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Effect of chlorhexidine application on shear bond strength of brackets bonded with a resin-modified glass ionomer
ORIGINAL ARTICLE
Effect of chlorhexidine application on shear bond strength of brackets bonded with a resinmodified glass ionomer Vittorio Cacciafesta,a Maria Francesca Sfondrini,b Paola Stifanelli,c Andrea Scribante,c and Catherine Klersyd Varese and Pavia, Italy Introduction: The purpose of study was to assess the effect of chlorhexidine application on the shear bond strength and bond failure site of a resin-modified glass ionomer (Fuji Ortho LC, GC Europe, Leuven, Belgium). Methods: Forty-five bovine permanent mandibular incisors were randomly divided into 3 groups of 15. Group 1 had no chlorhexidine treatment and served as the control; groups 2 and 3 had chlorhexidine application immediately before and 1 week before bonding, respectively. Stainless steel brackets (DB, Leone, Sesto Fiorentino, Italy) were bonded with the resin-modified glass ionomer. After bonding, all samples were stored in distilled water for 24 hours and subsequently tested in a shear mode on a testing machine. Analysis of variance (ANOVA) and the Scheffé test were applied to determine significant differences in the shear bond strength values, and the chi-square test was used to determine significant differences in the adhesive remnant index scores among the groups. Significance for all statistical tests was predetermined at P ⬍ .05. Results: Group 1 (no chlorhexidine application) showed significantly higher shear bond strength values than group 2 (chlorhexidine applied immediately before bonding). No significant differences were found between groups 1 and 3 (chlorhexidine applied 1 week before bonding). Moreover, significant differences in debond locations were found among the 3 groups. Conclusions: Chlorhexidine application immediately before bonding significantly lowered the bond strength values of Fuji Ortho LC but did not affect its bond strength when applied 1 week before bonding. (Am J Orthod Dentofacial Orthop 2006;129:273-6)
C
hlorhexidine is an antibacterial and antiseptic agent widely used in dentistry.1 In both shortterm2 and long-term studies,3-4 it has been shown to be effective for plaque control and gingivitis without developing resistant organisms in the oral flora. Caries and decalcification can be greatly reduced by maintaining good oral hygiene, applying topical fluorides, and using a fluoride-containing toothpaste during orthodontic treatment.5-9 Some authors10 suggested that, during a severe cariogenic challenge, even fluorides might have a limited effect in the prevention of decalcification. Therefore, fluoride agents could be a
Assistant clinical professor, Department of Orthodontics, University of Insubria, Varese and Pavia, Italy. b Assistant clinical professor, Department of Orthodontics, University of Pavia, Pavia, Italy. c Research fellow, Department of Orthodontics, University of Pavia, Pavia, Italy. d Statistician, Clinical Epidemiology and Biometry Unit, Scientific Direction, IRCCS San Matteo, Pavia, Italy. Reprint requests to: Dr Vittorio Cacciafesta, c/o Studio Prof Giuseppe Sfondrini, Via Libertà 17, 27100 Pavia, Italy; e-mail, [email protected]. Submitted, April 2004; revised and accepted, July 2004. 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2004.07.050
further improved by the addition of antibacterial agents, such as xylitol, triclosan, and chlorhexidine.10 Chlorhexidine has been used as an adjunct treatment for periodontal disease as both a mouth rinse and an ingredient in toothpastes.1-3,11 It has also been suggested that chlorhexidine combined with thymol in a varnish could have a desensitizing effect on the teeth, lower bacterial activity in plaque while maintaining an ecological balance, and have excellent adsorption on the tooth surface.12 Moreover, the application of chlorhexidine varnish before and during orthodontic treatment was found to affect the salivary Streptococcus mutans levels for at least 3 months and even up to 7 months after application.13 Applying chlorhexidine to the enamel surface could increase antibacterial protection, but it can adversely influence bond strength, depending on the method of application.12 Because people with significant carious and periodontal challenges might be candidates for orthodontic treatment, it would be of interest to determine whether the use of chlorhexidine mouth rinse for 1 week before the bonding procedure can affect the bond strength of an orthodontic adhesive. The effect of chlorhexidine on shear bond 273
274 Cacciafesta et al
Table I.
