In vitro evaluation of bonding effectiveness to dentin of all-in-one adhesives

Objectives

The study was aimed at assessing the bonding potential of all-in-one adhesives to dentin.

Methods

The microtensile bond strength of the all-in-one adhesives Bond Force (Tokuyama), AdheSE One (Ivoclar-Vivadent), and Xeno V (Dentsply) was measured in comparison with the etch-and-rinse system XP Bond (Dentsply). The ultrastructural characteristics of dentin–adhesive interface were observed under scanning electron microscope (SEM). Twenty human extracted third molars had their mid-coronal dentin exposed and ground with wet 600-grit SiC paper in order to create a standardized smear layer. Bonding procedures were performed according to the manufacturers’ instructions and microtensile beams were obtained with the “non-trimming” technique. The bond strengths in MPa were statistically analyzed including pre-test failures as “zero” values (Kolmogorov–Smirnov test, Levene's test, One-Way ANOVA, Tukey's test p < 0.05).

Results

The following bond strengths were recorded in MPa (mean ± standard deviation): AdheSE One 31.7 ± 21.3; Xeno V 42.8 ± 26.4; Bond Force 43.3 ± 22.1; XP Bond 51.9 ± 18.6. The statistical analysis demonstrated that the bond strengths achieved by Bond Force and Xeno V were similar to that of the etch-and-rinse adhesive, whereas the bond strength of AdheSE One was significantly lower. A distinct hybrid layer with resin tags was seen only in XP Bond specimens. All-in-one adhesives demonstrated a rather superficial interaction with the dentin substrate.

Conclusions

Although the strongest bond to dentin was established by the etch-and-rinse system, however the all-in-one adhesives containing organic solvents reached bond strength levels that were comparable from a statistical point of view.     

The effect of dimethyl sulfoxide (DMSO) on dentin bonding and nanoleakage of etch-and-rinse adhesives

Objective

The objective was to examine the effect of a solvent dimethyl sulfoxide (DMSO) on resin–dentin bond durability, as well as potential functional mechanisms behind the effect.

Methods

Microtensile bond strength (μTBS) was evaluated in extracted human teeth in two separate experiments. Dentin specimens were acid-etched and assigned to pre-treatment with 0.5 mM (0.004%) DMSO as additional primer for 30 s and to controls with water pre-treatment. Two-step etch-and-rinse adhesive (Scotchbond 1XT, 3M ESPE) was applied and resin composite build-ups were created. Specimens were immediately tested for μTBS or stored in artificial saliva for 6 and 12 months prior to testing. Additional immediate and 6-month specimens were examined for interfacial nanoleakage analysis under SEM. Matrix metalloproteinase (MMP) inhibition by DMSO was examined with gelatin zymography. Demineralized dentin disks were incubated in 100% DMSO to observe the optical clearing effect.

Results

The use of 0.5 mM DMSO had no effect on immediate bond strength or nanoleakage. In controls, μTBS decreased significantly after storage, but increased significantly in DMSO-treated group. The control group had significantly lower μTBS than DMSO-group after 6 and 12 months. DMSO also eliminated the increase in nanoleakage seen in controls. 5% and higher DMSO concentrations significantly inhibited the gelatinases. DMSO induced optical clearing effect demonstrating collagen dissociation.

Significance

DMSO as a solvent may be useful in improving the preservation of long-term dentin–adhesive bond strength. The effect may relate to dentinal enzyme inhibition or improved wetting of collagen by adhesives. The collagen dissociation required much higher DMSO concentrations than the 0.5 mM DMSO used for bonding.     

Adhesive performance of a multi-mode adhesive system: 1-Year in vitro study

Objectives

The aim of this study was to investigate the adhesive stability over time of a multi-mode one-step adhesive applied using different bonding techniques on human coronal dentine. The hypotheses tested were that microtensile bond strength (μTBS), interfacial nanoleakage expression and matrix metalloproteinases (MMPs) activation are not affected by the adhesive application mode (following the use of self-etch technique or with the etch-and-rinse technique on dry or wet dentine) or by ageing for 24 h, 6 months and 1 year in artificial saliva.

