Bonding effectiveness of self-adhesive composites to dentin and enamel

Abstract

Self-adhesive composites (SACs) are claimed to bond to tooth substrate without a separate adhesive. Bonding effectiveness data are however still limited.

Objectives

In SubProject 1, the hypothesis was tested that the micro-tensile bond strength (μTBS) to dentin of two flowable SACs was alike that of a one-step self-etch adhesive (1-SEa) combined with a flowable composite (flowC). In SubProject 2, the hypothesis was tested that the nature of the smear layer did not affect the μTBS of the SACs to dentin/enamel.

Methods

SubProject 1: The μTBS to bur-cut dentin of two SACs (Fusio Liquid Dentin, Pentron; Vertise Flow, Kerr) was measured and compared to that of four 1-SEa/flowC combinations (AdheSe One/Tetric EvoFlow, Ivoclar Vivadent; Adper Prompt L-Pop/Filtek Supreme XT Flowable, 3M ESPE; iBond/Venus flow, Heraeus Kulzer; Xeno V/X-flow, Dentsply) and of one 3-step etch-and-rinse adhesive (3-E&Ra: OptiBond FL, Kerr) combined with Premise Flowable (Kerr). The effect of pre-etching dentin with phosphoric acid on the μTBS of the SAC Vertise Flow (Kerr) was measured as well. SubProject 2: The μTBS of the two SACs and one 1-SEa/flowC combination (Adper Prompt L-Pop/Filtek Supreme XT Flowable, 3M ESPE) to either bur-cut or SiC-paper ground dentin/enamel was measured. The effect of pre-etching enamel with phosphoric acid on the μTBS of the SAC Vertise Flow (Kerr) was also measured.

Results

SubProject 1: The μTBS to dentin of both SACs was significantly lower than that of the 1-SEa/flowC and the 3-E&Ra/flowC combinations, of which the latter performed best. The SAC Fusio Liquid Dentin (Pentron) bonded significantly better to dentin than Vertise Flow (Kerr), except when dentin had additionally been pre-etched with phosphoric acid. SubProject 2: Surface smear did not interfere with bonding of the SACs to dentin/enamel, while their μTBS remained significantly lower than that of the 1-SEa/flowC combination. Prior phosphoric-acid etching of dentin/enamel significantly ameliorated the bonding effectiveness of Vertise Flow (Kerr).

Significance

The bonding effectiveness of flowable SACs underscores that of 1-SEa’s and one ‘gold-standard’ 3-E&Ra when combined with their proprietary flowable composite. Consequently, routine clinical application of SACs should be carefully considered.

Introduction

As today’s adhesives are often regarded as technique-sensitive , combining the benefits of adhesive and composite technology into a self-adhesive restorative composite was the next step clinicians have been waiting for . Especially simplification in clinical adhesive procedures is a major drive for current research-and-development efforts at dental industry . However, the hydrophobic–hydrophilic mismatch between dental composite and tooth substrate needs to be overcome in order to achieve a long-term lasting bond. The introduction of self-adhesive composite cements has led to the development of a new class of self-adhesive (restorative) composites (SACs) that are bonded to tooth enamel and dentin without a separate adhesive.

Since their introduction, data regarding physical properties of SACs , their shear bond strength and marginal sealing potential (micro-leakage studies) were published. Even more, SACs have been tested for orthodontic and endodontic purposes . However, so far no micro-tensile bond strength (μTBS) data are available in literature. Of high interest is for instance to know if the smear layer, typically prepared by bur clinically, may potentially interfere with the bonding effectiveness of this new group of composites. In addition, all publications have dealt with only one commercial SAC, namely Vertise Flow (Kerr).

Therefore, the aim of this study was to test in SubProject 1 hypothesis ‘1’ that the μTBS to bur-cut dentin of two (commercial) flowable SACs was alike that of a one-step self-etch adhesive (1-SEa) when combined with a flowable composite (flowC), and in SubProject 2 hypothesis ‘2’ that the smear layer did not affect the μTBS of the two SACs to dentin and enamel. In addition, the effect of pre-etching tooth enamel/dentin with phosphoric acid on the μTBS of the SAC Vertise Flow (Kerr) was tested as well, having hypothesized that pre-etching did not increase the μTBS (hypothesis ‘3’).

