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Biomedical subjects

F Lutz

Publications and source records attributed to F Lutz.

At least 19 recordsLinked to original sources
PubMed1992

Site-directed mutagenesis of the Pseudomonas aeruginosa cytotoxin for probing toxic activity.

The location of amino acids with direct influence on toxic activity in the pore-forming cytotoxin from Pseudomonas aeruginosa was tested by site-directed mutagenesis. Mutant fragments obtained by the polymerase-chain reaction were subcloned into a cytotoxin gene-bearing plasmid to minimize the possibility of amplification error. Our data suggest an important role of cysteines for toxic activity of cytotoxin. Furthermore, domain-facilitating-binding to plasma membranes is located on the C-terminal side of Cys215.

Bacteriophages↗
PubMed1992

Schistosoma mansoni: stage-dependent formation and repair of membrane pores induced by a cytotoxin from Pseudomonas aeruginosa.

Various stages of Schistosoma mansoni were treated with a cytotoxin from Pseudomonas aeruginosa and their response to the damaging effect was studied in detail. Marker release and membrane potential measurements showed that the cytotoxin formed stable pores in all developmental stages. However, in juvenile 27-day-old worms, which are refractory to the killing effect of the cytotoxin, the pores had a smaller functional diameter as compared to other stages including 31-day-old worms. Furthermore, these resistant 27-day-old worms, but not susceptible older juvenile worms were able to repair the membrane lesions as shown by restoration of the resting membrane potential. In contrast, older juvenile and adult parasites were unable to cope with the breakdown of the resting potential induced by the cytotoxin. The results demonstrate the existence in 27-day-old schistosomes of effective repair mechanisms dealing with damage to the surface membrane.

Animals↗
PubMed1992

A critical comparison of dentifrice abrasion scores on dentine recorded by gravimetric and radiotracer methods.

Dentifrice abrasivity on dentine is conventionally ranked by various in vitro methods. The abrasivity of selected dentifrices in Switzerland was ranked in 1985 by the gravimetric and in 1989 by the radiotracer method. Because same-named brands of dentifrices were differently ranked by these methods, Swiss clinicians were unsure which ranking to follow. This paper lists the errors known to occur in both techniques, but unfortunately it is difficult to quantitate the magnitudes of these errors. Consequently, it is impossible to determine which method yields the more reliable results. Thus, researchers should look into the problem of dentifrice abrasion scores and try to formulate tests which could simplify the selection of brand-named dentifrices by clinicians and the consumers.

Densitometry↗
PubMed1992

Human root caries: histopathology of arrested lesions.

The histopathology of arrested root caries lesions was examined in extracted human teeth. The main structural characteristics of arrested lesions were the completely mineralized surface area and the formation of a distinct sclerosis of the dentinal tubules. Intertubular dentin was, with the exception of the dentinal tubules, fully mineralized up to the surface. Dentinal tubules near the surface were either filled with ghosts of microorganisms or with crystals of different shapes. Sclerosis of the dentinal tubules was characterized by the presence of three different patterns of intratubular mineralization that occur in distinct regions of the zone of tubular sclerosis. The patterns were distinguishable by the type of crystals and their association with organic structures such as collagenous fibrils or odontoblast processes. It is suggested that arrested lesions are based on (1) the formation of an inner barrier that interrupts the diffusion of substrata from the pulp to invaded bacteria, (2) the formation of an outer barrier by a compact, highly mineralized surface region which blocks the diffusion of products of bacterial metabolism into dentin, and (3) an area of mineralization which extends from the outer barrier toward the root canal within demineralized dentin. The present study demonstrates the considerable potential of caries lesions in dentin to become arrested, and subsequently partially remineralized. These phenomena seem to depend on the severity of an active lesion and its location on the root surface. This should be taken into account when diagnosing root caries lesions. The potential of root caries lesions to become arrested indicates that the treatment concept of active root caries lesions should be reconsidered.

Adult↗
PubMed1992

Effect of contact area size on enamel and composite wear.

