This study evaluated the effect of using a warm versus cold air stream for solvent evaporation on the properties of two etch-and-rinse adhesive systems. Microtensile bond strength and nanoleakage patterns were compared between the two drying methods. Degree of conversion and solvent evaporation rates were also analyzed. The results showed that using a warm air stream improved bond strength and reduced nanoleakage, without affecting degree of conversion. This suggests that a warm air dry may help form a stronger polymer network within the hybrid layer.

1. JJOD 1249 1–8
journal of dentistry xxx (2008) xxx–xxx
available at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/jden
1
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2
3 Evaporating solvents with a warm air-stream: Effects on
adhesive layer properties and resin–dentin bond strengths
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5 Celso Afonso Klein Jr.a, Christiana Zander-Grande b, Roberto Amaral b,
6 Rodrigo Stanislawczuk b, Eugenio Jose Garcia b, Ricardo Baumhardt-Neto c,
ˆ ´
Marcia Margarete Meier , Alessandro Dourado Loguercio e,f, Alessandra Reis e,f,*
´ d
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7
a
8 School of Dentistry, Department of Dentistry, University Luterana do Brasil, Cachoeira do Sul, Rio Grande do Sul, Brazil
b
9 ´
School of Dentistry, Department of Restorative Dentistry, University Estadual de Ponta Grossa, Ponta Grossa, Parana, Brazil
c
10 School of Chemistry, Department of Chemistry and Materials Science, University Federal do Rio Grande do Sul,
11 Porto Alegre, Rio Grande do Sul, Brazil
d
12 FGM Dental Products, Department of Research and Development, Joinville, Santa Catarina, Brazil
13
14
e
Brazil
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School of Dentistry, Department of Dental Materials and Operative Dentistry, University of Oeste de Santa Catarina, Joacaba, Santa Catarina,
¸
f
15 ´
University Estadual de Ponta Grossa, Ponta Grossa, Parana, Brazil
article info summary
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Article history: Objectives: This study evaluated the effect of a warm or cold air-dry stream for solvent
Received 27 November 2007 evaporation on the microtensile resin–dentin bond strength (mTBS), nanoleakage pattern
Received in revised form (SEM), degree of conversion (DC) and solvent evaporation rates of an ethanol/water- (Adper
6 April 2008 Single Bond, [SB] 3MESPE) and an acetone-based (Prime & Bond 2.1, [PB] Dentsply), two-step
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Accepted 20 April 2008 etch-and-rinse adhesive system.
Materials and methods: Adhesives were applied on demineralized dentin surfaces. For SE, a
warm or cold air-dry stream (10 s) was applied prior to light-activation (10 s). Bonded sticks
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Keywords: (0.8 mm2) were tested in tension (0.5 mm/min). Two bonded sticks from each tooth were
Adhesive systems immersed in a 50% (w/v) solution of silver nitrate (24 h), photodeveloped (8 h) and analyzed
Bond strength by SEM. The DC and solvent evaporation rate of the adhesives were evaluated under FTIR
Solvent and analytical balance, respectively. Data were analyzed by two-way ANOVA and Tukey test
Evaporation (a = 0.05).
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Degree of conversion Results: Higher mTBS and lower nanoleakage were observed when the SE step was per-
Dentin formed with warm air-dry stream. However, the DC of the adhesives was not altered by the
use of a warm air-dry.
Conclusions: The use of a warm air-dry stream seems to be a clinical tool to improve the bond
strength and the quality of the hybrid layer (less nanoleakage infiltration), since it might
reduce the number of pores within the adhesive layer.
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18
16 # 2008 Elsevier Ltd. All rights reserved.
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19
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* Corresponding author at: Universidade do Oeste de Santa Catarina, Curso de Odontologia, Rua Getulio Vargas, 2125 Bairro Flor da Serra,
´
CEP 89600-000, Joacaba, SC, Brazil. Tel.: +55 49 3554 4452; fax: +55 49 3551 2004.
¸
E-mail address: reis_ale@hotmail.com (A. Reis).
