Effect of Saliva Contamination on the Shear Bond Strength of Orthodontic Brackets Bonded with a Self-Etching Primer
This study evaluates the effect of saliva contamination at different stages of the bonding brackets procedure using the self-etching primer Adper Prompt L-Pop (3M ESPE, Minneapolis, Minn) and the resin orthodontic adhesive system Transbond XT (3M). A total of 70 brackets were bonded to human extracted premolars, which were divided into four groups: group 1, uncontaminated (control); group 2, saliva application before priming; group 3, saliva application after priming; and group 4, saliva application before and after priming. Shear bond strength was measured with a universal test machine. The adhesive remnant on the tooth after debonding was determined using image analysis equipment. Significant differences were only observed between group 1 (12.42 ± 3.27) and groups 2 (9.93 ± 4.50) and 4 (9.59 ± 2.92) (P < .05). Concerning the adhesive remnant, no significant differences were found between the groups evaluated (P > .05).Abstract
INTRODUCTION
Different investigations have evaluated the effect of contamination through fluids, such as plasma, saliva, water,1 and blood,23 on the bonding procedure, causing a decrease in bond strengths. Contamination appears to be one of the most important causes of adhesive failures.
Saliva is the most frequently found contamination in the clinic. Saliva contamination on enamel etched for a duration of one second or more leaves a surface layer of saliva on the enamel that is resistant to rinsing.4 Furthermore, when the etched enamel becomes wet, most of the pores are blocked and the penetration of resin is altered, resulting in resin tags of insufficient number and length.5
Since the introduction of self-etching primers (SEPs) as an alternative to the traditional acid-etch method, many investigations have been carried out to evaluate their efficacy. These new systems include combining the conditioner and primer in only one product6; therefore, SEPs are of great interest. They imply an obvious clinical advantage because they reduce both chair time7 and the possible number of errors in intermediate steps. SEPs were initially used on dentin, but subsequent investigations have confirmed their efficacy on enamel8 and hence their orthodontic application.
There is controversy over the results reported by different authors. Some studies observed shear bond strengths similar to those obtained using the traditional acid-etch technique.910 Other studies observed that the bond strength of SEPs was lower.1112 Still other studies found that SEPs provided greater bond strengths than the traditional system.13
Most SEPs incorporate the 2-hydroxyethyl methacrylate (HEMA) molecule in their composition. Because of the hydrophilic properties of this molecule, it is interesting to evaluate the effect of moisture contamination on SEP, and authors such as Bishara et al,14 Cacciafesta et al,15 Larmour and Stirrups,16 Zeppieri et al,17 and Rajagopal et al18 have carried out research on this matter. However, further research is needed because of the continuous introduction of new and improved varieties of SEPs.
A new SEP has been recently introduced in the market, Adper Prompt L-Pop (Adper PLP, 3M ESPE, Minneapolis, Minn). This SEP is the improved version of its predecessor Promp L-Pop (3M ESPE). According to the manufacturer, Adper PLP introduces a better activation control and a perfected chemical composition.
This study evaluates the effect of saliva contamination at different stages of the bonding procedure using the SEP Adper PLP (3M ESPE) and the resin orthodontic adhesive system Transbond XT (3M).
MATERIALS AND METHODS
Teeth
Seventy human upper premolars free from caries and fillings were used. These had been extracted for reasons unrelated to the objectives of this study and with the informed consent of the patients. The project has been approved by the Murcia University Bio-ethical Commission.
The teeth were washed in water to remove any traces of blood and then placed in a 0.1% thymol solution. Afterward, they were stored in distilled water, which was changed periodically to avoid deterioration. In no case was a tooth stored for more than a month after extraction.
Brackets
Seventy metal upper premolar brackets were used (Victory Series, 3M Unitek Dental Products, Monrovia, Calif). The base area of each bracket was calculated (mean = 9.79 mm2) using image analysis equipment and MIP 4 software (Micron Image Processing Software, Digital Image Systems, Barcelona, Spain).
