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Experimental in vitro lesions adjacent to composite restorations in etched cavities
Experimental in vitro lesions adjacent to compositerestorations in etched cavities Ehar Hals, Dr.philos., Bergeq Norway DEPARTMENT
OF CARIOLOGY,
Candodont., SCHOOL
and OEav Laegreid,
OF DENTISTRY,
TJNIWRSITY
Cand.odont., OF BERGEN
Class V cavities and wedge-shaped cavities simulating erosions were prepared in thirty extracted, permanent human teeth. After being etched for 2 minutes with the pertinent cleanser, the wedge-shaped cavities were restored with Enamelite or Restodent. The Class V cavities were etched with 50 per cent phosphoric acid and restored with HL-72. Artificial lesions around the fillings were produced by immersing the teeth in an acid-gelatin system. Ground sections of the teeth with the fillings in situ were studied by polarized light microscopy and microradiography. All the teeth showed “outer lesions,” whereas the occurrence of a %vall lesion” was a rare exception.
M
icroretention of composite restorations based on the etch technique1 has been used in the clinic for some years. Etching has been used instead of conventional preparation in connection with restoration of fractured teeth and in cases of erosion, hypoplastic defects, discolored enamel, etc.2-5 The etch method has also been used in cavities in supplementation of preparation with rotating instruments.6 Experimental in vitro and in vivo lesions developing around composite restorations inserted without previous etching have been described by Hals and Kvinnsland.? All teeth showed “outer lesions,” whereas the tendency to the development of “cavity wall lesions” was negligible. For an explanation of these entities, see Fig. 1. The a.im of this study was to investigate in vitro lesions associated with composite restorations where the cavities had been etched, either as the only preparatory procedure or in supplementation of conventional preparation. MATERIAL
AND
METHODS
Fifty extracted human teeth were fixed in 10 per cent neutral formalin, stored in 1 per cent benzalkonium chloride, and not allowed to dry during any stage of the experiments. In order to simulate erosions, wedge-shaped cavities 225
Dentine
Fig. 1. Microscopic image (schematic) of experimental lesion adjacent to filling (lost during processing of section). Outer lesion, developing by action of acid on outer surface. Wall lesion, developing by penetration of acid into microspace between filling and cavity mall, tending to encompass fiIling.
were prepared on clinically sound buccal surfaces of twenty teeth. The occlusocervical extension was approximately 4 mm., and the depth of the cavities was 2 mm. In two cases the cervical limit was extended to the surface of the root. The cavities were prepared with an air-rotor with adequate water cooling, and the two facets were polished with fine sandpaper disks. After being etched for 2 minutes with the pertinent, cleanser, included in the Restodent and Enamelite kits, fifteen “erosion” cavities were restored with Enamelite and five with Restodent. In ten teeth, buccal Class V cavities, 2 by 2 mm. wide and 2 mm. deep, were prepared-also in these cases with an air-rotor with adequate water cooling. The ca,vity walls were finished with mounted stones and hand instruments and etched with 50 per cent phosphoric acid for 2 minutes before being restored with HI,-72. In all of these cases, etching and filling procedures were undertaken according to the manufacturers’ instructions. Four teeth served as controls of the effect of the preparation procedure on the cavity walls, and ten teeth for the effect of etching. These teeth were not filled. Three teeth served as controls of the interface between restoration and cavity wall and of the possible effect, of the filling materials on the cavit.y walls. All these procedures were undertaken by one examiner (0. JL) . In order to produce lesions around the fillings, we used the method described by Hals and Nernaes8 After polishing of the restorations 8 to 14 days after insertion, all experimental teeth were isolated with colored nail varnish, except for a narrow rim around the restorations. The teeth were stored in water for 24 hours and thereafter placed in acid gelatin!’ for 55 to 70 days. The concentration of the gelatin was 15 per cent. The pH of the solution was adjusted to 4.0 by the addition of 30 per cent lactic acid, and thymol was added to prevent bacterial growth.
Volume Number
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adjacent
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restorations
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Fig. B. Control. Transversally cut enamel prisms. Effect of etching with 50 per cent r phoric acid for 2 minutes. (Scanning electron microscope. Original magnification, ~3,000.)
