Effect of Salivary Contamination and Decontamination on Bond Strength of Two One-Step Self-Etching Adhesives to Dentin of Primary and Permanent Teeth Katharina Santschia / Anne Peutzfeldtb / Adrian Lussic / Simon Fluryd Purpose: To evaluate the effects of human saliva contamination and two decontamination procedures at different stages of the bonding procedure on the bond strength of two one-step self-etching adhesives to primary and permanent dentin. Materials and Methods: Extracted human primary and permanent molars (210 of each) were ground to mid-coronal dentin. The dentin specimens were randomly divided into 7 groups (n = 15/group/molar type) for each adhesive (Xeno V+ and Scotchbond Universal): no saliva contamination (control); saliva contamination before or after light curing of the adhesives followed by air drying, rinsing with water spray/air drying, or by rinsing with water spray/air drying/reapplication of the adhesives. Resin composite (Filtek Z250) was applied on the treated dentin surfaces. The specimens were stored at 37°C and 100% humidity for 24 h. After storage, shear bond strength (SBS) was measured and data analyzed with nonparametric ANOVA followed by exact Wilcoxon rank sum tests. Results: Xeno V+ generated significantly higher SBS than Scotchbond Universal when no saliva contamination occurred. Saliva contamination reduced SBS of Xeno V+, with the reduction being more pronounced when contamination occurred before light curing than after. In both situations, decontamination involving reapplication of the adhesive restored SBS. Saliva contamination had no significant effect on Scotchbond Universal. There were no differences in SBS between primary and permanent teeth. Conclusion: Rinsing with water and air drying followed by reapplication of the adhesive restored bond strength to saliva-contaminated dentin. Keywords: all-in-one adhesives, one-bottle adhesives, adhesion, dentin bonding, deciduous teeth. J Adhes Dent 2015; 17: 51–57. doi: 10.3290/j.jad.a33514
I
n order to generate a durable restoration using resin composites, successful adhesion without any contamination is required. Good moisture control keeps oral fluids, such as saliva, off the operation field. In clinical routine, however, ideal conditions are not always feasible, especially when rubber-dam isolation is not achievable.
a
Graduate Dentist, Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Switzerland. Idea, experimental work, wrote manuscript.
b
Senior Researcher, Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Switzerland. Idea, co-wrote manuscript.
c
Professor and Head, Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Switzerland. Proofread manuscript.
d
Research Associate, Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Switzerland. Idea, experimental design, supervision of the graduate dentist, co-wrote manuscript.
Correspondence: Simon Flury, Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Freiburgstrasse 7, CH-3010 Bern, Switzerland. Tel: +41-31-632-2581, Fax: +41-31632-9875. e-mail: [email protected]
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Submitted for publication: 19.08.14; accepted for publication: 18.01.15
Several studies have investigated the effect of saliva contamination on the bond strength to dentin of permanent teeth, but they did not reach consensus: While numerous authors detected a significant decrease in bond strength after salivary contamination,3,20,21 others did not.8,14,17 According to the studies by Johnson et al8 and Taskonak and Sertgöz,17 the bonding stage at which contamination occurs has no influence on bond strength. Other authors have reported significant differences depending on when the contamination occurred.3,6,9,11,21 Furthermore, various decontamination procedures have been recommended, going from blot drying11 to resurfacing of the cavity.3 While the effect of salivary contamination during the bonding procedure in permanent teeth has been studied relatively well, only a few studies have dealt with this problem in primary teeth,2,10 although this seems highly relevant. First, the risk of salivary contamination is increased in young children due to limited cooperation. Second, the effect of salivary contamination on bond strength may vary between the dentin of primary and permanent teeth, since the structure and morphology of the two have been 51
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shown to differ.16 Considering these differences, effects of salivary contamination on bond strength to permanent dentin may not automatically apply to primary dentin. The aim of the present in vitro study was to generate further knowledge about the effect of salivary contamination at different stages of the bonding procedure on bond strength of two one-step self-etching adhesives to primary and permanent dentin. Moreover, two decontamination procedures were investigated in an effort to restore any reduced bond strength. The null hypotheses to be tested were that (1) saliva contamination, (2) the two decontamination procedures, and (3) the bonding stage at which contamination occurs would have no influence on bond strength, (4) there would be no difference in bond strength between primary and permanent dentin, and (5) the two one-step self-etching adhesives would generate equal bond strengths.
MATERIALS AND METHODS Saliva Collection In order to achieve clinically relevant but at the same time standardized salivary contamination, unstimulated human saliva was collected from a single individual (K.S.) at least one hour after any consumption of food or drink. The collection of saliva took place on four subsequent days. Directly after collection, the saliva was centrifuged (Megafuge 1.0R, Heraeus Holding; Hanau, Germany) and stored at –80°C. On each day prior to preparation of shear bond strength (SBS) specimens, an equal amount of saliva from each of the four subsequent collecting days was thawed, pooled, and used at room temperature. Preparation of Dentin Specimens A final number of 210 extracted human primary molars and 210 extracted human permanent molars were used in this study (n = 15 primary and n = 15 permanent molars per group; 2 one-step self-etching adhesives; 7 groups [1 control group, 2 bonding stages at which contamination occurred: a) without or b) with 2 subsequent decontamination procedures]). Before extraction, patients and/or parents were informed about the use of the teeth for research purposes and verbal consent had been obtained. The molars were cleaned under tap water with a scaler and stored in 2% chloramine solution in the refrigerator (4°C) until needed. For preparation of dentin specimens, the molars were apically shortened with a water-cooled diamond saw (Isomet low-speed saw, Buehler; Lake Buff, IL, USA) and ground from the occlusal surface down to mid-coronal dentin. Grinding was performed with 220-grit followed by 500-grit silicon carbide (SiC) abrasive papers on a Struers LaboPol-21 grinding machine (Struers; Ballerup, Denmark). After grinding, to facilitate handling and allow fixation in the universal testing machine, the molars were embedded in self-curing acrylic resin (Paladur, Heraeus Kulzer; Hanau, Germany) in cylindrical stainless steel molds. After removal of the steel molds, the dentin speci52
