Status of current CAD/CAM technology in dental medicine.

This article provides an overview of the status of current CAD/CAM technology and possible development trends. In addition to a description of the different CAD/CAM components required for producing computer-assisted dental restorations, innovative design methods recently introduced into dental technology are also mentioned. In the description of the practical application of the current CAD/CAM systems, the possibilities and limits of the present-day techniques and future outlook are illustrated. In this context, the current range of materials available for the computer-assisted production of biocompatible and at the some time high-quality dental restorations is also discussed. In conclusion, the different economic concepts coming into consideration in view of the high investment costs of the current CAD/CAM systems are presented and discussed.

Marginal fit of alumina-and zirconia-based fixed partial dentures produced by a CAD/CAM system.

Clinical long-term success of all-ceramic dental restorations can be significantly influenced by marginal discrepancies. As a result, this in vitro study evaluated the marginal fit of alumina- and zirconia-based fixed partial dentures (FPDs) machined by the Precident DCS system. Different master steel models of three-, four- and five-unit posterior FPDs with an 0.8 mm chamfer preparation were produced. FPDs made of DC-Zirkon and In-Ceram Zirconia core ceramics were machined by the Precident DCS system. The marginal fit of the milled frameworks placed on the master steel models was determined by a replica technique using a light-body silicone to fill the discrepancies between crown and tooth and a heavy-body material to stabilize the light-body impression material. The impressions were poured into an epoxy resin material and each model was cross-sectioned with a low speed diamond saw to better visualize marginal discrepancies. The marginal fit of the FPDs was evaluated by scanning electron microscopy. The measurements of the marginal fit exhibited mean marginal discrepancies in a range between 60.5 and 74.0 microm, mean marginal gaps in a range from 42.9 to 46.3 microm, mean vertical discrepancies in a range from 20.9 to 48.0 microm and mean horizontal discrepancies in the range of 42.0 to 58.8 microm. Statistical data analysis was performed using the non-parametric test of Kruskal-Wallis and Mann-Whitney. The analysis revealed no significant differences (p>0.05) between the mean marginal gaps and vertical and horizontal discrepancies. However, for some FPDs the mean values of the marginal discrepancies were significantly different (p < or =0.05). The wide range of the measured values may be attributed to the complex geometrical design of long span FPDs and difficulties regarding the milling process of brittle ceramic materials. Based on the selection of 100 microm as the limit of clinical acceptability, the results of this study can conclude that the level of marginal fit for alumina- and zirconia-based FPDs achieved with the Precident DCS system meet the clinical requirements.

Fracture resistance of lithium disilicate-, alumina-, and zirconia-based three-unit fixed partial dentures: a laboratory study.

PURPOSE: The purpose of this study was to determine the fracture resistance of three-unit fixed partial dentures (FPD) made of new core ceramics. MATERIALS AND METHODS: A base metal three-unit master FPD model with a maxillary premolar and molar abutment was made. Tooth preparation showed 0.8-mm circumferential and 1.5-mm occlusal reduction and a chamfer margin design. FPDs were constructed with a uniform 0.8-mm-thick core ceramic and a porcelain veneer layer. In-Ceram Alumina, In-Ceram Zirconia, and DC-Zirkon core ceramics were machined by a computer-aided design/manufacturing system, whereas IPS Empress 2 core ceramic was indirectly built up using the fabrication technology of waxing and heat pressing. FPDs of IPS Empress were heat pressed as complete restorations without core material. To ensure standardized dimensions, the FPDs were controlled at different points. All FPDs were cemented with ZnPO4 on the master model and loaded on a universal testing machine until failure. The failure load and mode of failure were recorded. RESULTS: The highest failure loads, exceeding 2,000 N, were associated with FPDs of DC-Zirkon. FPDs of IPS Empress and In-Ceram Alumina showed the lowest failure loads, below 1,000 N, whereas intermediate values were observed for FPDs of IPS Empress 2 and In-Ceram Zirconia. Differences in mean values were statistically significant. CONCLUSION: The high fracture resistance evaluated for FPDs made of DC-Zirkon underscores the remarkable mechanical properties of high-performance ceramic, which could be useful for highly loaded all-ceramic restorations, especially in the molar region.

