In-Office Milling: Maximizing Aesthetics and Efficiency

Since this article was published, 3M has removed the crown indication for Lava Ultimate CAD/CAM Restorative. The product continues to be indicated for inlays, onlays (with an internal retentive design element), and veneer restoratives, per new instructions for use.

INTRODUCTION
With an aging population and the increasingly high aesthetic demands of patients, today’s dentists are faced with escalating restorative challenges. Fortunately, technology is keeping pace with these demands, and practitioners have more tools than ever before to provide patients with restorations that are strong, aesthetic, and long lasting. For many practices, intraoral scanning tools, in-office CAD/CAM milling systems, and their accompanying milling materials, are chief among these technologies.

Benefits of Chairside CAD/CAM Systems
The advantages of chairside CAD/CAM systems are considerable in a modern dental practice. While the initial start-up costs can be significant, dentists who accurately project the future use and time investment involved can decide if the chosen system will be a profitable addition. For many practices, these systems reach a break-even point at a relatively low number of restorations placed per month, when the practice’s savings in outside laboratory costs outweigh the costs of owning or leasing the machine.
Beyond this calculation, there are many other less quantifiable benefits to in-office milling systems. The ability to complete a restoration in just one visit is something that can be of great value to patients and it can also help in attracting new patients and retaining existing ones. Furthermore, with use of an intraoral scanning device, chairside milling systems can help increase patient comfort by eliminating the need for traditional impression materials.¹ Intraoral scanning may also help increase the accuracy of the restoration and reduce the need for adjustments or remakes. Finally, with the preparation and seating of the final restoration done in one visit, the temporization process is eliminated, increasing convenience for both the patient and dentist.²
An additional advantage of using an in-office milling system is the milling material itself. Regardless of what type of block material is selected, these blocks, by their nature, are fabricated using reproducible procedures; this produces homogenous, consistently dense blocks that are high in quality and with no porosities. Inherent in traditional laboratory-processed pressed ceramic and hand-layered porcelain restorations is the chance for human error, and electron micrographs have shown that these restorations may contain porosities.³ Due to the variance in handling conditions, the results of using hand-made restoration materials vary widely.⁴

What Makes a Great Milling Material?
Dentists currently have several varieties of chairside blocks from which to choose. The baseline qualifications for an acceptable block material include its ability to be milled quickly, resistance to damage from machining, and simple finishing steps.3 (This explains why zirconia is not classified as a chairside material, as its lengthy processing time makes it impractical for same-day procedures.⁵) These qualities help maximize the efficiency benefits of in-office CAD/CAM systems. Materials should also demonstrate good strength and low wear on opposing dentition.
Of course, dentistry has treated these technologies with prudent caution, and there are several concerns about chairside CAD/CAM restorations that have been raised throughout the years. However, by now, most of these concerns have been adequately addressed with clinical data. In the beginning, a top concern with these restorations was the possibility of postoperative sensitivity. However, reports of this issue have lessened throughout time with the advancements in adhesives and luting techniques. Additionally, because the scanning step of the chairside milling procedure requires careful isolation of the tooth, this can actually help reduce the possibility of postoperative sensitivity. Furthermore, the elimination of the temporization step also reduces the chances of contamination and therefore later sensitivity.⁶
Fracturing is a concern for any milling material, whether it is used with in-office systems, or is fabricated in a laboratory. As with laboratory-fabricated restorations, proper design of the preparation and the subsequently fabricated restoration are vital to prevent fracturing. Inadequate porcelain thickness has been shown to be a significant factor in premature material fractures. Overall, however, CAD/CAM restorations have demonstrated consistently low fracture rates.⁶

Helpful Materials
Of the variety of milling materials available for chairside use, one of the longest track records exists for Vitablocs Mark II (Vident). This feldspathic glass-ceramic material was introduced in 1991.⁷ Its strength, when polished, has been shown to be approximately 130 MPa; while its strength, when glazed, increases to 160 MPa, or more.³ Another popular material is lithium disilicate (such as e.max [Ivoclar Vivadent]), which has been getting significant attention in the past few years due to its aesthetics and flexural strength (360 MPa for the CAD/CAM version; 400 MPa for the pressed version). With this strength, restorations made with this material can be either adhesively bonded with composite resin cements, or placed with conventional cements. These blocks are distributed in a soft state that enables them to be milled with chairside equipment, and then they are put through a 2-stage firing process in order to achieve their final state.⁵
A new material, referred to as a resin nanoceramic, has recently been introduced (Lava Ultimate Restorative [3M ESPE]). This CAD/CAM block is indicated for fabricating aesthetic and strong (200 MPa) single-tooth permanent restorations including crowns, crowns over implants, inlays, onlays, and veneers.
Based on nanoceramic technology, this material has properties similar to both composite resin and glass ceramic. By weight, the nanoceramic material included accounts for approximately 80% of this restorative material. This heat-treated material, with its reinforced matrix consisting of resin and nanoparticles, makes it harder and more resistant to wear than a conventional composite resin material. Additionally, it also retains polish very well like a glass ceramic, with less wear to opposing dentition. It is interesting to note that this material is being offered with a 10-year manufacturer warranty, demonstrating the confidence that the manufacturer has in this newly introduced material.
There are productivity advantages to using this material as well. It requires no firing, and its compositelike qualities make it easy to mill, polish, and adjust. Because it is less brittle, it also provides better edge quality right out of the milling unit. It can also be repaired intraorally, either with a subtractive technique, or an additive technique with light-cured composite resin restoratives. The material must be bonded with an adhesive resin cement.
The following case report will demonstrate the use of this new milling material to create an aesthetic and strong onlay in a single-office visit.

