- Email: [email protected]
Effects of 2.5% TiF4 on microtensile bond strength: Influence of application method and degree of dentin mineralization
International Journal of Adhesion & Adhesives 54 (2014) 159–164
Contents lists available at ScienceDirect
International Journal of Adhesion & Adhesives journal homepage: www.elsevier.com/locate/ijadhadh
Effects of 2.5% TiF4 on microtensile bond strength: Influence of application method and degree of dentin mineralization Domingues LG, Real CM, Bridi EC, Amaral FLB, França FMG, Turssi CP, Basting RTn DDS, School of Dentistry and Research Institute, São Leopoldo Mandic, Campinas, SP, Brazil
art ic l e i nf o
a b s t r a c t
Article history: Accepted 30 May 2014 Available online 11 June 2014
Objectives: The aims of this study were to evaluate the effects of: (a) the application method of a 2.5% titanium tetrafluoride aqueous solution (TiF4) to dentin on the microtensile bond strength of a two-step self-etching adhesive system and (b) dentin pretreatment with 2.5% TiF4 on the microtensile bond strength of a two-step self-etching adhesive system to sound and demineralized dentin. Materials and methods: Thirty-two third molars were selected to evaluate the application method for dentin pretreatment with TiF4 (Study 1). The occlusal enamel surfaces were removed, the superficial dentin flattened and the teeth divided into four groups according to the application method (n ¼8): NO— no dentin pretreatment with TiF4; 60A—active application of TiF4 for 60 s; 30A—active application of TiF4 for 30 s; 60P—passive application of TiF4 for 60 s. Twenty-four teeth were used to evaluate the effects of TiF4 on sound and demineralized dentin (Study 2). The occlusal enamel of the teeth was removed and flattened. They were then divided into four groups according to the degree of dentin mineralization (sound or demineralized) and the presence or absence of dentin pretreatment with TiF4 (n ¼6). For dentin demineralization, the teeth were immersed in demineralizing solution for 1 h and in remineralizing solution for 23 h for 3 days. Dentin pretreatment with 2.5% TiF4 was performed actively for 1 min in Study 2. For Studies 1 and 2, after application of a two-step self-etching adhesive system (Clearfil SE Bond/Kuraray), a composite resin block was built up on the tooth. The tooth-resin samples were cut to obtain specimens with a bonding area of approximately 1 mm2. Microtensile bond strength testing was performed 24 h later. The fractured test specimens were visually examined to classify the failure mode. Photomicrographs of the tooth/restoration interface were taken using scanning electron microscopy. Results: For Study 1, ANOVA demonstrated no difference between application methods (p¼ 0.784). For Study 2, ANOVA revealed no significant difference in mean bond strength values between sound and demineralized dentin (p¼ 0.1982), or between the presence or absence of TiF4 (p¼ 0.1789). In addition, no significant interaction between the factors (p¼0.4284) was observed. The commonnest failure mode for both studies was adhesive. Hybrid layer formation was observed in all TiF4 application methods and degrees of dentin mineralization; however, the use of TiF4, independently of the application method, reduced the number and the extent of resin tags in the hybrid layer. Conclusions: Microtensile bond strength of a self-etching adhesive system to dentin was not influenced by the application method of TiF4. Dentin pretreatment with TiF4 had no influence on the bond strength of the two-step self-etching adhesive system to sound or demineralized dentin, despite the changes in hybrid layer micromorphology. & 2014 Elsevier Ltd. All rights reserved.
Keywords: A. Self-etch primers B. Dentin C. Micro-tensile D. Adhesion by mechanical interlocking D. Hybrid layer D. Demineralisation
1. Introduction
n Corresponding author at: Faculdade de Odontologia e Instituto de Pesquisas São Leopoldo Mandic, Departamento de Odontologia Restauradora—Dentística, Rua José Rocha Junqueira, 13, Bairro Swift, Campinas CEP: 13045-755, SP, Brazil. Tel.⧸fax: 55 19 3211 3600. E-mail addresses: [email protected] (L. Domingues), [email protected] (C. Real), [email protected] (E. Bridi), fl[email protected] (A.-n. FLB), [email protected] (F. FMG), [email protected] (. Turssi), [email protected] (R. Basting).
http://dx.doi.org/10.1016/j.ijadhadh.2014.06.005 0143-7496/& 2014 Elsevier Ltd. All rights reserved.
Titanium tetrafluoride (TiF4) varnishes and solutions have been used to prevent enamel demineralization [1] and dentin erosion [2–4], due to the formation of a layer of titanium oxide or stable organometallic compounds, which are resistant to acid and alkaline solutions [5,6]. The formation of a vitreous layer (glaze-like surface) has been observed for both enamel and dentin, conferring higher substrate resistance to demineralization [6,7]. When applied to dentin, following cavity preparation, a lower risk of secondary caries would be expected as a result of the change in
160
L. Domingues et al. / International Journal of Adhesion & Adhesives 54 (2014) 159–164
the smear layer [8,9], and therefore, pretreating the dentin with titanium tetrafluoride would benefit restorative procedures. As a dentin pretreatment, Dündar et al. [10] demonstrated that the application of TiF4 solution followed by acid etching reduced the bond strength to dentin, when using 4-META/MMA and Bis-GMA-based cements and, likewise, when an acidic monomer was used prior to an MMA-based cement. The reason for such low bond strength values was the pH of TiF4 (approximately 1.2), which may have favored bonding between the titanium and the oxygen from the phosphate group, resulting in the formation of a vitreous layer of titanium dioxide on the surface [11], thus preventing penetration of the bond monomers and formation of the hybrid layer. However, when TiF4 was used before acid etching in a conventional three-step adhesive system, Devabhaktuni and Manjunath [5] observed that titanium tetrafluoride did not significantly affect the bond strength between composite resin and dentin, just as Bridi et al. [9] did not observe any influence of TiF4 application when using two-step self etching or single-step adhesive systems on sound dentin. It could be postulated that TiF4 application method influences the formation of a glaze-like surface layer on dentin. Magalhães et al. [1] showed that the formation of such layer did not occur when a 4% TiF4 solution was actively applied using a disposable brush, rather than simply pipetting the solution. Application with a disposable brush, therefore, leads to surface wear rather than allowing the formation of a glaze-like surface layer. Basting et al. [6], however, showed the formation of a glaze-like surface layer when actively applying TiF4 solution, although the microtensile bond strength of two self-etching adhesive systems were not influenced by this application method [9]. Due to the lack of further studies in the literature investigating the influence of the TiF4 application method as a dentin pretreatment, an initial study, namely Study 1, was performed. It is important to highlight that the current principle of caries removal is based on completely eliminating superficial dentin, known as infected dentin, which contains a large amount of necrotic tissue and microorganisms. The inner layer is known as affected or demineralized dentin, and contains a reduced amount of bacteria and preserved collagen fibers and should, therefore, be maintained, since it can be remineralized [12–14]. Therefore, when using two-step self-etching adhesive systems on demineralized dentin, lower bond strength has been observed when compared to sound dentin [15,16], however, a lack of significant difference has also been reported for both dentinal substrates [17,18]. Considering that TiF4 may contribute to dental tissue remineralization, despite no reports on dentin with varying degrees of remineralization, a second experiment, namely Study 2, was conducted to evaluate the influence of TiF4 on bond strength to sound and demineralized dentin using a two-step self-etching adhesive system. The null hypotheses tested in these experiments were: - Study 1: there is no influence of TiF4 application method on the microtensile bond strength of a self-etching adhesive system to dentin;
- Study 2: (a) there is no influence of TiF4 use, in terms of bond strength, using a two-step self-etching adhesive system to dentin; b) there is no difference in bond strength of a twostep self-etching adhesive system to different types of dentin substrates.
