Aggressiveness of contemporary self-etching adhesives. Part II: etching effects on unground enamel.

OBJECTIVES: The aggressiveness of three self-etching adhesives on unground enamel was investigated. Ultrastructural features and microtensile bond strength were examined, first using these adhesives as both the etching and resin-infiltration components, and then examining their etching efficacy alone through substitution of the proprietary resins with the same control resins. METHODS: For SEM examination, buccal, mid-coronal, unground enamel from human extracted bicuspids were etched with either Clearfil Mega Bond (Kuraray), Non-Rinse Conditioner (NRC; Dentsply DeTrey) or Prompt L-Pop (ESPE). Those in the control group were etched with 32% phosphoric acid (Bisco) for 15s. They were all rinsed off prior to examination of the etching efficacy. For TEM examination, the self-etching adhesives were used as recommended. Unground enamel treated with NRC were further bonded using Prime&Bond NT (Dentsply), while those in the etched, control group were bonded using All-Bond 2 (Bisco). Completely demineralized, resin replicas were embedded in epoxy resin for examination of the extent of resin infiltration. For microtensile bond strength evaluation, specimens were first etched and bonded using the self-etching adhesives. A second group of specimens were etched with the self-etching adhesives, rinsed but bonded using a control adhesive. Following restoration with Z100 (3M Dental Products), they were sectioned into beams of uniform cross-sectional areas and stressed to failure. RESULTS: Etching patterns of aprismatic enamel, as revealed by SEM, and the subsurface hybrid layer morphology, as revealed by TEM, varied according to the aggressiveness of the self-etching adhesives. Clearfil Mega Bond exhibited the mildest etching patterns, while Prompt L-Pop produced an etching effect that approached that of the total-etch control group. Microtensile bond strength of the three experimental groups were all significantly lower than the control group, but not different from one another. When the self-etching adhesives were replaced with the control adhesive after etching, bond strengths of NRC/Prime&Bond NT and Prompt L-Pop were not significantly different from that of the control group, but were significantly higher than that of Clearfil Mega Bond. SIGNIFICANCE: Both etching efficacy and strength of the resins are important contributing factors in bonding of self-etching adhesives to unground enamel.     

Evaluation of the enamel etching capacity of six contemporary self-etching adhesives

OBJECTIVES: The purpose of this study was to evaluate the capacity of six contemporary self-etch primers/adhesives to demineralize ground enamel by means of ultrastructural analysis of the etching surface under SEM and by spectroscopic measurement of the percentage of calcium and phosphate ions dissolved. METHODS: Seventy non-carious extracted human third molars were sub-divided into 2 groups of 35 teeth each. The teeth of the first group were ground to expose flat, polished enamel surfaces 3-4mm thick. The samples thus obtained were treated with six self-etch bonding systems and a phosphoric acid gel (control group). The self-etch priming agent was then eliminated and the etched enamel surface observed by SEM. From the teeth of the second group, disc-shaped specimens were made from ground enamel and subjected to application of each of the six self-etchants. Once the etching product had been rinsed off, the rinse solution was analyzed by atomic flame spectroscopy to evaluate the percentage of calcium and phosphate ions dissolved. RESULTS: SEM images show that AdheSE, Adper Prompt L-Pop and Xeno III, despite having a less intensive etching efficacy than phosphoric acid, gave a regular pattern over a considerable surface area and depth. iBond and One-Up Bond F gave less regular demineralization. For Clearfil SE Bond, the demineralization was ineffective. Results of the percentage of mineral loss show that Adper Prompt L-Pop and Xeno III were the most efficient self-etch products. AdheSE, iBond and One-Up Bond F, respectively exhibited decreasing demineralizing capacity. Clearfil SE Bond, however, gave low proportions of calcium and phosphate ions loss and was considered unsatisfactory. CONCLUSION: The action on enamel was not the same for all self-etch systems tested. The etching potential of the self-etch adhesives was lower than that of phosphoric acid but some self-etch systems, particularly those with monomers containing phosphate derivatives, gave results close to those obtained with phosphoric acid.     

