Enamel loss during orthodontic bonding and subsequent loss during removal of filled and unfilled adhesives C. R. Lee Brown, D.D.S., and David C. Way, D.D.S., MS., F.R.C.D.(C) London,
Ontario,
Canada
S
ince Buonocore2 first reported, in 19.55, on the possibility of bonding acrylic resins to etched enamel surfaces, many different materials and techniques have been developed. 7, 8, ‘I* l8 During the last decade, these materials and procedures have gained widespread use for bonding orthodontic attachments directly to tooth surfaces.14* “3 25, 26 A number of different techniques have been suggested for removal of attachments and adhesive when orthodontic treatment is completed.6 Although several studies 3S‘* ” have demonstrated which debonding procedures cause the least scratching or faceting of the enamel, only two researchers5, 26 appear to have attempted to measure the actual amount of enamel loss that debonding produces. These two studies, which employed different debonding and measuring techniques, showed markedly different results, one concluding that 55.6 Frn is lost and the other that less than 5 pm is lost. This study, therefore, has two purposes: ( 1) to measure and compare in vivo the total enamel loss during bonding and debonding techniques with two popular adhesives (one a highly filled composite of quartz in a diacrylate resin* and the other an unfilled polymethylmethacrylatet) and (2) to measure in vitro the amount of enamel lost during each step of the procedure, namely, polishing, etching, and final debonding and clean-up. Materials and methods In order to make the precise measurements required in this study, a metal gauge (Fig. 1) was developed that could register the depth from the surface of the tooth to a recessed steel marker and which could be accurately measured in the optical system of a micrometer-stage microscope (Fig. 2). The first part of the study involved twenty-six first premolars from a group of eight orthodontic patients; the second part was conducted on twenty first premolars from another group of eight patients. All teeth in both groups were scheduled for extraction as part of the orthodontic treatment; none were carious or restored. The age of the patients in Group 1 ranged from 11 to 19; in Group 2 the range was from I 1 to 2.5. From the This study *Concise, +Directon
Division of Orthodontics, Faculty of Dentistry. The University was supported in part by an MRC General Support Grant. Minnesota Mining and Manufacturing Co., St. Paul, Minn. II, TP Laboratories, LaPorte, lnd.
900?-9416/?81120663+09$00.90/0
@
1978 The C. V. Mosby
Co
of Western
Ontario.
663
Am. J. Orthod. December I918
Fig. 1, The
Fig.
metal
gauge
2. Miniload
which
hardness
was used
tester
for all measurements
(Leitz),
with
micrometer
made
stage
in this study.
and graticle
(Magnification,
x 8.)
eyepiece
The twenty-six premolars in the first group were prepared by drilling two holes completely through the enamel with a No. 699M high-speed bur. The holes were positioned on the buccal developmental ridge, one above the other, 3 to 4 mm. apart. Tightly fitting stainless steel marker pins were then cemented into the holes with zinc phosphate cement. The face of each pin was recessed approximately 200 ,um below the enamel
Volume 74 Number 6
Enamel loss during orthodontic
Fig.
3. Initial
position
of the gauge
against
an embedded
Fig. 4. The final position of the gauge, with the steel pin (P) resting the face of the gauge resting on the surface of the enamel (Ej.
steel
bonding
665
marker.
on the embedded
marker(M)
and
surface with a No. 2 round bur. This step served two purposes; (1) it produced a smooth, concave steel reference point, in which the measuring gauge would be self-centering, and (2) it also removed any weakened enamel prisms around the pin hole, ensuring that the face of the gauge would rest on stable enamel during measurement. Immediately following pin placement. recessing, and removal of excess cement, the metal gauge and microscope were used to record and measure initial pin depth. The gauge was positioned as in Fig. 3 and then moved against the tooth until the metal face made maximum contact on the enamel (Fig. 4). Five measurements were made at each site
Am. J. Orthod. December 1978
Fig. 5. A diagrammatic (Magnification, x40.)
representation
of the appearance
of the gauge
and
graticle
in the microscope.
intraorally, and an average was taken. The standard error of the mean was calculated for each group of five measurements to serve as an error study. Each tooth was then polished with zirconium silicate* and water on a rotating bristle brush? for 10 to 15 seconds, after which the teeth were washed, isolated, and dried with an air syringe. Each tooth was then individually etched for 90 seconds with 37 percent orthophosphoric acid, washed, dried, and reisolated without contacting the etched surface with cotton rolls or lips. An orthodontic bracket on a foil-mesh pad was bonded immediately to each tooth, covering both steel markers. On each pair of premolars for each patient, the unfilled adhesive was used randomly on one side or the other, preceded by a vinyl silane primer-.$ The contralateral tooth was etched, dried, and bonded with the filled adhesive, preceded by an unfilled enamel sealant.§ Both adhesive systems were used in accordance with the manufacturers’ directions. After a period of 4 to 7 days, the brackets were carefully removed with bracketremoving pliers.” The pliers were not used to scrape the surface. As much of the remaining adhesive as possible was removed with a hand scaler. Any adhesive tags that could not be removed by hand were slowly abraded with a No. 7902 finishing bur until the surface of the tooth appeared clinically clean and shiny. Each tooth was then polished with zirconium silicate on a brush. Any adhesive still remaining in the pin holes was removed with a scaler. Five measurements of the final depth of each marker were taken again and averaged. The total enamel loss at each site was then calculated by subtraction of this value from the original depth. Statistical analysis was done to determine the presence of *Zircate, L. D. Caulk Co., Milford, Del. *Crescent Dental Mfg. Co., Chicago, Ill. *Directon 11 Primer. 5Enamel Bond, Minnesota Mining and Manufacturing “ETM. No. 349, Monrovia, Calif.
