[Facts, myths and future perspectives regarding amalgam., mercury and resins].
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Denmark↗
Biomedical subjects
E Asmussen
Publications and source records attributed to E Asmussen.
Improved efficacy of some phosphate-based dentin-bonding agents.
The gap-reducing efficacy of four phosphate-based dentin-bonding agents was tested after various treatments of the dentin and/or the bonding agents. The investigation was carried out on extracted human teeth. One of the root surfaces was ground flat, and a cylindrical butt-joint cavity was prepared in the ground dentin surface. It was found that the efficacy of two of the adhesives, presumably being chloro-substituted phosphates, could be markedly improved if the primed dentin was rinsed with copious amounts of water, dried by compressed air, and a second layer of bonding agent applied. The mechanism behind this improvement is assumed to be the formation of hydrogen chloride, which dissolves part of the smear layer.
Dental Bonding↗
Marginal adaptation of posterior resins: effect of dentin-bonding agent and hygroscopic expansion.
The wall-to-wall polymerization contraction of three composite resins, provisionally accepted by the American Dental Association for use in posterior teeth, was investigated in dentin cavities prepared in extracted human teeth. The marginal adaptation was measured in a light microscope 10 min after polymerization or after 28 days of water absorption. The three composites were tested with and without previous application of two dentin-bonding agents. Used as the control was a microfilled resin intended for use in anterior teeth. None of the two dentin-bonding agents could prevent the formation of a contraction gap of any of the four resins, but the results obtained with the anterior material were significantly better than those obtained with the posterior resins. The reason for the low efficacy of the dentin-bonding agents, when used with the posterior resins, is assumed to be the high viscosity of these restoratives, caused by both the high quantity of fillers and the composition of the organic components. As to the hygroscopic expansion, the contraction gaps of the anterior resin were closed within 28 days, while the posterior materials all had a residual gap. The reason for the smaller hygroscopic expansion of the posterior resins is assumed to be related to the reduced quantity of organic material in these composites.
Absorption↗
Aluminum oxalate/glycine solutions as pretreatment in the Gluma bonding system.
Dentin and enamel surfaces were treated with solutions of aluminum oxalate (AO), the pH of which was adjusted by glycine. Gluma as well as an enamel bonding agent were applied to the surfaces before the placement of a composite resin. On shear bond testing, there was obtained a strong adhesion that was influenced by the pH of the AO solutions. Dentin and enamel specimens for examination by scanning electron microscopy (SEM) were also prepared and treated as above. Enamel specimens showed a very definite etching pattern, and on the dentin surfaces a precipitate was observed. The amount of this product seemed to decrease as the pH increased.
Aldehydes↗
Effect of disinfecting solutions on accuracy of alginate and elastomeric impressions.
The effect of immersion in six disinfecting solutions on the accuracy of 10 impression materials was investigated. Impressions were taken of a truncated steel cone. After setting, the impressions were either stored at room temperature for 24 h, for control, or immediately immersed in a disinfecting agent for 60 min (in one case 10 min), and after 24 h poured with gypsum. A steel ring fitting the steel cone was placed on the resulting dies, and the discrepancy between the top surface of the ring and the die was measured. From these measurements the deviation between the base diameter of the die and of the impression was calculated to express the inaccuracy. All impressions except some in Blueprint exhibited a net shrinkage, giving rise to too large die stones and incomplete seating of the steel ring. Blueprint impressions, however, occasionally swelled and resulted in too small die stones and "overseating" of the steel ring. The disinfecting solutions had no significant impact on two impression materials. For the remaining eight materials the accuracy was decreased, increased, or unaffected by the immersion. Generally, the accuracy of the alginates investigated were more affected by the disinfecting solutions than were the elastomeric impression materials. The accuracy of the three alginates was drastically impaired by immersion in 70% ethanol, whereas the remaining five disinfecting solutions had a smaller, though sometimes statistically significant, effect on the accuracy. For the elastomeric materials only a few specific combinations of impression material and disinfecting solution reduced the accuracy.(ABSTRACT TRUNCATED AT 250 WORDS)
Alginates↗
Accuracy of alginate and elastomeric impression materials.
The accuracy of three alginates and seven elastomeric impression materials was determined. Impressions were taken of a truncated cone and poured with stone die. A steel ring fitting the steel cone was placed on the dies, and the discrepancy between the top surface of the ring and the die was measured. From these measurements the deviation between the base diameter of the die and that of the cone was calculated and used to express the accuracy of an impression material. All impressions showed a net shrinkage, resulting in too large a die stone and incomplete seating of the steel ring. The inaccuracy of the alginates varied between 44 and 188 microns. Blueprint regular was found to be significantly more accurate than the two other alginates investigated, and had a degree of accuracy comparable with that of the more accurate elastomeric impression materials. Within this group of materials the inaccuracy varied between 39 and 130 microns. Generally, the addition-curing silicones were more accurate than the polyethers. Baysilex and President regular body had the highest degree of accuracy of the elastomeric impression materials.