Maxillary sinus augmentation with the xenograft Bio-Oss and autogenous intraoral bone for qualitative improvement of the implant site: a histologic and histomorphometric clinical study in humans.

The aim of the present clinical study was to determine, through histologic and histomorphometric investigations of human bone specimens, whether the addition of autogenous bone to the bone substitute material Bio-Oss can produce a high-quality implant site. To improve vertical bone height, 13 sinus floor elevations were carried out in a total of 12 patients. Augmentation of the maxillary sinus floor was completed using a mixture of Bio-Oss and bone harvested intraorally from the mandibular symphysis, the retromolar space, or the tuberosity region. Following an average of 7.1 months of healing, 36 Brånemark System implants were placed. During this surgical intervention, 23 cylinder-shaped bone biopsies were taken from the augmented maxillary region using trephine burs. Histologic analysis of the bone biopsies revealed that the Bio-Oss granulate was well-integrated into the newly formed bone; 33.1% (+/- 12.4%) of the substitute material surface was in direct contact with bone. Histomorphometric analysis of the samples revealed an average percentage proportion of bone of 18.9% (+/- 6.4%). The bovine substitute material and soft tissue occupied, respectively, 29.6% (+/- 8.9%) and 51.5% (+/- 9.4%) of the measured surface. When the implants were uncovered after an average healing phase of 6 months, all 36 implants had become osseointegrated. The combination of osteoconductive Bio-Oss and osteoinductive autogenous bone thus proved to be a material suitable for application in sinus floor augmentation.

Application of laser measuring, numerical simulation and rapid prototyping to titanium dental castings.

OBJECTIVES: This paper describes a method of making titanium dental crowns by means of integrating laser measuring, numerical simulation and rapid prototype (RP) manufacture of wax patterns for the investment casting process. METHODS: Four real tooth crowns (FDI No. 24, 25, 26, 27) were measured by means of 3D laser scanning. The laser digitized geometry of the crowns was processed and converted into standard CAD models in STL format, which is used by RP systems and numerical simulation software. Commercial software (MAGMASOFT) was used to simulate the casting process and optimize the runner and gating system (sprue) design. RP crowns were 'printed' directly on a ModelMaker II 3D Plotting System. A silicone negative mold (soft tool) was made from the RP crowns, then more than hundreds wax crowns were duplicated. The duplicated crowns were joined to the optimized runner and gating system. By using the investment casting process 20-25 replicas of each crown were made on a centrifugal casting machine. All castings were examined for porosity by X-ray radiographs. RESULTS: By using the integrated scanning, simulation, RP pattern and casting procedure, cast crowns, free of porosity, with excellent functional contour and a smooth surface finish, were obtained from the first casting trial. SIGNIFICANCE: The coupling of laser digitizing and RP indicates a potential to replace the traditional 'impression taking and waxing' procedure in dental laboratory, with the quality of the cast titanium prostheses also being improved by using the numerically optimized runner and gating system design.

Clinical use of an intraoral silicoating technique.

UNLABELLED: A ceramic fracture rate of metal-ceramic fixed prosthodontics of up to almost 9% calls for an efficient and effective intraoral repair system. For the repair of fractured veneering material, an intraoral silicoating technique was introduced. In contrast to other repair techniques, the silicoating can successfully be used on a variety of dental restorative materials and, therefore, offers additional applications in the field of the intraoral adhesive technique. This silicoating technique, consisting of a chairside airabrasion device filled with a specific silica-coated air-abrasion medium, has been used intraorally by the authors since 1993 for clinical purposes. The clinical procedure is described for different applications in the field of the adhesive technique: intraoral repair, preconditioning of core buildups, implant abutments, and surfaces of fixed prosthodontics for the bonding of orthodontic brackets or periodontal splints. CLINICAL SIGNIFICANCE: The intraoral silicoating technique promotes reliable adhesion to the major part of metal alloy, composite, and ceramic surfaces of fixed prosthodontics. Preliminary clinical results of intraoral repairs conducted with this technique have shown that it presents a medium-term alternative to the replacement of the restoration. Also, the preliminary results of the clinical applications in other fields of adhesive dentistry are promising.

