Biomedical subjects

E Asmussen

Publications and source records attributed to E Asmussen.

At least 37 records · Page 2Linked to original sources

PubMed1997

Mechanical properties of endodontic posts.

Twenty-two commercially available endodontic posts were examined with regard to stiffness, elastic limit and resistance to fracture. Differences in mechanical properties were explained by differences in width, shape and surface structure. In the selection of an endodontic post, its stability rather than its retention should be of primary clinical concern. Accordingly, the authors advocate the use of endodontic posts that have a cylindrical coronal portion and a conical apical portion.

Dental Alloys↗

PubMed1997

Improved efficacy of dentin-bonding agents.

Dentin cavities, prepared in extracted human teeth, were treated with various proprietary dentin-bonding agents and then filled with a light-cured restorative resin for posterior use. All bonding agents were either treated in accordance with the manufacturers' instructions or combined with Gluma, which is an aqueous solution of glutaraldehyde and HEMA, a hydrophilic monomer. 10 min after polymerization, the width and the extent of the marginal contraction gap was measured approximately 0.1 mm below the free surface of the filling, using a light microscope. With nearly all dentin-bonding agents, the marginal contraction gap could be significantly reduced if Gluma was used after conditioning of the dentin. The reason for this improvement may be that glutaraldehyde cross-links the collagen fibers and thereby strengthens the organic part of the hybrid layer, however, other mechanisms might also play a rôle in the improvement found.

Acrylic Resins↗

PubMed1997

Visible-light curing units: correlation between depth of cure and distance between exit window and resin surface.

Study 1) The depth of proximal cavities was measured on previously taken bitewing radiographs. Study 2) By means of a scrape test, the relationship between depth of cure and irradiation distance was examined with four different curing units and two different restorative resins. Study 3) The microhardness of one of the polymerized resins was measured 0.5 mm below the free surface of the filling and then at 1.0 mm, 1.5 mm, 2.0 mm, and so forth until the resin became so soft that no hardness could be recorded. The hardness at each 0.5-mm level was recorded in relation to irradiation distance. 1) The cavity depth was most often 4-5 mm in lower premolars, 5 6 mm in upper premolars and lower molars, and 5-7 mm in upper molars. In the latter teeth, 15% of the cavities were > or =8 mm deep. 2 and 3) The depth of cure decreased moderately and in a linear manner with increasing irradiation distance. An irradiation distance of 12 mm reduced the depth of well-cured resin only by about 1 mm as compared with close contact between exit window and surface of resin.

Adult↗

PubMed1997

Surface hardness and wear of glass ionomers and compomers.

PURPOSE: To determine the surface hardness and in vitro wear of glass ionomer cements (GIC) and compomers in comparison with a resin composite and to test for a possible correlation between the determined hardness and wear values. MATERIALS AND METHODS: Samples were made of conventional GIC (Ketac-Fil, Fuji II, Fuji IX, Ketac-Prototype = Ketac-Molar), resin-modified GIC (Photac-Fil, Fuji II LC, Vitremer), compomers (Dyract, Compoglass) and resin composite (Z100) for the hardness test (n = 10) and for the wear test (n = 3). The materials were handled according to the manufacturers' instructions. The samples were stored in deionized water for 48 hours at 37 degrees C prior to the determination of Rockwell hardness and three-body in vitro wear. RESULTS: Hardness could not be measured on Ketac-Fil and Fuji II as the samples fractured before a reading was obtainable. Statistically significant differences were found in hardness and wear between brands and between the four types of material. Surface hardness: resin-modified GIC < conventional GIC = compomers < resin composite. In vitro wear: resin-modified GIC > compomers > conventional GIC > resin composite. A negative correlation between hardness and wear was recorded.

Analysis of Variance↗

PubMed1996

In vitro wear, hardness, and conversion of diacetyl-containing and propanal-containing resin materials.

