Dentin conditioned with a metal salt-based conditioner

ObjectivesUniversal adhesives (UAs) can optionally be applied in either an etch-and-rinse (E&R) or self-etch (SE) bonding mode. As the preferred bonding mode differs for enamel versus dentin, a universal conditioner for both enamel and dentin in replacement of the relatively aggressive phosphoric-acid etchant remains desirable. This study aimed to test if a metal salt-based etchant (ZrO(NO₃)₂) provides as durable bonding to dentin as a classic E&R or SE bonding modeMethodsBefore applying the UA Adhese Universal (‘AdU’; Ivoclar Vivadent) to bur-cut dentin of 24 teeth (n = 8), dentin was conditioned with either (1) an experimental metal salt-based conditioner (‘ZON’; Ivoclar Vivadent) or (2) 37% phosphoric acid (Total Etch gel, Ivoclar Vivadent), representing a classic ‘E&R′ mode; (3) a third experimental group involved AdU applied in SE mode. Bonding effectiveness was determined in terms of immediate (‘1w’) and aged (‘50k’ TC) micro-tensile bond strength (μTBS) to bur-cut dentin. Adhesive-conditioned dentin interfacial interactions were characterized by S/TEM.ResultsLinear mixed-effects modeling revealed significantly higher immediate μTBS to dentin of ZON_AdU than E&R_AdU, while ZON_AdU performed not significantly different from SE_AdU. No significant differences were found between the three experimental groups after 50k TC (aged μTBS). S/TEM disclosed less exposure of dentinal collagen fibrils when AdU was bonded upon ZON etching than when applied in E&R mode. Moreover, ZON resulted in more hydroxyapatite (HAp) crystals remaining at the bottom of the hybrid layer, while dentinal tubule orifices remained nearly fully closed, by which hardly any resin tags were formed.SignificanceThe alternative metal salt-based conditioner revealed at dentin a more HAp-protected hybrid layer with less exposure of collagen fibrils, while a comparable bond strength was obtained to that with a phosphoric-acid E&R as well as with an SE (no conditioner) bonding mode. These findings confirm that the metal salt-based conditioner can be considered as a suitable alternative (enamel/)dentin conditioner to classic phosphoric acid employed in an E&R bonding mode.     

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.     

Bonding to enamel using alternative Enamel Conditioner/etchants

ObjectiveEnamel bond durability of three new alternative etchants combined with three representative adhesives was determined.MethodsThe ‘immediate’ and ‘aged’ micro-tensile bond strength (μTBS) of the 3-step etch&rinse adhesive OptiBond FL (‘O-FL’, Kerr), 2-step self-etch (SE) adhesive Clearfil SE Bond 2 (‘C-SE2’, Kuraray Noritake) and universal adhesive Adhese Universal (‘ADU’, Ivoclar Vivadent) were measured when bonded to enamel following either a proprietary organic acid-containing Enamel Conditioner (‘EC’, Shofu), a phosphoric-acid monomer-containing Multi Etchant (‘ME’, Yamakin: 10-methacryloyloxy tetraethylene glycol dihydrogenphosphate or MTEGP), or a metal salt-based ZON etchant (‘ZON’, Ivoclar Vivadent: ZrO(NO₃)₂). All alternative etchants were used in replacement of phosphoric acid, the latter (K-Etchant, Kuraray Noritake) also used with O-FL and ADU, in addition to C-SE2 that was solely used in SE mode (controls). The enamel-etching patterns and de-bonded fracture surfaces were examined by SEM, while the interfaces with enamel were ultra-morphologically characterized by TEM.ResultsNo statistically significant difference in immediate and aged μTBS, obtained by combining the three alternative etchants with the three adhesives, was recorded as compared with the respective controls, except for ME combined with O-FL. Upon aging, significant reduction in μTBS was recorded for the ME/C-SE2 and ME/ADU combinations. The percentage of adhesive failures increased with aging. SEM revealed similar etching patterns produced by EC and ZON as by classic phosphoric-acid etching, for which also numerous micro-resin tags at the adhesive-enamel interface were disclosed.SignificanceDurable bonding to enamel was generally obtained for all etchant/adhesive combinations with the exception of the ME/O-FL combination.     