0300-5712/$ – see front matter # 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jdent.2008.04.014
Please cite this article in press as: Klein Jr CA, et al., Evaporating solvents with a warm air-stream: Effects on adhesive layer properties
and resin–dentin bond strengths, Journal of Dentistry (2008), doi:10.1016/j.jdent.2008.04.014

2. JJOD 1249 1–8
2 journal of dentistry xxx (2008) xxx–xxx
21
1. Introduction Bond, [SB] 3M ESPE) and an acetone-based (Prime & Bond 2.1, 65
[PB] Dentsply) two-step etch-and-rinse adhesive systems. The 66
22 Etch-and-rinse adhesives require a separate step of etching, degree of conversion and solvent evaporation rates of the 67
23 which is usually performed with 30–40% phosphoric acid. In adhesives after solvent evaporation with both protocols was 68
24 their original configuration they were released to be applied in also investigated. 69
25 a three-step procedure, in which after etching, the surfaces
26 were primed and then bonded with a flow, non-solvated 70
27 bonding resin.1 2. Materials and methods
28 In an attempt to reduce clinical steps and save time
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29 manufacturers produced simplified etch-and-rinse adhesives 2.1. Microtensile testing
30 by joining the components of the primer and the bonding resin
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31 into a single solution. If on one hand, this modification allowed Twenty extracted, caries-free human third molars were used. 72
32 the accomplishment of the bonding protocol in two steps,1 on The teeth were collected after obtaining the patient’s informed 73
33 the other hand, the hydrophilic features of these simplified consent under a protocol approved by the University of Oeste 74
34 adhesives were increased as the primer/bond solution should of Santa Catarina Institutional Review Board. The teeth were 75
35 be compatible to the intrinsically moist, acid-etched dentin. disinfected in 0.5% chloramine, stored in distilled water and 76
36 Consequently, the adhesive solutions became more perme- used within 6 months after extraction. A flat dentin surface 77
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37 able to water from the oral environment and from the was exposed after wet grinding the occlusal enamel on a # 180 78
38 underlying bonded dentin,2–4 leading to incompatibility grit SiC paper. The exposed dentin surfaces were further 79
39 issues5–7 and faster degradation of resin–dentin bonds polished on wet #600-grit silicon-carbide paper for 60 s to 80
40 comparatively to their three-step version.8–10 standardize the smear layer. 81
41 This is somewhat true, that a recent systematic review of Two solvent-based, etch-and-rinse adhesive systems were 82
42 current clinical trials has reported that in general, the two-step tested: Adper Single Bond (SB-3M ESPE, St. Paul, MN, USA), an 83
43
44
etch-and-rinse adhesives perform clinically less favorable
than the conventional three-step etch-and-rinse adhesives.11
ED ethanol/water-based and Prime & Bond 2.1 (PB–Dentsply De
Trey, Konstanz, Germany) an acetone-based system. The
84
85
45 While 79% of the two-step etch-and-rinse adhesives fulfilled composition, application mode and batch number are 86
46 the provisional acceptance ADA guidelines, only 51% fulfilled described in Table 1. 87
47 the full acceptance ADA guidelines.11 After acid etching with the respective etchants of each 88
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48 Resin–dentin bond strength and their durability seem to adhesive system, the surfaces were rinsed with distilled water 89
49 rely on the quality of the hybrid layer,12 i.e. on the proper for 15 s and air-dried for 15 s. The surfaces were, then, 90
50 impregnation of the dentin substrate and on the formation of a rewetted with water.20 Two coats of adhesive were slightly 91
51 high cross-linking polymer inside the collagen mesh. As a applied for 10 s. After each coat, the solvent evaporation was 92
52 result, different clinical approaches have been proposed to performed either with a warm (60 Æ 2 8C) or cold air (20 Æ 1 8C) 93
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53 achieve this goal, such as increased application times of for 10 s at a distance of 20 cm. In both cases, the air stream was 94
54 bonding agents,13 multiple adhesive coating,13 delayed poly- generated by a commercially hair-dresser (SC831, Black & 95
55 merization,15,16 adhesive rubbing17,18 and longer exposure Decker, Uberaba, MG, Brazil). The speed of the air was 5.50 m/s 96
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56 times of bonding systems.19 and the air flow 0.0138 m3/s. The air emitted by the hair- 97
57 Most of these approaches favors solvent evaporation and dresser in the cold condition was the same of the room 98
58 contributes to the formation of a strong polymer. The use of a temperature. 99
59 warm air-stream for solvent evaporation could theoretically The adhesives were light-cured for the respective recom- 100
60 improve solvent evaporation, but this approach has not been mended time using a quartz-tungsten halogen light set at 101
