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Preparations to prevent enamel decalcification during orthodontic treatment compared
Preparations to prevent enamel decalcification during orthodontic treatment compared An in vitro study David 0. Hughes, D.D.S., MS.,* John H. Hembrse, Jr., D.D.S.,** and Faustin N. Weber, D.D.S., M.S.*** Laurel,
Miss., Charleston,
S. C.. and Memphis. Twn.
T
he clinical orthodontist has many responsibilities; one of the most important is the detection and prevention of decalcification and dental caries that may occur during active orthodontic treatment. Because decalcification often develops in orthodontic patients, it is important to investigate methods of preventing it. At present, fluoride compounds are the most widely used preventive agents. Ever since the discovery that the presence of fluoride in the water supplies of certain communities had the bentilcial effect of reducing dental decay, fluoride has been applied in many forms in efforts to prevent decalcification. One of the methods most frequently employed in orthodontics has been the application of topical fluorides.‘~17 More recently, polymeric adhesive coating materials have been used following investigations which have shown them to be beneficial when applied to the surfaces of teeth that are to receive orthodontic appliances. ‘x-22 In a recent study comparing a polymeric adhesive coating to topical fluoride solutions, the polymeric material proved to be more effective in protecting against decalcification. 23 The investigation was a short-term pilot study. The purpose of this follow-up study was to evaluate the effectiveness of several materials, currently being manufactured for the prevention of decalcification of the enamel surfaces of teeth during orthodontic treatment. Several polymeric adhesive coating and resinous coating materials were selected for evaluation. A comparison of these materials could provide results that would prove helpful to orthodontists in their attempt to select the most effective agent for preventing dental decalcification. This study was carried out in partial fulfillment of the requirements for the degree of Master of Science in Orthodontics, University of Tennessee College of Dentistry. Requests for reprints may be addressed to Dr. Hembree. *In the practice of orthodontics, Laurel, Miss. **Professor and chairman, Department of Operative Dentistry. Medical University of South Carolina, College of Dental Medicine, Charleston, S. C. ***Chairman, Department of Orthodontics. University of Tennessee College of Dentistry, Memphis, Tenn.
416
0002.9416/79/040416+05$00.50/0
0
1979 The C. V. Mosby
Co
Volume 75 Number 4
Preparations
to prevent
enamel
dec~alcifkation
47 7
Methods and materials One hundred twenty extracted premolar teeth were selected; the buccal surfaces of all teeth were free of decalcification and caries. All were lightly pumiced and stored in sterile distilled water. After removal and drying, an adhesive dot was placed on the buccal surface of each tooth and carefully burnished to seal its edges. Each tooth was then immersed in nail polish and suspended to dry. After the nail polish dried, the adhesive dots were removed, exposing a symmetrical area of uncoated enamel. The teeth were divided into five groups, with twenty-four in each group. Teeth in the first group were treated with Product A,* an unfilled bis GMA resin. For this, the exposed, uncoated enamel was etched with 50 percent phosphoric acid solution for 90 seconds and then cleaned with tap water. After drying, Nuva-Seal was applied and polymerized with an ultraviolet light. Teeth in the second group were treated with Product B,t a copal resin varnish applied to the exposed, uncoated enamel surface. Product C,.$ a polymeric adhesive coating, was applied to teeth in the third group. After the exposed uncoated surfaces of enamel were prepared with an etching agent included in the kit, equal amounts of the pastes were mixed and applied to each tooth. Product DQ was applied to the exposed, uncoated enamel surfaces of teeth in the fourth group. The fifth group, untreated, served as the control. Orthodontic bands” were selected and loosely fitted to each of the 120 teeth. Bands were cemented to the teeth with zinc phosphate cement.7 After the cement had set, union between the exposed enamel surface and the orthodontic band was broken by the application of pressure to each band with posterior band-removing pliers; this step was designed to simulate a loose orthodontic band in vivo. The use of an in vitro technique to produce decalcification and carieslike lesions has been described by several investigators. “-” The technique of formulating a medium which will produce in vitro decalcification of teeth is as follows: A 20 percent solution of gelatin is adjusted to pH 4.0 by the addition of 30 percent lactic acid. Thymol is added to prevent bacterial growth. Before immersing in the gelatin, each tooth was thermocycled by alternately submerging it for one minute in water at temperatures of 4” C. and 58” C. 100 times to more closely simulate in vivo conditions. The teeth in each of the five groups were suspended in a gelatin solution prepared as described above. Each group of twenty-four teeth was further divided into three subgroups of eight teeth each. The teeth in Subgroup 1 were removed from the gelatin after being immersed for 7 weeks; those in Subgroup 2 after being immersed for 14 weeks; and those in Subgroup 3 after 21 weeks. The orthodontic bands were removed, and the nail polish adjacent to the exposed and treated surfaces was also removed for better determination of the presence or absence of white-spot decalcification. Macroscopically, the decalcification that developed closely resembles in vivo decalcification. The area of decalcification was *Nuva-Seal, the L. D. Caulk Co., Milford, Del. Kopalite, The Harry Bosworth Co., Chicago, Ill. .$Protecto, Lee Pharmaceuticals, South El Monte, Calif. $Portrait Veneer, Lorvic Corp., St. Louis, MO. “Maxillary and mandibular preformed premolar bands, Lancer Pacific, TZinc phosphate cement, Stratford-Cookson Co., College Park, Ga.
