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Table of Contents   
ORIGINAL RESEARCH  
Year : 2013  |  Volume : 24  |  Issue : 5  |  Page : 616-621
Effect of various commercially available mouthrinses on shear bond strength of orthodontic metal brackets: An in vitro study


1 Department of Orthodontics, Priyadarshini Dental College and Hospital, Thiruvallur, Tamil Nadu, India
2 Department of Orthodontics, Ragas Dental College and Hospital, Tamilnadu, India

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Date of Submission11-Jul-2010
Date of Decision10-Aug-2010
Date of Acceptance08-Jun-2013
Date of Web Publication21-Dec-2013
 

   Abstract 

Context: Alcohol is known to degrade and dissolve the bisphenol A glycidyl methacrylate present in the composite resin. The effect of alcohol containing mouthrinses on the shear bond strength of orthodontic metal brackets bonded with composite resin has not been verified until date and is the purpose of this study.
Aims: The aims and objectives of the present study were to evaluate (1) Whether there is a significant difference in the shear bond strength of metal orthodontic brackets after the 1 year (12 h) and 2 years simulation (24 h) of mouth rinsing with 4 different commercially available mouthrinses (2 alcoholic and 2 alcohol-free mouthrinses) when compared to the control. (2) Whether alcohol containing mouthrinses have more adverse effect on the shear bond strength when compared with alcohol-free mouthrinses. (3) To assess the site of bond failure using adhesive remnant index.
Setting and Design: Experimental - laboratory based.
Materials and Methods: A total of 100 upper premolars extracted for orthodontic purpose were collected immediately after extraction, cleared soft-tissue debris and blood and immediately stored in distilled water with 0.1% thymol crystals added to inhibit bacterial growth. Two alcohol containing mouthrinses and two alcohol-free mouthrinses were used and the bonded teeth were placed in the mouthrinses for a stipulated period of time (1 year simulation and 2 years simulation) and shear bond strength were tested using Lloyd Universal Testing Machine.
Statistical Analysis Used: The data were analyzed using analysis of variance and paired samples t-test.
Results: After the 1 year and 2 years simulation time, samples stored in alcohol containing mouthrinses showed lower bond strength (P < 0.05) when compared to samples stored in alcohol free mouthrinses and distilled water (control).
Conclusion: Alcohol containing mouthrinses affect the shear bond strength of the metal orthodontic brackets bonded with composite resin (Transbond XT in the present study), more when compared with alcohol-free mouthrinses. It is, therefore, highly advisable to avoid alcohol containing mouthrinses in patients undergoing orthodontic treatment and use alcohol-free mouthrinses as adjuncts to regular oral hygiene procedures for maintaining good enamel integrity and periodontal health, without compromising the shear bond strength of the bonded metal brackets.

Keywords: Alcohol-free mouthrinse, alcoholic mouthrinse, shear bond strength

How to cite this article:
Meeran NA, George AM. Effect of various commercially available mouthrinses on shear bond strength of orthodontic metal brackets: An in vitro study. Indian J Dent Res 2013;24:616-21

How to cite this URL:
Meeran NA, George AM. Effect of various commercially available mouthrinses on shear bond strength of orthodontic metal brackets: An in vitro study. Indian J Dent Res [serial online] 2013 [cited 2019 Sep 19];24:616-21. Available from: http://www.ijdr.in/text.asp?2013/24/5/616/123404
Mouthrinses are regularly being prescribed for orthodontic patients as an oral hygiene aid to prevent enamel decalcification, gingivitis and periodontal breakdown. Most mouthrinses contain 18-26% alcohol as a solvent, preservative and semi-active ingredient. Several studies [1],[2],[3],[4],[5],[6],[7],[8],[9],[10],[11] have proved that alcohol-containing mouthrinses degrade composite resin restorations and accelerate the resin wear by dissolving the bisphenol A glycidyl methacrylate (BIS-GMA) present in composite resin. However, the effect of these mouthrinses, used during orthodontic treatment, on the shear bond strength of orthodontic metal brackets has not been studied until now.