Methods

Human molars were cut to expose middle/deep dentine and assigned to one of the following bonding systems (N = 15): (1) Scotchbond Universal (3M ESPE) self-etch mode, (2) Scotchbond Universal etch-and-rinse technique on wet dentine, (3) Scotchbond Universal etch-and-rinse technique on dry dentine, and (4) Prime&Bond NT (Dentsply De Trey) etch-and-rinse technique on wet dentine (control). Specimens were processed for μTBS test in accordance with the non-trimming technique and stressed to failure after 24 h, 6 months or 1 year. Additional specimens were processed and examined to assay interfacial nanoleakage and MMP expression.

Results

At baseline, no differences between groups were found. After 1 year of storage, Scotchbond Universal applied in the self-etch mode and Prime&Bond NT showed higher μTBS compared to the other groups. The lowest nanoleakage expression was found for Scotchbond Universal applied in the self-etch mode, both at baseline and after storage. MMPs activation was found after application of each tested adhesive.

Conclusions

The results of this study support the use of the self-etch approach for bonding the tested multi-mode adhesive system to dentine due to improved stability over time.

Clinical significance

Improved bonding effectiveness of the tested universal adhesive system on dentine may be obtained if the adhesive is applied with the self-etch approach.     

Towards a better understanding of the adhesion mechanism of resin-modified glass-ionomers by bonding to differently prepared dentin

Objectives

The purpose of this study was to evaluate the bonding effectiveness of a resin-modified glass-ionomer (RMGI) to differently prepared dentin and how this restorative material interacts with these distinct substrates. Also the potential adhesion-promoting role of a polyalkenoic-acid conditioner was assessed.

Methods

Forty-eight dentin surfaces were prepared from sound human molars and randomly distributed among 6 experimental groups. Fuji II LC (GC) was applied on bur-cut (100 μm diamond), fractured and Er:YAG laser-irradiated (200 mJ, 10 Hz, 31.4 J/cm²) dentin with or without the beforehand application of the aqueous polyalkenoic-acid conditioner, Cavity Conditioner (GC). After 7 days of storage in water at 37 °C, specimens were prepared for microtensile bond strength testing (μTBS), as well as for TEM characterization of the resultant RMGI-dentin interface. Statistical analysis of the μTBS results was performed using ANOVA and Tukey's test (p < 0.05).

Results

The use of conditioner resulted in a significantly higher bond strength only when dentin was prepared by diamond bur (p < 0.05). Laser irradiation induced micro-cracks on the dentin surface and led to the lowest bond strength, irrespective of the use of conditioner (p < 0.05). Fuji II LC was able to partially demineralise (up to 2.0 μm) and infiltrate bur-cut and fractured dentin, but no evident interaction was observed at the interface between the RMGI and laser-irradiated dentin.

Conclusions

Laser-induced surface modifications impaired the interaction of the RMGI with dentin, thereby negatively influencing its bonding effectiveness. The use of a polyalkenoic-acid conditioner remains crucial for the RMGI to bond effectively to bur-cut dentin.     

Correlation between degree of conversion,resin–dentin bond strength and nanoleakage of simplified etch-and-rinse adhesives

Objectives

The aim of this study was to correlate the degree of conversion measured inside the hybrid layer (DC) with the microtensile resin–dentin bond strength (μTBS) and silver nitrate uptake or nanoleakage (SNU) for five simplified etch-and-rinse adhesive systems.

Methods

Fifty-five caries free extracted molars were used in this study. Thirty teeth were used for μTBS/SNU [n = 6] and 25 teeth for DC [n = 5]. The dentin surfaces were bonded with the following adhesives: Adper Single Bond 2 (SB), Ambar (AB), XP Bond (XP), Tetric N-Bond (TE) and Stae (ST) followed by composite resin build-ups. For μTBS and SNU test, bonded teeth were sectioned in order to obtain stick-shaped specimens (0.8 mm²), which were tested under tensile stress (0.5 mm/min). Three bonded sticks, from each tooth, were not tested in tensile stress and they were immersed in 50% silver nitrate, photo-developed and analyzed by scanning electron microscopy. Longitudinal 1-mm thick sections were prepared for the teeth assigned for DC measurement and evaluated by micro-Raman spectroscopy.

