The Journal of Adhesive Dentistry, 06/2013

Purpose: To evaluate the effect of different polymerization sequences employed during application of bis-GMAbased particulate filler composites (PFC) or a flowable resin (FR) on fiber-reinforced composite (FRC). Materials and Methods: Unidirectional, pre-impregnated S2-glass fibers (Dentapreg) and multidirectional preimpregnated E-glass fibers (Dentapreg) (length: 40 mm; thickness: 0.5 mm) were obtained (N = 144, n = 12 per group) and embedded in translucent silicone material with the adhesion surface exposed. The resulting specimens were randomly divided into 12 groups for the following application sequences: a) FRC+PFC (photopolymerized in one step), b) FRC+FR (photopolymerized in one step), c) FRC+PFC (photopolymerized individually), d) FRC+FR (photopolymerized individually), e) FRC (photopolymerized)+intermediate adhesive resin and PFC (photopolymerized in one step), f) FRC (photopolymerized)+intermediate adhesive resin and FR (photopolymerized in one step). The sequences of unidirectional (groups a to f) were repeated for multidirectional (groups g to l) FRCs. PFCs were debonded from the FRC surfaces using the shear bond test in a universal testing machine (1 mm/min). On additional specimens from each FRC type, thermogravimetric analysis (TGA) was performed to characterize the fiber weight content (Wf) (N = 6, n = 3 per group). After debonding, all specimens were analyzed using SEM to categorize the failure modes. The data were statistically analyzed using 3-way ANOVA and Tukey's tests (α = 0.05). Results: Significant effects of the FRC type (S2 or E-glass) (p 0.01), resin type (PFC or FR) (p 0.01) and polymerization protocol (p 0.05) were observed on the bond strength (MPa). Interaction terms were also significant (p 0.05). The multidirectional FRC groups (g to l) showed significantly lower bond strengths (2.3 ± 0.2 to 7.3 ± 0.3 MPa) than did the unidirectional FRC groups (a to f) (10.7 ± 0.6 to 24.4 ± 0.8 MPa). Among the unidirectional FRC groups, the highest values were obtained with protocol f (24.4 ± 0.8), followed by protocol e (18.6 ± 0.4). PFC adhesion to unidirectional FRC was lower when FRC and PFC were polymerized in one step (protocol a: 11.3 ± 0.5) than individual polymerization (protocol c: 14.1 ± 0.5). The opposite situation was true for FR (protocol b: 17.5 ± 0.4; protocol d: 10.7 ± 0.6). Groups a to f presented exclusively mixed failures (a combination of partial cohesive failure in the PFC and adhesive failure between the FRC and PFC) and groups g to l demonstrated only adhesive failure (intact FRC no cohesive failure of PFC). TGA revealed 55 ± 3 wt% fiber content for multidirectional and 60 ± 3 wt% for unidirectional FRCs tested. Conclusion: Multidirectional pre-impregnated E-glass fibers cannot be recommended in combination with the PFC and FR materials tested in this study. Application of an intermediate adhesive resin layer increases the adhesion of both PFC and FR to unidirectional FRC. FRC and FR can be polymerized in one step, but FRC and PFC combinations should be polymerized individually. Keywords: bond strength, dental materials, intermediate adhesive resin, fiber-reinforced-composites, flowable resin

Purpose: To introduce a new fixation method for stick-shaped specimens for use in microtensile tests and to evaluate the effect of this new method on microtensile bond strength, failure modes, and stress distribution. Materials and Methods: Flat mid-coronal dentin surfaces were prepared on 12 caries-free human third molars and randomly divided into two groups for testing with two dental adhesives (Adper Single Bond 2 [SB2] and Clearfil SE Bond [SEB]). Following adhesive application and composite buildups, the bonded teeth were sectioned into beams. Sticks from each tooth were then equally divided into two subgroups for microtensile bond testing according to the utilized gripping devices (a flat Ciucchi's jig and the experimental setup). Failure modes were examined with a field-emission scanning electron microscope (FESEM). Three-dimensional models of each gripping device and specimen were developed, and stress distributions were analyzed by finite element analysis (FEA). Statistical significance was set at α = 0.05 Results: Compared to those fixed using a flat Ciucchi's jig, sticks fixed with the experimental setup yielded lower bond strength values (p = 0.021 for SB2 and p = 0.007 for SEB) and more mixed failure patterns (p = 0.036 for both SB2 and SEB). In addition, the experimental setup guaranteed a uniaxial tensile force that was perpendicular to the bonding interface and produced a more uniform stress distribution at the bonding interface. Conclusion: An experimental setup for fixing microtensile sticks was proposed that was designed to provide a uniform stress distribution at the adhesive interface. FEA and failure mode analysis confirmed such uniform distribution, thus supporting the validity of the bond strength results obtained with this new fixture design. Keywords: microtensile bond strength, failure mode, stress distribution, FEA