600 mW/cm2 (VIP, Bisco, Schaumburg, IL, USA) (Table 1). Resin
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61 addressed yet. Therefore, the aim of this study was to compare 102
62 the effects of the air stream temperature for solvent evapora- composite build-ups (Filtek Z250, shade A2, 3M ESPE, St. Paul, 103
63 tion on the microtensile resin–dentin bond strength (mTBS) MN, USA) were constructed on the bonded surfaces in 3 104
64 and nanoleakage pattern of an ethanol/water- (Adper Single increments of 1 mm each that were individually light-cured 105
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Table 1 – Adhesive systems: composition, application mode and batch number
Adhesive systems Composition Application mode Batch number
Single Bond (3M ESPE) 1. Scotchbond etchant–35% phosphoric acid
2. Adhesive–Bis-GMA, HEMA, dimethacrylates, a, b, c, d, e, f, e, f, g 5FE
polyalkenoic acid copolymer, initiators, water and ethanol
Prime Bond 2.1 (Dentsply) 1. 32% phosphoric acid
2. Adhesive–UDMA, PENTA, Bis-GMA, butylated hydroxytoluene, a, b, c, d, e, f, e, f, g 707608
4-ethyl dimethyl aminobenzoate, cetylamine hydrofluoride,
initiator and acetone
(a) Acid-etching (15 s); (b) rinsing (15 s); (c) air-drying (30 s); (d) dentin rewetted with water; (e) one coat of adhesive; (f) air-dry for 10 s at 20 cm
for solvent evaporation; (g) light-curing (10 s–600 mW/cm2). BPDM: biphenyl dimethacrylate or 4,40-dimethacryloyloxyethyloxycarbonylbi-
phenyl-3,30-dicarboxylic acid; HEMA: 2-hydroxyethyl methacrylate; Bis-GMA: bisphenol A diglycidyl methacrylate; UDMA: urethane
dimethacrylate; PENTA: dipentaerythritol pentaacrylate monophosphate.
Please cite this article in press as: Klein Jr CA, et al., Evaporating solvents with a warm air-stream: Effects on adhesive layer properties
and resin–dentin bond strengths, Journal of Dentistry (2008), doi:10.1016/j.jdent.2008.04.014

3. JJOD 1249 1–8
journal of dentistry xxx (2008) xxx–xxx 3
106 for 30 s with the same light intensity. All the bonding intensities of aliphatic C C (peak height at 1640 cmÀ1) against 164
107 procedures were carried out by a single operator at a room internal standard before and after curing of the specimen. The 165
108 temperature of 20 8C and constant relative humidity. Five aromatic carbon–carbon bond (peak height at 1610 cmÀ1) 166
109 teeth were used for each combination of adhesive system and absorbance was used as an internal standard. The degree of 167
110 air temperature. conversion (DC) was determined by subtracting the % C C 168
111 After storage of the restored teeth in distilled water at 37 8C from 100%. Three specimens were tested for each group. 169
112 for 24 h, they were longitudinally sectioned in both a mesio-to- Degree of conversion results were evaluated statistically using 170
113 distal and buccal-to-lingual directions across the bonded two-way ANOVA and Tukey’s test at a pre-set significance 171
114 interface with a diamond saw in a Labcut 1010 machine (Extec level of 0.05. 172
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115 Corp., Enfield, CT, USA) to obtain approximately 25 bonded
116 sticks per tooth, each with a cross-sectional area of approxi- 2.3. Solvent evaporation rate 173
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117 mately 0.8 mm2. The number of premature debonded sticks
118 (D) per tooth during specimen preparation was recorded. Approximately 10 mL of each of the products, which corre- 174
119 Specimens originated from the areas immediately above the sponds to approximately one coat with saturated microbrush, 175
120 pulp chamber had their remaining dentin thickness (RDT) was obtained with a micropipette (Pipetman, Gilson, NY, USA) 176
121 measured with a digital caliper and recorded (Absolute from the original container and transferred to small light- 177
122 Digimatic, Mitutoyo, Tokyo, Japan). The cross-sectional area proof glass containers of known weight. They were immedi- 178
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123 of each stick was measured with the digital caliper to the ately placed in an analytical balance (Mettler, type H6; 179
124 nearest 0.01 mm for calculation of the actual bond strength Columbus, OH, USA; capacity to 160 g) and the baseline mass 180
125 values (BS). was recorded to the nearest 0.0001 mg. After 20 s, 1, 2, 3, 4 and 181
126 Only half of the specimens, from each tooth, were tested in 5 min, the mass was recorded again. No stopper that could 182
127 this study and they were randomly selected. Each bonded stick prevent evaporation was used. 183
128 was attached to a modified device for microtensile testing with The same procedure was repeated; however instead of 184
129
130
cyanoacrylate resin (Zapit, Dental Ventures of North America,
Corona, CA, USA) and subjected to a tensile force in a universal
ED leaving the adhesive undisturbed, a warm or cold air-stream
was applied for 10 s before placing the adhesive into the
185
186
131 ˜ ´
testing machine (EMIC, Sao Jose dos Pinhais, PR, Brazil) at a analytical balance. The mass was measured after 20 s, 1, 2, 3, 4 187
