Biomedical subjects

B Thonemann

Publications and source records attributed to B Thonemann.

14 recordsLinked to original sources

PubMed2004

Partial ceramic crowns. Influence of preparation design and luting material on margin integrity--a scanning electron microscopic study.

This in vitro study examines the effects of three preparation designs and different luting agents on the marginal integrity of partial ceramic crowns. One hundred forty-four extracted human molars were prepared according to the following preparation designs: A. Coverage of functional cusps, B. Horizontal reduction of functional cusps and C. Complete reduction of functional cusps. Partial ceramic crowns (Vita Mark II, Cerec 3 System) were bonded to the cavities with: Variolink II/Excite (Vivadent), Panavia F/ED primer (Kuraray), Dyract/Prime and Bond NT (Detrey/Dentsply), and Fuji Plus/GC cavity conditioner (GC). The specimens were exposed to thermocycling and mechanical loading. Marginal adaptation was assessed on replicas using quantitative margin analysis in the scanning electron microscope (SEM). Significant differences were observed between the preparation designs in general. Coverage of functional cusps with preparation of butt joints and use of Variolink as luting material showed a tendency toward the lowest values for compromised adhesion, especially within the dentin. Significant differences could be determined between luting systems: resin-modified glass ionomer cement (RMGIC) caused fracture of the restorations and revealed higher values than all other luting materials for compromised adhesion at ceramic-luting agent and tooth-luting agent interfaces. The dentin-luting material interface, in general, showed higher percentages of compromised adhesion (38-100%) than enamel- and ceramic-luting material interfaces (0-30%). In conclusion, the SEM data indicate that, with adhesively bonded partial ceramic crowns, retentive preparation is not contraindicated and the choice of luting material is more relevant than the preparation design. Margins below the cemento-enamel junction reveal significant loss of adhesion in spite of adhesive luting techniques. The RMGIC cannot be recommended as a luting material for feldspathic partial ceramic crowns.

Ceramics↗

PubMed2002

Responses of L929 mouse fibroblasts, primary and immortalized bovine dental papilla-derived cell lines to dental resin components.

OBJECTIVE: The use of adequate target cells for cytotoxicity testing of dental restorative materials has often been experimentally assessed with respect to the clinical relevance of the test results. In the present study, the responses in primary bovine dental papilla-derived cells (pulp cells) were compared with those in transformed dental papilla-derived cell lines and L929 mouse fibroblasts after exposure to various dental resin compounds. METHODS: Primary bovine dental papilla-derived cells (CPC), tCPC B (CPC cells transformed with SV40 T-antigen), tCPC E (CPC cells transformed with E6/E7 oncogen), and L929 mouse fibroblast cells were exposed to various compounds of dental resin materials for 24 h, and cytotoxicity was determined using the MTT assay. Bis-GMA, UDMA, 1,6 hexane diol dimethacrylate (HDDM), TEGDMA, HEMA, MMA, camphorquinone (CQ), bisphenol A (BPA), and glycidyl methacrylate (GMA) were tested. Concentrations leading to 50% cell survival (TC50 values) were calculated from fitted dose-response curves. RESULTS: The simple ranking of the cytotoxic effects of the dental resin compounds in the four cell types was identical, and TC50 values determined in L929 cells here were consistent with findings by other authors using continuous cell lines. However, the concentrations of the resin compounds necessary for eliciting cytotoxic responses in the various cells were clearly different. The analyses of TC50 values of the resin compounds revealed a linear correlation between cell lines, and the overall sensitivities increased as follows: CPC=tCPC B<tCPC E<L929. SIGNIFICANCE: The low sensitivities of primary cells and transformed tCPC B cells compared with the continuous L929 cell line and the transformed tCPC E cells indicates the presence of specific structural and functional properties relevant in vivo. The differences between the transformed tCPC B and tCPC E cells may indicate modifications of cellular functions caused by the different transformation processes.

Acrylates↗

PubMed2001

Clinical evaluation of packable composite resins in Class-II restorations.