Purpose: To evaluate the effect of three different liquids used for intrapulpal pressure (IPP) simulation on the microtensile bond strength (µTBS) of three adhesive systems to dentin. Materials and Methods: The occlusal surfaces of sound human molars were ground flat down to mid-dentin depth. The teeth were bonded under 15 mmHg simulated IPP using distilled water, phosphate buffered saline, or human plasma as a simulating liquid. Three adhesive systems were tested: a single-bottle etch-and-rinse adhesive (SingleBond, 3M ESPE), and two single-step self-etching adhesives (G-Bond, GC) and (iBond, Heraeus Kulzer). Resin composite (Tetric EvoCeram, Ivoclar Vivadent) buildups were made in 2 increments, each 2 mm in height. Specimens were stored in artificial saliva under 20 mmHg IPP at 37°C for 24 h prior to testing. µTBS (n = 15) was tested using a universal testing machine, and failure modes were determined. Data were statistically analyzed using ANOVA and Bonferroni post-hoc tests at p = 0.05. Results: With SingleBond adhesive, distilled water showed significantly higher µTBS compared to plasma and phosphate buffered saline. With G-Bond, no significant difference was found between distilled water and phosphate buffered saline, whereas plasma showed significantly lower µTBS values. In contrast, no significant difference was encountered between the three IPP liquids for iBond adhesive. Predominant modes of failure were adhesive and mixed. Conclusion: A difference in intrapulpal pressure simulating liquids influences the bonding of adhesives to dentin. Etch-and-rinse adhesives are more sensitive to intrapulpal simulating liquids than are self-etching adhesives. Adhesives containing protein-coagulating components perform better with plasma perfusion than those lacking such components. Keywords: intrapulpal pressure, human plasma, microtensile bond strength, adhesive systems

Purpose: This study evaluated the effect of residual water included within the FT-IR spectra on the calculation of the degree of conversion (DC) of a self-etching adhesive (SEA). Materials and Methods: FT-IR spectra of a SEA (Adper Prompt SE, 3M ESPE) were obtained for different amounts of dentin powder, agitation times, and light-curing times. The measured DC (mDC) obtained from the IR spectra was compared to the apparent DC (aDC) from the adjusted IR spectra using the water subtraction algorithm (WSA), by which the water absorption band was subtracted from the obtained IR spectrum. Results: When the SEA was mixed with 10 mg of dentin powder, the aDC was significantly higher than the mDC immediately after light curing (paired t-test, p 0.001). With the increase in the amount of dentin powder, the mDC immediately after curing and the difference between the mDC and the aDC gradually increased. The amount of dentin powder, light-curing time, square of light-curing time, and time until measurement were the variables that significantly affected the aDC (linear mixed model, p 0.05). However, the agitation time did not affect the aDC or the difference between the mDC and the aDC, except at 20 s. Conclusion: When the DC of SEA itself is measured with FT-IR, the mDC needs to be adjusted with the water subtraction algorithm. Clinically, SEA needs to be applied under conditions of prolonged contact with the dentin substrate and vigorous and prolonged drying. Keywords: Fourier transform infrared spectrophotometer (FT-IR), water subtraction algorithm, self-etching dentin adhesive, degree of conversion, generalized least squares model