132 crosshead speed of 0.5 mm/min. The failure modes were and 5 min. 188
133 evaluated at 400Â (HMV-2, Shimadzu, Tokyo, Japan) and Room temperature was set at 20 8C and the relative 189
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134 classified as cohesive (failure exclusive within dentin or resin humidity approximately at 50%. Protection from light radia- 190
135 composite, C), adhesive (failure at resin/dentin interface–A), or tion was assured by covering the analytical balance with 191
136 adhesive/mixed (failure at resin/dentin interface that included appropriate light filters. Five samples of each adhesive, in each 192
137 cohesive failure of the neighboring substrates, A/M). experimental condition, were used. 193
138 The mean bond strength of all sticks from the same tooth The percentage of loss of mass, based on the mean baseline 194
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139 was averaged for statistical purposes. The prematurely recording, was calculated for each experimental condition. 195
140 debonded specimens were included in the tooth mean. The The data was subjected to a two-way ANOVA and Tukey’s test 196
141 average value attributed to specimens that failed prematurely at a pre-set significance level of 0.05. 197
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142 during preparation was arbitrary and corresponded to
143 approximately half of the minimum bond strength value that 2.4. Scanning electron microscopy for nanoleakage 198
144 could be measured in this study (ca. 4.3 MPa).20 The BS mean evaluation 199
145 for every testing group was expressed as the average of the five
146 teeth used per group. The microtensile bond strength data was Approximately three or four sticks from each tooth were used 200
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147 subjected to a two-way analysis of variance (adhesive/air for nanoleakage evaluation. Bonded sticks were coated with 201
148 temperature) and a post hoc test Tukey’s test at a = 0.05 for two layers of nail varnish applied up to within 1 mm of the 202
149 pair-wise comparisons. bonded interfaces. The specimens were re-hydrated in 203
distilled water for 10 min prior to immersion in the tracer 204
150 2.2. Degree of conversion solution. Ammoniacal silver nitrate was prepared according to 205
the protocol previously described by Tay et al.21 The sticks 206
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151 One drop of each adhesive solution was placed between were placed in the ammoniacal silver nitrate in darkness for 207
152 acetate strips to achieve a thin film 8 mm in diameter. Before 24 h, rinsed thoroughly in distilled water, and immersed in 208
153 covering the adhesive with the upper acetate strip, they were photo developing solution for 8 h under a fluorescent light to 209
154 gently air-dried either with a warm or dry stream (10 s) to reduce silver ions into metallic silver grains within voids along 210
155 allow for solvent evaporation. A FTIR spectrum of the uncured the bonded interface. 211
156 material was recorded and then, the specimens were photo- All sticks were wet-polished with 600-grit SiC paper to 212
157 activated for 10 s. Each specimen was carefully removed with remove the nail varnish. Then, the specimens were placed 213
158 a narrow surgical knife and stored for 24 h in a dark, dry inside an acrylic ring, which was attached to a double-sided 214
159 environment until the FTIR analysis of the degree of conver- adhesive tape, and embedded in epoxy resin. After the epoxy 215
160 sion (FTIR-8300, Shimadzu, Tokyo, Japan). The spectrum was resin set, the thickness of the embedded specimens was 216
161 obtained with 32 scans at 1 cmÀ1 resolution in transmission reduced to approximately half by grinding with silicon carbide 217
162 method. The percentage of unreacted carbon–carbon double papers under running water. Specimens were polished with a 218
163 bonds (% C C) was determined from the ratio of absorbance 600-, 1000-, and 2000-grit SiC paper and 6, 3, 1 and 0.25 mm 219
Please cite this article in press as: Klein Jr CA, et al., Evaporating solvents with a warm air-stream: Effects on adhesive layer properties
and resin–dentin bond strengths, Journal of Dentistry (2008), doi:10.1016/j.jdent.2008.04.014

4. JJOD 1249 1–8
4 journal of dentistry xxx (2008) xxx–xxx
220 diamond paste (Buehler Ltd., Lake Bluff, IL, USA) using a polish Table 3 – Overall degree of conversion (%) and the
221 cloth. They were ultrasonically cleaned, air dried, mounted on respective standard deviations (MPa) obtained in each
222 stubs, and coated with carbon-gold (MED 010, Balzers Union, experimental conditiona
223 Balzers, Liechtenstein). Resin–dentin interfaces were analyzed Adhesive Air temperature
224 in a field-emission scanning electron microscope operated in Cold Warm
225 the backscattered electron mode (JSM 6060, JEOL, Tokyo,
226 Japan). SB 47.8 Æ 3.5 a 50.3 Æ 5.4 a
PB 36.2 Æ 5.2 b 39.3 Æ 6.3 b
a
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227 The same letters indicate statistically similar means ( p > 0.05).