Results

ST showed lowest DC, μTBS, and higher SNU (p < 0.05). All other adhesives showed similar DC, μTBS, and SNU (p > 0.05), except for TE which showed an intermediate SNU level. The DC was positively correlated with μTBS and negatively correlated with SNU (p < 0.05). SNU was also negatively correlated with μTBS (p < 0.05).

Significance

The measurement of DC inside the hybrid layer can provide some information about bonding performance of adhesive systems since this property showed a good correlation with resin–dentin bond strength and SNU values.     

Slow progression of dentin bond degradation during one-year water storage under simulated pulpal pressure

Objectives

To evaluate the dentin bond durability of simplified adhesives after one-year (1 y) under water storage and simulated pulpal pressure.

Methods

Class I cavities were prepared in sixty human third molars with the pulpal wall located in mid-coronal dentin. The roots were cut off to expose the pulpal chamber, and the teeth were assembled in a pulpal pressure simulator device. A two-step etch-and-rinse adhesive (Single Bond 2/SB), a two-step self-etch adhesive (Clearfil SE Bond/CSE), a three-step self-etch adhesive (Adper Scotchbond SE/SSE) and three all-in-one adhesives (Adper Easy Bond/EB, Clearfil S³ Bond/S3 and Adhese One/AO) were applied according to manufacturer? instructions. No enamel pre-etching was used for the self-etch systems. The cavities were filled with a composite (Z250, 3M ESPE) in four to five horizontal increments and individually cured. Immediately after the final cure, pulpal pressure was set to 15 cm H₂O. After 24 h and 1 y under simulate pulpal pressure the teeth were cut following a ‘nontrimming’ microtensile test technique (n = 30) and tested in tension. Kruskall–Wallis and post hoc multiple comparisons were used at α = 0.05. Weibull statistics was applied to SB, CSE and EB. Fractographic analysis of debonded specimens was performed using scanning electron microscopy.

Results

At 24 h and 1 y periods, SB showed higher bond strength means than all the others adhesives tested. CSE was not statistically different from EB at 24 h and from EB and SB at 1 y. EB showed bond strength statistically higher than the other three self-etch adhesives, which were not statistically different from each other at 24 h. AO showed significantly lower bond strength than all tested materials after 1 y. For all adhesives the mean bond strength at 1 y were not statistically different from the values measured at 24 h (p > 0.05). Shifts in failure mode patterns and Weibull modulus decrease indicate some degree of bond degradation after the 1 y storage period.

Conclusion

One-year of simulated pulpal pressure did not affect dentin bond strength of simplified adhesives in Class I restorations. Signs of degradation were only revealed by fractographic analysis and reliability parameters.     

Nanotube-modified dentin adhesive—Physicochemical and dentin bonding characterizations

Objective

The aim of this study was to investigate the effect of aluminosilicate clay nanotubes (Halloysite, HNT) incorporated into the adhesive resin of a commercially available three-step etch and rinse bonding system (Adper Scotchbond Multi-Purpose/SBMP) on dentin bond strength, as well as the effect on several key physicochemical properties of the modified adhesive.

Methods

Experimental adhesives were prepared by adding five distinct HNT amounts (5–30 wt.%) into the adhesive resin (w/v) of the SBMP dentin bonding system. Bond strength to human dentin, microhardness, and degree of conversion (DC) of the modified adhesives were assessed.

Results

From the shear bond strength data, it was determined that HNT incorporation at a concentration of 30 wt.% resulted in the highest bond strength to dentin that was statistically significant (p = 0.025) when compared to the control. Even though a significant increase in microhardness (p < 0.001) was seen for the 30 wt.% HNT-incorporated group, a significantly lower DC (p < 0.001) was recorded when compared to the control.

