Effect of primers on bonding agent polymerization

Influence of primer contamination on the bonding interface of enamel pre-etched with phosphoric acid

In this study, the influence of primer contamination on enamel bonding was analyzed. Adper Scotchbond Multi-Purpose (SMP), CLEARFIL SE Bond 2 (SE2), Scotchbond Universal (SBU) Adhesive, and Scotchbond Etchant (35% phosphoric acid; PA) were used. Ground bovine enamels were divided into eight groups based on the bonding protocols. The bonding interfaces after an acid-base challenge were observed via scanning electron microscopy to determine the acid-base resistant zone (ABRZ). Moreover, the bonding interfaces after the nanoleakage challenge were analyzed via energy-dispersive X-ray spectroscopy. ABRZ was observed in all the samples except PA_ONLY (applied PA etching, No primer and No adhesive resin). The funnel-shaped erosion was detected only in X_SBU (applied SBU without PA etching). The nanoleakage test revealed silver patterns in some groups. The nanoleakage, i.e., the penetration of the silver ions, was detected in the groups wherein primer was applied on PA-pre-etched enamel.

Does Shortened Application Time Affect Long-Term Bond Strength of Universal Adhesives to Dentin?

OBJECTIVE

This study evaluated the effect of shortened application time on long-term bond strength with universal adhesives.

METHODS AND MATERIALS

Three universal adhesives were used: Clearfil Universal Bond (CU, Kuraray Noritake Dental Inc, Tokyo, Japan), Scotchbond Universal Adhesive (SB, 3M ESPE, St Paul, MN, USA) or G-Premio Bond (GP, GC Corp, Tokyo, Japan). Sixty molars were cut to expose midcoronal dentin and prepared with a regular diamond bur. Each adhesive was applied either according to the manufacturer's instruction or with shortened time. Specimens were stored in distilled water at 37°C for 24 hours and then cut into resin-dentin sticks. Microtensile bond strength (μTBS) was tested after either 24 hours or 1 year of water storage. Data were analyzed by the three-way ANOVA and Duncan tests ( α=0.05). Fracture modes were analyzed under a scanning electron microscope (SEM). One dentin stick per group was selected after fracture mode analysis and further observed using transmission electron microscopy (TEM). Six additional dentin discs were prepared and conditioned with each adhesive under the different application time to observe the adhesive-smear layer interaction by SEM.

RESULTS

Shortened application time affected the μTBS ( p<0.001) while storage time did not affect bond strength ( p=0.187). A significant effect of shortened application time on μTBS was observed in the CU at 1 year and in the GP at both storage times.

CONCLUSIONS

One-year storage time had no effect on the μTBS of universal adhesives to bur-cut dentin. The performance of universal adhesives can be compromised when applied using a shortened application time.

Mechanical viscoelastic behavior of dental adhesives

OBJECTIVES

The purpose of the study was to evaluate the mechanical properties of dental adhesive materials at different testing temperatures after dry and wet storage.

METHODS

Specimens (d=1 mm, l=18 mm) from six materials were tested: Silorane Adhesive System (SL), Heliobond (HE), One-Step Plus (OS), Optibond Solo Plus (OP), cmf Adhesive System (CF) and Protobond (PR). Static and creep testing was performed by applying a constant torque below the proportional limit of the materials, while dynamic testing consisted of dynamic torsional loading. Experiments were performed after 24h of dry and wet storage under temperatures from 21°C to 50°C and various viscoelastic parameters were calculated.

RESULTS

Shear modulus ranged from 0.19 to 1.99 GPa, while flexural modulus from 0.67 to 5.69 GPa. Most of the materials were affected by the presence of water and increase of temperature. OP showed the highest recovery after creep, while SL exhibited the highest permanent deformation.

SIGNIFICANCE

Contact with water after polymerization and increase of temperature resulted in a decline of the mechanical properties, especially for the HEMA-containing adhesives.