Numerical simulation of the casting process of titanium tooth crowns and bridges.

The objectives of this paper were to simulate the casting process of titanium tooth crowns and bridges; to predict and control porosity defect. A casting simulation software, MAGMASOFT, was used. The geometry of the crowns with fine details of the occlusal surface were digitized by means of laser measuring technique, then converted and read in the simulation software. Both mold filling and solidification were simulated, the shrinkage porosity was predicted by a "feeding criterion", and the gas pore sensitivity was studied based on the mold filling and solidification simulations. Two types of dental prostheses (a single-crown casting and a three-unit-bridge) with various sprue designs were numerically "poured", and only one optimal design for each prosthesis was recommended for real casting trial. With the numerically optimized design, real titanium dental prostheses (five replicas for each) were made on a centrifugal casting machine. All the castings endured radiographic examination, and no porosity was detected in the cast prostheses. It indicates that the numerical simulation is an efficient tool for dental casting design and porosity control.

Metal-free inlay-retained fixed partial dentures.

OBJECTIVE: The treatment procedures used in conjunction with two different metal-free restorative systems are illustrated on the basis of clinical examples. In addition, a report on the initial clinical findings is provided. METHOD AND MATERIALS: Metal-free restorative materials are opening doors to new preparation methods because of their close link to the adhesive cementation technique. As a result of the developments over the past few years, various metal-free systems that can be used to fabricate short-span fixed partial dentures (FPD) are now available. Certain guidelines, however, must be observed in the process. Because of their minimal invasiveness, inlay-retained FPDs offer an interesting solution in cases where the residual dentition exhibits low caries activity. Since the beginning of 1997, a total of 23 metal-free inlay-retained FPDs made of two different types of framework material (11 of high-strength pressed ceramic and 12 of fiber-reinforced composite) have been examined in a clinical study. RESULTS: One inlay-retained FPD made of pressed ceramic had to be replaced because of a fracture. Because the materials have only been on the market for a short time, long-term results are not yet available. CONCLUSION: This type of restoration provides excellent esthetics and reduced invasiveness compared with complete crown-retained FPDs, although indications are limited by the special mechanical properties of the material.

Maxillary sinus augmentation using xenogenic bone substitute material Bio-Oss in combination with venous blood. A histologic and histomorphometric study in humans.

The aim of the present study was to evaluate bone formation following maxillary sinus augmentation using bovine bone substitute material Bio-Oss in combination with venous blood by means of histologic and histomorphometric examination of human biopsies. This involved a total of 15 sinus floor elevation procedures being carried out on 11 patients (average age of 49.6 years) according to the technique described by Tatum (1986). The subantral sinus cavity was augmented using bovine apatite combined with venous blood. After an average healing phase of 6.8 months, trephine burrs were used to take 22 bone biopsies from the augmented sinus region. Then 38 Brånemark implants were inserted in both the osteotomies resulting from bone sampling and in regular sites in the augmented posterior maxilla. Histomorphometric analysis of ground sections from the bone biopsies prepared according to the standard method of Donath & Breuner (1982) produced an average percentage of newly-formed bone of 14.7% (+/- 5.0%) and a proportion of residual xenogenic bone substitute material of 29.7% (+/- 7.8%). Some 29.1% (+/- 8.1%) of the surface of the Bio-Oss granulate was in direct contact with newly-formed bone. Histologically, newly-developed bone became evident, partly invaginating the particles of apatite and forming bridges in the form of trabeculae between the individual Bio-Oss particles. Despite the absence of osteoclastic activity, the inward growth of bone indicates slow resorption of the xenogenic bone graft material. When the implants were uncovered, after an average healing phase of 6 months, 4 of the 38 implants had become loose. Of these 4 implants, 1 had to be subsequently explanted, while the others remained as "sleeping implants" and were not included in the implants superstructure. Thus, the resulting clinical survival rate, prior to prosthetic loading, was 89.5%.

Ceramic abutments--a new era in achieving optimal esthetics in implant dentistry.