Significance

It was concluded that HNT can be incorporated up to 20 wt.% without jeopardizing important physicochemical properties of the adhesive. The modification of the SBMP dentin bonding agent with 20 wt.% HNT appears to hold great potential toward contributing to a durable dentin bond; not only from the possibility of strengthening the bond interface, but also due to HNT intrinsic capability of encapsulating therapeutic agents such as matrix metalloproteinase (MMP) inhibitors.     

A randomized controlled 5-year prospective study of two HEMA-free adhesives,a 1-step self etching and a 3-step etch-and-rinse,in non-carious cervical lesions

Objective

The aim of this study was to evaluate the 5 year clinical dentin bonding effectiveness of two HEMA-free adhesives in Class V non-carious cervical lesions.

Material and methods

A total of 169 Class V restorations were placed in 67 patients with a self-etching adhesive (G-Bond; 67), a 3-step HEMA and TEGDMA free etch-and-rinse (cfm; 51) and a control HEMA-containing etch-and-rinse adhesive (XP Bond; 51) in non-carious cervical lesions without intentional enamel involvement. The restorations were evaluated at baseline and yearly during a 5 year follow-up with modified USPHS criteria. Dentin bonding efficiency was determined by the percentage of lost restorations.

Results

During the 5 years, 159 restorations could be evaluated. Good short time dentin retention was observed for the three adhesives, there all adhesives fulfilled at 18 months the full acceptance ADA criteria. At 5 years a cumulative number of 22 lost restorations (13.8%) was observed. The HEMA-free adhesives showed significantly higher dentin retention compared to the HEMA-containing one. Loss of retention was observed for 5 G-Bond (7.9%), 4 cfm (8.3%) and 13 XP Bond (27.1%) restorations (p < 0.05). No post-operative sensitivity was reported by the participants. No secondary caries was observed.

Significance

The durability in non-carious cervical lesions of the HEMA-free adhesives was successful after 5 years. Despite concerns which have been raised, showed the 1-step SEA one of the best reported clinical dentin bonding effectiveness.     

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

Objectives

Zinc-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.

Methods

Caries-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.

Results

AAS 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.

Conclusion

These outcomes demonstrated that the excessive presence of zinc ions may jeopardise the bonding performance of MDP-containing self-etch adhesives.     

Cross-linking effect on dentin bond strength and MMPs activity

Objective

The objectives of the study were to evaluate the ability of a 1-ethyl-3 (3-dimethylaminopropyl) carbodiimide (EDC)-containing primer to improve immediate bond strength of either self-etch or etch-and-rinse adhesive systems and to stabilize the adhesive interfaces over time. A further objective was to investigate the effect of EDC on the dentinal MMPs activity using zymographic analysis.

Active application improves the bonding performance of self-etch adhesives to dentin

Objectives

To evaluate the effect of application method on immediate and 6-month resin–dentin microtensile bond strength (μTBS) and nanoleakage (NL) of three one-step self-etch adhesives systems (Clearfil S³ Bond (S3), Xeno III (XE) and Adper Prompt L-Pop (AD)).

Methods

The oclusal enamel of 30 human molar was removed in order to expose a flat dentin surface. The adhesives were applied under two modes: inactive (IN) or active (AC) application. After light-curing (600 mW/cm² for 10 s), composite buildups were constructed incrementally and sectioned to obtain bonded sticks (0.8 mm²) to be tested in tension immediately (IM) or after 6 months (6M) of water storage. For NL, three bonded sticks from each tooth at each time were coated with nail varnish, placed in silver nitrate and polished down with SiC paper. The μTBS data were submitted to a two-way ANOVA and Tukey’s test for each adhesive (α = 0.05).

Results

The AC showed higher μTBS to dentin when compared to IN in both periods of time (p = 0.001). Only for AD, lower μTBS was seen after 6M for IN and AC techniques. XE and S3 adhesives applied under IN showed a higher amount of silver penetration throughout the hybrid layer. Low silver nitrate deposition was seen for these adhesives under AC. After 6M, AD showed a higher amount of silver nitrate uptake under IN and AC techniques.

