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Influence of Acid Etching and Universal Adhesives on the Bond Strength to Dentin

Abstract

The purpose of this study was to evaluate the influence of the application mode of three universal adhesive systems on interfacial physical properties of indirect composite restorations adhesively cemented to dentin cavities. Seventy-eight bovine lower incisors were selected and a slice of dentin (thickness: 2 mm) between the buccal surface and pulp chamber was obtained for each tooth. Conical cavities were made on this surface. The internal walls of the cavities were then coated with a hydrophilic gel, filled with composite resin and photopolymerized. The dentin/cone sets were divided into 6 groups (n=10) according to type of universal adhesive (TETRI: Tetric N Bond, FUT: Futura Bond U, SBU: Single Bond Universal) and acid etching on dentin (A: with acid etching; WA: without acid etching). The acid etching and the adhesive systems were applied to the surface of the dentin. All composite resin cones were sandblasted (Al2O3, 20 s) and silanized. After surface treatment, the cones were cemented (RelyX Ultimate) into the dentin cavity and photopolymerized. After thermocycling (10,000 cycles), samples were submitted to marginal adaptation analysis (using caries detector dye), push-out test (0.5 mm/min), and failure mode analysis. Additional samples were prepared for nanoleakage analysis (SEM). The data (MPa) were analyzed by two-way ANOVA and Tukey’s post-test (5%). The groups in which the dentin was acid etched showed significantly lower bond strength values in the push-out test (p<0.01). Dentin acid etching significantly reduced the bond strength between universal adhesive systems and dentin in indirect restorative procedures.

Key Words:
indirect composite resin; push-out; universal adhesives; dentin

Resumo

O objetivo deste estudo foi avaliar a influência do modo de aplicação de três sistemas adesivos universais nas propriedades físicas interfaciais de restaurações indiretas de compósito adesivamente cimentadas a cavidades dentinária. Setenta e oito incisivos inferiores bovinos foram selecionados e uma fatia de dentina (espessura: 2 mm) entre a face vestibular e a câmara pulpar foi obtida para cada dente. Cavidades cônicas foram feitas nesta superfície. As paredes internas das cavidades foram então revestidas com um gel hidrofílico, preenchidas com resina composta, e fotopolimerizados. Os conjuntos dentina/cone foram divididos em 6 grupos (n=10) de acordo com o tipo de adesivo universal (TETRI: Tetric N Bond, FUT: Futura Bond U, SBU: Single Bond Universal) e ácido na dentina (A: com condicionamento ácido; WA: sem condicionamento ácido). O condicionamento ácido e os sistemas adesivos foram aplicados na superfície da dentina. Todos os cones de resina composta foram jateados (Al2O3, 20 s) e silanizados. Após o tratamento superficial, os cones foram cimentados (RelyX Ultimate) na cavidade dentinária e fotopolimerizados. Após a termociclagem (10.000 ciclos), as amostras foram submetidas a análise de adaptação marginal (usando corante detector de carie), teste push-out (0,5 mm/min) e análise do modo de falha. Amostras adicionais foram preparadas para análise de nanoinfiltração (MEV). Os dados (MPa) foram analisados por ANOVA dois fatores e pós-teste de Tukey (5%). Os grupos em que a dentina foi condicionada por ácido apresentaram valores significativamente menores de resistência de união no teste push-out (p<0,01). O condicionamento ácido da dentina reduziu significativamente a resistência de união entre sistemas adesivos universais e dentina em procedimentos restauradores indiretos.

Introduction

Direct composite resin restorations, as well as indirect or semi-direct restorations 11. Spreafico RC, Krejci I, Dietschi D. Clinical performance and marginal adaptation of class II direct and semidirect composite restorations over 3.5 years in vivo. J Dent 2005;33:499-507 have been an option in dental practice. Indirect and semi-direct techniques overcome some of the disadvantages of direct restorations, such as polymerization shrinkage and the cementation “gap”11. Spreafico RC, Krejci I, Dietschi D. Clinical performance and marginal adaptation of class II direct and semidirect composite restorations over 3.5 years in vivo. J Dent 2005;33:499-507. In addition, these restorations have better mechanical properties due to the additional polymerization with light or heat, lower microleakage, lower costs, and easier intraoral maintenance compared to dental ceramics 11. Spreafico RC, Krejci I, Dietschi D. Clinical performance and marginal adaptation of class II direct and semidirect composite restorations over 3.5 years in vivo. J Dent 2005;33:499-507. Several studies have evaluated the longevity of resins for indirect and semi-direct techniques, reporting good clinical performance in several situations, such as in class I and II restorations (95% in good conditions after 3 years of follow-up) 22. Van Dijken JWK, Kieri C, Carlén M. Longevity of extensive class II open-sandwich restorations with a resin-modified glass-ionomer cement. J Dent Res1999;78:1319-25., in inlays (80% after 10 years of follow-up) 33. Thordrup M, Isidor F, Hörsted-Bindslev P. A prospective clinical study of indirect and direct composite and ceramic inlays: ten-year results. Quintessence Int 2006;37:139-144., and in class II restorations using the semi-direct technique (100% after 3.5 years) 11. Spreafico RC, Krejci I, Dietschi D. Clinical performance and marginal adaptation of class II direct and semidirect composite restorations over 3.5 years in vivo. J Dent 2005;33:499-507.

