Influence of different etching modes on bond strength and fatigue strength to dentin using universal adhesive systems

Abstract

Objectives

The purpose of this study was to determine the dentin bonding ability of three new universal adhesive systems under different etching modes using fatigue testing.

Method

Prime & Bond elect [PE] (DENTSPLY Caulk), Scotchbond Universal [SU] (3M ESPE), and All Bond Universal [AU] (Bisco) were used in this study. A conventional single-step self-etch adhesive, Clearfil Bond SE ONE [CS] (Kuraray Noritake Dental) was also included as a control. Shear bond strengths (SBS) and shear fatigue strength (SFS) to human dentin were obtained in the total-etch mode and self-etch modes. For each test condition, 15 specimens were prepared for the SBS and 30 specimens for SFS. SEM was used to examine representative de-bonded specimens, treated dentin surfaces and the resin/dentin interface for each test condition.

Results

Among the universal adhesives, PE in total-etch mode showed significantly higher SBS and SFS values than in self-etch mode. SU and AU did not show any significant difference in SBS and SFS between the total-etch mode and self-etch mode. However, the single-step self-etch adhesive CS showed significantly lower SBS and SFS values in the etch-and-rinse mode when compared to the self-etch mode. Examining the ratio of SFS/SBS, for PE and AU, the etch-and-rinse mode groups showed higher ratios than the self-etch mode groups.

Significance

The influence of different etching modes on dentin bond quality of universal adhesives was dependent on the adhesive material. However, for the universal adhesives, using the total-etch mode did not have a negative impact on dentin bond quality.

Introduction

Because of increased patient desire for tooth color restorations and minimally invasive treatments, direct application of resin composites has become universally accepted and widespread over the past few decades. This treatment has relied heavily upon the development of adhesive technology, and both resin composite and adhesive technology have rapidly advanced over the years.

Currently, dental adhesives are generally classified into either “etch-and-rinse” or “self-etch” systems. Furthermore, the priming and bonding components can be separated or combined, resulting in three steps or two steps for etch and rinse systems, and two steps or one step for self-etch adhesives . In recent years, self-etch adhesive system have become very popular due to the efficiency offered by the simplified bonding procedures. In addition, it is thought that the incidence of post-operative sensitivity appears to be lower relative to etch-and-rinse systems thanks to chemical bonding and reduced demineralization of dentin . However, some laboratory studies have indicated that self-etch adhesive systems are not able to etch enamel as effectively as the phosphoric acids used in etch-and-rinse adhesive systems due to their lower acidity . In order to achieve a durable bond to enamel, when using self-etch adhesive systems, selective etching with phosphoric acid prior to application of the self-etch adhesive has been recommended . However, clinically, it may be difficult to precisely etch only the enamel region without affecting exposed dentin . Therefore, inadvertent pre-etching of dentin could be a clinical risk, as resin monomers of self-etch adhesives may not be able to penetrate the entire depth of the deeply demineralized dentin, resulting in reduced dentin bonding quality .

Recently, a new type of single-step self-etch adhesive has been introduced. This type of self-etch adhesive is categorized as “universal” or “multi-mode” as they can be used either with the etch-and-rinse or the self-etch approaches . Therefore, universal systems allow application of the adhesive with phosphoric acid pre-etching in the total-etch or selective-etch approaches, which purportedly enhances enamel bond durability. In addition, it also provides a simplified procedure of the self-etch approach on dentin.

Investigation of initial bonding effectiveness is considered essential to grasp the general characteristics of adhesive systems for screening purposes. Currently, the most widespread method for the evaluation of bonding performance is measuring bond strength by shear bond strength (SBS) or tensile bond strength testing (μ-TBS). However, clinical bonds between restorations and teeth are not typically subjected to a monotonically increasing force until the bond fails from tensile or shear forces, but rather bonded restorations are subjected to repeated sub-critical loading during normal function. The repeated loads typically encountered in the oral cavity are insufficient to provoke acute failure, but they induce damage by generating cracks that grow over time and eventually result in deterioration of adhesively bonded restorations through marginal failure or, in extreme cases, bulk fracture . Fatigue can be defined as the degradation or failure of mechanical properties after repeated applications of stress, at a level well below the ultimate fracture strength of the material or interface . Consequently, fatigue tests provide not only information on the ability of a material or interface to resist the development of cracks, but also the endurance characteristics of a bonding system.

