Comparison of depth of dentin etching and resin infiltration with single-step adhesive systems

Effect of Active Application on Bond Durability of Universal Adhesives

The purpose of this study was to determine the effect of different adhesive application methods and etching modes on the dentin bond durability of universal adhesives under thermal cycling (TC). All-Bond Universal (Bisco), Adhese Universal (Ivoclar Vivadent), and Scotchbond Universal (3M ESPE) were used as adhesives. In total, 600 bovine teeth with exposed dentin were divided into 12 groups according to the type of adhesive and subjected to the following bonding procedures: 1) etch-and-rinse mode with active application; 2) etch-and-rinse mode with inactive application; 3) self-etch mode with active application; and 4) self-etch mode with inactive application. Bonded specimens were stored in distilled water at 37°C for 24 hours and then subjected to 5000, 10,000, 30,000, or 50,000 TC between 5°C and 55°C before shear bond strength (SBS) testing, creating a division into a total of five different storage conditions. Baseline specimens were stored in distilled water at 37°C for 24 hours. The SBS test was performed at a cross-head speed of 1.0 mm/min. Three-way analysis of variance revealed that all the factors of application mode, adhesive, and thermal cycle period significantly influenced the SBS values (p<0.001), regardless of the etching mode. In the baseline groups, all of the tested adhesives with active application had higher SBS values than those with inactive application, regardless of etching mode. In the TC groups, significantly lower SBS values were observed at 50,000 TC with inactive application compared to those with active application, regardless of the etching mode. From the scanning electron microscopy observation of demineralized and deproteinized resin/dentin interfaces, dense resin tags longer than 50 μm were observed in the etch-and-rinse with active application group. On the other hand, the resin tags in self-etch mode were sparse, thin, and much shorter than those in etch-and-rinse mode. Comparing the penetration status of the resin tags with active and inactive application in self-etch mode, the resin tag penetration with inactive application was much lower than that with active application. Active application is effective in enhancing the dentin bond durability of universal adhesives. When using universal adhesives with different etching modes, practitioners should select the optimal etching mode and appropriate application method in accordance with the cavity conditions.

Nanoleakage evaluation at adhesive-dentin interfaces by different observation methods

The purpose of this study was to evaluate the capability and characteristics of different nanoleakage observation methods, including light microscope (LM), field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), and confocal laser scanning microscope (CLSM). Dentin specimens were bonded with either an etch-and-rinse adhesive (SBMP) or a self-etch adhesive (GB), and prepared for nanoleakge evaluation according to different observation methods. LM, FESEM and CLSM results demonstrated that the SBMP group showed more interfacial nanoleakage than the GB group (p<0.05); by contrast, no significant difference was found in TEM results (p>0.05), however, TEM illustrated concrete nanoleakage forms or patterns. The results suggested that different observation methods might exhibit distinct images and a certain degree of variations in nanoleakage statistical results. Researchers should carefully design and calculate the optimum assembly in combination with qualitative and quantitative approaches to obtain objective and accurate nanoleakage evaluation.

Effect of Phosphoric Acid Pre-etching on Fatigue Limits of Self-etching Adhesives

The purpose of this study was to use shear bond strength (SBS) and shear fatigue limit (SFL) testing to determine the effect of phosphoric acid pre-etching of enamel and dentin prior to application of self-etch adhesives for bonding resin composite to these substrates. Three self-etch adhesives—1) G- ænial Bond (GC Corporation, Tokyo, Japan); 2) OptiBond XTR (Kerr Corp, Orange, CA, USA); and 3) Scotchbond Universal (3M ESPE Dental Products, St Paul, MN, USA)—were used to bond Z100 Restorative resin composite to enamel and dentin surfaces. A stainless-steel metal ring with an inner diameter of 2.4 mm was used to bond the resin composite to flat-ground (4000 grit) tooth surfaces for determination of both SBS and SFL. Fifteen specimens each were used to determine initial SBS to human enamel/dentin, with and without pre-etching with a 35% phosphoric acid (Ultra-Etch, Ultradent Products Inc, South Jordan, UT, USA) for 15 seconds prior to the application of the adhesives. A staircase method of fatigue testing (25 specimens for each test) was then used to determine the SFL of resin composite bonded to enamel/dentin using a frequency of 10 Hz for 50,000 cycles or until failure occurred. A two-way analysis of variance and Tukey post hoc test were used for analysis of SBS data, and a modified t-test with Bonferroni correction was used for the SFL data. Scanning electron microscopy was used to examine the area of the bonded restorative/tooth interface. For all three adhesive systems, phosphoric acid pre-etching of enamel demonstrated significantly higher (p&lt;0.05) SBS and SFL with pre-etching than it did without pre-etching. The SBS and SFL of dentin bonds decreased with phosphoric acid pre-etching. The SBS and SFL of bonds using phosphoric acid prior to application of self-etching adhesives clearly demonstrated different tendencies between enamel and dentin. The effect of using phosphoric acid, prior to the application of the self-etching adhesives, on SBS and SFL was dependent on the adhesive material and tooth substrate and should be carefully considered in clinical situations.

