Original Article
Water and Saliva Contamination Effect on Shear Bond Strength of Brackets Bonded with a Moisture-Tolerant Light Cure System Ascensio´n Vicentea; Ana Menab; Antonio Jose´ Ortizc; Luis Alberto Bravoc ABSTRACT Objective: To evaluate the effects of water and saliva contamination on shear bond strength of brackets bonded with a moisture-tolerant light cure system. Materials and Methods: Brackets were bonded to 240 bovine lower incisors divided into 12 groups. Four bonding procedures were evaluated, including (1) TSEP/Transbond XT, (2) TMIP/ Transbond XT, (3) TSEP/Transbond PLUS, and (4) TMIP/Transbond PLUS, each under three different bonding conditions: without contamination, with water contamination, and with saliva contamination. Shear bond strength was measured with a universal testing machine. The adhesive remnant on the teeth was quantified with the use of image analyzing equipment. Results: Without contamination, bond strengths for the four procedures were similar (P ⬎ .05). TSEP/Tranbond PLUS and TMIP/Transbond PLUS left significantly less adhesive on the teeth after debonding than TSEP/Transbond XT and TMIP/Transbond XT (P ⬍ .008). Bond strength and adhesive remaining for TMIP/Transbond XT contaminated with water or saliva showed significantly worse performance than the other procedures evaluated (P ⬍ .008). Contamination (with water or saliva) did not affect either bond strength or adhesive remaining on the teeth for TSEP/ Transbond XT, TSEP/Transbond PLUS, or TMIP/Transbond PLUS (P ⬎ .017), although for TMIP/ Transbond XT, both variables showed significant reductions after contamination (P ⬍ .017). Conclusion: TSEP/Transbond PLUS, TMIP/Transbond PLUS, and TSEP/Transbond XT showed greater tolerance to wet conditions than was shown by TMIP/Transbond XT. (Angle Orthod. 2009; 79:127–132.) KEY WORDS: Moisture; Brackets; Shear bond strength
INTRODUCTION Because of the hydrophobic properties of resin bonding systems and the fact that adhesion is not in any way chemical, tooth enamel must remain dry after acid etching.1 In this way, penetration of hydrophobic resin into the microporous enamel is ensured for adequate mechanical retention.2 However, the reality of a Contracted Doctor, Docent Unit of Orthodontics, Dental Clinic, University of Murcia, Murcia, Spain. b Postgraduate Student, Docent Unit of Orthodontics, Dental Clinic, University of Murcia, Murcia, Spain. c Senior Lecturer, Integral Pediatric Dentistry Teaching Unit, Dental Clinic, The University of Murcia, Murcia, Spain. Corresponding author: Dr Ascensio´n Vicente, Docent Unit of Orthodontics, Dental Clinic, University of Murcia, Hospital Morales Meseguer, 2a planta. C/Marque´s de los Ve´lez s/n, Murcia, 30008 Spain (e-mail:
[email protected])
Accepted: February 2008. Submitted: January 2008. 2009 by The EH Angle Education and Research Foundation, Inc. DOI: 10.2319/012208-37.1
clinical conditions prevents the ideal of complete isolation from wet conditions during bracket bonding,2 especially when attachments are bonded to difficult to reach places.3 Under everyday clinical conditions, contamination may be produced through the presence of saliva, gingival exudation, or bleeding, or through the presence of water when teeth are washed.4 When brackets are bonded to enamel, two critical moments have been identified at which contamination may occur: (1) after the enamel surface has been etched, and (2) after primer has been applied.5 When the enamel surface is contaminated prior to primer application, plugging of the porosities of acid etching occurs, along with a reduction in surface energy. Penetration of the resin is impeded to the detriment of mechanical microretention, which, in turn, causes a reduction in bond strength between the resin and the etched enamel.6,7 In an attempt to overcome these difficulties, some manufacturers have introduced primers that are hydrophilic and that tolerate wet conditions; Transbond Plus