HISTOLOGK
OBSERVATIONS
One well-oriented buccolingual section in the longitudinal axis of the cr()wn was cut from all teeth with the restoration in situ. Details have been descri bed by Hals and Leth Simonsen. lo The sections were observed by means of polari lzed light microscopy and microradiography, which were used in the same way as described by Hals and Nernaes.” For examination and photography by polarized light, all sections were im-
Fig. 3. Control. Longitudinally cut enamel prisms. Effect of etching \vith 50 per cent phosphoric acid for 2 minutes. (Scanning electron microscope. Original magnification, x3,000. )
mersed in distilled water (n = 1.33) and guinoline (n = 1.62). Reexamination took place after mounting in Canada balsam (n = 1.53). Since it was soon realized that this study would be concerned, in parbicular, with very early stages of enamel caries, many sections were also examined in air in = 1.0) and methanol (n = 1.33) .I1 Occlusal or cervical cavity walls from three of the control teeth mere excised and examined by means of a scanning electron microscope.
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to composite restorations
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Fig. 4. Experimental tooth (56 days). Dentin wall etched with cleanser for 2 minutes. D, Dentin. I, Decalcified rim of dentin wall displaying increased birefringence. F, Filling (Enamelite) . (Polarized light. Gypsum compensator. Red. 1 order. Section immersed in distilled water. Original magnification, x500.) Fig. 5. Control. Dentin/cementum cavity wall (and surface of cementum) etched with 50 per cent phosphoric acid for 2 minutes. D, Dentin. C, Cementum. Ca, Cavity. (Polarized light. Gypsum compensator. Section immersed in distilled water. Original magnification, x60.) RESULTS Controls
No changes due to cavity preparation could be observed in any of the cavity walls. In transversally or obliquely cut prisms, etching had caused a honeycomb pattern and a denudation of crystallite structure which could be demonstrated by scanning electron microscopy (Fig. 2). Correspondingly, in sections of the cavity walls, a distinct relief could be observed by polarized light. In the occlusal enamel wall of the wedge-shaped cavities where the prisms were usually cut in a plane parallel with prism direction, the etched surface was characterized by the relief formed by the crystallite structure and by longitudinal ridges (Fig. 3). Comparison of nonfilled and filled etched cavities revealed no effect of the filling materials on the cavity walls. The effect of etching could also be demonstrated in filled cavities. The effect of etching on dentin walls not covered by a cement base appeared as an approximately 20 ,um wide border rim in which distinctly widened tubules could be discerned. In polarized light (Fig. 4) the rim displayed highly increased birefringence, whereas a narrow, pseudo-isotropic layer formed the transition to the intact dentin. By microradiography the rim had a translucent appearance.
Fig. 6. Experimental tooth (63 days). Outer lesion of enamel. Arrow, Interfare cavity wall/filling. (Microradiograph. Original magnification, x60.) Fig. 7. Experimental tooth (61 days). Cervical facet of wedge-shaped cavity extended to cementum (C). Etching for 2 minutes with cleanser. drrolr, &calcified rim of dentin/cementurn caused by etching. 0, Outer lesion of cementum/dentin. F, Filling (Enamelite). Cleft between filling and outer part of cavity wall due to shrinkage of outer lesion probably during processing of section. No wall lesion. (Polarized light. Gypsum compensator. Se(ation immersed in distilled nater Original magnification, x30.)
A corresponding demineralized area was observed in the cementum (Fig. 5). An intimate connection existed between the enamel wall and the border of the restoration. Corresponding to the relief of the wall shown in Fig. 2, cones and spicules of the border of the restoration fitted in with the roughened surface of enamel. In instances of longitudinally cut prisms the border of the restoration appeared plain. The restorative material had not penetrated into the demineralized border rim of the dentin wall (Fig. 4). ln instances of extension of the cavities to the root surface, the same situation was observed in the eementum. Consequently, in these areas the etching had led to a porous interface between the restoration and the cavity wall. Experiments
Outer lesions had developed in all “secondary caries risks.“” The enamel lesions (Fig. 6) were subsurface radiolucent, and according to all details completely similar to outer lesions associated with composite restorations in nonetched cavities7 Of the four lesions which had developed from the cementum, two were subsurface and two revealed a demineralized surface. All four lesions showed shrinkage, both relative to the root surface and to the cavity wall (Fig. 7). “Every
section represented
an occlusal and a cervical
secondary
caries risk.