Pomona,
Calif.
Table I. Comparison
of four methods of controlling
decalcification
beneath orthodontic
bands
at three time intervals 7 weeks
Decalcifcation
14 weeks
No decalcification
Decalcification
-II weeks
No decalcification
Decal1 cification
No de/ culcij?cation
8 0
0
8
0
8
0
8
0
8
0
0 8
8 0
0 8
8 7
x 0
ProductC$
8 0
Product DO
4
4
8
0
8
Untreated teeth (control) Product A* Product Bt
I 0
*Nuva-Seal, L. D. Caulk Co., Milford, Del. Kopalite, Harry Bosworth Co., Chicago, 111. Wrotecto, Lee Pharmaceuticals, South El Monte, Calif. #Portrait Veneer, Lorvic Corp., St. Louis, MO.
directly proportional to the amount of time the teeth were left in the gelatin solution (that is, teeth at 21 weeks showed much more decalcification than teeth at 7 weeks.) The results of the visual inspection were recorded and statistically evaluated. Discussion of results The results of this study are shown in Table I. The data obtained were analyzed statistically by means of the chi-square test. The analysis demonstrated whether there was a significant difference, at the 5 percent level of significance with one degree of freedom, between the groups being compared. Decalcification occurs most often on the buccal surface of the lower first molars and on the lingual surface of the upper incisors when the occlusion of opposing molars and on the lingual surface of the upper incisors where the occlusion of opposing teeth often breaks up the cement and allows it to be washed out. The groups were compared at three 7-week intervals of time. After the first 7 weeks there was a significant difference between teeth treated with Product A and the control and between those treated with Product C and the control, but there was no significant difference between those treated with Product B and the control and those treated with Product D and the control. Again, after 14 weeks, there was a significant difference between teeth treated with Products A and C and the control. In this study, Products B and D proved ineffective in preventing decalcification. After 21 weeks Product C no longer protected the teeth from decalcification. Products B and D once again proved ineffective in preventing decalcification. The teeth treated with Product A were, therefore, the only ones that continued free of decalcification. When the teeth treated with Products A and C (the acid-etch resin base materials) were compared (at 21 weeks) to those treated with non-acid-etch materials, there was a significant difference which proved that the acid-etch material was the only one used in the study that was effective after this length of time. A comparison was then made between the acid-etch materials themselves; Product A
Volume 75 Number
4
Preparations
to prevent
enamel
decalcification
419
proved to be significantly more effective in protecting against decalcification than Product C when compared after 21 weeks. From this investigation, it can be concluded that only materials using the acid etching method were effective in preventing in vitro decalcification under loose orthodontic bands. As demonstrated in a previous study, 23 Product C protected the enamel under orthodontic bands for short time periods; however, at 21 weeks the enamel seal provided by Product C had disintegrated and decalcification had developed. Further studies might attempt to evaluate the effectiveness of other materials in protecting the tooth surface against decalcification. Teeth could be observed for a longer period of time than was done in this study to determine the effectiveness of Product A. Histologic studies would be useful in determining the amount and depth of penetration of decalcification. This investigation did show that some materials protect teeth against decalcification when an in vitro technique of producing decalcification under loose orthodontic bands is employed. Summary One hundred twenty extracted premolar teeth were divided into five groups of equal size. One group of teeth was treated