Bond strength of a mild self-etch adhesive with and without prior acid-etching

SUMMARY: The self-etch approach provides dentists with a generation of user-friendly and less technique-sensitive adhesives. Nevertheless, some concern has been raised regarding their bonding effectiveness to enamel, in particular when so-called 'mild' self-etch adhesives are employed. OBJECTIVES: The purpose of this study was to test the hypothesis that the two-step self-etch adhesive Clearfil SE Bond (C-SE; Kuraray, Osaka, Japan) bonds equally effective to enamel/dentin either with or without prior etching with phosphoric acid. METHODS: Bur-cut enamel/dentin surfaces prepared from human molars were partially split in two halves by cutting a shallow groove. One half was first etched with 40% phosphoric acid (K-etchant), while protecting the other half by holding a razor blade in the groove. Next, C-SE was applied strictly following the manufacturer's instructions, after which the surface was built up using Z100 (3M Espe). After 24-h water storage, micro-specimens were prepared with the interface circularly constricted using a Micro-Specimen Former, prior to micro-tensile bond strength (MPa) measurement. In addition, interfaces of C-SE with enamel/dentin prepared with and without beforehand acid etching were examined by Feg-SEM and TEM. RESULTS: Beforehand etching significantly increased the bonding effectiveness of C-SE to enamel. A clearly more micro-retentive surface was revealed by TEM and Feg-SEM when enamel was etched. Phosphoric-acid etching prior to C-SE application on dentin significantly decreased the muTBS to dentin. TEM provided indications of a low-quality hybrid layer after beforehand phosphoric-acid etching. CONCLUSION: Using C-SE, additional etching with phosphoric acid to improve bonding effectiveness should be limited to enamel.     

Adhesive performance of a multi-mode adhesive system: 1-Year in vitro study

Objectives

The aim of this study was to investigate the adhesive stability over time of a multi-mode one-step adhesive applied using different bonding techniques on human coronal dentine. The hypotheses tested were that microtensile bond strength (μTBS), interfacial nanoleakage expression and matrix metalloproteinases (MMPs) activation are not affected by the adhesive application mode (following the use of self-etch technique or with the etch-and-rinse technique on dry or wet dentine) or by ageing for 24 h, 6 months and 1 year in artificial saliva.

Methods

Human molars were cut to expose middle/deep dentine and assigned to one of the following bonding systems (N = 15): (1) Scotchbond Universal (3M ESPE) self-etch mode, (2) Scotchbond Universal etch-and-rinse technique on wet dentine, (3) Scotchbond Universal etch-and-rinse technique on dry dentine, and (4) Prime&Bond NT (Dentsply De Trey) etch-and-rinse technique on wet dentine (control). Specimens were processed for μTBS test in accordance with the non-trimming technique and stressed to failure after 24 h, 6 months or 1 year. Additional specimens were processed and examined to assay interfacial nanoleakage and MMP expression.

Results

At baseline, no differences between groups were found. After 1 year of storage, Scotchbond Universal applied in the self-etch mode and Prime&Bond NT showed higher μTBS compared to the other groups. The lowest nanoleakage expression was found for Scotchbond Universal applied in the self-etch mode, both at baseline and after storage. MMPs activation was found after application of each tested adhesive.

Conclusions

The results of this study support the use of the self-etch approach for bonding the tested multi-mode adhesive system to dentine due to improved stability over time.

Clinical significance

Improved bonding effectiveness of the tested universal adhesive system on dentine may be obtained if the adhesive is applied with the self-etch approach.     