   Materials and Methods Top


  1. Teeth used for the study: A total of 100 upper premolars extracted for orthodontic purpose were collected immediately after extraction, cleared of soft-tissue debris and blood and immediately stored in distilled water with 0.1% thymol crystals added to inhibit bacterial growth. Only intact, non-carious, unrestored teeth with no developmental defects and no visible evidence of abnormal enamel cracking on the buccal surface were used
  2. Mouthrinses used in this study [Figure 1]a
    Figure 1

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    • Group A (control): Distilled water (white)
    • Group B (alcoholic mouthrinses)

      • Group B l: Listerine 12 h (light blue) [Figure 1]b
      • Group B 2: Listerine 24 h (dark blue)
      • Group B 3: Colgate Plax 12 h (light green)
      • Group B 4: Colgate Plax 24 h (dark green)


    • Group C (alcohol-free mouthrinses)


    • Group C l: Hexidine 12 h (orange) [Figure 1]b
    • Group C 2: Hexidine 24 h (red)
    • Group C 3: S Flo 12 h (grey)
    • Group C 4: S Flo 24 h (black)


    Listerine and Colgate Plax are alcoholic mouthrinses containing 21.6% and 12% alcohol respectively Hexidine and S Flo are alcohol-free mouthrinses
  3. Brackets: 0.022 Roth stainless steel premolar brackets with metallic fill-mesh backing were used [American Orthodontics]. Base dimensions −9.250 mm 2 (given by the manufacturers)
  4. Etchant 37% Orthophosphoric acid
  5. Primer and adhesive Transbond XT [Figure 2]
  6. Light cure kit: 3M Ortholux curing light, light output power −450 mW/cm 2 [Figure 3]
  7. Universal testing machine: (Lloyd). Capacity 100 kN [Figure 4].
Figure 2: Armamentarium used for bonding

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Figure 3: Ortholux XT Halogen curing unit

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Figure 4: Lloyd universal testing machine

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   Methodology Top


Bonding protocols of the study groups

All bonding procedures were carried out by the same operator and a standard protocol was followed. The teeth were etched with 37% orthophosphoric acid gel for 30 s, rinsed with water for 10 s and dried for 10 s. After applying primer to the tooth surface, composite was applied to the bracket base and bonded on the teeth. The excess composite was removed and then light cured for 40 s. All brackets were bonded with bracket base perpendicular to the buccal surface and parallel to the direction of shear debonding force. After bonding, the specimens were stored in distilled water at 37°C for 24 h in an incubator to allow full curing of the composite, before being put into one of the mouthrinses.

Various studies [4],[10],[11] have used this simulation time for evaluating the effect of alcoholic and alcohol-free mouthrinses on the composite resin. The simulation time for 1 year and 2-year mouthrinse use has been calculated as follows. To simulate a 1-year regimen of rinsing for 2 min/day, (2 min/day × 365 days = 730 min. Simulated by 12 h × 60 min = 720 min).

The 1-year simulation experimental groups were stored in 20 ml of one of the mouthrinses for a period of 12 h (which has been reported to be equivalent in time to 1 year of 2 min of mouth rinse use-once a day) as done by Gürgan et al. [4] , Gürdal et al. [10] and Yap et al. [11] [Figure 5]. The 2-year simulation experimental groups were stored in 20 ml of one of the mouthrinses for a period of 24 h (which has been reported to be equivalent in time to 2 year of 2 min of mouthrinse use-once a day) as done by Yap et al. [11] Specimens in mouthrinses were shaken every hour, to prevent chemical equilibrium around the composite bracket interface and kept at 37°C throughout the study. At the end of the specified time, the specimens were removed and submerged in distilled water. The teeth were mounted in cold curing acrylic resin [Figure 6] and bond strength evaluated using a Lloyd universal testing machine [Figure 7].
Figure 5: Samples placed in the mouthrinses

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Figure 6: Samples mounted in acrylic for shear bond strength testing

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Figure 7: Samples being tested for shear bond strength

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The force value at which the bond failure occurred was recorded from the display panel of the machine in Newtons(N) and was subsequently calculated in Megapascals (Mpa) using the formula below:



Statistical analysis

Descriptive statistics including the mean, standard deviation and minimum and maximum values were calculated for each of the nine test groups. Analysis of variance was used to determine if significant differences were present in the shear bond strength between the nine groups. If statistical differences were present, BONFERRONI multiple range tests were used to determine which of the means were significantly different from each other. Significance for all statistical tests was predetermined at P < 0.05.

