Digital dentistry: Unraveling the mysteries of computer-aided design computer-aided manufacturing in prosthodontic rehabilitation

Computer-aided design and computer-aided manufacturing (CAD/CAM) refers to computer software that is used to both design and fabricate prosthesis. This technology has revolutionized dentistry and has influenced every field of restorative/prosthetic dentistry. Most of the prosthodontic rehabilitation work is shifting toward CAD-CAM due to faster fabrication, passivity, and precise fit. The faster fabrication is also a boon to emerging market of dental tourism. Thus, it becomes imperative for the dental clinicians to get acquainted with the various components of this technology.

A basic CAD-CAM system requires that the information is provided to the computer in the digital format. This is done by a scanner, which can be intraoral (Optical Impression ex: Cerec) or with white light/laser beam laboratory scanners that can scan the models/dies/interocclusal records. These optical scanners work on the triangulation procedure. Here, the source of light (ex. laser) and the receptor unit are in a definite angle in their relationship to one another. Through this angle, the computer can calculate a three-dimensional data set from the image on the receptor unit.[1] Another variant of the scanner is a mechanical scanner in which the master cast is read mechanically line-by-line by means of a ruby ball, and the three-dimensional structure is measured (ex: The Procera Scanner from Nobel Biocare, Göteborg).

The digitized data are uploaded on a special dental software on which the designing can be done for different fixed prosthesis including single crowns, bridges, inlays, onlays, monolithic crowns (anatomic crowns), and telescopic primary copings. The occlusion also digitizes and a virtual articulator is also available in this software in which the values of horizontal condylar guidance and incisal guidance can be fed in. Most commonly, the designed data are stored in the standard transformation language format.

The designed data prepared virtually with CAD software have to be converted into reality using the milling process by CAM unit. These units currently available in dentistry are distinguished primarily on the basis of a number of axis, i.e., 3 axis, 4 axis, or 5 axis. The more the number of milling axis the greater is the accuracy. Another variation in the milling procedure can be on the basis of wet milling and dry milling.

Dry processing is applied mainly with respect to zirconium oxide blanks with a low degree of presintering.[2] In this process, the milling diamond or carbide cutter is protected by a spray of cool liquid against overheating of the milled material. This kind of processing is necessary for all metals and glass ceramic material to avoid damage through heat development.[2]

Additional accessories of CAD-CAM assembly include a suction unit with both wet and dry milling unit. In addition, in dry milling unit, the milled zirconia has to be sintered in a compatible sintering furnace. At present, a number of materials can be milled such as Titanium, Titanium alloys, chrome-cobalt alloys, resins, glass ceramics, infiltration ceramics, and yttrium stabilized zirconium oxide.

The applications of this technology initially were limited to tooth-supported restorations. However, implant dentistry has accepted this technology in a very enthusiastic way owing to no casting shrinkage, greater passivity of prosthesis, and ability to mill titanium that results in very light weight prosthesis. The field of maxillofacial prosthodontics is also using various software to design and wax mill the prosthesis before silicon duplication. The applications of this technology are immense, and all the rehabilitative and restorative dentists should understand this technology in greater depth for better clinical results.