The Journal of Adhesive Dentistry, 02/2008

Purpose: To evaluate the phase separation, extent of dentin demineralization, and curing efficiency of one-step self-etching adhesives placed on dentin and on inert substrate. Materials and Methods: The adhesives tested were G-Bond (GB), iBond (IB) and Clearfil S3 Bond (SB). Two groups (2 x 3) of dentin and inert (gold) specimens were prepared for each product. The films formed on inert surfaces were subjected to mild (1st group) or strong air drying (2nd group) and examined with near- and mid-FTIR microspectroscopy. On dentin (1st group), the extent of demineralization (%DM) was evaluated before and after adhesive treatment plus rinsing with water and acetone by mid-FTIR microspectroscopy. The films formed after strong air drying (2nd group) and 20 s of light curing were rinsed with acetone, and the degree of cure (%DC) was measured by micro-multiple internal reflection FTIR spectroscopy. ANOVA was used to assess the statistically significant differences in %DM and %DC (α = 0.05). Results: In GB and IB, mild air drying produced more water droplets and monomer separation than strong air drying. SB demonstrated the least separation. IB induced the highest %DM. All the adhesives demonstrated the greatest %DC on dentin. On both substrates SB showed the highest %DC values. Conclusion: Phase separation including water and/or monomers was found in all the adhesives. The extent of dentin demineralization and degree of cure varied among the products tested. The degree of cure was higher on dentin than on the inert substrate. Keywords: self-etching adhesives, phase separation, FTIR spectroscopy and imaging, demineralization, degree of cure

Purpose: Self-etching adhesives partly remove or dissolve the dentin smear layer, causing incomplete resin tag formation or low resin tag density. The quantitative contribution of properly formed resin tags to dentin adhesion was evaluated. Materials and Methods: We assessed how the presence or absence of resin tags affects tubules of human deepcoronal dentin. G-Bond was used to bond Gradia resin composite. To ensure deep tubule penetration, we used a vacuum exsiccator. For eliminating tag formation, dentin tubules were presealed with adhesive and reverse bonded after finishing. Microtensile bond strength (µTBS) was measured on flat specimens and on Class I cavity floors. Thermocyclic loading was used to estimate the influence of resin tags on long-term behavior. Confocal laser scanning microscopy was used to evaluate adhesive interface dimensions. Results: Hybrid layer thickness, tag length, and tag diameter increased under vacuum treatment. Presealing dentin tubules led to a residual tag area of 3.1% with a tag length of 10.8 µm. Under vacuum, 24.7% of the total dentin surface was covered with tags of 87.8 µm. Low C-factor preparations produced superior µTBS (71.8 to 92.7 MPa) compared with high C-factor Class I cavities (47.0 to 67.6 MPa). Thermocyclic fatigue differed from low to high C-factor situations. In Class I cavities, µTBS significantly decreased after thermocycling. On flat specimens, vacuum infiltration led to reduced µTBS after thermocyclic loading. Conclusion: Initially, resin tag formation did not influence the µTBS in either type of C-factor preparation. After thermocyclic loading, µTBS decreased with or without resin tags. Adhesive fracture patterns occurred at the hybrid layer/dentin interface. Keywords: dentin bonding, adhesion, tag formation, resin composites, hybrid layer, vacuum, C-factor