Morphological and chemical comparative analysis of the human and bovine dentin-adhesive layer

Micro energy-dispersive X-ray fluorescence spectrometry (µ-EDXRF) and scanning electron microscopy (SEM) were used to evaluate dentin treated with an etch and rinse adhesive (ER) and a self-etch adhesive (SE). Ten human molars (H) and ten bovine anterior teeth (B) were prepared (exposure of dentin and divided in the middle) and allocated into two different adhesion strategy groups per substrate (n=40). µ-EDXRF data and SEM images were obtained before and after treatment. Untreated dentin of both substrates did not differ in terms of Ca (p<0.1503), P (p<0.2986) or Ca/P ratio (p<0.1400). H-SE and B-SE specimens showed reduced P content (p<0.0001; p<0.0002), while H-ER and B-ER specimens showed reduced Ca and P content (p<0.0001; p<0.0001) when compared with untreated specimens. The Ca/P ratio was significantly higher in H-ER and B-ER specimens than in H-SE and B-SE specimens (p<0.0001; p<0.0080). Untreated dentin showed a homogeneous elemental distribution. However, after adhesive treatments, the surface of the dentin showed an irregular demineralization pattern. The resin tags and adhesive layer were shorter in bovine specimens than in human specimens due to morphological differences.

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 γS⁺ component increased slightly when drying was performed with a stream of warm air, whereas that of the γS⁻ 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.

Effect of warm air-drying on dentin bond strength of single-step self-etch adhesives

The effect of warm air-drying on the dentin bond strengths of the single-step self-etch adhesives was determined. The adhesives were applied to bovine dentin followed by drying in a stream of warm air for 5, 10, and 15 s at 37°C. Resin composites were condensed into a mold and polymerized. Specimens were stored in distilled water at 37°C for 24 h, then shear tested. The surface free-energies were determined by measuring the contact angles of three test liquids placed on the cured adhesives. The dentin bond strengths varied according to the air-drying time. The value of the acid component increased slightly when drying was performed with a stream of warm air, whereas that of the base component decreased significantly. These data suggested that warm air-drying was essential to obtain adequate bond strengths, although increasing the drying time did not significantly influence the bond strength.

Effect of air-drying dentin surfaces on dentin bond strength of a solvent-free one-step adhesive

The purpose was to evaluate the effect of air-drying dentin surfaces on the microtensile bond strength (μTBS) of a solvent-free onestep adhesive (Bond 1 SF). Twelve human molars were ground with 600-grit SiC paper. Before applying bonding agent, the dentin surface was rinsed with distilled water and blot-dried with tissue paper, followed by air-drying for 0, 3, 30, and 60 s using with a dental air syringe. After applying and curing Bond 1 SF, resin composite was incrementally built up. Specimens were then stored in distilled water for 24 h and then μTBSs were measured at a cross-head speed of 1 mm/min. Higher μTBS were observed when the dentin surface was air-dried for 3 s (33.2±6.8MPa)>0 s (26.7±4.5MPa)>30 s (22.6±5.5MPa)=60 s (20.4±5.0MPa). The results suggested that prolonged air-drying of the dentin surface removed water and decreased the bond strengths of Bond 1 SF.

