In vivo Effect of Oral Environment on Etched Enamel: A Scanning Electron Microscopic Study R. GARBEROGLIO and G. COZZANI University Dental School, Milan, Italy
After etching the enamel in teeth ofyoung children with 50% buffered phosphoric acid and allowing the teeth to remain in the oral environment for a few months, an irregular enamel surface similar to the morphology of recently etched enamel was noted by means of scanning electron microscopy. In addition, the enamel surfaces were covered with plaque. Accordingly, observations by other authors, that etched human enamel takes on a normal appearance after short exposure in the oral cavity, could not be confirmed. However, when the surface of the etched enamel was pumiced, the enamel reacquired both the shine and appearance of non-etched enamel.
J Dent Res 58(9):1859-1865, September 1979
Introduction. The technique of etching enamel with concentrated acids in order to bond composite restorative materials to teeth is a common procedure at the present time. The etching of the enamel by the acid creates a multitude of microscopic "irregularities" in the enamel rods. These irregularities are approximately 25 microns in depth and result from a selective dissolution of enamel rods. An appropriate composite resinl2 flows into these irregularities and polymerizes to form a tenacious mechanical bond.3 This technique has been used for sealing pits and fissures,4 5 for repairing fractured incisal edges,6 for improving marginal adaptation of restorations,7 and for bonding orthodontic brackets to enamel.8 Although clinical advantages of enamel etching resinous bonding procedures are apparent, a number of questions arise. One deals with the fate of enamel surfaces exposed to the oral cavity in procedures involving placement of pit and fissure sealants and composite restorations. In addition, the removal of the resin bonded orthodontic brackets also exposes etched enamel to the oral environment. Received for publication April 22, 1977 Accepted for publication October 30, 1978 For reprints: Corso Alfieri 336, Asti, Italy.
Some investigators refer to the ability of saliva to chemically remineralize demineralized enamel.9,11,12,13 Yet, only a few studies have described the microscopic morphology of the recovery of etched enamel in the presence of saliva.9'14,15,18 One possible reason is that most investigations were conducted before the advent of scanning electron microscopy (SEM). Accordingly, the purpose of this study is to investigate, by means of a scanning electron microscope, the effect of the oral environment on the morphology of etched enamel surfaces. Some teeth were treated with etching solution and extracted immediately after acid etching. These were compared with teeth that had been etched and left in place for a suitable period of time and those that had brackets bonded and later removed.
Materials and methods. Twenty-six upper premolar teeth, from thirteen children (age range 8-14 years) undergoing orthodontic treatment, were included in the study. The grouping of the patients was as follows: Group L - In two patients, the buccal surface of one premolar (upper) was etched with 50% phosphoric acid for 2 minutes. The contralateral premolar was left untreated as control. A total of four teeth were used, and all teeth were extracted immediately after acid etching. Group I. - In three patients, one premolar was treated as previously described while the contralateral premolar was left untreated as control. A total of six teeth were used and extracted 90 days after acid etching. Following extraction, the three etched teeth were longitudinally sectioned in a labio-lingual direction. In this manner, the etched portion of the enamel was divided into two equal halves. One half was placed 1859
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1860
J Detz t Res
GARBEROGLIO & CO/ZA NI
in 5% sodium hypochlorite for one hour in order to remove all organic materials. The other portion of the tooth was left with the organic materials on its surface. Group III. - In five patients, one premolar was subjected to the previously described acid etching procedure on the buccal surface with the contralateral premolar serving as a control. Following etching, orthodontic plastic brackets were attached to the buccal surfaces with UV activated resin bonding. After a period of one week, orthodontic pliers were used for the removal of the plastic brackets. Immediately after, these teeth were pumiced with a rotary prophylactic brush at low speed using fine grade pumice. All of the teeth remained in the mouth for a period of 90 days. They were then extracted. A total of 10 teeth were used as specimens. Group IV. - Three patients were used. The same acid etching, bracket placement and removal procedure as described for Group III was performed on one premolar of each patient. The contralateral premolar served as a control. Following bracket removal, the teeth were not pumiced. A total of six teeth were used. All extracted teeth were immediately stored in buffered neutral formalin. They were exposed to vacuum and plated with 250 A layer of palladium gold. They were then examined by a scanning electron microscope (Stereoscan Cambridge Mark 2A) with an accelerating voltage of 20-30 KV.