Alginates↗
Substitutes for N-phenylglycine in adhesive bonding to dentin.
Using bond strength measurements, we investigated a number of related compounds in order to elucidate the role of the surface-active ingredient, N-phenylglycine (NPG), in experimental two-step and three-step bonding protocols resulting in adhesive bonding to dentin. All active compounds identified for the two-step or the three-step protocol were N-aryl-alpha-amino acids, and the results delineate some of the key features of the NPG molecule for bonding. For the three-step protocol, there was a requirement for a secondary or tertiary aromatic amino group, a carboxylic acid group, and a single (secondary or tertiary) methylene unit between those two functional groups of the amino acid. For the two-step protocol, additional substitutions at the para position of the phenyl ring on the amine improved the bond strength. In both protocols, para-methyl- and para-chloro-substituted NPG analogues ranked higher than NPG. A "catalytic" effect of the aromatic tertiary amino group on the polymerization of the adhering resin in both procedures could not be ruled out.
Adhesiveness↗
Oxygen-inhibited surface layers on Microfill Pontic.
Radical polymerization of composite resins is inhibited by oxygen. For Microfill Pontic, a self- and photo-curing resin cement, irradiation is proposed as a means to reduce the thickness of the oxygen-inhibited surface layer. The thickness of the layer was measured by a dial gauge technique on irradiated and non-irradiated specimens, to determine a possible effect of irradiation. The results indicate that the depth of inhibition is reduced by irradiation and that an irradiation time of 20 sec is sufficient to give the maximum reduction.
Chemical Phenomena↗
Bonding and gap formation of glass-ionomer cement used in conjunction with composite resin.
Glass-ionomer cement has been suggested as liner in cavities restored with composite resin. The purpose of the present investigation was to measure 1) tensile bond strength between etched glass-ionomer cement and composite resin, and 2) gap formation as assessed by wall-to-wall polymerization contraction and by microleakage with a silver nitrate technique. The influence of the following variables was examined: type of glass-ionomer cement and composite resin, duration of acid etching, irradiation time of unfilled and composite resin, preparation of bevel, conditioning with polyacrylic acid, and storing time in water before gap measurement. Bond strengths varied from 0 MPa when etching was omitted to 3.9 MPa after etching. Glass-ionomer cement lining reduced wall-to-wall contraction and penetration of silver nitrate. A positive correlation was found between wall-to-wall contraction and silver nitrate penetration.
Composite Resins↗
Hardness of restorative resins: effect of camphorquinone, amine, and inhibitor.
The influence of the content of camphorquinone (CQ), amine (DABE), and inhibitor (MHQ) on the Wallace indentation hardness of light-curing polymers was investigated. The hardness was measured on disc-shaped specimens made from 50 bisphenol-A-glycidyl-dimethacrylate/triethyleneglycol-dimethacryla te-based monomers with various contents of CQ, DABE, and MHQ. When no MHQ had been added, the hardness number decreased with increasing content of CQ. This was also the case with increasing content of DABE, but to a lesser extent. In the presence of MHQ, the contents of CQ and DABE did not influence the hardness number significantly.
4-Aminobenzoic Acid↗
Efficacy of dentin-bonding agents in relation to application technique.
The gap-reducing efficacy of two dentin-bonding agents was examined in butt-joint dentin cavities prepared in extracted human teeth. The cavity wall and the surrounding dentin surface were treated with one of the dentin-bonding agents, and a light-activated microfilled restorative resin was either applied and polymerized or applied and then withdrawn from the cavity and once again applied before polymerization. Ten minutes after polymerization the width and the extent of the contraction gap were measured, using a light microscope, approximately 0.1 mm below the original free surface of the fillings. The marginal porosity was also registered and calculated in percentage of the total filling periphery. It was found that reapplication resulted in an increased marginal porosity and also that the width and extent of the contraction gap were increased when the restorative resin was reapplied.
Adhesives↗
[Retrograde root obturations employing composite and a dentin bonding agent: adaptions of the filling materials and bond strength].
Composite resin containing silver for radiopacity bonds to the dentin surface of a resected and slightly concave root pretreated with a dentin bonding agent (Gluma). The bond strength between composite and apical dentin is about 18 MPa and is not affected by a preceding root canal filling with eugenol-containing sealer. Contamination with saliva or serum of the Gluma-treated dentin surface reduced the bond strength significantly. No reduction in bond strength is observed when the contamination of the surface is performed before Gluma-application. Microscopy of the borderline between composite and dentin as well as SEM of the composite surface adjacent to dentin revealed a good adaptation which presumably does not allow bacterial penetration.
Composite Resins↗
Bonding to dentine with a simplified Gluma system.
