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Filled and unfilled restorative materials to reduce enamel decalcification during fixed-appliance orthodontic treatment
ORIGINAL ARTICLE
Filled and unfilled restorative materials to reduce enamel decalcification during fixed-appliance orthodontic treatment Melissa L. Farrow,a Sheldon M. Newman,b Larry J. Oesterle,c and W. Craig Shellhartd Aurora, Colo Introduction: Enamel decalcification is a potential problem that can compromise the esthetic results of orthodontic treatment. Patient compliance with preventive measures is frequently inadequate to resolve this issue. The purpose of this study was to determine the effectiveness of sealing around the bracket periphery in reducing decalcification. Methods: Sixty extracted teeth were collected and randomized to 4 groups: group 1, bonded and then sealed around the bracket with an unfilled sealant material; group 2, bonded and then sealed with a filled, flowable composite material; group 3, bonded and sealed with excess bracket adhesive contoured at bracket periphery; and group 4, conventional treatment with excess bonding material removed and no additional protection at the bracket periphery. Each group was subjected to mechanical, thermal, and decalcification challenges to simulate in-vivo conditions. Results: Groups 1 and 2 had the lowest incidence of decalcification; however, decalcification was not statistically significantly reduced by the use of an additional restorative/bracket adhesive material. An incidental finding was a statistically significant loss of bracket adhesive material beneath the bracket pads of group 4. Conclusions: Prophylactic sealing around the orthodontic bracket pad periphery with an unfilled sealant or a filled flowable composite restorative material did not significantly reduce the incidence of decalcification. (Am J Orthod Dentofacial Orthop 2007;132:577.e13-577.e18)
E
sthetics is a primary reason that patients come to an orthodontist. To achieve the goal of a beautiful smile, the orthodontist invests much time and expertise. The patients are also asked to devote their time, compliance, and finances to the success of treatment. Appliance removal is an exciting day for patients, families, and the treating orthodontist and staff. However, this revealing moment can be compromised by noticeable decalcification, resulting from inadequate oral hygiene during treatment. Enamel decalcification is a common negative sequela of orthodontic treatment when oral hygiene is inadequate. The presence of white spot lesions at the end of treatment can compromise an otherwise beautiful result.
From the Department of Orthodontics, University of Colorado at Denver and Health Sciences Center, Aurora, Colo. a Postgraduate resident. b Associate professor, Departments of Biomaterials and Restorative Dentistry and Orthodontics. c Professor and chair, Department of Orthodontics. d Associate professor, Department of Orthodontics. Reprint requests to: Larry Oesterle, Department of Orthodontics, University of Colorado, School of Dentistry, Mail Stop F849, PO Box 6508, Aurora, CO 80045; e-mail, [email protected]. Submitted, January 2007; revised and accepted, May 2007. 0889-5406/$32.00 Copyright © 2007 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2007.05.010
Not only can achieving optimum oral hygiene around orthodontic appliances be difficult, but also the resulting increase in plaque retention places patients at higher risk for enamel lesion development adjacent to the appliances. Therefore, orthodontic patients treated with fixed appliances are at increased risk for the development of clinically detectable areas of enamel decalcification. Decalcification occurs when specific bacteria are retained on the enamel surface for a long time. The bacteria metabolize fermentable carbohydrates and produce organic acids. These acids dissolve the calcium phosphate mineral of the enamel and dentin, resulting in decalcification. Decalcification is first observed clinically as white spot lesions. The demineralized area beneath the dental plaque and the body of the enamel lesion can lose as much as 50% of the original mineral content.1 Prevention of this condition is in the hands of both the orthodontist and the patient. The patient’s role is to perform adequate oral hygiene and use topical preventive measures. The orthodontist’s responsibility is to detect and prevent decalcification during active orthodontic treatment. Therefore, orthodontists must educate and intervene aggressively as needed. To date, the standard preventive treatment for decalcification during orthodontic treatment has been 577.e13
577.e14 Farrow et al
patient compliance, which often is clearly inadequate. Other methods have been studied to take the compliance issue out of the equation. Most recently, Hu and Featherstone2 found that Pro Seal, a filled light-cured sealant, reduced the incidence of demineralization. Vorhies et al3 found that hybrid orthodontic glass ionomer cements release fluoride and inhibit enamel demineralization. Fluoride varnishes have also been shown to decrease enamel demineralization.2,4 Another method is sealing the enamel surrounding an orthodontic appliance.2,5 Sealant use is a promising method of decreasing decalcification during fixed orthodontic appliance treatment. However, several factors might affect its success: duration of the protection, material thickness, distribution on the tooth surface, composition of the sealant material, and endurance to oral stresses such as abrasion and thermal changes. A sealant material with abrasion resistance strength and low material thickness that readily flows and adapts is required for effectiveness. A filled, flowable composite meets those requirements but has not been tested. Therefore, the purposes of this study were to investigate the use of an unfilled sealant restorative material, a filled flowable composite restorative material, and excess bracket adhesive to seal the bracket periphery to reduce the incidence of decalcification, and to determine the presence and condition of these materials after thermocycling, abrasion, and decalcification challenges. MATERIAL AND METHODS
Sixty recently extracted noncarious premolars and molars were collected and stored in refrigerated chloramine T solution (1% by weight). All calculus, bone, and soft tissue were removed with a scaler and a sterile #15 blade. The teeth were cleaned with a rubber prophylaxis cup with nonfluoridated pumice (Preppies, flour of pumice; Whip Mix, Louisville, Ky) and rinsed copiously with water. A small hole was drilled near the apex of each tooth, and nonfluoridated dental floss was fed through the hole to facilitate handling during testing. The teeth were then randomly assigned to 4 groups of 15 teeth each. The groups and their conditions were as follows. The teeth in group 1 were conventionally bonded with the addition of an unfilled sealant restorative material applied around the bracket periphery. Excess bracket adhesive material was removed with a sharp explorer; the teeth were light cured; the bracket periphery was etched; and unfilled sealant (Natural Elegance Pit and Fissure Sealant; Henry Schein, Melville, NY) was applied at the bracket periphery and light cured.
