Nanoleakage patterns of four dentin bonding systems

Lipopolysaccharide penetration analysis of two different resin cement systems to dentin and ceramic surface

Background/purpose

One of the challenges in adhesive ceramic restorations is deterioration of tooth-cement-ceramic interfaces. This study was to quantitatively investigate lipopolysaccharide (LPS) penetration through adhesive ceramic restorations.

Materials and methods

Standardized holes were formed on ceramic (IPS Empress CAD, Ivoclar Vivadent) and human dentin discs. Prepared discs were randomly assigned to experimental groups (n = 6/group): SC, self-adhesive resin cement (SmartCem 2, Dentsply Sirona) bonded to ceramic discs; ST, self-adhesive resin cement bonded to dentin discs; VC, etch-and-rinse resin cement (Variolink II, Ivoclar Vivadent AG) bonded to ceramic discs; VT, etch-and-rinse resin cement bonded to dentin discs. The specimens underwent thermocycling (10,000 cycles; 5-55 °C) then LPS penetration test until 5-weeks. A mixed effect analysis using R statistical language was performed for data analysis.

Results

Dentin and ceramic bonded with etch-and-rinse resin cements (groups VT and VC) showed significantly less penetration than those with self-adhesive resin cement (groups ST and SC) (P < 0.05). ST showed significantly lower penetration than SC (P < 0.05), that showed similar penetration with positive control (P > 0.05). VC showed minimal penetration during observed time of period (P < 0.05). Scanning electron microscope observations showed different interfacial characteristics among the groups.

Conclusion

Within the limitation of this study, etch-and-rinse resin cement showed less LPS penetration than self-adhesive resin cement on both ceramic and dentin surfaces.

Deep Margin Elevation: Current Concepts and Clinical Considerations: A Review

Dietschi and Spreafico first proposed deep margin elevation (DME) in 1998 to address the multiple clinical problems associated with sub-gingival margins, where sub-gingival margins will be repositioned coronally using composite resin restorations. Given that dentistry is directing towards conservatism, its use is currently trending. Materials and Methods: a search was performed through PubMed, Scopus, and Google Scholar search engines to obtain relevant articles with no time restriction. Results: With biological width taken into consideration, well-defined and polished sub-gingival restorations are compatible with periodontal health. Marginal integrity in the DME technique seems to be affected by the type of adhesive, restoration, and incremental layering of the restoration. Regarding fracture resistance, DME has no significant effects. Conclusion: The DME technique seems to be a minimally invasive alternative to surgical crown lengthening (SCL) and orthodontic extrusion (OE) with respect to biological width. Well-controlled clinical trials are limited in this field; further long-term follow-up studies emphasizing the periodontal outcomes and prevention of complications are needed.

Influence of the adhesive strategy in the sealing ability of resin composite inlays after deep margin elevation

Background

The aim of this study was to determine the influence of the gingival margin position and the adhesive strategy selected to perform deep margin elevation (DME) in marginal sealing of resin composite inlays by a nanoleakage test.

Material and Methods

12 sound third molars were selected and expulsive MOD cavities for inlays were prepared. Experimental groups were established according to gingival margin location (enamel: 1 mm above cemento-enamel junction (CEJ), dentin: 1 mm below CEJ, or DME, and the adhesive strategy used to lute inlays and elevate the gingival margin. Therefore, the six experimental groups were: 1) Enamel + etch-and-rinse adhesive (ERA) Adper Scotchbond 1XT (SB1XT); 2) Dentin + SB1XT; 3) DME + SB1XT; 4) Enamel + self-etching adhesive (SEA) with enamel selective etching Clearfil SE Bond (CSE); 5) Dentin + CSE; 6) DME + CSE. Resin composite inlays were constructed (Gradia Indirect) and all luted with the same resin cement (RelyX ARC). Specimens were submitted to nanoleakage test. Results were analyzed by Kruskal-Wallis and Mann-Whitney U tests with Bonferroni correction (p<0.05).

Results

A perfect sealing ability was evidenced for experimental groups with gingival margins on enamel. Similar nanoleakage values were determined when CSE adhesive was applied regardless the gingival margin position. The highest silver nitrate infiltration was detected for elevated margins with the ERA SB1XT.

Conclusions

The SEA Clearfil SE Bond showed higher sealing ability than the ERA Adper Scotchbond 1XT when margins were located on dentin, regardless margin elevation. Gingival margins on enamel together with enamel acid etching provided an excellent sealing with both adhesive systems. Key words:Adhesion, composite inlays, gingival margin, deep margin elevation, marginal seal, nanoleakage test.

Evaluating the Failure of Resin-based Materials on the Proximal Cervical Dentin

Background:

Resin-based materials are the popular restorative material in dentistry. The majority of these materials are light cured with a major disadvantage: marginal leakage.

Objective:

To evaluate the gap width of different resin-based materials at the cervical dentin when achieved mechanical force.

Methods:

Class II cavities were prepared on extracted premolar teeth with the gingival margin 1 mm below the Cementoenamel Junction (CEJ). In the first three experimental groups, three different lining materials (flowable resin composite, bulk-fill flowable resin composite, and resin-modified glass ionomer cement) were placed at the cervical dentin with a thickness of 1 mm. The rest of the cavities were restored with conventional resin composite. The other two groups were restored with conventional resin composite (control) or high viscosity bulk-fill resin composite, respectively. All groups were thermocycled and underwent vacuum pressure 2.6 KPa for 30 min in a Scanning Electron Microscope (SEM).

Results:

There was no gap formation at the cervical dentin on the external surface when restored with high-viscosity bulk fill resin composite. Almost all gaps occurred at the interface between restorative materials and the hybrid layer. The flowable bulk fill resin composite showed a significantly smaller gap width on both the external and internal surfaces compared to the other groups (p< 0.05). The resin-modified glass ionomer cement showed the largest gaps in the cervical dentin (p < 0.05).

Conclusion:

The different types of resin-based materials demonstrated a different failure of gap width under mechanical force. It clearly occurred at the restorative material-hybrid layer interface.

Influence of operator experience on bond strength of different adhesives to dentin

Aim

Application of adhesive systems on dentin is a multistep, technique-sensitive procedure. Thus, the aim was to assess the effect of operator experience on the shear bond strength of an etch-and-rinse adhesive system and a self-etch adhesive system on dentin.

Materials and Methods

Forty-eight extracted human molar teeth were used in the study. They were embedded in an acrylic resin after cutting off the roots. The mesial and distal enamels of the teeth were removed to expose dentin surfaces. The samples were allocated to four groups (n = 12): Group 1: restorative dentistry specialist with 13 years of experience, Group 2: with 6 years of experience, Group 3: postgraduate operator with 2 years of experience, and Group 4: undergraduate student with 1 year of experience and familiar with adhesive with systems. Each operator applied an etch-and-rinse adhesive system (Adper Single Bond 2) to mesial surface and a self-etch adhesive system (Clearfil SE Bond) to distal surface (n = 12). Then, a composite resin (Filtek Z250) was inserted with the aid of a plastic ring (2 mm × 2 mm) and light polymerized. The specimens were stored in distilled water before shear bond strength test. A two-way ANOVA test was used for statistical analysis.