Sep tem ber 1 9 79
4~~~~~~~~~~~~
F ig.
1
Scanning electron micrograph of
enamel surface after etching with 50C buffered
phosphoric acid. The entire surface has a pitted appearance (x 2.800).
trol teeth, the surface, at the same magnification (Fig. 4), is very smooth and shows depressions due to remnants of plaque. However, the depressions were much less than in the experimental teeth. Observation of the etched enamel treated with 5% sodium hypochlorite also showed a high degree of irregularity (Figs. 5, 6) but the surface projections were quite different from those observed in Fig. 4. These projections appear to
Results. Group 1. Enamel etched on teeth immediately extracted. - In the two teeth which were etched, there were the characteristic patterns of the demineralized enamel. In Fig. 1 the periphery of prisms has been etched to a greater extent than the central core of the prisms. On the control side (Fig. 2) the usual smooth featureless appearance of the intact enamel is seen. Group 2. Enamel etched, the teeth left in mouth 90 days.- Scanning examination of the enamel not treated with 57 sodium hypochlorite showed surface irregularities with large peaks and depressions (Fig. 3). These projections appeared to be rounded with weblike connections between the rounded elevations and with the appearance of plaque material. On the contralateral con-
Ad
Fig. 2
V.:
,4,
s:,:SUbS
Surface of an unetched control tooth
(x 1.350).
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Vol. S8 No. 9
USE OFACIDS TO ETCH TOOTH ENAMEL
Fig. 3 Surface of an unetched tooth left in the mouth for 90 days. Bacterial plaque covers the enamel (x 5.700).
Fig.
5
1861
Half of the same tooth of Fig. 3. The
tooth was placed in sodium hypochlorite which destroyed the plaque. The enamel appears irregular and has the characteristics of newly etched enamel
(x 5.800).
be sharp ridges consistent with the etched enamel seen immediately after acid etching. Group 3. Enamel etched, resin bonded brackets placed, then removed, surface pumiced, teeth leJt in mouth 90 days. There were two significant observations in these cases. The first was that the remnants
FIig. 4
-
Tooth: control (x 6.250).
of the resin sometimes remained on the enamel surface. This can be observed in the darker shade of the resin surface seen with
Fig. 6 (x 5.500).
Another
zone
of the
same
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tooth
1862
J Dciit Res Septemher 19 79 GARBEROGLIO & COZ/A NID
Fig. 7
Tooth surface wlhich was pumiced after remnoving an orthodontic bracket which was bonded by resin. Part of the resin (R) remained attached to the enamel and, on the surface, striations were produced by pumice abrasion (x 1 30). -
its diagonal striation shown to the right of
Fig. 7.
Fig. - Higher magnification of a part of the surface of the enamel shown in Fig. 7. The configuration is similar to that observed in Fig. 1. This may represent the deeper part of the etched enamel, while the superficial parts were removed by pumicing (x 2.700).
Fig. 9 - Tooth surface from which a bracket was removed and the tooth renained in the mouth 90 days. After bracket removal the toothl was not pumiced. Residual fragments of resin are apparent (R) which circle a zone of enamel (E) (x 50).
In higher magnification, the second salient observation, seen in Fig. 8, was that of a shallow irregular etching pattern. The enamel surface shown here demonstrates only slight irregularities at high magnification (x 2700).
Fig. 10 The central zone in Fig. 9. The enamel surface is highly irregular (x 260).
