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Microtensile bond strength of total-etch and self-etching adhesives to caries-affected dentine
Journal of Dentistry (2003) 31, 469–477
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Microtensile bond strength of total-etch and self-etching adhesives to caries-affected dentine ´n G. Camejob, M. Victoria Fuentesa, Raquel Osorioa, Laura Ceballosa, Defre Manuel Toledanoa, Ricardo M. Carvalhoc, David H. Pashleyd,* a
Department of Dental Mater, School of Dentistry, University of Granada, Granada, Spain ´rida, Venezuela School of Dentistry, University of Los Andes, Me c Department of Operative Dentistry, Endodontics and Dental Mater, Bauru School of Dentistry, ˜o Paulo, Sa ˜o Paulo, Brazil University of Sa d Department of Oral Biology/Physiology, School of Dentistry, Medical College of Georgia, Augusta, GA 30912-1129, USA b
Received 4 April 2003; accepted 24 April 2003
KEYWORDS Dentine bonding; Totaletch; Self-etch; Cariesaffected dentine; Microtensile bond strength; Microhardness; DIAGNOdent laser
Summary Objectives. To evaluate the microtensile bond strength of total-etch or selfetch adhesives to caries-affected versus normal dentine, and to correlate these bond strengths with DIAGNOdent laser fluorescence and Knoop microhardness (KH) measurements of the substrates. Methods. Extracted carious human molars were ground to expose flat surfaces where the caries lesion was surrounded by normal dentine. Surfaces were bonded with either Prime & Bond NT, Scotchbond 1, Clearfil SE Bond or Prompt L-Pop, according to manufacturers’ recommendations. A crown was built up using resin composite (Tetric Ceram). After storage in water (37 8C, 24 h), teeth were vertically serially sectioned into 0.7 mm thick slabs and trimmed to yield 1 mm2 test area that contained either caries-affected or normal dentine. Samples were tested in tension in an Instron machine at 1 mm/min. The quality of the dentine just beneath each fractured specimen was measured by laser fluorescence and KH. Results. Total-etch adhesives yielded higher bond strengths than self-etching systems. Significantly lower results were obtained with Prompt L-Pop. All the adhesives attained higher strengths in normal than in caries-affected dentine, but the differences were only significant for Prime & Bond NT and Clearfil SE Bond. Higher laser fluorescence values and lower KH ðp , 0:001Þ were recorded in caries-affected dentine compared to normal dentine. Conclusions. The total-etch adhesives evaluated produced higher bond strengths to normal and caries-affected dentine than self-etching systems. Laser fluorescence measurements discriminated caries-affected dentine from normal dentine, and were strongly correlated with KH. However, laser fluorescence and KH did not permit high correlations with resin-dentine bond strengths in caries-affected dentine. Q 2003 Elsevier Ltd. All rights reserved.
Introduction *Corresponding author. Tel.: þ1-706-721-2033; fax: þ1-706721-6252. E-mail address: [email protected]
The infiltration of resin monomers within the demineralized microporous collagen fibril scaffold
0300-5712/03/$ - see front matter Q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0300-5712(03)00088-5
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to establish a hybrid layer, and the formation of resin tags that seal the opened tubules constitute the major and most effective ways to bond resins to dentine.1 – 3 A number of new adhesive systems have been developed in an attempt to reduce the steps and simplify clinical bonding procedures. Two major simplified bonding approaches have been developed.4 The first utilizes the total-etching technique to simultaneously remove the smear layers from both enamel and dentine surfaces, followed by the application of a one-bottle agent that combines the primer and the adhesive in one solution.5 As the demineralized collagen fibril mesh is used as the bonding substrate, a wet bonding technique is required to insure its full expansion.6,7 The need for a moist dentine surface in complex cavity preparations often create overwet and underwet regions in the same tooth, making bonding to dentine with these adhesives very technique sensitive.8 – 10 The second approach is the use of self-etching primers.4,11 Their bonding mechanism is based upon the simultaneous etching and priming of the smear-covered dentine using an acidic primer,12,13 followed by the application of an adhesive resin. Self-etching primers eliminate the separate acid-etching and rinsing steps, simplifying bonding technique and reducing its techniquesensitivity.10,14,15 Recently, all-in-one adhesive systems have been also introduced to simplify the bonding procedure even more. These are also named self-etching adhesives and combine the etching, priming and bonding procedures into one solution and one step.14 The efficiency of these simplified bonding systems is still controversial4 and practically all published reports used normal dentine as the bonding substrate. However, most clinical adhesive procedures involve altered forms of dentine, such as sclerotic or caries-affected dentine.16,17 The development of the microtensile test method, that utilizes specimen cross-sectional areas of approximately 1 mm2, has allowed the determination of bond strengths of several bonding systems to cariesaffected dentine.16,18 – 21 Previous studies have reported that the bond strengths of self-conditioning systems seems to be markedly reduced on caries-affected dentine.18,21,22 . However, the adhesive properties of the new, all-in-one systems to caries-affected dentine have not yet been extensively reported. According to this method,16 after conducting the bond strength testing, the quality of the cariesaffected dentine, previously defined by combined criteria of visual examination and staining by
L. Ceballos et al.
a caries detector solution, is confirmed by measuring the Knoop hardness of the substrate. It has been demonstrated that microhardness measurements correlate well with the degree of mineralization,23 with caries-affected dentine being significantly softer than normal dentine.16,18,19,24 – 26 However, this technique is time-consuming and requires the use of a microhardness tester, which is not available in most laboratories. New non-invasive, optical instrument-based techniques for detection and quantification of demineralization have been recently developed.27 One example is the introduction of a device called the DIAGNOdent, based on the fluorescence of tooth structure when teeth are illuminated with a laser light (l ¼ 655 nm). This radiation is absorbed by both inorganic and organic tooth substance28 and by metabolites from oral bacteria.29 Emitted fluorescence is observed through a high-pass barrier filter that discriminates between sound and carious tissue. 30 If there is a significant relationship between Knoop hardness values and the fluorescence values of the DIAGNOdent, the latter device might be more convenient to estimate the quality of the caries-affected dentine in microtensile bond test studies. The aim of the present study was to evaluate the microtensile bond strength of two total-etch and two self-etching adhesive systems to normal and caries-affected dentine, and to compare DIAGNOdent laser fluorescence and Knoop microhardness measurements to quantitate the degree of demineralization of caries-affected dentine following resin-bonding. Two hypotheses were tested. The first hypothesis is that the bond strengths of adhesive systems to caries-affected dentine is lower than to normal dentine. The second is that the more carious the dentine (i.e. the softer or more demineralized the dentine), the lower will be its bond strength.
Materials and methods Specimen preparation Sixteen extracted human molars with coronal dentine caries extending approximately halfway through the dentine were used in this study. All teeth had been stored at 4 8C in physiological saline to which several crystals of thymol were added. Specimens were prepared as described by Nakajima et al.16 to perform microtensile bond strength tests on caries-affected dentine. Occlusal surfaces were ground perpendicular to the long axis of the tooth
Microtensile bond strength of total-etch and self-etching adhesives to caries-affected dentine
with #220 silicon carbide paper under running water (EXAKT- Apparatebau D-2000 Nerderstedt, Germany) to expose a flat surface where the caries lesion was surrounded by normal dentine. To obtain caries-affected dentine, the samples were ground using the combined criteria of visual examination and staining with 0.5% fucsin dye, until relatively hard, non-staining dentine was obtained. Four teeth were randomly allocated to each of the four treatment groups.
Bonding procedure and bond strength testing Four different adhesive systems were applied following the manufacturers’ recommendations (Table 1). Two were total-etch, one-bottle adhesives: Prime & Bond NT (Dentsply DeTrey, Konstanz, Germany) and Scotchbond 1 (3M-ESPE, St Paul, MN, USA); and two more were self-etching
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systems: Clearfil SE Bond (Kuraray Co. Ltd., Osaka, Japan) and the all-in-one adhesive system, Prompt L-Pop (3M-ESPE, St Paul, MN, USA). A composite crown was built up by applying several layers of Tetric Ceram (Ivoclar-Vivadent, Schaan, Liechtenstein) hybrid resin composite to a height of 3 –5 mm. Each increment was cured for 40 s. The teeth were stored in water at 37 8C for 24 h and then vertically serially sectioned perpendicularly to the bonded interface to produce several bonded sections of approximately 0.7 mm thick (Accutom-50, Struers, Copenhagen, Denmark). Each slice was carefully examined to separate those that contained caries-affected dentine from those containing normal dentine, following the visual criterion described above. About three slabs of normal dentine and two to three slabs of cariesaffected dentine were obtained per tooth (10 per group). All the slabs were trimmed to yield an hourglass shape with a 1 mm2 test area that contained either caries-affected or normal dentine.