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to composite restorations
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Fig. 8. Experimental tooth (63 days). 0, Outer lesion of enamel and dentin. No wall lesion. ATTOW,Radiolucent rim of dentin wall caused by etching with cleanser. No penetration of filling material (F, Enamelite) into this area. (Microradiograph. Original magnification, x40.) Fig. 9. Experimental tooth (70 days). 0, Outer lesion of enamel. F, Filling (Restodent). Microretention through resin tags into enamel wall (E) undamaged. No wall lesion. (Polarized light. Gypsum compensator. Section immersed in distilled mater. Original magnification, x250.) Fig. 20. Experimental tooth (63 days). Enamel from cervical facet of wedge-shaped cavity. No wall lesion. Br~ows, Zone of increased negative birrfringenee of enamel covered by dark zone of resin tags. Filling (Enamelite) lost during processing of section. (Polarized light. Gypsum compensator. Air-dried section. Original magnification, x100.)
Fig. 8 shows the typical image of the enamel/dentin cavity wall. There are no changes in the enamel. The empty, demineralized border rim of the dentin wall is clearly visible, but no changes due to the experiment are present. Fig. 9 (polarized light) shows that the “microretention” of the filling to the enamel is undamaged. In some sections, primarily where the prisms had been transversely or obliquely cut, a 5 to 15 pm wide zone at the surface of the enamel wall displayed increased negative birefringence relative to the underlying enamel, irrespective of the immersion medium used (Fig. 10). The zone appeared dark by incident light/dark-field examination, and in two inst,ances also showed increased radiopacitp by microradiography (Fig. 11). Only three cavity wall lesions out of sixty risks could be observed. One lesion was restricted to the enamel wall (Fig. 12)) a second one, to the dentin wall, and the third one had attacked both the enamel and the dentin wall. All lesions were radiolucent in microradiographs. Discussion
Unless carefully neutralized and controlled, formalin as a fixative may cause disintegration of the surface of enamel.I2 HalP found no indication that the
Fig. 12. Experimental tooth (70 days). Slight hypermineralieatio~1 of 15 pm wide zone (arrows) of enamel mall adjacent, to filling (Rcstodent, lost during processing of section). (Microradiograph. Original magnification, x250. ) Fig Id. Experimental tooth (57 days). Ehrmcl of occlusal cavity wall. 0, Outer lesion. Filling (HL-72) and surface of enamel lost during processing of section. II., Wall lesion. (Polarized light. Section immersed in distilled water. Original magnification, x60.) Fig. 23. Experimental tooth (70 days). Bonding of filling (F, Rrstodent) to enamel persists. No wall lesion. C, Crack of enamel created during processing of scction. (Polarized light. Gypsum compensator. Section immersed in distilled water. Original magnification, x250.)
10 per cent neutral formalin used by him had caused any damage to the mineralized tissue. In the present study the same type of formalin was used. Unlike the sit,uation with silicate cements, no penetration of ions from the composites in question into adjacent tooth tissue has been described. Apparently, these composites haye no anticariogenic properties. Except for the action of acids that may have taken place during the etching procedure, conditions for development of outer lesions in this study must have been the same as with conventional composites7 and amalgam.” Actually, the outer lesions of these studies corresponded closely to each other. The findings from the various examinations to which the enamel wall in Fig. 10 was subjected indicate a loss of pore volume of the enamel tissue. Probably, this has been created by reprecipitation of mineral salts dissolved by the acid used for etching of the enamel. Since the phenomenon was also observed in two of the control sections, any effect due to the acid gelatin can be disregarded. In this way a slight hypermineralization, detectable by polarized light, and occasionally even by microradiography, has developed. Thus, etching of the enamel has in some instances caused both surface and in-depth changes.