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1 863
USE OFA CIDS TO ETCH TOOTH ENAM1EL
Group 4. Enamel etched, resin bonding brackets placed and removed, teeth lef t in the mouth 90 days (no pumicing). - The remnants of the resin are clearly defined as dark shading on the right and left side of Fig. 9 (x 50). The enamel surface shown in Fig. 9 can be seen at higher magnification in Figs. 10, 11, 12. The enamel surface is clearly characterized by deep irregularities covered in many parts by plaque material. It should be noted in Fig. 9 (arrow below) that the enamel presents another type of surface configuration. This portion of the enamel has an irregularly grainy appearance clearly seen at higher magnification (Figs. 13, 14). In Fig. 14, this granular appearance simulates the prismatic structure of the enamel rods. The removal of the plastic brackets in this specinen appears to have fractured off the outer layer of enamel revealing the deeper prismatic enamel structure (Fig. 14).
Fig. 12 -Higher magnification of the material which covers the enamel in F ig. 1 1. It has the characteristics of bacterial plaque, with filamentous organisms and cocci (C) (x 6.000). _ a
Discussion. Previous studies reported that etched enamel which is exposed to the oral environment "remineralizes" in a short
time.3,5,10,14,15 The term remineralization was used mainly to indicate that an etched enamel surface had returned to its normal appearance. In this context, some investigators only examined the teeth visually.3,5'10
Fig. 11 At higher magnification, the irregular enamel surface appears partially covered with material (P) (x 2.700).
Fig. 13 Zone of enamel surface where a layer of enamel was fractured during the bracket removal procedure (x 270).
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1864
Fig.
GARBEROGLIO & COZZANI
14
Higher magnification
of
J Den t R es
fractured
enamel (x 2.800).
The mechanism whereby the etched enamel reassumes its intact appearance has never been clearly defined. Several hypotheses have been suggested, including that of the deposition of salivary mucoid material, the abrasion or erosion of the remaining fingerlike projections of the etched crevice, and the precipitation of inorganic constituents found in the saliva. Only the precipitation of the inorganic constituents would constitute actual mineralization. The other mechanisms principally alter the surface morphology. In the present study, we tried to distinguish between "true" nmineralization and alterations in surface morphology by selectively pumicing certain teeth. Teeth which were etched, left in the mouth 90 days and then pumiced, had smooth surfaces similar to those noted on the unetched teeth. These findings corroborate the studies of Miura et al.8 and Newman and Facq.16 Miura et al. showed that the etched enamel surfaces regain their original appearance after brushing 2,000 times with the electrically powered toothbrush. Newman and Facq, usirng SEM, reported that the pumice prophylaxis, after resin removal, restored the enamel surface to its original appearance. A possible explanation for this observation is
Sep tem ber 1 9 79
that the fine pumice, which represents an abrasive, removed the superficial layer. As such, only the deeper enamel layer can be observed upon SEM examination. Our study has shown that in the absence of prophylactic pumicing following bracket removal, there exists an organic layer which covers the surface (group 4). This organic material can mask the rough enamel so that clinically, the surface enamel appears glistening and intact. Similar findings were reported by Lenz and Miihlemann using a TEM investigation. 17 This does not preclude that there may be some uptake of mineral constituents from the saliva into the organic matrix. Mihlemann et aX.,18 in TEM investigations, found that in partially demineralized enamel surfaces, the intercrystalline spaces were filled with a finely grained amorphous precipitate, possibly inorganic in nature. Teeth which were used were exposed to a calcifying fluoridate solution for rehardening. They concluded that the amorphous precipitate cannot be considered as a "restitutio ad integrum" of demineralized enamel structures. On the other hand, when pumice was not applied to the surfaces of the teeth which were etched and left in the mouth 90 days, the enamel surfaces remained rough and were covered with an organic material comparable to the usual pattern of bacterial plaque (Group 2). The rough surface indicated that the effect of the acid etching was still present. This was more clearly shown after removing any organic material with sodium hypochlorite. The findings imply that remineralization of etched surfaces is, at best, incomplete after 3 months. Further studies are suggested to determine if better remineralization can be obtained. At the present time, fluoride applications seem to be very effective on enamel previously subjected to acid action: fluoride salts react chemically with the dissolving tissue, substituting for some of the hydroxylions and promoting the reprecipitation of a more resistent enamel rich in fluorides.20 Treatment with sodium fluoride results in significantly higher mean fluoride uptake than treatment with stannous fluoride.21 From the same study, it seems that, when 2% sodium fluoride is included in the acid, the highest fluoride incorporation in the enamel is achieved. Our observation also showed that in
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Vol. S8 No. 9
USE OFACIDS TO ETCH TOOTH ENAMEL
children undergoing orthodontic treatment, etched enamel maintained a rough surface which was easily covered by plaque-like material. This raises the possibility that the etched enamel may be harmful since caries can be initiated from plaque. Gedalia et al. 19 investigated the effect of citric acid as a factor of erosion of dental enamel. Thus, it appears important to clean and pumice teeth which were etched to restore a smooth surface. Otherwise the irregular surface that remains becomes an easy target for plaque accumulation. Accordingly, the use of an acid etched technique such as bonding orthodontic brackets should be followed by careful cleaning and pumicing with sodium fluoride to protect the tooth surface.