Although there are several studies of enamel and dentin bonding performance of universal adhesives , only limited information is available on the bonding quality of universal adhesives when used in different application modes . The purpose of this laboratory investigation was to determine the dentin bond quality of universal adhesives in different application modes using fatigue testing.

Methods

Study materials

The materials used in this study are shown in Table 1 . The three universal adhesives used were: (1) Prime & Bond elect [PE] (DENTSPLY Caulk, Milford, DE USA), (2) Scotchbond Universal [SU] (3M ESPE, St Paul, MN USA) and (3) All Bond Universal [AU)] (Bisco, Schaumburg, IL USA). A conventional single-step self-etch adhesive, (4) Clearfil Bond SE ONE [CS)] (Kuraray Noritake Dental, Tokyo, Japan) was used as a control. The phosphoric acid pre-etching agent used was Ultra-Etch (Ultradent, South Jordan, UT USA). Z100 Restorative [Z100] (3M ESPE, St Paul, MN USA) was used as a restorative material for bonding to dentin.

Table 1
Study materials.
Adhesive Manufacturer Main Components Code
Prime & Bond elect
Lot No. 130606
Dentsply Caulk Milford, DE 19963, USA Dipentaerythritol penta acrylate monophosphate, polymerizeable dimethacrylate resin, polymerizeable trimethacrylate resin, diketon, organic phosphine oxide, stabilizers, cetylamine, hydrofluoride, acetone, water PE
Scotchbond Universal
Lot No. 451192
3M ESPE Dental Products, St. Paul, MN 55144, USA MDP phosphate monomer, HEMA, dimethacrylate resins, Vitrebond copolymer, filler, ethanol, water, initiators, silane SU
All-Bond Universal
Lot No. 4483016
Bisco Inc., Schaumburg, IL 60193, USA MDP phosphate monomer, bis-GMA, HEMA, ethanol, water, initiators AU
Clearfil Bond SE ONE
Lot No. 4483016
Kuraray Noritake Dental Tokyo, Japan MDP phosphate monomer, bis-GMA, HEMA, ethanol, water, filler, CQ CS
Pre-etching agent
Ultra-Etch
Lot No.G017
Ultradent Products, Inc., South Jordan, UT 84095, USA 35% phosphoric acid
Resin composite
Z100 Restorative
Lot No. N416713
3M ESPE Dental Products, St. Paul, MN 55144, USA Zirconia/silica, 0.01–3.5 μm; Filler Load: 84.5% weight–66% volume

Specimen preparation

Extracted caries-free deidentified human molars were selected for use in this study under a protocol reviewed and approved by the Ethics Committee for Human Studies of the Nihon University School of Dentistry (#2015-06). The dentin bonding sites were prepared by sectioning the teeth medio-distally and then removing approximately two-thirds of the apical root structure. The buccal and lingual tooth sections were mounted with Triad DuaLine (DENTSPLY International, York, PA, USA) in 25 mm diameter brass rings. The dentin bonding surfaces were ground flat using a water coolant and a sequence of carbide polishing papers ending with 4000 grit (Struers Inc., Cleveland, OH, USA). Metal rings machined from 304 stainless steel with an inner diameter of 2.4 mm, an outer diameter of 4.8 mm and a length of 2.6 mm were used to confine resin composite on dentin surfaces for shear bond strength (SBS) and shear fatigue strength (SFS) tests. The bonding procedure resulted in a resin composite cylinder inside the ring that approximated 2.35 mm in diameter and 2.5 mm in height. The ring was left in place for the tests.