However, in spite of the excellent longevity, problems related to dentin adhesion have been reported 44. Toledano M, Cabello I, Aguilera FS, Osorio E, Toledano-Osorio M, Osorio R. Improved sealing and remineralization at the resin-dentin interface after phosphoric acid etching and load cycling. Microsc Microanal 2015;21:1530-1548.. Some factors, such as overdrying of dentin after acid etching, excess moisture, and excessive acid demineralization or acid undercorrosion, may decrease the flow of resinous monomers along the intertubular dentin, compromising the longevity of restorations 55. Marshall Sj, Bayne Sc, Baier R, Tomsia Ap, Marshall Gw. A review of adhesion science. Dent Mater 2009; 26:e11-e16.. Although the conventional approach for adhesive restorations, including dentin etching with phosphoric acid (35-37%), is an established and predictable clinical procedure, the acid corrosion of dentin is a definitive factor for adhesion quality, increasing wettability and surface roughness, and allowing the penetration of adhesives and resin cements through the smear layer 44. Toledano M, Cabello I, Aguilera FS, Osorio E, Toledano-Osorio M, Osorio R. Improved sealing and remineralization at the resin-dentin interface after phosphoric acid etching and load cycling. Microsc Microanal 2015;21:1530-1548..

Universal adhesive systems minimize problems associated to the substrate, ensuring a greater adhesion stability. These materials can be used by the self-etch (SE) technique, prior conditioning etch-and-rinse (ER) technique, or as SE adhesives in dentin and ER in enamel (commonly referred to as “selective enamel conditioning”) 66. 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;40:475-84.. All the components of universal adhesive systems come in a single vial, and the adhesive has the advantages of being effective on wet or dry dentin 77. Perdigao J, Sezinando A, Monteiro PC. Laboratory bonding ability of a multi-purpose dentin adhesive. Am J Dent 2012;25:153-158., being less technique-sensitive, and requiring fewer clinical steps 77. Perdigao J, Sezinando A, Monteiro PC. Laboratory bonding ability of a multi-purpose dentin adhesive. Am J Dent 2012;25:153-158.. Despite similarities with other adhesive systems, universal adhesives differ from the current SE systems by having phosphate monomers in their composition, among them MDP, which can produce chemical and micromechanical adhesion to dental substrates by ionically binding to calcium in hydroxyapatite (Ca10 [PO4]6 [OH]2) and increasing binding efficiency 66. 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;40:475-84.,77. Perdigao J, Sezinando A, Monteiro PC. Laboratory bonding ability of a multi-purpose dentin adhesive. Am J Dent 2012;25:153-158..

In addition to interacting with a hydrophilic substrate, the combination of properties allows the interaction with the hydrophobic restorative material under a variety of surface conditions 55. Marshall Sj, Bayne Sc, Baier R, Tomsia Ap, Marshall Gw. A review of adhesion science. Dent Mater 2009; 26:e11-e16.. The adhesion of composite restorations to dental substrates is still a challenge due to the presence of different interfaces: substrate/adhesive/cement system, in addition to the cement/composite resin interface. Moreover, the resin/dentin interface is constantly submitted to mechanical stress from chewing and swallowing 44. Toledano M, Cabello I, Aguilera FS, Osorio E, Toledano-Osorio M, Osorio R. Improved sealing and remineralization at the resin-dentin interface after phosphoric acid etching and load cycling. Microsc Microanal 2015;21:1530-1548. and to thermal variations from food. Limitations of materials and techniques may also contribute to a degradation of the tooth/restorative material interface, compromising longevity 88. De Munck J, Vargas M, Van Landuyt K, Hikita K, Lambrechts P, Van Meerbeek B. Bonding of an auto-adhesive luting material to enamel and dentin. Dent Mater 2004;20:963-971..

Studies have evaluated the bond strength between universal adhesive systems and dentin using direct composites 11. Spreafico RC, Krejci I, Dietschi D. Clinical performance and marginal adaptation of class II direct and semidirect composite restorations over 3.5 years in vivo. J Dent 2005;33:499-507. However, no study has evaluated the effects of dentin pretreatment for universal adhesive systems used for cementation of semi-direct resins to dentin. Thus, the objective of the present study was to evaluate the influence of three universal adhesive systems used with or without acid conditioning on the marginal adaptation, push-out bond strength, and nanoleakage of a semi-direct composite resin restoration adhesively cemented to bovine dentine. The hypotheses tested were: A) the type of adhesive system does not affect bond strength; B) acid conditioning does not significantly affect bond strength; C) the adhesive system and the acid conditioning technique will not affect the marginal adaptation or the nanoleakage.

Material and Methods

The materials (manufacturers, trademarks, chemical composition, and batch number) used in this study are presented in Table 1.

Table 1
Trademarks, manufacturers, chemical composition, and batch number of the materials used in the study

Teeth Selection and Preparation

Samples were prepared according to a method described previously for the push-out bond strength test 99. Borges BC, Vilela AR, da Silva-Junior CA, Souza-Junior EJ, Sinhoreti MA, Pinheiro FH, et al. Dual-cured etch-and-rinse adhesive systems increase the bond durability of direct coronal dentin restorations. Oper Dent 2013,38:512-518.. Seventy-eight intact bovine incisors were selected, cleaned from tissue and debris with a periodontal curette, disinfected with 0.1% aqueous thymol solution at 40°C for one week, and stored in distilled water at 4°C (ISO 11405). The roots were sectioned at the cementoenamel junction with a double-sided diamond disk (KG Sorensen, Barueri, SP, Brazil) in a straight handpiece and low speed micromotor, under constant irrigation (Fig 1A).

Figure 1
Sample preparation for the push-out test.

