Edna L. Pashley

Regional Measurement of Resin-Dentin Bonding as an Array

During the development of the microtensile bond-testing method, large variations in bond strengths were noted among serial sections. The reason for these variations is unknown. The purpose of this work was to determine the consistency of resin-dentin bond strengths across the occlusal surface of coronal dentin by dividing composite resin buildups into an array of 1 x 1 mm beams, the top half consisting of composite resin, and the bottom half consisting of dentin. Extracted human third molars had the occlusal enamel removed as a single section by means of a diamond saw. Resin composite buildups were made after the dentin was bonded with either One-Step or MacBond. After being stored in 37°C water for 1 day, the teeth were vertically sectioned at 1-mm increments into slabs of bonded teeth. Each slab was further subdivided by vertical sections into 1 x 1 x 8 mm beams. Each beam was assigned an x-y coordinate and tested for tensile bond strength. Two different clinicians (A and B) performed the same procedures using One-Step in a parallel study. Using One-Step, clinician A obtained a large number of zero bonds in superficial dentin but fewer in deep dentin. This resulted in a very large standard deviation in bond strengths (mean ± SD of 22 ± 20 MPa in superficial dentin and 27 ± 14 MPa in deep dentin). Clinician B obtained much higher (p < 0.001) and more uniform bond strengths with One-Step (56 ± 13 MPa in superficial dentin and 57 ± 12 MPa in deep dentin). With MacBond, there were no zero bonds and hence less variation, with a mean of 41 ± 13 MPa in superficial dentin and 27 ± 12 MPa (x ± SD) in deep dentin. When pairs of Z100 resin composite cylinders were bonded together with One-Step and then sectioned into an array, there was little variation in regional bond strength (37 ± 1 MPa). Dividing bonded resin composite buildups into an array of 20 to 30 1 x 1 x 8 mm beams allows for the evaluation of uniformity of resin-dentin bonds. The method used in this study detected local regional differences in resin-dentin bond strengths. The largest differences were shown to be related to technique rather than to material. The results indicate that resin-dentin bonds may not be as homogenous as was previously thought.

Effects of HEMA on water evaporation from water-HEMA mixtures.

OBJECTIVES The aims of this research were: (1) to determine the relative rates of evaporation of water and HEMA, and (2) to determine the effects of increasing concentrations of HEMA on the rate of evaporation of water from water and HEMA mixtures. METHODS Ten microliters of each solution (100% H2O, 75% H2O-25% HEMA, 50% H2O-50% HEMA, 25% HEMA, 100% HEMA) were placed on the pan of a thermogravimetric analysis instrument held at 37 degrees C. The rate of spontaneous weight loss was measured as a function of time and relative humidity (RH) and compared statistically using ANOVA and Scheffé F test. RESULTS The rate of evaporation of pure water was 32-fold higher than that of 100% HEMA. Addition of HEMA to water lowered the rate of evaporation of water from the water-HEMA mixtures in a manner that was proportional to its effect on lowering the vapor pressure of water (p < 0.05 comparing 50% HEMA with 75% HEMA). The rate of evaporation of water from water-HEMA mixtures was higher (p < 0.05) when the ambient gas was at 0% RH than when it was at 51% RH. SIGNIFICANCE The results indicate that as water evaporates from water-HEMA mixtures, the concentration of HEMA rises because it is relatively non-volatile. This rise in HEMA concentration lowers the vapor pressure of water making it more difficult to remove the last amounts of water. This residual water may interfere with polymerization of adhesive monomers, thereby lowering the quality of the hybrid layer.