Ethanol-wet bonding may improve root dentine bonding performance of hydrophobic adhesive

OBJECTIVES

The current study aimed to assess ethanol-wet dentine surfaces by atomic force microscopy (AFM), and to evaluate the efficacy of ethanol-wet bonding on root dentine by determining the shear bond strength (SBS) and interfacial nanoleakage expression.

METHODS

Flat dentine slices from human premolar roots were randomly grouped into five. All specimens were acid-etched, rinsed, and left moist. They were then treated with 100% ethanol for 0s (control group), 20s (Group 1), 60s (Group 2), three 60s periods (Group 3), or stepwise ethanol application (Group 4). After treatment, each group was bonded either with Adper™ Scotchbond™ Multi-Purpose (Scotchbond) or experimental hydrophobic adhesive. Nano-scale adhesion forces (Fad) were probed by AFM and analysed using one-way ANOVA. The SBS results were analysed using two-way ANOVA. Tukey's test was employed for multiple comparisons.

RESULTS

Ethanol-wet protocols significantly decreased the value of Fad (p<0.001). When bonded with Scotchbond, ethanol treatment did not affect the bond strength (p>0.05), but decreased the interfacial nanoleakage. The SBS values of the groups bonded with hydrophobic adhesive varied with different ethanol-wet protocols (p<0.05). Decreased nanoleakage was manifested in all experimental groups, except Group 1. Compared with the classical water-wet bonding with Scotchbond in the control group, Group 4 bonded with hydrophobic adhesive exhibited a significantly higher bond strength (p<0.05).

CONCLUSIONS

Ethanol-wet bonding using a stepwise ethanol application protocol may have potential benefits in the root dentine bonding of hydrophobic adhesive.

Influence of storage conditions of adhesive vials on dentin bond strength

This study was carried out to examine the effect of storage conditions of adhesive vials on the dentin bond strength of single-step self-etch adhesive systems. The adhesive/resin composite combinations used were: Absolute 2/Ceram.X(AB), Adper Prompt L-Pop/Filtek Supreme(AP), Bond Force/Estelite sigma Quick(BF), Clearfil tri-S Bond/Clearfil AP-X(CT) and G-Bond/Gradia Direct(GB). Vials of adhesives were stored at 5 degrees C, 23 degrees C or 40 degrees C. Specimens for the dentin bond strength tests were made after 0, 1, 2, 3, 4, 5 and 6 months. Labial bovine mandibular incisor dentin was wet ground with #600 SiC. The adhesives were applied according to the manufacturer's instructions. After adhesive light irradiation, resin composite cylinders were created (4 mm x 2 mm) and polymerized (n = 10). Samples were stored in 37 degrees C distilled water for 24 hours, then shear tested at a crosshead speed of 1.0 mm/minute. ANOVA and Dunnet tests were performed at a significance level of 0.05. Scanning electron microscopic (SEM) observations of the dentin surfaces were made. Bond strengths varied, with storage conditions ranging from 2.2 +/- 1.4 to 9.3 +/- 2.4 MPa for AB, 4.5 +/- 1.5 to 13.3 +/- 2.7 MPa for AP, 5.1 +/- 1.9 to 5.1 +/- 1.9 MPa for BF, 7.7 +/- 1.9 to 19.7 +/- 2.0 MPa for CT and 7.4 +/- 1.3 to 15.7 +/- 2.8 MPa for GB. With longer storage periods and higher temperatures, significant decreases in bond strength were found for all the adhesives. From SEM observation, the etching effect of the adhesives was weakened and the remaining smear layer was observed. The data suggests that the storage conditions of adhesive vials significantly affects the bond strengths of single-application self-etch adhesive systems.

Effects of Storage Temperature on the Shelf Life of One-step and Two-step Self-etch Adhesives

Storage temperature affects the alteration rate of one-step adhesives for all-in-one adhesive systems and self-etching primer for two-step adhesive systems. Their shelf life is strongly dependent on the storage temperature and time period. Storage under 20°C extends their shelf life.

Four-year water degradation of a total-etch and two self-etching adhesives bonded to dentin

OBJECTIVES

To evaluate effect of direct and indirect water storage on the microtensile dentin bond strength of one total-etch and two self-etching adhesives.