128 Self-Etching Primer (TSEP; 3M Unitek Dental Products, Monrovia, Calif) and the moisture-insensitive primer Transbond MIP (TMIP; 3M Unitek) are examples of such products. Some studies have shown that bond strength for TSEP8 and TMIP1–9 is not affected by enamel wetness; furthermore, in situations where water10 or saliva7,9 contamination occurs, both TSEP and TMIP provide bond strengths that are significantly greater than those of conventional primers. Contamination may be produced after primer application; in this situation, it is not only the hydrophilic capacity of the primer that is important, but also the bracket bonding resin. Recently, another innovation has been introduced—Transbond PLUS color change adhesive (3M Unitek), which, according to the manufacturer, is a moisture-tolerant light cure bonding system that, when used together with TSEP or TMIP, provides a completely moisture-tolerant system. As far as we are aware, nothing has been published about the bond capacity of this product. Therefore, the purpose of this study was to evaluate the effects on bond strength and on the adhesive remaining on teeth after debonding that results from the presence of water and saliva after applications of TSEP and TMIP, when brackets are bonded with a traditional adhesive bonding system (Transbond XT; 3M Unitek) and when a hydrophilic resin system is used (Transbond PLUS; 3M Unitek). MATERIALS AND METHODS Teeth A total of 240 bovine lower incisors were used. The teeth were washed in water, were placed in a 0.1% thymol solution, and later were stored in distilled water, which was changed periodically. No tooth was stored for longer than 1 month after extraction. Incisors were set in a 4 cm long copper cylinder with an internal diameter of 3 cm, and the roots were set in plaster. Brackets In all, 240 upper central incisor brackets were used (Victory Series; 3M Unitek). The base area of each bracket was calculated (mean ⫽ 10.25 mm2) through the use of image analysis equipment and Micro Image Processing 4 software (MIP 4; Digital Image Systems, Barcelona, Spain). Bracket Bonding The teeth were divided into 12 groups of 20 bovine incisors, and brackets were bonded onto the vestibular surfaces. Four bonding procedures—TSEP/Transbond XT,
VICENTE, MENA, ORTIZ, BRAVO Table 1. Bonding Procedures Group Group Group Group Group Group Group Group Group Group Group Group
1 TSEP 2 TSEP 3 TSEP 4 Acid etching 5 Acid etching 6 Acid etching 7 TSEP 8 TSEP 9 TSEP 10 Acid etching 11 Acid etching 12 Acid etching
TMIP TMIP TMIP
TMIP TMIP TMIP
Dry Water Saliva Dry Water Saliva Dry Water Saliva Dry Water Saliva
Transbond Transbond Transbond Transbond Transbond Transbond Transbond Transbond Transbond Transbond Transbond Transbond
XT XT XT XT XT XT PLUS PLUS PLUS PLUS PLUS PLUS
TMIP/Transbond XT, TSEP/Transbond PLUS, and TMIP/Transbond PLUS—were evaluated under three different bonding conditions: without contamination (dry), with water contamination, and with saliva contamination. The bonding procedure for each group is described in Table 1. The chemical composition of each adhesive according to the manufacturer is shown in Table 2. For all groups, buccal surfaces were polished with a rubber cup and polishing paste (De´tartrine; Septodont, Saint-Maur, France). The vestibular surfaces of teeth in groups 1, 2, 3, 7, 8, and 9 were treated with TSEP, which was rubbed gently onto the enamel for 5 seconds with the disposable supplied with the system. A moisture-free air source was used to deliver air to the primer. Although no contamination was present for groups 1 and 7, the teeth in groups 2 and 8 were contaminated with water, and those in groups 3 and 9 were contaminated with saliva. Both contaminants were applied to the entire vestibular surfaces of the teeth with a fine brush. Water was introduced by means of a dental syringe, and saliva was provided by one of the authors, who had been asked to clean her teeth and thereafter to refrain from eating for 1 hour before collecting the saliva. Then, for groups 1, 2, and 3, Transbond XT paste was applied to the base of each bracket, which then was placed on the teeth by pressing firmly. Excess adhesive