American Journal of Orthodontics and Dentofacial Orthopedics February 2006
Bonding procedures for groups
Group
Bonding procedure
1 2
— —
3
1 week chlorhexidine treatment
— 1 week chlorhexidine treatment 1 week physiologic solution
strength of orthodontic brackets bonded with composites has been assessed in vitro with toothpastes12 and varnishes,12 after initial prophylaxis,14 and incorporating the chlorhexidine in the primer15 or sealant.12 To our knowledge, however, no studies in the literature have evaluated the effect of chlorhexidine rinse before bracket bonding with a resin-modified glass ionomer cement. The purpose of this study was to assess the effect of chlorhexidine mouth-rinse treatment at 2 times (immediately before bonding and 1 week before bonding) on the shear bond strength and bond failure site of a resin-modified glass ionomer. The null hypothesis was that there is no significant difference in bond strength and debond site location among the different chlorhexidine application times. MATERIAL AND METHODS
Forty-five freshly extracted bovine permanent mandibular incisors were collected from a local slaughterhouse and stored in a solution of 0.1% (weight/volume) thymol for a week. The criteria for tooth selection included intact buccal enamel with no cracks caused by the extraction forceps and no caries. After extraction, all enamel surfaces were examined under a light stereomicroscope at 10-times magnification. The teeth were randomly assigned to 1 of 3 groups by using random number tables. Each group consisted of 15 specimens. The teeth were cleansed of soft tissue with curettes, embedded in cold-curing, fast-setting acrylic (Leocryl, Leone, Sesto Fiorentino, Italy), and placed in metal rings. Each tooth was oriented so that its labial surface would be parallel to the force during the shear bond test. Forty-five stainless steel maxillary central incisor brackets with an .018-inch slot (DB, Leone) were bonded by 1 operator (P.S.). The average bracket base surface area was determined to be 12.4 mm2. This was verified by measuring it with a digital calliper (Mitutoyo, Miyazaki, Japan). The areas of 15 brackets were recorded, and the mean value was calculated. All teeth were cleaned with a mixture of water and
Conditioning Bonding Conditioning Bonding
Light-curing Light-curing
Conditioning Bonding
Light-curing
pumice by using a rubber polishing cup. As described in Table I, chlorhexidine pretreatment was not used for the teeth in group 1 (control group). The teeth in group 2 were bonded immediately after 1 week of chlorhexidine treatment (Chlorhexidine 0.20%, Dentosan, Compo, Lainate, Italy; 2 rinses per day), whereas the teeth in group 3 were bonded after 1 week of the same chlorhexidine treatment, followed by 1 week of storage in physiologic solution. Before bonding, all teeth were dried with oil-free air and conditioned with 10% polyacrylic acid (GC Conditioner, GC Europe, Leuven, Belgium) for 20 seconds, followed by thorough washing and drying. All brackets were bonded by using a resin-modified glass ionomer adhesive (Fuji Ortho LC, GC Europe) according to the manufacturer’s guidelines. The adhesivefilled Fuji Ortho LC capsule was activated by manual squeezing and then triturated for 10 seconds at approximately 4000 rpm. The capsule was then loaded into an application gun, and the adhesive was squeezed onto the bracket base. The brackets were positioned on the teeth near the center of the facial surfaces with sufficient pressure to express excess adhesive, which was removed from the margins of the bracket base with a scaler before polymerization. All brackets were lightcured for 40 seconds with a halogen light-curing unit (Ortholux XT, 3M Unitek, Monrovia, Calif)—10 seconds each from the mesial, distal, gingival, and occlusal margins. After bonding, all samples were stored in distilled water at room temperature for 24 hours and tested in shear mode on a universal testing machine (Instron, Canton, Mass). For shear testing, the specimens were secured in the lower jaw of the machine so that the bracket base of the sample paralleled the direction of the shear force. The specimens were stressed in an occlusogingival direction with a crosshead speed of 1 mm/minute, according to previous studies.16-18 The maximum load necessary to debond or initiate bracket fracture was recorded in newtons and then converted into megapascals as a ratio of newtons to surface area of the bracket. After bond failure, the bracket bases and the enamel
Cacciafesta et al 275
American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 2
Table II. Descriptive statistics (in MPa) of shear bond strengths of groups (each group consisted of 15 specimens) Group
Mean
SD
Minimum
Median
Maximum
Scheffé*
1 2 3
11.67 9.20 10.12
2.40 2.84 1.82
8.45 6.44 7.73
10.79 8.34 9.38
14.85 15.06 14.11
A B A,B
*Means with same letter are not significantly different.