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4I 2
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The cleft shown in Fig. 7 indicates that bonding between filling and the etched dentin/cementum wall has been inadequate. Contrary to fillings bordering enamel walls both occlusally and cervically, fillings in cavities that were extended to the cementum were easily lost during processing of the sections. Wall lesions did not seem to have developed in these cases of supposed permeability. However, it ran be presumed that bonding would have been still less sufficient under clinical conditions due to the content of fluid in the tissues. By clinical restoration of cavities extending into the root surface, it is, therefore, recommended not to etch the dentin/cementum wall but to use conventional mechanical retention in this area. In the study of the in vitro lesions associated with composites in nonetched cavities, wall lesions were observed in only a few instances.’ It was supposed that the degree of microleakage must be less with composite than with silicate cement and amalgam restorations. Obviously, in the present study the almost total absence of wall lesions must go back to the intimate connection between the composite and the cavity walls that probably has prevented microleakage. Presumably, cavity walls cut in a plane parallel with prism direction would offer a retention of the filling inferior to that existing with walls cut perpendicular to prism direction. However, it seems as though bonding of composite to etched enamel, irrespective of prism direction, is stronger than the enamel itself. While bonding persisted during grinding of the sections, a break in the enamel adjacent to the filling could be observed in a few instances (Fig. 13). Jfirgensen, Asmussen, and ShimokobcT4 showed that contraction stresses in restorative resins bonded to the enamel of cavity walls readily broke the enamel surrounding the cavities. Both polymerization contra.ction and thermal contraction could cause the forces studied. Possibly, such defects have been the starting point for dcvclopmcnt of the cxccptional wall lesions in our expcrimcnts. SUMMARY Class V cavities and wedge-shaped cavities simulating erosions were prepared in thirty extracted, permanent human teeth. After being etched for 2 minutes with the pertinent cleanser, the wedge-shaped cavities were restored with Enamelite or Restodent. The Class V cavities were etched with 50 per cent phosphoric acid and restored with HI,-72. Artificial lesions around the fillings were produced by immersing the teeth in an acid-gelatin system. Ground sections of the teeth with the fillings in situ were studied by polarized light microscopy and microradiography. All the teeth showed “outer lesions,” whereas the occu~*~c~~ccof a “wall lesion” was a rare exception. REFERENCES
1. Buonocore, M. G.: A Simple Method of Increasing the Adhesion of Acrylic Filling Materials to Enamel Surfaces, J. Dent. Res. 34: 849-853, 1955. 2. Laswell, H. R., Welk, D. A., and Rugenos, J. W. : Attachment of Resin Restorations to Acid Pretreated Enamel, J. Am. Dent. Assoc. 82: 558-563, 1971. 3. Ibsen, R. L.: Conservative Restorations of Decalcified Enamel With an Adhesive Composite, J. S. Calif. Dent. Assoc. 40: 926-927, 1972. 4. Hindmg, J. H.: The Acid-etch Restoration: A Treatment for Fractured Anterior Teeth, J. Dent. Child. 40: 21-24, 1973. 5. Buonocore, M. G., and Davila, J.: Restoration of Fractured Anterior Teeth With Ultraviolet Light-Polymerized Bonding Matrrials : A New Technique, J. Am. Dent. Assoc. 86: 1349-1354, 1973.
6. Jergensen, K. D. : Personal communication, 1974. 7. Hals, E., and Kvinnsland, I.: Structure of Experimental In Vitro and In \.ivo Lesions Around Composite (Addent XV) Fillings, J. Dent. Res. 82: 517-526, 1974. Silwr .Imalg:nn 8. Hals, E., and Nernars, A.: Histopathology of In Vitro Grips Around Fillines. Caries Res. 5: 58-77. 1971. 9. Von ~artheld, F.: Membrane Phenomena in Carious Dissolution of the Teeth, Arcl~. Oral Biol., Special supplement 6: 284-303, 1961. 10. Hals, E., and Leth Simonsen, T. : Histopathology of In Vivo Caries Arouutl Hilrcr Amalgam Fillings, Caries Res. 6: 16-33, 1972. 11. Silverstone, L. M.: The Primary Translucent~ Zone of Enamrl Caries and of Artificial Caries-like Lesions, Br. Dent. J. 120: 461-471, 1966. 12. Crabb, H. S. M.: The Pattern of Enamel Mineralization, Thesis, University of Bristol,
-_-
1MX
13. Hals, E.: The Structure of Experimental In Vitro Lesions Around Silicate Fillings in Human Teeth, Arch. Oral Biol. 20: 283-289, 1975. 14. J#rgensen, h. D:, Asmussen, E., and Shrmokobe, H.: Enamel Dnmages Caused by Contracting Rest,oratrve Resins, &and. J. Dent. Res. 83: 120-122 ,I975 Reprint Yequests to : Dr. Einar Hals Department of Cariology School of Dentistry iirstadvei 17 N-5000 Bergen, Norway
OF CARIOLOGY,
Candodont., SCHOOL
and OEav Laegreid,
OF DENTISTRY,
TJNIWRSITY
Cand.odont., OF BERGEN
Class V cavities and wedge-shaped cavities simulating erosions were prepared in thirty extracted, permanent human teeth. After being etched for 2 minutes with the pertinent cleanser, the wedge-shaped cavities were restored with Enamelite or Restodent. The Class V cavities were etched with 50 per cent phosphoric acid and restored with HL-72. Artificial lesions around the fillings were produced by immersing the teeth in an acid-gelatin system. Ground sections of the teeth with the fillings in situ were studied by polarized light microscopy and microradiography. All the teeth showed “outer lesions,” whereas the occurrence of a %vall lesion” was a rare exception.