Bonding to dentin as a function of air-stream temperatures for solvent evaporation

This study evaluated the influence of solvent evaporation conditions of acid-etching adhesives. The medium dentin of thirty extracted human third molars was exposed and bonded to different types of etch-and-rinse adhesives: 1) Scotchbond Multi-Purpose (SBMP) ; water-based; 2) Adper Single Bond 2 (SB) ; ethanol/water-based, and 3) Prime & Bond 2.1 (PB) ; acetone-based. Solvents were evaporated at air-drying temperatures of 21ºC or 38ºC. Composite buildups were incrementally constructed. After storage in water for 24 h at 37ºC, the specimens were prepared for bond strength testing. Data were analyzed by two-way ANOVA and Tukey's test (5%). SBMP performed better when the solvents were evaporated at a higher temperature (p < 0.05). Higher temperatures did not affect the performance of SB or PB. Bond strength at room temperature was material-dependent, and air-drying temperatures affected bonding of the water-based, acid-etching adhesive.

Effects of water-storage on the physical and ultramorphological features of adhesives and primer/adhesive mixtures

The aims of this study were to evaluate the ultimate tensile strength (UTS) and elastic modulus (E) of adhesives, and primer/adhesive mixtures after aging for 6 months in water or oil; and to compare silver uptake patterns under the TEM. A one-step self-etching adhesive (One-up Bond F: OB), two two-step self-etching primers (SE Bond: SE and Protect Bond: CP), and two etch-and-rinse systems (Single Bond: SB and Prime&Bond NT: PB) were used. Bonding and primer solutions of self-etching systems were also mixed (SE+P and CP+P). Most adhesives presented decreased UTS after water-storage. Similar or increased UTS was observed after oil storage. Except for SB, E values did not change after water-storage, but they increased after storage in oil. OB, CP+P and SE+P presented more silver uptake. The effects of water-storage were material-dependent, and significantly affected the mechanical properties and silver uptake patterns of adhesives.

Effect of dentine smear layer on the performance of self-etching adhesive systems: A micro-tensile bond strength study

This study aimed to evaluate the effect of the smear layer on the micro-tensile bond strength when two self-etching adhesives were used with different techniques. Flat dentine surfaces were prepared using either medium grit diamond burs or tungsten carbide burs. Ten specimens from each prepared surfaces were subjected for smear layer evaluation under SEM. Forty specimens from each of the prepared surfaces were further divided into two groups, bonded with either Clearfil SE Bond (SE) or Clearfil S(3) Bond (S3) using one of four applications (as manufacturer's instructions, agitation, reapplication, and increased application time), restored with composites and subjected to a micro-tensile bond strength test. Smear layers created with diamond burs were thicker than those created with tungsten carbide burs. Surfaces prepared with tungsten carbide burs produced a higher bond strength than those prepared with diamond burs and the same type of adhesive resin. SE demonstrated a higher bond strength than S3 for all surfaces. S3 applied with the agitation technique demonstrated a higher bond strength to dentine prepared with tungsten carbide and diamond burs than that applied with other techniques. SE applied with increased time on dentine treated with carbide burs produced the highest bond strength. In conclusion, a thick smear layer decreased bond strength to dentine, and this might be improved by modification of application technique.

Bond Strength and Quality of the Hybrid Layer of One-step Self-etch Adhesives Applied with Agitation on Dentin

Vigorous application on the dentin surface is an excellent tool capable of improving the immediate performance of simplified self-etch adhesive systems.

Influence of drying time and temperature on bond strength of contemporary adhesives to dentine

OBJECTIVES

To evaluate the bond strength (microTBS) of self-etching adhesives in different solvent evaporation conditions.

METHODS

Flat dentine surfaces from extracted human third molars were bonded with: (1) 2 two-steps self-etching adhesives (Clearfil SE Bond-CSEB); (Protect Bond-PB) and (2) 2 one-step self-etch systems (Adper Prompt L Pop-ADPLP); (Xeno III-XIII). Bonded dentine surfaces were air-dried for 5s, 20s, 30s or 40s at either 21 degrees C or 38 degrees C. Composite build-ups were constructed incrementally. After storage in water for 24h at 37 degrees C, the specimens were prepared for microtensile bond strength testing. Data were analyzed by two-way ANOVA and Student-Newman-Keuls at alpha=0.05.