Effects of one versus two applications of an unfilled, all-in-one adhesive on dentine bonding

OBJECTIVES This study examined the null hypothesis that there is no difference between the effect of a one versus two-layer applications of Prompt L-Pop (3M ESPE, Seefeld, Germany) to sound, abraded human coronal dentine. METHODS In group I, the mixed adhesive was applied for 15s, and light-cured for 10s. In group II, after light-curing the first layer, the adhesive was re-applied and light-cured. Specimens bonded with a hybrid composite were sectioned into beams for microtensile bond strength evaluation. Additional teeth from each group were bonded similarly using a lining composite for transmission electron microscopy examination of the resin-dentine interfaces, and nanoleakage evaluation using ammoniacal silver nitrate. RESULTS A significant difference (p<0.001) was detected between microtensile bond strengths in the two groups. Stained, demineralized sections revealed 3-5 microm thick hybrid layers in both groups. An electron-lucent layer between 7 and 20 microm thick was present between the adhesive and the overlying composite. This layer was absent from the interfaces after removal with ethanol before composite placement. The use of a single application in group I resulted in the direct contact of the electron-lucent layer with the dentine surface and tubular orifices. In unstained, undemineralized sections used to evaluate nanoleakage, silver deposits were found mostly in the hybrid layer in group II, but throughout the entire adhesive layer in group I. CONCLUSION Bonding of this unfilled all-in-one adhesive to dentine may be improved by application of a second adhesive layer after light-curing the first layer. This ensures that the exposed dentine surface and dentinal tubules are coated with adhesive that is adequately polymerized.

In vitro study on the dimensional changes of human dentine after demineralization

Dentine rods measuring approximately 0.7 x 0.7 x 5.0 mm were prepared from dentine of extracted human third molars stored in saline containing 0.5% sodium azide at 4 degrees C until used. Forty specimens were demineralized in 10% citric acid plus 3% ferric chloride (w/w) solution for 8 h, then assigned to four groups (A, B, C and D) of 10 specimens each. Groups A and B were used to investigate volumetric changes after air-drying and further immersion in either water, an aqueous solution of 50% 2-hydroxymethylmethacrylate (HEMA) or 100% HEMA, followed by air-drying. Groups C and D were used to investigate the ability of 100% HEMA or 100% ethylene glycol to prevent shrinkage of demineralized dentine during exposure to air. Demineralization caused a small, non-significant (1.9%) reduction in dentine volume. Air-drying further reduced the volume by 65.6%. When demineralized, shrunken specimens were immersed in water for 24 h, they recovered their original demineralized volume. Immersion in 100% HEMA did not re-expand demineralized shrunken dentine. Specimens immersed in 50% HEMA yielded a 50% volume shrinkage when exposed to air for 24 h. Both 100% HEMA and 100% ethylene glycol were effective in preventing shrinkage of demineralized dentine. The technique used provided useful information about maximal dimensional changes that may occur at a microscopic level during adhesive dental restorative procedures.

The effects of dentin permeability on restorative dentistry

The permeability properties of dentin determine its sensitivity and the degree of pulpal response to restorative procedure materials and microleakage. Most pulpal reactions are due to bacteria or bacterial products that permeate across dentin. These reactions can be prevented if dentin is sealed with resins as soon as it is exposed. In the future, restorative dentists may employ topical application of biologic growth factors to permeate across dentin to modify the formation of reactionary or reparative dentin, thereby lowering dentin permeability and protecting the pulp.

Bond strengths to superficial, intermediate and deep dentin in vivo with four dentin bonding systems

The shear bond strength of four dentin bonding systems which remove or modify the smear layer were measured in vivo in dog canine and molar teeth as a function of dentin depth. Dentin bond strengths were higher with cuspid teeth compared to molar teeth. Most bonding systems gave higher bonds to superficial dentin and progressively lower bond strengths deeper dentin. The highest bond strengths were obtained with Clearfil Liner Bond, followed by Superbond C&B, Scotchbond 2 and Tenure. The former two bonding systems achieved shear bond strengths to cuspids that were > 10 MPa regardless of dentin depth while the latter two systems produced bond strengths < 10 MPa. In molars, the same ranking of bonding systems was noted but the value that separated the high from the low bonds was 5 MPa.

