The Effect of Dentin-Cleaning Agents on Resin Cement Bond Strength to Dentin
Duygu Saraç, DDS, PhD,
Bilinc Bulucu, DDS, PhD,
Y. Sinasi Saraç, DDS, PhD and
Safak Kulunk, DDS, PhD
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ABSTRACT
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Background. Provisional cement remnants on dentin affect the bond strength of resin cements to dentin. The authors investigated the effects of dentin-cleaning agents and etching systems on the bond strength of adhesive resin cement.
Methods. The authors removed the provisional cement from the dentin surfaces of the specimens and then cleaned the surfaces with the dentin-cleaning agents Sikko Tim (VOCO GmbH, Cuxhaven, Germany), Cavity Cleanser (Bisco, Schaumburg, Ill.) or Consepsis Scrub (Ultradent, South Jordan, Utah). They used adhesive resin cement after applying the different etching adhesive systems. Then they examined the dentin surfaces by using scanning electron microscopy.
Results. The authors analyzed data by means of a two-way analysis of variance with Tukey honestly significant difference tests (
= .05). They found that specimens cleaned with Sikko Tim and Consepsis Scrub had higher shear bond strength values than did those in the no-treatment control group or the group cleaned with Cavity Cleanser. The specimens treated with the total-etching adhesive system had higher shear bond strength than did those treated with the self-etching adhesive systems.
Conclusions. Sikko Tim and Consepsis Scrub were effective in removing provisional cement. Adhesive resin cement showed higher bond strength when used in conjunction with the total-etching adhesive system.
Clinical Implications. The use of an effective dentin cleaner before cementation with resin cement can increase bond strength.
Key Words: Dentin-cleaning agent; adhesive system; provisional cement; shear bond strengthAbbreviations: HEMA: Hydroxyethyl methacrylate. • SEM: Scanning electron microscope. • ZOE: Zinc oxide–eugenol.
Application of tooth-colored materials to anterior and posterior teeth has increased because of improvements in the bonding characteristics of luting systems, particularly for bonding to dentin.1 The integrity of the bond between dentin and resin adhesive systems is key to improving the success of restorations.2 The performance of final cements and the longevity of a restoration are affected by the preparation’s coarseness, and the type of provisional cement and dentin-cleaning agent used.3–5 The remnants of provisional restorative materials, debris and smear layer may have adverse effects on the bond strength between the dentin and resin adhesive systems.2,5,6 Although materials containing zinc oxide–eugenol (ZOE) are used extensively in dentistry, the results of studies have indicated that eugenol-containing materials have adverse effects including changes in the wettability and reactivity of the dentin and can alter resin cement adhesion and reduce bond strengths.2,7–9 Furthermore, remnants of ZOE on the surface may interact with the polymerization of resin-based composites.2,10–13
Eugenol is a phenolic compound that is insoluble in water.8 Phenolic hydrogen inhibits resin polymerization, reduces the microhardness, increases the surface roughness and decreases the color stability of resin composites polymerized on or near eugenol-containing cements.8,14 Although the results of some studies have indicated that the presence of eugenol substantially decreased the retention of resin-based composite to dentin, others are not in agreement with the effect of provisional ZOE materials on resin-based restorative materials.2,9 According to study results, eugenol-containing provisional cements may be used before resin-based cements are used, if the smear layer is modified or removed before dentin bonding.2,9
Mechanical removal of provisional cement has been only partially effective; cement remnants have been observed microscopically on surfaces that appeared to be clean macroscopically.8,10,15 Complete removal of the provisional cement before seating final restorations is optimal. Generally, practitioners use an excavator to remove the provisional cement, but this approach alone is not adequate.1 Thus, various methods for removing provisional cement have been studied. Several investigators have studied the removal of provisional cement in vitro by using pumice, an explorer and air-water spray, or soap; they found that none of these methods removed remnants of provisional cements effectively.1,3,10,16,17
For removal of debris and remnants from the dentin surface, different dentin-cleaning agents containing ethanol, ethyl acetate, acetone or chlorhexidine digluconate have been marketed. Water-miscible solvents such as acetone or ethanol have been used in bonding agents and are thought to behave as a water chaser to facilitate resin monomer penetration into the collagen network.18–20