Purpose: The aim of this study was to evaluate the ultrastructural characteristics and ionic profile of U937 cells after exposure to 2-hydroxyethyl methacrylate (HEMA) to shed light on the cytotoxicity of this dental adhesive and its relation to mechanisms of cell death. Materials and Methods: U937 human monoblastic cells were incubated in RPMI 1640 culture medium and exposed to HEMA at LD50. Structural changes after 5, 15, 30, 60, and 120 min were observed with transmission electron microscopy. Ionic content of Na, K, Cl, Mg, P and S was evaluated by quantitative electron probe X-ray microanalysis. Results: Our results in human monoblastic cell line U937 establish that exposure to HEMA at LD50 led to a singular mechanism of cell death characterized by changes in the morphology and ultrastructure of the cells (cell size, blebs, and organelle structure) compatible with apoptosis, but without changes in nuclear ultrastructure. These findings were consistent with our microanalytical data, which revealed a significant increase in intracellular Na and a decrease in K, along with a significant initial decrease in Cl concentration followed later (120 min) by an increase. Conclusion: All three lines of evidence (cell morphology, ultrastructural changes, and ionic profile) showed that HEMA at LD50 led to a hybrid process of cell death. We suggest that apoptosis and necrosis are part of a continuum comprising a single process of cell death. Keywords: HEMA, cell death, apoptosis Keywords: HEMA, cell death, apoptosis, necrosis, microanalysis, sodium, chlorine, potassium

Purpose: The aim of this study was to evaluate the effect of material technique, bevel placement, and aging on the fracture resistance of composite restorations bonded to sectioned incisal edges. Materials and Methods: For the retention test, the incisal thirds of 80 mandibular human incisors were sectioned. Ten sound incisors were used as a control group. Teeth were divided into two groups according to storage time (24 h and 180 days with 1000 thermal cycles). In each group, subgroups were randomly formed as follows: beveled or nonbeveled direct resin composite restorations (Adper Single Bond/Filtek Z250) and beveled or nonbeveled indirect composite restorations (prepolymerized Filtek Z250 cemented with Adper Single Bond/Rely X ARC). For each experimental group, 20 specimens were prepared (10 tested after 24 h and the remaining after 180 days). The specimens were subjected to shear testing in a universal testing machine with a crosshead speed of 0.5 mm/min. Failure patterns were analyzed by stereomicroscopy (30X). Data were statistically analyzed with ANOVA and Tukey's and Student's t-tests for retention resistance, and with Fisher's exact test for fracture patterns at the 0.05 level of significance for all tests. Results: After 24 h, beveled restorations exhibited higher fracture strength values than nonbeveled restorations and showed resistance similar to the sound teeth. After 6 months, beveled restorations still presented better results than nonbeveled restorations. Thermal cycling and water storage decreased the fracture resistance in the majority of the groups. Adhesive failures were mainly observed in nonbeveled restorations and mixed failures in beveled restorations. Conclusion: Within the limitations of the study, it was concluded that storage with thermal cycling decreased fracture resistance, beveling improved fracture resistance, and indirect restorations had a fracture resistance similar to direct restorations. Keywords: dentin bonding agents, composite resins, bevel, polymerization shrinkage

Purpose: To assess the effect of different peri- and intertubular dentin mineralization conditions and etching on shear bond strength in vitro. Materials and Methods: One hundred fifty crowns of extracted bovine incisors were embedded in resin and ground to expose the buccal coronal dentin. Sixty specimens were subjected to a demineralizing solution (DS) and another 60 teeth to a bacterial-based laboratory caries model (S. mutans, SM). Thirty specimens of each demineralization protocol (DS and SM) were randomly selected and remineralized (-R). Thirty sound dentin specimens served as control (C). Resin composite buildups (Tetric) were bonded after application of one of the following adhesives: a one-step self-etching adhesive (Xeno III), and a self-etching adhesive (Syntac Classic) without (three-step) and with prior additional 35% phosphoric acid etching (etch-and-rinse, four-step). Teeth were subjected to shear bond strength testing in a universal testing device at a crosshead speed of 0.5 mm/min (Ultradent method). Results: Bond strength value for group C ranged from 6.3 to 8.4 MPa (p > 0.05). DS and DS-R samples showed increased bond strength with the one-step adhesive (11.6 MPa, p 0.05), whereas the three-step adhesive with additional etching showed decreased bond strength (3.2 MPa, p 0.05). SM samples showed the lowest bond strength of all adhesive systems (range 1.1 to 1.5 MPa, p > 0.05). Remineralization showed no effect on the latter group. Conclusion: The degree of mineralization of the dentin is important for adhesion. Additional etching with phosphoric acid reduced bond strength of a three-step adhesive. Keywords: dentin, demineralization, S. mutans, adhesive, bond strength

