Abstract:

This study aimed to evaluate the bond strength of a universal adhesive system to enamel surrounding real-life carious cavities. Twenty-eight permanent molars (n = 7) with carious lesions in dentin were subjected to selective carious tissue removal to firm dentin and had their crowns sectioned longitudinally. A universal adhesive system (Single Bond Universal [SBU] used in either etch-and-rinse and self-etch strategies) was compared with an etch-and-rinse Adper Single Bond 2 (ASB) and a self-etch Clearfil SE Bond (CSE) adhesive systems (control systems). Adhesives were applied on the enamel, assumed demineralized, surrounding the cavity margins and on sound enamel (control substrate). Composite cylinders were built (0.72 mm²) and microshear bond strength (µSBS) test was performed after 24 h of water storage. The µSBS values (MPa) were analyzed using two-way ANOVA and Tukey's post hoc tests (α = 0.05). Bond strength values obtained in demineralized enamel surrounding carious cavity margins were significantly lower than that obtained in sound enamel (distant from carious cavity margins) (p = 0.035). The bonding strategy of the SBU did not influenced the bond strength values, which were higher than that obtained with ASB. CSE showed similar µSBS values to ASB and SBU in the self-etch mode. In conclusion, the bond strength to enamel assumed demineralized is lower than to sound enamel. The enamel surrounding carious cavities jeopardize the bonding of universal adhesive system. The bond strength of universal adhesive is similar, regardless to bonding strategy.

Keywords:
Dental Enamel; Dental Caries; Adhesives; Dental Materials; Dental Bonding

Introduction

The technique of selective removal of carious tissue¹1. Schwendicke F, Frencken JE, Bjørndal L, Maltz M, Manton DJ, Ricketts D, et al. Managing carious lesions: consensus recommendations on carious tissue removal. Adv Dent Res. 2016 May;28(2):58-67. https://doi.org/10.1177/0022034516639271
https://doi.org/10.1177/0022034516639271... , formerly known as partial caries removal, is widely adopted as a minimally invasive approach in the restorative treatment of primary and permanent teeth to reduce the risk of pulp exposure,²2. Franzon R, Guimarães LF, Magalhães CE, Haas AN, Araujo FB. Outcomes of one-step incomplete and complete excavation in primary teeth: a 24-month randomized controlled trial. Caries Res. 2014;48(5):376-83. https://doi.org/10.1159/000357628
https://doi.org/10.1159/000357628... ^,33. Lula EC, Monteiro-Neto V, Alves CM, Ribeiro CC. Microbiological analysis after complete or partial removal of carious dentin in primary teeth: a randomized clinical trial. Caries Res. 2009;43(5):354-8. https://doi.org/10.1159/000231572
https://doi.org/10.1159/000231572... ^,44. Maltz M, Koppe B, Jardim JJ, Alves LS, de Paula LM, Yamaguti PM, et al. Partial caries removal in deep caries lesions: a 5-year multicenter randomized controlled trial. Clin Oral Investig. 2018 Apr;22(3):1337-43. https://doi.org/10.1007/s00784-017-2221-0
https://doi.org/10.1007/s00784-017-2221-... treatment costs,⁵5. Schwendicke F, Stolpe M, Meyer-Lueckel H, Paris S, Dörfer CE. Cost-effectiveness of one- and two-step incomplete and complete excavations. J Dent Res. 2013 Oct;92(10):880-7. https://doi.org/10.1177/0022034513500792
https://doi.org/10.1177/0022034513500792... post-operative complications, and the overextension of the cavities that weakens tooth structure increasing the risk of restoration failure.⁶6. Zhang Z, Zheng K, Li E, Li W, Li Q, Swain MV. Mechanical benefits of conservative restoration for dental fissure caries. J Mech Behav Biomed Mater. 2016 Jan;53:11-20. https://doi.org/10.1016/j.jmbbm.2015.08.010
https://doi.org/10.1016/j.jmbbm.2015.08.... In selective removal of carious tissue, peripheral enamel and dentin should be prepared to hard/sound tissue while soft or firm carious tissue should be left over the pulp.⁷7. Schwendicke F. Contemporary concepts in carious tissue removal: A review. J Esthet Restor Dent. 2017 Nov;29(6):403-8. https://doi.org/10.1111/jerd.12338
https://doi.org/10.1111/jerd.12338... ^,88. Banerjee A, Frencken JE, Schwendicke F, Innes NP. Contemporary operative caries management: consensus recommendations on minimally invasive caries removal. Br Dent J. 2017 Aug;223(3):215-22. https://doi.org/10.1038/sj.bdj.2017.672
https://doi.org/10.1038/sj.bdj.2017.672... This strategy for carious tissue removal is the treatment of choice for both dentitions and, furthermore, it is a less time-consuming and user-friendly technique, along with the use of universal adhesive systems.