Conclusions

AC improves the bonding performance of all one-step self-etch adhesive systems tested regardless of the time and this tendency was maintained over time.     

Dicalcium phosphate (CaHPO4·2H2O) precipitation through ortho- or meta-phosphoric acid-etching: Effects on the durability and nanoleakage/ultra-morphology of resin–dentine interfaces

Objectives

To compare the effects of two etching procedures using meta-phosphoric (MPA) or ortho-phosphoric acid (OPA) on dentine demineralisation, resin–dentine bonds durability and interface nanoleakage/ultra-morphology.

Methods

Middle-dentine specimens were etched using 37% OPA (15 s) or 40% MPA (60 s) and submitted to infrared spectroscopy (FTIR) or ultra-morphology dye-assisted (calcium-staining) confocal microscopy (Ca-CLSM). A three-step etch-and-rinse adhesive was formulated, applied onto dentine and light-cured for 30 s before composite build-up. After 24 h, the dentine-bonded specimens were cut into 1 mm² beams; half were immediately submitted to microtensile bond strength (μTBS) and half stored in DW for six months. The μTBS results were analysed with repeated-measures ANOVA and Tukey's test (p < 0.05). Further teeth were bonded and prepared for interface nanoleakage/ultra-morphology confocal evaluation.

Results

FTIR and Ca-CLSM analyses showed dicalcium phosphate dihydrate (Brushite) precipitation in MPA-etched dentine and on the bottom (front of demineralisation) of the OPA-etched dentine. Statistical analysis showed similar μTBS for both etching procedures after 24 h. The μTBS of specimens in OPA-group dropped significantly (p < 0.05) after six month; the specimens in the MPA group showed no statistically difference (p > 0.05). CLSM depicted no evident sign of nanoleakage within the resin–dentine interface of the MPA-treated specimens, while the specimens in OPA-group presented intense nanoleakage and interface degradation.

Conclusion

The use of MPA (60 s) as an alternative dentine conditioning agent in etch-and-rinse bonding procedures may be a suitable strategy to create more durable resin–dentine bonds.     

Bonding performance of universal adhesives in different etching modes

Objectives

The aim of this study was to compare the microtensile bond strength (μTBS) and resin penetration into dentine of three universal adhesives (UAs) applied in two different etching modes (i.e. self-etch or etch-and-rinse). The effect of thermocycling on the μTBS was also evaluated.

Methods

The occlusal third of sound human molars was removed and the exposed surfaces were treated with three UAs (Futurabond Universal, Scotchbond Universal Adhesive and All-Bond Universal) in self-etch or etch-and-rinse mode. Two one-step self-etch adhesives (Futurabond DC and Futurabond M) were applied on additional teeth as reference. After composite build up, the specimens were stored for 24 h in distilled water at 37 °C or thermocycled for 5000 cycles. Composite/dentine beams were prepared (1 mm²) and μTBS test was performed. Data was analyzed using three-way ANOVA and Tukey's test (α = 0.05). One additional tooth was prepared for each group for evaluation of infiltration ability into dentine by dyeing the adhesives with a fluorochrome (Rhodamine B). After longitudinal sectioning, the generated interfaces were examined under confocal laser scanning microscopy.

Results

The addition of an etching step did not significantly affect the μTBS of none of the UAs, when compared to their self-etch application mode. All pre-etched specimens showed considerably longer resin tags and thicker hybrid layers. Thermocycling had no significant effect on the μTBS of the UAs.

Conclusions

Application of an etching step prior to UAs improves their dentine penetration, but does not affect their bond strength to dentine after 24 h or after thermocycling for 5000 cycles.

Clinical significance

Similar bond strength values were observed for the UAs regardless of application mode, which makes them reliable for working under different clinical conditions.     