Effects of cross-sectional area on resin-enamel tensile bond strength

OBJECTIVE It was hypothesized that there is an inverse relationship between resin-enamel bond strength and bonded cross-sectional area, and that there are regional differences in resin-enamel bond strength. METHODS The facial and lingual surfaces of extracted human third molars were ground down 0.3 mm using 240 grit abrasive paper and were then bonded with either Clearfil Liner Bond 2 or Scotchbond Multi-Purpose Plus adhesive systems using the manufacturers instructions. The bonded surfaces then received a resin composite build-up. After 24 h of storage in water, the bonded teeth were vertically serially sectioned into 1.0 mm thick slabs using a diamond saw, and the bonded surface area at the resin-enamel interface was varied from 0.5 to 3.0 mm2 using a diamond saw under microscopic observation. The trimmed region was varied from the occlusal third of the facial or lingual enamel to the middle third, to the cervical third. The trimmed specimens were then glued to a Bencor Multi-T device, placed in an Instron testing machine and stressed to failure at 1 mm/min. A three-factor ANOVA was used to compare bond strengths (buccal vs. lingual, occlusal vs. middle vs. cervical-third, vs. materials). Regression analysis was used to examine the relationship between bond strength and bonded cross-sectional area for each material on occlusal enamel. RESULTS For both bonding systems, there was a highly significant (p < 0.001) inverse exponential relationship between tensile bond strength (y axis) and bonded cross-sectional area (x axis) with y intercepts of 51 and 59 MPa for Clearfill Liner Bond 2 and Multi-Purpose Plus, respectively. Using both materials, the highest bond strengths were measured in the occlusal third, which were significantly higher (p < 0.05) than those made to cervical enamel. SIGNIFICANCE Like resin-dentin bonds, resin-enamel bonds exhibit an inverse relationship with cross-sectional area. This relationship becomes more apparent at bonded surface areas below 2 mm2 and is probably due to reductions in the number of interfacial stress-raisers as samples are made smaller.

Comparison of in vivo vs. in vitro Bonding of Composite Resin to the Dentin of Canine Teeth

Dogs were utilized in a study to compare the bond strengths of dentin bonding agents made to dentin in vivo and then again in vitro in the same teeth 30 min, one day, one week, and one month post-extraction. No statistically significant differences were observed between bonds made in vivo and those made in vitro at any time period. Contamination of the dentin surfaces with blood or saliva lowered the bond strengths, but these could be restored to control values by re-surfacing of the dentin with a bur.

In-vivo fluid movement across dentine in the dog

Abstract Conical chambers were cemented to dentine and connected via micropipettes to a pressure bottle to permit measurement of the rate of fluid movement across dentine under positive or negative hydrostatic pressures. Connecting the chamber to a pressure transducer permitted measurement of intra-pulpal tissue pressure through intact dentine, which averaged 24 mm Hg. Knowledge of the intra- and extra-pulpal pressures employed permitted calculation of the in-vivo hydraulic conductance of dog dentine. This was 1.35 × 10 −2 and 4.51 × 10 −3 μl cm −2 min −1 cm H 2 O −1 for molar and canine teeth respectively.

The sealing properties of temporary filling materials

R ecent articles suggest that many of the reported pulpal reactions to restorative materials may have been the result of microleakage of bacterial products around the restorations instead of the direct effect of the materials.‘-’ In such studies negative controls usually included cavities restored with zinc oxide-eugenol (ZOE) because it demonstrated little microleakage.6s7 However, Browne and Tobias,” in a review of the literature, suggested that the modest pulpal response reported beneath ZOE restorations may be the result of the antimicrobial properties of ZOE instead of its superior sealing qualities. Thus the sealing properties of ZOE and other temporary fillings warrant careful evaluation if investigators wish to use appropriate negative controls, namely, materials that seal perfectly. This study quantitatively evaluated the sealing properties of regular and reinforced ZOE, gutta-percha (GP), Cavit-G, (Premier Dental Products Co., Norristown, Pa.) and polycarboxylate cement placed in class I cavities prepared in extracted human third molars, by using the fluid filtration method described by Derkson et al.9 The results demonstrate the importance of the materials and their powder-to-liquid ratios in achieving a good seal between the filling materials and the cavity wall.