The effect of contact area dimensions on the wear of composite specimens and their opposing enamel cusps was evaluated in vitro. Thirty-six standardized cylindrical composite specimens were placed into metal cavities (8 mm x 2 mm) and divided randomly into five groups. The composite used was a fine-particle hybrid and was stressed as follows: storage in 75% aqueous ethanol solution for 24 h, toothbrush/toothpaste-abrasion for 30 min, followed by 300 thermal cycles in water ranging from 5 degrees to 55 degrees C and simultaneous 120,000 occlusal chewing loads at a frequency of 1.7 Hz at 53 N maximum force. In group 1 (n = 12), the occlusal chewing loads were applied by palatal cusps of extracted human maxillary molars with natural morphology. In groups 2 to 5 (n = 6), the cusp tips had standardized contact area dimensions of 0.26, 0.38, 1.18, and 4.10 mm2, respectively. Wear of composite specimens and antagonistic enamel cusps (means +/- SD) was assessed in microns by means of a 3-D scanner. Additionally, the contact surfaces of the restorations and of the antagonistic enamel cusps were evaluated by SEM. Increases in enamel contact areas after being loaded were measured by means of a digitizer and expressed in percent of the initial size before stress exposure. The wear of the composite specimens varied from 69.8 +/- 19.9 to 9.5 +/- 3.6 microns, and that of antagonistic enamel cusps from 31.3 +/- 3.4 to 8.8 +/- 1.5 microns. The increase in contact area varied between 27.8 and 0.1%.(ABSTRACT TRUNCATED AT 250 WORDS)

Cold Temperature↗
PubMed1992

Chewing pressure vs. wear of composites and opposing enamel cusps.

The effects of various chewing pressures on the wear of composites and enamel were assessed in vitro. Standardized composite discs (8 mm in diameter, 2 mm in height) were made of a fine-particle hybrid (FPH), a coarse-particle hybrid (CPH), and a homogeneous microfilled composite (HMC). The composite specimens were chemically degraded by immersion in 75% ethanol for 24 h, brushed for 30 min, and then thermocycled 300 times (5-55-5 degrees C) while being occlusally loaded 120,000 times at 1.7 Hz, with chewing forces of 25, 50, 75, and 100 N. Standardized human enamel cusps with a uniform contact area of 0.384 mm2 served as antagonists in the chewing machine. Wear of the composites and enamel cusps, their combined wear, and the increase of the enamel contact surfaces were quantified. An increase in chewing pressure significantly enhanced the wear of both composite and enamel in all groups except for the antagonists opposing a HMC. The FPH was most wear-resistant to in vitro chewing pressures in the range of 6.58 to 19.74 MN/m2, the CPH at 26.32 MN/m2, while the HMC was the most enamel-friendly of the three composites tested. The FPH composite had the least disintegration in the occlusal contact area. The ranking of the composites generally varied at the different chewing pressures with respect to the three types of quantified wear--that is, composite wear, enamel wear, and total wear.

Acrylic Resins↗
PubMed1992

Effects of cement-curing modes on dentin bonding of inlays.

The aim of this in vitro study was to evaluate dentin adhesion after cementation of immediate direct "All Purpose" Hybrid (AP.H) composite inlays (Dentsply) and Cerec Dicor-MGC (Dentsply) inlays with the dentin adhesive Prisma Universal Bond 2 (Dentsply) and the dual-curing Dicor-MGC luting composite (Dentsply). In 24 extracted human molars, standard MOD cavities were prepared with one approximal margin located in enamel and the other one located in dentin. They were divided into four groups: (I) AP.H inlays, luting composite only, chemically cured; (II) AP.H inlays, luting composite, immediately-light-cured; (III) AP.H inlays, luting composite, initially chemically and delayed-light-cured (15 min); and (IV) MGC inlays, luting composite, initially chemically and delayed-light-cured (15 min). In vitro load cycles corresponding to five years of clinical stress followed. Initially and after specimens were loaded, the margins were analyzed quantitatively by SEM. The tooth/cement and cement/inlay interfaces were scored separately. The initial percentages of "continuous margin"--at both the tooth/luting composite and luting composite/inlay interfaces--were higher than 94% for all groups. At the end of the load cycles, the quality of the margins at the tooth/luting composite interface significantly decreased for all groups. The highest decrease was found for the cervical margins located in dentin, where only 37%-61% were scored as "continuous margin". The AP.H inlay/luting composite interface showed almost no change. At the MGC inlay/luting composite interface, the percentage of "continuous margin" decreased to 74%. After specimens were loaded, the percentage of "continuous margin" in dentin was lower than in enamel, despite the use of a dentin bonding agent (PUB 2).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1992

