A new use for self-etching resin adhesives: Cementing bone fragments

Objectives

To evaluate the bond capacities of four self-etching resin cements and the self-etching adhesives of the same manufacturer when used to cement bone fragments and compare them with a well-known N-butyl-2-cyanoacrylate bone adhesive.

Methods

125 cylindrical bone specimens from pig mandibular ramus bone were prepared using terphane burs and cemented to the corticals of 125 other specimens obtained from pig mandibular body bone using the following bond systems: Group A: Adper PLP/Relyx; group B: Optibond/Maxcem; group C: Hystoacryl; group D: AdheSE/Multilink; group E: G-Bond/G-Cem. Shear bond strength was measured 15 min after cement application using a universal testing machine.

Results

Shear bond strength results: group A 2.54 ± 0.23 MPa; group B 4.83 ± 0.4 MPa; group C 2.90 ± 0.24 MPa; group D 2.10 ± 0.17 MPa; group E 4.22 ± 0.24 MPa. Values for shear bond strength were significantly greater for group B and E compared to groups A, C and D (p < 0.005, test Mann–Whitney). SEM images showed the presence of a hybrid layer similar to that formed by these bond systems when used on dentine.

Conclusion

Within the limitations of an in vitro investigation, results show that self-etching resin cements together with self-etching adhesives may be used for cementing bone fragments.     

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.     

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.     

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.     

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.     

Resistance to degradation of resin-modified glass-ionomer cements dentine bonds

Objective

To evaluate the effect of EDTA pre-treatment of dentine on resistance to degradation of the bond between dentine and resin-modified glass-ionomer cements.

Methods

Sixty non-carious human molars underwent cavity preparations. Teeth were restored with Fuji II LC or Vitremer. Half of the cavities were restored following manufacturers’ instructions whereas the other half was pre-treated with EDTA (0.1 M, pH 7.4) for 60 s. Teeth were stored in water at 37 °C for 24 h, 3 months or submitted to 10% NaOCl immersion for 5 h. Teeth were sectioned into beams (1 ± 0.1 mm) and tested to failure in tension at 0.5 mm/min. Bond strength data (MPa) were analyzed by ANOVA and SNK multiple-comparisons tests (p < 0.05).

Results

When EDTA was used for pre-treatment of dentine, higher bond strengths were observed for both cements. Degradation challenges produced a decrease in bond strength values only in the Vitremer group. This decrease was avoided when EDTA was used for dentine treatment before restoring with Vitremer.

Conclusions

EDTA pre-treatment of dentine increases bond strength of resin modified glass-ionomers cements to dentine and improves resistance to degradation of the bond between Vitremer and dentine.     

Prolonged exposure times of one-step self-etch adhesives on adhesive properties and durability of dentine bonds

Objectives

To evaluate the effect of prolonged exposure times on immediate and 6-month adhesive properties: degree of conversion (DC), nanoleakage (NL) and resin–dentine bond strength (μTBS) of three one-step self-etch adhesive systems (Adper Easy One [EO], Clearfil S³ Bond [CS3] and Go [GO]).

Material and methods

The adhesives were applied on exposed dentine surfaces of 90 human molars according to manufacturers’ instructions and light polymerized for 10, 20, and 40 s at 600 mW/cm². Bonded teeth were sectioned to obtain stick-shaped specimens (0.8 mm²) and tested under tensile stress (0.5 mm/min) immediately (IM) or after 6 months of water storage. Two bonded sticks from each tooth at each storage time interval were analysed by SEM for NL evaluation. The in situ DC was evaluated by micro-Raman spectroscopy. Data were analysed by appropriate ANOVA and Tukey's test (α = 0.05).

Results

Prolonged exposure times significantly increased the DC (%) (10 s [67.4 ± 17.3]; 20 s [85.9 ± 8.9] and 40 s [85.2 ± 9.0]) and decreased the NL (%) (10 s [24.8 ± 13.2]; 20 s [13.3 ± 7.5] and 40 s [13.5 ± 9.3]) for all adhesives; however it did not increase the IM μTBS for two (EO, GO) out of the three adhesives. Furthermore, this technique did not minimize dentine bond degradation.

