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Biomedical subjects

E C Munksgaard

Publications and source records attributed to E C Munksgaard.

At least 19 recordsLinked to original sources
PubMed1992

Permeability of protective gloves to (di)methacrylates in resinous dental materials.

Dentists may develop contact allergy induced by handling resinous dental materials, and vinyl and latex gloves may provide protection against the monomers of these materials only during the time it takes for a monomer to permeate the glove. The passage times and rates of penetration of four commonly used (di)methacrylates--HEMA, TEGDMA, BISGMA, and UEDMA--for 11 protective gloves were measured. The passage time for HEMA and TEGDMA through vinyl gloves was 1-3 min, and around 20 min for BISGMA and UEDMA. The rate of penetration of HEMA and TEGDMA in vinyl gloves was 0.5-4.5 mumol.min-1.cm-2. The passage time of HEMA and TEGDMA through most of the latex or the modified latex gloves was 5-8 min and the rate of penetration 0.5-3.1 mumol.min-1.cm-2. Latex or modified latex gloves provide a protection against BISGMA and UEDMA for 80 min or more with one exception (Elastyrene), which burst after about 50 min in contact with the resins. Of the tested gloves Ansell, Neutralon, Mediglove, and Biogel D provide protection against HEMA and TEGDMA for at least 5 min.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1992

Treatment of crown fractured incisors with laminate veneer restorations. An experimental study.

A method is described by which crown fractured incisors are restored with cast ceramic (Dicor) laminate veneers after initial treatment with either reattachment of the original crown fragment with a dentin bonding agent, with a composite resin build-up or no treatment (i.e. the veneer alone is used to restore the incisal edge). In order to elucidate the effect of the fragment/composite-tooth bonding interface on fracture strength of the restored teeth, the fracture strengths of the various treatment groups were compared to that of intact teeth supplied with Dicor laminate veneers. In an experimental investigation using central and lateral incisors from sheep, it was found that fracture strength (16.6 +/- 4.2 MPa) equal to that of intact incisors (16.1 +/- 2.6 MPa) could be achieved using laminate veneers made of porcelain on fractured teeth whose crown fragments were reattached using a dentin bonding agent (5). In the present investigation, using the same experimental model but using cast ceramic (Dicor) laminate veneers, the fracture strength of the restored incisors was significantly increased (21.0 +/- 3.7 MPa), exceeding that of intact teeth. The fracture strength of intact teeth was also exceeded in veneered incisors which were initially restored with a conventional composite resin build-up (20.2 +/- 5.6 MPa). However, the greatest fracture strength (28.2 +/- 8.9 MPa) was achieved when a Dicor laminate veneer alone was used to restore the fractured incisal edge.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Change in surface hardness of BisGMA/TEGDMA polymer due to enzymatic action.

The surface microhardness of specimens made of a BisGMA/TEGDMA polymer was measured before and during treatment for 60 days with phosphate buffer or phosphate-buffered esterase solution with an activity corresponding to the mean hydrolase activity of human saliva. The hardness of the buffer-treated specimens was unchanged during the incubation period, while that of the esterase-treated specimens decreased gradually. After about five days of treatment, no further change in hardness was observed for up to 60 days. Based on the difference in the calculated hardness of the specimens as a function of the applied load during measurement, it was estimated that the mean microhardness of the outermost surface layer of the esterase-treated specimens was diminished by about 15%, compared with that of the buffer-treated specimens. From these results, it was concluded that the wear resistance of a BisGMA/TEGDMA polymer is most likely diminished by hydrolases in saliva.

Analysis of Variance↗
PubMed1992

Toxicology versus allergy in restorative dentistry.

The frequency of side-effects among dental patients is very low and is seen mostly as mild allergic reactions. Among the dental staff, contact allergic eczema is occasionally seen, induced by certain metals and various organic materials.

Dental Alloys↗
PubMed1992

[Permeability of protective gloves to (di)methacrylates in resinous dental materials].

Dentists may develop contact allergy induced by handling resinous dental materials. Vinyl and latex gloves may provide protection against the monomers of these materials during the time it takes for a monomer to permeate the glove. The passage times and rates of penetration of four commonly used (di)methacrylates, HEMA, TEGDMA, BISGMA and UEDMA for 11 protective gloves were measured. The passage time in vinyl gloves for HEMA and TEGDMA was about 2 min, and around 20 min for BISGMA and UEDMA. The rates of penetration of HEMA and TEGDMA in vinyl gloves were between 1 and 4 mumol.min-1.cm-2. The passage times of HEMA and TEGDMA through most of the latex and modified latex gloves were between 5 and 8 min and the rates of penetration between 0.5 and 1 mumol.min-1.cm-2. Latex and modified latex gloves provide protection against BISGMA and UEDMA in 80 min or more with one exception (Elastyrene), which burst after about 50 min in contact with the resins. Of the tested gloves Ansell, Neutralon, Mediglove and Biogel D provide protection against HEMA and TEGDMA for at least 5 min.