Co.,
St. Paul,
Minn.
Volume 74 Number 6
Fig.
6. The
Enamel loss during orthodontic
appearance
of the tooth
after
debonding,
showing
the position
bonding
of the steel
667
markers.
any significant difference in enamel loss between the occlusal and gingival sites and between the teeth bonded with the filled resin compared to those bonded with the unfilled resin. The second part of the study was conducted in vitro to permit measurement of enamel loss during each step of the procedure with no risk of contamination of etched surfaces.24 The second group of eight patients provided twenty freshly extracted premolars. After extraction, but on the same day, markers were placed as before, and initial measurements were made. The teeth were polished, etched, and bonded by the same technique as for Group 1. Further measurements were taken immediately following polishing and again after etching. Brackets were bonded as before, with one tooth in each pair receiving the unfilled resin and the other receiving the filled adhesive. The teeth were stored in tap water for 3 to 5 days to permit complete polymerization. The brackets were removed; adhesive islands were removed with a hand scaler when possible and with a finishing bur when necessary. After polishing, final measurements were taken at each site. The amount of enamel loss due to polishing, etching, manual clean-up, and rotary clean-up was then calculated by subtracting each measurement from the previous measurement at the same site. Observed differences in enamel loss during the removal of the two adhesives were tested for significance. Results The accuracy of the measurement technique was determined by calculating the standard error of the mean for the five measurements taken at each site after each step was completed. In the first group, where all measurements were intraoral, the average of the standard errors was 3.07 pm. All measurements of the second group were done extraorally, with an average standard error of 2.44 pm. No brackets were lost during either part of the study. Although it appeared clinically
Am. J. Orrhod. December 1918
Table I. Total enamel loss in both groups Vnjlled
Group I (n = 23) Median loss 80 percent range Group2 (n = 19) Median loss 80 percent range
adhesive
(pm)
Filled
adhesive
(pm)
17.5 0.0 to 33.8
40.8 16.0 to 64.5
44.0 21.2 to 56.0
60.5 25.0 to 76.8
Table II. Enamel loss resulting from each procedure Loss due to
Polishing only Etching only Debonding of unfilled adhesive Debonding of filled adhesive
Median
(pm)
26.0 3.0 5.2 25.0
80 percent
range
10.0 to 43.8 0.2 to 11.7 0.0 to 32.4 0.0 to 46.8
(v)
n
42 42 19 19
that the bulk of the adhesive frequently remained on the foil-mesh pad after bracket removal, some adhesive remained on all teeth. The relatively soft polymethylmethacrylate resin was removed in all cases with a hand scaler and prophylaxis, whereas the filled composite resin required the use in every case of a tungsten carbide finishing bur to achieve a clinically clean appearance. The numerical results have been tabulated and are presented in Tables I and II. Because of the skewness of distribution of some of the results, median values and 80 percent ranges of values have been determined, instead of the more conventional mean values and standard deviation. For the same reason, a nonparametric analysis (Wilcoxon matched-pairs, signed-ranks test)23 was used. The Wilcoxon test showed that enamel loss at occlusal and gingival sites in both parts of the study was not significantly different. Therefore, the results from these sites have been pooled in Table I, which shows that enamel loss was greater during removal of the filled adhesive than with the unfilled adhesive. The total enamel loss was also somewhat greater in the extracted teeth treated in vitro than in those treated intraorally. For that reason, the results were not combined. The results of the second part of the study are shown in Table II, which shows once again that the teeth bonded with a filled adhesive lost more enamel than the teeth with an unfilled adhesive. It also shows that polishing with zirconium silicate on a rotating brush can remove a relatively large amount of enamel. The wide ranges indicated in Tables I and II indicate that a great variation exists between individuals, and even between teeth in the same individual. Discussion The study by Fitzpatrick and Way” showed enamel loss during etching, bonding, and debonding of an ultraviolet light-polymerized adhesive to be 55.6 pm, with a relatively narrow range of values. The present study, although demonstrating much more variation in different teeth, showed very similar results. The mean loss from teeth bonded with a
Enamel
loss
during
orrhodonfic
bonding
669
