Reduction In μTBS Research Articles

Dual-functional etchants that simultaneously demineralize and stabilize dentin render collagen resistant to degradation for resin bonding.

To develop dual-functional etchants that could demineralize and stabilize dentin collagen simultaneously, and to assess the effects of these etchants on collagen crosslinking, biostability and resin bonding properties under clinically relevant conditions. Dual-functional etchants were prepared by mixing 56% glycolic acid and 17% phosphoric acid and adding 1% of theaflavins (TF) or proanthocyanidins from grape seed extract (GSE). The etchant without crosslinker was used as control. The prepared human dentin specimens were treated with the 3 etchants for 30s and analyzed for chemical interaction using Fourier transform infrared spectroscopy and resistance of the demineralized layer to collagenase degradation using electron microscopy (EM). Resin-dentin interfacial bonding properties were evaluated after 24h and after 10,000 thermocycling through microtensile bond strength (μTBS), nanoleakage and matrix metalloproteinases (MMPs) activity via in situ zymography. Statistical analysis was done using ANOVA and post- hoc Tuckey's test. Compared to control, TF and GSE dual-functional etchants were able to demineralize dentin, induce collagen crosslinking and protect the demineralized layer from collagenase degradation within 30s. High resolution EM images showed better protection with TF etchant compared to GSE. There was a significant reduction in μTBS and an increase in nanoleakage and MMPs activity in control after thermocycling (p<0.05) while these changes weren't seen in dual-functional etchants. Dual-functional etchants, especially TF containing, provide collagen protection against degradation and result in stable μTBS and less nanoleakage and MMPs activity under clinically relevant conditions.

Bonding performance of experimental HEMA-free two-step universal adhesives to low C-factor flat dentin.

Experimental two-step universal adhesives (2-UAs) providing a particle-filled hydrophobic adhesive resin with a significant film thickness to hydrophobically seal the adhesive interface were designed and synthesized. This study aimed to characterize their interfacial interaction with dentin, to determine whether the 2-UA formulations achieve durable bonding to low C-factor flat dentin and to measure their water sorption. Bonding effectiveness of 2-UAs that combine a 10-MDP-based primer with hydrophobic adhesive resins differing only for filler (BZF-21, BZF-29, and BZF-29_hv) were comparatively investigated with the commercial adhesive Clearfil SE Bond 2 (C-SE2, Kuraray Noritake). Adhesive-dentin interfaces were characterized with TEM. Adhesive-resin disks were immersed in distilled water at 37°C for 1 week, 6 months and 1 year to measure water sorption and solubility. 'Immediate' and 'aged' micro-tensile bond strength (μTBS) of the adhesives applied in etch-and-rinse (E&R) and self-etch (SE) bonding mode to low C-factor flat dentin were measured. Statistical analyses involved linear mixed-effects (LME) modelling and Kruskal-Wallis testing (p<0.05). TEM revealed that E&R hybrid layers were more sensitive to aging than SE hybrid layers. Lower water sorption was recorded for all UAs compared with C-SE2. The immediate μTBS of BZF-21 and BZF-29 was not significantly different from that of C-SE2. The 1-year aged μTBS of all 2-UAs was significantly lower than that of C-SE2, except for BZF-29 applied in E&R mode. A significant reduction in μTBS upon 1-year aging was recorded for BZF-21 and BZF-29 applied in E&R mode. A significant difference in μTBS between E&R and SE bonding modes was recorded for all adhesives except BZF-21. Experimental 2-UAs with a hydrophobic adhesive-resin design produced±20-μm thick adhesive-resin layers, absorbed less water and resulted in bonding performance that was more aging-resistant when applied in SE than in E&R bonding mode. The silica-filled BZF-29 2-UA revealed the most comparable bonding performance with C-SE2 in a low C-factor condition (flat dentin).

Comparative evaluation of the effect of two natural collagen cross-linkers on microtensile bond strength of self-etch adhesive system to dentin after contamination with blood and hemostatic agent: An in vitro study.