American Journal of Orthodontics and Dentofacial Orthopedics November 2007
The teeth in group 2 were conventionally bonded with the addition of a filled, flowable composite restorative material applied around the bracket periphery. They were prepared as for group 1, and a filled, flowable composite (Natural Elegance; Henry Schein) was applied at the bracket periphery and light cured. The teeth in group 3 were conventionally bonded with excess bracket adhesive material contoured at the bracket periphery. The excess bracket adhesive material was not removed from the periphery of the bracket but was contoured adjacent to the bracket before light curing. The teeth in group 4 received conventional treatment; the excess bracket adhesive material was removed with an explorer before light curing. In all groups, the facial surfaces of the teeth near the brackets were etched with 37% phosphoric acid gel (Ultra-Etch; Ultradent Products, South Jordan, Utah) for 30 seconds and then rinsed copiously with water. Next, a thin layer of an unfilled bonding resin (Transbond XT Primer; 3M Unitek, Monrovia, Calif) was applied with a microbrush applicator (Microbrush International, Grafton, Wis) to the etched area and gently air thinned for 2 to 5 seconds. Precoated APC brackets (Victory; 3M Unitek) appropriate to either premolars or molars were positioned on the facial surface at the height of contour mesiodistally, in the middle third occlusogingivally, and the tie wings were oriented parallel to the long axis of the tooth. The brackets were ideally positioned and then compressed to express excess bracket adhesive material, which was then removed with a sharp explorer in all but group 3. Each bracket was then cured with a light-emitting diode curing light (Ortholux; 3M Unitek) for a total of 40 seconds, 20 seconds on the mesial and distal aspects to achieve optimal curing of the bracket adhesive.6 In group 3, the bracket was placed similarly, but the excess adhesive material was not removed after bracket placement. Instead, it was contoured adjacent to the bracket periphery to flow smoothly from bracket to tooth. It was then light cured in the same fashion. To simulate thermal stress and mechanical wear, all teeth were cycled between brushing and thermocycling to simulate 35 days of in-vivo conditions. Mechanical wear was simulated by brushing each tooth for 5 seconds 3 times a day for 35 days with a mediumbristled toothbrush (GUM Super Tip; Sunstar Butler, Chicago, Ill) with a nonfluoridated dentifrice Natural Antiplaque Tartar Control & Whitening Toothpaste (Tom’s of Maine, Kennebunk, Me). This was alternated with 3 cycles per day of thermocycling.
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American Journal of Orthodontics and Dentofacial Orthopedics Volume 132, Number 5
Table.
Polarized light microscopy observations
Restorative/ adhesive material present (n)
Yes
No
Decalcification
Yes
No
Lost adhesive
Yes
No
Loss under bracket pad
2 5
24 21
7.7% 19.2%
25 20
1 6
3.8% 23.1%
1 1
25 25
3.8% 3.8%
4 5
22 21
15.4% 19.2%
20 19
6 7
23.1% 26.9%
4 10
22 16
15.4% 38.5%*
Decalcification present (n) Sample Group 1: pit and fissure sealant Group 2: flowable composite Group 3: excess bonding material contoured Group 4: traditionally bonded
Adhesive material present beneath bracket pad (n)
*Statistically different from the other groups (chi-square test).
