Dent Mater 8:229-233, July, 1992

Dentin thickness, hardness, and Ca-concentration v$ bond strength of dentin adhesives L. Perinka ~, H. Sano 2, and H. Hosoda 2 i Department of Operative Dentistry, Charles University in Prague 1st Stomatological Clinic, Prague, Czechoslovakia 2Department of Operative Dentistry, Tokyo Medical and Dental University, Tokyo, Japan

Abstract. The relationship between the tensile bond strength experimental system was comprised of a conditioner contain(TBS) and three dentin characteristics: remaining dentin thickness ing an aqueous solution of 10% citric acid and 20% calcium (RDT), Ca-concentration, and hardness, were investigated. Sixty- chloride (10-20 Ca solution), and a primer consisting of 3% Ntwo extracted bovine incisors, divided into four groups, were methacryloyl 5-aminosalicylic acid in ethanol (3% NMSA) prepared using 600-grit SiC paper to create flat dentinal surfaces. (Hosoda etal., 1989). The materials tested in this study consisted of three commercially AdhesionTest: Sixty-two bovine lower permanent incisors available and one experimental dentin bonding systems. The TBS were used for the adhesion test. The teeth were stored at-24°C andmodesoffailureweredeterminedafterstoragefor24hin37°C and used within two weeks of the extraction. The labial water. Then RDT, Ca-concentration, and hardness were mea- surface of each tooth was ground using 600-grit SiC paper sured. Data were statistically compared with TBS of each group, under running water, removing the enamel to obtain a flat The mean bond strength of the commercial materials ranged from dentin surface for bonding. The area of adhesion was regu2.5+0.9 MPa to 7.7+2.8 M Pa. Correlations with Ca-concentration lated by placing vinyl tape with a hole 5.5 mm in diameter on and RDT varied, depending on the product. The bond strength of the dentin surface. In the case of the three commercial the experimental material was 9.2+4.4 MPa and significantly bonding systems (Groups 1, 2, and 3), the demarcated dentin correlated with RDT and hardness. With twoofthedentinbonding surfaces were conditioned and bonded according to each agents, specimens showed a high number of cohesive fractures manufacturer's instructions as follows: in dentin, 40% to 82%. It was concluded that the variability of TBS Group1: The dentin surface was etched using 37% phosphoric was influenced by dentinal characteristics in three of the four acid-gel (K-etchant) for 40 s, rinsed with water for 15 s, and materials tested, then air-dried for 10 s. Clearfil New Bond, chemical-cured bonding resin, was then applied to the surface and air-blown INTRODUCTION to evaporate the alcohol solvent followed by Clearfil FII A number of new dentin bonding systems has been developed composite. and marketed. These bonding systems were introduced to Group 2: The same etching procedure was followed as in increase the bond strength of composites to dentin, as well as Group 1. Clearfil Photo Bond was applied and the alcohol produce leak-free restorations. Bond strengths of these sys- solvent was evaporated by a gentle air stream for 10 s. The temshavebeeninvestigatedintensileorshearmodesinvitro, bonding agent was then light-cured (Quick Light, Kuraray The wide standard deviations observed in these tests might Co., Ltd.) for 30 s. Subsequently, Photo Clearfil Bright have been caused by differences in the substrate sites, composite was placed around 0.5 mm in thickness and irradiIt has been reported (Nakamichi et al., 1983; Nakamichi, ated for 60 s. 1984; Causton, 1984) that significant correlations exist be- Group 3: Scotchprep primer was applied to the dentin surface tween tensile bond strength (TBS) and both Ca-concentration for 60 s, during which it was constantly agitated. The primer and dentin depth. The bond strength was shown to be two was then dried with an air syringe. Scotchbond 2 adhesive was times greater in the more superficial dentinal layers when spread onto the primed surface, air-thinned and light-cured compared with the deeper portions. It has been reported for 30 s. Subsequently, Silux composite was placed as men(Suzuki and Finger, 1988) that the TBS is dependent upon the tioned above and irradiated for 60 s. percentage of total dentin thickness. However, it is still Group 4: In the case of the experimentalbonding system, the unclear whether the TBS is dependent upon the absolute dentin surface was conditioned using 10-20 Ca-solution for depth of the remaining dentin and dentinal hardness. 40 s, washed with water and air-dried for 10 s. Subsequently, The aim of this study was to investigate the relationship 3% NMSA solution was applied to the dentin surface for 30 s between three selected dentinal characteristics of thickness, and then air-dried. After this, Clearfil Photo Bond was placed hardness, Ca-concentration, and the TBS with bovine dentin, and left for 30 s prior to drying with compressed air and then using four dentin bonding systems, light-cured for 30 s. Finally, Photo Clearfil Bright composite was placed onto the bonded surface and irradiated for 60 s. MATERIALS AND METHODS Stainless steel rods (6.5 mm diameter) were attached Three commercially available and one experimental dentin perpendicularly to the resin surfaces using Panavia EX bonding systems were employed as indicated in Table 1. The (Kuraray Co., Ltd.) to facilitate the adhesion test. The bonded Dental Materials~July 1992 229

TABLE 1: MATERIALSTESTED

Group 1

Material K-etchant Clearfil Newbond

Manufacturer Kuraray Co., Ltd., Osaka, Japan

Clearfil FII 2

K-etchant

Kuraray Co., Ltd.