surfaces were examined by the same operator (P.S.) under a light stereomicroscope at 10-times magnification. The adhesive remnant index (ARI) was used to assess the amount of adhesive left on the enamel surfaces.19 The ARI has a range of 1 to 5 (1 ⫽ all adhesive, with an impression of the bracket base, remained on the tooth; 2 ⫽ more than 90% of the adhesive remained; 3 ⫽ more than 10% but less than 90% of the adhesive remained on the tooth; 4 ⫽ less than 10% of the adhesive remained on the tooth surface; 5 ⫽ no adhesive remained on the enamel). The ARI scores were used as a more complex method of defining the site of bond failure between enamel, adhesive, and bracket base. Statistical analysis was performed with the Stata 7 program (Stata, College Station, Tex). Descriptive statistics that included the mean, standard deviation, median, minimum, and maximum values were calculated for each of the 3 groups. Analysis of variance (ANOVA) was applied to determine whether significant differences existed among the various groups. For the post-hoc test, the Scheffé test was used. The chi-square test was used to determine significant differences in the ARI scores among the different groups. Significance for all statistical tests was predetermined at P ⬍.05. RESULTS
The descriptive statistics for the shear bond strengths of the 3 groups are given in Table II. Shear forces are in megapascals (MPa). The results of ANOVA indicated significant differences among the groups (P ⫽ .000). The Scheffé test showed that the bond strengths of group 1 (no chlorhexidine treatment) were significantly higher than those of group 2 (chlorhexidine treatment immediately before bonding) (P ⫽ .007). No significant differences were found between groups 1 and 3 (P ⫽ .06), and between groups 2 and 3 (P ⫽ .6). The ARI scores for the 3 groups are listed in Table III. The chi-square test results indicated significant differences among the groups (P ⫽ .03). Groups 1 and
Table III.
Frequency of distribution of ARI scores (%)
Group
ARI ⫽ 1
ARI ⫽ 2
ARI ⫽ 3
ARI ⫽ 4
ARI ⫽ 5
1 2 3
0 (0.0%) 0 (0.0%) 0 (0.0%)
0 (0.0%) 0 (0.0%) 0 (0.0%)
2 (13.3%) 6 (40.0%) 4 (26.7%)
4 (26.7%) 7 (46.7%) 3 (20.0%)
9 (60.0%) 2 (13.3%) 8 (53.3%)
3 showed a significantly higher frequency of ARI score 5, whereas group 2 showed a significantly higher frequency of ARI scores 3 and 4 (P ⫽ .01). DISCUSSION
The null hypothesis was partially rejected. Bond strengths of group 1 were significantly higher than those of group 2. No significant differences were found between groups 1 and 3, and between groups 2 and 3. In the literature, no studies have evaluated the effect of chlorhexidine treatment on the shear bond strength of a resin-modified glass ionomer cement. Bishara et al14 compared prophylaxis with pumice only and pumice prophylaxis followed by application of 0.12% chlorhexidine paste, and found no significant differences in bond strength values. Damon et al15 evaluated the effect of a chlorhexidine varnish incorporated in the primer solution, showing no significant differences in shear bond strengths compared with the control group. Other authors evaluated the effect of a chlorhexidine toothpaste and varnish on the shear bond strength of orthodontic brackets.12 The findings showed that the shear bond strength was not significantly affected when chlorhexidine was applied after bonding or as a prophylactic paste over unetched enamel, or when the varnish was premixed with the sealant and applied on the etched enamel surface. On the other hand, when chlorhexidine varnish was applied as a separate layer on the etched enamel surface or over the sealant, shear bond strength values and bracket failure rates became clinically unacceptable. Reynolds20 suggested that a minimum bond strength of 6 to 8 MPa was adequate for most clinical orthodontic needs. These bond strengths are considered able to withstand masticatory and orthodontic forces. In our study, all bond strength values were above this minimum requirement. The ARI scores of the 3 groups indicated that groups 1 and 3 had a significantly higher percentage of score 5, whereas group 2 had a significantly higher frequency of scores 3 and 4. Bishara et al14 found no significant differences in ARI scores between pumice prophylaxis only and pumice prophylaxis followed by chlorhexidine paste (ARI scores 3). Other authors evaluated the effect of
276 Cacciafesta et al
American Journal of Orthodontics and Dentofacial Orthopedics February 2006
chlorhexidine varnish incorporated in the primer and found no significant differences in ARI scores with the control group (ARI scores 3).15 Another investigation showed ARI scores 2 and 3 when chlorhexidine was applied after the bonding procedure or as a prophylactic paste over unetched enamel, and when the varnish was premixed with the sealant and applied on the etched enamel surface.12 On the other hand, a higher frequency of ARI scores 4 and 5 were reported when chlorhexidine varnish was applied as a separate layer on the etched enamel surface or over the sealant. The variability of the results can be attributed to differences in the mechanical and physical properties of the materials tested in each study (composite resins in the previous studies and resin-modified glass ionomer in ours).
