Hybrid Layer Formation Research Articles

Mineral distribution and CLSM analysis of secondary caries inhibition by fluoride/MDPB-containing adhesive system after cariogenic challenges

Objective To evaluate the inhibition zone formation (IZ) and mineral distribution along the interface of adhesive systems either containing fluoride and antibacterial primer or not, after chemical and biological artificial caries challenges. Methods Forty-eight third molars were used. Artificial caries was developed with S. mutans in a 4 mm × 4 mm area of occlusal dentin surface. Carious dentin was removed and cavities were restored with Adper Scotchbond Multi-Purpose (SBM) and Clearfil Protect Bond (CPB) ( n = 24). Samples were submitted to secondary caries development by chemical (C) (acidic gel) or biological (B) ( S. mutans culture) methods for 5 days. Four groups were tested ( n = 12): (1) SC (SBM + C); (2) SB (SBM + B); (3) CC (CPB + C); (4) CB (CPB + B). The IZ and outer lesion (OL) formations were analyzed by confocal laser scanning microscopy (CLSM). The distribution of calcium (Ca) and phosphorus (P) content along the interface was analyzed by micro X-ray fluorescence spectrometer by energy-dispersive (μEDX). Results The frequency of IZ formation and mean values of IZ thickness differed among the groups. The CC group presented the lowest OL depth. μEDX analysis showed that CPB had the highest mineral loss by the biological method, but the lowest mineral loss by the chemical method. SC and SB groups showed intermediate values of mineral loss. Conclusion The mineral loss along the dentin/restoration interface was affected by the artificial caries method, and hybrid layer formation by adhesive systems used. The adhesive system containing fluoride and antibacterial primer did not prevent secondary caries formation.

Hybrid layers of etch-and-rinse versus self-etching adhesive systems

To evaluate the effectiveness in the formation of resin tags, adhesive lateral branches and hybrid layers of five adhesive systems, when bonding to dentine. Flat dentin surfaces from 25 molars were bonded with several adhesive systems according to the manufacturers' instructions. Composite build-ups were constructed incrementally with Tetric Ceram. The Specimens were sectioned parallel to the long axis. One section was treated with phosphoric acid and sodium hypochlorite in order to reveal the hybrid layer formation. The other section was stored in 30% hydrochloric acid to detect resin tags and adhesive lateral branch formation. The two etch-and-rinse self-priming adhesives exhibited thicker hybrid layers than those found in self-etching adhesive systems. The all-in-one adhesive showed droplet formation between the adhesive and the resin composite. The resin tags formed with the etch-and-rinse adhesives were much longer than those found with the self-etching adhesives. Lateral branch formation was observed in etch-and-rinse adhesives and in one of the self-etch adhesives Clearfil SE Bond (SEB). The formed hybrid layer obtained with the two-step self-etching adhesives and the etch-and-rinse systems were continuous and uniform in thickness. Droplets within the all-in-one adhesive layer may occur as a result of water absorption from dentin through osmosis, and may interfere with proper resin polymerization. Resin tags obtained with SEB and the etch-and-rinse adhesive systems showed lateral branches, which is a sign of proper resin infiltration.

Limited Decalcification/Diffusion of Self-adhesive Cements into Dentin

Resin cement diffusion into dentin may differ as a function of the pre-treatment regimen. Since self-adhesive cements do not require substrate pre-treatment for luting, penetration of and interaction with the underlying dentin are questioned. We hypothesized that differences in the resin cement diffusion into dentin may exist among current commercial adhesive cements. Composite cylinders were luted on mid-coronal dentinal surfaces by an etch-and-rinse cement (Calibra), a self-etching system (Panavia F 2.0), and 4 self-adhesive cements (Multilink Sprint, Rely X Unicem, G-Cem, Bis-Cem). Dentin/cement interfacial characteristics were analyzed by a staining technique (Masson's trichrome) and by scanning electron microscopy. Conventional acid etching resulted in partially infiltrated adhesive interfaces differing from those achieved with the application of self-etching primer. No hybrid layer and/or resin tag formation was detectable at the interfaces bonded with self-adhesive cements. Limited decalcification/infiltration was observed for self-adhesive cements into the underlying dentin. Self-adhesive cements were not able to demineralize/dissolve the smear layer completely.