In the visible dental region in particular, implant-prosthetic restorations filling single-tooth gaps make exacting demands on function and esthetics. One crucial factor influencing the esthetic outcome is the emergence profile of the restoration. The introduction of aluminum oxide or zirconium oxide abutments, which can be milled to meet individual requirements, provides new opportunities for reconstruction adapted to anatomic findings. Tooth-matched coloring combined with customized preparation and dimensioning make for optimal mucogingival esthetics in implant-supported single-tooth restorations. The aim of the present article is to give a general survey and to illustrate the use of ceramic abutments with clinical case reports.

Cell culture tests for assessing the tolerance of soft tissue to variously modified titanium surfaces.

The aim of our research project was to achieve an improvement in the integration of enossal dental implants in the region of peri-implantary soft tissue. Improvement in the adhesion of the gingiva of the surface of enossal implants was to be achieved by modification of the titanium surface. The effect of different modifications on the biocompatibility of the modified titanium surfaces was tested: sulfur dioxide plasma treatment of titanium; acetylene plasma treatment of titanium followed by sulfur dioxide plasma etching; plasma nitration of titanium; replacement of titanium by glycidoxypropyltrimethoxy silane; coating titanium with poly[(ethene-co-vinyl acetate)-graft-vinyl chloride] and coating titanium with fibronectin. Determination of the chemical composition of the surface was carried out using X-ray photospectroscopy. The adsorption of fibronectin at the surface of the titanium was tested using an Enzyme Linked Immunosorbent Assay. In selected in vitro tests with human gingival fibroblasts, cell morphology was assessed using scanning electron microscopy and light microscopy. Cell proliferation and protein synthesis, as well as the activity of mitochondrial dehydrogenases were evaluated. By means of centrifugation and by determining initial cell adhesion, the adhesion of gingival fibroblasts was investigated. According to the kind of modification made to the titanium surfaces, it was possible to observe differences in the cellular behavior of gingiva fibroblasts on the differently modified surfaces of the implants. Coating the titanium using fibronectin produced optimization of cell growth and improvement in the adhesion of gingiva fibroblasts to the implant surface. In contrast, modification of the titanium with poly[(ethene-co-vinyl acetate)-graft-vinyl chloride] generally resulted in a deterioration of the biocompatibility of the surface. A marked correlation between the cellular compatibility of the modified titanium and the surface modification made did not become apparent. One reason for this is the large number of parameters determining the interaction between implant and tissue.

Numerical simulation of porosity-free titanium dental castings.

The objective of this research was to analyse, predict and control the porosity in titanium dental castings by the use of numerical simulation. A commercial software package (MAGMASOFT) was used. In the first part of the study, a model casting (two simplified tooth crowns connected by a connector bar) was simulated to analyse shrinkage porosity. Secondly, gas pores were numerically examined by means of a ball specimen with a "snake" sprue. The numerical simulation results were compared with the experimental casting results, which were made on a centrifugal casting machine. The predicted shrinkage levels coincided well with the experimentally determined levels. Based on the above numerical analyses, an optimised running and gating system design for the crown model was proposed. The numerical filling and solidification results of the ball specimen showed that this simulation model could be helpful for the explanation of the experimentally indicated gas pores. It was concluded that shrinkage porosity in titanium dental casting was predictable, and it could be minimised by improving the running and gating system design. Entrapped gas pores can be explained from the simulation results of the mould filling and solidification.

Maxillary sinus augmentation prior to placement of endosseous implants: A histomorphometric analysis.