mouthrinse on orthodontic patients aged 11 through 17 with established gingivitis. Am J Orthod Dentofacial Orthop 1991;100:324-9. Sheykholeslam Z, Buonocore MG, Gwinnett AJ. Effect of fluorides on the bonding of resins to phosphoric acid-etched bovine enamel. Arch Oral Biol 1972;17:1037-45. Shannon IL. Prevention of decalcification in orthodontic patients. J Clin Orthod 1981;15:694-705. Wang WN, Sheen DH. The effect of pretreatment with fluoride on the tensile bond strength of orthodontic bonding. Angle Orthod 1991;61:31-4. Aboush YE, Tareen A, Elderton RJ. Resin-to-enamel bonds: effect of cleaning the enamel surface with prophylaxis pastes containing fluoride or oil. Br Dent J 1991;171:207-9. Garcia-Godoy F, Hubbard GW, Storey AT. Effect of a fluoridated etching gel on enamel morphology and shear bond strength of orthodontic brackets. Am J Orthod Dentofacial Orthop 1991; 100:163-70. Øgaard B, Rølla G. Cariogenical aspects of treatment with fixed orthodontic appliances. Part II. New concept on cariostatic mechanism of topical fluoride. Kieferorthopädische Mitterlungen 1993;6:45-51. Barkvoll P, Rølla G, Svendsen AK. Interaction between chlorhexidine digluconate and sodium lauryl sulfate in vivo. J Clin Periodontol 1989;16:593-5. Bishara SE, Vonwald L, Zamtua J, Damon PL. Effects of various methods of chlorhexidine application on shear bond strength. Am J Orthod Dentofacial Orthop 1998;114:150-3. Sandham HJ, Nadeau L, Phillips HI. The effect of chlorhexidine varnish treatment on salivary mutans streptococcal levels in child orthodontic patients. J Dent Res 1992;71:32-5. Bishara SE, Damon PL, Olsen ME, Jakobsen JR. Effect of applying chlorhexidine antibacterial agent on the shear bond strength of orthodontic brackets. Angle Orthod 1996;66:313-6. Damon PL, Bishara SE, Olsen ME, Jakobsen JR. Bond strength following the application of chlorhexidine on etched enamel. Angle Orthod 1997;67:169-72. Jobalia SB, Valente RM, de Rijk WG, BeGole EA, Evans CA. Bond strength of visible light-cured glass ionomer orthodontic cement. Am J Orthod Dentofacial Orthop 1997;112:205-8. Millett DT, Cattanach D, McFadzean R, Pattison J, McColl J. Laboratory evaluation of a compomer and a resin-modified glass ionomer cement for orthodontic bonding. Angle Orthod 1999; 69:58-63. Sfondrini MF, Cacciafesta V, Pistorio A, Sfondrini G. Effects of conventional and high-intensity light-curing on enamel shear bond strength of composite resin and resin-modified glass ionomer. Am J Orthod Dentofacial Orthop 2001;119:30-5. Oliver RG. The effect of different methods of bracket removal on the amount of residual adhesive. Am J Orthod Dentofacial Orthop 1988;93:196-200. Reynolds IR. A review of direct orthodontic bonding. Br J Orthod 1975;2:171-8.
5.
6. 7.
8.
9.
10.
CONCLUSIONS
This study demonstrated the following: 1. Fuji Ortho LC showed the highest bond strengths when used without chlorhexidine or when bonded 1 week after chlorhexidine treatment. 2. Chlorhexidine application immediately before bonding significantly lowered the bond strength of Fuji Ortho LC and increased the amount of adhesive remaining on enamel after debonding. 3. All combinations tested showed clinically acceptable bond strengths. 4. Significant differences were found among the ARI scores of the 3 groups. We thank Leone, GC Europe, and Dentosan for providing the materials tested in this study, and G. Scommegna and E. Ladani (Leone) for their excellent technical assistance.
11.
12.
13.
14.
15.
16.
17.
REFERENCES 1. Mandel ID. Antimicrobial mouthrinses: overview and update. J Am Dent Assoc 1994;125:2S-10S. 2. Löe H, Schiött CR. The effect of mouthrinses and topical application of chlorhexidine on the development of dental plaque and gingivitis in man. J Periodontal Res 1970;5:79-83. 3. Löe H, Schiött CR, Karring G, Karring T. Two years oral use of chlorhexidine in man. I. General design and clinical effects. J Periodontal Res 1976;11:135-44. 4. Brightman LJ, Terezhalmy GT, Greenwell H, Jacobs M, Enlow DH. The effects of a 0.12 percent chlorhexidine gluconate
18.