Thermocycling consisted of 3 cycles per day for 35 days. A thermocycle consisted of placing the teeth in a mesh basket and submerging them in water at a temperature of 4°C for 1 minute, followed by submergence in 60°C water for 1 minute to complete the cycle. Previous studies cycled for 100 cycles1,7; this is comparable with the thermal stress in this study. After mechanical and thermal stresses and before decalcification, all teeth were painted with a thin coat of acid-resistant varnish covering all surfaces except the 2-mm margin around each bracket pad, leaving an exposed window of enamel similar to previous studies.2,5,8 All teeth were then submerged in a decalcification solution of 3% gelatin with 85% lactic acid at a pH of 3.98 and stored at 37°C. All 4 groups were suspended in the gelatin solution for 10 days and then removed, rinsed thoroughly, and returned to their respective storage jars with distilled water and refrigerated; this is comparable to previous studies.4,5,7,8 After the thermal, mechanical, and decalcification challenges, all teeth were prepared for sectioning. Each tooth was mounted in a metal sleeve with sticky wax before sectioning with a hard-tissue microtome (Silverstone-Taylor, Denver, Colo). Several sections of each tooth were cut perpendicular to the enamel surface. A longitudinal section was made through the orthodontic bracket and the tooth with the microtome. Sections were approximately 130 to 210 m thick. The molars were excluded from sectioning and further evaluation because of our inability to adequately section the larger buccal molar bracket with the microtome. Therefore, each group was reduced to 13 experimental teeth. After sectioning, specimens, with the bonded bracket intact, were selected for analysis. Some brackets were debonded in the sectioning process. However, if a section of the tooth with the bracket intact was not available, a section with intact enamel was analyzed.
By using water as the suspension medium, the specimens were examined under a polarizing light microscope. Each sample was observed under the microscope, and several photomicrographs were made from the incisal aspect in small increments to the gingival aspect of each section. Observations were made for the presence or absence of decalcification and additional restorative material at the bracket periphery. Upon evaluating for decalcification and additional restorative/bracket adhesive material, we found a significant loss of bracket adhesive material beneath the bracket pads in group 4. Therefore, based on this finding, all groups were reexamined for the loss of adhesive material beneath the bracket pad. The microscopic observations were recorded as either yes or no at 2 representative measurements, gingivally and occlusally to the bracket. The results of the 6 observations for each tooth were then averaged to give an overall evaluation of the presence or absence of decalcification, the presence or absence of additional restorative/bracket adhesive material beneath the bracket pad, and the condition of the remaining restorative/bracket adhesive material. The chi-square test was used to compare the nonparametric data and evaluate the statistical differences between the groups. RESULTS
The results are summarized in the Table. Chisquare analyses were performed on each variable and group. Each group had 26 observations for 3 measurements: presence or absence of decalcification, presence or absence of restorative/bracket adhesive material at the bracket periphery, and loss or maintenance of bracket adhesive material beneath the bracket pad. Group 1 had the least amount of decalcification at 7.7%, whereas groups 2 and 4 had equal incidences of 19.2% (Fig 1). Group 3 had decalcification incidence of 15.4%. The chi-square analysis showed that the these
577.e16 Farrow et al
American Journal of Orthodontics and Dentofacial Orthopedics November 2007
Fig 1. Group 4: traditionally bonded with bracket adhesive and showing the highest levels of decalcification adjacent to the bracket and adhesive. A, Enamel; B, bracket adhesive; C, decalcification.
Fig 3. Group 3: tooth bonded with excess bracket adhesive material contoured for enamel protection. Bracket adhesive intact with no decalcification. A, Enamel; B, bracket adhesive.
Fig 2. Group 1: bracketed tooth with adhesive and sealant intact with no loss under bracket pad. A, Enamel; B, bracket adhesive; D, Bracket adhesive and sealant intact around the bracket pad.
Fig 4. Group 4: traditionally bonded group demonstrating loss of bracket adhesive material beneath the bracket pad. A, Enamel; B, bracket adhesive; D, loss of bracket adhesive beneath the bracket pad.
findings for decalcification were not statistically significant (P ⫽ .621). The observations of the presence or absence of additional restorative/bracket adhesive material at the bracket periphery showed that group 1 had the most remaining material after testing; material loss at the bracket periphery occurred in only 3.8% of the observations (Fig 2). Groups 2 and 3 showed loss of the additional material in 23.1% of the observations (Fig 3), and group 4, which had no additional material placed, showed a loss of the adhesive material around the bracket periphery in 26.9% of the observations. The chi-square analysis demonstrated no statistically insignificant difference between any of these findings (P ⫽ .142).