Conclusions. A SEM study was performed to evaluate the morphology of the enamel surface of teeth which were etched with 5 0% phosphoric acid and left in the oral environment for 90 days. Orthodontic brackets were placed on some of the teeth using UV activated resin and were subsequently removed. The results demonstrated that the etched enamel surfaces do not show, microscopically, a "restitutio ad integrum" of the structure. Rather, the enamel surface appeared to maintain surface irregularities consistent with those noted immediately after acid etching. The action of fine grade pumice appears to smooth the irregularities caused by the action of the acid, and it is a suggested procedure to avoid plaque accumulation on the rough surface of the teeth. In addition, the application of sodium fluoride may enhance the remineralization process.
1.
2.
3. 4.
REFERENCES JORGENSEN, K. D. and SHIMOKOBE, H: Adaptation of Resinous Restorative Materials to Acid Etched Enamel Surfaces, Scand J Dent Res 83:31-36, 1975. CASTAGNOLA, L.; WIRZ, J.; and GARBEROGLIO, R.: Die Schmelzitzung fuir die konservierende Zahnbehandlung, Sch weiz Mschr Zahnheilk 85:975-1011, 1975. RETIEF, D.H.: Effect of Conditioning the Enamel Surface with Phosphoric Acid, J Dent Res 52:333-341, 1973. LUTZ, F.: Die Adhisiv Versiegelung, Schweiz Mschr Zahnheilk 84:1082-1090, 1974.
1865
5. GWINNETT, A.J. and BUONOCORE, M.G.: Adhesives and Caries Prevention, Brit Dent J 119:77-80, 1965. 6. GROPER, J.N.: The Etch Technique for Anterior Tooth Restoration, J So Cal Dent Assn 39:756-760, 1971. 7. BAHARLOO, D. and MOORE, D.L.: Effect of Acid Etching on Marginal Penetration of Composite Resin Restoration, J Prosth Dent 32:2-10, 1974. 8. MIURA, F.; NAKAGAWA, K.; and MASUHARA, E.: New Direct Bonding System for Plastic Brackets, Am J Orthodont
59:350-361, 1971. 9. WEI, S.H.Y.: Remineralization of Enamel and Dentine-A Review, J Dent Children 34:444451, 1967. 10. ARANA, M.E.: Clinical Observations of Enamel after Acid-etch Procedure, JADA 89:1102-1106, 1974. 11. JOHANSSON, B.: Remineralization of Slightly Etched Enamel, JDent Res 44:64-70. 12. MC DOUGALL, W.A. and ADKINS, K.F.: A Method for the in vitro Study of Demineralization and Remineralization of the Subsurface Enamel, Austr Dent J 11: 20-26, 1966. 13. SOGNNAES, R. F.: Dental Hard Tissue Destruction with Special Reference to Idiopathic Erosion, Washington, D.C., AAAS 91-153, 1963. 14. ALBERT, M. and GRENOBLE, D.E.: An in vivo Study of Enamel Remineralization after Acid Etching, J So Cal Dent Assoc 39:747-755, 1971. 15. LEE, H., et al.: Application of Scanning Electron Microscopy to in vivo Remineralization Studies of Human Enamel, Lee Pharmaceuticals, Res Rep n° 70-147,1970. 16. NEWMAN, G.V. and FACQ, J.M.: The Effect of Adhesive Systems on Tooth Surfaces, Amer JOrthQdont 59:67-75, 1971. 17. LENZ, H. and MUHLEMANN, H. R.: Repair of Etched Enamel Exposed to the Oral Environment, Helv Odontol Acta 7:4749, 1963. 18. MUHLEMANN, H.R.; LENZ, H.; and ROSSINSKY, K.: Electron Microscopic Appearance of Rehardened Enamel, Helv Odontol Acta 8:108-111, 1964. 19. GEDALIA, I.; ANAISE, V.: WESTREICH, V.; and FUKS, A.: Predisposition to Caries in Hamsters Following the Erosive Effect of a Commercial Citrus Beverage Administered With and Without Supplemental Fluoride, J Dent Res 54:496-499, 1975. 20. KATZ, S.; MUHLER, J.C.; and BECK, C.W.: Enamel Conditioning for Fluoride Treatments, J Dent Res 50:816-820, 1971. 21. KOCHAVI, D.; GEDALIA, I.; and ANAISE, J.: Effect of Conditioning with Fluoride and Phosphoric Acid on Enamel Surface as Evaluated By Scanning Electron Microscopy and Fluoride Incorporation, J Dent Res 54:304-309, 1975.