Resin tag length of one-step and self-etching adhesives bonded to unground enamel

Length of resin tags yielded by utilization of an one-step conventional adhesive system and self-etching adhesive system on unground enamel was observed. In study Groups I and III, the enamel surface was etched for 60 seconds with 35% phosphoric acid gel and adhesive systems PQ1 (Ultradent Products, Inc) and Adper Prompt L Pop (3M/ESPE) were applied. Adper Prompt L Pop (3M/ESPE) was also applied in Group II in accordance with the manufacturer's recommendations. After application of these adhesive systems to dental enamel, specimens were prepared for light microscopy analysis to ascertain degree of penetration (x400). The results were submitted to an analysis of variance at the 5% level; whenever there was significance, the Tukey test was applied at the 5% level. It was found that acid etching prior to application of conventional and self-etching adhesive materials provided higher penetration of the adhesive into the unground enamel surface compared to that achieved solely by application of self-etching adhesive.     

SEM evaluation of contemporary self-etching primers applied to ground and unground enamel

PURPOSE: This study evaluated the etching effect of self-etching priming agents applied to intact and ground enamel. MATERIALS AND METHODS: Thirty-two human molars were used. Each tooth was divided into two halves. The buccal or lingual mid-coronal surface of 32 half-teeth was ground with 600-grit silicon carbide paper. The other half-teeth were left intact (control). Teeth were treated with Clearfil SE Bond (SE), Prompt L-Pop (PLP) or Adper (AD). Those in the control group were etched with 35% phosphoric acid. The etching effect of such systems on enamel surfaces was assessed by three different approaches using scanning electron microscopy: 1) in situ or direct morphological examination of the etched enamel; 2) indirect morphological examination, that is, evaluation of the etching pattern left on resin reproductions; 3) adhesive interface examination. RESULTS: SE exhibited the least aggressive dissolution of the intact and ground enamel, with many sites of the intact enamel remaining completely unetched. SE monomer infiltration into etched enamel was restricted to the superficial layer. PLP and AD produced equivalent etching patterns on intact and ground enamel, which resemble that produced by the phosphoric acid control group. PLP and AD monomer penetration extended along the porous subsurface enamel layer. CONCLUSION: SE produced mild morphological changes on intact and ground enamel surface, resulting in a very superficial resin infiltration particularly into intact enamel. No differences were evident among the etching and resin infiltration pattern produced by both all-in-one self-etching adhesives, PLP and AD, and the phosphoric acid system.     

Aggressiveness of self-etch adhesives on unground enamel

Manufacturers of mild self-etch adhesives advocate the adjunctive use of phosphoric acid etching when bonding to unground enamel. This study tested the null hypothesis that there is no difference between the recently introduced, more aggressive self-etch adhesives and a total-etch adhesive in bonding to unground enamel. The ultrastructure and microtensile bond strengths (microTBS) of Xeno III (Dentsply) and Simplicity (Apex Dental Materials), bonded to unground enamel, were examined after thermocycling. Clearfil SE Bond (Kuraray), a mild self-etch adhesive, was used as the negative control, and One-Step (BISCO), a total-etch adhesive bonded to phosphoric acid-etched unground enamel, was used as the positive control. Differences in the thickness of enamel hybrid layers were observed and the aggressiveness of apatite dissolution in the four adhesives.     

Comparison of bonding ability of single-step self-etching adhesives with different etching aggressiveness to root dentin

The aim of this study was to compare the bonding ability of single-step self-etching adhesives with different degrees of etching aggressiveness to root dentin. Composite restorations were placed on sound or caries-affected root dentin using a "strong" (Adper Prompt L-Pop, Absolute) or "mild" (Clearfil Tri-S Bond, Reactmer Bond) system. Immediately after restoration placement and after 24-hour storage in distilled water, the bonding interface was examined by scanning electron microscopy. Microtensile bond strength (MTBS) on sound root dentin was also measured with each storage condition. The adhesives with strong etching aggressiveness demonstrated interfacial integrity immediately after restoration and also after 24 hours of storage. Conversely, the "mild" adhesives showed debonding immediately after restoration. There were no statistical differences in MTBS among the four systems, nor between the two storage periods for each material. For restorations on root dentin using single-step adhesives, "strong" systems were thus recommended as they favorably produced a stable bond since the early stage.     

