Chairside Vs. Laboratory Milling: What Factors Into a Clinician’s Decision?

An investment in high-end milling devices (initially a PrograMill PM3 and, subsequently, a PrograMill PM7, Ivoclar Vivadent, ivoclarvivadent.com) has afforded the practice a highly predictable workflow that allows full control of the technical aspects associated with both esthetic and reconstructive patient treatments. Beginning with the digital design of the esthetic mock-ups as the prototype for milled provisional restorations, through to definitive lithium-disilicate or monolithic zirconia restorations, the versatility of the in-office laboratory mill when utilized by skilled in-office digital laboratory technical personnel has been a "game changer."

The chairside milling process should provide the same level of precision of fit, longevity of restorative material, and esthetics as a laboratory-milled restoration. In that respect, our chairside-milled restoration is in actualitya laboratory-milled restoration.

Perhaps the most efficient and cost-effective use of our in-office laboratory mills is the single-tooth ceramic restoration that can be delivered on a same-day basis, again with the high level of laboratory-quality precision. The typical scenario involves the patient who presents with a fractured tooth and requires either a partial- or full-coverage fixed prosthesis. The tooth may be prepared, an intraoral scan obtained, the restoration designed and milled and then definitively cemented in place, all in 2 to 3 hours.

Throughout the process, the patient is able to see the capturing of an image of the prepared tooth and observe the digital design of the restoration. This portion of the process is, indeed, accomplished chairside,while the laboratory phase then creates the high-quality definitive restoration. Patients typically are fascinated to observe the process and appreciate the technical and artistic skills involved in the provision of their care. Also, they see the value of this single-visit service. This is truly a hybrid approach: chairside image and data capture followed by laboratory-quality milled in-office restorations.

While the initial expenses required to ramp up in-office laboratory milling technology may seem daunting, with each high-end mill acquisition our practice has seen a rapid return on that investment. Mill technology continues to improve as costs continue to go down. With the introduction of smaller high-quality milling units, the ability to provide laboratory-quality single-tooth restorations has been "democratized" for a reasonable cost, while precision and delivery time have been optimized.

In today's digital world clearly it is advantageous to have a digital process, whether in the clinical environment or laboratory environment. All of the various aspects that are encompassed in digital dentistry-the transfer of information, accuracy, duplication, and repeatability-are benefited. Certainly, the chairside component clinically is valuable because of the time-saving element for the patient. However, one could argue that the final esthetic restorative result may be inferior to what a quality laboratory can produce or become highly time-consuming for the clinical staff to create. What is often oversimplified in the dental profession-and can be misleading-is the idea that dentists or technicians can simply plug something (ie, material) into a digital space and have it produce a human body part. Even in a clinical environment someone must be steering the ship, so to speak, acting as the coordinator or serving as the technician, with a hand in the skilled, artistic aspect of the production of the restoration.

This same challenge is applicable in the laboratory. Somehow, it seems those on the clinical side of dentistry think lab technicians have all the answers, or that clinicians can just "send the file" and technicians will make everything happen, almost magically. However, there is a bit more to it than that. It is true that digital methods are light-years ahead of manual approaches when it comes to repeatability. But, speaking as a lab technician, with regard to the actual input of information, to create an esthetic restoration the time differential between manual and digital can be argued.

Surely, there are many benefits to chairside CAD/CAM. Of course, in the most demanding esthetic cases, the lab technician should be totally involved. But for immediate situations-for example, a broken tooth or repair-chairside can more than suffice. The realm of dentures may offer an even greater opportunity for chairside CAD/CAM. Consider that, hypothetically, in an optimal setting, one could take a digital scanner and scan, for example, every denture in a nursing home and have the ability to replace any denture any time it was lost! Thus, from an immediacy standpoint, it is invaluable. Again, the challenge is the esthetic input into the system, and technology has advanced such that even edentulous scans are now more accurate than ever before.

The digital platform will continue to grow, even though only a small percentage of the market is currently utilizing it to its maximum. It has undoubtedly helped improve the clinical setting. For example, a digital impression or scan can be enlarged to reveal a full-volume view of all the detail. This helps improve the dentist's level of accuracy due to the ability to see the field more clearly.

I have worked with digital platforms now for well over a decade, and currently operate a six-person laboratory with three scanners, two milling machines, and a printer-a lot of digital equipment for a small laboratory. Yet we still produce many of the final esthetic outcomes by hand, with the aid of the digital components. Communication remains the key-regarding material options, esthetic requirements, functional parameters, and the needs of the patient. Communication in the dental profession in general, I believe, needs improvement. Just because one sends files digitally instead of writing out a prescription doesn't mean the case is already better.

When considering the decision of chairside milling versus laboratory milling related to private practice, both the technology and its multiple effects on the operation of the practice must be evaluated. Even with the myriad of existing hardware and software choices, there are still a number of processes involved with all of these programs.

The first step in CAD/CAM dentistry is the acquisition of dental arches and sending these files to a design program. This is the initial involvement for a dental laboratory when a lab is used to complete the entire manufacturing process. For in-office milling, an intraoral scan is sent to a specific design program, or the program may have the design software embedded in the acquisition module. Regardless, the clinical acquisition needs to be performed adequately, and then the crown designed. (It is hoped that there will soon be complete automatic intelligence-fabricated design of the crown.) The mill then has to be prepared and the design sent to and cut by the milling machine, which at present is a relatively simple process. After completion of the milling, the crown has to be finished and/or stained and glazed, and then, of course, properly prepared and cemented/bonded to the tooth.

Each of these steps requires the proper amount of time, with consideration given to system performance, human engagement, and operator qualifications. These factors can vary greatly because every business is staffed by uniquely knowledgeable and talented individuals. A series of practice runs (either on a typodont or patient) can be performed to fine-tune and record the time and resources an office may need to manufacture and deliver the crown.

A number of observations may be considered regarding the utilization of an intraoral scanner and in-office mill. First, patient satisfaction is highly dependent on results. Obviously, the digital process is meant to simplify the patient experience. If this is not happening, alternative techniques and pathways should be available. The more experience the doctor and staff acquire, the better the results should be.

Second, these people-oriented tasks usually are divided up among the staff and doctor(s) and will intersect and/or interfere with other job responsibilities. The office schedule may need to allow for additional workload, and/or consideration may be given to hiring another appropriately trained clinical staff member(s). Alternatively, more classical dental laboratory pathways could be used to process crowns. Assuming dental anatomical knowledge and correct material selection and handling, the quality of the produced crown, whether from laboratory milling or chairside milling, should be comparable.

Third, technology is an evolution in which dentistry is in midstride. The dental profession has overcome many of the earlier clinical outcome disappointments of the digital process, but more improvements are still needed to make it easier and timelier. These improvements will likely be significant enough to prompt hardware changes and related expenses in the future.

In summary, if a dental practice is at peak performance and employee utilization, then staying with present techniques may be the easiest and most cost-effective approach. But, if an ample supply of monetary and manpower resources are available, then implementation of a chairside milling option should be seriously considered.

Lawrence E. Brecht, DDS
Clinical Associate Professor, New York University College of Dentistry, New York, New York; Private Practice limited to Prosthodontics and Maxillofacial Prosthetics, New York, New York

Peter Pizzi, MDT, CDT
Owner, Pizzi Dental Studio Inc., Staten Island, New York; Editor-In-Chief, Inside Dental Technology

Vincent J. Prestipino, DDS
Private Practice limited to Prosthetic and Implant Dentistry, Bethesda, Maryland