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Biomedical subjects

K D Jörgensen

Publications and source records attributed to K D Jörgensen.

At least 19 recordsLinked to original sources
PubMed1986

Non-restraining factors affecting setting expansion of phosphate-bonded investments.

Only a few studies on the setting expansion of phosphate-bonded investments have been published. In the present work the effect on the non-restrained setting expansion of mixing time, mixing liquid, mixing device, and volume mixed was investigated for selected brands of this type of investment. It was found that all variables studied may greatly affect the setting expansion, and that the use of the special liquid delivered by the manufacturers in most cases causes an unacceptably high expansion. A modification of the brands studied appears necessary before they can be employed in a precision-requiring technique.

Chemical Phenomena↗
PubMed1986

Gingival and alveolar bone reaction to marginal fit of subgingival crown margins.

Interproximal subgingival marginal discrepancies of full coverage restorations were compared with adjacent crevicular fluid flow and percentage radiographic periodontal bone loss. A total of 88 patients with 116 premolar crowns were evaluated. Patients were selected at random from student treatment records, Institute of Dental Prosthetics, Royal Dental College, Copenhagen, Denmark. Crevicular fluid collected on filter paper strips from the interproximal area was stained with 0.2% ninhydrin solution and the length of the area measured. Marginal fit was determined by measuring the marginal excess or deficit recorded in a polyether impression. The amount of bone around each crowned tooth was measured on five times magnified prints of radiographs. Percentage bone loss was calculated by dividing the distance from the alveolar crest to the most coronal level at which the periodontal space retained its normal width by the distance from the alveolar crest to the root apex. Correlating marginal fit with crevicular fluid within gingival index scores showed r = 0.32 (G.I.1) and r = 0.42 (G.I.2). Fit vs percentage bone loss showed r = 0.68 and r = 0.59, respectively (P less than or equal to 0.001). Differentiation was further made within the 0.0-0.2 mm range discrepancy by categorizing the data in four groups. Comparing fit relative to crevicular fluid and bone loss, most of these groups were significantly different when analyzed statistically using the Mann-Whitney U-Test. Small defects less than or equal to 0.050 mm were associated with significantly less fluid flow and bone loss than defects exceeding this value.

Age Factors↗
PubMed1986

Restraining factors affecting setting expansion of phosphate-bonded investments.

The effects of several factors on the setting expansion of a phosphate-bonded investment used in a steel casting ring were studied. The results show that the setting expansion under the conditions analyzed can be characterized only as a most unreliable means to partly compensate for the solid thermal contraction of casting alloys in a precision-requiring technique.

Chemical Phenomena↗
PubMed1986

A new phosphate bonded investment.

A new type of phosphate bonded investment has been studied. The setting expansion was found to be 0.03-0.05%, the thermal expansion was 1.54-1.85% depending upon the mixing liquid used: water or aqueous glycerol solutions, 5, 10, or 20%. Trial castings of alloys with a thermal expansion room to solidus temperature ranging from 1.60 to 1.91% showed either a very high accuracy or the possibility of improving the accuracy actually found by modifying the glycerol content of the mixing liquid used. To prevent cracking, heating of the investment mould in the temperature range 200-300 degrees C must be slow, probably not faster than 2-3 degrees per min.

Chemical Phenomena↗
PubMed1985

Composite wall-to-wall polymerization contraction in dentin cavities treated with various bonding agents.

Extracted human teeth are frequently used in studies on bonding of composites to dentin. However, little is known about the effect of storing conditions on the results recorded. The purpose of the present work was to measure the wall-to-wall polymerization contraction of a light-cured composite material with and without the use of five different dentin bonding agents in cylindrical dentin cavities prepared in extracted human teeth, either fresh or after storing for up to 4 wk in four different media. No effect of the storing conditions on the width of contraction gaps could be demonstrated when the teeth were stored in tap water or in a 1.0% aqueous chloramine solution. Aqueous solutions of either 0.1% benzalkonium chloride or 0.9% sodium chloride did occasionally affect the size of the contraction gap.

Adhesives↗
PubMed1985

Dimensional and phase changes of dental amalgams.

The relationship of long-term expansion to phase changes of dental amalgams was examined. Using multiple regression analysis, a predictive equation was found which showed that the linear dimensional change was dependent on the alterations in the content of gamma 2 and beta 1.

Chemical Phenomena↗
PubMed1985

Effect of combining dentin bonding agents.

The wall-to-wall polymerization contraction of a light-cured composite was measured in cylindrical dentin cavities treated with the bonding agents: Scotchbond, Clearfil Bond, Gluma/Scotchbond, Gluma/Silux Enamel Bond or Gluma/Clearfil Bond. Marginal gaps were prevented in 29 out of 30 cases when Gluma was used in combination with Clearfil Bond. This combination mediates a mean bond strength between composite and dentin of 20 MPa.

Adhesives↗
PubMed1985

Dentin-polymer bond in resin fillings tested in vitro by thermo- and load-cycling.

The effect of stress applied by thermo- and load-cycling to the bond between composite- and bonding-agent-treated dentin was tested. Cylindrical cavities in extracted human teeth, approximately one-half of the margins in dentin, were etched and treated with two bonding agents - Gluma and Clearfil Bond - before being filled with Silux composite. Forty specimens, some provided with cavity floor lining, were cycled several hundred times between 15 degrees and 50 degrees C, either immediately after light-curing or upon 24 hr of water storage. In all cases, microscopic inspection revealed unchanged adaptation at the dentin margins. Teeth with Class 3 and Class 5 cavities, ten of each and with the gingival margins entirely in dentin, were pre-treated and filled as above. The teeth were covered with a dye during loading and unloading in a manner simulating biting and chewing. Inspection of the cavity margins revealed absence of percolation at the dentin margins. It is concluded that effective bonding agents are necessary to prevent contraction gaps in resin-filled cavities where the margins are partly or entirely located in dentin.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1984

Distortion of wax crowns.

