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Biomedical subjects

F Lutz

Publications and source records attributed to F Lutz.

At least 37 records · Page 2Linked to original sources
PubMed1999

Consistency in the amount of linear polymerization shrinkage in syringe-type composites.

OBJECTIVES: The purpose of this study was to investigate whether the composite resin in a syringe showed a consistent shrinkage through its content. Additionally, the amount of linear shrinkage was compared between materials. METHODS: Five brands of syringe-type and one brand of carpule-type composite resins were used in this study. To each brand, two to three syringes were assigned. In the carpule-type composite, 15 carpules were used. The linear polymerization shrinkage was measured using a custom-made linometer. In this linometer, the amount of displacement of an aluminum disk, which was caused by the linear shrinkage of composite resin, was recorded by a computer every second for 90 s. RESULTS: The syringe-type composites showed similar consistencies in the amount of linear shrinkage except one. The linear shrinkage of the carpule-type Tetric Ceram showed more consistency compared with syringe-type composites. The amount of linear polymerization shrinkage varied between materials. SIGNIFICANCE: This investigation demonstrates that the use of carpule-type composites is recommended instead of syringe-types, because of the consistency in its linear shrinkage. The custom-made linometer provides an effective way to study polymerization shrinkage.

Analysis of Variance↗
PubMed1999

The influence of antagonist standardization on wear.

For differences among materials to be easily detected, low variation in in vitro wear tests is desirable. The working hypothesis of this paper was that antagonists standardized for shape and size and according to materials would show mean values similar to those found in natural, non-standardized cusps, and that standardization would lead to a reduction in mean variation. First, the shapes and sizes of palatal cusps of non-erupted human upper third molars were measured. The cusp cupola was best described by the formula y = 0.001 x2 and was symmetrical around the axis of rotation. Up to 200 microm of the y-axis, this parabola corresponded best to a ball radius of 0.6 mm. Based on this information, standardized antagonists were fabricated from both human enamel and steatite. Wear in the occlusal contact area and the wear of opposing conventional ceramic and fine hybrid composite, respectively, were quantified in a computerized chewing simulator. As a control, natural human enamel cusps were used. Standardization of enamel cusps did not reduce the variation of the resulting wear compared with that of non-standardized enamel antagonists. Furthermore, standardization led to significantly different results both in the antagonists and in the opposing restorative materials. Thus, natural enamel antagonists are preferable for the simulation of wear in the occlusal contact area.

Analysis of Variance↗
PubMed1999

[The type testing of light-polymerization equipment, I: the testing protocol].

With the spread of light polymerisation in dentistry for curing light-activated filling and luting materials the visible-light curing unit has become a standard device in the dental office. The light intensity is the main factor for the degree of polymerisation. However, there are other factors like comfort, handling and intensity control influencing daily use. The light curing unit industry is large and always changing. Consumer information is rare and often out of date. Considering these facts the present study presents a concept of investigating light curing units. In a further study all light curing units available on the Swiss market will be investigated using this protocol. Newly released light curing units should be investigated in this manner to actualize the existing results. Initially specifications and features are summarised using a questionnaire. Several tests are performed to investigate the parameters of the units. The light intensity emitted from the curing tip is analysed by the radiant power, the radiance and the light distribution across the face of the light curing tip as a function of time. Precise radiometers and a camera for picture processing are used for these measurements. Density filters are used to reduce the radiant power. The measurements of the precise radiometer are compared with those of the integrated radiometer of the light-curing unit. In this way the precision of integrated radiometers is controlled at maximum and reduced output. For evaluating the presence and the quality of integrated voltage stabilizer, the line voltage is varied from 230 V down to 207 V and up to 244 V and the radiant power is measured. The integrated timer is measured for its accuracy in each unit. The time intervals are controlled using a stopwatch. Finally the cooling device is tested. Using a phonometer the noise of the cooling fan is measured. Furthermore, the overheating protector is controlled by recording the activating and resetting time.

Dental Equipment↗
PubMed1999

Resin composite polishing--filling the gaps.

OBJECTIVE: The search for the ideal polishing agent for resin composite materials is still ongoing. A new polishing brush with abrasive bristles for polishing resin-based restorations was tested to determine if it polishes restorations, including those with concave surfaces, macrostructured occlusal surfaces, and textured surfaces, without destroying their delicate texture or microstructure. METHOD AND MATERIALS: The polishing effectiveness and the ultimate destructive potential of these brushes were assessed quantitatively and subjectively in vitro. In addition, the durability of the brushes after repeated use and autoclaving was also evaluated. RESULTS: The brushes were nondestructive to resin-based restorative, enamel, dentin, and the restoration interface. They produced a shiny surface on resin-based restorative materials without destroying the surface texture. The abrasive brushes were autoclavable and demonstrated satisfactory durability, despite multiple heat sterilization cycles. CONCLUSION: These brushes can be considered to be key products to polish concave surfaces, anatomically shaped occlusal surfaces, and textured surfaces without damaging the surface characteristics.

