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.     

Ethanol-wet bonding may improve root dentine bonding performance of hydrophobic adhesive

Objectives

The current study aimed to assess ethanol-wet dentine surfaces by atomic force microscopy (AFM), and to evaluate the efficacy of ethanol-wet bonding on root dentine by determining the shear bond strength (SBS) and interfacial nanoleakage expression.

Methods

Flat dentine slices from human premolar roots were randomly grouped into five. All specimens were acid-etched, rinsed, and left moist. They were then treated with 100% ethanol for 0 s (control group), 20 s (Group 1), 60 s (Group 2), three 60 s periods (Group 3), or stepwise ethanol application (Group 4). After treatment, each group was bonded either with Adper™ Scotchbond™ Multi-Purpose (Scotchbond) or experimental hydrophobic adhesive. Nano-scale adhesion forces (Fad) were probed by AFM and analysed using one-way ANOVA. The SBS results were analysed using two-way ANOVA. Tukey's test was employed for multiple comparisons.

Results

Ethanol-wet protocols significantly decreased the value of Fad (p < 0.001). When bonded with Scotchbond, ethanol treatment did not affect the bond strength (p > 0.05), but decreased the interfacial nanoleakage. The SBS values of the groups bonded with hydrophobic adhesive varied with different ethanol-wet protocols (p < 0.05). Decreased nanoleakage was manifested in all experimental groups, except Group 1. Compared with the classical water-wet bonding with Scotchbond in the control group, Group 4 bonded with hydrophobic adhesive exhibited a significantly higher bond strength (p < 0.05).

Conclusions

Ethanol-wet bonding using a stepwise ethanol application protocol may have potential benefits in the root dentine bonding of hydrophobic adhesive.     

Effect of ethanol-wet bonding with hydrophobic adhesive on caries-affected dentine

Frequently encountered in clinical practice, caries-affected dentine (CAD) is the most challenging bonding substrate. This study evaluated the effect of ethanol-wet bonding with hydrophobic adhesive to sound dentine and to CAD. In the control groups, prepared sound dentine and CAD were bonded with Adper Single Bond 2 using a traditional water-wet bonding technique. In the experimental groups, the specimens were treated as follows: Group 1, rinsed with stepwise ethanol dehydration; Group 2, immersion in 100% ethanol, three times, for 20 s each time; and Group 3, immersion in 100% ethanol for 20 s. Microtensile bond strength (μTBS) testing was used to evaluate the effects of the different protocols on bonding. The microhardness of debonded dentine surfaces was measured to ensure the presence of CAD. Interfacial nanoleakage was evaluated by field-emission scanning electron microscopy. Treatment significantly improved the μTBS in CAD in Groups 1 and 2, but had no effect on Group 3. Conversely, treatment significantly reduced the μTBS in sound dentine in Groups 2 and 3, but had no effect in Group 1. The presence of nanoleakage varied with the ethanol-wet protocol used. In conclusion, ethanol-wet bonding can potentially improve bond efficacy to CAD when an appropriate protocol is used.     

Bonding ability of 4-META self-etching primer used with 4-META/MMA-TBB resin to enamel and dentine: Primary vs permanent teeth

Objectives

The present study compared the efficacies of the self-etching Teeth Primer (TP: 4-META), and the etchants Red Activator (RA; 65% phosphoric acid) and Green Activator (GA; 10% citric acid with 3% ferric chloride), for bonding to enamel and dentine of human primary and permanent teeth, when used with 4-META/MMA-TBB resin (Bondfill SB).

Methods

Forty-eight non-carious primary canines and third molars were used. Eight groups were prepared: Group 1 (primary enamel with RA), Group 2 (permanent enamel with RA), Group 3 (primary enamel with TP), Group 4 (permanent enamel with TP), Group 5 (primary dentine with GA), Group 6 (permanent dentine with GA), Group 7 (primary dentine with TP) and Group 8 (permanent dentine with TP). Micro-tensile bond strengths (MTBS) were measured and analyzed statistically using ANOVAs and Tukey HSD tests at α = 0.05. Efficacy of etching/priming and the morphology of bonded interfaces were observed with SEM.