These versatile adhesives, also called multi-mode systems,⁹9. Hanabusa M, Mine A, Kuboki T, Momoi Y, Van Ende A, Van Meerbeek B, et al. Bonding effectiveness of a new ‘multi-mode’ adhesive to enamel and dentine. J Dent. 2012 Jun;40(6):475-84. https://doi.org/10.1016/j.jdent.2012.02.012
https://doi.org/10.1016/j.jdent.2012.02.... ^,1010. Perdigão J, Sezinando A, Monteiro PC. Laboratory bonding ability of a multi-purpose dentin adhesive. Am J Dent. 2012 Jun;25(3):153-8. can be used in strategies with total or selective acid conditioning in enamel or in self-etch mode. Recently, some studies evaluated the performance of these adhesives to dental enamel and most of them indicated that etch-and-rinse strategy provided higher bond strength to enamel.¹¹11. de Goes MF, Shinohara MS, Freitas MS. Performance of a new one-step multi-mode adhesive on etched vs non-etched enamel on bond strength and interfacial morphology. J Adhes Dent. 2014 Jun;16(3):243-50. https://doi.org/10.3290/j.jad.a32033
https://doi.org/10.3290/j.jad.a32033... ^,1212. Antoniazzi BF, Nicoloso GF, Lenzi TL, Soares FZ, Rocha RO. Selective acid etching improves the bond strength of universal adhesive to sound and demineralized enamel of primary teeth. J Adhes Dent. 2016;18(4):311-6. https://doi.org/10.3290/j.jad.a36154
https://doi.org/10.3290/j.jad.a36154... ^,1313. Cardenas AM, Siqueira F, Rocha J, Szesz AL, Anwar M, El-Askary F, et al. Influence of conditioning time of universal adhesives on adhesive properties and enamel-etching pattern. Oper Dent. 2016 Sep-Oct;41(5):481-90. https://doi.org/10.2341/15-213-L
https://doi.org/10.2341/15-213-L... ^,1414. Suzuki T, Takamizawa T, Barkmeier WW, Tsujimoto A, Endo H, Erickson RL, et al. Influence of etching mode on enamel bond durability of universal adhesive systems. Oper Dent. 2016 Sep-Oct;41(5):520-30. https://doi.org/10.2341/15-347-L
https://doi.org/10.2341/15-347-L... ^,1515. Vermelho PM, Reis AF, Ambrosano GM, Giannini M. Adhesion of multimode adhesives to enamel and dentin after one year of water storage. Clin Oral Investig. 2017 Jun;21(5):1707-15. https://doi.org/10.1007/s00784-016-1966-1
https://doi.org/10.1007/s00784-016-1966-...

More attention has been given to the dentin-pulp complex when referring to the selective removal of carious tissue, including the arrest of the caries process³3. Lula EC, Monteiro-Neto V, Alves CM, Ribeiro CC. Microbiological analysis after complete or partial removal of carious dentin in primary teeth: a randomized clinical trial. Caries Res. 2009;43(5):354-8. https://doi.org/10.1159/000231572
https://doi.org/10.1159/000231572... ^,1616. Lula EC, Almeida LJ Jr, Alves CM, Monteiro-Neto V, Ribeiro CC. Partial caries removal in primary teeth: association of clinical parameters with microbiological status. Caries Res. 2011;45(3):275-80. https://doi.org/10.1159/000325854
https://doi.org/10.1159/000325854... and preservation of pulp vitality.²2. Franzon R, Guimarães LF, Magalhães CE, Haas AN, Araujo FB. Outcomes of one-step incomplete and complete excavation in primary teeth: a 24-month randomized controlled trial. Caries Res. 2014;48(5):376-83. https://doi.org/10.1159/000357628
https://doi.org/10.1159/000357628... ^,33. Lula EC, Monteiro-Neto V, Alves CM, Ribeiro CC. Microbiological analysis after complete or partial removal of carious dentin in primary teeth: a randomized clinical trial. Caries Res. 2009;43(5):354-8. https://doi.org/10.1159/000231572
https://doi.org/10.1159/000231572... ^,44. Maltz M, Koppe B, Jardim JJ, Alves LS, de Paula LM, Yamaguti PM, et al. Partial caries removal in deep caries lesions: a 5-year multicenter randomized controlled trial. Clin Oral Investig. 2018 Apr;22(3):1337-43. https://doi.org/10.1007/s00784-017-2221-0
https://doi.org/10.1007/s00784-017-2221-... However, bonding to enamel should be a concern, since the stability of the resin-bonded dentin¹⁷17. Torkabadi S, Nakajima M, Ikeda M, Foxton RM, Tagami J. Influence of bonded enamel margins on dentin bonding stability of one-step self-etching adhesives. J Adhes Dent. 2009 Oct;11(5):347-53. and effectiveness of marginal sealing¹⁸18. Heintze SD. Clinical relevance of tests on bond strength, microleakage and marginal adaptation. Dent Mater. 2013 Jan;29(1):59-84. https://doi.org/10.1016/j.dental.2012.07.158
https://doi.org/10.1016/j.dental.2012.07... depends on the bonding to surrounding enamel. In both the non-selective and selective removal to firm dentin approaches, the excavation of carious dentin is performed only with manual or low-speed rotary instruments¹⁶16. Lula EC, Almeida LJ Jr, Alves CM, Monteiro-Neto V, Ribeiro CC. Partial caries removal in primary teeth: association of clinical parameters with microbiological status. Caries Res. 2011;45(3):275-80. https://doi.org/10.1159/000325854
https://doi.org/10.1159/000325854... ^,1919. Dalpian DM, Ardenghi TM, Demarco FF, Garcia-Godoy F, De Araujo FB, Casagrande L. Clinical and radiographic outcomes of partial caries removal restorations performed in primary teeth. Am J Dent. 2014 Apr;27(2):68-72. and the access to the lesion is performed with high-speed rotary instruments only when needed.⁴4. Maltz M, Koppe B, Jardim JJ, Alves LS, de Paula LM, Yamaguti PM, et al. Partial caries removal in deep caries lesions: a 5-year multicenter randomized controlled trial. Clin Oral Investig. 2018 Apr;22(3):1337-43. https://doi.org/10.1007/s00784-017-2221-0
https://doi.org/10.1007/s00784-017-2221-... Thus, it is possible that this conservative enamel preparation may result in some degree of demineralized enamel left at the cavity margins. Furthermore, the visual-tactile inspection is a subjective yet widely used criteria to determine the end-point of caries removal.²⁰20. Kidd EA, Joyston-Bechal S, Beighton D. Microbiological validation of assessments of caries activity during cavity preparation. Caries Res. 1993;27(5):402-8. https://doi.org/10.1159/000261571
https://doi.org/10.1159/000261571... ^,2121. Ntovas P, Loubrinis N, Maniatakos P, Rahiotis C. Evaluation of dental explorer and visual inspection for the detection of residual caries among Greek dentists. J Conserv Dent. 2018 May-Jun;21(3):311-8. https://doi.org/10.4103/JCD.JCD_67_17
https://doi.org/10.4103/JCD.JCD_67_17...

