Practical Advice for Incorporating CAD/CAM Into the Operatory

In terms of technology, incorporating computer-aided design/computer-aided manufacturing (CAD/CAM) dentistry (eg, CEREC^®, Sirona Dental Inc., www.sirona.com; E4D, D4D Technologies, www.e4d.com) probably has the most significant impact on a dental practice. Not only does it affect the way restorative dentistry is performed, but it also impacts patients, practice marketing, and the practice’s financial bottom line.

CAD/CAM dentistry is a significant investment, and the thought of having an expensive, high-tech piece of machinery become a dormant, dust-collecting object can be disconcerting. However, the upside is gaining the ability to deliver complete dentistry in one visit that can transform the patient’s experience from negative to positive. Patients typically don’t like having an impression taken and wearing a temporary for 2 weeks, and then having to return. Once patients experience one-visit dentistry, they will likely be repeat customers.

Once a dental practice decides to commit to CAD/CAM dentistry, as with any new endeavor, a systematic approach to incorporating it into the practice can ease the transition. The first step is deciding on the system that seems best for the individual practice—such as either the CEREC system or the E4D system. It would be prudent to have each system brought into the office and “test-drive” the equipment on a willing patient or staff member. (The representative will provide needed assistance.) This may require several restorations until a decision can be made. Both systems can produce the same end-result; their differences lie in the manner in which it is accomplished.

CAD/CAM systems are composed of the acquisition unit and the milling unit. The acquisition unit can move room to room, whereas the milling unit should be located in an area in the office where it can be put on display. It is exciting for patients to watch their own crown being milled. Other patients in the office will also be interested in watching the milling process. Exposing the patient base to this high-tech equipment creates a perception that the office is on the “the leading edge.” Patients tend to tell others when their dentists offer new procedures, such as making a new crown in one visit; this can, in turn, be a highly effective marketing tool.

Scheduling must also be considered. As with any new procedure, the learning curve can be steep and the time allotted for it in the schedule can become problematic. Simply doubling the normal time allowed for a single-crown appointment may serve as a guide for the first few restorations. As the clinician and assistant perform more procedures, the scheduling time can be adjusted. Keep in mind that the normal second insertion appointment is eliminated, therefore that time now becomes available.

Clinicians have several different types of restorative materials to choose from, including millable blocks of laboratory-processed resins, porcelains, and high-strength ceramics. Paradigm™ MZ100 (3M ESPE, www.3MESPE.com) is an all-resin material. Lava™ Ultimate Restorative (3M ESPE) is a combination resin/porcelain material that has properties of a resin and strength of a porcelain restoration. Several leucite-reinforced blocks are available, either in solid shades or multi-layered shades that offer variations in color for the anterior region. Lithium-disilicate blocks such as IPS e.max® (Ivoclar Vivadent, www.ivoclarvivadent.com) are also available in all shades.

There are several new items becoming available to the CAD/CAM practice. Clinicians will have multiple-size blocks, shades, and translucencies to choose from that allow the fabrication of a fixed bridge in one appointment. The IPS e.max CAD B32 size block will be available in a variety of low translucency shades and can be used for up to three-unit anterior bridges—premolar forward—offering high durability and esthetics.

IPS e.max CAD Abutment Solutions will offer clinicians the ability to create a chairside implant abutment in one visit using the “block with a hole in it,” according to the manufacturer. The shade offering allows for supragingival margins, unmatched esthetics, and predictable clinical success.

Technology has increased the use of monolithic restorations utilizing lithium disilicate and zirconia dioxide. Both materials require further processing after the milling phase is completed. Crystallization of the lithium-disilicate restorations can be completed in a porcelain furnace in 20 minutes. Zirconia dioxide, on the other hand, has a much longer sintering process (more than 2 hours in a sintering oven) that does not fit the chairside one-appointment crown scenario. Although zirconia-dioxide restorations can be fabricated in the dental office, the time and equipment required makes it more feasible to outsource them to a laboratory that can utilize facilities that specialize in these types of restorations.