The final observation was added as a result of the earlier microscopic findings to evaluate the loss of bracket adhesive material beneath the bracket pad. A statistically significant difference was found (P ⫽ .001) between group 4 and the remaining groups. Groups 1 and 2 with the additional restorative/bracket adhesive material at the bracket periphery had no significant loss of bracket adhesive material beneath the bracket pads. Only 3.8% of these observations had loss of material beneath the bracket compared with 38.5% in group 4 (Fig 4). Group 3 had less loss (15.4%) of bracket adhesive material beneath the bracket pad than did group 4, but more than groups 1 and 2. There was no observable correlation between loss of bracket adhesive
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American Journal of Orthodontics and Dentofacial Orthopedics Volume 132, Number 5
material or loss of additional restorative material and decalcification in this study. DISCUSSION
In previous studies, the authors sought to prevent demineralization around orthodontic brackets without reliance on patient compliance.2,4,5 Application of restorative sealants on the enamel surface around and beneath the orthodontic brackets was suggested as a method of preventing demineralization. However, Zachrisson et al9 found that many sealants failed to protect the enamel around orthodontic brackets because of oxygen inhibiting the polymerization of the thin sealant coating. Another important consideration in sealant placement is the sensitivity of the technique and the risk of breaks in the sealant layer, resulting from the sealant shearing from the surface due to differences in the coefficients of thermal expansion and eventual decalcification under the sealant. Another factor is the longevity of the sealant protection due to lack of abrasion resistance on the exposed sealant surfaces. Ceen and Gwinnett10 stated that current sealants, with their thin, weak films and low abrasion resistance, cannot provide long-standing protection of the enamel surface against demineralization and concluded that there is a need to develop sealants for orthodontic use with durable, protective films. Hu and Featherstone2 found that a composite based on acrylates instead of methacrylates and containing a relatively small amount of filler (25%) could reduce enamel demineralization under their test conditions compared with a varnish and an orthodontic sealant. They suggested that the significant filler content led to greater abrasion resistance and thus less demineralization, but they reported no data on the amount of remaining resin to support this conclusion. In addition, they did not thermocycle, which can crack and debond the resin due to thermal expansion differences, and bonded brackets were not used. This study indicated that a 64% filled flowable composite made no significant difference in decalcification under our test conditions. Filler alone is not a likely explanation for the differences in the results of these 2 studies. Poststudy observations of the acrylate-based sealant used in the study of Hu and Featherstone2 vs the restorative sealant used in our study showed no obvious difference between the viscosities of these materials. Polymerization of both products produced a hard coating material, even after washing away any oxygeninhibited layer. An explanation for the differences in the results of these 2 studies is elusive. Prophylactic sealing around the orthodontic bracket is worthwhile if the additional time to seal
around the bracket limits the amount of decalcification. However, our results did not conclusively indicate that using either a filled flowable composite or an unfilled sealant, or removing or not removing excess bracket adhesive material, eliminates or significantly reduces the incidence of decalcification. A statistically significant incidental microscopic finding in this study was the bracket adhesive material loss beneath the bracket pads in the conventional treatment group. The bracket adhesive material beneath the bracket pads in groups 1, 2, and 3 treated with additional restorative/bracket adhesive was largely maintained. This appeared to have occurred from the washout of the adhesive material secondary to the mechanical challenges to the unprotected enamel/bracket interface. The additional restorative/bracket adhesive material around the bracket periphery appears to protect from this washout. The washout phenomenon might contribute to the decalcification observed clinically around the bracket pad. Further research is necessary to determine the benefit of sealing around the periphery of the orthodontic bracket. These researchers might find that any sealing at the bracket periphery can also benefit bond strength because of retention of the bracket adhesive material beneath the bracket pad. Although in this study a discrete area around the bracket base was sealed, in clinical use, a large area of coverage, particularly gingivally, would be required to minimize decalcification. CONCLUSIONS
Three methods of protecting the bracket periphery with a restorative/bracket adhesive material were tested to determine their effectiveness in reducing decalcification. None was found to be statistically significantly effective in reducing the incidence of decalcification. However, we identified a significant correlation with the addition of a restorative/bracket adhesive material at the bracket periphery and the reduction in the loss of bracket adhesive material beneath the bracket pad; this might be an alternate benefit to prophylactic sealing around the bracket pad periphery.
REFERENCES 1. Hughes D, Hembree JH, Weber FN. Preparations to prevent enamel decalcification during orthodontic treatment compared. Am J Orthod 1979;76:416-20. 2. Hu W, Featherstone DB. Prevention of enamel demineralization: an in-vitro study using light-cured filled sealant. Am J Orthod Dentofacial Orthop 2005;128:592-600. 3. Vorhies AB, Donly KJ, Staley RN, Wefel JS. Enamel demineralization adjacent to orthodontic brackets bonded with hybrid glass ionomer cements: an in vitro study. Am J Orthod Dentofacial Orthop 1998;114:668-74.
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4. Todd MA, Staley RN, Kanellis MJ, Donly KJ, Wefel JS. Effect of a fluoride varnish on demineralization adjacent to orthodontic brackets. Am J Orthod Dentofacial Orthop 1999;116:159-67. 5. Frazier MC, Southard TE, Doster PM. Prevention of enamel demineralization during orthodontic treatment: an in vitro study using pit and fissure sealants. Am J Orthod Dentofacial Orthop 1996;110:459-65. 6. Oesterle LJ, Messersmith ML, Devine SM, Ness CF. Light and setting times of visible-light cured orthodontic adhesives. J Clin Orthod 1995;29:31-6.
American Journal of Orthodontics and Dentofacial Orthopedics November 2007
7. Younis O, Hughes DO, Weber FN. Enamel decalcification in orthodontic treatment. Am J Orthod 1979;75:678-81. 8. Schmit JL, Staley RN, Wefel JS, Kanellis M, Jakobsen JR, Keenan PJ. Effect of fluoride varnish on demineralization adjacent to brackets bonded with RMGI cement. Am J Orthod Dentofacial Orthop 2002;122:125-33. 9. Zachrisson BU, Hemigard E, Ruyter EI, Mjor IA. Problems with sealants for bracket bonding. Am J Orthod 1979;75:641-9. 10. Ceen RF, Gwinnett AJ. Microscopic evaluation of the thickness of sealants used in orthodontic bonding. Am J Orthod 1980;78:623-9.