In the present study, a number of modifications were introduced in the so-called Gluma resin--a new, simplified bonding system. The amount of acetone in its formulation was altered, or the acetone as well as part of the water were substituted by one of several volatile compounds with the purpose of obtaining a pretreatment of easier clinical application. Some modifications of the pH of the mixtures were also tried. Dentine specimens for shear bond testing were prepared and conditioned with an aluminium oxalate/glycine solution. The dentine surfaces were then treated with the modified Gluma resin mixtures before the placement of the composite resin. Gluma resin formulations containing tetrahydrofuran resulted in acceptable bond strengths, and with formulations of reduced pH, high bond strengths were obtained.
Acetates↗
[Compatibility between stone and alginate].
The compatibility between three alginates and three die stones was measured with a surface analyser and observed in the scanning electron microscope. For all nine combinations of alginate and die stone, the relief of the roughness standard was only partly reproduced. The compatibility of certain combinations was so poor that these should be avoided. Thus, Blueprint should not be poured with white Vel-Mix. Furthermore, it is recommendable to use combinations of alginate and die stone that result in the highest Ra-values possible.
Alginates↗
Silicoating: evaluation of a new method of bonding composite resin to metal.
Silicoating is a new type of pretreatment of the metal in the resin-bonded bridge technique. The size of bond strength between resin cement and silicoated metal was investigated. Different resin cements, types of metal, and grain sizes of sand used for roughening the metal surface were tested. Furthermore, the effect on the bond strength of contamination with saliva and of thermocycling was measured. There was no difference of importance between the two resin cements tested. Bond strengths obtained with Wirobond were the highest and insensible to changes in resin cement, grain size of sand, and to thermocycling. It was found that sand of the smallest grain size used brought about the highest bond strengths. Contamination with saliva did not significantly reduce the size of the bond strengths. Rinsing the metal surfaces with water or ethanol after contamination restored the bond strengths to their original magnitude. By silicoating, a greater resistance to thermocycling was obtained. Nevertheless, except for Wirobond, a fall in bond strength was measured after thermocycling. Bond strengths of the size of those between etched enamel and composite resin were measured, and the Silicoater method seems a reliable pretreatment of the metal.
Composite Resins↗
Impression materials: effect of hydrophilicity and viscosity on ability to displace water from dentin surfaces.
The water-displacing ability of hydrophilic and hydrophobic impression materials was determined and related to the hydrophilicity and viscosity of the materials. The water-displacing ability of the materials was determined on a network of grooves in a dentin surface covered by a drop of water. After setting of the material, the number of crossings reproduced in the impression was calculated in percent of the total number of crossings. The hydrophilicity was assessed by measuring the contact angle between water and impression material. To determine viscosity, a rotoviscosimeter was used. Impression materials with contact angles less than 70 degrees showed a significant negative correlation between water-displacing ability and contact angle, i.e. the reproducing ability decreased with decreasing hydrophilicity of the materials. Impression materials with contact angles above 70 degrees showed a significant positive correlation between water-displacing ability and viscosity, i.e. the water-displacing ability improved with increasing viscosity.
Chemical Phenomena↗
Effect of postponed polishing on marginal adaptation of resin used with dentin-bonding agent.
Dentin cavities, prepared in extracted human teeth, were treated with two different dentin-bonding agents and filled with a light-activated microfilled resin. The maximum width of the contraction gap (MG) and the extent of the gap (GP) were then measured, using a light microscope, approximately 0.1 mm below the original free surface of the filling. The contraction gap was measured 30 s, 10 min or 60 min, and remeasured 65 min, after stop of irradiation. A positive correlation was found between the two variables, MG and GP. The product of MG and GP was chosen as basis for the statistical analyses. This "marginal index" was significantly reduced when polishing of the marginal area was postponed for 10 min with one of the dentin-bonding agents and for 60 min with the other. Even though the improvement in marginal adaptation was statistically significant, this improvement was considered clinically irrelevant. It is concluded that polishing of the marginal area should not be done before the hygroscopic expansion of the resin restoration has closed the contraction gap.
Chemical Phenomena↗
Adhesion to dentin by means of Gluma resin.
In its present version, the Gluma system for bonding restorative resin to dentin involves the application of an enamel bonding agent prior to the composite resin. Conceivably, pretreating the dentin with solutions of amino acids, and incorporating camphorquinone and selected methacrylic monomers into the Gluma adhesive would nullify the need for the enamel bonding agent. A bond strength to dentin of 13.4 MPa was obtained in the control experiment. Using a solution of pyruvic acid and glycine as pretreatment, and an optimized adhesive mixture containing glutaraldehyde, HEMA, BIS-GMA, camphorquinone, and water, bond strengths to dentin of 14.5 MPa and to enamel of 23.3 MPa were obtained. Thus, the new Gluma bonding system gave acceptable bond strengths without the prior application of enamel bonding agents.
Adhesiveness↗