19.
20.
Effect of chlorhexidine application on shear bond strength of brackets bonded with a resinmodified glass ionomer Vittorio Cacciafesta,a Maria Francesca Sfondrini,b Paola Stifanelli,c Andrea Scribante,c and Catherine Klersyd Varese and Pavia, Italy Introduction: The purpose of study was to assess the effect of chlorhexidine application on the shear bond strength and bond failure site of a resin-modified glass ionomer (Fuji Ortho LC, GC Europe, Leuven, Belgium). Methods: Forty-five bovine permanent mandibular incisors were randomly divided into 3 groups of 15. Group 1 had no chlorhexidine treatment and served as the control; groups 2 and 3 had chlorhexidine application immediately before and 1 week before bonding, respectively. Stainless steel brackets (DB, Leone, Sesto Fiorentino, Italy) were bonded with the resin-modified glass ionomer. After bonding, all samples were stored in distilled water for 24 hours and subsequently tested in a shear mode on a testing machine. Analysis of variance (ANOVA) and the Scheffé test were applied to determine significant differences in the shear bond strength values, and the chi-square test was used to determine significant differences in the adhesive remnant index scores among the groups. Significance for all statistical tests was predetermined at P ⬍ .05. Results: Group 1 (no chlorhexidine application) showed significantly higher shear bond strength values than group 2 (chlorhexidine applied immediately before bonding). No significant differences were found between groups 1 and 3 (chlorhexidine applied 1 week before bonding). Moreover, significant differences in debond locations were found among the 3 groups. Conclusions: Chlorhexidine application immediately before bonding significantly lowered the bond strength values of Fuji Ortho LC but did not affect its bond strength when applied 1 week before bonding. (Am J Orthod Dentofacial Orthop 2006;129:273-6)
C
hlorhexidine is an antibacterial and antiseptic agent widely used in dentistry.1 In both shortterm2 and long-term studies,3-4 it has been shown to be effective for plaque control and gingivitis without developing resistant organisms in the oral flora. Caries and decalcification can be greatly reduced by maintaining good oral hygiene, applying topical fluorides, and using a fluoride-containing toothpaste during orthodontic treatment.5-9 Some authors10 suggested that, during a severe cariogenic challenge, even fluorides might have a limited effect in the prevention of decalcification. Therefore, fluoride agents could be a
Assistant clinical professor, Department of Orthodontics, University of Insubria, Varese and Pavia, Italy. b Assistant clinical professor, Department of Orthodontics, University of Pavia, Pavia, Italy. c Research fellow, Department of Orthodontics, University of Pavia, Pavia, Italy. d Statistician, Clinical Epidemiology and Biometry Unit, Scientific Direction, IRCCS San Matteo, Pavia, Italy. Reprint requests to: Dr Vittorio Cacciafesta, c/o Studio Prof Giuseppe Sfondrini, Via Libertà 17, 27100 Pavia, Italy; e-mail, [email protected]. Submitted, April 2004; revised and accepted, July 2004. 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2004.07.050
further improved by the addition of antibacterial agents, such as xylitol, triclosan, and chlorhexidine.10 Chlorhexidine has been used as an adjunct treatment for periodontal disease as both a mouth rinse and an ingredient in toothpastes.1-3,11 It has also been suggested that chlorhexidine combined with thymol in a varnish could have a desensitizing effect on the teeth, lower bacterial activity in plaque while maintaining an ecological balance, and have excellent adsorption on the tooth surface.12 Moreover, the application of chlorhexidine varnish before and during orthodontic treatment was found to affect the salivary Streptococcus mutans levels for at least 3 months and even up to 7 months after application.13 Applying chlorhexidine to the enamel surface could increase antibacterial protection, but it can adversely influence bond strength, depending on the method of application.12 Because people with significant carious and periodontal challenges might be candidates for orthodontic treatment, it would be of interest to determine whether the use of chlorhexidine mouth rinse for 1 week before the bonding procedure can affect the bond strength of an orthodontic adhesive. The effect of chlorhexidine on shear bond 273
274 Cacciafesta et al
Table I.