Conclusion

Although longer exposure times than those recommended could not prevent degradation of dentine bonds, they could increase DC within the hybrid layer and reduced NL for all adhesives tested.     

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.     

The influence of temporary cements on dental adhesive systems for luting cementation

Objective

This study tested the hypothesis that bond strength of total- and self-etching adhesive systems to dentine is not affected by the presence of remnants from either eugenol-containing (EC) or eugenol-free (EF) temporary cements after standardized cleaning procedures.

Methods

Thirty non-carious human third molars were polished flat to expose dentine surfaces. Provisional acrylic plates were fabricated and cemented either with EC, EF or no temporary cements. All specimens were incubated for 7 days in water at 37 °C. The restorations were then taken out and the remnants of temporary cements were mechanically removed with a dental instrument. The dentine surfaces were cleaned with pumice and treated with either total-etching (TE) or self-etching (SE) dental adhesive systems. Atomic force microscopy was used to examine the presence of remnants of temporary cements before and after dentine cleaning procedures. Composite resin build-ups were fabricated and cemented to the bonded dentine surfaces with a resin luting cement. The specimens were then sectioned to obtain 0.9 mm² beams for microtensile bond strength testing. Fractographic analysis was performed by optical and scanning electron microscopy.

Results

ANOVA showed lower mean microtensile bond strength in groups of specimens treated with EC temporary cement than in groups treated with either no cement or an EF cement (p < 0.05). Mean microtensile bond strength was lower in groups employing the SE rather than the TE adhesive system (p < 0.001). SE samples were also more likely to fail during initial processing of the samples. There was no evidence of interaction between cement and adhesive system effects on tensile strength. Fractographic analysis indicated different primary failure modes for SE and TE bonding systems, at the dentine-adhesive interface and at the resin cement-resin composite interface, respectively.

Conclusion

The use of eugenol-containing temporary cements prior to indirect bonding restorations reduce, to a statistically similar extent, the bond strength of both total- and self-etching adhesive systems to dentine.     

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.     

Effect of application mode on interfacial morphology and chemistry between dentine and self-etch adhesives

Objective

To investigate the influence of application mode on the interfacial morphology and chemistry between dentine and self-etch adhesives with different aggressiveness.

Methods

The occlusal one-third of the crown was removed from un-erupted human third molars, followed by abrading with 600 grit SiC under water. Rectangular dentine slabs were prepared by sectioning the tooth specimens perpendicular to the abraded surfaces. The obtained dentine slabs were treated with one of the two one-step self-etch adhesives: Adper Easy Bond (AEB, pH ∼ 2.5) and Adper Prompt L-Pop (APLP, pH ∼ 0.8) with (15 s, active application) or without (15 s, inactive application) agitation. The dentine slabs were fractured and the exposed adhesive/dentine (A/D) interfaces were examined with micro-Raman spectroscopy and scanning electron microscopy (SEM).

Results

The interfacial morphology, degree of dentine demineralization (DD) and degree of conversion (DC) of the strong self-etch adhesive APLP showed more significant dependence on the application mode than the mild AEB. APLP exhibited inferior bonding at the A/D interface if applied without agitation, evidenced by debonding from the dentine substrate. The DDs and DCs of the APLP with agitation were higher than those of without agitation in the interface, in contrast to the comparable DD and DC values of two AEB specimen groups with different application modes. Raman spectral analysis revealed the important role of chemical interaction between acid monomers of self-etch adhesives and dentine in the above observations.

Conclusion

The chemical interaction with dentine is especially important for improving the DC of the strong self-etching adhesive at the A/D interface. Agitation could benefit polymerization efficacy of the strong self-etch adhesive through enhancing the chemical interaction with tooth substrate.     