Influence of Dentin Smear Layer Created by Chemo-Mechanical or Bur Excavation Methods on Adhesion of Self-Etching Primers and a Conventional Adhesive

This study evaluated the influence of chemo-mechanical or bur excavation methods on bond strength of dentin bonding agents, micromorphology of the treated-dentin surfaces, and the bonded interfaces. Smear layer-free surfaces were used as control. The methods of cavity preparation (chemo-mechanical and rotary burs) were used under specific parameters and four commercial dentin bonding agents (three two-step self-etching primers and one “etch-and-rinse” adhesive system) were applied to treated surfaces, according to manufacturers' instructions. Composite blocks were built on bonded surfaces and restored teeth were vertically, serially sectioned to obtain bonded slices for interfacial micromorphologic analysis or to produce beam specimens for micro-tensile bond testing. A clear difference of the preparation of dentin surfaces and formation of hybrid layer and resin tags are noted. The use of burs or chemo-mechanical methods did not affect the bond strength for etch-and-rinse system and for a self-etching primer with a very low pH (0.5). However, dentin surface preparations decreased the bond strength for the milder versions (pH of around 2) of self-etching adhesive systems. The manner of dentin preparation prior to bonding procedures can influence the effectiveness of some self-etching primers, which dissolve the smear layer and dentin surface only partially.

Influence of Diamond Sono-Abrasion, Air-Abrasion and Er:YAG Laser Irradiation on Bonding of Different Adhesive Systems to Dentin

Different surface treatments may affect bonding performance of adhesive systems to dentin. This study evaluated the influence of different methods of surface treatment on adhesion of bonding agents to dentin. Dentin surfaces abraded with #600-grit SiC paper were used as control. Three methods of surface treatment (sono-abrasion, air-abrasion and Er:YAG laser irradiation) were used under specific parameters. Four adhesive systems (Tyrian, Clearfil SE Bond, Unifil Bond and Single Bond) were applied to treated surfaces, according to the manufacturers' instructions. Composite blocks were built on bonded surfaces, then restored teeth were vertically and serially sectioned to obtain bonded slices for interfacial micromorphologic analysis or to produce beam specimens for mu-TBS bond test. Data were analyzed with two-way ANOVA and Tukey test at a significance level of 5%. The results indicated that the preparation of dentin with sono-abrasion or laser did not affect the bond strength, while the preparation of dentin with SiC paper and air-abrasion influenced the bond strength for some systems. A clear difference of the preparation of dentin surfaces and formation of hybrid layer and resin tags were noted. Bonding effectiveness of both the etch-and-rinse and the self-etch adhesives can be influenced by different methods of dentin preparation.

Gel Phase Formation at Resin-modified Glass-ionomer/Tooth Interfaces

Ionic bonding between polyalkenoic acid and hydroxyapatite may explain the excellent bonding retention of glass-ionomers in clinical trials. We have here investigated the extent to which the self-adhesiveness of resin-modified glass-ionomers (RMGIs) can be attributed to this chemical bonding capacity. Therefore, the interaction of 3 RMGIs with tooth substrates was comprehensively characterized, with electron and atomic force microscopy correlated with x-ray photoelectron spectroscopy (XPS). Interfacial ultrastructural analysis for 2 RMGIs disclosed a shallow hybridization of hydroxyapatite-coated collagen, on which a submicron gel phase was deposited through reaction of the polyalkenoic acid with calcium extracted from the dentin surface. One RMGI, however, bonded to dentin without hybrid layer or gel phase formation. XPS indicated that polycarboxylic acids included in the RMGIs electrostatically interacted with hydroxyapatite. We conclude that the self-adhesiveness of RMGIs should be attributed to ionic bonding to hydroxyapatite around collagen, and to micro-mechanical interlocking for those RMGIs that additionally hybridize dentin.

To what extent does the longevity of fixed dental prostheses depend on the function of the cement? Working Group 4 materials: cementation