Purpose: This study evaluated the bond strength of two etch-and-rinse adhesive systems (two- and three-step) and a self-etching system to coronal and root canal dentin. Materials and Methods: The root canals of 30 human incisors and canines were instrumented and prepared with burs. The posts used for luting were duplicated with dual resin cement (Duo-link) inside Aestheti Plus #2 molds. Thus, three groups were formed (n = 10) according to the adhesive system employed: All-Bond 2 (TE3) + resin cement post (rcp) + Duo-link (Dl); One-Step Plus (TE2) + rcp + Dl; Tyrian/One-Step Plus (SE) + rcp + Dl. Afterwards, 8 transverse sections (1.5 mm) were cut from 4 mm above the CEJ up to 4 mm short of the root canal apex, comprising coronal and root canal dentin. The sections were submitted to push-out testing in a universal testing machine EMIC (1 mm/min). Bond strength data were analyzed with two-way repeated measures ANOVA and Tukey's test (p 0.05). Results: The relationship between the adhesives was not the same in the different regions (p 0.05). Comparison of the means achieved with the adhesives in each region (Tukey; p 0.05) revealed that TE3 (mean ± standard deviation: 5.22 ± 1.70) was higher than TE2 (2.60 ± 1.74) and SE (1.68 ± 1.85). Conclusion: Under the experimental conditions, better bonding to dentin was achieved using the three-step etch-andrinse system, especially in the coronal region. Therefore, the traditional etch-and-rinse three-step adhesive system seems to be the best choice for teeth needing adhesive endodontic restorations. Keywords: bond strength, push-out test, coronal dentin, root canal dentin, dental adhesives

Purpose: The aim of this study was to evaluate the effect of using 5.25% commercial sodium hypochlorite treatment prior to the application of etch-and-rinse and self-etching adhesives on dentin surface microtopography and tensile bond strength. Materials and Methods: Thirty-two noncarious, nonrestored human third molars were collected. The occlusal enamel of all teeth was removed using diamond disks to expose flat dentin surfaces. The exposed dentin surfaces were abraded using 600-grit SiC disks, to create a uniform dentin smear layer. For AFM characterization, 12 teeth were equally divided into 4 groups according to the proposed dentin surface treatment. Three dentin disks, 2 mm thick, were evaluated per group using tapping mode assessment. Twenty teeth were used for TBS and SEM evaluation and were equally divided into 4 groups, according to the proposed dentin surface treatment. For TBS, 8 dentin/composite slabs, 2 mm thick, were used in each group, while for SEM evaluation 2 slabs were used. Each slab was tested in tension at a crosshead speed of 0.5 mm/min until failure occurred. The samples were examined using SEM operated at 30 kv to evaluate the hybrid layer photographically at 1500X. Statistical analysis was carried out using StatsDirect 2.5.7. One-way ANOVA followed by Tukey-Kramer multiple-comparison post-hoc tests were performed to test the difference between roughness parameters and TBS between groups. Results: Sodium hypochlorite followed by the application of 37% phosphoric acid significantly increased the arithmetic average of the absolute values of surface height deviations (Sa), the surface area ratio which expresses the ratio between the surface area (taking the z height into account) and the area of the flat x,y plane (Sdr), and the surface bearing index (Sbi) parameters, while the application of sodium hypochlorite prior to the application of the selfetching primer significantly increased the valley fluid retention index (Svi) parameter. Self-etching primer without sodium hypochlorite pretreatment significantly increased the core fluid retention index (Sci) parameter. Sodium hypochlorite/AdheSE (7.42 ± 2.16 MPa) significantly increased TBS value compared to other groups. However, no statistically significant difference was found between sodium hypochlorite/Excite (4.68 ± 1.26 MPa), AdheSE (4.42 ± 1.36), and Excite (4.06 ± 1.35). Remnants of smear layer were detected with areas devoid of resin tags in SEM images of samples bonded with AdheSE self-etching adhesive, in contrast to samples bonded with sodium hypochlorite followed by AdheSE self-etching adhesive. Conclusion: The application of 5.25% commercial sodium hypochlorite with rubbing action for 60 s (total application time 120 s) seems to positively influence the TBS of the self-etching adhesive; however, it has no significant effect on TBS of etch-and-rinse single-bottle adhesive to dentin. The addition of functional roughness parameters to study the dentin surface was shown to be of importance in evaluating the relationship between bond strength and surface topography of conditioned dentin Keywords: sodium hypochlorite, dentin adhesives, AFM, tensile bond strength