Micro-tensile bond strength of two adhesives to Erbium:YAG-lased vs. bur-cut enamel and dentin

The purpose of the study was to assess the hypotheses that laser irradiation is equally effective for bonding as traditional acid-etch procedures, and that tooth substrate prepared either by Erbium:YAG laser or diamond bur is equally receptive to adhesive procedures. Buccal/oral enamel and mid-coronal dentin were laser-irradiated using an Erbium:YAG laser. A total-etch adhesive (OptiBond FL) applied with and without prior acid-etching and a self-etch adhesive (Clearfil SE Bond) were employed to bond the composite. The micro-tensile bond strength (microTBS) was determined after 24 h of storage in water. Failure patterns were analysed using a stereo-microscope, and samples were processed for Field-emission Scanning Electron Microscopy (Fe-SEM) evaluation. Unbonded, lased enamel and dentin surfaces were evaluated using Fe-SEM as well. The total-etch adhesive bonded significantly less effectively to lased than to bur-cut enamel/dentin. Laser 'conditioning' was clearly less effective than acid-etching. Moreover, acid etching lased enamel and dentin significantly improved the microTBS of OptiBond FL. The self-etch adhesive performed equally to lased as to bur-cut enamel, but significantly less effectively to lased than to bur-cut dentin. It is concluded that cavities prepared by laser appear less receptive to adhesive procedures than conventional bur-cut cavities.     

Current aspects on bonding effectiveness and stability in adhesive dentistry

Improved dental adhesive technology has extensively influenced modern concepts in restorative dentistry. In light of minimal-invasive dentistry, this new approach promotes a more conservative cavity design, which basically relies on the effectiveness of current enamel-dentine adhesives. Nowadays, the interaction of adhesives with the dental substrate is based on two different strategies, commonly described as an etch-and-rinse and a self-etch approach. In an attempt to simplify the bonding technique, manufacturers have decreased the number of steps necessary for the accomplishment of the bonding procedure. As a consequence, two-step etch-and-rinse and one-step (self-etch) adhesives were introduced and gained rapid popularity in the dental market due to their claimed user-friendliness and lower technique sensitivity. However, many concerns have been raised on the bonding effectiveness of these simplified adhesives, especially in terms of durability, although this tends to be very material dependent. In order to blend all the adhesive components into one single solution, one-step adhesives were made more acidic and hydrophilic. Unfortunately, these properties induce a wide variety of seemingly unrelated problems that may jeopardize the effectiveness and stability of adhesion to the dental substrate. Being more susceptible to water sorption and thus nanoleakage, these adhesives are more prone to bond degradation and tend to fail prematurely as compared to their multi-step counterparts. Incidentally, another factor that may interfere with the bonding effectiveness of adhesives is the technique used for caries removal and cavity preparation. Several tools are on the market today to effectively remove carious tissue, thereby respecting the current trend of minimum intervention. Despite their promising performance, such techniques modify the tooth substrate in different aspects, possibly affecting bonding effectiveness. Altogether, we may conclude that not only the adhesive formulation, but also substrate nature must be taken into account to achieve a stable bonding interface, rendering the restorative treatment more predictable in terms of clinical performance. In this review, we analyse the current theoretical and clinical aspects of adhesion to enamel and dentine, and discuss the diverse possibilities to overcome problems which nowadays still challenge clinicians in their achievement of a more stable and effective bond to tooth enamel and dentine.     

Effect of acid etching time on bond strength of an etch-and-rinse adhesive to primary tooth dentine affected by amelogenesis imperfecta

Background.  Dentine affected by amelogenesis imperfecta (AI) is histologically altered following loss of the hypoplastic enamel and becomes hypermineralized, which would make bonding less predictable.
Aim.  This study examined the effect of etching time on the microtensile bond strength (µTBS) to AI-affected primary dentine.
Design.  Flat coronal dentine surface was obtained from extracted AI-affected and noncarious primary molars. Teeth were etched either for 15 or for 30 s using 34% phosphoric acid. Prime & Bond® NT™ (Dentsply De Trey), an etch-and-rinse adhesive, was applied to dentine surfaces, air-dried and light-cured, followed by composite build-ups. The bonded teeth were sectioned into beams of 0.8 mm² and stressed to failure under tension. Representative fractured beams from each group were examined under scanning electron microscopy.
Results.  The extended etching time had an adverse effect on the µTBS for the normal dentine, while no significant difference was found for AI-affected dentine. When the AI-affected dentine was etched for 30 s, the fracture occurred in the demineralized dentine at the base of the hybrid layer.
Conclusion.  Bonding to AI-affected dentine compromised the bonding of the etch-and-rinse adhesive. The bonding could not be improved by increasing etching time.     

