Abstracts
The aim of this study was to assess the tensile bond strength of four adhesive systems to enamel and dentin: Clearfil Liner Bond 2V - C, Prime&Bond NT/NRC - PB, Single Bond - SB and All Bond 2 -AB. For such purpose, 40 sound human molars were selected. Crowns were bisected in a mesiodistal direction and each half was ground until flat enamel (E) or dentin (D) surfaces were obtained. A total of 80 specimens were randomly assigned to 4 groups (n=20, 10 in enamel and 10 in dentin). After surface treatment, a composite resin (Z250; 3M) cone was prepared using a split Teflon® matrix. Bond strength was tested in an universal testing machine (0.5 mm/min). Bond strength means in MPa were: C - E: 18.66 (±2.67) and D: 21.62 (±5.29); PB - E: 18.13 (±2.96) and D: 3.19 (±1.40); SB - E: 20.06 (±6.11) and D: 16.95 (±2.57); AB - E: 18.20 (±3.94) and D: 15.94 (±4.72). Statistical analysis of data by two-way ANOVA showed that C presented the best results followed by SB. In conclusion, among the tested materials, Clearfil Liner Bond 2V self-etching primer adhesive syetem had the best performance. The substrate type influenced bond strength, being higher to enamel.
bond strength; enamel; dentin; adhesive systems
Este estudo avaliou a resistência à tração de diferentes sistemas adesivos ao esmalte/dentina: Clearfil Liner Bond 2V - C, Prime&Bond NT/NRC - PB, Single Bond -SB and All Bond 2 -AB. Quarenta molares humanos hígidos tiveram suas coroas seccionadas no sentido mesio-lingual, e posteriormente lixadas até que fossem obtidas superfícies lisas de esmalte (E) ou dentina (D). Oitenta espécimes foi aleatoriamente dividido em 4 grupos (n=20, 10 em esmalte e 10 em dentina). Após o tratamento da superfície de acordo com cada sistema adesivo testado, um cone de resina composta Z250 (3M) foi preparado com uma matriz de Teflon®. O teste de tração foi realizado em uma máquina universal de ensaios (0.5 mm/min). As médias de resistência à tração (em MPa) foram: C - E: 18,66 (±2,67) e D: 21,62 (±5,29); PB - E: 18,13 (±2,96) e D: 3,19 (±1,40); SB - E: 20,06 (±6,11) e D: 16,95 (±2,57); AB - E: 18,20 (±3,94) e D: 15,94 (±4,72). A análise estatística (ANOVA a critérios e teste de Tukey) mostrou que C obteve os melhores resultados, seguido por SB. Concluiu-se que, dentre os materiais testados, o Clearfil Liner Bond 2V teve melhor desempenho, e que o tipo de substrato tratado influenciou na resistência adesiva, sendo esta maior em esmalte.
Tensile bond strength of different adhesive systems to enamel and dentin
Wanessa Christine SouzaZaroni; Letícia Caliento Seixas; Juliane Cristina CicconeNogueira; Daniela Thomazatti Chimello; Regina Guenka PalmaDibb
Department of Restorative Dentistry, School of Dentistry of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil
Correspondence Correspondence: Profa. Dra. Regina Guenka Palma Dibb Faculdade de Odontologia de Ribeirão Preto,USP, Departamento de Odontologia Restauradora Avenida do Café, S/N, 14040904 Ribeirão Preto, SP, Brasil Tel: +551636024016. Fax:+551636330999 email: rgpalma@forp.usp.br
ABSTRACT
The aim of this study was to assess the tensile bond strength of four adhesive systems to enamel and dentin: Clearfil Liner Bond 2V C, Prime&Bond NT/NRC PB, Single Bond SB and All Bond 2 AB. For such purpose, 40 sound human molars were selected. Crowns were bisected in a mesiodistal direction and each half was ground until flat enamel (E) or dentin (D) surfaces were obtained. A total of 80 specimens were randomly assigned to 4 groups (n=20, 10 in enamel and 10 in dentin). After surface treatment, a composite resin (Z250; 3M) cone was prepared using a split Teflon® matrix. Bond strength was tested in an universal testing machine (0.5 mm/min). Bond strength means in MPa were: C E: 18.66 (±2.67) and D: 21.62 (±5.29); PB E: 18.13 (±2.96) and D: 3.19 (±1.40); SB E: 20.06 (±6.11) and D: 16.95 (±2.57); AB E: 18.20 (±3.94) and D: 15.94 (±4.72). Statistical analysis of data by twoway ANOVA showed that C presented the best results followed by SB. In conclusion, among the tested materials, Clearfil Liner Bond 2V selfetching primer adhesive syetem had the best performance. The substrate type influenced bond strength, being higher to enamel.