Results

No statistically significant difference was found between each operator type with respect to etch-and-rinse adhesive system (P > 0.05); however, the undergraduate student performed better than 2-year experienced operator with respect to self-etch system application (P < 0.05).

Conclusion

The shear bond strength of a self-etch system might vary according to the operator's experience.

Improvement of Total Etching Dentin Bonding with Subpressure

This study aimed to investigate the effects of subpressure on the bond properties of total-etching adhesive to dentin. Thirty-six caries-free premolars were sectioned parallel to the occlusal plane and randomly divided into four groups (n = 9): a control group (C, no treatment) and three subpressure groups, which were treated under 0.8, 0.6 or 0.4 bar after applying adhesives, named S8, S6 and S4, respectively. Afterward, resin was bonded to the dentin surface, and 27 beams (1.0 mm × 1.0 mm) of each group were sectioned. One was selected to observe the bonding interface from each group by SEM. Each group was divided into two subgroups (n = 13): 24 hours of water storage (I) and 10,000 thermocycling (A). The microtensile bond strength (μTBS), failure modes and nanoleakage expression were evaluated. SEM results showed that the subpressure groups had longer and denser resin tags. The μTBS of the subpressure groups was higher than that of the control group (p < 0.05). The subpressure groups were dominated by mixed failure, whereas main interfacial failure appeared in group C. The subpressure groups showed less silver deposition than the control group (p < 0.05). The subpressure technique may remarkably improve bonding strength and decrease nanoleakage on total-etching bonding.

The innovative applications of therapeutic nanostructures in dentistry

Nanotechnology has paved multiple ways in preventing, reversing or restoring dental caries which is one of the major health care problems. Nanotechnology aided in processing variety of nanomaterials with innovative dental applications. Some showed antimicrobial effect helping in the preventive stage. Others have remineralizing potential intercepting early lesion progression as nanosized calcium phosphate, carbonate hydroxyapatite nanocrystals, nanoamorphous calcium phosphate and nanoparticulate bioactive glass particularly with provision of self-assembles protein that furnish essential role in biomimetic repair. The unique size of nanomaterials makes them fascinating carriers for dental products. Thus, it is recentlyclaimedthat fortifying the adhesives with nanomaterials that possess biological meritsdoes not only enhance the mechanical and physical properties of the adhesives, but also help to attain and maintain a durable adhesive joint and enhanced longevity. Accordingly, this review will focus on the current status and the future implications of nanotechnology in preventive and adhesive dentistry.

Nanoleakage evaluation at adhesive-dentin interfaces by different observation methods

The purpose of this study was to evaluate the capability and characteristics of different nanoleakage observation methods, including light microscope (LM), field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), and confocal laser scanning microscope (CLSM). Dentin specimens were bonded with either an etch-and-rinse adhesive (SBMP) or a self-etch adhesive (GB), and prepared for nanoleakge evaluation according to different observation methods. LM, FESEM and CLSM results demonstrated that the SBMP group showed more interfacial nanoleakage than the GB group (p<0.05); by contrast, no significant difference was found in TEM results (p>0.05), however, TEM illustrated concrete nanoleakage forms or patterns. The results suggested that different observation methods might exhibit distinct images and a certain degree of variations in nanoleakage statistical results. Researchers should carefully design and calculate the optimum assembly in combination with qualitative and quantitative approaches to obtain objective and accurate nanoleakage evaluation.

In vitro remineralization of hybrid layers using biomimetic analogs

Resin-dentin bond degradation is a major cause of restoration failures. The major aim of the current study was to evaluate the impact of a remineralization medium on collagen matrices of hybrid layers of three different adhesive resins using nanotechnology methods. Coronal dentin surfaces were prepared from freshly extracted premolars and bonded to composite resin using three adhesive resins (FluoroBond II, Xeno-III-Bond, and iBond). From each tooth, two central slabs were selected for the study. The slabs used as controls were immersed in a simulated body fluid (SBF). The experimental slabs were immersed in a Portland cement-based remineralization medium that contained two biomimetic analogs (biomineralization medium (BRM)). Eight slabs per group were retrieved after 1, 2, 3, and 4 months, respectively and immersed in Rhodamine B for 24 h. Confocal laser scanning microscopy was used to evaluate the permeability of hybrid layers to Rhodamine B. Data were analyzed by analysis of variance (ANOVA) and Tukey's honest significant difference (HSD) tests. After four months, all BRM specimens exhibited a significantly smaller fluorescent area than SBF specimens, indicating a remineralization of the hybrid layer (P≤0.05). A clinically applicable biomimetic remineralization delivery system could potentially slow down bond degradation.

Effect of Storage Time on Bond Strength and Nanoleakage Expression of Universal Adhesives Bonded to Dentin and Etched Enamel

PURPOSE

To investigate bond strength and nanoleakage expression of universal adhesives (UA) bonded to dentin and etched enamel.

METHODS

Extracted human third molars were sectioned and ground to obtain flat surfaces of dentin (n = 36) and enamel (n = 48). Dentin and etched enamel surfaces were bonded with one of two UAs, All-Bond Universal (ABU) or Scotchbond Universal (SBU); or a two-step self-etching adhesive, Clearfil SE Bond (CSEB). A hydrophobic bonding resin, Adper Scotchbond Multi-Purpose Bond (ASMP Bond) was applied only on etched enamel. Following each bonding procedure, resin composite blocks were built up incrementally. The specimens were sectioned and subjected to microtensile bond strength (MTBS) testing after 24 hours or one year water storage, or immersed into ammoniacal silver nitrate solution after aging with 10,000 thermocycles and observed using scanning electron microscopy. The percentage distribution of silver particles at the adhesive/tooth interface was calculated using digital image-analysis software.

RESULTS

The MTBS (CSEB = SBU > ABU, for dentin; and CSEB > ABU = SBU = ASMP Bond, for etched enamel) differed significantly between the adhesives after 24 hours. After one year, MTBS values were reduced significantly within the same adhesive for both substrates (analysis of variance, Bonferroni post hoc, p<0.05), and no significant differences were found among the adhesives for etched enamel. Silver particles could be detected within the adhesive/dentin interface of all specimens tested. Kruskal-Wallis mean ranks for nanoleakage in ABU, SBU, and CSEB were 16.9, 18.5 and 11, respectively (p>0.05).

CONCLUSIONS

In the short term, MTBS values were material and dental-substrate dependent. After aging, a decrease in bonding effectiveness was observed in all materials, with nanoleakage at the adhesive/dentin interface. The bonding of the UAs was equal or inferior to that of the conventional restorative systems when applied to either substrate and after either storage period.

The Impact of Expasyl® Gingival Retraction Paste on the Bond Strength of Self-etch and Total-etch Systems

OBJECTIVE

To evaluate the influence of Expasyl® gingival retraction paste on the shear bond strength of self-etch and total-etch adhesive systems.

MATERIALS AND METHODS

Twenty-four specimens of extracted, caries-free, sound human molars were used in this study. The molars were then cut vertically into halves through the buccal and lingual cusps. Forty-eight specimens were divided into four groups (total-etch, total-etch with Expasyl application, self-etch, self-etch with Expasyl application) and the shear bond strength was tested.