One-day bonding effectiveness of new self-etch adhesives to bur-cut enamel and dentin

Self-etch adhesives try to solve difficulties commonly associated with the clinical application of etch-and-rinse adhesives. Their application procedure is considered less time-consuming and, more importantly, less technique-sensitive. The main objective of this study was to determine the bonding effectiveness to and the interaction with enamel/dentin of three contemporary one- and two-step self-etch adhesives by microtensile bond strength testing (microTBS), Fe-SEM and TEM when compared to a control two-step self-etch and a three-step etch-and-rinse adhesive. The one-step self-etch adhesive, Adper Prompt (3M ESPE), scored the lowest microTBS of all experimental and control adhesives tested. Conversely, the two-step self-etch adhesives Clearfil SE (Kuraray) and OptiBond Solo Plus Self-Etch (Kerr) approached the values obtained by the three-step etch-and-rinse control (OptiBond FL, Kerr) when bonded to enamel and dentin. Ultramorphological characterization showed that interfacial morphology and the pH of the self-etch primer/adhesive are strongly associated. The interaction with dentin varied from the formation of a submicron, hydroxyapatite-containing hybrid layer for the "mild" self-etch adhesive Clearfil SE to a 3-5 microm thick, hydroxyapatite-depleted hybrid layer for the "strong" self-etch adhesive Adper Prompt. The two-step self-etch adhesives AdheSE and OptiBond Solo Plus Self-Etch presented with a hybrid layer with a hydroxyapatite-depleted top part and a hydroxyapatite-containing base part and were therefore classified into a new group of self-etch adhesives, namely "intermediary strong" self-etch adhesives.     

Effects of different orthodontic adhesives and resin removal techniques on enamel color alteration

Objective: To investigate the color alterations in enamel following the use of different orthodontic bonding resins and adhesive residue–removal burs.Materials and Methods:Metal brackets were bonded to extracted human premolars (n  =  175) by using an etch-and-rinse adhesive system, a self-etch adhesive system (SEP), or a resin-modified glass ionomer cement (RMGIC). After 24 hours of photoaging, the brackets were removed and the adhesive residue on the tooth surfaces was cleaned with either a tungsten carbide bur or a Stainbuster bur. Tooth colors were measured with a spectrophotometer at baseline, after adhesive removal, and after additional photoaging. Color evaluation was made, and color differences induced by photoaging were calculated. Statistical evaluation was made using the Kruskal-Wallis test and the Mann-Whitney U-test, with Bonferroni correction.Results:All specimens showed discoloration at varying levels. The highest color change was observed in the etch-and-rinse adhesive/tungsten carbide bur group. When the etch-and-rinse and self-etch adhesives were used, adhesive-remnant removal with Stainbuster burs resulted in significantly lower discoloration. The type of bur did not affect the extent of enamel discoloration in the RMGIC group.Conclusions:Orthodontic treatment alters the original color of enamel, and both the adhesive system and the resin-removal methods are responsible for this change. When brackets are bonded with the etch-and-rinse system or the SEP, cleaning the adhesive residuals with Stainbuster burs is recommended for minimal change. RMGIC can be safely cleaned with tungsten carbide burs.     

Self-etch adhesives for the bonding of orthodontic brackets: faster, stronger, safer?

Objectives

This study aimed to evaluate the performance of accelerating procedures for bonding of orthodontic brackets in vitro by comparing different adhesives (etch-and-rinse, self-etch) and polymerization procedures (curing devices, time). The performance was characterized by three parameters: (1) the bond strength achieved, (2) the incidence of enamel damage, and (3) the extent of residual composite on the tooth.