2. Materials and methods Both studies were approved by the Research Ethics Committee of the Sao Leopoldo Mandic Research Institute (process numbers 521.180 and 420.932). 2.1. Study 1 Thirty-two sound recently extracted human third molars were cleaned using a periodontal curette and maintained in a 0.1% aqueous thymol solution. The occlusal surface of all teeth was removed to obtain a flat superficial dentin surface. The roots were removed at 2 mm below the cementoenamel junction using diamond disks mounted on a precision saw (Isomet 1000 Precision Diamond Saw, Buehler Ltd, Lake Bluff, Illinois, USA) and the pulp chamber exposed was filled with composite resin (Filtek Z350 XT, 3M Espe, Saint Paul, MN, USA), using a two-step self-etching adhesive system (Clearfil SE Bond, Kuraray Medical Inc., Kurashiki, Okayama, Japan). The dentin surfaces were flattened using a water-cooled polisher (Politriz Aropol 2V, Arotec, Cotia, SP, Brazil), using aluminum oxide sandpaper (Imperial Wetordry, 3M, Sumaré, SP, Brazil) in descending order of abrasiveness (400, 600 and 1200). The teeth were divided into groups according to the TiF4 application method (n ¼8) (Table 1). TiF4 was obtained in the pro analysi (P.A.) form and prepared in distilled deionized water at a concentration of 2.5% pH 1.4 (Table 2), as described by Dündar et al. [10], as a dentin pretreatment solution. The solution was applied to the dentin surfaces of the respective groups for 30 or 60 s, either actively (smearing) or passively, using a disposable brush (Table 1). Active application was performed with a disposable brush, using light pressure and sweeping movements along the entire dentin surface, while passive application was achieved using a disposable brush with sweeping movements, but without pressure. Following the desired application time, each specimen was lightly air-dried for 5 s. After applying the two-step self-etching adhesive system (Clearfil SE Bond) to the dentin surface, a 5 mm high and 5 mm wide composite resin block (Filtek Z350 XT, 3M Espe, Saint Paul, MN, USA) was prepared in increments over the hybridized dentin surface. Light-curing was then performed using a halogen light source (Demetron Research Corporation, Danbury, CT, USA), with a mean radiance of 487 mW/cm2 (minimum 438 mW/cm2 and maximum 597 mW/cm2), measured using a radiometer (Newdent Equipament Ltd., Ribeirão Preto, SP, Brazil) after every five specimens.
Table 1 Group and treatment for studies 1 and 2. Study
Study 1
Study 2
Abbreviation
Treatment
NO 60A 30A 60P SD þ Clear DD þClear SD þ TiF4 þ Clear DD þTiF4 þ Clear
No pretreatment followed by a two-step self-etching adhesive system Pretreatment with TiF4 actively for 60 s followed by a two-step self-etching adhesive system Pretreatment with TiF4 actively for 30 s followed by a two-step self-etching adhesive system Pretreatment with TiF4 passively for 60 s followed by a two-step self-etching adhesive system Sound dentin and application of two-step self-etching adhesive system Demineralized dentin and application of two-step self-etching adhesive system Sound dentin, pretreatment with TiF4 and application of two-step self-etching adhesive system Demineralized dentin, pretreatment with TiF4 and application of two-step self-etching adhesive system
L. Domingues et al. / International Journal of Adhesion & Adhesives 54 (2014) 159–164
161
Table 2 Titanium tetrafluoride, adhesive system and demineralizing and remineralizing solutions used, composition, method of use and manufacturer.
Material
Composition
Method of use
2.5% Titanium tetrafluoride pH1.4
TiF4 P.A.þdistilled deionized water
Clearfil SE bond pH 2
Primer: MDP, HEMA, Hydrophilic dimethacrylate, camphorquinone, N,N-diethanol-Ptoluidine, water. Bond: MDP, Bis-GMA, HEMA, Hydrophobic dimethacrylate, camphorquinone, N,N-diethanol-P-toluidine, silanized colloid silica
Demineralizing 2 mM Ca, 2 mM P, acetate buffer 74 mM solution* pH 4.3 Remineralizing 1.5 mM Ca, 0.9 mM P, Tris buffer 20 mM, 150 mM KCl solution* pH 7.0
Apply product actively for 60 s [1] Dry cavity; Apply primer for 20 s; Gently air-dry; Apply bond; Gently air-dry; Light-cure for 10 s.
Manufacturer (city, state, country) Sigma Aldrich (Saint Louis, MO, United States of America)
Kuraray Medical Inc. (1621 Sakazu, Kurashiki, Okayama, Japan)
1 h1.5 ml/mm2
Prepared in the laboratory
23 h1.5 ml/mm2
Prepared in the laboratory
Bis-GMA: bisphenol-glycidyl-methacrylate; HEMA: 2-hydroxydoethyl methacrylate; MDP: 10-methacryloiloxy decyl dihydrogen phosphate. n
According to Featherstone et al. [21] and modified by Serra and Cury [22].
The tooth blocks were fixed onto acrylic plates for positioning in a precision saw (Isomet 1000 Precision Diamond Saw, Buehler Ltd, Lake Bluff, Illinois, USA), in order to cut sections in the buccal-lingual plane. One slice of each toothresin set was prepared to evaluate the hybrid layer under scanning electron microscopy, while the remaining slices were used for microtensile bond strength testing, cut in the mesiodistal plane, to obtain specimens with a cross-section of approximately 1 mm2. On average, five to seven specimens were obtained per tooth. Microtensile bond strength tests were performed after 24 h using a universal testing machine (DL2000, EMIC, São José dos Pinhais, PR, Brazil) at a speed of 0.5 mm/min and load cell of 50 N. The interface area of each specimen was measured using a digital gauge (Mitutoyo Sul Americana Ltd, Suzano, SP, Brazil). The specimens were glued (Superbonder, Henkel Loctite Ltd., São Paulo, SP, Brazil) onto specific devices by their extremities and the bond strength values were obtained in MPa, by dividing the force needed to break the adhesive interface (Newtons) by the area of the adhesive interface (mm2). Failure mode was assessed by visual examination using a stereoscopic loupe (Eikonal, São Paulo, SP, Brazil), with a magnification power of 30 times. The failure modes were adhesive (adhesive failure), dentin cohesion (failure of the tooth substrate), resin cohesion (failure of the composite resin), or mixed (adhesive and resin cohesion failure). One or two slices from each tooth-resin block were set aside for evaluation of the tooth/restoration interface using scanning electronic microscopy (SEM) (Jeol 5900LV, Jeol Ltd., Tokyo, Japan), as per Radovic et al. [19]. The samples were mounted on aluminum blocks, sputter-coated with gold and examined under SEM at an operating voltage of 10 kV. Observations were carefully performed on the entire adhesive interface of the slice at 500 magnification and images of the most representative area of each specimen were taken at 1000 magnification. Differences in hybrid layer formation, shape, length and number of resin tags were ascertained according to the application method tested and the influence of pretreatment with TiF4 was evaluated. The microtensile bond strength values recorded for all specimens of the same tooth were averaged in order to obtain a single value for each tooth. After checking normality and homogeneity of variance, one-way analysis of variance (ANOVA) was applied, with a significance level set at 5%. Data analysis was performed using SPSS 20 (SPSS Inc., Chicago, IL, USA).
2.2. Study 2 Twenty-four sound, recently extracted human third molars were cleaned using periodontal curettes and stored in 0.1% aqueous thymol solution, and prepared as described for Study 1. The teeth were then divided into groups according to presence or absence of TiF4 application, in addition to degree of dentin mineralization (n ¼6) (Table 1). The demineralized dentin substrate was obtained using the dynamic model described by Hara et al. [20]. The dentin surface for adhesion was measured at 5 5 mm and the remainder of the tooth block was made impermeable using modeling wax. Each tooth block was then immersed individually for 1 h in demineralizing solution, rinsed in distilled deionized water and immersed in remineralizing solution (Table 2), completing the cycle in 23 h. Three cycles were performed over three days in an incubator at 37 1C in individual receptacles. TiF4 solution was prepared as described in Study 1 and applied to groups SDþ TiF4 þClear and DDþTiF4 þClear (Table 1). The solution was actively applied onto the dentin surface for 60 s using a disposable brush [1], followed by gentle air-drying for 5 s (Table 1). The adhesive system was then applied according to the manufacturers’ instructions, and the composite resin block was made in order to prepare specimens for microtensile bond strength testing, as described for Study 1. Microtensile bond strength test, failure mode and SEM of the hybrid layer were also evaluated. The microtensile bond strength values, which were recorded for all specimens of the same tooth, were averaged in order to obtain a single value for each tooth. After checking normality and homogeneity of variance, one-way analysis of variance (ANOVA) was applied, with a significance level set at 5%. Data analysis was performed using SPSS 20 (SPSS Inc., Chicago, IL, USA).
