Osmotic blistering in enamel bonded with one-step self-etch adhesives

Does the Application of Additional Hydrophobic Resin to Universal Adhesives Increase Bonding Longevity of Eroded Dentin?

This paper evaluates the effect of an additional hydrophobic resin coat (extra HL) associated with universal adhesives on sound and eroded dentin and evaluated immediately or after 2 years of water storage to improve the microtensile bond strength (μTBS) and nanoleakage (NL) when compared to the use of universal adhesives only. Sixty-four molars were assigned to eight groups using the following combinations: 1. dentin substrate, including sound and eroded dentin; 2. treatment, including the control and extra HL and storage time (immediately and after two-years of storage). Two universal adhesives (Prime & Bond Active or Scotchbond Universal) were evaluated. Before restoration, half of the teeth were subjected to soft-drink erosion. Composite buildups were bonded; specimens were stored (37 °C/24 h), sectioned into resin−dentin bonded sticks and tested for microtensile bond strength and nanoleakage using SEM (immediately and after two-years of storage). Three-way ANOVA and Tukey’s test (α = 0.05%) were used. In the immediate testing, the application of extra HL did not increase microtensile bond strength values compared with the control group in either substrate (p > 0.05). However, extra HL significantly decreased nanoleakage values when applied to eroded and sound dentin (p = 0.0001). After two years, the application of extra HL produced significantly higher microtensile bond strength and lower nanoleakage values than the control group for both adhesives (p = 0.0001). In all cases, sound dentin showed higher microtensile bond strength and lower nanoleakage values than eroded dentin (p = 0.000001). An extra HL increased the bond strength and reduced nanoleakage in eroded dentin after two-years of storage.

Adhesive dentistry: Current concepts and clinical considerations

OBJECTIVES

To address contemporary concepts in adhesive dental materials with emphasis on the evidence behind their clinical use.

OVERVIEW

Adhesive dentistry has undergone major transformations within the last 20 years. New dental adhesives and composite resins have been launched with special focus on their user-friendliness by reducing the number of components and/or clinical steps. The latest examples are universal adhesives and universal composite resins. While clinicians prefer multipurpose materials with shorter application times, the simplification of clinical procedures does not always result in the best clinical outcomes. This review summarizes the current evidence on adhesive restorative materials with focus on universal adhesives and universal composite resins.

CONCLUSIONS

(a) Although the clinical behavior of universal adhesives has exceeded expectations, dentists still need to etch enamel to achieve durable restorations; (b) there is no clinical evidence to back some of the popular adjunct techniques used with dental adhesives, including glutaraldehyde-based desensitizers and matrix metalloproteinase inhibitors; and (c) the color adaptation potential of new universal composite resins has simplified their clinical application by combining multiple shades without using different translucencies of the same shade.

CLINICAL SIGNIFICANCE

New adhesive restorative materials are easier to use than their predecessors, while providing excellent clinical outcomes without compromising the esthetic quality of the restorations.

Impact of Different Etching Strategies on Margin Integrity of Conservative Composite Restorations in Demineralized Enamel

Good margin integrity with a tight seal of the adhesive interface is considered one of the key factors for the clinical success of composite restorations. This study investigated the effect of enamel etching with phosphoric acid on the margin integrity of self-etch bonded composite restorations in demineralized enamel. Crowns of bovine incisors were assigned into 14 groups (n = 10 per group) of which ten groups (groups 1–5 and 8–12) were demineralized (21 days, acid buffer, pH 4.95) to create artificial carious lesions. Standardized Class V cavities were prepared in all specimens. Demineralized groups were either etched with phosphoric acid for 10, 30, 60, or 120 s (groups 2–5 and 9–12), or no etching was performed (groups 1 and 8). The non-demineralized (sound) groups were etched for 10 s (groups 7 and 14) or remained non-etched (groups 6 and 13). Resin composite restorations were then placed using either a one-step (iBond Self Etch, groups 1–7) or two-step self-etch adhesive (Clearfil SE Bond, groups 8–14). Margin integrity of the restorations was assessed after thermocycling (5000×, 5–55 °C) using scanning electron microscopy, and the percentage of continuous margins (%CM) was statistically analyzed (α = 0.05). Phosphoric acid etching significantly increased %CM in both demineralized and sound enamel. For iBond Self Etch, a significant increase in %CM in demineralized enamel was observed with increased etching times. All etched groups treated with Clearfil SE Bond and those etched for 60 or 120 s and treated with iBond Self Etch showed similar %CM in demineralized enamel as in etched sound enamel, and significantly higher %CM than in non-etched sound enamel. In conclusion, enamel etching with phosphoric acid improves margin integrity of composite restorations in demineralized enamel when bonded with the examined adhesives.

Current perspectives on dental adhesion: (1) Dentin adhesion - not there yet

The essential goal of any adhesive restoration is to achieve a tight and long-lasting adaptation of the restorative material to enamel and dentin. The key challenge for new dental adhesives is to be simultaneously effective on two dental substrates of conflicting nature. Some barriers must be overcome to accomplish this objective. While bonding to enamel by micromechanical interlocking of resin tags within the array of microporosities in acid-etched enamel can be reliably achieved and can effectively seal the restoration margins against leakage, bonding effectively and durably to organic and humid dentin is the most puzzling task in adhesive dentistry.

