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Biomedical subjects

M Behr

Publications and source records attributed to M Behr.

At least 37 records · Page 2Linked to original sources
PubMed2001

Glass fiber-reinforced abutments for dental implants. A pilot study.

Titanium abutments in dental implants shine through all-ceramic crowns and therefore limit excellent esthetic results. Prototypes of tooth-colored fiber-reinforced abutments were investigated to avoid the shining-through effect. In vitro, the fracture strength was determined after thermal cycling and mechanical loading of all-ceramic single crowns and four-unit bridges made of a fiber-reinforced composite. The suprastructures were adhesively fixed onto fiber-reinforced implant abutments and compared with those fixed on standard titanium abutments. The median of the fracture strength of the titanium-supported all-ceramic crowns was significantly higher than the median of crowns fixed onto the prototypes. But this value was still more than twice as high as the maximum loading force under oral conditions. No statistical difference was found between four-unit bridges made by fiber-reinforced composite inserted onto titanium abutments and those inserted onto fiber-reinforced abutments. Fiber-reinforced abutment prototypes for dental implants avoided the shining-through effect associated with metal abutments. Their load-bearing capacity after in vitro stress simulation was higher than the maximum oral loading force. With some improvements, the fiber-reinforced implant abutments are therefore a promising alternative to titanium abutments.

Composite Resins↗
PubMed2001

Glass-fibre-reinforced-composite fixed partial dentures on dental implants.

UNLABELLED: The objective was to investigate the fracture strength and marginal fit of implant suprastructures made of fibre-reinforced composite which were fixed onto the implants using cementation or screws. A sample (n=8) of 4-unit bridges, made of the fibre-reinforced composite Vectris/Targis, were adhesively cemented onto titanium conical implant abutments. The second sample consisted of eight screwable Vectris/Targis bridges which were based on prototypes of titanium crown bases. After a 5 year simulation of thermal cycling and mechanical loading (TCML), all specimen were loaded to fracture. Marginal fit was investigated using a semiquantitative SEM analysis. The cemented 4-unit bridges showed a fracture strength of 1553 N (Q1=1498 N, Q3=1825 N) and the screw-fixed bridges had a median of 1457 N (Q1=1223 N, Q3= 1781 N). The analysis of the marginal adaptation showed similar results of cemented and screwed bridges. The bond between the Targis facing-material and the composite cement was significantly deteriorated after TCML. CONCLUSION: Suprastructures made of glass-fibre-reinforced composite could become an alternative to reconstructions with a metal-framework. Both, fixation onto the implants with screws or cementation, are possible.

Composite Resins↗
PubMed2001

Interferon-stimulated response element (ISRE)-binding protein complex DRAF1 is activated in Sindbis virus (HR)-infected cells.

To elucidate the host cell defense mechanisms in response to Sindbis viral infection, we have started to characterize interferon (IFN)-stimulated response element (ISRE)-binding proteins activated in infected cells that are involved in the transcriptional induction of IFN type I-inducible genes. Using electromobility shift assays (EMSA), we detected several protein complexes with a human IFN-stimulated gene 15 (ISG15) ISRE in extracts from virus-infected L929 cells that were absent in extracts from uninfected cells. Comigration with Newcastle disease virus-activated ISRE-binding complexes, ISRE-binding specificity, supershift experiments, and conditions of formation indicate that the complexes activated by Sindbis viral infection in L929 cells correspond to DRAF1 and ISG factor 3 (ISGF3). Transfection of L929 cells with poly rI:rC induced only ISGF3. DRAF1 could be detected in Sindbis virus-infected mouse embryo fibroblasts derived from IFNR type I and type II KO mice. Viral RNA synthesis is required for activation of DRAF1.

Animals↗
PubMed2000

Comparison of failure rates of adhesive-fixed partial dentures for in vivo and in vitro studies.