Immediate enamel bond strength of universal adhesives to unground and ground surfaces in different etching modes

The purpose of this study was to determine the immediate bond effectiveness of universal adhesives to unground and ground enamel surfaces in different etching modes, through shear bond strength (SBS) tests and scanning electron microscopy observations. Three universal adhesives, a conventional two‐step self‐etch adhesive, and a conventional single‐step self‐etch adhesive were compared. Human enamel specimens from lower anterior teeth were divided into four groups and subjected to the following treatments: (i) unground enamel in self‐etch mode; (ii) ground enamel in self‐etch mode; (iii) unground enamel in etch‐&‐rinse mode; and (iv) ground enamel in etch‐&‐rinse mode. Bonded assemblies were subjected to SBS testing. All the adhesives showed significantly higher SBS values in etch‐&‐rinse mode than in self‐etch mode, regardless of whether enamel was unground or ground. The influence of the enamel surface condition on SBS was different in different etching modes. Without pre‐etching, all tested materials showed lower SBS values in unground enamel than in ground enamel. In etch‐&‐rinse mode, no significant differences in SBS values were observed between unground enamel and ground enamel for any of the adhesives tested. Phosphoric acid pre‐etching before application of self‐etch adhesives to an unground enamel surface is essential to enhance initial enamel bond effectiveness.     

Hydroxyapatite effect on photopolymerization of self-etching adhesives with different aggressiveness

Objective

To understand the correlation of the acidic monomer/hydroxyapatite (HAp) reaction with the photopolymerization behaviour of self-etching adhesives with different aggressiveness.

Methods

Two commercial self-etching adhesives the strong Adper Prompt L-Pop (APLP, pH ∼ 0.8) and the mild Adper Easy Bond (AEB, pH ∼ 2.5) were used. HAp powders were incorporated into both adhesives to acquire solutions with concentrations of 0, 1, 3, 5, 7 wt%. The attenuated total reflectance Fourier transform infrared (ATR/FT-IR) technique was employed to collect the in situ spectra during light-curing, from which the degree of conversion (DC) and polymerization rate (PR) were calculated. The pH of each tested solution was also measured.

Results

Without HAp incorporation, the DC and PR of the strong APLP (7.8% and 0.12%/s, respectively) were much lower than those of the mild AEB (85.5% and 5.7%/s, respectively). The DC and PR of APLP displayed an apparent increasing trend with the HAp content. For example, the DC increased from 7.8% to 58.4% and the PR increased from 0.12 to 3.8%/s when the HAp content increased from 0 to 7 wt%. In contrast, the DC and PR of AEB were much less affected by the HAp content. The observations were correlated well with the spectral and pH changes, which indicated that APLP underwent a higher extent of chemical reaction with HAp than AEB.

Conclusions

The results disclosed the important role of the acidic monomer/HAp chemical reaction in improving the photopolymerization of the strong (low-pH) self-etching adhesives such as APLP. The phenomenon of polymerization improvement strongly depended on the adhesive aggressiveness.     

Wetting ability of single-component self-etching adhesives on enamel and dentin

PURPOSE: To assess the contact angle, volume loss and nanoleakeage profile of five one-component self-etching adhesive formulations that differed in their HEMA content, on enamel and dentin. METHODS: Contact angles of drops from each adhesive system were measured over 40 enamel and dentin flat surfaces. Volumetric changes were measured as well. The adhesives were then applied over repolished surfaces according to manufacturers' recommendations, covered with a microfilled restorative composite and the samples were silver infiltrated and prepared for evaluation in a scanning electron microscope. RESULTS: On enamel and dentin surfaces, the contact angles decreased with increasing HEMA content. A correlation was observed between contact angle, volume loss and HEMA content on both substrates.     