mens were stored in a humid chamber in the refrigerator (100% humidity; 4°C) until needed. Preparation of SBS Specimens One hour before adhesive treatment, the dentin specimens were taken out of the refrigerator and kept in tap water at room temperature. Before preparation of each SBS specimen, the dentin surface was wet ground for 5 s with 500-grit SiC abrasive papers (Struers) to obtain a standardized smear layer, changing the 500-grit SiC abrasive paper each time after grinding 10 specimens. Subsequently, the specimen was air dried and the bonding area defined and isolated by use of perforated self-adhesive tape (diameter of the perforation approximately 2 mm). The bonding area was then treated with one of the two adhesives as listed in Table 1. For the control groups (groups 1X/1S; Fig 1), the adhesives were applied according to the manufacturers’ instructions (Table 1). For the groups including contamination before light curing (groups 2X/2S to 4X/4S; Fig 1), the adhesives were applied as described for groups 1X/1S, with the exception that a drop of saliva (6 μl) was applied with a pipette (Eppendorf Research; Hamburg, Germany) and left undisturbed for 5 s. For the contamination groups (groups 2X/2S), saliva was solely air dried and the adhesive then light cured. For decontamination (groups 3X/3S and 4X/4S), saliva was rinsed with water spray for 2 s followed by gentle air drying and light curing of the adhesive (groups 3X/3S), or saliva was rinsed with water spray for 2 s, followed by gentle air drying, reapplication and light curing of the adhesive (groups 4X/4S; Table 1). For the groups including contamination after light curing (groups 5X/5S to 7X/7S; Fig 1), the adhesives were applied as described for groups 1X/1S. After light curing, a drop of saliva was applied as described above. As regards contamination in groups 5X/5S, saliva was solely air dried. For decontamination (groups 6X/6S and 7X/7S), saliva in groups 6X/6S was rinsed with water spray for 2 s followed by gentle air drying. For groups 7X/7S, saliva was rinsed with water spray for 2 s followed by gentle air drying, reapplication and light curing of the adhesive (Table 1). All groups were prepared for both primary and permanent molars. After the adhesive treatment, a split Teflon mold (inner diameter 1.5 mm ≈ bonding area 1.8 mm2; height: 2 mm) was clamped to the dentin surface, filled with resin composite (Filtek Z250, 3M ESPE; St Paul, MN, USA; shade A2, lot No.: N505287), and covered with a Mylar strip (Hawe Stopstrip Straight, KerrHawe; Bioggio, Switzerland). The resin composite was light cured for 20 s and the SBS specimen was placed in a black photoresistant box in order to avoid any additional effect of ambient light on the polymerization process. Five minutes after completion of light curing, the specimen was freed from the Teflon mold at room temperature. Light curing was always performed with the LED curing unit bluephase polywave G2 (Ivoclar Vivadent; Schaan, Lichtenstein). All specimens were then stored in black photoresistant boxes in an incubator (Memmert UM 500, Memmert & Co; Schwabach, Germany) at 37°C and 100% humidity for 24 h. The Journal of Adhesive Dentistry
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Table 1
Adhesives used
Adhesive
Composition (manufacturers’ information)
Treatment steps
Time
Xeno V+ (DENTSPLY DeTrey; Konstanz, Germany) Lot No.: 1306004071
Bifunctional acrylate; acidic acrylate; ethyl 2-[5-dihydrogen phosphoryl-5,2-dioxapentyl]acrylate; initiator; stabilizer; tertiary butanol; water
Apply and agitate
20 s
Air dry thoroughly
>5s
Light cure
10 s
Scotchbond Universal (3M ESPE; Neuss, Germany) Lot No.: 530720
Bisphenol A diglycidyl ether dimethacrylate (bis-GMA); hydroxyethylmethacrylate (HEMA); 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP); 2-propenoic acid-, 2-methyl-, reaction products with 1,10-decanediol and phosphorous oxide; copolymers; silane treated silica; initiators; stabilizer; ethanol; water
Apply and agitate
20 s
Air dry
(~ 5 s)
Light cure
10 s
Xeno V+ (X) or Scotchbond Universal (S) Application of adhesive, air dry Saliva contamination
Air dry
Water spray, air dry
Water spray, air dry
Reapply adhesive
Light curing Saliva contamination
Air dry
Water spray, air dry
Water spray, air dry
Reapply adhesive, light cure
Resin composite, light curing Group 1X/1S Fig 1
Group 2X/2S
Group 3X/3S
Group 4X/4S
Group 5X/5S
Group 6X/6S
Group 7X/7S
Flowchart of the adhesive treatments resulting in groups 1X/1S to 7X/7S.
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Shaer bond strength values (MPa)
Shaer bond strength values (MPa)
Santschi et al
30 25 20 15 10 5 0 1X
1S
2X
2S 3X
3S
4X
4S 5X
5S 6X
6S
7X
7S
Groups
30 25 20 15 10 5 0 1X
1S
2X
2S 3X
3S
4X
4S 5X
5S 6X
6S
7X
7S
Groups
Fig 2 Shear bond strength (MPa; medians, lower and upper quartiles as well as minima and maxima) of primary molars (n = 15) for groups 1X/1S to 7X/7S (X = Xeno V+, S = Scotchbond Universal). For definition of groups, see Fig 1.
Fig 3 Shear bond strength (MPa; medians, lower and upper quartiles as well as minima and maxima) of permanent molars (n = 15) for groups 1X/1S to 7X/7S (X = Xeno V+, S = Scotchbond Universal). For definition of groups, see Fig 1.
SBS Testing and Failure Mode Determination After storage, specimens were subjected to SBS testing by use of a wire (stainless steel, diameter 0.6 mm) in a universal testing machine (Zwick Z010, Zwick; Ulm, Germany) at a crosshead speed of 1 mm/min. The maximum force (Fmax [N]) was recorded (testXpert software V9.0, Zwick) and the SBS values (MPa) were calculated (Fmax [N])/bonding area [mm2]), resulting in 15 SBS values per group for statistical analyses. After SBS testing, the failure mode of each specimen was determined under a stereomicroscope (Leica ZOOM 2000, Leica; Buffalo, NY, USA) at 40X magnification and classified as 1) cohesive failure in dentin, 2) adhesive failure at the dentin/adhesive interface, 3) cohesive failure within adhesive layer, 4) adhesive failure at the adhesive/resin composite interface, 5) cohesive failure in resin composite, or 6) mixed failure (combinations of failure modes 1 to 5).
molars are shown in Fig 2 and for permanent molars in Fig 3. The nonparametric ART ANOVA showed a significant effect on SBS of the factor adhesive (ie, Xeno V+ or Scotchbond Universal) and a significant effect of the factor adhesive treatment (ie, groups 1X/1S to 7X/7S) (both at p < 0.0001), but no significant effect of the factor tooth type (ie, primary molars or permanent molars; p = 1.00). Thus, SBS of primary and permanent molars were pooled. Finally, there was a significant interaction between the factors adhesive and adhesive treatment (p < 0.0001). The post-hoc analysis showed that for Xeno V+, saliva contamination (groups 2X and 5X) significantly lowered SBS (both p < 0.0001) compared to the control group (group 1X). For Scotchbond Universal, saliva contamination (groups 2S and 5S) had no significant influence on SBS (p = 0.51 to 0.87) compared to the SBS of the control group (group 1S). Regarding the two decontamination procedures (water spray/air drying in groups 3X/3S and 6X/6S; water spray/ air drying/reapplication of the adhesive in groups 4X/4S and 7X/7S), the post-hoc analysis showed that for Xeno V+, decontamination with water spray/air drying still resulted in a significantly lower SBS compared to the SBS of the control group, regardless of the bonding stage at which contamination occurred, ie, before light curing of the adhesive (group 3X; p < 0.0001) or after (group 6X; p = 0.049). However, decontamination with water spray/ air drying/reapplication of the adhesive restored SBS with no significant differences in SBS compared to that of the control group, regardless of the bonding stage at which contamination had occurred (group 4X: p = 0.19; group 7X: p = 0.54). For Scotchbond Universal, decontamination with water spray/air drying led to a similar SBS compared to that of the control group, regardless of the bonding stage at which contamination occurred (group 3S: p = 0.26; group 6S: p = 0.85). Decontamination with water spray/air drying/reapplication of the adhesive before light curing of the adhesive (group 4S) led to significantly higher SBS com-
Statistical Analyses Failure modes after SBS testing were analyzed descriptively, whereas SBS values were analyzed with nonparametric ANOVA (aligned rank transformation [ART] ANOVA)5 and the p-values were corrected with Bonferroni-Holm adjustment for multiple testing. For post-hoc analysis, exact Wilcoxon rank sum tests were performed with no correction for multiple testing. Thus, significant differences must be interpreted in an explorative context. All calculations were performed with R version 3.0.2 (The R Foundation for Statistical Computing; Vienna, Austria). Data of preliminary tests were statistically analyzed with NCSS/PASS 2005 (NCSS; Kaysville, UT, USA) for sample size determination, with the level of significance set at _ = 0.05.
