CAD/CAM dentistry

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

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,^[1][2] especially dental prostheses, including crowns, crown lays, veneers, inlays and onlays, fixed bridges, dental implant restorations, dentures (removable or fixed), and orthodontic appliances. CAD/CAM complements earlier technologies used for these purposes by any combination of increasing the speed of design and creation; increasing the convenience or simplicity of the design, creation, and insertion processes; and making possible restorations and appliances that otherwise would have been infeasible. Other goals include reducing unit cost and making affordable restorations and appliances that otherwise would have been prohibitively expensive. However, to date, chairside CAD/CAM often involves extra time on the part of the dentist, and the fee is often at least two times higher than for conventional restorative treatments using lab services.CAD/CAM is one of the highly competent dental lab technology.^[3]

Like other CAD/CAM fields, CAD/CAM dentistry uses subtractive processes (such as CNC milling) and additive processes (such as 3D printing) to produce physical instances from 3D models.

History

Although CAD/CAM dentistry was used in the mid-1980s, early efforts were considered a cumbersome novelty, requiring an inordinate amount of time to produce a viable product. This inefficiency prevented its use within dental offices and limited it to labside use (that is, use within dental laboratories). As adjunctive techniques, software, and materials improved, the chairside use of CAD/CAM (use within dental offices/surgeries) increased.^[4] For example, the commercialization of Cerec by Siemens made CAD/CAM available to dentists who formerly would not have had avenues for using it.

The article 'CEREC' CAD/CAM in Dentistry^[5] original dissertation Data capture stabilising device for the CEREC CAD/CAM chairside camera^[6] fully explains all pros and cons of the system and is detailed in (materials, fit, software, hardware etc).

Difference from conventional restoration

Chairside CAD/CAM restoration differs from conventional dentistry in that the prosthesis is typically luted or bonded the same day. Conventional prosthesis, such as crowns, have temporaries placed from one to several weeks while a dental laboratory or in house dental lab produces the restoration.^[7] The patient returns later to have the temporaries removed and the laboratory-made crown cemented or bonded in place. An in-house CAD/CAM system enables the dentist to create a finished inlay in as little as an hour in some cases.^[8] Bonded veneer CAD/CAM restorations are more conservative in their preparation of the tooth. As bonding is more effective on tooth enamel than the underlying dentin, care is taken not to remove the enamel layer. Though one-day service is a benefit that is typically claimed by dentists offering chairside CAD/CAM services, the dentist's time is commonly doubled and the fee is therefore doubled.

Process

Typically CAD/CAM dental restorations are milled from solid blocks of ceramic or composite resin that closely match the basic shade of the restored tooth. Metal alloys may also be milled or digitally produced.

After decayed or broken areas of the tooth are corrected by the dentist, an image (scan) is taken of the prepared tooth and the surrounding teeth. This image, called a digital impression, draws the data into a computer. Proprietary software then creates a replacement part for the missing areas of the tooth, creating a virtual restoration. This is called reverse engineering. The software sends this virtual data to a milling machine where the replacement part is carved out of a solid block of ceramic or composite resin. Stains and glazes are fired to the surfaces of the milled ceramic crown or bridge to correct the otherwise monochromatic appearance of the restoration. The restoration is then adjusted in the patient’s mouth and cemented or bonded in place.

As in other fields, additive manufacturing (3D printing) first entered CAD/CAM dentistry in the form of laboratory experiments, but its use has since expanded; and chairside use, although not yet widespread, is advancing.

Drawbacks

As machine-built substitutes, CAD/CAM treatments have some aesthetic drawbacks, whether they are created at the dental practice or outsourced to a dental laboratory fabricating service. They rely mostly on superficial staining to achieve a more natural appearance, unlike hand-layered porcelain restorations, which possess a deep-set coloration due to the multi-layering. Depending on the dentist or technician, CAD/CAM restorations can be layered to give a deeper more natural look. However, traditional restorations also vary in aesthetic value. 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, this porcelain is layered onto a metal substructure and often display color 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.^[9]

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 and some composite resin 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.

Finally, the accuracy of restorations using CAD/CAM technology is not as consistent as in other dental fabricating processes. Crowns and bridges require an extremely precise fit on tooth abutments or stumps. Scanning and mathematically calculating the stump surface topography has accuracy limitations, as does milling by computer-numeric-control (CNC) machines. 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. Current standards require an accuracy of fit less than 10 µm, meaning the deviation from "perfect fit" is less than 10/1000ths of a millimeter. Currently, CAD/CAM and hand-made dental processes can not consistently achieve this kind of accuracy. Only "electrophoretic deposition" of glass-infiltrated aluminum oxide processes can consistently produce the coveted 10 µm fit.

List of CAD/CAM dental software products

• ISUS, CAD/CAM metal frameworks in Chrome-cobalt and Titanium.
• CEREC, software for manufacturing crowns, veneers, onlays and inlays using different types of ceramic material.
• Delcam dental solutions, for the design and manufacture of copings and bridge frameworks, including full crowns, abutments, dental bars, inlays and onlays, and implant bridges.
• Renishaw plc CAD/CAM systems, from a company that started in industrial metrology with patented probes.
• WorkNC Dental from Sescoi, CAD/CAM for automatic machining of prosthetic appliances, implants, bridges or dental structures.^[10]

References