Key Words: bond strength, enamel, dentin, adhesive systems.
RESUMO
Este estudo avaliou a resistência à tração de diferentes sistemas adesivos ao esmalte/dentina: Clearfil Liner Bond 2V C, Prime&Bond NT/NRC PB, Single Bond SB and All Bond 2 AB. Quarenta molares humanos hígidos tiveram suas coroas seccionadas no sentido mesiolingual, e posteriormente lixadas até que fossem obtidas superfícies lisas de esmalte (E) ou dentina (D). Oitenta espécimes foi aleatoriamente dividido em 4 grupos (n=20, 10 em esmalte e 10 em dentina). Após o tratamento da superfície de acordo com cada sistema adesivo testado, um cone de resina composta Z250 (3M) foi preparado com uma matriz de Teflon®. O teste de tração foi realizado em uma máquina universal de ensaios (0.5 mm/min). As médias de resistência à tração (em MPa) foram: C E: 18,66 (±2,67) e D: 21,62 (±5,29); PB E: 18,13 (±2,96) e D: 3,19 (±1,40); SB E: 20,06 (±6,11) e D: 16,95 (±2,57); AB E: 18,20 (±3,94) e D: 15,94 (±4,72). A análise estatística (ANOVA a critérios e teste de Tukey) mostrou que C obteve os melhores resultados, seguido por SB. Concluiuse que, dentre os materiais testados, o Clearfil Liner Bond 2V teve melhor desempenho, e que o tipo de substrato tratado influenciou na resistência adesiva, sendo esta maior em esmalte.
INTRODUCTION
In composite restorations, stable adhesion to the tooth is essential for clinical success. Recently, many adhesive systems, such as wetbonding and selfetching primer systems have been launched to market.
In great part of currently available adhesive systems the primer and bonding agent are combined in a single bottle, in an attempt to reduce the number of steps and make these products more practical than the multiplebottle bonding agents (1). Although commonly marketed as "onestep" systems, indeed most of them require a separate acid conditioning/rinsing step and the application of several coats of primer/adhesive.
Recent developments in dentin bonding have reintroduced the concept of utilizing the smear layer as a bonding substrate, but with novel insights and improved formulations that can etch beyond the smear layer into the underlying dentin matrix (2). This promising approach to dentin adhesion involves the use of acidic primers, which combine the acid etching and priming steps. The goal of the socalled selfetching primers adhesive systems was to simplify the bonding procedure and to reduce the sensitivity technique of the adhesive protocol by eliminating the acid conditioning step (3). Although the most reliable conclusions on the performance of bonding systems in the mouth must be derived from longterm clinical trials, laboratory assays are still useful to compare their bonding performance and the most common method to evaluate adhesive properties of restorative materials is bond strength assessment.
Given the great variability in formulation, characteristics and acting mode of commercially available bonding agents, it is of interest to establish the most appropriate bonding protocol. This study assessed the bond strength of different adhesive systems (multibottle, onebottle and selfetching primer systems) to enamel and dentin.
MATERIAL AND METHODS
Forty sound human molars, extracted within a sixmonth period and stored in thymolized saline at 4ºC, were selected and cleaned with scaler and rubber cup pumice prophylaxis. Roots were sectioned 2 mm below the cementoenamel junction and crowns were bisected longitudinally in a mesiodistal direction with a watercooled diamond saw in a sectioning machine, providing a total of 80 halves. Surfaces were identified to avoid both buccal and lingual halves of the tooth being assigned to the same experimental group. Then, halves were individually embedded in acrylic resin using PVC cylinders (2.1 cm diameter; 1.1 cm height) and ground using #120600 sandpapers until flat enamel (E) or dentin (D) surfaces were obtained.
Specimens were randomly assigned to 4 groups of equal size, according to the adhesive system used: Clearfil Liner Bond 2V (C); Prime&Bond NT/NRC (PB); Single Bond (SB) and All Bond 2 (AB). The tested materials with their compositions, specifications and manufacturers are given on Table 1. Each main group was divided into two subgroups (n=10), according to the substrate, enamel (E) or dentin (D).
The tooth surfaces were treated and the adhesives were applied to a delimited surface area of the enamel or dentin, according to each manufacturer's instructions.
