JADA Continuing Education
The effect of a dental unit waterline treatment regimen on the shear bond strength of resin-based composite
JAMES S. KNIGHT, D.D.S.,
STEPHEN B. DAVIS, D.D.S. and
JOHN G. McROBERTS, D.M.D.
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ABSTRACT
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Background. Numerous methods of disinfecting dental waterlines have been suggested. This study evaluates the effects of one disinfecting technique on the strength of resin-based composite’s bond to enamel and to dentin.
Methods. The authors bonded resin-based composite cylinders to enamel and dentin surfaces similarly mounted and prepared using three irrigation solutions. After undergoing acid etching, the tooth surface was rinsed with either distilled water, water from a municipal water source or a mixture of distilled water and mouthwash concentrate. The authors shear-tested the samples and analyzed the data statistically.
Results. The group rinsed with distilled water mixed with mouthwash exhibited the lowest shear bond strengths. However, a one-way ANOVA indicated no statistically significant differences in the mean values among the treatment groups for either enamel (P = .295) or dentin (P = .393). Specimens bonded to enamel demonstrated primarily adhesive fracture at the tooth/composite interface. Those bonded to dentin showed a similar pattern, with some sites of cohesive fracture in the resin-based composite.
Conclusions. There was no significant difference in shear bond strengths of resin-based composite to tooth structure when rinsed with distilled water mixed with mouthwash, distilled water or water from a municipal source.
Clinical Implications. Dental unit waterlines disinfected using a diluted mouthwash solution may be used while bonding resin-based composite to either enamel or dentin.
Dental unit waterline, or DUWL, contamination has received much attention recently in the professional literature, from dental manufacturers and in the public media. Many authors have defined and described DUWL contamination, and all have found it to be a widespread phenomenon.1–6 The American Dental Association addressed the problem in 1996 by issuing the ADA Statement on Dental Unit Waterlines,7 which called for a maximum of 200 colony-forming units of aerobic mesophilic heterotrophic bacteria per milliliter of water, or CFU/mL, in unfiltered DUWL output by the year 2000.
Dental unit waterlines disinfected using a diluted mouthwash solution may be used while bonding resin-based composite to either enamel or dentin.
Many methods and protocols have been developed to reduce, control and monitor waterline contamination in the dental operatory.8–14 A simple technique described by Eleazer and colleagues15 used dilute Scope mouthwash (Procter & Gamble) to effectively and inexpensively control DUWL contamination in dental units having a self-contained water system. Although the bacteria were controlled, the authors raised the question of effects of this technique on bond strengths of dental restorative materials.
Meiers and Shook16 examined the effects of two cavity disinfectants on resin-based composite/dentin bond strengths. They found the bond strength of one of the two composites tested to be reduced and concluded that the effects of these disinfectants were material-specific. Roberts and colleagues17 tested effects on dentin bond strength of several DUWL disinfectants, one of which was Listerine mouthwash (Warner-Lambert Consumer Group, Pfizer). They found that all antimicrobial agents tested reduced bond strength, but that only citric acid and diluted Listerine mouthwash significantly lowered bond strength relative to the distilled water control.
Based on the Eleazer and colleagues15 study, the division of endodontics at the Medical University of South Carolina College of Dental Medicine, Charleston, S.C., began using Scope mouthwash concentrate diluted in distilled water in self-contained dental unit water systems. The purpose of our study was to test this disinfection regimen to determine any effects on bond strength of resin-based composite to both dentin and enamel.
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MATERIALS AND METHODS
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We randomly divided 60 extracted human teeth, which had been stored in distilled water continuously since extraction, into two groups of 30 each. The teeth were embedded in autopolymerizing acrylic; we left exposed an intact facial or lingual crown surface that we ground flat into enamel or dentin, depending on the test grouping, using a grinder/polisher (Ecomet, Buehler). Initial rough grinding was accomplished with 120-grit sandpaper, followed by polishing with 240- and 320-grit sandpaper, successively. We used three test groups of 10 teeth each to test shear bond strength, or SBS, to enamel, and we used three similar groups to test SBS to dentin.