Bonding procedure
The 70 upper premolars were divided into four groups, and brackets were bonded on the buccal surface according to the instructions supplied by the manufacturer of each product. For all groups, the buccal surfaces were polished with a rubber cup and polishing paste (Détartrine, Septodont, Saint-Maur, France).
Group 1 (n = 25)—Uncontaminated (control)
Adper PLP was gently brushed onto the enamel for 15 seconds with the disposable tools supplied with the system. A moisture-free air source was used to deliver a gentle burst of air to the primer. The SEP was light cured for 10 seconds. Transbond XT paste was applied to the base of the bracket, which was then pressed firmly on to the tooth. Excess adhesive was removed from around the base of the bracket, and the adhesive was light cured by positioning the light guide of an Ortholux XT lamp (3M Unitek Dental Products) on each interproximal side for 10 seconds.
Group 2 (n = 15)—Saliva application before priming
Human saliva was applied with a brush to the labial surface until it was totally contaminated. Then, the bracket was bonded with Adper PLP and Transbond XT paste as in group 1.
Group 3 (n = 15)—Saliva application after priming
Adper PLP was gently brushed onto the enamel for 15 seconds with the disposable tools supplied with the system. A moisture-free air source was used to deliver a gentle burst of air to the primer. The SEP was light cured for 10 seconds. Then, the enamel surface was contaminated with saliva as in group 2. Afterward, the bracket was bonded with Transbond XT paste as in group 1.
Group 4 (n = 15)—Saliva application before and after priming
The enamel surface was contaminated with saliva as in group 2. Then, Adper PLP was gently brushed onto the enamel for 15 seconds with the disposable tools supplied with the system. A moisture-free air source was used to deliver a gentle burst of air to the primer. The SEP was light cured for 10 seconds. Afterward, the contamination procedure was repeated once more. Then, the bracket was bonded with Transbond XT paste as in group 1.
Saliva was collected from one of the authors of this study, who was instructed to brush her teeth and not to eat for one hour before the saliva was collected. One coat of saliva was applied on the tooth with a brush. After saliva contamination, the enamel surface was not blown off.
Storage of test specimens
The specimens were immersed in distilled water at a temperature of 37°C for 24 hours.19
Bond strength test
Shear bond strength was measured with a universal test machine (Autograph AGS-1KND, Shimadzu, Kyoto, Japan) with a one-kN load cell connected to a metal rod with one end angled at 30°. The crosshead speed was one mm/min.19
The teeth were set at the base of the machine so that the sharp end of the rod incised in the area between the base and the wings of the bracket, exerting a force parallel to the tooth surface in an occlusoapical direction.
The force required to debond each bracket was registered in newtons (N) and converted into megapascals as a ratio of the force to debond to the surface area of the bracket (MPa = N/mm2). We believe that to properly compare different bond test studies in orthodontics, it is necessary to determine bond strength because use of the debond force does not help compare brackets with different geometries.
Percentage of tooth area occupied by adhesive
The percentage of the surface of the bracket base covered by adhesive was determined using an image analysis equipment (Sony dxc 151-ap video camera, connected to an Olympus SZ11 microscope) and MIP software.
The percentage of the area still occupied by adhesive remaining on the tooth after debonding was obtained by subtracting the area of adhesive covering the bracket base from 100%.
Statistical analysis
The Kolmogorov-Smirnov normality test and the Levene variance homogeneity test were applied to the bond strength data. Because the data showed a normal distribution and there was homogeneity of variances, they were analyzed using one-way ANOVA, finding those groups that were significantly different with the Differences minimum significance, DMS, test (P < .05).
The Kolmogorov-Smirnov test and the Levene homogeneity test of variances were applied to the data for percentage of area of adhesive remaining on tooth. As there was not homogeneity of variances or a normal distribution, they were analyzed using the Kruskal-Wallis test (P < .05).