A 2-mm-thick dentin slice, between the buccal surface and pulp chamber, was obtained from each tooth. The teeth were ground with #200, #400 and #600 grit sanding paper in a polishing machine (AROTEC, Cotia, SP, Brazil), and the thickness measured with a digital caliper (Fig. 1B and 1C). Then, standardized conical cavities (larger Ø: 2 mm, smaller Ø: 1.5 mm) were prepared using tapered diamond burs (#3131, KGSorensen) in a high-speed handpiece adapted to a dental surveyor (Fig. 1D,E), so that the active tip was perpendicular to the buccal surface of the disc; the perforation was done in a single lowering movement by a single operator (Fig. 1D,E). The diamond bur was replaced after preparation of 50% of the samples.

Preparation of Composite Resin Cones

Opallis composite resin (FGM, Joinville, SC, Brazil) was used to fill the dentin cavities. The dentin samples were individually positioned on a glass surface and a hydrophilic gel (K-Y Gel Johnson & Johnson, New Jersey, USA) was applied to the internal walls of the cavities with a microbrush. The cavities were filled with a single increment of composite resin (2 mm) (Fig 1F) and partially photopolymerized for 3 s on each side to allow removal of excess resin (Fig 1G). Resin cones were then removed from the perforation and subjected to final polymerization for 40 s using a LED light (Radii-Cal - SDI 1200 mW/cm2) (Fig 1H). Afterwards, polymerization of the resin cones was further complemented in a microwave oven for 3 min at maximum power (Fig. 1I). The hydrophilic gel from the internal walls of the cavities was removed with an air/water spray. Dentin/composite cone sets were stored for 24 h in distilled water at room temperature and then finished and polished with Sof-lex discs (3M ESPE, St. Paul, MN, USA). The sets were randomly divided into 6 groups (n=10) according to the “adhesive system” factor (3 levels), and “acid conditioning” factor (2 levels, with and without): Futura Bond U (FUT); acid+FUT (A+FUT); Scotchbond Universal Adhesive (SBU); A+SBU; Tetric N-Bond Universal (TETRI); and A+TETRI.

Cementation Techniques

Surface Treatment of Composite Resin Cones

Cones were cleaned in an ultrasonic bath (Cristófoli, Campo Mourão, Paraná, Brazil) with 10% isopropyl alcohol for 5 min and then sandblasted with 50 µm aluminum oxide particles for 20 s (2.5 bar), slope of 90°, at a distance of 10 mm from the bonding surface. Using a microjet device (Microjato Standard, Bioart, São Carlos, SP, Brazil) attached to a dental surveyor (Fig 1J), the cones were rotated during the air-abrasion, so that only the bonding surfaces were sandblasted. After treatment, the surfaces were again cleaned in ultrasonic bath with distilled water for 2 min and air-dried. A layer of Silane (Dentsply International Inc., York, PA, USA) was applied to the sandblasted surfaces of the cones with the aid of a microbrush (Dentsply), according to the manufacturer’s recommendation.

Dentin Surface Treatment

Prior to cementation, prophylaxis was performed in the dentin cavity with pumice stone and water using a Robinson mini brush (Ø: 1.5mm) (Microtuft; Dhpro, Paraguaná, PR, Brazil) at low speed. Samples were then washed with water-air jet for 30 s and the excess moisture removed with absorbent paper. In three groups, the adhesive systems were directly applied according to the experimental group. In the other groups, the dentin surface was conditioned with 37% phosphoric acid (Dentsply Conditioner) for 15 s, carefully washed with water jet for 30 s (Fig 1K) and partially dried with absorbent paper. The adhesive systems were applied according to the manufacturer’s recommendations (Fig 1 K,L):

  • SBU: one layer was actively applied for 20 s, followed by a light jet of air for 5 s for solvent evaporation, and photopolymerization for 10 s using a LED light curing device (1200 mW/cm2) (Radii Cal, SDI, Australia).

  • FUTURA BOND U: One layer of the adhesive was actively applied for 20 s, followed by a light air jet for 5 s and photopolymerization as the previous group.

  • TETRIC N BOND: One layer of the adhesive was actively applied for 20 s, followed by a light air jet for 5 s and photopolymerization as the previous group.

Cementation of Resin Cones

The dual resin cement RelyX Ultimate (3M ESPE, St. Paul, MN, USA) was used for the cementation of cones. The dentin samples were placed individually on a glass plate. Equal amounts of base and catalyst pastes were dispensed, mixed, and immediately applied to the cementation surface of the cone, which was positioned into the dentin cavity (Fig 1M). The top of the cone was covered with a polyester strip and a 750 g weight was applied, simulating the adhesive cementation protocol (Fig 1N). Both sides of the restoration were light cured for 40 s using a LED device (1200 mW/cm2) (Radii Cal, SDI). The surfaces were then polished with polishing systems Sof-Lex Pop-On (3M ESPE). The specimens were stored in distilled water at 37°C for 24 h and then submitted to a thermocycling aging protocol of 10,000 cycles of alternating 30-s baths of 5 and 55°C, with a 2 s interval between immersions.