Filled and unfilled restorative materials to reduce enamel decalcification during fixed-appliance orthodontic treatment Melissa L. Farrow,a Sheldon M. Newman,b Larry J. Oesterle,c and W. Craig Shellhartd Aurora, Colo Introduction: Enamel decalcification is a potential problem that can compromise the esthetic results of orthodontic treatment. Patient compliance with preventive measures is frequently inadequate to resolve this issue. The purpose of this study was to determine the effectiveness of sealing around the bracket periphery in reducing decalcification. Methods: Sixty extracted teeth were collected and randomized to 4 groups: group 1, bonded and then sealed around the bracket with an unfilled sealant material; group 2, bonded and then sealed with a filled, flowable composite material; group 3, bonded and sealed with excess bracket adhesive contoured at bracket periphery; and group 4, conventional treatment with excess bonding material removed and no additional protection at the bracket periphery. Each group was subjected to mechanical, thermal, and decalcification challenges to simulate in-vivo conditions. Results: Groups 1 and 2 had the lowest incidence of decalcification; however, decalcification was not statistically significantly reduced by the use of an additional restorative/bracket adhesive material. An incidental finding was a statistically significant loss of bracket adhesive material beneath the bracket pads of group 4. Conclusions: Prophylactic sealing around the orthodontic bracket pad periphery with an unfilled sealant or a filled flowable composite restorative material did not significantly reduce the incidence of decalcification. (Am J Orthod Dentofacial Orthop 2007;132:577.e13-577.e18)
E
sthetics is a primary reason that patients come to an orthodontist. To achieve the goal of a beautiful smile, the orthodontist invests much time and expertise. The patients are also asked to devote their time, compliance, and finances to the success of treatment. Appliance removal is an exciting day for patients, families, and the treating orthodontist and staff. However, this revealing moment can be compromised by noticeable decalcification, resulting from inadequate oral hygiene during treatment. Enamel decalcification is a common negative sequela of orthodontic treatment when oral hygiene is inadequate. The presence of white spot lesions at the end of treatment can compromise an otherwise beautiful result.
From the Department of Orthodontics, University of Colorado at Denver and Health Sciences Center, Aurora, Colo. a Postgraduate resident. b Associate professor, Departments of Biomaterials and Restorative Dentistry and Orthodontics. c Professor and chair, Department of Orthodontics. d Associate professor, Department of Orthodontics. Reprint requests to: Larry Oesterle, Department of Orthodontics, University of Colorado, School of Dentistry, Mail Stop F849, PO Box 6508, Aurora, CO 80045; e-mail, [email protected]. Submitted, January 2007; revised and accepted, May 2007. 0889-5406/$32.00 Copyright © 2007 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2007.05.010
Not only can achieving optimum oral hygiene around orthodontic appliances be difficult, but also the resulting increase in plaque retention places patients at higher risk for enamel lesion development adjacent to the appliances. Therefore, orthodontic patients treated with fixed appliances are at increased risk for the development of clinically detectable areas of enamel decalcification. Decalcification occurs when specific bacteria are retained on the enamel surface for a long time. The bacteria metabolize fermentable carbohydrates and produce organic acids. These acids dissolve the calcium phosphate mineral of the enamel and dentin, resulting in decalcification. Decalcification is first observed clinically as white spot lesions. The demineralized area beneath the dental plaque and the body of the enamel lesion can lose as much as 50% of the original mineral content.1 Prevention of this condition is in the hands of both the orthodontist and the patient. The patient’s role is to perform adequate oral hygiene and use topical preventive measures. The orthodontist’s responsibility is to detect and prevent decalcification during active orthodontic treatment. Therefore, orthodontists must educate and intervene aggressively as needed. To date, the standard preventive treatment for decalcification during orthodontic treatment has been 577.e13
577.e14 Farrow et al
patient compliance, which often is clearly inadequate. Other methods have been studied to take the compliance issue out of the equation. Most recently, Hu and Featherstone2 found that Pro Seal, a filled light-cured sealant, reduced the incidence of demineralization. Vorhies et al3 found that hybrid orthodontic glass ionomer cements release fluoride and inhibit enamel demineralization. Fluoride varnishes have also been shown to decrease enamel demineralization.2,4 Another method is sealing the enamel surrounding an orthodontic appliance.2,5 Sealant use is a promising method of decreasing decalcification during fixed orthodontic appliance treatment. However, several factors might affect its success: duration of the protection, material thickness, distribution on the tooth surface, composition of the sealant material, and endurance to oral stresses such as abrasion and thermal changes. A sealant material with abrasion resistance strength and low material thickness that readily flows and adapts is required for effectiveness. A filled, flowable composite meets those requirements but has not been tested. Therefore, the purposes of this study were to investigate the use of an unfilled sealant restorative material, a filled flowable composite restorative material, and excess bracket adhesive to seal the bracket periphery to reduce the incidence of decalcification, and to determine the presence and condition of these materials after thermocycling, abrasion, and decalcification challenges. MATERIAL AND METHODS
Sixty recently extracted noncarious premolars and molars were collected and stored in refrigerated chloramine T solution (1% by weight). All calculus, bone, and soft tissue were removed with a scaler and a sterile #15 blade. The teeth were cleaned with a rubber prophylaxis cup with nonfluoridated pumice (Preppies, flour of pumice; Whip Mix, Louisville, Ky) and rinsed copiously with water. A small hole was drilled near the apex of each tooth, and nonfluoridated dental floss was fed through the hole to facilitate handling during testing. The teeth were then randomly assigned to 4 groups of 15 teeth each. The groups and their conditions were as follows. The teeth in group 1 were conventionally bonded with the addition of an unfilled sealant restorative material applied around the bracket periphery. Excess bracket adhesive material was removed with a sharp explorer; the teeth were light cured; the bracket periphery was etched; and unfilled sealant (Natural Elegance Pit and Fissure Sealant; Henry Schein, Melville, NY) was applied at the bracket periphery and light cured.
