Clinical effectiveness of fluoride-releasing elastomers. I: Salivary Streptococcus mutans numbers

Thomas G. Wilson, DDS, a and Richard L. Gregory, PhD b Des Moines, Iowa, and Indianapolis, Ind.

The purpose of this study was to examine the effect of fluoride-releasing elastomers on salivary Streptococcus rnutans numbers. Twenty-four patients with fixed orthodontic appliances were randomly divided into experimental and control groups consisting of 12 patients each. Conventional elastomers were in place while two baseline whole saliva samples were collected from each subject in both groups at their regular appointments. After the second baseline sample was taken, conventional elastomers were replaced with fluoride-releasing elastomers in the experimental group, whereas conventional elastomers were continued in the control group. Three saliva samples were then collected from all subjects at 1-week intervals. Conventional elastomers were placed in all subjects while two postexperimental saliva samples were collected at regular appointments. Results showed that the control group demonstrated no significant changes (/3 > 0.05) in the percentage of S. mutans over the 13-week study period. However, after the fluoride-releasing elastomers were placed, the percent of salivary S. mutans decreased significantly (p < 0.01) in the experimental group. There was no significant effect after the fluoride-releasing elastomers were in place for 2 or more weeks. (AM J ORTHOD DENTOFAC ORTHOP 1995;107:293-7.)

T h e presence of fixed orthodontic appli- ances leads to an increase in the absolute number of salivary Streptococcus mutans, as well as an increase in the percentage of S. mutans.l'2 These changes may be responsible for decalcification or white spot formation during orthodontic therapy. 3-7 Decalcification or white spot formation during orthodontic treatment has been a problem since the introduction of fixed appliances. Enamel decal- cification results from an imbalance between the demineralization and remineralization of enamel. The white spot lesion is considered to be the precurser of enamel caries. In orthodontics it has been attributed to prolonged accumulation and retention of bacterial plaque on the enamel surface adjacent to the appliances. ~ Plaque retention sur- rounding orthodontic appliances leads to enamel demineralization caused by organic acids, produced by bacteria in the dental plaque. 9 Plaque develops after the placement of a fixed appliance because the appliance often impedes the maintenance of good oral hygiene for the orthodontic patient. The components of the appliance create many new retention areas for microorganisms and impede

qn private practice of orthodontics and pediatric dentistry, Des Moines, Iowa. bAssociate Professor, Department of Oral Microbiology, Indiana Univer- sity School of Dentistry. Copyright © 1995 by the American Association of Orthodontists. 0889-5406/95/$3.00 + 0 8/1/50018

proper access to the tooth surfaces for optimal cleaning. 1° Decalcification may then occur. White spot formation represents an unesthetic side effect of orthodontic treatment that may counteract the beneficial results of such treatment. Thus, preven- tion of white spot formation is important for the orthodontist to consider.

One possible method of reducing the risk of decalcification during orthodontic treatment would be through topical application of fluoride. Al- though stannous fluoride has traditionally been thought to prevent caries by remineralizing enamel, studies have also shown that it exhibits antibacte- rial properties at low concentrations. 11-13 There are several theories regarding the antibacterial effects of stannous fluoride. Camosci and Tinanoff 13 be- lieved the unique antibacterial properties of SnF 2 are associated with the intracellular retention of tin. They found that tin is transported into the bacteria where it disrupts metabolism. Ota et al) a found that stannous fluoride preparations inhibited cell-to-cell coherence of S. mutans at concentra- tions as low as 0.001%. Whitford et al) ~ believed that stannous fluoride inhibits S. mutans growth through its low pH.

With this knowledge it would seem prudent to provide a constant supply of stannous fluoride over the duration of orthodontic treatment. Since cari- ous lesion formation most commonly occurs adja- cent to the orthodontic bracket, it would seem

293

294 Wilson and Gregory American Journal of Orthodontics and Dentofacial Orthopedics March 1995

15

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Fig. 1. Percent of S. mutans in 12 patients from control group reported as ratio of number of S. mutans/number of total oral streptococci x 100, over 13-week study period. Conventional elastomers were used throughout study period in these sub- jects.

appropriate for the fluoride source to be in close proximity to the bracket. This would serve to maxi- mize the antibacterial and remineralizing benefits associated with stannous fluoride. Recently, fluo- ride-releasing elastomers (OrthoArch Company, Inc., Hoffman Estates, Ill.) have been made avail- able for orthodontic patients. In vitro studies by Joseph et al. 14 have indicated that fluoride released from elastic chain was initially high, but dropped to low levels after 1 week. The current study was designed to determine the effect fluoride-releasing elastomers would have on salivary Streptococcus rnutans numbers.