Much of the research and development of dental adhesives has focused on making the clinical procedure more user-friendly by reducing the number of bottles and/or steps. Although clinicians certainly prefer less complicated and more versatile adhesive materials, there is a trade-off between simplification of dental adhesives and clinical outcomes. Likewise, new materials are launched with claims of being novel and having special properties without much supporting evidence.

This review article discusses dental adhesion acknowledging pioneer work in the field, highlights the substrate as a major challenge to obtain durable adhesive restorations, as well as analyzes the three adhesion strategies and their shortcomings. It also reviews the potential of chemical/ionic dental adhesion, discusses the issue of extensively published laboratory research that does not translate to clinical relevance, and leaves a few thoughts in regard to recent research that may have implications for future adhesive materials.

Laboratory evaluation of the effect of unfilled resin after the use of self-etch and total-etch dentin adhesives on the Shear Bond Strength of composite to dentin

BACKGROUND

Based on the frequent application of composite resins as tooth-colored fillings, this method is considered a viable alternative to dental amalgam. However, this method has the low bond strength of the composite to dentin. To solve this issue, various dental adhesive systems with different characteristics have been developed by dentistry experts.

AIM

To assess the effect of an additional layer of unfilled resin in self-etch and total-etch dentin adhesives on the shear bond strength (SBS) of composite to dentin. Moreover, we assessed the effects of sample storage in artificial saliva on the SBS of composite to dentin.

METHODS

Methods: This experimental study was conducted on 160 freshly extracted human first or second premolar teeth, which were randomly divided into 16 groups. The teeth were prepared from Mashhad University of Medical Sciences, Mashhad, Iran (2008-2009). Scotchbond Multi-purpose (SBMP), single bond (SB), Clearfil SE Bond, and Clearfil S3 Bond were applied to dentin surface with or without the placement of hydrophobic resin (Margin Bond) in accordance with the instructions of the manufacturers. To expose the coronal dentin, the teeth were abraded with 600 grit SiC paper. Immediately after restoration, half of the samples were tested in terms of SBS, while the other samples were evaluated in terms of SBS after three months of storage in artificial saliva. SBS rates of dental composites evaluated by universal testing machine and samples were studied by optical stereomicroscopy to verify the failure type. Data analysis was performed in SPSS V.16 using Kolmogorov-Smirnov test, independent-samples t-test, ANOVA, and Duncan's logistic regression test.

RESULTS

In this study, a significant reduction was observed in the SBS rates of SB and S3 bond adhesive systems after storage with and without hydrophobic resin (p>0.000). Without storage in normal saline, a significant increase was observed in the SBS rate of the SE bond (p=0.013). In addition, SBS rate of SBMP significantly increased after storage with hydrophobic resin (p=0.001). Finally, the highest and lowest rates of SBS were observed in the SE and S3 bonds in all the experimental groups, respectively.

CONCLUSION

The effects of using a hydrophobic resin layer on shear bond strength values seem to be effective. The mild self-etch adhesive exhibited the best resin-dentine bond strength after aging.

Effect of an extra layer of hydrophobic resin on the microleakage of Cl V composite resin restorations with a universal adhesive system

AIM

The aim of the present study was to evaluate the effect of the application of a hydrophobic resin on the microleakage of Cl V composite resin restorations using a universal adhesive system applied in the self-etch (SE) and etch-and-rinse (ER) modes.

METHOD

Cl V cavities were prepared on the buccal surfaces of 64 human premolar teeth and divided into four groups (n = 16): ER, ER with hydrophobic resin (ERH), SE, and SE with hydrophobic resin (SEH). Microleakage at occlusal and gingival margins was evaluated using 0.5% methylene blue dye penetration technique under stereomicroscope at 40 × magnification. Data were analyzed using Kruskal-Wallis and Mann-Whitney U-tests (P < 0.05).

RESULTS

At the enamel margins, the ER group had significantly less microleakage than the SE and SEH groups (P < 0.001), but had no significant difference compared with the ERH group (P > 0.05). There was also no statistically-significant difference between the SE and SEH groups (P > 0.05). At the dentinal margins, the SE group had significantly less microleakage compared with the ER (P < 0.001) and ERH groups (P = 0.005). Furthermore, microleakage of the SEH group was significantly less than the SE group (P < 0.001).

CONCLUSION

Applying an extra layer of hydrophobic resin significantly decreased microleakage in the SE mode at the dentinal margin, but had no significant effect in the ER mode.

Randomized clinical trial of four adhesion strategies in posterior restorations-18-month results

PURPOSE

To evaluate the 18-month clinical performance of four adhesive strategies in posterior composite restorations placed in private practice.

