CAD/CAM dentistry

CAD/CAM dentistry is a field of dentistry and prosthodontics using CAD/CAM (computer-aided-design and computer-aided-manufacturing) to improve the design and creation of dental restorations, especially dental prostheses, including crowns, crown lays, veneers, inlays and onlays, fixed dental prostheses bridges, dental implant supported restorations, dentures (removable or fixed), and orthodontic appliances.

Indirect prostheses can be made of cast alloys, sintered ceramics, or polymerized resins. Each material that is used for making a prosthesis requires a process that often takes two or more patient appointments to complete. CAD/CAM systems offer an alternative method that can produce metal, ceramic, or composite restorations in one appointment. In addition, CAD/CAM technology allows a technician or dentist to use higher quality ceramics, which are produced under nearly ideal conditions. Such materials exhibit several improved properties compared with conventional sintered or hot-pressed ceramics.

The dental application of CAD/CAM became available in the early 1980s to produce ceramic inlays and crowns during one chairside appointment. This technology has since been improved and expanded as an alternative to the metal-casting and ceramic sintering processes, since computer-aided milling or grinding of a metal or a ceramic block can be performed by a CAD-CAM process or by electrolytic or electrical discharge removal of metal.

Chrome-cobalt disc with bridges and crowns manufactured using WorkNC Dental CAD/CAM

Process

A CAD/CAM system electronically or digitally records surface coordinates of the prepared teeth and stores these data in the memory of a computer. The image data can be retrieved immediately to mill or grind a metal, ceramic, or composite prosthesis by computer control from a solid block of the chosen material. Within minutes, the prosthesis can be fabricated and placed on prepared teeth and bonded or cemented in the mouth of the patient in a time ranging from 10 minutes to 1 hour.

The optical scanning procedure eliminates the need for an impression. An advantage of ceramics is that homogeneous, high-quality materials with minimal porosity and few other defects are used for CAD/CAM applications. The computer controlled milling machine can then perform the milling or grinding for fabrication of a ceramic prosthesis within a few minutes. Note that all-ceramic prostheses suffer from some degree of near-surface damage that is directly related to material selection and machining parameters with CAD/CAM fabrication. Any surface damage increases the probability of catastrophic failure. Understanding and managing the damage phenomena are critical to the success of ceramic prostheses made by CAD/CAM.

The CAD/CAM technique can also be used to prepare prostheses from CP Ti or titanium alloy, which do not contain bulk casting defects or the hard α case found near the surface of cast titanium prostheses.

Advantages and drawbacks

CAD/CAM has improved the quality of prostheses in dentistry and standardised the production process. It has increased productivity and the opportunity to work with new materials with a high level of accuracy. It has decreased chair time for the patient by the use of intra-oral scanning systems which allow the dentist to send electronic impressions to the lab. The restorations are milled from a block of ceramic which has fewer flaws.

However, CAD/CAM requires a large initial investment. Occlusal detail isn't always the best and has to be amended by hand. Most doctors that use chair side technology find the level of detail to be more than adequate in a clinical setting.

Though CAD/CAM is a major technological advancement, it is important that the dentists’ technique is suited to CAD/CAM milling. This includes: correct tooth preparation with a continuous preparation margin (which is recognisable to the scanner e.g. in the form of a chamfer); avoiding the use of shoulderless preparations and parallel walls and the use of rounded incisor and occlusal edges to prevent the concentration of tension.

Depending on the material, CAD/CAM treatments may have aesthetic drawbacks, whether they are created at the dental practice or outsourced to a dental laboratory. Depending on the dentist or technician, CAD/CAM restorations can be layered to give a deeper more natural look. Just like traditional restorations, CAD/CAM restorations also vary in aesthetic value. Many are monochrome. In some hand-layered crowns and bridges, feldspathic porcelain is fused to glass-infiltrated aluminum oxide (alumina) or zirconium-oxide (zirconia) creating a high-strength, highly aesthetic, metal-free crown or bridge. In other traditional restorations, the porcelain is layered onto a metal substructure and often display colour brightness, an opaque "headlight", and dark oxide lines (a "black line" in the vicinity of the gum line). As these dark metal substructures are not conducive to a natural appearance, metal-free restorations are typically more aesthetically pleasing to the patient.

There are also different medical repercussions for each restorative technique. If the CAD/CAM restorative material is zirconia, the restoration becomes "radio-opaque", just as metal restorations are, blocking x-rays. Only alumina, lithium disilicate materials are "radio-lucent", allowing dentists to track potential decay. Zirconia, conventional porcelain-to-metal, and traditional gold and other all-metal crowns block x-ray radiation, disallowing evaluation over time. Therefore, doctors have to examine restorations visually and with a dental explorer to diagnose decay.

Crowns and bridges require a precise fit on tooth abutments or stumps. Fit accuracy varies according to the CAD/CAD system utilized and from user to user. Some systems are designed to attain higher standards of accuracy than others and some users are more skilled than others. It is estimated that 20 new systems are expected to become available by 2020.

Further research is needed to evaluate CAD/CAM technology compared to the other attachment systems (such as ball, magnetic and telescopic systems), as an option for attaching overdentures to implants.

CAD/CAM dentistry Resources
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