For the first group (E and D), Clearfil Liner Bond 2V selfetching primer adhesive system was used. Equal drops of primer liquids A and B were dispensed into a well of the mixing dish and mixed immediately before application. The resultant mixture was applied to the entire surface with a disposable brush tip, left undisturbed for 30 s and gently airdried to evaporate the volatile ingredients. No rinsing was accomplished. Then, Bond liquid A was applied to the entire dental substrate, slightly thinned with a mild oilfree air stream and lightcured for 20 s, with a visible light curingunit with a 450 mW/cm2 output. The second group (E and D) was bonded with Prime&Bond NT/NRC, also a selfetching primer adhesive. NRC mixture was applied and left undisturbed for 20 s. The excess was removed with air spray and NT was applied, left undisturbed for 20 s and gently airdried to evaporate the volatile ingredients for 5 s, then lightcured for 10 s. The third group used an ethanolbased, singlebottle bonding agent, Single Bond. Tooth surface was etched with a 35% phosphoric acid gel for 15 s, rinsed for 10 s and gently dried with a cotton pellet to remove water excess and keep the tooth surface moist. Bonding agent was applied using a small brush, dried with a gentle stream of air for 5 s and lightcured for 10 s. For the last group, the adhesive protocol was accomplished using All Bond 2, a multiplebottle system. The tooth surface was etched with a 35% phosphoric acid gel for 15 s, rinsed for 10 s and gently dried with a cotton pellet to remove water excess and keep tooth surface moist. Equal drops of primer liquids A and B were dispensed into a well of the mixing dish and mixed immediately before application. The resultant mixture was applied to the entire substrate with a disposable brush tip for five times, and gently airdried. Then, bond liquid was applied to the entire surface, slightly thinned with a mild oilfree air stream and lightcured for 20 s.
After bonding, each specimen was fixed in a metallic clamping device (developed by The Houston Biomaterial Research Center) keeping the demarcated site parallel to a flat surface. A split bisected Teflon® matrix was positioned over the tooth/resin block resulting in an inverted conical cavity with the smaller diameter coincident to the delimited bonding area (Æ 3mm).
A hybrid lightcured composite resin (Filtek Z250) was inserted into the matrix in three increments, polymerized for 40 s each. As the matrix cavity was completely filled, the specimen was removed from the clamping device and the matrix was opened and separated, leaving adhered to the limited dentin surface an inverted, composite resin cone with a diameter of 6 mm tapering to a diameter of 3 mm and 4 mm high.
After 24hour storage in distilled water at 37ºC, each coneshaped composite/acrylic resin blocks placed into an apparatus with an internal taper corresponding to the specimen shape. This configuration was loaded in tension in an universal testing machine at a crosshead speed of 0.5 mm/min and 50 kgf load cell until fracture. Bond strength means (in MPa) and standard deviation were determined and analyzed statistically by twoway ANOVA and Tukey's test at 5% significance level.
The debonded enamel and dentin sites were viewed under a stereoscopic magnifier (40x) to assess the failure mode. Adhesive failure was considered to be the one at the specimen/adhesive interface; cohesive failure occurred in the material or substrate, with no damage to the interface; mixed failure was the one involving at the same time the interface and the material.
RESULTS
Bond strength means and standard deviation are givenin Table 2. Bond strength to enamel was higher than to dentin independently of adhesive system.
Clearfil Liner Bond 2V presented statistically significant higher bond strength than the other materials (p<0.05). The lowest bond strength means, especially to dentin, was obtained for Prime&Bond, which differed significantly to the other adhesive systems (p<0.05). In the adhesive system x substrate interaction, all materials had similar results in enamel and differed in dentin, Clearfil Liner Bond 2V, presenting the best result.
Failure after testing mostly occurred involving at the same time the bonding interface and the adhesive system/composite resin (mixed failure) or only the adhesive interface (adhesive failure), except for Clearfil Liner Bond 2V in dentin, which showed mixed or cohesive failures in composite for most specimens.
DISCUSSION
In this study, no difference in bond strength to enamel was found among totaletch adhesive systems, wetbonding and selfetching primer adhesive systems. These results are in accordance with those of previous studies (46), which also found no significant difference in bond strength to ground enamel conditioned by phosphoric acid and selfetching primer. However, it has been reported (3,7,8) that there is a great difference in the morphology of enamel treated with phosphoric acid versus selfetching primer when observed under scanning electron microscopy. Phosphoric acid etching creates a deep etching pattern on enamel surface, with thick taglike extensions, while selfetching primer selectively decalcifies the interprismatic enamel, presenting thin taglike extensions (3,4).
The concept of infiltrating the hydrated demineralized dentin matrix with a hydrophilic resin capable of interweaving with the exposed collagen network has been supported by several studies as being the principle to achieve appropriate dentin bonding. Acid etching opens and widens the orifices of dentinal tubules, increases intratubular dentin exposure/permeability and demineralizes intertubular dentin, reportedly to a depth of 7 micrometers (9). The subsequent infiltration and polymerization of the monomer results in a resindentin interdiffusion zone or hybrid layer, which is the source of bonding to acidetched dentin (1,10,11).