The microtensile bond strength of self-etching adhesives to ground enamel

It is uncertain whether single-phase self-etching adhesives form bonds to enamel as reliable as those of etch-and-rinse adhesives. This study compared the microtensile bond strengths to ground enamel of three self-etching adhesive systems, a self-etching primer system and an etchand-rinse adhesive system. Human enamel was ground flat with 320-grit silicone carbide paper. The self-etching adhesives iBond (Heraeus Kulzer), Prompt L-Pop (3M ESPE) and Xeno III (Caulk/Dentsply), the adhesive with a self-etching primer Clearfil SE Bond (Kuraray) and the etch-and-rinse adhesive Scotchbond Multipur-pose (3M/ESPE) were applied as directed, followed by a core of the same manufacturers' hybrid resin composite. A microtensile bond strength evaluation was performed after 48 hours of water storage, using untrimmed beams approximately 0.9 mm2 in cross-sectional area at a crosshead speed of 0.6 mm/minute. There were no pretest failures in any group, and failures were predominately adhesive or mixed. Adhesion to enamel of Clearfil SE was not significantly different from Scotchbond Multi-Purpose, while the three self-etching adhesive systems demonstrated significantly lower bond strengths (One-way ANOVA, Tukey-Kramer Multiple-Comparison Test, p < 0.00001).     

Microtensile bond strength of self-etching adhesives to enamel and dentin

PURPOSE: To measure the microtensile bond strength to enamel and dentin of three self-etching adhesives in comparison with a total-etch two-step system as a control. MATERIALS AND METHODS: A total of 40 extracted human molars were stored in saline solution until use, then divided into 4 groups of 10 teeth (one group per adhesive system). Half of each of these groups underwent bond strength tests on enamel, and the other half was used for adhesion testing on dentin. The following experimental groups (n = 5) were then formed: E(1) Adper Prompt-L-Pop (AP, 3M ESPE) on enamel; E(2) Xeno CF II (X, Sanking Kogyo) on enamel; E(3) AdheSE (AS, Ivoclar-Vivadent) on enamel; E(4) Excite (EX, Ivoclar-Vivadent) on enamel; D(1) AP on dentin; D(2): X on dentin; D(3) AS on dentin; D(4) EX on dentin. Each tooth yielded 15 to 20 sticks about 0.9 x 0.9 mm in cross-sectional area for microtensile testing. Specimens were loaded in tension at a crosshead speed of 0.5 mm/minute, and bond strength at failure was calculated in MPa. A two-way ANOVA was applied to test for significance of the differences among the groups. RESULTS: The bond strength values of Excite (the control) were significantly higher than those of the test products on enamel (42.92+/-4.8 MPa) and on dentin (45.80+/-5.79 MPa). The self-etching adhesives AdheSE (28.48+/-4.71 MPa) and Xeno CF II (27.22+/-2.74 MPa) revealed significantly stronger adhesion than Adper Prompt-L-Pop (20.16+/-2.07 MPa) on dentin. On enamel, all self-etching test materials performed similarly. The substrate did not appear to have a significant influence on adhesion, as each material reached comparable levels of bond strength on enamel and dentin. CONCLUSION: On both substrates the self-etching adhesives tested performed significantly worse than did the total-etch system.     