Materials and methods

Bracket bonding was performed on 500 extracted human teeth after application of either an etch-and-rinse adhesive or a one-step self-etch adhesive. Two different two-component self-etch adhesives (Clearfil SE and Transbond Plus) and two single-component self-etch adhesives (Ideal and iBond) were investigated after using different polymerization procedures (light-emitting diode for 10 or 20 s or plasma arc curing device for 3 or 6 s). The bond strength, incidence of enamel damage, and extent of residual composite on the tooth were measured.

Results

Single-component self-etch adhesives gave the lowest bond strengths. No significant difference in bond strength could be detected between the two-component self-etch adhesives and the etch-and-rinse method. There was a 70.3 % risk for enamel damage at bond strengths above 12 MPa, but only 5 % risk below 12 MPa and no risk below 8.2 MPa. The risk of enamel damage increased by an odds ratio increment of 1.3 for each additional MPa above 8.2 MPa.

Conclusion

Single-component self-etch adhesives showed the lowest bond strengths, caused limited enamel damage, and generally left less residual composite on the tooth.

Clinical relevance

The nature of the adhesive greatly influences the resultant bond strength, the risk of enamel damage, and the extent of residual composite on the teeth.     

Dentin-smear remains at self-etch adhesive interface

ObjectiveThe bonding potential of ‘mild’ self-etch adhesives may be compromised due to smear interference, as they may not dissolve/penetrate the smear layer effectively due to their relatively low acidity. We observed that the thickness of the dentin smear layer differed depending on the surface-preparation methodology used.MethodsThe interaction of an (ultra-)mild self-etch adhesive (Clearfil S3 Bond, Kuraray Noritake) with human dentin, prepared either using a medium-grit diamond bur (‘thick’, clinically relevant smear layer) or 600-grit SiC-paper (‘thin’ smear layer), or just fractured (smear-free), was evaluated using high-resolution transmission electron microscopy (TEM). Non-demineralized/demineralized 30–100 nm interfacial cross-sections were prepared following common TEM-specimen processing and diamond-knife ultra-microtomy.ResultsThe adhesive did not dissolve the bur-cut, nor the SiC-ground smear layer, but impregnated it. Within this ‘resin-smear complex’, hydroxyapatite was abundantly present. At fractured dentin, this complex was not present, while the actual layer of interaction of the adhesive was limited to about 100 nm. Non-demineralized ‘ultra-thin’ (30–50 nm) sections confirmed the interfacial ultra-structure to differ for the three surface-preparation methods. An electron dense band was consistently disclosed at the adhesive interface, most likely representing the documented chemical interaction of the functional monomer 10-MDP with Ca.SignificanceThe dentin surface-preparation method significantly affects the nature of the smear layer and the interaction with the ultra-mild self-etch adhesive.     

Fatigue of enamel bonds with self-etch adhesives

ObjectiveFatigue testing of adhesive bonds to tooth structures in conjunction with bond strength testing can provide more useful information for examining the effectiveness of dental adhesives. The purpose of this study was to determine the shear bond strength (SBS) and shear fatigue limit (SFL) of composite to enamel bonds using modern adhesive systems.MethodsTwelve specimens each were used to determine 24-h resin composite (Z100-3M ESPE) to enamel shear bond strengths with an etch-and-rinse system (ERA), Adper Single Bond Plus (SB), and four self-etch adhesives (SEA)—Adper Prompt-L-Pop (PLP), Clearfil SE (CSE), Clearfil S³ (CS3) and Xeno IV (X4). A staircase method of fatigue testing was used in a four-station fatigue cycler to determine the SFL of composite to enamel bonds with the adhesives (16–20 specimens for each adhesive) at 0.25 Hz for 40,000 cycles. ANOVA and Tukey's post hoc test were used for the SBS data and a modified t-test with Bonferroni correction was used for comparisons of the SFL.ResultsThe SBS and SFL of the etch-and-rinse system were significantly greater (p < 0.05) than those of the four self-etch adhesives. The SBS and SFL of CSE were also significantly greater than for the other three self-etch systems. The ratio of SFL to SBS was highest with the etch-and-rinse system and the ratio became increasing smaller in the same order that the values for SBS decreased with the self-etch systems.SignificanceThe lower fatigue limits for composite to enamel bonds obtained with the self-etch adhesive systems may indicate that greater enamel margin breakdown will occur with restorations where these systems are used for bonding.     