Composite Resins↗
PubMed1999

[The type testing of light-polymerization equipment, II: the 1998 status].

In this study 16 different light curing units, available on the Swiss market, were tested for their features, radiant power and light distribution across the face of the curing tip and components like integrated radiometer, timer and cooling device. The basis of this study was the test protocol published in the november edition (11/1999). The features of the light curing units differed from one another. The Optilux 500 had all conceivable features that it could be designated the standard in features. If all these technical options are necessary has to be decided by the consumer. However, the components such as the timer, radiometer and voltage stabilizer are important because they influence the time of irradiation and the radiant power. The radiant power (mW) i.e., the radiance (mW/cm2) were measured in 2 spectral areas which are important for visible light polymerisation. The absolute values for the standard curing tip at a voltage of 230 V lay between 143.4 and 389.7 mW for the wavelengths between 400-520 nm and between 17.7 and 41.8 mW for the wavelengths between 462-472 nm. The resultant specific radiance values were between 268.3 and 862.6 mW/cm2 in the broad spectrum of 400-520 nm and 33.5 and 95.4 mW/cm2 in the narrow spectrum of 462-472 nm. Where the standard curing tips were replaced by guides with other diameters, tips with larger entrances showed more radiant power, light guides with smaller exits also showed more radiance. Turbo tips have larger entrances than exits and therefore combine both positive effects. The intensity wasn't distributed equally across the face of the curing light guide. Characteristically there was a concentric distribution of the intensity, with the maximum found in the centre and a decrease to the margin. Corresponding to the radiance values, curing light tips with decreasing diameters showed more homogeneous distribution patterns. Only Turbo tips showed worse distribution. Comparing the light intensity at a voltage of 207 V and 244 V to the normal voltage of 230 V it was found that not all curing units had an integrated voltage stabilizer. Just 9 out of the 16 tested units had an integrated radiometer. Comparison of the evaluated radiance values to the values given by the integrated radiometer revealed an agreement in just two cases. The marginal values, programmed by the manufacturer varied between 70 and 300 mw/cm2 and lie therefore, too low.

Dental Equipment↗
PubMed1999

Resin composites in the post-amalgam age.

Resin-based composites are now being used as either amalgam substitutes or amalgam alternatives for the direct placement of box-shaped, stress-bearing restorations in posterior teeth. The expected longevity of these restorations is 8 years. With amalgam substitutes, preservation of enamel and dentin and restoration of tooth form and function must be warranted for the full length of the envisaged service life. In addition, with amalgam alternatives, the restoration must be, and must remain, imperceptible at a normal talking distance. The limiting factor with amalgam substitutes is the elevated risk of secondary caries, which is a result of the marginal openings that are unavoidably associated with the nature of the operative technique. Restorations in permanent teeth using amalgam substitutes most likely fail in some critical aspect of the Swiss Dental Society quality guidelines. With amalgam alternatives, the high cost and the demanding operative technique remain the main criticisms. However, amalgam alternatives, if they are placed using a sophisticated operative technique resulting in perfectly adapted restorations, meet the high expectations outlined in the Swiss Dental Society quality guidelines and fit the clinical concept of the post-amalgam age.

Bicuspid↗
PubMed1998

Control of effective expression of the phage phiCTX-encoded ctx gene in Pseudomonas aeruginosa by a promoter upstream of the cos site.

In the DNA of bacteriophage phiCTX, the attachment site (attP), the cohesive end site (cos), and the gene (ctx) encoding the pore-forming cytotoxin, are clustered. Deletion variants and PCR-generated fragments of the DNA were cloned into the Pseudomonas aeruginosa and Escherichia coli vector pHA10. Recombinant plasmids carrying the chloramphenicol acetyltransferase gene, cat, were used for promoter studies. Two promoters responsible for ctx expression are located between attP and cos and between cos and ctx, the promoter upstream of cos being stronger than the one downstream. The promoters and the ribosomal binding site are recognized by both the P. aeruginosa and E. coli transcriptional systems. The results indicate that chromosomal integration of phiCTX DNA, which requires cos site ligation, is necessary for high ctx expression in phiCTX-infected P. aeruginosa strains.

Base Sequence↗
PubMed1998

Preparation of the apical part of the root canal by the Lightspeed and step-back techniques.