MATERIALS AND METHODS

Upon approval by an institutional review board, 144 restorations were inserted in 45 subjects (average age = 32.6) to treat caries lesions or to replace existing restorations in vital molars and premolars. The adhesives OptiBond FL (three-step etch-and-rinse), OptiBond SOLO Plus (two-step etch-and-rinse), OptiBond XTR (two-step self-etch), and OptiBond All-in One (one-step self-etch) were applied as per manufacturer's (Kerr Co.) instructions followed by a nanofilled resin composite (Filtek Z350XT, 3M ESPE) under rubber dam isolation. Restorations were evaluated at baseline and at 18 months using United States Public Health Service (USPHS)-modified criteria and high-resolution digital photographs. Statistical analyses included the McNemar and the Mann-Whitney non-parametric tests (p < 0.05).

RESULTS

A total of 137 restorations were evaluated after 18 months. The number of alfa ratings did not change significantly from baseline to 18 months for any of the adhesion strategies. When the 18-month evaluation criteria were pooled by pairs of adhesives, none of the adhesives resulted in a significantly different number of alfa ratings for any of the criteria compared with the other adhesives.

CONCLUSION

Bonding strategy did not influence the clinical performance of posterior composite restorations under the clinical conditions used in this study.

CLINICAL SIGNIFICANCE

When used in ideal clinical conditions, the composition of current dentin adhesives may be more clinically relevant than their adhesion strategy.

Evaluating Resin-Dentin Bond by Microtensile Bond Strength Test: Effects of Various Resin Composites and Placement Techniques

Objectives:

This in vitro study evaluated the microtensile bond strength (MTBS) of a methacrylate-based compared to a silorane-based resin composite in Class I cavity using different placement techniques.

Materials and Methods:

Class I cavities with dimension of (4 mm long, 4 mm wide, 3 mm deep) were prepared in extracted sound human molars. The teeth were randomly divided into six groups. The first three groups were filled with Filtek P90 using three methods of insertion; bulk, incremental and snow-plow, and the remaining three groups were filled with Clearfil AP-X using the same three placement techniques. After 24 hours of storage in water at 37°C, the specimens were thermocycled to 1000 cycles. Specimens were prepared for MTBS testing by creating bonded beams obtained from the pulpal floor. Statistical analysis used: Statistical analyses of data were performed by two-way ANOVA/Tukey (α=.05).

Results:

The experiment showed significant differences between the two resin composites with regard to filling techniques (P<0.05). The MTBS was significantly higher in each of Filtek P90 subgroup compared to Clearfil AP-X ones (P<0.05). With respect to filling technique in both resin composites, bulk insertion showed the significantly lowest MTBS (P<0.05), while no significant difference was found between the outcome of incremental and snow-plow techniques (P>0.05).

Conclusion:

Silorane-based resin composite as opposed to methacrylate based resin composite and layering placements in contrast to bulk filling method had higher microtensile bond strength.

Immediate adhesive properties to dentin and enamel of a universal adhesive associated with a hydrophobic resin coat

OBJECTIVES

To evaluate the effect of acid etching and application of a hydrophobic resin coat on the enamel/dentin bond strengths and degree of conversion (DC) within the hybrid layer of a universal adhesive system (G-Bond Plus [GB]).

METHODS

A total of 60 extracted third molars were divided into four groups for bond-strength testing, according to the adhesive strategy: GB applied as a one-step self-etch adhesive (1-stepSE); GB applied as in 1-stepSE followed by one coat of the hydrophobic resin Heliobond (2-stepSE); GB applied as a two-step etch-and-rinse adhesive (2-stepER); GB applied as in 2-stepER followed by one coat of the hydrophobic resin Heliobond (3-stepER). There were 40 teeth used for enamel microshear bond strength (μSBS) and DC; and 20 teeth used for dentin microtensile bond strength (μTBS) and DC. After restorations were constructed, specimens were stored in water (37°C/24 h) and then tested at 0.5 mm/min (μTBS) or 1.0 mm/min (μSBS). Enamel-resin and dentin-resin interfaces from each group were evaluated for DC using micro-Raman spectroscopy. Data were analyzed with two-way analysis of variance for each substrate and the Tukey test (α=0.05).

RESULTS

For enamel, the use of a hydrophobic resin coat resulted in statistically significant higher mean enamel μSBS only for the ER strategy (3-stepER vs 2-stepER, p<0.0002). DC was significantly improved for the SE strategy (p<0.00002). For dentin, the use of a hydrophobic resin coat resulted in significantly higher dentin mean μTBS only for the SE strategy (2-stepSE vs 1-stepSE, p<0.0007). DC was significantly improved in groups 2-stepSE and 3-stepER when compared with 1-stepSE and 2-stepER, respectively (p<0.0009).

CONCLUSIONS

The use of a hydrophobic resin coat may be beneficial for the selective enamel etching technique, because it improves bond strengths to enamel when applied with the ER strategy and to dentin when used with the SE adhesion strategy. The application of a hydrophobic resin coat may improve DC in resin-dentin interfaces formed with either the SE or the ER strategy. On enamel, DC may benefit from the application of a hydrophobic resin coat over 1-stepSE adhesives.

Effect of changes to the manufacturer application techniques on the shear bond strength of simplified dental adhesives

PURPOSE

The aim of this work was to assess the shear bond strength (SBS) between a composite resin and dentin, promoted by two dental adhesive systems (one-step self-etching adhesive Easy Bond [3M ESPE], and two-step etch-and-rinse adhesive Scotchbond 1XT [3M ESPE]) with different application protocols (per manufacturer's instruction (control group); with one to four additional adhesive layers; or with an extra hydrophobic adhesive layer).