Results

Etching/priming efficacy of TP on enamel was low. The MTBS of Group 2 was significantly higher than the other groups (Groups 1, 3 and 4). For dentine, significant differences in MTBS were observed, in the order of Groups 6 > 8 > 7 = 5 (p < 0.05). The MTBSs of permanent dentine were significantly higher than primary dentine. For primary teeth, there was no significant difference in the MTBSs between enamel and dentine, irrespective of primer or etchant (p > 0.05).

Conclusion

TP primer/Bondfill SB may be used as an alternative to other adhesive/resin composite systems for bonding to enamel and dentine of primary teeth.     

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.     

Influence of glutaraldehyde priming on bond strength of an experimental adhesive system applied to wet and dry dentine

Objectives

This study tested the following null hypotheses: (1) there is no difference in resin–dentine bond strength when an experimental glutaraldehyde primer solution is added prior to bonding procedures and (2) there is no difference in resin–dentine bond strength when experimental glutaraldehyde/adhesive system is applied under dry or wet demineralized dentine conditions.

Methods

Extracted human maxillary third molars were selected. Flat, mid-coronal dentine was exposed for bonding and four groups were formed. Two groups were designated for the dry and two for the wet dentine technique: DRY: (1) Group GD: acid etching + glutaraldehyde primer (primer A) + HEMA/ethanol primer (primer B)-under dried dentine + unfilled resin; (2) Group D: the same as GD, except for primer A application; WET: (3) Group GW: the same as GD, but primer B was applied under wet dentine condition; (4) Group W: the same as GW, except for primer A application. The bonding resin was light-cured and a resin core was built up on the adhesive layer. Teeth were then prepared for microtensile bond testing to evaluate bond strength. The data obtained were submitted to ANOVA and Tukey's test (α = 0.05).

Results

Glutaraldehyde primer application significantly improved resin–dentine bond strength. No significant difference was observed when the same experimental adhesive system was applied under either dry or wet dentine conditions. These results allow the first null hypothesis to be rejected and the second to be accepted.

Conclusion

Glutaraldehyde may affect demineralized dentine properties leading to improved resin bonding to wet and dry substrates.     

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.     

Shear bond strength of porcelain laminate veneers to enamel,dentine and enamel–dentine complex bonded with different adhesive luting systems

Objectives

The aim of this study was to evaluate the shear bond strength of porcelain laminate veneers to 3 different surfaces by means of enamel, dentine, and enamel–dentine complex.

Methods

One hundred thirty-five extracted human maxillary central teeth were used, and the teeth were randomly divided into 9 groups (n = 15). The teeth were prepared with 3 different levels for bonding surfaces of enamel (E), dentine (D), and enamel–dentine complex (E–D). Porcelain discs (IPS e.max Press, Ivoclar Vivadent) of 2 mm in thickness and 4 mm in diameter were luted to the tooth surfaces by using 2 light-curing (RelyX Veneer [RV], 3M ESPE; Variolink Veneer [VV], Ivoclar Vivadent) and a dual-curing (Variolink II [V2], Ivoclar Vivadent) adhesive systems according to the manufacturers’ instructions. Shear bond strength test was performed in a universal testing machine at 0.5 mm/min until bonding failure. Failure modes were determined under a stereomicroscope, and fracture surfaces were evaluated with a scanning electron microscope. The data were statistically analysed (SPSS 17.0) (p = 0.05).

Results

Group RV-D exhibited the lowest bond strength value (5.42 ± 6.6 MPa). There was statistically no difference among RV-D, V2-D (13.78 ± 8.8 MPa) and VV-D (13.84 ± 6.2 MPa) groups (p > 0.05). Group VV-E exhibited the highest bond strength value (24.76 ± 8.8 MPa).

Conclusions

The type of tooth structure affected the shear bond strength of the porcelain laminate veneers to the 3 different types of tooth structures (enamel, dentine, and enamel–dentine complex).

Clinical significance

When dentine exposure is necessary during preparation, enough sound enamel must be protected as much as possible to maintain a good bonding; to obtain maximum bond strength, preparation margins should be on sound enamel.     

Six-month evaluation of adhesives interface created by a hydrophobic adhesive to acid-etched ethanol-wet bonded dentine with simplified dehydration protocols

Objectives

To evaluate the efficacy of simplified dehydration protocols, in the absence of tubular occlusion, on bond strength and interfacial nanoleakage of a hydrophobic experimental adhesive blend to acid-etched, ethanol-dehydrated dentine immediately and after 6 months.