Bonding to ground versus unground enamel in fluorosed teeth.

OBJECTIVES: To determine the effect of grinding on the bonding effectiveness of a self-etch and an etch-and-rinse adhesive to fluorosed enamel. METHODS: The teeth were classified using the Thylstrup and Fejerskov index (TFI). Fluorosed teeth (TFI=5) obtained from Isparta (Turkey) and control teeth (TFI=0) obtained from Leuven (Belgium) were used. Using a depth-marking diamond bur, 0.3mm of enamel was removed from mid-buccal and mid-palatal/lingual surfaces of the teeth, whereas the area adjacent to the ground area was left unprepared. A two-step self-etch (Clearfil Protect Bond, Kuraray) and a three-step etch-and-rinse adhesive (Optibond FL, Kerr) were used to bond the resin composite to the ground and unground enamel. Rectangular micro-specimens were prepared using the slow-speed diamond saw and tested in tensile to determine the micro-tensile bond strength (microTBS). RESULTS: The microTBS to unground fluorosed enamel was significantly lower than to ground fluorosed enamel for Clearfil Protect Bond (15.8+/-15.2 and 45.0+/-12.4MPa, p<0.0001) and for Optibond FL (35.5+/-21.4 and 50.5+/-12.3MPa, p<0.05), respectively. In control teeth, Clearfil Protect Bond bonded better to ground enamel (p<0.01), whereas OptiBond FL exhibited a similar bonding effectiveness to ground and unground enamel (p=0.0634). SIGNIFICANCE: Preparation of enamel improved the resin-enamel bond strength in fluorosed teeth. The bonding effectiveness to unground enamel was lower in fluorosed teeth than in control teeth for the self-etch adhesive tested.     

Clinical effectiveness of contemporary adhesives: a systematic review of current clinical trials.

OBJECTIVES: The purpose of this paper was to review current literature on the clinical effectiveness of contemporary adhesives when used to restore cervical non-carious class-V lesions. Restoration retention in function of time was recorded in order to find out if adhesives with a simplified application procedure are as clinically effective as conventional three-step adhesives. DATA SOURCES: Literature published from January 1998 up to May 2004 was reviewed for university-centred clinical trials that tested the clinical effectiveness of adhesives in non-carious class-V lesions. Restoration-retention rates per adhesive reported in peer-reviewed papers as well as IADR-AADR abstracts and ConsEuro abstracts were included and depicted as a function of time in graphs for each of the five adhesive classes (three- and two-step etch-and-rinse adhesives, two- and one-step self-etch adhesives, and glass-ionomers). The guidelines for dentin and enamel adhesive materials advanced by the American Dental Association were used as a reference. Per class, the annual failure rate (%) was calculated. Kruskal-Wallis analysis and Dwass-Steel-Chritchlow-Fligner pairwise comparisons were used to determine statistical differences between the annual failure percentages of the five adhesive categories. RESULTS: Comparison of retention of class-V adhesive restorations as a measure to determine clinical bonding effectiveness of adhesives revealed that glass-ionomers most effectively and durably bond to tooth tissue. Three-step etch-and-rinse adhesives and two-step self-etch adhesives showed a clinically reliable and predictably good clinical performance. The clinical effectiveness of two-step etch-and-rinse adhesives was less favourable, while an inefficient clinical performance was noted for the one-step self-etch adhesives. SIGNIFICANCE: Although there is a tendency towards adhesives with simplified application procedures, simplification so far appears to induce loss of effectiveness. Clinical performance can be correlated with, and predicted by, appropriate types of laboratory study.     

Self-etch vs etch-and-rinse adhesives: effect of thermo-mechanical fatigue loading on marginal quality of bonded resin composite restorations.

