Internal
enamel
reinforcement
through
micromechanical
bonding Gerald E. Denehy, D.D.S., f&S.,* and Dennis 1. Torney, University of Iowa, College of Dentistry, loafa City, Iowa
D.D.S., M.S.**
lhe current emphasis on prevention, patient awareness of tooth preservation, and improved dental restorative materials has directed operative dentistry concepts toward more conservative cavity preparations. 1, 2 Proximal walls of Class II cavity preparations are no longer routinely extended to the external line angles of the tooth nor are occlusal preparation widths routinely cut one third to one half of the width of the occlusal table. The emphasis is now on preserving as much tooth structure as possible while still maintaining those principles of cavity preparation necessary for long-lasting restorations. In the past, it has been impossible to conserve undermined enamel. A basic rule of cavity preparation is the removal of all unsupported enamel to prevent fracture.” Frequently, undermined enamel is limited to the cavosurface marginal areas, and removal involves only minor overextension of the preparation. At other times, however, dentinal destruction and enamel undermining are extensive or exist in an area where the only alternative is total removal of a cusp or removal of a large area of labial enamel. If a true dental adhesive were developed, one that would adequately bond to tooth structure, it would not be necessary to remove undermined enamel. In bonding to the undermined enamel, the adhesive restorative material would lend the weakened area the support necessary to withstand masticatory forces. The a.cid-etch technique closely approaches adhesive dentistry. With this technique, bonding occurs between an unfilled resin and the retentive areas created by etching the enamel. This micromechanical bond supports and retains the resin.4, ’ Current research in progress at the University of Iowa, College of Dentistry, indicates that the opposite principle also may be true. If the resin is adequately retained, it may lend support and retention to the enamel. *Associate Professor,Department of Operative Dentistry. **Assistant Professor,Department of Operative Dentistry. 171
172
Denehy
Fig. 1. Etched x2,000.)
J. Prosthet. Dent. August, 1976
and Torney
internal
enamel
showing
inner
surface
irregularity.
Fig. 2. Unetched internal enamel surface showing grinding of surface irregularity. (Original magnification X2,000.)
Fig. 3. Unetched enamel magnification X500.) Fig. 4. Etched enamel tion X500.)
(UE).
Resin
(R) interface
(E) . Resin (R) interface
(Original
magnification
rills from the bur, but no evidence
shows a space or opening.
shows a close adaptation.
(Original
(Original magnifica-
MATERIALS AND METHODS An autopolymerizing unfilled/filled composite resin acid-etch system* was used in a pilot program to qualitatively study the effects of etching the internal aspects of enamel. Samples of enamel with the dentinal support removed by use of a No. 8 round bur in a slow-speed handpiece were etched internally with 50 per cent phosphoric acid. After etching, rinsing with tap water, and drying with air, the enamel was coated with the unfilled resin and then overlaid with the filled resin. Control samples were also prepared without etching the internal enamel surface. The interface between the enamel and the resin was then examined under the scanning electron microscope. Fig. 1 shows the internal enamel surface after etching for 1 minute. When com*Concise,
3M Manufacturing
Company,
St. Paul, Minn.
Volume 36 Number 2
Enamel
reinforced
by micromecltanical
bond
173
Fig. 5. Diagram of a completed Class III preparation with undermined labial wall.