Distortion of wax crown patterns is unavoidable. This distortion is sufficient to reduce the fit of the final restoration to a degree that is clinically unacceptable. The wax distortion may be ignored only by use of die-investing technique. However, an ideal investment for this technique is at present not available.

Crowns↗
PubMed1983

Curing contraction of addition-type silicone impression materials.

The curing contraction of addition-type silicone impression materials was measured by the mercury bath method. The results point to a classification of this group of materials into the following two types: 1: materials with maximum 0.08% polymerization contraction at 22 degrees C 15 min after mixing and maximum 0.03% contraction at 22 degrees C during storage from 15 min to 24 h (Permagum, President, Reflect and Reprosil). 2: materials with more than 0.08% polymerization contraction at 22 degrees C 15 min after mixing and significantly more than 0.03% contraction during storage at 22 degrees C from 15 min to 24 h (Exaflex, Xantogum).

Chemical Phenomena↗
PubMed1983

Abrasion of microfill restorative resins in Class 1 cavities.

Abrasion of Class 1 microfill restorations has been studied over a period 2 years. The materials used were the commercial products Isomolar (Ivoclar, Liechtenstein) and Silar (3 M Co., U.S.A.). All fillings were placed in permanent mandibular first molars of Copenhagen schoolchildren. The abrasion for Isomolar (29 fillings) was found to be 9.8 +/- 10.3 (range -9 to 28) micrometers per year, and for Silar (27 fillings) 11.8 +/- 13.0 (range -5 to 41) micrometers per year. Statistically no difference could be demonstrated between the two products.

Child↗
PubMed1983

Working time of dental amalgams.

The purpose of the present work was to study the setting of amalgams made from several different commercial alloys by recording the rate of initial mercury consumption, and then to compare the findings with those from other methods of defining the early setting process. The results show that the rate of initial mercury consumption is well correlated with clinicians' classification of the rate of setting of amalgams, but not correlated with mechanical tests like early compressive strength and guillotine setting time used till now in estimating the working time of amalgams. Based on these findings an appropriate method of determining the mercury:alloy proportion and working time of dental amalgams is suggested.

Chemical Phenomena↗
PubMed1983

Porosity in microfill restorative composites cured by visible light.

Previous studies indicate that porosity in dental microfill composite restoratives reduces the clinical qualities of this group of materials. Porosity may decrease the optical quality of restorations and is probably a strong factor in reducing wear resistance of Class 1 fillings. In view of possibly eliminating this disturbing factor it was the purpose of the present work to study the effect of variables in the clinical technique on porosity. Initially it was found that filling by spatula as well as paste-paste mixing of non-porous microfill materials caused high porosity, and that the visible light curing microfill brands studied were pore-free as delivered by manufacturers. Consequently only this type of material was studied in detail and only when applied by syringing technique. Poor adaptation of composite to tube inside and to cavity walls as well as too small diameter of the tube tip were found to be factors greatly adding to porosity. In cylindrical cavities, 3 mm in diameter and 2 mm deep, porosity could be consistently reduced to zero by wetting the inside of the tube as well as the cavity walls by a drop of visible light curing monomer and by use of tube with a tip opening of 1.0 mm. Similar positive results were obtained for simulated Class 1 fillings. No adverse effects of this technique were found.

Chemical Phenomena↗
PubMed1982

Microscopical analysis of fractured restorative resin/etched enamel bonds.

The purpose of the present work was to analyze the boundary structures of fractured restorative resin/etched enamel bonds. The fracture patterns were studied by scanning electron and optical microscopy. The three main types of failure observed were classified as: apparent interfacial failure, failure in the bulk of the restorative resin and failure in the bulk of the enamel. The fracture of the resin/etched enamel bond in the case of the apparent interfacial failure was located in the resin very near the interface. No true interfacial debonding occurred in any of the bonds studied.

Acid Etching, Dental↗
PubMed1982

Fatigue strength of some resinous materials.

The fatigue properties of resinous materials may be interesting from several points of view. A good resistance to fatigue failure is desirable in a denture base material. The possible relationship between fatigue strength and wear constitutes another aspect of interest. The purpose of the present work was to investigate the fatigue strength of various types of resinous materials used in dentistry. It was found that heat-cured denture base materials do not necessarily have higher fatigue strength than cold-cured materials. At low levels of stress a tendency was demonstrated for microfilled resins to show higher fatigue strength than other types of resinous materials. On this basis a connection between wear and fatigue properties may be surmised.

Acrylic Resins↗
PubMed1981

Stoichiometric and X-ray diffraction analysis on the gamma 2 leads to eta' transformation in a dispersant phase silver amalgam.

Phase composition of an amalgam prepared form a two-particle alloy was determined over a 2-year period by X-ray diffraction. The gamma 2-content decreased from 3.6% to 0.3% and eta' increased from 3.9% to 10.0%. These alterations in phase content agreed with stoichiometric calculations performed on the basis of the solid state reaction: gamma 2 + Ag/Cu leads to eta' + gamma 1.

Copper↗