The aim of this prospective study was to histomorphometrically evaluate at various time intervals the mineralization stage and process of an allogeneic-xenogeneic bone graft used in sinus augmentation procedures. One biopsy was taken from 20 patients at either 6, 8, 10, or 12 months after sinus augmentation. Immediately following the biopsy, an endosseous implant was placed into the biopsy site. This protocol provided 4 groups of 5 patients each, based on healing time following sinus augmentation. Using backscattered electron image analysis, the specimens were histomorphometrically analyzed to determine the volume fractions of residual cancellous bone, newly formed bone, soft tissue, bovine hydroxyapatite, and "remineralized" freeze-dried demineralized bone allograft (rDFDBA). "Remineralization" of DFDBA particles was observed in a few areas in all specimens. Polarized light microscopy showed that only the 12-month biopsies had a predominance of lamellar bone formation. The area within the biopsies that represented the residual alveolar ridge consisted of 32.6% +/- 8.6% (mean +/- SD) of bone. In the grafted area of the biopsies the volume fraction of newly formed bone at 12 months (20.7% +/- 8.3%) was significantly higher (P < .05, analysis of variance) than at 6 months (8.1% +/- 3.0%). There was no statistically significant difference between newly formed bone in the inferior, central, and superior grafted areas in all 4 time intervals. This prospective study indicates that the mineralization process of an allogeneic-xenogeneic sinus graft is incomplete 6 months after the sinus augmentation procedure. New bone formation increased up to 12 months postaugmentation; however, it remained lower than the volume of residual bone.

Numerical study of porosity in titanium dental castings.

A commercial software package, MAGMASOFT (MAGMA Giessereitechnologie GmbH, Aachen, Germany), was used to study shrinkage and gas porosity in titanium dental castings. A geometrical model for two simplified tooth crowns connected by a connector bar was created. Both mold filling and solidification of this casting model were numerically simulated. Shrinkage porosity was quantitatively predicted by means of a built-in feeding criterion. The risk of gas pore formation was investigated using the numerical filling and solidification results. The results of the numerical simulations were compared with experiments, which were carried out on a centrifugal casting machine with an investment block mold. The block mold was made of SiO2 based slurry with a 1 mm thick Zr2 face coat to reduce metal-mold reactions. Both melting and casting were carried out under protective argon (40 kPa). The finished castings were sectioned and the shrinkage porosity determined. The experimentally determined shrinkage porosity coincided with the predicted numerical simulation results. No apparent gas porosity was found in these model castings. Several running and gating systems for the above model casting were numerically simulated. An optimized running and gating system design was then experimentally cast, which resulted in porosity-free castings.

Clinical and microbial findings on osseo-integrated implants; comparisons between partially dentate and edentulous subjects.

Clinical and microbiological parameters in partially dentate and edentulous patients treated with oral implants were compared in this study. Twenty-four subjects including 9 males and 15 females, aged 33 to 70 were treated with 98 Brånemark fixtures. Plaque index, gingival index, pocket depth, implant mobility and crevicular fluid flow rate were measured. Latex agglutination tests identified the presence of Actinobacillus Actinomycetem-comitans, Porphyromonas gingivalis and Prevotella intermedia. Partially dentate patients accumulated more plaque than edentulous patients (P = 0.05), whereas crevicular fluid flow rate was significantly higher (P < 0.001) in the partially dentate population. Porphyromonas gingivalis and Prevotella intermedia were more frequently detected (P < 0.01) in partially dentate patients. These results indicate that the presence of natural teeth alter clinical and microbiological parameters which could in turn affect the long term success rate of implants.

[Characterization of the properties of differentially modified titanium surfaces for dental implantology. 2: In vitro biocompatibility studies]. / Charakterisierung der Eigenschaften unterschiedlich modifizierter Titanoberflächen für die zahnärztliche Implantologie. Teil 2: In-vitro-Biokompatibilitätsuntersuchungen.

The aim of the present study was to determine whether specific surface modifications are capable of improving the biocompatibility of a titanium surface, and whether there is a correlation between the physico-chemical properties of the implant material and its biocompatibility. To this end, the properties of titanium surfaces were modified using various methods or the latter were coated with various materials. Plasma treatments under different atmospheric conditions (N2-plasma, SO2-plasma, acetylene plasma) as well as plasma polymerization were used to affect the biological response. Characterization of the physico-chemical surface properties by means of X-ray photoelectron spectroscopy (XPS), contact angle measurements and the calculation of surface tensions or surface energy provided important information on the interactions at the interface between the implant material and the aqueous environment. The influence of the respective surface modification on cell proliferation, cell viability and the activity of mitochondrial dehydrogenases was evaluated in specific in vitro tests with human gingiva fibroblasts. It was show that different modifications of the titanium samples induce different biological responses of the gingiva fibroblasts. The results confirm the existence of correlations between thermodynamic surface properties and cellular reactions under in vitro conditions.