highly filled composite resin was 42.7 pm in Group 1 and 54.5 pm in Group 2. The proximity of the results would seem to indicate that the findings of Fitzpatrick and Way can be confirmed. Zachrisson,26 however, making reference to his own studies and to the reports of Mannerberg,‘” suggests that total loss in bonding and debonding procedures is less than 5 pm. He measured the height of perikymata at 5 pm and, by demonstrating their presence on scanning electron micrographs after debonding, has concluded that virtually no enamel had been lost. The difference could be at least partially accounted for as a result of the entirely different measuring technique employed. Another experimental difference between the two studies was that Zachrisson used a low-speed, six-fluted tungsten carbide bur for clean-up, whereas Fitzpatrick and Way used a high-speed, twelve-fluted tungsten carbide finishing bur. Gwinnett and Gorelick” have estimated the scratch hardness of intact enamel at 5 on the Mohs scale. Tungsten carbide (rated at S), steel (ranging from 7 to 9), and zirconium silicate (rated at 7) are therefore all capable of scratching or abrading intact enamel. Abandoning these materials, they tried new approaches to resin removal. By trial-anderror testing, they searched for a rubber wheel which “would abrade the resin, unfilled or highly filled composite, without abrading the enamel. None such was found.” If their exhaustive study found no instrument which could remove resin without removing enamel, we can assume that some enamel will be lost in any clean-up technique. One other variable is the subjective determination by the operator of the point at which the surface of the tooth is clinically clean. In this study, the teeth were dried and examined with a magnifying glass and with a dental explorer during the clean-up procedure, and polishing was continued until the tooth looked and felt smooth, shiny, and clean. The teeth treated in vitro lost more enamel than those which were treated completely intraorally. The difference may be the result of better drying and illumination and easier examination, leading to a more thorough (and more destructive) clean-up of the debonded teeth. If the acid-etch procedure has produced microporosities 20 to 50 mm. in depth,“, ** I8 and if the resins have filled the porosities completely,” then some resin tags are undoubtedly left on any teeth which lost less than 20 pm during clean-up. This assumption is in agreement with recent energy-dispersive x-ray analysis studies. Caspersen3 found that on debonded teeth which appeared clean to the naked eye, the SEM could disclose the presence of acrylic islands, flakes, or diffuse membranes. He believes that the close adaptation of acrylic to the rough surface of the etched enamel is unlikely to permit discoloration and leakage. In the second part of this study, approximately half of the sites measured showed a loss of less than 20 pm during clean-up and must, therefore, still contain some adhesive tags. In addition, four sites bonded with the unfilled resin and two bonded with the filled resin showed a net gain. The presence of this layer of adhesive is of iittle consequence for two reasons. Studies of restorative procedures using acid etch and various resins have indicated that an unfilled acrylic resin is very resistant to discoloration in a clean oral environment. 7, ‘I* 25 Also, the low abrasion resistance of an unfilled acrylic should permit the rapid elimination of the remaining layer of resin by normal toothbrushing.7 Since the thickness of the enamel in the areas measured in this study is approximately 1,500 to 2,000 pm,‘” the mean loss of 27.5 pm when an unfilled resin is used or 48.0 pm when a filled adhesive is used seems at first to be clinically insignificant. However, it is
Am. J. Orthod. December I978
not definitely known if removal of the fluoride-rich surface layer may have a deleterious effect on the future health of the tooth. Numerous studies” g, “L rR,‘l of the thickness of the fluoride layer have produced different results, but all studies agree that the gradient from the surface inward is very steep, with the highest fluoride concentration at the surface, and a rapid decline in concentration in the first 20 Frn of enamel. It would therefore seem undesirable to remove that much enamel in any procedure. There is some disagreement about the rate at which the protective layer will be restored.‘, I6 Since the results of the second part of this study showed that prophylaxis of an intact tooth with zirconium silicate on a rotating brush can remove 10.0 to 43.8 pm of enamel in only 15 seconds, and other studies have shown that pumice in a rubber cup removes only 3 to 4 ,um in 30 seconds, *Oit would appear that the latter procedure is to be preferred to the former. Conclusions
1. The techniques required in the removal of highly filled composite adhesives at the end of orthodontic treatment on an average cause more loss of enamel than removal of an unfilled polymethylmethacrylate adhesive. 2. The amount of enamel lost during the removal of either adhesive may be of clinical significance because of the removal of a major part of the protective fluoride-rich layer of enamel. 3. The use of zirconium silicate on a rotating bristle brush may cause considerable abrasion of enamel. The authors wish to express sincere appreciation for the assistancereceived from K. A. Galil, W. S. Hunter, the study and
L. N. Johnson, in the preparation
R. E. Jordan, of the article
and J. M. Wanklin. Their is gratefully acknowledged.