Although few studies have considered the demineralized enamel as a substrate in bond strength evaluations, bonding to demineralized enamel seems to be lower than to sound enamel,¹²12. Antoniazzi BF, Nicoloso GF, Lenzi TL, Soares FZ, Rocha RO. Selective acid etching improves the bond strength of universal adhesive to sound and demineralized enamel of primary teeth. J Adhes Dent. 2016;18(4):311-6. https://doi.org/10.3290/j.jad.a36154
https://doi.org/10.3290/j.jad.a36154... ^,2222. Tedesco TK, Soares FZ, Grande RH, Filho LE, Rocha RO. Effect of cariogenic challenge on bond strength of adhesive systems to sound and demineralized primary and permanent enamel. J Adhes Dent. 2014 Oct;16(5):421-8. probably due lower mineral content, higher porosity of the surface,²³23. Silverstone LM. Structure of carious enamel, including the early lesion. Oral Sci Rev. 1973;3:100-60. widened intercrystalline spaces, and consequently a larger pore volume than sound enamel,²⁴24. Kidd EAM, Fejerskov O. What constitutes dental caries? Histopathology of carious enamel and dentin related to the action of cariogenic biofilms. J Dent Res. 2004;83(1 Suppl):35-8. https://doi.org/10.1177/154405910408301s07
https://doi.org/10.1177/154405910408301s... ^,2525. Palamara J, Phakey PP, Rachinger WA, Orams HJ. Ultrastructure of the intact surface zone of white spot and brown spot carious lesions in human enamel. J Oral Pathol. 1986 Jan;15(1):28-35. https://doi.org/10.1111/j.1600-0714.1986.tb00560.x
https://doi.org/10.1111/j.1600-0714.1986... producing an unsatisfactory etching pattern and infiltration of resin monomers.²²22. Tedesco TK, Soares FZ, Grande RH, Filho LE, Rocha RO. Effect of cariogenic challenge on bond strength of adhesive systems to sound and demineralized primary and permanent enamel. J Adhes Dent. 2014 Oct;16(5):421-8.

Therefore, considering that enamel surrounding carious cavities after carious tissue removal is probably demineralized despite the absence of clinical signs of demineralization, this study aimed to evaluate the bond strength of a universal adhesive system to enamel surrounding real-life carious cavities. The null hypothesis was that there is no difference in the bonding values regardless the enamel proximity of carious cavities.

Methodology

The influence of the enamel proximity to cavities on the bond strength values was assessed by microshear bond strength (µSBS) test. Enamel surrounding caries was assumed demineralized and enamel distant from caries was considered sound enamel. The experimental design of the study is presented in Figure 1. The research protocol received previous approval from the Local Ethics Committee.