Cavity preparation often causes gingival bleeding which can be controlled by hemostatic agents (HAs). These along with blood act as contaminants and hamper the bonding mechanism. Collagen cross-linkers (CCLs) are agents known to increase the bond strength (BS) to dentin. Hence, the purpose of this in vitro study was to determine the effect of two different CCLs, proanthocyanidin (grape seed extract [GSE]) and hesperidin on the microtensile BS (μTBS) of a self-etch adhesive (SEA) system to dentin which was contaminated with blood and a HA. Thirty-six extracted human molars were collected, and their occlusal surfaces were sectioned to expose the dentin. The teeth were randomly divided into four groups: Group I - Control, Group II - Contamination with blood and HA, Group III - Application of GSE after contamination, and Group IV - Application of hesperidin extract after contamination. The SEA was applied, followed by the use of a nanocomposite. Dentin-composite rods were obtained from each group, and μTBS testing was done. The fracture pattern was visually classified as an adhesive failure at the interface, cohesive failure in composite, or dentin. The scanning electron microscope (SEM) analysis was done for two samples from each group. Statistical analysis was done using the Student's unpaired "t" and ANOVA test. Group II showed a statistically significant reduction in μTBS in comparison to Group I. This was overcome in Groups III and IV. Hesperidin showed marginally better results than GSE. The use of GSE and hesperidin increases the μTBS of composite resin to dentin postcontamination with blood and ViscoStat Clear with Single Bond Universal Adhesive.

Experimental two-step universal adhesives bond durably in a challenging high C-factor cavity model.

To determine the bonding effectiveness of experimental 2-step universal adhesives (UAs) to high C-factor class-I cavity-bottom dentin and to assess the potential bond-strength contribution of an additional flowable composite layer. Three experimental 2-step UA formulations, involving the application of a 10-MDP-based primer followed by a hydrophobic adhesive resin with a 15-to-20-µm film thickness and differing only for filler, referred to as BZF-21 (silica and bioglass filler), BZF-29 (silica filler) and BZF-29_hv (higher silica-filler loading resulting in a higher viscosity), all prepared by GC, along with three representative commercial adhesives, Clearfil SE Bond 2 (C-SE2, Kuraray Noritake), G-Premio Bond (G-PrB, GC) and OptiBond FL (Opti-FL, Kerr), were comparatively investigated for their 'immediate' and 'aged' (50,000 thermocycles) micro-tensile bond strength (μTBS), when applied either in etch-and-rinse (E&R) or self-etch (SE) mode, to high C-factor class-I cavity-bottom dentin (n=10; 10 experimental groups). Four additional experimental groups involved the extra application of the flowable composite G-ænial Universal Flo (GC), employed as an intermediate liner in combination with the adhesives BZF-29 and G-PrB and again applied both in E&R or SE mode. Statistical analysis was performed using linear mixed-effects (LME) modelling and linear regression analysis (p<0.05). All 2-step UAs performed similarly when compared to the gold-standard E&R Opti-FL and SE C-SE2 adhesives, except for the aged μTBS of BZF-29_hv applied in E&R mode, and significantly outperformed the 1-step UA G-PrB. Significant reduction in μTBS upon aging was only recorded for 2-step UAs applied in E&R mode. The extra flowable composite layer significantly improved G-PrB's μTBS. The experimental 2-step UAs revealed favorable bonding performance in the challenging high C-factor class-I cavity model, comparable to that of the multi-step gold-standard E&R and SE adhesives and superior to that of the 1-step UA investigated. An additionally applied flowable composite layer compensated for the lower bonding effectiveness of the 1-step UA in the high C-factor cavity model.

Delayed light activation of resin composite affects the bond strength of adhesives under dynamic simulated pulpal pressure.

To evaluate the effect of a time delay before the light activation of resin composite on the microtensile bond strength (µTBS) of self-etch adhesives under dynamic simulated pulpal pressure. One hundred twenty crown segments were prepared from human third molars. Dentin surfaces were prepared with coarse diamond burs and connected to a dynamic pulpal pressure device. The self-etch adhesives used were Clearfil SE Bond (CSE), G2-Bond Universal (G2B), Clearfil Universal Bond Quick (CBQ), and G-Premio Bond (GPB). Each adhesive was divided into 3 subgroups: immediate light activation of resin composite (T0), delayed light activation for 150s (T1), and 300s (T2). The µTBS data were obtained after 24-h water storage. Scanning electron microscopy was used to evaluate the nanoleakage at the resin-dentin surface. The µTBS data were analyzed using two-way ANOVA and Duncan's multiple comparisons. All adhesives demonstrated a significant reduction in µTBS at T2, except for CBQ where the bond strength was not affected by the delayed light activation times. The two-step self-etch adhesives (CSE and G2B) demonstrated higher bond strength than the one-step adhesives at all conditions. Nanoleakage was observed in all adhesives at T2; however, nanoleakage was detected only in CBQ and GPB at T1. Delayed light activation of resin composite adversely affected the dentin bond strength of self-etch adhesives. Two-step self-etch adhesives had better bonding performance than one-step self-etch adhesives. After adhesive application, resin composite should be adapted and cured as soon as possible.

