Role of preliminary etching for one‐step self‐etch adhesives

Taschner M, Nato F, Mazzoni A, Frankenberger R, Krämer N, Di Lenarda R, Petschelt A, Breschi L. Role of preliminary etching for one‐step self‐etch adhesives.
Eur J Oral Sci 2010; 118: 517–524. © 2010 Eur J Oral Sci The aim of this study was to analyse the effect of preliminary phosphoric acid etching of enamel and dentine before the application of two, one‐step self‐etch adhesive systems. The systems were applied onto acid‐etched or smear‐layer‐covered enamel and dentine. The treatment groups were as follows: group 1, Adper Easy Bond (3M ESPE) on etched substrate; group 2, Adper Easy Bond (control); group 3, iBond Self‐Etch (Heraeus Kulzer) on etched substrate; and group 4, iBond Self‐Etch (control). Enamel and dentine bond strengths were calculated using microshear and microtensile bond‐strength tests. Additional specimens were prepared to evaluate nanoleakage at the dentine–adhesive interface and were investigated using light microscopy or transmission electron microscopy. Both adhesives demonstrated higher microshear bond strengths when enamel was pre‐acid‐etched with phosphoric acid (Adper Easy Bond 28.7 ± 4.8 MPa; iBond Self‐Etch 19.7 ± 3.6 MPa) compared with controls (Adper Easy Bond 19.2 ± 3.3 MPa; iBond Self‐Etch 17.5 ± 2.7 MPa) and increased microtensile bond strength when applied on acid‐etched (Adper Easy Bond 35.8 ± 5.7 MPa; iBond Self‐Etch 24.3 ± 7.9 MPa) vs. smear‐layer‐covered dentine (Adper Easy Bond 26.9 ± 6.2 MPa; iBond Self‐Etch 17.6 ± 4.3 MPa). Adper Easy Bond showed lower nanoleakage than iBond Self‐Etch, irrespective of preliminary etching. The results of this study support the use of phosphoric acid etching before the application of one‐step self‐etch adhesive systems.     

Comparison between universal adhesives and two‐step self‐etch adhesives in terms of dentin bond fatigue durability in self‐etch mode

This aim of this study was to compare universal adhesives and two‐step self‐etch adhesives in terms of dentin bond fatigue durability in self‐etch mode. Three universal adhesives – Clearfil Universal, G‐Premio Bond, and Scotchbond Universal Adhesive – and three‐two‐step self‐etch adhesives – Clearfil SE Bond, Clearfil SE Bond 2, and OptiBond XTR – were used. The initial shear bond strength and shear fatigue strength of resin composite bonded to adhesive on dentin in self‐etch mode were determined. Scanning electron microscopy observations of fracture surfaces after bond strength tests were also made. The initial shear bond strength of universal adhesives was material dependent, unlike that of two‐step self‐etch adhesives. The shear fatigue strength of Scotchbond Universal Adhesive was not significantly different from that of two‐step self‐etch adhesives, unlike the other universal adhesives. The shear fatigue strength of universal adhesives differed depending on the type of adhesive, unlike those of two‐step self‐etch adhesives. The results of this study encourage the continued use of two‐step self‐etch adhesive over some universal adhesives but suggest that changes to the composition of universal adhesives may lead to a dentin bond fatigue durability similar to that of two‐step self‐etch adhesives.     

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.     