Materials and methods

Micro-specimen preparation

The experimental set-up is schematically presented in Fig. 1 . Non-carious and non-restored human third molars (gathered following informed consent approved by the Commission for Medical Ethics of KU Leuven) were stored in 0.5% chloramine in water at 4 °C and used within 1 month after extraction. Ninety-five teeth, 5 teeth per group, were mounted in gypsum blocks in order to facilitate manipulation. For the dentin specimens, the occlusal third of the molar crowns was removed by means of a water-cooled slow-speed diamond saw (Isomet 1000, Buehler, Lake Bluff, IL, USA). A standard smear layer was produced by removing a thin layer of the surface using a water-cooled, high-speed medium-grit diamond bur (842, Komet, Lemgo, Germany) mounted in a custom-adapted MicroSpecimen Former (“BUR-CUT”; thick and compact smear layer) or using 600-grit silicon-carbide paper under running water (“SiC-GROUND”; thin smear layer; solely in SubProject 2). For the enamel specimens (solely in SubProject 2), lingual and buccal enamel was flattened using the above-mentioned BUR-CUT or SiC-GROUND procedure. The teeth were randomly divided in groups according to the SubProject and the specific adhesive material tested ( Table 1 ): In SubProject 1, the μTBS to BUR-CUT dentin of the two SACs, Fusio Liquid Dentin (Pentron Clinical, Orange, CA, USA) and Vertise Flow (Kerr, Orange, CA, USA) was measured and compared to that of four 1-SEa/flowC combinations (AdheSe One/Tetric EvoFlow, Ivoclar Vivadent, Schaan, Liechtenstein; Adper Prompt L-Pop/Filtek Supreme XT Flowable, 3M ESPE, Seefeld, Germany; iBond/Venus flow, Heraeus Kulzer, Hanau, Germany; Xeno V/X-flow, Dentsply, Konstanz, Germany) and of one 3-step etch-and-rinse adhesive (3-E&Ra: OptiBond FL, Kerr) combined with Premise Flowable (Kerr). The effect of pre-etching BUR-CUT dentin with phosphoric acid (Kerr, Orange, CA, USA) on the μTBS of the SAC Vertise Flow (Kerr) was measured as well. In SubProject 2, the μTBS of the two SACs and one 1-SEa/flowC combination (Adper Prompt L-Pop/Filtek Supreme XT Flowable, 3M ESPE) to either BUR-CUT or SiC-GROUND dentin and enamel was measured. The effect of pre-etching BUR-CUT and SiC-GROUND enamel with phosphoric acid (Kerr, Orange, CA, USA) on the μTBS of the SAC Vertise Flow (Kerr) was also measured. All bonding and restorative procedures were performed strictly according to the manufacturer’s instructions ( Table 1 ). After adhesive treatment, the surfaces were built up to a height of 5 mm with the respective flowC (shade A2). Each layer of 1.5 mm was light-cured for 40 s using an Optilux 500 light-curing unit (Demetron/Kerr, Danbury, CT, USA) with a light output of not less than 600 mW/cm 2 . After storage of the teeth for 1 week in 0.5% chloramine at 37 °C, they were sectioned perpendicular to the bonding surface into square specimens of 1 mm × 1 mm using a fully automated precision water-cooled diamond saw (Accutom-50, Struers A/S, Ballerup, Denmark). For each tooth, only the 4 to 9 central sticks were used, resulting in 24 to 35 sticks per group. Specific measures were taken to reduce the incidence of pre-testing failures (ptf) by supporting the slices with alginate (Alginot, Kerr, Orange, CA, USA) during sectioning. The width and thickness of each specimen were measured to the nearest 0.01 mm using a digital calliper (Mitutoyo, Tokyo, Japan). For each micro-specimen, a bonding surface of about 1 mm 2 was obtained.

