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(c)2001-2018 R.G.Luthardt, S.Quaas, H.Rudolph, V. von Koenigsmarck, A.Weber
CAD/CAM systems
Computer-aided design and manufacturing processes (CAD/CAM - Computer Aided Design/Computer Aided Manufacturing) are used in dentistry for single-tooth restorations (inlays, onlays, veneers, crown frameworks and crowns). It is also possible to manufacture bridge frameworks of different sizes, implant superstructures, primary telescopes, bars and various connecting elements. Removable dentures cannot yet be fabricated using commercial CAD/CAM systems. The illustration compares the conventional approach with the possible ways of using CAD/CAM systems.
Conventional dental technology compared to CAD/CAM procedures
Conventional procedure CAD/CAM procedure
In principle, dental restorations must fulfil certain requirements. These do not differ depending on whether the restorations are fabricated conventionally or using CAD/CAM. These include
- Internal accuracy of fit
- The surface of the prepared die should match the inner surface of the crown. A gap of less than 100 µm is required under laboratory conditions, which is filled with a luting material.
- Occlusal/proximal accuracy of fit
- The restorations must have adequate contact with the neighbouring teeth (proximal contacts) and the teeth of the opposite row of teeth (antagonists) (occlusal contacts). The latter must take into account both the normal occlusion (static occlusion) and jaw movements (dynamic occlusion). The majority of CAD/CAM systems do not take the occlusion into account. Instead, the occlusal surfaces are designed manually by the dental technician.
- Aesthetics
- Clinical reliability
- Biocompatibility
- Standardised quality
Irrespective of the fact that conventionally and CAD/CAM-fabricated restorations must fulfil the same clinical requirements, individual manufacturing procedures and materials have specific requirements. These must be taken into account by the dentist during planning and preparation or by the dental technician during fabrication.
Indications
Not every system on the market can fabricate every type of restoration, which is why an overview of the indications is provided here. Apart from the technical possibilities of the various systems, the range of application also depends on the mechanical properties of the materials.
Overview of systems for the computer-aided fabrication of ceramic restorations and their indications.
The fabrication of dental restorations to restore or replace destroyed or missing teeth is a complex craft that requires a high degree of precision. If you consider the large number of individual steps in the conventional casting manufacturing process, it becomes clear how many possibilities there are for errors to occur. Although the individual steps in the process chain are very precisely coordinated today, casting errors such as unflowed margins or cavities as well as crowns and bridges that are too narrow, too wide or distorted in shape can still occur. The subsequent veneering with dental ceramic materials is another source of errors.
An attempt was therefore made to eliminate potential sources of error in the manual procedure by developing various technologies. The idea of developing computer-aided manufacturing techniques for the fabrication of crowns and bridges and their frameworks is not new. The first considerations in this regard were already made in the 1970s. In the meantime, the term CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) has become established. At the beginning of this development, the term CIM (Computer Integrated Manufacturing) was also commonly used.
Dr Francois Duret, who is now known as the "father of dental CAD/CAM technology", began his initial theoretical and experimental research work in 1971. Other researchers such as Heitlinger and Rodder had also been working on CAD/CAM since 1979 and Mörmann and Brandestini since 1980 (CEREC®). The first prototype of a dental CAD/CAM system was presented at the "Garanciere conference" in France in 1983. In the 1980s, Fujita et al came to the conclusion that the experience gained in the industry could not be transferred to the production of crowns and bridges without restrictions.
The oldest procedures apart from the CEREC system, Sopha (Duret) and DentiCAD (Rekow), did not become established. Other systems that grew beyond the experimental stage were the CELAY copy grinding process, the Procera process and the DCS system. To summarise, it can be said that the development stages of dental CAD/CAM procedures were always closely linked to material development.
Historical overview
1971 First experimental research work by Duret
1979 Heitlinger and Rodder experiment
1980Mörmann and Brandestini begin developing CEREC
1984 Fujita attempts to transfer industrial manufacturing processes to the dental sector
1985 CEREC (Siemens Dental, now Sirona Dental Systems, Bensheim, D)
1989 DCS Precident (CDS Dental AG, Allschwil, CH), Procera (Nobel Biocare AB, Gothenburg, SE)
1991 Celay (Mikrona Technologie AG, Spreitenbach, CH)
1993 Cicero (Cicero Dental Systems B.V., Hoorn, NL)
1995 Cercon smart ceramics (DCS, now DeguDent GmbH, Hanau, D)
1998 cad.esthetics (DECIM, now CAD.ESTHETICS AB, Skelleftea, S
Pro 50 (Cynovad, Montreal, CAN)
1999 Digident (Girrbach Dental GmbH, Pforzheim, D)
GN-1 (GC Corporation, Tokyo, J)
2001Etkon (Etkon AG, Gräfelfing, D)
Everest (KaVo, Leutkirch, D)
Lava (3M ESPE Dental AG, Seefeld, D)
EDC (Wieland Dental, Pforzheim, D)
Wol-Ceram (Wol-Dent GmbH, Ludwigshafen, D)
2002 Bego Medifacturing (Bego Medical, Bremen, D)
2003 ce.novation (Inocermic, Hermsdorf/Thuringia, D)
Perfactory (envisiontec, Gladbeck, D)
Xawex Dental System (ZFN-Verfahren; I-Mes, Eiterfeld, D)
HintELs DentaCAD Systeme (Hint-ELs® GmbH, Griesheim, D)
Triclone 90 (Renishaw, Gloucestershire, UK)
20053Shape Dental Designer (3Shape A/S, Copenhagen, DK)
ADG - SW Automatic Denture Generation - System Weigl (ADS GmbH, Frankfurt, D)
CADCOM4 (Schütz Dental GmbH, Rosbach, D)
diadem (diadem sas, Louey, F)
alkom digital (Luxembourg, L)
Diener Scan Tec (Diener Scan Tec Ltd., Embrach, CH)
Speedscan (smartoptics Sensortechnik GmbH, Bochum, D)
Zeno Tec System (Wieland Dental GmbH, Pforzheim, D)
Further development led to an exponential increase in the number of CAD/CAM systems and providers and, in turn, to numerous mergers.
There are now numerous solutions and collaborations for many interfaces between the components of the digitising device, design software (CAD), transfer to machine control (CAM) and production through to material support, especially among the market-leading providers.
A current market overview (as of 2018) can be found here:
digital-dental-magazin.de/category/marktubersichten/
www.dentalkompakt-online.de/produkte-fuer-das-dentallabor/cadcam-technik.html
The preparation of the tooth or teeth is followed by the first CAD/CAM step: digitisation. There are a number of different procedures for data acquisition. Starting with the data of a single tooth, it depends on the planned restoration whether and if so, which additional digital information (e.g. neighbouring teeth, opposing jaw) must be recorded.
With indirect, extraoral digitisation, a model (usually made of plaster) is first produced using an impression.
The captured digital raw data must be processed (e.g. filtering, spatial allocation) before the computer-aided design of the restoration (CAD). Such steps are often carried out automatically and unnoticed by the user in the respective system.
The computer design of the restoration ranges from simple inlays or crown frameworks with a standard layer thickness to 14-unit bridges (indications). Which design can be sensibly realised in a restoration depends - apart from clinical requirements - on the respective system, the implied shaping procedure and the selected material.
Depending on the manufacturing process, the CAD restoration must be converted into machine-understandable language (into so-called milling paths or CNC paths) for duplicate dies, moulds or the restorations themselves. This is where the CAM part begins - computer-aided manufacturing.
The necessary post-processing depends on the material and CAD/CAM system. Larger restorations and areas where the highest level of aesthetics is required usually require a ceramic veneer.
