Birger Thonemann

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.

Clinical evaluation of packable composite resins in Class-II restorations

Abstract. 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.

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.

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.

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.

SEM analysis of marginal expansion and gap formation in Class II composite restorations

OBJECTIVES Morphological changes in terms of marginal expansion have been observed at the dentin-composite interface of resin composite restorations with the scanning electron microscope (SEM), which could not be described with the criteria conventionally used for quantitative marginal analysis. The purpose of the present study was to elucidate the influence of marginal expansion upon marginal integrity and clarify the cause of these morphological changes. METHODS A total of 22 extracted human molars were restored with Class II resin composite restorations, with and without the use of a dentin bonding agent. The cervical restoration margin was located below the cemento-enamel-junction (CEJ). The marginal adaptation at the dentin- and enamel-composite interfaces was evaluated and measured on replicas using quantitative SEM analysis after different storage periods. The chemical composition of the marginal expansion was determined qualitatively by EDX (Energy Dispersive X-Ray) analysis using original tooth samples. The results obtained from quantitative SEM analysis were statistically analyzed by applying the Mann-Whitney U-test and the error rates method. RESULTS Significantly less marginal expansion occurred at the enamel interface than at the dentin-composite interface (p < or = 0.01). Within the dentin, less marginal expansion was observed with the use of a dentin bonding agent than without a dentin bonding agent (p < or = 0.05). At 1 y, a significant (p < or = 0.05) decrease in marginal expansion was observed in both groups. EDX analysis revealed that the chemical composition of the marginal expansion is comparable to the resin composite, since peaks for silicon, barium and ytterbium could be found at these sites. SIGNIFICANCE In Class II resin composite restorations below the CEJ, partial disruption of the adhesive bond may occur initially when curing the restoration. Water sorption causes gap reduction by hygroscopic expansion, seen in the SEM as a volume increase. Thus, the observed morphological changes can be regarded as an early sign of insufficient adhesion between composite and dentin at sites where disruption of the bond occurred initially, whether or not a dentin bonding agent was used.

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.

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

Abstract 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≤0.5). SEM analysis revealed that the ceramic-composite interface exhibited significantly (p≤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.

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.

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

Abstract 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.