One‐year clinical evaluation of a two‐step self‐etch adhesive with and without additional enamel etching technique in cervical lesions

Background: The aim of this study was to determine the clinical performance of a two‐step self‐etch adhesive with and without additional enamel etching technique to advanced non‐carious cervical sclerotic lesions. Methods: Twenty‐two patients (mean age = 51.5) having at least two pairs of non‐carious cervical erosion/attrition/abfraction lesions with incisal or occlusal margins in enamel and gingival margins in dentine/cementum were included in the study. The two‐step self‐etch adhesive (AdheSE; Ivoclar‐Vivadent) was either applied following the self‐etch approach on both enamel and dentine (AdheSE non‐etch), or a similar application including additional acid‐etching of the enamel cavity margins with 37% phosphoric acid (AdheSE etch). Resin composite Point 4 was used for all 104 restorations. Restorations were evaluated at baseline and at one year according to the modified United States Public Health Service (USPHS) criteria. Data were analysed by using McNemar’s test (p <0.05). Results: There were no significant differences in the marginal adaptation both at the cervical and enamel margins between AdheSE non‐etch and AdheSE etch groups (p >0.05). At one year, marginal discolouration was evident in the AdheSE non‐etch group but it was not statistically significant from the AdheSE etch group (p = 0.12). Postoperative sensitivity was 5% at baseline and reduced to 2% at one year. Conclusions: At one year, the two‐step self‐etch adhesive with and without additional enamel etching technique showed excellent clinical results to advanced non‐carious cervical sclerotic lesions.     

Effect of a functional monomer (MDP) on the enamel bond durability of single‐step self‐etch adhesives

The present study aimed to determine the effect of the functional monomer, 10‐methacryloxydecyl dihydrogen phosphate (MDP), on the enamel bond durability of single‐step self‐etch adhesives through integrating fatigue testing and long‐term water storage. An MDP‐containing self‐etch adhesive, Clearfil Bond SE ONE (SE), and an experimental adhesive, MDP‐free (MF), which comprised the same ingredients as SE apart from MDP, were used. Shear bond strength (SBS) and shear fatigue strength (SFS) were measured with or without phosphoric acid pre‐etching. The specimens were stored in distilled water for 24 h, 6 months, or 1 yr. Although similar SBS and SFS values were obtained for SE with pre‐etching and for MF after 24 h of storage in distilled water, SE with pre‐etching showed higher SBS and SFS values than MF after storage in water for 6 months or 1 yr. Regardless of the pre‐etching procedure, SE showed higher SBS and SFS values after 6 months of storage in distilled water than after 24 h or 1 yr. To conclude, MDP might play an important role in enhancing not only bond strength but also bond durability with respect to repeated subcritical loading after long‐term water storage.     

Effects of thermocycling and use of ElectroBond on microtensile strength and nanoleakage using commercial one‐step self‐etch adhesives

The aim of this study was to determine the effect of thermocycling and the use of an electronically assisted application technique on the microtensile bond strength and nanoleakage of bonded interfaces created using one‐step self‐etch adhesives. Composite build‐ups were bonded coronally to sectioned human molars using XENO III or Clearfil S³Bond. Adhesives were applied following the manufacturers’ instructions (control) or with the aid of an electrical application device (ElectroBond). Teeth were sectioned into non‐trimmed bonded beams for microtensile testing. Half of the specimens were subjected to 20,000 thermocycles, and the controls were not thermocycled. All specimens were tested to failure and peak stress was calculated. Additional specimens were prepared for nanoleakage analysis using transmission electron microscopy (TEM). The immediate bond strength of both adhesives increased as a result of using the ElectroBond device (XENO III 38.9 ± 8.1 MPa; Clearfil S³Bond 46.2 ± 9.9 MPa) compared with no use of the device (XENO III 26.7 ± 7.8 MPa; Clearfil S³Bond 38.9 ± 8.1 MPa). Thermocycling significantly decreased the bond strength of XENO III (27.1 ± 7.9 MPa with the use of ElectroBond; 20.7 ± 9.2 MPa without the use of ElectroBond); however, thermocycling did not affect the Clearfil S³Bond strength (47.2 ± 8.6 MPa with the use of ElectroBond; 33.6 ± 8.3 MPa without the use of ElectroBond). Reduced nanoleakage was found for both resins as a result of the use of the ElectroBond device, with or without thermocycling. Application of one‐step, self‐etch adhesives with the ElectroBond device significantly increased microtensile bond strength and reduced nanoleakage, but the effect of thermocycling was found to be brand‐dependent.     