RESULTS Shear bond strength (SBS; medians, lower and upper quartiles as well as minima and maxima) for primary 54
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Table 2 Distribution of failure modes after shear bond strength testing for primary molars (n = 15/group) / permanent molars (n = 15/group) Groups
1) Cohesive failure in dentin (%)
2) Adhesive failure at dentin/ adhesive interface (%)
3) Cohesive failure within adhesive layer (%)
4) Adhesive failure at adhesive/resin composite interface (%)
5) Cohesive failure in resin composite (%)
6) Mixed failure (%)
Group 1X
87 / 53
0 / 20
0/0
0/0
0/0
13 / 27
Group 2X
0/0
100 / 100
0/0
0/0
0/0
0/0
Group 3X
0/0
100 / 100
0/0
0/0
0/0
0/0
Group 4X
73 / 87
7/0
13 / 13
0/0
0/0
7/0
Group 5X
0/0
7/0
93 / 100
0/0
0/0
0/0
Group 6X
27 / 20
0/7
13 / 33
0/0
0/0
60 / 40
Group 7X
80 / 60
0/0
0/7
0/0
0/0
20 / 33
Xeno V+
Scotchbond Universal Group 1S
60 / 53
0 / 20
0/0
0/0
0/0
40 / 27
Group 2S
47 / 73.3
6 / 13.3
0/0
0/0
0/0
47 / 13.3
Group 3S
47 / 33
13 / 20
0/0
0/0
0/0
40 / 47
Group 4S
67 / 80
0/0
0/0
6/0
0/0
27 / 20
Group 5S
47 / 87
6/0
0/0
0/0
0/0
47 / 13
Group 6S
40 / 53.3
13 / 13.3
0/0
0/0
0/0
47 / 33.3
Group 7S
80 / 73
0/0
0/0
0/0
0/0
20 / 27
pared to that of the control group (p = 0.01), whereas after light curing of the adhesive (group 7S), SBS was similar to that of the control group (p = 0.47). The bonding stage at which contamination occurred highly influenced SBS of Xeno V+ (ART ANOVA p < 0.0001) but did not influence SBS of Scotchbond Universal (ART ANOVA p = 0.795). Generally, Xeno V+ showed less reduction in SBS when contamination (without or with subsequent decontamination procedures) took place after light curing the adhesive (groups 5X to 7X) compared to before light curing (groups 2X to 4X). However, the influence on SBS of the bonding stage at which contamination occurred varied depending on the adhesive treatment applied. Saliva contamination before light curing of Xeno V+ (group 2X) led to a significantly lower SBS than did saliva contamination after light curing (group 5X; p < 0.0001). Subsequent decontamination with water spray/air drying led to significantly lower SBS before light curing of Xeno V+ (group 3X) than after light curing (group 6X; p < 0.0001), whereas subsequent decontamination with water spray/ air drying/reapplication of the adhesive led to similar SBS before light curing (group 4X) compared to that after light curing (group 7X; p = 0.39). As indicated above, SBS of Xeno V+ and Scotchbond Universal differed markedly depending on the adhesive Vol 17, No 1, 2015
treatment. Regarding the control groups, Xeno V+ generated a significantly higher SBS than did Scotchbond Universal (p = 0.0007). However, Scotchbond Universal showed a significantly higher SBS than did Xeno V+, not only when saliva contamination occurred before light curing (groups 2X/2S; p < 0.0001), but also when it occurred after light curing (groups 5X/5S; p = 0.003). When the decontamination procedure with water spray/air drying was applied before light curing (groups 3X/3S), Scotchbond Universal resulted in a significantly higher SBS than did Xeno V+ (p < 0.0001), whereas after light curing (groups 6X/6S) Xeno V+ showed a significantly higher SBS than did Scotchbond Universal (p = 0.03). When the decontamination procedure with water spray/air drying/reapplication of the adhesive was applied before light curing (groups 4X/4S), Scotchbond Universal resulted in a SBS similar to that of Xeno V+ (p = 0.90), whereas after light curing (groups 7X/7S) Xeno V+ resulted in significantly higher SBS than that of Scotchbond Universal (p = 0.002). The distribution of failure modes after SBS testing is shown in Table 2 for primary molars and permanent molars. Xeno V+ showed marked differences in failure mode between the groups, reflecting the influence of the adhesive treatments. Specimens of the control group (group 1X) and of the groups in which decontamination 55
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with water spray/air drying/reapplication of the adhesive was applied (groups 4X/7X) mostly showed a combination of cohesive failure in dentin and mixed failure. All specimens of the contamination groups (groups 2X/5X) showed adhesive failure at the dentin/adhesive interface or cohesive failure within the adhesive layer. The specimens of the groups in which decontamination with water spray/air drying was applied (groups 3X/6X) all showed either adhesive failure at the dentin/adhesive interface (group 3X) or varying failure modes (group 6X; Table 2). For Scotchbond Universal, the predominant failure modes of all groups were cohesive failure in dentin and mixed failure (Table 2).