American Journal of Orthodontics and Dentofacial Orthopedics February 2006
Bonding procedures for groups
Group
Bonding procedure
1 2
— —
3
1 week chlorhexidine treatment
— 1 week chlorhexidine treatment 1 week physiologic solution
strength of orthodontic brackets bonded with composites has been assessed in vitro with toothpastes12 and varnishes,12 after initial prophylaxis,14 and incorporating the chlorhexidine in the primer15 or sealant.12 To our knowledge, however, no studies in the literature have evaluated the effect of chlorhexidine rinse before bracket bonding with a resin-modified glass ionomer cement. The purpose of this study was to assess the effect of chlorhexidine mouth-rinse treatment at 2 times (immediately before bonding and 1 week before bonding) on the shear bond strength and bond failure site of a resin-modified glass ionomer. The null hypothesis was that there is no significant difference in bond strength and debond site location among the different chlorhexidine application times. MATERIAL AND METHODS
Forty-five freshly extracted bovine permanent mandibular incisors were collected from a local slaughterhouse and stored in a solution of 0.1% (weight/volume) thymol for a week. The criteria for tooth selection included intact buccal enamel with no cracks caused by the extraction forceps and no caries. After extraction, all enamel surfaces were examined under a light stereomicroscope at 10-times magnification. The teeth were randomly assigned to 1 of 3 groups by using random number tables. Each group consisted of 15 specimens. The teeth were cleansed of soft tissue with curettes, embedded in cold-curing, fast-setting acrylic (Leocryl, Leone, Sesto Fiorentino, Italy), and placed in metal rings. Each tooth was oriented so that its labial surface would be parallel to the force during the shear bond test. Forty-five stainless steel maxillary central incisor brackets with an .018-inch slot (DB, Leone) were bonded by 1 operator (P.S.). The average bracket base surface area was determined to be 12.4 mm2. This was verified by measuring it with a digital calliper (Mitutoyo, Miyazaki, Japan). The areas of 15 brackets were recorded, and the mean value was calculated. All teeth were cleaned with a mixture of water and
Conditioning Bonding Conditioning Bonding
Light-curing Light-curing
Conditioning Bonding
Light-curing
pumice by using a rubber polishing cup. As described in Table I, chlorhexidine pretreatment was not used for the teeth in group 1 (control group). The teeth in group 2 were bonded immediately after 1 week of chlorhexidine treatment (Chlorhexidine 0.20%, Dentosan, Compo, Lainate, Italy; 2 rinses per day), whereas the teeth in group 3 were bonded after 1 week of the same chlorhexidine treatment, followed by 1 week of storage in physiologic solution. Before bonding, all teeth were dried with oil-free air and conditioned with 10% polyacrylic acid (GC Conditioner, GC Europe, Leuven, Belgium) for 20 seconds, followed by thorough washing and drying. All brackets were bonded by using a resin-modified glass ionomer adhesive (Fuji Ortho LC, GC Europe) according to the manufacturer’s guidelines. The adhesivefilled Fuji Ortho LC capsule was activated by manual squeezing and then triturated for 10 seconds at approximately 4000 rpm. The capsule was then loaded into an application gun, and the adhesive was squeezed onto the bracket base. The brackets were positioned on the teeth near the center of the facial surfaces with sufficient pressure to express excess adhesive, which was removed from the margins of the bracket base with a scaler before polymerization. All brackets were lightcured for 40 seconds with a halogen light-curing unit (Ortholux XT, 3M Unitek, Monrovia, Calif)—10 seconds each from the mesial, distal, gingival, and occlusal margins. After bonding, all samples were stored in distilled water at room temperature for 24 hours and tested in shear mode on a universal testing machine (Instron, Canton, Mass). For shear testing, the specimens were secured in the lower jaw of the machine so that the bracket base of the sample paralleled the direction of the shear force. The specimens were stressed in an occlusogingival direction with a crosshead speed of 1 mm/minute, according to previous studies.16-18 The maximum load necessary to debond or initiate bracket fracture was recorded in newtons and then converted into megapascals as a ratio of newtons to surface area of the bracket. After bond failure, the bracket bases and the enamel
Cacciafesta et al 275
American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 2
Table II. Descriptive statistics (in MPa) of shear bond strengths of groups (each group consisted of 15 specimens) Group
Mean
SD
Minimum
Median
Maximum
Scheffé*
1 2 3
11.67 9.20 10.12
2.40 2.84 1.82
8.45 6.44 7.73
10.79 8.34 9.38
14.85 15.06 14.11
A B A,B
*Means with same letter are not significantly different.