MATERIALS AND METHODS Patients and experimental design

Twenty-four patients ranging from 13 to 35 years of age from the postgraduate orthodontic clinic at Emory University were included in this study. All patients had been undergoing full orthodontic treatment with edge- wise appliances for at least 4 months. Subjects were randomly divided into experimental and control groups, each consisting of 12 patients. Two baseline unstimulated whole saliva samples were collected from the subjects in each group at their routine orthodontic appointments, which were scheduled at 3-week intervals. After the second baseline sample was taken, conventional elas-

tomers (Ormco Corp., Glendora, Calif.) were replaced with fluoride-releasing elastomers in the experimental group, whereas conventional elastomers were used in the control group. Three whole saliva samples were then collected from all subjects in each group at I-week intervals. Elastomers were not changed for either group while the weekly samples were collected. Conventional elastomers were placed at week 7 in all subjects and two postexperimental saliva samples were collected at rou- tine orthodontic appointments at weeks 10 and 13. A total of seven saliva samples were collected from each subject over a 13-week period.

Quantitation of oral streptococci and S. mutans

Each saliva sample was vortexed for 30 seconds and serially diluted from 10-' to 10 -2 in sterile deionized distilled water. From each dilution a Spiral Plater (Spiral Systems Inc., Cincinnati, Ohio) was used to deposit 0.0492 ml on the surface of duplicate agar plates. For cultivation of total oral streptococci organisms, dilutions were plated on Mitis salivarius (Difco Laboratories, De- troit, Mich.) plus 15% sucrose (MSS) plates. For deter- mination of S. mutans, a selective medium consisting of MSS agar containing bacitracin (0.2 units/ml) (MSSB) was used. All plates were incubated in a 5% CO2 enriched incubator at 37 ° C for 48 hours. A Spiral System Counting Grid (Spiral Systems Inc., Cincinnati, Ohio) was used to count individual colonies of bacteria. The percent of S. mutans was calculated by dividing the number of S. mutans on MSSB plates by the number of total oral streptococci on MSS plates x 100.

Statistical analysis

Data from both groups were subjected to a two tailed t test with BMDP (BMDP Statistical Software, Inc., Los Angeles, Calif.). Baseline bacteria counts, weeks 1 and 4, were compared with all other weeks. All variances are reported as standard deviations. Differences among means were analyzed by the Students t test for two group comparisons and Mann-Whitney U test or Kruskal-Wallis one-way analysis of variance for multigroup comparisons.

RESULTS

Figs. 1 and 2 illustrate the individual percent S. mutans (number of S. mutans /number total oral streptococci x 100) from the control and experi- mental groups, respectively. The control group showed no significant change (p > 0.05) in the percentage of S. mutans over the 13-week study period. However, after the fluoride-releasing elas- tomeres were placed at the 4-week mark, the per- cent of S. mutans decreased significantly (p < 0.01) in the experimental group at the 5-week interval (Fig. 3). By week 6 through week 13 there was no significant effect. Fig. 4 presents the data as group means with standard error bars, showing a signifi-

American Journal of Orthodontics and Dentofacial Orthopedics Wilson and Gregory 295 l/olume 107, No. 3

50 * F luor ide e l a s t o m e r s p l aced

45 # ConvenLional e lasLomers p l aced

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Fig. 2. Percent of S. mutans in 12 patients from experimental group, reported as ratio of number of S. mutans/number of total oral streptococci x 100, over 13-week study period. Fluoride-containing elastomers were placed after fourth week collection and replaced after seventh week collection with conventional elastomers.

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Fig, 3. Percent of S. mutans in 12 patients from experimental group from week 4 to week 5. Fluoride-containing elastomers were placed after fourth week collection.

cant dep re s s ion (p < 0.01) f rom the four th w e e k to the fifth week intervals in the expe r imen t a l g roup and no significant d i f fe rences b e t w e e n the groups at the o t h e r t ime intervals .

DISCUSSION

T h e dep re s s ion of S. mutans n o t e d at the week 5 sample in the expe r imen ta l g roup suggests tha t the s t annous f luor ide did exhibi t an t ibac te r i a l p rop -

2 9 6 Wilson and Gregory American Journal of Orthodontics and Dentofacial Orthopedics March 1995

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* Fluoride e l a s t o m e r s p laced # Convent ional e l a s t o m e r s p laced

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2 4 6 8 10 12 * # Weeks

14

Fig. 4. Group means _+ standard errors of means of percent of S. mutans in experimental and control groups. Fluoride- containing elastomers were placed in experimental group after fourth week collection and replaced after seventh week col- lection with conventional etastomers. Significant reductions (p < 0.01) were observed in experimental group between weeks 4 and 5.

erties. This finding agrees with previous research that showed a reduction in oral bacteria after exposure to low concentrations of stannous fluo- ride. 15-I7 Other studies have demonstrated a selec- tive inhibition of S. mutans in the presence of stannous fluoride. I8'19 Previous research noted a prolonged suppression in the percentage of salivary S. mutans for up to 4 weeks after discontinuing topical stannous fluoride applications. 2° The fact that S. mutans levels returned to baseline levels at week 6 suggests that (1) little or no stannous fluoride was being released; or (2) S. mutans were becoming resistant to the antibacterial effects of stannous fluoride. Research conducted by Klock et al. 21 tends to discount this latter theory. They reported a reduction of S. mutans in patients rins- ing with stannous fluoride daily was still evident after 2 years.