Test for debonding characteristics

The surface of the debonded specimens was studied under a stereomicroscope under ×10 magnification to identify the site of bond failures between enamel, adhesive and bracket base. [13],[14],[15] The samples were mounted in acrylic and color coded by an operator who was blind to the purpose of this study. Shear bond strength testing and adhesive remnant index (ARI) scores determination were performed by the examiners, who were blinded to the color coding of the samples (to which group the teeth belonged), in order to eliminate observer bias. If there were any variation in the ARI scores between the observers, a third examiner determined the score.

The score for ARI are given below:

ARI

0: No adhesive left on the tooth

1: Less than half of the adhesive left on the tooth

2: More than half of the adhesive left on the tooth

3: Entire adhesive left on the tooth, with a distinct impression of the bracket mesh.

Results and statistical inference

The mean and standard deviation of various groups studied are as given below [Table 1].
Table 1: Oneway


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  • Group A: Distilled water (control) =9.205 + 1.03 MPa
  • Group B (Alcoholic mouthrinses)
  • Group B l: Listerine 12 h = 7.141 + 0.87 MPa
  • Group B 2: Listerine 24 h = 6.604 + 0.80 MPa
  • Group B 3: Colgate Plax 12 h = 8.131 + 1.10 MPa
  • Group B 4: Colgate Plax 24 h = 7.645 + 0.84 MPa
  • Group C (alcohol-free mouthrinses)
  • Group C l: Hexidine 12 h = 8.340 + 1.11 MPa
  • Group C 2: Hexidine 24 h = 7.781 + 1.11 MPa
  • Group C 3 S Flo 12 h = 8.992 + 0.75 MPa
  • Group C 4 S Flo 24 h = 8.665 + 0.69 MPa.


The results of the analysis of variance indicated significant differences in the shear bond strength between the different groups. BONFERRONI multiple comparison test indicated that,

  • Group B 1 had significantly lower bond strength than the control
  • Group B 2 had significantly lower bond strength than the control
  • Group B 4 had significantly lower bond strength than the control
  • Group C 2 had significantly lower bond strength than the control
  • Group B 1 had significantly lower bond strength than Group C 3
  • Group B 2 had significantly lower bond strength than Group C 4.


The comparison of shear bond strength has been shown in the form of a bar chart [Figure 8].
Figure 8: Bar chart

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Paired t-test [Table 2] between the same groups indicated that there was no significant difference between the 12-h bond strength and the 24-h bond strength for the same mouthrinse groups.
Table 2: Analysis of variance


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ARI scores

Group A: For 70% samples, the entire adhesive was left on the enamel and for 30% half or more than half of adhesive was left on enamel.

Group B 1: For 50% more than half of adhesive was left on enamel and for 40% all adhesive was left on the enamel and 10% less than half of adhesive was left on enamel.

Group B 2: For 50% more than half of adhesive was left on enamel and for 30% all adhesive was left on the enamel and 20% less than half of adhesive was left on enamel.

Group B 3: For 60% all adhesive was left on enamel and for 40% more than half of adhesive was left on the enamel.

Group B 4: For 60% all adhesive was left on enamel and for 40% more than half of adhesive was left on the enamel.

Group C 1: For 60% all adhesive was left on enamel and for 40% more than half of adhesive was left on the enamel.

Group C 2: For 50% all adhesive was left on enamel and for 50% more than half of adhesive was left on the enamel.

Group C 3: For 70% all adhesive was left on enamel and for 30% more than half of adhesive was left on the enamel.

Group C 4: For 60% all adhesive was left on enamel and for 40% more than half of adhesive was left on the enamel.


   Discussion Top


Ethanol has been known to have a softening effect on the BIS-GMA matrix copolymer and lower the wear resistance of composite resins. This is due to the diffusion of ethanol into the composite, which results in micro cracking. Ethanol has solubility characteristics similar to BIS-GMA and this may promote the infusion of ethanol into the composite leading to further damage.