OBJECTIVE: This study evaluated the marginal integrity of dentine adhesives bonded to enamel and dentine, before and after thermo-mechanical loading (TML). METHODS: MO cavities with proximal boxes beneath the CEJ were prepared in extracted human third molars. Direct resin composite restorations (Tetric Ceram) were bonded with 3-step etch-and-rinse (Syntac Classic, Solobond Plus, OptiBond FL), 2-step etch-and-rinse (Admira Bond, Single Bond), 2-step self-etch (AdheSE, Clearfil SE Bond), and 1-step self-etch (all-in-one) adhesives (Adper Prompt, Xeno III, iBond). Marginal gaps were analyzed using SEM of epoxy resin replicas. Bonded interfaces before TML were examined with TEM to identify pre-existing attributes for subsequent marginal disintegration. RESULTS: In enamel, high percentages of gap-free margins were initially identified for all adhesives. After TML, etch-and-rinse adhesives exhibited significantly higher percentages of gap-free margins (approximately 90%) compared with two-step self-etch (approximately 75%) and all-in-one (approximately 55%) adhesives (p<0.05). iBond did not completely etch through the enamel smear layer. In dentine, 89-100% gap-free margins were initially observed. After TML, there were no statistical differences among etch-and-rinse (62-70%) and two-step self-etch (62-63%) adhesives (p>0.05). The all-in-one adhesives exhibited significantly less gap-free margins (<40%) in dentine (p<0.05), with iBond showing the worst marginal integrity (15%). The presence of pre-existing water channels within the adhesives probably expedited water sorption when restorations were under functional stresses. CONCLUSION: Enamel bonding was more effective with phosphoric acid-etching. Etch-and-rinse and 2-step self-etch adhesives showed promising marginal adaptation to dentine and may have a better clinical prognosis than the all-in-one bonding approach.     

Clinical effectiveness of a one-step self-etch adhesive in non-carious cervical lesions at 2 years

A 2-year randomized, controlled prospective study evaluated the clinical effectiveness of a one-step self-etch adhesive and a “gold-standard” three-step etch-and-rinse adhesive in non-carious Class-V lesions. The null hypothesis tested was that the one-step self-etch adhesive does perform clinically equally well as the three-step etch-and-rinse adhesive. A total of 161 lesions in 26 patients were restored with Clearfil AP-X (Kuraray). The restorations were bonded either with the “all-in-one” adhesive Clearfil S3 Bond (Kuraray) or with the three-step etch-and-rinse adhesive Optibond FL (Kerr). The restorations were evaluated at baseline and after 6 months, 1 and 2 years, regarding their retention, marginal adapation, marginal discoloration, caries occurrence, preservation of tooth vitality and post-operative sensivity. Retention loss, severe marginal defects and/or discoloration that needed intervention (repair or replacement) and the occurrence of caries were considered as clinical failures. The recall rate at 2 years was 93.8%. Only one Clearfil S3 Bond restoration was lost at the 2-year recall. All other restorations were clinically acceptable. The number of restorations with defect-free margins decreased severely during the 2-year study period (to 6.7% and 25.3% for Clearfil S3 Bond and Optibond FL, respectively). The Clearfil S3 Bond restorations presented significantly more small marginal defects at the enamel side than the Optibond FL restorations (Clearfil S3 Bond: 93.3%; Optibond FL: 73.3%; p = 0.000). Superficial marginal discoloration increased in both groups (to 53.3% and 36% for Clearfil S3 Bond and Optibond FL, respectively) and was also more pronounced in the Clearfil S3 Bond group (p = 0.007). After 2 years, the simplified one-step self-etch adhesive Clearfil S3 Bond and the three-step etch-and-rinse adhesive Optibond FL were clinically equally successful, even though both adhesives were characterized by progressive degradation in marginal integrity. Clearfil S3 Bond exhibited more small enamel marginal defects and superficial marginal discolorations.