Adhesion to dentin depends on the adhesive system and the dentin substrate. Thus, the authors of a study investigated materials and techniques for improving adhesion, and, consequently, adhesive restorative treatment.1 Among several factors that may interfere with the bonding quality, the type of adhesive system used is important.21,22 To increase the bond strength of adhesive resin, acids have been used to demineralize the dentin surface and remove remnants from the dentin surface.6,11 The smear layer must be removed, modified or impregnated by the resin to allow for bonding between the tooth and the restorative material.23
Modern adhesives can be grouped into two categories according to their interaction with the smear layer and etching technique: total-etching and self-etching.21,22 Total-etching adhesive systems, in which a separate acid-etching step is used, are more sensitive to the dentin depth than are self-etching adhesive systems.24 Moreover, the numerous steps involved in the application procedure increase the risk of human error.25 Self-etching adhesive systems overcome the adverse effects of total-etching adhesive systems.26 They contain both acidic and hydrophilic monomers and do not require rinsing after etching.22 In self-etching adhesive systems, the acidic monomer penetrates into the demineralized dentin, forming a hybrid layer that includes the dissolved smear layer.27 One-step self-etching bonding systems exhibit high permeability, resulting in water flow through the adhesive. This water flow has been attributed to the systems’ hydrophilic nature and the lack of a cured hydrophobic layer lining the adhesive. Ultramorphologically, the presence of so-called water trees is thought to be a manifestation of this permeability.28
We conducted this study to evaluate the shear bond strength of resin cement to dentin surfaces cleaned with three different dentin-cleaning agents and treated with three different adhesive systems. We also analyzed the cleanliness of the resulting dentin surfaces by using a field emission scanning electron microscope (SEM). We hypothesized that we would find significantly different shear bond strength values between dentin and resin cement after the dentin was contaminated with provisional cement and then cleaned with different adhesive systems and different dentin-cleaning agents.
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MATERIALS AND METHODS
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In our study, we used 60 unrestored and caries-free extracted third molars. We stored the teeth in 0.5 percent chloramine at room temperature until we needed them. We sectioned the roots at the cementoenamel junction and separated the coronal parts of teeth mesiodistally at the central fossa by using a water-cooled diamond-coated disk. We used autopolymerizing resin in plastic holders to mount 120 specimens with their buccal or lingual surfaces facing upward. We ground the buccal and lingual surfaces with a standard-grit diamond rotary cutting instrument until we reached the dentin surface. We then ground the exposed dentin surface with a 320-grit silicon carbide abrasive paper under running water to ensure a smooth surface. The dentin-cleaning agents and the etching systems used in our study are presented in Table 1
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To simulate provisional restorations, we made 120 5- x 7- x 1-millimeter acrylic resin plates by using a provisional restoration material. We cemented the acrylic resin plates to the dentin surfaces of the specimens by using eugenol-containing provisional cement under a 2.5-kilogram static load for five minutes. We stored these specimens in distilled water at 37°C ± 2°C for five days.
We removed the acrylic resin plates and mechanically removed the provisional cement by using a carving instrument until the dentin surface was macroscopically clean. We then rinsed the specimens thoroughly with water. We randomly divided the specimens into four groups of 30 specimens each and subjected the teeth in three groups to chemical cleaning with a different dentin-cleaning agent for 15 seconds. We scrubbed the dentin surfaces of specimens in the first group with a cotton pellet soaked in Sikko Tim (VOCO GmbH, Cuxhaven, Germany), which contains ethanol, ethyl acetate and acetone-based disinfectant. We scrubbed the dentin surfaces of the specimens in the second group with a cotton pellet soaked in Cavity Cleanser (Bisco, Schaumburg, Ill.), which contains 2 percent chlorhexidine digluconate. We cleaned the specimens in the third group with Consepsis Scrub (Ultradent, South Jordan, Utah), which contains 2 percent chlorhexidine digluconate and glass particles; we applied the cleaning agent by using rotary instrument with a rubber cup at 5,000 rotations per minute under water-cooling. The teeth in the fourth group, the control group, received no treatment. After applying the dentin-cleaning agents, we divided all groups into three subgroups, which we treated with different etching adhesive systems. We used one-step self-etching, two-step self-etching and total-etching adhesive systems in the first, second and third subgroups, respectively.
