Stannous Fluoride Preventive Effect on Enamel Erosion: An In Vitro Study.

The aim of this in vitro study was to evaluate the effects of a single dose application of two daily toothpastes on enamel exposed to acid attack. The research was conducted on human molars enamel fragments (n = 72). The two different toothpastes active ingredients were sodium fluoride (NaF) and stannous fluoride (SnF2). They were compared in protecting the surface of the enamel exposed to three acids: citric acid, lactic acid and hydrochloric acid. A spectrophotometer was used to measure the calcium ions and phosphate released in the solutions by the enamel specimens. Afterward, ionic concentrations were analyzed through the t-Student test, in order to estimate the significance level (p < 0.05) of the solubility differences obtained between the treatment and control groups. Finally, sample surfaces were analyzed with scanning electron microscopy and X-ray energy dispersive spectroscopy (SEM/EDX). The two analyzed toothpastes did not reveal any statistically significant variation in the release of calcium and phosphate (p > 0.05). Nevertheless, acid-resistant deposits were detected in samples treated with stannous fluoride and exposed to lactic acid, though the presence of tin ion deposits on samples treated with stannous fluoride was not shown. A single dose of a fluoride-based toothpaste before different acids attack, in simulated oral cavity conditions, did not show a significant preventive effect.

Outcome of secondary root canal treatment filled with Thermafil: a 5-year follow-up of retrospective cohort study.

OBJECTIVES: The aim of the present retrospective cohort study was to assess the 5-year outcome and survival of secondary root canal treatments (2°RCT), exploring the influence of pre-, intra-, and post-operative variables. MATERIALS AND METHODS: One hundred thirty-two endodontically retreated teeth were radiographically and clinically re-examined after 5 years. 2°RCT had been performed during a Masters program following standardized protocols and filled with AH Plus/Thermafil (TF). Pre-, intra-, and post-operative data were collected. The 5-year outcome was blindly evaluated and categorized as healed/diseased on the basis of the periapical index. Bivariate analysis and chi-square test evaluated the association between outcome and 31 demographic/clinical parameters. Multilevel analysis was performed at both patient and tooth level. Statistical significance was calculated at 5% level. RESULTS: At 5-year evaluation, survival rate was 80% with 7.5% lost for endodontic reasons. Eighty-three percent of the teeth were classified as healed. Multilevel analysis identified significant predictors of increased survival: female gender (p = 0.012), absence of a pre-operative metal post (p = 0.017), conservative apical preparation (diameter size < #35) (p = 0.039), teeth restored with a crown (p = 0.009), and final PAI (after 5 years) ≤ 2 (p = 0.001). Multilevel analysis identified as predictor healing: not being a smoker (p = 0.048) and conservative apical preparation < size #35 (p = 0.037). CONCLUSIONS: Outcome of 2°RCT filled with Thermafil was successful at 5 years, showing a high rate of survived and healed teeth comparable to that reported previously for other obturation techniques. CLINICAL RELEVANCE: Present findings confirm 2°RCT as a valid therapeutic option to retain natural teeth.

Long-term outcome of non-surgical root canal treatment: a retrospective analysis.

This study investigated the long-term clinical outcome of root canal treatment. 240 root-treated teeth (n = 61 patients) were initially classified on the basis of radiographic presence/absence of initial apical periodontitis (IAP) and clinical data. The final outcome measure was the periapical healing (healed/disease). The outcome at 6-9 months was correlated with the outcome at 10 years following treatment. Prognostic factors for the periapical healing were assessed. Extraction data were recorded. Univariate and multivariate logistic regression analysis was used to identify risk indicators for apical periodontitis (AP) development. Chi-square analysis was performed to evaluate a possible relationship between the 6-9 months outcome and the final outcome related to IAP. Mean observation time was 14 ± 3.7 years. Survival rate was 84.6% and healing rate was 79% (10-19 years). Predictors of outcome (p < .05) were considered statistically significant. Multivariate logistic regression analysis showed that initial pulpal and periapical status and the quality of root canal filling as assessed two-dimensionally were independent predictors of outcome. The 6-9 months evaluation appears to be an indicator for the final outcome of primary root canal treatment both in the presence and in the absence of IAP. An initial radiolucency associated with an unsatisfactory quality and extent of root canal filling significantly diminishes the possibility of achieving long-term radiographic success. For those with uncertain healing at 6-9 months (91%), clinicians should consider the high healing rate when estimating the prognosis and adjust the decision making accordingly.