Methods

Molars were randomly assigned to 6 treatment groups (n = 5). Under pulpal pressure simulation, dentine crowns were acid-etched with 35% H₃PO₄ and rinsed with water. Adper Scotchbond Multi-Purpose was used for the control group. The remaining groups had their dentine surface dehydrated with ethanol solutions: group 1 = 50%, 70%, 80%, 95% and 3 × 100%, 30 s for each application; group 2 the same ethanol sequence with 15 s for each solution; groups 3, 4 and 5 used 100% ethanol only, applied in seven, three or one 30 s step, respectively. After dehydration, a primer (50% BisGMA + TEGDMA, 50% ethanol) was used, followed by the neat comonomer adhesive application. Resin composite build-ups were then prepared using an incremental technique. Specimens were stored for 24 h, sectioned into beams and stressed to failure after 24 h or after 6 months of artificial ageing. Interfacial silver leakage evaluation was performed for both storage periods (n = 5 per subgroup).

Results

Group 1 showed higher bond strengths at 24 h or after 6 months of ageing (45.6 ± 5.9^a/43.1 ± 3.2^a MPa) and lower silver impregnation. Bond strength results were statistically similar to control group (41.2 ± 3.3^ab/38.3 ± 4.0^ab MPa), group 2 (40.0 ± 3.1^ab/38.6 ± 3.2^ab MPa), and group 3 at 24 h (35.5 ± 4.3^ab MPa). Groups 4 (34.6 ± 5.7^bc/25.9 ± 4.1^c MPa) and 5 (24.7 ± 4.9^c/18.2 ± 4.2^c MPa) resulted in lower bond strengths, extensive interfacial nanoleakage and more prominent reductions (up to 25%) in bond strengths after 6 months of ageing.

Conclusions

Simplified dehydration protocols using one or three 100% ethanol applications should be avoided for the ethanol-wet bonding technique in the absence of tubular occlusion, as they showed decreased bond strength, more severe nanoleakage and reduced bond stability over time.     

Effect of smear layer deproteinizing on resin–dentine interface with self-etch adhesive

Objectives

This study aimed to investigate deproteinizing effect of sodium-hypochlorite (NaOCl) and mild acidic hypochlorous-acid (HOCl) pretreatment on smear layer-covered dentine and to evaluate their effects on morphological characteristics of resin–dentine interface with self-etch adhesive.

Methods

Human coronal-dentine discs with standardized smear layer were pretreated with 6% NaOCl or 50 ppm HOCl for 15 s or 30 s. Their deproteinizing effects at the treated smear layer-covered dentine surfaces were determined by the measurement of amide:phosphate ratio using ATR-FTIR analysis. In addition, using TEM, micromorphological alterations of hybridized complex and nanoleakage expression were evaluated at the interface of a self-etch adhesive (Clearfil SE Bond) to the pretreated dentine surface with or without subsequent application of a reducing agent (p-Toluenesulfinic acid salt; Accel^®).

Results

Both pretreatments of NaOCl and HOCl significantly reduced the amide:phosphate ratio as compared with the no-pretreated group (p < 0.05), coincident with the elimination of the hybridized smear layer on their bonded interfaces. Nanoleakage within the hybrid layer was found in the no-pretreated and NaOCl-pretreated groups, whereas the subsequent reducing agent application changed the reticular nanoleakage to spotted type. HOCl-pretreated groups showed less nanoleakage expression in a spotted pattern, regardless of reducing agent application.

Conclusions

NaOCl and HOCl solutions could remove the organic component on the smear layer-covered dentine, which could eliminate the hybridized smear layer created by self-etch adhesive, leading to the reduction of nanoleakage expression within hybrid layer.

Clinical significance

Smear layer deproteinizing could modify dentine surface, giving an appropriate substrate for bonding to self-etch adhesive system.     

Effect of 2% chlorhexidine on dentin microtensile bond strengths and nanoleakage of luting cements

Objectives

The aim of this study was to investigate the effect of pre-treatment by chlorhexidine on the microtensile bond strength (mTBS) of resin cements and nanoleakage at the resin–dentine interfaces.