METHODS

Proximal enamel was removed from ninety caries-free human molars to obtain two dentin discs per tooth, which were randomly assigned to twelve experimental groups (n=15). After adhesion protocol, the composite resin (Filtek Z250 [3M ESPE]) was applied. Specimens were mounted in the Watanabe test device and shear bond test was performed in a universal testing machine with a crosshead speed of 5 mm/min. Data were analyzed with ANOVA followed by Student-Newman-Keuls tests (P<0.05).

RESULTS

The highest SBS mean value was attained with the Easy Bond three layers group (41.23±2.71 MPa) and the lowest with Scotchbond 1XT per manufacturer's instructions (27.15±2.99 MPa). Easy Bond yielded higher SBS values than Scotchbond 1XT. There were no statistically significant differences (P>0.05) between the application protocols tested, except for the three and four layers groups, that presented higher SBS results compared to manufacturer's instruction groups (P<0.05). No statistically significant differences were detected between the three and four layers groups (P≥0.05).

CONCLUSION

It is recommendable to apply three adhesive layers when using Easy Bond and Scotchbond 1XT adhesives, since it improves SBS values without consuming much time.

The addition of nanostructured hydroxyapatite to an experimental adhesive resin

OBJECTIVES

Was produced nanostructured hydroxyapatite (HAnano) and evaluated the influence of its incorporation in an adhesive resin.

METHODS

HAnano was produced by a flame-based process and was characterized by scanning electron microscopy. The surface area, particle size, micro-Raman and cytotoxicity were evaluated. The organic phase was formulated by mixing 50 wt.% Bis-GMA, 25 wt.% TEGDMA, and 25 wt.% HEMA. HAnano was added at seven different concentrations: 0; 0.5; 1; 2; 5; 10 and 20 wt.%. Adhesive resins with hydroxyapatite incorporation were evaluated for their radiopacity, degree of conversion, flexural strength, softening in solvent and microshear bond strength. The data were analyzed by one-way ANOVA and Tukey's post hoc test (α=0.05), except for softening in solvent (paired t-test) and cytotoxicity (two-way ANOVA and Bonferroni).

RESULTS

HAnano presented 15.096 m(2)/g of specific surface area and a mean size of 26.7 nm. The radiopacity values were not different from those of 1-mm aluminium. The degree of conversion ranged from 52.2 to 63.8%. The incorporation of HAnano did not influence the flexural strength, which ranged from 123.3 to 143.4MPa. The percentage of reduction of the microhardness after immersion in the solvent became lower as the HAnano concentration increased. The addition of 2% nanostructured hydroxyapatite resulted in a higher value of microshear bond strength than the control group (p<0.05).

CONCLUSIONS

The incorporation of 2% of nanostructured hydroxyapatite into an adhesive resin presented the best results.

CLINICAL SIGNIFICANCE

The incorporation of nanostructured hydroxyapatite increases the adhesive properties and may be a promising filler for adhesive resin.

Quantitative analysis of aqueous phase composition of model dentin adhesives experiencing phase separation

There have been reports of the sensitivity of our current dentin adhesives to excess moisture, for example, water-blisters in adhesives placed on over-wet surfaces, and phase separation with concomitant limited infiltration of the critical dimethacrylate component into the demineralized dentin matrix. To determine quantitatively the hydrophobic/hydrophilic components in the aqueous phase when exposed to over-wet environments, model adhesives were mixed with 16, 33, and 50 wt % water to yield well-separated phases. Based upon high-performance liquid chromatography coupled with photodiode array detection, it was found that the amounts of hydrophobic BisGMA and hydrophobic initiators are less than 0.1 wt % in the aqueous phase. The amount of these compounds decreased with an increase in the initial water content. The major components of the aqueous phase were hydroxyethyl methacrylate (HEMA) and water, and the HEMA content ranged from 18.3 to 14.7 wt %. Different BisGMA homologues and the relative content of these homologues in the aqueous phase have been identified; however, the amount of crosslinkable BisGMA was minimal and, thus, could not help in the formation of a crosslinked polymer network in the aqueous phase. Without the protection afforded by a strong crosslinked network, the poorly photoreactive compounds of this aqueous phase could be leached easily. These results suggest that adhesive formulations should be designed to include hydrophilic multimethacrylate monomers and water compatible initiators.

Restoration of noncarious cervical lesions: when, why, and how

At this time, restoration of noncarious cervical lesions (NCCLs) is a common occurrence in clinics nowadays. Some reasons for this are the growth of the elderly population, a smaller rate of tooth loss, and possibly the increase of some etiologic factors. These factors include inadequate brushing techniques in gingival recession cases, corrosive food and drink consumption, and occlusal stress concentrating factors (occlusal interferences, premature contacts, habits of bruxism, and clenching). Unfortunately, Class V restorations also represent one of the less durable types of restorations and have a high index of loss of retention, marginal excess, and secondary caries. Some causes for these problems include difficulties in isolation, insertion, contouring, and finishing and polishing procedures. This work aims to help dentists in choosing the best treatment strategy, which necessarily involves steps of problem identification, diagnosis, etiological factor removal or treatment, and, if necessary, restoration. Finally, appropriate restorative techniques are suggested for each situation.