Composite Resins↗
PubMed1991

Effect of human saliva on surface degradation of composite resins.

The amount of methacrylic acid produced by incubation of the dimethacrylate ester TEGDMA in human whole saliva was measured. The conversion rate of TEGDMA was determined in stimulated saliva from dental students and in unstimulated saliva from both dental students and patients. The differences in mean conversion rate measured in the three groups were not statistically significant (P = 0.346). The mean conversion rate +/- SD for all saliva samples was 4.54 +/- 3.24 mumol MAA/L.h. The surface of BISGMA/TEGDMA-polymer specimens treated with porcine liver esterase in activities equivalent to those found in human saliva exhibited a lower Wallace microhardness than the surface of untreated specimens. Polymer specimens incubated in human saliva exhibited a similar reduction in the microhardness. The results demonstrated that enzymes in human saliva are capable of softening the surface of dimethacrylate polymers presumably by inducing a hydrolysis of methacrylate ester bonds. The mechanical removal of a surface layer softened by hydrolases will expose a new surface layer to enzymatic attack. The enzymatic softening may thus contribute to the in vivo wear of composite restorations.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1991

Enamel-dentin crown fractures bonded with various bonding agents.

A method is described, by which the fracture strength of bonded, previously fractured incisors can be measured. The study employed incisors from sheep, which could be obtained in suitable numbers and with limited variation in size. The incisors were fractured parallel to the incisal edge. The mean fracture area +/- SD of central incisors was 8.45 +/- 0.89 mm2 and of lateral incisors 6.50 +/- 0.64 mm2. The enamel area constituted about 30% of the total fracture area. Acid etching of the enamel and bonding of the fractures with an unfilled resin yielded a fracture strength, which was approximately 38% of the fracture strength of fractured teeth restored with acid etching of enamel, Gluma treatment of dentin and bonding with the unfilled resin. Teeth restored in this way, but using the dentin bonding agent Tenure or Scotchbond2 instead of Gluma, exhibited mean fracture strengths which were not significantly different from that obtained when Gluma was employed as the bonding agent. The mean fracture strength by using one of the three bonding agents in combination with acid etching of enamel was about 8 MPa, which is approximately 50% of the fracture strength of intact teeth.

Acid Etching, Dental↗
PubMed1991

Reinforcement of bonded crown fractured incisors with porcelain veneers.

A method is described by which porcelain laminate veneers are used to reinforce crown-fractured incisors which have been restored by reattachment of enamel-dentin fragments using enamel etching and a dentin bonding system. In an experimental model using sheep incisors, it was found that fracture strength equal to that of intact incisors could be achieved by employing this method. This is in contrast to fracture strengths of reattached enamel-dentin tooth fragments without porcelain laminates which were only 50% of intact incisors. It is suggested that porcelain laminate veneers may be used to supplement fragment bonding, thereby enhancing dental esthetics and function.

Acid Etching, Dental↗
PubMed1991

Retrograde root filling with composite and a dentin-bonding agent. 1.

A method is described, by which retrograde root filling with a composite resin can be performed. The cavity design is a slightly concave dissection of the apical part of the root, which is treated with the bonding agent Gluma followed by an application of Retroplast. Retroplast is a chemically curable composite containing silver for radiopacity and aerosil to obtain a suitable consistency. Endodontically treated teeth with a eugenol-containing root canal sealer did not affect the strength of the bond between Retroplast and apical dentin. A tight seal between the composite and the cavity surface was observed by light and SEM microscopy, and histology of tissue surrounding fillings placed in monkeys revealed absence of inflammatory cells around the filling and a close contact between filling and fibroblasts with collagenous fibers. In some cases, cementum and Sharpey's fibers formed in contact with the filling. Fillings placed in humans performed successfully in most cases, and the main causes of failure were either inadequate hemostasis during filling, or root fracture unnoticed by the time of filling. The retrograde technique promises a new treatment principle, with a root canal effectively sealed and the periapical ligament restored after apicoectomy.

Adolescent↗
PubMed1991

Retrograde root filling with composite and a dentin-bonding agent. 2.

Investigations on retrograde root filling using a composite resin, Retroplast, bonded to the root surface with the dentin-bonding agent Gluma have been described. Here, detailed information is given about the surgical procedures. The aim was to obtain a thin retrograde composite filling on the root apex, made slightly concave, sealing the main root canal, accessory canals as well as dentinal tubules. Hemostasis was obtained primarily by applying 1% adrenaline and by using a needle suction tip, and care was taken not to damage the surrounding tissues by the various chemicals. The healing results, after up to 1 year, of 388 cases of various tooth types, treated with either retrograde composite or with amalgam were compared. The healing classification included four categories: 1) complete healing; 2) fibrous healing; 3) uncertain; and 4) failures. In the composite group, the healing rates were as follows: 74% showed complete healing, 4% fibrous healing, 15% uncertain, and 7% were failures. In the amalgam group, 59% showed complete healing, 3% fibrous healing, 30% uncertain, and 8% were failures. Complete healing occurred significantly more often after filling with Retroplast than after filling with amalgam (p less than 0.00005). Significantly fewer cases with complete healing occurred in lower front teeth in proportion to other tooth types. The number of immediate postoperative complications did not differ significantly between the composite and the amalgam groups.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1991

[Bonding of crown fragments with dentin bonding agents and porcelain veneers].