Fig. 1
Schematic illustrating the study design.

Table 1
Materials used in this study.
Material Composition a [lot number] Application
Self-adhesive flowable composite Fusio Dentin Liquid (Pentron Clinical, Orange, CA, USA) UDMA, TEGDMA, HEMA, 4-MET, nano-sized amorphous silica, silane treated barium glass, minor additives, photo curing system [3479986] Dispense a 1 mm increment and agitate to condition the tooth for 20 s prior to light curing for 10 s; syringe additional material in increments of 1.5–2 mm and light cure each increment for 10 s.
Vertise Flow (Kerr, Orange, CA, USA) GPDM, HEMA, prepolymerized filler, nano-sized ytterbium fluoride, 1-μm barium glass filler, nano-sized colloidal silica [3435242] Dispense a thin layer (<0.5 mm) on a forcefully dried surface; use a provided applicator with a brushing motion for 15–20 s; light cure for 20 s; syringe additional material in increments of less than 2 mm and light cure each increment for 20 s.
One-step self-etch adhesive AdheSe One (Ivoclar Vivadent, Schaan, Liechtenstein) Derivatives of bis-acrylamide, water, bis-methacrylamide dihydrogen phosphate, amino acid acrylamide, hydroxyalkyl-methacrylamide, highly dispersed silicon dioxide, catalysts, stabilizers [L49718] Brush onto the surface for >30 s; disperse excess with a strong stream of air; light cure for 10 s.
Adper Prompt L-Pop (3M ESPE, Seefeld, Germany) First blister : methacrylic phosphates, bis-GMA photo initiator [412924]
Second blister : water, HEMA, polyalkenoic acid polymer [412924]
Brush onto the surface; massage for 15 s applying pressure; gentle stream of air to thoroughly dry to a thin film; apply a second coat without massage; gentle stream of air to thoroughly dry to a thin film; light cure for 10 s.
iBond (Heraeus Kulzer, Hanau, Germany) UDMA, 4-meta, glutaraldehyde, acetone, water, photoinitiators, stabilizer [010075] Application for 20 s with agitation; start with gentle air blow, followed by a strong air blow for at least 5 s; light cure for 20 s.
Xeno V (Dentsply, Konstanz, Germany) Bifunctional acrylic amides, acryloamido alkylsulfonic acid, functionalized phosphoric acid ester, acrylic acid, camphorquinone, butylated benzenediol, water, tert-butanol, photoinitiators, stabilizer [0908001751] Apply adhesive twice; gently agitate for 20 s; carefully air blow for 5 s; light cure for 20 s.
Three-step etch-and-rinse adhesive OptiBond FL (Kerr, Orange, CA, USA) Etching : 37.5% phosphoric acid, silica thickener [3034827]
Primer : HEMA, GPDM, PAMM, ethanol, water, photo-initiator [3457744]
Adhesive : TEGDMA, UDMA, GPDM, HEMA, bis-GMA, filler, photo initiator [3461592]
Etch for 15 s; rinse thoroughly for 15 s; gently air dry for 3 s; apply primer with light brushing motion for 15 s; air dry for 5 s; apply adhesive with light brushing motion for 15 s; air thin for 3 s; light cure for 20 s.
Flowable composite Filtek Supreme XT Flowable (3M ESPE, St. Paul, MN, USA) Bis-GMA, TEGDMA, bis-EMA, functionalized dimethacrylate polymer, silane treated ceramic, silane treated silica, silane treated zirconium oxide [N110837] Apply in layers of max 2 mm and light cure for 20 s.
Premise Flowable (Kerr, Orange, CA, USA) Bis-EMA, TEGDMA, silica nanofiller [3044072] Apply in layers of max 2 mm and polymerize for 20 s.
Tetric EvoFlow (Ivoclar Vivadent, Schaan, Liechtenstein) Bis-GMA, UDMA, decamethylene dimethacrylate, barium glass, ytterbium trifluoride, highly dispersed silicon dioxide, mixed oxide and copolymer [L36209] Apply in layers of max 2 mm and light cure for 20 s (>500 mW/cm 2 ) or 10 s (>1000 mW/cm 2 ).
Venus flow (Heraeus-Kulzer, Hanau, Germany) Bis-GMA, TEGDMA, barium glass [010122] Apply in thin layers (max 2 mm, baseliner max 1 mm); apply a gentle stream of air and light cure for 20 s.
X-flow (Dentsply, Konstanz, Germany) DGDMA, di- and multifunctional acrylate and methacrylate resins, strontium alumino sodium fluoro phosphor silicate glass, highly dispersed silicon dioxide, UV stabilizer, ethyl-4-dimethylaminobenzoate, camphorquinone, butylated hydroxyl toluene, iron pigments, titanium oxide [0808001149] Incremental placement in 2 mm layers or less; polymerization for at least 20 s.