METHODS

The adhesive materials were: one total-etch adhesive; 'Admira Bond' and two self-etch adhesives; 'Clearfil SE Bond' and 'Hybrid Bond'. Freshly extracted human third molar teeth were used. In each tooth, a Class I cavity (4mmx4mm) was prepared in the occlusal surface with the pulpal floor extending approximately 1mm into dentin. The teeth were divided into three groups (n=18). Each group was restored with the resin composite 'Clearfil APX' using one of the tested adhesives. For each experimental group 3 test procedures (n=6) were carried out: Procedure A: the teeth were stored in water for 24h (control), then sectioned longitudinally, buccolingually and mesiodistally to get rectangular slabs of 1.0-1.2mm thickness on which a microtensile test was carried out. Procedure B: the teeth were also sectioned; however, the slabs were stored in water at 37 degrees C for 4 years before microtensile testing (direct water storage). Procedure C: the teeth were kept in water at 37 degrees C 4 years before sectioning and microtensile testing (Indirect water storage). During microtensile testing the slabs were placed in a universal testing machine and load was applied at cross-head speed of 0.5mm/min.

RESULTS

For the 24h control, there was no significant difference in bond strength between the three tested adhesives. After 4 years of indirect water storage, the bond strength decreased but the reduction was not significantly different from those of 24h. After 4 years of direct water storage, the bond strengths of all tested adhesives were significantly reduced compared to their 24h results.

CONCLUSION

All the tested adhesives showed no reduction in bond strength after indirect water exposure for 4 years. After 4-year direct water exposure, the bond produced by all tested adhesives was unable to resist deterioration.

Influence of thermal cycling on dentin bond strengths of single-step self-etch adhesive systems

This study investigated the influence of thermal cycling on the dentin bond strengths of single-step self-etch adhesive systems. The Absolute, Clearfil Tri-S Bond, G-Bond and One-Up Bond F Plus systems were used. Bovine mandibular incisors were mounted in self-curing resin, and the facial surfaces were wet ground with #600 SiC paper. Adhesives were applied to the prepared dentin surfaces, and they were light irradiated according to each manufacturer's instructions. Resin composites were condensed into a mold (4 mm in diameter and 2 mm in height) and light irradiated for 30 seconds. Bonded specimens were divided into three groups and subjected to different storage conditions as follows: 37 degrees C water for 24 hours; 37 degrees C water for 24 hours followed by 10,000 thermal cycles between 5 degrees C and 60 degrees C or 37 degrees C water for 24 hours followed by 20,000 thermal cycles between 5 degrees C and 60 degrees C. Ten samples per group were tested in a shear mode at a crosshead speed of 1.0 mm/minute. Analysis of variance and Tukey's HSD test at the 0.05 significance level were used to compare the three storage conditions for each adhesive system. After 24 hours storage in water, the mean dentin bond strengths ranged from 11.4 MPa to 17.1 MPa. The Clearfil Tri-S Bond system showed the highest bond strength. After 10,000 thermal cycles, the mean bond strengths remained unchanged except for those of the Clearfil Tri-S Bond system, which significantly increased. Significant decreases in bond strength were observed for the Absolute and One-Up Bond F Plus systems after 20,000 thermal cycles. Failure mode was commonly due to adhesive breakdown associated with partial cohesive failure of the adhesive resin. From the results of this study, in terms of simplifying the clinical procedure, the benefit of using single-step self-etch systems might be acceptable.

Hardness and Elasticity of Sound and Caries-affected Primary Dentin Bonded with One-step Self-etch Adhesive

Biomechanical properties of bonded dentin are important for resin restorations. We hypothesized that there are no differences in the hardness and elasticity of sound and caries-affected primary dentin bonded with a one-step self-etch adhesive. Resin-dentin interfaces in sound and caries-affected primary dentin were measured with a nano-indentation tester and observed with SEM and TEM. Interfacial dentin hardness was similar for sound and caries-affected dentin, but significantly lower than the underlying intact dentin. As for the Young's modulus of interfacial dentin, both substrates exhibited significantly lower values than the subsurface dentin. Further, the Young's modulus of interfacial dentin was significantly lower in caries-affected dentin. TEM revealed extensive interfacial nanoleakage in bonded sound dentin, while it was minimal in bonded caries-affected dentin. However, in the latter, silver deposits were identified within the porous substrate. Shorter application time and/or improvement of the adhesive components may be required to obtain stable adhesion in primary dentin.