Marginal Adaptation

To determine the marginal adaptation, a dye technique was used 1010. Alonso RC, Correr GM, Cunha LG, De Moraes Souto Pantoja CA, Puppin-Rontani RM, Sinhoreti MA. Modulated photoactivation methods--effect on marginal and internal gap formation of restorations using different restorative composites. J Biomed Mater Res B Appl Biomater 2007;82:346-351.. After thermocycling, before the push-out test, a 1% solution of red propylene glycol (caries detector dye, Kuraray Co., Osaka, Japan) was applied to the margins of the restoration for 5 s. Specimens were then rinsed in tap water and gently dried. They were then attached vertically to a holding device coupled with a lateral ruler of 2 cm, allowing calibration. Subsequently, photographs of the top and bottom of the restoration were obtained with a Canon EOS Rebel T5i Camera, positioned at a focal distance of 60 cm. The amount of stained margins was analyzed using Image Pro-Plus 7.0 (Media Cybernetic) software. The perimeter of the cementation line was measured in the photographs of each sample using a micrometric scale, which allowed following the contour of the restoration. The stained areas in the margins were then measured in both sides of each sample. This technique stained the gaps so they could easily be quantified 1010. Alonso RC, Correr GM, Cunha LG, De Moraes Souto Pantoja CA, Puppin-Rontani RM, Sinhoreti MA. Modulated photoactivation methods--effect on marginal and internal gap formation of restorations using different restorative composites. J Biomed Mater Res B Appl Biomater 2007;82:346-351.. Data were entered in an EXCEL spreadsheet to calculate the percentage of gaps in each sample and analyzed statistically. The marginal adaptation evaluation was done by a single trained evaluator. After, the samples were submitted to the push-out test.

Push-Out Bond Strength Test

The push-out bond strength test was performed using a universal testing machine (model 4411; Instron Corp., Canton, MA, USA). A metal device with a central hole (Ø: 1mm) was adapted to the base of the machine. Specimens were placed in the device with the larger diameter in contact with the lower metal surface of the device and the smaller diameter in contact with the metal piston (Ø: 1 mm). A 50-KgF load cell was positioned at the center of the composite resin cone at a speed of 0.5 mm/min until failure (Fig. 1)O. The load required for failure was recorded by the test machine and subsequently converted to MPa values. The resistance values were calculated (in MPa) by dividing the force (in N) at time of failure by the area: p (R1+R2) H (R1+R2) 2+h2, where R1 represents the smaller radius, R2 is the larger radius, and h, the height of the cavity.

Failure Mode Analysis

Specimens were examined by stereomicroscopy (20×) (Stereo Discovery V20, Zeiss, Göttingen, Germany) and failure modes were classified with the following scores: AD, adhesive failure between dentin and cement; AR, adhesive failure between cement and composite resin; C1, cohesive failure in dentin; C2, cohesive failure in composite resin; C3, cohesive failure in cement and mixed failures: (Cohesive + AR or AD).

Nanoleakage (NL)

For nanoleakage analysis, three extra samples from each group were made following the same parameters. After thermocycling (10,000 TC), the samples were immersed in distilled water and stored for 24 h at 37°C in an oven. The specimens were then removed from the water, dried with absorbent paper and impermeabilized with two layers of nail polish (Colorama, CEIL, São Paulo, SP, Brazil), leaving a 1-mm space from the edge without nail polish. The specimens were immersed in distilled water for 20 min and subsequently in silver nitrate solution (prepared with 25 g of silver nitrate crystals; Sigma Chemical Co., St. Louis, MO, USA), pH =11.0, in a dark container for 24 h. Afterwards, specimens were washed with distilled water and immersed in Kodak Developer Solution (Carestream Health Inc. NY, USA) for 8 h under fluorescent light. Again, specimens were washed in distilled water and polished under water in a polishing machine (Metaserv 2000, USA) using #600, 1200, 2000 grit sand paper (Carbimet Disc Set, USA) and 0.3 µm and 1 µm polishing pastes (Alumina Polishing Abrasives - PACE Technologies, Tucson, AZ, USA) using a felt disc (Buehler, Lake Bluff, IL, USA). Samples were examined in SEM / EDS (JEOL-JSM 5600LV, Tokyo, Japan) at 600, 800, and 1000× increments. Silver penetration at the bonding interface, the hybrid layer, and adhesive layer were examined by a single evaluator.

Statistical Analysis

Data were submitted to the Kolmogorov-Smirnov normality test using the computer program Assistat 7.7. The push-out bond strength data were submitted to the parametric test of two-way analysis of variance (ANOVA) and Tukey’s post-test (5% significance level). Failure modes and complementary data were analyzed descriptively. The marginal adaptation data were submitted to three-way ANOVA, followed by Mann-Whitney test and t-test (5% significance level). Data from nanoleakage were analyzed descriptively.

Results

Push-Out Bond Strength

The results indicated that the data were normally distributed (p>0.05). The interaction between factors (adhesive system x acid conditioning) was non-significant (p=0.514). The “adhesive system” factor (p=0.532) did not present a significant effect on results. On the other hand, the “acid conditioning” factor (p=0.0001) was statistically significant. The ​​results of the push-out test and the comparison between groups are shown in Table 2. Acid-etching the dentine prior to cementation significantly decreased bond strength of the three adhesive systems compared to no conditioning.

Table 2
Means (SD) of the push out strength values in the studied groups

Uppercase letters mean comparisons between columns in the same lines. Lowercase letters mean comparisons between lines in the same columns.

Marginal Adaptation

In general, no significant difference in gaps percentage was found between groups with and without acid etching (p>0.05, Tukey test); the exception was in the FUT groups, where the acid etching group showed significantly more gaps than the non-etching groups. Significant differences were also found for the non-etching SBU group in the larger diameter region, which showed significantly greater gaps than the non-etching groups. The smaller diameter region showed a significantly higher percentage of gaps in the acid groups of the FUT and TETRI adhesive systems. Between-group comparisons are presented in Figure 2.