DISCUSSION During the restoration of a cavity with resin composite, good moisture control is not always feasible and contamination of the operation field with saliva is a constant risk, particularly when treating young children who may not cooperate well. Thus, it would be beneficial for clinicians to have simplified one-step self-etching adhesives at their disposal, which would generate successful adhesion to dentin even if salivary contamination occurs, or which would still provide successful adhesion after a simple decontamination procedure such as air drying or rinsing of saliva with water spray. In the present study, the effect of salivary contamination on the bond strength of two simplified one-step self-etching adhesives to dentin of primary and permanent teeth was investigated along with two decontamination procedures. First and foremost, the present study showed no significant differences in shear bond strength (SBS) between primary and permanent dentin, leading to failure to reject the fourth null hypothesis (ie, that there would be no difference in bond strength between primary and permanent dentin). This finding is in accordance with the results of previous studies,7,15 and it seems that the reported differences in structure and morphology between primary and permanent dentin are of limited importance for the bond strength when adhesives of the self-etching type are used. Self-etching adhesives are applied on dentin directly after the preparation of the cavity, that is, directly on the smear layer. Before the adhesive can reach and interact with the dentin surface underneath, it has to penetrate and modify this smear layer. During this process, the acidity of the self-etching adhesive is buffered via the mineral component of the smear layer, leaving less acidity available to etch the underlying dentin. This results in a more superficial interaction of self-etching adhesives with the dentin, which may explain the lack of influence of dentin type (primary or permanent), especially with mild (pH > 2) self-etching adhesives.12,19 Whereas saliva contamination significantly lowered the SBS of Xeno V+, it had no significant effect on the SBS of Scotchbond Universal. Consequently, the first null hypothesis – that saliva contamination would have no influence on bond strength – was rejected for Xeno V+ but not re56
jected for Scotchbond Universal. The difference in behavior towards saliva of Xeno V+ and Scotchbond Universal may be explained by differences in the chemical composition of the two adhesives. Scotchbond Universal contains several components which have the potential to positively affect resistance to moisture: 10-methacryloyloxydecyl dihydrogenphosphate (10-MDP) decreases susceptibility to hydrolysis and forms a strong ionic bond with calcium and therefore with the hydroxyapatite of dentin. An optimized amount of the hydrophilic monomer 2-hydroxyethyl methacrylate (HEMA) promotes adhesion through improved wetting and keeps other components in solution.18 Finally, Scotchbond Universal contains Vitrebond copolymer; other adhesive systems containing this copolymer (eg, Scotchbond Multi-Purpose or Adper Easy Bond) have previously been shown to be less sensitive towards the effects of varying moisture.4,14 For Xeno V+ only limited information about the composition is available (Table 1), making it difficult to discuss possible chemical reasons for the increased sensitivity towards saliva or moisture in general. It may be that a different content of water, the use of tertiary butanol as solvent instead of ethanol, and/ or the use of different (functionalized) acidic monomers render the Xeno V+ more sensitive to moisture. Regarding the decontamination procedures, the present study showed marked differences between the two adhesives used. For Xeno V+, the decontamination with water spray/air drying did not restore SBS to that of the control group, whereas the decontamination with water spray/air drying/reapplication of the adhesive did. For Scotchbond Universal, both decontamination procedures led to equal or even higher SBS compared to that of the control group. The second null hypothesis (ie, that the two decontamination procedures would have no influence on bond strength) was therefore rejected for Xeno V+ and for Scotchbond Universal. The distinct behavior of the two adhesives may again be explained by their different chemical composition, which caused varied sensitivity to rinsing with water spray. Previous studies which investigated the effect of comparable decontamination procedures following contamination with saliva at different steps of the adhesive treatment found that decontamination with water spray/air drying led to lower SBS compared to the control group.1,11,21 On the other hand, decontamination with water spray/air drying/reapplication did in some cases restore SBS.1,3,11,13,21 It can be summarized that the result of a decontamination procedure depended on the type of adhesive used, but that in the present study a decontamination procedure including water spray/air drying/reapplication seemed effective in restoring SBS. Xeno V+ was less sensitive towards contamination (with or without subsequent decontamination) when contamination took place after as opposed to before light curing. This implies that the sensitivity of Xeno V+ towards saliva contamination and rinsing with water spray may be reduced by light curing, resulting in a polymerized adhesive layer in which the previously water-soluble components are retained and are thus less prone to dilution and elution by water or saliva. The SBS of Scotchbond The Journal of Adhesive Dentistry
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Universal was not influenced by the stage at which contamination occurred (before or after light curing) and the third null hypothesis – that the bonding stage at which contamination occurs would have no influence on bond strength – was consequently rejected for Xeno V+ but not for Scotchbond Universal. As metioned previously, the SBS of Xeno V+ and Scotchbond Universal markedly varied depending on the adhesive treatment. Xeno V+ showed a significantly higher SBS than did Scotchbond Universal in the control group. After salivary contamination without or with a decontamination procedure, Xeno V+ showed a broad range of SBS values, and SBS was comparable to the control group only when the second decontamination procedure, including reapplication of the adhesive, had been performed. Scotchbond Universal showed more consistent behavior, with SBS values not significantly differing from that of the control group. Thus, the fifth null hypothesis (ie, that the two onestep self-etching adhesives would generate equal bond strengths) was rejected. Finally, regarding the distribution of failure modes, for Xeno V+, the predominant failure mode in the control group was cohesive failure in dentin for both primary and permanent teeth. This failure mode was also predominant in the two groups involving decontamination with water spray/ air drying/reapplication of the adhesive, reflecting the high SBS of these three groups. Within the other groups, the adhesive layer was the weakest link and most failure modes occurred within the adhesive layer or at the dentin/ adhesive interface. Generally, the distribution of failure modes in these groups related well to the SBS behavior of Xeno V+. For Scotchbond Universal, all groups showed predominantly cohesive failure in dentin or mixed failure regardless of the type of teeth, reflecting the very few significant differences in SBS of this adhesive. Indeed, cohesive failures in dentin imply that instead of assessing the adhesive interface, the strength of the dentin substrate is actually measured, which can be regarded as a limitation of the SBS testing method used in the present study.
REFERENCES
CONCLUSIONS
19.
Within the limitations of the present in vitro study, the following conclusions can be drawn: sensitivity to saliva contamination varied between the two adhesives, and decontamination with water spray, air drying and reapplication of the adhesive proved effective in restoring shear bond strength to primary and permanent dentin.
ACKNOWLEDGMENTS The authors would like to thank 3M ESPE and DENTSPLY DeTrey for providing the materials needed. We also thank L. Martig, Institute of Mathematical Statistics and Actuarial Science, University of Bern for the statistical analyses.
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20.
21.