The objective of this review was to define the impact of cementation mode on the longevity of different types of single tooth restorations and fixed dental prostheses (FDP). Literature search by PubMed as the major database was used utilizing the terms namely, adhesive techniques, all-ceramic crowns, cast-metal, cement, cementation, ceramic inlays, gold inlays, metal-ceramic, non-bonded fixed-partial-dentures, porcelain veneers, resin-bonded fixed-partial-dentures, porcelain-fused-to-metal, and implant-supported-restorations together with manual search of non-indexed literature. Cementation of root canal posts and cores were excluded. Due to lack of randomized prospective clinical studies in some fields of cementation, recommendations had to be based on lower evidence level (Centre of Evidence Based Medicine, Oxford) for special applications of current cements. One-hundred-and-twenty-five articles were selected for the review. The primary function of the cementation is to establish reliable retention, a durable seal of the space between the tooth and the restoration, and to provide adequate optical properties. The various types of cements used in dentistry could be mainly divided into two groups: Water-based cements and polymerizing cements. Water-based cements exhibited satisfying long-term clinical performance associated with cast metal (inlays, onlays, partial crowns) as well as single unit metal-ceramic FDPs and multiple unit FDPs with macroretentive preparation designs and adequate marginal fit. Early short-term clinical results with high-strength all-ceramic restorations luted with water-based cements are also promising. Current polymerizing cements cover almost all fields of water-based cements and in addition to that they are mainly indicated for non-retentive restorations. They are able to seal the tooth completely creating hybrid layer formation. Furthermore, adhesive capabilities of polymerizing cements allowed for bonded restorations, promoting at the same time the preservation of dental tissues.

Analysis of surfaces and adhesive interfaces of enamel and dentin after different treatments

The purpose of this study was to analyze, by Scanning Electron Microscopy (SEM), the surface topography and the morphology of the adhesive interfaces of enamel and dentin after different treatments. The enamel-dentin discs were randomly assigned into three groups according to the surface treatment: I-37% phosphoric acid; II-air-abrasion; III-air-abrasion followed by 37% phosphoric acid. After surface treatment, discs were divided in two: one hemi-disc was separated for surface analysis; the other hemi-disc received the Single Bond/Filtek Z-250 restorative system. The restored sections were bisected perpendicularly to the surface and prepared for interface analysis. Results disclosed that when the surface treatment was performed by air-abrasion, irregularities were observed at the enamel surface; microcracks and occluded tubules at dentin surface and lack of hybrid layer at adhesive/dentin interface. The air-abrasion treatment followed by acid etching provided an enamel etching pattern similar to the acid etching; microfissures and open tubules at dentin surface, and formation of hybrid layer at adhesive-dentin interface. It may be concluded that the treatment with air-abrasion followed by acid etching is an effective procedure to obtain an adequate surface for resin adhesion.

Scanning electron microscopy and energy-dispersive X-ray analysis of self-etching adhesive systems to ground and unground enamel

The morphological analysis of the ground and unground enamel was treated with three different self-etching adhesive systems. Ultrastructural features were observed by using the field emission scanning electron microscope (FESEM) in combination with Energy Dispersive X-Ray Spectroscopy (EDS) analysis. Thirty extracted human molars were used for this study. Teeth were divided into two groups. In the first group unground enamel was etched with either Clearfil SE Bond (Kuraray-Japan), G Bond (GC-Japan) or Tri S Bond (Kuraray-Japan) according to the manufactures instructions. In the second group ground enamel was treated as above. In addition 24 ungrounded and grounded enamel specimens were etched and bonded with the three self-etching adhesives and restored with composite resin (Clearfil ST-Kuraray). Then they were cross-sectioned and interfacial analysis was done with the combination of EDS analysis. Etching patterns of the enamel varied according to the self-etching adhesive. Clearfil SE Bond produced micro-irregular etching pattern creating crater like area in ground enamel while other two produced mild etching pattern. All three adhesives produced incomplete etching on unground enamel. Interfacial studies showed demineralization for the bonding agent penetration and the formation of hybrid layer. The self-etching adhesives produced different specific SEM morphologies on unground and ground enamel.

A confocal microscopic evaluation of the hybrid layer and resin tag formation of a total etch technique in comparison with self etching primers with three different pH

<b>Aim:</b> A Confocal Microscopic Evaluation of the hybrid layer and resin tag formation -of a total etch technique in comparison with self etching primers with three different ph.<br><b>Materials and Methods:</b> 20 non carious human premolars stored in normal saline were used for the study. Occlusal surfaces of all the teeth were ground using slow speed diamond disc with copious <i> water </i> supply, <i> so </i> as to expose a flat surface of dentin with an approximate residual dentin thickness of 1.5-2mm. The teeth were then randomly divided into 4 groups of 5 specimens each. Group 1: (Blot dry)­<i> Prime and Bond NT (Dentsply), </i> Group 2; Strong self etch adhesives usually have a ph of 1 or below {<i> Adper Prompt L- Pop (3M ESPP)}, Group 3; </i> Intermediary self etch adhesives have a ph of about 1.5 {<i> AdheSE (Vvadent)}, </i> Group 4; Mild self etch systems have a ph of about <i> 2- {Cleatfil SE bond plus primer (knraray)}. </i> Bonding agents mixed with Rodhamine B dye was applied according to the manufacture's instructions and cured using a light curing unit. All the bonded surfaces were restored with 2mm of resin composite Z 350 (3M) and cured for 40 seconds, to protect the bonding layer. All the specimens were stored in normal saline. After 24 hrs of storage the teeth were longitudinally sectioned using a slow speed diamond disc under copious water supply. The sectioned surface was polished' with a' 600 grit silicon carbide paper. The dentin/adhesive interfacial region was examined using a Confocal Laser Scanning Microscope (CLSM). Statistical analysis was done to compare the values among the groups using Kruskal-Wallis One way ANOVA appropriately by testing the means.<br><b>Results:</b> Statistical analysis demonstrated that Mean length of resin tag formation and thickness of hybrid layer formation in Group I was maximum followed by Group IV; Group II and Group III respectively.<br><b> Conclusion: </b> Within the parameters of this study the Prime and Bond NT (Group 1) performed better than all the three self etching primers in terms of resin tag formation and hybrid layer thickness.