OBJECTIVES: This study was conducted to determine the effect of diacetyl or propanal activities: 1) on the in vitro wear of 22 experimental resin composites; and 2) on the Wallace indentation hardness of the unfilled resins. The objective was to examine the correlation between wear, hardness, and quantity of remaining double bonds (determined previously). METHODS: Diacetyl or propanal agents were added in varying concentrations to monomer mixtures. The resins were made light-curing and those used for measurement of wear were loaded with filter. The results were analyzed by ANOVA and Newman-Keuls' multiple range tests. RESULTS: In the composite systems, adding diacetyl or propanal resulted in decreased in vitro wear. The quantity of remaining double bonds in the dental polymers with these additives was also reduced. Their effect on Wallace indentation depth was less clear-cut. Low concentrations of additives decreased indentation depth of the unfilled materials, whereas high concentrations increased indentation depth. If it assumed that differences in the polymer have a major influence on the wear when the filter content and particle matrix interface are kept constant, then the hardness data on the unfilled resin can be used to correlate property changes of the polymer in the composite. A three-dimensional regression analysis found that in vitro wear decreased with decreasing Wallace indentation depth and decreasing quantity of remaining double bonds. SIGNIFICANCE: Addition of diketone or monoaldehyde to resin monomers may provide a means of increasing wear resistance of composites and allow their use in stress-bearing areas.

Aldehydes↗

PubMed1996

Effect of propanal and diacetyl on quantity of remaining double bonds of chemically cured BisGMA/TEGDMA resins.

The aim of the present study was to determine the effect of propanal and diacetyl addition on the quantity of remaining double bonds of chemically cured dental resins. Propanal (propionaldehyde) or diacetyl (2,3-butanedione) was added to monomer mixtures, which were then made chemically curable. The monomer mixtures were varied with respect to content of propanal or diacetyl. Addition of propanal or diacetyl to chemically curable resins resulted in a decrease in the quantity of remaining double bonds from 19.6% to 1.9% and from 19.6% to 11.4%, respectively. A negative correlation of statistical significance was found between content of propanal and quantity of remaining double bonds, while the relationship between content of diacetyl and quantity of remaining double bonds was found not to be linear. Propanal was equally effective in reducing the quantity of remaining double bonds in chemically cured and in the light cured resins studied previously. As regards diacetyl, a more pronounced effect on quantity of remaining double bonds was noted for light cured resins as compared with chemically cured resins. The most likely common reaction mechanism of propanal and diacetyl seemed to be that of chain transfer reactions. Furthermore, analysis of the data indicated a possible additional photoinitiating function of diacetyl.

Aldehydes↗

PubMed1996

Distortion of alloy by sandblasting.

PURPOSES: To measure distortion of alloy plates caused by sandblasting, and to determine the influence on degree of distortion of type of alloy, plate thickness, and sandblasting conditions i.e. particle size of alumina, air pressure, and duration of blasting period. MATERIALS AND METHODS: Plates were cast in a noble alloy and in a Co-Cr alloy. One end of the plates was fastened in a device, and the projecting 20 mm of the plates was sandblasted. Distortion was determined as the deflection of the plates at a distance of 20 mm from the mounting device. RESULTS: The mean deflections varied between 0.37 mm and 1.72 mm. Plates of Co-Cr alloy showed less deflection than did plates of noble alloy. Deflection was increased by an increase in duration of the blasting, pressure, particle size of the alumina, and by a decrease in plate thickness.

Analysis of Variance↗

PubMed1995

Factors affecting the adherence energy of experimental resin cements bonded to a nickel-chromium alloy.

Reliable adherence of resin-based cements is of prime importance for the longevity of cemented restorations. The present study investigated whether a relationship exists between adherence energy to a metal substrate and the degree of cross-linking and wetting characteristics of resin-based luting agents. The adherence energies between a sand-blasted metal surface and a series of experimental resin cements were measured by means of the wedge test. The degree of cross-linking was calculated from the monomer composition of the resin cements. The measured wetting characteristics were work of adhesion and surface tension, and their dispersive and polar components. Adherence energy varied between 22 and 81 J/m2 and was influenced by the nature of the resin cements: Those with a low degree of cross-linking resulted in high adherence values. Furthermore, resin cements whose monomers were relatively polar gave rise to high adherence values. Although other metals may not behave in exactly the same way, these results may help in the formulation of new, more retentive resin cements.

Acrylamides↗

PubMed1994

Bonding of resin cements to an aluminous ceramic: a new surface treatment.