Cobanoglu N, Unlu N, Ozer F, Blatz M. Bond strength of self-etch adhesives after saliva contamination at different application steps. Oper Dent 2013;38:505-511. Fakhri M, Seraj B, Shaarabi M, Motahhary P, Hooshmand T. Effect of salivary contamination on microleakage of resin composites placed with self-etch adhesive in primary teeth: an in vitro study. Pediatr Dent 2009;31:334-339. Fritz UB, Finger WJ, Stean H. Salivary contamination during bonding procedures with a one-bottle adhesive system. Quintessence Int 1998;29:567-572. Furuse AY, Cunha LF, Moresca R, Paganell G, Mondelli RF, Mondelli J. Enamel wetness effects on bond strength using different adhesive systems. Oper Dent 2011;36:274-280. Higgins JJ. Introduction to modern nonparametric statistics. Pacific Grove, California: Duxbury Press, 2003. Hitmi L, Attal JP, Degrange M. Influence of the time-point of salivary contamination on dentin shear bond strength of 3 dentin adhesive systems. J Adhes Dent 1999;1:219-232. Ilie N, Schöner C, Bücher K, Hickel R. An in-vitro assessment of the shear bond strength of bulk-fill resin composites to permanent and deciduous teeth. J Dent 2014;42:850-855. Johnson ME, Burgess OJ, Hermesch CB, Buikema DJ. Saliva contamination of dentin bonding agents. Oper Dent 1994;19:205-210. Kermanshan H, Ghabraei Sh, Bitaraf T. Effect of salivary contamination during different bonding stages on shear bond strength of one-step selfetch and total-etch adhesive. J Dent (Tehran) 2010;7:132-138. Ozer L, Ozalp N, Okte Z, Oztas D. Effects of saliva contamination on shear bond strength of compomer to dentin in primary teeth. Am J Dent 2006;19:28-30. Park JW, Lee KC. The influence of salivary contamination on shear bond strength of dentin adhesive systems. Oper Dent 2004;29:437-442. Pashley DH, Carvalho RM. Dentine permeability and dentine adhesion. J Dent 1997;25:355-372. Sattabanasuk V, Shimada Y, Tagami J. Effects of saliva contamination on dentin bond strength using all-in-one adhesives. J Adhes Dent 2006;8:311-318. Sheikh H, Heymann HO, Swift EJ, Ziemiecki TL, Ritter AL. Effect of saliva contamination and cleansing solutions on the bond strengths of self-etch adhesives to dentin. J Esthet Restor Dent 2010;22:402-410. Soares FZ, Rocha Rde O, Raggio DP, Sadek FT, Cardoso PE. Microtensile bond strength of different adhesive systems to primary and permanent dentin. Pediatr Dent 2005;27:457-462. Sumikawa DA, Marshall GW, Gee L, Marshall SJ. Microstructure of primary tooth dentin. Pediatr Dent 1999;21:439-444. Taskonak B, Sertgöz A. Shear bond strengths of saliva contaminated ’one-bottle’ adhesives. J Oral Rehabil 2002;29:559-564. 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. Biomaterials 2007;28:3757-3783. Van Meerbeek B, Yoshihara K, Yoshida Y, Mine A, De Munck J, Van Landuyt KL. State of the art of self-etch adhesives. Dent Mater 2011;27:17-28. Xie J, Powers JM, McGuckin RS. In vitro bond strength of two adhesives to enamel and dentin under normal and contaminated conditions. Dent Mater 1993;9:295-299. Yoo HM, Oh TS, Pereira PN. Effect of saliva contamination on the microshear bond strength of one-step self-etching adhesive systems to dentin. Oper Dent 2006;31:127-134.
Clinical relevance: Based on the in vitro results obtained in the present study, it is recommended to decontaminate saliva-contaminated dentin by rinsing with water spray, air drying and reapplying the adhesive.
57
I
n order to generate a durable restoration using resin composites, successful adhesion without any contamination is required. Good moisture control keeps oral fluids, such as saliva, off the operation field. In clinical routine, however, ideal conditions are not always feasible, especially when rubber-dam isolation is not achievable.
a
Graduate Dentist, Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Switzerland. Idea, experimental work, wrote manuscript.
b
Senior Researcher, Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Switzerland. Idea, co-wrote manuscript.
c
Professor and Head, Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Switzerland. Proofread manuscript.
d
Research Associate, Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Switzerland. Idea, experimental design, supervision of the graduate dentist, co-wrote manuscript.
Correspondence: Simon Flury, Department of Preventive, Restorative and Pediatric Dentistry, School of Dental Medicine, University of Bern, Freiburgstrasse 7, CH-3010 Bern, Switzerland. Tel: +41-31-632-2581, Fax: +41-31632-9875. e-mail: [email protected]
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Submitted for publication: 19.08.14; accepted for publication: 18.01.15
Several studies have investigated the effect of saliva contamination on the bond strength to dentin of permanent teeth, but they did not reach consensus: While numerous authors detected a significant decrease in bond strength after salivary contamination,3,20,21 others did not.8,14,17 According to the studies by Johnson et al8 and Taskonak and Sertgöz,17 the bonding stage at which contamination occurs has no influence on bond strength. Other authors have reported significant differences depending on when the contamination occurred.3,6,9,11,21 Furthermore, various decontamination procedures have been recommended, going from blot drying11 to resurfacing of the cavity.3 While the effect of salivary contamination during the bonding procedure in permanent teeth has been studied relatively well, only a few studies have dealt with this problem in primary teeth,2,10 although this seems highly relevant. First, the risk of salivary contamination is increased in young children due to limited cooperation. Second, the effect of salivary contamination on bond strength may vary between the dentin of primary and permanent teeth, since the structure and morphology of the two have been 51
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shown to differ.16 Considering these differences, effects of salivary contamination on bond strength to permanent dentin may not automatically apply to primary dentin. The aim of the present in vitro study was to generate further knowledge about the effect of salivary contamination at different stages of the bonding procedure on bond strength of two one-step self-etching adhesives to primary and permanent dentin. Moreover, two decontamination procedures were investigated in an effort to restore any reduced bond strength. The null hypotheses to be tested were that (1) saliva contamination, (2) the two decontamination procedures, and (3) the bonding stage at which contamination occurs would have no influence on bond strength, (4) there would be no difference in bond strength between primary and permanent dentin, and (5) the two one-step self-etching adhesives would generate equal bond strengths.