Unlike in the dental laboratory, where the technician can “fudge” inconsistencies with a preparation, the computer software does not have as much flexibility. One of the most common complaints from dental technicians is insufficient occlusal reduction, especially toward the lingual aspect of the second molar preparations. In the case of a ceramo-metal crown, the technician can either create a reduction coping that the clinician would use to modify the preparation at the insertion appointment or fabricate the crown with a metal occlusal island. The clinician does not have that ability to compensate for an under-reduction problem when fabricating CAD/CAM restorations.

The preparation must be corrected and rescanned with new images. Otherwise, the restoration will have an insufficient ceramic thickness and be destined to fail. Therefore, the preparations need to be adapted to what the computer is designed to see and mill. There are certain parameters that are put into the design program that the clinician selects, one of which is the minimal thickness of the crown. When the computer knows that the final restoration lacks this thickness, it will notify the dentist before moving into the milling phase. Flat margins with a 90-degree exit angle are easier to scan than a reverse or trough margin. Feather-edge margins are not only difficult to read, but they are also difficult to mill. Sharp line angles, undercuts, unclear margins, or insufficient interproximal reduction can all be potential problems in the scanning, design, and milling process. Once these concerns are recognized during the preparation phase, the whole process is streamlined.

For a novice, scanning the preparation for the different digital views required might take the same amount of time that is needed for a fast-setting triple-tray impression. Where the procedure can become time-consuming is the actual step-by-step crown design created on the computer. Like anything new, the more this step is practiced, the more proficient the clinician will become.

The time to fabricate the restoration will also depend on the type of restorative material used. For completing a non-stained, non-oven–glazed, leucite-reinforced ceramic restoration, the patient’s time can remain in the same scheduling column. It becomes a drill, scan, design, mill, and insert procedure. If the clinician desires to add external staining and possibly glazing, then some additional “oven time” must be accounted for. Using lithium disilicate will also require oven time.

If the clinician wants to offer ceramic restorations (IPS e.max), a porcelain oven will need to be incorporated into the office. A porcelain oven will also allow the practitioner to bring ceramic restorations to a higher level of esthetics by using chairside staining techniques. Another advantage of having a porcelain oven in the office is economics. For example, if a single all-ceramic crown for a maxillary central incisor is needed and the shade is off, it must be returned to the laboratory and the patient must return for a second appointment. Each additional patient visit and laboratory correction further erodes profit margin; it also increases the patient’s disappointment and inconvenience. However, with a porcelain-staining oven in the office, the clinician can correct the shade during the first appointment, thus preserving the profit margin and satisfying the patient. A porcelain oven is a practice asset that clinicians should learn to use.

There are other pieces of equipment that will aid the clinician in isolation, preparation, and cementation. For example, the success of the restoration depends on the ability of the acquisition unit to capture the preparation detail and offer a clear view of the margin. Using a diode laser unit easily exposes the margin and is less time-consuming than packing retraction cord. Additionally, LED light retraction devices help keep the patient’s tongue and cheek clear during the preparation and scanning steps, and flat-end diamond burs are needed for the correct margin design.

Before committing to CAD/CAM, it is important to assess all the costs. Once the unit is purchased, a service contract is highly recommended, which is an additional expense. Also, the cost of the supplies necessary to mill the ceramic blocks must be considered—these include diamond burs, milling liquid, polishing wheels, and the blocks themselves. Some of these expenses are fixed and some are variable. The fixed expenses—ie, the monthly service plan and lease payment—remain the same no matter how many units are produced in a month. The variable expenses parallel the number of restorations made; therefore, the cost of the fixed expenses decreases as the number of restorations increases. It is not enough to justify the expense based on a desire to eliminate the laboratory bill; care should be taken to calculate the cost differential between the monthly lab bill and the fixed and variable expenses of using a CAD/CAM unit to determine whether the purchase makes financial sense.

CAD/CAM dentistry is exciting and is the future of dentistry. Clinicians should engage it and see for themselves the transformation of not only their office but also their patients.

Gregg A. Helvey, DDS
Adjunct Associate Professor, Virginia Commonwealth
University School of Dentistry, Richmond, Virginia;
Private Practice Middleburg, Virginia