Collagen Cross-Linking Lignin Improves the Bonding Performance of Etch-and-Rinse Adhesives to Dentin.

To evaluate the biomodification ability of lignin used as pre-treatment in human dentin before the application of an etch-and-rinse adhesive. Experimental hydroethanolic solutions with different cross-linking agents were used: 6.5% proanthocyanidins (PAC, from grape-seed extract); 2% cardanol (CARD, from cashew-nut shell liquid); lignin (LIG, from eucalyptus) at 1, 2 or 4% concentrations. The negative control (NC) was ethanol 50 v%. Extracted molars were prepared, and dentin microtensile bond strength (μTBS) was evaluated after 24 h water storage or 10,000 thermocycling aging. Further specimens were processed for SEM nanoleakage, micropermeability confocal microscopy evaluation and in situ degree of conversion (DC) through micro-Raman spectroscopy. Demineralized dentin sticks were submitted to a three-point bending test to evaluate the elastic modulus (E) before and after 1 min biomodification using the tested solutions. Moreover, it was also evaluated the mass changes and hydroxyproline (HYP) release after 4-weeks of water storage. Vibrational collagen crosslinking identification was evaluated through micro-Raman spectroscopy. The results were analyzed by analysis of variance (ANOVA) and Tukey’s test (α = 0.05). A significant reduction in μTBS was observed in groups NC (p < 0.001) and CARD (p = 0.026). LIG-4% showed no significant reduction in μTBS after aging (p = 0.022). Nanoleakage micrographs showed hybrid layer protection with all agents, but reduced micropermeability was attained only with lignin. Polymerization was negatively affected in the presence of all tested cross-linking agents, except LIG-1%. Lignin and cardanol increased the dentin E values, but only lignin reduced the mass loss in dentin specimens. Effective collagen crosslinking (1117 cm−1 and 1235 cm−1) was detected for all agents. HYP release was significantly lower with LIG-1% than NC (p < 0.001). Lignin was able to perform collagen cross-linking and prevent the degradation of unprotected dentin collagen, thereby improving the bonding performance of the composite restorations performed in this study.

Effect of grape seed extract on the bond strength and adhesion durability of universal adhesive to dentin

The effects of grape seed extract (GSE) on the microtensile bond strength (µTBS) and resin-dentin bond durability of universal adhesive to dentin were investigated, while the resin-dentin interface was evaluated using a scanning electron microscope (SEM). Flat occlusal dentin surfaces of 80 sound human molars assigned to, control and GSE-pretreated groups & further divided into etch-and-rinse (E&R) and self-etch (SE) adhesion subgroups. In each subgroup, molars tested immediately (t0; n = 10) & after 6 months (t6; n = 10). In GSE-pretreated group, 10% GSE was prepared in hot water & then used for 1 min pretreatment after etching (15s) in the E&R subgroup or before application of adhesion in the SE subgroup. Composite build-ups made incrementally, and dentin beams sectioned and tested for µTBS at the baseline (24 h) and 6 months. Sections were obtained for SEM analysis. In the 6-month treatment, beams stored in artificial saliva, subjected to thermal cycling, and then tested. The failure modes of fracture surfaces were identified with a stereomicroscope. Comparing the t0 and t6 timepoints, significant reduction in µTBS in all groups compared with their respective controls after aging, but the percentage of bond loss due to aging in the GSE-pretreated groups was less than controls. Most failure modes were mixed. GSE (10%) pretreatment for 1 min before adhesion enhanced the durability of the resin-dentin bond but did not completely eliminate loss of bond strength.