with a copal resin varnish, another was treated with an unfilled bis GMA resin; the third was treated with a polymeric adhesive coating; the fourth received a protective application of an ultraviolet-light-activated bis GMA resin; and the fifth was left untreated. Each tooth then had an orthodontic band loosely fitted and cemented into place, after which the cement seal was broken to simulate a loose orthodontic band in vivo. Next, all teeth were thermocycled and immediately immersed in a decalcifying gelatin. At the end of 7 weeks, one third of the teeth in each group were removed and examined. At 14 weeks, the second third of the teeth in each group were removed and evaluated. The final third of the teeth in each group were evaluated at 21 weeks. At each time interval the teeth were studied to determine whether any decalcification had taken place. The chi-square test was used to note differences among the five groups of teeth; differences between groups of teeth treated with acid-etch products and the nonetched group; and among the acid-etched groups themselves. For a one-application technique, the ultraviolet-light-activated bis GMA resin used in this study provided more protection against in vitro decalcification of teeth under loose orthodontic bands than did any other product in the study. REFERENCES 1. Fischer, R. B., Muhler, J. C., and Wust, C. J.: Effects of several fluoride reagents on the surface structure of powdered dental enamel, J. Dent. Res. 33: 50-54, 1954. 2. Howell, C. L., Gish, C. W., Smiley, R. D., and Muhler, J. C.: Effect of topically applied stannous fluoride on dental caries experience in children, J. Am. Dent, Assoc. 50: 1417, 1955. 3. Slack, G. L.: The effect of topical application of stannous fluoride solution in the prevention of dental caries, J. Dent. Res. 34: 785, 1955. 4. Slack, G. L.: The effect of topical application of stannous fluoride solution on the incidence of dental caries in six-year-old children, Br. Dent, J. 101: 7- 11, 1956. 5. Walsh, R. H., Mebergall, W. H., Muhler, J. C., and Day, H. G.: Effects of buffered solutions of sodium
6. 7.
8. 9. 10. II. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.
fluoride and stannous fluoride on the solubilit) o1 po~~~tlered enamel using repeated decalclll~~atlc!n. J. I)ent Res. 36: 118-123. 1957. Gish. C. W.. Howell, C. L., and Muhler. J. C.: A new approach to the ruplcal application ot Huorldc\ tor the reduction of dental caries in children, J. Dent. Rcs. 46: 784-786. 1957 Gray, J. A., Schweizer. H. C., Roscverar, F. B.. and Broge. R. W.: Electron microscopic obser\atlon of’ the differences in the effects of stannous fluoride and sodium fluoride on dental enamel. J. Dent. Rch. 37: 63X-648. 1958. Brudevold. F.: Action of topically applied fluoride. J. Dent. Child. 26: 1X6- 190. 1959. Jorden, W. A., Snyder, J. R., and Wilson, V.: A study of a hingle apphcatlon of eight percent stannous fluoride, J. Dent. Child. 26: 355-359, 1959. Mercer, V. H., and Muhler, J. C.: Comparison of a single application of stannous fluoride with a single application of sodium fluoride or two applications of stannous fluoride, J. Dent. Child. 28: 84-86, 1961. Gish, C. W.. Howell, C. L.. and Muhler, J. C.: A new approach to the topical application of fluorides for the reduction ofdental caries in children: Results at the end of five years, J. Dent. Child. 26: 65-71. 1962. Brudevold, F.. Savory, A., Gardner, D. E., Spinelli, M., and Speris, R.: A study of acldulated fluoride solutions. I, Arch. Oral Biol. 8:167-177, 1963. Wellock, W. P., and Brudevold. F.: A study of acidulated fluoride solutions. II, Arch. Oral Biol. 8: 179-182, 1963. Pameijer, J. H., Brudevold, F.. and Hunt. E. E.: A study of acidulated fluoride solutions. 111. Arch. Oral Biol. 8: 183-185, 1963. Meckel, A. H., and Frances, M. D.: Intraoral transfer of topically applied stannous fluoride, J. Dent. Res. 43: 78-85. 