Shear bond strength tests (SBS)

Fifteen specimens were used for each test group to determine the SBS to dentin in total-etch mode (phosphoric acid was applied for 15 s, prior to the application of the adhesive) or in self-etch mode (without phosphoric acid etching). The adhesive agents were used in accordance with the manufacturers’ instructions as shown in Table 2 . Following the treatment of the flat ground dentin surface with the adhesive agent, the metal ring was positioned over the bonding site and secured in place by clamping in a custom fixture. The resin composite (Z100) was confined in the ring and polymerized for 40 s with the Spectrum 800 Curing Unit (DENTSPLY Caulk, Milford, DE USA) set at a light irradiance average of 600 mW/cm 2 . The bonded specimens were stored for 24 h in distilled water at 37 °C before testing. The specimens were loaded to failure at 1.0 mm per minute using an MTS Insight machine using TestWorks 4 software (MTS Systems Corporation, Eden Prairie, MN USA). A metal rod with a chisel-shaped end was used to apply the load to the metal ring immediately adjacent to the flat ground tooth surface. The SBS values (MPa) were calculated from the peak load at failure divided by the bonded surface area. After testing, the bonding site tooth surfaces and resin composite cylinders were observed under an optical microscope (MZ16; Leica Microsystems Ltd., Heerbrugg, Switzerland) at a magnification of ×20 to determine the bond failure mode. Based on the percentage of substrate area (adhesive–resin composite–dentin) observed on the de-bonded cylinders and tooth bonding sites, the types of bond failure were recorded as (1) adhesive failure, (2) cohesive failure in composite, (3) cohesive failure in dentin, or (4) mixed failure—partially adhesive and partially cohesive.

Table 2
Application protocol for pre-etching and self-etching adhesives.
Method code Pre-etching protocol
Total-etch mode Enamel/dentin surface was phosphoric acid conditioned for 15 s. Conditioned surface was rinsed with water for 15 s (three-way dental syringe) and air-dried
Self-etch mode Phosphoric acid pre-etching was not performed
Adhesive Adhesive application protocol
PE Adhesive applied to tooth surface (do not desiccate) with rubbing action for 20 s. Gentle stream of air applied over the liquid for at least 5 s. Light irradiate for 10 s
SU Adhesive applied to air-dried tooth surface with rubbing action for 20 s and then medium air pressure applied to surface for 5 s. Adhesive light cured for 10 s
AU Adhesive applied to tooth surface (do not desiccate) with rubbing action for 10–15 s per coat. No light cure between coats. Gentle stream of air applied over the liquid for at least 10 s. Light irradiate for 10 s
CS Adhesive applied to air-dried tooth surface for 10 s and then medium air pressure applied to surface for 5 s. Adhesive light cured for 10 s

Shear fatigue strength testing (SFS)

The staircase method of fatigue testing reported by Draughn was used for SFS testing. Test specimens were made as described above for the SBS testing. The lower load limit was set near zero (0.4 N) and the initial maximum load applied was 50–60% of the SBS determined for each of the adhesive systems tested. The load was applied at a frequency rate of 10 Hz with an ElectroPuls E1000 machine (Instron Worldwide Headquarters, Norwood, MA USA) using a sine wave for 50,000 cycles or until failure occurred. The load was incrementally adjusted upward or downward (depending on survival or failure) by approximately 10% of the initial load. For each test condition 30 specimens were used to determine the SFS. Using the calculation described by Draughn , the test stress that is likely to produce 50% failure is termed the fatigue strength . After testing, the specimens were examined to determine the type of bond failure in the same manner as for the SBS, described above.