pared with a nonetched sample (Fig. 2), it can be seen that the grinding rills were removed and the internal surface presented the irregularities caused by etching. The interface between the composite resin and the normal internal enamel surface of the control sample is seen in Fig. 3. A space or opening exists between the resin and the enamel. In contrast, the interface junction seen in Fig. 4, typical of specimens with etched internal enamel surfaces, is closely adapted. It would appear from these interface scannings by electron microscope that micromechanical bonding does occur between the resin system and the internally etched surface of enamel, much the same as it does between the resin system and externally etched surface of enamel. CLINICAL
TECHNIQUE
Unsupported enamel is commonly encountered by the dentist when restoring anterior teeth. It may result from several causes: gross dentinal caries and/or preexisting restorations; incisal attrition where the dentin is exposed and worn away leaving a surrounding collar of enamel; or traumatic fractures leaving an enamel shelf. Class III, IV, or VI cavities may be involved. If enamel support is to be achieved through the internal acid-etch procedure, certain conditions must prevail and certain procedures must be followed. Dentinal support must be lost to the degree that enamel is exposed on the internal aspects of the tooth. No effective micromechanical bonding occurs between the unfilled resins and etched dentin.“, 7 If the composite resin restoration is to properly support the undermined enamel through the internal acid-etch techniqre, the dentist must design the cavity preparation to be sure the resin restoration itself is firmly retained by the tooth. Conventional retention and resistance form in the cavity preparation are often necessary. However, if sufficient bulk of tooth structure is left, an excellent way to retain the restoration is through a combination of the internal and external acid-etch tech-
174
Denehy
J. I’roathct. Dent.
and Torney
Auqut,
Fig. 6. Class VI lesions exhibiting
undermined
Fig. 7. Class VI
with
lesions restored
niques. This is best accomplished
l!lili
enamel walls.
the internal
by beveling
acid-etch
technique.
all enamel
cavosurface
margins
(Fig.
5). Usually, when the enamel has been extensively undermined, the axial and pulpal walls are deeper than ideal. Although the effect of acid penetration through dentinal tubules has been shown not to have a direct effect on the pulp,+1° it is best to place a protective, sealing calcium hydroxide base in the deep areas before etching. The acid is then applied to the enamel cavosurface margins and internal undermined enamel areas. It is allowed to remain on the enamel for 90 seconds, then it is thoroughly rinsed with water and air dried. A white hazy or chalky appearance to the enamel indicates proper etching. If this is not evident, etching should be repeated. Either an ultraviolet light-polymerized or self-curing composite resin may be used with internal acid etching. The unfilled resin is painted over the internally etched enamel and over the etched bevel on the cavosurface margin. The filled resin is then added to build the restoration to the approximate contour and allowed to overlap the unfilled resin on the cavosurface margins (Figs. 6 and 7). These overlapped margins not only achieve added retention but also provide an excellent interfacial seal for the restoration.ll After the resin has properly polymerized, the restoration may be finished in a conventional manner. Proper contour and function should be established in the finished restoration. Care should be taken to maintain the featheredge of composite resin over the beveled cavosurface areas. The internal acid-etch technique also offers interesting possibilities for posterior undermined enamel. The greater masticatory forces and the wear associated with composite resin in posterior teeth, however, pose problems which must be answered before its use is advocated. Research is currently in progress at the University of Iowa which hopefully will answer some of these questions.12 SUMMARY The internal acid-etch technique is not proposed relating to unsupported enamel. It is, however, one treatment when the proper situation arises. Rather undermined enamel in anterior restorations, interior acid-etch bonding deserves consideration.
as the answer to all problems useful method of conservative than the extensive removal of enamel reinforcement through
Volume 36 Number 2
Enamel
reinforced
by micromechanical