Enamel structural changes induced by hydrochloric and phosphoric acid treatment.

PURPOSE: The aim of this study was to evaluate enamel acid-induced structural changes after 2 different treatments, by means of Raman and infrared (IR) spectroscopy analyses, and to correlate these findings with permeability measured as fluid discharge from outer enamel. METHODS: Two different treatments were investigated: 10 enamel slices were etched with 15% hydrochloric acid (HCl) for 120 seconds and 10 slices with 37% phosphoric acid gel (H3PO4) for 30 seconds, rinsed for 30 seconds and then air-dried for 20 seconds. Powders of enamel treated as previously described were produced. Replicas of enamel subjected to the same treatments were obtained to evaluate the presence of fluid droplets on enamel surface. RESULTS AND CONCLUSIONS: Raman and IR spectroscopy showed that the treatment with both hydrochloric and phosphoric acids induced a decrease in the carbonate content of the enamel apatite. At the same time, both acids induced the formation of HPO42- ions. After H3PO4 treatment, the bands due to the organic component of enamel decreased in intensity, while they increased after HCl treatment. Replicas of H3PO4 treated enamel showed a strongly reduced permeability. Replicas of HCl 15% treated samples showed a maintained permeability. A decrease of the enamel organic component, as resulted after H3PO4 treatment, involves a decrease in enamel permeability, while the increase of the organic matter (achieved by HCl treatment) still maintains enamel permeability.The results suggested a correlation between organic matter and enamel permeability. Permeability was affected by etching technique and could be involved in marginal seal, gap and discoloration at the enamel interface, still causes of restoration failure.

Effects of long-term water storage on the microtensile bond strength of five experimental self-etching adhesives based on surfactants rather than HEMA.

OBJECTIVES: The purpose of this study is to evaluate the hypothesis that replacing 2-hydroxyethyl methacrylate (HEMA) for surfactant dimethacrylates (SD) does not affect the immediate and long-term microtensile bond strength (µTBS) of experimental two-step self-etch HEMA-free adhesive systems applied on dentin. MATERIALS AND METHODS: Five experimental HEMA-free two-step self-etching systems containing different SD (ethoxylated bisphenol A diglycidyl dimethacrylate (Bis-EMA 10, B10), Bis-EMA 30 (B30), poly-ethyleneglycol (400) dimethacrylate (PEG 400, P400), PEG 1000 (P1000), and PEG 400 urethane dimethacrylate (UDMA) (UP400)) and a HEMA-containing system (control) (HA) were formulated. Specimens were subjected to the µTBS test after 24 h and 6 and 12 months of storage. Data (in megapascals) were analyzed by Kruskal-Wallis and Dunn tests (α = 0.05). RESULTS: Medians of the µTBS data after 24 h of storage are: HA = 57.2(A), B10 = 26.2(BC), B30 = 24.0(C), P400 = 32.6(BC), P1000 = 37.3(B), and UP400 = 57.9(A); after 6 months are: HA = 47.9(A), B10 = 18.5(B), B30 = 7.8(C), P400 = 16.1(B), P1000 = 14.6(BC), and UP400 = 51.6(A); and after 12 months are: HA = 31.2(A), B10 = 15.2(B), B30 = 9.0(B), P400 = 9.1(B), P1000 = 13.3(B), and UP400 = 35.7(A). Between the HEMA-free groups, the adhesive system formulated with PEG 400 UDMA produced similar µTBS to the HEMA-containing group. Also, the storage of specimens decreased the µTBS (p < 0.05). CONCLUSION: Replacing HEMA for PEG 400 UDMA in an adhesive system formulation generated a satisfactory µTBS to dentin. CLINICAL RELEVANCE: Surfactant dimethacrylates have a potential use in the development of HEMA-free self-etching adhesive systems, which are more chemically stable.

The effect of the NRT files instrumentation on the quality of the surface of the root canal wall.