In the present study Listerine, containing 21.6% ethanol, reduced the shear bond strength significantly compared with the control. This may be attributed to the high ethanol content present in Listerine. This is supported by various studies performed by Cavalcanti et al., [2] Roberts et al., [7] and Yap et al. [11] that proved Listerine softens the composite resin and reduces composite hardness.

Colgate Plax reduced the shear bond strength for both 12 h (1-year simulation) and 24 h (2-year simulation), but statistical significance was present only for the 2-year simulation. This reduction in shear bond strength could be due to the ethanol present in the mouthrinse. The reason it does not affect shear bond strength as drastically as Listerine may be due to the fact that the alcohol content in Colgate Plax is less (12% ethanol) when compared to Listerine (21.6%). This reduction in the shear bond strength is supported by the study done by Cavalcanti et al., [2] which showed that Colgate Plax softens composite resin and reduces composite hardness.

Hexidine, containing 0.2% chlorhexidine, showed reduced bond strength for both 12 h (1-year simulation) and 24 h (2-year simulation), when compared to the control, but statistical significance was present only for the 24 h (2-year simulation) period. However, this bond strength was higher when compared to alcohol containing mouthrinses (Listerine and Colgate Plax) for the same period.

S Flo, containing 0.2% sodium fluoride, showed a very negligible reduction in the bond strength for both 1 year simulation and 2 year simulation when compared to the control, but it was not statistically significant. However, this bond strength was higher when compared to alcohol containing mouthrinses.

According to Reynolds, [12] maximum bond strength of 5.9-7.9 Mpa is adequate in the oral cavity. For Transbond XT, various studies report a shear bond strength ranging between 9.2 Mpa and 10.5 Mpa. ARI values indicated that bond failures for all the groups occurred in a similar manner. However, it was found that Group B1 (Listerine 12 h) and Group B4 (Listerine 24 h) showed more cohesive failures within the composite while the other groups showed more failures at the bracket adhesive interface although it was not statistically significant. This could be due to the fact that the ethanol in Listerine was capable of dissolving the BIS-GMA in the composite, thereby inducing cohesive failure within the composite.

The results of this study indicated that Listerine (21.6% ethanol) significantly lowers the bond strength over a 12 h (1 year simulation) and 24 h (2 year simulation) period when compared to the control. Colgate Plax (12% ethanol) does not affect the bond strength over a 12 h (1 year simulation) period, but significantly reduces the bond strength over a 24 h (2 year simulation) period when compared to the control.

Hexidine does not affect the bond strength over a 12 h (1 year simulation) period, but significantly reduces the bond strength over a 24 h (2 year simulation) period when compared to the control. However, the 24 h bond strength for Hexidine was higher than the alcoholic mouth rinse groups (Listerine and Colgate Plax) for the same 24 h period. Listerine significantly lowers the bond strength over a 12 h (1 year simulation) period when compared to S Flo for the same 12 h (1-year simulation) period. Listerine significantly lowers the bond strength over a 24 h (2 year simulation) period when compared to S Flo for the same 24 h (2 year simulation) period.

The results of the present study, conclusively proves that alcohol containing mouthrinses affect the shear bond strength of metal orthodontic brackets bonded with composite resin (Transbond XT in the present study), more when compared to alcohol-free mouthrinses. The limitations of this study are this being an in vitro study; it does not truly reflect the oral environment. Since the in vitro testing can never simulate oral conditions precisely, direct extrapolation of the findings to the in vitro conditions may not be possible. Clinically, the effects of mouthrinses on shear bond strength may be modified by many factors that could not be replicated in this study. Saliva may dilute or buffer the mouth rinse and salivary pellicle might have a protective effect. Thus, the variables are numerous and the results need to be interpreted with care. Extensive clinical trials over extended periods are needed to evaluate the in vitro effects of alcoholic and alcohol-free mouthrinses on the bond strength and bracket failure rates in orthodontic patients.