The results demonstrate that the use of Scope mouthwash (Procter & Gamble) as a waterline disinfectant creates no problems relative to bond strengths.
We further divided the 30 teeth with prepared enamel into three groups of 10 each. After undergoing acid-etching with 37 percent phosphoric acid (Etch-37, Bisco Dental Products) for 30 seconds, the teeth were washed for 30 seconds each with a flow rate of 195 milliliters per minute using one of three different wash solutions:
- – Group 1: distilled water mixed with Scope mouthwash concentrate (Table
), 30 mL concentrate added to 720 mL of distilled water;
- – Group 2: distilled water alone (control);
- – Group 3: untreated municipal water.
We dried the specimens with moisture-free compressed air for five seconds and applied a coat of OptiBond FL adhesive resin (SDS Kerr). We thinned the bonding resin with dry air for approximately two seconds and light-polymerized it for 30 seconds. A hybrid resin-based composite (Prodigy, shade B-2, Kerr), was loaded into a length of plastic tubing that had a lumen diameter of 3.46 millimeters; we placed the composite on the tooth surface with finger pressure. We removed excess composite while holding the plastic cylinder in place on the tooth surface. We light-polymerized the composite using a curing light (Optilux, Demetron), which had a light intensity greater than 320 milliwatts per square centimeter, from four different angles for 20 seconds at each angle. Thus, each composite specimen was polymerized for 80 seconds.
We also divided the 30 teeth with prepared dentin into three groups of 10 each and bonded resin-based composite samples to them as we did with the enamel group, except that we acid-etched them for only 15 seconds and used dentin primer. After we washed the dentin specimens with one of the test solutions, we lightly dried the tooth surface for two seconds with compressed air, making sure the dentin surface still was damp. We applied primer (Opti-Bond FL Primer, Kerr) with a light scrubbing motion for 30 seconds and gently air-dried it for less than five seconds. We then placed the adhesive and the resin-based composite as previously described.
The specimens were stored in distilled water at 37 C for 14 days before testing. With a universal mechanical testing system (MTS 810 material testing system, MTS Systems) that had a linear displacement of 1.0 mm per minute, we fractured the resin-based composite from the tooth. The force to failure was recorded in newtons and converted to shear strength in megapascals, or MPa. We calculated the mean shear strength and standard deviation for each group and ran a one-way analysis of variance, or ANOVA, on the collected data.
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RESULTS
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The table presents a summary of the data. An ANOVA indicated no statistically significant differences in the mean SBS values among the groups of either the specimens bonded to enamel (P = .295) or those bonded to dentin (P = .393).
In both the enamel specimens and the dentin specimens, those in Group 1 exhibited the lowest mean SBS, those in Group 3 had the highest SBS, and those in Group 2 had an SBS between those of the other two groups.
We examined the specimens using a dissecting microscope at x25 magnification to evaluate the location of fracture. Specimens bonded to enamel revealed primarily adhesive fracture at the tooth/composite interface; 20 percent or less of the samples in each group showed cohesive fracture within the resin-based composite material. Only one sample exhibited cohesive fracture in the enamel, and that sample was in Group 3. Specimens bonded to dentin exhibited a similar adhesive fracture pattern, with some sites of cohesive fracture in the resin-based composite. No dentin cohesive failure was observed in any group.
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DISCUSSION
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Although the mean SBS for the Group 1 specimens was the lowest among those of the three groups for both enamel and dentin bonding, there was no statistically significant difference among the respective groups. These results demonstrate that the use of Scope mouthwash as a waterline disinfectant creates no problems relative to bond strengths.
The standard deviation in the data for the enamel bonding strength of Group 2 was slightly high (Figure) because of one particularly low value. This was caused by incorporation of air at the bonding interface with a concomitant reduction in composite surface area available for bonding. Eliminating this aberrant value from the data analysis did not change the original group relationships.
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Figure. Bond strengths (with standard deviation) to enamel and dentin using three irrigating solutions. MPa: Megapascals. Scope is manufactured by Procter & Gamble.