1964. Wells. W. R.: Effect of phosphated acidulated fluoride on caries susceptibility of orthodontic patients. Unpublished Master’s Thesis, University of Tennessee, 1970, pp. 46-4X. De Paola, P. F., and Mellberg, J. R.: Caries experience and fluoride uptake in children receiving semiannual prophylaxes with an acidulated phosphate fluoride paste, J. Am. Dent. Assoc. 87: l55- 159, 1973. Gwinnett, A. J., and Buonocore, M. G.: Adhesives and caries protection. Br. Dent. J. 119: 79-80, 1965. Buonocore, M. G., Matsui. A., and Gwinnett, A. J.: Penetration of resin dental materials into enamel surfaces with reference to bonding, Arch. Oral Biol. 13: 61-70, 1968. Buonocore, M. G.: Adhesive sealing of pits and fissures for caries prevention, with the use of ultra violet light, J. Am. Dent. Assoc. 80: 324-30, 1970. Buonocore, M. G.: Caries prevention in pits and fissures sealed with an adhesive resin polymerized by ultraviolet light: A two year study of a single adhesive application, J. Am. Dent. Assoc. 82: 1090-3, 197 1. Lee, H. L., Orlowski, J. A., and Kobashigawa, A. 1.: A protective coating for combating decalcification in orthodontic practice, J. Clin. Orthod. 7: 249-56, 1973. Tillery, T. J., Hembree, J. H., and Weber, F. N.: Preventing enamel decalcification during orthodontic treatment, AM. J. ORTHOD. 70: 435-439, 1976. Silverstone, L. M.: Caries-like lesions produced in vitro, Br. Dent. J. 125: 145-157, 1968. Hals. E., and Nernaes, A.: Histopathology of in vitro caries developing around silver amalgam fillings, Caries Res. 5: 58-77, 1971. Hals, E., and Simonsen, T. L.: Histopathology of experimental in viva caries around silver amalgam fillings, Caries Res. 6: 1633, 1972. Grieve, A. R.: The occurrence of secondary caries-like lesions in vitro. Br. Dent. J. 134: 530-536. 1973.
Miss., Charleston,
S. C.. and Memphis. Twn.
T
he clinical orthodontist has many responsibilities; one of the most important is the detection and prevention of decalcification and dental caries that may occur during active orthodontic treatment. Because decalcification often develops in orthodontic patients, it is important to investigate methods of preventing it. At present, fluoride compounds are the most widely used preventive agents. Ever since the discovery that the presence of fluoride in the water supplies of certain communities had the bentilcial effect of reducing dental decay, fluoride has been applied in many forms in efforts to prevent decalcification. One of the methods most frequently employed in orthodontics has been the application of topical fluorides.‘~17 More recently, polymeric adhesive coating materials have been used following investigations which have shown them to be beneficial when applied to the surfaces of teeth that are to receive orthodontic appliances. ‘x-22 In a recent study comparing a polymeric adhesive coating to topical fluoride solutions, the polymeric material proved to be more effective in protecting against decalcification. 23 The investigation was a short-term pilot study. The purpose of this follow-up study was to evaluate the effectiveness of several materials, currently being manufactured for the prevention of decalcification of the enamel surfaces of teeth during orthodontic treatment. Several polymeric adhesive coating and resinous coating materials were selected for evaluation. A comparison of these materials could provide results that would prove helpful to orthodontists in their attempt to select the most effective agent for preventing dental decalcification. This study was carried out in partial fulfillment of the requirements for the degree of Master of Science in Orthodontics, University of Tennessee College of Dentistry. Requests for reprints may be addressed to Dr. Hembree. *In the practice of orthodontics, Laurel, Miss. **Professor and chairman, Department of Operative Dentistry. Medical University of South Carolina, College of Dental Medicine, Charleston, S. C. ***Chairman, Department of Orthodontics. University of Tennessee College of Dentistry, Memphis, Tenn.