In vitro bonding effectiveness of self-etch adhesives with different application techniques: A microleakage and scanning electron microscopic study

Aim:

To evaluate and compare the microleakage of self-etch adhesives placed under different clinical techniques and to analyze the resin–dentin interfacial ultrastructure under scanning electron microscope (SEM).

Materials and Methods:

100 extracted human premolars were divided into two groups for different adhesives (Clearfil S³ and Xeno III). Class V cavities were prepared. Each group was further divided into four subgroups (n = 10) according to the placement technique of the adhesive, i.e. according to manufacturer's directions (Group 1), with phosphoric acid etching of enamel margins (Group 2), with hydrophobic resin coat application (Group 3), with techniques of both groups 2 and 3 (Group 4). The cavities were restored with composite. Ten samples from each group were subjected to microleakage study. Five samples each of both the adhesives from groups 1 and 3 were used for SEM examination of the micromorphology of the resin–dentin interface.

Results:

At enamel margins for both the adhesives tested, groups 2 and 4 showed significantly lesser leakage than groups 1 and 3. At dentin margins, groups 3 and 4 depicted significantly reduced leakage than groups 1 and 2 for Xeno III. SEM observation of the resin–dentin interfaces revealed generalized gap and poor resin tag formation in both the adhesives. Xeno III showed better interfacial adaptation when additional hydrophobic resin coat was applied.

Conclusions:

In enamel, prior phosphoric acid etching reduces microleakage of self-etch adhesives, while in dentin, hydrophobic resin coating over one-step self-etch adhesives decreases the microleakage.

Ternary phase diagram of model dentin adhesive exposed to over-wet environments

When adhesives and/or composites are bonded to the tooth, water in the environment can interfere with proper interface formation. Formation of water blisters and phase separation at the adhesive/dentin interface have appeared as new types of bond defects. To better understand this problem, we determined the near-equilibrium partition of the hydrophobic/hydrophilic components when exposed to over-wet environments. Model methacrylate-based adhesives were mixed with different amounts of water to yield well-separated aqueous and resin phases. It was found that less than 0.1% BisGMA but nearly one-third of the HEMA diffused into the aqueous phase, leaving the remaining resin phase relatively hydrophobic. A partial phase diagram was created for the ternary BisGMA/HEMA/water system. All the experimental phase partitioning data were plotted, and the points lay on a binodal curve that separated the single-phase region from the two-phase region. We obtained the 3 tie lines by connecting the 2 points of each conjugate pair of the phase partitioning data from the 3 sets of tripartite mixtures. Information about solubility, water miscibility, distribution ratio, and phase partitioning behavior could be obtained quantitatively. This type of phase diagram will provide a more thorough understanding of current adhesive performance and elucidate directions for further improvement.

A review--micromorphological evidence of degradation in resin-dentin bonds and potential preventional solutions

Resin adhesion to dentin was first achieved in 1982 through mechanical hybridization between resin and collagen fibrils using an adhesive resin containing a functional monomer. Over the last 2 decades, newly developed adhesive resins have attempted to improve the bond strength at least in the first 24 h after bonding. Although much is known about the initial bond strength, learned through morphological analysis, the long-term durability of bonds has not yet been established analytically. However, numerous recent studies have shown chemical biodegradation of resin-dentin bonds under various testing regimes. In general, studies have shown that dentin bond strength decreases over time due to degradation of the resin and the collagen fibrils within the bonds. Furthermore, crystal formation around cured bonding resins has been reported in a number of adhesives after long-term water storage. However, the extent and process of degradation or crystallization is adhesive type specific. This review mainly summarizes the most recent and state of the art work in degradation of the bonding of dental restorative compounds with dentin based on micromorphological data of scanning and transmission electron microscopy.

Improving clinical retention of one-step self-etching adhesive systems with an additional hydrophobic adhesive layer

BACKGROUND

The durability of restorations bonded with one-step self-etching (OSSE) adhesive systems is inferior compared with that of restorations bonded with conventional adhesives. The authors conducted an 18-month randomized clinical study to evaluate the clinical performance of two OSSE systems in noncarious cervical lesions applied as recommended or with an extra layer of hydrophobic adhesive layer after 18 months of clinical service.

METHODS

Thirty participants, each of whom had at least two pairs of similar-sized noncarious cervical lesions, took part in this study. The authors placed 120 restorations, 30 in each of four groups: Clearfil S3 Bond (Kuraray, Osaka, Japan) (CS) and iBond Gluma inside (Heraeus Kulzer, Hanau, Germany) (IB), and Clearfil S3 Bond (CSB) and iBond Gluma inside (IBB) with an extra layer of hydrophobic adhesive applied on top of them. They placed the restorations incrementally, using a resin-based composite. The authors evaluated the restorations at baseline and at 18 months following modified U.S. Public Health Service criteria.