RESULTS

Expasyl significantly reduced the shear bond strength of the self-etch and total-etch adhesive systems. The self-etch system showed relatively lower performance compared with the total-etch adhesive system. The shear bond strength values of the total-etch adhesive without Expasyl showed the highest bond strength (21.48 ± 2.89), while the self-etching group adhesive treated with Expasyl showed the lowest shear bond strength value (14.89 ± 1.81).

CONCLUSION

From the observations of this in vitro study, it can be concluded that the use of Expasyl® gingival retraction system can negatively affect bond strength of adhesives. The total-etch system showed better compatibility to the Expasyl gingival retraction system than the self-etch.

Does the use of a novel self-adhesive flowable composite reduce nanoleakage?

Objective

The aim of the study reported here was to evaluate the performance of a self-adhesive flowable composite and two self-etching adhesive systems, when subjected to cyclic loading, in preventing the nanoleakage of Class V restorations.

Methods

Wedge-shape Class V cavities were prepared (4×2×2 mm [length × width × depth]) on the buccal surfaces of 90 sound human premolars. Cavities were divided randomly into three groups (n=30) according to the used adhesive (Xeno^® V [self-etching adhesive system]) and BOND-1^® SF (solvent-free self-etching adhesive system) in conjunction with Artiste^® Nano Composite resin, and Fusio™ Liquid Dentin (self-adhesive flowable composite), consecutively. Each group was further divided into three subgroups (n=10): (A) control, (B) subjected to occlusal cyclic loading (90N for 5,000 cycles), and (C) subjected to occlusal cyclic loading (90N for 10,000 cycles). Teeth then were coated with nail polish up to 1 mm from the interface, immersed in 50% silver nitrate solution for 24 hours and tested for nanoleakage using the environmental scanning electron microscopy and energy dispersive analysis X-ray analysis. Data were statistically analyzed using two-way analysis of variance and Tukey’s post hoc tests (P≤0.05).

Results

The Fusio Liquid Dentin group showed statistically significant lower percentages of silver penetration (0.55 μ) compared with the BOND-1 SF (3.45 μ) and Xeno V (3.82 μ) groups, which were not statistically different from each other, as they both showed higher silver penetration.

Conclusion

Under the test conditions, the self-adhesive flowable composite provided better sealing ability. Aging of the two tested adhesive systems, as a function of cyclic loading, increased nanoleakage.

Effects of sonic application of adhesive systems on bonding fiber posts to root canals

INTRODUCTION

Luting posts inside the root canal is still a challenge because of the difficulty of bonding adhesive materials in the apical third of roots. This study evaluated the effect of the application mode of 3 simplified etch-and-rinse adhesives on the push-out bond strength (PBS), nanoleakage (NL), and in situ degree of conversion (DC) of fiber posts in the root canal.

METHODS

The roots of human premolars were endodontically prepared and divided into 6 groups according to the combination of the main factors: adhesive (Ambar, FGM, Joinville, SC, Brazil; Adper Single Bond 2, 3MESPE, St Paul, MN; and XP Bond+self-cure activator, DeTrey Dentsply, Konstanz, Germany) and application mode (manual or sonic). The posts were cemented and the PBS tested at 0.5 mm/min. The NL was evaluated by scanning electron microscopy after the immersion of specimens in 50% silver nitrate. Micro-Raman spectroscopy was used to measure the in situ DC. Root third was also considered in the statistical evaluation. Data were analyzed by 3-way repeated measures analysis of variance and Tukey tests (5%).

RESULTS

Under sonic application, the PBS and the in situ DC increased, whereas NL decreased significantly for all groups in the middle and apical thirds (P < .05).

CONCLUSIONS

The application of simplified adhesives by sonic mode in the root canal is a feasible tool to increase the fiber post bond to root canals.

Fracture strength and nanoleakage of weakened roots reconstructed using relined glass fiber-reinforced dowels combined with a novel prefabricated core system

PURPOSE

The aim of this study was to evaluate fracture strength and nanoleakage of endodontically treated weakened teeth after being restored with relined glass fiber-reinforced dowels and two types of cores.

MATERIALS AND METHODS

Sixty sound human decoronated and endodontically treated teeth were embedded in epoxy resin blocks, then divided into three groups (n = 20) according to the method of root reconstruction. Group 1 (control): nonweakened roots were restored with glass fiber-reinforced dowels (UNIC); group 2: weakened roots restored with glass fiber-reinforced dowels relined with composite resin; group 3: weakened roots restored with glass fiber-reinforced dowels and a thick layer of luting cement. Dowels were cemented using Corposit, a dual-cured adhesive resin cement, then each group was assigned into two subgroups (n = 10) according to the type of core used; subgroup a: custom-made core using the same luting cement, subgroup b: prefabricated glass fiber-reinforced core (UNIC). Half the specimens of each subgroup were individually mounted at 45° angles and statically compressed until fracture at a 0.5 mm/min crosshead speed with a 5 kN load cell. The type of failure was assessed using a magnification lens. The other half of the specimens were removed from the block, placed in silver nitrate solution for 24 hours followed by photo developer for 8 hours, then examined using environmental scanning electron microscope/energy dispersive analytical X-ray for nanoleakage evaluation. Data were statistically analyzed.

RESULTS

The nonweakened group recorded the highest fracture strength values. The composite relined group showed significantly higher fracture strength values than the cement group. The prefabricated core yielded higher fracture strength values than the custom-made core. All groups showed a degree of nanoleakage, with higher scores recorded for the composite group.

CONCLUSIONS

The fracture resistance of wide root canals can be improved by using glass fiber-reinforced dowels relined with composite resin as an alternative to increasing the thickness of luting cement; however, the percentage nanoleakage would increase. On the other hand, the recently introduced prefabricated glass fiber-reinforced core can be considered a promising technique, but further investigations are necessary.

A new concept in hybridization: Bromelain enzyme for deproteinizing dentin before application of adhesive system

Objective:

The objective of this study is to assess the deproteinizing effect of bromelain enzyme and compare it with neodymium-doped yttrium aluminum garnet (Nd:YAG) laser and 10% sodium hypochlorite (NaOCl) by using scanning electron microscope (SEM) and polarized microscope.

Materials and Methods:

A total of 60 extracted human upper premolars were selected to be given standardized buccal and lingual class V cavities. The teeth were divided into three groups each one consisted of 20 teeth. Thirty teeth were recruited for SEM study and the other 30 for polarized microscope. Group 1: Teeth were deproteinized with Nd:YAG laser, Group 2: Teeth were deproteinized with bromelain enzyme and Group 3: Teeth were deproteinized with 10% NaOCl.

Results and Conclusions:

Application of bromelain enzyme has led to removing collagen network and significantly decreased the global leakage scores of the adhesive system.