OBJECTIVES: The purpose of the work reported here was to develop a surface treatment of an alumina-based ceramic (In Ceram) that would make reliable bonding to a resin-based luting agent possible. METHODS: The surface treatment studied was the application of a suspension of a fine-grained, refractory powder, which after drying was sintered to the surface at 960 degrees C. The adherence potential of the surface was determined by measurement of bond energy. RESULTS: It was found that the surface treatment, in conjunction with a heat-treated, silane coupling agent, resulted in mean bond energies of 47 (+/- 19), 56 (+/- 22), and 525 (+/- 116) J/m2 for the three resin cements studied. SIGNIFICANCE: It was concluded that the new surface treatment makes reliable bonding possible, which may allow new indications for this material.

Aluminum Oxide↗

PubMed1994

Effects of surface treatment on the free surface energy of dentin.

OBJECTIVES: The purpose of this study was to evaluate the influence of six treatments on the dispersive, acid, and base components of the free surface energy of dentin. METHODS: Occlusal dentin surfaces were polished with 4000 grit abrasive paper, washed and air dried. Characteristics of the surface energy were calculated by measuring contact angles of the four following liquids:alpha-bromonaphtalene, glycerol, ethylene glycol, and water. The dentin was then treated with aqueous solutions containing: (1) oxalic acid and glycine (OX/GLY),(2) oxalic acid, glycine, and HEMA (OX/GLY/HEMA), (3) phosphoric acid (PA), (4) maleic acid (MA),(5) EDTA, or (6) NaCIO. After treatment, washing and air drying, the energy characteristics of the samples were evaluated again. RESULTS: Three kinds of wetting behavior were observed: an increase (OX/GLY/HEMA), a stabilization (PA, NaCIO) or a decrease (OX/GLY, MA, EDTA) of the wettability of the dentin surface. The calculations demonstrated that dentin surfaces are basic. SIGNIFICANCE: This study of the evolution of the surface energy components gave information on adhesion mechanisms involving hydrophilic and hydrophobic interactions. The results may be helpful in the formulation of conditioners and primers.

Acid Etching, Dental↗

PubMed1994

Bonding of luting materials for resin-bonded bridges: clinical relevance of in vitro tests.

A retrospective clinical study on 78 resin-bonded bridges placed between 1981 and 1992 was used to validate the wedge test in the assessment of the bonding of resin-based luting material. According to the correlation obtained between the findings of the in vivo and the in vitro studies, the wedge test may be considered to be predictive of the clinical performance of resin bonds. The life expectancy of resin-bonded bridges bonded with the 4 META containing material tested appears to be longer than that for bridges bonded with conventional resin cements.

Aluminum Oxide↗

PubMed1994

Effect of wettability of adhesive resins on bonding to dentin.

The purpose of this study was to investigate on human dentin the relationships between, on the one hand, the wettability of five adhesive compounds, characterized by different solubility parameters delta, and on the other, the thickness of the resin impregnated dentin layer (RIL) and the shear bond strength (SBS). Cut dentin surfaces were treated with conditioners of pH 1.25, 3.6 or 7.4. Shear bond strength was measured on 20 specimens each. RIL was determined by scanning electron microscope on specimens fractured perpendicularly to the bonding interface. When resins with delta 32, 30 or 39 (MJ1/2/m3/2) were used RILs were consistently 4 microns and 1 micron on dentin pretreated with the two acidic conditioners. No clearly measurable RIL was shown after application of the conditioner with pH 7.4, and when resins with delta-values of 20 and 25 were applied. For the same adhesive no difference in SBS was found, when applied on the differently conditioned dentin sites. Resins with delta > 30 produced significantly higher SBS than the two adhesives with smaller delta.

Analysis of Variance↗

PubMed1993

Reliability of three dental radiometers.

The light intensity from 80 different curing units was recorded on three dental radiometers. Even though the correlation between the recordings obtained with the three testers was rather high, some units were categorized as good units by one radiometer and poor ones by another. It was also found that, in some case, there was a pronounced difference between the output within the same type of new units. Cavities were made in extracted third molars, filled with a microfilled resin, irradiated for 40 s with 20 of the curing units, and the depth of cure was measured. The radiometers were not able to rank the 20 units in accordance with their depth of cure. We conclude that the three radiometers are not fully reliable. However, they may become very useful tools for monitoring the output from a curing unit if the radiometer and the unit are calibrated.

Composite Resins↗

PubMed1993

Correlation between depth of cure and surface hardness of a light-activated resin.