We used a plastic transparent mold with a hole in the center (3 mm in diameter and 2 mm in height) to place the resin cement on the dentin surfaces. We polymerized the adhesive resin cement for 20 seconds. Then we stored the specimens distilled water at 37°C ± 2°C for five days. We subjected them to 500 thermal cycles between 5°C and 55°C, with a dwell time of 30 seconds.
We measured shear bond strengths of the cylindrical adhesive resin cement by using a universal testing machine with a crosshead speed of 0.5 mm per minute. We conducted statistical analyses and used the Kolmogorov-Smirnov test to determine normal distribution; we found that the data were of a normal distribution (P > .05). We used Levene’s test to determine homegeneity of variance (F, 1.074; P > .05), and we calculated means and standard deviations of bond strengths. We analyzed data by using two-way analysis of variance (ANOVA). We calculated post hoc Tukey intervals at the =.05 level to compare the dentin-cleaning agents and the etching adhesive systems.
To evaluate the effect of the dentin-cleaning agents and the adhesive systems on the dentin surfaces, we prepared eight additional specimens. To see the effect of the cleaning agents, we prepared four of the specimens as described previously. We mechanically removed the remnants of the provisional cement of the other four specimens and then applied total-etching, one-step self-etching and two-step self-etching adhesive systems to the second, third and fourth specimens, respectively. The first specimen received no treatment and served as the control. Then we subjected these eight specimens to gold sputtering and examined them under an SEM at 15.0 kilovolts. We made SEM micrographs at x2,000 magnification so we could visually inspect them.
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RESULTS
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We performed a power calculation and determined that 120 specimens for 12 groups would provide sufficient statistical data at a = .05 level. The results of the two-way ANOVA we used to test the shear bond strength values are shown in Table 2, and shear bond strength values and the differences among groups are shown in Table 3. The dentin-cleaning agents and the etching and adhesive systems significantly affected the shear bond strength of resin-based composite cement to dentin (P < .001). However, we found no interaction between the dentin-cleaning agents and the etching and adhesive systems (P > .05). In all dentin-cleaning agent groups, while the total-etching adhesive system had the highest shear bond strength values, we found no significant differences between one-step and two-step self-etching adhesive systems (P > .05).
When we compared the dentin-cleaning agents, we found no significant differences between shear bond strengths of the specimens cleaned with Sikko Tim and Consepsis Scrub (P > .05). There also was no significant difference between control and Cavity Cleanser specimens (P > .05). The Sikko Tim and Consepsis Scrub groups had higher shear bond strength values than did the control and Cavity Cleanser groups.
The type and frequency of failures for specimens are presented in Table 3
. The specimens had three types of failures: adhesive, cohesive and mixed. Mixed and adhesive fractures were the most common types of failure for all groups. However, only the specimens cleaned with Sikko Tim and Consepsis Scrub had cohesive failures.
We observed extensive remnants of provisional cement on the micrographs of untreated dentin surfaces and surfaces cleaned with Cavity Cleanser; however, we observed smoother and cleaner surfaces on the dentin surfaces that were cleaned with Sikko Tim and Consepsis Scrub (Figure 1). We saw droplets, which formed when the solvent in the adhesive evaporated,28 on the micrographs of the specimens treated with the one-step and two-step self-etching adhesive systems after we cleaned the specimens with the dentin-cleaning agents (Figure 2). The droplets on the micrograph of the specimen treated with the one-step self-etching adhesive system (Figure 2B) were bigger and had more regular shapes, which indicated the amount of evaporation of the solvent, than did those seen on the specimen treated with the two-step self-etching adhesive system (Figure 2C). The dentin surface of the specimen treated with the total-etching adhesive system was covered completely by resin (Figure 2D).