Table 1 Dentine adhesive systems tested. Adhesive system
Principle ingredients
Mode/steps of application
Prime & Bond NT (Dentsply De Trey GmbH, Konstanz, Germany)
PENTA, UDMA resin, Resin R5-62-1, T-resin, D-resin, nanofiller, initiators, stabilizer, cetylamine hydrofluoride, acetone
Etch for 15 sec with 35% phosphoric acid. Rinse with water for 15 s and remove excess water with 1 s air blast. Apply ample adhesive to saturate moist surface, reapply if necessary. Leave surface undisturbed for 20 s; Remove solvent gently with air for 5 s. Light-cure 10 s
Scotchbond 1 (3M, St Paul, MN, USA)
Bis-GMA, HEMA, dimethacrylates, polyalkenoic acid copolymer, initiator, water, ethanol
Etch 15 s with 35% phosphoric acid. Rinse with water for 10 s. Apply two consecutive coats of the adhesive to moist dentine with a saturated brush tip. Dry gently for 2–5 sec; Light cure 10 s
Clearfil SE Bond (Kuraray Co, Osaka, Japan)
Primer. 10-methacryloyloxydecyl dihydrogen phosphate; 2-hydroxyethyl methacrylate; hydrophilic dimethacrylate; dl-camphorquinone; N,N-diethanol-p-toluidine; water Adhesive. 10-methacryloxydecyl dihydrogen phosphate; Bis-phenol A diglycidylmethacrylate; 2-hydroxyethyl methacrylate; hydrophobic dimethacrylate; di-camphorquinone; N,N-diethanol-p-toluidine; silanated colloidal silica
Apply Primer for 20 s; Evaporate water with mild air; Apply adhesive, Gentle air stream. Light cure 10 s
Prompt L-Pop (3M-ESPE, St Paul, MN, USA)
Water, methacrylated phosphoric acid esters, phosphine oxide, stabilizer, zinc fluoride complex, parabenes
Apply with scrubbing for 15 s. Gently air dry, Light cure 10 s
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Samples were attached to a Bencor Multi-T testing apparatus with a cyanoacrylate adhesive (Zapit, DVA, Anaheim, CA, USA) and subjected to tensile stress in an universal testing machine (Model 4411, Instron Corp., Canton, MA) at a cross-head speed of 1 mm/min until failure. The bond strengths were expressed in MPa after measuring the cross-sectional area at the site of fracture with a digital caliper (Mitutoyo, Tokyo, Japan).
DIAGNOdent laser and microhardness measurements: After performing the microtensile test, the lateral aspect (i.e. the non-bonded surface) of each dentine-half of the fractured specimens was highly polished with #4000 silicon paper in a circular grinding machine (EXAKT-Apparatebau D-2000 Nerderstedt, Germany) to permit subsequent microhardness measurements. Prior to microhardness measurements, the degree of demineralization of the specimen was measured with the laser fluorescence system (DIAGNOdent, KaVo, Biberach, Germany). Before the start of the measurements, the laser was calibrated against a porcelain standard as indicated in the manufacturer’s instructions. The measurements were performed using the smallest conical tip (1.2 mm diameter) that was held against the specimen at right angles to the surface. The maximum fluorescence reading was recorded just beneath the fractured site. Progression of the carious process is reflected in an increase in the amount of fluorescence.31 The numerical range of the DIAGNOdent instrument is from 0 to 100. Finally, Knoop microhardness measurements were done 50 mm below the adhesive/dentine interface using an Instron Wolpert hardness tester (V-testor 4021, Instron Wolpert GmbH, Ludwgshafen, Germany), under a load of 30 g and a duration of 30 s. During the test, dentine desiccation was
avoided.32 Each specimen received approximately five indentations and were averaged.
Statistical analysis A two-way ANOVA was performed to evaluate the effect of the adhesive and the type of dentine tested, and their interactions, on microtensile bond strength. Statistical significance was set in advance at the 0.05 probability level. Multiple post-hoc comparisons were done using Student-Newman – Keuls test. Comparison of the values obtained by either laser fluorescence or microhardness tests, on normal dentine and caries-affected dentine were performed by Student’s t test. The correlation between laser fluorescence values and Knoop microhardness numbers, as well as the correlations between microtensile bond strength and fluorescence values and between bond strength and microhardness measurements were analyzed by calculating Pearson’s correlation coefficient. All data were analyzed by means of SPSS 10.0 for Windows software (SPSS Inc., Chicago, IL, USA).
Results The results of microtensile bond strength test are shown in Table 2. Two-way ANOVA revealed a significant influence of both the adhesive systems tested ðF ¼ 40:857; p , 0:0001Þ and the type of dentine ðF ¼ 22:088; p , 0:0001Þ on microtensile bond strength values. However, the interaction of these two factors was not statistically significant (F ¼ 1.282; p ¼ 0.287). ANOVA analysis showed significant differences among the adhesive systems evaluated for normal ðF ¼ 21:892; p , 0:0001Þ and caries-affected dentine ðF ¼ 23:701; p , 0:0001Þ: In normal dentine, Prime & Bond NT attained the highest microtensile bond strength. Intermediate, statistically similar bond strengths were obtained in normal
Table 2 Mean microtensile bond strengths (MPa) and standard deviation (SD) to normal and caries-affected dentine. Adhesive system
Normal dentine
Sig.
Caries-affected dentine
Prime & Bond NT Scotchbond 1 Clearfil SE Bond Prompt L Pop
56.3 (11.1) a 43.9 (11.4) b 35.5 (11.6) b 18.2 (9.6) c
,0.05a NS ,0.05a NS
41.3 (10.7) A 36.3 (12.2) A 21.5 (5.5) B 13.4 (1.9) C
For each column, means designated by the same letter are not significantly different ðp . 0:05Þ: NS: not significantly different. Values are mean ^ SD in MPa. a Shows statistical differences between normal and caries-affected dentine ðp , 0:05Þ:
Microtensile bond strength of total-etch and self-etching adhesives to caries-affected dentine
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Table 3 Failure modes for the adhesives in normal and caries-affected dentin. Adhesive system
Adhesive
Cohesive in dentine
Cohesive in composite
10% 33.3%
10% 33.3%
80% 33.3%
25% 71.4%
12.5% 14.3%
62.5% 14.3%
46.7% 63.6%
13.3% 36.4%
13.3% 0
100% 90%
0 10%
0 0
Prime & Bond NT Normal dentine Caries-affected dentine Scotchbond 1 Normal dentine Caries-affected dentine Clearfil SE Bond Normal dentine Caries-affected dentine Prompt L-Pop Normal dentine Caries-affected dentine
dentine with Scotchbond1 and Clearfil SE Bond, while Prompt L-Pop showed the lowest strengths (Table 2). In caries-affected dentine, the totaletch adhesive systems, Prime & Bond NT and Scotchbond 1, yielded statistically higher ðp , 0:05Þ bond strengths than Clearfil SE Bond. Significantly lower ðp , 0:05Þ strengths were obtained with Prompt L-Pop. In normal dentine, the major mode of failure in specimens showing low bond strengths was adhesive failure, while cohesive fractures in dentine or composite were seen at higher bond strengths (Table 3). In caries-affected dentine, adhesive and cohesive failures in dentine were seen in specimens showing low bond strengths, while cohesive failures in resin composite were seen more frequently in specimens with high bond strengths. All the adhesives tested showed higher strengths in normal dentine than in caries-affected, but these differences were only significant for Prime & Bond NT and Clearfil SE Bond. The results of laser fluorescence and Knoop hardness numbers for normal and caries-affected dentine are shown in Table 4. Significantly lower fluorescent values were obtained for normal dentine ðt : 19:289; p , 0:0001Þ; compared with the values recorded in caries-affected dentine. Mean hardness results for normal dentine were statistically significant higher ðt : 17:495; p , 0:0001Þ than those of caries-affected dentine. Comparison between laser fluorescence values recorded and Knoop hardness numbers (KHN) of all of the specimens (Fig. 1) revealed a high correlation ðr ¼ 20:85; p , 0:0001Þ: However, the correlation between all resindentine bond strengths and fluorescence values
was low (r ¼ 20:334; data not shown) but was significant ðp , 0:01Þ: Similarly, the correlation between microtensile bond strength and KH values, while significant ðp , 0:001Þ; was low (r ¼ 0:412; data not shown). These correlations were done excluding the specimens bonded with Prompt LPop, as the bond strengths attained with this adhesive were so low. Thus, the potential utility of using KHN or fluorescence values for predicting bond strength using all combined types of dentine is poor. If the correlation of bond strength and KHN is limited to caries-affected specimens, then the correlation becomes even weaker ðr ¼ 0:119; p ¼ 0:554Þ: Similarly, the correlation between bond strengths of caries-affected dentine and fluorescence values was insignificant (r ¼ 20:023; p ¼ 0:90 data not shown). When these correlations were done for each adhesive separately, they were not significant for Scotchbond 1 or for Prompt L-P. However, the correlation between bond strength and KH for Prime & Bond NT was moderate ðr ¼ 0:548; p , 0:05Þ and the same was observed for Clearfil SE Bond ðr ¼ 0:472; p , 0:01Þ: Similarly, the correlations between bond strength and fluorescence Table 4 DIAGNOdent values and Knoop microhardness numbers obtained in normal and caries-affected dentine. DIAGNOdent values
Knoop microhardness number
Normal dentine 8.5 (12.6) a 74.6 (9.1) A Caries-affected dentine 61.6 (20.9) b 33.9 (6.7) B For each column, values with different letters indicate statistically significant difference ðp , 0:05Þ:
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Figure 1
L. Ceballos et al.
Correlation between Knoop hardness values and DIAGNOdent fluorescent values on the same specimens.
values for Prime & Bond NT and Clearfil SE Bond were also relatively low, but were significant (r ¼ 20:49; p , 0:05 and r ¼ 20:514; p , 0:01; respectively).