American Journal of Orthodontics and Dentofacial Orthopedics November 2007
The teeth in group 2 were conventionally bonded with the addition of a filled, flowable composite restorative material applied around the bracket periphery. They were prepared as for group 1, and a filled, flowable composite (Natural Elegance; Henry Schein) was applied at the bracket periphery and light cured. The teeth in group 3 were conventionally bonded with excess bracket adhesive material contoured at the bracket periphery. The excess bracket adhesive material was not removed from the periphery of the bracket but was contoured adjacent to the bracket before light curing. The teeth in group 4 received conventional treatment; the excess bracket adhesive material was removed with an explorer before light curing. In all groups, the facial surfaces of the teeth near the brackets were etched with 37% phosphoric acid gel (Ultra-Etch; Ultradent Products, South Jordan, Utah) for 30 seconds and then rinsed copiously with water. Next, a thin layer of an unfilled bonding resin (Transbond XT Primer; 3M Unitek, Monrovia, Calif) was applied with a microbrush applicator (Microbrush International, Grafton, Wis) to the etched area and gently air thinned for 2 to 5 seconds. Precoated APC brackets (Victory; 3M Unitek) appropriate to either premolars or molars were positioned on the facial surface at the height of contour mesiodistally, in the middle third occlusogingivally, and the tie wings were oriented parallel to the long axis of the tooth. The brackets were ideally positioned and then compressed to express excess bracket adhesive material, which was then removed with a sharp explorer in all but group 3. Each bracket was then cured with a light-emitting diode curing light (Ortholux; 3M Unitek) for a total of 40 seconds, 20 seconds on the mesial and distal aspects to achieve optimal curing of the bracket adhesive.6 In group 3, the bracket was placed similarly, but the excess adhesive material was not removed after bracket placement. Instead, it was contoured adjacent to the bracket periphery to flow smoothly from bracket to tooth. It was then light cured in the same fashion. To simulate thermal stress and mechanical wear, all teeth were cycled between brushing and thermocycling to simulate 35 days of in-vivo conditions. Mechanical wear was simulated by brushing each tooth for 5 seconds 3 times a day for 35 days with a mediumbristled toothbrush (GUM Super Tip; Sunstar Butler, Chicago, Ill) with a nonfluoridated dentifrice Natural Antiplaque Tartar Control & Whitening Toothpaste (Tom’s of Maine, Kennebunk, Me). This was alternated with 3 cycles per day of thermocycling.
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Table.
Polarized light microscopy observations
Restorative/ adhesive material present (n)
Yes
No
Decalcification
Yes
No
Lost adhesive
Yes
No
Loss under bracket pad
2 5
24 21
7.7% 19.2%
25 20
1 6
3.8% 23.1%
1 1
25 25
3.8% 3.8%
4 5
22 21
15.4% 19.2%
20 19
6 7
23.1% 26.9%
4 10
22 16
15.4% 38.5%*
Decalcification present (n) Sample Group 1: pit and fissure sealant Group 2: flowable composite Group 3: excess bonding material contoured Group 4: traditionally bonded
Adhesive material present beneath bracket pad (n)
*Statistically different from the other groups (chi-square test).