M
icroretention of composite restorations based on the etch technique1 has been used in the clinic for some years. Etching has been used instead of conventional preparation in connection with restoration of fractured teeth and in cases of erosion, hypoplastic defects, discolored enamel, etc.2-5 The etch method has also been used in cavities in supplementation of preparation with rotating instruments.6 Experimental in vitro and in vivo lesions developing around composite restorations inserted without previous etching have been described by Hals and Kvinnsland.? All teeth showed “outer lesions,” whereas the tendency to the development of “cavity wall lesions” was negligible. For an explanation of these entities, see Fig. 1. The a.im of this study was to investigate in vitro lesions associated with composite restorations where the cavities had been etched, either as the only preparatory procedure or in supplementation of conventional preparation. MATERIAL
AND
METHODS
Fifty extracted human teeth were fixed in 10 per cent neutral formalin, stored in 1 per cent benzalkonium chloride, and not allowed to dry during any stage of the experiments. In order to simulate erosions, wedge-shaped cavities 225
Dentine
Fig. 1. Microscopic image (schematic) of experimental lesion adjacent to filling (lost during processing of section). Outer lesion, developing by action of acid on outer surface. Wall lesion, developing by penetration of acid into microspace between filling and cavity mall, tending to encompass fiIling.
were prepared on clinically sound buccal surfaces of twenty teeth. The occlusocervical extension was approximately 4 mm., and the depth of the cavities was 2 mm. In two cases the cervical limit was extended to the surface of the root. The cavities were prepared with an air-rotor with adequate water cooling, and the two facets were polished with fine sandpaper disks. After being etched for 2 minutes with the pertinent, cleanser, included in the Restodent and Enamelite kits, fifteen “erosion” cavities were restored with Enamelite and five with Restodent. In ten teeth, buccal Class V cavities, 2 by 2 mm. wide and 2 mm. deep, were prepared-also in these cases with an air-rotor with adequate water cooling. The ca,vity walls were finished with mounted stones and hand instruments and etched with 50 per cent phosphoric acid for 2 minutes before being restored with HI,-72. In all of these cases, etching and filling procedures were undertaken according to the manufacturers’ instructions. Four teeth served as controls of the effect of the preparation procedure on the cavity walls, and ten teeth for the effect of etching. These teeth were not filled. Three teeth served as controls of the interface between restoration and cavity wall and of the possible effect, of the filling materials on the cavit.y walls. All these procedures were undertaken by one examiner (0. JL) . In order to produce lesions around the fillings, we used the method described by Hals and Nernaes8 After polishing of the restorations 8 to 14 days after insertion, all experimental teeth were isolated with colored nail varnish, except for a narrow rim around the restorations. The teeth were stored in water for 24 hours and thereafter placed in acid gelatin!’ for 55 to 70 days. The concentration of the gelatin was 15 per cent. The pH of the solution was adjusted to 4.0 by the addition of 30 per cent lactic acid, and thymol was added to prevent bacterial growth.
Volume Number
41 2
1% vitro
lesions
adjacent
to
composite
restorations
227
Fig. B. Control. Transversally cut enamel prisms. Effect of etching with 50 per cent r phoric acid for 2 minutes. (Scanning electron microscope. Original magnification, ~3,000.)