counsel
and advice
during
REFERENCES I. Brudevold, F.: Interaction of fluoride with human enamel, Symposium on Chemistry and Physiology of Enamel, Ann Arbor, 197 1, University of Michigan, pp. 73-90. 2. Buonocore, M. G.: A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces, J. Dent. Res. 34: 849-853, 1955. 3. Caspersen, I.: Residual acrylic adhesive after removal of plastic orthodontic brackets: A scanning electron microscope study. AM. J. ORTHOD. 71: 637-650, 1977. 4. Dogon, I. L.: Studies demonstrating the need for an intermediary resin of low viscosity for the acid etch technique. In Silverstone, L. M., and Dogon, I. L. (editors): Proceedings of an International Symposium on Acid Etch Technique, St. Paul. 1975, North Central Publishing Company, pp. 100-l 18. 5. Fitzpatrick, D. A., and Way, D. C.: The effects of wear, acid etching, and bond removal on human enamel, AM.
J. ORTHOD.
6. Gwinnett, AM.
72:
671-681,
A. J.. and Gorelick,
J. ORTHOD.
71: 651-655,
1977.
L.: Microscopic
evaluation
of enamel
after debonding
clinical
application,
1977.
7. Jordan, R. E., Suzuki, M., Gwinnett, A. J., and Hunter, J. K.: Restoration of fractured and hypoplastic incisors by the acid-etch technique: A three-year report, J. Am. Dent. Assoc. 95: 795-803, 1977. 8. Jorgensen, K. D.: The adaptation of composite and non-composite resins to acid etched enamel surfaces. In Silverstone, L. M., and Dogon, I. L., (editors): Proceedings of an International Symposium on Acid Etch Technique, St. Paul, 1975, North Central Publishing Company, pp. 93-99. 9. Koch, G., and Friberger, P.: Fluoride content of outermost enamel layers in teeth exposed to topical fluoride application, Odontol. Revy 22: 351-362, 1971. 10. Koch, G., and Petersson, L. G.: Fluoride content of enamel surface treated with a varnish containing sodium fluoride, Odontol. Revy 23: 437-446, 1972.
VoIume 74 Number 6
Il. 12. 13. 14. 15. 16. 17. 18.
19. 20. 21.
22. 23. 24.
25. 26.
Ennmel
loss
during
orthodontic
bonding
671
Leinfelder, K. F., Sluder, T. B., Sockwell, C. L., Strickland, W. D., and Wall, J. T.: Clinical evaluation of composite resins as anterior and posterior restorative materials, J. Prosthet. Dent. 33: 407-416, 1975. Mannerberg, F.: Appearance of tooth surface, Odontol. Revy 11: Supp. 6, 1960. Mellberg, J. R., Nicholson, C. R., and Law, F. E.: Fluoride concentrations in deciduous tooth enamel of children chewing sodium fluoride tablets, J. Dent. Res. 15: 551-554, 1972. Newman, G. V., and Facq. J. M.: The effect.. of adhesive systems on tooth surfaces, AM. J. ORTHOD. 5% 67-75, 197 1. Sicher, H., and Bhaskar. S. N. (editors): Orban’s oral histology and embryology, ed. 7. St. Louis, 1972, The C. V. Mosby Company. Petersson, L. G.: fluorine gradients in outermost surface enamel after various forms of topical application of fluorides in viva, Odontol. Revy 27: 25.50, 1976. Retief, D. H., and Sadowsky, P. L.: Clinical experience with the acid-etch technique in orthodontics, AM. J. ORTHOD. 68: 645-654, 1975. Silverstone. L. M.: The acid etch technique: In vitro studies with special reference to the enamel surface and the enamel-resin interface. In Silverstone, L. M., and Dogon, 1. L. (editors): Proceedings of an Intemational Symposium on Acid Etch Technique, St. Paul, 1975, NorthCentral Publishing Company, pp. 13-39. Silverstone, L. M.: Fissure sealants: Laboratory studies, Caries Res. 8: 2-26, 1974. Vrbic, V., Brudevold, F., and McCann, H. G.: Acquisition of fluoride by enamel from fluoride pumice pastes, Helv. Odontol. Acta 11: 21-33, 1967. Weatherell, J. A., Robinson, C., and Hallsworth, A. S.: Microanalytical studies on single sections of enamel. In Fearnhead, R. W., and Stack, M. V. (editors): Tooth Enamel, II, Bristol, 1971, John Wright & Sons, Ltd. Wickwire, N. A., and Rentz, D.: Enamel pretreatment: A critical variable in direct bonding systems, AM. J. ORTHOD. 64: 499-512, 1973. Wilcoxon, F.: Individual comparisons by ranking methods, Biometrics Bull. 1: 80-83, 194.5. Yankelson, M.: The acid etch technique in orthodontics: The problem. In Silverstone, L. M., and Dogon, I. L. (editors) Proceedings of an International Symposium on Acid Etch Technique, St. Paul, 1975, North Central Publishing Company, pp. 255-264. Zachrisson, B. U.: A posttreatment evaluation of direct bonding in orthodontics, AM. .I. ORTHOD. 71: 173-189, 1977. Zachrisson, B. U.: Unpublished research, presented in a paper at Anaheim on April 15, 1978, prior to the A.A.O. convention.