Methods

Cylindrical composite blocks were luted to human dentine using resin cements (RelyX ARC, 3M ESPE: ARC; Panavia F, Kuraray Medical Inc.: PF; RelyX Unicem, 3M ESPE: UN) with/without pre-treatment by 2% chlorhexidine digluconate (CAVITY CLEANSER, Bisco, Inc., Schaumburg, IL, USA). CAVITY CLEANSER was applied on the acid etched dentine for 60 s in the ARC group, and on smear layer-covered dentine in the PF and UN groups. After storage in water for 24 h, the bonded teeth were sectioned into 1 mm thick slabs and further into 0.9 mm × 0.9 mm beams. After immersion in water or ammoniacal silver nitrate for 24 h, the beams were stressed to failure in tension. The fractured surfaces were examined by field-emission scanning electron microscopy (FE-SEM) using backscattered electron mode. The silver-stained slabs were used to examine nanoleakage within the bonded interface by FE-SEM.

Results

The resin cement and chlorhexidine treatment had significant effects (p < 0.0001) on mTBS; while the storage media had no significant effect (p = 0.435). The mTBS of ARC was significantly higher than the other cements. Chlorhexidine reduced mTBS and produced pronounced nanoleakage when PF and UC were luted to dentine.

Conclusions

Pre-treatment with chlorhexidine affected the integrity of dentine bonding with PF and UC, while there was no adverse effect on coupling of ARC.     

Effects of chlorhexidine-containing adhesives on the durability of resin–dentine interfaces

Objectives

This study evaluated the effect of addition of diacetate CHX in different concentrations into two simplified etch-and-rinse (ER) adhesive systems (XP Bond [XP] and Ambar {AM}) on the ultimate tensile strength (UTS), degree of conversion (DC), 60-day cumulative water sorption (WS), solubility (SO) and CHX release (CR) as well as the immediate (IM) and 1-year (1Y) resin–dentine bond strength (μTBS) and nanoleakage (NL).

Methods

Ten experimental adhesive systems were formulated according to the addition of CHX diacetate (0 [control], 0.01, 0.05, 0.1 and 0.2%) in the two ER. For UTS and DC, specimens were constructed and tested after 24 h. For WS, SO and CR, after specimens build-up, they were stored in water and the properties measured after 60 days. The occlusal enamel of fifty molars was removed and the adhesives were applied in dentine surface after 37% phosphoric acid etching. After composite resin build-ups, specimens were longitudinally sectioned to obtain resin–dentine bonded sticks (0.8 mm²). Specimens were tested in tension at 0.5 mm/min in the IM or 1Y. For NL, 2 bonded sticks from each tooth were prepared and analyzed under SEM. The data were submitted to appropriate statistical analysis (α = 0.05).

Results

The addition of CHX did not influence UTS, DC, WS and SO (p < 0.05). Higher CR was observed in adhesives with higher concentration of CHX (p < 0.05). After 1Y, significant reductions of μTBS and increases of NL were observed in the control groups (p < 0.05). Reductions of μTBS and increase of NL over time were not observed (AM) for CHX-containing adhesives or it was less pronounced than the control (XP) regardless of the CHX concentration.

Conclusions

The addition of CHX diacetate in concentrations until 0.2% in the simplified ER adhesive systems may be an alternative to increase the long-term stability of resin–dentine interfaces, without jeopardizing the adhesives’ mechanical properties evaluated.     

Influence of proanthocyanidins combined with ethanol-wet bonding on the bonding quality of fibre posts to root dentine

This study evaluated the influence of a bonding approach using proanthocyanidins (PAs) combined with ethanol-wet bonding (EWB) and a hydrophobic adhesive on the bonding quality of fibre posts. After endodontic treatment and post-space preparation, 72 single-rooted extracted human teeth were etched, thoroughly rinsed, and then treated using the following procedures (n = 24 teeth per group): group 1, no pretreatment; group 2, pretreatment with absolute ethanol three times, for 30 s each time; or group 3, pretreatment with absolute ethanol solution containing 5% PAs three times, for 30 s each time. Six teeth per group were dried according to a dry and a wet drying protocol and then observed using field emission-scanning electron microscopy. The remaining 18 teeth in each group were cemented with fibre posts: All-Bond 3 and Duo-Link cement were used for group 1; and hydrophobic adhesive and Duo-Link cement were used for groups 2 and 3. Push-out bond strength, failure mode, and nanoleakage were evaluated immediately and after collagenase treatment. Higher push-out bond strength and less nanoleakage were observed in the two ethanol-pretreatment groups, regardless of storage conditions. Teeth pretreated with PAs + ethanol exhibited significantly higher push-out bond strength after collagenase treatment than did teeth pretreated with ethanol alone. Within the limits of this study, the bonding approach of PAs combined with EWB and a hydrophobic adhesive synergistically improved the durability of fibre post bonds.     