The results of the current study should be considered with the results of a previous study that compared the use of elastomeres and steel ligation techniques. Forsberg et al. 1° found that teeth at- tached to the arch wire with an elastomeric ring exhibited a greater number of microorganisms in the plaque than teeth ligated with steel wire. They even recommended that for patients who demon-

strate inadequate oral hygiene, elastomeric ligation rings should not be used as they will significantly increase microbial accumulation on tooth surfaces adjacent to the brackets. This accumulation will increase the chances of decalcification and gingivi- tis. Further research is needed to determine whether the antibacterial properties exhibited by fluoride-releasing elastomeres will offset their pro- pensity for plaque accumulation.

The results of the current study suggest that for those clinicians who do choose to use elastomers, fluoride-releasing elastomers will temporarily re- duce the levels of S. mutans. Whether this depres- sion of S. rnutans translates to less decalcification during orthodontic therapy will be addressed in future studies.

We express our appreciation to the Emory Orth- odontic Study Club for the financial support provided to this project. These studies were carried out with in- formed consent and were approved by the Human Use Committee of Emory University.

REFERENCES

1. Mattingty JR, Sauer G J, Yancy JM, Arnold RR. Enhance- ment of Streptococcus mutans colonization by direct bonded orthodontic appliances. J Dent Res 1983;62:1209-11.

2. Rosenbloom RG, Tinanoff N. Salivary Streptococcus mutans levels in patients before, during, and after orthodontic treatment. AM J DENTOFAC ORTHOP 1991;100:35-7.

3. Gorelick L, Geiger AM, Gwinnett AJ. Incidence of white spot formation after bonding and banding. AM J ORTHOD 1982;81:93-8.

4. Zachrisson BU, Zachrisson S. Caries incidence and oral hygiene during orthodontic treatment. Scand J Dent Res 1971;79:394-401.

5. Ingervall B. The influence of orthodontic appliances on caries frequency. Odontol Revy 1962;13:185-90.

6. Artun J, Brobakken O. Prevalence of carious white spots after orthodontic treatment with multibonded appliances. Eur J Orthod 1986;8:229-34.

7. Ogaard B. Prevalence of white spot lesions in 19-year-olds: a study on untreated and orthodontically treated persons 5 years after treatment. AM J ORTHOD 1989;96:423-7.

8. O'Reilly MM, Featherstone JDB. Demineralization and remineralization around orthodontic appliances: an in vivo

study. AM J ORTHOD DENTOFAC ORTHOP 1987;92:33-40. 9. Arends J, Christofferson I. The nature of early caries lesions

in enamel. J Dent Res 1986;65:2-11. 10. Forsberg CM, Brattstr6m V, Malmberg E, Nord CE. Liga-

ture wires and etastomeric rings: two methods of ligation, and their association with microbial colonization of StreFto - coccus mutans and lactobacilli. Eur J Orthod 1991;13:416-20.

11. Whitford GM, Schuster GS, Paschley DH, Venkateswarlu P. Fluoride uptake by Streptococcus mutans 6715. Infect Im- mun 1977;18:660-87.

12. Ota K, Kikuchi S, Beierle JW. Stannous fluoride and its effects on oral microbial adhesive properties in vitro. Ped Dent 1989;11:21-4.

American Journal of Orthodontics and Dentofacial Orthopedics Wilson and Gregory 297 Volume 107, No. 3

13. Camosci DA, Tinanoff N. Anti-bacterial determinants of stannous fluoride. J Dent Res 1984;63:1121-5.

14. Joseph VR Grobler SR, Rossouw PE. Fluoride release from orthodontic elastic chain. J Clin Orthod 1993;27:101-5.

15. Bibby BG, VonKesternen M. The effect of fluorine on mouth bacteria. J Dent Res 1940;19:391-402.

16. Konig KG. Dental caries and plaque accumulation in rats treated with stannous fluoride and penicillin. Helv Odont Acta 1959;3:39-44.

17. Shern RJ, Couet KM, Kingman A. Effects of various fluo- ride rinses on dental plaque in rats. J Dent Res 1978;57: All4.

18. Svanberg M, Westergren G. Effect of SnFz, administered as mouth rinses or topically applied, on Streptococcus mutans, Streptococcus sanguis and Lactobacilli in dental plaque and saliva. Scand J Dent Res t983;91:123-9.

19. Tinanoff N, Klock B, Camosci DA, Manwell MA. Microbio-

logic effects of SnF 2 and NaF mouthrinses in subjects with high caries activity: results after one year. J Dent Res 1983;62:907-11.

20. Svanberg M, Rolla G. Streptococcus mutans in plaque and saliva after mouthrinsing with SnF 2. Scand J Dent Res 1982;90:292-8.

21. Klock B, Serling J, Kinder S, Manwell MA, Tinanoff N. Comparison of effect of SnF2 and NaF mouthrinses on caries incidence, salivary S. mutans and gingivitis in high caries prevalent adults. Stand J Dent Res 1985;93:213-7.

Reprint requests to: Dr. Thomas G. Wilson 8515 Douglas Omega Place, Suite 26 Des Moines, IA 50322

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