[Characterization of the properties of differently modified titanium surfaces for dental implantology. 1: Methods for surface analysis]. / Charakterisierung der Eigenschaften unterschiedlich modifizierter Titanoberflächen für die zahnärztliche Implantologie. Teil 1: Oberflächenanalytische Verfahren.

Contact between the biological environment and biomaterials takes place at their surfaces. The biocompatibility of a material is determined by interactions at the interface between implant and biological system. The physicochemical surface properties of the materials used, for example, chemical composition, wettability, surface energy and electrical surface charge, therefore play an important role. Within the framework of the investigations described here, specific modifications of the surfaces properties of titanium are effected using various methods with the aim of achieving a positive influence on cell growth and cell attachment. To characterize the physicochemical surface properties, X-ray photoelectron spectroscopy (XPS) have been used. In addition to the clearly altered chemical composition of the modified material surface, it proved possible to determine significant changes in the thermodynamic properties with the aid of contact angle measurements and the determination of surface energy. On the basis of these results, important information about possible interactions at the interface between implant and tissue can be obtained.

Computer aided prediction and control of shrinkage porosity in titanium dental castings.

OBJECTIVES: The main objectives were to investigate the possibility and reliability of quantitative prediction and control of the concentrated shrinkage porosity (macroporosity) in titanium dental castings by means of a numerical simulation technique; and finally to optimize the filling and feeding system design for dental castings. METHODS: A commercial software, MAGMASOFT (Giessereitechnologie GmbH, Germany), was employed to simulate the mold filling and solidification process, and predict the shrinkage tendency in a sample dental casting, two simplified tooth crowns with a connector bar between them. The numerically predicted shrinkages were compared with the experimental results. The experiments were carried out on a centrifugal casting machine. The same geometric and processing parameters of the casting as in the simulations were strictly controlled. RESULTS: The computer predicted shrinkage porosity coincided with the performed experiments, demonstrating the reliability of the numerical model and the thermal physical data chosen for the calculations. Based on the above numerical model, several filling and feeding systems for the same casting were numerically simulated and compared. Finally an optimized design for this sample casting was proposed, and porosity-free castings were obtained. SIGNIFICANCE: It was expected that the numerical simulation technique could be further developed for dental laboratories to aid the real dental casting design.

Simultaneous hard and soft tissue augmentation for implant-supported single-tooth restorations.

The replication of nature in the rehabilitation of a single missing anterior tooth is primarily a surgical challenge, as hard and soft tissue deficiencies compromise the achievement of functional and aesthetic implant-supported restorations. Bone defects can be treated using guided bone regeneration (GBR), with or without bone graft materials. The successful application of the GBR technique has been documented in several experimental and clinical studies; the primary challenge associated with single tooth replacement is the creation of an adequate soft tissue recipient site. However, the increased morbidity and prolonged healing period involved in performing hard and soft tissue grafting procedures in two consecutive appointments do not achieve patient expectations. The learning objective of this article is to master a single-tooth replacement technique that allows surgical treatment of bony and soft tissue deficiencies in a single procedure, during either an immediate or delayed implant placement.

Removable partial denture production in western Germany.

Removable partial denture production in western Germany was studied by analyzing 1,082 photographs taken in consecutive series at five large dental laboratories. The photographic technique was standardized, enabling evaluation of the casts as well as the design of the dentures. Of the casts, 47.2% were maxillary and 52.8% were mandibular. The mean number of teeth present was 6.29 in the maxilla and 6.57 in the mandible. In the maxilla, 52.9% of the molar regions were edentulous; i.e., they had distal-extension free-end spaces. The corresponding figure for the mandibles was 72.7%. Most of the maxillary removable partial dentures had a palatal strap or a palatal plate, and most of the mandibular dentures had a lingual bar. Of the removable partial dentures, 53.1% were retained by telescopic crowns, 15.3% had precision attachments, and 36.1% were retained by clasps only.