HISTOLOGK
OBSERVATIONS
One well-oriented buccolingual section in the longitudinal axis of the cr()wn was cut from all teeth with the restoration in situ. Details have been descri bed by Hals and Leth Simonsen. lo The sections were observed by means of polari lzed light microscopy and microradiography, which were used in the same way as described by Hals and Nernaes.” For examination and photography by polarized light, all sections were im-
Fig. 3. Control. Longitudinally cut enamel prisms. Effect of etching \vith 50 per cent phosphoric acid for 2 minutes. (Scanning electron microscope. Original magnification, x3,000. )
mersed in distilled water (n = 1.33) and guinoline (n = 1.62). Reexamination took place after mounting in Canada balsam (n = 1.53). Since it was soon realized that this study would be concerned, in parbicular, with very early stages of enamel caries, many sections were also examined in air in = 1.0) and methanol (n = 1.33) .I1 Occlusal or cervical cavity walls from three of the control teeth mere excised and examined by means of a scanning electron microscope.
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In vitro
lesions adjacent
to composite restorations
229
Fig. 4. Experimental tooth (56 days). Dentin wall etched with cleanser for 2 minutes. D, Dentin. I, Decalcified rim of dentin wall displaying increased birefringence. F, Filling (Enamelite) . (Polarized light. Gypsum compensator. Red. 1 order. Section immersed in distilled water. Original magnification, x500.) Fig. 5. Control. Dentin/cementum cavity wall (and surface of cementum) etched with 50 per cent phosphoric acid for 2 minutes. D, Dentin. C, Cementum. Ca, Cavity. (Polarized light. Gypsum compensator. Section immersed in distilled water. Original magnification, x60.) RESULTS Controls
No changes due to cavity preparation could be observed in any of the cavity walls. In transversally or obliquely cut prisms, etching had caused a honeycomb pattern and a denudation of crystallite structure which could be demonstrated by scanning electron microscopy (Fig. 2). Correspondingly, in sections of the cavity walls, a distinct relief could be observed by polarized light. In the occlusal enamel wall of the wedge-shaped cavities where the prisms were usually cut in a plane parallel with prism direction, the etched surface was characterized by the relief formed by the crystallite structure and by longitudinal ridges (Fig. 3). Comparison of nonfilled and filled etched cavities revealed no effect of the filling materials on the cavity walls. The effect of etching could also be demonstrated in filled cavities. The effect of etching on dentin walls not covered by a cement base appeared as an approximately 20 ,um wide border rim in which distinctly widened tubules could be discerned. In polarized light (Fig. 4) the rim displayed highly increased birefringence, whereas a narrow, pseudo-isotropic layer formed the transition to the intact dentin. By microradiography the rim had a translucent appearance.
Fig. 6. Experimental tooth (63 days). Outer lesion of enamel. Arrow, Interfare cavity wall/filling. (Microradiograph. Original magnification, x60.) Fig. 7. Experimental tooth (61 days). Cervical facet of wedge-shaped cavity extended to cementum (C). Etching for 2 minutes with cleanser. drrolr, &calcified rim of dentin/cementurn caused by etching. 0, Outer lesion of cementum/dentin. F, Filling (Enamelite). Cleft between filling and outer part of cavity wall due to shrinkage of outer lesion probably during processing of section. No wall lesion. (Polarized light. Gypsum compensator. Se(ation immersed in distilled nater Original magnification, x30.)
A corresponding demineralized area was observed in the cementum (Fig. 5). An intimate connection existed between the enamel wall and the border of the restoration. Corresponding to the relief of the wall shown in Fig. 2, cones and spicules of the border of the restoration fitted in with the roughened surface of enamel. In instances of longitudinally cut prisms the border of the restoration appeared plain. The restorative material had not penetrated into the demineralized border rim of the dentin wall (Fig. 4). ln instances of extension of the cavities to the root surface, the same situation was observed in the eementum. Consequently, in these areas the etching had led to a porous interface between the restoration and the cavity wall. Experiments
Outer lesions had developed in all “secondary caries risks.“” The enamel lesions (Fig. 6) were subsurface radiolucent, and according to all details completely similar to outer lesions associated with composite restorations in nonetched cavities7 Of the four lesions which had developed from the cementum, two were subsurface and two revealed a demineralized surface. All four lesions showed shrinkage, both relative to the root surface and to the cavity wall (Fig. 7). “Every
section represented
an occlusal and a cervical
secondary
caries risk.