A 2-year in vitro evaluation of a chlorhexidine-containing acid on the durability of resin-dentin interfaces

Objective

This study evaluated the effect of 2% chlorhexidine-containing acid (Ac/CHX) and 2% chlorhexidine digluconate solution (CHX) on immediate (IM) and 2-year (2Y) resin-dentin bond strength (BS) and silver nitrate uptake (SNU) for two simplified etch-and-rinse adhesives.

Methods

Forty-two caries-free extracted molars had a flat dentin surface exposed. In the control groups (groups 1), the surfaces were acid etched with conventional phosphoric acid and the adhesives Prime&Bond NT (PB) or Adper Single Bond 2 (SB) was applied after rinsing, drying and rewetting with water. In groups 2, Ac/CHX groups the adhesives were applied in a similar manner; however a 2% CHX-containing acid was previously applied. In groups 3, the adhesives were applied according to the control group; however the rewetting procedure was performed with an aqueous solution of 2% CHX for 60 s. Composite build-ups were constructed incrementally and microtensile specimens (0.8 mm²) were prepared for microtensile bond strength testing in the IM or 2Y periods at 0.5 mm/min. For SNU, 2 bonded sticks from each tooth were coated with nail varnish, placed in the silver nitrate, polished down with SiC papers and analysed by EDX-SEM. The data from each adhesive was submitted to a two-way repeated measures ANOVA and Tukey's test (α = 0.05).

Results

After 2Y, significant reductions of BS were observed for both adhesives in the control group (p < 0.05). In Ac/CHX or CHX groups the BS remained stable for both systems. SNU was more evident in the control than in the experimental groups (p < 0.05) both in IM and 2Y periods. The use of CHX in an aqueous solution or associated with the acid conditioner was effective to reduce the degradation of dentin bonds over a 2-year period.

Significance

The addition of CHX digluconate in the acidic conditioner may be an excellent tool to increase the long-term stability of collagens fibrils within the hybrid layer against host-derived metalloproteinases without the need for additional steps for the bonding protocol.     

Differential bonds degradation of two resin-modified glass-ionomer cements in primary and permanent teeth

Objectives

To evaluate the effect of chemical degradation on bond strength of resin-modified glass-ionomer cements bonded to primary and permanent dentin.

Methods

Class I cavities of permanent and primary extracted human molars were restored with two resin-modified glass-ionomer cements: Fuji II LC and Vitremer, and stored in water for 24 h. Half samples were immersed in 10% NaOCl aqueous solution for 5 h. Teeth were sectioned into beams and tested for microtensile bond strengths. Results were analyzed with multiple ANOVA and Tukey's tests (p < 0.05). Analysis of debonded surfaces was performed by SEM.

Results

24 h bond strengths for Vitremer and Fuji II LC were similar. For Fuji II, bond strength values were higher for primary than for permanent dentin. Vitremer bond strength was similar for both. Chemical degradation did not affect Fuji II LC bond strength to dentin. However, decreases in bond strength were found for Vitremer groups after NaOCl immersion. Signs of glass ionomer–dentin interaction were evident by SEM analysis for Fuji II LC specimens.

Conclusions

Vitremer and Fuji II presented similar bond strength at 24. Vitremer dentin bonds were prone to chemical degradation. Fuji II LC–dentin bonds showed typical features of glass-ionomer dentin interaction at the bonded interfaces, and were resistant to in vitro degradation.     

Effect of waiting interval on chemical activation mode of dual-cure one-step self-etching adhesives on bonding to root canal dentin

Objectives

The purpose of this study was to evaluate the effect of waiting interval on the chemical activation of dual-cure one-step self-etching adhesives before placing resin core materials on the regional bond strength to root canal dentin.

Materials and methods

Forty-eight post spaces prepared in human lower premolars were applied with four dual-cure one-step self-etching adhesives Estelite Core Quick: ECB/ECQ, Clearfil DC Core Automix: CDB/CDC, Unifil Core EM: UNB/UNC, BeautiCore: BTB/BTC as the manufacturers’ instructions. These adhesives were cured with light activation for 10 s, or chemical activation with 0, 10, and 30 s waiting intervals prior to placing resin core material. Resin core materials were then placed into the post space and light-cured for 60 s. After 24 h water storage, each specimen was serially sliced into 8, 0.6 mm × 0.6 mm thick beams for the μTBS test. The regional μTBS data were analyzed using three-way ANOVA and Dunnett's T3 test (p < 0.05).

