Patricia N.R. Pereira

Long-term Durability of Dentin Bonds Made with a Self-etching Primer, in vivo

The long-term durability of bonds between adhesive resins and dentin is of significant importance for the longevity of bonded restorations. We carried out an in vivo one-year study to evaluate the durability of resin-dentin bonds in the oral cavity, as well as to test the hypothesis that the adhesive interface would show morphological changes in vivo over time. Very shallow saucer-shaped dentin cavities were prepared in 12 intact teeth of one Japanese monkey (Macaca fuscata) under general anesthesia. The cavities were restored with Clearfil Liner Bond II and Clearfil Photo Posterior resin composite. The teeth were extracted at three different times: immediately, and 180 and 360 days after placement of the restorations. One day after the monkey was killed, specimens of the three time periods were subjected to the micro-tensile bond test at a crosshead speed of 1 mm/min. The surfaces of the failed bonds were observed under a field emission scanning electron microscope (FE-SEM). Bond strength measurements in this study were successfully performed and were stable at approximately 19 MPa during the one-year testing. Scanning electron microscopic observations of the failed surfaces revealed, at the top of the hybrid layer and within the adhesive resin, porosity which increased over time. Long-term bonds can be assessed in vivo by the combined evaluation of the microtensile bond strength and SEM morphological examination of the adhesive interface.

Effects of mechanical properties of adhesive resins on bond strength to dentin.

OBJECTIVES The purpose of this study was to evaluate the relationship between the micro-tensile bond strength to dentin and mechanical properties of the cured adhesive resins. METHODS Coronal dentin surfaces of extracted human teeth were treated with four commercial self-etching priming systems (Clearfil SE Bond; UniFil Bond; Tokuso Mac-Bond II; and Imperva Fluoro Bond) and bonded with a resin composite. After 24h storage in water at 37 degrees C, the bonded specimens were trimmed and subjected to micro-tensile bond strength testing at a cross-head speed of 1mm/min. Debonded surfaces were observed under a FE-SEM. For testing mechanical properties, 0.7-mm thick slabs of each adhesive resin were prepared, light-cured, and stored dry at the room temperature for 24h. After trimming, ultimate micro-tensile strength was measured. The nano-hardness and Youngs modulus were also evaluated using cured adhesives that were prepared in the same manner as described above. RESULTS The micro-tensile bond strengths to dentin and ultimate micro-tensile strengths of the resins were not significantly different among all systems (P>0.05). However, the nano-hardness and Youngs modulus of Clearfil SE Bond and Imperva Fluoro Bond adhesive resins were significantly higher than those of UniFil Bond and Tokuso Mac-Bond II resins (P<0.05). The micro-tensile bond strength significantly correlated with the ultimate micro-tensile strength of the resins (r(2)=0.77; P<0.05), but was not correlated with the nano-hardness or Youngs modulus (P>0.05). SEM observation of the debonded surfaces revealed a mixed type of fracture with a combination of interfacial and cohesive failure within the adhesive resin. SIGNIFICANCE The four self-etching priming systems exhibited similar dentin bond strengths, which also correlates with the ultimate strength of the adhesive resins.