RESULTS

At 18 months, the retention rate for the IB group was statistically lower than those for the CS, IBB and CSB groups. Marginal discoloration occurred in all groups and was statistically worse in the IB group.

CONCLUSIONS

The conversion of the iBond Gluma inside and Clearfil S3 Bond adhesive systems into two-step systems by means of applying an extra hydrophobic adhesive layer improved the clinical performance of these materials after 18 months of clinical service.

CLINICAL IMPLICATIONS

The application of an extra hydrophobic adhesive layer over OSSE adhesive systems, layers improved the OSSE systems clinical performance, mainly in terms of retention rate.

Effects of opacity and oxygen inhibition of coating resin composites on bond strength to enamel

The purpose of this in vitro investigation was to study the effects on bond strength to primed human enamel stemming from opacity and polymerization inhibition by oxygen due to two coating resins. The coating resins and primers used were White Coat and an experimental material, SIR. The bond strengths on fine-ground enamel were evaluated for three shades of each of these coating resins after 24-hour storage in water. In addition, their degrees of opacity and oxygen inhibition depths were measured. The mild self-etch primer solutions produced very shallow but distinct etching patterns for micromechanical retention of the coating resin. Significant linear relationships between bond strength on the one hand and opacity and oxygen inhibition depth on the other were found for the three shades of each coating resin. Generally, the bond strength mediated on enamel is sufficiently high when these resins are combined with their proprietary adhesives. Therefore, the decrease in bond strength with increasing opacity of the coating resin shades has to be taken into account during application and light-curing.

Durability of enamel bonding using one-step self-etch systems on ground and unground enamel

OBJECTIVE

To examine the morphological, early and long-term microtensile bond strengths (microTBS) of one-step self-etch systems to unground and ground enamel.

MATERIALS AND METHODS

Resin composite (Filtek Z250) buildups were bonded to the buccal and lingual enamel surfaces (unground, bur-cut or SiC-roughened enamel) of third molars after adhesive application using the following adhesives: Clearfil S3 Bond (CS3); Adper Prompt L-Pop (ADP); iBond (iB) and, as the control, Clearfil SE Bond (CSE). Six tooth halves were assigned for each condition. After storage in water (24 hours/37 degrees C), the bonded specimens were sectioned into beams (0.8 mm2) and subjected to microTBS (0.5 mm/min) either immediately (IM) or after six (6 M) or 12 months (12 M) of water storage. The data were analyzed by three-way repeated measures ANOVA and Tukey's test (alpha = 0.05). Surface conditioning was observed under scanning electron microscopy (SEM).

RESULTS

The microTBS in the Si-C paper and diamond bur groups were similar and higher than the unground group. No significant difference was observed among the different storage periods, except for CS3, which showed an increase in the microTBS after 12 M. The etching pattern was more retentive on ground enamel.

CONCLUSIONS

One-step self-etch adhesives showed higher bond strengths on ground enamel and no reductions in resin-enamel bonds were observed after 12 M of water storage.

Microtensile bond strength of fiber-reinforced composite with semi-interpenetrating polymer matrix to dentin using various bonding systems

This study investigated the microtensile bond strength (microTBS) of fiber-reinforced composite (FRC) to dentin using various adhesive systems. Forty eight (n = 8/group) human molars were flattened to expose dentin. A layer of preimpregnated unidirectional FRC (everStick) was applied on the dentin surface after treatment with either a single-step self-etching adhesive, two-step self-etching system, or a conventional three-step adhesive system. For the control, particulate filler composite (PFC) (Filtek Z250) layering without FRC was used. After 24-hour water storage at 37 degrees C, the specimens were sectioned, further water-stored at 37 degrees C for 30 days and then tested. Data were analyzed using ANOVA and Tukey's test, and reliability was analyzed with Weibull distribution. microTBS values differed significantly according to the adhesive material used (p < 0.05). Single-step self-etching adhesive showed the lowest bond reliability and microTBS values with both FRC and PFC, whereas conventional three-step and two-step self-etching systems showed higher bond reliability and microTBS with both materials.

Morphology of the smear layer after the application of simplified self-etch adhesives on enamel and dentin surfaces created with different preparation methods

Mild self-etching adhesive systems modify and/or incorporate the smear layer into the resin-infiltrated demineralised dentin. Some factors such as type of bur and use of water spray might affect the thickness of the smear layer on substrates, enamel and dentin. Because of this, the present study evaluated the thickness of smear layers created by different finishing procedures, after the application of three simplified self-etching primers (Adper Prompt L-Pop and two experimental formulations) on enamel and dentin. After the application and removal of the primers' resinous component, the specimens were prepared for examination under a scanning electron microscope. Smear layers were thicker on enamel than on dentin, irrespective of the finishing methods used. Therefore, different thicknesses of smear layer on enamel/dentin might be an important factor to consider when evaluating the bonding efficacy of self-etching adhesives to both tooth substrates.