Results

For the chemical activation with 10 and 30 s waiting intervals, ECB and CDB exhibited significantly improved μTBS, whereas for UNB and BTB, the μTBS were not significantly different but increased with waiting interval. On the other hand, light-activation of all the adhesives produced significantly higher μTBS to root canal dentin than chemical activation (p < 0.05), except for the UNB group.

Conclusions

For the chemical activation of dual-cure one-step self-etching adhesives, a waiting interval prior to placing resin core material improved μTBS to root canal dentin. Polymerising the adhesives before polymerisation reaction of resin core material would be effective for bonding to root canal dentin.

Clinical relevance

For chemical activation mode as well as light activation mode, pre-curing of adhesive layer before proceeding polymerisation of resin filling material would produce higher bonding performance to dentin in the cavity.     

Adjunctive application of chlorhexidine and ethanol-wet bonding on durability of bonds to sound and caries-affected dentine

Objectives

To examine the effect of adjunctive application of chlorhexidine (CHX) and ethanol-wet bonding (EWB) on bond durability and nanoleakage of hydrophobic adhesive to sound (SD) and caries-affected dentine (CAD).

Methods

Dentine surfaces of molars were etched after caries removal and randomly allocated to four groups (n = 12). In Groups 1 and 2, dentine surfaces were saturated with either 2 ml of 100% ethanol or 2 ml of ethanol with 2% CHX for 60 s. In Groups 3 and 4, dentine surfaces were saturated with either 15 μL of distilled water or 15 μL of distilled water with 2% CHX for 60 s. Two coats of primer, followed by neat resin were applied and light-cured for 40 s. Resin composite build-ups were placed and bonded specimens were sectioned for bond strength testing after 24 h and 12 months’ storage in artificial saliva. Bond strength data were analyzed using 3-way ANOVA and SNK tests. Interfacial nanoleakage was evaluated after 24 h and 12 months using a field-emission scanning electron microscopy and data were analyzed using Kruskal–Wallis test.

Results

Significant differences were observed for the three factors: “substrate” (p < 0.001), “rewetting agents” (p < 0.001) and “time” (p < 0.001) on bond strength. Incorporation of 2% CHX to EWB preserved bond strength to SD and CAD and reduced interfacial nanoleakage after 12 months. Incorporation of 2% CHX to WWB also preserved bond strength to SD after ageing.

Conclusions

Incorporation of chlorhexidine to ethanol-wet bonding has an interaction effect on preservation of bond durability to sound and caries-affected dentine.

Clinical significance

Incorporation of chlorhexidine to ethanol-wet bonding with hydrophobic adhesive enhances the success rate of aesthetic bonded restorations.     

The inhibition effect of non-protein thiols on dentinal matrix metalloproteinase activity and HEMA cytotoxicity

Objectives

Phosphoric acid (PA) etching used in etch-and-rinse adhesives is known to activate host-derived dentinal matrix-metalloproteinases (MMPs) and increase dentinal permeability. These two phenomena will result, respectively; in degradation of dentine-adhesive bond and leaching of some monomers especially 2-hydroxyethyl methacrylate (HEMA) into the pulp that would negatively affect the viability of pulpal cells. This study is the first to investigate the inhibitory effect of non-protein thiols (NPSH); namely reduced glutathione (GSH) and N-acetylcysteine (NAC) on dentinal MMPs and compare their effects on HEMA cytotoxicity.

Methods

Dentine powder was prepared from human teeth, demineralized with 1% PA and then treated with 2% GSH, 2% NAC or 2% chlorhexidine (CHX). Zymographic analysis of extracted proteins was performed. To evaluate the effect of GSH, NAC and CHX on HEMA cytotoxicity, solutions of these compounds were prepared with or without HEMA and rat pulpal cells were treated with the tested solutions for (6 and 24 h). Cells viability was measured by means of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cytotoxicity data were analysed by one-way ANOVA and Tukey post hoc tests (p < 0.05).