Methacrylamide–methacrylate hybrid monomers for dental applications

ObjectivesThe susceptibility of methacrylates to hydrolytic and enzymatic degradation may be a contributing factor limiting the clinical lifespan of resin composite restorations. The elimination of labile ester bonds is a potential advantage of methacrylamides, which have been shown to produce more stable restorative interfaces. The rationale of this study is to design hydrolytically and enzymatically stable adhesive monomers, with the added benefit of being able to form crosslinked networks. The objective of this study was to synthesize difunctional, hybrid methacrylate-methacrylamide monomers, and evaluate them as potential monomers for dental adhesives. Materials and methodsHEMA, TEGDMA (controls) or secondary methacrylamides (HEMAM – commercially available, 2EM and 2dMM – newly synthesized) either bearing a hydroxyl group or a methacrylate functionality (Hybrids-Hy), were added at 40mass% to bisGMA. The photoinitiator system consisted of 2-dimethoxyphenyl acetophenone (DMPA) and diphenyl iodonium hexafluorophosphate (DPI-PF6) at 0.2 and 0.4mass%, respectively. Polymerization kinetics were followed in real-time by near-IR spectroscopy during light activation at 630mW/cm2 for 300s. Water sorption and solubility (WS, SL) were measured according to ISO 4049. Storage modulus in shear (G′) for 300s was obtained by oscillatory rheometry. For the microtensile bond strength (μTBS), fully formulated adhesives containing 40vol% ethanol were used to restore caries-free human third molars. Bonded specimens with 1mm2 cross-sectional area were tested after 48h and 6 months storage in water at 37°C. Single bond (SB) was tested as a commercial control. Data were analysed with one-way ANOVA and Tukey's test and Student's t-test (α=0.05). ResultsIn general, hybrid versions showed lower polymerization rate and degree of conversion, whereas the methacrylate controls, HEMA and TEGDMA, showed the highest values. The hybrid versions showed lower values of WS and SL than their monofunctional versions. HEMAM Hy showed the highest values of G′ and TEGDMA, 2EM, and 2dMM-Hy the lowest. The μTBS values between 48h and 6 months were statistically reduced only for the HEMA and both 2dMM materials. The formulation containing the monofunctional methacrylamide (HEMAM) showed only 9% reduction in μTBS after 6 months of aging, while the other groups showed a decrease ranging between 18% and 33%. ConclusionOverall, hybrid monomers showed lower reactivity than their analogous monofunctional versions, but had markedly lower water sorption. Shear storage modulus was affected differently by the addition of the second functionality. HEMAM-containing systems were able to maintain stable long-term dentin bond strength, which demonstrates that bonding stability is a result of the complex interplay among the factors studied. Clinical significanceThe novel monomers showed here are potential alternatives to the current methacrylate adhesives, with selected formulations presenting greater bond stability.

Characterization and Antibacterial Effect of an Experimental Adhesive Containing Different Concentrations of Proanthocyanidin.

To evaluate the degree of conversion (DC%), water sorption (Sp), solubility (Sl), dentin bond strength (μTBS) (immediate and after 12 months of storage), and the antibacterial effect of an experimental adhesive containing different concentrations (%) of proanthocyanidin (PA): 0, 1%, 2%, 4.5%, and 6% (PA0, PA1%, PA2%, PA4.5% and PA6%, respectively). DC% was measured by FT-IR and the Sp and Sl were determined based on the ISO 4049 specification. For μTBS, resin composite buildups were constructed incrementally and specimens (n = 8) were sectioned to obtain sticks (1 mm2). The μTBS was evaluated after 24 h and 12 months of water storage at 37°C. The failure mode was analyzed. The antibacterial effects were evaluated by analyzing the bacterial growth (S. mutans) (n = 5) and antibiofilm activity (n = 5) of the adhesives by spectrophotometry. The incorporation of PA did not affect the Sp, Sl, or DC%. Immediate μTBS was similar for all groups. After 12 months, PA4.5% presented significantly higher μTBS than PA0, while the other groups did not differ from PA0 and PA4.5%. Groups PA0 and PA1% underwent significant reduction in μTBS. In the experimental groups PA2%, PA4.5% and PA6%, μTBS was maintained after storage. All groups showed antibacterial activity. Incorporation of 2%, 4.5%, and 6% PA maintained the dentin μTBS after 12-month storage, without affecting the Sp, Sl, or DC% of experimental adhesives. PA4.5% presented higher μTBS values than PA0 after 12 months. The adhesive presented antibacterial effect irrespective of PA concentration.