Discussion The results of the present study show that bond strength to normal and caries-affected dentine is dependent on the adhesive system used. In normal dentine, the total-etch adhesives tended to produce higher bond strength values than the selfetching adhesives, confirming the observations of Inoue et al.33 Prime & Bond NT exhibited the highest bond strengths compared with the other total-etch adhesive, Scotchbond 1. Prime and Bond is filled with nanoparticles that may help to establish a thicker more uniform resin film thickness that stabilizes the hybrid layer,14 although this effect is still somewhat controversial.34,35 The lowest microtensile bond strengths were attained with Prompt L-Pop, that exclusively yielded adhesive failures. These results are in agreement with previous reports that this product produces inconsistent results.11,14,36,37 Prompt LPop produces an etching pattern similar to phosphoric acid, being classified as a strong self-etching adhesive, in contrast with the mild etching ability of Clearfil SE Bond.14,15 Both bonding systems form authentic hybrid layers. However, Prompt L-Pop dissolves the smear layer and plugs while Clearfil SE
Bond preserves and incorporates them into the hybridized complex.15 This etching aggressiveness is unrelated to the bond strengths attained.11 One explanation may be the formation of dry spots where the low viscosity Prompt L-Pop had spread so thin that it may not be properly polymerized.36,37 Higher strengths have been reported for this adhesive when it is applied in multiple coats38 or is experimentally filled.36,37 In caries-affected dentine, the total etch adhesives performed better than the self-etching systems. Caries-affected dentine contains dentinal tubules that are filled with acid-resistant whitlockite minerals25,39,40 – 42 that interfere the infiltration of adhesive resins and the formation of resin tags.42,43 The application of 32 – 37% phosphoric acid seems to solubilize the intratubular mineral deposits in caries-affected dentine19 – 21 better than weaker acids, thereby contributing to better resin retention.3 It may be that Clearfil SE Bond is not acidic enough to dissolve the mineral casts. Moreover, the smear layer formed on caries-affected dentine includes acid resistant crystals that may hamper the diffusion of the self-etching primer into the underlying intact dentine.21 However, since the presence of these deposits in dentinal tubules has been shown to reduce dentine permeability44 to near zero and hence constitutes a protective barrier for the pulp tissue by reducing the ingress of bacteria, and/or bacterial products,40,42 it should be retained in conservative cavity preparations,42 as it is generally not infected and can remineralize.45
Microtensile bond strength of total-etch and self-etching adhesives to caries-affected dentine
The low bond strengths produced by Prompt LPop may not be related to its etching aggressiveness but to its degree of conversion. All-in-one systems do not yet possess all the requirements to provide optimal adhesion to tooth structure.11 Modifications in its formulation or mode of application are needed.36 – 38 It is noteworthy that Prompt L-Pop has been ported to be relatively ineffective in retention of resin composite restorations to noncarious cervical sites in a clinical trial.46 Caries-affected intertubular dentine is partially demineralized due to the caries process,25,41,44 and is more porous, allowing deeper penetration of monomers.22 This fact is reflected in the establishment of thicker hybrid layers.16,18 – 22 However, the thickness of the hybrid layer is unrelated to bond strengths in dentine.16,18 – 22 Even when the adhesive systems are capable of infiltrating deep into intertubular dentine, there would be always a porous and demineralized underlying zone that was not infiltrated.42 Moreover, caries-affected dentine presents lower nanomechanical properties44 and a lower cohesive strength22 (Fuentes, unpublished observations) as they are dependent on the properties of intertubular dentine.47 Thus, the weakest link in the resin-caries-affected dentine assembly may be the cohesive strength of caries-affected dentine. Knoop hardness testing revealed the cariesaffected dentine to be about half as hard as normal dentine, in agreement with previously reported results.16,18 – 20,25 This relative softness of caries-affected dentine is due to the partial demineralization of the intertubular dentine even though tubules become filled with mineral.16,25,48 In the present study, lower Knoop hardness values in caries-affected dentine were strongly correlated with higher laser fluorescence values (Fig. 1), confirming the results of Banerjee et al.49 Therefore, these results reveal the capacity of the laser fluorescence device to estimate the quality of caries-affected dentine relative to normal dentine. Its non-destructive nature, in addition to its repeatability and validity have been claimed to make it an useful tool in a clinical and laboratory situation.30,50 – 53 The mechanism underlying the enhanced fluorescence in the presence of caries has not been fully clarified.54 Unlike Knoop hardness,23 no relationship between autofluorescence and the mineral content of caries lesions has been found. This may be due to the contribution of exogenous fluorescent molecules imported during the carious process.55 The DIAGNOdent instructions describe a scale which correlates the numerical values with histological findings, and provide treatment recommendations. However, this scale makes no
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distinction between acute or active carious lesions versus chronic or arrested lesions. Moreover, it has been reported that high laser fluorescence readings may also be obtained on dentine surfaces which are stained.51,56 It must be borne in mind that caries-affected dentine presents a glassy, dark yellow or slightly brown appearance. This may produce higher DIAGNOdent scores49,56 than less colored caries lesions with the same degree of demineralization. This potential source of error of DIAGNOdent has been previously be pointed out to be a distinct disadvantage,57 compared with the visual system, as laser fluorescence system can only detect carious lesions but cannot judge their activity.51 In caries-affected dentine, the relationship between bond strength and hardness or fluorescence values were not significant when all the specimens were considered. Even using the smallest laser probe, the DIAGNOdent sampled an area of about 1 mm2 or a volume **(for a 0.7 mm thick specimen) of 0.7 mm3 that was located subjacent to the bonded surface area. That is, it only gives an average fluorescence value of dentine at some distance below the bonded surface. Fig. 1 shows that the fluorescence values varied from 35 to 98 in cariesaffected dentine, yet the resin-dentine bond strengths did not vary as much as the fluorescence values (data not shown). Although the KH numbers were also measured below the bonded surface, it was only 50 mm below, instead of 500 mm or more as was the case with the DIAGNOdent. The Knoop hardness measurements are made with a large indenter that crushes both intertubular and peritubular dentine. That is, it measures an average hardness. In caries-affected dentine, the tubules are filled with mineral crystals that prevent resin tag formation and make these tubules harder than fluid-filled tubules.44 Dentine bond strengths under these conditions are probably due to hybridization of intertubular dentine.58 Better correlations between bond strengths and hardness of caries-affected dentine may require use of nanohardness techniques.4,43
Conclusions All the adhesives evaluated in the present study showed higher strengths to normal dentine than in caries-affected, but these differences were only significant for Prime & Bond NT and Clearfil SE Bond. The occlusion of dentinal tubules by the acidresistant mineral deposits that interferes with
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the formation of retentive resin tags and the intrinsic weakness of caries-affected dentine may have contributed these results. In caries-affected dentine, total-etch adhesives performed better than self-etching systems. Higher laser fluorescence values were strongly correlated with lower Knoop hardness values in caries-affected dentine. Thus, although both the DIAGNOdent and KH values correlate well to each other and can measure differences in the quality of dentine, the regions that they sample may be too far removed from the resin-dentine interface to permit high correlations with resin-dentine bond strengths.
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13. 14.
15.
16.
17.
Acknowledgements This research project was supported by grant DEO14911 from the National Institute of Dental and Craniofacial Research, by grant MAT 2001-2843-CO2; RED CYCTED VIII.J. from the CICYT, Spain. The authors wish to thank Gertrudis Go ´mez-Villaescusa for her help with specimen preparation.
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References 1. Nakabayashi N, Kojima K, Masuhara E. The promotion of adhesion by infiltration of monomers into tooth substrates. J Biomed Mater Res 1982;16:265—73. 2. Van Meerbeek B, Dhem A, Goret-Nicaise M, Braem M, Lambrechts P, Vanherele G. Comparative SEM and TEM examination of the ultrastructure of the resin-dentin interdiffusion zone. J Dental Res 1993;72:495—501. 3. Pashley DH, Carvalho RM. Dentine permeability and dentine adhesion. J Dent 1997;25:355—72. 4. Van Meerbeek B, Perdiga ˜o J, Lambrechts P, Vanherle G. The clinical performance of adhesives. J Dent 1998;26:1—20. 5. Li H, Burrow MF, Tyas MJ. Nanoleakage patterns of four dentin bonding systems. Dent Mater 2000;16:48—56. 6. Gwinnett AJ. Moist versus dry dentin: Its effect on shear bond strength. Am J Dent 1992;5:127—9. 7. Kanka J. Resin bonding to wet substrate. I. Bonding to dentin. Quintessence Int 1992;5:127—9. 8. Tay FR, Gwinnett JA, Wei SHY. The overwet phenomenon: a transmission electron microscopic study of surface moisture in the acid-conditioned, resin—dentin interface. Am J Dent 1996;9:161—6. 9. Van Meerbeek B, Yoshida Y, Lambrechts P, Duke ES, Eick JD, Robinson SJ. A TEM study of two water-based adhesive systems bonded to dry and wet dentin. J Dent Res 1998;77: 50—9. 10. Miyazaki M, Onose H, Moore BK. Effect of operator variability on dentin bond strength of two-step bonding systems. Am J Dent 2000;13:101—4. 11. Bouillaguet S, Gysi P, Wataha JC, Ciucchi B, Cattani M, Godin CH, Meyer JM. Bond strength of composite to dentin using
22.