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After etching the enamel in teeth ofyoung children with 50% buffered phosphoric acid and allowing the teeth to remain in the oral environment for a few months, an irregular enamel surface similar to the morphology of recently etched enamel was noted by means of scanning electron microscopy. In addition, the enamel surfaces were covered with plaque. Accordingly, observations by other authors, that etched human enamel takes on a normal appearance after short exposure in the oral cavity, could not be confirmed. However, when the surface of the etched enamel was pumiced, the enamel reacquired both the shine and appearance of non-etched enamel.
J Dent Res 58(9):1859-1865, September 1979
Introduction. The technique of etching enamel with concentrated acids in order to bond composite restorative materials to teeth is a common procedure at the present time. The etching of the enamel by the acid creates a multitude of microscopic "irregularities" in the enamel rods. These irregularities are approximately 25 microns in depth and result from a selective dissolution of enamel rods. An appropriate composite resinl2 flows into these irregularities and polymerizes to form a tenacious mechanical bond.3 This technique has been used for sealing pits and fissures,4 5 for repairing fractured incisal edges,6 for improving marginal adaptation of restorations,7 and for bonding orthodontic brackets to enamel.8 Although clinical advantages of enamel etching resinous bonding procedures are apparent, a number of questions arise. One deals with the fate of enamel surfaces exposed to the oral cavity in procedures involving placement of pit and fissure sealants and composite restorations. In addition, the removal of the resin bonded orthodontic brackets also exposes etched enamel to the oral environment. Received for publication April 22, 1977 Accepted for publication October 30, 1978 For reprints: Corso Alfieri 336, Asti, Italy.
Some investigators refer to the ability of saliva to chemically remineralize demineralized enamel.9,11,12,13 Yet, only a few studies have described the microscopic morphology of the recovery of etched enamel in the presence of saliva.9'14,15,18 One possible reason is that most investigations were conducted before the advent of scanning electron microscopy (SEM). Accordingly, the purpose of this study is to investigate, by means of a scanning electron microscope, the effect of the oral environment on the morphology of etched enamel surfaces. Some teeth were treated with etching solution and extracted immediately after acid etching. These were compared with teeth that had been etched and left in place for a suitable period of time and those that had brackets bonded and later removed.