PURPOSE: To analyze in vitro, trough scanning electron microscope (SEM), the shaping ability of NRT NiTi rotary system (Mani, Inc, Toshigi-Ken, Japan). METHODS: Ten extracted human teeth were cut at the level of the CEJ and prepared with Gates-Glidden burs 4-3-2 and NRT rotary files up to size #35. Irrigation was performed with 7.5 mL of 5% NaOCl and 7.5 mL of 10% EDTA during each canal instrumentation. Following the shaping sequence, a final irrigation was performed with EDTA followed by NaOCl, each left in situ for three minutes. Teeth were then fractured longitudinally, and the coronal, middle, and apical thirds of the canals were inspected with SEM. Three parameters, divided into four different levels (Alfa and Bravo, considered clinically acceptable; Charlie and Delta, considered clinically unacceptable), were used to score the canal morphology: presence and amount of smear layer; presence of organic and inorganic debris; surface profile. RESULTS: SEM assessment revealed that in the coronal and middle third the majority of canals shaped with NRT rotary system presented a clinically acceptable surface. The apical third presented a higher amount of smear layer and dentinal debris instead, compared to the coronal and middle third. CONCLUSIONS: NRT files demonstrated that they provided good instrumentation of the coronal and middle third, while being unable to obtain a defects-free surface in the apical third.

A new approach in self-etching adhesive formulations: replacing HEMA for surfactant dimethacrylate monomers.

This study evaluated the influence of surfactant dimethacrylates (SD) on the resin-to-dentin microtensile bond strength (µTBS) and characterized the interfacial micromorphology of the hybrid layer of the experimental HEMA-free self-etching systems. Five experimental HEMA-free two-step self-etching systems containing different SD (Bis-EMA 10, Bis-EMA 30, PEG 400, PEG 1000, and PEG 400 UDMA) and a HEMA-containing system (control) were compared. Each experimental adhesive system was applied and resin composite restorations were incrementally built up in bovine incisors. After 24 h, restored teeth were sectioned to obtain 24 sticks per group. Thereafter, the specimens were subjected to the µTBS test. Data (MPa) were analyzed by One-way ANOVA and Tukey's test. Adhesive-dentin interfaces were analyzed through Scanning Electron Microscopy (SEM). The adhesive system formulated with PEG 400 UDMA produced µTBS similar to the HEMA-containing group and statistically higher than the HEMA-free groups. Similar failure percentages were observed in the PEG 400 UDMA and the control group. In the SEM analysis, all the adhesive systems presented similar partially demineralized hybrid layer (1.5-3.0 µm thickness) with well-formed resin tags. All SD presented reasonable initial µTBS, with the PEG 400 UDMA being a promising monomer to be considered as a HEMA substitute in adhesive systems compositions.

Cyclic fatigue testing and metallographic analysis of nickel-titanium rotary instruments.

INTRODUCTION: The aim of this study was to compare cyclic fatigue resistance of four nickel-titanium rotary systems and to evaluate their surface, fractographic, and matrix morphology. METHODS: Four models of endodontic rotary files (EasyShape [Komet/Gebr. Brasseler, Lemgo, Germany], ProTaper [Dentsply Maillefer, Ballaigues, Switzerland], NRT [MANI Inc, Toshigi-Ken, Japan], and AlphaKite [Komet/Gebr. Brasseler]) were subjected to fatigue testing in artificial canals with angle of curvature of 45° and 60° and a radius of curvature of 5 mm until fracture occurred. Nickel-titanium (NiTi) alloy properties were investigated by light microscopy, environmental scanning electron microscopy (ESEM), and energy dispersive x-ray spectrophotometry (EDS). ESEM analysis was conducted on new files to examine surface characteristics and on fractured samples to identify the crack origin and the fractographic features. RESULTS: Analysis of variance testing revealed significant differences (P < .001) among the groups. NRT files had the highest fatigue resistance followed by AlphaKite, EasyShape, and ProTaper. All the new files presented surface imperfections. Fractographic analysis found the crack initiation to originate at the level of surface irregularities. Optical microscope inspection of the NiTi alloy matrix disclosed different-sized nonmetallic inclusions among models. EDS analysis of these inclusions showed that they were composed of carbon and oxygen in addition to nickel and titanium. Under light microscopy, austenitic grains appeared larger near the handle and smaller near the tip in all instruments. CONCLUSIONS: NRT files presented the longest fatigue life. All samples showed surface irregularities and nonmetallic inclusions. Austenitic grains were smaller near the tip than near the handle. The angle of curvature was confirmed to influence the fatigue life of NiTi instruments.