23.
24.
25.
26.
27.
28. 29. 30.
31.
32.
conventional, one-step, and self-etching adhesive systems. J Dent Res 2001;29:55—61. Hayakawa T, Nemoto K, Horie K. Adhesion of composite to polished dentin retaining its smear layer. Dent Mater 1995; 11:218—22. Nakabayahi N, Saimi Y. Bonding to intact dentin. J Dent Res 1996;75:1706—15. Inoue S, Van Meerbeek B, Vargas M, Yoshida Y, Lambrechts P, Vanherle G. Adhesion mechanism of self-etching adhesives. In: Tagami J, Toledano M, Prati C, et al., editors. Advanced adhesive dentistry. Cirimido, Italia; 2000. p. 131—48. Tay FR, Pashley DH. Aggressiveness of contemporary selfetching systems. I. Depth of penetration beyond dentin smear layers. Dent Mater 2001;17:296—308. Nakajima M, Sano H, Burrow MF, Yoshiyama M, Ebisu S, Ciucchi B, Russell CM, Pashley DH. Tensile bond strength and SEM evaluation of caries-affected dentin using dentin adhesives. J Dent Res 1995;74:1679—88. Marshall GW, Marshall SJ, Kinney JH, Balooch M. The dentin substrate: structure and properties related to bonding. J Dent 1997;25:441—58. Nakajima M, Ogata M, Tagami J, Sano H, Pashley DH. Bonding to caries-affected dentin using self-etching primers. Am J Dent 1999;12:309—14. Nakajima M, Sano H, Zheng L, Tagami J, Pashley DH. Effect of moist vs dry bonding to normal vs caries-affected dentin with scotchbond multi-purpose plus. J Dent Res 1999;78: 1298—303. Nakajima M, Sano H, Urabe I, Tagami J, Pashley DH. Bond strengths of single-bottle dentin adhesives to cariesaffected dentin. Oper Dent 2000;25:2—10. Yoshiyama M, Urayama A, Kimochi T, Motsuo T, Pashley DH. Comparison of conventional vs. self-etching adhesive bonds to caries-affected dentin. Oper Dent 2000;25:163—9. Yoshiyama M, Tay FR, Doi J, Nishitani Y, Yamada T, Itou K, Carvalho RM, Nakajima M, Pashley DH. Bonding of selfetching and total-etch adhesives to carious dentin. J Dent Res 2000;81:556—60. Panighi M, G’Sell C. Influence of calcium concentration on the dentin wettability by an adhesive. J Biomed Mater Res 1992;26:1081—9. Fusayama T, Okuse K, Hosoda H. Relationship between hardness, discoloration and microbial invasion in carious dentin. J Dent Res 1966;45:1033—46. Ogawa K, Yamashita Y, Ichijo T, Fusayama T. The ultrastructure and hardness of the transparent layer of human carious dentin. J Dent Res 1983;62:7—10. Hosoya Y, Marshall SJ, Watanabe LG, Marshall GW. Microhardness of carious deciduous dentin. Oper Dent 2000;25: 81—9. Hafstro ¨m-Bjo ¨rkman U, Sundstro ¨m F, de Josselin de Jong E, Angmar-Ma ˚nsson B. Comparison of laser fluorescence and longitudinal microradiography for quantitative assessment of in vitro enamel caries. Caries Res 1999;26:241—7. Hibst R, Gall R. Development of a diode laser-based fluorescence caries detector. Caries Res 1998;32:294. Hibst R, Paulus R. Molecular basis of red excited caries fluorescence. Caries Res 2000;34:323. Ando M, Hall AF, Eckert GJ, Schemehorn Br, Amaloui M, Stookey GK. Relative ability of laser fluorescence techniques to quantitate early mineral loss in vitro. Caries Res 1997;31: 125—31. Shi XQ, Welander U, Angmar-Ma ˚nsson. Occlusal caries detection with KaVo DIAGNOdent and radiography: an in vitro comparison. Caries Res 2000;34:151—8. Xu HHK, Smith DT, Jahanmir S, Romberg E, Kelly JR, Thompson VP, Rekow ED. Indentation damage and
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33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
mechanical properties of human enamel and dentin. J Dent Res 1998;77:472—80. Inoue S, Vargas MA, Abe Y, Yoshida Y, Lambrechts P, Vanherle G, Sano H, Van Meerbeek B. Microtensile bond strength of eleven contemporary adhesives to dentin. J Adhes Dent 2001;3:237—45. Braga RR, Cesar PF, Gonzaga CC. Tensile bond strength of filled and unfilled adhesives to dentin. Am J Dent 2001;13: 73—6. Nunes FM, Swift EJ, Perdiga ˜o J. Effects of adhesive composition on microtensile bond strength to human dentin. Am J Dent 2001;14:340—3. Perdiga ˜o J, Frankenberger R, Rosa BT, Breschi L. New trends in dentin/enamel adhesion. Am J Dent 2000;13: 25D—30D. Frankenberger R, Perdiga ˜o J, Rosa BT, Lopes M. No-bottle vs. multi-bottle dentin adhesives-a microtensile bond strength and morphological study. Dent Mater 2001;17: 373—80. Pashley EL, Agee KA, Pashley DH, Tay FR. Effects of one versus two applications of an unfilled, all-in-one adhesive on dentine bonding. J Dent 2002;30:83—90. Frank RM, Voegel JC. Ultrastructure of the human odontoblast process and its mineralisation during dental caries. Caries Res 1980;14:367—80. Pashley EL, Talman R, Horner JA, Pashley DH. Permeability of normal versus carious dentin. Endod Dent Traumatol 1991;7:207—11. Fusayama T. A simple pain-free adhesive restorative by system by minimal reduction and total etching. Tokyo: Ishiyaku EuroAmerica; 1993. Marshall GW, Chang YJ, Gansky SA, Marshall SJ. Demineralization of caries-affected transparent dentin by citric acid: an atomic force microscopy study. Dent Mater 2001;17: 45—52. Marshall GW, Habelitz S, Gallagher R, Balooch M, Blooch G, Marshall SJ. Nanomechanical properties of hydrated carious human dentin. J Dent Res 2001;80:1768—71. Tagami J, Hosoda H, Burrow MF, Nakajima M. Effect of aging and caries on dentin permeability. Proc Finnish Dent Soc 1992;88(Suppl 1):149—54. Ohgushi K, Fusayama T. Electron microscopic structure of the two layers of carious dentin. J Dent Res 1975;54: 1019—26.
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46. Brackett WW, Covey DA, St Germain HA. One-year clinical performance of a self-etching adhesive in Class V resin composites cured by two methods. Oper Dent 2002;27: 218—22. 47. Kinney JH, Balooch M, Marshall GW, Marshall SJ. A micromechanics model of the elastic properties of human dentine. Arch Oral Biol 1999;44:813—22. 48. Shimizu C, Yamashita Y, Ichijo T, et al. Carious change of dentin observed on Longspan ultrathin sections. J Dent Res 1981;60:1826—31. 49. Banerjee A, Sherriff M, Kidd EAM, et al. A confocal microscopic study relating the autofluorescence of carious dentine to its microhardness. Br Dent J 1999;187:206—10. 50. De Josselin de Jong E, Sundstro ¨m F, Westerling H, Tranaeus S, ten Bosch JT, Angmar-Ma ˚nsson B. A new method for in vivo quantification of changes in initial enamel caries with laser fluorescence. Caries Res 1995;29:2—7. 51. Sheeny EC, Brailsford SR, Kidd EAM, et al. Comparison between visual examination and a laser fluorescence system for in vivo diagnosis of occlusal caries. Caries Res 2001;35: 421—6. 52. Lussi A, Megert B, Longbotton C, Beighton D, Zoitopoulos L. Clinical performance of a laser fluorescence device for detection of occlusal caries lesions. Eur J Oral Sci 2001;109: 14—9. 53. Alwas-Danowska HM, Plasschaert AJM, Suliborski S, et al. Reliability and validity issues of laser fluorescence measurements in occlusal caries diagnosis. J Dent 2002;30:129—34. 54. Shi XQ, Tranæus A, Angmar-Ma ˚nsson B. Comparison of QLF and DIAGNOdent for quantification of smooth surface caries. Caries Res 2001;35:21—6. 55. Banerjee A, Boyde A. Autofluorescence and mineral content of carious dentine: Scanning optical and backscattered electron microscopic studies. Caries Res 1998;32:219—26. 56. Welsh GA, Hall AF, Hannah AJ, Foye RH. Variation in DIAGNOdent measurements of stained artificial caries lesions. Caries Res 2000;34:324. 57. Lussi A, Imwinkelried S, Pitts NB, Longbottom C, Reich E, Performance and reproducibility of a laser fluorescence system for detection of occlusal caries in vitro. Caries Res 1999;33:261—6. 58. Pashley DH, Ciucchi B, Sano H, Carvalho RM, Russell CM. Bond strength versus dentine structure: a modelling approach. Arch Oral Biol 1995;40:1109—18.