Detection of marginal leakage of Class V restorations in vitro by micro-computed tomography

This in vitro study evaluated the efficacy of micro-computed tomography (CT) in marginal leakage detection of Class V restorations. Standardized Class V preparations with cervical margins in dentin and occlusal margins in enamel were made in 20 extracted human molars and restored with dental bonding agents and resin composite. All teeth were then immersed in 50% ammoniacal silver nitrate solution for 12 hours, followed by a developing solution for eight hours. Each restoration was scanned by micro-CT, the depth of marginal silver leakage in the central scanning section was measured, and the three-dimensional images of the silver leakage around each restoration were reconstructed. Afterward, all restorations were cut through the center and examined for leakage depth using a microscope. The silver leakage depth of each restoration obtained by the micro-CT and the microscope were compared for equivalency. The silver leakage depth in cervical walls observed by micro-CT and microscope showed no significant difference; however, in certain cases the judgment of leakage depth in the occlusal wall in micro-CT image was affected by adjacent enamel structure, providing less leakage depth than was observed with the microscope (p<0.01). Micro-CT displayed the three-dimensional image of the leakage around the Class V restorations with clear borders only in the dentin region. It can be concluded that micro-CT can detect nondestructively the leakage around a resin composite restoration in two and three dimensions, with accuracy comparable to that of the conventional microscope method in the dentin region but with inferior accuracy in the enamel region.

Nanoleakage in primary teeth prepared by laser irradiation or bur

The aim of this in vitro study was to analyze hybrid layer and nanoleakage of composite resin restorations in cavities prepared by either Er,Cr:YSGG laser or bur, followed by acid etching in primary teeth. Ten extracted primary molar teeth were randomly allocated into two groups consisting of ten cavities according to surface treatment regimen: Er,Cr:YSGG laser + acid etching(group 1) and bur + acid etching(group 2). Restorations of all samples were completed. Then, teeth were sectioned and immersed to ammoniacal silver nitrate solution. After polishing, hybrid layer thicknesses were examined under scanning electron microscopy (SEM) and ion analysis was carried out with SEM/energy dispersive X-ray spectroscopy preparation in terms of nanoleakage. Hybrid layer thickness and the amount of silver ions were assessed for the acid-etched groups. The collected data were analyzed with independent sample t test and Spearman's rank correlation. In groups 1 and 2, the mean hybrid layer thicknesses were 4.25 ± 1.41 and 5.24 ± 1.07 μm and the silver ion percentages were 10.97 ± 13.81 and 22.79 ± 21.62 %, respectively. Although no significant correlation was observed between the increase of hybrid layer thickness and the amount of silver ions, more silver ions were observed in group 2 (p < 0.05). According to the results of this study, acid-etched cavities prepared with laser promoted better results when compared to the acid-etched cavities prepared with bur.

Effects of functional monomers and photo-initiators on the degree of conversion of a dental adhesive

Besides functional and cross-linking monomers, dental adhesives contain a photo-initiator system for polymerization, thereby providing physico-mechanical strength to the adhesive-tooth interface. Few studies have investigated the effect of the functional monomer and polymerization-initiation system on the polymerization efficiency of the adhesive. Here, we tested the effect of two different functional monomers (MAC-10 vs. SR) and two photo-initiator systems, camphorquinone-amine (CQ) vs. borate (BO), on the degree of conversion (DC) of different adhesive formulations. The DC of the CQ-cured adhesive formulations was significantly affected by the MAC-10 monomer. This should be ascribed to the known inactivation of the amine co-initiator through acid-base reaction. However, the SR monomer did not decrease the DC, which could be attributed to a "gel effect" or the so-called "Trommsdorff-Norrish" phenomenon of enhanced DC with more viscous resins, and to the more favorable availability of CC double bonds. In contrast, the DC of the BO-cured adhesive formulations was not affected by any acidic monomer. It is concluded that the degree of conversion of an adhesive can be affected by the functional monomer, but this depends on the kind of photo-initiator system used. As bond durability depends, among other factors, on the strength and thus degree of conversion of the adhesive, potential interaction between adhesive ingredients and the photo-initiator system definitely needs to be studied further.

Microleakage resistance of minimally invasive Class I flowable composite restorations

Minimally invasive flowable composite Class I restorations are widely used. However, flowable composites are characterized by low filler contents, modified resin formulations, low moduli of elasticity, low viscosity, generally poor mechanical properties, and decreased long-term stability. The purpose of this study was to compare the microleakage resistance of a wide variety of flowable composites used with their manufacturers' recommended bonding systems to that of a long-used and widely studied microhybrid composite when placed as minimally invasive occlusal restorations. Molar teeth were prepared in a standardized manner, restored, artificially aged, stained, sectioned, evaluated, and analyzed. Microleakage varied substantially, by a whole order of magnitude, among the material groups tested. The control group, a conventional microhybrid composite material, leaked significantly less than all the flowable composite groups. Microleakage varied very slightly among measurement site locations. Tiny microscopic bubbles were seen within many of the flowable composite specimens, as were a few voids.

Adhesive temperature: effects on adhesive properties and resin-dentin bond strength

OBJECTIVES

To evaluate the effect of adhesive temperature on the resin-dentin bond strength (μTBS), nanoleakage (NL), adhesive layer thickness (AL), and degree of conversion (DC) of ethanol/water- (SB) and acetone-based (PB) etch-and-rinse adhesive systems.

METHODS

The bottles of the two adhesives were kept at each temperature (5°C, 20°C, 37°C, and 50°C) for 2 hours before application to demineralized dentin surfaces of 40 molars. Specimens were prepared for μTBS testing. Bonded sticks (0.8 mm(2)) were tested under tension (0.5 mm/min). Three bonded sticks from each tooth were immersed in silver nitrate and analyzed by scanning electron microscopy. The DC of the adhesives was evaluated by Fourier transformed infrared spectroscopy.

RESULTS

Lower μTBS was observed for PB at 50°C. For SB, the μTBS values were similar for all temperatures. DC was higher at 50°C for PB. Higher NL and thicker AL were observed for both adhesives in the 5°C and 20°C groups compared to the 37°C and 50°C groups. The higher temperatures (37°C or 50°C) reduced the number of pores within the adhesive layer of both adhesive systems.

CONCLUSIONS

It could be useful to use an ethanol/water-based adhesive at 37°C or 50°C and an acetone-based adhesive at 37°C to improve adhesive performance.

Long-term nanoleakage depth and pattern of cervical restorations bonded with different adhesives

PURPOSE

This study investigated the effect of water storage on nanoleakage depth and the pattern of cervical cavities bonded with different adhesives.

METHODS

For nanoleakage depth evaluation, standardized cervical cavities (2 mm in diameter) were prepared on the buccal and lingual surfaces of 36 intact human premolars. Specimens were divided into three groups (n=12) according to the three adhesive systems used: an etch-and-rinse adhesive (SBMP, Adper Scotchbond Multi-Purpose, 3M ESPE) and two single-step self-etch adhesives; one was mild and acetone based (IB-iBond, Kulzer), while the other was strong water based (PL, Adper Prompt L-Pop, 3M ESPE). All cavities were restored using Filtek Z250 (3M ESPE) resin composite. For each adhesive, specimens (n=12 with 24 restored cavities) were subdivided into three subgroups (n=4 with eight cavities) according to the storage period before examination (24 hours, three or six months). Another duplicate of teeth was prepared in the same way for nanoleakage pattern evaluation. After storage, the specimens were placed in 50%W/V silver nitrate solution for 24 hours and immersed in a photo-developing solution for eight hours. Thereafter, the specimens were sectioned buccolingually, polished, and examined by scanning electron microscopy. For nanoleakage pattern, specimens were treated in the same way as for nanoleakage depth except that they were additionally immersed in 10% EDTA for five seconds after polishing. Silver penetration percentage was calculated to the total length of the tooth-restoration interface. Data were analyzed with two-way analysis of variance, Kruskal-Wallis, and post hoc tests.