Finally, the restoration is tried in on the patient, the internal and occlusal accuracy of fit is checked and the restoration is seated using a suitable luting material (adhesive, conventional cementation).
In order to manufacture dental prosthetic restorations using CAD/CAM technologies, it is necessary to digitise the clinical situation in the mouth or as a model. The geometric structure of existing physical objects is recorded and transferred to a computerised data model.
There is a fundamental correlation between the restoration to be fabricated and the method and scope of digitisation.
Crown frameworks:
- Data of the prepared die,
- if applicable, data of the antagonists and the adjacent teeth
Bridge frameworks:
- Data of the prepared dies,
- the gingiva in the area of the pontics,
- data of the antagonists and neighbouring teeth, if applicable.
Restorations with occlusal surfaces:
- Data of the prepared die/prepared stumps,
- the gingiva in the area of the pontics, if applicable, and
- the data of the antagonists and neighbouring teeth is mandatory
Objective of digitisation:
- Complete shape acquisition of the surface including the preparation margin,
- consistent accuracy for x, y, z over the entire surface and
- sufficient measuring point density.
In general, a distinction is made between tactile (mechanical scanning of the surface) and non-contact optical digitisation methods (optical measurement):
intraoral:optical -> prepared dies, quadrants, assignment via buccal scan
Whole jaw (mainly orthodontic application)
extraoral:mechanical -> prepared dies
optical -> prepared dies, opposing jaw, registration, complete model
Mechanical digitisation
Tactile methods use a probe to capture the shape of the object line by line or outline by outline. The shape and size of the stylus are decisive for the precise detection of the object and its fine structures. A probe tip that is too large will not resolve fine structures, while a small probe and excessive contact pressure can damage the surface of the object. Automatic systems should be favoured over manually guided systems.
Examples:
www.renishaw.de/de/renishaw-dental-studio--24222
www.zeiss.de/messtechnik/produkte/systeme/optische-messtechnik/o-inspect.html
Mechanical scanning of the surface with Triclone 90 dental scanning system from Renishaw
Optical digitisation
Optical data acquisition can be performed intraorally from the prepared tooth or extraorally from the model. Compared to tactile systems, they generally have shorter digitisation times but lower measurement accuracy. Optical digitisation methods are based on projection and detection units arranged at a known angle to each other. It is used
- point-by-point (scanner)
- linear► with white light or laser
- imaging-areal
projected onto the object to be digitised. Light-sensitive sensors (CCD, CMOS) are used as detectors. The point coordinates are determined using the triangulation principle from the 2D image of the object in the detector and the known geometry of the measuring arrangement.
Extraoral optical digitisation
Line-based systems
- One-dimensional scanning
- Rotation of the measurement object required
Imaging surface systems
- Projection of stripe patterns (e.g. grey code)
Intraoral optical digitisation
Intraoral optical digitisation procedures are used in an attempt to avoid impression taking and model fabrication. The limited space available and 100% humidity limit the possibilities of the digitising device. Systems with only one viewing direction have to use small triangulation angles and accept large height errors. Very short digitisation times are required due to patient and practitioner movements.
Based on existing experience with extraoral digitisation technology for single dies and jaw models, several measuring positions are required to capture the entire shape. These are currently combined using known rotation angles of the individual positions or freely using matching methods. The result of the digitisation is a point cloud, which is further processed into a CAD model in a subsequent step (data processing).
The raw data obtained using various digitisation methods requires appropriate processing in order to achieve the quality required for computer-aided design (CAD).
In the case of non-contact optical processes, stray points (noise) caused by measurements must be removed. This process is called filtering. Such filters are usually integrated into the software for operating the respective measuring system. The combination of different partial images from different directions is also usually automated.
Raw data sets based on mechanical digitisation do not contain this type of noise.
Common to all raw data sets - regardless of the measuring system used - is superfluous data (e.g. digitally recorded areas below the preparation margin) that must be removed either automatically or interactively (trimming the data sets). This step is usually linked to the preparation margin determination, for which a correctable suggestion is usually made by the respective software (see also: CAD).
If the size of a measuring field or volume is not sufficient to digitise the entire relevant area, several overlapping images can also be lined up; this is referred to as "matching". A variant of this is the arrangement of high-resolution partial images (e.g. a single tooth) in a coarser overall image (e.g. an entire jaw). It should be noted that each match is subject to a more or less large error (ranging from a few micrometres to several tenths of a millimetre). The further the assigned area is from the centre of the assignment and the more partial images are combined, the greater the error.
Individual "data holes", i.e. missing digitised data, can be closed using suitable algorithms. If the "hole" is not too large, the probable course is extrapolated from the data in the immediate vicinity. Similarly, undercutting areas can be virtually blocked out.
Triangulation with holes Triangulation, holes closed
Conversely, overrepresented areas of a data set can be thinned out: such a measure serves to accelerate subsequent calculation steps.
Despite all the anatomical and functional similarities, natural teeth have a wide variety of individual shapes, which - apart from their respective correlates in the opposite half of the jaw - are unique. Their shape can only be described by computer technology using free-form surfaces with many, often pronounced changes in curvature in a small space. After data preparation, the workpiece to be produced must be designed with computer support. In principle, the design can be divided into designing the inner surface, determining the preparation margin, designing the outer contour and, if necessary, the occlusion. Many systems can determine the preparation margin automatically. The die surface is generally used as the inner contour, the offset for the cement gap is programmed or can be entered individually. Depending on the system, simple offset copings (the die surface is scaled according to the required coping thickness), anatomical copings (the coping is designed according to the opposing jaw and the neighbouring teeth so that a uniform thickness of the veneering material can be achieved) or crowns/bridges with an occlusal surface can be designed. In systems where the design of full crowns is possible, the occlusal surface is mostly designed by selecting a system-specific occlusal surface or a library occlusal surface created by the user, which is then automatically adjusted (e.g. moving the cusps until contact with the opposing tooth is achieved). Individual manipulation (e.g. virtual wax-up instrument) is possible. Another option is to scan a restoration fabricated conventionally in wax.
When creating crown and bridge frameworks, the occlusal and proximal relationship does not need to be taken into account, as the reconstruction of the final external shape is not designed on the computer, but conventionally using the dental technician's ceramic veneer. In the case of bridge constructions, the basic shape of one or more pontics and the position, shape and size of the connector cross-sections must be determined. If a computer-aided design of the restoration is used, current CAD/CAM systems are usually based on interactive software.
Occlusion
In the patient's final bite, i.e. when the teeth are fully clenched, the upper and lower teeth meet at specific, individually different contact points (static occlusion). Chewing movements, which are determined on the one hand by the masticatory muscles and the temporomandibular joint, are also guided by the shape of the teeth on the other. The teeth slide along defined paths from the final bite to the side and back (laterotrusion and mediotrusion paths, dynamic occlusion). These points and paths differ from patient to patient and therefore require a customised design of the restoration.
Both static and dynamic occlusion should be taken into account when designing occlusal surfaces. To check the static occlusion, an impression is taken of the opposing jaw and the plaster model is digitised. With the help of a registration in the final bite, the upper and lower jaws can be assigned to each other. If there are sufficient impressions, digitisation of the registration may also be sufficient. Few systems have implemented a virtual articulator to check the dynamic occlusion. An alternative approach is to register using the FGP technique (the occlusal surface of the opposing bite is placed in the patient's mouth with functional back and forth movements of the
The lower jaw was moulded, i.e. every possible position of the lower jaw in relation to the upper jaw was coded).