MATERIALS AND METHODS Saliva Collection In order to achieve clinically relevant but at the same time standardized salivary contamination, unstimulated human saliva was collected from a single individual (K.S.) at least one hour after any consumption of food or drink. The collection of saliva took place on four subsequent days. Directly after collection, the saliva was centrifuged (Megafuge 1.0R, Heraeus Holding; Hanau, Germany) and stored at –80°C. On each day prior to preparation of shear bond strength (SBS) specimens, an equal amount of saliva from each of the four subsequent collecting days was thawed, pooled, and used at room temperature. Preparation of Dentin Specimens A final number of 210 extracted human primary molars and 210 extracted human permanent molars were used in this study (n = 15 primary and n = 15 permanent molars per group; 2 one-step self-etching adhesives; 7 groups [1 control group, 2 bonding stages at which contamination occurred: a) without or b) with 2 subsequent decontamination procedures]). Before extraction, patients and/or parents were informed about the use of the teeth for research purposes and verbal consent had been obtained. The molars were cleaned under tap water with a scaler and stored in 2% chloramine solution in the refrigerator (4°C) until needed. For preparation of dentin specimens, the molars were apically shortened with a water-cooled diamond saw (Isomet low-speed saw, Buehler; Lake Buff, IL, USA) and ground from the occlusal surface down to mid-coronal dentin. Grinding was performed with 220-grit followed by 500-grit silicon carbide (SiC) abrasive papers on a Struers LaboPol-21 grinding machine (Struers; Ballerup, Denmark). After grinding, to facilitate handling and allow fixation in the universal testing machine, the molars were embedded in self-curing acrylic resin (Paladur, Heraeus Kulzer; Hanau, Germany) in cylindrical stainless steel molds. After removal of the steel molds, the dentin speci52
mens were stored in a humid chamber in the refrigerator (100% humidity; 4°C) until needed. Preparation of SBS Specimens One hour before adhesive treatment, the dentin specimens were taken out of the refrigerator and kept in tap water at room temperature. Before preparation of each SBS specimen, the dentin surface was wet ground for 5 s with 500-grit SiC abrasive papers (Struers) to obtain a standardized smear layer, changing the 500-grit SiC abrasive paper each time after grinding 10 specimens. Subsequently, the specimen was air dried and the bonding area defined and isolated by use of perforated self-adhesive tape (diameter of the perforation approximately 2 mm). The bonding area was then treated with one of the two adhesives as listed in Table 1. For the control groups (groups 1X/1S; Fig 1), the adhesives were applied according to the manufacturers’ instructions (Table 1). For the groups including contamination before light curing (groups 2X/2S to 4X/4S; Fig 1), the adhesives were applied as described for groups 1X/1S, with the exception that a drop of saliva (6 μl) was applied with a pipette (Eppendorf Research; Hamburg, Germany) and left undisturbed for 5 s. For the contamination groups (groups 2X/2S), saliva was solely air dried and the adhesive then light cured. For decontamination (groups 3X/3S and 4X/4S), saliva was rinsed with water spray for 2 s followed by gentle air drying and light curing of the adhesive (groups 3X/3S), or saliva was rinsed with water spray for 2 s, followed by gentle air drying, reapplication and light curing of the adhesive (groups 4X/4S; Table 1). For the groups including contamination after light curing (groups 5X/5S to 7X/7S; Fig 1), the adhesives were applied as described for groups 1X/1S. After light curing, a drop of saliva was applied as described above. As regards contamination in groups 5X/5S, saliva was solely air dried. For decontamination (groups 6X/6S and 7X/7S), saliva in groups 6X/6S was rinsed with water spray for 2 s followed by gentle air drying. For groups 7X/7S, saliva was rinsed with water spray for 2 s followed by gentle air drying, reapplication and light curing of the adhesive (Table 1). All groups were prepared for both primary and permanent molars. After the adhesive treatment, a split Teflon mold (inner diameter 1.5 mm ≈ bonding area 1.8 mm2; height: 2 mm) was clamped to the dentin surface, filled with resin composite (Filtek Z250, 3M ESPE; St Paul, MN, USA; shade A2, lot No.: N505287), and covered with a Mylar strip (Hawe Stopstrip Straight, KerrHawe; Bioggio, Switzerland). The resin composite was light cured for 20 s and the SBS specimen was placed in a black photoresistant box in order to avoid any additional effect of ambient light on the polymerization process. Five minutes after completion of light curing, the specimen was freed from the Teflon mold at room temperature. Light curing was always performed with the LED curing unit bluephase polywave G2 (Ivoclar Vivadent; Schaan, Lichtenstein). All specimens were then stored in black photoresistant boxes in an incubator (Memmert UM 500, Memmert & Co; Schwabach, Germany) at 37°C and 100% humidity for 24 h. The Journal of Adhesive Dentistry
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Table 1
Adhesives used
Adhesive
Composition (manufacturers’ information)
Treatment steps
Time
Xeno V+ (DENTSPLY DeTrey; Konstanz, Germany) Lot No.: 1306004071
Bifunctional acrylate; acidic acrylate; ethyl 2-[5-dihydrogen phosphoryl-5,2-dioxapentyl]acrylate; initiator; stabilizer; tertiary butanol; water
Apply and agitate
20 s
Air dry thoroughly
>5s
Light cure
10 s
Scotchbond Universal (3M ESPE; Neuss, Germany) Lot No.: 530720
Bisphenol A diglycidyl ether dimethacrylate (bis-GMA); hydroxyethylmethacrylate (HEMA); 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP); 2-propenoic acid-, 2-methyl-, reaction products with 1,10-decanediol and phosphorous oxide; copolymers; silane treated silica; initiators; stabilizer; ethanol; water
Apply and agitate
20 s
Air dry
(~ 5 s)
Light cure
10 s
Xeno V+ (X) or Scotchbond Universal (S) Application of adhesive, air dry Saliva contamination
Air dry
Water spray, air dry
Water spray, air dry
Reapply adhesive
Light curing Saliva contamination
Air dry
Water spray, air dry
Water spray, air dry
Reapply adhesive, light cure
Resin composite, light curing Group 1X/1S Fig 1
Group 2X/2S
Group 3X/3S
Group 4X/4S
Group 5X/5S
Group 6X/6S
Group 7X/7S
Flowchart of the adhesive treatments resulting in groups 1X/1S to 7X/7S.
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Shaer bond strength values (MPa)
Shaer bond strength values (MPa)
Santschi et al
30 25 20 15 10 5 0 1X
1S
2X
2S 3X
3S
4X
4S 5X
5S 6X
6S
7X
7S
Groups
30 25 20 15 10 5 0 1X
1S
2X
2S 3X
3S
4X
4S 5X
5S 6X
6S
7X
7S
Groups
Fig 2 Shear bond strength (MPa; medians, lower and upper quartiles as well as minima and maxima) of primary molars (n = 15) for groups 1X/1S to 7X/7S (X = Xeno V+, S = Scotchbond Universal). For definition of groups, see Fig 1.
Fig 3 Shear bond strength (MPa; medians, lower and upper quartiles as well as minima and maxima) of permanent molars (n = 15) for groups 1X/1S to 7X/7S (X = Xeno V+, S = Scotchbond Universal). For definition of groups, see Fig 1.
SBS Testing and Failure Mode Determination After storage, specimens were subjected to SBS testing by use of a wire (stainless steel, diameter 0.6 mm) in a universal testing machine (Zwick Z010, Zwick; Ulm, Germany) at a crosshead speed of 1 mm/min. The maximum force (Fmax [N]) was recorded (testXpert software V9.0, Zwick) and the SBS values (MPa) were calculated (Fmax [N])/bonding area [mm2]), resulting in 15 SBS values per group for statistical analyses. After SBS testing, the failure mode of each specimen was determined under a stereomicroscope (Leica ZOOM 2000, Leica; Buffalo, NY, USA) at 40X magnification and classified as 1) cohesive failure in dentin, 2) adhesive failure at the dentin/adhesive interface, 3) cohesive failure within adhesive layer, 4) adhesive failure at the adhesive/resin composite interface, 5) cohesive failure in resin composite, or 6) mixed failure (combinations of failure modes 1 to 5).