Microfilled test specimens were polymerized for 40 s with 10 different curing units. The specimens were stored for 7 days at 36 +/- 0.5 degrees C, and then the hardness of the surface was measured. The depth of cure of the 10 units was also measured, but no correlation was found between surface hardness and depth of cure. Even inferior curing units were able to polymerize the surface just as effectively as good light sources. The conclusion is that one cannot use the surface hardness of an irradiated resin to assess the quality of a curing unit.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1993

Correlation between depth of cure and temperature rise of a light-activated resin.

The temperature rise, caused by 10 different curing units, in a prepolymerized resin specimen was examined. For all units, the temperature increase in a 60-s cycle followed a logarithmic curve, with the most effective light sources giving the highest temperature rise. In the surface layer the change of temperature ranged between 3.6 and 29.2 degrees C, and 3.2 mm below the irradiated surface between 1.5 and 12.3 degrees C. The use of a 2-mm-thick isolating layer of glass ionomer resulted in a significant reduction in the temperature increase. The correlation between the depth of cure and the temperature rise was of an exponential or power nature; i.e., a small increase of the depth of cure was followed by a disproportionately high increase in temperature.

Chemical Phenomena↗

PubMed1993

Solubility parameters, fractional polarities, and bond strengths of some intermediary resins used in dentin bonding.

An effective bonding of resin composites to dentin is generally preceded by a conditioning of the surface of the dentin. Previous studies have indicated that the intermediary or adhesive resin should have specific wetting characteristics matching those of the conditioned dentin, in order that optimum bonding can be ensured. The wetting characteristics may be expressed in terms of solubility parameter (delta) and polarity (p) of the resin. The aims of the present study were to determine these variables for a number of compounds used in adhesive resins and to investigate the effects of delta and p on the shear bond strength to dentin. Solubility parameters were obtained according to the method of Small. Fractional polarities were calculated on the basis of measurements of refractive index and dielectric constant of the resins. In the measurements of bond strength, Scotchprep, EDTA + Gluma, or Al2Ox3/glycine were used as dentin conditioners in combination with intermediary resins having various delta and p. For each conditioner, the shear bond strength (BS) could be "explained" by an exponential expression of the form BS = e(a + bx), where x = (delta + cp + d)2, and where a-d are constants depending on the conditioned dentin. It may be concluded that solubility parameter and polarity of the intermediary resins are important variables in the process of bonding to dentin.

Acrylamides↗

PubMed1993

Adherence of resin-based luting agents assessed by the energy of fracture.

The present study assessed the adherence of nine commercial resin cements by means of the wedge test. The beams of the test were made of a Ni-Cr-Be alloy, and the adhering surfaces were sandblasted with 250 microns Al2O3. The energy of fracture of the investigated cements varied from less than 10 J/m2 to 121 J/m2. The fracture energies were not influenced by 1) the thickness of the joint, 2) the width of the beams, 3) the use of an intermediary noncomposite resin, or 4) storage in water beyond 24 h. In spite of a rather high variability within groups, it is concluded that the wedge test may give relevant data on the performance of adhesive joints.

Analysis of Variance↗

PubMed1993

Cusp fracture of endodontically treated posterior teeth restored with amalgam. Teeth restored in Denmark before 1975 versus after 1979.

The aim of the present study was to analyze the frequency and the severity of cuspal fracture for posterior teeth endodontically treated by 91 Danish dentists and restored with amalgam either before 1975 or after 1979. A database from a previous study was analyzed (1584 teeth with an MO, a DO, or an MOD amalgam restoration without cuspal overlays). Teeth restored before 1975 had a significantly lower frequency of cusp fracture than teeth restored after 1979. Moreover, when comparing the frequency of subcrestal fractures, that of the second group (after 1979) was more than twice as high as that of the first group (before 1975). Two factors with a bearing on these findings changed in the time period 1975-1979; the high-copper amalgams took over in Denmark, and the use of Gates-Glidden burs to achieve straight-line access to the root canal was introduced. It is suggested that the weakening of the coronal part of the root, caused by the use of Gates-Glidden burs, and the expansion and low creep of high-copper amalgams may be two of the reasons for the increased frequency and severity of cuspal fracture found in the past decade in Denmark.

Bicuspid↗