Construction of occlusal surfaces
Three different strategies were pursued for our own investigations:
In the first step, the occlusal surface was positioned, rotated and, if necessary, scaled in size. The proximal contacts and the marginal ridges of the neighbouring dentition were then adjusted. The control points in the polygon mesh were used to modify the occlusal surface in order to emphasise or, if necessary, reduce contact points with the opposing dentition. The static occlusion is then checked. Contact is made at the points of surface penetration of the upper (green/blue) and lower jaw (yellow). The dynamic occlusion is checked using the FGP: With the exception of the contact points, further interference between the restoration and FGP is undesirable
It is necessary to modify digitised data for the production of dental restorations. This involves creating surface models from the digitised data set (point cloud) and converting the data into a suitable format. The common formats of CAD/CAM technologies are available for this purpose. The most commonly used data format for point clouds is the ASCII format (ASCII - American Standard Code for Information Interchange) and the STL format (STL - Standard Transformation Language) for CAD models (surface data). Other data formats such as the Autocad format DXF (Drawing Interchange Format) or IGES (Initial Graphics Exchange Specification), on the other hand, are more error-prone for detailed information during data exchange due to the variability of interpretation options. With the increasing centralisation of production, technologies for data transfer are required, whereby existing Internet technologies can be used in the dental industry. For this reason, standardisation of export formats in the dental industry is desirable. Looking at the CAD/CAM process chain for the production of dental/technical restorations, there are several options for implementing interfaces between the process steps.
1. interface between the digitiser after the application of process-dependent procedures and algorithms (primary processing of raw data: Filtering, quality weighting of individual points, selection and determination of transformation parameters for the matching of several data sets) and the application of largely process-independent procedures (execution of matching, generation of surfaces). In addition to customer and order information, data from the point clouds and transformation parameters could be transmitted. The ASCII format is often used to transfer data via this interface.
2. interface between the application of process-independent procedures (see above) and partially production-specific procedures (determination of preparation margin and a prosthetic axis, construction of CAD models, generation of bridge pontics and connectors, occlusal surface design, etc.). Surfaces or bodies can be transferred as CAD models. STL and IGES are the favoured data formats for this interface.
3. interface between the partially fabrication-specific procedures (see above) and the procedures for fabrication-specific adaptations and corrections (milling path generation, milling cutter radius corrections, etc.). All common CAD/CAM data formats that can represent surfaces are also used at this interface.
A basic distinction can be made between additive (constructive) and subtractive (ablative) processes. Typical examples of additive processes are stereolithography or the direct shaping of ceramics by master moulding.
Primary moulding:
- the workpiece is created from a ceramic ("shapeless") starting material, e.g. powder or slip, possibly using a mould. Examples: Electrophoresis, dry pressing, injection moulding (additive process).
Moulding:
- The workpiece is created from a blank, e.g. bar material (moulded), which is formed without removing material.
Cutting:
- the workpiece is created from a blank, e.g. bar or block material, by removing material (subtractive process).
Among the manufacturing processes integrated into dental CAD/CAM systems, so-called rapid prototyping processes (stereolithography, selective laser sintering, fused deposition modelling) have become increasingly important in recent years. These processes are used in industry, for example, to produce sample parts or small series during the development process.
Subtractive processes (separating processes)
Hard machining:
- The densely sintered or additionally hipped oxide ceramic blank requires long machining times and high tool wear.
Green machining:
- The blanks used were only moulded (e.g. pressing) and dried. The rather soft material offers little resistance to machining and is not very dimensionally stable. During subsequent post-processing (sintering, glass infiltration), it is subject to complete sintering shrinkage.
White processing:
- The blank has been partially sintered. The higher the degree of sintering, the greater the resistance to processing, but the lower the remaining sintering shrinkage. This results in an optimum degree of sintering where the reduced machining effort outweighs the additional effort required for two-stage sintering.
The blanks are processed in two steps:
Roughing:
- Removal of large quantities of material as quickly as possible (contour-limited).
Finishing:
- During subsequent finishing, a high dimensional, shape and surface quality should be achieved (surface-guided).
Subsequent grinding is carried out with rotating multi-edged tools without geometrically defined cutting edges. The following requirements must be placed on the CNC machine for hard machining:
- Use of a ceramic-optimised CNC machine (high-frequency spindle, high machine rigidity)
- Use of optimum software to create the milling paths for the geometries to be produced
- Cooling to prevent overheatingCooling to avoid overheating of the poorly thermally conductive ceramics
- Use of small grinding pins to avoid cavities in the incisal/occlusal area during internal machining
- Use of machining parameters adapted to the meshing conditions.
The majority of CAD/CAM systems currently available on the market work subtractively, so this procedure is described here.
Additive processes
Additive processes include, for example, the electrophoretic deposition of ceramic slurry, the pressing of aluminium oxide or zirconia ceramics onto enlarged duplicate dies with subsequent mechanical external contouring and sintering or master moulding. Technologies taken from the field of rapid prototyping include stereolithography, 3D printing, selective laser sintering and injection moulding.
Electrophoresis:
- Deposition of ceramic slurry (ions or particles with a surface charge) in an electric field at the oppositely charged electrode. A duplicate die that equalises the sintering shrinkage is used as a cathode (conductive silver coating). Subsequent sintering and glass infiltration are necessary.
Pressing and milling:
- Ceramic slip or powder is applied to a slightly enlarged duplicate die that compensates for the expected sintering shrinkage. The outer contour is then reworked and finally sintered.
Stereolithography:
- Liquid monomers or resins are solidified locally by polymerisation using exposure to a laser. Layers of different thicknesses are produced, which are bonded together. In photopolymerisation with light in the visible range, an acrylate is hardened layer by layer by means of mask projection (Digital Light Processing technology - DLP). The accuracy depends on the layer thickness and also influences the speed.
3D printing:
- The virtual model is broken down into individual, superimposed sections, which are then produced layer by layer on top of each other (z-direction). Two heated extrusion nozzles distribute build or support material in the x-y plane in each layer. The model is very accurate in the construction plane (x-y direction), while the accuracy in the z direction depends on the selected layer thickness. The production speed also depends on the layer thickness. The restorations are then fabricated using the conventional casting technique.
Selective laser sintering (SLS):
- The frameworks are built up layer by layer in SLS. A roller distributes the powdery material (preheated to just below the melting temperature) in thin layers on the working plane. This is compacted by a laser beam, which is controlled along the component cross-section according to the specifications of the CAD model. At present, precious and non-precious metal alloys can be sintered; laser sintering of ceramics is not yet ready for the market. LaserCUSING® uses only original materials without additives, which are melted by laser to create a strong material bond, high density and a high surface quality (e.g. processing of titanium).
Injection moulding:
- A powder-binder mixture is hydraulically pressed into injection moulding tools at approx. 100° C. After cooling, the green compact can be removed from the mould. This must be debinded (brown moulding) and then sintered (finished part).
The implementation requires process-specific procedures.
From a medical, biological and aesthetic point of view, ceramic materials have great future potential as biocompatible and cost-effective materials in dental prosthetics. The CAD/CAM systems currently being developed or available on the market are primarily aimed at processing ceramic materials (glass ceramics, infiltration ceramics, high-performance ceramics). In the case of metals, the machining of titanium is of particular interest. Titanium is characterised by good biocompatibility, high corrosion resistance and low density. Another advantage is the low material costs compared to precious metal alloys. In contrast to the casting technique, CAD/CAM procedures offer the possibility of producing cavity-free restorations by using industrially prefabricated blanks.
Industrially prefabricated raw materials, which are produced under constant, optimal and reproducible conditions, fulfil the highest demands in terms of purity, homogeneity and quality of the material. Quality can be further improved by using fine-grained powders, clean room technology, high primary compaction before sintering (green body), controlled grain size processing and hot isostatic post-compaction ("hipping") to further reduce residual porosity. The full potential of a material in terms of its material properties can therefore be utilised.