Materials and methods. Twenty-six upper premolar teeth, from thirteen children (age range 8-14 years) undergoing orthodontic treatment, were included in the study. The grouping of the patients was as follows: Group L - In two patients, the buccal surface of one premolar (upper) was etched with 50% phosphoric acid for 2 minutes. The contralateral premolar was left untreated as control. A total of four teeth were used, and all teeth were extracted immediately after acid etching. Group I. - In three patients, one premolar was treated as previously described while the contralateral premolar was left untreated as control. A total of six teeth were used and extracted 90 days after acid etching. Following extraction, the three etched teeth were longitudinally sectioned in a labio-lingual direction. In this manner, the etched portion of the enamel was divided into two equal halves. One half was placed 1859
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1860
J Detz t Res
GARBEROGLIO & CO/ZA NI
in 5% sodium hypochlorite for one hour in order to remove all organic materials. The other portion of the tooth was left with the organic materials on its surface. Group III. - In five patients, one premolar was subjected to the previously described acid etching procedure on the buccal surface with the contralateral premolar serving as a control. Following etching, orthodontic plastic brackets were attached to the buccal surfaces with UV activated resin bonding. After a period of one week, orthodontic pliers were used for the removal of the plastic brackets. Immediately after, these teeth were pumiced with a rotary prophylactic brush at low speed using fine grade pumice. All of the teeth remained in the mouth for a period of 90 days. They were then extracted. A total of 10 teeth were used as specimens. Group IV. - Three patients were used. The same acid etching, bracket placement and removal procedure as described for Group III was performed on one premolar of each patient. The contralateral premolar served as a control. Following bracket removal, the teeth were not pumiced. A total of six teeth were used. All extracted teeth were immediately stored in buffered neutral formalin. They were exposed to vacuum and plated with 250 A layer of palladium gold. They were then examined by a scanning electron microscope (Stereoscan Cambridge Mark 2A) with an accelerating voltage of 20-30 KV.
Sep tem ber 1 9 79
4~~~~~~~~~~~~
F ig.
1
Scanning electron micrograph of
enamel surface after etching with 50C buffered
phosphoric acid. The entire surface has a pitted appearance (x 2.800).
trol teeth, the surface, at the same magnification (Fig. 4), is very smooth and shows depressions due to remnants of plaque. However, the depressions were much less than in the experimental teeth. Observation of the etched enamel treated with 5% sodium hypochlorite also showed a high degree of irregularity (Figs. 5, 6) but the surface projections were quite different from those observed in Fig. 4. These projections appear to
Results. Group 1. Enamel etched on teeth immediately extracted. - In the two teeth which were etched, there were the characteristic patterns of the demineralized enamel. In Fig. 1 the periphery of prisms has been etched to a greater extent than the central core of the prisms. On the control side (Fig. 2) the usual smooth featureless appearance of the intact enamel is seen. Group 2. Enamel etched, the teeth left in mouth 90 days.- Scanning examination of the enamel not treated with 57 sodium hypochlorite showed surface irregularities with large peaks and depressions (Fig. 3). These projections appeared to be rounded with weblike connections between the rounded elevations and with the appearance of plaque material. On the contralateral con-
Ad
Fig. 2
V.:
,4,
s:,:SUbS
Surface of an unetched control tooth
(x 1.350).
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Vol. S8 No. 9
USE OFACIDS TO ETCH TOOTH ENAMEL
Fig. 3 Surface of an unetched tooth left in the mouth for 90 days. Bacterial plaque covers the enamel (x 5.700).
Fig.
5
1861
Half of the same tooth of Fig. 3. The
tooth was placed in sodium hypochlorite which destroyed the plaque. The enamel appears irregular and has the characteristics of newly etched enamel
(x 5.800).
be sharp ridges consistent with the etched enamel seen immediately after acid etching. Group 3. Enamel etched, resin bonded brackets placed, then removed, surface pumiced, teeth leJt in mouth 90 days. There were two significant observations in these cases. The first was that the remnants
FIig. 4
-
Tooth: control (x 6.250).
of the resin sometimes remained on the enamel surface. This can be observed in the darker shade of the resin surface seen with
Fig. 6 (x 5.500).