Figure 2
Box Plot of medians (Q1-Q3) of marginal adaptation of the three adhesive systems in both sides of the specimen according to etching acid: etching (A) and no etching (B) . Uppercase letters indicate significant differences between with and without acid conditioning, in the same adhesive, and same side. Lowercase letters indicate significant differences between different adhesive system, in the same side and with the same acid protocol (acid conditioning or no acid-conditioning). *significant differences between different sides.

Nanoleakage

SEM images showing silver particles in the adhesive systems are shown in Figures 3 A-F. Elemental silver was identified by EDS analysis, confirming the obtained results. Different patterns of silver nitrate nanoleakage were found along the adhesive layer for the three universal adhesive systems. The deposition of silver ions was found throughout the adhesive layer at the cement/dentin interface. The TETRI-A group (Fig. 3E) demonstrated a thicker layer of silver ions compared to the non-conditioned group (Fig. 3F).

Figure 3
Representative EDS / SEM (200-1000×) micrographs of nanoleakage at the cement/dentin/resin interface after adhesive universal with and without acid conditioning. A: Futura Bond U with acid conditioning; B: Futura Bond U without acid conditioning; C: Scotch Bond Universal (SBU) applied with acid conditioning; D: SBU without acid conditioning; E: Tetric N-Bond Universal with acid conditioning; F: Tetric N-Bond Universal without acid conditioning. Δ: Dentin; *: composite resin →: silver ions at the interface, ◊: resin cement.

Failure Analysis

Different failure patterns were observed for the three adhesive systems tested according to absence or presence of acid conditioning. The groups with acid etching demonstrated mixed failures (cohesive in cement and adhesive at the cement/dentin interface) (Fig. 4A). In groups without acid etching, failures occurred mainly at the cement/resin interface (Fig. 4B). Adhesive failures at the cement/dentin interface were common for the SBU-A and TETRI-A groups (Fig. 4C). Cohesive failures in dentin were also observed in the SBU and TETRI groups (Fig. 4D). Failure modes for each group are shown in Table 3.

Figure 4
Stereomicroscopy (20×) micrograph representing failure modes. A: cohesive failure in cement and adhesive failure at the cement/dentin interface; B: cohesive failure in cement and adhesive failure at the cement/resin interface; C: adhesive failure at the cement/dentin interface; D: cohesive failure in dentin and adhesive failure at the cement/dentin interface. Right: composite resin cone; Left: dentin.

Table 3
Number (N) and percentage (%) of pre-test failure (PTF) during thermal aging, total number of samples submitted to the push-out bond strength test, and failure mode (%) of the groups after bond strength test

Discussion

In the present study, the influence of acid etching on the bond strength between three universal adhesive systems and bovine dentin was investigated. Cavities in coronary bovine dentin were standardized at 2 mm thickness to simulate a clinical situation of high C-factor, similar to a semi-direct composite resin restoration performed clinically. Besides, the method allowed the evaluation of marginal adaptation, bond strength, and nanoleakage in the same cavity 1111. Oliveira Jr FO, Kunz PVM, B Filho F, Correr GM, Cunha LFC, Gonzaga CC. Influence of pre-curing different adhesives on the color stability of cemented thin ceramic veneers. Braz Dent J2018;29:275-281.,1212. Hu M, Weiger R, Fischer J. Comparison of two test designs for evaluating the shear bond strength of resin composite cements. Dent Mater 2016;32:223-232..

According to results of this study, the first hypothesis that the type of adhesive system does not affect bond strength was accepted, as no significant difference between the three universal adhesives was found. Tetric N Bond, SBU, and Futura Bond U are universal one-component adhesives with similar indications, applications, and chemical compositions. All have phosphated acid monomers in their composition and are considered ‘ultra mild’ based on their pH (SBU: pH=2.7; FTU: pH=2.5 and TET: pH=2.5-3.0) 131. Spreafico RC, Krejci I, Dietschi D. Clinical performance and marginal adaptation of class II direct and semidirect composite restorations over 3.5 years in vivo. J Dent 2005;33:499-507,1), which makes them capable of demineralizing and diffusing in the dentin, forming a hybrid layer that is more stable to hydrolytic degradation due to changes in their chemical composition 1111. Oliveira Jr FO, Kunz PVM, B Filho F, Correr GM, Cunha LFC, Gonzaga CC. Influence of pre-curing different adhesives on the color stability of cemented thin ceramic veneers. Braz Dent J2018;29:275-281.. The phosphated functional monomers in their composition chemically interact with hydroxyapatite forming hydrolytic and more stable bonds with calcium 1414. Araújo AMM, Januário ANB, Moura DMD, Tribst JPM, Özcan M, Assunção ROA. Can the application of multimode adhesive be a substitute to silicatized/ silanized Y-TZP ceramics? Braz Dent J. 2018; 29:275-281.,1515. Cuevas-Suárez CE, Ramos TS, Rodrigues SB, Collares FM, Zanchi CH, Lund RG, et al. Impact of shelf-life simulation on bonding performance of universal adhesive systems. Dent Mater 2019;3379.,1616. Makishi P, André CB, Ayres A, Martins AL, Giannini M. Effect of storage time on bond strength and nanoleakage expression of universal adhesives bonded to dentin and etched enamel. Oper Dent 2016;41:305-317.. It is reported that adhesive systems containing MDP phosphated monomers chemically interact with hydroxyapatite forming 10-MDP-Ca salts that have low solubility, better resistance to hydrolysis, and are more stable. However, in this study, the adhesive systems that contained this monomer (SBU and TETRIC) did not significantly influence the bond strength.