Invitro evaluation of the effect of sodium hypochlorite on shear bond strength of dentin bonding agent on demineralized and remineralized dentin

Background & Objectives Formation of hybrid layer is thought to be the main mode of adhesion between dentin and resin. But, the longetivity of this hybrid layer is questionable as it is subjected to hydrolytic degradation over time. Hence, the concept of reverse hybrid layer on application of NaOCI is contemplated to bring about better bonding. Studies till date, have focused on the effects of NaOCI on sound tooth structure. Hence, this comparative study evaluated the effect of NaOCI on shear bond strength of two fifth generation single bottle adhesive agents on demineralized and remineralized dentin surfaces. Method 88 humans premolars were taken and divided into two main groups (group 1 and 2) and bonded with two fifth generation bonding agents Adper Single Bond 2 and Excite respectively.. Each of these groups were further divided into three subgroups Control, Demineralizing and reminerlizing group. The specimens in each subgroups were subjected to either acid etching alone or acid etching and NaOCI pretreatment. The teeth were then stored in distilled water for I month and subjected to shear bond testing. Stereomicroscopic evaluation of the fracture mode at debonded interfaces was done. SEM was used to evaluate the resin-dentin interface. Result No statistically significant difference existed between the two bonding agents (group I and 2) when the three subgroups were compared either without or with NaOCI application. A statistical significant difference existed for each of the bonding agents between the demineralized and remineralized subgroups. The subgroups subjected to NaOCI pretreatment showed better bond strength values, though statistically not significant. Interpretation and conclusion Bond strength values to demineralized dentin surface was higher than remineralized dentin surface both without and with NaOCI application. Sodium hypochlorite is an effective deproteinizing agent and its application results in the formation of a Reverse Hybrid Layer. This formed a more stable interface and would delay the process of hydrolytic degradation overtime.

Interfacial characteristics of adhesive luting resins and composites with dentine

Purpose To evaluate the interfacial characteristics of five adhesive resin luting agents with dentine including tensile bond strength, failure mode, extent of demineralisation, morphological changes and hybrid layer formation. Materials and methods The products tested were Bistite II DC (BDC), C&B Super-Bond (CBM), M-Bond (MBD), Panavia-F (PAF) and Rely-X Unicem (RXU). For tensile bond strength measurements (TBS), metallic rods were bonded to standardised dentine surface areas ( n = 10), thermal-cycled (3000× 5–55 °C, 4 cycles/min) and debonded at 1 mm/min crosshead speed. The failure mode was examined on dentine surfaces by LV-SEM ( n = 10), whereas the thickness of the hybrid layer by HV-SEM ( n = 4). FT-IR microscopy ( n = 4) and ESEM ( n = 4) were used to assess the extent of demineralisation and the morphological changes induced on dentine by the conditioning and priming treatments. Results TBS (MPa) values were BDC (13.01), MBD (9.19) and PAF (7.07) significantly different from CBM (4.79) and RXU (4.47). The percentage of debonded dentine area covered with resin showed the highest values in BDC (47.80) and MBD (38.12) significantly different from CBM (17.20), PAF (16.47), and RXU (16.50). The extent of demineralisation for CBM was 100%. No statistical differences were found among BDC (60.86%), MBD (60.22%) and PAF (51.99%). RUX (45.03%) showed the lowest value. CBM induced the most pronounced tubule funneling and intertubular dissolution, followed by PAF, BDC and MDB. RXU partially removed the smear layer without opening tubule orifices. The thickest hybrid layer was found in CBM (4.17 μm) followed by MBD (2.39 μm). No statistically significant differences were found between PAF (0.95 μm) and BDC (1.12 μm), whereas RXU showed no detectable hybrid layer. Significance Significant differences were found in the interfacial properties among the materials tested, that may lead to differences in their clinical performance.