The potential of novel primers and universal adhesives to bond to zirconia

Objectives

To investigate the adhesive potential of novel zirconia primers and universal adhesives to surface-treated zirconia substrates.

Methods

Zirconia bars were manufactured (3.0 mm × 3.0 mm × 9.0 mm) and treated as follows: no treatment (C); air abrasion with 35 μm alumina particles (S); air abrasion with 30 μm silica particles using one of two systems (Rocatec or SilJet) and; glazing (G). Groups C and S were subsequentially treated with one of the following primers or adhesives: ZP (Z-Prime Plus), AZ (AZ Primer); MP (Monobond Plus); SU (ScotchBond Universal) and; EA (an Experimental Adhesive). Groups Rocatec and SilJet were silanized prior to cementation. Samples form group G were further etched and silanized. Bars were cemented (Multilink) onto bars of a silicate-based ceramic (3.0 mm × 3.0 mm × 9.0 mm) at 90° angle, thermocycled (2.500 cycles, 5–55 °C, 30 s dwell time), and tested in tensile strength test. Failure analysis was performed on fractured specimens to measure the bonding area and crack origin.

Results

Specimens from group C did not survive thermocycling, while CMP, CSU and CEA groups survived thermocycling but rendered low values of bond strength. All primers presented a better bond performance after air abrasion with Al₂O₃ particles. SilJet was similar to Rocatec, both presenting the best bond strength results, along with SMP, SSU and CEA. G promoted intermediate bond strength values. Failure mode was predominately adhesive on zirconia surface combined to cohesive of the luting agent.

Conclusions

Universal adhesives (MP, SU, EA) may be a considerable alternative for bonding to zirconia, but air abrasion is still previously required. Air abrasion with silica particles followed by silane application also presented high bond strength values.     

Effect of water-ageing on dentine bond strength and anti-biofilm activity of bonding agent containing new monomer dimethylaminododecyl methacrylate

Objectives

The objectives of this study were to develop bonding agent containing a new antibacterial monomer dimethylaminododecyl methacrylate (DMADDM) as well as nanoparticles of silver (NAg) and nanoparticles of amorphous calcium phosphate (NACP), and to investigate the effects of water-ageing for 6 months on dentine bond strength and anti-biofilm properties for the first time.

Methods

Four bonding agents were tested: Scotchbond Multi-Purpose (SBMP) Primer and Adhesive control; SBMP + 5% DMADDM; SBMP + 5% DMADDM + 0.1% NAg; and SBMP + 5% DMADDM + 0.1% NAg with 20% NACP in adhesive. Specimens were water-aged for 1 d and 6 months at 37 °C. Then the dentine shear bond strengths were measured. A dental plaque microcosm biofilm model was used to inoculate bacteria on water-aged specimens and to measure metabolic activity, colony-forming units (CFUs), and lactic acid production.

Results

Dentine bond strength showed a 35% loss in 6 months of water-ageing for SBMP control (mean ± sd; n = 10); in contrast, the new antibacterial bonding agents showed no strength loss. The DMADDM–NAg–NACP containing bonding agent imparted a strong antibacterial effect by greatly reducing biofilm viability, metabolic activity and acid production. The biofilm CFU was reduced by more than two orders of magnitude, compared to SBMP control. Furthermore, the DMADDM–NAg–NACP bonding agent exhibited a long-term antibacterial performance, with no significant difference between 1 d and 6 months (p > 0.1).

Conclusions

Incorporating DMADDM–NAg–NACP in bonding agent yielded potent and long-lasting antibacterial properties, and much stronger bond strength after 6 months of water-ageing than a commercial control. The new antibacterial bonding agent is promising to inhibit biofilms and caries at the margins. The method of DMADDM–NAg–NACP incorporation may have a wide applicability to other adhesives, cements and composites.     

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.     

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.     

