Search PubMed⌕ Search

Biomedical subjects

E K Hansen

Publications and source records attributed to E K Hansen.

At least 37 records · Page 2Linked to original sources
PubMed1990

In vivo fractures of endodontically treated posterior teeth restored with amalgam.

The cumulative survival rate (retention of both cusps) and the fracture pattern of 1639 endodontically treated posterior teeth were assessed in a retrospective study. All teeth had an MO/DO or an MOD cavity restored with amalgam without cuspal overlays. The 20-year survival rate of teeth with an MO/DO cavity was markedly higher than that of teeth with an MOD cavity. The lowest survival rate was found for the upper premolars with an MOD cavity: 28% of these teeth fractured within 3 years after endodontic therapy, 57% were lost after 10 years, and 73% after 20 years. Generally, the cusp most prone to fracture was the lingual one, and lingual fractures caused significantly more damage to the periodontal tissues than did facial or total crown fractures. The severity of periodontal damage increased with posterior location of the tooth. By far the most serious failures, irrespective of the cavity type, were found for the upper second molar, as 10 of 29 fractures led to extraction. It is concluded that amalgam, especially in MOD cavities, is an unacceptable material for restoration of endodontically treated posterior teeth if used without cuspal overlays.

Analysis of Variance↗
PubMed1990

In vivo fractures of endodontically treated posterior teeth restored with enamel-bonded resin.

The cumulative survival rate of 190 endodontically treated posterior teeth were assessed in a retrospective study; all teeth had an MO/DO or an MOD cavity restored with a composite resin without cuspal overlays after previous acid-etching of the enamel. In contrast to our previous study on endontically treated posterior teeth restored with amalgam, the survival rate of the MOD resin-restored teeth was equal to that of MO/DO teeth. Teeth restored with a light-activated resin had a much lower survival rate than teeth restored with a chemically-activated material, the cause presumably being that the light-activated resins were insufficiently irradiated. Nearly 25% of the teeth had been restored with a microfilled resin for anterior use and these teeth had a lower survival rate than had teeth restored with a macrofilled or hybrid resin. It was also found that a beveling technique did not decrease the fracture rate while the use of an intermediate layer of low-viscosity resin resulted in a significant improvement.

Bicuspid↗
PubMed1989

Saliva contamination vs. efficacy of dentin-bonding agents.

The efficacy of two dentin-bonding agents (Gluma and Scotchbond Dual Cure) was investigated in vitro with or without saliva contamination of the dentin before or after application of the adhesive. The efficacy of the bonding agents was evaluated by a shear-bond strength test and a cavity test. When the dentin surface was contaminated, either before or after application of one of the bonding agents, the shear bond strength was reduced, but the difference between contaminated and non-contaminated specimens was not statistically significant. In the cavity test, the width and the extent of the marginal contraction gap were markedly increased when the dentin was contaminated with saliva before the bonding agent was applied. If the contamination happened after application of the adhesive, the efficacy of Gluma was further reduced, while that of Scotchbond was significantly improved. (This phenomenon has been investigated in detail in an accompanying paper.) The clinical consequence of saliva contamination seems to be that when Gluma is used as dentin-bonding agent, the contaminated area must be removed operatively, and then each of the various bonding procedures must be repeated.

Dental Bonding↗
PubMed1989

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↗
PubMed1989

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↗
PubMed1989

Three-year study of cervical erosions restored with resin and dentin-bonding agent.

Cervical erosions without undercuts and traditional cavity preparation were restored with a light-activated microfilled resin in combination with two different dentin-bonding agents, Gluma and the chemically activated version of Scotchbond. In the Gluma group the final polishing was postponed for at least 1 day; in the Scotchbond group polishing was performed 5 to 15 min after polymerization. The results of the two clinical tests are therefore not comparable. Under these experimental conditions the cumulative 3-year survival rate for the fillings in the two groups were 96% (Gluma) and 66% (Scotchbond). It is concluded that cervical erosions should be restored without undercuts or traditional cavity preparation on the condition that the enamel is acid-etched, polishing of the gingival area is postponed, and an effective dentin-bonding agent is used.

Acid Etching, Dental↗
PubMed1989

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↗
PubMed1988

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↗
PubMed1987

Effect of Gluma in acid-etched dentin cavities.

The marginal adaptation of a restorative resin in combination with a dentin bonding agent was investigated in dentin cavities treated either with a strong solution of phosphoric acid or with an 0.5 M EDTA solution neutralized to pH 7.4 with NaOH. It was found that both the maximum marginal contraction gap and the extent of the gap were significantly increased in acid-etched cavities when compared to cavities cleaned with the EDTA solution.

Acid Etching, Dental↗
PubMed1987

Influence of temporary filling materials on effect of dentin-bonding agents.

Dentin cavities, prepared in extracted human teeth, were filled with a dry mixture of zinc oxide-eugenol (ZOE) or a commercial temporary filling cement without eugenol (Cavit). The ZOE was removed 3 h later while the Cavit was removed after 7 days. The cavity wall and the surrounding dentin were then treated with a dentin-bonding agent before application of a restorative resin. The width and the extent of the marginal contraction gap were measured, using a light microscope, approximately 0.1 mm below the original free surface of the filling. It was found that the contraction gap was markedly increased in cavities previously filled with ZOE while the non-eugenol cement had no influence on the effect of the two dentin-bonding agents tested. The short-term test applied in the present study indicates that ZOE should not be used in cavities later to be restored with dentin-bonding agent and resin.

Adhesives↗
PubMed1987

Wall-to-wall polymerization contraction of composite resins versus filler content.

Various amounts of microfiller, condensed microfiller, prepolymer plus microfiller, or macrofiller were added to an unfilled light-curable resin. The marginal adaptation of these experimental resin/filler mixtures was studied by measuring the wall-to-wall polymerization contraction (wtw-contraction) in dentin cavities in vitro. The investigation showed that increasing amounts of microfiller did not affect the wtw-contraction. However, mixtures made by the three other fillers showed a decreasing wtw-contraction with increasing filler concentration.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1987

Influence of irradiation time on effect of a light-activated dentin-bonding agent.

The marginal adaptation to dentin cavities of a microfilled restorative resin was measured with and without previous use of a light-activated dentin-bonding agent. The investigation was carried out on butt-joint cavities prepared in extracted human teeth. Increasing the irradiation time of the bonding agent from 10 to 80 sec reduced significantly both the width and the extent of the marginal contraction gap.

Adhesives↗