3. Results One-way analysis of variance (ANOVA) revealed no significant difference in bond strength between the methods with and without application of TiF4 (p ¼0.784) (Table 3). ANOVA also showed no significant difference in bond strength to dentin in MPa between sound and demineralized dentin (p ¼0.1982) or between the presence and absence of TiF4 (p ¼0.1789). Interaction between factors was also not significant (p ¼0.4284) (Table 4).
162
L. Domingues et al. / International Journal of Adhesion & Adhesives 54 (2014) 159–164
Table 3 Mean values of bond strength (MPa) to dentin (standard deviation) according to the different TiF4 application methods. Application method
Bond strength (MPa)
NO 60A 30A 60P
11.1 12.0 14.0 13.5
(7.2) A (7.3) A (6.0) A (5.6) A
Table 4 Mean values of bond strength (MPa) to dentin (standard deviation) in terms of groups. TiF4 Dentin
Sound Demineralized
Presence
Absence
9.3 (4.2) Aa 8.4 (3.8) Aa
13.1 (3.4) Aa 9.4 (5.2) Aa
Mean followed by the same letters, no significant difference (p 40.05).
Table 5 Failure pattern distribution of the specimens according to group (Study 1). Failure pattern
NO 30A 60A 60P
Adhesive (%)
Mixed (%)
Dentin cohesion (%)
Resin cohesion (%)
77.8 81.8 62.2 67.4
14.8 15.2 27.0 14.0
0.0 0.0 2.7 7.0
7.4 3.0 8.1 11.6
Table 6 Failure pattern distribution of the specimens according to group (Study 2). Failure pattern Dentin
Sound
TiF4
Presence Absence Demineralized Presence Absence
Adhesive (%)
Mixed (%)
Dentin cohesion (%)`
Resin cohesion (%)
85.3 68.8 88.2 94.1
0.0 6.2 0.0 0.0
2.9 3.1 0.0 0.0
11.8 21.9 11.8 5.9
The commonest failure type was adhesive for all application methods for both Study 1 and Study 2 (84.3%), followed by mixed (Table 5) and resin cohesion (12.7%), respectively (Table 6). The formation of a hybrid layer was observed for all types of TiF4 application method to dentin (Fig. 1) as well as for the degree of dentin mineralization (Fig. 2). TiF4 application, however, regardless of the method, reduced the number and extension of resin tags in the hybrid layer (B, C and D) when compared to group NO, where TiF4 was not applied (A). For sound (A) and demineralized dentin (C), when only Clearfil SE Bond was used, resin tags were formed uniformly throughout the adhesive interface. TiF4 application reduced the number and length of resin tags in the hybrid layer in sound (B) and demineralized dentin (D).
4. Discussion Some studies using TiF4 have demonstrated its capacity to prevent erosion and demineralization of the enamel [1,3,4] by inducing the formation of a protective layer composed of titanium
oxide or organometallic compounds [23,24]. When in contact with organic material present in the dentin, this substance can rapidly form a stable and resistant coating to acids and alkaline solutions, promoting higher tooth substrate resistance to demineralization [5,6]. Therefore, pretreatment with TiF4 could contribute to tooth remineralization and a reduced risk of secondary caries due to the changes induced in the smear layer [6]. Dundar et al. [10] were the first to show that dentin pretreatment with TiF4 prevented the formation of a hybrid layer when using resin cements, which contradicts the results of the present study and those of Bridi et al. [9]. These variations may rely on the fact that Dündar et al. [10] used different adhesive systems and resin cement compositions, following TiF4 pretreatment. For the 4-META/MMA cement groups, the dentin was etched with citric acid and FeCl3 gel (Green Activator, Sun Medical) once TiF4 had been applied. Basting et al. [6], observed that the vitreous surface that formed after TiF4 application was resistant to etching with citric acid, therefore, opening the possibility that this layer was not removed in the Dündar et al. [10] study. In addition, for Bis-GMA resin cements, the differences may be accounted for by the use of a primer (Syntac Primer/Ivoclar Vivadent) containing different components to that of Clearfil SE Bond/Kuraray Medical Inc, which contain acetone, triethyleneglycol dimethacrylate, polyethylene glycol dimethacrylate and maleic acid, and a composition based on 10-methacryloiloxy decyl dihydrogen phosphate, hydroxydoethyl methacrylate, hydrophilic dimethacrylate, camphorquinone, N,Ndiethanol-P-toluidine and water, respectively. Although the acidity of the adhesive may also contribute to the different mechanisms of hybrid layer formation, with Clearfil SE Bond adhesive being weakly acidic (pH¼2), while Syntac Primer is moderately acidic (pH¼ 1.3) [25,26], Clearfil SE Bond also contains 10-MDP functional monomer, which may have significantly contributed to the chemical bond to dentin [27]. Bridi et al. [9] also observed that pretreatment with TiF4 did not influence the microtensile bond strength to dentin when using a one or two-step self-etching adhesive system. This was reported as being due to the low pH of the TiF4 solution associated to active application, which may dissolve the smear layer and improve the infiltration of resin monomers into the dentin. The results of the present study, however, demonstrated that the TiF4 application method, whether active or passive, did not lead to a difference in the micromorphology of the hybrid layer, nor did it influence bond strength. The suggestions by Magalhães et al. [1] that the formation of a glaze-like surface layer did not occur when TiF4 solution was applied with a microbrush is contradicted by Basting et al. [6], who showed that 2.5% TiF4 has the ability to improve the mechanical properties of the dentin surface. Furthermore, the glaze-like surface layer was not only reported to be homogenous, but also abundantly deposited. Independently of the TiF4 application method, Clearfil SE Bond was effective in penetrating the glaze-like surface, due to its moderate acidity, managing to demineralize the superficial dentin in addition to the TiF4-layer. Although Bridi et al. [9] showed that the TiF4 solution did not interfere with the micromorphological characteristics of the hybrid layer when using a two or a one-step self-etching adhesive system, the present study demonstrated fewer and shorter resin tags when this solution was applied as a pre-treatment. It is well known that resin tags do not contribute significantly to resin‐dentin bonding, and that it occurs mainly to peri‐and inter‐tubular dentin [28], which explains why there were no differences in bond strength values. Dentin cohesion failure was also only observed when TiF4 was actively (2.7%) or passively (7%) applied for 60 s onto the dentin, whilst no dentin failure was observed in other groups. The results of Study 1 accepted the null hypothesis, since there was no influence of the TiF4 application method on the
L. Domingues et al. / International Journal of Adhesion & Adhesives 54 (2014) 159–164
163
Fig. 1. SEM image of the adhesive interface: (A) No treatment with TiF4 (group NO); (B) TiF4 actively applied for 30 s onto dentin (group 30A); (C) TiF4 actively applied for 60 s onto dentin (group 60A); (D) TiF4 passively applied for 60 s onto dentin (group 60P).
Fig. 2. SEM image of the adhesive interface: (A) sound dentin without pretreatment; (B) sound dentin with TiF4 application; (C) demineralized dentin without pretreatment; (D) demineralized dentin with TiF4 application.