Sample preparation

Twenty-eight extracted human permanent molars were selected from a pool of extracted teeth according the following inclusion criteria: presence of carious cavities involving dentin on occlusal or occlusal-proximal surfaces (International Caries Detection and Assessment System - ICDAS 5 or 6);²⁶26. Ismail AI, Sohn W, Tellez M, Amaya A, Sen A, Hasson H, et al. The International Caries Detection and Assessment System (ICDAS): an integrated system for measuring dental caries. Community Dent Oral Epidemiol. 2007 Jun;35(3):170-8. https://doi.org/10.1111/j.1600-0528.2007.00347.x
https://doi.org/10.1111/j.1600-0528.2007... no restorations, cracks, enamel defects or signs of previous restorative intervention. Teeth were stored in 0.5% chloramine T solution at 4ºC for up to 30 days before being used.

Teeth were randomly allocated into four groups (n = 7) by a program to generate random number list (Random.org - Randomness and Integrity Services Ltd., Dublin, Ireland) according to the adhesive system: Single Bond Universal (SBU) (3M ESPE; St Paul, USA) in both self-etch (SE) and etch-and-rinse (ER) application modes; Adper Single Bond 2 (ASB) (3M ESPE; St Paul, USA) an etch-and-rinse system; and Clearfil SE Bond (CSE) (Kuraray Noritake; Tokyo, Japan), a self-etch system.

A single experienced operator performed the selective removal of the carious tissue. The decayed tissue of the sidewalls was completely removed by using low-speed metal burs and/or hand excavator, according to the size of the cavity⁴4. Maltz M, Koppe B, Jardim JJ, Alves LS, de Paula LM, Yamaguti PM, et al. Partial caries removal in deep caries lesions: a 5-year multicenter randomized controlled trial. Clin Oral Investig. 2018 Apr;22(3):1337-43. https://doi.org/10.1007/s00784-017-2221-0
https://doi.org/10.1007/s00784-017-2221-... using the visual-tactile criteria in assessing the end-point of carious tissue removal. On the cavity floor, carious tissue removal was continued until firm dentin (‘leathery’ consistency) was encountered and was left over the pulp.²⁷27. Schwendicke F, Meyer-Lueckel H, Dörfer C, Paris S. Failure of incompletely excavated teeth—a systematic review. J Dent. 2013 Jul;41(7):569-80. https://doi.org/10.1016/j.jdent.2013.05.004
https://doi.org/10.1016/j.jdent.2013.05....

The presence/absence of white spot lesion in the enamel was verified after the selective carious tissue removal. If the enamel surrounding cavity margins presented some visible white spot lesion (opaque enamel with a dull-whitish aspect) the tooth was excluded from the study and replaced. Afterwards, the crowns of all teeth were longitudinally sectioned at the center of the cavities using a low-speed water-cooled diamond saw in a cutting machine (Labcut 1010, Extec Co., Enfield, USA) to obtain at least two sections (specimens) of each tooth. Thereby, flat transversal enamel surfaces were obtained, as required for the microshear bond test, preserving the presumed-demineralized enamel. Each section was glued with cyanoacrylate in PVC rings embedded with self-curing acrylic resin (JET Clássico^®, São Paulo, Brazil), constituting a specimen. Specimens were manually ground with 600-grit SIC paper under running water for 60 s to create standardized flat enamel surfaces.²⁸28. Loguercio AD, Moura SK, Pellizzaro A, Dal-Bianco K, Patzlaff RT, Grande RH, et al. Durability of enamel bonding using two-step self-etch systems on ground and unground enamel. Oper Dent. 2008 Jan-Feb;33(1):79-88. https://doi.org/10.2341/07-42
https://doi.org/10.2341/07-42...

Bonding and restorative procedures

The adhesive systems were applied to enamel according to the manufacturers’ instructions (Table 1). Starch tubes (Isabela, Ind. e Com. Food, São Paulo, Brazil) with 0.96 mm of internal diameter and 1.0 mm in height,²⁹29. Tedesco TK, Montagner AF, Skupien JA, Soares FZ, Susin AH, Rocha RO. Starch tubing: an alternative method to build up microshear bond test specimens. J Adhes Dent. 2013 Aug;15(4):311-5. https://doi.org/10.3290/j.jad.a28602
https://doi.org/10.3290/j.jad.a28602... were positioned over the enamel surface prior the light curing the adhesives with a light emitting diode curing unit (Emitter B, Schuster, Santa Maria, Brazil) with a light output of at least 1,250 mW/cm². The devices own radiometer quantified the output power. The tubes were carefully filled with composite resin (Filtek Z250 XT, 3M ESPE, St Paul, USA; shade A2) and light cured for 20 s. At least two cylinders of composite resin were built in each specimen, one over the enamel surrounding carious cavity (as close as possible to the outer surface) and one over the sound enamel (at the opposite side of the carious cavity). A single trained operator performed all adhesive and restorative procedures at room temperature.

Microshear Bond Strength (µSBS) Test

The specimens were stored in distilled water at 37°C for 24 h. After this period, the starch tubes were gently removed using air/water spray and a probe. Cylinders of composite resin were examined under a stereomicroscope (Stereo Discovery V20, Carl Zeiss do Brazil Ltda., Rio de Janeiro, Brazil) at 10× magnification to verify the presence of bubbles and gaps in the interface or other defects. When defects were found, all the specimens from the tooth were excluded and the tooth was replaced.