Effect of intrinsic wetness and regional difference on dentin bond strength

OBJECTIVES The aim of this investigation was to determine the influence of intrinsic wetness on regional bond strengths of adhesive resins to dentin. METHODS Human caries-free third molars were randomly divided into three groups for bonding: Group 1--no pulpal pressure; Group 2--pulpal pressure of 15 cm H2O; and Group 3--dentin dried overnight in a desiccator. Clearfil Liner Bond II (Kuraray) or One Step (Bisco) adhesive resins systems were applied to the flat dentin surfaces and the teeth were restored with APX resin composite (Kuraray). After 24 h in water at 37 degrees C, the specimens were sectioned into 0.7 mm thick slabs and divided into three regional subgroups according to the remaining dentin thickness and visual criteria: pulp horn, center, and periphery. The slabs were then trimmed for the micro-tensile bond test and subjected to a tensile force and crosshead of 1 mm/min. The data were analyzed with ANOVA and Fishers PLSD test at a confidence level of 95%. The fracture modes were determined under a scanning electron microscope (JXA-840, JEOL, Japan). RESULTS No significant regional difference was observed for the Group 1 and 2 specimens restored with Clearfil Liner Bond II (p > 0.05). However, bond strengths significantly decreased at the pulp horn region of the Group 1 and 2 specimens restored with One Step (p > 0.01). All bond strengths of Group 3 decreased significantly and regional differences were not evident (p > 0.05). SIGNIFICANCE The dentin adhesive system should be chosen according to the substrate and region to be bonded, since bond strengths can vary according to the intrinsic wetness, region, and the adhesive system.

In vitro secondary caries inhibition around fluoride releasing materials

Objectives of the study were to compare the capacity of fluoride releasing materials to inhibit in vitro caries formation and to measure the width and height of the inhibition zones. Box-shaped cavities were prepared on bovine root dentine and restored with Fuji II, Fuji II LC. Vitremer, or Clearfil Liner Bond II system with a fluoride releasing composite. After immersion in a buffered demineralizing solution of 50 mmol/L acetic acid adjusted to pH 4.5 for 3 days, longitudinal sections were cut and imbibed in quinoline for analysis under a polarized light microscope (PLM). The contours of the lesions and inhibition zones were traced and their depth, width and height calculated. The data were analyzed by one-way ANOVA and Fishers PLSD test at 95% level of confidence. The polarized light microscopy results showed a distinct inhibition zone adjacent to both conventional and resin-modified glass ionomer cements; however, it was not observed around the adhesive resin system. The width and height of this inhibition zone were significantly greater for Fuji II than for Fuji II LC and Vitremer. An inhibition zone was not observed adjacent to the adhesive resin system with fluoride releasing composite. The resin-modified glass ionomer cements produced less protection against in vitro secondary caries formation than the conventional glass ionomer cement. The recent bonding system that releases fluoride failed to produce an inhibition zone along the cavity wall adjacent to the restoration.

Collagen cross-linking and ultimate tensile strength in dentin

Several studies have indicated differences in bond strength of dental materials to crown and root dentin. To investigate the potential differences in matrix properties between these locations, we analyzed upper root and crown dentin in human third molars for ultimate tensile strength and collagen biochemistry. In both locations, tensile strength tested perpendicular to the direction of dentinal tubules (undemineralized crown = 140.4 ± 48.6/root = 95.9 ± 26.1; demineralized crown = 16.6 ± 6.3/root = 29.0 ± 12.4) was greater than that tested parallel to the tubular direction (undemineralized crown = 73.1 ± 21.2/root = 63.2 ± 22.6; demineralized crown = 9.0 ± 3.9/root = 16.2 ± 8.0). The demineralized specimens showed significantly greater tensile strength in root than in crown. Although the collagen content was comparable in both locations, two major collagen cross-links, dehydrodihydroxylysinonorleucine/its ketoamine and pyridinoline, were significantly higher in the root (by ~ 30 and ~ 55%, respectively) when compared with those in the crown. These results indicate that the profile of collagen cross-linking varies as a function of anatomical location in dentin and that the difference may partly explain the site-specific tensile strength.