164
L. Domingues et al. / International Journal of Adhesion & Adhesives 54 (2014) 159–164
microtensile bond strength of a self-etching adhesive system to dentin. Therefore, active TiF4 application for 30 s may be a reasonable and time-saving method to treat dentin prior to restoration. Both conventional and self-etching adhesive systems may be used for sound dentin [18], however, it has been demonstrated that two-step self-etching adhesive systems, particularly Clearfil SE Bond, presented similar [15] or higher bond strength values [16] than the conventional two-step adhesive onto sound dentin. Furthermore, it has been reported that one-step self-etching adhesive systems present significantly lower bond strength values than the two-step systems [15]. The superior adhesion obtained with two-step self-etching systems may be attributed to the presence of the MDP monomer, which is characterized by its link with hydroxyapatite, thus promoting a chemical bond in addition to the mechanical adhesion [27]. The present study demonstrated that, for demineralized dentin, the bond strength obtained when using a two-step self-etching adhesive system did not show a significant difference when compared to sound dentin. Furthermore, the predominant failure mode (adhesive) was similar for all groups. These findings corroborate those reported in the literature, which also demonstrated no difference in bond strength for two-step self-etching adhesive systems to dentin, regardless of its degree of mineralization [17,18]. It is speculated that the adhesive system may create an adequate bond in either substrate because it induces a superficial demineralization of the dentin, which is sufficient to create a porous surface for mechanical imbrication [29], as well as to maintain the residual hydroxyapatite linked with collagen, which may work as an additional receptor for chemical bonding with the functional monomer 10-MDP from the two-step self-etching adhesive system Clearfil SE Bond [27]. The results from Study 2 provided grounds to accept the null hypothesis, since there was no influence of TiF4 application in terms of bond strength for a two-step self-etching system to dentin and there was no difference in bond strength for the same adhesive system to different types of dentin substrates. Nonetheless, although the micromorphology observations revealed that the use of Clearfil SE Bond lead to the formation of resin tags uniformly throughout the adhesive interface for both sound and demineralized dentin, TiF4 application reduced the number and extension of resin tags in the hybrid layer. Consequently, despite the variation in hybrid layer micromorphology, bond strength did not appear to be related to the extent of resin tags or the penetration of the adhesive through the tubules, but to the interaction of the adhesive system with the intertubular dentin, particularly if one considers that the substrate was the superficial dentin [28]. In terms of clinical relevance, the use of TiF4, regardless of the application method (actively for 30 or 60 s, or passively for 60 s), could be an important step in pretreatment for both sound and demineralized dentin due to the good bond strength values obtained when using a two-step self-etching adhesive system.
5. Conclusions Regardless of the application method, dentin pretreatment with TiF4 had no influence on the bond strength of the Clearfil SE Bond self-etching adhesive system to either sound or demineralized dentin, however, TiF4 seemed to provide a hybrid layer with a reduced number and extension of resin tags.
Acknowledgments The authors would like to thank LME/LNNano/CNPEM for the technical support during the electron microscopy study.
References [1] Magalhães AC, Comar LP, Rios D, Delbem ACB, Buzalaf MAR. Effect of a 4% titanium tetrafluoride (TiF4) varnish on demineralisation and remineralisation of bovine enamel in vitro. J Dent 2008;36:158–62. [2] Schlueter N, Ganss C, Mueller U, Klimek J. Effect of titanium tetrafluoride and sodium fluoride on erosion progression in enamel and dentine in vitro. Caries Res 2007;41:141–5. [3] Magalhães AC, Levy FM, Rios D, Buzalaf MA. Effect of a single application of TiF (4) and NaF varnishes and solutions on dentin erosion in vitro. J Dent 2010;38:153–7. [4] Hove LH, Holme B, Stenhagen KR, Tveit AB. Protective effect of TiF4 solutions with different concentrations and pH on development of erosion-like lesions. Caries Res 2011;45:64–8. [5] Devabhaktuni S, Manjunath MK. Effect of 4% titanium tetrafluoride application on shear bond strength of composite resin: an in vitro study. J Conserv Dent 2011;14:43–5. [6] Basting RT, Leme AA, Bridi EC, Amaral FLB, França FMG, Turssi CP, BedranRusso AK. Nanomechanical properties, SEM and EDS microanalysis of dentin treated with 2.5% titanium tetrafluoride, before and after an erosive challenge. J Biomed Mater Res Part B 2014 (In press). [7] Wei SH, Soboroff DM, Wefel JS. Effects of titanium tetrafluoride on human enamel. J Dent Res 1976;55:426–31. [8] Kazemi RB, Sen BH, Spångberg LS. Permeability changes of dentine treated with titanium tetrafluoride. J Dent 1999;27:531–8. [9] Bridi EC, Amaral FL, França FM, Turssi CP, Basting RT. Influence of dentin pretreatment with titanium tetrafluoride and self-etching adhesive systems on microtensile bond strength. Am J Dent 2013;26:121–6. [10] Dündar M, Ozcan M, Cömlekoglu ME, Sen BH. Nanoleakage inhibition within hybrid layer using new protective chemicals and their effect on adhesion. J Dent Res 2011;90:93–8. [11] Sen BH, Büyükyilmaz T. The effect of 4% titanium tetrafluoride solution on root canal walls—a preliminary investigation. J Endod 1998;24:239–43. [12] Fusayama T. Two layers of carious dentin: diagnosis and treatment. Oper Dent 1979;4:63–70. [13] Yip HK, Beeley JA, Stevenson AG. Mineral content of the dentine remaining after chemomechanical caries removal. Caries Res 1995;29:111–7. [14] Wambier DS, Santos FA, Guedes-Pinto AC, Jaeger RG, Simionato MR. Ultrastructural and microbiological analysis of the dentin layers affected by caries lesions in primary molars treated by minimal intervention. Pediatr Dent 2007;29:228–34. [15] Wei S, Sadr A, Shimada Y, Tagami J. Effect of caries-affected dentin hardness on the shear bond strength of current adhesives. J Adhes Dent 2008;10:431–40. [16] Xuan W, Hou BX, Lü YL. Bond strength of different adhesives to normal and caries-affected dentins. Chin Med J 2010;123:332–6. [17] Mobarak EH, El-Korashy DI, Pashley DH. Effect of chlorhexidine concentrations on micro-shear bond strength of self-etch adhesive to normal and cariesaffected dentin. Am J Dent 2010;23:217–22. [18] Scholtanus JD, Purwanta K, Dogan N, Kleverlaan CJ, Feilzer AJ. Microtensile bond strength of three simplified adhesive systems to caries-affected dentin. J Adhes Dent 2010;12:273–8. [19] Radovic I, Vulicevic ZR, García-Godoy F. Morphological evaluation of 2- and 1-step self-etching system interfaces with dentin. Oper Dent 2006;31:710–8. [20] Hara AT, Magalhães CS, Rodrigues Jr AL, Serra MC. Cariostatic effect of adhesive restorations in root surfaces: an in vitro study. Pesqui Odontol Bras 2000;14:113–8. [21] Featherstone JD, O’Really MM, Shariati M, Brugler S. Enhancement of remineralization in vitro and in vivo. In: Leach SA, editor. Factors relating to demineralization and remineralization of the teeth. IRL, Oxford; 1986. p. 23–34. [22] Serra MC, Cury JA. The in vitro effect of glass-ionomer cement restoration on enamel subjected to a demineralization and remineralization model. Quintessence Int 1992;23:39–44. [23] (21) Wiegand A, Magalhães AC, Sener B, Waldheim E, Attin T. TiF(4) and NaF at pH 1.2 but not at pH 3.5 are able to reduce dentin erosion. Arch Oral Biol 2009;54:790–5. [24] Wiegand A, Waldheim E, Sener B, Magalhães AC, Attin T T. Comparison of the effects of TiF4 and NaF solutions at pH 1.2 and 3.5 on enamel erosion in vitro. Caries Res 2009;43:269–77. [25] Van Meerbeek B, Van Landuyt K, De Munck J, Hashimoto M, Peumans M, Lambrechts P, Yoshida Y, Inoue S, Suzuki K. Technique-sensitivity of contemporary adhesives. Dent Mater J 2005;24:1–13. [26] Tay FR, Pashley DH. Aggressiveness of contemporary self-etching systems I: Depth of penetration beyond dentin smear layers. Dent Mater 2001;17: 296–308. [27] Van Landuyt KL, Snauwaert J, De Munck J, Peumans M, Yoshida Y, Poitevin A, Coutinho E, Suzuki K, Lambrechts P, Van Meerbeek B. Systematic review of the chemical composition of contemporary dental adhesives. Biomater 2007;28: 3757–85. [28] Lohbauer U, Nikolaenko SA, Petschelt A, Frankenberger R. Resin tags do not contribute to dentin adhesion in self-etching adhesives. J Adhes Dent 2008;10:97–103. [29] Van Meerbeek B, De Munck J, Yoshida Y, Inoue S, Vargas M, Vijay P, Van Landuyt K, Lambrechts P, Vanherle G. Buonocore memorial lecture. Adhesion to enamel and dentin: current status and future challenges. Oper Dent 2003;28:215–35.