surfaces were examined by the same operator (P.S.) under a light stereomicroscope at 10-times magnification. The adhesive remnant index (ARI) was used to assess the amount of adhesive left on the enamel surfaces.19 The ARI has a range of 1 to 5 (1 ⫽ all adhesive, with an impression of the bracket base, remained on the tooth; 2 ⫽ more than 90% of the adhesive remained; 3 ⫽ more than 10% but less than 90% of the adhesive remained on the tooth; 4 ⫽ less than 10% of the adhesive remained on the tooth surface; 5 ⫽ no adhesive remained on the enamel). The ARI scores were used as a more complex method of defining the site of bond failure between enamel, adhesive, and bracket base. Statistical analysis was performed with the Stata 7 program (Stata, College Station, Tex). Descriptive statistics that included the mean, standard deviation, median, minimum, and maximum values were calculated for each of the 3 groups. Analysis of variance (ANOVA) was applied to determine whether significant differences existed among the various groups. For the post-hoc test, the Scheffé test was used. The chi-square test was used to determine significant differences in the ARI scores among the different groups. Significance for all statistical tests was predetermined at P ⬍.05. RESULTS
The descriptive statistics for the shear bond strengths of the 3 groups are given in Table II. Shear forces are in megapascals (MPa). The results of ANOVA indicated significant differences among the groups (P ⫽ .000). The Scheffé test showed that the bond strengths of group 1 (no chlorhexidine treatment) were significantly higher than those of group 2 (chlorhexidine treatment immediately before bonding) (P ⫽ .007). No significant differences were found between groups 1 and 3 (P ⫽ .06), and between groups 2 and 3 (P ⫽ .6). The ARI scores for the 3 groups are listed in Table III. The chi-square test results indicated significant differences among the groups (P ⫽ .03). Groups 1 and
Table III.
Frequency of distribution of ARI scores (%)
Group
ARI ⫽ 1
ARI ⫽ 2
ARI ⫽ 3
ARI ⫽ 4
ARI ⫽ 5
1 2 3
0 (0.0%) 0 (0.0%) 0 (0.0%)
0 (0.0%) 0 (0.0%) 0 (0.0%)
2 (13.3%) 6 (40.0%) 4 (26.7%)
4 (26.7%) 7 (46.7%) 3 (20.0%)
9 (60.0%) 2 (13.3%) 8 (53.3%)
3 showed a significantly higher frequency of ARI score 5, whereas group 2 showed a significantly higher frequency of ARI scores 3 and 4 (P ⫽ .01). DISCUSSION
The null hypothesis was partially rejected. Bond strengths of group 1 were significantly higher than those of group 2. No significant differences were found between groups 1 and 3, and between groups 2 and 3. In the literature, no studies have evaluated the effect of chlorhexidine treatment on the shear bond strength of a resin-modified glass ionomer cement. Bishara et al14 compared prophylaxis with pumice only and pumice prophylaxis followed by application of 0.12% chlorhexidine paste, and found no significant differences in bond strength values. Damon et al15 evaluated the effect of a chlorhexidine varnish incorporated in the primer solution, showing no significant differences in shear bond strengths compared with the control group. Other authors evaluated the effect of a chlorhexidine toothpaste and varnish on the shear bond strength of orthodontic brackets.12 The findings showed that the shear bond strength was not significantly affected when chlorhexidine was applied after bonding or as a prophylactic paste over unetched enamel, or when the varnish was premixed with the sealant and applied on the etched enamel surface. On the other hand, when chlorhexidine varnish was applied as a separate layer on the etched enamel surface or over the sealant, shear bond strength values and bracket failure rates became clinically unacceptable. Reynolds20 suggested that a minimum bond strength of 6 to 8 MPa was adequate for most clinical orthodontic needs. These bond strengths are considered able to withstand masticatory and orthodontic forces. In our study, all bond strength values were above this minimum requirement. The ARI scores of the 3 groups indicated that groups 1 and 3 had a significantly higher percentage of score 5, whereas group 2 had a significantly higher frequency of scores 3 and 4. Bishara et al14 found no significant differences in ARI scores between pumice prophylaxis only and pumice prophylaxis followed by chlorhexidine paste (ARI scores 3). Other authors evaluated the effect of
276 Cacciafesta et al
American Journal of Orthodontics and Dentofacial Orthopedics February 2006
chlorhexidine varnish incorporated in the primer and found no significant differences in ARI scores with the control group (ARI scores 3).15 Another investigation showed ARI scores 2 and 3 when chlorhexidine was applied after the bonding procedure or as a prophylactic paste over unetched enamel, and when the varnish was premixed with the sealant and applied on the etched enamel surface.12 On the other hand, a higher frequency of ARI scores 4 and 5 were reported when chlorhexidine varnish was applied as a separate layer on the etched enamel surface or over the sealant. The variability of the results can be attributed to differences in the mechanical and physical properties of the materials tested in each study (composite resins in the previous studies and resin-modified glass ionomer in ours).