www.elsevier.com/locate/jdent
Microtensile bond strength of total-etch and self-etching adhesives to caries-affected dentine ´n G. Camejob, M. Victoria Fuentesa, Raquel Osorioa, Laura Ceballosa, Defre Manuel Toledanoa, Ricardo M. Carvalhoc, David H. Pashleyd,* a
Department of Dental Mater, School of Dentistry, University of Granada, Granada, Spain ´rida, Venezuela School of Dentistry, University of Los Andes, Me c Department of Operative Dentistry, Endodontics and Dental Mater, Bauru School of Dentistry, ˜o Paulo, Sa ˜o Paulo, Brazil University of Sa d Department of Oral Biology/Physiology, School of Dentistry, Medical College of Georgia, Augusta, GA 30912-1129, USA b
Received 4 April 2003; accepted 24 April 2003
KEYWORDS Dentine bonding; Totaletch; Self-etch; Cariesaffected dentine; Microtensile bond strength; Microhardness; DIAGNOdent laser
Summary Objectives. To evaluate the microtensile bond strength of total-etch or selfetch adhesives to caries-affected versus normal dentine, and to correlate these bond strengths with DIAGNOdent laser fluorescence and Knoop microhardness (KH) measurements of the substrates. Methods. Extracted carious human molars were ground to expose flat surfaces where the caries lesion was surrounded by normal dentine. Surfaces were bonded with either Prime & Bond NT, Scotchbond 1, Clearfil SE Bond or Prompt L-Pop, according to manufacturers’ recommendations. A crown was built up using resin composite (Tetric Ceram). After storage in water (37 8C, 24 h), teeth were vertically serially sectioned into 0.7 mm thick slabs and trimmed to yield 1 mm2 test area that contained either caries-affected or normal dentine. Samples were tested in tension in an Instron machine at 1 mm/min. The quality of the dentine just beneath each fractured specimen was measured by laser fluorescence and KH. Results. Total-etch adhesives yielded higher bond strengths than self-etching systems. Significantly lower results were obtained with Prompt L-Pop. All the adhesives attained higher strengths in normal than in caries-affected dentine, but the differences were only significant for Prime & Bond NT and Clearfil SE Bond. Higher laser fluorescence values and lower KH ðp , 0:001Þ were recorded in caries-affected dentine compared to normal dentine. Conclusions. The total-etch adhesives evaluated produced higher bond strengths to normal and caries-affected dentine than self-etching systems. Laser fluorescence measurements discriminated caries-affected dentine from normal dentine, and were strongly correlated with KH. However, laser fluorescence and KH did not permit high correlations with resin-dentine bond strengths in caries-affected dentine. Q 2003 Elsevier Ltd. All rights reserved.
Introduction *Corresponding author. Tel.: þ1-706-721-2033; fax: þ1-706721-6252. E-mail address: [email protected]
The infiltration of resin monomers within the demineralized microporous collagen fibril scaffold
0300-5712/03/$ - see front matter Q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0300-5712(03)00088-5
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to establish a hybrid layer, and the formation of resin tags that seal the opened tubules constitute the major and most effective ways to bond resins to dentine.1 – 3 A number of new adhesive systems have been developed in an attempt to reduce the steps and simplify clinical bonding procedures. Two major simplified bonding approaches have been developed.4 The first utilizes the total-etching technique to simultaneously remove the smear layers from both enamel and dentine surfaces, followed by the application of a one-bottle agent that combines the primer and the adhesive in one solution.5 As the demineralized collagen fibril mesh is used as the bonding substrate, a wet bonding technique is required to insure its full expansion.6,7 The need for a moist dentine surface in complex cavity preparations often create overwet and underwet regions in the same tooth, making bonding to dentine with these adhesives very technique sensitive.8 – 10 The second approach is the use of self-etching primers.4,11 Their bonding mechanism is based upon the simultaneous etching and priming of the smear-covered dentine using an acidic primer,12,13 followed by the application of an adhesive resin. Self-etching primers eliminate the separate acid-etching and rinsing steps, simplifying bonding technique and reducing its techniquesensitivity.10,14,15 Recently, all-in-one adhesive systems have been also introduced to simplify the bonding procedure even more. These are also named self-etching adhesives and combine the etching, priming and bonding procedures into one solution and one step.14 The efficiency of these simplified bonding systems is still controversial4 and practically all published reports used normal dentine as the bonding substrate. However, most clinical adhesive procedures involve altered forms of dentine, such as sclerotic or caries-affected dentine.16,17 The development of the microtensile test method, that utilizes specimen cross-sectional areas of approximately 1 mm2, has allowed the determination of bond strengths of several bonding systems to cariesaffected dentine.16,18 – 21 Previous studies have reported that the bond strengths of self-conditioning systems seems to be markedly reduced on caries-affected dentine.18,21,22 . However, the adhesive properties of the new, all-in-one systems to caries-affected dentine have not yet been extensively reported. According to this method,16 after conducting the bond strength testing, the quality of the cariesaffected dentine, previously defined by combined criteria of visual examination and staining by
L. Ceballos et al.
a caries detector solution, is confirmed by measuring the Knoop hardness of the substrate. It has been demonstrated that microhardness measurements correlate well with the degree of mineralization,23 with caries-affected dentine being significantly softer than normal dentine.16,18,19,24 – 26 However, this technique is time-consuming and requires the use of a microhardness tester, which is not available in most laboratories. New non-invasive, optical instrument-based techniques for detection and quantification of demineralization have been recently developed.27 One example is the introduction of a device called the DIAGNOdent, based on the fluorescence of tooth structure when teeth are illuminated with a laser light (l ¼ 655 nm). This radiation is absorbed by both inorganic and organic tooth substance28 and by metabolites from oral bacteria.29 Emitted fluorescence is observed through a high-pass barrier filter that discriminates between sound and carious tissue. 30 If there is a significant relationship between Knoop hardness values and the fluorescence values of the DIAGNOdent, the latter device might be more convenient to estimate the quality of the caries-affected dentine in microtensile bond test studies. The aim of the present study was to evaluate the microtensile bond strength of two total-etch and two self-etching adhesive systems to normal and caries-affected dentine, and to compare DIAGNOdent laser fluorescence and Knoop microhardness measurements to quantitate the degree of demineralization of caries-affected dentine following resin-bonding. Two hypotheses were tested. The first hypothesis is that the bond strengths of adhesive systems to caries-affected dentine is lower than to normal dentine. The second is that the more carious the dentine (i.e. the softer or more demineralized the dentine), the lower will be its bond strength.
Materials and methods Specimen preparation Sixteen extracted human molars with coronal dentine caries extending approximately halfway through the dentine were used in this study. All teeth had been stored at 4 8C in physiological saline to which several crystals of thymol were added. Specimens were prepared as described by Nakajima et al.16 to perform microtensile bond strength tests on caries-affected dentine. Occlusal surfaces were ground perpendicular to the long axis of the tooth
Microtensile bond strength of total-etch and self-etching adhesives to caries-affected dentine
with #220 silicon carbide paper under running water (EXAKT- Apparatebau D-2000 Nerderstedt, Germany) to expose a flat surface where the caries lesion was surrounded by normal dentine. To obtain caries-affected dentine, the samples were ground using the combined criteria of visual examination and staining with 0.5% fucsin dye, until relatively hard, non-staining dentine was obtained. Four teeth were randomly allocated to each of the four treatment groups.
Bonding procedure and bond strength testing Four different adhesive systems were applied following the manufacturers’ recommendations (Table 1). Two were total-etch, one-bottle adhesives: Prime & Bond NT (Dentsply DeTrey, Konstanz, Germany) and Scotchbond 1 (3M-ESPE, St Paul, MN, USA); and two more were self-etching
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systems: Clearfil SE Bond (Kuraray Co. Ltd., Osaka, Japan) and the all-in-one adhesive system, Prompt L-Pop (3M-ESPE, St Paul, MN, USA). A composite crown was built up by applying several layers of Tetric Ceram (Ivoclar-Vivadent, Schaan, Liechtenstein) hybrid resin composite to a height of 3 –5 mm. Each increment was cured for 40 s. The teeth were stored in water at 37 8C for 24 h and then vertically serially sectioned perpendicularly to the bonded interface to produce several bonded sections of approximately 0.7 mm thick (Accutom-50, Struers, Copenhagen, Denmark). Each slice was carefully examined to separate those that contained caries-affected dentine from those containing normal dentine, following the visual criterion described above. About three slabs of normal dentine and two to three slabs of cariesaffected dentine were obtained per tooth (10 per group). All the slabs were trimmed to yield an hourglass shape with a 1 mm2 test area that contained either caries-affected or normal dentine.