RESULTS

After 24 hours, the least amount of nanoleakage depth was recorded for IB, while the highest was recorded for PL. For stored specimens, there was no significant difference among the nanoleakage depths of all adhesives. The tested adhesives recorded different nanoleakage patterns; however, there was an increase in the intensity and continuity of silver deposition by time.

CONCLUSIONS

After 24 hours, the nanoleakage depth/pattern varied with the type of adhesive used; however, after water storage, all adhesives performed equally.

Bond Strength and Quality of the Hybrid Layer of One-step Self-etch Adhesives Applied with Agitation on Dentin

Vigorous application on the dentin surface is an excellent tool capable of improving the immediate performance of simplified self-etch adhesive systems.

Nanoleakage phenomenon on deproteinized human dentin

OBJECTIVE

The purpose of this study was to evaluate the influence of dentin deproteinization on the nanoleakage phenomenon.

MATERIAL AND METHODS

Class V cavities were prepared in 12 human molars with cervical margins located in dentin. The cavities were assigned to 2 groups (n=6) according to dentin treatment: Group I - dentin treated in accordance with the manufacturer's instructions and Group II - dentin treated following the manufacturer's instructions + 10% NaOCl. Each group was sub-divided into three groups, according to the DBS (dentin bonding system) used: Scotchbond Multi Purpose (SBMP), Prime & Bond NT (PB) and Clearfil SE Bond (SE), which were applied according to manufacturer's instructions. The cavities were restored with composite resin, and the specimens were immersed in a tracer agent (AgNO3 50%) for 24 h. The teeth were sectioned buccolingually through the center of the restorations, and nanoleakage pattern was evaluated by scanning electron microscopy (SEM) using the backscattered electron image mode.

RESULTS

SEM analysis showed different nanoleakage patterns for each DBS. Irrespective of dentin treatments, all SBMP specimens showed nanoleakage. SE did not show any nanoleakage with both dentin treatments used. PB showed nanoleakage within the hybrid layer only in Group I.

CONCLUSIONS

The influence of dentin deproteinization on the nanoleakage phenomenon was dependent on dentin bonding system formulation and bonding strategies.

Chlorhexidine release and water sorption characteristics of chlorhexidine-incorporated hydrophobic/hydrophilic resins

OBJECTIVES

The aim of this study was to evaluate chlorhexidine release from unfilled non-solvated methacrylate-based resins of increasing hydrophilicity and to examine relationships among Hoy's solubility parameters, water sorption, solubility and the rate of chlorhexidine release.

METHODS

Resin discs were prepared from light-cured, experimental resin blends (R1, R2, R3, R4 and R5) containing 0.0, 0.2, 1.0 and 2.0 wt.% chlorhexidine diacetate (CDA). Discs were immersed in distilled water at 37 degrees C, and mass changes were recorded at different periods. Spectral measurements were made to follow change in optical densities of storage solution to examine chlorhexidine release kinetics. After a 28-day period, water sorption, solubility, and the cumulative chlorhexidine release were obtained. Additionally, antibacterial study was performed by observing the presence of inhibition zone against Streptococcus mutans.

RESULTS

The most hydrophilic resin (R5) exhibited the highest chlorhexidine release rate. The most hydrophobic resin (R1) exhibited the lowest rate. However, no inhibition zone was produced by any specimens stored in water for 2 weeks. The addition of CDA increased solubility significantly but had no effect on water sorption. Significant positive correlations were seen between water sorption and the cumulative chlorhexidine release.

SIGNIFICANCE

Chlorhexidine release from resins may be related to water-induced swelling, which in turn is enhanced by the hydrophilicity of cured polymer matrix.

Hybridization quality in cervical cementum and superficial dentin using current adhesives

OBJECTIVES

The aim of this research was to determine the hybridization quality of adhesives to gingival cementum and close superficial dentin using both total-etch and self-etch, one-step and two-step adhesives in vitro.

METHODS

Five adhesive systems were used and evaluated in this study; three kinds of two-step adhesives (total-etch--Single Bond and self-etch--Clearfil SE Bond and Clearfil Protect Bond) and two one-step adhesives (Clearfil S3 Bond, G Bond). Fifteen extracted intact human third molars were used in this study. A diagonal cut which was approximately 45 degrees to the long axis of the roots, with the initiating point located 2 mm below the buccal enamel-cementum junction and ascending towards the pulp chamber was prepared on each tooth. Flat cervical cementum and dentin surfaces were ground with wet 600-grit silicon carbide paper, and bonded with one of the adhesives and finished by applying a flowable resin composite. After 24 h storage at 37 degrees C in water, the bonded assemblies were sectioned into approximately 1mm thick slabs. Two central slabs from each tooth were chosen. One slab was totally demineralized in 0.5 M EDTA and the other was not demineralized and immersed into 50% (w/v) solution of ammoniacal silver nitrate for 24 h, and successively exposed to photodeveloping solution for 8 h. The specimens were then processed for TEM observation. Both the stained demineralized silver unchallenged and unstained non-demineralized silver challenged resin-cervical cementum/proximal superficial dentin interface were observed and evaluated under a transmission electron microscope.

RESULTS

The nanoleakage pathway and extent vary among the different adhesives used and also between the resin-cementum interface and resin-dentin interface. Two-step self-etch adhesives showed better hybridization quality both in cementum and proximal superficial dentin as compared to those of two-step total-etch adhesive and one-step self-etch adhesives.

SIGNIFICANCE

Two-step self-etch adhesives may provide a better sealing in cervical cementum and the proximal superficial dentin region.

Micropermeability of current self-etching and etch-and-rinse adhesives bonded to deep dentine: a comparison study using a double-staining/confocal microscopy technique

Water sorption decreases the mechanical properties and the bond strengths of resin-bonded dentine. The aim of this study was to evaluate the micropermeability of several self-etching and etch-and-rinse adhesives. Optibond FL, Silorane, Scotchbond 1XT, G-Bond, and DC-Bond were bonded under simulated pulpal pressure. A 10 wt% solution of ammoniacal silver nitrate and a 1 wt% solution of rhodamine B were injected into the pulp chamber at 20 cm of water pressure. The dentine-adhesive interfaces were examined using a confocal scanning microscope. Micropermeability was detected in all the adhesives. DC-Bond, G-Bond, and Scotchbond 1XT showed voids along the resin-bonded interface. Silorane and Optibond FL showed an adhesive layer that was free from water trees and micropermeability. The double staining technique is a method that gives accurate results in the study of the resin-dentine micropermeability. Each class of adhesive has a different distribution of micropermeability. The higher the micropermeability, the higher the risk of defects at the resin-dentine interface, which may represent the pathway for hydrolytic and enzymatic degradation of resin-dentine bonds over time.

Leakage Pathway of Class V Cavities Restored With Different Flowable Resin Composite Restorations

The flowable resins evaluated in this study showed leakage patterns (micro and nano), indicating that the bonding system used did not achieve perfect sealing at the restortion/dentin interface.