Purpose: To evaluate the effect of dentin pretreatment with epigallocatechin-3-gallate solution on the preservation of the resin/dentin interface with etch-and-rinse adhesives. Materials and Methods: Thirty extracted human molars were prepared to expose the dentin surface and divided into 5 groups according to the pretreatment solution. Dentin surfaces were etched (35% phosphoric acid for 15 s), rinsed, and air dried. Dentin was rewetted either with distilled water, 3 different epigallocatechin-3-gallate solutions (EGCG; 0.02%, 0.1%, or 0.5% w/v), or 2% chlorhexidine digluconate solution for 60 s. Adper Single Bond 2 was applied and a subsequent 5-mm-thick resin crown was built up. Bonded teeth were longitudinally sectioned to obtain sticks with a cross-sectional area of 1.0 mm2. Half of the specimens were immediately tested, while the remaining specimens were tested after storage in 3 mMol/l sodium azide solution at 37°C for six months. The mode of fracture was examined. Bond strength values were analyzed with ANOVA and Student-Newman-Keuls tests. Results: After 24 h of storage, mean bond strengths of 0.5% EGCG were significantly lower than those found for the other groups (p 0.05), except for 0.02% EGCG (p > 0.05). Resin-dentin bond strengths after 6 months were not significantly different among the experimental groups (p > 0.05). Storage in water for 6 months resulted in a significant decrease in bond strength for the water control group only (p 0.05). The bond strengths of the experimental groups remained stable after 6 months of water storage (p > 0.05). Conclusion: Pretreatment with EGCG preserved the bond of Adper Single Bond 2 to dentin after six months of storage equally well as pretreatment with chlorhexidine digluconate. Keywords: resin-dentin bond degradation, epigallocatechin-3-gallate, green tea, matrix metalloproteinases

Purpose: To evaluate the biocompatibility of a glass-ionomer (GIC) and a resin-modified glass-ionomer cement (RM-GIC), cell viability was examined in a model of human gingival fibroblasts using morphological, biochemical, and ionic patterns by means of phase contrast microscopy, lactate dehydrogenase (LDH) release, and quantitative x-ray microanalysis (EPXMA). Materials and Methods: The GIC Ketac-Molar Easymix (3M ESPE) and the RM-GIC Vitrebond (3M ESPE) were compared in human gingival fibroblasts exposed to the cements for 72 h. As controls, fibroblasts cultured with DMEM culture medium (negative control) and with 1% triton × (positive control) were used. Results: Light microscopic findings showed greater morphological alterations in cells exposed to RM-GIC than to GIC. The relative percentage of LDH released from the cells to the supernatant was significantly higher in RMGIC cultures than in the control. Quantitative x-ray microanalysis showed that cultures exposed to RM-GIC were characterized by an increase in intracellular Na and a decrease in intracellular Cl and K. These changes in ion composition were significant compared to control and GIC cultures. Conclusion: The three indicators of cellular biocompatibility after 72 h of exposure showed that RM-GIC led to more marked alterations than GIC in human gingival fibroblasts. Keywords: glass-ionomer cements, biocompatibility, intracellular, electron probe microanalysis, human gingival fibroblast, LDH

Purpose: This study examined the effect of selecting a single-peak blue vs a polywave blue/violet emission LED curing light on the degree of conversion (DC) and Knoop microhardness (KHN) of resin cements when light cured through a ceramic disk. Materials and Methods: Two shades (A1 and A4) of resin cement (Variolink II) were placed in a 0.5-mm-thick ring. The top surfaces were covered with a Mylar strip and further covered with a disk of 1-mm-thick Empress Esthetic ceramic, shade A2. The specimens were light cured by means of an Elipar-S10 (3M ESPE, single-peak blue LED) or BluePhase-G2 (Ivoclar Vivadent, polywave blue/violet LED) curing light, both for 20 s, directly on the surface of an attenuated total reflectance FT-IR plate at 30°C. The DC of the resin was calculated after 100 s. The specimens were removed, and the Knoop microhardness was tested immediately and again after 24-h storage in the dark at 37°C and 100% humidity. Five specimens were made in each group. The DC and Knoop microhardness results were analyzed with ANOVA and Fisher's PLSD at α = 0.05. Results: The choice of curing light had no significant effect on the DC and only a small effect on the immediate and 24-h KHN values. Shade A4 of the resin cement was harder and had a higher DC than shade A1. Conclusion: When light cured for 20 s, Variolink II resin cement can be light cured with either the single-peak or the polywave curing light. Shade A4 of the cement was slightly harder than A1. Keywords: polymerization, cement hardness, degree of conversion, LED, ceramic

