CAD/CAM

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 IN-OFFICE MILLING

When using CEREC and E4D, clinicians can fabricate their own restorations chairside. This capability can be an advantage in most cases; however, excellent patient scheduling is needed, and the dentist or staff person is required to take the total responsibility for the restoration fabrication. Clinicians state that all current dental CAD/CAM systems can be improved, including both the chairside and laboratory aspects of the process. The level of consistency and accuracy of restorations can occasionally be less than acceptable and can require extra time if the restoration proposals are not adequate for quick and simple modification. We are told by CAD/ CAM mechanical engineers that the current level of accuracy and consistency for CAD/CAM systems in dentistry is below that of some other industries, such as medical, electronic, automotive, machining, etc. Despite this limitation, the current dental systems have proven to be clinically acceptable in most situations when attention to detail is provided by the clinician.

Currently, there are about 12,000 in-office milling devices in the US, the majority of which are CEREC systems and a growing number are E4D systems. Although there is the expected competition and marketing claims from both companies, CR has demonstrated that both systems can provide an excellent restoration. Both devices have advantages over their competitor and both have areas of improvement. We expect many new and exciting innovations as the technology continues to evolve.

What are the differences in clinical techniques when a dentist decides to use digital impressions and in-office milling instead of conventional techniques? The following steps show that there can be significant differences in the clinical procedure. Steps 3 to 8 can be legally accomplished by staff persons in most states:



1. Seat the patient, select the color of the restoration, and anesthetize the patient.

2. Make the tooth preparation to a specified design, which may be slightly different depending on the type of ceramic or composite used for the restoration.

3. Place reflective powder if required. CEREC requires a thin dusting of powder, while E4D does not require the use of powder. (Sometimes a liquid contrast agent on enamel or metal restorations is needed with the E4D.) Both preimpression techniques are minimal and require little time and effort.

4. Make a digital impression of the tooth preparation. The length of impression time varies by system. 

5. Design the restoration using the computer program. This task can require from a few minutes to 20 minutes, related to the quality of the impression, the accuracy need of the proposed restoration, and the number of changes the clinician desires. 

6. Mill the restoration from standardized blocks. There are a variety of materials from which to choose, with most materials coming from Vident, Ivoclar Vivadent, or 3M ESPE. The introduction of IPS e.max CAD (Ivoclar Vivadent) for chairside milling has allowed the clinician to provide a stronger restoration, but requires a furnace to fully crystallize (bake) the material.

7. Adjust the restoration clinically.

8. Characterize and/or stain the restoration as desired or needed. Several furnaces are available with one of the most popular being the Programat CS (Ivoclar Vivadent).

9. Cement the restoration (resin cement is the most commonly used for these mostly ceramic or polymer restorations). Most clinicians are using either a self-adhesive (such as RelyX Unicem 2 or Maxcem Elite, or separate self-etching resin cement (such as Multilink Automix).

10. Evaluate and adjust the occlusion with fine diamonds and porcelain polishing instruments (such as Brasseler USA or KOMET). 

11. Finish and polish the restoration where adjustments were made with porcelain polishing paste (such as Diashine by VH Technologies).



CR research has shown for more than nearly 25 years that the quality of restorations made from digital impressions and milled in-office are the same as or better than restorations made in the conventional manner when strict attention to the protocol is provided. Digital impressions and chairside milling should not be considered to allow less attention to detail or require less clinical expertise. When those using these concepts follow the manufacturers’ instructions and develop excellent clinical skills, these chairside digital devices can deliver a great restoration.

How soon this concept will become commonplace in dentistry is unknown. We appear to be somewhat behind other areas in adapting to this popular and growing concept. More innovative planning and development requiring more manufacturer investment is suggested to make the systems more accurate, faster, easier, and definitely less expensive. For some dental practices, the move to in-office milling can be efficient, predictable, and profitable.