In addition to the predominantly used glass ceramics (e.g. IPS Empress) and infiltration ceramics based on aluminium oxide, the ceramic materials used in dentistry increasingly include high-performance ceramics (Al2O3, ZrO2), which are already used in other areas of medical technology. These are characterised above all by their outstanding strength properties, which clearly sets them apart from all other materials.
Glass-ceramics have aesthetically pleasing translucency and colour matching as well as easy machinability, but are limited in terms of their mechanical properties. Infiltration ceramics can be processed favourably, but must be glass-infiltrated after processing to achieve sufficient fracture strength. Densely sintered aluminium oxide or zirconium oxide ceramics require long processing times and result in high tool wear. To circumvent this problem, several newer systems also use prefabricated, but partially sintered, e.g. chalk-hard material, which reduces machining time and tool wear. Machining processes with geometrically defined cutting edges (milling) can be used here. With this method, the expected shrinkage of the material during the final sintering process must be taken into account during the design of the dental prosthesis. Comparative studies that test these materials with densely sintered materials with regard to homogeneity and fracture strength as well as the effects of sintering shrinkage on the accuracy of fit are not yet available.
In the future, there is a need for research into the special problem of manufacturing real dental geometries (crown and bridge frameworks) from metallic and ceramic materials with particular attention to the accuracy of fit and reproducibility of the results.
Recently, manufacturing processes from rapid prototyping have also become increasingly important for dental CAD/CAM technology (e.g. stereolithography, selective laser sintering, fused deposition modelling).
From the clinic's point of view, the range of applications for CAD/CAM-fabricated restorations is determined by the mechanical properties of the materials and the technical options of the systems. In principle, the range of indications extends from inlays to multi-unit bridges for the anterior and posterior region. Customised implant abutments are offered by several systems. There is a general trend towards the predominant use of ceramic materials.
Due to the brittleness of ceramic materials, different requirements are placed on the preparation for ceramic restorations than for restorations made of metal or metal-ceramic. Sharp edges and thin tapered margins should be avoided in any case, round shapes should be favoured. Of course, special attention must be paid to the preparation margin; parallel or undercutting parts must be avoided.
Special attention should be paid to the following four factors when preparing ceramic restorations:
- Type of cementation (conventional, adhesive)
- Digitisation method (mechanical/optical) or digitisation parameters (size of the scanning sphere, triangulation angle)
- Fabrication by the CAD/CAM system (subtractive, additive)
As shown in the table below, the different systems follow different preparation rules. Systems that work additively (e.g. with duplicate dies) (Procera, WOL-Ceram, ce.novation) place less stringent demands on the preparation than those that fabricate the restoration from prefabricated (ceramic) blocks. Procedures that work subtractively, i.e. mill or grind the restorations from a block, are characterised by considerably larger gaps between the die and the inside of the crown. The required removal of hard substance in the area of the preparation margin of 1 mm should not be exceeded if possible (preservation of substance, preservation of vitality). Marginal gaps between the abutment and crown margin as well as unphysiological contours of the restoration favour secondary caries and periodontal diseases (increased plaque accumulation in micro-ecological niches).
Computer-aided methods of design, planning and production have been established in mechanical engineering production technology for many years. Due to the need for one-off production in the manufacture of dental restorations, their use in dentistry is still in its infancy. Restorations produced by hand using conventional methods still dominate over those produced using CAD/CAM. At the IDS 2009 (International Dental Show in Cologne), innovative solutions were once again presented, as they had been two years previously, which suggest that CAD/CAM-manufactured restorations will become increasingly important.
For our working group, research work on CAD/CAM procedures formed the starting point for a wide range of applications of CAD/CAM technologies in dental research.
Optical and mechanical digitisation processes, together with corresponding software programs, allow dental materials to be analysed with regard to dimensional accuracy (biomaterial research). In clinical studies, it is even possible to analyse the accuracy of materials and their handling properties. However, clinical research and experimental biomaterial research in dentistry are usually conducted independently of each other and show little interaction. From a clinical point of view, close networking and interaction of these research areas towards a continuous development chain would be desirable. The focus of the working group is to initiate and further develop this interaction of research areas (Simulation and Testing in Oral Medicine - SimTOM).
Research projects of the working group in recent years
- Modular system solution for the production of all-ceramic dental restorations - ce.mosyst (Pro Inno II). Sub-project: Biological design and analysis of bridge frameworks and implant superstructures on natural teeth or implants - ce.mosyst-ZAHN. Project sponsor: AIF (Arbeitsgemeinschaft industrieller Forschungsvereinigungen) "Otto von Guericke" e.V.(2005-2007, funding code: KF 0107601 VTS)
- Collaborative project: High-performance manufacturing process for the master moulding of high-strength materials using the example of fixed individual dentures (ZAHN).Project Management Agency: Karlsruhe Research Centre, BMBF Project Management Agency for Production and Manufacturing Technologies (2001-2004, funding code: 02 PD 2171)
- Development of a reverse engineering CAM process chain for the design and manufacture of dental prosthetic restorations. Project sponsor: AIF (Arbeitsgemeinschaft industrieller Forschungsvereinigungen) "Otto von Guericke" e.V. (2001-2003, grant award AZ: VL A 2 - 40 42 40/7)
- Simulation and evaluation of intraoral digitisation and functional occlusal surface design - further development of a reverse engineering CAM process chain for fixed dental restorations. Project sponsor: AIF (Arbeitsgemeinschaft industrieller Forschungsvereinigungen) "Otto von Guericke" e.V. (2003-2005, grant notification AZ: VL A 2 - 40 42 40/7) The project was funded from the budget of the Federal Ministry of Economics and Labour via the German Federation of Industrial Research Associations (AiF) (funding reference: 13893BR). Final Report Part I and Part II
- Statistical analysis of a survey on CAD/CAM technology among dentists and dental technicians in Germany. funded by: Deutsche Gesellschaft für Zahn-, Mund- und Kieferheilkunde, DGZMK, (2006)
- Testing the accuracy of an impression material with different impression procedures by comparing the digitised data of duplicate dies of a real model with its CAD master model.
- Testing the accuracy of three corrective impression materials by comparing the digitised data of duplicate dies of a real model.
- Testing the time regime of fast-set polyether impression materials in vivo based on the change in three-dimensional dimensional accuracy.
- Clinical testing of the flow-out of light/ultralight-body silicones during corrective moulding.
- Testing the three-dimensional dimensional accuracy and optical digitisation capability of different plasters by comparing the digitisation data of duplicate dies of a real model with its CAD model.
- Comparative investigation of intraoral and extraoral digitisation as well as after model fabrication with CEREC 3D.
- Comparative investigation of the three-dimensional, polymerisation-related size changes of denture teeth.
- Testing the accuracy of different impression materials and procedures by comparing the digitisation data of duplicate dies of a real model with its CAD model.
Materials
- Rosentritt M, Behr M, Thaller C, Rudolph H, Feilzer A. Fracture performance of computer-aided manufactured zirconia and alloy crowns. Quintessence Int. 2009; 40(8):655-62
- Luthardt RG, Rudolph H, Johannes M, Sandkuhl O, Arnold J, Hieke T, et al. Fabrication of crown and bridge frameworks from Y-TZP zirconia by direct shaping. Dtsch Zahnärztl Z 2006; 61: 84-87.
- Luthardt RG, Rudolph H, Quaas S, Herold V, Sandkuhl O, Johannes M. Material properties of high-performance ceramics processed by direct ceramic shaping (master moulding).Dtsch Zahnärztl Z 2006; 61:489-493.