3. Results
228
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3.1. Microtensile bond strength
229 Approximately 21–26 sticks could be obtained per tooth
230 including those with premature debonding. The mean
231 cross-sectional area ranged from 0.82 to 0.98 mm2 and no
232 difference among groups was detected ( p > 0.05). The percen-
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233 tage of specimens with premature debonding and the
234 frequency of each fracture pattern mode are shown in Table 2.
235 Table 2 also depicts the overall means and the respective
236 standard deviations of the resin–dentin bond strengths for all
237 experimental groups. Neither the interaction adhesive vs. air
238 temperature nor the main factor Adhesive was statistically
239
240
significant ( p > 0.05). Only the main factor air temperature was
statistically significant ( p = 0.001). Higher bond strength values
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241 were observed for both adhesives when the solvent evaporation
242 step was performed with a warm air-stream. However, the
243 means were only statistically significant for the SB system.
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244 3.2. Degree of conversion
Fig. 1 – Loss of mass (%) in function of different solvent
evaporation methods during 300 s in: (a) Prime & Bond 2.1;
245 The means and standard deviations of the degree of conver-
(b) Single Bond.
246 sion for both adhesives under the experimental conditions of
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247 this study are shown in Table 3. The degree of conversion of
248 the adhesives was not affected by the air temperature one can observe the percentage of mass of both adhesives 258
249 ( p = 0.36). Only the main factor adhesive was statistically after 20 s was significantly improved by the application of an 259
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250 significant ( p = 0.005). air-dry stream. The use of a cold or warm air-dry was not 260
significant for PB. However, the application of a warm air-dry 261
251 3.3. Solvent evaporation rate significantly favored the evaporation rate of SB compared to 262
the use of a cold air-stream. Nonetheless, in none of the 263
252 In Fig. 1A and B it can be see the mean percentages values of conditions, the evaporation rate of SB was similar to PB. 264
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253 loss of mass for both adhesives during 5 min. Table 4 depicts
254 the mean percentages values of loss of mass for both 3.4. Scanning electron microscopy 265
255 adhesives 20 s after being dispensed. The interaction adhesive
256 vs. air temperature was statistically significant as well as the Representative SEM images at the resin–dentin interfaces for 266
257 main factors Adhesive and Air Temperature ( p < 0.0001). As the experimental conditions are depicted in Fig. 2. Single Bond, 267
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Table 2 – Number of specimens and their respective percentages (%) distributed according to the fracture pattern mode as
well as the percentage of premature debonded specimens for each experimental condition as well as the overall
microtensile bond strength values and the respective standard deviations (MPa) obtained in each experimental conditiona
Adhesive Air temperature A/Mb C Debonded mTBS
SB Cold 39 (79.6) 6 (12.2) 4 (8.2) 34.9 Æ 8.5 b
Warm 31 (66) 9 (19.1) 7 (14.9) 48.7 Æ 6.3 a
PB Cold 32 (80) 3 (7.5) 5 (12.5) 37.3 Æ 5.7 ab
Warm 27 (65.9) 5 (12.1) 9 (22) 44.7 Æ 5.2 ab
a
Statistically similar means are represented by the same letters ( p > 0.05).
b
A/M: adhesive/mixed fracture mode; C: dentin or resin cohesive fracture mode.
Please cite this article in press as: Klein Jr CA, et al., Evaporating solvents with a warm air-stream: Effects on adhesive layer properties
and resin–dentin bond strengths, Journal of Dentistry (2008), doi:10.1016/j.jdent.2008.04.014

5. JJOD 1249 1–8
journal of dentistry xxx (2008) xxx–xxx 5
Table 4 – Mean percentages of mass (%) and the nation can still be observed in base of the hybrid layer (Fig. 2b) 275
respective standard deviations obtained in each experi- the magnitude of the silver nitrate penetration was not as 276
mental condition after dispensea evident as in Fig. 1a. Similarly, Prime & Bond 2.1 showed a very 277
Adhesive Without air Air temperature dense deposition of silver nitrate when the solvent was 278
Cold Warm evaporated with a cold air-dry (Fig. 2c). However, contrary to 279
Single Bond, this intense deposition did not occur in the entire 280
SB 95.4 Æ 1.5 a 90.0 Æ 2.2 b 69.4 Æ 2.0 c thickness of the adhesive layer but only at the hybrid layer. 281
PB 87.0 Æ 2.1 b 33.6 Æ 2.3 d 32.2 Æ 3.0 d
This deposition was significantly reduced when the solvent 282
a
evaporation of PB was performed with a warm air-stream 283
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The same letters indicate statistically similar means ( p > 0.05).