Effects of diphenyliodonium salt addition on the adhesive and mechanical properties of an experimental adhesive

Objectives

The aim of this study was to assess the microtensile bond strength (μTBS), nanoleakage (NL), nano-hardness (NH) and Young's modulus (YM) of resin–dentine bonding components formed by an experimental adhesive system with or without inclusion of diphenyliodonium salt (DPIH) in the camphorquinone–amine (CQ) system.

Methods

On 12 human molars, a flat superficial dentine surface was exposed by wet abrasion. A model simplified adhesive system was formulated (40 wt.% UDMA/MDP, 30 wt.% HEMA and 30 wt.% ethanol). Two initiator systems were investigated: 0.5 mol% CQ + 1.0 mol% EDMAB and 0.5 mol% CQ + 1.0 mol% EDMAB + 0.2 mol% DPIH. Each adhesive was applied and light-cured (10 s; 600 mW/cm²). Composite build-ups were constructed incrementally and resin–dentine specimens (0.8 mm²) were prepared. For NL, 3 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. NH and YM were performed on the hybrid layer in 2 bonded sticks from each teeth. The remaining bonded sticks were tested on μTBS (0.5 mm/min). The data from each test were submitted to a Student t-test (α = 0.05).

Results

No significant difference was found for μTBS between groups (p > 0.05). Significant lower NL and higher NH and YM were found in the hybrid layer and adhesive layer produced with the iodinium salt-containing adhesive (p < 0.05).

Conclusions

The inclusion of the DPIH to the traditional CQ is a good strategy to improve the adhesive and mechanical properties of a simplified etch-and-rinse adhesive system.     

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.     

Effects of the application sequence of calcium-containing desensitising pastes during etch-and-rinse adhesive restoration

Objectives

To evaluate the effects of different application sequence of calcium-containing desensitising pastes on bonding effectiveness and tubule occlusion during etch-and-rinse (E&R) adhesive restoration.

Methods

Seventy molars were sectioned parallel to the occlusal plane, polished and randomly divided into seven groups (n = 10). Group 1 was etched with 35% phosphoric acid for 15 s. Groups 2–4 were treated with different calcium-containing desensitisers, including an arginine-calcium carbonate (Arg-CaCO₃)-containing paste, a casein phosphopeptide-amorphous calcium phosphate (CPP-ACP)-containing paste and a calcium-sodium phosphosilicate (Novamin)-containing paste, respectively. Afterward, these groups were etched with 35% phosphoric acid for 15 s. Groups 5–7 were initially etched and then treated with Arg-CaCO₃-, CPP-ACP- and Novamin-containing desensitisers, respectively. In each group, samples were equally distributed into two subgroups (n = 5) to bond with either a two-step E&R adhesive Adper SingleBond 2 (SB) or a three-step E&R adhesive Adper ScotchBond Multi-Purpose (SBMP). The microtensile bond strengths (MTBS) were tested and fracture modes were analyzed by stereomicroscopy and field-emission scanning electron microscopy (FESEM). Eight additional dentine disks were prepared to evaluate tubule occlusion prior to bonding using FESEM.

Results

The application sequence of calcium-containing desensitising pastes did not significantly affect MTBS irrespective of two-step SB (P > 0.05) or three-step SBMP E&R adhesives (P > 0.05). Effective dentinal tubule occlusion was observed in the mode of etching-desensitising.

Conclusions

Applying calcium-containing desensitisers (particularly Arg-CaCO₃- and Novamin-based) after etching during E&R adhesive restoration could achieve effective tubule occlusion without affecting the bonding strength.     

Effect of natural cross-linkers incorporation in a self-etching primer on dentine bond strength

Objectives

The aim of this in vitro study was to investigate the effect of incorporation of natural cross-linkers into the primer of a self-etching adhesive on resin–dentine bond strength.