This study investigated the clinical performance of two packable composite resins in Class-II restorations. One hundred and four Class-II restorations were placed in 52 patients by five dentists (four in dental practices and one in a university clinic) in a controlled prospective multicentre clinical trial. Each patient received one Definite/Etch & Prime 3.0 (D-EP) and one Solitaire/Solid Bond (S-SB) restoration, which were examined clinically according to modified USPHS-criteria after 1 week (baseline) and after 1 year. Statistical analysis was performed using the Wilcoxon rank sum test and the error rates method. The significance level was set to 0.05. At baseline both materials performed equally according to the evaluated criteria. After 1 year D-EP showed significantly worse marginal adaptation compared to S-SB. Both materials displayed significant deterioration for the criteria marginal adaptation, marginal discolouration, approximal contact, and fracture of restoration after 1 year compared to baseline. With a failure rate of 9.6% after 1 year, D-EP did not fulfill ADA acceptance criteria for restorative materials. It is proposed that at least 1-year data of clinical testing should be available before a new material is broadly marketed.

Adolescent↗

PubMed2001

Dentin barrier test with transfected bovine pulp-derived cells.

Growth kinetics of SV40 large T-antigen-transfected bovine pulp-derived cells on dentin were investigated. These cells were used in a dentin barrier test device, and the system was evaluated by testing a set of dental filling materials. Cells (120 cells/mm2) were seeded on dentin slices and incubated for up to 21 days. Cell proliferation was recorded using MTT assay. For cytotoxicity tests 3500 cells/mm2 were seeded on dentin discs, which were then incorporated into the dentin barrier test device. After 72 h preincubation test materials were applied. After a 24 h exposure with or without perfusion of the pulpal part of the test device, cell survival was evaluated using MTT assay. The cells revealed similar growth kinetics on dentin slices and on tissue culture plates. In cytotoxicity tests the cells were more sensitive toward the test materials than previously used three-dimensional cultures of human foreskin fibroblasts and as anticipated from clinical experience. Further improvement is expected by using three-dimensional cultures of pulp-derived cells.

Animals↗

PubMed2001

Cytotoxicity testing with three-dimensional cultures of transfected pulp-derived cells.

SV40 large T-antigen-transfected bovine pulp-derived cells were grown three-dimensionally on polyamide meshes. For optimal cell growth, various cell numbers and mesh coatings were tested. Next the three-dimensional cultures were used in a dentin barrier test device, and the system was evaluated by testing a set of dental filling materials. After 24 hr exposure with or without perfusion of the pulpal part of the test device, cell survival was evaluated using an MTT assay. In all experiments pulp-derived cells transfected with SV40 large T-antigen grew three-dimensionally on polyamide meshes and showed growth kinetics similar to those on cell culture plates with lag, log, and plateau phases (reached after about 14 days of incubation). Cross-sections of the three-dimensional cell cultures revealed about 15 to 20 cell layers. In vitro cytotoxicity tests resulted in cell survival rates which are in good agreement with in vivo data and with results obtained from cytotoxicity tests with three-dimensional cultures of human foreskin fibroblasts.

Animals↗

PubMed2000

Inserts--megafillers in composite restorations: a literature review.

Modern insert systems have been available on the dental market since the late 1980s. In general, two major systems can be distinguished: those with and those without preparation instruments in combination with matching standardized inserts. It is claimed that one of the advantages of insert systems is the better marginal adaptation of insert/composite restorations compared to mere composite restorations: the integration of inserts reduces the polymerization shrinkage stress and lowers the overall coefficient of thermal expansion. In vitro data indicate that adapting the insert size to the most precise fit produces a quality of marginal adaptation comparable to that of ceramic inlays. Inserts also facilitate the establishment of a proximal contact. With respect to wear, no significant differences are detected between composite and insert restorations. The bond between insert and composite is susceptible to contamination during operative procedures. Short-term clinical investigations confirm in vitro findings regarding improved marginal adaptation and increased wear resistance. Long-term controlled clinical studies are in progress, but data are not yet available. Based upon the present in vitro and in vivo data it can be concluded that the insert technology shows promising results, but further investigations regarding, for example, stability of the insert/composite bond, fracture resistance of the overall restoration, and wear behavior are necessary to predict the clinical success of this alternative restoration procedure.