molars are shown in Fig 2 and for permanent molars in Fig 3. The nonparametric ART ANOVA showed a significant effect on SBS of the factor adhesive (ie, Xeno V+ or Scotchbond Universal) and a significant effect of the factor adhesive treatment (ie, groups 1X/1S to 7X/7S) (both at p < 0.0001), but no significant effect of the factor tooth type (ie, primary molars or permanent molars; p = 1.00). Thus, SBS of primary and permanent molars were pooled. Finally, there was a significant interaction between the factors adhesive and adhesive treatment (p < 0.0001). The post-hoc analysis showed that for Xeno V+, saliva contamination (groups 2X and 5X) significantly lowered SBS (both p < 0.0001) compared to the control group (group 1X). For Scotchbond Universal, saliva contamination (groups 2S and 5S) had no significant influence on SBS (p = 0.51 to 0.87) compared to the SBS of the control group (group 1S). Regarding the two decontamination procedures (water spray/air drying in groups 3X/3S and 6X/6S; water spray/ air drying/reapplication of the adhesive in groups 4X/4S and 7X/7S), the post-hoc analysis showed that for Xeno V+, decontamination with water spray/air drying still resulted in a significantly lower SBS compared to the SBS of the control group, regardless of the bonding stage at which contamination occurred, ie, before light curing of the adhesive (group 3X; p < 0.0001) or after (group 6X; p = 0.049). However, decontamination with water spray/ air drying/reapplication of the adhesive restored SBS with no significant differences in SBS compared to that of the control group, regardless of the bonding stage at which contamination had occurred (group 4X: p = 0.19; group 7X: p = 0.54). For Scotchbond Universal, decontamination with water spray/air drying led to a similar SBS compared to that of the control group, regardless of the bonding stage at which contamination occurred (group 3S: p = 0.26; group 6S: p = 0.85). Decontamination with water spray/air drying/reapplication of the adhesive before light curing of the adhesive (group 4S) led to significantly higher SBS com-
Statistical Analyses Failure modes after SBS testing were analyzed descriptively, whereas SBS values were analyzed with nonparametric ANOVA (aligned rank transformation [ART] ANOVA)5 and the p-values were corrected with Bonferroni-Holm adjustment for multiple testing. For post-hoc analysis, exact Wilcoxon rank sum tests were performed with no correction for multiple testing. Thus, significant differences must be interpreted in an explorative context. All calculations were performed with R version 3.0.2 (The R Foundation for Statistical Computing; Vienna, Austria). Data of preliminary tests were statistically analyzed with NCSS/PASS 2005 (NCSS; Kaysville, UT, USA) for sample size determination, with the level of significance set at _ = 0.05.
RESULTS Shear bond strength (SBS; medians, lower and upper quartiles as well as minima and maxima) for primary 54
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Table 2 Distribution of failure modes after shear bond strength testing for primary molars (n = 15/group) / permanent molars (n = 15/group) Groups
1) Cohesive failure in dentin (%)
2) Adhesive failure at dentin/ adhesive interface (%)
3) Cohesive failure within adhesive layer (%)
4) Adhesive failure at adhesive/resin composite interface (%)
5) Cohesive failure in resin composite (%)
6) Mixed failure (%)
Group 1X
87 / 53
0 / 20
0/0
0/0
0/0
13 / 27
Group 2X
0/0
100 / 100
0/0
0/0
0/0
0/0
Group 3X
0/0
100 / 100
0/0
0/0
0/0
0/0
Group 4X
73 / 87
7/0
13 / 13
0/0
0/0
7/0
Group 5X
0/0
7/0
93 / 100
0/0
0/0
0/0
Group 6X
27 / 20
0/7
13 / 33
0/0
0/0
60 / 40
Group 7X
80 / 60
0/0
0/7
0/0
0/0
20 / 33
Xeno V+
Scotchbond Universal Group 1S
60 / 53
0 / 20
0/0
0/0
0/0
40 / 27
Group 2S
47 / 73.3
6 / 13.3
0/0
0/0
0/0
47 / 13.3
Group 3S
47 / 33
13 / 20
0/0
0/0
0/0
40 / 47
Group 4S
67 / 80
0/0
0/0
6/0
0/0
27 / 20
Group 5S
47 / 87
6/0
0/0
0/0
0/0
47 / 13
Group 6S
40 / 53.3
13 / 13.3
0/0
0/0
0/0
47 / 33.3
Group 7S
80 / 73
0/0
0/0
0/0
0/0
20 / 27
pared to that of the control group (p = 0.01), whereas after light curing of the adhesive (group 7S), SBS was similar to that of the control group (p = 0.47). The bonding stage at which contamination occurred highly influenced SBS of Xeno V+ (ART ANOVA p < 0.0001) but did not influence SBS of Scotchbond Universal (ART ANOVA p = 0.795). Generally, Xeno V+ showed less reduction in SBS when contamination (without or with subsequent decontamination procedures) took place after light curing the adhesive (groups 5X to 7X) compared to before light curing (groups 2X to 4X). However, the influence on SBS of the bonding stage at which contamination occurred varied depending on the adhesive treatment applied. Saliva contamination before light curing of Xeno V+ (group 2X) led to a significantly lower SBS than did saliva contamination after light curing (group 5X; p < 0.0001). Subsequent decontamination with water spray/air drying led to significantly lower SBS before light curing of Xeno V+ (group 3X) than after light curing (group 6X; p < 0.0001), whereas subsequent decontamination with water spray/ air drying/reapplication of the adhesive led to similar SBS before light curing (group 4X) compared to that after light curing (group 7X; p = 0.39). As indicated above, SBS of Xeno V+ and Scotchbond Universal differed markedly depending on the adhesive Vol 17, No 1, 2015
treatment. Regarding the control groups, Xeno V+ generated a significantly higher SBS than did Scotchbond Universal (p = 0.0007). However, Scotchbond Universal showed a significantly higher SBS than did Xeno V+, not only when saliva contamination occurred before light curing (groups 2X/2S; p < 0.0001), but also when it occurred after light curing (groups 5X/5S; p = 0.003). When the decontamination procedure with water spray/air drying was applied before light curing (groups 3X/3S), Scotchbond Universal resulted in a significantly higher SBS than did Xeno V+ (p < 0.0001), whereas after light curing (groups 6X/6S) Xeno V+ showed a significantly higher SBS than did Scotchbond Universal (p = 0.03). When the decontamination procedure with water spray/air drying/reapplication of the adhesive was applied before light curing (groups 4X/4S), Scotchbond Universal resulted in a SBS similar to that of Xeno V+ (p = 0.90), whereas after light curing (groups 7X/7S) Xeno V+ resulted in significantly higher SBS than that of Scotchbond Universal (p = 0.002). The distribution of failure modes after SBS testing is shown in Table 2 for primary molars and permanent molars. Xeno V+ showed marked differences in failure mode between the groups, reflecting the influence of the adhesive treatments. Specimens of the control group (group 1X) and of the groups in which decontamination 55
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with water spray/air drying/reapplication of the adhesive was applied (groups 4X/7X) mostly showed a combination of cohesive failure in dentin and mixed failure. All specimens of the contamination groups (groups 2X/5X) showed adhesive failure at the dentin/adhesive interface or cohesive failure within the adhesive layer. The specimens of the groups in which decontamination with water spray/air drying was applied (groups 3X/6X) all showed either adhesive failure at the dentin/adhesive interface (group 3X) or varying failure modes (group 6X; Table 2). For Scotchbond Universal, the predominant failure modes of all groups were cohesive failure in dentin and mixed failure (Table 2).