Effect of dentin depth on hybridization quality using different bonding tactics in vivo

OBJECTIVES

Incomplete resin infiltration and polymerization of adhesive contributed to nanoleakage formation. This study tested the null hypothesis that adoption of different bonding tactics and dentine depth will not affect hybridization quality in vivo.

METHODS

Class V cavities were prepared on the labial/buccal surface of monkey teeth. They were bonded by Single Bond (a two-step total-etch adhesive), Clearfil SE Bond (a two-step self-etch adhesive), or Clearfil S(3) Bond (an all-in-one self-etch adhesive). Combined nanoleakage analysis and quantitative immunolabeling evaluation were carried out in the hybrid layer formed in both cervical superficial and deep dentine.

RESULTS

Single Bond showed reticular and spotted nanoleakage while Clearfil SE Bond and Clearfil S(3) Bond presented only a spotted one. While Single Bond showed increased concentration of labeling of type I collagen within the deep part of the hybrid layer, two self-etch adhesives-Clearfil SE Bond and Clearfil S(3) Bond revealed a homogeneous labeling pattern, even if the latter presented a significantly increased labeling index in deep dentine.

CONCLUSIONS

Different bonding tactics showed different nanoleakage patterns and immunolabeling index, and was influenced by dentine depth at different levels in vivo.

Qualitative analysis of adhesive interface nanoleakage using FE-SEM/EDS

OBJECTIVES

The purpose of this study was to evaluate the quality of short term sealing of current adhesives.

METHODS

Five adhesive systems were used and evaluated in this study; two kinds of two-step adhesives (Single Bond and Clearfil SE Bond) and three one-step adhesives (Clearfil S3 Bond, G Bond and One-Up Bond F-plus). Flat occlusal superficial dentin surfaces from extracted human third molars were finished with wet 600-grit silicon-carbide paper and bonded with one of the adhesives. After 24h storage at 37 degrees C in water, the bonded assemblies were sectioned into approximately 1mm thick slabs. Two central slabs from each tooth were chosen and immersed into 50% (w/v) solution of silver ammoniacal nitrate for 18 h and exposed to photodeveloping solution for 6h. The specimens were then slightly polished, argon ion-etched. In order to examine the nanoleakage within the resin/dentin interface, penetration of silver was observed in a field emission (FE)-SEM using yttrium-aluminium-garnet (YAG) backscattered electron mode. EDS analysis was also carried out in parallel to identify the existence of metallic silver particles.

RESULTS

The penetration pattern of silver depended on the adhesive used, indicating different nanoleakage in different adhesive systems. Single Bond, One-Up Bond F-plus and G Bond showed clear silver uptake in both the adhesive and hybrid layer. Clearfil SE Bond showed less silver penetration and slight silver peak on the elemental energy spectroscopy of EDS. Clearfil S3 Bond did not display clear silver penetration under 2000x magnification by FE-SEM, and no existence of metallic silver of the Clearfil S3 Bond group by EDS, could be detected.

SIGNIFICANCE

The nanoleakage, as well as its location depends on the adhesives. Different nanoleakage expressions were revealed between two-step and one-step adhesives and also among one-step adhesives themselves.

Modulated photoactivation methods—Effect on marginal and internal gap formation of restorations using different restorative composites

This study evaluated the effect of modulated photoactivation methods on gap formation of restorations using different composites.

METHODS

Sixty human third molars were selected, sectioned (two fragments), and ground to expose a flat enamel area. A cavity (5 mm long x 2 mm wide x 2 mm deep--outer margins in enamel and inner margins in dentin) was prepared on the central area of flattened surface. Single bond adhesive system was applied according to manufacturer's instructions. The specimens were assigned into 12 groups (n = 10), according to the restorative composite (Filtek Z250, Herculite XRV, and Heliomolar) and the photoactivation method [continuous light (CL); soft-start (SS); pulse delay (PD); and intermittent light (IL)]. Outer margins were stained using Caries Detector, observed under stereomicroscope, and images were transferred to a computer measurement program. Then, the specimens were sectioned in slices and the internal gaps were assigned using the same method. The length of gaps was expressed as a percentage of total length of the margins. Data (internal adaptation) were submitted to ANOVA and Tukey's test.

RESULTS

All restorations showed perfect seal of the enamel outer margins. Modulated photoactivation methods (SS, PD, and IL) showed a significant reduction on internal gap formation when compared with CL, regardless of the composite. Filtek Z250 showed the best internal adaptation, regardless of the photoactivation method.

CONCLUSION

Modulated photoactivation methods decrease the internal gap formation of composite restorations, and should be encouraged on clinical practice.

Quantitative Comparison of the Water Permeable Zone Among Four Types of Dental Adhesives Used with a Dual-cured Composite

When placing a dual-cured composite, variation in the permeability of adhesive interfaces may affect bonding quality and longevity.

Effect of bur type and conditioning on the surface and interface of dentine

The purpose of this in vitro study was to evaluate the surface and resin-dentine interface characteristics of permanent tooth dentine cut with diamond or carbide burs and treated with phosphoric acid (PA) or an acidic conditioner. Labial surfaces of permanent incisors were prepared into dentine with high-speed carbide or diamond burs and divided into two halves. Phosphoric acid 36% was applied on one half and non-rinse conditioner (NRC) was applied on the other half. Ten randomly selected scanning electron microscopy (SEM) fields from each specimen (n = 15) were evaluated. Occlusal surfaces of third molars were divided in two halves for evaluation of the resin-dentine interface. The halves were randomly assigned to one of each conditioner and restored with Prime & Bond NT/Spectrum. Ten specimens were analysed by SEM to evaluate hybrid layer formation and interfacial seal. We observed that surfaces prepared with carbide bur presented less residual smear plugs (P < 0.05) than surfaces prepared with diamond burs. Surfaces conditioned with NRC, which is a smear layer modifier, presented more residual smear plugs than surfaces conditioned with PA (P < 0.05). Treatment with PA resulted in more sealed interfaces than specimens treated with NRC. Within the limitations of this study the results showed that carbide burs leave a surface that is more conducive to bonding than diamond burs.

Seven-year dentin bond strengths of a total- and self-etch system

The aim of this study was to determine the durability of tensile bond strengths of a conventional 3-step bonding system (Superbond D-liner Plus) and a self-etching priming bonding system (Clearfil Liner Bond II) to bovine dentin over a 7 yr period. Superficial bovine dentin finished with 600-grit SiC paper was bonded with one of the two adhesive materials. A 4 mm diameter area was bonded, covered with resin composite and stored in 37 degrees C deionized water containing gypsum chips and 0.4% sodium azide as an antibacterial. Bonds were stressed in tension at a crosshead speed of 1 mm min(-1). Mean bond strengths were observed at 1 d, at 1, 3, and 6 months, and at 1, 2, 3, 6 and 7 yr. Ten specimens were tested for the first 3 yr and 15 specimens were tested for 6 and 7 yr. The bond strength of Superbond D-liner Plus significantly decreased over the 7 yr period, whereas Liner Bond II showed a slight but, insignificant, decrease. The fracture mode changed with time for Superbond D-liner Plus, but not for Liner Bond II. It was concluded that systems which use a strong acid for demineralizing the dentin may show greater deterioration of the bond to dentin compared with a self-etching priming system.