A confocal microscopic evaluation of resin-dentin interface using adhesive systems with three different solvents bonded to dry and moist dentin—An in vitro study

<h3>Objective</h3> Total dehydration of acid-etched dentin is known to cause the collapse of collagen fiber, which leads to poor hybridization. Dentin-bonding systems with water as a solvent are found to rehydrate the collapsed collagen. Acetone-based adhesives are found to compete with moisture, and the acetone carries the resin deep into the dentin. The question arises whether to dry the dentin and use a water-based adhesive, or to keep the dentin moist and use an acetone- or alcohol-based adhesive. The aim of this study was to compare different bonding systems and techniques to assess which is most successful. A confocal microscope was used to evaluate the amount of hybrid layer formation and the depth of resin tag formation. <h3>Method and Materials</h3> Superficial occlusal dentin specimens from 120 noncarious, freshly extracted human premolars were used for the study. The dentin was etched using 36% phosphoric acid for 15 seconds and then rinsed. The specimens were then randomly divided into 4 groups for different drying procedures; group I: air-dried for 30 seconds; group II: air-dried for 3 seconds; group III: blotted dry; group IV: overwet. The specimens were further subdivided into 3 groups to be tested with different bonding systems: subgroup A: acetone-based adhesive (Prime & Bond NT); subgroup B: water-based adhesive (Syntac Single Component); subgroup C: water- and ethanol-based adhesive (Single Bond). The resulting resin-dentin interfaces were then examined and categorized via confocal microscopy, and relative values were assigned to each specimen. <h3>Results</h3> Group IV (overwet) showed the lowest values, and the highest values were obtained in group III. The highest values were seen in group III, subgroup A (blotted dry, acetone-based bonding agent, Prime & Bond NT). <h3>Conclusion</h3> Under these conditions, using these three bonding systems, maximum hybridization and resin tag formation were achieved using acetone-based adhesive on etched dentin kept moist by blot drying.—<i>Reprinted with permission of Quintessence Publishing.</i>

Influence of dentin pre-treatment with NaOCl on the morphology of adhesive interface of self-etching adhesive systems

The aim of this in vitro study was to evaluate the influence of pre-treatment using NaOCl in the morphology of dentin/resin interface. The three self-etching adhesive systems were selected: One-Up Bond F (Tokuyama, Tokyo, Japan), Prime & Bond NT/NRC (Dentsply, Konstanz, Germany) and Clearfil SE Bond (Kuraray, Osaka, Japan). Nine dentin disks were used in this study. Half disk was treated strictly following manufacturers’ instructions (control groups). The other half was treated with a solution of 2.5% NaOCl (experimental groups). After the bonding protocols were accomplished, a low viscosity resin (Flow-it/Jeneric Pentron) was inserted and light-cured. Specimens were prepared for SEM. Morphological aspects were observed, comparing both the groups. The analysis of the photomicrographs revealed formation of a hybrid layer for both controls groups along the interface. The experimental groups showed a resin/dentin interface more irregular and produced topographical features with funnel-shaped dentin tubules. Areas with absence of hybrid layer formation were observed, mainly for One-Up Bond F, although tubules their lateral branches were filled with Prime & Bond NT/NRC and Clearfil Se Bond adhesive systems. It was concluded that the use of NaOCl influenced negatively in the formation of the hybrid layer, mainly for the One-Up Bond F.

Development of a Self-etch Adhesive for Resin-modified Glass Ionomers

The favorable self-adhesiveness of resin-modified glass ionomers (RMGIs) might be even further improved if the time-consuming and technically sensitive etch-and-rinse pre-treatment step with polyalkenoic acids could be avoided. We undertook this study to assess the effectiveness of an experimental self-etch adhesive for RMGIs that does not need to be rinsed off. Ultrastructural analysis and micro-tensile bond strength testing to enamel and dentin of a RMGI restorative material and a RMGI adhesive were performed after 4 different surface pre-treatments: no conditioning; 25% polyalkenoic acid; an experimental self-etch adhesive; and 37.5% phosphoric acid followed by the experimental self-etch adhesive. The use of an experimental self-etch adhesive increased the bond strength of RMGIs, especially after an additional conditioning step. Interfacial analysis showed the formation of a thin hydroxyapatite-containing hybrid layer. The self-etch technique enhances the user-friendliness of RMGIs and lowers their technique-sensitivity, while maintaining desirable characteristics of the conventional etch-and-rinse approach with polyalkenoic acids.