Solubilization of the binding protein from Ehrlich ascites cells and erythrocytes to Pseudomonas aeruginosa cytotoxin.

The binding protein for pore-forming Pseudomonas aeruginosa cytotoxin was solubilized from Ehrlich ascites cell plasma membranes and rabbit and bovine erythrocyte ghosts using nonionic and zwittergent detergents. Analysis of solubilized plasma membranes from Ehrlich cells by a ligand-blot technique after separation by SDS-PAGE/electrophoretic transfer to nitrocellulose or affinity chromatography showed a protein of 70 kDa molecular mass, which binds to cytotoxin. The binding protein solubilized from rabbit erythrocyte ghosts showed a molecular mass of 50 kDa and that from bovine ghosts 55 kDa according to the former test. The binding proteins could be characterized as acidic. They contain a glycan moiety which is, however, not involved in the interaction of cytotoxin with the binding site.

ADP Ribose Transferases↗
PubMed1992

The importance of proximal curing in posterior composite resin restorations.

This in vitro study compared the marginal adaptation of enamel-bonded mesio-occlusodistal composite resin restorations placed using two different insertion techniques (one-step and two-step) and three different curing techniques (occlusal using opaque matrix and wedge systems and interproximal using transparent matrix systems and either transparent, non reflecting, or transparent, laterally reflecting wedges). The micromorphology of the enamel-restoration interface and the marginal seal were evaluated after the restorations were exposed to mechanical and thermal stresses. Although the difference was not statistically significant, the marginal quality of the restorations placed with the two-step technique was better than that of the restorations placed with the one-step technique. The restorations cured from the interproximal direction had significantly better marginal adaptation than did restorations cured only from the occlusal direction. The quality among the groups of interproximally cured restorations was not significantly different, because all the restorative techniques that were evaluated resulted in generally poor marginal quality.

Analysis of Variance↗
PubMed1992

Restoration quality in relation to wedge-mediated light channeling.

Thirty large mesio-occlusodistal cavities with their margins totally in enamel were restored using the three-sited light-curing technique in five different ways: group 1 = Mark I version of a light-reflecting wedge; groups 2 and 3 = interproximal curing with transparent, nonreflecting wedges; groups 4 and 5, Mark II version of the light-reflecting wedge with increased resiliency. In groups 3 and 5, the light that was not conducted by the transparent wedges was shielded by a piece of aluminum foil. It was found that, when used directly and unshielded, both Mark I and Mark II versions of the light-reflecting wedge induced significantly better marginal adaptation than the transparent, nonreflecting wedge, especially gingiovproximally. With both the nonreflecting and reflecting wedges, the shielding had no effect on the overall percentage of excellent margin. However, gingivoproximally, the shielding significantly improved the marginal quality in the nonreflecting wedge groups, leading to the conclusion that the first increment should be cured as thoroughly as possible from a gingivoproximal direction, preferably indirectly via light-conducting wedges. Direct irradiation from a lingual or buccal direction is less favorable.

Composite Resins↗
PubMed1992

In vitro evaluation of dentinal bonding agents in mixed Class V cavity preparations.

The effect of ten dentinal bonding agents on composite resin restorations was tested in mixed Class V cavity preparations. The marginal quality of the restorations was quantified under a scanning electron microscope before and after thermocycling. In addition, the marginal seal was semiquantitatively evaluated with a dye penetration technique. Marginal adaptation in dentin was poor in seven test groups. Three products showed values of excellent margin in dentin exceeding 50% after thermocycling. Furthermore, some dentinal bonding agents had a deleterious effect on marginal adaptation to the etched enamel surfaces.