This study measured in vitro the displacement of natural canal centres in 18 human teeth before and after shaping by the step-back or Lightspeed techniques. Experimental roots (n = 9 per group), embedded in clear plastic, were cross-sectioned using a 0.1-mm-thick band saw at distances 1.25 mm, 3.25 mm and 5.25 mm from the apices. A stereo microscope was used to take 35 mm slides of the cut surfaces of the sectioned roots and canals. The slides of the uninstrumented canals were scanned into a computer and saved. Each sectioned root was then reassembled and the canals shaped by the step-back or Lightspeed technique. File size 40 and instrument size 50 were selected as the master apical file and master apical rotary for the step-back and Lightspeed groups, respectively. The 18 prepared canals were photographed, and the 35 mm slides scanned and computer stored as previously. This allowed the positions of the pre- and postinstrumented roots to be electronically superimposed for subsequent analyses. Displacements of the root canal centres before and after preparation were assessed in relation to the cross-sectional diameter of the files or instruments used. In addition, increases in cross-sectional area of the root canals after preparation were evaluated in relation to the cross-sectional area of the files or instruments used. Engine-driven nickel-titanium Lightspeed instruments caused significantly less (P < 0.001) displacement of the canal centres, so roots in the Lightspeed group remained better centred than those in the step-back group. The mean cross-sectional area after preparation in the Lightspeed group was significantly less (P < 0.001) than that recorded in the step-back group. Clinically, this implies less apical transportation and less dentine destruction with the Lightspeed technique than with the step-back technique.

Dental Instruments↗
PubMed1998

[Hazardous materials and work safety in veterinary practice. 1: Hazardous material definition and characterization, practice documentation and general rules for handling].

In the last years the standards for professional handling of hazardous material as well as health and safety in the veterinary practice became considerably more stringent. This is expressed in various safety regulations, particularly the decree of hazardous material and the legislative directives concerning health and safety at work. In part 1, a definition based on the law for hazardous material is given and the potential risks are mentioned. The correct documentation regarding the protection of the purchase, storage, working conditions and removal of hazardous material and of the personal is explained. General rules for the handling of hazardous material are described. In part 2, particular emphasis is put on the handling of flammable liquids, disinfectants, cytostatica, pressurised gas, liquid nitrogen, narcotics, mailing of potentially infectious material and safe disposal of hazardous waste. Advice about possible unrecognized hazards and references is also given.

Germany↗
PubMed1998

[Hazardous material and safety conditions in veterinary practice. 2: Flammable liquid, disinfectants and cleansing media, cytostatics, pressurized gases, liquid nitrogen, narcotic gases, mailing of diagnostic samples, hazardous waste].

In the last years the standards for professional handling of hazardous material as well as health and safety in the veterinary practice became considerably more stringent. This is expressed in various safety regulations, particularly the decree of hazardous material and the legislative directives concerning health and safety at work. In part 1, a definition based on the law for hazardous material was given and the potential risks were mentioned. The correct documentation regarding the protection of personal and the purchase, storage, working conditions and removal of hazardous material was explained. General rules for the handling of hazardous material were described. In part 2, partial emphasis is put on the handling of flammable liquids, disinfectants, cytostatica, pressurised gases, liquid nitrogen, narcotics, mailing of potentially infectious material and safe disposal of hazardous waste. Advice about possible unrecognized hazards and references are also given.

Animals↗
PubMed1998

Adhesive crowns and fixed partial dentures fabricated of ceromer/FRC: clinical and laboratory procedures.

Ceramic optimized polymer and fiber-reinforced composite materials represent a significant development in prosthetic dentistry. When utilized in conjunction with adhesive luting techniques, exceptionally conservative crown and bridge restorations may be achieved. This article discusses utilization of these materials in inlay and onlay restorations, as well as clinical and laboratory procedures for fabrication, preparation, and seating of adhesive crown and bridge restorations. The initial results of restorations utilizing these innovative materials are presented.

Ceramics↗
PubMed1998

Scanning electron microscope appearances of Lightspeed instruments used clinically: a pilot study.

The cutting heads of the first 18 instruments in six sets of clinically used Lightspeed instruments (sizes 20-65) were examined in a scanning electron microscope (SEM). Three sets had been used by full-time faculty and discarded as follows: instrument sizes 20-32.5 after 18 treated root canals; instrument sizes 35-47.5 after 36 treated root canals; and instrument sizes 50-65 after 54 treated root canals. Three other sets had been used by a private clinician who discarded all Lightspeed instruments after preparing 20 root canals. The cutting heads of the 108 instruments were examined for the presence of surface debris, metal strips, metal flash, disrupted cutting edges, microfractures, tears, pitting and fretting and fatigue cracks. Fewer instruments ultrasonically cleaned before examination in the SEM had debris than those not cleaned before examination. The prevalence of metal strips and metal flash was similar for both groups. In contrast, microfractures and tears were more prevalent in instruments used by the full-time faculty group, who used their instruments more frequently before discarding them. Pitting and fretting occurred equally frequently in both groups whilst no fatigue cracks were noted in any of the 108 instruments. Overusage of Lightspeed instruments may predispose the flutes of the cutting heads to microfractures and clinicians should be aware of this possibility.

Alloys↗