Table 1 Dentine adhesive systems tested. Adhesive system
Principle ingredients
Mode/steps of application
Prime & Bond NT (Dentsply De Trey GmbH, Konstanz, Germany)
PENTA, UDMA resin, Resin R5-62-1, T-resin, D-resin, nanofiller, initiators, stabilizer, cetylamine hydrofluoride, acetone
Etch for 15 sec with 35% phosphoric acid. Rinse with water for 15 s and remove excess water with 1 s air blast. Apply ample adhesive to saturate moist surface, reapply if necessary. Leave surface undisturbed for 20 s; Remove solvent gently with air for 5 s. Light-cure 10 s
Scotchbond 1 (3M, St Paul, MN, USA)
Bis-GMA, HEMA, dimethacrylates, polyalkenoic acid copolymer, initiator, water, ethanol
Etch 15 s with 35% phosphoric acid. Rinse with water for 10 s. Apply two consecutive coats of the adhesive to moist dentine with a saturated brush tip. Dry gently for 2–5 sec; Light cure 10 s
Clearfil SE Bond (Kuraray Co, Osaka, Japan)
Primer. 10-methacryloyloxydecyl dihydrogen phosphate; 2-hydroxyethyl methacrylate; hydrophilic dimethacrylate; dl-camphorquinone; N,N-diethanol-p-toluidine; water Adhesive. 10-methacryloxydecyl dihydrogen phosphate; Bis-phenol A diglycidylmethacrylate; 2-hydroxyethyl methacrylate; hydrophobic dimethacrylate; di-camphorquinone; N,N-diethanol-p-toluidine; silanated colloidal silica
Apply Primer for 20 s; Evaporate water with mild air; Apply adhesive, Gentle air stream. Light cure 10 s
Prompt L-Pop (3M-ESPE, St Paul, MN, USA)
Water, methacrylated phosphoric acid esters, phosphine oxide, stabilizer, zinc fluoride complex, parabenes
Apply with scrubbing for 15 s. Gently air dry, Light cure 10 s
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Samples were attached to a Bencor Multi-T testing apparatus with a cyanoacrylate adhesive (Zapit, DVA, Anaheim, CA, USA) and subjected to tensile stress in an universal testing machine (Model 4411, Instron Corp., Canton, MA) at a cross-head speed of 1 mm/min until failure. The bond strengths were expressed in MPa after measuring the cross-sectional area at the site of fracture with a digital caliper (Mitutoyo, Tokyo, Japan).
DIAGNOdent laser and microhardness measurements: After performing the microtensile test, the lateral aspect (i.e. the non-bonded surface) of each dentine-half of the fractured specimens was highly polished with #4000 silicon paper in a circular grinding machine (EXAKT-Apparatebau D-2000 Nerderstedt, Germany) to permit subsequent microhardness measurements. Prior to microhardness measurements, the degree of demineralization of the specimen was measured with the laser fluorescence system (DIAGNOdent, KaVo, Biberach, Germany). Before the start of the measurements, the laser was calibrated against a porcelain standard as indicated in the manufacturer’s instructions. The measurements were performed using the smallest conical tip (1.2 mm diameter) that was held against the specimen at right angles to the surface. The maximum fluorescence reading was recorded just beneath the fractured site. Progression of the carious process is reflected in an increase in the amount of fluorescence.31 The numerical range of the DIAGNOdent instrument is from 0 to 100. Finally, Knoop microhardness measurements were done 50 mm below the adhesive/dentine interface using an Instron Wolpert hardness tester (V-testor 4021, Instron Wolpert GmbH, Ludwgshafen, Germany), under a load of 30 g and a duration of 30 s. During the test, dentine desiccation was
avoided.32 Each specimen received approximately five indentations and were averaged.
Statistical analysis A two-way ANOVA was performed to evaluate the effect of the adhesive and the type of dentine tested, and their interactions, on microtensile bond strength. Statistical significance was set in advance at the 0.05 probability level. Multiple post-hoc comparisons were done using Student-Newman – Keuls test. Comparison of the values obtained by either laser fluorescence or microhardness tests, on normal dentine and caries-affected dentine were performed by Student’s t test. The correlation between laser fluorescence values and Knoop microhardness numbers, as well as the correlations between microtensile bond strength and fluorescence values and between bond strength and microhardness measurements were analyzed by calculating Pearson’s correlation coefficient. All data were analyzed by means of SPSS 10.0 for Windows software (SPSS Inc., Chicago, IL, USA).
Results The results of microtensile bond strength test are shown in Table 2. Two-way ANOVA revealed a significant influence of both the adhesive systems tested ðF ¼ 40:857; p , 0:0001Þ and the type of dentine ðF ¼ 22:088; p , 0:0001Þ on microtensile bond strength values. However, the interaction of these two factors was not statistically significant (F ¼ 1.282; p ¼ 0.287). ANOVA analysis showed significant differences among the adhesive systems evaluated for normal ðF ¼ 21:892; p , 0:0001Þ and caries-affected dentine ðF ¼ 23:701; p , 0:0001Þ: In normal dentine, Prime & Bond NT attained the highest microtensile bond strength. Intermediate, statistically similar bond strengths were obtained in normal
Table 2 Mean microtensile bond strengths (MPa) and standard deviation (SD) to normal and caries-affected dentine. Adhesive system
Normal dentine
Sig.
Caries-affected dentine
Prime & Bond NT Scotchbond 1 Clearfil SE Bond Prompt L Pop
56.3 (11.1) a 43.9 (11.4) b 35.5 (11.6) b 18.2 (9.6) c
,0.05a NS ,0.05a NS
41.3 (10.7) A 36.3 (12.2) A 21.5 (5.5) B 13.4 (1.9) C
For each column, means designated by the same letter are not significantly different ðp . 0:05Þ: NS: not significantly different. Values are mean ^ SD in MPa. a Shows statistical differences between normal and caries-affected dentine ðp , 0:05Þ:
Microtensile bond strength of total-etch and self-etching adhesives to caries-affected dentine
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Table 3 Failure modes for the adhesives in normal and caries-affected dentin. Adhesive system
Adhesive
Cohesive in dentine
Cohesive in composite
10% 33.3%
10% 33.3%
80% 33.3%
25% 71.4%
12.5% 14.3%
62.5% 14.3%
46.7% 63.6%
13.3% 36.4%
13.3% 0
100% 90%
0 10%
0 0
Prime & Bond NT Normal dentine Caries-affected dentine Scotchbond 1 Normal dentine Caries-affected dentine Clearfil SE Bond Normal dentine Caries-affected dentine Prompt L-Pop Normal dentine Caries-affected dentine
dentine with Scotchbond1 and Clearfil SE Bond, while Prompt L-Pop showed the lowest strengths (Table 2). In caries-affected dentine, the totaletch adhesive systems, Prime & Bond NT and Scotchbond 1, yielded statistically higher ðp , 0:05Þ bond strengths than Clearfil SE Bond. Significantly lower ðp , 0:05Þ strengths were obtained with Prompt L-Pop. In normal dentine, the major mode of failure in specimens showing low bond strengths was adhesive failure, while cohesive fractures in dentine or composite were seen at higher bond strengths (Table 3). In caries-affected dentine, adhesive and cohesive failures in dentine were seen in specimens showing low bond strengths, while cohesive failures in resin composite were seen more frequently in specimens with high bond strengths. All the adhesives tested showed higher strengths in normal dentine than in caries-affected, but these differences were only significant for Prime & Bond NT and Clearfil SE Bond. The results of laser fluorescence and Knoop hardness numbers for normal and caries-affected dentine are shown in Table 4. Significantly lower fluorescent values were obtained for normal dentine ðt : 19:289; p , 0:0001Þ; compared with the values recorded in caries-affected dentine. Mean hardness results for normal dentine were statistically significant higher ðt : 17:495; p , 0:0001Þ than those of caries-affected dentine. Comparison between laser fluorescence values recorded and Knoop hardness numbers (KHN) of all of the specimens (Fig. 1) revealed a high correlation ðr ¼ 20:85; p , 0:0001Þ: However, the correlation between all resindentine bond strengths and fluorescence values
was low (r ¼ 20:334; data not shown) but was significant ðp , 0:01Þ: Similarly, the correlation between microtensile bond strength and KH values, while significant ðp , 0:001Þ; was low (r ¼ 0:412; data not shown). These correlations were done excluding the specimens bonded with Prompt LPop, as the bond strengths attained with this adhesive were so low. Thus, the potential utility of using KHN or fluorescence values for predicting bond strength using all combined types of dentine is poor. If the correlation of bond strength and KHN is limited to caries-affected specimens, then the correlation becomes even weaker ðr ¼ 0:119; p ¼ 0:554Þ: Similarly, the correlation between bond strengths of caries-affected dentine and fluorescence values was insignificant (r ¼ 20:023; p ¼ 0:90 data not shown). When these correlations were done for each adhesive separately, they were not significant for Scotchbond 1 or for Prompt L-P. However, the correlation between bond strength and KH for Prime & Bond NT was moderate ðr ¼ 0:548; p , 0:05Þ and the same was observed for Clearfil SE Bond ðr ¼ 0:472; p , 0:01Þ: Similarly, the correlations between bond strength and fluorescence Table 4 DIAGNOdent values and Knoop microhardness numbers obtained in normal and caries-affected dentine. DIAGNOdent values
Knoop microhardness number
Normal dentine 8.5 (12.6) a 74.6 (9.1) A Caries-affected dentine 61.6 (20.9) b 33.9 (6.7) B For each column, values with different letters indicate statistically significant difference ðp , 0:05Þ:
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Figure 1
L. Ceballos et al.
Correlation between Knoop hardness values and DIAGNOdent fluorescent values on the same specimens.
values for Prime & Bond NT and Clearfil SE Bond were also relatively low, but were significant (r ¼ 20:49; p , 0:05 and r ¼ 20:514; p , 0:01; respectively).