RESULTS
The one-way ANOVA test found significant differences (P = .04) in shear bond strength between the different groups evaluated. The DMS test detected these differences between the control group and the group in which contamination occurred before priming (P = .03) and the control group and the group which was contaminated before and after priming (P = .01) (Table 1).
The values of the percentage of tooth area occupied by adhesive remnant are shown in Table 2. The Kruskal-Wallis did not show significant differences (P = .44) between the different groups.
DISCUSSION
This study evaluated the effect of saliva contamination on the bond strength of Adper PLP at different stages of the bonding procedure. This SEP contains methacrylated phosphoric esters, Bisphenol A-glycidyl methacrylate, Bis-GMA, initiators based on camphorquinone, water, HEMA, polyalkenoic acid, and stabilizers.
Significant differences were found between the control group and the group in which contamination occurred before the application of Adper PLP. Although the bond strength values of the group in which contamination occurred before priming were not significantly different from those in which contamination occurred after priming, significant differences were not found between this last group and the control group. Adper PLP was light cured before contamination with saliva, so penetration of the primer into the enamel pores was not altered. This could explain why the reduction in bond strength at contamination after priming was not as great as that before priming.
Significant differences were also observed between the control group and the group in which saliva contamination occurred before and after the application of the SEP.
To our knowledge, there are no studies that evaluate the effect of saliva contamination on Adper PLP. However, there are similar investigations that evaluate other SEPs. Bishara et al14 used the SEP Angel I (3M ESPE). Our results concur with the results obtained by these authors. They observed significant differences between the control group and the group contaminated before and after priming. However, they also found significant differences between the group contaminated before priming and the group in which contamination occurred before and after the application of the SEP.
Cacciafesta et al15 studied Transbond Plus Self Etching Primer (3M Unitek). Our results also concur with the results obtained by these authors. They observed significant differences between the control group and the group contaminated before and after priming. Furthermore, they found differences between the control group and the group contaminated after priming.
Larmour and Stirrups16 and Rajagopal et al18 evaluated the effect of saliva contamination before the application of Transbond Plus Self Etching Primer (3M Unitek), and once more, our results concur with theirs. They found significant differences between the control group and the group in which saliva contamination occurred before priming.
Zeppieri et al17 found that saliva contamination at different stages of the bonding brackets procedure did not affect the bond strength of Transbond Plus Self Etching Primer.
Therefore, we can appreciate that the results obtained in these different studies are highly disparate. The differences in results could be because of the application of different products as well as the varied materials and methods used by each of the authors.
Regarding the adhesive remnant, no significant differences were obtained between the groups evaluated. This result concurs with the results obtained by Cacciafesta et al,15 Larmour and Stirrups,16 Zeppieri et al,17 and Rajagopal et al.18
In our study we can observe that the bond strength decreases from 12.42 MPa in the control group to 9.93 MPa in the group contaminated before priming and to 9.59 MPa in the group contaminated before and after priming. The strengths of the last two groups were significantly lower than the strengths of the control group. However, the bond strength values of these two experimental groups are still greater than the estimated values of 5.9 and 7.8 MPa suggested by Reynolds20 as the minimum values required for clinical needs. However, we must be cautious when extrapolating in vitro results to the clinical situation. Therefore, in vivo research must be carried out to confirm laboratory results.
CONCLUSIONS
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The greatest bond strength values were obtained when contamination did not occur.
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Significant differences were observed between the bond strengths of the control group and the group in which contamination occurred before the application of Adper PLP. Significant differences were also observed between the control group and the group in which saliva contamination occurred before and after the application of the SEP.
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No significant differences were observed in the adhesive remnant index between the groups evaluated.
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Our results suggest that contamination after photocuring of SEPs has a lesser influence on the reduction of the shear bond strength than contamination before priming.
Contributor Notes
Corresponding author: Ascensión Vicente, DDS, PhD, Docent Unit of Orthodontic, Dental Clinic, University of Murcia, Hospital Morales Meseguer, 2a planta, C/Marqués de los Vélez s/n, Murcia, Murcia 30008, Spain (ascenvi@um.es)