RESULTS

CSEB and PB performed better at warm temperature with only 20s of air-blowing. The bond strength increased when XIII was performed at warm temperature at 40s air-blowing. Extended air-blowing not affect the performance of ADPLP, except at 30s air-blowing time at warm temperature.

CONCLUSIONS

The use of a warm air-dry stream seems to be a clinical tool to improve the bond strength to self-etching adhesives.

Quantification of monomer elution and carbon-carbon double bonds in dental adhesive systems using HPLC and micro-Raman spectroscopy

OBJECTIVES

To quantify monomer elution from different adhesive systems using reverse-phase high-performance liquid chromatography (HPLC) and correlate this elution with the ratio of carbon-carbon double bonds from monomer to polymer (RDB) obtained using micro-Raman spectroscopy.

METHODS

Thirty dentine discs were cut from 30 human, intact, third molars and randomly allocated to five groups according to the adhesive applied: total-etch, Excite (Ivoclar Vivadent), two-bottle self-etch, Clearfil SE (Kuraray), one-bottle self-etch, Clearfil 3S (Kuraray), ormocer-based, Admira (Voco) and Filtek Silorane adhesive system (FS) (3M ESPE). Monomer elution was studied 1h, 6h, 24h, 96h and 7 days after immersion in 75% ethanol/water. The RDB was calculated immediately after light-curing and thereafter at 24h and 7 days. The data were statistically analysed using one-way ANOVA and Pearson's correlation coefficient (p<0.05).

RESULTS

More than 90% of the whole elution occurred during the first 1h, except for BisGMA in FS, with the highest absolute amount from Clearfil SE and the highest wt% from Admira. Initial RDB was in the ascending order FS<Admira<Excite<Clearfil SE<Clearfil 3S. In all groups, the RDB was significantly higher after 24h and 7 days than immediately after light-curing (p<0.05). Negative correlation was found only for the elution of HEMA and the RDB of Clearfil 3S.

CONCLUSIONS

Different adhesive systems showed different monomer elution kinetics. In all systems, the RDB increased after monomer elution. Overall, no direct correlation exists between the RDB of adhesives and the elution of unreacted monomers.

Bond strength and etching pattern of adhesive systems to enamel: effects of conditioning time and enamel preparation

STATEMENT OF THE PROBLEM

The performance of self-etch systems on enamel is controversial and seems to be dependent on the application technique and the enamel preparation.

PURPOSE OF THE STUDY

To examine the effects of conditioning time and enamel surface preparation on bond strength and etching pattern of adhesive systems to enamel.

MATERIALS AND METHODS

Ninety-six teeth were divided into 16 conditions (N=6) in function of enamel preparation and conditioning time for bond strength test. The adhesive systems OptiBond FL (Kerr, Orange, CA, USA), OptiBond SOLO Plus (Kerr), Clearfil SE Bond (Kuraray, Osaka, Japan), and Adper Prompt L-Pop (3M ESPE, St. Paul, MN, USA) were applied on unground or ground enamel following the manufacturers' directions or doubling the conditioning time. Cylinders of Filtek Flow (0.5-mm height) were applied to each bonded enamel surface using a Tygon tube (0.7 mm in diameter; Saint-Gobain Corp., Aurora, OH, USA). After storage (24 h/37 degrees C), the specimens were subjected to shear force (0.5 mm/min). The data were treated by a three-way analysis of variance and Tukey's test (alpha=0.05). The failure modes of the debonded interfaces and the etching pattern of adhesives were observed using scanning electron microscopy.

RESULTS

Only the main factor "adhesive" was statistically significant (p<0.001). The lowest bond strength value was observed for OptiBond FL. The most defined etching pattern was observed for 35% phosphoric acid and for Adper Prompt L-Pop. Mixed failures were observed for all adhesives, but OptiBond FL showed cohesive failures in resin predominantly.

