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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
PubMed1995

Ceramic inlay movement during polymerization of resin luting cements.

In cavities with no support for inlays, polymerization contraction of the resin cement may move the ceramic inlay axially. The purpose of this study was to determine the velocity and extent of such movement. Cylindrical ceramic inlays were placed in dentin cavities filled with one of four commercially available resin composite cements. An initial standardized 200-microns-thick cement film was created. The movement of the ceramic inlay during polymerization of one of the resin cements was measured by a dial gauge. The velocity of the inlay movement decreased exponentially with time and with a velocity constant of 0.09 min-1. The majority of the movement occurred within the first 12 min after photopolymerization and probably continued for several days, reaching an estimated value of 5.8 microns. After 1-2 d of water storage, 1-2-microns contraction gaps at the cavity floors were observed microscopically for every cement used. It is concluded that in cavities without support for the inlay, about 2/3 of the resin cement contraction results in movement of the inlay and about 1/3 results in formation of gaps at the cavity floors.

Analysis of Variance↗
PubMed1995

Interfacial gaps of resin cemented ceramic inlays.

A method was developed for measuring presence, location and extent of interfacial contraction gaps of resin-cemented ceramic inlays in dentin cavities. Cylindrical ceramic inlays were cemented using one of 12 commercially available resin composite cements to make a film thickness of 200-microns. Cross-sections revealed absence of marginal gaps but contraction gaps occurred at all dentin-cement interfaces at the cavity floors and ranged from 1.6 to 7.1 microns. This was equivalent to 0.8-3.5% of the cement film thickness and was 3-10 times greater than the wall-to-wall contraction in percent observed when resin composites are used as filling materials in 3-5 mm butt-joint dentin cavities. The results support the theory that contraction gaps developing adjacent to thin films of resin cements reach a size equivalent to the cement film thickness multiplied by the volumetric polymerization shrinkage of the cement.

Adhesiveness↗
PubMed1995

Adherence of chewing gum to dental restorative materials.

PURPOSE: To describe a method whereby chewing gum tackiness can be measured. MATERIALS AND METHODS: The chewing gum used for the experiment was V6 (Freshmint). Paladur denture base material, Silux Plus, P-50 and Heliomolar resin composites and Luxalloy amalgam were used. Squared specimens (15 x 15 x 2 mm) composed of the polymerized materials tested or set amalgam were made with a mold. As gold specimen, a gold-plated brass specimen was used, having the same dimension as specified above. A tooth enamel specimen (5 x 5 mm) was made out of flat ground human enamel from an incisor. All specimens were stored for more than 7 days in water before use, and wet ground on paper No 320 immediately before testing. The adhesion was measured by a balance equipped with a recorder and a bottom attachment, to which a chain was mounted. The end of the chain was attached to a quadratic brass plate, to which one of the above described specimen was glued by cyanoacrylate. Another brass plate, with an attached specimen of the same material, was mounted in a small vise in such way that the two specimens were parallel with and facing each other. A motor drive enabled parallel removal of the two plates from each other. The gum was chewed approximately 1 second between bites and for various periods of time. It was then pressed between the two parallel squares (mentioned above) of restorative materials or enamel, reaching a final distance of 1 mm between the plates and occupying the entire space between the plates. The study was carried out at 36 degrees C, and the two plates were wetted with fresh saliva or water immediately before placement of the chewing gum. Excess liquid was removed after the wetting, leaving a thin film. The maximal force during parallel removal of the two plates from each other was recorded. The measurements were performed eight times in each group, and the mean adhesion per surface area and SD was expressed as mN/mm(2). The measurements were repeated for some of the groups. The significance of differences between each group was tested by Newman-Keul's Multiple Range Test at a 5% level of significance. RESULTS: Adherence of chewing gum to dental restorative materials and enamel was found to decrease as follows: denture base material > resin composites = silver amalgam > gold > human enamel. The adhesion was dependent on gum base and not on the sweetening additives and reached a maximum after about 2 minutes' chewing.

Adhesiveness↗
PubMed1993

Periodontal tissue regeneration including cementogenesis adjacent to dentin-bonded retrograde composite fillings in humans.

The roots of two incisors were treated by apicoectomy and a retrograde dentin-bonded composite filling. Periapical healing was observed a few months later by radiography. Later, due to root fracture and marginal bone resorption, the apical parts were removed including adjacent periapical bone. A histological and scanning electron microscopic examination of the tissue showed reformation of periodontium adjacent to the composite, including reformation of a lamina dura, inserting Sharpey's fibers and cementum deposited in intimate contact with the composite. This finding is in agreement with previous observations of tissue surrounding retrograde dentin-bonded composite fillings placed in monkeys, indicating that tissue regeneration including cementogenesis may occur on composite material and consequently form a biological closure of the root canal.

Adult↗
PubMed1993

Bonding of enamel-dentin crown fragments after crown fracture. An experimental study using bonding agents.

Previous experimental studies into the use of dentin bonding agents for reattachment of enamel-dentin crown fragments have demonstrated fracture strength about 50-60% of that of intact teeth. In the clinic this has been reflected in the frequent need of repeated bonding of the treated incisors due to refracture. Recently newer bonding agents have been developed which can bond equally well with enamel and dentin. Employing the same experimental model, these bonding agents (All-Bond 2, Scotchbond MP) were used to reattach crown fragments to the remaining portion of sheep incisors. Loading of teeth bonded with these agents in an Instron testing machine at a speed of 1 mm/min demonstrated similar fracture strengths as those previously achieved with Gluma, Scotchbond 2 or Tenure. A second study was carried out whereby fragments were bonded with Scotchbond MP and loaded at various speeds. The results demonstrated that the fracture strength decreased exponentially with increased loading speed. By extrapolation, it was concluded that the strength was nil at a loading speed of approximately 2 m/min. It was concluded that the weak link in the bond between tooth fragment and remaining tooth structure is the bonding resin. Theoretically, a resin which is slightly elastic might act as a shock absorber to withstand functional stress. However, studies carried out with resins of varying moduli of elasticity gave disappointing results probably due to their low flexural strength.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1993

Dentin bonding agents and composite retrograde root filling.

The purpose of this in vitro study was to evaluate the applicability of five different commercial dentin bonding agents to the composite retrograde root filling technique. The evaluation was performed by bond strength measurements and by the tendency of retrograde composite fillings to develop gaps during exposure to thermal stress. Bond strength was measured in shear and the interface between retrograde filling and dentin was examined microscopically. In adaptation tests the apical cavity design was performed as a slightly concave dissection of the root area. Gaps were found between retrograde filling and resected root as a consequence of thermocycling when using Scotchbond 2, Prisma Universal Bond 3 and XR-Bonding System, while Tenure Solution and Gluma maintained gap-free interfaces in all test specimens. A directly proportional relationship was found between the percentage of thermocycled specimens exhibiting no gaps and the mean bond strength. Based upon these results, it is advisable to apply the dentin bonding systems Tenure Solution or Gluma for retrograde composite root filling.

Analysis of Variance↗
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↗