was removed from around the base of the brackets, and the adhesive was light cured while the light guide of an Ortholux XT lamp (3M Unitek) was positioned on each interproximal side for 10 seconds. In groups 7, 8, and 9, brackets were bonded with Transbond PLUS in the same way as with Transbond XT. The vestibular enamel of the teeth in groups 4, 5, 6, 10, 11, and 12 was etched with a 37% o-phosphoric acid gel (Total Etch; Ivoclar Vivadent, Schaan, Liechtenstein) for 30 seconds. Then, the enamel was thoroughly washed and dried. Afterward, TMIP was applied onto the enamel, and a moisture-free air source was used to deliver a gentle burst of air to the primer. In groups 4 and 10, no contamination was introduced;
129
BRACKETS BONDED WITH A MOISTURE-TOLERANT ADHESIVE Table 2. Composition of Adhesives According to Manufacturer Adhesive Transbond XT
Transbond PLUS
TSEP TMIP
Composition
% by Wt
Silane-treated quartz Bisphenol A diglycidyl ether dimethacrylate Bisphenol A bis(2-hydroxyethyl ether) dimethacrylate Dichlorodimethylsilane reaction product with silica Silane-treated quartz Glass reacted with hydrolyzed silane Polyethylene glycol dimethacrylate Citric acid dimethacrylate oligomer Silane-treated silica Bisphenol A diglycidyl ether dimethacrylate Methacrylate ester derivative Water Ethyl alcohol Bisphenol A diglycidyl ether dimethacrylate 2-Hydroxyethyl methacrylate 2-Hydroxy-1,3-dimethacryloxypropane Copolymer itaconic and acrylic acid Diurethane dimethacrylate Water
70–80 10–20 5–10 ⬍2 35–45 35–45 5–15 1–10 ⬍2 ⬍2 75–85 15–25 30–40 10–30 10–30 7–13 7–13 3–7 3–7
groups 5 and 11 were contaminated with water, and groups 6 and 12 were contaminated with saliva. Then, in groups 4, 5, and 6, brackets were bonded with Transbond XT, and in groups 10, 11, and 12, they were bonded with Transbond PLUS. Storage of Test Specimens Specimens were immersed in distilled water at a temperature of 37⬚C for 24 hours.11 Bond Strength Test Shear bond strength was measured with a universal test machine (Autograph AGS-1KND; Shimadzu, Kyoto, Japan) with a 1 KN load cell connected to a metal rod and one end angled at 30 degrees. The crosshead speed was 1 mm/min.11 The teeth were set at the base of the machine so that the sharp end of the rod was incised in the area between the base and the wings of the bracket, exerting a force parallel to the tooth surface in an occlusal-apical direction. The force required to debond each bracket was registered in Newtons (N) and was converted into megaPascals as a ratio of Newtons to surface area of the bracket (MPa ⫽ N/mm2). Evaluation of Residual Adhesive The percentage of the surface of the bracket base covered by adhesive was determined with the use of image analysis equipment (a Sony DXC 151-ap video camera, connected to an Olympus SZ11 microscope, Tokyo, Japan) and MIP 4 software. The percentage of the area still occupied by adhe-
sive that remained on the tooth after debonding was obtained by subtracting the area of adhesive covering the bracket base from 100%. Statistical Analysis Values for shear bond strength obtained by the four bonding procedures and the percentage of area occupied by adhesive material on the teeth after debonding were compared for the three different bonding conditions: without contamination, with water contamination, and with saliva contamination. Bond strength and the percentage of area occupied by adhesive material on the teeth after debonding were compared individually for each bonding procedure under the three bonding conditions. The Kolmogorov-Smirnov normality test and Levene’s homogeneity of variance test were applied to the data for bond strength and for the percentage of area of adhesive remaining on the teeth after debonding. When data fulfilled the criteria for normality and homogeneity of variance, the existence of significant differences was analyzed by means of variance analysis (ANOVA) for one factor, and the Scheffe´ test was used for multiple comparisons (P ⬍ .05). When data were not distributed normally or failed to fulfill the criteria for variance homogeneity, they were analyzed with the Kruskall-Wallis test (P ⬍ .05) so those groups could be located that were significantly different when the Mann-Whitney test was applied to two independent samples. To avoid an accumulation of errors resulting from multiple comparisons, the significance level was modified by dividing this (P ⬍ .05) by the number of comparisons made (Bonferroni correction); P ⬍ .017 was considered significant when three compari-