Shear Bond Strengths of Self-etching Adhesives to Caries-affected Dentin on the Gingival Wall

The purpose of this study was to evaluate the bonding ability of five current self-etching adhesives to caries-affected dentin on the gingival wall. Seventy extracted human molars with approximal dentin caries were employed in this study. In order to obtain caries-affected dentin on the gingival wall, grinding was performed under running water. Following which, specimens mounted in acrylic blocks and composite resins of the bonding systems were bonded to dentin with plastic rings and then debonded by shear bond strength. With Clearfil SE Bond, bonding to caries-affected dentin showed the highest bond strength. With Optibond Solo Plus Self-Etch, bonding to caries-affected dentin showed higher shear bond strength than AQ Bond, Tyrian SPE & One-Step Plus, and Prompt-L-Pop (p<0.05). Further, the bond strengths of Clearfil SE Bond and Optibond Solo Plus Self-Etch to sound dentin were higher than those of Prompt-L-Pop, AQ Bond, and Tyrian SPE & One-Step Plus (p<0.05). In conclusion, besides micromechanical interlocking through hybrid layer formation, bond strength of self-etch adhesives to dentin may be increased from additional chemical interaction between the functional monomer and residual hydroxyapatite. The results of this study confirmed that differences in bond strength among self-etching adhesives to both caries-affected and sound dentin were due to chemical composition rather than acidity.

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.

Hybrid layer thickness and resin tag length of a self-etching adhesive bonded to sound dentin

the purpose of this study is to employ optical microscopy to measure the thickness of the hybrid layer and the penetration (tags) of an aggressive self-etching adhesive system into sound dentin. occlusal cavities were prepared in 40 extracted human posterior teeth. The prepared teeth were randomly assigned to four experimental groups with 10 specimens each. The self-etching adhesive system Adper Prompt L-Pop was applied to the dentin surface as follows: Group 1: cavosurface enamel was etched for 60 s and dentin for 20 s with 35% phosphoric acid gel, immediately followed by application of the self-etching adhesive with a brush to the entire cavity for 15 s; Groups 2, 3, and 4: no pre-etching was performed, and the self-etching adhesive was applied to both enamel and dentin for 15, 30 and 45 s, respectively. After curing, the cavities were filled with composite resin Filtek Z250. Afterwards, the teeth were decalcified and the restorations were carefully removed for later embedding in paraffin. The specimens were serially sectioned at 6 microm of thickness and sequentially mounted in glass slides. These sections were stained with Brown and Brenn staining for posterior analysis and measurement of the hybrid layer and resin tags on a light microscope with a micrometric ocular 40/075. The results were submitted to analysis of variance at the 5% level. whenever there was significance, the Tukey test was applied at the 5% level. The specimens receiving application of acid etching before the self-etching adhesive displayed a larger thickness of the hybrid layer; on the other hand, specimens receiving only application of the self-etching adhesive on dentin for 15, 30 and 45 s exhibited similar thickness of the hybrid layer. As regards the resin tags, no statistically significant differences could be found between the study groups. it could be concluded that the increase in the time of application of the self-etching adhesive Adper Prompt L-Pop did not significantly influence the formation and thickness of hybrid layer, as well as its penetration into the sound dentin surface.

Technique-Sensitivity of Contemporary Adhesives

Besides micro-mechanical interlocking through hybrid-layer formation, self-etch adhesives may benefit from additional chemical interaction between the functional monomer and residual hydroxyapatite. One-step adhesives are commonly associated with lower bonding effectiveness, which must be attributed in part to the dissolution of hydrophilic and hydrophobic monomers in a relatively highly concentrated solvent. In this 'difficult' mixture, also water is essential as ionization medium to enable self-etching activity. Due to the high hydrophilicity, one-step self-etch adhesives have been reported to behave as semi-permeable membranes, allowing fluids to pass through and seriously jeopardizing bond durability. Recent research has also revealed that HEMA-free one-step adhesives are prone to phase-separation, which may also account for their lower bonding effectiveness. Employing an appropriate air-drying technique may, however, improve the bonding effectiveness of such phase-separating adhesives by getting rid of substantially more interfacial water than HEMA-containing adhesives, of which water might be more difficult to remove from.

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.