It has been shown that the depth of the demineralized intact dentin relates to the concentration of the acidic monomer in the primer and the application time of primer (11). The overall acidity of a primer mixture will determine its selfetching potential (12). A minimum pH value would be required for any primer solution to counteract the buffering capacity of the smear layer and intact dentin before it can etch beyond those substrates. One of the selfetching primer systems tested in this study, Clearfil Liner Bond 2V, has in its composition MDP, an acidic phosphate resin monomer that replaced the phenylP from the original formulation (2). The primer acidity (2.8 pH), although less than that of 3237% phosphoric acid gels is sufficient to etch through the smear layer into the underlying dentin.
That improved etching potential of nonrinsed, selfetching primers coupled to the application of a polymerizable adhesive layer forms a thin hybridized complex, comprising an upper and a lower portion. The upper portion is the result of resin infiltration into the demineralized smear layer, the socalled hybridized smear layer. The lower, thinner portion is due to the formation of a true hybrid layer through the interweaving the of resin monomer with the collagen web within the demineralized dentin matrix. The only material connecting these two layers is the diffused resin. Although the hybridized complex is usually thinner than the hybrid layer formed by adhesive agents using phosphoric acid etching (generally less than 2micrometerthick) it has been shown that selfetching primers produce relatively high bond strength to dentin (13,14).
The findings of a previous investigation (2) with a selfetching primer (Clearfil SE Bond) showed that the thickness of the underlying true hybrid layer remained reasonably consistent (ca 400 to 500 nm), despite great variation in thickness of the surface hybridized smear layer (0 to 4.1 micrometers). This thin layer is possibly mainly responsible for the high bond strength produced by this adhesive system, which may indicate that hybrid layers do not have to be thick to be strong, as long as the collagen fibrils are optimally infiltrated by resin. No correlation between hybrid layer thickness/morphology and bond strength could be found (15,16).
In the present study, the selfetching systems showed different bond strength to dentin, i.e., Clearfil had higher means than Prime&Bond NT/NRC. On the other hand, there was no difference between Clearfil and Single Bond totaletch system in enamel. Another work (17) found higher bond strength to dentin with Prime&Bond NT/NRC than that of the present study, as well as similar bond strength for Prime&Bond NT/NRC and Single Bond, and similar incidence of adhesive failures for both systems. In the present study, most tested systems showed a large number of mixed failures in enamel and cohesive in dentin, except for All Bond 2, which showed adhesive failures in both substrates, as published elsewhere (18).
A suitable explanation for the better performance of Clearfil Liner Bond 2V would be that selfetching primers are generally less techniquesensitive than totoaletch bonding agents because the acidic monomer of selfetching systems demineralizes superficially dentin surface by partially dissolving mineral crystals around the collagen fibrils and simultaneously permitting monomer infiltration, as the demineralizing component of the primer is also the infiltrating resin (1,2). Because the tooth surface is not rinsed following treatment with acidic primers, there is no loss of dentin mass. This is thought to minimize the susceptibility to shrinkage or collapse of the collagen network (10), thereby providing optimal bonding. On the other hand, the poor performance of Prime&Bond NT/NRC system in dentin is probably related to the use of maleic acid as a component of the selfpriming. It was observed (19) that when applying weak acids (maleic acid or NaEDTA) to dentin for 15 s, bond strength significantly decreased compared to 60s applications, given that the highest bond strength was obtained with application of maleic acid for 60 s, or phosphoric acid for 15 s.
Additionally, adhesive systems with waterbased primers seem less critical as far as the wetness of the acidconditioned dentin is concerned (20). Adhesive systems with ethanol or acetonebased primers show a restricted "windows of opportunity" since a precise amount of water should be retained postconditionally on dentin surface for efficient bonding to be achieved (20). Depending on the water content of the primer system, different sensitivity ranges or shifts in the "windows" for optimal adhesion have been observed. Differences in the bond strength of the tested systems may be a result of different primer formulations.
Current developments in dentin bonding have focused on simplifying the application methods by decreasing the time and steps required for placement. While these simplified adhesive systems are convenient, some of them had their efficacy for stable bonding already demonstrated. Although, longterm clinical trials are needed to fully understand the performance of the newly developed bonding systems.
Accepted February 4, 2004
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Correspondence:
Publication Dates
-
Publication in this collection
25 Oct 2007 -
Date of issue
2007
History
-
Received
04 Feb 2004 -
Accepted
04 Feb 2004