130
VICENTE, MENA, ORTIZ, BRAVO
Table 3. Mean Shear Bond Strength (MPa) and Standard Deviation (SD) for Each Group (n ⫽ 20)
Group TSEP/Transbond XT TMIP/Transbond XT TSEP/Transbond PLUS TMIP/Transbond PLUS
Dry
Water
Saliva
Mean ⫾ SD
Mean ⫾ SD
Mean ⫾ SD
8.15 8.23 6.93 7.89
⫾ ⫾ ⫾ ⫾
4.22 3.77 3.34 2.71
Aa Aa Aa Aa
6.80 2.20 6.14 7.83
⫾ ⫾ ⫾ ⫾
2.91 1.54 2.40 2.54
Aa Bb Aa Aa
7.50 1.81 7.78 7.51
⫾ ⫾ ⫾ ⫾
3.21 1.29 4.45 3.18
Aa Bb Aa Aa
Within the same column, identical upper case letters indicate no differences (P ⬎ .05), and different upper case letters show significant differences (P ⬍ .008). For each row, matching lower case letters indicate no differences (P ⬎ .05), and different lower case letters show significant differences (P ⬍ .017).
sons were made, and P ⬍ .008 was significant for six comparisons. RESULTS Table 3 shows bond strength values for each of the groups evaluated. When no contamination was present, no significant differences were found (P ⫽ .61) between the four bonding procedures. However, with water and saliva contamination, bond strength was significantly less for TMIP/Transbond XT than for the three other bonding procedures (TSEP/Transbond XT, P ⫽ .000; TSEP/Transbond PLUS, P ⫽ .000; and TMIP/Transbond PLUS, P ⫽.000). When bond strength for each procedure was evaluated under variable conditions, significant differences were observed only for the TMIP/Transbond XT bonding procedure, which, when no contamination was present, achieved significantly greater bond strength values than after water contamination (P ⫽ .00) or saliva (P ⫽ .00). Significant differences (P ⫽ .45) were not found between water contamination and saliva contamination for this bonding procedure. The percentages of tooth area occupied by adhesive material after debonding are shown in Table 4. When no contamination was found, both TSEP/Tranbond PLUS and TMIP/Transbond PLUS left significantly less adhesive material on the teeth than did TSEP/Transbond XT (P ⫽.00 and P ⫽.00, respectively) and TMIP/Transbond XT (P ⫽.00 and P ⫽.00, respectively). With the presence of water, TMIP/Transbond XT left less adhesive on the teeth than was left by the other bonding procedures (TSEP/Transbond XT, P ⫽ .000; TSEP/Transbond PLUS, P ⫽ .000; and TMIP/Transbond PLUS, P ⫽ .000). TSEP/Transbond XT left the greatest amount of adhesive material, which was significantly more than was left by the other bonding procedures (TMIP/Transbond XT, P ⫽ .000; SEP/Transbond PLUS, P ⫽ .000; and TMIP/Transbond PLUS, P ⫽ .000). After saliva contamination, TMIP/Transbond XT left the least adhesive material on the teeth, followed by TSEP/Transbond Plus. TMIP/Transbond XT left sig-
nificantly less bond material than was left by the other procedures (TSEP/Transbond XT, P ⫽ .000; TSEP/ Transbond PLUS, P ⫽ .000; and TMIP/Transbond PLUS, P ⫽ .000); however, TSEP/Transbond PLUS left significantly less adhesive than was left by TSEP/ Transbond XT (P ⫽ .000) and TMIP/Transbond PLUS (P ⫽ .000). When the percentage of area occupied by adhesive that remained on the teeth after debonding was evaluated for each procedure under the three different conditions, significant differences were observed only for the TMIP/Transbond XT bonding procedure, which left significantly more adhesive without contamination than with contamination by water (P ⫽ .00) or saliva (P ⫽ .00). This bonding procedure did not show significant differences (P ⫽ 1.00) between contamination by water and contamination by saliva. DISCUSSION One of the most frequent causes of bracket bond failure is contamination during the bonding process. It has been