Another
zone
of the
same
Downloaded from jdr.sagepub.com at UNIV CALIFORNIA SAN DIEGO on April 13, 2015 For personal use only. No other uses without permission.
tooth
1862
J Dciit Res Septemher 19 79 GARBEROGLIO & COZ/A NID
Fig. 7
Tooth surface wlhich was pumiced after remnoving an orthodontic bracket which was bonded by resin. Part of the resin (R) remained attached to the enamel and, on the surface, striations were produced by pumice abrasion (x 1 30). -
its diagonal striation shown to the right of
Fig. 7.
Fig. - Higher magnification of a part of the surface of the enamel shown in Fig. 7. The configuration is similar to that observed in Fig. 1. This may represent the deeper part of the etched enamel, while the superficial parts were removed by pumicing (x 2.700).
Fig. 9 - Tooth surface from which a bracket was removed and the tooth renained in the mouth 90 days. After bracket removal the toothl was not pumiced. Residual fragments of resin are apparent (R) which circle a zone of enamel (E) (x 50).
In higher magnification, the second salient observation, seen in Fig. 8, was that of a shallow irregular etching pattern. The enamel surface shown here demonstrates only slight irregularities at high magnification (x 2700).
Fig. 10 The central zone in Fig. 9. The enamel surface is highly irregular (x 260).
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Vol. 58 No. 9
1 863
USE OFA CIDS TO ETCH TOOTH ENAM1EL
Group 4. Enamel etched, resin bonding brackets placed and removed, teeth lef t in the mouth 90 days (no pumicing). - The remnants of the resin are clearly defined as dark shading on the right and left side of Fig. 9 (x 50). The enamel surface shown in Fig. 9 can be seen at higher magnification in Figs. 10, 11, 12. The enamel surface is clearly characterized by deep irregularities covered in many parts by plaque material. It should be noted in Fig. 9 (arrow below) that the enamel presents another type of surface configuration. This portion of the enamel has an irregularly grainy appearance clearly seen at higher magnification (Figs. 13, 14). In Fig. 14, this granular appearance simulates the prismatic structure of the enamel rods. The removal of the plastic brackets in this specinen appears to have fractured off the outer layer of enamel revealing the deeper prismatic enamel structure (Fig. 14).
Fig. 12 -Higher magnification of the material which covers the enamel in F ig. 1 1. It has the characteristics of bacterial plaque, with filamentous organisms and cocci (C) (x 6.000). _ a
Discussion. Previous studies reported that etched enamel which is exposed to the oral environment "remineralizes" in a short
time.3,5,10,14,15 The term remineralization was used mainly to indicate that an etched enamel surface had returned to its normal appearance. In this context, some investigators only examined the teeth visually.3,5'10
Fig. 11 At higher magnification, the irregular enamel surface appears partially covered with material (P) (x 2.700).
Fig. 13 Zone of enamel surface where a layer of enamel was fractured during the bracket removal procedure (x 270).
Downloaded from jdr.sagepub.com at UNIV CALIFORNIA SAN DIEGO on April 13, 2015 For personal use only. No other uses without permission.
1864
Fig.
GARBEROGLIO & COZZANI
14
Higher magnification
of
J Den t R es
fractured
enamel (x 2.800).