Contents lists available at ScienceDirect
International Journal of Adhesion & Adhesives journal homepage: www.elsevier.com/locate/ijadhadh
Effects of 2.5% TiF4 on microtensile bond strength: Influence of application method and degree of dentin mineralization Domingues LG, Real CM, Bridi EC, Amaral FLB, França FMG, Turssi CP, Basting RTn DDS, School of Dentistry and Research Institute, São Leopoldo Mandic, Campinas, SP, Brazil
art ic l e i nf o
a b s t r a c t
Article history: Accepted 30 May 2014 Available online 11 June 2014
Objectives: The aims of this study were to evaluate the effects of: (a) the application method of a 2.5% titanium tetrafluoride aqueous solution (TiF4) to dentin on the microtensile bond strength of a two-step self-etching adhesive system and (b) dentin pretreatment with 2.5% TiF4 on the microtensile bond strength of a two-step self-etching adhesive system to sound and demineralized dentin. Materials and methods: Thirty-two third molars were selected to evaluate the application method for dentin pretreatment with TiF4 (Study 1). The occlusal enamel surfaces were removed, the superficial dentin flattened and the teeth divided into four groups according to the application method (n ¼8): NO— no dentin pretreatment with TiF4; 60A—active application of TiF4 for 60 s; 30A—active application of TiF4 for 30 s; 60P—passive application of TiF4 for 60 s. Twenty-four teeth were used to evaluate the effects of TiF4 on sound and demineralized dentin (Study 2). The occlusal enamel of the teeth was removed and flattened. They were then divided into four groups according to the degree of dentin mineralization (sound or demineralized) and the presence or absence of dentin pretreatment with TiF4 (n ¼6). For dentin demineralization, the teeth were immersed in demineralizing solution for 1 h and in remineralizing solution for 23 h for 3 days. Dentin pretreatment with 2.5% TiF4 was performed actively for 1 min in Study 2. For Studies 1 and 2, after application of a two-step self-etching adhesive system (Clearfil SE Bond/Kuraray), a composite resin block was built up on the tooth. The tooth-resin samples were cut to obtain specimens with a bonding area of approximately 1 mm2. Microtensile bond strength testing was performed 24 h later. The fractured test specimens were visually examined to classify the failure mode. Photomicrographs of the tooth/restoration interface were taken using scanning electron microscopy. Results: For Study 1, ANOVA demonstrated no difference between application methods (p¼ 0.784). For Study 2, ANOVA revealed no significant difference in mean bond strength values between sound and demineralized dentin (p¼ 0.1982), or between the presence or absence of TiF4 (p¼ 0.1789). In addition, no significant interaction between the factors (p¼0.4284) was observed. The commonnest failure mode for both studies was adhesive. Hybrid layer formation was observed in all TiF4 application methods and degrees of dentin mineralization; however, the use of TiF4, independently of the application method, reduced the number and the extent of resin tags in the hybrid layer. Conclusions: Microtensile bond strength of a self-etching adhesive system to dentin was not influenced by the application method of TiF4. Dentin pretreatment with TiF4 had no influence on the bond strength of the two-step self-etching adhesive system to sound or demineralized dentin, despite the changes in hybrid layer micromorphology. & 2014 Elsevier Ltd. All rights reserved.
Keywords: A. Self-etch primers B. Dentin C. Micro-tensile D. Adhesion by mechanical interlocking D. Hybrid layer D. Demineralisation
1. Introduction
n Corresponding author at: Faculdade de Odontologia e Instituto de Pesquisas São Leopoldo Mandic, Departamento de Odontologia Restauradora—Dentística, Rua José Rocha Junqueira, 13, Bairro Swift, Campinas CEP: 13045-755, SP, Brazil. Tel.⧸fax: 55 19 3211 3600. E-mail addresses: [email protected] (L. Domingues), [email protected] (C. Real), [email protected] (E. Bridi), fl[email protected] (A.-n. FLB), [email protected] (F. FMG), [email protected] (. Turssi), [email protected] (R. Basting).
http://dx.doi.org/10.1016/j.ijadhadh.2014.06.005 0143-7496/& 2014 Elsevier Ltd. All rights reserved.
Titanium tetrafluoride (TiF4) varnishes and solutions have been used to prevent enamel demineralization [1] and dentin erosion [2–4], due to the formation of a layer of titanium oxide or stable organometallic compounds, which are resistant to acid and alkaline solutions [5,6]. The formation of a vitreous layer (glaze-like surface) has been observed for both enamel and dentin, conferring higher substrate resistance to demineralization [6,7]. When applied to dentin, following cavity preparation, a lower risk of secondary caries would be expected as a result of the change in
160
L. Domingues et al. / International Journal of Adhesion & Adhesives 54 (2014) 159–164
the smear layer [8,9], and therefore, pretreating the dentin with titanium tetrafluoride would benefit restorative procedures. As a dentin pretreatment, Dündar et al. [10] demonstrated that the application of TiF4 solution followed by acid etching reduced the bond strength to dentin, when using 4-META/MMA and Bis-GMA-based cements and, likewise, when an acidic monomer was used prior to an MMA-based cement. The reason for such low bond strength values was the pH of TiF4 (approximately 1.2), which may have favored bonding between the titanium and the oxygen from the phosphate group, resulting in the formation of a vitreous layer of titanium dioxide on the surface [11], thus preventing penetration of the bond monomers and formation of the hybrid layer. However, when TiF4 was used before acid etching in a conventional three-step adhesive system, Devabhaktuni and Manjunath [5] observed that titanium tetrafluoride did not significantly affect the bond strength between composite resin and dentin, just as Bridi et al. [9] did not observe any influence of TiF4 application when using two-step self etching or single-step adhesive systems on sound dentin. It could be postulated that TiF4 application method influences the formation of a glaze-like surface layer on dentin. Magalhães et al. [1] showed that the formation of such layer did not occur when a 4% TiF4 solution was actively applied using a disposable brush, rather than simply pipetting the solution. Application with a disposable brush, therefore, leads to surface wear rather than allowing the formation of a glaze-like surface layer. Basting et al. [6], however, showed the formation of a glaze-like surface layer when actively applying TiF4 solution, although the microtensile bond strength of two self-etching adhesive systems were not influenced by this application method [9]. Due to the lack of further studies in the literature investigating the influence of the TiF4 application method as a dentin pretreatment, an initial study, namely Study 1, was performed. It is important to highlight that the current principle of caries removal is based on completely eliminating superficial dentin, known as infected dentin, which contains a large amount of necrotic tissue and microorganisms. The inner layer is known as affected or demineralized dentin, and contains a reduced amount of bacteria and preserved collagen fibers and should, therefore, be maintained, since it can be remineralized [12–14]. Therefore, when using two-step self-etching adhesive systems on demineralized dentin, lower bond strength has been observed when compared to sound dentin [15,16], however, a lack of significant difference has also been reported for both dentinal substrates [17,18]. Considering that TiF4 may contribute to dental tissue remineralization, despite no reports on dentin with varying degrees of remineralization, a second experiment, namely Study 2, was conducted to evaluate the influence of TiF4 on bond strength to sound and demineralized dentin using a two-step self-etching adhesive system. The null hypotheses tested in these experiments were: - Study 1: there is no influence of TiF4 application method on the microtensile bond strength of a self-etching adhesive system to dentin;
- Study 2: (a) there is no influence of TiF4 use, in terms of bond strength, using a two-step self-etching adhesive system to dentin; b) there is no difference in bond strength of a twostep self-etching adhesive system to different types of dentin substrates.