seen that the presence of water9,10 or saliva9,12,13 drastically reduces bond strength in orthodontic resin bonding systems. With the aim of improving the hydrophilic properties of traditional adhesives, hydrophilic monomers (HEMA, 4-PENTA, etc.) and solvents have been incorporated to produce greater tolerance to wet conditions. This study showed that when bracket bonding is carried out without any contamination, the shear bond strength produced by the different combinations of adhesives tested was similar. However, when Transbond XT was used, it showed better tolerance to contamination in combination with TSEP than with TMIP. The better performance of TSEP may be due to the facts that (1) etching and priming take place simultaneously so that the depth of the etch and the degree of resin penetration will be identical, and (2) self-etching primers based on esters of phosphoric acid have a capacity to adhere chemically to hydroxyapatite, in addition to micromechanical hybridation.14 Bond strength values obtained for TSEP/Transbond XT when no contamination was present were similar
131
BRACKETS BONDED WITH A MOISTURE-TOLERANT ADHESIVE Table 4. Mean and Standard Deviation (SD) of the Percentage of Tooth Area Occupied by Adhesive for Each Group (n ⫽ 20)
Group TSEP/Transbond XT TMIP/Transbond XT TSEP/Transbond PLUS TMIP/Transbond PLUS
Dry
Water
Saliva
Mean ⫾ SD
Mean ⫾ SD
Mean ⫾ SD
59.42 66.06 32.84 34.81
⫾ ⫾ ⫾ ⫾
12.47 13.12 10.72 12.40
Aa Aa Ba Ba
61.51 0.00 29.78 38.43
⫾ ⫾ ⫾ ⫾
15.23 Aa 0.00 Bb 8.98 Ca 11.49 Ca
49.64 0.00 26.01 43.76
⫾ ⫾ ⫾ ⫾
22.01 Aa 0.00 Bb 9.26 Ca 12.08 Aa
Within the same column, identical upper case letters indicate no differences (P ⬎ .05), and different upper case letters show significant differences (P ⬍ .008). For each row, matching lower case letters indicate no differences (P ⬎ .05), and different lower case letters show significant differences (P ⬍ .017).
to those obtained with water or saliva contamination. It could be true that the presence of water as a solvent in the composition of TSEP lends a certain tolerance to wet conditions. Only recently have self-etching primers been introduced for orthodontic use, and various studies have shown that they perform adequately for bracket bonding, achieving bond strengths that are similar to those achieved through traditional etching techniques.15,16 Few studies have evaluated the effects of contamination after TSEP is applied.2,9 Our results differ from those of Cacciafesta et al,9 who found a significant decrease in the bond strength of TSEP in the presence of water or saliva. Zeppieri et al2 found that saliva contamination did not affect bond strengths achieved by TSEP/Transbond XT, although these results are not comparable with ours because Zeppieri’s group applied an additional layer of TSEP after contamination had been introduced. It is difficult to compare the bond strength results generated by different studies of bond capacity in dry conditions because of the variety of methods used, but when contamination is introduced, the difficulty of comparison is even greater because of the lack of standardization involved in introducing the contamination. This has caused different studies to generate varying results. The hydrophilic character of TMIP could result from the ethanol solvent of the primer, the addition of HEMA to the primer, or both. It would seem that whenever contamination takes place before primer application, TMIP bond strength is not affected.10 In our study, in which water or saliva contamination was introduced after primer application, bond strength for TMIP/Transbond XT was significantly less than that produced when no contamination was present. Furthermore, when water or saliva contamination was present, TMIP/Transbond XT produced bond strength values that were significantly lower than those of the other groups tested. Cacciafesta et al9 found that when no contamination was present, TMIP/Transbond XT provided significantly greater bond strength than was noted after water or saliva contamination following primer application. On the other hand, Zeppieri et al2 found