(Fig. 2d). 284
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268 after solvent evaporation with a cold air-dry stream showed a 285
269 poor seal, as many dentinal tubules were filled with silver 4. Discussion
270 (Fig. 2a). Besides that, the entire thickness of the hybrid and
271 adhesive layers, formed under this condition, was throughout Current adhesive systems are generally formulated with 286
272 impregnated with silver nitrate. This situation was not hydrophilic and hydrophobic resin monomers dissolved in 287
273 observed in the adhesive layer formed by Single Bond air- acetone, ethanol and water or in solvent combinations.22 288
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274 dried with a warm stream (Fig. 2b). Although silver impreg- Solvents act as a transport medium and lower resin viscosity. 289
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Fig. 2 – Representative backscattered SEM images of the interface bonded with Single Bond (a and b) and Prime & Bond 2.1 (c
and d) to demineralized dentin. In (a and c), the solvent was evaporated with a cold air-dry stream, while in (b and d), a
warm air-dry stream was employed. (a) Silver deposition occurred almost throughout the entire thickness of the hybrid
layer. Intense penetration of silver nitrate can also bee seen into the tubules. (b) It can be seen that the amount of silver
penetration was lower and practically occurred at the base of the hybrid layer. Only few dentin tubules were infiltrated by
silver nitrate. (c) A higher amount of silver penetration can be observed at the base of the hybrid for PB. (d) The amount of
silver nitrate penetration seems to be quite low and it was restricted to the base of the hybrid layer.
Please cite this article in press as: Klein Jr CA, et al., Evaporating solvents with a warm air-stream: Effects on adhesive layer properties
and resin–dentin bond strengths, Journal of Dentistry (2008), doi:10.1016/j.jdent.2008.04.014

6. JJOD 1249 1–8
6 journal of dentistry xxx (2008) xxx–xxx
290 This allows greater penetration of resins into the micropor- system (PB). Different molecules differ in the amount of 350
291 osites of the prepared tooth surface23 as well as enhances the attraction that exists between them. For instance, the mutual 351
292 mobility of radicals and growing polymer chains.24 The resin attraction between water molecules and ethanol molecules 352
293 surface wetting capabilities are also improved and help to are stronger than that of acetone, because it involves hydrogen 353
294 displace surface moisture without collapsing the deminer- bonding forces. As a result, the boiling temperature and the 354
295 alized collagen network.22 vapor pressure of ethanol and water are higher than that of 355
296 On the other hand, the presence of residual solvent might acetone, which turns their evaporation more difficult. A recent 356
297 have an adverse effect on the performance of the resin–dentin study that examined the effect of organic solvent and water 357
298 bonds. It was already demonstrated that high solvent retention in comonomer blends with different hydrophilicity 358
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299 concentration within the adhesive polymer prior to light- demonstrated that significantly more solvent and water were 359
300 curing prevents the attainment of a high cross-linking retained in ethanol-based adhesives when compared to 360
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301 polymer inside the hybrid layer25,26 and leads to pores and acetone-based mixtures.30 This could be the reason of why 361
302 interfacial layers,27 affecting the overall performance of resin– the acetone-based system (PB) was less affected by the 362
303 dentin bonds.28 increase in the air temperature. 363
304 Ideally, solvents and water (from the moist demineralized Interestingly, the increase in bond strengths was not 364
305 dentin) should be completely eliminated from the dentin accompanied by an increase in the degree of conversion of 365
306 surface before light-curing. On this basis, there is often an air- the adhesive system as observed in the present study. 366
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307 drying process recommended as part of the clinical regimen Previous studies evaluating the effect of solvent concentration 367
308 for dentin bonding while using adhesives that contain on the degree of conversion of adhesive films have observed 368
309 solvents. However, the removal of solvents with a simple that increasing amounts of solvents led to a reduction of their 369
310 air-drying stream is not an easy task to be accomplished under degree of conversion.27,28 However, one may consider that a 370
311 clinical application. As water/solvent evaporates from the wide range of solvent concentration was investigated being 371
312 adhesive, the monomer density is found to increase sharply, them not representative of the amount of solvent presented in 372
313
314
creating a monomer concentration gradient which acts as a
barrier for further solvent evaporation and thus, reduces the
ED the adhesive layer before and after application of a cold or
warm air-drying procedures.