Adhesive sealing of the pulp chamber

The purpose of this in vitro study was to evaluate quantitatively the ability of four different filling materials to seal the orifices of root canals as a secondary seal after root canal therapy. Forty extracted human molar teeth were used. The top of pulp chambers and distal halves of the roots were removed using an Isomet saw. The canal orifices were temporarily sealed with a gutta-percha master cone without sealer. The pulp chambers were then treated with a self-etching primer adhesive system (Clearfil SE Bond), a wet bonding system (One-Step), a 4-methacryloyloxyethyl trimellitate anhydride adhesive system (C&B Metabond), or a reinforced zinc oxide-eugenol (IRM). The specimens were randomly divided into four groups of 10 each. A fluid filtration method was used for quantitative evaluation of leakage. Measurements of fluid movement were made at 2-min intervals for 8 min. The quality of the seal of each specimen was measured by fluid filtration immediately and after 1 day, 1 wk, and 1 month. Even after 1 month the resins showed an excellent seal. Zinc oxide-eugenol had significantly more leakage when compared with the resin systems (p < 0.05). Adhesive resins should be considered as a secondary seal to prevent intraorifice microleakage.

Microleakage Evaluation of a New Low-shrinkage Composite Restorative Material

PURPOSE This study compared the microleakage of an experimental low-shrinkage resin composite (Hermes), a nanofilled resin composite material (Filtek Supreme) and a hybrid resin composite (Tetric Ceram) using a dye penetration method. METHODS AND MATERIALS Class I cavities prepared in 60 human molars were randomly divided into 3 groups according to the restorative material used. The preparations were restored using a bulk or an incremental technique. Half of the specimens from each group were subjected to 200,000 cycles of loading at 50 N, while the other half were stored in distilled water for 24 hours at 37 degrees C. All specimens were immersed in 1% methylene blue (pH = 7.0) for 24 hours and sectioned into 3 slabs. The margins were evaluated for microleakage using an ordinal scoring system (0-4) under a stereomicroscope at 40x magnification. Data were subjected to the non-parametric Kruskal-Wallis analysis of variance and Mann-Whitney test (p<0.05). Data were expressed as median leakage scores and mean ranks. RESULTS All of the restorative systems had microleakage, regardless of the insertion technique and mechanical load cycling. Incremental placement significantly reduced microleakage as compared to the bulk technique, regardless of the restorative system used. Load cycling significantly affected incrementally placed restorations, except for the Hermes system.

Dimensional changes of demineralized dentin treated with HEMA primers

OBJECTIVES The purpose of this study was to measure the dimensional changes of demineralized dentin before and after application of HEMA (2-hydroxyethyl methacrylate) by confocal laser scanning microscopy (CLSM). METHODS The middle portion of bovine dentin was ground, polished, and covered with a vinyl tape with a 4-mm hole punched through it. A strip of polysiloxane impression material was then placed across the center of the dentin surface to preserve a strip of the original unetched surface. Dentin surfaces were etched with 32% phosphoric acid for 60 s and rinsed with water. The impression material was then removed and the following sequential steps were performed: the dentin surface was mildly air-dried, then strongly air-dried, then treated with either 35 wt.% HEMA/water or 100 wt.% HEMA and mildly air-dried, and then strongly dried again. The shrinkage of the demineralized dentin surface from the original unetched level was measured by CLSM in each step and results analyzed by one-way ANOVA. RESULTS The dimensional changes of demineralized dentin after mild air drying were approximately -1 micron and, following strong air drying, resulted in -5 microns shrinkage. Following the application of 35 wt.% HEMA/water, the height of the demineralized dentin changed to a level of -3.3 microns, but then shrank to -4.8 microns after strong drying. ANOVA indicated that re-expansion of the shrunken etched dentin was significant (p < 0.05); however, the treated surface collapsed when it was strongly dried again (p < 0.05). 100% HEMA did not re-expand the shrunken demineralized dentin under any of the application on protocols (p > 0.05). SIGNIFICANCE Thirty-five wt.% HEMA in water re-expanded the collapsed demineralized dentin matrix, however not to the original level. One hundred wt.% HEMA did not cause any re-expansion.