416
0002.9416/79/040416+05$00.50/0
0
1979 The C. V. Mosby
Co
Volume 75 Number 4
Preparations
to prevent
enamel
dec~alcifkation
47 7
Methods and materials One hundred twenty extracted premolar teeth were selected; the buccal surfaces of all teeth were free of decalcification and caries. All were lightly pumiced and stored in sterile distilled water. After removal and drying, an adhesive dot was placed on the buccal surface of each tooth and carefully burnished to seal its edges. Each tooth was then immersed in nail polish and suspended to dry. After the nail polish dried, the adhesive dots were removed, exposing a symmetrical area of uncoated enamel. The teeth were divided into five groups, with twenty-four in each group. Teeth in the first group were treated with Product A,* an unfilled bis GMA resin. For this, the exposed, uncoated enamel was etched with 50 percent phosphoric acid solution for 90 seconds and then cleaned with tap water. After drying, Nuva-Seal was applied and polymerized with an ultraviolet light. Teeth in the second group were treated with Product B,t a copal resin varnish applied to the exposed, uncoated enamel surface. Product C,.$ a polymeric adhesive coating, was applied to teeth in the third group. After the exposed uncoated surfaces of enamel were prepared with an etching agent included in the kit, equal amounts of the pastes were mixed and applied to each tooth. Product DQ was applied to the exposed, uncoated enamel surfaces of teeth in the fourth group. The fifth group, untreated, served as the control. Orthodontic bands” were selected and loosely fitted to each of the 120 teeth. Bands were cemented to the teeth with zinc phosphate cement.7 After the cement had set, union between the exposed enamel surface and the orthodontic band was broken by the application of pressure to each band with posterior band-removing pliers; this step was designed to simulate a loose orthodontic band in vivo. The use of an in vitro technique to produce decalcification and carieslike lesions has been described by several investigators. “-” The technique of formulating a medium which will produce in vitro decalcification of teeth is as follows: A 20 percent solution of gelatin is adjusted to pH 4.0 by the addition of 30 percent lactic acid. Thymol is added to prevent bacterial growth. Before immersing in the gelatin, each tooth was thermocycled by alternately submerging it for one minute in water at temperatures of 4” C. and 58” C. 100 times to more closely simulate in vivo conditions. The teeth in each of the five groups were suspended in a gelatin solution prepared as described above. Each group of twenty-four teeth was further divided into three subgroups of eight teeth each. The teeth in Subgroup 1 were removed from the gelatin after being immersed for 7 weeks; those in Subgroup 2 after being immersed for 14 weeks; and those in Subgroup 3 after 21 weeks. The orthodontic bands were removed, and the nail polish adjacent to the exposed and treated surfaces was also removed for better determination of the presence or absence of white-spot decalcification. Macroscopically, the decalcification that developed closely resembles in vivo decalcification. The area of decalcification was *Nuva-Seal, the L. D. Caulk Co., Milford, Del. Kopalite, The Harry Bosworth Co., Chicago, Ill. .$Protecto, Lee Pharmaceuticals, South El Monte, Calif. $Portrait Veneer, Lorvic Corp., St. Louis, MO. “Maxillary and mandibular preformed premolar bands, Lancer Pacific, TZinc phosphate cement, Stratford-Cookson Co., College Park, Ga.
Pomona,
Calif.
Table I. Comparison
of four methods of controlling
decalcification
beneath orthodontic
bands
at three time intervals 7 weeks
Decalcifcation
14 weeks
No decalcification
Decalcification
-II weeks
No decalcification
Decal1 cification
No de/ culcij?cation
8 0
0
8
0
8
0
8
0
8
0
0 8
8 0
0 8
8 7
x 0
ProductC$
8 0
Product DO
4
4
8
0
8
Untreated teeth (control) Product A* Product Bt
I 0
*Nuva-Seal, L. D. Caulk Co., Milford, Del. Kopalite, Harry Bosworth Co., Chicago, 111. Wrotecto, Lee Pharmaceuticals, South El Monte, Calif. #Portrait Veneer, Lorvic Corp., St. Louis, MO.