DISCUSSION During the restoration of a cavity with resin composite, good moisture control is not always feasible and contamination of the operation field with saliva is a constant risk, particularly when treating young children who may not cooperate well. Thus, it would be beneficial for clinicians to have simplified one-step self-etching adhesives at their disposal, which would generate successful adhesion to dentin even if salivary contamination occurs, or which would still provide successful adhesion after a simple decontamination procedure such as air drying or rinsing of saliva with water spray. In the present study, the effect of salivary contamination on the bond strength of two simplified one-step self-etching adhesives to dentin of primary and permanent teeth was investigated along with two decontamination procedures. First and foremost, the present study showed no significant differences in shear bond strength (SBS) between primary and permanent dentin, leading to failure to reject the fourth null hypothesis (ie, that there would be no difference in bond strength between primary and permanent dentin). This finding is in accordance with the results of previous studies,7,15 and it seems that the reported differences in structure and morphology between primary and permanent dentin are of limited importance for the bond strength when adhesives of the self-etching type are used. Self-etching adhesives are applied on dentin directly after the preparation of the cavity, that is, directly on the smear layer. Before the adhesive can reach and interact with the dentin surface underneath, it has to penetrate and modify this smear layer. During this process, the acidity of the self-etching adhesive is buffered via the mineral component of the smear layer, leaving less acidity available to etch the underlying dentin. This results in a more superficial interaction of self-etching adhesives with the dentin, which may explain the lack of influence of dentin type (primary or permanent), especially with mild (pH > 2) self-etching adhesives.12,19 Whereas saliva contamination significantly lowered the SBS of Xeno V+, it had no significant effect on the SBS of Scotchbond Universal. Consequently, the first null hypothesis – that saliva contamination would have no influence on bond strength – was rejected for Xeno V+ but not re56
jected for Scotchbond Universal. The difference in behavior towards saliva of Xeno V+ and Scotchbond Universal may be explained by differences in the chemical composition of the two adhesives. Scotchbond Universal contains several components which have the potential to positively affect resistance to moisture: 10-methacryloyloxydecyl dihydrogenphosphate (10-MDP) decreases susceptibility to hydrolysis and forms a strong ionic bond with calcium and therefore with the hydroxyapatite of dentin. An optimized amount of the hydrophilic monomer 2-hydroxyethyl methacrylate (HEMA) promotes adhesion through improved wetting and keeps other components in solution.18 Finally, Scotchbond Universal contains Vitrebond copolymer; other adhesive systems containing this copolymer (eg, Scotchbond Multi-Purpose or Adper Easy Bond) have previously been shown to be less sensitive towards the effects of varying moisture.4,14 For Xeno V+ only limited information about the composition is available (Table 1), making it difficult to discuss possible chemical reasons for the increased sensitivity towards saliva or moisture in general. It may be that a different content of water, the use of tertiary butanol as solvent instead of ethanol, and/ or the use of different (functionalized) acidic monomers render the Xeno V+ more sensitive to moisture. Regarding the decontamination procedures, the present study showed marked differences between the two adhesives used. For Xeno V+, the decontamination with water spray/air drying did not restore SBS to that of the control group, whereas the decontamination with water spray/air drying/reapplication of the adhesive did. For Scotchbond Universal, both decontamination procedures led to equal or even higher SBS compared to that of the control group. The second null hypothesis (ie, that the two decontamination procedures would have no influence on bond strength) was therefore rejected for Xeno V+ and for Scotchbond Universal. The distinct behavior of the two adhesives may again be explained by their different chemical composition, which caused varied sensitivity to rinsing with water spray. Previous studies which investigated the effect of comparable decontamination procedures following contamination with saliva at different steps of the adhesive treatment found that decontamination with water spray/air drying led to lower SBS compared to the control group.1,11,21 On the other hand, decontamination with water spray/air drying/reapplication did in some cases restore SBS.1,3,11,13,21 It can be summarized that the result of a decontamination procedure depended on the type of adhesive used, but that in the present study a decontamination procedure including water spray/air drying/reapplication seemed effective in restoring SBS. Xeno V+ was less sensitive towards contamination (with or without subsequent decontamination) when contamination took place after as opposed to before light curing. This implies that the sensitivity of Xeno V+ towards saliva contamination and rinsing with water spray may be reduced by light curing, resulting in a polymerized adhesive layer in which the previously water-soluble components are retained and are thus less prone to dilution and elution by water or saliva. The SBS of Scotchbond The Journal of Adhesive Dentistry
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Universal was not influenced by the stage at which contamination occurred (before or after light curing) and the third null hypothesis – that the bonding stage at which contamination occurs would have no influence on bond strength – was consequently rejected for Xeno V+ but not for Scotchbond Universal. As metioned previously, the SBS of Xeno V+ and Scotchbond Universal markedly varied depending on the adhesive treatment. Xeno V+ showed a significantly higher SBS than did Scotchbond Universal in the control group. After salivary contamination without or with a decontamination procedure, Xeno V+ showed a broad range of SBS values, and SBS was comparable to the control group only when the second decontamination procedure, including reapplication of the adhesive, had been performed. Scotchbond Universal showed more consistent behavior, with SBS values not significantly differing from that of the control group. Thus, the fifth null hypothesis (ie, that the two onestep self-etching adhesives would generate equal bond strengths) was rejected. Finally, regarding the distribution of failure modes, for Xeno V+, the predominant failure mode in the control group was cohesive failure in dentin for both primary and permanent teeth. This failure mode was also predominant in the two groups involving decontamination with water spray/ air drying/reapplication of the adhesive, reflecting the high SBS of these three groups. Within the other groups, the adhesive layer was the weakest link and most failure modes occurred within the adhesive layer or at the dentin/ adhesive interface. Generally, the distribution of failure modes in these groups related well to the SBS behavior of Xeno V+. For Scotchbond Universal, all groups showed predominantly cohesive failure in dentin or mixed failure regardless of the type of teeth, reflecting the very few significant differences in SBS of this adhesive. Indeed, cohesive failures in dentin imply that instead of assessing the adhesive interface, the strength of the dentin substrate is actually measured, which can be regarded as a limitation of the SBS testing method used in the present study.
REFERENCES
CONCLUSIONS
19.
Within the limitations of the present in vitro study, the following conclusions can be drawn: sensitivity to saliva contamination varied between the two adhesives, and decontamination with water spray, air drying and reapplication of the adhesive proved effective in restoring shear bond strength to primary and permanent dentin.
ACKNOWLEDGMENTS The authors would like to thank 3M ESPE and DENTSPLY DeTrey for providing the materials needed. We also thank L. Martig, Institute of Mathematical Statistics and Actuarial Science, University of Bern for the statistical analyses.
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20.
21.
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Clinical relevance: Based on the in vitro results obtained in the present study, it is recommended to decontaminate saliva-contaminated dentin by rinsing with water spray, air drying and reapplying the adhesive.
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