to be designed and milled were 24 and 25. After exiting the milling units, all crowns were treated in the same manner as the premolars except some minor line contouring.


Finishing for the crowns began with cleaning and gentle blow-drying. Any necessary minor adjustments were made with a fine needle diamond. The spurs were removed and the crowns were pre-polished. Polishing paste was then applied with a soft bristle brush and a low speed handpiece. A natural luster appeared after a brief polishing and the crowns were then buffed with a muslin rag wheel. Following this, the interiors of the restorations were sandblasted and 3M ESPE Scotchbond Universal Adhesive was applied and scrubbed for 20 seconds, then air thinned.

The preparations were then etched with phosphoric acid for 15 seconds. The etchant was rinsed and the teeth were dried. Scotchbond Universal adhesive was applied to the preps and rubbed in for 20 seconds, briefly air thinned and then light cured. 3M ESPE RelyX Ultimate Adhesive Resin Cement was then dispensed into each crown and the crowns were seated on the preps. Excess cement was briefly light cured to reach a gel stage and then cleaned away. A 20-second light cure was then performed on each crown and final polishing was completed (Figs. 6 and 7). The restorations were seated starting with numbers 24 and 25, followed by 23-26, then 22 and 27, 21 and 28, and lastly, 20 and 29.

Discussion

The patient was extremely pleased with the outcome of the treatment, which was a significant improvement both in terms of aesthetics and function. The complete 10-unit treatment was performed in approximately five hours, a strong testament to the speed of working with this milling material. Not only does it save time due to the fact that it does not require firing, it is also extremely fast to polish and adjust. Additionally, the shade used in this case was an ideal match in the aesthetically sensitive anterior area.

The adhesive and cement also helped contribute to the speed of completion. Scotchbond Universal adhesive works as both a primer and adhesive, and can be applied to both enamel and dentin with no worries about post-operative sensitivity. RelyX Ultimate cement is well suited for CAD/CAM and glass ceramic restorations, and works with the adhesive to form strong and durable bonds.

With this combination of materials, the patient's needs were met and exceeded. Not only were the final crowns a vast aesthetic improvement for the patient, the resin nano-ceramic will also be kinder to the patient's opposing teeth, an important consideration given his bruxism. This one-day treatment is an outstanding example of the capabilities of this fast and easy-to-use milling material.

  Author's Bio
Dr. Bart McFarland graduated in 1987 from the University of Kentucky College of Dentistry. He has been a CEREC user since 1998 and is one of the CEREC trainers in the state of Kentucky for Patterson Dental. He has completed more than 14,000 CEREC restorations. Dr. McFarland has invented several techniques with CEREC, single visit root canals crowns and how Invisalign and CEREC compliment each other. He has been published numerous times in national dental journals and magazines on procedures involving CEREC. He patented the Safemate Dental Needle (self sheathing needle used in dental schools private practices and hospitals). Dr. Mcfarland has been in practice for 26 years in Paris, Kentucky.
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