that even when TMIP was reapplied after saliva contamination, it produced significantly lower bond strength.2 Sayinsu et al3 showed that when contamination with saliva was introduced after the primer had been polymerized, bond strength was significantly greater than if it had not been polymerized. However, the bond strength was still less than when no contamination was present. When contamination takes place on already polymerized TMIP and another layer of the product is applied a second time, bond strength is similar to that achieved when no contamination is present.5 For Transbond PLUS, bond strength was similar in all three bonding conditions, regardless of whether it was used in combination with TMIP or TSEP. When bond strengths were evaluated for TSEP/Transbond PLUS and TMIP/Transbond PLUS individually under the three differing conditions, no significant differences were found with or without contamination by water or saliva. Until now, no studies of Transbond PLUS have been carried out. This adhesive contains fewer hydrophilic monomers than Transbond XT, and this fact could explain in part its better performance in wet conditions. Although Transbond PLUS contains less than 2% in weight of bisphenol A diglycidyl ether dimethacrylate (bis-GMA), Transbond XT contains 10% to 20%. On the other hand, Transbond PLUS includes polyethylene glycol dimethacrylate (PEGDMA) in its composition, which might enhance its tolerance of wet conditions. In studies of bonding onto dentin, in which the bonding process is complex because of the unpredictable quantity of water in this tissue, it has been seen that the addition of PEGDMA allows the bond material to tolerate greater concentrations of water. Diffusion of bis-GMA monomers over an area of wet demineralized dentin is less than with adhesives without PEGDMA18 because the relatively hydrophobic bisGMA cannot adequately infiltrate demineralized dentin under wet bonding conditions.19 Thus, the addition of PEGDMA might favor the infiltration of bis-GMA– based adhesives into the wet enamel and might pro-
132 mote homogeneous distribution of hydrophobic components throughout the interface. Brackets bonded with Transbond PLUS showed that when no contamination was present, significantly less adhesive was left on the teeth than when brackets were bonded with Transbond XT. This is an important advantage because the orthodontist needs less time to remove leftover bond material, and the risk of damage to tooth enamel diminishes. Consistent with results for bond strength, the system that was most affected by contamination from water or saliva was TMIP/Transbond XT, which left the entire adhesive on the bracket.
VICENTE, MENA, ORTIZ, BRAVO
6.
7.
8.
9.
CONCLUSIONS • When the risk of contamination by water or saliva during bracket bonding is foreseeable, the use of Transbond PLUS, combined to equal effect with TSEP or TMIP, is advisable. • However, when Transbond XT is used for resin bracket bonding, it shows a certain tolerance to wet conditions only when used in combination with TSEP.
10.
11.
12.
13.
ACKNOWLEDGMENT Our thanks to 3M Unitek Dental Products for providing the brackets and adhesives used in this study.
14.
REFERENCES
15.
1. Grandhi RK, Combe EC, Speidel TM. Shear bond strength of stainless steel orthodontic brackets with a moisture-insensitive primer. Am J Orthod Dentofacial Orthop. 2001; 119:251–255. 2. Zeppieri IL, Chung C-H, Mante FK. Effect of saliva on shear bond strength of an orthodontic adhesive used with moisture-insensitive and self-etching primers. Am J Orthod Dentofacial Orthop. 2003;124:414–419. 3. Sayinsu K, Isik F, Sezen S, Aydemir B. Light curing the primer—beneficial when working in problem areas? Angle Orthod. 2006;76:310–313. 4. Littlewood SJ, Mitchell L, Greenwood DC, Bubb NL, Wood DJ. Investigation of a hydrophilic primer for orthodontic bonding: an in vitro study. J Orthod. 2000;27:181–186. 5. Schaneveldt S, Foley TF. Bond strength comparison of
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