Scanning electron microscopy (SEM) observations

Treated dentin surfaces, restorative/dentin interfaces, and representative fracture sites after the SFS testing were observed by field-emission microscopy (FE-SEM) [ERA-8800FE, Elionix Ltd., Tokyo, Japan]. For observations of treated dentin surfaces, sample preparation, in both total-etch mode and self-etch mode, was carried out in accordance with each manufacturer’s instructions, followed by three alternating rinses of acetone and water. For ultrastructure observations of the restorative/dentin interface, bonded specimens (stored in 37 °C distilled water for 24 h) were embedded in epoxy resin and then longitudinally sectioned with a diamond saw (Isomet Low Speed Saw, Buehler, Lake Bluff, IL, USA). The sectioned surfaces were polished to a high gloss with abrasive discs (Fuji Star Type DDC, Sankyo Rikagaku Co. Ltd., Saitama, Japan) followed by diamond pastes down to 0.25 μm particle size (DP-Paste, Struers, Ballerup, Denmark). Fracture sites were prepared directly for FE-SEM. All SEM specimens were dehydrated in ascending grades of tert -butyl alcohol (50% for 20 min, 75% for 20 min, 95% for 20 min, and 100% for 2 h) and then transferred from the final 100% bath to a critical-point dryer (Model ID-3, Elionix, Tokyo, Japan) for 30 min. Resin/dentin interface specimens were then subjected to argon-ion beam etching (EIS-200ER, Elionix, Tokyo, Japan) for 40 s with the ion beam (accelerating voltage 1.0 kV, ion current density 0.4 mA/cm 2 ) directed perpendicular to the polished surfaces. Finally, all of the SEM specimens were coated in a vacuum evaporator, Quick Coater (Type SC-701, Sanyu Denchi Inc., Tokyo, Japan) with a thin film of gold. Observations were carried out using an operating voltage of 10 kV.

Statistical analysis

A two-way analysis of variance (ANOVA) followed by Tukey’s honestly significant difference (HSD) test ( α = 0.05) was used for analysis of the SBS data. The statistical analysis for SBS was performed with the Sigma Plot software system (Ver. 11.0; SPSS Inc., Chicago, IL, USA). A modified t -test with Bonferoni correction was used for the SFS data using a custom program.

Methods

Study materials

The materials used in this study are shown in Table 1 . The three universal adhesives used were: (1) Prime & Bond elect [PE] (DENTSPLY Caulk, Milford, DE USA), (2) Scotchbond Universal [SU] (3M ESPE, St Paul, MN USA) and (3) All Bond Universal [AU)] (Bisco, Schaumburg, IL USA). A conventional single-step self-etch adhesive, (4) Clearfil Bond SE ONE [CS)] (Kuraray Noritake Dental, Tokyo, Japan) was used as a control. The phosphoric acid pre-etching agent used was Ultra-Etch (Ultradent, South Jordan, UT USA). Z100 Restorative [Z100] (3M ESPE, St Paul, MN USA) was used as a restorative material for bonding to dentin.

Table 1
Study materials.
Adhesive Manufacturer Main Components Code
Prime & Bond elect
Lot No. 130606
Dentsply Caulk Milford, DE 19963, USA Dipentaerythritol penta acrylate monophosphate, polymerizeable dimethacrylate resin, polymerizeable trimethacrylate resin, diketon, organic phosphine oxide, stabilizers, cetylamine, hydrofluoride, acetone, water PE
Scotchbond Universal
Lot No. 451192
3M ESPE Dental Products, St. Paul, MN 55144, USA MDP phosphate monomer, HEMA, dimethacrylate resins, Vitrebond copolymer, filler, ethanol, water, initiators, silane SU
All-Bond Universal
Lot No. 4483016
Bisco Inc., Schaumburg, IL 60193, USA MDP phosphate monomer, bis-GMA, HEMA, ethanol, water, initiators AU
Clearfil Bond SE ONE
Lot No. 4483016
Kuraray Noritake Dental Tokyo, Japan MDP phosphate monomer, bis-GMA, HEMA, ethanol, water, filler, CQ CS
Pre-etching agent
Ultra-Etch
Lot No.G017
Ultradent Products, Inc., South Jordan, UT 84095, USA 35% phosphoric acid
Resin composite
Z100 Restorative
Lot No. N416713
3M ESPE Dental Products, St. Paul, MN 55144, USA Zirconia/silica, 0.01–3.5 μm; Filler Load: 84.5% weight–66% volume