- Luthardt RG, Rudolph H, Quaas S, Herold V, Haronska P, Johannes M, et al. Individualised fixed dentures made of high-performance ceramics - development of a process for precision master moulding. Hermsdorf: Gesellschaft für innovative Keramik mbH; 2005. Luthardt RG. Crown and bridge frameworks made of zirconia ceramics by direct moulding. DZW 2005 15.06.2005.
- Rudolph H, Johannes M, Luthardt RG. Low-pressure injection moulding of high-performance ceramics. Dtsch Zahnärztl Z 2005; 60(3): 172-175.
- Luthardt R, Rudolph H, Quaas S, Holzhüter M, Walter M. Influencing the mechanical properties of zirconia ceramics in simulated crown fabrication. Biomaterials 2004; 5 (S1): 80-81.
- Brick EM, Rudolph H, Johannes M, Sandkuhl O, Luthardt RG. Use of nanoceramics for crown frameworks. ZWR 2003; 112: 93-96.
- Johannes M, Rudolph H, Sandkuhl O, Herold V, Luthardt RG. High-performance ceramics in restorative dentistry. In: Schnapp JD, Glatzel U, Jandt KD, Knake H, (Eds.). Thüringer Werkstofftag 2002; October 2002; Jena: Verlag Dr Köster; 2002: 46-53.
- Luthardt RG: Status and perspectives of the processing of zirconium oxide ceramics. In: Rech A, (ed.). dental-labor Fachbuchreihe: Vollkeramik. Munich: Verlag Neuer Merkur; 2002: 191-199.
- Luthardt RG, Holzhüter M. Investigations on the 3D accuracy of polyether single-phase impressions. Zahnärztl Welt Reform 2002; 111: 224-230.
- Bornemann G, Lemelson S, Claas H, Luthardt RG. Analysis of the internal 3D accuracy of fit of all-ceramic crowns (Cerec-3®). Dtsch Zahnärztl Z 2001; 56: 619-622.
- Luthardt R, Rudolph H, Sandkuhl O, Walter M: The right material. ZWP Spezial 2001; Sonderdruck(4):12-16.
- Luthardt RG, Rudolph H, Sandkuhl O, Walter M. Materials for CAD/CAM technology. Zahnarzt-Wirtschaft-Praxis 2001; 1: 12-16.
- Luthardt R, Holzhüter M, Sandkuhl O, Herold V, Walter M: Strength and marginal zone damage of Zirconia-TZP ceramics after simulated internal machining of crowns. Dtsch Zahnärztl Z 2000; 55: 785-789.
- Tolykpayewa A, Luthardt RG, Richter G, Walter M, Kästner K. On the quality of dental castings made of titanium. dental-labor 2000; 48: 717-722.
- Luthardt RG, Sandkuhl O, Reitz B: Zirconia-TZP and Alumina - Advanced Technologies for the Manufacturing of Single Crowns. Eur J Prosthodont Rest Dent 1999; 7: 113-119.
- Göbel R, Luthardt RG, Welker D. Experimental investigations on the cementation of zirconia and titanium restorations. Dtsch Zahnärztl Z 1998; 53: 295-298.
- Luthardt RG, Herold V, Sandkuhl O, Reitz B, Knaak J-P, Lenz, E. Kronen aus Hochleistungskeramik Zirkondioxid-Keramik, ein neuer Werkstoff in der Kronenprothetik, Dtsch Zahnärztl Z 1998; 53: 280-285.
- Luthardt RG, Holzhüter M, Reitz B, Knaak J-P, Sandkuhl O, Herold V. Comparison of different procedures for the fabrication of crown frameworks made of high-performance ceramics. Swiss Dent 1998; 19: 5-12.
- Luthardt RG, Musil R. CAD/CAM fabricated zirconia ceramic frameworks. Dtsch Zahnärztl Z 1997; 52(5): 380-384.
- Luthardt RG, Rieger W, Musil R. Grinding of Zirconia-TZP in Dentistry - CAD/CAM-Technology for the Manufacturing of fixed Dentures. In: Seder L, Rey C, (Eds.). 10th International Symposium on Ceramics in Medicine Bioceramics 10. Paris, France: Elsevier Science Ltd; 1997: 437-440.
- Luthardt RG. The Precident DCS system - status and perspectives of processing zirconia ceramics. dental-labor 1997; XLV: 2187-2195.
Digitisation and CAD
- Rudolph H, Luthardt RG, Walter MH. Computer-aided analysis of the influence of digitising and surfacing on the accuracy in dental CAD/CAM-technology. Comput Biol Med 2007; 37(5):579-87.
- Quaas S, Rudolph H, Luthardt RG. Direct mechanical data acquisition of dental impressions for the manufacturing of CAD/CAM restorations. J Dent 2007; 35(12):903-8.
- Rudolph H, Luthardt RG, Walter M. Computer-aided analysis of the influence of digitising and surfacing on the accuracy in dental CAD/CAM-technology. Comput Biol Med 2006 (accepted).
- Quaas S, Weber A, Rudolph H, Luthardt RG. Influence of digitising and surfacing on the precision of machine-made duplicate teeth. (Influence of digitizing and surfacing on the precision of machine-made duplicate teeth.) Int J Comp Dent 2006; 9: 45-48.
- Luthardt RG, Heyder S, Weber A, Quaas S, Rudolph H. Interactive Design of occlusal Surfaces 2D vs. 3D Display (Interactive modelling of occlusal surfaces: Conventional monitor versus 3D display). Int J Comput Dent 2006; 9: 37-40.
- Luthardt RG, Loos R, Quaas S. Accuracy of Intraoral Data Acquisition in Comparison to the Conventional Impression. Int J Comput Dent 2005; 8: 283-294.
- Quaas S, Loos R, Sporbeck H, Luthardt RG. Analysis of the influence of powder application on the accuracy of optical digitisation. Dtsch Zahnärztl Z 2005; 60: 96-99.
- Weber A, Heyder S, Quaas S, Rudolph H, Luthardt RG. Computer-aided design (CAD) of prosthetic restorations with the aid of a 3D display - comparison of conventional versus 3D display. In: Paul L, Stanke G, editors. Proceedings of the 8th application-related workshop on the acquisition, processing, modelling and evaluation of 3D data of 3D-NordOst; 2005. Berlin: Gesellschaft zur Förderung angewandter Informatik e. V. (GFaI); 2005. p. 67-74.
- Luthardt RG, Loos R, Quaas S. Accuracy of intraoral data acquisition compared to conventional impression taking. Int J Comput Dent 2005; 8: 283-294.
- Luthardt RG, Quaas S. Analysis of the influence of the digitisation procedure on clinical measurements of impression accuracy. Dtsch Zahnärztl Z 2004; 59: 531-534.
- Brick E-M, Rudolph H, Arnold J, Luthardt RG. Analysis of three-dimensional sinter shrinkage of copings made from alumina in an innovative direct shaping process. Comput Med Imag Graph 2004; 28: 159-165.
- Luthardt RG, Bornemann G, Lemelson S, Claas H, Walter MH, Hüls A. An Innovative Method for the Evaluation of the Three-Dimensional Internal Fit of CAD/CAM-Crowns Fabricated after Direct Optical vs. Indirect Laser Scan Digitising. Int J Prosthodont 2004; 17: 680-685.
- Quaas S, Loos R, Sporbeck H, Luthardt RG. What influence does the matting of freeform surfaces by powder application have on the accuracy of optical digitisation? In: Proceedings of the 7th Application-Related Workshop on the Acquisition, Processing, Modelling and Evaluation of 3D Data; Gesellschaft zur Förderung angewandter Informatik e.V. (GFaI); Eigenverlag, Berlin (2004), 13-17.