Bonding characteristics of self-etching adhesives to intact versus prepared enamel

Purpose: This study tested the null hypothesis that the preparation of the enamel surface would not affect the enamel microtensile bond strengths of self‐etching adhesive materials. Materials and Methods: Ten bovine incisors were trimmed with a diamond saw to obtain a squared enamel surface with an area of 8 × 8 mm. The specimens were randomly assigned to five adhesives: (1) ABF (Kuraray), an experimental two‐bottle self‐etching adhesive; (2) Clearfil SE Bond (Kuraray), a two‐bottle self‐etching adhesive; (3) One‐Up Bond F (Tokuyama), an all‐in‐one adhesive; (4) Prompt L‐Pop (3M ESPE), an all‐in‐one adhesive; and (5) Single Bond (3M ESPE), a two‐bottle total‐etch adhesive used as positive control. For each specimen, one half was roughened with a diamond bur for 5 seconds under water spray, whereas the other half was left unprepared. The adhesives were applied as per manufacturers' directions. A universal hybrid composite resin (Filtek Z250, 3M ESPE) was inserted in three layers of 1.5 mm each and light‐cured. Specimens were sectioned in X and Y directions to obtain bonded sticks with a cross‐sectional area of 0.8 ± 0.2 mm². Sticks were tested in tension in an Instron at a cross‐speed of 1 mm per minute. Statistical analysis was carried out with two‐way analysis of variance and Duncan's test at p <. 05. Ten extra specimens were processed for observation under a field‐emission scanning electron microscope. Results: Single Bond, the total‐etch adhesive, resulted in statistically higher microtensile bond strength than any of the other adhesives regardless of the enamel preparation (unprepared = 31.5 MPa; prepared = 34.9 MPa, not statistically different at p < 05). All the self‐etching adhesives resulted in higher microtensile bond strength when enamel was roughened than when enamel was left unprepared. However, for ABF and for Clearfil SE Bond this difference was not statistically significant at p > 05. When applied to ground enamel, mean bond strengths of Prompt L‐Pop were not statistically different from those of Clearfil SE Bond and ABF. One‐Up Bond F did not bond to unprepared enamel. Commercial self‐etching adhesives performed better on prepared enamel than on unprepared enamel. The field‐emission scanning electron microscope revealed a deep interprismatic etching pattern for the total‐etch adhesive, whereas the self‐etching systems resulted in an etching pattern ranging from absent to moderate. CLINICAL SIGNIFICANCE For the recently introduced all‐in‐one self‐etching dental adhesives, instrumentation of enamel may be critical for their ability to optimally bond to enamel.     

Inter-crystallite nanoretention of self-etching adhesives at enamel imaged by transmission electron microscopy

The purpose of this in vitro study was to analyse the mode of action of self-etching adhesive systems when applied for resin-to-enamel bonding. Transmission electron microscopy was used to investigate the enamel-resin interface after application of non-rinsing self-etching adhesive systems based on phosphoric acid estered methacrylates (Clearfil Liner Bond 2, Clearfil SE Bond, Etch & Prime 3.0 and Resulcin AquaPrime) compared with conventional phosphoric acid etching and bonding (Heliobond). Non-decalcified ultrathin sections from the interface between enamel and self-etching adhesive systems revealed a 1.5-3.2-microm deep enamel surface layer characterized by a less-dense arrangement of enamel crystallites separated from each other by nanometer-sized spaces. A 1.5-3.2-microm wide, netlike resinous structure was observed in corresponding decalcified specimens, indicating that self-etching priming agents dissolve the peripheral and central part of the enamel crystallites, while simultaneously promoting inter- and intra-crystallite monomer infiltration. A similar pattern, but greater depth (6.9 microm) of enamel surface hybridization was found in the phosphoric acid-etched and bonded specimens. The nanoretentive interlocking between enamel crystallites and resin could explain the potential of self-etching adhesive systems in resin-to-enamel bonding despite the less distinct enamel etching pattern observed in scanning electron microscopy investigations.     