Discussion The results of the present study show that bond strength to normal and caries-affected dentine is dependent on the adhesive system used. In normal dentine, the total-etch adhesives tended to produce higher bond strength values than the selfetching adhesives, confirming the observations of Inoue et al.33 Prime & Bond NT exhibited the highest bond strengths compared with the other total-etch adhesive, Scotchbond 1. Prime and Bond is filled with nanoparticles that may help to establish a thicker more uniform resin film thickness that stabilizes the hybrid layer,14 although this effect is still somewhat controversial.34,35 The lowest microtensile bond strengths were attained with Prompt L-Pop, that exclusively yielded adhesive failures. These results are in agreement with previous reports that this product produces inconsistent results.11,14,36,37 Prompt LPop produces an etching pattern similar to phosphoric acid, being classified as a strong self-etching adhesive, in contrast with the mild etching ability of Clearfil SE Bond.14,15 Both bonding systems form authentic hybrid layers. However, Prompt L-Pop dissolves the smear layer and plugs while Clearfil SE
Bond preserves and incorporates them into the hybridized complex.15 This etching aggressiveness is unrelated to the bond strengths attained.11 One explanation may be the formation of dry spots where the low viscosity Prompt L-Pop had spread so thin that it may not be properly polymerized.36,37 Higher strengths have been reported for this adhesive when it is applied in multiple coats38 or is experimentally filled.36,37 In caries-affected dentine, the total etch adhesives performed better than the self-etching systems. Caries-affected dentine contains dentinal tubules that are filled with acid-resistant whitlockite minerals25,39,40 – 42 that interfere the infiltration of adhesive resins and the formation of resin tags.42,43 The application of 32 – 37% phosphoric acid seems to solubilize the intratubular mineral deposits in caries-affected dentine19 – 21 better than weaker acids, thereby contributing to better resin retention.3 It may be that Clearfil SE Bond is not acidic enough to dissolve the mineral casts. Moreover, the smear layer formed on caries-affected dentine includes acid resistant crystals that may hamper the diffusion of the self-etching primer into the underlying intact dentine.21 However, since the presence of these deposits in dentinal tubules has been shown to reduce dentine permeability44 to near zero and hence constitutes a protective barrier for the pulp tissue by reducing the ingress of bacteria, and/or bacterial products,40,42 it should be retained in conservative cavity preparations,42 as it is generally not infected and can remineralize.45
Microtensile bond strength of total-etch and self-etching adhesives to caries-affected dentine
The low bond strengths produced by Prompt LPop may not be related to its etching aggressiveness but to its degree of conversion. All-in-one systems do not yet possess all the requirements to provide optimal adhesion to tooth structure.11 Modifications in its formulation or mode of application are needed.36 – 38 It is noteworthy that Prompt L-Pop has been ported to be relatively ineffective in retention of resin composite restorations to noncarious cervical sites in a clinical trial.46 Caries-affected intertubular dentine is partially demineralized due to the caries process,25,41,44 and is more porous, allowing deeper penetration of monomers.22 This fact is reflected in the establishment of thicker hybrid layers.16,18 – 22 However, the thickness of the hybrid layer is unrelated to bond strengths in dentine.16,18 – 22 Even when the adhesive systems are capable of infiltrating deep into intertubular dentine, there would be always a porous and demineralized underlying zone that was not infiltrated.42 Moreover, caries-affected dentine presents lower nanomechanical properties44 and a lower cohesive strength22 (Fuentes, unpublished observations) as they are dependent on the properties of intertubular dentine.47 Thus, the weakest link in the resin-caries-affected dentine assembly may be the cohesive strength of caries-affected dentine. Knoop hardness testing revealed the cariesaffected dentine to be about half as hard as normal dentine, in agreement with previously reported results.16,18 – 20,25 This relative softness of caries-affected dentine is due to the partial demineralization of the intertubular dentine even though tubules become filled with mineral.16,25,48 In the present study, lower Knoop hardness values in caries-affected dentine were strongly correlated with higher laser fluorescence values (Fig. 1), confirming the results of Banerjee et al.49 Therefore, these results reveal the capacity of the laser fluorescence device to estimate the quality of caries-affected dentine relative to normal dentine. Its non-destructive nature, in addition to its repeatability and validity have been claimed to make it an useful tool in a clinical and laboratory situation.30,50 – 53 The mechanism underlying the enhanced fluorescence in the presence of caries has not been fully clarified.54 Unlike Knoop hardness,23 no relationship between autofluorescence and the mineral content of caries lesions has been found. This may be due to the contribution of exogenous fluorescent molecules imported during the carious process.55 The DIAGNOdent instructions describe a scale which correlates the numerical values with histological findings, and provide treatment recommendations. However, this scale makes no
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distinction between acute or active carious lesions versus chronic or arrested lesions. Moreover, it has been reported that high laser fluorescence readings may also be obtained on dentine surfaces which are stained.51,56 It must be borne in mind that caries-affected dentine presents a glassy, dark yellow or slightly brown appearance. This may produce higher DIAGNOdent scores49,56 than less colored caries lesions with the same degree of demineralization. This potential source of error of DIAGNOdent has been previously be pointed out to be a distinct disadvantage,57 compared with the visual system, as laser fluorescence system can only detect carious lesions but cannot judge their activity.51 In caries-affected dentine, the relationship between bond strength and hardness or fluorescence values were not significant when all the specimens were considered. Even using the smallest laser probe, the DIAGNOdent sampled an area of about 1 mm2 or a volume **(for a 0.7 mm thick specimen) of 0.7 mm3 that was located subjacent to the bonded surface area. That is, it only gives an average fluorescence value of dentine at some distance below the bonded surface. Fig. 1 shows that the fluorescence values varied from 35 to 98 in cariesaffected dentine, yet the resin-dentine bond strengths did not vary as much as the fluorescence values (data not shown). Although the KH numbers were also measured below the bonded surface, it was only 50 mm below, instead of 500 mm or more as was the case with the DIAGNOdent. The Knoop hardness measurements are made with a large indenter that crushes both intertubular and peritubular dentine. That is, it measures an average hardness. In caries-affected dentine, the tubules are filled with mineral crystals that prevent resin tag formation and make these tubules harder than fluid-filled tubules.44 Dentine bond strengths under these conditions are probably due to hybridization of intertubular dentine.58 Better correlations between bond strengths and hardness of caries-affected dentine may require use of nanohardness techniques.4,43
Conclusions All the adhesives evaluated in the present study showed higher strengths to normal dentine than in caries-affected, but these differences were only significant for Prime & Bond NT and Clearfil SE Bond. The occlusion of dentinal tubules by the acidresistant mineral deposits that interferes with
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the formation of retentive resin tags and the intrinsic weakness of caries-affected dentine may have contributed these results. In caries-affected dentine, total-etch adhesives performed better than self-etching systems. Higher laser fluorescence values were strongly correlated with lower Knoop hardness values in caries-affected dentine. Thus, although both the DIAGNOdent and KH values correlate well to each other and can measure differences in the quality of dentine, the regions that they sample may be too far removed from the resin-dentine interface to permit high correlations with resin-dentine bond strengths.
L. Ceballos et al.
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Acknowledgements This research project was supported by grant DEO14911 from the National Institute of Dental and Craniofacial Research, by grant MAT 2001-2843-CO2; RED CYCTED VIII.J. from the CICYT, Spain. The authors wish to thank Gertrudis Go ´mez-Villaescusa for her help with specimen preparation.
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References 1. Nakabayashi N, Kojima K, Masuhara E. The promotion of adhesion by infiltration of monomers into tooth substrates. J Biomed Mater Res 1982;16:265—73. 2. Van Meerbeek B, Dhem A, Goret-Nicaise M, Braem M, Lambrechts P, Vanherele G. Comparative SEM and TEM examination of the ultrastructure of the resin-dentin interdiffusion zone. J Dental Res 1993;72:495—501. 3. Pashley DH, Carvalho RM. Dentine permeability and dentine adhesion. J Dent 1997;25:355—72. 4. Van Meerbeek B, Perdiga ˜o J, Lambrechts P, Vanherle G. The clinical performance of adhesives. J Dent 1998;26:1—20. 5. Li H, Burrow MF, Tyas MJ. Nanoleakage patterns of four dentin bonding systems. Dent Mater 2000;16:48—56. 6. Gwinnett AJ. Moist versus dry dentin: Its effect on shear bond strength. Am J Dent 1992;5:127—9. 7. Kanka J. Resin bonding to wet substrate. I. Bonding to dentin. Quintessence Int 1992;5:127—9. 8. Tay FR, Gwinnett JA, Wei SHY. The overwet phenomenon: a transmission electron microscopic study of surface moisture in the acid-conditioned, resin—dentin interface. Am J Dent 1996;9:161—6. 9. Van Meerbeek B, Yoshida Y, Lambrechts P, Duke ES, Eick JD, Robinson SJ. A TEM study of two water-based adhesive systems bonded to dry and wet dentin. J Dent Res 1998;77: 50—9. 10. Miyazaki M, Onose H, Moore BK. Effect of operator variability on dentin bond strength of two-step bonding systems. Am J Dent 2000;13:101—4. 11. Bouillaguet S, Gysi P, Wataha JC, Ciucchi B, Cattani M, Godin CH, Meyer JM. Bond strength of composite to dentin using
22.