Influence of warm air‐drying on enamel bond strength and surface free‐energy of self‐etch adhesives

We examined the effect of warm air‐drying on the enamel bond strengths and the surface free‐energy of three single‐step self‐etch adhesives. Bovine mandibular incisors were mounted in self‐curing resin and then wet ground with #600 silicon carbide (SiC) paper. The adhesives were applied according to the instructions of the respective manufacturers and then dried in a stream of normal (23°C) or warm (37°C) air for 5, 10, and 20 s. After visible‐light irradiation of the adhesives, resin composites were condensed into a mold and polymerized. Ten samples per test group were stored in distilled water at 37°C for 24 h and then the bond strengths were measured. The surface free‐energies were determined by measuring the contact angles of three test liquids placed on the cured adhesives. The enamel bond strengths varied according to the air‐drying time and ranged from 15.8 to 19.1 MPa. The trends for the bond strengths were different among the materials. The value of the component increased slightly when drying was performed with a stream of warm air, whereas that of the component decreased significantly. These data suggest that warm air‐drying is essential to obtain adequate enamel bond strengths, although increasing the drying time did not significantly influence the bond strength.     

Enzymatic degradation of adhesive–dentin interfaces produced by mild self‐etch adhesives

De Munck J, Mine A, Van den Steen PE, Van Landuyt KL, Poitevin A, Opdenakker G, Van Meerbeek B. Enzymatic degradation of adhesive–dentin interfaces produced by mild self‐etch adhesives.
Eur J Oral Sci 2010; 118: 494–501. © 2010 Eur J Oral Sci Endogenous matrix metalloproteinases (MMPs) released by adhesive procedures may degrade collagen in the hybrid layer and so compromise the bonding effectiveness of etch‐and‐rinse adhesives. In this study, endogenous enzymatic degradation was evaluated for several simplified self‐etch adhesives. In addition, primers were modified by adding two MMP inhibitors: chlorhexidine, a commonly used disinfectant, but also a non‐specific MMP inhibitor; and SB‐3CT, a specific inhibitor of MMP‐2 and MMP‐9. Gelatin zymography of fresh human dentin powder was used to identify the enzymes released by the adhesives. Micro‐tensile bond strength (μTBS) testing was used to assess the mechanical properties of resin–dentin interfaces over time. In none of the experimental groups treated with the mild self‐etch adhesives was MMP‐2 and/or MMP‐9 identified. Also, no difference in the μTBS was measured for the inhibitor‐modified and the control inhibitor‐free adhesives after 6 months of water storage. It is concluded that in contrast to etch‐and‐rinse adhesives, the involvement of endogenous MMP‐2 and MMP‐9 in the bond‐degradation process is minimal for mild self‐etch adhesives.     

Effect of a one‐step self‐etch adhesive on endogenous dentin matrix metalloproteinases

Degradation of the hybrid layer created in dentin by dentin adhesives is caused by enzyme activities present within the dentin matrix that destroy unprotected collagen fibrils. The aim of the present study was to evaluate the effect of a one‐step self‐etch adhesive system on dentinal matrix metalloproteinases 2 and 4 (MMP‐2 and MMP‐9, respectively) using in situ zymography and an enzymatic activity assay. The null hypothesis tested was that there are no differences in the activities of dentinal MMPs before and after treatment with a one‐step adhesive system. The MMP‐2 and MMP‐9 activities in dentin treated with the one‐step adhesive, Adper Easy Bond, were quantified using an enzymatic activity assay system. The MMP activities within the hybrid layer created by the one‐step adhesive tested were also evaluated using in situ zymography. The enzymatic assay revealed an increase in MMP‐2 and MMP‐9 activities after treatment with adhesive. In situ zymography indicated that gelatinolytic activity is present within the hybrid layer created with the one‐step self‐etch adhesive. The host‐derived gelatinases were localized within the hybrid layer and remained active after the bonding procedure. It is concluded that the one‐step self‐etch adhesive investigated activates endogenous MMP‐2 and MMP‐9 with the dentin matrix, which may cause collagen degradation over time.     