a Composition as provided by respective manufacturer: bis-EMA, ethoxylated bisphenol A glycol dimethacrylate; bis-GMA, bisphenol-glycidyl methacrylate; DGDMA, diethylene glycol dimethacrylate; GPDM, glycerol phosphate dimethacrylate; HEMA, hydroxyethylmethacrylate; PAMM, phthalic acid monoethyl methacrylate; TEGDMA, triethylene glycol dimethacrylate; UDMA, urethane dimethacrylate; 4-MET, 4-methacryloxyethyltrimetellitic acid.

μTBS

The micro-specimens were fixed with cyanoacrylate glue (Model Repair II Blue, Dentsply-Sankin, Ohtawara, Japan) onto a notched BIOMAT jig . The μTBS of each micro-specimen was determined in a universal testing machine (Instron 5848 Micro Tester, High Wycombe, Bucks, UK) using a load cell of 500 N and a crosshead speed of 1 mm/min. The μTBS of each specimen was calculated in MPa, by dividing the imposed force (in N) at the time of fracture by its cross-sectional bond area (in mm 2 ). All specimens were maintained moist throughout the whole preparation and test procedure.

Failure analysis and Feg-SEM examination

All specimens tested were semi-quantitatively analyzed for the mode of failure using a stereomicroscope at a magnification of 50× (Wild M5A, Heerbrug, Switzerland). Failures were recorded as either ‘cohesive in dentin’, ‘adhesive at the interface with the self-adhesive flowable composite or adhesive’, ‘cohesive in the adhesive’, ‘adhesive at the interface between the adhesive and flowable composite’, and ‘cohesive in the (self-adhesive) flowable composite’. Representative specimens were selected for fractographic examination by Feg-SEM (Philips XL30, Eindhoven, The Netherlands), and processed appropriately, including fixation in glutaraldehyde, dehydration in ascending concentrations of ethanol, and chemical drying following the protocol described in detail by Perdigão et al. .

Statistical analysis

One-way analysis of variance (ANOVA) in SubProject 1 and two-way ANOVA in SubProject 2, and Tukey HSD multiple comparisons test (both subprojects) were used to determine statistical differences in μTBS. All data were analyzed at a significance level of 0.05 using a software package (R2.12, R Foundation for Statistical Computing, Vienna, Austria).