The objective was to investigate associations between the results of an in vitro and an in vivo study using an artificial mouth and a study of adhesive fixed partial dentures (AFPD) begun in 1985 [1]. Twenty extracted human molars and 20 human upper incisors were inserted into PMMA resin, 6 mm apart to represent a gap. Two preparation methods (identical to those in in vivo conditions) were used: a retentive preparation technique (posterior) and a non-retentive preparation technique (anterior). The frameworks of the bridges consisted of CoCr-alloy with a ceramic veneered pontic to replace the missing tooth. The bonding surfaces of the posterior AFPDs were conditioned with a tribochemical system, while the anterior AFPDs were sandblasted. All AFPDs were inserted using a dual curing composite cement. During thermal-cycling and mechanical loading (TCML: 6000 x 5 degrees C, 1.2 x 10(6) x 50 N, 1.66 Hz) in an artificial environment, the frequency and type of failures were observed. The above mentioned loading parameters were hypothesized to represent a period of 5 years under oral conditions. The results were compared to those of similar bridge-types in the in vivo study. The Kaplan-Meier estimations showed similar graphs for in vivo and in vitro with both types of AFPDs. In vivo and in vitro, the retentively prepared AFPDs were markedly more successful. With regard to the failure types, the simulation-parameters seemed to represent a loading stress that was comparable to in vivo conditions.

Acid Etching, Dental↗
PubMed2000

Technical failure rates of double crown-retained removable partial dentures.

Removable partial dentures (RPD) can be retained using conical crowns or parallel-sided telescopic double crowns. The purpose of this study was to evaluate and compare the technical failure rate of the two retainer systems. One hundred seventeen dentures made by dentists of the medical school were included. Seventy-four RPD were retained with parallel-sided crowns (n = 251) and 43 with conical crowns (n = 160). Following the medical report follow-ups from January 1992 to December 1998, technical RPD failures were noted and analyzed. Technical problems occurred during the observation time in 48.8% of the conical retained dentures and 34.2% of the parallel-sided retained dentures. In both cases, loss of cementation was most frequently noted, while loss of the facings occurred only with conical crowns. Other technical failures did not depend on the type of retainer system used. These were most frequently problems with the denture base, e.g., fracture of artificial teeth or the metal framework. We conclude that there were different technical failures of both double crown retainer systems. These problems were not insignificant in number but treatable.

Cementation↗
PubMed2000

Experimental design of FPD made of all-ceramics and fibre-reinforced composite.

OBJECTIVES: This study was carried out to combine flexural properties of FRC materials with aesthetic values of ceramics. METHODS: The bonding strength of fibre-reinforced composite to ceramic was determined. Afterwards, 8 three unit and 8 four unit FPDs (fixed partial dentures) were manufactured based on the experimental design and were then adhesively luted onto human molars. After thermal cycling and mechanical loading in an artificial environment, the fracture strength and marginal adaptation was determined. FPDs made of FRC (fibre-reinforced composite) materials were used as a control. RESULTS: The most reliable bonding strength of ceramic to FRC material was achieved using acid etching in combination with adhesive luting techniques. Median fracture strength values of 575 N for three unit FPD and 876 N for four unit FPD were established. More than 85% of the experimental FPDs showed a perfect margin while less than 15% revealed a marginal gap, even after thermal cycling and mechanical loading (TCML). The strongest influence of TCML on the marginal adaptation of the experimental design FPD was determined within the four unit system showing approximately a 10% change in marginal gap and perfect margin. SIGNIFICANCE: Assuming an improvement in adhesive bonding between the ceramic and the FRC material and, in addition, an enhancement of the contact surface between pontic and abutment, the hybrid technique could represent an interesting procedure for further investigations and, eventually, clinical implication.

Acid Etching, Dental↗
PubMed2000

Flexural properties of fiber reinforced composite using a vacuum/pressure or a manual adaptation manufacturing process.