Specimen preparation

Extracted caries-free deidentified human molars were selected for use in this study under a protocol reviewed and approved by the Ethics Committee for Human Studies of the Nihon University School of Dentistry (#2015-06). The dentin bonding sites were prepared by sectioning the teeth medio-distally and then removing approximately two-thirds of the apical root structure. The buccal and lingual tooth sections were mounted with Triad DuaLine (DENTSPLY International, York, PA, USA) in 25 mm diameter brass rings. The dentin bonding surfaces were ground flat using a water coolant and a sequence of carbide polishing papers ending with 4000 grit (Struers Inc., Cleveland, OH, USA). Metal rings machined from 304 stainless steel with an inner diameter of 2.4 mm, an outer diameter of 4.8 mm and a length of 2.6 mm were used to confine resin composite on dentin surfaces for shear bond strength (SBS) and shear fatigue strength (SFS) tests. The bonding procedure resulted in a resin composite cylinder inside the ring that approximated 2.35 mm in diameter and 2.5 mm in height. The ring was left in place for the tests.

Shear bond strength tests (SBS)

Fifteen specimens were used for each test group to determine the SBS to dentin in total-etch mode (phosphoric acid was applied for 15 s, prior to the application of the adhesive) or in self-etch mode (without phosphoric acid etching). The adhesive agents were used in accordance with the manufacturers’ instructions as shown in Table 2 . Following the treatment of the flat ground dentin surface with the adhesive agent, the metal ring was positioned over the bonding site and secured in place by clamping in a custom fixture. The resin composite (Z100) was confined in the ring and polymerized for 40 s with the Spectrum 800 Curing Unit (DENTSPLY Caulk, Milford, DE USA) set at a light irradiance average of 600 mW/cm 2 . The bonded specimens were stored for 24 h in distilled water at 37 °C before testing. The specimens were loaded to failure at 1.0 mm per minute using an MTS Insight machine using TestWorks 4 software (MTS Systems Corporation, Eden Prairie, MN USA). A metal rod with a chisel-shaped end was used to apply the load to the metal ring immediately adjacent to the flat ground tooth surface. The SBS values (MPa) were calculated from the peak load at failure divided by the bonded surface area. After testing, the bonding site tooth surfaces and resin composite cylinders were observed under an optical microscope (MZ16; Leica Microsystems Ltd., Heerbrugg, Switzerland) at a magnification of ×20 to determine the bond failure mode. Based on the percentage of substrate area (adhesive–resin composite–dentin) observed on the de-bonded cylinders and tooth bonding sites, the types of bond failure were recorded as (1) adhesive failure, (2) cohesive failure in composite, (3) cohesive failure in dentin, or (4) mixed failure—partially adhesive and partially cohesive.

Table 2
Application protocol for pre-etching and self-etching adhesives.
Method code Pre-etching protocol
Total-etch mode Enamel/dentin surface was phosphoric acid conditioned for 15 s. Conditioned surface was rinsed with water for 15 s (three-way dental syringe) and air-dried
Self-etch mode Phosphoric acid pre-etching was not performed
Adhesive Adhesive application protocol
PE Adhesive applied to tooth surface (do not desiccate) with rubbing action for 20 s. Gentle stream of air applied over the liquid for at least 5 s. Light irradiate for 10 s
SU Adhesive applied to air-dried tooth surface with rubbing action for 20 s and then medium air pressure applied to surface for 5 s. Adhesive light cured for 10 s
AU Adhesive applied to tooth surface (do not desiccate) with rubbing action for 10–15 s per coat. No light cure between coats. Gentle stream of air applied over the liquid for at least 10 s. Light irradiate for 10 s
CS Adhesive applied to air-dried tooth surface for 10 s and then medium air pressure applied to surface for 5 s. Adhesive light cured for 10 s
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Nov 23, 2017 | Posted by in Dental Materials | Comments Off on Influence of different etching modes on bond strength and fatigue strength to dentin using universal adhesive systems
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