373
374
315 ability of water and solvents to evaporate from the adhesive.29 There is a solvent concentration at which maximum 375
316 This situation is even worse for simplified adhesives such as conversion is reached; more or less solvent than this amount 376
317 the two-step etch-and-rinse adhesives evaluated in the would decrease monomer conversion,24 and this seems to be 377
related to the viscosity of the adhesive film.28 It is likely that
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318 present investigation, since the extent of solvent and water 378
319 retention in polymer networks seems to be directly correlated non-solvated versions of adhesive systems might present a 379
320 with the hydrophilicity of the resin blends.30 In addition to lower degree of conversion due to the increased viscosity of 380
321 that, the recommended clinical time for solvent evaporation is the solution. An increased viscosity restricts the mobility of 381
322 rather short as some studies have demonstrated that only reactive components during polymerization.28 On the other 382
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323 periods of time longer than 12–20 min can ensure an almost extreme, excess of solvents would cause a dilution of the 383
324 complete solvent evaporation.15,31 components preventing the collision of reactive components. 384
325 In face of that some alternative methods to maximize Unfortunately, no attempt was made in the present investiga- 385
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326 solvent evaporation should be investigated, such as the one tion to determine the amount of residual solvent in the 386
327 evaluated in the present study. One way to accelerate solvent adhesive films after using the two different modes of air- 387
328 evaporation, at least for water/ethanol-based systems is the drying and this deserves further investigations. 388
329 use of a warm dry set at approximately 60 8C. Although a Based on the results of the present investigation we cannot 389
330 previous study has not observed any beneficial effect of warm assume that the increase in resin–dentin bond strength is due 390
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331 air-dry on solvent evaporation rate, the temperature of the air to an increase in the degree of conversion of the adhesives. It is 391
332 was half of that employed in the present investigation.32 likely that the increase in the resin–dentin bonds is due to an 392
333 The use of a warm air-stream allowed an increase of 20 and increase in the mechanical properties of the adhesive layer 393
334 40% in the resin–dentin bonds for PB and SB, respectively. This due to more solvent evaporation rates. An earlier study 394
335 could be attributed to the fact that when heat is delivered to a observed that although the solvent content did not affect the 395
336 substance, energy comes in. That energy can be used either to degree of conversion of bulk adhesive specimens, the flexural 396
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337 increase the kinetic energy of the molecules, which causes an strength of these specimens, which is a mechanical property 397
338 increase in temperature or that heat can be used to increase of the adhesive layer, were significantly reduced, since 398
339 the potential energy of the molecules causing a change in the residual solvent might leave more pores in the specimens.27 399
340 state.33 One could hypothesize that under the conditions of This correlation between mechanical properties and resin– 400
341 the study the heat delivered by the warm air-dry could have dentin bonds was also observed in other studies. For instance, 401
342 altered the manner molecules bond to one another. Conse- a significant and positive correlation was observed between 402
343 quently, this increased the evaporation rate of solvents from resin–dentin bond strength values and the ultimate strength 403
344 bonding interface allowing the achievement of higher resin– of the adhesives.34,35 404
345 dentin bonds, as observed in the present investigation. The presence of solvent-rich pores can be reinforced by the 405
346 However, the adhesives did not respond homogeneously to FE-SEM findings of the present study. The amount of silver 406
347 the delivered heat. Although a numerical increase in the resin– nitrate penetration was significantly higher in the specimens 407
348 dentin bond strengths was observed for both adhesives, this that were cold air-dried, as this caused a higher amount of 408
349 increase was not statistically significant for the acetone-based water/solvent retention within the adhesive layer. It is 409
Please cite this article in press as: Klein Jr CA, et al., Evaporating solvents with a warm air-stream: Effects on adhesive layer properties
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7. JJOD 1249 1–8