     

Effects of surface wetness of etched dentin on bonding durability of a total-etch adhesive system: comparison of conventional and dumbbell-shaped specimens

The dentin bonding durability of a total-etch adhesive system (Prime & Bond NT) was investigated by tensile bond test using conventional and dumbbell-shaped specimens. Two bonding techniques were compared. After etching and rinsing, dentin surface was either blotted by cotton ball (wet-bonding) or air-dried (dry-bonding) before bonding agent was applied. The bond strength of wet-bonding specimens was significantly higher than that of dry-bonding for both conventional and dumbbell-shaped specimens after one day. The bond strength of wet-bonded conventional specimens did not decrease after two years of water immersion, but cohesive failure in demineralized dentin was observed after two years. Wet-bonded dumbbell-shaped specimens showed cohesive failure within demineralized dentin after only one day. The bond strength of dry-bonded conventional specimens decreased significantly after one year, and cohesive failure in demineralized dentin was confirmed after three months. As for dry-bonded dumbbell-shaped specimens, they showed cohesive failure in demineralized dentin after one month. The results of the present study showed that the bonding durability of dry-bonded Prime & Bond NT restorations was lower than that of wet-bonded restorations. Further, by using tensile bond test, cohesive failure in demineralized dentin was detected earlier in dumbbell-shaped specimens than in conventional specimens.     

Influence of preliminary etching on the stability of bonds created by one-step self-etch bonding systems

We evaluated the effects of preliminary etching of dentine on the stability of the bond created by one-step self-etch adhesives under different storage conditions. Adper Easy Bond (3M ESPE) and iBond Self-Etch (iBond SE; Heraeus Kulzer) were applied with an etch-and-rinse (i.e. after preliminary phosphoric acid etching for 15 s) or a self-etch approach. Resin-dentine bonded specimens were sectioned perpendicularly to the adhesive interface according to the 'non-trimming technique'. Beams were stored in artificial saliva for 24 h, 6 months, or 1 yr at 37°C, or in 10% NaOCl for 5 h at room temperature, and then stressed until failure; the microtensile bond strengths were calculated. Interfacial nanoleakage of additional teeth was evaluated using light microscopy or transmission electron microscopy. Adper Easy Bond showed higher bond strength than iBond SE, regardless of the dentine treatment. Similar microtensile bond strength results were obtained for teeth subjected to artificial ageing in 10% NaOCl for 5 h at room temperature and for teeth stored in artificial saliva for 6 months at 37°C. The additional etching step increased the microtensile bond strength for Adper Easy Bond and iBond SE. This study supports the use of one-step adhesives on etched dentine because of the increased bond strength compared with their application onto smear-layer-covered dentine, regardless of storage conditions.     

The role of HEMA in one-step self-etch adhesives

In spite of its high allergenic potential, 2-hydroxyethyl methacrylate (HEMA), a low-molecular-weight monomer, is frequently used in adhesives for its positive influence on the bond strength. In addition, the presence of HEMA in one-component one-step adhesives can prevent phase separation. OBJECTIVES: In search of improved bonding effectiveness, the 24-h bond strength of four experimental one-step self-etch adhesives with different concentrations of HEMA to bur-cut enamel and dentin was determined using a micro-tensile bond strength protocol. METHODS: The tested experimental adhesives (Exp-0, Exp-10, Exp-19 and Exp-36) only differed in their concentration of HEMA, which was 0, 10, 19 and 36%, respectively. With an increasing concentration of HEMA, the concentration of acetone was decreased. Besides bond strength, the adhesives were also examined by light-microscopy for phase separation. The interface was investigated by SEM and TEM. RESULTS: Regarding bond strength, Exp-10 performed best. Even though Exp-36 was the only adhesive formulation that did not exhibit phase separation on a glass plate, it yielded the lowest bond strength. Accordingly, droplets could be observed by SEM and TEM in the adhesive layers of all adhesives, except for Exp-36 on enamel. CONCLUSION: A small amount of HEMA (10%) improved the bond strength of a one-step self-etch adhesive. When added in higher concentrations, this beneficial effect of HEMA on the bond strength is lost due to increased osmosis, which resulted in many droplets; due to reduced polymerization conversion; and sub-optimal physico-mechanical properties of the resultant poly-HEMA containing adhesive interface.