The mechanism whereby the etched enamel reassumes its intact appearance has never been clearly defined. Several hypotheses have been suggested, including that of the deposition of salivary mucoid material, the abrasion or erosion of the remaining fingerlike projections of the etched crevice, and the precipitation of inorganic constituents found in the saliva. Only the precipitation of the inorganic constituents would constitute actual mineralization. The other mechanisms principally alter the surface morphology. In the present study, we tried to distinguish between "true" nmineralization and alterations in surface morphology by selectively pumicing certain teeth. Teeth which were etched, left in the mouth 90 days and then pumiced, had smooth surfaces similar to those noted on the unetched teeth. These findings corroborate the studies of Miura et al.8 and Newman and Facq.16 Miura et al. showed that the etched enamel surfaces regain their original appearance after brushing 2,000 times with the electrically powered toothbrush. Newman and Facq, usirng SEM, reported that the pumice prophylaxis, after resin removal, restored the enamel surface to its original appearance. A possible explanation for this observation is
Sep tem ber 1 9 79
that the fine pumice, which represents an abrasive, removed the superficial layer. As such, only the deeper enamel layer can be observed upon SEM examination. Our study has shown that in the absence of prophylactic pumicing following bracket removal, there exists an organic layer which covers the surface (group 4). This organic material can mask the rough enamel so that clinically, the surface enamel appears glistening and intact. Similar findings were reported by Lenz and Miihlemann using a TEM investigation. 17 This does not preclude that there may be some uptake of mineral constituents from the saliva into the organic matrix. Mihlemann et aX.,18 in TEM investigations, found that in partially demineralized enamel surfaces, the intercrystalline spaces were filled with a finely grained amorphous precipitate, possibly inorganic in nature. Teeth which were used were exposed to a calcifying fluoridate solution for rehardening. They concluded that the amorphous precipitate cannot be considered as a "restitutio ad integrum" of demineralized enamel structures. On the other hand, when pumice was not applied to the surfaces of the teeth which were etched and left in the mouth 90 days, the enamel surfaces remained rough and were covered with an organic material comparable to the usual pattern of bacterial plaque (Group 2). The rough surface indicated that the effect of the acid etching was still present. This was more clearly shown after removing any organic material with sodium hypochlorite. The findings imply that remineralization of etched surfaces is, at best, incomplete after 3 months. Further studies are suggested to determine if better remineralization can be obtained. At the present time, fluoride applications seem to be very effective on enamel previously subjected to acid action: fluoride salts react chemically with the dissolving tissue, substituting for some of the hydroxylions and promoting the reprecipitation of a more resistent enamel rich in fluorides.20 Treatment with sodium fluoride results in significantly higher mean fluoride uptake than treatment with stannous fluoride.21 From the same study, it seems that, when 2% sodium fluoride is included in the acid, the highest fluoride incorporation in the enamel is achieved. Our observation also showed that in
Downloaded from jdr.sagepub.com at UNIV CALIFORNIA SAN DIEGO on April 13, 2015 For personal use only. No other uses without permission.
Vol. S8 No. 9
USE OFACIDS TO ETCH TOOTH ENAMEL
children undergoing orthodontic treatment, etched enamel maintained a rough surface which was easily covered by plaque-like material. This raises the possibility that the etched enamel may be harmful since caries can be initiated from plaque. Gedalia et al. 19 investigated the effect of citric acid as a factor of erosion of dental enamel. Thus, it appears important to clean and pumice teeth which were etched to restore a smooth surface. Otherwise the irregular surface that remains becomes an easy target for plaque accumulation. Accordingly, the use of an acid etched technique such as bonding orthodontic brackets should be followed by careful cleaning and pumicing with sodium fluoride to protect the tooth surface.
Conclusions. A SEM study was performed to evaluate the morphology of the enamel surface of teeth which were etched with 5 0% phosphoric acid and left in the oral environment for 90 days. Orthodontic brackets were placed on some of the teeth using UV activated resin and were subsequently removed. The results demonstrated that the etched enamel surfaces do not show, microscopically, a "restitutio ad integrum" of the structure. Rather, the enamel surface appeared to maintain surface irregularities consistent with those noted immediately after acid etching. The action of fine grade pumice appears to smooth the irregularities caused by the action of the acid, and it is a suggested procedure to avoid plaque accumulation on the rough surface of the teeth. In addition, the application of sodium fluoride may enhance the remineralization process.
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