CONCLUSIONS

The increase in the conditioning time as well as the enamel pretreatment did not provide an increase in the resin-enamel bond strength values for the studied adhesives.

CLINICAL SIGNIFICANCE

The surface enamel preparation and the conditioning time do not affect the performance of self-etch systems to enamel.

Effect of air-drying and solvent evaporation on the strength of HEMA-rich versus HEMA-free one-step adhesives

OBJECTIVES

The objectives of this study were (1) to clarify the relationship between the duration of air-drying of one-step self-etch adhesives (1-SEAs) and the evaporation degree (ED) of solvents, and (2) to evaluate the effect of ED on the ultimate micro-tensile strength (microTS) of the adhesives.

METHODS

The ED of one HEMA-rich 1-SEA, Clearfil S3 Bond (Kuraray), and two HEMA-free 1-SEAs, iBond (Heraeus-Kulzer) and G-Bond (GC), was determined without air-drying and after, respectively, 5- and 10-s air-drying using a gravimetric method. Next, the microTS of the adhesives at ED equivalent to 0-, 5- and 10-s air-drying was measured.

RESULTS

The ED increased with extension of air-drying time. Among the adhesives tested, iBond showed the largest ED, followed by G-Bond and Clearfil S3 Bond in this order. A longer air-drying time for 10-s resulted in a statistically significantly higher microTS for the HEMA-rich Clearfil S3 Bond. The microTS of the latter was higher than that of the other two HEMA-free adhesives for each air-drying time.

SIGNIFICANCE

Air-drying of 1-SEAs had a significant effect on the degree of solvent evaporation (ED) and also on the mechanical properties (microTS) of the 1-SEAs upon setting. It is therefore beneficial to remove solvents of the 1-SEAs as much as possible by thorough, strong air-drying in order to achieve a strong adhesive layer at the interface.

Influence of water-storage time on the sorption and solubility behavior of current adhesives and primer/adhesive mixtures

This study evaluated the effects of water-storage on the water sorption and solubility behavior of five commercially available dental adhesive systems and two primer/adhesive mixtures. The adhesives comprised three different approaches to bonding to hard tooth tissues: a one-step self-etching adhesive (One-up Bond F), two two-step self-etching primers (Clearfil SE Bond and Clearfil Protect Bond) and two etch-and-rinse systems: a water/ethanol-based (Single Bond) and an acetone-based filled adhesive (Prime&Bond NT). The bonding agents and primers of the two-step self-etching systems were mixed in a 1:1 volume ratio. Water sorption and solubility values were determined after 1, 7, 30, 90 and 180 days. The results showed that, except for SB, all adhesives presented increased water sorption with increased storage time. The one-step self-etching adhesive and self-etching primer/adhesive mixtures presented the highest water sorption and solubility values. Equilibrium in the water sorption values was observed for all adhesives after 90 days of water-storage. However, solubility values continued to increase for some materials until 180 days. The sorption and solubility behavior of the materials tested seem to be related to hydrophilicity of the adhesive resin solution and might influence the long-term performance of resin-based composite restorations.

Systematic review of the chemical composition of contemporary dental adhesives

Dental adhesives are designed to bond composite resins to enamel and dentin. Their chemical formulation determines to a large extent their adhesive performance in clinic. Irrespective of the number of bottles, an adhesive system typically contains resin monomers, curing initiators, inhibitors or stabilizers, solvents and sometimes inorganic filler. Each one of these components has a specific function. The aim of this article is to systematically review the ingredients commonly used in current dental adhesives as well as the properties of these ingredients. This paper includes an extensive table with the chemical formulation of contemporary dental adhesives.

Water sorption/solubility of dental adhesive resins

OBJECTIVES

This study evaluated the water sorption, solubility and kinetics of water diffusion in commercial and experimental resins that are formulated to be used as dentin and enamel bonding agents.