Summary and Conclusion

Within the limitations of this study, the following conclusions can be made:

  • Alcoholic mouthrinses showed reduced bond strength when compared to alcohol-free mouthrinses
  • Listerine reduced the shear bond strength significantly for 12 h (1 year simulation) and for 24 h (2 year simulation)
  • Colgate Plax did not significantly affect shear bond strength for 1 year simulation, but it significantly affected shear bond strength for 2 year simulation period
  • Hexidine did not significantly affect shear bond strength for 1 year simulation, but it significantly affected shear bond strength for 2 year simulation period
  • S Flo showed higher bond strength when compared to Listerine for both 1 year simulation and 2 year simulation period
  • On comparison between the 1 year simulation and 2 year simulation bond strength for the same mouth rinse group, it was found that there was no significant difference in the bond strength for the same mouth rinse group
  • Listerine affected the shear bond strength most, followed by Colgate Plax and Hexidine. S Flo affected the shear bond strength least
  • ARI scores revealed there was no significant difference in the site of the bond failure between the different groups.


It has been found in this study that alcohol-containing mouthrinses affect the shear bond strength, of metal brackets bonded with composite resin adhesives, more when compared to alcohol-free mouthrinses. It is therefore highly advisable to avoid alcohol containing mouthrinses in patients undergoing orthodontic treatment and use alcohol-free mouthrinses as adjuncts to regular oral hygiene procedures for maintaining good enamel integrity and periodontal health without compromising the shear bond strength of the bonded metal brackets.

 
   References Top

1.Asmussen E. Softening of BISGMA-based polymers by ethanol and by organic acids of plaque. Scand J Dent Res 1984;92:257-61.  Back to cited text no. 1
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2.Cavalcanti AN, Mitsui FH, Ambrosano GM, Mathias P, Marchi GM. Effect of different mouthrinses on Knoop hardness of a restorative composite. Am J Dent 2005;18:338-40.  Back to cited text no. 2
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3.Ferracane JL, Berge HX. Fracture toughness of experimental dental composites aged in ethanol. J Dent Res 1995;74:1418-23.  Back to cited text no. 3
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4.Gürgan S, Onen A, Köprülü H. In vitro effects of alcohol-containing and alcohol-free mouthrinses on microhardness of some restorative materials. J Oral Rehabil 1997;24:244-6.  Back to cited text no. 4
    
5.Hobson RS, McCabe JF, Hogg SD. The effect of food simulants on enamel-composite bond strength. J Orthod 2000;27:55-9.  Back to cited text no. 5
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7.Roberts HW, Karpay RI, Mills SE. Dental unit waterline antimicrobial agents' effect on dentin bond strength. J Am Dent Assoc 2000;131:179-83.  Back to cited text no. 7
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8.Wu W, McKinney JE. Influence of chemicals on wear of dental composites. J Dent Res 1982;61:1180-3.  Back to cited text no. 8
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9.McKinney JE, Wu W. Chemical softening and wear of dental composites. J Dent Res 1985;64:1326-31.  Back to cited text no. 9
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10.Gürdal P, Akdeniz BG, Hakan Sen B. The effects of mouthrinses on microhardness and colour stability of aesthetic restorative materials. J Oral Rehabil 2002;29:895-901.  Back to cited text no. 10
    
11.Yap AU, Tan BW, Tay LC, Chang KM, Loy TK, Mok BY. Effect of mouthrinses on microhardness and wear of composite and compomer restoratives. Oper Dent 2003;28:740-6.  Back to cited text no. 11
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12.Reynolds IA. A review of direct orthodontic bonding. Br J Orthod 1975;2:171-8.  Back to cited text no. 12
    
13.Iijima M, Ito S, Yuasa T, Muguruma T, Saito T, Mizoguchi I. Bond strength comparison and scanning electron microscopic evaluation of three orthodontic bonding systems. Dent Mater J 2008;27:392-9.  Back to cited text no. 13
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14.Nemeth BR, Wiltshire WA, Lavelle CL. Shear/peel bond strength of orthodontic attachments to moist and dry enamel. Am J Orthod Dentofacial Orthop 2006;129:396-401.  Back to cited text no. 14
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Correspondence Address:
Nazeer Ahmed Meeran
Department of Orthodontics, Priyadarshini Dental College and Hospital, Thiruvallur, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.123404

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