In vivo effects of fluoride on enamel permeability.

This in vivo study evaluated the effects of topical fluoride application on enamel by repeated scanning electron microscopy analysis of replicas. Baseline fluid droplets were employed as qualitative indication of enamel permeability. CaF(2)-like globules were detected in vivo after fluoride application and were not found after professional brushing, ultrasound action, or chemical extraction. Absence of water permeability of enamel was demonstrated even after removal of CaF(2)-like globules. Droplets reappeared within 1 h in sodium fluoride-treated teeth, but they did not reappear even after 1 week following topical enamel treatment with acidulated phosphate fluoride. Teeth treated with an acidulate fluoride-free solution showed lack of CaF(2)-like globules and no droplets for at least 1 week as detected in acidulate phosphate fluoride-treated teeth. The caries-preventing action of fluoride may be due to its ability to decrease permeability and diffusion pathways. CaF(2)-like globules seem to be indirectly involved in enamel protection over time maintaining an impermeable barrier, and phosphoric acid seemed to play an unexpected fluoride-independent preventive role.

Development of experimental HEMA-free three-step adhesive system.

OBJECTIVE: To evaluate the influence of Bis-EMA 30 on the resin-to-dentin microtensile bond strength (microTBS) and structural reliability of the experimental three-step etch-and-rinse adhesive systems. METHODS: Five experimental primers containing different dimethacrylate monomer concentrations (0, 10, 20, 40, 60 wt% of the Bis-EMA 30, P0.P60) added to acid monomer and solvents (ethanol/water), and a resin bond (Bis-GMA/TEGDMA, 50/50 wt%) were formulated. The adhesive system Scotchbond MultiPurpose (SBMP, 3M ESPE) was tested as commercial reference. Sixty bovine incisors were randomly separated into six groups, and their superficial coronal dentin was exposed. After acid etching and rinsing, the excess water was removed from the surface with absorbent paper. Each experimental primer was actively applied (30 s), followed by a mild air stream (10 s). The experimental adhesive resin was applied and light activated for 20 s. Resin composite restorations were incrementally built up. The restored teeth were stored in distilled water at 37 degrees C for 24 h, and then sectioned to obtain sticks with a cross-sectional area of approximately 0.5 mm(2), after which 24 specimens per group were subjected to the microTBS test. Data (MPa) were analyzed by One-way ANOVA, Tukey test (alpha=0.05) and Weibull analysis. RESULTS: The P40 group showed microTBS means similar to those of the control (SBMP), whereas both had statistically higher values when compared with the other groups (p<0.001). Moreover, P40 showed higher structural reliability, represented by the high Weibull modulus and characteristic strength values. The lowest microTBS was observed in the P0, P10 and P20 groups, which also had low structural reliability. SIGNIFICANCE: Bis-EMA 30 is a promising monomer to be considered as a substitute for HEMA in adhesive system compositions.

In vivo enamel fluid movement.

The aim of this study was to visualize fluid movement through dental enamel in vivo. Fifty permanent upper central incisors, from subjects aged 10-70 yr, and 5 permanent central just-erupted incisors, from subjects aged 6-7 yr, were included in the study. An impression was obtained by vinyl polyxiloxane, and replicas were then obtained by polyether impression material. The hydrophobic vinyl polyxiloxane material yielded a morphological image in situ of outward fluid flow through tooth enamel. The study confirmed in vivo that enamel is a permeable substrate, as shown by the presence of droplets on its surface, and demonstrated that age and enamel permeability are closely related. Samples from subjects of different ages showed a decreasing number and size of droplets with increasing age: freshly erupted permanent teeth showed many droplets covering the entire enamel surface. Droplets in permanent teeth were prominent along enamel perikymata.

Effect of simulated pulpal pressure on dentin permeability and adhesion of self-etch adhesives.