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Ia Gtro lesiom adjacent
to composite restorations
231
Fig. 8. Experimental tooth (63 days). 0, Outer lesion of enamel and dentin. No wall lesion. ATTOW,Radiolucent rim of dentin wall caused by etching with cleanser. No penetration of filling material (F, Enamelite) into this area. (Microradiograph. Original magnification, x40.) Fig. 9. Experimental tooth (70 days). 0, Outer lesion of enamel. F, Filling (Restodent). Microretention through resin tags into enamel wall (E) undamaged. No wall lesion. (Polarized light. Gypsum compensator. Section immersed in distilled mater. Original magnification, x250.) Fig. 20. Experimental tooth (63 days). Enamel from cervical facet of wedge-shaped cavity. No wall lesion. Br~ows, Zone of increased negative birrfringenee of enamel covered by dark zone of resin tags. Filling (Enamelite) lost during processing of section. (Polarized light. Gypsum compensator. Air-dried section. Original magnification, x100.)
Fig. 8 shows the typical image of the enamel/dentin cavity wall. There are no changes in the enamel. The empty, demineralized border rim of the dentin wall is clearly visible, but no changes due to the experiment are present. Fig. 9 (polarized light) shows that the “microretention” of the filling to the enamel is undamaged. In some sections, primarily where the prisms had been transversely or obliquely cut, a 5 to 15 pm wide zone at the surface of the enamel wall displayed increased negative birefringence relative to the underlying enamel, irrespective of the immersion medium used (Fig. 10). The zone appeared dark by incident light/dark-field examination, and in two inst,ances also showed increased radiopacitp by microradiography (Fig. 11). Only three cavity wall lesions out of sixty risks could be observed. One lesion was restricted to the enamel wall (Fig. 12)) a second one, to the dentin wall, and the third one had attacked both the enamel and the dentin wall. All lesions were radiolucent in microradiographs. Discussion
Unless carefully neutralized and controlled, formalin as a fixative may cause disintegration of the surface of enamel.I2 HalP found no indication that the
Fig. 12. Experimental tooth (70 days). Slight hypermineralieatio~1 of 15 pm wide zone (arrows) of enamel mall adjacent, to filling (Rcstodent, lost during processing of section). (Microradiograph. Original magnification, x250. ) Fig Id. Experimental tooth (57 days). Ehrmcl of occlusal cavity wall. 0, Outer lesion. Filling (HL-72) and surface of enamel lost during processing of section. II., Wall lesion. (Polarized light. Section immersed in distilled water. Original magnification, x60.) Fig. 23. Experimental tooth (70 days). Bonding of filling (F, Rrstodent) to enamel persists. No wall lesion. C, Crack of enamel created during processing of scction. (Polarized light. Gypsum compensator. Section immersed in distilled water. Original magnification, x250.)
10 per cent neutral formalin used by him had caused any damage to the mineralized tissue. In the present study the same type of formalin was used. Unlike the sit,uation with silicate cements, no penetration of ions from the composites in question into adjacent tooth tissue has been described. Apparently, these composites haye no anticariogenic properties. Except for the action of acids that may have taken place during the etching procedure, conditions for development of outer lesions in this study must have been the same as with conventional composites7 and amalgam.” Actually, the outer lesions of these studies corresponded closely to each other. The findings from the various examinations to which the enamel wall in Fig. 10 was subjected indicate a loss of pore volume of the enamel tissue. Probably, this has been created by reprecipitation of mineral salts dissolved by the acid used for etching of the enamel. Since the phenomenon was also observed in two of the control sections, any effect due to the acid gelatin can be disregarded. In this way a slight hypermineralization, detectable by polarized light, and occasionally even by microradiography, has developed. Thus, etching of the enamel has in some instances caused both surface and in-depth changes.