CASE REPORT
Diagnosis and Treatment Planning
A female patient presented with a large area of interproximal decay on No. 30, as well as decay on the adjacent tooth No. 28 (Figure 1).
It was decided to restore the bicuspid, No. 28, with a direct composite restoration using a direct nanocomposite resin (Filtek Supreme [3M ESPE]), then our attention turned to the larger area of caries on tooth No. 30.
While removing the decay, it was discovered that its extent ran deeper than upon first appearance. The initial plan was to stay conservative while removing the decay on the buccal cusp; however, it was necessary to remove decay not only from the buccal cusp but from the lingual cusp as well (Figure 2). Despite this, it was still possible to avoid having to create a full-coverage preparation, and the preparation design was kept as conservative as possible.

Figure 1. The patient presented with a large area of interproximal decay on a first molar.	Figure 2. Caries removal was completed.
Figure 3. A digital impression using CEREC Bluecam (Sirona Dental Systems) was taken.	Figure 4. Margins were drawn electronically using the system’s software.

Following the preparation step, the area was etched with phosphoric acid, and Scotchbond Universal adhesive (3M ESPE) was applied and cured. It should be noted here that, when Lava Ultimate Restorative is used with RelyX Ultimate Adhesive Resin Cement (3M ESPE) and Scotchbond Universal Adhesive as recommended by the manufacturer, the clinician can take advantage of a system that includes the primer and adhesive in one bottle. The clinician can choose between a self-etch, selective-etch, or total-etch technique, providing clinical flexibility. Next, a felt-tipped syringe (Ultradent Products) filled with alcohol was used to clean off the air-inhibited layer of the resin to facilitate the removal of the opaquing medium, and then a cord was packed around the preparation margin. A contrast medium (Optispray [Sirona Dental Systems]) was sprayed on the preparation area and the tooth was scanned with the CEREC (Sirona Dental Systems) wand.
Our chairside CAD/CAM system software (CEREC 4.03 [Sirona Dental Systems]) was used to design the restoration (Figures 3 to 6), and an A2-HT/14L Lava Ultimate block was selected and milled. After removal of the sprue, the restoration was tried in the mouth to confirm good interproximal contacts and occlusion (Figure 7). The restoration was then polished and the internal aspects were abraded with a surface treatment system. The restoration was then steam cleaned.

Figure 5. Restoration design.	Figure 6. Milling preview displayed.
Figure 7. After milling and subsequent removal of the sprue, the restoration was tried-in.	Figure 8. The final restoration (Lava Ultimate Restorative [3M ESPE]), after adhesive cementation.

Next, internal aspects of the onlay were coated with adhesive (Scotchbond Universal), and then the restoration was subsequently covered to prevent premature photo initiation. An additional application of adhesive was applied to the tooth for 20 seconds and then air thinned. A dual-cured universal adhesive resin cement (RelyX Ultimate) was then applied to the preparation, and the onlay was seated. Excess material was removed from the margins and the restoration was then fully light-cured (Figure 8).
The patient was very satisfied with the final aesthetic result and was also pleased that this restoration was completed in only one office visit.

CLOSING COMMENTS
The ability to offer an aesthetic and long-lasting restoration in a single visit is something that, in the author’s opinion, will become increasingly important for many dental practices. Within the space of one CAD/CAM appointment, a significant opportunity exists for dentists to increase operative efficiency by significantly decreasing the waiting time between preparation and delivery of a restoration. Depending on the alternative block material or technique, use of this newly introduced resin nanoceramic CAD/CAM block, as demonstrated in this case report, can save nearly 20 minutes in a restorative procedure due to its fast milling time and the elimination of the firing step necessary with conventional ceramics. Advances in materials are definitely helping dentists meet the ever-increasing and sophisticated demands of today’s patients.

References

1. Lowe RA. CAD/CAM dentistry and chairside digital impression making. cnpg.com/Video/flatFiles/-1172/dropbox_pdf/cadent-cadcamlowe.pdf. Accessed August 24, 2012.
2. Klim J, Corrales EB. Innovation in dentistry: CAD/CAM restorative procedures. cadstar.org/category/downloads/cerec-articles. Accessed August 24, 2012.
3. Giordano R. Materials for chairside CAD/CAM-produced restorations. J Am Dent Assoc. 2006;137(suppl):14S-21S.
4. Giordano RA. Building Blocks: An overview of the various types of machinable blocks for laboratory-based CAD/CAM systems. Inside Dental Technology. 2011;2:46-50.
5. Fasbinder DJ. Materials for chairside CAD/CAM restorations. Compend Contin Educ Dent. 2010;31:702-709.
6. Fasbinder DJ. Clinical performance of chairside CAD/CAM restorations. J Am Dent Assoc. 2006;137(suppl):22S-31S.
7. Fasbinder DJ. Chairside CAD/CAM: an overview of restorative material options. Compend Contin Educ Dent. 2012;33:50, 52-58.

Dr. Fleming is a 1978 graduate of The Ohio State University College of Dentistry. He maintains a full-time practice in Scottsdale, Ariz. Dr. Fleming has spoken to several international groups on CEREC technology and has served on the board of an international academy which furthered the understanding and use of computerized technologies and machinable restorative materials in dentistry. He serves as a consultant to a variety of dental manufacturers helping in product evaluation and design. Dr. Fleming has been a CEREC user since 2001, and a beta tester for the CEREC software since 2004. He is a faculty member in the CAD/CAM dentistry department at the prestigious Scottsdale Center for Dentistry. Dr. Fleming also serves as faculty on cerecdoctors.com, the largest online CEREC training in the world. He is editor for cerecdoctors.com the Magazine. He can be reached at mjfddsinc@aol.com.

Disclosure: Dr. Fleming received an honorarium from 3M ESPE for this article.