Each specimen was individually attached to a universal testing machine (Emic, São José dos Pinhais, Brazil), equipped with a 100 N load cell (10 kgf), with 0.01 N reading resolution and minimum sensitivity of 2 N. A stainless steel wire (0.20 mm diameter) was looped around the composite resin cylinder as closer as possible to the resin/enamel interface. A shear load was applied at a crosshead speed of 1.0 mm/min until failure. To avoid bias, a single and blinded operator carried out bond strength measurement procedures.

Failure mode

All debonded specimens were observed under stereomicroscope at 40× magnification by a trained and blinded examiner to determine failure mode: cohesive failure within enamel or resin and interfacial failure.¹⁷17. Torkabadi S, Nakajima M, Ikeda M, Foxton RM, Tagami J. Influence of bonded enamel margins on dentin bonding stability of one-step self-etching adhesives. J Adhes Dent. 2009 Oct;11(5):347-53. Only specimens with interfacial fractures were considered in the calculation of bond strength values.

Four representative specimens from each experimental group were prepared for failure mode evaluation under scanning electron microscope (SEM). Specimens were dehydrated in ascending degrees of ethanol (50, 75, and 90% for 5 min each, and 100% for 3 h)³⁰30. Montagner AF, Skupien JA, Borges MF, Krejci I, Bortolotto T, Susin AH. Effect of sodium hypochlorite as dentinal pretreatment on bonding strength of adhesive systems. Indian J Dent Res. 2015 Jul-Aug;26(4):416-20. https://doi.org/10.4103/0970-9290.167633
https://doi.org/10.4103/0970-9290.167633... and kept in vacuum for 24 h. Subsequently, they were gold sputter-coated for SEM observation.

Statistical analysis

The tooth was considered the experimental unit. Thus, the µSBS values of all composite cylinders from the same tooth, according the enamel location, were averaged for statistical purposes. The sample size of 7 teeth per group was estimated previously considering an 80% power, a coefficient of variation of 20%, and assuming a two-sided 5% significance level for comparisons. Pretest failures (PTFs) that occurred during specimens’ testing preparation were not included in the statistical analysis because were equally distributed in all groups.

The normal distribution of the data and equality of variances were confirmed with Kolmogorov-Smirnov and Cochran tests, respectively. The µSBS means were submitted to two-way ANOVA with pairwise comparisons (enamel location vs. adhesive system) and Tukey's post hoc tests at a significance level of 5%. All statistical analyses were performed using the Minitab software (Minitab Inc., State College, USA).

Results

Descriptive statistics, including means, standard deviations, and the number of tested specimens per group are presented in Table 2. The cross-interaction product “enamel location vs. adhesive system” was not significant (p = 0.62). However, the main factors “enamel location” (p = 0.03) and “adhesive system” (p < 0.00) significantly influenced the µSBS values. Bond strength of adhesive system to enamel surrounding carious cavities, assumed as demineralized enamel, was approximately 10% lower than that obtained to sound enamel. SBU presented similar values in ER (12.3 ± 1.8) and SE (10.5 ± 0.8) strategies, and higher values than those obtained with ASB (8.1 ± 0.4). CSE (8.7 ± 0.5) showed similar µSBS values to ASB and the SBU in the SE mode. PTFs occurred in all groups (Table 3).

All specimens showed interfacial failures, regardless of the enamel location (Figure 2).

Discussion

The current investigation has demonstrated that bond strength of adhesive systems to enamel assumed demineralized was lower than those obtained to sound enamel. Thus, the proximity to the carious lesions can influence negatively the bond strength values to enamel. Moreover, since the use of artificial lesions decreased external validity,³¹31. Schwendicke F, Kern M, Blunck U, Dörfer C, Drenck J, Paris S. Marginal integrity and secondary caries of selectively excavated teeth in vitro. J Dent. 2014 Oct;42(10):1261-8. https://doi.org/10.1016/j.jdent.2014.08.002
https://doi.org/10.1016/j.jdent.2014.08.... the evaluation of the performance of adhesive systems to enamel surrounding real-life carious cavities, consequence of natural caries process, increases the external validity of our findings, besides being original and clinically relevant.