Ceramics↗

PubMed2000

Immortalization of bovine dental papilla cells with simian virus 40 large t antigen.

Primary cultures of dental papilla-derived cells have a limited lifespan in vitro and can be maintained only up to passage 7-9 before showing senescence, but in vitro investigations often require a large number of cells showing phenotypic characteristics of the original tissue. To overcome this shortcoming, second-passage cells established from calf molar tooth germs by enzymatic pretreatment of the dental papilla were transfected by electroporation with pSV3neo, coding for the oncogene simian virus 40 large t antigen and a neomycin-resistance gene. Under selection by G418 (neomycin), four cell clones were isolated by single cell dilution at passage 15. Integration of simian virus 40 large t antigen and expression of the gene products were determined in cell clones by polymerase chain reaction (PCR) and immunohistochemistry. Four transfected cell lines (clones B, C, D and no. 12) were maintained in culture for over 1.5 years. For cell characterization, gene expression of procollagen alpha1 (I) and osteocalcin was evaluated by reverse transcriptase (RT)-PCR with cDNA obtained from the established cell lines at passage 20. Expression of collagen type I, osteocalcin and dentine phosphoprotein was evaluated immunohistochemically at passage 20 and after 1.5 years of continuous cell culture. Gene expression and the expression of mineralized tissue-specific proteins was demonstrated with RT-PCR and immunohistochemistry within all four immortalized cell lines. Expression of dentine phosphoprotein was observed in three simian virus 40 large t antigen-transfected cell lines, suggesting the immortalization of odontoblast-like cells in vitro. Thus, transfection of bovine dental papilla-derived cells resulted in immortal cell lines exhibiting phenotypic characteristics of the original tissue.

Animals↗

PubMed2000

Bovine dental papilla-derived cells immortalized with HPV 18 E6/E7.

In vitro investigations of cell-specific metabolism and cell interactions as well as biocompatibility studies are often hampered by the limited lifespan of primary cells originating from target tissues like the oral mucosa, gingiva or pulp. Pulp cells, as do other primary cells, undergo senescence after several passages in vitro. However, senescence can be overcome by transfection of primary cells with oncogenes like the HPV 18 (human papillomavirus 18) E6/E7 oncogene, resulting in immortalized cell lines. The purpose of our study was to establish and preliminary characterize an immortalized bovine dental papilla-derived cell line by transfection with HPV 18 E6/E7 for future use in biocompatibility testing of dental materials. First passage dental papilla-derived cells from molar tooth germs of 6-month-old calves were transfected by electroporation with pUC18 LCR E6/E7 coding for the HPV 18 E6/E7 oncogene. Cells underwent crisis after 5 wk in culture. Distinct cell colonies arose after about 9 wk. Cells were cloned by single cell dilution in passage 15 and 17. Out of three cell clones maintained in culture, two cell clones showed cell death after 28 and 30 wk, respectively. One cell clone overcame a second crisis after 38 wk and was maintained in culture until passage 75. Stable gene expression of HPV 18 E6/E7 oncogenes was verified by polymerase chain reaction (PCR) and immunohistochemistry. Reverse transcription (RT)-PCR revealed that the established cell line (passage 50) expresses procollagen type I, alkaline phosphatase and osteocalcin. This suggests that the immortalization with HPV 18 E6/E7 results in a cell line, which maintained phenotypic characteristics of odontoblast-like cells.

Alkaline Phosphatase↗

PubMed1998

Clinical evaluation of different adhesive systems for restoring teeth with erosion lesions.