Ontario,
Canada
S
ince Buonocore2 first reported, in 19.55, on the possibility of bonding acrylic resins to etched enamel surfaces, many different materials and techniques have been developed. 7, 8, ‘I* l8 During the last decade, these materials and procedures have gained widespread use for bonding orthodontic attachments directly to tooth surfaces.14* “3 25, 26 A number of different techniques have been suggested for removal of attachments and adhesive when orthodontic treatment is completed.6 Although several studies 3S‘* ” have demonstrated which debonding procedures cause the least scratching or faceting of the enamel, only two researchers5, 26 appear to have attempted to measure the actual amount of enamel loss that debonding produces. These two studies, which employed different debonding and measuring techniques, showed markedly different results, one concluding that 55.6 Frn is lost and the other that less than 5 pm is lost. This study, therefore, has two purposes: ( 1) to measure and compare in vivo the total enamel loss during bonding and debonding techniques with two popular adhesives (one a highly filled composite of quartz in a diacrylate resin* and the other an unfilled polymethylmethacrylatet) and (2) to measure in vitro the amount of enamel lost during each step of the procedure, namely, polishing, etching, and final debonding and clean-up. Materials and methods In order to make the precise measurements required in this study, a metal gauge (Fig. 1) was developed that could register the depth from the surface of the tooth to a recessed steel marker and which could be accurately measured in the optical system of a micrometer-stage microscope (Fig. 2). The first part of the study involved twenty-six first premolars from a group of eight orthodontic patients; the second part was conducted on twenty first premolars from another group of eight patients. All teeth in both groups were scheduled for extraction as part of the orthodontic treatment; none were carious or restored. The age of the patients in Group 1 ranged from 11 to 19; in Group 2 the range was from I 1 to 2.5. From the This study *Concise, +Directon
Division of Orthodontics, Faculty of Dentistry. The University was supported in part by an MRC General Support Grant. Minnesota Mining and Manufacturing Co., St. Paul, Minn. II, TP Laboratories, LaPorte, lnd.
900?-9416/?81120663+09$00.90/0
@
1978 The C. V. Mosby
Co
of Western
Ontario.
663
Am. J. Orthod. December I918
Fig. 1, The
Fig.
metal
gauge
2. Miniload
which
hardness
was used
tester
for all measurements
(Leitz),
with
micrometer
made
stage
in this study.
and graticle
(Magnification,
x 8.)
eyepiece
The twenty-six premolars in the first group were prepared by drilling two holes completely through the enamel with a No. 699M high-speed bur. The holes were positioned on the buccal developmental ridge, one above the other, 3 to 4 mm. apart. Tightly fitting stainless steel marker pins were then cemented into the holes with zinc phosphate cement. The face of each pin was recessed approximately 200 ,um below the enamel
Volume 74 Number 6
Enamel loss during orthodontic
Fig.
3. Initial
position
of the gauge
against
an embedded
Fig. 4. The final position of the gauge, with the steel pin (P) resting the face of the gauge resting on the surface of the enamel (Ej.
steel
bonding
665
marker.
on the embedded
marker(M)
and
surface with a No. 2 round bur. This step served two purposes; (1) it produced a smooth, concave steel reference point, in which the measuring gauge would be self-centering, and (2) it also removed any weakened enamel prisms around the pin hole, ensuring that the face of the gauge would rest on stable enamel during measurement. Immediately following pin placement. recessing, and removal of excess cement, the metal gauge and microscope were used to record and measure initial pin depth. The gauge was positioned as in Fig. 3 and then moved against the tooth until the metal face made maximum contact on the enamel (Fig. 4). Five measurements were made at each site
Am. J. Orthod. December 1978
Fig. 5. A diagrammatic (Magnification, x40.)
representation
of the appearance
of the gauge
and
graticle
in the microscope.
intraorally, and an average was taken. The standard error of the mean was calculated for each group of five measurements to serve as an error study. Each tooth was then polished with zirconium silicate* and water on a rotating bristle brush? for 10 to 15 seconds, after which the teeth were washed, isolated, and dried with an air syringe. Each tooth was then individually etched for 90 seconds with 37 percent orthophosphoric acid, washed, dried, and reisolated without contacting the etched surface with cotton rolls or lips. An orthodontic bracket on a foil-mesh pad was bonded immediately to each tooth, covering both steel markers. On each pair of premolars for each patient, the unfilled adhesive was used randomly on one side or the other, preceded by a vinyl silane primer-.$ The contralateral tooth was etched, dried, and bonded with the filled adhesive, preceded by an unfilled enamel sealant.§ Both adhesive systems were used in accordance with the manufacturers’ directions. After a period of 4 to 7 days, the brackets were carefully removed with bracketremoving pliers.” The pliers were not used to scrape the surface. As much of the remaining adhesive as possible was removed with a hand scaler. Any adhesive tags that could not be removed by hand were slowly abraded with a No. 7902 finishing bur until the surface of the tooth appeared clinically clean and shiny. Each tooth was then polished with zirconium silicate on a brush. Any adhesive still remaining in the pin holes was removed with a scaler. Five measurements of the final depth of each marker were taken again and averaged. The total enamel loss at each site was then calculated by subtraction of this value from the original depth. Statistical analysis was done to determine the presence of *Zircate, L. D. Caulk Co., Milford, Del. *Crescent Dental Mfg. Co., Chicago, Ill. *Directon 11 Primer. 5Enamel Bond, Minnesota Mining and Manufacturing “ETM. No. 349, Monrovia, Calif.