2. Materials and methods Both studies were approved by the Research Ethics Committee of the Sao Leopoldo Mandic Research Institute (process numbers 521.180 and 420.932). 2.1. Study 1 Thirty-two sound recently extracted human third molars were cleaned using a periodontal curette and maintained in a 0.1% aqueous thymol solution. The occlusal surface of all teeth was removed to obtain a flat superficial dentin surface. The roots were removed at 2 mm below the cementoenamel junction using diamond disks mounted on a precision saw (Isomet 1000 Precision Diamond Saw, Buehler Ltd, Lake Bluff, Illinois, USA) and the pulp chamber exposed was filled with composite resin (Filtek Z350 XT, 3M Espe, Saint Paul, MN, USA), using a two-step self-etching adhesive system (Clearfil SE Bond, Kuraray Medical Inc., Kurashiki, Okayama, Japan). The dentin surfaces were flattened using a water-cooled polisher (Politriz Aropol 2V, Arotec, Cotia, SP, Brazil), using aluminum oxide sandpaper (Imperial Wetordry, 3M, Sumaré, SP, Brazil) in descending order of abrasiveness (400, 600 and 1200). The teeth were divided into groups according to the TiF4 application method (n ¼8) (Table 1). TiF4 was obtained in the pro analysi (P.A.) form and prepared in distilled deionized water at a concentration of 2.5% pH 1.4 (Table 2), as described by Dündar et al. [10], as a dentin pretreatment solution. The solution was applied to the dentin surfaces of the respective groups for 30 or 60 s, either actively (smearing) or passively, using a disposable brush (Table 1). Active application was performed with a disposable brush, using light pressure and sweeping movements along the entire dentin surface, while passive application was achieved using a disposable brush with sweeping movements, but without pressure. Following the desired application time, each specimen was lightly air-dried for 5 s. After applying the two-step self-etching adhesive system (Clearfil SE Bond) to the dentin surface, a 5 mm high and 5 mm wide composite resin block (Filtek Z350 XT, 3M Espe, Saint Paul, MN, USA) was prepared in increments over the hybridized dentin surface. Light-curing was then performed using a halogen light source (Demetron Research Corporation, Danbury, CT, USA), with a mean radiance of 487 mW/cm2 (minimum 438 mW/cm2 and maximum 597 mW/cm2), measured using a radiometer (Newdent Equipament Ltd., Ribeirão Preto, SP, Brazil) after every five specimens.
Table 1 Group and treatment for studies 1 and 2. Study
Study 1
Study 2
Abbreviation
Treatment
NO 60A 30A 60P SD þ Clear DD þClear SD þ TiF4 þ Clear DD þTiF4 þ Clear
No pretreatment followed by a two-step self-etching adhesive system Pretreatment with TiF4 actively for 60 s followed by a two-step self-etching adhesive system Pretreatment with TiF4 actively for 30 s followed by a two-step self-etching adhesive system Pretreatment with TiF4 passively for 60 s followed by a two-step self-etching adhesive system Sound dentin and application of two-step self-etching adhesive system Demineralized dentin and application of two-step self-etching adhesive system Sound dentin, pretreatment with TiF4 and application of two-step self-etching adhesive system Demineralized dentin, pretreatment with TiF4 and application of two-step self-etching adhesive system
L. Domingues et al. / International Journal of Adhesion & Adhesives 54 (2014) 159–164
161
Table 2 Titanium tetrafluoride, adhesive system and demineralizing and remineralizing solutions used, composition, method of use and manufacturer.
Material
Composition
Method of use
2.5% Titanium tetrafluoride pH1.4
TiF4 P.A.þdistilled deionized water
Clearfil SE bond pH 2
Primer: MDP, HEMA, Hydrophilic dimethacrylate, camphorquinone, N,N-diethanol-Ptoluidine, water. Bond: MDP, Bis-GMA, HEMA, Hydrophobic dimethacrylate, camphorquinone, N,N-diethanol-P-toluidine, silanized colloid silica
Demineralizing 2 mM Ca, 2 mM P, acetate buffer 74 mM solution* pH 4.3 Remineralizing 1.5 mM Ca, 0.9 mM P, Tris buffer 20 mM, 150 mM KCl solution* pH 7.0
Apply product actively for 60 s [1] Dry cavity; Apply primer for 20 s; Gently air-dry; Apply bond; Gently air-dry; Light-cure for 10 s.
Manufacturer (city, state, country) Sigma Aldrich (Saint Louis, MO, United States of America)
Kuraray Medical Inc. (1621 Sakazu, Kurashiki, Okayama, Japan)
1 h1.5 ml/mm2
Prepared in the laboratory
23 h1.5 ml/mm2
Prepared in the laboratory
Bis-GMA: bisphenol-glycidyl-methacrylate; HEMA: 2-hydroxydoethyl methacrylate; MDP: 10-methacryloiloxy decyl dihydrogen phosphate. n
According to Featherstone et al. [21] and modified by Serra and Cury [22].
The tooth blocks were fixed onto acrylic plates for positioning in a precision saw (Isomet 1000 Precision Diamond Saw, Buehler Ltd, Lake Bluff, Illinois, USA), in order to cut sections in the buccal-lingual plane. One slice of each toothresin set was prepared to evaluate the hybrid layer under scanning electron microscopy, while the remaining slices were used for microtensile bond strength testing, cut in the mesiodistal plane, to obtain specimens with a cross-section of approximately 1 mm2. On average, five to seven specimens were obtained per tooth. Microtensile bond strength tests were performed after 24 h using a universal testing machine (DL2000, EMIC, São José dos Pinhais, PR, Brazil) at a speed of 0.5 mm/min and load cell of 50 N. The interface area of each specimen was measured using a digital gauge (Mitutoyo Sul Americana Ltd, Suzano, SP, Brazil). The specimens were glued (Superbonder, Henkel Loctite Ltd., São Paulo, SP, Brazil) onto specific devices by their extremities and the bond strength values were obtained in MPa, by dividing the force needed to break the adhesive interface (Newtons) by the area of the adhesive interface (mm2). Failure mode was assessed by visual examination using a stereoscopic loupe (Eikonal, São Paulo, SP, Brazil), with a magnification power of 30 times. The failure modes were adhesive (adhesive failure), dentin cohesion (failure of the tooth substrate), resin cohesion (failure of the composite resin), or mixed (adhesive and resin cohesion failure). One or two slices from each tooth-resin block were set aside for evaluation of the tooth/restoration interface using scanning electronic microscopy (SEM) (Jeol 5900LV, Jeol Ltd., Tokyo, Japan), as per Radovic et al. [19]. The samples were mounted on aluminum blocks, sputter-coated with gold and examined under SEM at an operating voltage of 10 kV. Observations were carefully performed on the entire adhesive interface of the slice at 500 magnification and images of the most representative area of each specimen were taken at 1000 magnification. Differences in hybrid layer formation, shape, length and number of resin tags were ascertained according to the application method tested and the influence of pretreatment with TiF4 was evaluated. The microtensile bond strength values recorded for all specimens of the same tooth were averaged in order to obtain a single value for each tooth. After checking normality and homogeneity of variance, one-way analysis of variance (ANOVA) was applied, with a significance level set at 5%. Data analysis was performed using SPSS 20 (SPSS Inc., Chicago, IL, USA).
2.2. Study 2 Twenty-four sound, recently extracted human third molars were cleaned using periodontal curettes and stored in 0.1% aqueous thymol solution, and prepared as described for Study 1. The teeth were then divided into groups according to presence or absence of TiF4 application, in addition to degree of dentin mineralization (n ¼6) (Table 1). The demineralized dentin substrate was obtained using the dynamic model described by Hara et al. [20]. The dentin surface for adhesion was measured at 5 5 mm and the remainder of the tooth block was made impermeable using modeling wax. Each tooth block was then immersed individually for 1 h in demineralizing solution, rinsed in distilled deionized water and immersed in remineralizing solution (Table 2), completing the cycle in 23 h. Three cycles were performed over three days in an incubator at 37 1C in individual receptacles. TiF4 solution was prepared as described in Study 1 and applied to groups SDþ TiF4 þClear and DDþTiF4 þClear (Table 1). The solution was actively applied onto the dentin surface for 60 s using a disposable brush [1], followed by gentle air-drying for 5 s (Table 1). The adhesive system was then applied according to the manufacturers’ instructions, and the composite resin block was made in order to prepare specimens for microtensile bond strength testing, as described for Study 1. Microtensile bond strength test, failure mode and SEM of the hybrid layer were also evaluated. The microtensile bond strength values, which were recorded for all specimens of the same tooth, were averaged in order to obtain a single value for each tooth. After checking normality and homogeneity of variance, one-way analysis of variance (ANOVA) was applied, with a significance level set at 5%. Data analysis was performed using SPSS 20 (SPSS Inc., Chicago, IL, USA).