Materials and methods

Micro-specimen preparation

The experimental set-up is schematically presented in Fig. 1 . Non-carious and non-restored human third molars (gathered following informed consent approved by the Commission for Medical Ethics of KU Leuven) were stored in 0.5% chloramine in water at 4 °C and used within 1 month after extraction. Ninety-five teeth, 5 teeth per group, were mounted in gypsum blocks in order to facilitate manipulation. For the dentin specimens, the occlusal third of the molar crowns was removed by means of a water-cooled slow-speed diamond saw (Isomet 1000, Buehler, Lake Bluff, IL, USA). A standard smear layer was produced by removing a thin layer of the surface using a water-cooled, high-speed medium-grit diamond bur (842, Komet, Lemgo, Germany) mounted in a custom-adapted MicroSpecimen Former (“BUR-CUT”; thick and compact smear layer) or using 600-grit silicon-carbide paper under running water (“SiC-GROUND”; thin smear layer; solely in SubProject 2). For the enamel specimens (solely in SubProject 2), lingual and buccal enamel was flattened using the above-mentioned BUR-CUT or SiC-GROUND procedure. The teeth were randomly divided in groups according to the SubProject and the specific adhesive material tested ( Table 1 ): In SubProject 1, the μTBS to BUR-CUT dentin of the two SACs, Fusio Liquid Dentin (Pentron Clinical, Orange, CA, USA) and Vertise Flow (Kerr, Orange, CA, USA) was measured and compared to that of four 1-SEa/flowC combinations (AdheSe One/Tetric EvoFlow, Ivoclar Vivadent, Schaan, Liechtenstein; Adper Prompt L-Pop/Filtek Supreme XT Flowable, 3M ESPE, Seefeld, Germany; iBond/Venus flow, Heraeus Kulzer, Hanau, Germany; Xeno V/X-flow, Dentsply, Konstanz, Germany) and of one 3-step etch-and-rinse adhesive (3-E&Ra: OptiBond FL, Kerr) combined with Premise Flowable (Kerr). The effect of pre-etching BUR-CUT dentin with phosphoric acid (Kerr, Orange, CA, USA) on the μTBS of the SAC Vertise Flow (Kerr) was measured as well. In SubProject 2, the μTBS of the two SACs and one 1-SEa/flowC combination (Adper Prompt L-Pop/Filtek Supreme XT Flowable, 3M ESPE) to either BUR-CUT or SiC-GROUND dentin and enamel was measured. The effect of pre-etching BUR-CUT and SiC-GROUND enamel with phosphoric acid (Kerr, Orange, CA, USA) on the μTBS of the SAC Vertise Flow (Kerr) was also measured. All bonding and restorative procedures were performed strictly according to the manufacturer’s instructions ( Table 1 ). After adhesive treatment, the surfaces were built up to a height of 5 mm with the respective flowC (shade A2). Each layer of 1.5 mm was light-cured for 40 s using an Optilux 500 light-curing unit (Demetron/Kerr, Danbury, CT, USA) with a light output of not less than 600 mW/cm 2 . After storage of the teeth for 1 week in 0.5% chloramine at 37 °C, they were sectioned perpendicular to the bonding surface into square specimens of 1 mm × 1 mm using a fully automated precision water-cooled diamond saw (Accutom-50, Struers A/S, Ballerup, Denmark). For each tooth, only the 4 to 9 central sticks were used, resulting in 24 to 35 sticks per group. Specific measures were taken to reduce the incidence of pre-testing failures (ptf) by supporting the slices with alginate (Alginot, Kerr, Orange, CA, USA) during sectioning. The width and thickness of each specimen were measured to the nearest 0.01 mm using a digital calliper (Mitutoyo, Tokyo, Japan). For each micro-specimen, a bonding surface of about 1 mm 2 was obtained.

Fig. 1
Schematic illustrating the study design.