Co.,
St. Paul,
Minn.
Volume 74 Number 6
Fig.
6. The
Enamel loss during orthodontic
appearance
of the tooth
after
debonding,
showing
the position
bonding
of the steel
667
markers.
any significant difference in enamel loss between the occlusal and gingival sites and between the teeth bonded with the filled resin compared to those bonded with the unfilled resin. The second part of the study was conducted in vitro to permit measurement of enamel loss during each step of the procedure with no risk of contamination of etched surfaces.24 The second group of eight patients provided twenty freshly extracted premolars. After extraction, but on the same day, markers were placed as before, and initial measurements were made. The teeth were polished, etched, and bonded by the same technique as for Group 1. Further measurements were taken immediately following polishing and again after etching. Brackets were bonded as before, with one tooth in each pair receiving the unfilled resin and the other receiving the filled adhesive. The teeth were stored in tap water for 3 to 5 days to permit complete polymerization. The brackets were removed; adhesive islands were removed with a hand scaler when possible and with a finishing bur when necessary. After polishing, final measurements were taken at each site. The amount of enamel loss due to polishing, etching, manual clean-up, and rotary clean-up was then calculated by subtracting each measurement from the previous measurement at the same site. Observed differences in enamel loss during the removal of the two adhesives were tested for significance. Results The accuracy of the measurement technique was determined by calculating the standard error of the mean for the five measurements taken at each site after each step was completed. In the first group, where all measurements were intraoral, the average of the standard errors was 3.07 pm. All measurements of the second group were done extraorally, with an average standard error of 2.44 pm. No brackets were lost during either part of the study. Although it appeared clinically
Am. J. Orrhod. December 1918
Table I. Total enamel loss in both groups Vnjlled
Group I (n = 23) Median loss 80 percent range Group2 (n = 19) Median loss 80 percent range
adhesive
(pm)
Filled
adhesive
(pm)
17.5 0.0 to 33.8
40.8 16.0 to 64.5
44.0 21.2 to 56.0
60.5 25.0 to 76.8
Table II. Enamel loss resulting from each procedure Loss due to
Polishing only Etching only Debonding of unfilled adhesive Debonding of filled adhesive
Median
(pm)
26.0 3.0 5.2 25.0
80 percent
range
10.0 to 43.8 0.2 to 11.7 0.0 to 32.4 0.0 to 46.8
(v)
n
42 42 19 19
that the bulk of the adhesive frequently remained on the foil-mesh pad after bracket removal, some adhesive remained on all teeth. The relatively soft polymethylmethacrylate resin was removed in all cases with a hand scaler and prophylaxis, whereas the filled composite resin required the use in every case of a tungsten carbide finishing bur to achieve a clinically clean appearance. The numerical results have been tabulated and are presented in Tables I and II. Because of the skewness of distribution of some of the results, median values and 80 percent ranges of values have been determined, instead of the more conventional mean values and standard deviation. For the same reason, a nonparametric analysis (Wilcoxon matched-pairs, signed-ranks test)23 was used. The Wilcoxon test showed that enamel loss at occlusal and gingival sites in both parts of the study was not significantly different. Therefore, the results from these sites have been pooled in Table I, which shows that enamel loss was greater during removal of the filled adhesive than with the unfilled adhesive. The total enamel loss was also somewhat greater in the extracted teeth treated in vitro than in those treated intraorally. For that reason, the results were not combined. The results of the second part of the study are shown in Table II, which shows once again that the teeth bonded with a filled adhesive lost more enamel than the teeth with an unfilled adhesive. It also shows that polishing with zirconium silicate on a rotating brush can remove a relatively large amount of enamel. The wide ranges indicated in Tables I and II indicate that a great variation exists between individuals, and even between teeth in the same individual. Discussion The study by Fitzpatrick and Way” showed enamel loss during etching, bonding, and debonding of an ultraviolet light-polymerized adhesive to be 55.6 pm, with a relatively narrow range of values. The present study, although demonstrating much more variation in different teeth, showed very similar results. The mean loss from teeth bonded with a
Enamel
loss
during
orrhodonfic
bonding
669
highly filled composite resin was 42.7 pm in Group 1 and 54.5 pm in Group 2. The proximity of the results would seem to indicate that the findings of Fitzpatrick and Way can be confirmed. Zachrisson,26 however, making reference to his own studies and to the reports of Mannerberg,‘” suggests that total loss in bonding and debonding procedures is less than 5 pm. He measured the height of perikymata at 5 pm and, by demonstrating their presence on scanning electron micrographs after debonding, has concluded that virtually no enamel had been lost. The difference could be at least partially accounted for as a result of the entirely different measuring technique employed. Another experimental difference between the two studies was that Zachrisson used a low-speed, six-fluted tungsten carbide bur for clean-up, whereas Fitzpatrick and Way used a high-speed, twelve-fluted