Purpose: To evaluate the fracture resistance of teeth restored using an adhesive core material placed under artificial crowns without pins or posts and to assess the effect of different preparation designs and cementation techniques (glass ionomer compared with adhesive cementation) used for the crowns. Materials and Methods: Eighty-three intact molars were collected. Sixty-seven teeth were decoronated (test groups and one control group), a 2-mm circular ferrule design was prepared, and four different preparation designs (2-mm- or 1-mm-deep cavities and 2-mm- or 1-mm-thick walls) were used. Three control groups were also established. Cores were built up using an adhesive material. After preparation, standardized artificial crowns (cobalt-chromium alloy) were fabricated. Half of the crowns in the test group (n = 32) were cemented using Panavia (P group); glass-ionomer cement was used for the other half (KC group). All teeth were exposed to 10,000 thermal cycles and loaded until fracture. Statistical analysis was performed, including nonparametric tests (Mann-Whitney U-test) and ANOVA. Results: In the P group, the fracture strength was significantly (p = 0.004) higher (591.75 ± 177.95 N) than in the KC group (430.18 ± 193.67 N). The effect of the preparation design was more pronounced in the KC group. In all groups simulating the most moderate type of tooth decay (2-mm-deep cavity and a 2-mm-thick wall), the fracture strength was comparable with that of intact teeth. Results from ANOVA showed that the type of cementation of the crowns affected fracture strength. Conclusion: Fracture strengths of adhesive core/crown complexes are greater when an adequate cavity for retention (at least 2 mm deep) is prepared and the crown is luted. Keywords: cores, cementation technique, fracture strength, artificial crown, preparation design

Purpose: To study the microstructure of sealant penetration in the enamel of in vivo sealed approximal noncavitated incipient caries lesions with and without a preceding bonding step. Materials and Methods: A total of 26 proximal noncavitated caries lesions were sealed in vivo, using a sealant in 13 premolars with orthodontic indication of extraction. Each tooth was randomly assigned to mesial or distal surface application of a sealant in the lesion area and in surrounding sound enamel, with or without a bonding system. Four groups were analyzed: a nonbonding group in the lesion area (NBL); a nonbonding group in sound enamel (NBS); a bonding group in the lesion area (BL) and a bonding group in sound enamel (BS). The premolars were extracted after two weeks. All sealed areas were cut and demineralized with 37% hydrochloric acid for 24 h. For each group, the resin tags were observed and measured by scanning electron microscopy. Results: The lesion areas showed a very irregular resin network with twisted and curved tags in contrast to the sound enamel where a regular etching pattern was observed. The length of resin tags in microns for each group (mean ± SD) was: NBG-L = 4.19 ± 1.59; NBG-S = 5.49 ± 2.49; BG-L = 4.57 ± 1.99; and BG-S = 4.21 ± 1.87. The differences between the groups were not statistically significant (p=0.34). Conclusion: The use of a bonding system prior to the application of a pit and fissure sealant on both lesion and sound enamel areas does not increase the resin penetration length under non-contaminated conditions. Keywords: approximal initial caries, in vivo, prevention, sealant, SEM analysis