3. Results One-way analysis of variance (ANOVA) revealed no significant difference in bond strength between the methods with and without application of TiF4 (p ¼0.784) (Table 3). ANOVA also showed no significant difference in bond strength to dentin in MPa between sound and demineralized dentin (p ¼0.1982) or between the presence and absence of TiF4 (p ¼0.1789). Interaction between factors was also not significant (p ¼0.4284) (Table 4).
162
L. Domingues et al. / International Journal of Adhesion & Adhesives 54 (2014) 159–164
Table 3 Mean values of bond strength (MPa) to dentin (standard deviation) according to the different TiF4 application methods. Application method
Bond strength (MPa)
NO 60A 30A 60P
11.1 12.0 14.0 13.5
(7.2) A (7.3) A (6.0) A (5.6) A
Table 4 Mean values of bond strength (MPa) to dentin (standard deviation) in terms of groups. TiF4 Dentin
Sound Demineralized
Presence
Absence
9.3 (4.2) Aa 8.4 (3.8) Aa
13.1 (3.4) Aa 9.4 (5.2) Aa
Mean followed by the same letters, no significant difference (p 40.05).
Table 5 Failure pattern distribution of the specimens according to group (Study 1). Failure pattern
NO 30A 60A 60P
Adhesive (%)
Mixed (%)
Dentin cohesion (%)
Resin cohesion (%)
77.8 81.8 62.2 67.4
14.8 15.2 27.0 14.0
0.0 0.0 2.7 7.0
7.4 3.0 8.1 11.6
Table 6 Failure pattern distribution of the specimens according to group (Study 2). Failure pattern Dentin
Sound
TiF4
Presence Absence Demineralized Presence Absence
Adhesive (%)
Mixed (%)
Dentin cohesion (%)`
Resin cohesion (%)
85.3 68.8 88.2 94.1
0.0 6.2 0.0 0.0
2.9 3.1 0.0 0.0
11.8 21.9 11.8 5.9
The commonest failure type was adhesive for all application methods for both Study 1 and Study 2 (84.3%), followed by mixed (Table 5) and resin cohesion (12.7%), respectively (Table 6). The formation of a hybrid layer was observed for all types of TiF4 application method to dentin (Fig. 1) as well as for the degree of dentin mineralization (Fig. 2). TiF4 application, however, regardless of the method, reduced the number and extension of resin tags in the hybrid layer (B, C and D) when compared to group NO, where TiF4 was not applied (A). For sound (A) and demineralized dentin (C), when only Clearfil SE Bond was used, resin tags were formed uniformly throughout the adhesive interface. TiF4 application reduced the number and length of resin tags in the hybrid layer in sound (B) and demineralized dentin (D).
4. Discussion Some studies using TiF4 have demonstrated its capacity to prevent erosion and demineralization of the enamel [1,3,4] by inducing the formation of a protective layer composed of titanium
oxide or organometallic compounds [23,24]. When in contact with organic material present in the dentin, this substance can rapidly form a stable and resistant coating to acids and alkaline solutions, promoting higher tooth substrate resistance to demineralization [5,6]. Therefore, pretreatment with TiF4 could contribute to tooth remineralization and a reduced risk of secondary caries due to the changes induced in the smear layer [6]. Dundar et al. [10] were the first to show that dentin pretreatment with TiF4 prevented the formation of a hybrid layer when using resin cements, which contradicts the results of the present study and those of Bridi et al. [9]. These variations may rely on the fact that Dündar et al. [10] used different adhesive systems and resin cement compositions, following TiF4 pretreatment. For the 4-META/MMA cement groups, the dentin was etched with citric acid and FeCl3 gel (Green Activator, Sun Medical) once TiF4 had been applied. Basting et al. [6], observed that the vitreous surface that formed after TiF4 application was resistant to etching with citric acid, therefore, opening the possibility that this layer was not removed in the Dündar et al. [10] study. In addition, for Bis-GMA resin cements, the differences may be accounted for by the use of a primer (Syntac Primer/Ivoclar Vivadent) containing different components to that of Clearfil SE Bond/Kuraray Medical Inc, which contain acetone, triethyleneglycol dimethacrylate, polyethylene glycol dimethacrylate and maleic acid, and a composition based on 10-methacryloiloxy decyl dihydrogen phosphate, hydroxydoethyl methacrylate, hydrophilic dimethacrylate, camphorquinone, N,Ndiethanol-P-toluidine and water, respectively. Although the acidity of the adhesive may also contribute to the different mechanisms of hybrid layer formation, with Clearfil SE Bond adhesive being weakly acidic (pH¼2), while Syntac Primer is moderately acidic (pH¼ 1.3) [25,26], Clearfil SE Bond also contains 10-MDP functional monomer, which may have significantly contributed to the chemical bond to dentin [27]. Bridi et al. [9] also observed that pretreatment with TiF4 did not influence the microtensile bond strength to dentin when using a one or two-step self-etching adhesive system. This was reported as being due to the low pH of the TiF4 solution associated to active application, which may dissolve the smear layer and improve the infiltration of resin monomers into the dentin. The results of the present study, however, demonstrated that the TiF4 application method, whether active or passive, did not lead to a difference in the micromorphology of the hybrid layer, nor did it influence bond strength. The suggestions by Magalhães et al. [1] that the formation of a glaze-like surface layer did not occur when TiF4 solution was applied with a microbrush is contradicted by Basting et al. [6], who showed that 2.5% TiF4 has the ability to improve the mechanical properties of the dentin surface. Furthermore, the glaze-like surface layer was not only reported to be homogenous, but also abundantly deposited. Independently of the TiF4 application method, Clearfil SE Bond was effective in penetrating the glaze-like surface, due to its moderate acidity, managing to demineralize the superficial dentin in addition to the TiF4-layer. Although Bridi et al. [9] showed that the TiF4 solution did not interfere with the micromorphological characteristics of the hybrid layer when using a two or a one-step self-etching adhesive system, the present study demonstrated fewer and shorter resin tags when this solution was applied as a pre-treatment. It is well known that resin tags do not contribute significantly to resin‐dentin bonding, and that it occurs mainly to peri‐and inter‐tubular dentin [28], which explains why there were no differences in bond strength values. Dentin cohesion failure was also only observed when TiF4 was actively (2.7%) or passively (7%) applied for 60 s onto the dentin, whilst no dentin failure was observed in other groups. The results of Study 1 accepted the null hypothesis, since there was no influence of the TiF4 application method on the
L. Domingues et al. / International Journal of Adhesion & Adhesives 54 (2014) 159–164
163
Fig. 1. SEM image of the adhesive interface: (A) No treatment with TiF4 (group NO); (B) TiF4 actively applied for 30 s onto dentin (group 30A); (C) TiF4 actively applied for 60 s onto dentin (group 60A); (D) TiF4 passively applied for 60 s onto dentin (group 60P).
Fig. 2. SEM image of the adhesive interface: (A) sound dentin without pretreatment; (B) sound dentin with TiF4 application; (C) demineralized dentin without pretreatment; (D) demineralized dentin with TiF4 application.