OBJECTIVES: Dentin bonds made with one-bottle etch-and-rinse and self-etch adhesives are affected by the formation of interfacial blisters, porosities and deterioration. The first objective of this study was to evaluate the fluid flow through resin-dentin interfaces created by self-etching adhesives applied to deep dentin using a replica technique and by directly measuring dentin permeability (P). The second objective was to examine the effect of intrapulpal pressure on the microtensile bond strength of these adhesives. METHODS: A fluid-transport model was used to measure the fluid permeability (%P) through different adhesives. Impressions of bonded dentin were taken with a polyvinylsiloxane impression material to monitor fluid transudation from the surface of the adhesive. Positive replicas were fabricated for SEM examination. Two groups of resin-bonded specimens (pulpal pressure versus no pulpal pressure) were created for microtensile bond strength evaluation. Adhesive application was performed under 0 cm H(2)O. Pulpal pressure group was submitted to 20 cm H(2)O of pulpal pressure during build-up procedures. RESULTS: Clearfil Protect Bond exhibited the lowest permeability and fewest numbers of fluid droplets over the surface of the bonded dentin. G-Bond and Clearfil-S3 Bond were more permeable than Clearfil Protect Bond. One Up Bond F was the most permeable adhesive. A highly significant correlation was observed between the relative permeability of these adhesives (%P) and the number of fluid droplets on the adhesive surfaces. The application of pulpal pressure significantly reduced bond strength. SIGNIFICANCE: Resin-dentin bonds created by contemporary self-etch adhesives are susceptible to fluid permeation induced by pulpal pressure. HEMA-based adhesives showed the largest reductions in bond strengths after pulpal pressure application.

The effect of application sustained seating pressure on adhesive luting procedure.

OBJECTIVES: To evaluate the effect of short versus long application seating pressure on the bond strength of resin blocks, luted with a dual-cured resin cement (Panavia F) to pre-coated or non pre-coated dentin with an hydrophobic light-cured adhesive (Clearfil Protect Bond). METHODS: Sixteen non-carious human third molars were randomly divided into six Groups (four teeth each). Cylindrical composite blocks were luted with Panavia F (Group Ia) and with Clearfil Protect Bond with Panavia F (Group IIa) and seating pressure was applied for 5s. In Groups Ib and IIb, the two bonding procedures were respectively repeated, but the resin cylinder was maintained under constant pressure during the entire 3min polymerization period for the resin cement. After storing in distilled water for 24h, 0.9mmx0.9mm sticks were produced from these luted specimens for microtensile bond testing and SEM examination. RESULTS: The use of Clearfil Protect Bond with Panavia F produced higher bond strengths than the use of Panavia F (p<0.05). Extending the time of pressure application up to 3min increased the bond strength (p<0.001) and improved the integrity of the interfacial quality. SIGNIFICANCE: The application of sustained seating pressure during luting procedures and the additional use of a hydrophobic light-cured adhesive both improve the final bond strength of the resin cement.

Single-bottle adhesives behave as permeable membranes after polymerisation. II. Differential permeability reduction with an oxalate desensitiser.

OBJECTIVES: This study examined the changes in hydraulic conductance and ultrastructure of dentine bonded with simplified etch-and-rinse adhesives to oxalate desensitiser pre-treated acid-etched dentine. METHODS: Human dentine disks were acid-etched, treated with an oxalate desensitiser (BisBlock, Bisco), and bonded with One-Step (OS), Single Bond (SB), OptiBond Solo Plus (OB) or Prime and Bond NT (PB). Similar disks from each group were acid-etched, and bonded without oxalate pre-treatment. Hydraulic conductance of the specimens was measured at 20 cm of water pressure and analysed with nonparametric statistical methods. Epoxy resin replicas of the smear layer-covered dentine and bonded dentine were examined with SEM for the extent of fluid transudation. Specimens bonded under perfusion were examined with TEM after tracer immersion. RESULTS: OB and PB exhibited a highly significant reversal of the reduced hydraulic conductance obtained with BisBlock on unbonded acid-etched dentine. Profuse water transudation across the bonded dentine was observed from the replicas. Adhesive interfaces were covered with spherical globules that interfered with dentine hybridization. Conversely, no significant difference in hydraulic conductance was observed in SB, between Bisblock pre-treated, unbonded and bonded acid-etched dentine. Significantly lower hydraulic conductance was shown on application of OS to Bisblock-treated acid-etched dentine. Water transudation was sparse, interfering surface globular structures were absent, and only angular subsurface crystals were seen in the dentinal tubules. CONCLUSIONS: Convective water fluxes through dentine may be reduced by applying Bisblock to acid-etched dentine before bonding with One-Step or Single Bond. However, reducing adhesive permeability with the use of oxalate desensitiser is not applicable to low acidity adhesives such as OptiBond Solo Plus and Prime and Bond NT.