Bonding to enamel using alternative Enamel Conditioner/etchants

ObjectiveEnamel bond durability of three new alternative etchants combined with three representative adhesives was determined. MethodsThe ‘immediate’ and ‘aged’ micro-tensile bond strength (μTBS) of the 3-step etch&rinse adhesive OptiBond FL (‘O-FL’, Kerr), 2-step self-etch (SE) adhesive Clearfil SE Bond 2 (‘C-SE2’, Kuraray Noritake) and universal adhesive Adhese Universal (‘ADU’, Ivoclar Vivadent) were measured when bonded to enamel following either a proprietary organic acid-containing Enamel Conditioner (‘EC’, Shofu), a phosphoric-acid monomer-containing Multi Etchant (‘ME’, Yamakin: 10-methacryloyloxy tetraethylene glycol dihydrogenphosphate or MTEGP), or a metal salt-based ZON etchant (‘ZON’, Ivoclar Vivadent: ZrO(NO3)2). All alternative etchants were used in replacement of phosphoric acid, the latter (K-Etchant, Kuraray Noritake) also used with O-FL and ADU, in addition to C-SE2 that was solely used in SE mode (controls). The enamel-etching patterns and de-bonded fracture surfaces were examined by SEM, while the interfaces with enamel were ultra-morphologically characterized by TEM. ResultsNo statistically significant difference in immediate and aged μTBS, obtained by combining the three alternative etchants with the three adhesives, was recorded as compared with the respective controls, except for ME combined with O-FL. Upon aging, significant reduction in μTBS was recorded for the ME/C-SE2 and ME/ADU combinations. The percentage of adhesive failures increased with aging. SEM revealed similar etching patterns produced by EC and ZON as by classic phosphoric-acid etching, for which also numerous micro-resin tags at the adhesive-enamel interface were disclosed. SignificanceDurable bonding to enamel was generally obtained for all etchant/adhesive combinations with the exception of the ME/O-FL combination.

Effect of Phosphoric Acid Containing MMP-Inactivator on the Properties of Resin Bonding to Eroded Dentin.

To evaluate the effect of two phosphoric acids containing protease inactivators (chlorhexidine and proanthocyanidin) on the resin/eroded-dentin microtensile bond strength (μTBS), nanoleakage (NL), and in situ degree of conversion (DC) of three universal adhesives applied in the etch-and-rinse mode. One hundred twenty-six molars were randomly assigned to 18 experimental conditions according to the combination of the independent variables: eroded dentin (soft drink and citric acid), adhesive (Prime&Bond Elect [PBE, Dentsply Sirona], Scotchbond Universal Adhesive [SBU, 3M Oral Care], and Tetric N-Bond Universal [TEU, Ivoclar Vivadent]), and acid pretreatment (conventional phosphoric acid [CP acid]; chlorhexidine acid [CHX acid]; and proanthocyanidin acid [PA acid]). After restorations, specimens were sectioned into resin-dentin sticks (ca 0.8 mm2) that were then tested under tension (crosshead speed: 0.5 mm/min). Selected sticks from each tooth were used to evaluate NL and DC. Data from all tests were subjected to three-way ANOVA and Tukey's test (α=0.05). Dentin eroded with citric acid showed a significant reduction in μTBS for each adhesive in comparison to dentin eroded with the soft drink (p < 0.001). For dentin eroded with CHX acid and PA acid, the μTBS (p > 0.03) significantly improved and NL decreased for all adhesives (p < 0.004); in addition, the DC improved for two of the three adhesives tested (SBU and TEU) (p < 0.03) when CHX acid and PA acid were compared to CP acid. The addition of chlorhexidine and proanthocyanidin to phosphoric acid improved the adhesive performance when compared with conventional phosphoric acid, without jeopardizing adhesive polymerization at the resin/eroded-dentin interface.

Effect of epigallocatechin-3- gallate solutions on bond durability at the adhesive interface in caries-affected dentin

Hydrolytic and enzymatic degradation by matrix metalloproteinases (MMPs) reduces the durability of composite resin restorations on caries-affected dentin (CAD). The use of MMP inhibitors such as epigallocatechin-3-gallate (EGCG) could increase the longevity of the bond to dentin. This study aimed to evaluate the use of EGCG at different aqueous concentrations on the resin-dentin microtensile bond strength (μTBS), fracture pattern and nanoleakage (NL) in immediate (IM) time interval and after 12-months of water storage (1Y) when using a two-step etch-and-rinse adhesive system on CAD. Dentin surfaces of 40 human molars were submitted to a microbiological caries induction protocol and randomized into 5 groups (n = 8) (0.02% EGCG; 0.2% EGCG; 0.5% EGCG; 2% Chlorhexidine [CHX] and no treatment as Control Group - [NT]). After acid etching, the solutions were applied for 60 s followed by application of dental adhesive (Adper Single Bond 2, 3 M ESPE) to CAD surfaces. Subsequently, a resin composite (4 mm) block was built on the dentin. After 24 h, the teeth were sectioned into beam-shaped specimens (cross-sectional area of 1 mm2 and 8-mm high). Half of the specimens were tested in IM and the other half after 1Y. Two samples per tooth were submitted to SEM for NL evaluation. Data were statistically analyzed by two-way ANOVA and Tukey tests (α = 0.05). The results showed that use of EGCG and CHX did not affect μTBS in IM (p > 0.05). After 1Y, there was a reduction in μTBS for all experimental groups (p < 0.05). Adhesive fractures predominated in IM in all groups, except for 0.05% EGCG and NT. After 1Y, there was an increase in these adhesive fractures in all groups. For NL, all agents applied reduced NL in comparison with CT (p < 0.001). CHX showed lower NL (p < 0.001), followed by 0.02% and 0.5% EGCG. NT showed highest NL for both time intervals (p < 0.001). Thus, although the use of EGCG at different concentrations and CHX reduced the NL, they were unable to reduce degradation of μTBS to CAD over time.