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The data for the Group 1 specimens bonded to dentin also exhibited a high standard deviation. With three values less than 20 MPa and the highest value more than 30 MPa, this group showed the greatest range in dentin SBS values. Possible causes for this variation include differences in the quality of dentin among the tooth samples, in the bonding methodology or in the interaction between components in the mouthwash (Box, "Ingredients of Scope Mouthwash Concentrate") and the dentin surface.
Our bond strengths to dentin for the distilled water control (Group 2) compared favorably with the findings by Roberts and colleagues,17 but our dentin mean SBS for Scope mouthwash (Group 1) was significantly higher than those authors’ finding for Listerine mouthwash. They suggested that essential oils (such as thymol, menthol and eucalyptol), which are active ingredients in Listerine, might contribute to the low SBS they observed. The mode of failure for the mouthwash-treated group was similar in their study and in ours—that is, adhesive failure at the resin-dentin interface.
We contracted with a commercial laboratory to perform the waterline analysis and determine the water quality before the study began. Water samples were collected using aseptic technique, and a chain of custody for the samples was maintained. The water treated with Scope as previously described showed no detectable microbial growth, while the DUWL supplied by a municipal water source showed more than 30,000 CFU/mL. The distilled water was tested in two ways: removed from a new container using sterile technique and dispensed from a 5-gallon container using a plastic pump dispenser that remained attached to the top of the container. Using sterile technique, the laboratory detected no growth during testing. This finding is consistent with the findings of Eleazer and colleagues15 and Williams and colleagues.18 When the pump dispenser was used for the distilled water, the test showed a microbial level of 13,200 CFU/mL.
The mode of dentin bond failure for the mouthwash-treated group was adhesive failure at the resin-dentin interface.
In our study, the mixture of Scope concentrate and distilled water created a final concentration of 3.8 percent mouthwash, whereas in the study by Eleazer and colleagues,15 the final concentration was 2.8 percent. The difference was unintentional and occurred because our original calculation of the amount of concentrate to be added was figured on the basis of a bottle size of 1,000 mL. It was only at the time of writing this article that we realized that the bottles are 750 mL, rather than 1,000 mL, in volume. Inasmuch as the results of our study showed no statistically significant effect of Scope-treated water on strengths of resin-based composite’s bond to enamel and dentin, we consider the difference in concentration between Eleazer and colleagues’15 study and our study inconsequential.
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CONCLUSION
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Diluted Scope mouthwash has been shown to be an effective waterline disinfectant in dental units that have an independent, self-contained water supply.15 When this solution is used as an irrigant during operative procedures, it might affect bond strengths of resin-based composite to enamel or dentin.
Under the conditions of our study, the use of distilled water disinfected by means of Scope mouthwash did provide slightly lower enamel/composite and dentin/composite bond strengths. However, the difference in bond strengths was not statistically significant when compared with those using the distilled water control or untreated municipal water.
The results of this study demonstrate that Scope mouthwash may be used as a waterline disinfectant during bonding procedures; however, further study is required to answer questions dealing with possible long-term effects on the restoration and any possible restorative material specificity.
Other mouthwash products with different ingredients also may be considered for use as waterline disinfectants. However, additional research is required to determine any effects these different product formulations might have on bond strengths.
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FOOTNOTES
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Dr. Knight is an associate professor and the director, Division of Operative Dentistry, Medical University of South Carolina College of Dental Medicine, 173 Ashley Ave., Charleston, S.C. 29425, e-mail "knightjs{at}musc.edu". Address reprint requests to Dr. Knight.
Dr. Davis is the director, Endodontic Residency Program, Long Beach Veterans Affairs Medical Center, Long Beach, Calif.
Dr. McRoberts has a private practice in general dentistry, Clemson, S.C.
The authors thank Dr. Robert Draughn, D.Sc., M.S., Department of Materials Science, Medical University of South Carolina College of Dental Medicine, for his assistance.
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REFERENCES
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ABSTRACT
MATERIALS AND METHODS