METHODS

Four commercial adhesives were selected along with their solvent-monomer combination: the bonding resins were of Adper Scotchbond Multi-Purpose (MP) and Clearfil SE Bond (SE) systems, and the "one-bottle" systems, Adper Single Bond (SB) and Excite (EX). Five experimental methacrylate-based resins of known hydrophilicities (R1, R2, R3, R4 and R5) were used as reference materials. Specimen disks were prepared by dispensing the uncured resin into a mould (5.8mm x 0.8mm). After desiccation, the cured specimens were weighed and then stored in distilled water for evaluation of the water diffusion kinetics over a 28-day period.

RESULTS

Resin composition and hydrophilicity (ranked by their Hoy's solubility parameters) influenced water sorption, solubility and water diffusion in both commercial and experimental dental resins. The most hydrophilic experimental resin, R5, showed the highest water sorption, solubility and water diffusion coefficient. Among the commercial adhesives, the solvated systems, SB and EX, showed water sorption, solubility and water diffusion coefficients significantly greater than those observed for the non-solvated systems, MP and SE (p<0.05). In general, the extent and rate of water sorption increased with the hydrophilicity of the resin blends.

SIGNIFICANCE

The extensive amount of water sorption in the current hydrophilic dental resins is a cause of concern. This may affect the mechanical stability of these resins and favor the rapid and catastrophic degradation of resin-dentin bonds.

Effect of metal conditioners on polymerization behavior of bonding agents

This study aimed to determine the influence of metal conditioners on the polymerization behavior of bonding agents. Bonding agents of two-step self-etching primer systems and metal conditioners for adhesion of dental metal alloys were used. Double bond conversion was determined by Fourier transform-ation infrared spectroscopy. The percentage of residual double bonds, including pendant and monomeric double bonds, was calculated by comparing the obtained ratio with that of the uncured bonding agent. The degree of conversion of the bonding agents was obtained by subtracting the remaining double bonds from 100%. ANOVA followed by a Tukey HDS test was performed. Degree of conversion of the bonding agents ranged from 86.0 to 87.8%. When the bonding agents were mixed with metal conditioners or solvents of the metal conditioners, double bond conversion of the bonding agents tended to decrease. Within the limitations of this study, which was far removed from clinical situations, the presence of metal conditioners and remaining solvents had adverse effects on the polymerization reaction of bonding agents. Clinicians should be cognizant of the various factors that can influence bond strength of restorative resins to dentin.

Effect of evaporation of primer components on ultimate tensile strengths of primer-adhesive mixture

OBJECTIVE

The purpose of the present study was to evaluate the effect of evaporation of primer components on the ultimate tensile strength (UTS) of primer-adhesive mixtures.

METHODS

The UTSs of 1:3 by weight primer-adhesive mixtures and of the pure adhesives (controls) were measured after 0-, 2-, 5-min and 24-h storage in a 37 degrees C oven for the three-step etch&rinse adhesive OptiBond FL (Kerr) and the two-step self-etch adhesive Clearfil SE (Kuraray).

RESULTS

Evaporation of primer components increased with time for both adhesives investigated. OptiBond FL showed a higher evaporation of primer components than Clearfil SE at the 2-, 5-min and 24-h storage time. As compared to the pure adhesive, the UTS of the primer-adhesive mixture was lower after 0- and 2-min storage for OptiBond FL and after 0-, 2- and 5-min storage for Clearfil SE. The UTS of OptiBond FL was higher than that of Clearfil SE at the 0- and 2-min storage time, though there was no difference at the 5-min and 24-h storage time.

SIGNIFICANCE

The degree of evaporation of primer components depended largely on the primer solvents employed. The significant decrease in UTS of adhesive resin when mixed with primer must be attributed to incomplete evaporation of primer components. Complete evaporation of solvents is hard to achieve, even by thorough air drying.

Effect of fracture strength of primer–adhesive mixture on bonding effectiveness

OBJECTIVE

The purpose of this study was to measure the micro-tensile bond strength (microTBS) of two adhesives to dentin and to correlate this microTBS with the micro-tensile fracture strength (microTFS) of primer-adhesive mixtures of the two adhesives.