directly proportional to the amount of time the teeth were left in the gelatin solution (that is, teeth at 21 weeks showed much more decalcification than teeth at 7 weeks.) The results of the visual inspection were recorded and statistically evaluated. Discussion of results The results of this study are shown in Table I. The data obtained were analyzed statistically by means of the chi-square test. The analysis demonstrated whether there was a significant difference, at the 5 percent level of significance with one degree of freedom, between the groups being compared. Decalcification occurs most often on the buccal surface of the lower first molars and on the lingual surface of the upper incisors when the occlusion of opposing molars and on the lingual surface of the upper incisors where the occlusion of opposing teeth often breaks up the cement and allows it to be washed out. The groups were compared at three 7-week intervals of time. After the first 7 weeks there was a significant difference between teeth treated with Product A and the control and between those treated with Product C and the control, but there was no significant difference between those treated with Product B and the control and those treated with Product D and the control. Again, after 14 weeks, there was a significant difference between teeth treated with Products A and C and the control. In this study, Products B and D proved ineffective in preventing decalcification. After 21 weeks Product C no longer protected the teeth from decalcification. Products B and D once again proved ineffective in preventing decalcification. The teeth treated with Product A were, therefore, the only ones that continued free of decalcification. When the teeth treated with Products A and C (the acid-etch resin base materials) were compared (at 21 weeks) to those treated with non-acid-etch materials, there was a significant difference which proved that the acid-etch material was the only one used in the study that was effective after this length of time. A comparison was then made between the acid-etch materials themselves; Product A
Volume 75 Number
4
Preparations
to prevent
enamel
decalcification
419
proved to be significantly more effective in protecting against decalcification than Product C when compared after 21 weeks. From this investigation, it can be concluded that only materials using the acid etching method were effective in preventing in vitro decalcification under loose orthodontic bands. As demonstrated in a previous study, 23 Product C protected the enamel under orthodontic bands for short time periods; however, at 21 weeks the enamel seal provided by Product C had disintegrated and decalcification had developed. Further studies might attempt to evaluate the effectiveness of other materials in protecting the tooth surface against decalcification. Teeth could be observed for a longer period of time than was done in this study to determine the effectiveness of Product A. Histologic studies would be useful in determining the amount and depth of penetration of decalcification. This investigation did show that some materials protect teeth against decalcification when an in vitro technique of producing decalcification under loose orthodontic bands is employed. Summary One hundred twenty extracted premolar teeth were divided into five groups of equal size. One group of teeth was treated with a copal resin varnish, another was treated with an unfilled bis GMA resin; the third was treated with a polymeric adhesive coating; the fourth received a protective application of an ultraviolet-light-activated bis GMA resin; and the fifth was left untreated. Each tooth then had an orthodontic band loosely fitted and cemented into place, after which the cement seal was broken to simulate a loose orthodontic band in vivo. Next, all teeth were thermocycled and immediately immersed in a decalcifying gelatin. At the end of 7 weeks, one third of the teeth in each group were removed and examined. At 14 weeks, the second third of the teeth in each group were removed and evaluated. The final third of the teeth in each group were evaluated at 21 weeks. At each time interval the teeth were studied to determine whether any decalcification had taken place. The chi-square test was used to note differences among the five groups of teeth; differences between groups of teeth treated with acid-etch products and the nonetched group; and among the acid-etched groups themselves. For a one-application technique, the ultraviolet-light-activated bis GMA resin used in this study provided more protection against in vitro decalcification of teeth under loose orthodontic bands than did any other product in the study. REFERENCES 1. Fischer, R. B., Muhler, J. C., and Wust, C. J.: Effects of several fluoride reagents on the surface structure of powdered dental enamel, J. Dent. Res. 33: 50-54, 1954. 2. Howell, C. L., Gish, C. W., Smiley, R. D., and Muhler, J. C.: Effect of topically applied stannous fluoride on dental caries experience in children, J. Am. Dent, Assoc. 50: 1417, 1955. 3. Slack, G. L.: The effect of topical application of stannous fluoride solution in the prevention of dental caries, J. Dent. Res. 34: 785, 1955. 4. Slack, G. L.: The effect of topical application of stannous fluoride solution on the incidence of dental caries in six-year-old children, Br. Dent, J. 101: 7- 11, 1956. 5. Walsh, R. H., Mebergall, W. H., Muhler, J. C., and Day, H. G.: Effects of buffered solutions of sodium
6. 7.