A three-year clinical evaluation of two-bottle versus one-bottle dentin adhesives

BACKGROUND

The authors conducted an in vivo investigation to compare the clinical performance of two commercial one-bottle adhesives and a two-bottle adhesive for restoration of noncarious cervical lesions (NCCLs).

METHOD

The patient pool consisted of 57 patients and 171 teeth (three teeth per patient), with one NCCL per tooth. Each patient received three resin-based composite restorations, each with a different adhesive: one tooth with a two-bottle, water-based adhesive as the control; another tooth with a one-bottle, ethanol-based adhesive; and a third tooth with a one-bottle, solvent-free adhesive. The authors assessed restorations in terms of retention, marginal integrity, margin discoloration and air sensitivity at baseline, six months, one year, two years and three years after initial placement.

RESULTS

The retention rates at 36 months were 88 percent for the first adhesive, 81 percent for the second adhesive and 90 percent for the third adhesive. No statistically significant differences in retention rates could be shown, with 86 percent of restorations retained overall. Measures of marginal integrity, marginal discoloration and sensitivity also had no statistically significant differences between the three adhesives (P > .05).

CONCLUSIONS

All three adhesives performed with acceptable outcomes after a 36-month period, with small differences between the one- and two-bottle systems and between the various solvents. Retention rate was moderately high and air sensitivity was markedly reduced; however, superficial marginal discoloration and marginal degradation was notable. Certain lesion, tooth and patient characteristics may predispose restorations to retention failure.

CLINICAL IMPLICATIONS

The type of solvent may not be a major factor in retention of Class V restorations in NCCLs. Both single-bottle adhesives and conventional two-bottle adhesives performed acceptably.

Adhesiveness of dental resin-based restorative materials investigated with atomic force microscopy

This study aimed to show that the polymerization contraction of dental methacrylate-based materials, when used as adhesives on hard substrate, produces voids at the material-substrate interface. This phenomenology is closely related with the nanoleakage and the sealing ability of these materials. One prime/bond system, three restorative composite resins, and one orthodontic bonding system were cured by using mirror-like glass slides as a compliance-free reference substrate. The adhesive surface was analyzed by atomic force microscopy, and the polymerization contraction of bulk material was tested by laser beam-scanning method. Nanoperiodic structure of three-dimensional (3D) images, section analysis, and roughness characteristics (R(a) and R(z)) indicated that polymerization contraction produced voids at the interface. When the adhesive surface was exposed to oral simulating fluids (water, ethanol, and lactic acid solutions), hydrolytic degradation involved some hundreds of nanometers in depth. In visible light-cured (VLC) materials, the interface porosity decreased when an irradiation pause ( approximately 2 min) was carried out during gelation.

Water movement in the hybrid layer after different dentin treatments

The aim of this study was to examine the morphology of the hybrid layer (HL) of bonded water-stored specimens after different chemical pre-treatments of dentin.

MATERIALS AND METHODS

Twenty-seven recently extracted human molars were selected. Fifty-four dentin disks in middle/deep dentin were obtained with a slow speed saw with a diamond-impregnated disk under water lubrication. Smear layers were created with 180 grit silicon carbide under running water for 1 min. Different pre-treatments of dentin were: Group (1) no treatment; Group (2) 35% H3PO4 etch for 15 s followed by 10% glutaraldehyde for 120 s; Group (3) 37% H3PO4 etch for 15 s followed by 5% NaOCl for 120 s. Three dentin bonding agents (DBAs), Prime and Bond NT (P and B), AdmiraBond (AB), and Clearfil SE Bond (SEB) were applied in association with a resin composite following the manufacturers' directions. Each specimen was then longitudinally sectioned and polished with wet SiC papers (up to #4000 grit). Impressions of the polished dentin were immediately taken with a silicone impression material. Bonded specimens were then stored for 3 or 12 h in deionized water. Further impressions of stored specimens were taken after air-drying of specimens for 10 s. Positive replicas were obtained using a polyether impression material. All the replicas and the original specimens were inspected by SEM.

RESULTS

A line of droplets (0.5-4 microm in diameter) was observed along the region of the adhesive-HL junction in all replicas of specimens stored in water, except in group 3, when P and B and AB were used. When SEB was used in each group the droplet were found in all groups except the zone of droplets was thinner. No differences in droplets dimensions were seen between 3 or 12 h water storage, or between the different dentin treatments.

CONCLUSIONS

The replica procedure used in this study was able to detect water trapped in the adhesive-HL region that was released during the setting of the impression material. The droplets observed in this region support the hypothesis that there can be bidirectional water movement within the adhesive-HL complex.

Evaluation of silver methenamine method for nanoleakage

OBJECTIVES

The aim of this study was to evaluate nanoleakage patterns following silver methenamine staining of restorations bonded with a total-etch single bottle system, a self-etching primer system and a total-etch single bottle system after collagen depletion.

METHODS

The dentin bonding systems used in this study were Prime and bond 2.1 (PB) and Clearfil SE Bond (CSEB). Cavities were made in grounded labial surfaces of 15 extracted bovine lower incisors, randomly divided into 3 Groups. Group 1 (PB), Group 2 (CSEB) and Group 3 (PB/SH) PB after collagen depletion with sodium hypochlorite (SH). The specimens were restored, sectioned and submitted to silver methenamine staining, polished and observed with low-vacuum back-scattered SEM. One way ANOVA and multiple-comparison Tukey's test were used for statistical analysis of the leakage scores.

RESULTS

PB presented significantly greater silver deposition and a distinct pattern when compared to CSEB. No silver deposition was detected for PB after collagen depletion.

SIGNIFICANCE

The dentine bonding systems tested were unable to prevent nanoleakage when used according to the manufacturers' instructions; however, CSEB presented a lower level of silver deposition. Collagen depletion prior to PB application may prevent nanoleakage occurrence in dentine walls. Silver methenamine staining may be a useful method for detection of nanoleakage in dentine when the collagen fibrils remain exposed within the hybrid layers.

Adhesive restorative materials: A review

'Adhesive' restorative dentistry originated with the work of Buonocore in 1955 in bonding resin to etched enamel. Since then, adhesive materials and techniques have developed at a rapid rate. The first chemically adhesive material (zinc polycarboxylate cement) was marketed in the late 1960s, and glass-ionomer cements and dentine bonding agents have since become available. This review focuses on the latter two products. Glass-ionomer cements have a particular role in adhesive dentistry because of their reliable chemical adhesion to enamel and dentine, and because of their apparent ability to promote the remineralization of 'affected' dentine. Dentine bonding agents have undergone marked changes in presentation over the last 15 years, but all have an essentially similar bonding system, that of hybrid layer formation. However, the most recent systems have limited clinical data supporting their use.