- Luthardt RG, Kühmstedt P, Walter MH. A new method for the computer aided evaluation of three-dimensional changes of dental materials. Dent Mater 2003; 19: 19-24.
- Quaas S, Sporbeck H, Luthardt RG. Analysis of the digitisation accuracy of complete models with multiple measurements. Dtsch Zahnärztl Z 2003; 58: 543-5.
- Luthardt RG, Kühmstedt P, Schimpf K. Methodical accuracy of the clinical analysis of shape deviations when using digitisation procedures. Dtsch Zahnärztl Z. 2003 Sep; 58(9): 538-42.
- Bornemann G, Lemelson S, Luthardt RG. Innovative Method for the Analysis of the Internal 3D Fitting Accuracy of CEREC 3 Crowns. Int J Comput Dent 2002; 5: 177-182.
- Rudolph H, Bornemann G, Quaas S, Schöne C, Weber A, Benzinger S, Luthardt RG. Innovative model for testing the internal and occlusal accuracy of fit of CAD/CAM-fabricated restorations. Dtsch Zahnärztl Z 2002; 57: 540-544.
- Rudolph H, Quaas S, Luthardt RG. Matching Point Clouds: Limits and Possibilities. Int J Comp Dent 2002; 5: 155-164.
- Luthardt RG, Sandkuhl O, Herold V, Walter MH: Accuracy of mechanical digitising with a CAD/CAM system for fixed restorations. Int J Prosthodont 2001; 14: 146-151.
- Luthardt RG, Sandkuhl O, Brakhage P, Kühmstedt P, Lazarek K. Analysis of individual sources of error within the process chain impression taking - model fabrication - digitisation. Dtsch Zahnäztl Z 1999; 54(10): 627-630.
- Luthardt RG, Kühmstedt P, Sandkuhl O, Brackhage P: Optical digitisation of complete jaw models and CAD-modelled occlusal surfaces. ZWR 1999; 108: 574-580.
CAM
- Rudolph H, Johannes M, Luthardt RG: Low-pressure injection moulding of high-performance ceramics. Dtsch Zahnärztl Z 2005; 60: 172-175.
- Luthardt RG, Holzhüter MS, Rudolph H, Herold V, Walter M. Analysis of CAD/CAM-machining Effects on Y-TZP zirconia ceramic crowns. Dent Mater 2004; 20: 655-662.
- Rudolph H, Schöne C, Luthardt RG. Influence of digitalisation on the achievable precision of CAD/CAM-fabricated dental restorations. Dtsch Zahnärztl Z 2004; 59: 73-77.
- Luthardt RG, Sandkuhl O, Holzhüter M, Herold V, Walter M. Grinding of Zirconia-TZP ceramics for restorative appliances. J Dent Res 2002; 81: 487-491.
- Luthardt R, Sandkuhl O, Johannes M. Material and processing investigations on the fabrication of crown and bridge frameworks made of high-performance ceramics with CAD/CAM systems. Final report for the research project of the Thuringian Ministry of Science, Research and Culture; 1998.
- Luthardt RG, Musil R. High-performance ceramics and CAD/CAM technology in dentistry: On the question of the dental-technological machinability of zirconia ceramics. Swiss dent 1996; 11-S: 37-41.
Review article
- Luthardt RG. Single-tooth restorations Part 2: Laboratory-fabricated restorations in the anterior region. Dtsch Zahnärztl Z 2006; 61(3): 115-117.
- Luthardt RG. Single-tooth restorations Part 3: Plastic fillings versus indirect restorations in the posterior region. Dtsch Zahnärztl Z 2006; 61:331-333.
- Luthardt RG. Aesthetic restorations made of zirconia ceramics in dental prosthetics. Zahnärztliche Mitteilungen 2005; 95(1.11.2005): 62-66.
- Walter MH, Luthardt RG. Differential therapeutic criteria and treatment options for bilaterally shortened dentition. ZWR 2005; 114: 220-228.
- Luthardt RG. Single-tooth restorations Part 1: Laboratory-fabricated restorations in the posterior region. Dtsch Zahnärztl Z 2005; 60: 603-604.
- Luthardt RG. Is prosthetic therapy necessary for bilateral shortened dentition with molar loss? Dtsch Zahnärztl Z 2005; 60: 369-370.
- Luthardt RG. Status and perspectives of impression taking and digitisation procedures in restorative dentistry. today 2005, 31.
- Luthardt RG, Weber A. Survey among dental technicians on the state of knowledge. Dental-labor 2005; LIII(4): 687.
- Walter MH, Luthardt RG. Shortened rows of teeth: Which teeth to replace and how? Zahnärztliche Mitteilungen 2005; 95 (1 November 2005): 48-52.
- Luthardt RG. CAD/CAM in restorative dentistry - An overview. In: Weber H. (ed.). Proceedings of the 33rd conference of the Arbeitsgemeinschaft Dentale Technologie e.V. Tübingen: Eigenverlag, 2004. 4-15.
- Luthardt RG, Rudolph H, Brick EM, Quaas S. CAD/CAM technology 2003: materials and their processing in the focus of development. ZAHNARZT & PRAXIS international 2004; 7: 14-16.
- Quaas S, Rudolph H, Luthardt R. Quo vadis CAD/CAM? Dentalzeitung 2004; 5 (9): 38-40.
- Luthardt RG: Are adhesive build-up fillings superior to other materials/procedures in the fabrication of indirect restorations in vital teeth? Dtsch Zahnärztl Z 2004; 59: 607-608.
- Rudolph H, Quaas S, Luthardt RG. CAD/CAM - New technologies and developments in dentistry and dental technology. Dtsch Zahnärztl Z. 2003; 58: 559-569.
- Quaas S, Rudolph H, Luthardt R. What can current CAD/CAM systems achieve in the manufacture of dental prostheses? ZWL 2003; 6: 24-30
- Kern M, Luthardt RG. Current status of CAD/CAM technology for dental restorations. ZWR 2002; 111, 557-560.
- Luthardt RG, Weber A, Rudolph H, Schöne C, Quaas S, Walter M. Design and production of dental prosthetic restorations: basic research on dental CAD/CAM-technology. Int J Comp Dent 2002; 5: 165-176.
- Luthardt R, Rudolph H, Schöne C, Weber A, Quaas S, Walter M. Development of a reverse engineering CAM process chain for the design and production of dental prosthetic restorations. In: 3rd Workshop of the Working Group for Applied Computer Science in Dentistry, Oral and Maxillofacial Medicine; 2002; Münster; 2002.
- Rudolph H, Schöne C, Weber A, Benzinger S, Quaas S, Sporbeck H, et al. Evaluation of restorations with functional occlusal surfaces - Presentation of a novel test method. In: 3rd Workshop of the Working Group for Applied Computer Science in Dentistry, Oral and Maxillofacial Medicine; 2002; Münster; 2002.
- Luthardt RG, Rudolph H, Sandkuhl O, Walter M: Current CAD/CAM systems for the fabrication of ceramic dental restorations - Part 1: Systems without additional processing of the ceramic base material. ZWR 2001; 11: 747-754.
- Luthardt RG, Rudolph H, Sandkuhl O, Walter M: Current CAD/CAM systems for the fabrication of ceramic dental restorations - Part 2: Systems with additional sintering of the ceramic base material. ZWR 2001; 12: 797-802.
- Luthardt RG: CAD/CAM for restorative applications in dentistry. In: Heidemann D, (ed.). German Dental Calendar 2001. Munich: Hanser, 2000: 93-105.
- Schöne C, Rudolph H, Luthardt R. Development of a reverse engineering CAM process chain for the design and manufacture of dental prosthetic restorations. In: Rapromed 2001; 2001 24 October 2001; Beckmann-Institut Lichtenstein; 2001.