Water uptake of bonding systems applied on root dentin surfaces: a SEM and confocal microscopic study.

OBJECTIVES: Dentin adhesives have been proposed as desensitizing agents to seal exposed root dentin surfaces. Simplified 'one-step' dentin adhesives are highly permeable to water. The authors hypothesized that a lactic acid challenge may increase permeability of simplified adhesives and may induce fast degradation of bonding. This phenomenon adversely affects their durability as long term desensitizing agents. The aim of this in vitro study was to evaluate the ability of four dentin adhesives to seal root dentin surfaces that were exposed to water and lactic acid challenges. METHODS: Four commercially-available dentin adhesives were applied with a small sponge to the root dentin of extracted human molars as de-sensitizing agents. Impression replicas of the adhesive-covered root dentin were fabricated after water immersion, as a control, and after lactic acid challenge. The replicas were examined with SEM for quantitative comparison of fluid droplet formation on the surfaces. The bonded specimens were also examined using reflected light confocal microscopy. RESULTS: Replicas of water droplets were observed on the adhesive surfaces, by SEM which corresponded with direct confocal observation of blisters and voids from the surface of the bonded specimens. There were significantly more water droplets from samples that were subjected to lactic acid challenge than water only immersion. SIGNIFICANCE: Although the dentin adhesives examined were able to cover exposed root dentin, they all exhibited fluid transudation through the polymerized adhesives. Dentin adhesives were also susceptible to surface degradation after lactic acid challenge. As simplified self-etch adhesives were highly water permeable and exhibited the most extensive surface damage, they may not be the best adhesives to be used for long-term dentin desensitization. These preliminary in vitro findings warrant validation in vivo.

Effect of the seating pressure on the adhesive bonding of indirect restorations.

PURPOSE: To evaluate the effect of two different techniques of seating pressure application on the adhesive-dentin bond of indirect restorations. METHODS: Eight non-carious human third molars were randomly divided in two treatment groups (four teeth each). Cylindrical composite blocks were luted with a resin cement (Panavia F). In Group 1, the seating pressure was applied for 5 seconds. In Group 2, the resin cylinder was maintained under constant pressure during the entire 3-minute polymerization period of the resin cement. After storing in distilled water for 24 hours, 0.9 x 0.9 mm sticks were produced from these luted specimens for microtensile bond testing and SEM examination. RESULTS: The Student t-test showed a significant difference (P < 0.05) in bond strength between Groups 1 and 2. SEM revealed the presence of structural defects and resin globules on the seating surface of the composites. These features were exclusively identified from Group 1 specimens and were probably caused by fluid transudation from the underlying dentin through the simplified self-etch adhesive (ED primer).

Does hybridization of intraradicular dentin really improve fiber post retention in endodontically treated teeth?

This study tested the hypothesis that hybridization of intraradicular dentin eliminates interfacial gaps, thereby improving the coronal seal and retention of teeth restored with fiber posts. Post spaces were bonded with two types of fiber posts, using the corresponding etch-and-rinse adhesives and dual-cured resin cements. Longitudinal sections of the interfaces were examined for dentin hybridization in the coronal- and middle-thirds of the root canals. Resin replicas of these sections were evaluated for interfacial gap formation. Although intraradicular dentin hybridization was not compromised irrespective of whether the adhesives were light-cured before cementation, the universal occurrence of interfacial gaps along the hybrid layer surface or the post-cement interface reflects the challenge in bonding to post spaces with low compliance and high C-factors. The clinical success associated with bonded fiber posts is probably due predominantly to frictional retention.

Permeability of marginal hybrid layers in composite restorations.