8. 9. 10. II. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.
fluoride and stannous fluoride on the solubilit) o1 po~~~tlered enamel using repeated decalclll~~atlc!n. J. I)ent Res. 36: 118-123. 1957. Gish. C. W.. Howell, C. L., and Muhler. J. C.: A new approach to the ruplcal application ot Huorldc\ tor the reduction of dental caries in children, J. Dent. Rcs. 46: 784-786. 1957 Gray, J. A., Schweizer. H. C., Roscverar, F. B.. and Broge. R. W.: Electron microscopic obser\atlon of’ the differences in the effects of stannous fluoride and sodium fluoride on dental enamel. J. Dent. Rch. 37: 63X-648. 1958. Brudevold. F.: Action of topically applied fluoride. J. Dent. Child. 26: 1X6- 190. 1959. Jorden, W. A., Snyder, J. R., and Wilson, V.: A study of a hingle apphcatlon of eight percent stannous fluoride, J. Dent. Child. 26: 355-359, 1959. Mercer, V. H., and Muhler, J. C.: Comparison of a single application of stannous fluoride with a single application of sodium fluoride or two applications of stannous fluoride, J. Dent. Child. 28: 84-86, 1961. Gish, C. W.. Howell, C. L.. and Muhler, J. C.: A new approach to the topical application of fluorides for the reduction ofdental caries in children: Results at the end of five years, J. Dent. Child. 26: 65-71. 1962. Brudevold, F.. Savory, A., Gardner, D. E., Spinelli, M., and Speris, R.: A study of acldulated fluoride solutions. I, Arch. Oral Biol. 8:167-177, 1963. Wellock, W. P., and Brudevold. F.: A study of acidulated fluoride solutions. II, Arch. Oral Biol. 8: 179-182, 1963. Pameijer, J. H., Brudevold, F.. and Hunt. E. E.: A study of acidulated fluoride solutions. 111. Arch. Oral Biol. 8: 183-185, 1963. Meckel, A. H., and Frances, M. D.: Intraoral transfer of topically applied stannous fluoride, J. Dent. Res. 43: 78-85. 1964. Wells. W. R.: Effect of phosphated acidulated fluoride on caries susceptibility of orthodontic patients. Unpublished Master’s Thesis, University of Tennessee, 1970, pp. 46-4X. De Paola, P. F., and Mellberg, J. R.: Caries experience and fluoride uptake in children receiving semiannual prophylaxes with an acidulated phosphate fluoride paste, J. Am. Dent. Assoc. 87: l55- 159, 1973. Gwinnett, A. J., and Buonocore, M. G.: Adhesives and caries protection. Br. Dent. J. 119: 79-80, 1965. Buonocore, M. G., Matsui. A., and Gwinnett, A. J.: Penetration of resin dental materials into enamel surfaces with reference to bonding, Arch. Oral Biol. 13: 61-70, 1968. Buonocore, M. G.: Adhesive sealing of pits and fissures for caries prevention, with the use of ultra violet light, J. Am. Dent. Assoc. 80: 324-30, 1970. Buonocore, M. G.: Caries prevention in pits and fissures sealed with an adhesive resin polymerized by ultraviolet light: A two year study of a single adhesive application, J. Am. Dent. Assoc. 82: 1090-3, 197 1. Lee, H. L., Orlowski, J. A., and Kobashigawa, A. 1.: A protective coating for combating decalcification in orthodontic practice, J. Clin. Orthod. 7: 249-56, 1973. Tillery, T. J., Hembree, J. H., and Weber, F. N.: Preventing enamel decalcification during orthodontic treatment, AM. J. ORTHOD. 70: 435-439, 1976. Silverstone, L. M.: Caries-like lesions produced in vitro, Br. Dent. J. 125: 145-157, 1968. Hals. E., and Nernaes, A.: Histopathology of in vitro caries developing around silver amalgam fillings, Caries Res. 5: 58-77, 1971. Hals, E., and Simonsen, T. L.: Histopathology of experimental in viva caries around silver amalgam fillings, Caries Res. 6: 1633, 1972. Grieve, A. R.: The occurrence of secondary caries-like lesions in vitro. Br. Dent. J. 134: 530-536. 1973.