Clearfil Photo Bond 3

Photo Clearfil Bright Scotchprep Scotchbond2 Silux

4

10-20 Ca

3% N-methacryloyl 5 aminosalicylic acid in ethanol (NMSA)

3M Dental Products Division, St Paul, MN USA Kuraray C o . , Ltd.

Clearfil Photo Bond Photo Clearfil Bright

Batch No. EG 0141 FC 1191, FU 1291 NC 556, NU 656 EG 0142 107, 207 01-1001 8AC3 28AB 5N2 experimental experimental

107, 207 01-1001

assemblies were stored in water for 24 h at 37°C prior to testingthe TBSusingauniversaltestingmachine (Autograph AG-500B, Shimadzu, Kyoto, Japan) at a cross-head speed of 2 mm/min. Mean values of the TBS determined were statistically analyzed by Duncan's new m u l t i p l e range test at the 99% confidence ]eve]. After testing, the specimens were visually examined to determine the modes of fracture. To investigate the bond failures more closely, two specimens from each group were randomly selected for SEM examination. CorrelationAnalysis: In order to evaluate the relationship between the TBS and the three dentin characteristics, the debonded specimens were trimmed, embedded in epoxy resin and cut perpendicularly to the bonded surface using a diamond saw microtome (Leitz 1600 Saw Microtome, Ernst Leitz, GMBH, Wetzlar, Germany). The cut surfaces were then polished with diamond pastes. The polished dentin was scanned vertically from the center of bonded area toward the pulp chamber. Using a microhardness tester (Akashi MVKE Hardness Tester, Tokyo, Japan) loading at 50 g for 15 s (Fig. 1), the Knoop hardness measurements were made starting 50 pm just below the bonded surface and then at 50 pm intervals. The average ofKHN was calculated from the first five measurements. The remaining dentin thickness (RDT) was then measured by a micrometer attached to the hardness tester. For measuring Ca-concentration, the same specimensurfaceswerevapor-coatedwithAuandthenscanned by using an x-ray energy dispersive analyzer (JXA 840, JEOL Ltd., Tokyo, Japan), which recorded the percentage of dentinal calcium compared against a standard concentration crystal ofsintered hydroxyapatite. The calcium concentration was determined at intervals of 25 pm along the same line as the hardness measurements. The average Ca-concentration was then calculated from the first 10 results obtained. The relations between the TBS and the three dentin characteristics were evaluated using first order regression analysis. 230

Perinka et al./Dentin characteristics vs bond strength

TABLE 2: DENTIN CHARACTERISTICS OF EACH GROUP RDT (mm) KHN Ca-Concentration (%) Group mean (SD) 1 1.86 (0.40) 52.3(8.11) 65.8(2.07) 2 3

1.65 (0.42) 1.64 (0.27)

52.8(4.99) 48.5(4.02)

65.3(1.66) 64.3(2.74)

4 1.61 (0.40) 52.1(6.03) 61.0(7.65) Mean values connected by the vertical line differ significantly. TABLE 3: TENSILE BOND STRENGTH (MPa) AND RATE OF COHESIVE FAILURE IN DENTIN TBS (MPa) Group Mean(SD) Minimum Maximum CohesiveFailure 1 2

2.5 (0.9) 5.2 (2.1)

1.1 2.8

4.5 10.7

0/15 (0%) 0/15 (0%)

3 7.7 (2.8) 3.6 12.1 6/15 (40%) 4 9.2 (4.4) 3.1 19.1 14/17 (82%) Mean values connected by the vertical line do not differ significantly.

TABLE 4: CORRELATIONBETWEEN TBS AND THREE DENTINAL CHARACTERISTICS Group RDT

Ca-ConcentrationHardness

1 2

Not Significant 0.61 (p

Dentin thickness, hardness, and Ca-concentration vs bond strength of dentin adhesives.

The relationship between the tensile bond strength (TBS) and three dentin characteristics: remaining dentin thickness (RDT), Ca-concentration, and har...
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