tungsten carbide finishing bur. Gwinnett and Gorelick” have estimated the scratch hardness of intact enamel at 5 on the Mohs scale. Tungsten carbide (rated at S), steel (ranging from 7 to 9), and zirconium silicate (rated at 7) are therefore all capable of scratching or abrading intact enamel. Abandoning these materials, they tried new approaches to resin removal. By trial-anderror testing, they searched for a rubber wheel which “would abrade the resin, unfilled or highly filled composite, without abrading the enamel. None such was found.” If their exhaustive study found no instrument which could remove resin without removing enamel, we can assume that some enamel will be lost in any clean-up technique. One other variable is the subjective determination by the operator of the point at which the surface of the tooth is clinically clean. In this study, the teeth were dried and examined with a magnifying glass and with a dental explorer during the clean-up procedure, and polishing was continued until the tooth looked and felt smooth, shiny, and clean. The teeth treated in vitro lost more enamel than those which were treated completely intraorally. The difference may be the result of better drying and illumination and easier examination, leading to a more thorough (and more destructive) clean-up of the debonded teeth. If the acid-etch procedure has produced microporosities 20 to 50 mm. in depth,“, ** I8 and if the resins have filled the porosities completely,” then some resin tags are undoubtedly left on any teeth which lost less than 20 pm during clean-up. This assumption is in agreement with recent energy-dispersive x-ray analysis studies. Caspersen3 found that on debonded teeth which appeared clean to the naked eye, the SEM could disclose the presence of acrylic islands, flakes, or diffuse membranes. He believes that the close adaptation of acrylic to the rough surface of the etched enamel is unlikely to permit discoloration and leakage. In the second part of this study, approximately half of the sites measured showed a loss of less than 20 pm during clean-up and must, therefore, still contain some adhesive tags. In addition, four sites bonded with the unfilled resin and two bonded with the filled resin showed a net gain. The presence of this layer of adhesive is of iittle consequence for two reasons. Studies of restorative procedures using acid etch and various resins have indicated that an unfilled acrylic resin is very resistant to discoloration in a clean oral environment. 7, ‘I* 25 Also, the low abrasion resistance of an unfilled acrylic should permit the rapid elimination of the remaining layer of resin by normal toothbrushing.7 Since the thickness of the enamel in the areas measured in this study is approximately 1,500 to 2,000 pm,‘” the mean loss of 27.5 pm when an unfilled resin is used or 48.0 pm when a filled adhesive is used seems at first to be clinically insignificant. However, it is
Am. J. Orthod. December I978
not definitely known if removal of the fluoride-rich surface layer may have a deleterious effect on the future health of the tooth. Numerous studies” g, “L rR,‘l of the thickness of the fluoride layer have produced different results, but all studies agree that the gradient from the surface inward is very steep, with the highest fluoride concentration at the surface, and a rapid decline in concentration in the first 20 Frn of enamel. It would therefore seem undesirable to remove that much enamel in any procedure. There is some disagreement about the rate at which the protective layer will be restored.‘, I6 Since the results of the second part of this study showed that prophylaxis of an intact tooth with zirconium silicate on a rotating brush can remove 10.0 to 43.8 pm of enamel in only 15 seconds, and other studies have shown that pumice in a rubber cup removes only 3 to 4 ,um in 30 seconds, *Oit would appear that the latter procedure is to be preferred to the former. Conclusions
1. The techniques required in the removal of highly filled composite adhesives at the end of orthodontic treatment on an average cause more loss of enamel than removal of an unfilled polymethylmethacrylate adhesive. 2. The amount of enamel lost during the removal of either adhesive may be of clinical significance because of the removal of a major part of the protective fluoride-rich layer of enamel. 3. The use of zirconium silicate on a rotating bristle brush may cause considerable abrasion of enamel. The authors wish to express sincere appreciation for the assistancereceived from K. A. Galil, W. S. Hunter, the study and
L. N. Johnson, in the preparation
R. E. Jordan, of the article
and J. M. Wanklin. Their is gratefully acknowledged.
counsel
and advice
during
REFERENCES I. Brudevold, F.: Interaction of fluoride with human enamel, Symposium on Chemistry and Physiology of Enamel, Ann Arbor, 197 1, University of Michigan, pp. 73-90. 2. Buonocore, M. G.: A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces, J. Dent. Res. 34: 849-853, 1955. 3. Caspersen, I.: Residual acrylic adhesive after removal of plastic orthodontic brackets: A scanning electron microscope study. AM. J. ORTHOD. 71: 637-650, 1977. 4. Dogon, I. L.: Studies demonstrating the need for an intermediary resin of low viscosity for the acid etch technique. In Silverstone, L. M., and Dogon, I. L. (editors): Proceedings of an International Symposium on Acid Etch Technique, St. Paul. 1975, North Central Publishing Company, pp. 100-l 18. 5. Fitzpatrick, D. A., and Way, D. C.: The effects of wear, acid etching, and bond removal on human enamel, AM.