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410 accepted that one of the sources of nanoleakage expression and dentin: current status and future challenges. Operative 457
411 within adhesive interfaces are the remnant water/solvent and Dentistry 2003;28:215–35. 458
2. Tay FR, Pashley DH. Dentin adhesives: have they become 459
412 the water flux from the underlying dentin.7 They represent
too hydrophilic? Journal of Canadian Dental Association 460
413 areas within the adhesive layer in which water or solvent are
2003;69:724–31. 461
414 incompletely removed resulting in regions of incomplete 3. Tay FR, Pashley DH. Water treeing—a potential mechanism 462
415 polymerization and/or hydrogel formation.7,36 They are there- for degradation of dentin adhesives. American Journal of 463
416 fore highly prone for deposition of silver nitrate as can be seen Dentistry 2003;16:6–12. 464
417 in the micrographs of the present investigation. 4. Tay FR, Frankenberger R, Krejci I, Bouillaguet S, Pashley DH, 465
418 One important issue that should be mentioned is the Carvalho RM, et al. Single-bottle adhesives behave as 466
F
permeable membranes after polymerization. I. In vivo 467
419 potential effects of high temperature in the W-air dry group on
evidence. Journal of Dentistry 2004;32:611–21. 468
420 pulp as well as on dentinal fluid flow. The most widely 5. Tay FR, Suh BI, Pashley DH, Prati C, Chuang SF, Li F. Factors 469
OO
421 accepted mechanism of dentin hypersensitivity is the hydro- contributing to the incompatibility between simplified-step 470
422 dynamic theory proposed by Brannstrom et al.,37 whereby
¨ ¨ adhesives and self-cured or dual-cured composites. Part II. 471
423 fluid flow within dentinal tubules is altered (increased or Single-bottle, total-etch adhesive. Journal of Adhesive 472
424 changed directionally) by thermal, tactile or chemical stimuli Dentistry 2003;5:91–105. 473
6. Suh BI, Feng L, Pashley DH, Tay FR. Factors contributing to 474
425 near the exposed surface of the tubules. This alteration would
the incompatibility between simplified-step adhesives and 475
426 lead to stimulation of the A-d fibres surrounding the
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chemically-cured or dual-cured composites. Part III. Effect 476
427 odontoblasts. Therefore, the use of the warm temperature of acidic resin monomers. Journal of Adhesive Dentistry 477
428 either in superficial, medium and deep cavities should be 2003;5:267–82. 478
429 matter of further investigation to determine the clinical 7. Tay FR, Pashley DH, Suh BI, Hiraishi N, Yiu CHY. Water 479
430 viability of the studied clinical approach. ´ ˜
treeing in simplified dentin adhesives–deja vu? Operative 480
431 The use of a warm air-stream seems to be a useful tool to Dentistry 2005;30:561–79. 481
8. De Munck J, Van Meerbeek B, Yoshida Y, Inoue S, Vargas M, 482
432 help clinicians to improve the quality of the resin–dentin
ED Suzuki K, et al. Four-year water degradation of total-etch 483
433 bonds. However, further studies are still required in order to
adhesives bonded to dentin. Journal of Dental Research 484
434 elucidate some of the hypothesis raised in this study and 2003;82:136–40. 485
435 evaluate the effects of a warm air-dry stream in the long-term 9. Frankenberger R, Strobel WO, Lohbauer U, Kramer N, 486
436 resin–dentin bonds. Petschelt A. The effect of six years of water storage on resin 487
composite bonding to human dentin. Journal of Biomedical 488
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437 10. Gamborgi GP, Loguercio AD, Reis A. Influence of enamel 490
5. Conclusions
border and regional variability on durability of resin–dentin 491
bonds. Journal of Dentistry 2007;35:371–6. 492
438 The resin–dentin bond strength and the quality of the hybrid 11. Peumans M, Kanumilli P, De Munck J, Van Landuyt K, 493
439 layer (less nanoleakage infiltration) of adhesives can be Lambrechts P, Van Meerbeek B. Clinical effectiveness of 494
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E
440 improved by the use of a warm air-stream for solvent 495
441 evaporation, mainly for water/ethanol-based systems. This clinical trials. Dental Materials 2005;21:864–81. 496
12. De Munck J, Van Landuyt K, Peumans M, Poitevin A, 497
442 seems to be mainly attributed to more solvent evaporation
RR
Lambrechts P, Braem M, et al. A critical review of the 498
443 rather than improvement in the degree of conversion of the
durability of adhesion to tooth tissue: methods and results. 499
444 adhesive layer. Journal of Dental Research 2005;84:118–32. 500
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Please cite this article in press as: Klein Jr CA, et al., Evaporating solvents with a warm air-stream: Effects on adhesive layer properties
and resin–dentin bond strengths, Journal of Dentistry (2008), doi:10.1016/j.jdent.2008.04.014