164
L. Domingues et al. / International Journal of Adhesion & Adhesives 54 (2014) 159–164
microtensile bond strength of a self-etching adhesive system to dentin. Therefore, active TiF4 application for 30 s may be a reasonable and time-saving method to treat dentin prior to restoration. Both conventional and self-etching adhesive systems may be used for sound dentin [18], however, it has been demonstrated that two-step self-etching adhesive systems, particularly Clearfil SE Bond, presented similar [15] or higher bond strength values [16] than the conventional two-step adhesive onto sound dentin. Furthermore, it has been reported that one-step self-etching adhesive systems present significantly lower bond strength values than the two-step systems [15]. The superior adhesion obtained with two-step self-etching systems may be attributed to the presence of the MDP monomer, which is characterized by its link with hydroxyapatite, thus promoting a chemical bond in addition to the mechanical adhesion [27]. The present study demonstrated that, for demineralized dentin, the bond strength obtained when using a two-step self-etching adhesive system did not show a significant difference when compared to sound dentin. Furthermore, the predominant failure mode (adhesive) was similar for all groups. These findings corroborate those reported in the literature, which also demonstrated no difference in bond strength for two-step self-etching adhesive systems to dentin, regardless of its degree of mineralization [17,18]. It is speculated that the adhesive system may create an adequate bond in either substrate because it induces a superficial demineralization of the dentin, which is sufficient to create a porous surface for mechanical imbrication [29], as well as to maintain the residual hydroxyapatite linked with collagen, which may work as an additional receptor for chemical bonding with the functional monomer 10-MDP from the two-step self-etching adhesive system Clearfil SE Bond [27]. The results from Study 2 provided grounds to accept the null hypothesis, since there was no influence of TiF4 application in terms of bond strength for a two-step self-etching system to dentin and there was no difference in bond strength for the same adhesive system to different types of dentin substrates. Nonetheless, although the micromorphology observations revealed that the use of Clearfil SE Bond lead to the formation of resin tags uniformly throughout the adhesive interface for both sound and demineralized dentin, TiF4 application reduced the number and extension of resin tags in the hybrid layer. Consequently, despite the variation in hybrid layer micromorphology, bond strength did not appear to be related to the extent of resin tags or the penetration of the adhesive through the tubules, but to the interaction of the adhesive system with the intertubular dentin, particularly if one considers that the substrate was the superficial dentin [28]. In terms of clinical relevance, the use of TiF4, regardless of the application method (actively for 30 or 60 s, or passively for 60 s), could be an important step in pretreatment for both sound and demineralized dentin due to the good bond strength values obtained when using a two-step self-etching adhesive system.
5. Conclusions Regardless of the application method, dentin pretreatment with TiF4 had no influence on the bond strength of the Clearfil SE Bond self-etching adhesive system to either sound or demineralized dentin, however, TiF4 seemed to provide a hybrid layer with a reduced number and extension of resin tags.
Acknowledgments The authors would like to thank LME/LNNano/CNPEM for the technical support during the electron microscopy study.
References [1] Magalhães AC, Comar LP, Rios D, Delbem ACB, Buzalaf MAR. Effect of a 4% titanium tetrafluoride (TiF4) varnish on demineralisation and remineralisation of bovine enamel in vitro. J Dent 2008;36:158–62. [2] Schlueter N, Ganss C, Mueller U, Klimek J. Effect of titanium tetrafluoride and sodium fluoride on erosion progression in enamel and dentine in vitro. Caries Res 2007;41:141–5. [3] Magalhães AC, Levy FM, Rios D, Buzalaf MA. Effect of a single application of TiF (4) and NaF varnishes and solutions on dentin erosion in vitro. J Dent 2010;38:153–7. [4] Hove LH, Holme B, Stenhagen KR, Tveit AB. Protective effect of TiF4 solutions with different concentrations and pH on development of erosion-like lesions. Caries Res 2011;45:64–8. [5] Devabhaktuni S, Manjunath MK. Effect of 4% titanium tetrafluoride application on shear bond strength of composite resin: an in vitro study. J Conserv Dent 2011;14:43–5. [6] Basting RT, Leme AA, Bridi EC, Amaral FLB, França FMG, Turssi CP, BedranRusso AK. Nanomechanical properties, SEM and EDS microanalysis of dentin treated with 2.5% titanium tetrafluoride, before and after an erosive challenge. J Biomed Mater Res Part B 2014 (In press). [7] Wei SH, Soboroff DM, Wefel JS. Effects of titanium tetrafluoride on human enamel. J Dent Res 1976;55:426–31. [8] Kazemi RB, Sen BH, Spångberg LS. Permeability changes of dentine treated with titanium tetrafluoride. J Dent 1999;27:531–8. [9] Bridi EC, Amaral FL, França FM, Turssi CP, Basting RT. Influence of dentin pretreatment with titanium tetrafluoride and self-etching adhesive systems on microtensile bond strength. Am J Dent 2013;26:121–6. [10] Dündar M, Ozcan M, Cömlekoglu ME, Sen BH. Nanoleakage inhibition within hybrid layer using new protective chemicals and their effect on adhesion. J Dent Res 2011;90:93–8. [11] Sen BH, Büyükyilmaz T. The effect of 4% titanium tetrafluoride solution on root canal walls—a preliminary investigation. J Endod 1998;24:239–43. [12] Fusayama T. Two layers of carious dentin: diagnosis and treatment. Oper Dent 1979;4:63–70. [13] Yip HK, Beeley JA, Stevenson AG. Mineral content of the dentine remaining after chemomechanical caries removal. Caries Res 1995;29:111–7. [14] Wambier DS, Santos FA, Guedes-Pinto AC, Jaeger RG, Simionato MR. Ultrastructural and microbiological analysis of the dentin layers affected by caries lesions in primary molars treated by minimal intervention. Pediatr Dent 2007;29:228–34. [15] Wei S, Sadr A, Shimada Y, Tagami J. Effect of caries-affected dentin hardness on the shear bond strength of current adhesives. J Adhes Dent 2008;10:431–40. [16] Xuan W, Hou BX, Lü YL. Bond strength of different adhesives to normal and caries-affected dentins. Chin Med J 2010;123:332–6. [17] Mobarak EH, El-Korashy DI, Pashley DH. Effect of chlorhexidine concentrations on micro-shear bond strength of self-etch adhesive to normal and cariesaffected dentin. Am J Dent 2010;23:217–22. [18] Scholtanus JD, Purwanta K, Dogan N, Kleverlaan CJ, Feilzer AJ. Microtensile bond strength of three simplified adhesive systems to caries-affected dentin. J Adhes Dent 2010;12:273–8. [19] Radovic I, Vulicevic ZR, García-Godoy F. Morphological evaluation of 2- and 1-step self-etching system interfaces with dentin. Oper Dent 2006;31:710–8. [20] Hara AT, Magalhães CS, Rodrigues Jr AL, Serra MC. Cariostatic effect of adhesive restorations in root surfaces: an in vitro study. Pesqui Odontol Bras 2000;14:113–8. [21] Featherstone JD, O’Really MM, Shariati M, Brugler S. Enhancement of remineralization in vitro and in vivo. In: Leach SA, editor. Factors relating to demineralization and remineralization of the teeth. IRL, Oxford; 1986. p. 23–34. [22] Serra MC, Cury JA. The in vitro effect of glass-ionomer cement restoration on enamel subjected to a demineralization and remineralization model. Quintessence Int 1992;23:39–44. [23] (21) Wiegand A, Magalhães AC, Sener B, Waldheim E, Attin T. TiF(4) and NaF at pH 1.2 but not at pH 3.5 are able to reduce dentin erosion. Arch Oral Biol 2009;54:790–5. [24] Wiegand A, Waldheim E, Sener B, Magalhães AC, Attin T T. Comparison of the effects of TiF4 and NaF solutions at pH 1.2 and 3.5 on enamel erosion in vitro. Caries Res 2009;43:269–77. [25] Van Meerbeek B, Van Landuyt K, De Munck J, Hashimoto M, Peumans M, Lambrechts P, Yoshida Y, Inoue S, Suzuki K. Technique-sensitivity of contemporary adhesives. Dent Mater J 2005;24:1–13. [26] Tay FR, Pashley DH. Aggressiveness of contemporary self-etching systems I: Depth of penetration beyond dentin smear layers. Dent Mater 2001;17: 296–308. [27] Van Landuyt KL, Snauwaert J, De Munck J, Peumans M, Yoshida Y, Poitevin A, Coutinho E, Suzuki K, Lambrechts P, Van Meerbeek B. Systematic review of the chemical composition of contemporary dental adhesives. Biomater 2007;28: 3757–85. [28] Lohbauer U, Nikolaenko SA, Petschelt A, Frankenberger R. Resin tags do not contribute to dentin adhesion in self-etching adhesives. J Adhes Dent 2008;10:97–103. [29] Van Meerbeek B, De Munck J, Yoshida Y, Inoue S, Vargas M, Vijay P, Van Landuyt K, Lambrechts P, Vanherle G. Buonocore memorial lecture. Adhesion to enamel and dentin: current status and future challenges. Oper Dent 2003;28:215–35.