May 2016
Volume 37, Issue 5

Eying the Future: Digital Dentistry in Your Sights?

Brian Schroder, DDS; Christopher A. Hooper, DDS; and David G. Gratton, BSc, DDS, MS

Q: Is chairside CAD/CAM the future?

A: Dr. Schroder

As CAD/CAM is but a small part of the overall involvement of computers in dentistry, I’d like to rephrase the question. No, digital dentistry is not the future; it is the present. I replaced the use of conventional impression material with a dedicated digital impressioning system in my practice in January 2009, and since that time have made every impression for indirect restorations, from a single crown to a full-mouth rehabilitation, with the use of a digital impressioning system (first with the Lava Chairside Oral Scanner C.O.S. [3M ESPE, www.3M.com] and then evolving into the 3M TrueTM Definition Scanner [3M ESPE]). (I have yet to adapt chairside CAD/CAM to my practice.) I did not make this change because of the clinical challenges involved in making good impressions but rather because of the inherent errors found in conventional systems. Tray selection and seating, accurate material placement, undisturbed setting of the impression, disinfection of the final impression, transport of that impression to the laboratory, creation of a gypsum stone master cast, die separation and ditching, and articulation all challenged my results when I was an impression materials user. The change has been productive for my efficiency. My calculations suggest that my switch to digital impressioning has eliminated more than 80% of those areas for distortion potential. My experience has enabled me to conclude that the gains in the accuracy of digital systems are found in the elimination of the impression material and the replacement of the gypsum die stone cast with a resin or polyurethane model.

Please do not infer that digital systems excuse outstanding clinical technique. Accurate preparation and isolation remain mandatory for precise data capture. Digital systems are accurate, consistent, and efficient, performing exactly the same with each use. The data that they acquire are archived and able to be infinitely recalled and remain unchanged. A digital system can be used to design and mill restorations, create master models for more conventional restoration fabrication, mill wax, print resin, laser sinter metal, and provide a myriad of other current and future applications. In our practice, we now use STL files merged with CBCT to fabricate surgical guides (www.implantconcierge.com), enabling far greater confidence and accuracy in implant placement. We scan those implants using scanning abutments at the time of surgery, thereby enabling creation of final crowns far sooner and with fewer appointments for the patient. We are using the digital data to design and fabricate RPD frameworks that have demonstrated greater precision and fit, reducing delivery times.

The applications for digital-data use just continue to expand. The incorporation of digital systems into the daily practices of restorative dentists is no longer an outlier limited to those that exist on the fringes of conventionally accepted techniques. It has proven to be worthy of a place in mainstream dentistry.

A: Dr. Hooper

CAD/CAM procedures are neither new nor unique to dentistry and can be found through many aspects of contemporary manufacturing and design. When we consider the usefulness in dentistry, or any business for that matter, we also must consider the drawbacks. Without question, digital impressions have the ability to impress patients. Even more striking is the ability to deliver a completed restoration in one dental visit, instead of the traditional return visit after the restoration has been fabricated in the laboratory.

Many proponents of digital impressioning and computerized milling mention how laborious conventional methods are: tray selection, messy impression materials, transportation to and from the laboratory, stone models, etc. In reality, I do not find placing a triple tray in the mouth with fast-setting impression material to be laborious or messy. It is certainly no messier than the preparation itself, or the steps needed to place composite resin restorations and the use of phosphoric-acid etchant.

These proponents also discuss the inherent superiority of CAD/CAM crowns in terms of marginal integrity. This implies that conventionally fabricated crowns must somehow be subpar; however, we have all seen conventionally fabricated crowns still functioning well in our patients’ mouths for 30-, 40-, and even 50-plus years. Many studies show conventional techniques produce crowns with marginal gaps in the 25-µm to 30-µm range, a gap thinner than the resulting gap after proper cementation utilizing good cements.

Proponents also like to point to how the technology may help reduce the number of appointments. Most dentists with busy restorative practices can prepare, impress, and temporize teeth in short order. I generally allow approximately 1 hour to prepare, impress, and temporize a quadrant of crowns, and I schedule 20 minutes for the delivery appointment 2 weeks later. During this temporary phase, good things can happen. If we utilize ZOE temporary cements, symptomatic teeth many times settle down. If they do not quickly settle, we can extend the delivery appointment an additional week, or consider endodontic therapy prior to final crown delivery. Also, I have never seen a dentist complete 3 to 4 crowns in 1 hour and 20 minutes utilizing digital impressioning and computerized milling. Plus, in my state of Virginia, as well as in many other states, the doctor is required to make the final impression, which is not to be delegated to a staff member. So rather than scan, I can simply place the final impression, examine, or treat another patient, and then return 3 minutes later to remove and evaluate the impression, which is time very well utilized. Moreover, the final esthetic result is generally superior when using a good ceramist with experience and attention to detail.

We must not at all forget about the cost to purchase, maintain, and service the CAD/CAM device, which must be wheeled between operatories. First there is the $100,000 plus for initial “investment” (I generally consider investments as instruments that spin off cash), approximately $40 to $50 per crown for materials, burs, and other items, and then of course the maintenance and software upgrades on the system. Contrast this to the cost of a triple tray, impression material, and perhaps $79 to $99 cost for a commercially made ceramic or zirconia posterior crown. Many insurance-based practices even utilize PFM restorations that are available for an even lower price point.

Doctors may, indeed, find this technology exciting, and some may even find it beneficial for their practices and patients. I, however, am not quite ready to jump on board for the reasons listed above.

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