Purpose: To evaluate the influence of fluoride delivery and restoration time point on the microshear bond strength (mSBS) and degree of conversion (DC) values of an adhesive applied on bleached enamel. Materials and Methods: Fifty-four enamel specimens were submitted to bleaching and divided into 3 groups of n = 18: group HP: 35% hydrogen peroxide (HP); group HPF: HP + 1.23% sodium fluoride application (F); group PF: 38% HP with F. A control group of n = 6 was neither bleached nor fluoridated. Subsequently, each group except the control was subdivided into 3 subgroups (n = 6) to be restored immediately, or at 7 or 14 days. Tygon tubes were filled with composite resin and placed on enamel surfaces, then the mSBS test was performed. The DC of the interface was observed with Raman spectroscopy. The data were submitted to two-way ANOVA and Tukey's and Dunnet's post-hoc test (α = 0.05). Results: The mSBS results showed higher values for groups HP and HPF at 14 days compared with immediate and 7 days (p 0.05). Lower DC values were obtained in the immediately restored groups HP and HPF, which were significantly different from 7 and 14 days (p 0.05). mSBS and DC for group PF was similar at all restoration time points and to the control group (p > 0.05). Conclusion: Only the use of a fluoridated in-office bleaching agent (Opalescence Boost PF) proved to be effective for immediately reversing the side effects of low mSBS and DC values when in-office bleaching is used. Keywords: tooth bleaching, hydrogen peroxide, dental adhesives, fluoride

Purpose: To evaluate the influence of resin cements and aging on cuspal deflection, fracture resistance, and mode of failure of endodontically treated teeth restored with composite resin inlays. Materials and Methods: Seventy-two maxillary premolars were divided into 6 groups: 1: sound teeth as control (C); 2: preparations without restoration (WR); 3: inlays luted with RelyX ARC (ARC); 4: inlays luted with RelyX Unicem (RLXU); 5: inlays luted with Maxcem Elite (MCE); 6: inlays luted with SeT (ST). Groups 2 to 6 received mesio-occlusal-distal preparations and endodontic treatment. Stone casts were made for groups 3 to 6. Composite resin inlays were built over each cast and luted with the resin cements. A 200-N load was applied on the occlusal aspect and the cuspal deflection was measured using a micrometer before and after 500,000 cycles of fatigue loading (200 N; 500,000 cycles). The specimens were then submitted to an axial load until failure. Results: The median cuspal deflection (µm) and median fracture resistance (N) were calculated and statistically analyzed using Kruskal-Wallis and Mann-Whitney tests (p 0.01). Values followed by the same letter represent no statistically significant difference. Cuspal deflection before cyclic loading: C = 3 µma; ARC = 4 µmab; RLXU= 5 µmab; MCE = 21 µmb; ST = 51 µmbc; WR = 69 µmc. Cuspal deflection after cyclic loading: ARC = 6 µma; RLXU = 19 µmab; MCE = 33 µmb; ST = 62 µmb. Fracture resistance in N: C = 1902a; ARC = 980b; RLXU = 670c; MCE = 533c; ST = 601c; WR = 526c. According to the Wilcoxon test, there was no statistical difference between the cuspal deflection before and after cyclic loading only for ARC (p = 0.015). There was a predominance of recovery fractures for the restored groups. Conclusion: Composite resin inlays luted with RelyX ARC maintained cuspal deflection stability and showed higher fracture resistance of the teeth than did inlays luted with the other cements tested. Keywords: resin cements, cuspal deflection, fracture resistance