The goal of adhesive dentistry is to restore the peripheral seal of dentin lost from removal of enamel. Unfortunately, the hybrid layer (HL) that is used to create that seal is permeable to small ions or molecules, even in the absence of detectable, interfacial gap formation via nanoleakage. This nanoleakage results from several mechanisms including incomplete infiltration of adhesive monomers into demineralized collagen matrix, presence of hydrophilic monomers, and insufficient removal of solvent or water that remains trapped inside the HL. These mechanisms lead to a porous interface with nanometer-sized channels that increase the permeability of the HL. The null hypothesis tested in this study was that water and acidic solution storage are able to alter in vitro the resin-dentin interface, further increasing the marginal hybrid layer (MHL) permeability. Class II cavities were made in vitro. The specimens were stored in water for 1 week and in lactic acid solution for 3 days. Polyvinyl siloxane impressions of restoration margins were taken before and after storage in water and lactic acid solution. Polyether replicas were obtained using the silicon impressions as molds. Replicas and original samples were observed under scanning electron microscopy. Lines of water droplets were detected on MHLs and overlying adhesive only after storage. Replicas obtained after acidic solution storage showed great numbers of irregularities such as gaps, voids, and degradation of the dentin-restoration surface margin, but also a great number of droplets. Dentin-restoration resin interfaces absorb water and are damaged by storage in dilute lactic acid. The presence of water droplets probably indicates water that flows out of the interface during the setting time of the impression and thus represents an index of marginal HL water permeability.

Nanoleakage within the hybrid layer: a correlative FEISEM/TEM investigation.

The aim of this study was to compare the nanoleakage patterns of the resin-dentin interfaces of three dentin bonding systems at both TEM and field emission in lens SEM (FEI-SEM) levels. A standardized smear layer was created with 180-grit silicon carbide paper (SiC) on dentin disks obtained from 18 noncarious human third molars. Specimens were randomly divided into three groups and bonded with a two-step total etching adhesive (Single Bond, SB), a two-step, self-etching adhesive (Clearfil SE BOND, SEB), and a one-step, self-etching adhesive (XENO III, XEIII). Nanoleakage was evaluated by using an ammoniacal silver-nitrate solution. Specimens were processed for TEM and FEI-SEM observation. The TEM of SB revealed silver deposits in adhesive and hybrid layers (HL). High-magnification FEI-SEM micrographs clearly identified these deposits as spherical clusters mainly associated with nonembedded collagen fibrils. TEM and FEI-SEM examination of SEB revealed some clusters of silver deposits within porosities and small channels of the HL. Additional silver deposits were observed between the peritubular dentin walls and the resin tags. XEIII revealed very fine and diffuse silver grains throughout the entire HL. SEM visualization of nanoleakage at a high level of resolution has not been previously described. FEI-SEM technology supported the TEM visualization with three-dimensional morphological data of the relations between the HL constituents and nanoleakage. The results of the present study confirm the hypothesis that both total- and self-etch adhesives are not able to fully infiltrate the dentin substrate.

A challenge to the conventional wisdom that simultaneous etching and resin infiltration always occurs in self-etch adhesives.

This study provided morphological evidence that discrepancies between the depth of demineralisation and the depth of resin infiltration can occur in some mild self-etch adhesives. Sound dentine specimens derived from extracted human third molars were bonded with 5 one-step and 5 two-step self-etch adhesives. One millimeter thick slabs containing the resin-dentine interfaces were immersed in 50 wt% aqueous ammoniacal silver nitrate and processed for TEM examination. A zone of partially etched but uninfiltrated dentine was identified beneath the hybrid layers in the milder versions of both one-step and two-step self-etch adhesives. This zone was characterised by the occurrence of silver deposits along the interfibrillar spaces of mineralised collagen fibrils. The silver infiltrated interfibrillar spaces were clearly identified from the one-step self-etch adhesives Xeno III, iBond, Brush&Bond and the experimental adhesive, and were thinner and only occasionally observed in the two-step self-etch adhesives Clearfil SE Bond and Clearfil Protect Bond. The more aggressive one-step and two-step adhesives that exhibit more abrupt transitions from completely demineralised to mineralised dentin were devoid of these silver-infiltrated interfibrillar spaces beneath the hybrid layers. Incomplete resin infiltration observed in some self-etch adhesives may be caused by the reduced etching potential of the acidic monomers toward the base of hybrid layers, or the presence of acidic but non-polymerisable hydrolytic adhesive components, creating potential sites for the degradation of the bonded created by these self-etch adhesives.