Methods

Flat dentine surfaces were prepared from extracted human molar teeth and were applied with the following self-etching primers. The 0.5% hesperidin (HPN), 0.5% chlorhexidine (CHX) or 0.5% grape seed extract (GSE) was incorporated into Clearfil SE primer (Kuraray Medical, Inc.) to formulate three experimental primers. The original SE primer served as control. Following primer application, the teeth were bonded with Clearfil SE bond, restored with resin composite and stored in water for 24 h at 37 °C. The bonded specimens were sectioned into beams and subjected to micro tensile bond testing (μTBS). Failure analysis and morphological evaluation of the dentine surfaces were performed using a scanning electron microscope (SEM). Hardness (H) and elastic modulus (EM) were measured using nano-indentation technique to examine the mechanical properties of the bonded interfaces.

Results

One-way ANOVA showed significant differences in μTBS, H and EM among the tested and control groups (p < 0.001). Tukey post hoc test revealed that incorporation of HPN significantly increased μTBS, H and EM, when compared with the other groups (p < 0.006). The GSE-incorporated group significantly decreased μTBS, H and EM, when compared with the other groups (p < 0.006); while CHX-incorporated group did not show any statistical significant difference when compared with the control group.

Conclusion

Incorporation of HPN into Clearfil SE primer had a positive influence on the immediate μTBS and mechanical properties of the bonded interface.     

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.     

Wettability of root canal sealers on intraradicular dentine treated with different irrigating solutions

Objectives

The aim of this in vitro study was to evaluate the wettability of AH Plus and ThermaSeal Plus sealers on intraradicular dentine treated with different irrigating solutions.

Methods

Fifty anterior teeth were decoronated and split longitudinally. Each root half was divided into 5 groups (n = 10). Group I: 5 mL of 2.5% NaOCl + QMix. Group II: 5 mL of 2.5% NaOCl + 17% EDTA. Group III: 5 mL of 2.5% NaOCl + 7% maleic acid. Group IV: 5 mL of 2.5% NaOCl. Group V: 5 mL of distilled water. Irrigation regimens were performed for 1 min. Each specimen was placed inside a Dynamic Contact Angle Analyser. A controlled-volume droplet of sealer was placed on each specimen and the static contact angle was analysed.

Results

The contact angle made by both sealers with EDTA-irrigated dentine was significantly larger when compared to the other irrigants (P < 0.05). For ThermaSeal Plus, contact angles produced on maleic acid-, NaOCl- and distilled water-irrigated dentine were not significantly different, but were all significantly larger than the contact angle produced on QMix-irrigated dentine (P < 0.05). For AH Plus, contact angles produced on NaOCl- and distilled water-irrigated dentine were not significantly different, but were significantly larger than those made by maleic acid and QMix.

Conclusion

When used as a final irrigant, QMix favours the wetting of root canal dentine by both AH Plus and ThermaSeal Plus sealers. Maleic acid shows a promising result when compared to EDTA and NaOCl. Wettability of both sealers is the worst on EDTA-irrigated dentine.

Clinical significance

The present study highlights the effect of newer endodontic irrigating solutions on the wettability of sealers on to the root canal dentine, which is required for obtaining good obturation seal.     

Effects of C-factor and resin volume on the bonding to root canal with and without fibre post insertion

Objectives

The aim of this study was to evaluate the effects of C-factor and resin volume on the regional bond strength of dual-cure luting resin to root canal dentine.

Methods

Twelve single-root human premolars were decoronated and post space prepared to a depth of 8 mm, with a diameter of 1.5 mm for six roots and 1.75 mm for the other six. Root canal dentine was treated with a dual-cure bonding system and light-cured for 20 s. Specimens were filled with a dual-cure resin composite with or without insertion of 1.4-mm-diameter light-transmitting glass fibre posts, followed by light-curing for 60 s from the coronal direction. After 24 h water storage, each specimen was serially sliced into eight 0.6 mm × 0.6 mm thick beams for a microtensile bond strength test. Failure modes were observed using SEM. Bond strength data were divided into coronal and apical regions and statistically analysed.

Results

For both sizes of post space, bond strengths dramatically decreased when fibre posts were inserted. There were no significant differences in microtensile bond strength between 1.5 mm and 1.75 mm canal width, regardless of fibre post insertion. Regional differences in bond strength were found only in the resin-filled canals.

Conclusions

: The increase of C-factor of the root canal system by insertion of a fibre post had a detrimental effect on the bond strength to root canal dentine. On the other hand, the change of resin volume had no significant effect on bonding.