Long-term durability of one-step adhesive-composite systems to enamel and dentin

This study evaluated the long-term durability of three one-step adhesive-composite systems to ground enamel and dentin. Twenty-seven teeth were randomly divided into three groups of nine. The first group had its crowns sectioned to expose superficial dentin, which was then ground with 600 grit SiC paper. One of three one-step adhesives: a trial bonding agent, OBF-2; i Bond or Adper Prompt L-Pop was applied to the dentin of three teeth and built-up with the corresponding resin composite (Estelite sigma, Venus or Filtek Supreme). The second group of nine teeth had their enamel approximal surfaces ground with wet 600-grit SiC paper, then one of the three one-step adhesives was applied and built-up with resin composite. The bonded specimens were sliced into 0.7 mm-thick slabs. After 24 hours and one year of water storage at 37 degrees C, the slabs were sectioned into beams for the microtensile bond strength test. Failure modes were observed using optical and electron scanning microscopy. The third group of nine teeth had approximal wedge-shaped cavities prepared above the CEJ into dentin. Two-to-three grains of rhodamine B were added to each of the three adhesives prior to restoring the cavities with resin composite. After 24 hours storage, the teeth were sectioned and their interfaces examined with a laser scanning confocal microscope. The bond strengths of the three adhesive-composite systems to both enamel and dentin significantly lessened after one year of water storage, however, there was no significant difference between the materials.

In vitro bonding performance of self-etch adhesives: II--ultramorphological evaluation

OBJECTIVE

To study the interfacial ultra-morphology formed by "all-in-one" self-etch adhesives.

METHODS

Forty-nine extracted molars were assigned to one of five all-in-one adhesives: Adper Prompt L-Pop (AP, 3M ESPE); Clearfil S3 Bond (S3, Kuraray); G-Bond (GB, GC America); iBond (iB, Heraeus Kulzer) and Xeno IV (XE, Dentsply Caulk). Adper Single Bond Plus (SB, 3M ESPE), a two-step etch&rinse adhesive, and Clearfil SE Bond (SE, Kuraray), a two-step self-etch adhesive, were used as controls. Dentin, unground enamel and ground enamel were used as bonding substrates. Dentin specimens were processed for FESEM and TEM analyses. Enamel specimens were processed for FESEM.

RESULTS

Dentin: GB, iB, S3, SE and XE resulted in a submicron-thick hybrid layer (0.2-0.7 microm), but only S3 and SE did not result in interfacial gaps. AP resulted in the thickest hybrid layer (1.7-2.9 microm) among the self-etch adhesives. SB resulted in a 3.4-5.2 pm thick hybrid layer. Unground enamel-GB, iB and SE resulted in a mostly featureless morphology resembling that of untreated enamel with areas in which the superficial enamel layer was removed without dissolving the subsurface enamel. XE resulted in areas of intra-prismatic etching and areas without any etching pattern. S3 resulted in frequent shallow intra-prismatic etching, while AP was able to unveil the enamel crystallites across the entire enamel surface. Phosphoric acid in SB resulted in the deepest intra- and inter-prismatic demineralization. Ground enamel--AP resulted in a well-defined inter-prismatic etching pattern. iB, GB, SE and S3 resulted in islands of superficially dissolved enamel within areas without evidence of enamel dissolution. XE resulted in etched enamel areas with mild intraprismatic exposure of crystallites. Phosphoric acid in SB resulted in deep enamel etching.

CONCLUSIONS

Only AP, an aggressive self-etch adhesive, showed enamel morphological features that resemble those created by etch & rinse adhesives. S3 and SE were the only self-etch adhesives that did not result in dentin interfacial debonding.

Effect of Double-application or the Application of a Hydrophobic Layer for Improved Efficacy of One-step Self-etch Systems in Enamel and Dentin

The double-application and placement of a hydrophobic resin coat can improve the performance (μTBS) of one-step self-etch systems to tooth substrates, mainly in dentin.

Clinical Evaluation of an All-in-one Adhesive in Non-Carious Cervical Lesions with Different Degrees of Dentin Sclerosis

Lower scores for marginal discoloration and adaptation were noted when an all-in-one self-etching adhesive was applied to non-carious cervical lesions and compared to a three-step total-etch adhesive.

Sealing Ability of Dentin Adhesives/Desensitizer

Depending on the application of the individual adhesives used, dentin adhesives seal dentin surfaces and reduce dentinal permeability. Dentin adhesives possessing a high sealing ability for dentin surfaces are suggested for the treatment of dentin hypersensitivity.

Origin of interfacial droplets with one-step adhesives

Contemporary one-step self-etch adhesives are often documented with interfacial droplets. The objective of this study was to research the origin of these droplets. Two HEMA-rich and one HEMA-free adhesive were applied to enamel and dentin, with the lining composite either immediately cured or cured only after 20 min. All one-step adhesives exhibited droplets at the interface; however, the droplets had two different origins. With the HEMA-free adhesives, droplets were located throughout the adhesive layer and were stable in number over time. With the HEMA-rich adhesives, the droplets were observed exclusively at the adhesive resin/composite interface, and their number increased significantly when the composite was delay-cured. Only the latter droplets caused a significant drop in bond strength after delayed curing. While the droplets in the HEMA-free one-step adhesives should be ascribed to phase separation, those observed with HEMA-rich adhesives resulted from water absorption from dentin through osmosis.