Results

The inhibitory effect of GSH and NAC on dentinal MMPs was confirmed. GSH showed similar effectiveness to NAC regarding HEMA cytotoxicity inhibition.

Conclusion

NPSH were effective to inhibit dentinal MMPs and HEMA cytotoxicity.

Clinical significance

The tested properties of NPSH provide promising clinical use of these agents which would enhance dentine-bond durability and decrease post-operative sensitivity.     

Load cycling enhances bioactivity at the resin–dentin interface

Objectives

The purpose of this study was to evaluate if mechanical loading promotes bioactivity at the resin interface after bonding with three different adhesive approaches.

Methods

Dentin surfaces were subjected to three different treatments: demineralisation by (1) 37% phosphoric acid (PA) followed by application of an etch-and-rinse dentin adhesive Single Bond (SB) (PA + SB), (2) by 0.5 M ethylenediaminetetraacetic acid (EDTA) followed by SB (EDTA + SB), (3) application of a self-etch dentin adhesive: Clearfil SE Bond (SEB). Bonded interfaces were stored in simulated body fluid during 24 h or 3 w. One half of each tooth was submitted to mechanical loading. Remineralisation of the bonded interfaces was assessed by AFM imaging/nano-indentation, Raman spectroscopy/cluster analysis, dye assisted confocal microscopy evaluation (CLSM) and Masson's trichrome staining.

Results

Loading cycling for 3 w promoted an increase of mechanical properties at the resin–dentin interface. Cluster analysis demonstrated an augmentation of the mineral–matrix ratio in SB-loaded specimens. CLSM showed an absent micropermeability and nanoleakage after loading EDTA + SB and SEB specimens. Trichrome staining reflected a narrow demineralised dentin matrix after loading, almost not observable in EDTA + SB and SEB.

Significance

In vitro mechanical loading promoted mineralization in the resin–dentin interfaces, at 24 h and 3 w of storage.     

Hydrolytic degradation of the resin–dentine interface induced by the simulated pulpal pressure,direct and indirect water ageing

Objectives

The aim of this study was to compare the hydrolytic effects induced by simulated pulpal pressure, direct or indirect water exposure within the resin–dentine interfaces created with three “simplified” resin bonding systems (RBSs).

Methods

A two-step/self-etching (CSE: Clearfil SE Bond), one-step/self-etching (S3: Clearfil S3) and etch-and-rinse/self-priming (SB: Single-bond 2) adhesives were applied onto dentine and submitted to three different prolonged (6 or 12 months) ageing strategies: (i) Simulated Pulpal Pressure (SPP); (ii) Indirect Water Exposure (IWE: intact bonded-teeth); (iii) Direct Water Exposure (DWE: resin–dentine sticks). Control and aged specimens were submitted to microtensile bond strength (μTBS) and nanoleakage evaluation. Water sorption (WS) survey was also performed on resin disks. Results were analysed with two-way ANOVA and Tukey's test (p < 0.05).

Results

The μTBS of CS3 and SB dropped significantly (p < 0.05) after 6 months of SPP and DWE. CSE showed a significant μTBS reduction only after 12 months of DWE (p = 0.038). IWE promoted no statistical change in μTBS (p > 0.05) and no evident change in nanoleakage. Conversely, SPP induced a clear formation of “water-trees” in CS3 and SB. WS outcomes were CS3 > SB = CSE.

Conclusion

The hydrolytic degradation of resin–dentine interfaces depend upon the type of the in vitro ageing strategy employed in the experimental design. Direct water exposure remains the quickest method to age the resin–dentine bonds. However, the use of SPP may better simulate the in vivo scenario. However, the application of a separate hydrophobic solvent-free adhesive layer may reduce the hydrolytic degradation and increase the longevity of resin–dentine interfaces created with simplified adhesives.