- Luthardt R, Spieckermann J, Böning K, Walter M. Therapie der verkürzten Zahnreihe -Eine systematische Literaturübersicht-. Dtsch Zahnärztl Z 2000; 55(9): 592-609.
- Luthardt RG, Musil R. The Precident DCS system for crowns and bridges, CAD/CAM-fabricated titanium and zirconium oxide restorations. Phillip-Journal 1996; 13: 217-225.
- Quaas S, Rudolph H, Schöne C, Sporbeck H, Luthardt RG. Design and fabrication of dental prosthetic restorations - development and validation of a test chain. In proceedings of the 6th application-related workshop on the acquisition, processing, modelling and evaluation of 3D data of 3D-NordOst, pages 87-91.
- Luthardt RG, Weber A, Walter, M. Nationwide survey launched. zm 95; 6: 692.
Systems
- Weber A, Rudolph H, Quaas S, Thöne A, Luthardt RG. Survey among dentists and dental technicians on CAD/CAM technology in Germany, Dtsch Zahnärztl Z, 2007; 62:679-84.
- Weber A, Rudolph H, Quaas S, Luthardt RG. CAD/CAM-fabricated dental prostheses: A current assessment from the perspective of dentists in Germany. ZM 2006; 24:52-55.
- Rudolph H, Quaas S, Luthardt RG. The choice is great: Which CAD/CAM system suits me? ZWL 2006; 9:30-34.
- Luthardt RG, Rudolph H, Johannes M, Sandkuhl O, Arnold J, Hieke T, et al. Fabrication of crown and bridge frameworks from Y-TZP zirconia by direct moulding. Dtsch Zahnärztl Z 2006; 61: 84-87.
- Luthardt RG, Johannes M, Sankkuhl O, Quaas S, Lemcke J, Rudolph H. CAD/CAM-Manufacturing of FPDs of Alumina and Zirconia by Direct Shaping. J Dent Res 2005(SI): (in press).
- Luthardt RG, Rudolph H, Quaas S, Herold V, Haronska P, Johannes M, et al. Customised fixed prostheses made of high-performance ceramics - development of a process for precision shaping. Hermsdorf: Gesellschaft für innovative Keramik mbH; 2005.
- Luthardt RG. Crown and bridge frameworks made of zirconia ceramics by direct moulding. DZW 2005 15.06.2005.
- Luthardt R, Musil R: The Precident DCS system for crowns and bridges CAD/CAM-fabricated titanium and zirconium oxide restorations. Phillip Journal 1996; 13: 217-225.
3D analyses
- Luthardt RG, Walter H, Quaas S, Koch R, Rudolph H. Clinical trial on the three-dimensional accuracy of full mouth impressions made with three different techniques. Quintessence Int 2010;
- Haim M, Luthardt RG, Rudolph H, Koch R, Walter MH, Quaas S. Randomised controlled clinical study on the accuracy of two stage-putty-and-wash impression materials. Int J Prosthodont 2009; 22(3):296-302.
- Luthardt RG, Walter MH, Weber A, Koch R, Rudolph H. Clinical parameters influencing the accuracy of 1- and 2-stage impressions: a randomised controlled trial. Int J Prosthodont 2008; 21(4):322-7.
- Rudolph H, Luthardt RG, Walter MH. Computer-aided analysis of the influence of digitising and surfacing on the accuracy in dental CAD/CAM-technology. Comput Biol Med 2007; 37(5):579-87.
- Quaas S, Rudolph H, Luthardt RG. Direct mechanical data acquisition of dental impressions for the manufacturing of CAD/CAM restorations. J Dent 2007; 35(12):903-8.
- Quaas S, Weber A, Rudolph H, Luthardt RG. Influence of digitizing and surfacing on the precision of machine-made duplicate teeth. Int J Comp Dent 2006; 9:45-48.
- Luthardt RG, Heyder S, Weber A, Quaas S, Rudolph H. Interactive Design of occlusal Surfaces 2D vs. 3D Display (Interactive modelling of occlusal surfaces: Conventional monitor versus 3D display). Int J Comp Dent 2006; 9:37-40.
- Moldovan O, Rudolph H, Luthardt RG. Internal 3D accuracy of fit of CAD/CAM-fabricated zirconia frameworks for the posterior region. Dtsch Zahnärztl Z 2006; 61:412-18.
- Luthardt RG, Koch R, Rudolph H, Walter MH: Qualitative computer aided evaluation of dental impressions in vivo. Dent Mater 2006 Jan; 22(1): 69-76.
- Quaas S, Rudolph H, Preissler J, Koch M, Koch R, Luthardt RG. Randomised controlled clinical blind study on the accuracy of corrective impression materials. Dtsch Zahnärztl Z 2006; 61:43-47
- Luthardt RG, Loos R, Quaas S. Accuracy of Intraoral Data Acquisition in Comparison to the Conventional Impression. Int J Comp Dent 2005; 8:283-94.
- Luthardt RG, Rudolph H, Benzinger S, Walter MH. Comparison of validity and reliability of the conventional replica technique versus a 3D replica technique. Dtsch Zahnärztl Z 2004; 59: 462-467.
- Luthardt RG, Bornemann G, Lemelson S, Claas H, Walter MH, Hüls A. An Innovative Method for the Evaluation of the Three-Dimensional Internal Fit of CAD/CAM-Crowns Fabricated after Direct Optical vs. Indirect Laser Scan Digitising. Int J Prosthodont 2004; 17: 680-685.
- Luthardt RG, Kühmstedt P, Walter MH. A new method for the computer aided evaluation of three-dimensional changes of dental materials. Dent Mater 2003; 19: 19-24.
- Bornemann G, Lemelson S, Luthardt RG. Innovative Method for the Analysis of the Internal 3D Fitting Accuracy of CEREC 3 Crowns. Int J Comput Dent 2002; 5: 177-182.
- Rudolph H, Bornemann G, Quaas S, Schöne C, Weber A, Benzinger S, Luthardt RG. Innovative model for testing the internal and occlusal accuracy of fit of CAD/CAM-fabricated restorations. Dtsch Zahnärztl Z 2002; 57: 540-544.
Finite element method
- Rudolph H, Hieke T, Luthardt RG. Development of a study model considering clinical Parameter for material testing of dental restorations. Int J Comp Dent 2006;9:41-44
Clinical studies
- Luthardt RG, Walter H, Quaas S, Koch R, Rudolph H. Clinical trial on the three-dimensional accuracy of full mouth impressions made with three different techniques. Quintessence Int 2010;
- Haim M, Luthardt RG, Rudolph H, Koch R, Walter MH, Quaas S. Randomised controlled clinical study on the accuracy of two stage-putty-and-wash impression materials. Int J Prosthodont 2009; 22(3):296-302
- Luthardt RG, Walter MH, Weber A, Koch R, Rudolph H. Clinical parameters influencing the accuracy of 1- and 2-stage impressions: a randomised controlled trial. Int J Prosthodont 2008; 21(4):322-7.
- Ludwig A, Heydecke G, Aggstaller H, Böning K, Busche E, Ebenhöh J, Eschbach S, Gerds T, Gitt I, Hannak W, Lazarek K, Luthardt RG, Marré B, Pospiech P, Reinhardt W, Schädler M, Stark H, Tauche G, Wöstmann B, Walter M. Influence of different prosthetic restoration concepts of the shortened tooth row on the target criteria caries, vitality and tooth loss. 3-year results of the pilot phase of a multicentre study. Dtsch Zahnärztl Z 2006; 61 (12):650-661.