Effects of saliva contamination on resin-resin bond strength

OBJECTIVE The purpose of this study is to evaluate the effects of saliva contamination on microtensile bond strength (microTBS) between resin interfaces and to determine which decontamination methods best re-established the original resin-resin bond strength. MATERIALS AND METHODS Ninety-six light-cured resin composite cylinders of Z-250, Renew, Clearfil APX, and Pertac II were randomly divided into six groups. For each material, one group of specimens was not contaminated, serving as the control. For the other specimens, the top surface of each block was treated with saliva that was slowly dried (Treatment 1); dried forcefully (Treatment 2); slowly dried, rinsed, and dried (Treatment 3); slowly dried, rinsed, dried, and bonded with Single Bond, One-Step, Clearfil SE Bond, or Prompt L-Pop (Treatment 4); or slowly dried, but not rinsed, and bonded using the same adhesives (Treatment 5). Two 2-mm increments of resin composite were applied and light-cured. After 24 h, the assemblies were trimmed for microtensile bond testing and were loaded to failure at 1 mm/min. Data were analyzed using two-way and one-way ANOVA and Fishers PLSD (p<0.05). RESULTS Control values ranged from 45.1 MPa for Pertac II to 71.5 MPa for APX. Treatment 1 caused significant reduction in resin-resin bond strength for all materials tested but for two of the materials in treatment 2. Pertac II was the only material that did not show a statistical difference from control group for treatment 3. Treatment 4 re-established the control values for Z-250 and Renew and treatment 5 was the only one to show no statistical difference for all materials tested. SEM observation revealed a smooth surface in treatment 1, but treatment 3 showed a few craters. Treatment 4 and 5 showed a mixture of cohesive failure in the composite and adhesive. SIGNIFICANCE The most reliable method for decontaminating saliva from resin surfaces involves the application of adhesives.

Fluoride-containing adhesive: durability on dentin bonding.

OBJECTIVES To evaluate (1) the influence of fluoride-containing adhesive on microtensile bond strength (microTBS) and (2) in vitro secondary caries inhibition at the resin-dentin interface after 24 h and 3 months water-storage and (3) the degree of conversion of different adhesives after 24h 1 month. METHODS Flat surfaces of human teeth were ground and randomly assigned to six groups: (SBMP-24) Scotchbond Multi-Purpose control [SBMP], 24 h; (SE-24) SBMP etch and primer+Clearfil SE Bond adhesive [SE], 24h; (PB-24) SBMP etch and primer+Clearfil Protect Bond adhesive [PB], 24h; (SBMP-3) SBMP, 3 months; (SE-3) SBMP+SE, 3 months; and (PB-3) SBMP+PB, 3 months. To evaluate the effect of the adhesive resin alone, all teeth were etched with 35% phosphoric acid and primed with SBMP primer prior to applying the adhesive resin. Bonded assemblies were prepared for microTBS and stored in distilled water at 37 degrees C for 24h and 3 months. Sections of restored teeth of each group were exposed to an acid challenge. The specimens were sectioned, polished, and then observed with polarized light microscopy (PLM). Also, the degree of conversion (DC) of the adhesives was measured using Fourier Transform-Infrared spectroscopy (FTIR) at 24 h and 1 month, after polymerization. RESULTS microTBS values obtained in MPa (24h/3m) were: (MP) 61.5+/-10.5/52.9+/-8.9, (SE) 55.5+/-11.8/55.6+/-13, and (PB) 50.3+/-9.9/61.0+/-13.6. For interface analysis by PLM, an inhibition zone (IZ) adjacent to the hybrid layer was created only when the fluoride-containing adhesive (PB) was used. The DC in percentage (24 h, 1 month) were: (MP) 60.5+/-2.8/61.3+/-0.6, (SE) 69.6+/-1.3/70.7+/-0.05, and (PB) 53.1+/-0.4/58.3+/-1.6. SIGNIFICANCE The fluoride-containing adhesive demonstrated significant increase of bond strength values after water-storage. This material was also able to create an acid inhibition zone in dentin. There was a significant increase of degree of conversion after 1 month only for PB.