New developments in dental adhesion

Numerous simplified adhesives have been introduced to the dental market within the last few years, sometimes without comprehensive testing to validate the performance claimed by the respective manufacturers. Mild self-etch adhesives are unable to etch enamel to provide adequate retention for bonded restorations. Although high early resin-dentin bond strength values can be achieved with some self-etch adhesives, their resistance to thermal and mechanical stresses over time is disappointing. In light of the current drawbacks attributed to all-in-one self-etch adhesives, etch-and-rinse adhesives are still the benchmark for dental adhesion in routine clinical use. This article summarizes current issues and factors related to the performance of adhesives.

Increases in Dentin-bond Strength If Doubling Application Time of an Acetone-containing One-step Adhesive

When treating dentin surfaces with Futurabond one-step self-etch bonding agent, in order to obtain higher microtensile bond strength, doubling the application time of the adhesive should be considered.

New concept of resin-dentin interfacial adhesion: the nanointeraction zone

The purpose of this study was to evaluate the morphological appearance of resin-dentin interface produced by 1-step adhesive systems in order to classify them, using TEM. It was hypothesized that all interfaces produced by each 1-step adhesive show characteristics similar to that produced by the conventional self-etching system rather than that produced by etch-and-rinse system. The flattened dentin surfaces were subjected to bonding treatment using either a 2-step adhesive: single bond, mega bond, unifil bond; or a 1-step adhesive: Prompt L-Pop, absolute, xeno CF, AQ bond, one-up bond F, G bond, and SSB-200. A flowable resin was then applied to these surfaces. The results revealed that resin-dentin interfaces produced by 1-step systems were classified into three categories. Additionally, the interface produced by G bond and SSB-200 showed a different morphological appearance from that of the others. The interface produced by these adhesives was thinner and less demineralized, with the presence of hydroxyapatite-coated collagen fibrils. It is proposed that "Nanointeraction Zone (NIZ)" is a new complementary classification for partially demineralized resin-dentin interdiffusion zones. Thus, one-step self-etching adhesive systems can be classified into three categories, etch-and-rinse type, mild self-etching type, and NIZ type, by their morphological appearance of the interface.

Extension of a one-step self-etch adhesive into a multi-step adhesive

One-step self-etch adhesives are undoubtedly the most user-friendly adhesives, but have been associated with lower bonding effectiveness as compared to two-step and three-step adhesives. Conversion of a one-step self-etch system into a two-step self-etch adhesive by adding a bonding step, or into a three-step etch&rinse adhesive by adding a beforehand etching step and a bonding step might be tempting in order to improve bond strength.

OBJECTIVES

The objective of this study was to investigate whether adding application steps influences the bond strength of a one-step self-etch adhesive.

METHODS

In this study, the bonding effectiveness of two experimental one-step self-etch adhesives and three different commercial adhesives to enamel and dentin was determined using a micro-tensile bond-strength protocol. This procedure was repeated for the experimental adhesives transformed into two-step self-etch and three-step etch&rinse adhesives. In addition, their interaction with tooth tissue was investigated using TEM and Feg-SEM.

RESULTS

Transforming a one-step into a two-step self-etch adhesive did improve the bond strength to enamel and dentin, though not significantly. By adding a preceding etching step, the bond strength to enamel was significantly improved, but that to dentin was decreased considerably. The latter must be attributed to hampered resin infiltration of the one-step self-etch adhesive within the relatively deeply exposed collagen fibril network.

SIGNIFICANCE

Additional application of a hydrophobic bonding agent slightly improved bonding effectiveness. Adding a preceding etching step is beneficial for enamel but should be avoided for dentin as this will decrease bond strengths, and may even jeopardize the bonding durability.

Secondary caries-like lesions at fissure sealings with Xeno III and Delton—an in vitro study

OBJECTIVES

The aim of the study was to establish a bacterial based in vitro caries model to test the caries preventive effect of fissure sealants and to investigate whether a self-etching adhesive (Xeno III) used as fissure sealant is equally effective in preventing secondary caries compared to a conventional sealant (Delton) when applied on saliva contaminated and non-contaminated fissures.

METHODS

Forty caries-free upper premolars were randomly divided into two groups. Group A was sealed with a conventional resin-based fissure sealant (Delton) after phosphoric acid etching. Group B was sealed with a self-etching adhesive (Xeno III) without prior etching. To simulate the clinical situation of saliva contamination, the distal part of each tooth was slightly moistened with saliva before sealant application. After thermo-cycling, the specimens were exposed to a cariogenic Streptococcus mutans biofilm in an artificial mouth model. Depths of demineralization were measured on serial sections by confocal laser scanning microscopy. If a demineralization was detected underneath the whole fissure sealing the sample was rated as 'total failure'.

RESULTS

Significantly higher numbers of total failures could be found in the Xeno III group compared to the Delton group in areas without saliva contamination. On contaminated areas, no significant difference could be found. There was no significant difference regarding the depth of the primary carious lesions between groups.

CONCLUSION

The study supports our recent findings that our caries model is capable to produce secondary caries-like lesions at fissure sealings. Based on the present in vitro data, it cannot be recommended to use the self-etching adhesive Xeno III solely as a fissure sealant.

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.