Effect of chlorhexidine incorporation into a self-etching primer on dentine bond strength of a luting cement

Objectives

This study investigated the effect of incorporating chlorhexidine in a self-etching primer on the bond strength of an adhesive resin cement to dentine and on antibacterial activity.

Methods

Experimental self-etching primers were prepared by adding chlorhexidine (CHX) diacetate to ED primer 2.0 (Kuraray Medical Inc.) to obtain chlorhexidine concentrations of 1.0 wt% and 2.0 wt%. Human occlusal dentine surfaces were conditioned for 30 s using the experimental primers or pure ED primer. Composite blocks were luted using Panavia F 2.0 (Kuraray Medical Inc.). After storage in water for 24 h, the bonded teeth were sectioned into 0.9 mm × 0.9 mm beams and stressed to failure in tension to examine microtensile bond strength (μTBS). Fractured surfaces were examined with a field-emission scanning electron microscopy (FE-SEM). The morphology of dentine surfaces that were conditioned with each primer was also observed under FE-SEM. An agar diffusion test was performed to examine the antibacterial effect of each primer against Streptococcus mutans and Enterococcus faecalis.

Results

Addition of chlorhexidine to the primer had significant effects (p < 0.001) on μTBS and antibacterial effect. No significant difference in μTBS was found between the groups that contained 0% and 1% chlorhexidine in the primer (p = 0.095). Conversely, the group that contained 2% chlorhexidine showed significantly lower μTBS and pronounced cohesive failures within the thin layer of the primer.

Conclusions

Incorporation of chlorhexidine into ED primer 2.0 showed significant antibacterial activities. Conditioning with the 1% chlorhexidine-containing primer had no adverse effect on μTBS.     

MMPs activity and bond strength in deciduous dentine–resin bonded interfaces

Objectives

To determine effect of ageing on deciduous dentine–resin interfaces bond strength and the metalloproteinases (MMPs) activity at the hybrid layer compared to permanent dentine.

Methods

Microtensile bond strength (MTBS) tests were performed in human deciduous and permanent dentine after 24 h, 3 and 6 months using an etch and rinse adhesive. C-terminal telopeptide concentrations (ICTP) were calculated, in order to determine MMPs mediated collagen degradation at the hybrid layer.

Results

The highest MMPs-mediated collagen degradation values occurred in phosphoric acid demineralized dentine, ICTP values were similar for deciduous and permanent dentine after 1 week. Resin infiltration decreased collagen degradation in both dentins and ICTP values were similar to those attained by for untreated dentine. In resin infiltrated and untreated dentine specimens collagen degradation was always higher for deciduous dentine. At 24 h, MTBS was higher in permanent dentine. After ageing MTBS decreased and performed similarly in both dentins.

Conclusions

Higher collagenollytic activity is found in deciduous than in permanent dentine. At 24 h, collagen cleavage by MMPs at the hybrid layer is higher in deciduous dentine leading to a lower MTBS.

Clinical significance

The presence of resin monomers reduced collagen degradation when applied on demineralized dentine, but exerted protection was lower in deciduous dentine.     

Improved degree of conversion of model self-etching adhesives through their interaction with dentine

Objective

To investigate the correlation of the chemical interaction between model self-etching adhesives and dentine with the degree of conversion (DC) of the adhesives.

Methods

The model self-etching adhesives contained bis[2-methacryloyloxy)ethyl] phosphate (2MP) and 2-hydroxyethyl methacrylate (HEMA) with a mass ratio of 1/1, and 0-40% water contents, respectively. The adhesives were applied either onto the prepared dentine surface or unreactive substrates (such as glass slides), agitated for 15 s, then light-cured for 40 s. The DCs of the adhesives were determined using micro-Raman spectral and mapping analysis.