Purpose: To evaluate the influence of heat treatment (HT) procedures of a pre-hydrolyzed silane on bond strength of resin cement to a feldspathic ceramic. Materials and Methods: Ceramic and composite blocks (N = 30) were divided into six groups (n = 5) and subjected to the following conditioning procedures: G1: 9.6% hydrofluoric acid (HF) for 20 s + silane (RelyX Ceramic Primer, 3M ESPE) + resin cement (Panavia F2.0, Kuraray) (control); G2: HF (20 s) + silane + heat treatment in furnace (HTF) (100°C, 2 min) + resin cement; G3: silane + HTF + resin cement; G4- HF (20 s) + silane + heat treatment with hot air (HTA) (50 ± 5°C for 1 min) + resin cement; G5: silane + HTA + resin cement; G6: silane + resin cement. The microtensile bond strength (MTBS) test was performed using a universal testing machine (1 mm/min). After debonding, the substrate and adherent surfaces were analyzed using a stereomicroscope and SEM to categorize the failure types. The data were statistically evaluated using one-way ANOVA and Tukey's test (5%). Results: The control group (G1) showed no pre-test failures and presented significantly higher mean MTBS (16.01 ± 1.12 MPa) than did other groups (2.63 ± 1.05 to 12.55 ± 1.52 MPa) (p = 0.0001). In the groups where HF was not used, HTF (G3: 12.55 ± 1.52 MPa) showed significantly higher MTBS than did HTA (G5: 2.63 ± 1.05 MPa) (p 0.05). All failure types were mixed, ie, adhesive between the resin cement and ceramic accompanied by cohesive failure in the cement. Conclusion: Heat treatment procedures for the pre-hydrolyzed silane either in a furnace or with the application of hot air cannot replace the use of HF gel for the adhesion of resin cement to feldspathic ceramic. Yet when mean bond strengths and incidence of pre-test failures are considered, furnace heat treatment delivered the second best results after the control group, being considerably better than hot air application. Keywords: adhesion, cementation, ceramics, microtensile bond strength, silane coupling agent

Purpose: This study investigated the effect of a low-viscosity adhesive resin (Icon) applied after either hydrochloric (HCl) or phosphoric acid (H3PO4) on the adhesion of metal brackets to enamel. Failure types were analyzed. Materials and Methods: The crowns of bovine incisors (N = 20) were sectioned mesio-distally and inciso-gingivally, then randomly assigned to 4 groups according to the following protocols to receive mandibular incisor brackets: 1) H3PO4 (37%)+TransbondXT (3M UNITEK); 2) H3PO4 (37%)+Icon+TransbondXT; 3) HCl (15%)+Icon (DMG)+TransbondXT 4) HCl (15%)+Icon+Heliobond (Ivoclar Vivadent)+TransbondXT. Specimens were stored in distilled water at 37°C for 24 h and thermocycled (5000x, 5°C to 55°C). The shear bond strength (SBS) test was performed using a universal testing machine (1 mm/min). Failure types were classified according to the Adhesive Remnant Index (ARI). Contact angles of adhesive resins were measured (n = 5 per adhesive) on ceramic surfaces. Results: No significant difference in SBS was observed, implying no difference between combinations of adhesive resins and etching agents (p = 0.712; ANOVA). The Weibull distribution presented significantly lower Weibull modulus (m) of group 3 (m = 2.97) compared to other groups (m = 5.2 to 6.6) (p 0.05). The mean SBS results (MPa) in descending order were as follows: group 4 (46.7 ± 10.3) > group 1 (45.4 ± 7.9) > group 2 (44.2 ± 10.6) > group 3 (42.6 ± 15.5). While in groups 1, 3, and 4 exclusively an ARI score of 0 (no adhesive left on tooth) was observed, in group 2, only one specimen demonstrated score 1 (less than half of adhesive left on tooth). Contact angle measurements were as follows: Icon (25.86 ± 3.81 degrees), Heliobond (31.98 ± 3.17 degrees), TransbondXT (35 ± 2.21 degrees). Conclusion: Icon can be safely used with the conventional adhesives tested on surfaces etched with either HCl or H3PO4. Keywords: adhesion, enamel, Icon, sealant, white spot lesion

Purpose: To evaluate the clinical effectiveness of indirect composite restorations in permanent molars with excessive substance loss in pediatric patients who have undergone root canal treatments. Materials and Methods: Molars of 29 pediatric patients underwent endodontic treatment. Sixteen molars were restored with an indirect posterior composite resin restoration and 13 molars were restored with a direct posterior composite resin restoration. The success of the restorations was evaluated for 2 years based on United States Public Health Service (USPHS) criteria, photographs after staining with basic fuchsine, and radiographic data. Data obtained from both groups were compared using the Mann-Whitney U-test and Wilcoxon signed rank test. Results: Evaluation of the clinical and radiographic data revealed no observable, statistically significant differences between the posterior and the indirect posterior composites (p > 0.05). However, evaluation of photos taken of the patients' molars after staining with basic fuchsin revealed that direct posterior composites showed increased staining on the margins of the restorations after six months (p 0.05). Conclusion: Considering the difficulties of restoring endodontically treated permanent teeth with excessive substance loss in child patients, indirect restorations may be seen as a better option. Keywords: indirect posterior composite, inlay, direct posterior composite, root canal treatment