Thermocycling consisted of 3 cycles per day for 35 days. A thermocycle consisted of placing the teeth in a mesh basket and submerging them in water at a temperature of 4°C for 1 minute, followed by submergence in 60°C water for 1 minute to complete the cycle. Previous studies cycled for 100 cycles1,7; this is comparable with the thermal stress in this study. After mechanical and thermal stresses and before decalcification, all teeth were painted with a thin coat of acid-resistant varnish covering all surfaces except the 2-mm margin around each bracket pad, leaving an exposed window of enamel similar to previous studies.2,5,8 All teeth were then submerged in a decalcification solution of 3% gelatin with 85% lactic acid at a pH of 3.98 and stored at 37°C. All 4 groups were suspended in the gelatin solution for 10 days and then removed, rinsed thoroughly, and returned to their respective storage jars with distilled water and refrigerated; this is comparable to previous studies.4,5,7,8 After the thermal, mechanical, and decalcification challenges, all teeth were prepared for sectioning. Each tooth was mounted in a metal sleeve with sticky wax before sectioning with a hard-tissue microtome (Silverstone-Taylor, Denver, Colo). Several sections of each tooth were cut perpendicular to the enamel surface. A longitudinal section was made through the orthodontic bracket and the tooth with the microtome. Sections were approximately 130 to 210 m thick. The molars were excluded from sectioning and further evaluation because of our inability to adequately section the larger buccal molar bracket with the microtome. Therefore, each group was reduced to 13 experimental teeth. After sectioning, specimens, with the bonded bracket intact, were selected for analysis. Some brackets were debonded in the sectioning process. However, if a section of the tooth with the bracket intact was not available, a section with intact enamel was analyzed.
By using water as the suspension medium, the specimens were examined under a polarizing light microscope. Each sample was observed under the microscope, and several photomicrographs were made from the incisal aspect in small increments to the gingival aspect of each section. Observations were made for the presence or absence of decalcification and additional restorative material at the bracket periphery. Upon evaluating for decalcification and additional restorative/bracket adhesive material, we found a significant loss of bracket adhesive material beneath the bracket pads in group 4. Therefore, based on this finding, all groups were reexamined for the loss of adhesive material beneath the bracket pad. The microscopic observations were recorded as either yes or no at 2 representative measurements, gingivally and occlusally to the bracket. The results of the 6 observations for each tooth were then averaged to give an overall evaluation of the presence or absence of decalcification, the presence or absence of additional restorative/bracket adhesive material beneath the bracket pad, and the condition of the remaining restorative/bracket adhesive material. The chi-square test was used to compare the nonparametric data and evaluate the statistical differences between the groups. RESULTS
The results are summarized in the Table. Chisquare analyses were performed on each variable and group. Each group had 26 observations for 3 measurements: presence or absence of decalcification, presence or absence of restorative/bracket adhesive material at the bracket periphery, and loss or maintenance of bracket adhesive material beneath the bracket pad. Group 1 had the least amount of decalcification at 7.7%, whereas groups 2 and 4 had equal incidences of 19.2% (Fig 1). Group 3 had decalcification incidence of 15.4%. The chi-square analysis showed that the these
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Fig 1. Group 4: traditionally bonded with bracket adhesive and showing the highest levels of decalcification adjacent to the bracket and adhesive. A, Enamel; B, bracket adhesive; C, decalcification.
Fig 3. Group 3: tooth bonded with excess bracket adhesive material contoured for enamel protection. Bracket adhesive intact with no decalcification. A, Enamel; B, bracket adhesive.
Fig 2. Group 1: bracketed tooth with adhesive and sealant intact with no loss under bracket pad. A, Enamel; B, bracket adhesive; D, Bracket adhesive and sealant intact around the bracket pad.
Fig 4. Group 4: traditionally bonded group demonstrating loss of bracket adhesive material beneath the bracket pad. A, Enamel; B, bracket adhesive; D, loss of bracket adhesive beneath the bracket pad.
findings for decalcification were not statistically significant (P ⫽ .621). The observations of the presence or absence of additional restorative/bracket adhesive material at the bracket periphery showed that group 1 had the most remaining material after testing; material loss at the bracket periphery occurred in only 3.8% of the observations (Fig 2). Groups 2 and 3 showed loss of the additional material in 23.1% of the observations (Fig 3), and group 4, which had no additional material placed, showed a loss of the adhesive material around the bracket periphery in 26.9% of the observations. The chi-square analysis demonstrated no statistically insignificant difference between any of these findings (P ⫽ .142).