Table 1
Materials used in this study.
Material Composition a [lot number] Application
Self-adhesive flowable composite Fusio Dentin Liquid (Pentron Clinical, Orange, CA, USA) UDMA, TEGDMA, HEMA, 4-MET, nano-sized amorphous silica, silane treated barium glass, minor additives, photo curing system [3479986] Dispense a 1 mm increment and agitate to condition the tooth for 20 s prior to light curing for 10 s; syringe additional material in increments of 1.5–2 mm and light cure each increment for 10 s.
Vertise Flow (Kerr, Orange, CA, USA) GPDM, HEMA, prepolymerized filler, nano-sized ytterbium fluoride, 1-μm barium glass filler, nano-sized colloidal silica [3435242] Dispense a thin layer (<0.5 mm) on a forcefully dried surface; use a provided applicator with a brushing motion for 15–20 s; light cure for 20 s; syringe additional material in increments of less than 2 mm and light cure each increment for 20 s.
One-step self-etch adhesive AdheSe One (Ivoclar Vivadent, Schaan, Liechtenstein) Derivatives of bis-acrylamide, water, bis-methacrylamide dihydrogen phosphate, amino acid acrylamide, hydroxyalkyl-methacrylamide, highly dispersed silicon dioxide, catalysts, stabilizers [L49718] Brush onto the surface for >30 s; disperse excess with a strong stream of air; light cure for 10 s.
Adper Prompt L-Pop (3M ESPE, Seefeld, Germany) First blister : methacrylic phosphates, bis-GMA photo initiator [412924]
Second blister : water, HEMA, polyalkenoic acid polymer [412924]
Brush onto the surface; massage for 15 s applying pressure; gentle stream of air to thoroughly dry to a thin film; apply a second coat without massage; gentle stream of air to thoroughly dry to a thin film; light cure for 10 s.
iBond (Heraeus Kulzer, Hanau, Germany) UDMA, 4-meta, glutaraldehyde, acetone, water, photoinitiators, stabilizer [010075] Application for 20 s with agitation; start with gentle air blow, followed by a strong air blow for at least 5 s; light cure for 20 s.
Xeno V (Dentsply, Konstanz, Germany) Bifunctional acrylic amides, acryloamido alkylsulfonic acid, functionalized phosphoric acid ester, acrylic acid, camphorquinone, butylated benzenediol, water, tert-butanol, photoinitiators, stabilizer [0908001751] Apply adhesive twice; gently agitate for 20 s; carefully air blow for 5 s; light cure for 20 s.
Three-step etch-and-rinse adhesive OptiBond FL (Kerr, Orange, CA, USA) Etching : 37.5% phosphoric acid, silica thickener [3034827]
Primer : HEMA, GPDM, PAMM, ethanol, water, photo-initiator [3457744]
Adhesive : TEGDMA, UDMA, GPDM, HEMA, bis-GMA, filler, photo initiator [3461592]
Etch for 15 s; rinse thoroughly for 15 s; gently air dry for 3 s; apply primer with light brushing motion for 15 s; air dry for 5 s; apply adhesive with light brushing motion for 15 s; air thin for 3 s; light cure for 20 s.
Flowable composite Filtek Supreme XT Flowable (3M ESPE, St. Paul, MN, USA) Bis-GMA, TEGDMA, bis-EMA, functionalized dimethacrylate polymer, silane treated ceramic, silane treated silica, silane treated zirconium oxide [N110837] Apply in layers of max 2 mm and light cure for 20 s.
Premise Flowable (Kerr, Orange, CA, USA) Bis-EMA, TEGDMA, silica nanofiller [3044072] Apply in layers of max 2 mm and polymerize for 20 s.
Tetric EvoFlow (Ivoclar Vivadent, Schaan, Liechtenstein) Bis-GMA, UDMA, decamethylene dimethacrylate, barium glass, ytterbium trifluoride, highly dispersed silicon dioxide, mixed oxide and copolymer [L36209] Apply in layers of max 2 mm and light cure for 20 s (>500 mW/cm 2 ) or 10 s (>1000 mW/cm 2 ).
Venus flow (Heraeus-Kulzer, Hanau, Germany) Bis-GMA, TEGDMA, barium glass [010122] Apply in thin layers (max 2 mm, baseliner max 1 mm); apply a gentle stream of air and light cure for 20 s.
X-flow (Dentsply, Konstanz, Germany) DGDMA, di- and multifunctional acrylate and methacrylate resins, strontium alumino sodium fluoro phosphor silicate glass, highly dispersed silicon dioxide, UV stabilizer, ethyl-4-dimethylaminobenzoate, camphorquinone, butylated hydroxyl toluene, iron pigments, titanium oxide [0808001149] Incremental placement in 2 mm layers or less; polymerization for at least 20 s.
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Nov 28, 2017 | Posted by in Dental Materials | Comments Off on Bonding effectiveness of self-adhesive composites to dentin and enamel
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