The histological structure of demineralized enamel is different from sound enamel,²³23. Silverstone LM. Structure of carious enamel, including the early lesion. Oral Sci Rev. 1973;3:100-60.^,2424. Kidd EAM, Fejerskov O. What constitutes dental caries? Histopathology of carious enamel and dentin related to the action of cariogenic biofilms. J Dent Res. 2004;83(1 Suppl):35-8. https://doi.org/10.1177/154405910408301s07
https://doi.org/10.1177/154405910408301s... ^,2525. Palamara J, Phakey PP, Rachinger WA, Orams HJ. Ultrastructure of the intact surface zone of white spot and brown spot carious lesions in human enamel. J Oral Pathol. 1986 Jan;15(1):28-35. https://doi.org/10.1111/j.1600-0714.1986.tb00560.x
https://doi.org/10.1111/j.1600-0714.1986... which should be related to reduced bond strength due to unsatisfactory conditioning pattern and infiltration of resin monomers.²²22. Tedesco TK, Soares FZ, Grande RH, Filho LE, Rocha RO. Effect of cariogenic challenge on bond strength of adhesive systems to sound and demineralized primary and permanent enamel. J Adhes Dent. 2014 Oct;16(5):421-8. This fact may justify the lower bond strength of adhesive systems to enamel adjacent to dentin carious lesions. This is in line with previous studies that compared sound and demineralized enamel substrates, exhibiting significant differences in bond strength values.¹²12. Antoniazzi BF, Nicoloso GF, Lenzi TL, Soares FZ, Rocha RO. Selective acid etching improves the bond strength of universal adhesive to sound and demineralized enamel of primary teeth. J Adhes Dent. 2016;18(4):311-6. https://doi.org/10.3290/j.jad.a36154
https://doi.org/10.3290/j.jad.a36154... ^,2222. Tedesco TK, Soares FZ, Grande RH, Filho LE, Rocha RO. Effect of cariogenic challenge on bond strength of adhesive systems to sound and demineralized primary and permanent enamel. J Adhes Dent. 2014 Oct;16(5):421-8. Considering that the enamel condition may compromise adhesion, it may be suggested changes in the treatment of enamel surrounding cavities subjected to non-selective and selective removal approaches in teeth with ‘open’ cavities (ICDAS 5 or 6). Since the mineral loss suffered by enamel is not always clinically visible,³²32. Cury JA, Tenuta LM. Enamel remineralization: controlling the caries disease or treating early caries lesions? Braz Oral Res. 2009;23 Suppl 1:23-30. https://doi.org/10.1590/S1806-83242009000500005
https://doi.org/10.1590/S1806-8324200900... the enamel suspected of mineral loss and unintentionally left after dentin carious removal could be carefully prepared prior the adhesive procedures with rotary instruments at high speed.

The enamel surrounding carious cavities requires more attention in non-selective and selective excavation technique. Despite that the enamel surrounding open cavities is less demineralized than that in closed lesions,³³33. Neves AA, Vargas DO, Santos TM, Lopes RT, Sousa FB. Is the morphology and activity of the occlusal carious lesion related to the lesion progression stage? Arch Oral Biol. 2016 Dec;72:33-8. https://doi.org/10.1016/j.archoralbio.2016.08.004
https://doi.org/10.1016/j.archoralbio.20... it is still very demineralized and this condition could jeopardize the adhesion, as previously seen in laboratory studies.¹²12. Antoniazzi BF, Nicoloso GF, Lenzi TL, Soares FZ, Rocha RO. Selective acid etching improves the bond strength of universal adhesive to sound and demineralized enamel of primary teeth. J Adhes Dent. 2016;18(4):311-6. https://doi.org/10.3290/j.jad.a36154
https://doi.org/10.3290/j.jad.a36154... ^,2222. Tedesco TK, Soares FZ, Grande RH, Filho LE, Rocha RO. Effect of cariogenic challenge on bond strength of adhesive systems to sound and demineralized primary and permanent enamel. J Adhes Dent. 2014 Oct;16(5):421-8. Besides that, the presence of enamel margins is relevant, because dentinal margins showed more marginal imperfections, gaps, and microleakage.³¹31. Schwendicke F, Kern M, Blunck U, Dörfer C, Drenck J, Paris S. Marginal integrity and secondary caries of selectively excavated teeth in vitro. J Dent. 2014 Oct;42(10):1261-8. https://doi.org/10.1016/j.jdent.2014.08.002
https://doi.org/10.1016/j.jdent.2014.08....

