International Journal of Computerized Dentistry, 01/2007

When three-dimensional imaging is necessary in dentistry, oral surgery or maxillofacial surgery, conventional computed tomography or cone beam computed tomography is chosen regularly. However, there are two obvious drawbacks. Metallic restorations lead to pronounced streak artefacts in conventional computed tomography. Moreover, the resolution of both conventional computed tomography and cone beam computed tomography is limited to 0.3 mm. This resolution is not sufficient for the fabrication of dental restorations. In order to improve the quality of the two different computed tomography techniques and to eliminate streak artefacts, fusion with optical 3D images can be considered. The resolution of optical 3D images can reach the range of some µms depending on the calibration of the sensor. Metal artefacts do not occur. The fusion of computed tomography images without artefacts and optical 3D images leads to a mean deviation of corresponding points for the two imaging techniques of 0.1262 ± 0.0301 mm. When computed tomography images with metal artefacts are used, the deviation increases up to 0.2671 ± 0.0580 mm. The accuracy of image fusion is significantly reduced by metal artefacts (p 0.0005). When image fusion of computed tomography and optical 3D images is used in clinical studies, the mean deviation of corresponding points for the two imaging techniques for mandible and maxilla is 0.66 ± 0.49 mm and 0.56 ± 0.48 mm, respectively. The available data on image fusion show that the quality of computed tomography data without streak artefacts can be significantly improved by registration with optical 3D images. The precision of the fused images exceeds the resolution of the original computed tomography. When streak artefacts are present, image fusion makes it possible to increase the quality of the data to the level of the original resolution of computed tomography without artefacts. Keywords: computed tomography, cone beam computed tomography, optical 3D image, triangulation, registration, fusion of image data

Orthodontic biomechanics started in the early 1960s with the work of Burstone and later Nikolai. Experimental and theoretical studies using finite element methods (FEM) focused on the determination of the position of the center of resistance of single and multi-rooted teeth. Due to the complex structure of the system tooth/ periodontal ligament/ alveolar bone and because of the limited power of computers, the first numerical models were quite simple. Improved FE software, sophisticated programs for model generation and the explosion of computer power in the last decade resulted in more complex tooth-periodontium models and model assumptions. This paper describes the application of finite element methods in orthodontic biomechanics with the help of several typical examples. The examples cover aspects from basic orthodontic biomechanics to possible future applications in treatment planning using bone remodelling theories: determination of the mechanical properties of the periodontal ligament in a combined numerical and experimental study, calculation of the centers of resistance of different teeth, and simulation of orthodontic tooth movements. The examples show that nowadays finite element methods are a useful and easy-to-handle tool for the solution of a larger number of structure-mechanical and biomechanical problems. Nevertheless, in spite of the enormous technical progress in the last decade, many problems in orthodontic biomechanics remain to be solved. Keywords: orthodontics, biomechanics, finite element methods, center of resistance, bone remodelling theories, laser scanning, geometry reconstruction, surface matching

The purpose of this study was to investigate clinical applications of the three-dimensional reverse engineering technologies for the analysis of orthodontic models. The measuring accuracy and the process of the 3D model scanning technique were evaluated with respect to linear, surface and volumetric parameters. Orthodontically induced dentoalveolar changes, which have been traditionally evaluated by cephalometric analysis, were assessed by the registration function of Rapidform 2002®, a 3D-reverse modeling software in scanned maxillary casts. Threedimensional digital models are valuable alternatives to conventional casts for model analysis and also yield information which could previously be gathered only by cephalometric superimposition. Keywords: digital models, virtual model, 3D digital model analysis, cephalometry, 3D scanning, superimposition

SureSmile is an all-digital system which uses new 3-D imaging and computer techniques for diagnostics and treatment planning and uses robotics to customize fixed orthodontic appliances. Treatment can be simulated in advance and different treatment strategies can be visualized; this allows detailed treatment planning. The application of CAD/CAM aims at improving reproducibility, efficiency, and quality of orthodontic treatment. Keywords: SureSmile, CAD/CAM, intraoral scanning, orthodontic treatment, robotics

Certain diagnostic tools (eg, extra- and intraoral photographs, orthopantogram, lateral radiograph and model photos) are necessary at the start and during the course of an orthodontic treatment. These tools can now be shared with other medical professionals (eg, oral surgeon, dentist and orthodontist) involved in the treatment of a particular patient via the internet. This program creates better communication among the professionals concerned. The records of the patient are protected by a user name and a password. They make it possible for the patient to have access to his/her personal records at any time to see the progress of his/her treatment. This way, a patient can identify with the treatment, which should consequently improve the motivation and cooperation of the patient. Keywords: orthodontic diagnostics, internet, quality circle, motivation

Restoration of a mandibular first molar with an all-ceramic partial crown in a single treatment session is described in the present case. The Cerec 3D system (Sirona) was used with biogeneric technology. Keywords: Cerec, articulation, partial crown, biogeneric technology, single session treatment

VITA CAD-Temp is a composite block which enables highquality provisional restorations to be created using the Sirona milling units. The new Cerec MC XL and inLab MC XL units are the preferred choice on account of their significantly higher milling speeds. The technical requirements are described and an illustrated practical example presented. CAD-Temp constitutes a good example of rapid and efficient collaboration between dentists and dental technicians. This is illustrated on the basis of an example relating to the field of implant prosthetics. Keywords: Cerec, inLab, CAD/CAM material, provisional restoration, CAD-Temp

The new software for Cerec and inLab represents a new milestone in terms of occlusal surface design and ease of use. The graphical user interface has been streamlined and visually enhanced. All the functions intended for experienced users have been grouped together under the menu item "Master mode". The software now provides an occlusal-surface design function based on the biogeneric tooth model developed by Professors A. Mehl and V. Blanz. This function is superior to traditional methods.

Cerec 3 and inLab will soon be augmented by the new CEREC MC XL and inLab MC XL milling machines. Dentists and dental technicians who are on the threshold of introducing CAD (Computer Aided Dentistry) to their practice or laboratory can either opt for a low-cost solution or for a system which offers an extended range of indications as well as enhanced reliability and ease of use. The Cerec 3 and inLab milling machines are well-tried, accepted and proven. They offer an interesting balance between price and performance. The MC XL series is not only faster and more precise, but is also quieter and easier to use.

Unfortunately, there is no such thing as a universal material for every application - neither in engineering nor in dentistry. Instead, it is a matter of selecting the right material for each individual case and deploying this material in the appropriate way. For this reason, Sirona Dental Systems has decided to augment the existing product portfolio of its material suppliers (Vita Zahnfabrik and Ivoclar Vivadent) and has launched its own range of ceramics for chairside applications, as well as for the fabrication of crowns and bridges in dental laboratories. Keywords: materials, cerec, feldspar ceramic, sintered ceramic, zirconium oxide

Thanks to the compatibility of Cerec and inLab, the "impression-free" dental practice is just around the corner. Some final details remain to be clarified. An easy-touse web portal is under development.