The final observation was added as a result of the earlier microscopic findings to evaluate the loss of bracket adhesive material beneath the bracket pad. A statistically significant difference was found (P ⫽ .001) between group 4 and the remaining groups. Groups 1 and 2 with the additional restorative/bracket adhesive material at the bracket periphery had no significant loss of bracket adhesive material beneath the bracket pads. Only 3.8% of these observations had loss of material beneath the bracket compared with 38.5% in group 4 (Fig 4). Group 3 had less loss (15.4%) of bracket adhesive material beneath the bracket pad than did group 4, but more than groups 1 and 2. There was no observable correlation between loss of bracket adhesive
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material or loss of additional restorative material and decalcification in this study. DISCUSSION
In previous studies, the authors sought to prevent demineralization around orthodontic brackets without reliance on patient compliance.2,4,5 Application of restorative sealants on the enamel surface around and beneath the orthodontic brackets was suggested as a method of preventing demineralization. However, Zachrisson et al9 found that many sealants failed to protect the enamel around orthodontic brackets because of oxygen inhibiting the polymerization of the thin sealant coating. Another important consideration in sealant placement is the sensitivity of the technique and the risk of breaks in the sealant layer, resulting from the sealant shearing from the surface due to differences in the coefficients of thermal expansion and eventual decalcification under the sealant. Another factor is the longevity of the sealant protection due to lack of abrasion resistance on the exposed sealant surfaces. Ceen and Gwinnett10 stated that current sealants, with their thin, weak films and low abrasion resistance, cannot provide long-standing protection of the enamel surface against demineralization and concluded that there is a need to develop sealants for orthodontic use with durable, protective films. Hu and Featherstone2 found that a composite based on acrylates instead of methacrylates and containing a relatively small amount of filler (25%) could reduce enamel demineralization under their test conditions compared with a varnish and an orthodontic sealant. They suggested that the significant filler content led to greater abrasion resistance and thus less demineralization, but they reported no data on the amount of remaining resin to support this conclusion. In addition, they did not thermocycle, which can crack and debond the resin due to thermal expansion differences, and bonded brackets were not used. This study indicated that a 64% filled flowable composite made no significant difference in decalcification under our test conditions. Filler alone is not a likely explanation for the differences in the results of these 2 studies. Poststudy observations of the acrylate-based sealant used in the study of Hu and Featherstone2 vs the restorative sealant used in our study showed no obvious difference between the viscosities of these materials. Polymerization of both products produced a hard coating material, even after washing away any oxygeninhibited layer. An explanation for the differences in the results of these 2 studies is elusive. Prophylactic sealing around the orthodontic bracket is worthwhile if the additional time to seal
around the bracket limits the amount of decalcification. However, our results did not conclusively indicate that using either a filled flowable composite or an unfilled sealant, or removing or not removing excess bracket adhesive material, eliminates or significantly reduces the incidence of decalcification. A statistically significant incidental microscopic finding in this study was the bracket adhesive material loss beneath the bracket pads in the conventional treatment group. The bracket adhesive material beneath the bracket pads in groups 1, 2, and 3 treated with additional restorative/bracket adhesive was largely maintained. This appeared to have occurred from the washout of the adhesive material secondary to the mechanical challenges to the unprotected enamel/bracket interface. The additional restorative/bracket adhesive material around the bracket periphery appears to protect from this washout. The washout phenomenon might contribute to the decalcification observed clinically around the bracket pad. Further research is necessary to determine the benefit of sealing around the periphery of the orthodontic bracket. These researchers might find that any sealing at the bracket periphery can also benefit bond strength because of retention of the bracket adhesive material beneath the bracket pad. Although in this study a discrete area around the bracket base was sealed, in clinical use, a large area of coverage, particularly gingivally, would be required to minimize decalcification. CONCLUSIONS
Three methods of protecting the bracket periphery with a restorative/bracket adhesive material were tested to determine their effectiveness in reducing decalcification. None was found to be statistically significantly effective in reducing the incidence of decalcification. However, we identified a significant correlation with the addition of a restorative/bracket adhesive material at the bracket periphery and the reduction in the loss of bracket adhesive material beneath the bracket pad; this might be an alternate benefit to prophylactic sealing around the bracket pad periphery.
REFERENCES 1. Hughes D, Hembree JH, Weber FN. Preparations to prevent enamel decalcification during orthodontic treatment compared. Am J Orthod 1979;76:416-20. 2. Hu W, Featherstone DB. Prevention of enamel demineralization: an in-vitro study using light-cured filled sealant. Am J Orthod Dentofacial Orthop 2005;128:592-600. 3. Vorhies AB, Donly KJ, Staley RN, Wefel JS. Enamel demineralization adjacent to orthodontic brackets bonded with hybrid glass ionomer cements: an in vitro study. Am J Orthod Dentofacial Orthop 1998;114:668-74.
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4. Todd MA, Staley RN, Kanellis MJ, Donly KJ, Wefel JS. Effect of a fluoride varnish on demineralization adjacent to orthodontic brackets. Am J Orthod Dentofacial Orthop 1999;116:159-67. 5. Frazier MC, Southard TE, Doster PM. Prevention of enamel demineralization during orthodontic treatment: an in vitro study using pit and fissure sealants. Am J Orthod Dentofacial Orthop 1996;110:459-65. 6. Oesterle LJ, Messersmith ML, Devine SM, Ness CF. Light and setting times of visible-light cured orthodontic adhesives. J Clin Orthod 1995;29:31-6.
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7. Younis O, Hughes DO, Weber FN. Enamel decalcification in orthodontic treatment. Am J Orthod 1979;75:678-81. 8. Schmit JL, Staley RN, Wefel JS, Kanellis M, Jakobsen JR, Keenan PJ. Effect of fluoride varnish on demineralization adjacent to brackets bonded with RMGI cement. Am J Orthod Dentofacial Orthop 2002;122:125-33. 9. Zachrisson BU, Hemigard E, Ruyter EI, Mjor IA. Problems with sealants for bracket bonding. Am J Orthod 1979;75:641-9. 10. Ceen RF, Gwinnett AJ. Microscopic evaluation of the thickness of sealants used in orthodontic bonding. Am J Orthod 1980;78:623-9.