Volume Numlwr
4I 2
In vifro
lesions
udjtrce?if
fo cmposife
resfornfims
233
The cleft shown in Fig. 7 indicates that bonding between filling and the etched dentin/cementum wall has been inadequate. Contrary to fillings bordering enamel walls both occlusally and cervically, fillings in cavities that were extended to the cementum were easily lost during processing of the sections. Wall lesions did not seem to have developed in these cases of supposed permeability. However, it ran be presumed that bonding would have been still less sufficient under clinical conditions due to the content of fluid in the tissues. By clinical restoration of cavities extending into the root surface, it is, therefore, recommended not to etch the dentin/cementum wall but to use conventional mechanical retention in this area. In the study of the in vitro lesions associated with composites in nonetched cavities, wall lesions were observed in only a few instances.’ It was supposed that the degree of microleakage must be less with composite than with silicate cement and amalgam restorations. Obviously, in the present study the almost total absence of wall lesions must go back to the intimate connection between the composite and the cavity walls that probably has prevented microleakage. Presumably, cavity walls cut in a plane parallel with prism direction would offer a retention of the filling inferior to that existing with walls cut perpendicular to prism direction. However, it seems as though bonding of composite to etched enamel, irrespective of prism direction, is stronger than the enamel itself. While bonding persisted during grinding of the sections, a break in the enamel adjacent to the filling could be observed in a few instances (Fig. 13). Jfirgensen, Asmussen, and ShimokobcT4 showed that contraction stresses in restorative resins bonded to the enamel of cavity walls readily broke the enamel surrounding the cavities. Both polymerization contra.ction and thermal contraction could cause the forces studied. Possibly, such defects have been the starting point for dcvclopmcnt of the cxccptional wall lesions in our expcrimcnts. SUMMARY Class V cavities and wedge-shaped cavities simulating erosions were prepared in thirty extracted, permanent human teeth. After being etched for 2 minutes with the pertinent cleanser, the wedge-shaped cavities were restored with Enamelite or Restodent. The Class V cavities were etched with 50 per cent phosphoric acid and restored with HI,-72. Artificial lesions around the fillings were produced by immersing the teeth in an acid-gelatin system. Ground sections of the teeth with the fillings in situ were studied by polarized light microscopy and microradiography. All the teeth showed “outer lesions,” whereas the occu~*~c~~ccof a “wall lesion” was a rare exception. REFERENCES
1. Buonocore, M. G.: A Simple Method of Increasing the Adhesion of Acrylic Filling Materials to Enamel Surfaces, J. Dent. Res. 34: 849-853, 1955. 2. Laswell, H. R., Welk, D. A., and Rugenos, J. W. : Attachment of Resin Restorations to Acid Pretreated Enamel, J. Am. Dent. Assoc. 82: 558-563, 1971. 3. Ibsen, R. L.: Conservative Restorations of Decalcified Enamel With an Adhesive Composite, J. S. Calif. Dent. Assoc. 40: 926-927, 1972. 4. Hindmg, J. H.: The Acid-etch Restoration: A Treatment for Fractured Anterior Teeth, J. Dent. Child. 40: 21-24, 1973. 5. Buonocore, M. G., and Davila, J.: Restoration of Fractured Anterior Teeth With Ultraviolet Light-Polymerized Bonding Matrrials : A New Technique, J. Am. Dent. Assoc. 86: 1349-1354, 1973.
6. Jergensen, K. D. : Personal communication, 1974. 7. Hals, E., and Kvinnsland, I.: Structure of Experimental In Vitro and In \.ivo Lesions Around Composite (Addent XV) Fillings, J. Dent. Res. 82: 517-526, 1974. Silwr .Imalg:nn 8. Hals, E., and Nernars, A.: Histopathology of In Vitro Grips Around Fillines. Caries Res. 5: 58-77. 1971. 9. Von ~artheld, F.: Membrane Phenomena in Carious Dissolution of the Teeth, Arcl~. Oral Biol., Special supplement 6: 284-303, 1961. 10. Hals, E., and Leth Simonsen, T. : Histopathology of In Vivo Caries Arouutl Hilrcr Amalgam Fillings, Caries Res. 6: 16-33, 1972. 11. Silverstone, L. M.: The Primary Translucent~ Zone of Enamrl Caries and of Artificial Caries-like Lesions, Br. Dent. J. 120: 461-471, 1966. 12. Crabb, H. S. M.: The Pattern of Enamel Mineralization, Thesis, University of Bristol,
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13. Hals, E.: The Structure of Experimental In Vitro Lesions Around Silicate Fillings in Human Teeth, Arch. Oral Biol. 20: 283-289, 1975. 14. J#rgensen, h. D:, Asmussen, E., and Shrmokobe, H.: Enamel Dnmages Caused by Contracting Rest,oratrve Resins, &and. J. Dent. Res. 83: 120-122 ,I975 Reprint Yequests to : Dr. Einar Hals Department of Cariology School of Dentistry iirstadvei 17 N-5000 Bergen, Norway