Bicuspid↗
PubMed1992

[The effects of the processing technic on dentinal adhesion].

In this in vitro study, the effect of application techniques on marginal adaptation of thermal cycled class V restorations restored with an actual dentinal adhesive were quantitated using SEM and dye penetration. Under optimal application conditions, excellent results were generated: though a simple bulk insertion technique was used, no difference was found between enamel and dentin margins before and after thermal loading. On the other hand, contamination of the bonding agent with saliva before composite resin insertion dramatically decreased the percentage of "excellent margin" in dentin and in enamel. Similar effects were found after protecting the bonding agent with an insulating gel. No improvement in marginal adaptation was found after reapplication of the bonding agent. The class V inlay did not show better results than the direct filling technique. However, postcured inlays performed better than their non-postcured counterparts. Without etching enamel with a phosphoric acid gel, but by priming its surface, approximately 80% of "excellent margin" were found in enamel before thermal cycling. This percentage decreased significantly after thermal loading. Restorations totally confined to dentin had slightly lower percentages of "excellent margin" than the mixed class V fillings. The results of this study indicated, that by using dentinal adhesives, little changes and deviations from the correct procedure result in significant alterations in marginal adaptation.

Composite Resins↗
PubMed1992

[Composite inlays: clinical and scanning electron microscopic research after a 1-year functional period].

24 composite inlays placed and documented for post-graduate education purposes in 1990 were reassessed clinically and by means of SEM. The clinical examination after 1 year of clinical service gave excellent results. The quantitative SEM evaluation of the marginal adaptation in the replicable areas revealed 6.6% of marginal gaps at the tooth/cement- and 27.1% at the cement/inlay-interface. To be able to compare these findings to the initial situation, additional five inlays were placed and examined in the SEM immediately after placement. This group exhibited next to gap-free margins. The results were selectively analyzed according to fabrication technique, type and localization of the restorations. No significant difference was found among molars and premolars. On the other hand, higher percentages of marginal gaps at the cement/inlay interface were observed with multi-surfaced, indirect lab-made inlays.

Composite Resins↗
PubMed1992

[Marginal adaptation of adhesive inlays after removal of unpolymerized composite cement].

The removal of polymerized excess resin cement around adhesive inlays is very time consuming and often tooth-destructive. In this study we evaluated, if brushing away of the unset resin cement produced any marginal imperfections. It was found that this procedure caused underfilled margins especially in the occlusal portion of the inlay margins. For this reason the use of this method to remove excess resin cement is not recommended.

Cementation↗
PubMed1992

[Substance ablation with a superpulsed CO2 laser].

In this study a new, superpulsed CO2-laser was evaluated to remove enamel, dentin and several dental restorative materials. In the first part of the experiment, superpulsed mode was compared with pulsed and continuous wave using semiquantitative test methods. It was found that only superpulse was suitable for the purpose. In the following second part of the experiment, temperature rise, crater depth and crater diameter were quantitated for the superpulsed mode in a range of parameters defined in the first experimental part. It is concluded that superpulsed CO2-laser basically has the potential for a mechanical drill substitute, provided that the output power is limited to about 1 W and short pulses of 0.2-0.3 s duration are applied. In the present form the system is not adapted to clinical use. Cooling of the substrate and flexible beam delivery must be developed.

Dental Amalgam↗
PubMed1992

Clinical evaluation of a new pressed glass ceramic inlay material over 1.5 years.

Ten IPS/Empress pressed glass ceramic inlays were cemented in box-shaped, non-beveled, Class II, posterior cavities. They were evaluated clinically according to modified US Public Health Service criteria after 1.5 years in vivo. In addition, quantitative marginal analysis was performed immediately after placement of the inlays and at the 1.5-year recall. Clinical evaluation revealed that the inlays performed well after 1.5 years; all inlays received scores of Alfa or Beta for all criteria evaluated. Scanning electron microscopic examination indicated that the excellent initial marginal adaptation decreased significantly over 1.5 years.

Adhesiveness↗