Relationship between degree of polymerization and enamel bonding strength with self-etching adhesives

PURPOSE: To investigate the relationship between the degree of conversion of double bonds of all-in-one adhesives and their shear bond strength on ground human enamel. MATERIALS AND METHODS: Six commercially available systems and one experimental adhesive were tested: Absolute (ABS; Dentsply-Sankin), Clearfil S3 Bond (CSB; Kuraray), G-Bond (GBO; GC), Hybrid Bond (HYB; Sun Medical), iBond (IBO; Heraeus Kulzer), Xeno IV (XEN; Dentsply Caulk), and experimental iBond NG (ING; Heraeus Kulzer). Conventional shear bond strengths (SBS, n=8) of adhesive-coated enamel specimens bonded to Venus composite (Heraeus Kulzer) and degrees of conversion (DC) (FTIR, n=5) were determined after 1 and 10 min, 1, 2, and 24 h of storage. Data were statistically analyzed using ANOVA and Duncan's post hoc test (0 < 0.05). RESULTS: The adhesives' SBS (MPa) and DC (%) by testing time followed logarithmic regression lines established by the least square method. Mean shear bond strengths after 1 min/24 h were: ABS 9.8/14.9; CSB 14.7/23.4; GBO 14.8/22.0; HYB 9.7/17.0; IBO 11.3/22.3; XEN 9.1/17.3; ING 9.7/25.6. The corresponding mean DC values were: ABS 51.3/66.2; CSB 83.1/90.8; GBO 75.8/87.7; HYB 49.6/67.2; IBO 72.6/93.7; XEN 61.6/74.1; ING 64.9/89.1. Linear regressions for the relationship DC vs. SBS were significant with coefficients of determination (r2) between 0.72 and 0.97. CONCLUSION: Despite similar acidity, the adhesives showed different SBSs on enamel. Based on the relationships between DC and SBS, the cohesive failure patterns observed, and the composition-property relations discussed, it is concluded that the percentage DC is the main parameter influencing an adhesive's bonding efficacy to ground enamel.     

Sealant and composite bond strength to enamel with antibacterial/self-etching adhesives

INTRODUCTION: The enamel in pits and fissures undergoing preventive or ultraconservative resin restorations may be affected by secondary caries. An antibacterial adhesive bond may be a useful choice to prevent and reduce demineralization. OBJECTIVES: The purpose of this study was to determine the shear bond strength of an experimental antibacterial bond, a self-etch bond, and an ormocer-based adhesive bond using an ormocer-based fissure sealant and a composite resin on intact enamel. METHODS: Twenty-four extracted human molars were sectioned bucco-lingually to obtain two flat and sound enamel surfaces. Forty-eight specimens were randomly assigned into four groups. The groups were prepared to receive the following treatments: (1) Admira Bond + Admira Seal (n = 10); (2) ABF Bond + Admira Seal (n = 11); (3) Clearfil SE Bond + Clearfil AP-X (n = 12); and (4) ABF Bond + Clearfil AP-X (n = 11). A cylindrical mould was placed over the bonded surface, and both materials were applied according to the instructions. The teeth were thermocycled 500 cycles between 5 and 55 degrees with a dwell time of 30 s. For shear bond strength testing, the load was applied vertically to the base of the mould. The cross-head speed was 5 mm min(-1). RESULTS: The maximum load that a specimen can withstand until failure was determined and shear bond strength was calculated by dividing the load at failure by the surface area of the mould. The results (median, minimum and maximum, respectively) for the four groups were: (1) 7.9, 4.2 and 13.6 MPa; (2) 8.6, 2.6 and 15.9 MPa; (3) 5.9, 5.3 and 8.2 MPa; and (4) 8.8, 3.0 and 19.2 MPa. Kruskal-Wallis and Mann-Whitney U-tests were performed for the statistical analysis. Groups 3 and 4 were statistically significantly different (P = 0.005; P < 0.05). There was no statistically significant difference between the sealant and composite groups for ABF (P = 0.375). Fracture sites were viewed by microscope under x 16 magnification to determine if the mode of failure was adhesive or cohesive. The results (number of adhesive failed specimens and number of cohesive failed specimens, respectively) for the four groups were: (1) 7 and 3; (2) 3 and 8; (3) 2 and 9; and (4) 8 and 3. CONCLUSION: The ABF bond has sufficiently physical qualities to be used under fissure sealant and composite resin on uncut enamel, its antibacterial efficiency notwithstanding.