This investigation evaluated the performance of a resin-modified glass ionomer, a compomer, and a bonding system/composite combination for the restoration of cervical erosion lesions without cavity preparation. Forty-eight lesions (11 patients) were restored with a bonding agent/composite combination [Prime & Bond 2.1/PrismaTPH (P & B/TPH); DeTrey/Dentsply], a compomer (Dyract; DeTrey/Dentsply), or a light-curing glass ionomer (Fuji II LC; Fuji). The materials were randomly assigned to the patients in triplets. No cavity preparation was performed. The procedures strictly followed the manufacturers' instructions. The restorations were evaluated clinically, using modified USPHS criteria, and by quantitative scanning electron microscope (SEM) analysis, at baseline and 12 months. The clinical data were statistically evaluated with the Pearson chi-square test, the SEM data (criterion gap formation) were analyzed with the Mann-Whitney U-test and error rates method. Clinically, two restorations could not be evaluated. One Dyract restoration failed. With respect to marginal discoloration, recurrent caries and contour, no significant differences could be found between the materials. The surface texture of P & B/TPH and Dyract was significantly better than that of Fuji II LC at baseline and 12 months. Compared to P & B/TPH and Fuji II LC, Dyract revealed a significant decrease in marginal integrity between baseline and 12 months. In SEM analysis, gap formation was determined as follows: baseline, enamel interface: 4% Dyract= 4% Fuji >2% P & B/TPH and dentin interface: 11% Dyract >9% P & B/TPH >2% Fuji; 12 months, enamel interface: 15% Dyract >4% Fuji >3% P & B/TPH and dentin interface: 11% P & B/TPH >6% Fuji >5% Dyract. The error rates method revealed no significant differences, in general, between the three materials with regard to gap formation. In conclusion, the restorations of erosion lesions with different classes of adhesive materials were well retained after 12 months. None of the materials studied revealed superiority over the other materials. All materials revealed shortcomings with respect to either surface texture, marginal integrity or color stability clinically and for all materials gap formation was recorded in the SEM evaluation.

Acetone↗

PubMed1997

Clinical evaluation of heat-pressed glass-ceramic inlays in vivo: 2-year results.

In the present study, the 2-year clinical and scanning electron microscope (SEM) results for heat-pressed ceramic inlays are reported. In a selected patient population, 51 cavities were restored with all-ceramic inlays. All margins were located within the enamel. The inlays were luted to the cavities with a high-viscosity, dual-cure luting composite. After 2 days, 1 year, and 2 years, the restorations were evaluated clinically, using the modified USPHS criteria. Quantitative margin analysis was performed in the SEM on the replicas fabricated at the recall times. The data were tested for significant differences, using the chi-square test for the clinical evaluation and the Mann-Whitney U-test for the margin analysis. After 2 years, the clinical evaluation of the margin adaptation revealed Bravo ratings for 14 restorations (27.5%); 37 restorations (72.5%) were rated Alfa. Compared to the baseline data, this difference was statistically significant (p < or = 0.5). SEM analysis revealed that the ceramic-composite interface exhibited significantly (p < or = 0.01) more gap formation than the enamel-composite interface at all times of evaluation. Wear of the luting composite could be determined along 50% of the restoration interface during the first year, 53% during the second year. The inlay restorations controlled in this study perform well after a period of 2 years.

Adult↗

PubMed1995

Resin-modified glass ionomers for luting posterior ceramic restorations.

OBJECTIVES: Until recently, esthetic inlay restorations in posterior teeth have been limited to cavities surrounded by enamel. Dentin adhesive systems in combination with luting composites and light-cured resin-modified glass ionomer cements offer a possibility for bonding ceramic inlays to cavities when the cervical margin is in dentin. This study was designed to compare in vitro marginal integrity of ceramic inlays bonded to dentin to restorations placed in cavities with margins located entirely in the enamel. METHODS: In the present in vitro study, the sealing abilities of a dentin bonding agent/luting composite combination (Syntac/Dual Cement, Vivadent) and resin-modified glass ionomers (Photac Fil, Photac Bond, ESPE; Dyract, De Trey Dentsply; Fuji II LC, GC Dental Industrial Corp.; and Vitremer, 3M Dental Products) used as luting agents in cavities extending beyond the cemento-enamel junction, were compared to the sealing abilities of a conventional luting composite (Vita Cerec Duo Cement, Vita) in cavities within sound enamel. SEM analysis and dye penetration were performed to evaluate marginal integrity at the cervical cavity margins. RESULTS: The dentin bonding agent/luting composite combination (Syntac/Dual Cement) rendered a marginal seal within the dentin similar to the quality obtained with the conventional luting procedures within sound enamel. When three out of the five resin-modified glass ionomers were used as luting agents (Dyract, Fuji II LC and Vitremer), the results were comparable to those reported for the dentin bonding agents and the conventional method. SIGNIFICANCE: Light-cured resin-modified glass ionomer cements may be considered as an alternative to dentin bonding agents when the cavity margins of ceramic inlay restorations are within the dentin. However, further studies, e.g., wear resistance, must be performed.

