Biomedical subjects
Publications and source records attributed to E C Munksgaard.
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.
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.
Gluma-treated dentin was covered with various resins before a microfilled composite was applied. The strength of the bond between dentin and composite established by this procedure was measured in shear and tensile tests. The effectiveness of the bonding was further tested by the width of the marginal contraction gap around fillings made in dentin by the above procedure. Resins containing propanal promoted shear bond strength of about 15 MPa. The tensile bond strength exceeded 22 MPa by one of the resins, but could not be measured because of frequent rupture in the composite. Between 30 and 70% of the fillings were without contraction gaps when propanal or p-toluenesulfinate-containing resins were used. It is proposed that oxygen inhibition of the polymerization on the dentin surface suppresses the bonding. Resins containing reducing agents may reduce oxygen inhibition and increase bonding by the adhesive.
Effective bonding between restorative resins and hard dental tissues would eliminate the need for retentive undercuts and prevent the formation of marginal gaps. While bonding to enamel has found a satisfactory solution with the advent of the acid etch technique, bonding to dentine has been more elusive. Restorative resins may bond to dentine through mechanisms involving either the inorganic or the organic constituents of the dentine. In the present work the possibility of bonding to the organic part of dentine was investigated. Since the water present in the surface of moist dentine may impede bonding, the research was focused on adhesives that are operational in aqueous environments. Aqueous mixtures of aldehydes and certain active monomers constitute such adhesives. The strength of the bond between a restorative resin and dentine was measured using the mixtures as intermediaries. To remove the smear layer the dentine was pretreated with 0.5 M EDTA, pH = 7.4. Among the aliphatic aldehydes especially propionic aldehyde and glutaraldehyde were found to be effective. Aromatic aldehydes resulted in bonds of low strength. Among the monomers investigated HEMA (hydroxyethyl-methacrylate) gave rise to the bond of highest strength. Using an adhesive based on HEMA and propionic aldehyde or HEMA and glutaraldehyde bond strengths of 15 and 18 MN/m2, respectively, were obtained. The latter adhesive significantly reduced the width of the polymerization contraction gaps between resin and dentine.
The bonding of restorative resins to dentin by means of formaldehyde used in conjunction with an OH-containing monomer as intermediary was investigated. In this way a bonding to the organic constituent of dentin is conceivable. Mean bond strengths of 0.6 kg/mm2 were obtained. Bond strengths of this order of size may be of clinical interest.
Cylindric dentin cavities ranging from 2 to 6 mm in diameter were treated with different dentin adhesives: Clearfil, Gluma, NPG-GMA + PMDM, Scotchbond or Superbond before filling with Silux. The maximal contraction gap was measured 10 min after curing and compared with results from cavities where an adhesive was omitted. The effectiveness in reducing contraction gaps increased in the following order: Clearfil, Scotchbond, NPG-GMA + PMDM, Superbond and Gluma.
We investigated the bond strength between restorative resin and dentin pre-treated with mixtures of HEMA and glutaraldehyde. It is suggested that the mixture acts by forming a chemical bond of HEMA molecules to a collagen-glutaraldehyde reaction complex. Subsequently applied resin will then co-polymerize with the collagen-linked methacrylate groups. Statistical analysis of the results from varying mixtures of HEMA and glutaraldehyde revealed that the bond strength was highly dependent on the HEMA concentration, with a maximum at 35%, and nearly independent of the glutaraldehyde concentration when greater than 3%. The highest mean bond strength was about 1.8 kg/mm2, and bond strength of this order of size may be attractive for clinical use.
The bonding of restorative resins to dentin by means of an intermediary monomer containing a carboxylic acid chloride or an isocyanate group was investigated. Such intermediary monomers are supposed to react with the organic constituent of dentin. Bond strengths were enhanced by the use of the intermediary monomers, resulting in mean bond strengths of 0.13 kg/mm 2. Bond strengths of this order of size are probably too low to be of clinical interest.
Collagen synthesis in serially propagated cultures of rat mucosal keratinocytes (line RTK-I) was investigated. Analysis of biosynthetically labeled cell and media proteins retrieved after limited pepsin digestion revealed seven or eight collagen chains originating from four distinct collagens (types I, III, IV, V). Type III collagen was identified as the predominant species based on its electrophoretic and chromatographic behavior in the reduced and unreduced states, on the peptide pattern generated by limited cleavage with CNBr and with trypsin, and on the immunofluorescent detection of intracellular, collagen type III-reactive material. Evidence for the synthesis of two type IV collagen chains (155 k and 160 k after limited pepsin digestion) was provided by immunofluorescent and electrophoretic studies. Type V collagen was revealed by immunofluorescence, and two, possibly three, component chains were resolved in native type V collagen isolated from the harvest medium. Type I collagen, identified by comigration with authentic carriers, was a constant but quantitatively variable synthetic product. This study provides evidence that keratinocytes produce collagens normally found in mesenchymal matrices (type I and III) in addition to collagens characteristic of basement membranes (type IV) and of pericellular structures (type V). These findings reveal a hitherto unrecognized complexity and heterogeneity of the collagens synthesized by a highly differentiated epithelial cell type.
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One of the most abundant noncollagenous proteins of dentin is a phosphoprotein rich in aspartic acid and phosphoserine. This protein occurs in soluble and inextractable forms, the latter being associated with the insoluble collagenous matrix. This protein is capable of tightly binding a relatively high level of calcium. Biosynthetic and radioautographic data suggest that shortly after its biosynthesis, the phosphoprotein is transported and bound to the collagen at the predentin-dentin junction. This event is probably central to the mineralization process, though other glycoproteins may be involved.
The collagen synthesized by cultured odontoblasts related to dentin, was identified as type I and as type I trimer in nearly equal amounts. Analysis of in vivo synthesized collagen extracted from unerupted bovine teeth confirmed that type I trimer is a constituent of dentin, but presumably in small amount compared to type I collagen.
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Phosphorprotein extracted from rat incisors was purified by passage through a sulfonated polystyrene column. The phosphoprotein that emerged in the void volume contained 54% phosphoserine + serine and 36% aspartic acid and, in contrast to that obtained by DEAE-cellulose chromatography, was devoid of proline, valine, isoleucine, leucine, tyrosine, phenylalanine and arginine. Gel electrophoresis of the material purified on sulfonated polystyrene columns gave one major phosphate-containing band which would not stain with Coomassie Blue. EDTA or acetic acid demineralization yielded phosphoprotein preparations with identical compositions and electrophoretic properties. These data show that purification procedures reported earlier are insufficient.
The phosphoprotein of continually erupting rabbit incisors was extracted from decalcified teeth and purified by gel filtration and ion-exchange chromatography. Chemical characterization revealed that its composition was very similar to that of rat incisor and bovine molar phosphoproteins. The presence of similar acidic proteins in the dentin of various mammals is consistent with the suggestion that they are involved in the mineralization process.
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