The inner enamel surface was used in the present study, since the cut of slices was transversal. Moreover, the enamel surface was ground with 600-grit silicon carbide paper, which affected the nature of enamel smear layer, turning the substrate more receptive to bonding with self-etch systems.³⁴34. Mine A, De Munck J, Vivan Cardoso M, Van Landuyt KL, Poitevin A, Kuboki T, et al. Enamel-smear compromises bonding by mild self-etch adhesives. J Dent Res. 2010 Dec;89(12):1505-9. https://doi.org/10.1177/0022034510384871
https://doi.org/10.1177/0022034510384871... ^,3535. Perdigão J, Geraldeli S. Bonding characteristics of self-etching adhesives to intact versus prepared enamel. J Esthet Restor Dent. 2003;15(1):32-41. https://doi.org/10.1111/j.1708-8240.2003.tb00280.x
https://doi.org/10.1111/j.1708-8240.2003... Thereby, the performance of Single Bond Universal in both strategies was similar, in agreement with previous studies that evaluated universal adhesives.¹⁰10. Perdigão J, Sezinando A, Monteiro PC. Laboratory bonding ability of a multi-purpose dentin adhesive. Am J Dent. 2012 Jun;25(3):153-8.^,3636. Loguercio AD, Muñoz MA, Luque-Martinez I, Hass V, Reis A, Perdigão J. Does active application of universal adhesives to enamel in self-etch mode improve their performance? J Dent. 2015 Sep;43(9):1060-70. https://doi.org/10.1016/j.jdent.2015.04.005
https://doi.org/10.1016/j.jdent.2015.04.... ^,3737. Torres CR, Zanatta RF, Silva TJ, Huhtala MF, Borges AB. Influence of previous acid etching on bond strength of universal adhesives to enamel and dentin. Gen Dent. 2017 Mar-Apr;65(2):e17-21. However, recent studies evaluating the performance of Single Bond Universal to enamel¹¹11. de Goes MF, Shinohara MS, Freitas MS. Performance of a new one-step multi-mode adhesive on etched vs non-etched enamel on bond strength and interfacial morphology. J Adhes Dent. 2014 Jun;16(3):243-50. https://doi.org/10.3290/j.jad.a32033
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https://doi.org/10.2341/15-213-L... ^,1313. Cardenas AM, Siqueira F, Rocha J, Szesz AL, Anwar M, El-Askary F, et al. Influence of conditioning time of universal adhesives on adhesive properties and enamel-etching pattern. Oper Dent. 2016 Sep-Oct;41(5):481-90. https://doi.org/10.2341/15-213-L
https://doi.org/10.2341/15-213-L... ^,1414. Suzuki T, Takamizawa T, Barkmeier WW, Tsujimoto A, Endo H, Erickson RL, et al. Influence of etching mode on enamel bond durability of universal adhesive systems. Oper Dent. 2016 Sep-Oct;41(5):520-30. https://doi.org/10.2341/15-347-L
https://doi.org/10.2341/15-347-L... ^,1515. Vermelho PM, Reis AF, Ambrosano GM, Giannini M. Adhesion of multimode adhesives to enamel and dentin after one year of water storage. Clin Oral Investig. 2017 Jun;21(5):1707-15. https://doi.org/10.1007/s00784-016-1966-1
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https://doi.org/10.1016/j.jdent.2015.10.... stated that the enamel bond strength values are higher when used with the etching strategy.

The results of the two-step self-etch adhesive system (Clearfil SE Bond) did not differ from bond strength values of the Single Bond Universal in the self-etch mode. Both adhesives contain 10-MPD (10-methacryloxydecyl dihydrogen phosphate) as acidic monomer. This monomer contains phosphate groups able to produce ionic chemical bonds with calcium in hydroxyapatite, which may explain the similar performance. Previous studies also found similar bond strength to these adhesive systems.¹¹11. de Goes MF, Shinohara MS, Freitas MS. Performance of a new one-step multi-mode adhesive on etched vs non-etched enamel on bond strength and interfacial morphology. J Adhes Dent. 2014 Jun;16(3):243-50. https://doi.org/10.3290/j.jad.a32033
https://doi.org/10.3290/j.jad.a32033... ^,1212. Antoniazzi BF, Nicoloso GF, Lenzi TL, Soares FZ, Rocha RO. Selective acid etching improves the bond strength of universal adhesive to sound and demineralized enamel of primary teeth. J Adhes Dent. 2016;18(4):311-6. https://doi.org/10.3290/j.jad.a36154
https://doi.org/10.3290/j.jad.a36154... Besides that, the way the enamel prisms were exposed in axial longitudinal sections may have influenced the bond strength results,³⁹39. Ikeda T, Uno S, Tanaka T, Kawakami S, Komatsu H, Sano H. Relation of enamel prism orientation to microtensile bond strength. Am J Dent. 2002 Apr;15(2):109-13. favouring the Single Bond Universal, which has the additional chemical interaction of 10-MDP and hydroxyapatite, compared to Adper Single Bond 2.¹¹11. de Goes MF, Shinohara MS, Freitas MS. Performance of a new one-step multi-mode adhesive on etched vs non-etched enamel on bond strength and interfacial morphology. J Adhes Dent. 2014 Jun;16(3):243-50. https://doi.org/10.3290/j.jad.a32033
https://doi.org/10.3290/j.jad.a32033... ^,4040. Carvalho MP, Morari VH, Susin AH, Rocha RO, Valandro LF, Soares FZ. Endodontic irrigation protocols: effects on bonding of adhesive systems to coronal enamel and dentin. J Esthet Restor Dent. 2017 May;29(3):222-8. https://doi.org/10.1111/jerd.12289
https://doi.org/10.1111/jerd.12289... However, both the two-step self-etch system (Clearfil SE Bond) and the etch-and-rinse adhesive (Adper Single Bond 2) presented similar performance on permanent enamel, in accordance with previous studies.²²22. Tedesco TK, Soares FZ, Grande RH, Filho LE, Rocha RO. Effect of cariogenic challenge on bond strength of adhesive systems to sound and demineralized primary and permanent enamel. J Adhes Dent. 2014 Oct;16(5):421-8.^,2929. Tedesco TK, Montagner AF, Skupien JA, Soares FZ, Susin AH, Rocha RO. Starch tubing: an alternative method to build up microshear bond test specimens. J Adhes Dent. 2013 Aug;15(4):311-5. https://doi.org/10.3290/j.jad.a28602
https://doi.org/10.3290/j.jad.a28602... ^,3434. Mine A, De Munck J, Vivan Cardoso M, Van Landuyt KL, Poitevin A, Kuboki T, et al. Enamel-smear compromises bonding by mild self-etch adhesives. J Dent Res. 2010 Dec;89(12):1505-9. https://doi.org/10.1177/0022034510384871
https://doi.org/10.1177/0022034510384871... They are considered as control adhesives (gold standards) to self-etch and etch-and-rinse strategies, respectively, and frequently used in bond strength studies.⁴¹41. El Zohairy AA, Saber MH, Abdalla AI, Feilzer AJ. Efficacy of microtensile versus microshear bond testing for evaluation of bond strength of dental adhesive systems to enamel. Dent Mater. 2010 Sep;26(9):848-54. https://doi.org/10.1016/j.dental.2010.04.010
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https://doi.org/10.1016/j.jdent.2014.01.... ^,4343. Senawongse P, Harnirattisai C, Shimada Y, Tagami J. Effective bond strength of current adhesive systems on deciduous and permanent dentin. Oper Dent. 2004 Mar-Apr;29(2):196-202.^,4444. Soares FZ, Rocha RO, Raggio DP, Sadek FT, Cardoso PE. Microtensile bond strength of different adhesive systems to primary and permanent dentin. Pediatr Dent. 2005 Nov-Dec;27(6):457-62.^,4545. Vinagre A, Ramos J, Messias A, Marques F, Caramelo F, Mata A. Microtensile bond strength and micromorphology of bur-cut enamel using five adhesive systems. J Adhes Dent. 2015 Apr;17(2):107-16. https://doi.org/10.3290/j.jad.a34060
https://doi.org/10.3290/j.jad.a34060... ^,4646. Hoshika S, Kameyama A, Suyama Y, De Munck J, Sano H, Van Meerbeek B. GPDM- and10-MDP-based self-etch adhesives bonded to bur-cut and uncut enamel: “immediate”and “aged” µTBS. J Adhes Dent. 2018;20(2):113-20. https://doi.org/10.3290/j.jad.a40307
https://doi.org/10.3290/j.jad.a40307...