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Figure 1. Scanning electron micrographs of eugenol-contaminated dentin surfaces. A. Untreated control. B. Cleaned with Cavity Cleanser (Bisco, Schaumburg, Ill.). C. Cleaned with Consepsis Scrub (Ultradent, South Jordan, Utah). D. Cleaned with Sikko Tim (VOCO GmbH, Cuxhaven, Germany). Original magnification x2,000; bar 10 micrometers.
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Figure 2. Scanning electron micrographs of eugenol-contaminated dentin surfaces after application of etching systems. A. Unetched control. B. Etched with one-step self-etching adhesive system. C. Etched with two-step self-etching adhesive system. D. Etched with total-etching adhesive system. Original magnification x2,000; bar 10 micrometers.
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DISCUSSION
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In this study, we hypothesized that different dentin-cleaning agents and etching and adhesive systems used to remove provisional cement remnants from dentin surfaces affect the bond strength of adhesive resin cement to dentin. The results of this study support that hypothesis. We found significant differences in shear bond strengths among the dentin-cleaning agents and among the etching and adhesive systems (P < .0001).
The control group had the lowest shear bond strength values (P < .001). When we compared all the groups, we found no significant differences between the control and Cavity Cleanser groups (P > .05) or between the Consepsis Scrub and Sikko Tim groups (P > .05). In a previous study, we found no significant difference between the untreated specimens and the specimens treated with Cavity Cleanser.4 Grasso and colleagues3 used 0.12 percent chlorhexidine gluconate to remove provisional cement from the dentin surface and found that 0.12 percent chlorhexidine gluconate had similar effects as an explorer and air-water spray. Cavity Cleanser contains 2 percent chlorhexidine digluconate in a water-based gel. Consepsis Scrub, which contains 2 percent chlorhexidine digluconate and glass fillers that act as an abrasive, has higher shear bond strength values than did Cavity Cleanser. Although these two dentin-cleaning agents contain the same amount of chlorhexidine digluconate, their application procedures are different. We applied Cavity Cleanser with a cotton pellet and Consepsis Scrub with a rubber cup by using a rotary instrument. The use of a rubber cup and a rotary instrument may clean the surface more effectively than the use of a cotton pellet soaked in a dentin-cleaning agent.
The specimens cleaned with Sikko Tim had significantly higher shear bond strength values than did those cleaned with Cavity Cleanser and untreated specimens (P < .001). The specimens cleaned with Sikko Tim also had higher bond strength values than did the specimens cleaned with Consepsis Scrub, but we found no significant difference between the two groups (P > .05). Sikko Tim’s chemical composition includes ethanol, ethyl acetate and acetone. Thus, Sikko Tim acts as a solvent for the remnants of provisional cement. Since Sikko Tim contains water-miscible solvents, it probably removes water from the dentin, allowing resin-based composite to penetrate better into dentinal tubules and interfibrillar spaces and to achieve strong dentin bonding. Sarac and colleagues4 compared different dentin-cleaning agents, including two that contain chlorhexidine digluconate or water-miscible solvents such as ethanol and acetone. The agents containing water-miscible solvents had higher bond strength values and lower contact angle values (9.3° ± 0.1) than did those containing chlorhexidine digluconate (20.1° ± 0.1).4
Generally, after tooth preparation, dentin was covered with a smear layer, which was composed mainly of cut, mineralized collagen fibrils.6,8 There was no structural continuity between the smear layer particles and the underlying dentin. When the eugenol-containing provisional cement was put on the smear layer, eugenol leached into and through the smear layer to the dentin tubules, contaminating the dentin surface. After removal of the provisional cement, the dentin surface still was covered by the smear layer, which contained the absorbed eugenol and cement remnants.6,8 Ganss and Jung,9 however, reported that pretreatment of dentin with eugenol-containing or