Measurements of fracture strengths of incisors from sheep, previously fractured and then restored by reattaching the fragments with a light-curable resin, revealed that pretreatment of the fracture surfaces with dentin bonding agents such as Gluma, Tenure or Scotchbond2 and acid-etching of the enamel, gave values of about half the fracture strength of intact teeth. Measurements furthermore demonstrated that pretreatment by a combination of dentin bonding agents and acid-etching of the enamel yielded higher fracture strengths of the restored teeth, than that of teeth restored using only one of the two pretreatments. Fractured incisors, restored by Gluma-treatment of the dentin, acid-etching of the enamel and fragment-bonding with a light-curable resin, were further restored with porcelain veneers after preparation. Fracture strength measurements of such restored teeth revealed strength not significantly different from that of intact teeth. It is suggested that such restorations, could have a reasonably long period of function clinically.

Acid Etching, Dental↗
PubMed1990

Enzymatic hydrolysis of (di)methacrylates and their polymers.

Di- and monomethacrylates hydrolyze to methacrylic acid and the alcohol part at neutral pH catalyzed by an unspecific esterase (hydrolase) and by enzymes in saliva. The rate constants of the enzymatic hydrolysis of various (di)methacrylates increase in the following order: HPMA less than BISGMA less than LAMA less than DECMA less than TEGDMA less than UEDMA less than DEGDMA. Esterase added to aqueous slurries of various powders made of polymerized BISGMA/TEGDMA-mixtures gave rise to liberation of methacrylic acid, presumably deriving from degradation of those of the dimethacrylates only bonded in the matrix by one end of the molecule. It was estimated that a TEGDMA-polymer will be hydrolyzed faster than a BISGMA-polymer. It is proposed that hydrolases in saliva increase the wear rate of composite resin fillings.

Acrylates↗
PubMed1990

Enzymatic degradation of BISGMA/TEGDMA-polymers causing decreased microhardness and greater wear in vitro.

The microhardness of the surfaces of BISGMA/TEGDMA-polymers decreased after treatment with pork liver esterase for 48 h in concentrations greater than or equal to 0.05 U/ml. This softening effect on BISGMA/TEGDMA-polymer surfaces was also shown as an increased wear rate of the polymers in the presence of esterase measured by a laboratory abrasion method. In this method, polymer cylinders were vigorously shaken in an aqueous slurry containing abrasive particles. The shaking was performed for 3 s followed by a rest period of either 100 or 200 s. This was repeated for 24 h. A greater mean loss of weight of the cylinders was measured when esterase was present in the slurry and the loss of weight increased significantly from 6.7% to 23.8% (P less than 0.001) when the rest period was increased from 100 s to 200 s. The results indicate that enzymatic hydrolytic activity in the mouth will contribute to a breakdown of composite resin fillings.

Acrylates↗
PubMed1990

Amine-induced polymerization of aqueous HEMA/aldehyde during action as a dentin bonding agent.

Aqueous mixtures of HEMA with glutaraldehyde or propionaldehyde polymerize by addition of catalytic amounts of amines or amino acids. The maximal reaction velocity of the transformation of HEMA/glutaraldehyde with glycine was obtained at pH 0.8. Kinetic data suggested a second-order reaction between glutaraldehyde and glycine, and solubility data suggested formation of a cross-linked polymer. A relatively high bond strength between dentin and resin composite was obtained by pre-treatment of dentin with Gluma (35% HEMA, 5% glutaraldehyde in water) adjusted to pH 1.0 with hydrochloric acid. It is proposed that on application of Gluma, amino-group-containing substances in dentin react with glutaraldehyde and start the formation of a HEMA polymer. This product may be cross-linked by an alpha,beta-unsaturated glutaraldehyde aldol condensation product and may bond to dentin by aldehyde fixation to dentin proteins. Resin composite will bond to this product by copolymerization.

Acrylates↗
PubMed1990

[Contact dermatitis, due to (di)methacrylates, on the hands of dental personnel].

Eight dentists and one dental assistant have developed allergic contact dermatitis caused by exposure to (di)methacrylates, especially those found in resins, in dentin bonding agents, in rebasement and in prosthetic materials. The eczema is characterized by its location on the first, second and third finger of the left hand showing redness, desquamation, fissuring and excoriations. Patch testing with various test substances revealed positive reactions towards EGDMA in eight cases. It is suggested that this reaction was a cross-reaction and that the sensibilization was caused by MMA, TEGDMA, HEMA and/or BUDMA. One of the eight dentists had to give up practising.

Acrylates↗
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↗