J. ORTHOD.
6. Gwinnett, AM.
72:
671-681,
A. J.. and Gorelick,
J. ORTHOD.
71: 651-655,
1977.
L.: Microscopic
evaluation
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clinical
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7. Jordan, R. E., Suzuki, M., Gwinnett, A. J., and Hunter, J. K.: Restoration of fractured and hypoplastic incisors by the acid-etch technique: A three-year report, J. Am. Dent. Assoc. 95: 795-803, 1977. 8. Jorgensen, K. D.: The adaptation of composite and non-composite resins to acid etched enamel surfaces. In Silverstone, L. M., and Dogon, I. L., (editors): Proceedings of an International Symposium on Acid Etch Technique, St. Paul, 1975, North Central Publishing Company, pp. 93-99. 9. Koch, G., and Friberger, P.: Fluoride content of outermost enamel layers in teeth exposed to topical fluoride application, Odontol. Revy 22: 351-362, 1971. 10. Koch, G., and Petersson, L. G.: Fluoride content of enamel surface treated with a varnish containing sodium fluoride, Odontol. Revy 23: 437-446, 1972.
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Il. 12. 13. 14. 15. 16. 17. 18.
19. 20. 21.
22. 23. 24.
25. 26.
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Leinfelder, K. F., Sluder, T. B., Sockwell, C. L., Strickland, W. D., and Wall, J. T.: Clinical evaluation of composite resins as anterior and posterior restorative materials, J. Prosthet. Dent. 33: 407-416, 1975. Mannerberg, F.: Appearance of tooth surface, Odontol. Revy 11: Supp. 6, 1960. Mellberg, J. R., Nicholson, C. R., and Law, F. E.: Fluoride concentrations in deciduous tooth enamel of children chewing sodium fluoride tablets, J. Dent. Res. 15: 551-554, 1972. Newman, G. V., and Facq. J. M.: The effect.. of adhesive systems on tooth surfaces, AM. J. ORTHOD. 5% 67-75, 197 1. Sicher, H., and Bhaskar. S. N. (editors): Orban’s oral histology and embryology, ed. 7. St. Louis, 1972, The C. V. Mosby Company. Petersson, L. G.: fluorine gradients in outermost surface enamel after various forms of topical application of fluorides in viva, Odontol. Revy 27: 25.50, 1976. Retief, D. H., and Sadowsky, P. L.: Clinical experience with the acid-etch technique in orthodontics, AM. J. ORTHOD. 68: 645-654, 1975. Silverstone. L. M.: The acid etch technique: In vitro studies with special reference to the enamel surface and the enamel-resin interface. In Silverstone, L. M., and Dogon, 1. L. (editors): Proceedings of an Intemational Symposium on Acid Etch Technique, St. Paul, 1975, NorthCentral Publishing Company, pp. 13-39. Silverstone, L. M.: Fissure sealants: Laboratory studies, Caries Res. 8: 2-26, 1974. Vrbic, V., Brudevold, F., and McCann, H. G.: Acquisition of fluoride by enamel from fluoride pumice pastes, Helv. Odontol. Acta 11: 21-33, 1967. Weatherell, J. A., Robinson, C., and Hallsworth, A. S.: Microanalytical studies on single sections of enamel. In Fearnhead, R. W., and Stack, M. V. (editors): Tooth Enamel, II, Bristol, 1971, John Wright & Sons, Ltd. Wickwire, N. A., and Rentz, D.: Enamel pretreatment: A critical variable in direct bonding systems, AM. J. ORTHOD. 64: 499-512, 1973. Wilcoxon, F.: Individual comparisons by ranking methods, Biometrics Bull. 1: 80-83, 194.5. Yankelson, M.: The acid etch technique in orthodontics: The problem. In Silverstone, L. M., and Dogon, I. L. (editors) Proceedings of an International Symposium on Acid Etch Technique, St. Paul, 1975, North Central Publishing Company, pp. 255-264. Zachrisson, B. U.: A posttreatment evaluation of direct bonding in orthodontics, AM. .I. ORTHOD. 71: 173-189, 1977. Zachrisson, B. U.: Unpublished research, presented in a paper at Anaheim on April 15, 1978, prior to the A.A.O. convention.