Bicuspid↗

PubMed1995

Dental mineralization.

Extracellular matrix components and cell-derived microstructures are implicated in mineralization processes which occur in dental tissues. The respective role(s) of collagenic and non-collagenic matrix components are reviewed: phosphorylated and non-phosphorylated proteins, proteoglycans and phosphpholipids. Space-filling amphiphilic molecules seem to play an important role in the preorganization and oriented deposition of calcium phosphate on structures serving more or less as passive support in dentine as well as in enamel.

Amelogenesis↗

PubMed1994

Biological and clinical investigations of a glass ionomer base material.

OBJECTIVES: The purpose of this study was to investigate the biological properties of a new glass ionomer base material containing strontium glass. METHODS: The glass ionomer base material (Base Line, De Trey Dentsply) was tested for cytotoxicity using a standard agar diffusion test, for its effect upon the pulp in subhuman primates, and in a clinical study as base beneath both composite fillings and amalgam fillings. RESULTS: The material showed a cytotoxicity pattern similar to reference materials, a zinc phosphate cement and a reference glass ionomer base material, which are used successfully in clinical applications. With the pulp/dentin usage test in subhuman primates, there were no statistically significant differences between the experimental glass ionomer base material and the negative control group if bacterial contamination of the cavity floor or direct contact with the pulp was avoided. The results of the clinical study also indicated no pulp damage after one year. SIGNIFICANCE: The experimental glass ionomer base material proved to be acceptable both biologically and clinically.

Analysis of Variance↗

PubMedDate not supplied

Total bonding vs selective bonding: marginal adaptation of Class 2 composite restorations.

For improving the marginal integrity of composite restorations, a total bonding method has been advocated besides the conventional selective bonding method. Total bonding avoids the placement of a base. The entire internal cavity surface is available for the adhesive bond. Selective bonding involves the placement of a base covering the pulpal floor as well as the pulpoaxial wall. In this study, five dentin/enamel bonding system/composite combinations were used to restore 60 class 2 cavities with their cervical margins below the cementoenamel junction (CEJ); six teeth per material were restored according to the total bonding and the selective bonding methods. Before and after simultaneous thermo-cycling and mechanical loading (TCML) marginal adaptation was evaluated on replicas in the SEM. Microleakage was determined by dye penetration on the original samples after TCML. The data were statistically evaluated with the Mann-Whitney U-test and the Wilcoxon test. The error rates method was applied. In SEM analysis the error rates method indicated a significant difference between the two restoration methods in general. In the pairwise comparisons, no significant differences between the selective bonding and total bonding methods were found for Syntac/Tetric, Gluma 2000/Pekafill, and Gluma/Pekafill. With Scotchbond Multi-Purpose (SBMP) and All-Bond 2 (AB2), total bonding revealed significantly (P < or = 0.01) less gap formation before and after TCML than selective bonding. Accordingly, total bonding showed significantly less (P < or = 0.01) dye penetration with Scotch-bond Multi-Purpose and All-Bond 2 compared to selective bonding. In conclusion, the reduction of microleakage by application of the total bonding method depended upon the bonding system used. Total bonding could be an alternative procedure for the adhesive restoration of class 2 cavities when their gingival margins are apical to the cementoenamel junction, provided the proper system is used and pulp damage is prevented.

Composite Resins↗