eugenol-free provisional materials had no adverse effects on the shear bond strength of dual-curing luting composite when the smear layer was modified with primer and an adhesive-containing system. The primer they used consisted of tetraethylene glycol dimethacrylate, maleic acid and dimethylacetone. The acidic primer modified the smear layer, and, at the same time, the solvent component ensured wetting of the dentin surface by the resin.9 The adhesive consisted mainly of polyethylene glycol dimethacrylate, maleic acid and glutaraldehyde. The adhesive acted as a link between the hydrophilic dentin and the relatively hydrophobic bonding resin, whereas the glutaralde-hyde may have reacted with the organic portion of the dentin matrix.9
Acid-etching and rinsing procedures remove components of the dentin surface and, therefore, might underlie the elimination of the alleged negative effect of eugenol on the bond strength.2 Acid-etching has been reported to dissolve microscopic remnants of residual eugenol.8 In our study, the total-etching adhesive systems had higher bond strength values. To obtain efficient dentin bonding, the mineral phase of the dentin must be extracted from the dentin substrate without damaging the collagen matrix, and the voids left by the mineral must be filled with an adhesive resin that penetrates the exposed collagen fibril network.29 Unlike total-etching adhesives, self-etching systems do not completely dissolve or remove the smear layer. Instead, they partly integrate it into the hybrid layer.29–31
In our study, when we compared self-etching adhesive systems, we found no significant differences between one- and two-step self-etching adhesive systems (P > .05). Bouillaguet and colleagues26 reported that the low bond strengths associated with self-etching adhesive systems may indicate that the single component material cannot yet fulfill all requirements for the production of effective adhesive layers. Although we found no differences between one- and two-step self-etching adhesive systems in terms of resin cement bonding, we saw more droplets on the micrograph of the two-step self-etching adhesive specimen. The two-step self-etching adhesive system we used contains hydroxyethyl methacrylate (HEMA), but the onestep self-etching adhesive system does not. Authors of a previous study stated that more and bigger droplets were seen on the SEM micrographs of HEMA-rich adhesive specimens than on those of HEMA-free specimens.28 They also stated that the HEMA-rich adhesives contained water that was absorbed from the underlying dentin, so an osmotic process caused these droplets.
The limitations of our study were that we used only one type of adhesive resin cement, and that we performed the tests in in vitro conditions. Different results might be have been obtained if we had used a different adhesive resin cement or different dentin-cleaning agents. These topics should be investigated further.
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CONCLUSION
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Within the limitations of this study, we found significant differences among the different dentin-cleaning agents and etching systems (P < .001). We found that specimens in the Sikko Tim and Consepsis Scrub groups had higher shear bond strength values than did specimens in the Cavity Cleanser and the control groups (P < .001). We found no significant differences between the one- and two-step self-etching adhesive systems (P > .05).
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FOOTNOTES
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Dr. Duygu Saraç is an associate professor, Department of Prosthetic Dentistry, Faculty of Dentistry, Ondokuz Mayis University, Samsun, 55139 Turkey, e-mail "dsarac{at}omu.edu.tr". Address reprint requests to Dr. Saraç.
Dr. Bulucu is a professor, Department of Operative Dentistry, Faculty of Dentistry, Ondokuz Mayis University, Samsun, Turkey.
Dr. Y. Sinasi Saraç is a an associate professor, Department of Prosthetic Dentistry, Faculty of Dentistry, Ondokuz Mayis University, Samsun, Turkey.
Dr. Kulunk is an assistant professor, Department of Prosthetic Dentistry, Faculty of Dentistry, Ondokuz Mayis University, Samsun, Turkey.
Disclosures. None of the authors reported any disclosures.
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ABSTRACT
MATERIALS AND METHODS