A recent study 1717. Awad MM. Assessment of resin-dentin interfacial morphology of two ethanol-based universal adhesives: A scanning electron microscopy study. Eur J Dent 2017;11:206-209. evaluated the bond strength of the resin/dentin interface using two of these systems (SBU and Tetric N Bond) and the authors found no difference between them. The authors report that the interfacial morphology of both adhesives can be affected by the similarity of their compositions, as both contain water, ethanol, and hydroxyethyl methacrylate (HEMA). Water is essential to ionize acid monomers and trigger the demineralization process 1313. Van Landuyt KL1, Snauwaert J, De Munck J, Peumans M, Yoshida Y, Poitevin A, et al. Systematic review of the chemical composition of contemporary dental adhesives. Biomaterials 2007;28:3757-3785.. The water-ethanol combination can also dilute the viscous monomers and help their infiltration into the dentin. In another study 1818. Diniz AC, Bandeca MC, Pinheiro LM, Dos Santosh Almeida LJ Jr, Torres CR et al. Influence of different etching modes on bond strength to enamel using universal adhesive systems. J Contemp Dent Pract2016;17:820-825., the authors report that Futura Bond U (FUT) presented significantly higher values ​​of bond strength compared to other universal adhesives, such as Clearfil Universal and SBU, and they associate the results ​​to a greater interaction of FUT with the resin.

The second hypothesis tested in this study that acid etching does not significantly affect bond strength was not accepted. The universal adhesives are known for their versatility and by being effective either with or without prior acid conditioning. Thus, it is expected that bond strength would not be compromised by acid conditioning 1919. Matos AB, Trevelin LT, Silva BTFD, Francisconi-Dos-Rios LF, Siriani LK, Cardoso MV. Bonding efficiency and durability: current possibilities. Braz Oral Res 2017;31:e57.. However, prior acid etching of dentin significantly decreased the adhesion values ​​of the three universal adhesive systems. According to the concept of adhesion-decalcification (A-D) proposed for self-adhesives 1919. Matos AB, Trevelin LT, Silva BTFD, Francisconi-Dos-Rios LF, Siriani LK, Cardoso MV. Bonding efficiency and durability: current possibilities. Braz Oral Res 2017;31:e57., dentin demineralization by strong acids will result in a higher dissolution rate of calcium salts. This suppresses the potential of establishing a chemical bond between resinous monomers and apatite crystals, and creating calcium precipitates nano-layers with phosphate monomers 2020. Van Meerbeek B, Vargas S, Inoue S, Yoshida Y, Peumans M, Lambrechts P. Adhesives and cements to promote preservation dentistry. Oper Dent 2001;26:119-144.. When the conditioning and simultaneous infiltration of adhesive systems into the dentin, as proposed by the universal adhesives, is replaced by a diffusion mechanism to achieve micromechanical retention (as in acid corrosion) 2121. Perdigão J, Muñoz MA, Sezinando A, Luque-Martinez IV, Staichak R, Reis A. Immediate adhesive properties to dentin and enamel of a universal adhesive associated with a hydrophobic resin coat. Oper Dent 2014;39:489-499., an incomplete infiltration of resinous monomers within a matrix of thickened or completely demineralized collagen may occur.

Varied results are found in the literature 1919. Matos AB, Trevelin LT, Silva BTFD, Francisconi-Dos-Rios LF, Siriani LK, Cardoso MV. Bonding efficiency and durability: current possibilities. Braz Oral Res 2017;31:e57.,2121. Perdigão J, Muñoz MA, Sezinando A, Luque-Martinez IV, Staichak R, Reis A. Immediate adhesive properties to dentin and enamel of a universal adhesive associated with a hydrophobic resin coat. Oper Dent 2014;39:489-499.,1515. Cuevas-Suárez CE, Ramos TS, Rodrigues SB, Collares FM, Zanchi CH, Lund RG, et al. Impact of shelf-life simulation on bonding performance of universal adhesive systems. Dent Mater 2019;3379.. One study 2222. Takamizawa T, Barkmeier WW, Tsujimoto A, Berry TP, Watanabe H, Erickson RL2, et al. Influence of different etching modes on bond strength and fatigue strength to dentin using universal adhesive systems. Dent Mater 2016;32:e9-21. reported that dentin conditioning had no negative impact on adhesion. Corroborating these findings, another study 22. Van Dijken JWK, Kieri C, Carlén M. Longevity of extensive class II open-sandwich restorations with a resin-modified glass-ionomer cement. J Dent Res1999;78:1319-25. concluded that the prior acid etching of dentin did not significantly affect bond strength of two universal adhesive systems, Futura Bond U and SBU. The authors reported that the additional application of acid monomers on dentin surface enhanced by the active friction of the adhesive system seems to improve the contact area of ​​the adhesive solution on the surface and provide a higher concentration of free H+ ions to interact with the mineral components of dentin 222. Van Dijken JWK, Kieri C, Carlén M. Longevity of extensive class II open-sandwich restorations with a resin-modified glass-ionomer cement. J Dent Res1999;78:1319-25.,2). Additional studies 2222. Takamizawa T, Barkmeier WW, Tsujimoto A, Berry TP, Watanabe H, Erickson RL2, et al. Influence of different etching modes on bond strength and fatigue strength to dentin using universal adhesive systems. Dent Mater 2016;32:e9-21. also found no difference between universal adhesives (All-Bond Universal, Scotchbond Universal, and Futura Bond U) when used with different conditioning techniques. On the other hand, one study 2323. Poggio C, Beltrami R, Colombo M, Chiesa M, Scribante A. Influence of dentin pretreatment on bond strength of universal adhesives. Acta Biomater Odontol Scand2017;3:30-35. reported that prior acid etching reduced dentin bond strength values ​​only for some of the universal adhesive systems tested, such as Futura Bond U, but stated that universal adhesives have specific application methods and that acid pretreatment should be performed only on enamel. Another relevant factor that was accounted for in this study is the perforation simulating a clinical situation, as the adherent surface of the mineralized dentin depends on cavity configuration (Factor C), that is, the option of pre-conditioning is determined based on cavity size and depth 2323. Poggio C, Beltrami R, Colombo M, Chiesa M, Scribante A. Influence of dentin pretreatment on bond strength of universal adhesives. Acta Biomater Odontol Scand2017;3:30-35..