The effect of dentine pre-treatment using bioglass and/or polyacrylic acid on the interfacial characteristics of resin-modified glass ionomer cements

ObjectiveTo evaluate the effect of load-cycle aging and/or 6 months artificial saliva (AS) storage on bond durability and interfacial ultramorphology of resin-modified glass ionomer cement (RMGIC) applied onto dentine air-abraded using Bioglass 45S5 (BAG) with/without polyacrylic acid (PAA) conditioning. MethodsRMGIC (Ionolux, VOCO) was applied onto human dentine specimens prepared with silicon-carbide abrasive paper or air-abraded with BAG with or without the use of PAA conditioning. Half of bonded-teeth were submitted to load cycling (150,000 cycles) and half immersed in deionised water for 24 h. They were cut into matchsticks and submitted immediately to microtensile bond strength (μTBS) testing or 6 months in AS immersion and subsequently μTBS tested. Results were analysed statistically by two-way ANOVA and Student–Newman–Keuls test (α = 0.05). Fractographic analysis was performed using FE-SEM, while further RMGIC-bonded specimens were surveyed for interfacial ultramorphology characterisation (dye-assisted nanoleakage) using confocal microscopy. ResultsRMGIC applied onto dentine air-abraded with BAG regardless PAA showed no significant μTBS reduction after 6 months of AS storage and/or load cycling (p > 0.05). RMGIC–dentine interface showed no sign of degradation/nanoleakage after both aging regimens. Conversely, interfaces created in PAA-conditioned SiC-abraded specimens showed significant reduction in μTBS (p < 0.05) after 6 months of storage and/or load cycling with evident porosities within bonding interface. ConclusionsDentine pre-treatment using BAG air-abrasion might be a suitable strategy to enhance the bonding performance and durability of RMGIC applied to dentine. The use of PAA conditioner in smear layer-covered dentine may increase the risk of degradation at the bonding interface. Clinical significanceA combined dentine pre-treatment using bioglass followed by PAA may increase the bond strength and maintain it stable over time. Conversely, the use of PAA conditioning alone may offer no significant contribute to the immediate and prolonged bonding performance.

Glutaraldehyde collagen cross-linking stabilizes resin-dentin interfaces and reduces bond degradation.

This study evaluated the stability of resin-dentin interfaces treated with glutaraldehyde-containing agents, and assessed collagen degradation in dentin matrices treated with Gluma. Microtensile bond strength (μTBS) was evaluated 24 h and 6 months after treatment with three desensitizers (Gluma Desensitizer, Gluma Desensitizer Power Gel, and MicroPrime G) and two etch-and-rinse adhesives (Comfort Bond & Desensitizer and iBond TE). Demineralized beams of human dentin were treated with water or Gluma, and the degradation of collagen in these beams was assessed by quantification of the dry mass loss and of the amount of hydroxyproline released from hydrolyzed specimens after 1 or 4 wk. All groups demonstrated significant reduction in μTBS after 6 months, except for Gluma Desensitizer and iBond TE groups, which showed decreases of 7.2% and 10.8%, respectively. The most prevalent failure mode was 'mixed'. Significantly less hydroxyproline was released from Gluma-treated beams than from control beams after 4 wk. Beams treated with Gluma yielded significantly less dry mass loss than did beams in the control group. Collagen cross-linking with glutaraldehyde-containing agents may assist in the stabilization of resin-dentin bonds by reducing the amount of collagen solubilized from dental matrices in the hybrid layer. In turn, this may contribute to the preservation of adhesive interfaces.

