The Use of CAD CAM in Dentistry

Computer-aided design (CAD) and computer-aided manufacturing (CAM) have become an increasingly popular part of dentistry over the past 25 years. The technology, which is used in both the dental laboratory and the dental office, can be applied to inlays, onlays, veneers, crowns, fixed partial dentures, implant abutments, and even full-mouth reconstruction. This article discusses the history of CAD/CAM in dentistry and gives an overview of how it works. It also provides information on the advantages and disadvantages, describes the main products available, discusses how to incorporate the new technology into your practice, and addresses future applications.

History of dental CAD/CAM

Computer-aided design and manufacturing were developed in the 1960s for use in the aircraft and automotive industries, and were first applied to dentistry a decade later.

Some of the most important figures in dental CAD/CAM development are Drs François Duret of France, Werner Mörmann of Switzerland, Dianne Rekow of the United States, and Matts Andersson of Sweden.

Dr Duret was the first person to develop a dental CAD/CAM device, making crowns based on an optical impression of the abutment tooth and using a numerically controlled milling machine as early as 1971. He produced the first dental CAD/CAM restoration in 1983 and demonstrated his system at the French Dental Association's international congress in November 1985 by creating a posterior crown restoration for his wife in less than an hour. Dr Duret later developed the Sopha system.

Dr Mörmann was the developer of the first commercial CAD/CAM system. He consulted with Dr Marco Brandestini, an electrical engineer, who came up with the idea of using optics to scan the teeth. By 1985, the team had performed the first chairside inlay using a combination of their optical scanner and milling device. They called the device CEREC, an acronym for computer-assisted ceramic reconstruction.

Dr Rekow worked on a dental CAD/CAM system in the mid-1980s with colleagues at the University of Minnesota. This system was designed to acquire data using photographs and a high-resolution scanner, and to mill restorations using a 5-axis machine.

Early technology permitted the creation of inlays, onlays, veneers, and crowns. More recently, CAD/CAM systems have been able to provide fixed partial dentures and implant abutments.

Another use of CAD/CAM is in orthodontics. CAD/CAM systems are becoming increasingly popular in dental offices. 

Overview of CAD/CAM

In brief, in-office dental CAD/CAM systems consist of a handheld scanner, a cart that houses a personal computer together with a monitor, and a milling machine.

The scanner head is placed intraorally above the tooth preparation and the resulting data appear on the monitor as 2-dimensional (2-D) or 3-dimensional (3-D) images. Design work is done on the monitor and the instructions are sent to a computer-assisted processing machine for milling.

Restorations are milled from prefabricated blocks of porcelain. Options include feldspathic, leucite, or lithium disilicate materials as well as blocks of composite. After the restoration is examined and approved, it is polished and inserted using conventional bonding techniques.

Results with in-office milling machines appear to be as good as those from laboratory milling machines. 

Advantages and disadvantages of CAD/CAM

The use of CAD/CAM technology for dental restorations has numerous advantages over traditional techniques. These advantages include speed, ease of use, and quality.

Digital scans have the potential to be faster and easier than conventional impressions because casts, wax-ups, investing, casting, and firing are eliminated. According to Sirona, half-arch impressions with the most recent version of CEREC take 40 seconds and full-arch impressions take 2 minutes. 

CAD/CAM also makes design and fabrication faster; a full-contour crown takes just 6 minutes to mill.

Having a milling machine on site means that patients can receive their permanent restoration the same day they come in, without making a second appointment. Patients no longer need to have provisional restorations, which take time to fabricate and fit. If anesthetics are needed, they only need to be administered once.

The quality of CAD/CAM restorations is extremely high because measurements and fabrication are so precise. In a study of 117 subjects by Henkel, each subject had 2 crowns made. One crown was made based on physical impressions using standard trays and impression material and another was made based on electronic impressions. Without knowing which one was which, dentists chose the crown based on the electronic impression 68% of the time.

Perhaps this difference in the finished product should not be surprising, given the wide variation in quality of traditional impressions. Writing in a 2005 article, Christensen stated that he had seen impressions sent to laboratories in which more than 50% of the preparation margins were not discernible. Traditional impressions suffer from problems, such as bubbles and tears in the impression material, cords or other debris embedded in the impression material, and missing teeth.

CAD/CAM restorations have a natural appearance because the ceramic blocks have a translucent quality that emulates enamel, and they are available in a wide range of shades. Ceramic wears well in the mouth, even when used for posterior teeth; because it is no more abrasive than conventional and hybrid posterior composite resins, it causes minimal wear to the opposing teeth.

Finally, quality is consistent because prefabricated ceramic blocks are free from internal defects and the computer program is designed to produce shapes that will stand up to wear.

Savings in time and labor have the potential to reduce costs, and the promise of faster, high-quality restorations should appeal to patients and patients are also happy to avoid the need for gag-inducing impressions.

Another benefit is that all the scans can be stored on the computer; whereas, standard stone models take up space and can chip or break if stored improperly.

Still, CAD/CAM systems have disadvantages. The initial cost of the equipment and software is high, and the practitioner needs to spend time and money on training. Dentists without a large enough volume of restorations will have a difficult time making their investment pay off.

Just as with conventional impressions, in taking an optical scan the dentist needs to obtain an accurate recording of the tooth in need of restoration. The scan needs to emphasize the finish line and precisely duplicate the surrounding and occlusive teeth. Digital scanning requires the same type of soft-tissue management, retraction, moisture control, and hemostasis that is so important for conventional impressions.

Digital impression systems may not save time as they are currently used because of the need for multiple steps. For example, dentists who use certain scanners must first send the images for a cleanup process, which is followed by setting of the margins by a dental technician. The images next go to the clinician's dental laboratory for review and then back for model milling. Finally, the models and dies are then sent to the clinician's dental laboratory for fabrication of the restoration.