The third hypothesis that acid conditioning does not affect marginal adaptation or the nanoleakage was partially accepted. The caries detecting stain analysis was used to evaluate the marginal adaptation. Based on a previous study 1010. Alonso RC, Correr GM, Cunha LG, De Moraes Souto Pantoja CA, Puppin-Rontani RM, Sinhoreti MA. Modulated photoactivation methods--effect on marginal and internal gap formation of restorations using different restorative composites. J Biomed Mater Res B Appl Biomater 2007;82:346-351., measuring the margin gaps using the staining technique provides results comparable to scanning electron microscopy. According to the results of this study, acid etching, especially for Futura Bond U groups, significantly increased the percentage of gaps in relation to the acid-free groups. On the other hand, SBU groups showed significantly more gaps in the acid-free groups. Larger stained areas around the margins of the restoration indicate larger gaps 1010. Alonso RC, Correr GM, Cunha LG, De Moraes Souto Pantoja CA, Puppin-Rontani RM, Sinhoreti MA. Modulated photoactivation methods--effect on marginal and internal gap formation of restorations using different restorative composites. J Biomed Mater Res B Appl Biomater 2007;82:346-351., which are the first signs of failure of a restoration, clinically detectable by marginal staining.

With regard to nanoleakage, SEM images and EDS analysis demonstrated the infiltration of silver ions along the adhesive layer (dentin/adhesive interface) in samples with and without acid conditioning of the three adhesive systems. However, for the TETRI + acid conditioning group, a thicker hybrid layer with a higher concentration of silver ions along the adhesive interface was observed compared to TETRI (without acid conditioning) samples. Silver nitrate can lodge into nanometer-sized spaces around exposed collagen fibers where monomers fail to infiltrate or where residual water is not displaced by the adhesive, or even in areas with incomplete monomer conversion 99. Borges BC, Vilela AR, da Silva-Junior CA, Souza-Junior EJ, Sinhoreti MA, Pinheiro FH, et al. Dual-cured etch-and-rinse adhesive systems increase the bond durability of direct coronal dentin restorations. Oper Dent 2013,38:512-518., which are important factors for degradation of the bonding interface. Adhesive systems that contain both MDP and HEMA, such as Tetric N-Bond, may create interfaces bound for nanoleakage, as monomers compete for the interaction with calcium on the dentin surface, resulting in markedly reduced nano-layering of 10-MDP-calcium salts within the resin-dentin interface 2424. Yoshida Y, Yoshihara K, Hayakawa S, Nagaoka N, Okihara T, Matsumoto T. HEMA inhibits interfacial nano-layering of the functional monomer MDP. J Dent Res 2012;91:1060-1065.. In addition, thermocycling can accelerate aging degradation and cause expansion and tension stresses due to the different thermal expansion coefficients between substrates and restorative materials, favoring interface degradation 1616. Makishi P, André CB, Ayres A, Martins AL, Giannini M. Effect of storage time on bond strength and nanoleakage expression of universal adhesives bonded to dentin and etched enamel. Oper Dent 2016;41:305-317..

Failure mode analysis demonstrated different failure patterns between acid and acid-free groups. In general, failures were of mixed mode. The groups with acid conditioning showed inferior adhesion at the cement/dentin interface because they presented a higher rate of mixed failures. The opposite was observed for acid-free groups. The process of nucleation is the failure of materials or interfaces, i.e., it refers to weak points where high stresses can lead to overload. Acid etching dentin prior to universal adhesive application creates weak regions in the interface between resin and adhesive layer or between the adhesive layer and decalcified dentin 2424. Yoshida Y, Yoshihara K, Hayakawa S, Nagaoka N, Okihara T, Matsumoto T. HEMA inhibits interfacial nano-layering of the functional monomer MDP. J Dent Res 2012;91:1060-1065.. In addition, such vulnerable regions and flawed bonding may adversely affect long-term adherence 2222. Takamizawa T, Barkmeier WW, Tsujimoto A, Berry TP, Watanabe H, Erickson RL2, et al. Influence of different etching modes on bond strength and fatigue strength to dentin using universal adhesive systems. Dent Mater 2016;32:e9-21..

The results of this study showed that the three universal adhesive systems presented similar performance. However, acid conditioning dentin significantly reduced bond strength of the adhesives used in semi-direct composite restorations. The marginal adaptation analysis demonstrated that groups with acid etching, especially for Futura Bond U, had significantly increased percentage of gaps compared to the acid-free groups. With regard to nanoleakage, the three adhesive systems demonstrated infiltration of silver ions along the adhesive layer with and without acid conditioning. Further controlled randomized studies are required to evaluate adhesion and longevity of universal adhesive systems and to complement these laboratory findings.

Acknowledgements

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.

