9.2. CAD-CAM and milling technology
Improvements in ceramic materials and processing techniques have facilitated the development and application of ceramics with superior properties. CAD/CAM allows the use of materials that cannot be used with conventional processing techniques. This kind of ceramic processing process provides a reduction in regular microstructural structure, higher density, lower porosity and residual stresses.
CAD/CAM systems have become synonymous with zirconia, However, there are systems that can process any type of ceramic such as glass ceramics, infiltration ceramics and solid sintered monophase ceramics such as zirconia.
By using CAD/CAM technologies, full ceramic inlays, onlays, crowns and bridges in a single Patient appointment in the clinic can be produced. Ceramic restorations produced with this method showed perfect harmony, resistance and long life. Two basic techniques are available for CAD/CAM restorations.
1. Bedside (clinical) single appointment technique.
2. Bebside (clinical) - laboratory technique
Bedside (clinical) single appointment technique: This technique means the production of ceramic restorations in the clinic. Preparation is applied with titanium dioxide contrast powder spray. An infrared camera record the powder and creates a 3D optical image on the computer. The colour of the ceramic is selected and recorded by the physician. Then the computer tells you which ceramic block shouldbe used. This block is milled in the clinic according to computer design. The restoration is taken from the milling machine. Then, it is tested in the mouth.
Proximal contact points and occlusal connection may need to be adjusted. If the restoration is enough and aesthetic, it can be cemented. Since there is no need for measure in this technique, the patient does not feel any discomfort and a potential source of error is cleared away.
Bedside (clinical) - laboratory technique: This technique requires two appointments. The preparation is scanned directly and then sent to the laboratory. or a plaster model is obtained and the plaster model is scanned in the laboratory and the data is transformed to the computer in the laboratory.
The design of the virtual restoration is similar to the traditional practice in the laboratory. Margin limits are fixed, and restoration design is executed. However, rather than forming restoration by using ceramic layers, a fully contoured 3D model of the restoration that need finer arrangements are acquired.
By entering a comprehensive natural dentition into the database, the design recommended by the computer is evaluated. In addition to occlusion, the compliance of the preparation with gingival limits and adjacent teeth can be confirmed.
Any regulations deemed necessary by the dentist are performed by the computer software design tools. By using the CAD software, an interproximal contact point can be created and the occlusions connections before milling process can be checked.
Using CAD/CAM restoration technique provides many steps to be simplified or removed. A scan device digitally recording the form and limits of the preparation instead of conventional measure is used. To prevent the occurrence of errors make sure that all the preparation is scanned. As in the conventional measure, soft tissue retraction and haemostasis are prior condition for obtaining a correct result.
The material used depends on the production of CAD/CAM restoration at bedside (clinical) or laboratory CAD/CAM restoration together with functional and aesthetic requirements. In the CAD/CAM restorations, an aesthetic and strong material that needs minimal aesthetic adjustment after milling is necessary to shorten the time spent by the patient as much as possible. Glass ceramics reinforced with leucite (IPS Empress CAD*) and glass ceramics with lithium disilicate (IPS e.max*) can be used for single restorations in bedside (clinical) and laboratory CAD/CAM systems. The material reinforced with leucite is designed to match the dentition in terms of strength and surface smoothness and to provide aesthetic results with light scattering similar to tooth enamel.
For bedside (clinical) applications where resistance is important, lithium disilicate CAD restorations offer a power of 400 MPa against to ceramic reinforced with leucite with 120 to 160 MPa and provide good aesthetic appearance. Lithium Disilicate is used as a resistant monolithic material.
*Ivoclar Vivadent, Lichtenstein
**Sirona Dental System Gmbh, Bensheim, Germany