- Moldovan O, Rudolph H, Quaas S, Bornemann G, Luthardt RG. Internal and external accuracy of fit of CAM-fabricated zirconia bridge frameworks - pilot study. Dtsch Zahnärztl Z 2006; 61: 38-42.
- Luthardt RG, Koch R, Rudolph H, Walter MH. Qualitative computer aided evaluation of dental impressions in vivo. Dent Mater 2006; 22(1):69-76
- Quaas S, Rudolph H, Preissler J, Koch M, Koch R, Luthardt RG. Randomised controlled clinical blind study on the accuracy of corrective impression materials. Dtsch Zahnärztl Z 2006; 61: 43-47.
- Luthardt RG. Quality assurance in clinical trials: a template for the design of randomised clinical trials in restorative dentistry. Dtsch Zahnärztl Z 2005; 60: 105-107.
- Wolfart S, Heydecke G, Luthardt RG, Marre B, Freesmeyer WB, Stark H, et al. Effects of prosthetic treatment for shortened dental arches on oral health-related quality of life, self-reports of pain and jaw disability: results from the pilot-phase of a randomised multicentre trial. J Oral Rehabil 2005; 32(11): 815-22.
- Rudolph H, Quaas S, Koch M, Preißler J, Koch R, Luthardt RG. Randomised, controlled clinical blind study: time regime versus 3D accuracy of impressions. Dtsch Zahnärztl Z 2005; 60: 695-701.
- Luthardt RG. The accuracy of dental impressions for fixed prostheses. Dtsch Zahnärztl Z 2004; 7; 59: 372-380.
- Luthardt RG. Randomised, controlled study on 3D impression accuracy - relation prepared tooth/neighbouring teeth. Dtsch Zahnärztl Z 2003; 58: 337-342.
- Walter M, Böning K, Butz F, Hannak W, Kern M, Köpcke W, Luthardt RG, Marré B, Mundt T, Pospiech P, Reiber Th, Richter E-J, Schädler M, Severin RM. The randomised multicenter study of prosthetic treatment options of the shortened dental arch. In: Merker N, Göpfert P, Kirch W, (eds.). Public health research and practice: report of the public health research association Saxony 2000-2001. Regensburg: Roderer Verlag; 2002. 289-301.
- Boening KW, Kaestner KI, Luthardt RG, Walter MH. Burs with guide pins for standardised tooth preparation. Quintessence Int 2001; 32: 191-197.
- Luthardt RG. Randomised, controlled clinical study on three-dimensional impression accuracy - results of the pilot study. Dtsch Zahnärztl Z 2001; 56: 603-607.
- Luthardt RG, Stößel M, Hinz M, Rüdiger V. Clinical performance and periodontal outcome of temporary crowns and fixed partial dentures: a randomised clinical trial. J Prosthet Dent 2000; 83: 32-39.
- Luthardt RG, Stößel M, Hinz M, Vollandt R, Lenz E. Clinical study on the quality and processing of temporary crown and bridge resins. Dtsch Zahnärztl Z 1998; 53: 633-638.
- Luthardt RG, Hinz M, Stößel M. Comparative clinical study of temporary C&B resins. Phillip Journal 1996; 13: 367-373.
- Wolfart S, Heydecke G, Luthardt RG, Marre B, Freesmeyer WB, Stark H, Wöstmann B, Mundt T, Pospiech P, Jahn F, Gitt I, Schädler M, Aggstaller H, Talebpur F, Busche E, Bell M: Effects of Prosthetic Treatment for Shortened Dental Arches on Oral Health-related Quality of Life, Self-Reports of Pain and Jaw Disability. Results from the Pilot-Phase of a Randomised Multicenter Trial. JOS (accepted).
- Luthardt RG. A quantitative and qualitative analysis of the 3D accuracy of dental impressions. Habilitation thesis for the award of the academic degree doctor medicinae dentariae habilitatus (Dr med. dent. habil.) of the Carl Gustav Carus Medical Faculty of the Technical University of Dresden.
Literature research and methodological work
- Luthardt R, Brick EM, Ullmann K, Roediger J, Quaas S, Walter MH. A novel method for measuring treatment success in clinical studies. Dtsch Zahnärztl Z 2005; 60(2): 105-107.
- Luthardt RG. Quality assurance in clinical trials: A template for the design of randomised clinical trials in restorative dentistry. Dtsch Zahnärztl Z 2005; 60: 105-107.
- Luthardt RG, Brick EM, Ullmann K, Roediger J, Quaas S, Walter M. A novel method for measuring treatment success in clinical trials. Dtsch Zahnärztl Z 2004; 59: 596-599.
- Luthardt, RG. Seek and ye shall find. Dental Magazin 2004; 22: 100-103.
- Luthardt RG, Kuhlisch, E. Ein Beitrag zum Nutzen verschiedener medizinischer Datenbanken in der systematischen Literatursuche. Dtsch Zahnärztl Z 2003; 58:351-357.
- Luthardt RG, Roediger J, Siedentop H, Rychlik R, Walter M. Evaluation of the cost-effectiveness of different dental-prosthetic therapy procedures in reduced dentition. Gesundh ökon Qual manag 2001; 6: 1-10.
- Luthardt RG, Spieckermann J, Böning K, Walter M. Systematic review of prosthetic literature -options and problems-. ZWR 2001; 110: 388-393.
- Walter M, Roediger J, Kästner K, Luthardt R, Siedentop H, Rychlik R. Kosten und Lebensqualität in der zahnärztlichen Prosthetik. In: Kirch W, (ed.). 2nd Workshop Health Economics. Regensburg: S. Roderer; 1999. 60-89.
Book contributions
- Moldovan O, Luthardt RG. Chapter 5: Crowns and bridges; CAD/CAM procedures. In: Marxkors 5th edition.
- Luthardt RG, Quaas S, Rudolph H. Chapter 5: Machined fabrication of dental restorations. In: Oxide ceramics and CAD/CAM technologies, J. Tinschert, G. Natt (Eds.). Deutscher Ärzteverlag, Cologne, 2007; 5:253-56 ISBN 978-3-7691-3342-4.
- Luthardt RG, Quaas S, Rudolph H. Chapter 3: Machined fabrication of dental prostheses. In: Oxide ceramics and CAD/CAM technologies, J. Tinschert, G. Natt (Eds.). Deutscher Ärzteverlag, Cologne, 2007; 3:67-94 ISBN 978-3-7691-3342-4.
- Weber A, Heyder S, Quaas S, Rufoloh H, Luthardt RG. Computer-aided design (CAD) of prosthetic restorations with the aid of a 3D display - comparison of conventional versus 3D display. In Proceedings of the 8th application-related workshop on the acquisition, processing, modelling and evaluation of 3D data of 3D-NordOst; 2005:67-74.
- Quaas S, Loos R, Sporbeck H, Luthardt RG. What influence does the matting of free-form surfaces by powder application have on the accuracy of optical digitisation. In Proceedings of the 7th application-related workshop on the acquisition, processing, modelling and evaluation of 3D data of 3D-NordOst; 2004:13-17.
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- Johannes M, Rudolph H, Sandkuhl O, Herold V, Luthardt RG. High-performance ceramics in restorative dentistry. In: Schnapp JD, Glatzel U, Jandt KD, Knake H, (Eds.). Thüringer Werkstofftag 2002; October 2002; Jena: Verlag Dr Köster; 2002:46-53.
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- Luthardt RG. Status and perspectives of zirconium oxide ceramic processing. In: Rech A, (ed.) Dental-labor Fachbuchreihe; Vollkeramik. Munich: Verlag Neuer Merkur; 2002:191-199
- Luthardt RG. CAD/CAM for restorative applications in dentistry. In: Heidemann D, (ed.). German Dental Calendar 2001. Munich: Hanser, 2000:93-105