References

  • 1
    Spreafico RC, Krejci I, Dietschi D. Clinical performance and marginal adaptation of class II direct and semidirect composite restorations over 3.5 years in vivo. J Dent 2005;33:499-507
  • 2
    Van Dijken JWK, Kieri C, Carlén M. Longevity of extensive class II open-sandwich restorations with a resin-modified glass-ionomer cement. J Dent Res1999;78:1319-25.
  • 3
    Thordrup M, Isidor F, Hörsted-Bindslev P. A prospective clinical study of indirect and direct composite and ceramic inlays: ten-year results. Quintessence Int 2006;37:139-144.
  • 4
    Toledano M, Cabello I, Aguilera FS, Osorio E, Toledano-Osorio M, Osorio R. Improved sealing and remineralization at the resin-dentin interface after phosphoric acid etching and load cycling. Microsc Microanal 2015;21:1530-1548.
  • 5
    Marshall Sj, Bayne Sc, Baier R, Tomsia Ap, Marshall Gw. A review of adhesion science. Dent Mater 2009; 26:e11-e16.
  • 6
    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;40:475-84.
  • 7
    Perdigao J, Sezinando A, Monteiro PC. Laboratory bonding ability of a multi-purpose dentin adhesive. Am J Dent 2012;25:153-158.
  • 8
    De Munck J, Vargas M, Van Landuyt K, Hikita K, Lambrechts P, Van Meerbeek B. Bonding of an auto-adhesive luting material to enamel and dentin. Dent Mater 2004;20:963-971.
  • 9
    Borges BC, Vilela AR, da Silva-Junior CA, Souza-Junior EJ, Sinhoreti MA, Pinheiro FH, et al. Dual-cured etch-and-rinse adhesive systems increase the bond durability of direct coronal dentin restorations. Oper Dent 2013,38:512-518.
  • 10
    Alonso RC, Correr GM, Cunha LG, De Moraes Souto Pantoja CA, Puppin-Rontani RM, Sinhoreti MA. Modulated photoactivation methods--effect on marginal and internal gap formation of restorations using different restorative composites. J Biomed Mater Res B Appl Biomater 2007;82:346-351.
  • 11
    Oliveira Jr FO, Kunz PVM, B Filho F, Correr GM, Cunha LFC, Gonzaga CC. Influence of pre-curing different adhesives on the color stability of cemented thin ceramic veneers. Braz Dent J2018;29:275-281.
  • 12
    Hu M, Weiger R, Fischer J. Comparison of two test designs for evaluating the shear bond strength of resin composite cements. Dent Mater 2016;32:223-232.
  • 13
    Van Landuyt KL1, Snauwaert J, De Munck J, Peumans M, Yoshida Y, Poitevin A, et al. Systematic review of the chemical composition of contemporary dental adhesives. Biomaterials 2007;28:3757-3785.
  • 14
    Araújo AMM, Januário ANB, Moura DMD, Tribst JPM, Özcan M, Assunção ROA. Can the application of multimode adhesive be a substitute to silicatized/ silanized Y-TZP ceramics? Braz Dent J. 2018; 29:275-281.
  • 15
    Cuevas-Suárez CE, Ramos TS, Rodrigues SB, Collares FM, Zanchi CH, Lund RG, et al. Impact of shelf-life simulation on bonding performance of universal adhesive systems. Dent Mater 2019;3379.
  • 16
    Makishi P, André CB, Ayres A, Martins AL, Giannini M. Effect of storage time on bond strength and nanoleakage expression of universal adhesives bonded to dentin and etched enamel. Oper Dent 2016;41:305-317.
  • 17
    Awad MM. Assessment of resin-dentin interfacial morphology of two ethanol-based universal adhesives: A scanning electron microscopy study. Eur J Dent 2017;11:206-209.
  • 18
    Diniz AC, Bandeca MC, Pinheiro LM, Dos Santosh Almeida LJ Jr, Torres CR et al. Influence of different etching modes on bond strength to enamel using universal adhesive systems. J Contemp Dent Pract2016;17:820-825.
  • 19
    Matos AB, Trevelin LT, Silva BTFD, Francisconi-Dos-Rios LF, Siriani LK, Cardoso MV. Bonding efficiency and durability: current possibilities. Braz Oral Res 2017;31:e57.
  • 20
    Van Meerbeek B, Vargas S, Inoue S, Yoshida Y, Peumans M, Lambrechts P. Adhesives and cements to promote preservation dentistry. Oper Dent 2001;26:119-144.
  • 21
    Perdigão J, Muñoz MA, Sezinando A, Luque-Martinez IV, Staichak R, Reis A. Immediate adhesive properties to dentin and enamel of a universal adhesive associated with a hydrophobic resin coat. Oper Dent 2014;39:489-499.
  • 22
    Takamizawa T, Barkmeier WW, Tsujimoto A, Berry TP, Watanabe H, Erickson RL2, et al. Influence of different etching modes on bond strength and fatigue strength to dentin using universal adhesive systems. Dent Mater 2016;32:e9-21.
  • 23
    Poggio C, Beltrami R, Colombo M, Chiesa M, Scribante A. Influence of dentin pretreatment on bond strength of universal adhesives. Acta Biomater Odontol Scand2017;3:30-35.
  • 24
    Yoshida Y, Yoshihara K, Hayakawa S, Nagaoka N, Okihara T, Matsumoto T. HEMA inhibits interfacial nano-layering of the functional monomer MDP. J Dent Res 2012;91:1060-1065.

Publication Dates

  • Publication in this collection
    13 July 2020
  • Date of issue
    2020

History

  • Received
    24 July 2019
  • Accepted
    17 Dec 2019
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