mouthrinse on orthodontic patients aged 11 through 17 with established gingivitis. Am J Orthod Dentofacial Orthop 1991;100:324-9. Sheykholeslam Z, Buonocore MG, Gwinnett AJ. Effect of fluorides on the bonding of resins to phosphoric acid-etched bovine enamel. Arch Oral Biol 1972;17:1037-45. Shannon IL. Prevention of decalcification in orthodontic patients. J Clin Orthod 1981;15:694-705. Wang WN, Sheen DH. The effect of pretreatment with fluoride on the tensile bond strength of orthodontic bonding. Angle Orthod 1991;61:31-4. Aboush YE, Tareen A, Elderton RJ. Resin-to-enamel bonds: effect of cleaning the enamel surface with prophylaxis pastes containing fluoride or oil. Br Dent J 1991;171:207-9. Garcia-Godoy F, Hubbard GW, Storey AT. Effect of a fluoridated etching gel on enamel morphology and shear bond strength of orthodontic brackets. Am J Orthod Dentofacial Orthop 1991; 100:163-70. Øgaard B, Rølla G. Cariogenical aspects of treatment with fixed orthodontic appliances. Part II. New concept on cariostatic mechanism of topical fluoride. Kieferorthopädische Mitterlungen 1993;6:45-51. Barkvoll P, Rølla G, Svendsen AK. Interaction between chlorhexidine digluconate and sodium lauryl sulfate in vivo. J Clin Periodontol 1989;16:593-5. Bishara SE, Vonwald L, Zamtua J, Damon PL. Effects of various methods of chlorhexidine application on shear bond strength. Am J Orthod Dentofacial Orthop 1998;114:150-3. Sandham HJ, Nadeau L, Phillips HI. The effect of chlorhexidine varnish treatment on salivary mutans streptococcal levels in child orthodontic patients. J Dent Res 1992;71:32-5. Bishara SE, Damon PL, Olsen ME, Jakobsen JR. Effect of applying chlorhexidine antibacterial agent on the shear bond strength of orthodontic brackets. Angle Orthod 1996;66:313-6. Damon PL, Bishara SE, Olsen ME, Jakobsen JR. Bond strength following the application of chlorhexidine on etched enamel. Angle Orthod 1997;67:169-72. Jobalia SB, Valente RM, de Rijk WG, BeGole EA, Evans CA. Bond strength of visible light-cured glass ionomer orthodontic cement. Am J Orthod Dentofacial Orthop 1997;112:205-8. Millett DT, Cattanach D, McFadzean R, Pattison J, McColl J. Laboratory evaluation of a compomer and a resin-modified glass ionomer cement for orthodontic bonding. Angle Orthod 1999; 69:58-63. Sfondrini MF, Cacciafesta V, Pistorio A, Sfondrini G. Effects of conventional and high-intensity light-curing on enamel shear bond strength of composite resin and resin-modified glass ionomer. Am J Orthod Dentofacial Orthop 2001;119:30-5. Oliver RG. The effect of different methods of bracket removal on the amount of residual adhesive. Am J Orthod Dentofacial Orthop 1988;93:196-200. Reynolds IR. A review of direct orthodontic bonding. Br J Orthod 1975;2:171-8.
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CONCLUSIONS
This study demonstrated the following: 1. Fuji Ortho LC showed the highest bond strengths when used without chlorhexidine or when bonded 1 week after chlorhexidine treatment. 2. Chlorhexidine application immediately before bonding significantly lowered the bond strength of Fuji Ortho LC and increased the amount of adhesive remaining on enamel after debonding. 3. All combinations tested showed clinically acceptable bond strengths. 4. Significant differences were found among the ARI scores of the 3 groups. We thank Leone, GC Europe, and Dentosan for providing the materials tested in this study, and G. Scommegna and E. Ladani (Leone) for their excellent technical assistance.
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REFERENCES 1. Mandel ID. Antimicrobial mouthrinses: overview and update. J Am Dent Assoc 1994;125:2S-10S. 2. Löe H, Schiött CR. The effect of mouthrinses and topical application of chlorhexidine on the development of dental plaque and gingivitis in man. J Periodontal Res 1970;5:79-83. 3. Löe H, Schiött CR, Karring G, Karring T. Two years oral use of chlorhexidine in man. I. General design and clinical effects. J Periodontal Res 1976;11:135-44. 4. Brightman LJ, Terezhalmy GT, Greenwell H, Jacobs M, Enlow DH. The effects of a 0.12 percent chlorhexidine gluconate
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