METHODS

The three-step etch&rinse adhesive OptiBond FL (Kerr) and the two-step self-etch adhesive Clearfil SE Bond (Kuraray) were used to bond Filtek Z100 (3M ESPE) to twenty mid-coronal dentin surfaces. The microTBS was determined at 1 and 24 h after light-curing. In addition, the microTFS of primer-adhesive mixtures (primer:adhesive=1:3 by weight) and of the pure adhesives (controls) were measured after the same time intervals.

RESULTS

The microTBS to dentin of OptiBond FL at 24 h was significantly higher than at 1 h and than the microTBS of Clearfil SE Bond at 24 h. The mean microTFS of the primer-adhesive mixtures was always lower than the microTFS of the respective adhesives. The highest reduction in microTFS due to mixing primer with the adhesive resin was measured for Clearfil SE Bond. Both the microTFS of the primer-adhesive mixtures and the pure adhesives of OptiBond FL and Clearfil SE Bond increased with time.

SIGNIFICANCE

The early 1 h microTBS to dentin was lower than the 24 h microTBS for OptiBond FL, but not for Clearfil SE Bond. Differences in polymerization efficiency as well as in the resulting interfacial strength may explain such varying early bond strengths to dentin.

Effect of smear layer thickness and acidity of self-etching solutions on early and long-term bond strength to dentin

OBJECTIVES

To evaluate the effect of smear layer thickness (SL) on early and 6-month bond strength (BS) of self-etching adhesives to dentin and to measure the ultimate microtensile strength (UTS) of the adhesives.

METHODS

Clearfil SE Bond; Optibond Solo Plus Self-Etch Primer; Tyrian Self Priming Etchant (TY) and as controls, Single Bond (SB) and Scotchbond Multi-Purpose Plus (SBMP) were applied on flat superficial dentin surface with thick and thin SL thicknesses. After adhesive's application (n=6) a resin build-up was made. After 24h, resin-dentin beams (0.8mm(2)) were prepared to be tested immediately and after 6-month (6M) at 0.5mm/min. For the UTS measurement, hour-glass specimens were prepared with the bonding resin alone or after mixing (1:1). BS values were analyzed by three-way repeated measures ANOVA and Tukey's multiple comparison tests. Two-way ANOVA (bonding resin and bonding resin+self-etching primer) and Tukey's test were used for the UTS values. The bonding resins were re-evaluated separately by a one-way ANOVA and Tukey's test, since Single Bond is a one-bottle adhesive (alpha=0.05).

RESULTS

The SL thickness was not significant (p=0.64). BS values were reduced after 6M, except for the SBMP. TY provided the lowest BS mean while SB and SBMP the highest BS. The UTS of the SBMP was the highest. TY yielded the lowest UTS. Regression analysis revealed a linear and significant relationship between the UTS of self-etch systems and the mean BS (R=0.95, p=0.02).

CONCLUSIONS

The performance of a self-etching system does not seem to be dependent on the SL thickness. The total-etch, three-step system provided the highest BS to dentin and maintained the BS stable over 6 months. The performance of the self-etching systems can be envisaged by their UTS.

Tensile bond strength of adhesive systems--effects of primer and thermocycling

The objective of this study was to evaluate the effects of primer and thermocycling on the bond strength of multi-purpose adhesive systems applied to enamel, under tensile stress. The following bonding systems were applied, according to the manufacturers' instructions, on unground enamel buccal surfaces of 96 premolars, with or without the application of primer: Scotchbond MP, OptiBond FL, Amalgambond Plus and OptiBond (dual-cure). A composite resin (Z100, 3M) was applied and light-cured in a cast metal hollow cone, which was previously fixed to the enamel surfaces. Half of the sample was subjected to 3,000 thermocycles (5-37 degrees C; 37-55 degrees C, dwell time of 60 s), and the other half was stored in water at 37 degrees C for the same period. The data were treated by means of ANOVA and no significant effects were detected, which indicates that tensile bond strength was not affected by the adhesive systems, application of primer or thermocycling.