Hardness, elasticity, and ultrastructure of bonded sound and caries-affected primary tooth dentin

Biomechanical properties of bonded dentin are important factors for resin restoration. We evaluated the hardness and elastic modulus of bonded sound and caries-affected primary tooth dentin using a one-step adhesive system, and observed the microstructure of the bonded interface. Six sound and six carious primary teeth were used. For sound teeth, flat occlusal dentin surfaces were prepared with a water-cooled high-speed diamond bur. For carious teeth, infected dentin was stained with a caries detector and removed with a water-cooled low-speed round steel bur and hand instruments. The prepared dentin was bonded with One-Up Bond F Plus (Tokuyama Dental Co., Tokyo, Japan). The resin-dentin interface and dentin beneath the interface were measured with a nano-indentation tester and observed with SEM and TEM. For both the carious and sound teeth, there was no significant difference between the hardness of the interfacial dentin and dentin 10-80 microm beneath the interface. However, the Young's modulus of the interfacial dentin was significantly lower than the dentin 40-80 microm (carious teeth) or 50-80 microm (sound teeth) beneath the interface. Both the hardness and Young's modulus of the interfacial dentin were not significantly different between the carious and sound teeth. Compared to the sound dentin, the hybrid layer on the caries-affected dentin was thicker and exhibited more complicated morphologic features. The thickness of the hybrid layers was generally less than 1 microm.

Bonding Efficacy of Single-step Self-etch Systems to Sound Primary and Permanent Tooth Dentin

Single-step self-etch systems are capable of producing a predictable bond to primary dentin, although the bond strength was found to be lower than permanent dentin.

Hardness and elasticity of bonded carious and sound primary tooth dentin

OBJECTIVE

Although biomechanical properties of bonded dentin are important for resin restorations, no information for primary teeth has been reported. This study evaluated the hardness and elastic modulus of bonded carious and sound primary tooth dentin using two adhesive systems.

METHODS

Twelve sound primary molars and 17 carious primary molars were bonded with Clearfil SE Bond (SE: Kuraray) or Single Bond (SB: 3M) and the resin-dentin interface was measured with a nano-indentator and observed with a SEM. Data was statistically analyzed using ANOVA subsequent application of Fisher's PLSD at p<0.01.

RESULTS

Compared to the dentin beneath the interface, the hardness of the interface dentin was not significantly different (carious-SE, sound-SE and sound-SB groups) or was significantly higher (carious-SB group). Young's modulus of the interface dentin was not significantly different (carious-SE, carious-SB and sound-SB groups) or was significantly lower (sound-SE group) than that for the dentin beneath the interface. In the comparison of the measurement on the interface dentin, the hardness showed no significant differences among all the groups. The Young's modulus of the sound-SE group was significantly lower than that of the carious-SE and sounds-SB groups, but no significant difference was observed between the carious-SB and other groups.

CONCLUSIONS

Physical properties of bonded primary tooth dentin might differ from that of permanent tooth dentin.

Effect of thermal cycling on bond strengths of single-step self-etch adhesives to bovine dentin

The purpose of this study was to clarify the effect of thermal cycling on dentin bond strengths of single-step self-etch adhesives. Five commercially available single-step self-etch systems were used. The adhesives were applied to the dentin surfaces of bovine incisors, and then light-irradiated. Resin composites were condensed into a mold and light-irradiated. Bonded specimens were divided into two groups and stored in water at 37 degrees C for 24 h without thermal cycling, or in water at 37 degrees C for 24 h followed by 10,000 thermal cycles between 5 degrees C and 60 degrees C. Ten samples per group were tested for shear strength at a crosshead speed of 1.0 mm/min. The data were analyzed by Student's t test and Tukey HSD test at a probability level of 0.05. After 24 h of storage in water, the mean dentin bond strengths ranged from 9.3 MPa to 14.0 MPa. After 10,000 thermal cycles, the mean bond strengths remained unchanged. Failure after the test was commonly due to adhesive breakdown associated with partial cohesive failure of the resin. The present results suggest that the benefit of using single-step self-etch systems, in terms of simplifying the clinical procedure, might be acceptable even after thermal stresses.