PURPOSE: This study investigated the influence of fiber content and water storage on the flexural strength of beams made of two fiber-reinforced composites (FRC), the Vectris and the FibreKor system. MATERIAL AND METHODS: A manual adaptation method (FibreKor, n=30) and a vacuum/pressure process (Vectris, n=30) were compared using 25x4x2mm(3) beams. One group of the Vectris (n=10) and the FibreKor beams (n=10) was stored in water for 24h, a further group was thermal-cycled (TC) 6000x5 degrees C/55 degrees C, and a third group was stored in water for 30days at 37 degrees C. All beams were then loaded to failure using a three-point bending test and the flexural strength was calculated. Finally, the fiber volume percent (vol%) was determined. RESULTS: Generally, the flexural strength decreased significantly with increasing storage time independent of the investigated fiber- and/or manufacturing system. With the parameters 24h/TC/30days, the mean of flexural strength for the Vectris beams was 618/579/545N/mm(2), and for FibreKor 585/534/499N/mm(2). A fiber content of 28.1+/-0.4vol% was assessed for the Vectris beams and 12.8+/-0.6vol% for the FibreKor beams. After 24h storage in water, the Vectris and the FibreKor beams demonstrated a statistically significant higher flexural strength than after 30days storage in water. CONCLUSIONS: A vacuum/pressure manufacturing process in contrast to manual adaptation, resulted in a markedly higher fiber content, but did not necessarily lead to significantly higher flexural strength. Not only the fiber content, but also matrix composition as well as the bond between fibers and matrix determined the properties of FRC.

Analysis of Variance↗
PubMed2000

Comparison of in vitro fracture strength of metallic and tooth-coloured posts and cores.

In root-treated anterior teeth a better aesthetic can be achieved by using translucent and tooth-coloured post and core restorations instead of traditional metal post systems. The aim of this in vitro study was to compare the fracture strength of tooth-coloured ceramic and fibre-reinforced posts as well as titanium posts with clinically proven gold alloy posts as a control. Two all-ceramic, one gold alloy and three combined post restoration systems (titanium and ceramic, respectively, fibre-reinforced posts with composite core) were each applied to upper incisors and after thermal cycling and mechanical loading (TCML) the fracture strength was determined. The variant providing the most reliable fracture strength values and the experimental fibre-reinforced composite (FRC) posts were - in combination with adhesively luted crowns - used to determine the fracture strength of the restoration after thermal cycling and mechanical loading. The median fracture strength of the luted posts and cores fluctuated between 114 and 546 N. Posts with composite cores demonstrate a higher fracture strength in comparison to the all-ceramic and gold alloy systems. Typical failure of metal systems was marked by loosening of the bonding and pulling out of the post in contrast to fracture of the ceramic posts. After the application of the crowns the ceramic system with composite core provided a fracture strength of 338 N and the FRC system a fracture strength of 228 N. Regarding fracture strength, the ceramic posts with composite cores are an alternative to commonly used gold posts and cores. A standardized technical manufacture of FRC posts and cores would provide better fracture strength results of this new dental material. Post and core restorations with tooth-coloured, translucent material offer an improved aesthetic especially in anterior restorations. Because of the high fracture strength prefabricated ceramic posts in combination with composite cores should prove their clinical applicability.

Aluminum Silicates↗
PubMed2000

In vitro repair of all-ceramic and fibre-reinforced composite crowns.

Shear bond strength between fibre reinforced composite and all-ceramic frameworks and veneering/repair composites was investigated after different surface treatments for evaluating the possibility of a repair. Then, 24 crowns were adhesively luted on human teeth and artificially aged. Repair quality was characterized by a loading to fracture test, where undamaged crowns were compared to repaired crowns. To simulate repeated damage, aging and repair, the procedure was performed three times for each crown. A combined silicate-silane treatment of the fibre-reinforced composite frameworks and the hydrofluoric acid etching of the ceramic showed good repair qualities and a sufficient fracture strength for clinical application.

Analysis of Variance↗
PubMed1999

In-vitro study of fracture strength and marginal adaptation of fibre-reinforced adhesive fixed partial inlay dentures.