Comparative evaluation of the microtensile bond strength of bulk fill and low shrinkage composite for different depths of Class II cavities with the cervical margin in cementum: An in vitro study.

Aim:The aim of this study was to evaluate the microtensile bond strength (μTBS) of bulk fill and low shrinkage composite for different depths of Class II cavities with the cervical margin in cementum.Materials and Methods:Standardized conservative box-shaped Class II cavities were prepared on sixty sound-impacted human third molars. The samples were randomly divided into two groups: Group I (n = 30) - horizontal incremental technique and Group II (n = 30) - bulk fill technique (SonicFill). They were further subdivided into three subgroups of (n = 10) samples each according to the different occluso-gingival height: subgroup (A - 4 mm, B - 5 mm, and C - 6 mm). The gingival margins for all the samples were located 1 mm below the cementoenamel junction. The restored samples were subjected to thermocycling (500 cycles) followed by μTBS testing. The scores were statistically analyzed using ANOVA and post hoc test using SPSS software version 16.Results:Subgroups IA and IB showed lower μTBS than subgroups IIA and IIB (P < 0.05) whereas subgroup IC showed higher μTBS than subgroup IIC (P < 0.05). SonicFill showed a significant reduction in μTBS as the depth increased.Conclusion:SonicFill should be used in two increments for cavities with a depth of more than 5 mm.

Chemical interaction of 10-MDP (methacryloyloxi-decyl-dihydrogen-phosphate) in zinc-doped self-etch adhesives

ObjectivesZinc-doped dentine adhesives have been recently advocated to interfere with metallo-proteinases-mediated collagen degradation. Nevertheless, there is a little information about the effects of zinc ions on the chemical interaction of self-etch functional monomers to dentine. The aim of this study was to assess if the inclusion of zinc into the primers of self-etch adhesives containing MDP (10-methacryloyloxi-decyl-dihydrogen-phosphate) may interfere with their chemical interaction to calcium/dentine. MethodsCaries-free human molars were bonded using two commercial self-etching adhesives [Clearfil SE bond (CSE) and S3 bond (S3)] doped with zinc nitrate and submitted to microtensile bond strength (μTBS) and interface nanoleakage evaluation. Moreover, MDP was synthesised to evaluate the chemical interaction with calcium/dentine through atomic absorption spectroscopy (AAS) and SEM-EDX in the presence or absence of zinc ions. ResultsAAS showed increasing formation of MDP–zinc rather than MDP–calcium salts (p=0.002) in the presence of zinc. SEM-EDX confirmed the formation of zinc-rich phosphate deposits that were probably responsible for the significant reduction in μTBS and increased interfacial nanoleakage attained with zinc-doped CSE and S3. ConclusionThese outcomes demonstrated that the excessive presence of zinc ions may jeopardise the bonding performance of MDP-containing self-etch adhesives.

Bioactive effects of a calcium/sodium phosphosilicate on the resin–dentine interface: a microtensile bond strength, scanning electron microscopy, and confocal microscopy study

This study evaluated, through microtensile bond strength (μTBS) testing, the bioactive effects of a calcium/sodium phosphosilicate (BAG) at the resin-dentine interface after 6 months of storage in phosphate buffer solution (PBS). Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were also performed. Three bonding protocols were evaluated: (i) RES-Ctr (no use of BAG), (ii) BAG containing adhesive (BAG-AD), and (iii) BAG/H (3) PO (4) before adhesive (BAG-PR). The dentin-bonded specimens were prepared for μTBS testing, which was carried out after 24 h or 6 months of storage in PBS. Scanning electron microscopy ultramorphology analysis was performed after debonding. Confocal laser scanning microscopy was used to evaluate the morphological and nanoleakage changes induced by PBS storage. High μTBS values were achieved in all groups after 24 h of storage in PBS. Subsequent to 6 months of storage in PBS the specimens created using the BAG-AD bonding approach still showed no significant reduction in μTBS. Moreover, specimens created using the BAG-AD or the BAG-PR approach showed an evident reduction of nanoleakage after prolonged storage in PBS. The use of BAG-containing adhesive may enhance the durability of the resin-dentine bonds through therapeutic/protective effects associated with mineral deposition within the bonding interface and a possible interference with collagenolytic enzyme activity (matrix metalloproteinases) responsible for the degradation of the hybrid layer.