The failure mode analysis found interfacial failures in all experimental groups. Moreover, in general, the failures occurred within the limits of the composite cylinder, excepted in specimens from demineralized enamel groups, which presented larger areas of substrate involvement in the fracture. This was expected, since the microshear bond strength test used in this study is associated to few cohesive failures in tooth substrate or composite.⁴⁷47. Andrade AM, Garcia EJ, El-Askary FS, Reis A, Loguercio AD, Grande RH. Influence of different test parameters on the microshear bond strength of two simplified etch-and-rinse adhesives. J Adhes Dent. 2014 Aug;16(4):323-31. https://doi.org/10.3290/j.jad.a32071
https://doi.org/10.3290/j.jad.a32071... ^,4848. Münchow EA, Bossardi M, Priebe TC, Valente LL, Zanchi CH, Ogliari FA, et al. Microtensile versus microshear bond strength between dental adhesives and the dentin substrate. Int J Adhes Adhes. 2013 Oct;46:95-9. https://doi.org/10.1016/j.ijadhadh.2013.06.005
https://doi.org/10.1016/j.ijadhadh.2013.... The frequency of pretest failure was very low and it was not prevalent in a specific group. The use of starch tubes to build the specimens may be the reason for the low occurrence of premature failure. The procedure of starch tube removal is very easy, does not require a blade or other cutting instrument, and does not cause pressure or stress in the interface of resin composite cylinder, which is a great advantage.²⁹29. Tedesco TK, Montagner AF, Skupien JA, Soares FZ, Susin AH, Rocha RO. Starch tubing: an alternative method to build up microshear bond test specimens. J Adhes Dent. 2013 Aug;15(4):311-5. https://doi.org/10.3290/j.jad.a28602
https://doi.org/10.3290/j.jad.a28602...

This study has limitations, such as the lack of an initial quantitative assessment of enamel surrounding cavities to validate the enamel condition (sound or demineralized), and the use of only visual inspection to assess the enamel condition. Moreover, the enamel surrounding carious cavities was assumed demineralized, because of the suspicion that it presented mineral loss before the start of the carious process. However, future studies should confirm this assumption.

Within the limitations of an in vitro study, the results obtained suggest that more attention should be given to the treatment of enamel surrounding carious cavities, since the presence of undetected demineralized enamel might be the cause of failures in adhesive restorations performed after selective caries removal. Further studies evaluating the enamel adjacent to cavities submitted to selective excavation approach are required.

Conclusions

The bond strength of adhesive systems to enamel assumed demineralized is lower than that to sound enamel. The proximity to carious cavities with little or no enamel preparation may jeopardize the bonding of adhesives to enamel.

The bonding strategy does not influence the enamel bond strength of universal adhesive system.

Acknowledgments

We thank the CAPES for the financial support and scholarship. The authors declare no conflict of interest with respect to the authorship and publication of this article.

References

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