Results

The DCs of the adhesives cured on the dentine substrate were found to be significantly higher than those on the unreactive glass substrate. Moreover, the DCs of the adhesives displayed a decreasing trend as the distance from the dentine surface became greater. The chemical interaction of the acidic 2MP/HEMA adhesives with the mineral apatite in dentine was proposed to play a significant role for the observations. The chemical interaction could be validated by the spectral comparison in the phosphate regions of 1100 cm⁻¹ and 960 cm⁻¹ in the Raman spectra. The results also revealed a notable influence of water content on the DC of adhesives. The DCs of the adhesive at 10% water content exhibited the highest DC level for both substrates.

Conclusions

Interaction with dentine dramatically improved the degree of conversion of self-etching adhesives. Our ability to chemically characterise the a/d interface including in situ detection of the DC distribution is very important in understanding self-etching adhesive bonding under in vivo conditions.     

Resin–dentine interfacial morphology following CPP–ACP treatment

Objectives

To evaluate the quality of bonded resin–dentine interfaces produced by two self-etching primer adhesives after casein phosphopeptide–amorphous calcium phosphate (CPP–ACP) treatment, in comparison to untreated dentine.

Methods

Thirty-four adult molar teeth were sectioned to obtain dentine with tubule orientations parallel/oblique or perpendicular to the surface. The specimens were divided into ‘smear layer’ (1A, 1B) and ‘no smear layer’ groups, after treatment with 15% EDTA (2A, 2B). The specimens were then left either untreated (1A, 2A) or treated (1B, 2B) with CPP–ACP paste (Tooth Mousse, GC Corp.) for 60 min × 7 days. Each treatment group was divided into three subgroups and specimens etched/conditioned (no conditioning; 30–40% phosphoric acid (H₃PO₄); 20% polyacrylic acid) and bonded with either a 2-step self-etching primer adhesive (Clearfil SE Bond, Kuraray Medical) or an ‘all-in-one’ adhesive (G-Bond, GC Corp.) and a hybrid resin composite. After 24-h water storage, the bonded specimens were sectioned, polished up to 4000-grit abrasive silicon carbide paper and 0.25-μm diamond paste, prepared for FE-SEM using the acid–base technique, critical point-dried, gold-coated and examined. Bonded and fractured dentine interfaces were also prepared and examined.

Results

The 2-step adhesive produced a similar appearance of bonded resin–dentine interface irrespective of smear layer group, treatment or etching/conditioning. After polyacrylic acid conditioning, the ‘all-in-one’ adhesive exhibited more areas with bond failures. The bond failures were within the hybrid layer and more pronounced following CPP–ACP treatment.

Conclusion

The quality of the bonded resin–dentine interface produced after CPP–ACP treatment may depend on the adhesive system used.     

Bond strengths, degree of conversion of the cement and molecular structure of the adhesive-dentine joint in fibre post restorations

Objectives

Because fibre post restorations are influenced by multiple factors such as the types of bonding materials, the dentine region and the time under moist exposure, this study sought to determine the bond strength of endodontic restorations and its relation to the degree of conversion of the cement layer and the molecular structure of the dentine-bonded joints.

Methods

The performance of 2 etch-and-rinse (All-Bond 2 and One-Step Plus) and 2 self-etch (Clearfil SE Bond and Xeno III) adhesives at post spaces regions, after 7 d or 4 m, was evaluated. FRC Postec Plus posts were cemented to the root canal with a dual-cure resin cement (Duo-Link). Transverse sections of the tooth were subjected to push-out testing, to degree-of-conversion measurements and to hybrid layer evaluation through μ-Raman spectroscopy.

Results

Coronal bonding was higher than cervical and middle bonding. The hybrid layer was thicker for the etch-and-rinse systems, with thicknesses decreasing towards the middle region. The degree of conversion measured for the 3-step etch-and-rinse group after 4 m was significantly higher than that for the self-etching groups.

Conclusions

Although not totally stable at the adhesive–dentine interface, the 3-step etch-and-rinse adhesive in the coronal dentine provided the best bond strength, degree of conversion of the cement and hybrid layer thickness in post restorations, in both short- and long-term analyses.