Influence of air‐abrasion executed with polyacrylic acid‐Bioglass 45S5 on the bonding performance of a resin‐modified glass ionomer cement

The aim of this study was to test the microtensile bond strength (μTBS), after 6 months of storage in PBS, of a resin-modified glass ionomer cement (RMGIC) bonded to dentine pretreated with Bioglass 45S5 (BAG) using various etching and air-abrasion techniques. The RMGIC (GC Fuji II LC) was applied onto differently treated dentine surfaces followed by light curing for 30 s. The specimens were cut into matchsticks with cross-sectional areas of 0.9 mm(2). The μTBS of the specimens was measured after 24 h or 6 months of storage in PBS and the results were statistically analysed using two-way anova and the Student-Newman-Keuls test (α = 0.05). Further RMCGIC-bonded dentine specimens were used for interfacial characterization, micropermeability, and nanoleakage analyses by confocal microscopy. The RMGIC-dentine interface layer showed no water absorption after 6 months of storage in PBS except for the interdiffusion layer of the silicon carbide (SiC)-abraded/polyacrylic acid (PAA)-etched bonded dentine. The RMGIC applied onto dentine air-abraded with BAG/H(2)O only or with BAG/PAA-fluid followed by etching procedures (10% PAA gel) showed no statistically significant reduction in μTBS after 6 months of storage in PBS. The abrasion procedures performed using BAG in combination with PAA might be a suitable strategy to enhance the bonding durability and the healing ability of RMGIC bonded to dentine.

Micro-tensile bond strength and interfacial characterization of an adhesive bonded to dentin prepared by contemporary caries-excavation techniques

Objectives To evaluate the micro-tensile bond strength (μTBS) and interfacial characteristics of adhesive–dentin bonds produced after caries-removal with contemporary techniques. Methods Carious molars were cut at the base of the fissure, exposing ‘sound’ and ‘carious’ dentin at different spots. After caries-excavation, a composite was bonded using a 2-step self-etch adhesive. The μTBS was measured and the mode of fracture analyzed using a stereomicroscope and imaged by Feg-SEM, while additional non-fractured specimens were histologically analyzed after Masson's trichrome staining in order to identify potentially incompletely resin-enveloped collagen. Results μTBS to residual caries-excavated dentin was lower than to sound dentin. The different caries-removing techniques had a significant effect on the μTBS. Er:YAG laser guided by a LIF-feedback system (Kavo) resulted in the lowest μTBS (26.8% lower than to ‘sound’ dentin) and a distinct layer of incompletely resin-enveloped collagen at the interface. Although different degrees of collagen exposure were seen for other caries-removing techniques, such as a thick layer for CeraBur (Komet-Brasseler), some unprotected collagen areas for Cariex (Kavo), or completely resin-enveloped collagen for a tungsten-carbide-bur (Komet), the μTBS appeared not directly affected (10%, 16.6%, and 15.3% lower than to ‘sound’ dentin, respectively). Carisolv (MediTeam) resulted in the highest μTBS (only 1% reduction compared to that to ‘sound’ dentin), followed by the tungsten-carbide-bur aided by Caries Detector (Kuraray) (4.8% reduction). Enzymatic caries excavation using the experimental SFC-VIII (3M-ESPE) aided by a disposable plastic instrument resulted in a 19.4% reduction in μTBS as compared to that to ‘sound’ dentin. Significance The dentin bonding receptiveness depends to a large extent on the caries-excavation method employed.

Effect of smear layer characteristics on dentin bonding durability of HEMA-free and HEMA-containing one-step self-etch adhesives

The purpose of this study was to evaluate the effect of smear layer characteristics on the dentin bonding durability of HEMA-free and HEMA-containing one-step self-etch adhesives. Xeno V (XV; HEMA-free), G BOND PLUS (GB; HEMA-free) and Clearfil S(3 )Bond (S(3); HEMA-containing), were applied to dentin surfaces prepared with either #180- or #600-grit SiC paper according to manufacturers' instructions. Bond strengths to dentin were determined using µTBS test after 24-hour, 6-month, and 1-year water storage. In addition, nanoleakage evaluation was performed using an SEM. The smear layer characteristics affected water-tree nanoleakage formation in the adhesive layers of XV and GB, which contributed to a reduction in µTBS after 6-month water storage, while the characteristics did not affect the µTBS of S(3). However, regardless of the smear layer characteristics, 1-year water storage significantly reduced the µTBS of all the adhesives and was associated with an increase in failures at the adhesive-composite interface.