The aim of this study was to examine in-vitro whether adhesive fixed posterior inlay dentures (AFPID) made with the fibreglass-reinforced Vectris/Targis system (Ivoclar, Schaan, FL) have a fracture strength and a satisfactory marginal adaptation which can occur under clinical conditions. Extracted human third molars were embedded in a PMMA resin 10 mm apart to represent a molar gap. Two preparation methods were used: a box-shaped preparation technique (n = 8) and a tub-shaped preparation technique (n = 8). All AFPIDs were adhesively inserted using the dual curing composite cement, Variolink-high-viscosity (Vivadent, Schaan, FL). After thermocycling and mechanical loading (TCML: 6000 x 5 degrees C/55 degrees C, 1.2 Mio x 50 N, 1.66 Hz) in an artificial environment, the bridges were loaded to failure. Marginal adaption was investigated before and after TCML with the replica technique. After TCML, no significant difference was found in fracture strength between tub-shaped-preparation (median = 722 N, bending median = 0.9 mm) and box-shaped preparation (median = 696 N, bending median = 1.2 mm). A 'perfect margin' was observed in more than 60% of the investigated areas in both preparation techniques. With these values, the bridges can occur under clinical conditions and thus a clinical employment should be considered.

Acid Etching, Dental↗
PubMed1999

Veneering composites - a thermoanalytical examination.

Differential thermal analysis and thermal gravimetric analysis were used to characterize veneering composites. Samples weighing 4-20 mg, made from the composite materials Visio-Gem (Espe, Germany), Sinfony (Espe, Germany), Artglass (Kulzer, Germany), Dentacolor (Kulzer, Germany) and Targis (Ivoclar, Liechtenstein), were examined. The samples were subjected to various thermal curing times of between 4 s and 25 min, using the relevant devices of the manufacturers. As a control group, samples of all materials were examined unreacted. In order to avoid post-curing during storage, all samples were subjected, immediately after manufacture, to the appropriate dynamic temperature programme of the thermoanalytical unit at a heating rate of 10 degrees C min(-1). The materials showed specific material characteristics which can, for instance, be used to analyse the curing behaviour of the materials. The position of the glass transition, polymerization and post-polymerization peaks at temperatures between 30 and 100 degrees C, as well as 150 and 300 degrees C, and the filler and matrix content, allow the classification of the veneering composites.

Journal Article↗
PubMed1999

In vitro study of the effect of thermo- and load-cycling on the bond strength of porcelain repair systems.

Fracture of porcelain fused to metal veneering may cause premature failure of fixed partial prosthodontics. Through the use of intra-oral composite bonded porcelain repair systems, the replacement of the prosthetic reconstruction can be avoided. The aim of this study was to evaluate the shear bond strength of porcelain repair systems currently in use and the effect of thermocycling and mechanical loading (TCML) on the adhesion of composite to ceramic surfaces in comparison with the composite to metal bonding system Rocatec. Specimens were fabricated by fusing the veneering ceramic VMK-68 (Vita) to Co-Cr-Mo-alloy base plates. Twenty cylindrically shaped composite samples in each series were bonded to the porcelain surface using porcelain repair systems currently in use. The shear bond strength of 10 samples was evaluated after 24 h (baseline) and after loading in an artificial oral environment. The repair systems Z 100 Kit, Monobond S/Tetric and Porcelain Etch were not impaired by TCML and exhibited a shear bond strength of greater than 12 MPa, which was comparable to the control group Rocatec. The shear strength of the repair systems Silistor and All-Bond 2 decreased significantly after TCML. Using the appropriate repair system, the repair of ceramic-veneered fixed partial prosthodontics can be recommended as a medium term alternative to a new reconstruction.

Adhesiveness↗
PubMed1999

Finishing and polishing of the ceromer material Targis. Lab-side and chair-side methods.