23.
24.
25.
26.
27.
28. 29. 30.
31.
32.
conventional, one-step, and self-etching adhesive systems. J Dent Res 2001;29:55—61. Hayakawa T, Nemoto K, Horie K. Adhesion of composite to polished dentin retaining its smear layer. Dent Mater 1995; 11:218—22. Nakabayahi N, Saimi Y. Bonding to intact dentin. J Dent Res 1996;75:1706—15. Inoue S, Van Meerbeek B, Vargas M, Yoshida Y, Lambrechts P, Vanherle G. Adhesion mechanism of self-etching adhesives. In: Tagami J, Toledano M, Prati C, et al., editors. Advanced adhesive dentistry. Cirimido, Italia; 2000. p. 131—48. Tay FR, Pashley DH. Aggressiveness of contemporary selfetching systems. I. Depth of penetration beyond dentin smear layers. Dent Mater 2001;17:296—308. Nakajima M, Sano H, Burrow MF, Yoshiyama M, Ebisu S, Ciucchi B, Russell CM, Pashley DH. Tensile bond strength and SEM evaluation of caries-affected dentin using dentin adhesives. J Dent Res 1995;74:1679—88. Marshall GW, Marshall SJ, Kinney JH, Balooch M. The dentin substrate: structure and properties related to bonding. J Dent 1997;25:441—58. Nakajima M, Ogata M, Tagami J, Sano H, Pashley DH. Bonding to caries-affected dentin using self-etching primers. Am J Dent 1999;12:309—14. Nakajima M, Sano H, Zheng L, Tagami J, Pashley DH. Effect of moist vs dry bonding to normal vs caries-affected dentin with scotchbond multi-purpose plus. J Dent Res 1999;78: 1298—303. Nakajima M, Sano H, Urabe I, Tagami J, Pashley DH. Bond strengths of single-bottle dentin adhesives to cariesaffected dentin. Oper Dent 2000;25:2—10. Yoshiyama M, Urayama A, Kimochi T, Motsuo T, Pashley DH. Comparison of conventional vs. self-etching adhesive bonds to caries-affected dentin. Oper Dent 2000;25:163—9. Yoshiyama M, Tay FR, Doi J, Nishitani Y, Yamada T, Itou K, Carvalho RM, Nakajima M, Pashley DH. Bonding of selfetching and total-etch adhesives to carious dentin. J Dent Res 2000;81:556—60. Panighi M, G’Sell C. Influence of calcium concentration on the dentin wettability by an adhesive. J Biomed Mater Res 1992;26:1081—9. Fusayama T, Okuse K, Hosoda H. Relationship between hardness, discoloration and microbial invasion in carious dentin. J Dent Res 1966;45:1033—46. Ogawa K, Yamashita Y, Ichijo T, Fusayama T. The ultrastructure and hardness of the transparent layer of human carious dentin. J Dent Res 1983;62:7—10. Hosoya Y, Marshall SJ, Watanabe LG, Marshall GW. Microhardness of carious deciduous dentin. Oper Dent 2000;25: 81—9. Hafstro ¨m-Bjo ¨rkman U, Sundstro ¨m F, de Josselin de Jong E, Angmar-Ma ˚nsson B. Comparison of laser fluorescence and longitudinal microradiography for quantitative assessment of in vitro enamel caries. Caries Res 1999;26:241—7. Hibst R, Gall R. Development of a diode laser-based fluorescence caries detector. Caries Res 1998;32:294. Hibst R, Paulus R. Molecular basis of red excited caries fluorescence. Caries Res 2000;34:323. Ando M, Hall AF, Eckert GJ, Schemehorn Br, Amaloui M, Stookey GK. Relative ability of laser fluorescence techniques to quantitate early mineral loss in vitro. Caries Res 1997;31: 125—31. Shi XQ, Welander U, Angmar-Ma ˚nsson. Occlusal caries detection with KaVo DIAGNOdent and radiography: an in vitro comparison. Caries Res 2000;34:151—8. Xu HHK, Smith DT, Jahanmir S, Romberg E, Kelly JR, Thompson VP, Rekow ED. Indentation damage and
Microtensile bond strength of total-etch and self-etching adhesives to caries-affected dentine
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
mechanical properties of human enamel and dentin. J Dent Res 1998;77:472—80. Inoue S, Vargas MA, Abe Y, Yoshida Y, Lambrechts P, Vanherle G, Sano H, Van Meerbeek B. Microtensile bond strength of eleven contemporary adhesives to dentin. J Adhes Dent 2001;3:237—45. Braga RR, Cesar PF, Gonzaga CC. Tensile bond strength of filled and unfilled adhesives to dentin. Am J Dent 2001;13: 73—6. Nunes FM, Swift EJ, Perdiga ˜o J. Effects of adhesive composition on microtensile bond strength to human dentin. Am J Dent 2001;14:340—3. Perdiga ˜o J, Frankenberger R, Rosa BT, Breschi L. New trends in dentin/enamel adhesion. Am J Dent 2000;13: 25D—30D. Frankenberger R, Perdiga ˜o J, Rosa BT, Lopes M. No-bottle vs. multi-bottle dentin adhesives-a microtensile bond strength and morphological study. Dent Mater 2001;17: 373—80. Pashley EL, Agee KA, Pashley DH, Tay FR. Effects of one versus two applications of an unfilled, all-in-one adhesive on dentine bonding. J Dent 2002;30:83—90. Frank RM, Voegel JC. Ultrastructure of the human odontoblast process and its mineralisation during dental caries. Caries Res 1980;14:367—80. Pashley EL, Talman R, Horner JA, Pashley DH. Permeability of normal versus carious dentin. Endod Dent Traumatol 1991;7:207—11. Fusayama T. A simple pain-free adhesive restorative by system by minimal reduction and total etching. Tokyo: Ishiyaku EuroAmerica; 1993. Marshall GW, Chang YJ, Gansky SA, Marshall SJ. Demineralization of caries-affected transparent dentin by citric acid: an atomic force microscopy study. Dent Mater 2001;17: 45—52. Marshall GW, Habelitz S, Gallagher R, Balooch M, Blooch G, Marshall SJ. Nanomechanical properties of hydrated carious human dentin. J Dent Res 2001;80:1768—71. Tagami J, Hosoda H, Burrow MF, Nakajima M. Effect of aging and caries on dentin permeability. Proc Finnish Dent Soc 1992;88(Suppl 1):149—54. Ohgushi K, Fusayama T. Electron microscopic structure of the two layers of carious dentin. J Dent Res 1975;54: 1019—26.
477
46. Brackett WW, Covey DA, St Germain HA. One-year clinical performance of a self-etching adhesive in Class V resin composites cured by two methods. Oper Dent 2002;27: 218—22. 47. Kinney JH, Balooch M, Marshall GW, Marshall SJ. A micromechanics model of the elastic properties of human dentine. Arch Oral Biol 1999;44:813—22. 48. Shimizu C, Yamashita Y, Ichijo T, et al. Carious change of dentin observed on Longspan ultrathin sections. J Dent Res 1981;60:1826—31. 49. Banerjee A, Sherriff M, Kidd EAM, et al. A confocal microscopic study relating the autofluorescence of carious dentine to its microhardness. Br Dent J 1999;187:206—10. 50. De Josselin de Jong E, Sundstro ¨m F, Westerling H, Tranaeus S, ten Bosch JT, Angmar-Ma ˚nsson B. A new method for in vivo quantification of changes in initial enamel caries with laser fluorescence. Caries Res 1995;29:2—7. 51. Sheeny EC, Brailsford SR, Kidd EAM, et al. Comparison between visual examination and a laser fluorescence system for in vivo diagnosis of occlusal caries. Caries Res 2001;35: 421—6. 52. Lussi A, Megert B, Longbotton C, Beighton D, Zoitopoulos L. Clinical performance of a laser fluorescence device for detection of occlusal caries lesions. Eur J Oral Sci 2001;109: 14—9. 53. Alwas-Danowska HM, Plasschaert AJM, Suliborski S, et al. Reliability and validity issues of laser fluorescence measurements in occlusal caries diagnosis. J Dent 2002;30:129—34. 54. Shi XQ, Tranæus A, Angmar-Ma ˚nsson B. Comparison of QLF and DIAGNOdent for quantification of smooth surface caries. Caries Res 2001;35:21—6. 55. Banerjee A, Boyde A. Autofluorescence and mineral content of carious dentine: Scanning optical and backscattered electron microscopic studies. Caries Res 1998;32:219—26. 56. Welsh GA, Hall AF, Hannah AJ, Foye RH. Variation in DIAGNOdent measurements of stained artificial caries lesions. Caries Res 2000;34:324. 57. Lussi A, Imwinkelried S, Pitts NB, Longbottom C, Reich E, Performance and reproducibility of a laser fluorescence system for detection of occlusal caries in vitro. Caries Res 1999;33:261—6. 58. Pashley DH, Ciucchi B, Sano H, Carvalho RM, Russell CM. Bond strength versus dentine structure: a modelling approach. Arch Oral Biol 1995;40:1109—18.