Overestimating hybrid layer quality in polished adhesive/dentin interfaces

The most popular techniques for determining the quality of the hybrid layer (HL) have relied on morphologic characterization of the polished adhesive/dentin (a/d) interfaces before and after acid-bleach chemical treatment. Using these techniques, the existence of smooth, acid-resistant layers has been consistently reported for most adhesive systems. The purpose of this study was to determine whether popular specimen preparation techniques that include polishing and acid-bleach treatment modify the a/d interface, mask the complexity of the HL, and lead to inaccurate assessment of the quality of the HL. To understand the impact of specimen preparation techniques on the morphology of the resin-dentin interface, polished and unpolished specimens from the same tooth were closely compared after different acid-bleach chemical treatment procedures. Two one-bottle adhesives, that is, 3M Single Bond and Pulpdent UNO, exhibiting distinct differences in hydrophilic/hydrophobic composition, were used in this investigation. Using specimens from the same tooth, the effect of chemical treatments on the morphology of the resin-dentin interdiffusion zone and the differences in the morphology of polished and unpolished specimens after these same treatments were studied with scanning electron microscopy. It was shown that conventional specimen preparation techniques that include polishing and acid-bleach treatment can adversely affect and even obscure the structural detail of the a/d interface in specimens that possess a porous HL. The results indicated that the Pulpdent UNO/dentin interface had better quality than the 3M Single Bond/dentin interface. The difference in the quality of HL can be attributed to factors such as compositional differences that impact the adhesive interaction with water, that is present within the substrate during wet bonding. The inability of the conventional acid-bleach procedure to reveal the differences in the scanning electron microscopy interfacial morphology was overcome in this investigation by using a multistep technique.

Ultramorphological analysis of resin-dentin interfaces produced with water-based single-step and two-step adhesives: Nanoleakage expression

This study evaluated the nanoleakage patterns in bonded interfaces using two single-step, self-etching adhesives (Adper Prompt-AD, and One-up Bond F-OB), two two-step, self-etching primers (Clearfil SE Bond-CF, and Unifil Bond-UB), and one two-step, total-etch adhesive (Single Bond-SB). Dentin surfaces were bonded with the adhesive systems and stored in water at 37 degrees C for 1 week and 6 months. After storage periods, teeth were sectioned into 0.8 mm-thick slabs, coated with nail varnish except for the bonded interfaces, and immersed in ammoniacal AgNO(3) for 24 h. After immersion in photodeveloping solution, bonded sections were prepared and observed under a SEM using the backscattered electron mode. Undemineralized, unstained, epoxy resin-embedded sections were prepared for TEM. Nanoleakage patterns were qualitatively compared between periods. Nanoleakage was observed in all bonded specimens at both periods. CF and UB presented silver deposits predominantly restricted to the thin (0.5 microm) hybrid layer (HL) at both periods. Although no evident differences were observed in the nanoleakage pattern of UB at 7 days and 6 months, CF presented enlarged areas of silver impregnation after 6 months. SB presented accumulation of silver particles mostly within the HL at 7 days, which was intensified after 6 months. AD and OB presented massive silver accumulation within the HL and the overlying adhesive layer. No evident differences were noticed between storage periods. Silver impregnation increased for all adhesive systems from 7 days to 6 months, except for UB.

Microtensile bond strength of total-etch and self-etching adhesives to caries-affected dentine

OBJECTIVES

To evaluate the microtensile bond strength of total-etch or self-etch adhesives to caries-affected versus normal dentine, and to correlate these bond strengths with DIAGNOdent laser fluorescence and Knoop microhardness (KH) measurements of the substrates.

METHODS

Extracted carious human molars were ground to expose flat surfaces where the caries lesion was surrounded by normal dentine. Surfaces were bonded with either Prime & Bond NT, Scotchbond 1, Clearfil SE Bond or Prompt L-Pop, according to manufacturers' recommendations. A crown was built up using resin composite (Tetric Ceram). After storage in water (37 degrees C, 24 h), teeth were vertically serially sectioned into 0.7 mm thick slabs and trimmed to yield 1 mm(2) test area that contained either caries-affected or normal dentine. Samples were tested in tension in an Instron machine at 1 mm/min. The quality of the dentine just beneath each fractured specimen was measured by laser fluorescence and KH.

RESULTS

Total-etch adhesives yielded higher bond strengths than self-etching systems. Significantly lower results were obtained with Prompt L-Pop. All the adhesives attained higher strengths in normal than in caries-affected dentine, but the differences were only significant for Prime & Bond NT and Clearfil SE Bond. Higher laser fluorescence values and lower KH (p<0.001) were recorded in caries-affected dentine compared to normal dentine.

CONCLUSIONS

The total-etch adhesives evaluated produced higher bond strengths to normal and caries-affected dentine than self-etching systems. Laser fluorescence measurements discriminated caries-affected dentine from normal dentine, and were strongly correlated with KH. However, laser fluorescence and KH did not permit high correlations with resin-dentine bond strengths in caries-affected dentine.

In vitro degradation of resin-dentin bonds analyzed by microtensile bond test, scanning and transmission electron microscopy

Our knowledge of the mechanisms responsible for the degradation of resin-dentin bonds are poorly understood. This study investigated the degradation of resin-dentin bonds after 1 year immersion in water. Resin-dentin beams (adhesive area: 0.9mm(2)) were made by bonding using a resin adhesive, to extracted human teeth. The experimental beams were stored in water for 1 year. Beams that had been stored in water for 24h were used as controls. After water storage, the beams were subjected to microtensile bond testing. The dentin side of the fractured surface was observed using FE-SEM. Subsequently, these fractured beams were embedded in epoxy resin and examined by TEM. The bond strength of the control specimens (40.3+/-15.1MPa) decreased significantly (p<0.01) after 1 year of water exposure (13.3+/-5.6MPa). Loss of resin was observed within fractured hybrid layers in the 1 year specimens but not in the controls. Transmission electron microscopic examination revealed the presence of micromorphological alterations in the collagen fibrils after 1 year of water storage. These micromorphological changes (resin elution and alteration of the collagen fibrils) seem to be responsible for the bond degradation leading to bond strength reduction.

Deproteinizing effects on resin-tooth bond structures

This study investigated the effects of NaOCl on resin-tooth bonds to simulate the situations of long-term durability and caries invasion. Resin-tooth bonded specimens were produced with the use of two resin adhesives (Excite and One-Bond). Resin-tooth bonded beams (adhesive area; 0.9 mm2) were serially sectioned and the specimens were immersed in 10% NaOCl medium for 0 (control), 2, 4, and 6 h after being stored in water for 24 h. After immersion, microtensile bond tests were performed. SEM fractography was conducted to calculate each failure mode by image analysis. In addition, the adhesive interface was examined with the use of TEM. In the control specimens, enamel bond strengths had no difference between Excite (45.6 +/- 15.0) and One-Bond (56.9 +/- 12.9). On the other hand, dentin bond strengths had significant difference between Excite (80.6 +/- 21.2) and One-Bond (50.7 +/- 11.2). The bond strengths decreased with increased storage time for both systems with enamel and dentin bonds. The deteriorated mineralized dentin of beams resulted in bond-strength reduction for resin-enamel bonds. For dentin bonding, the adhesive interface was gradually dissolved from the outer to the center portion of the beam. The depletion of collagen fibrils within the demineralized dentin or hybrid layer deformation was found under SEM and TEM examinations. These morphological changes are responsible for bond strength reduction of resin-dentin bonds.