UNLABELLED: The aim of the study was to check four lab-side and four chair-side methods for finishing and polishing the ceromer material Targis. Eighty bar-shaped specimens (20 mm x 10 mm x 2 mm) of Vectris were produced; 72 were covered with a 2 mm (thickness) layer of the Ceromer Targis and eight samples with the composite Tetric. All specimens were ground plane parallel with 320 Silicium carbide grit sandpaper in order to start with the same level of roughness. Then the specimens were finished and polished using the following methods: (1) Artglass toolkit, (2) pumice-stone and brushes/linen brush and polishing paste P3, (3) Robinson brush/Ivoclar Universal paste and wool brush, (4) Silicone wheel and rag wheel, (5) Shofu Rainbow set, (6) Sof-Lex discs, (7) Vivadent Politip set and (8) Nupro-pastes and brushes. The surface roughness was determined with a profilometer. The arithmetical roughness value Ra was calculated. From each group one specimen was randomly chosen and sputtered with gold in order to observe the surface with a scanning electron microscope to evaluate its smoothness. The methods were ranked as followed: 2, 3 and 5 with the lowest roughness, then 8, 6, 7, 4, 1. The best ranked chair-side method (5) and the best ranked lab-side methods (2, 3) did not differ significantly between the Ra values. No difference was observed between the composite Tetric and the ceromer Targis when these materials were polished using the same method. CONCLUSION: the lab-side-methods 2 and 3 and the chair-side-method 5 can be recommended for finishing and polishing the new ceromer material Targis.

Carbon Compounds, Inorganic↗
PubMed1998

Colour stability of provisional crown and bridge restoration materials.

OBJECTIVE: In an in vitro study to determine the colour stability of provisional restoration materials, the PMMA synthetics Trimm and Cronsin and the bis-acrylic composites Protemp Garant, Protemp Garant NF, Protemp II and Provipont DC were investigated. MATERIALS AND METHODS: The colour changes of the cylindrical untreated samples were measured in comparison with samples after 24 and 72 hours of artificial ageing in a Suntest CPS+ UV ageing device using the Minolta CM 3500d spectrophotometer according to the CIE-L*a*b* system. RESULTS: Trimm (light), Cronsin (brown, yellow and universal), Provipont DC (yellow) and Protemp Garant NF (extra light) displayed the greatest discoloration with values > or = 4-21 delta E, where discoloration toward yellow could be discerned. The remaining materials showed lower luminance reflectance values of < or = 1-4 delta E, and therefore greater colour stability. CONCLUSIONS: Because of their colour stability the materials Cronsin (grey), Protemp Garant (yellow), Protemp II (light), Protemp Garant NF (yellow, light and extra light) could also be used as long-term interim prosthetics.

Analysis of Variance↗
PubMed1998

Cloning of a functional promoter of the human sodium/iodide-symporter gene.

We have cloned and sequenced genomic DNA from a human library extending 1300 bp upstream the 5'-untranslated sequence of the cDNA coding for the sodium/iodide symporter. In transient transfection assays this sequence exhibited promoter activity, which could be confined to nucleotides -443 to -395 relative to the ATG start codon. This minimal promoter, including a putative GC- and TATA- box, was preferentially activated in the rat thyroid cell line FRTL-5, but was also active in non-thyroidal cells, such as COS-7 and Chinese-hamster ovary, albeit to a markedly lower extent.

Animals↗
PubMed1998

Adhesive-fixed partial dentures in anterior and posterior areas. Results of an on-going prospective study begun in 1985.

Within the framework of an on-going prospective clinical study begun in 1985, 120 adhesive-fixed partial dentures (AFPD) continued to be examined. The manufacture and the fitting of the AFPDs were carried out following a standard procedure. The preparation technique and the metal framework conditioning (silica-coating, sand-blasting and electrochemical etching) has varied throughout the duration of the study. Using Kaplan-Meier analysis, the survival rate was determined and an analysis of risk with regard to location factors (anterior, posterior; maxilla, mandible), conditioning and preparation techniques (retentive/non-retentive) was determined using the Cox regression model. The location of the AFPD had no influence on the survival rate. The survival time was determined mainly by the preparation technique. Strict preparation of seating grooves and pin holes made a 95% survival rate possible after 10 years (Kaplan-Meier estimation). Without retention, the risk of failure increased by a factor of 3.7.

Adolescent↗