Surface free‐energy measurements as indicators of the bonding characteristics of single‐step self‐etching adhesives

Inoue N, Tsujimoto A, Takimoto M, Ootsuka E, Endo H, Takamizawa T, Miyazaki M. Surface free‐energy measurements as indicators of the bonding characteristics of single‐step self‐etching adhesives.
Eur J Oral Sci 2010; 118: 525–530. © 2010 Eur J Oral Sci This study examined the surface free‐energy of dentin treated with the single‐step self‐etching adhesives Bond Force, Clearfil tri‐S Bond, and G‐Bond Plus. The labial dentin surfaces of bovine mandibular incisors were wet ground with #180‐, #600‐, and #2,000‐grit silicon carbide paper. The adhesives were applied to the ground dentin, and then rinsed with acetone and distilled water. The surface free‐energies were determined by measuring the contact angles of three test liquids placed on the adhesive‐treated dentin. The surface free‐energies of the samples treated with the G‐Bond Plus and Clearfil tri‐S Bond adhesives increased as the surface roughness decreased. No significant differences in the surface free‐energy were found for the samples treated with the Bond Force adhesive, regardless of the surface roughness. These results indicated that dentin surfaces treated with adhesives did not promote a higher surface‐energy state, and that differences in the components of surface energy were apparent for the adhesives tested.     

Optimization of direct currents to enhance dentine bonding of simplified one‐step adhesive

The aim of this study was to investigate the effects of different direct current intensities on dentine bonding effectiveness of Clearfil S³ Bond and on cell viability of human dental pulp cells (HDPCs). Thirty‐five‐third molars were sectioned and ground to provide flat surfaces. Clearfil S³ Bond was applied under different current conditions for 30 s and then resin composite was built up. Specimens were processed for microtensile bond strength (µTBS) testing and for nanoleakage investigation using scanning electron microscopy. Primary HDPCs isolated from premolars were stimulated with different intensities of electric current for 30 s. Then, cell viability was tested using the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide (MTT) assay. Specimens bonded with application of electrical current intensities of 50, 60, 70, and 90 µA exhibited a significant increase in immediate µTBS compared with all other groups. Bonded interfaces prepared using electrically assisted current application showed reduced interfacial nanoleakage upon scanning electron microscopy. Electric current application, from 20 to 70 µA, had no effect on the viability of HDPCs. This study provides further evidence for its future clinical use.     

Influence of methyl mercaptan on the repair bond strength of composites fabricated using self‐etch adhesives

The influence of methyl mercaptan on the repair bond strength of composites fabricated using self‐etch adhesives was investigated. The surface free‐energies were determined by measuring the contact angles of test liquids placed on composites that had been immersed in different concentrations of methyl mercaptan (0.01, 0.1, and 1.0 M). To determine the repair bond strength, self‐etch adhesives were applied to the aged composite, and then newly added composites were condensed. Ten samples of each specimen were subjected to shear testing at a crosshead speed of 1.0 mm min^?1. Samples were analyzed using two‐way anova followed by Tukey's honestly significant difference (HSD) test. Although the dispersion force of the composites remained relatively constant, their polar force increased slightly as the concentration of methyl mercaptan increased. The hydrogen‐bonding forces were significantly higher after immersion in 1.0 M methyl mercaptan, leading to higher surface‐free energies. However, the repair bond strengths for the repair restorations prepared from composites immersed in 1.0 M methyl mercaptan were significantly lower than for those immersed in 0.01 and 0.10 M methyl mercaptan. Considering the results of this study, it can be concluded that the repair bond strengths of both the aged and newly added composites were affected by immersion in methyl mercaptan solutions.