bond
175
References 1. Almquist, T. C., Cowan, R. D., and Lambert, R. L.: Conservative Amalgam Restorations, J. I’ROSTHET. DENT. 29: 524-528, 1973. 2. Eames, W. B., O’Neal, S., Black, J., and Rodgers, L. B.: The Incisal Edge Repair Bonanza, J. Am. Dent. Assoc. 90: 369-372, 1975. Publishing Company, 3. Black, G. V.: Operative Dentistry, Chicago, 1908, Medico-Dental p. 115. 4. Nelson, S. R., Till, M. J., and Hinding, J. H.: Comparison of Materials and Methods Used in Acid-Etch Restorative Procedures, J. Am. Dent. Assoc. 89: 1123-1127, 1974. 5. Mitcham, J. C., and Turner, L. R.: The Retentive Strengths of Acid-Etched Retained Resins, J. Am. Dent. Assoc. 89: 1107-1110, 1974. 6. Ibsen, R. L., and Neville, K.: Adhesive Restorative Dentistry, Philadelphia, 1974, W. B. Saunders Company, p. 126. 7. Torney, D. L.: The Retentive Value of Dentin in the Acid Etch Technique, Unpublished Master’s Thesis, University of Iowa, 1974. 8. Jennings, R. F., and Ranly, D. M.: Autoradiographic Studies of Pss Penetration Into Enamel and Dentin During Acid Etching, J. Dent. Child. 39: 69-71, 1972. 9. Lee, H. L., Orlowski, J. A., Scheidt, J. C., and Lee, J. R.: Effects of Acid Etchants on Dentin, J. Dent. Res. 52: 1228-1233, 1973. 10. Winson, D. E.: Autoradiographic Studies of the Penetration of Externally Placed Cads and Ps2 Into the Enamel and Dentin, Georgetown Dent. J. 31: 3-7, 1965. 11. Buonocore, M. G., Sheykholeslam, Z., and Glena, R.: Evaluation of an Enamel Adhesive to Prevent Marginal Leakage: An in Vitro Study, J. Dent. Child. 40: 35-40, 1973. 12. Espinosa, H. D.: Resin Supported Enamel Via Internal Acid Etching, Master’s Thesis, University of Iowa, 1976. UNIVERSITY OF IOWA COLLEGE OF DENTISTRY DENTAL SCIENCE BUILDING IOWA CITY, IOWA 52242
ARTICLES TO APPEAR IN FUTURE ISSUES Development
of new polishing
Takao Fusayama, D.D.S., D.D.Sc., D.D.Sc.
Effect of rapid Lawrence son, M.S.
curing
Gettleman,
Constructing Albert
D.D.S., D.M.Sc., Yoshihiro Sakai,
A silicone dentures
rubber
Gary R. Goldstein,
D.D.S.,
Nagata, D.D.Sc.,
on polymer
M.S.D.,
amalgam D.D.S., D.D.Sc., Masaaki and Hisashi Hisamitsu,
implant
Dan Nathanson,
to fit existing M.S.,
attachment D.D.S.
for dental
Naohiro D.D.S.,
procedures
D.M.D.,
cast crowns
T. Goldberg,
agents
materials
D.M.D.,
removable
Iwaku, D.D.S.,
and Richard
partial
L. Myer-
denture
clasps
of removable
partial
and Rex D. Jones, D.D.S.
for primary
retention
enamel
reinforcement
through
micromechanical
bonding Gerald E. Denehy, D.D.S., f&S.,* and Dennis 1. Torney, University of Iowa, College of Dentistry, loafa City, Iowa
D.D.S., M.S.**
lhe current emphasis on prevention, patient awareness of tooth preservation, and improved dental restorative materials has directed operative dentistry concepts toward more conservative cavity preparations. 1, 2 Proximal walls of Class II cavity preparations are no longer routinely extended to the external line angles of the tooth nor are occlusal preparation widths routinely cut one third to one half of the width of the occlusal table. The emphasis is now on preserving as much tooth structure as possible while still maintaining those principles of cavity preparation necessary for long-lasting restorations. In the past, it has been impossible to conserve undermined enamel. A basic rule of cavity preparation is the removal of all unsupported enamel to prevent fracture.” Frequently, undermined enamel is limited to the cavosurface marginal areas, and removal involves only minor overextension of the preparation. At other times, however, dentinal destruction and enamel undermining are extensive or exist in an area where the only alternative is total removal of a cusp or removal of a large area of labial enamel. If a true dental adhesive were developed, one that would adequately bond to tooth structure, it would not be necessary to remove undermined enamel. In bonding to the undermined enamel, the adhesive restorative material would lend the weakened area the support necessary to withstand masticatory forces. The a.cid-etch technique closely approaches adhesive dentistry. With this technique, bonding occurs between an unfilled resin and the retentive areas created by etching the enamel. This micromechanical bond supports and retains the resin.4, ’ Current research in progress at the University of Iowa, College of Dentistry, indicates that the opposite principle also may be true. If the resin is adequately retained, it may lend support and retention to the enamel. *Associate Professor,Department of Operative Dentistry. **Assistant Professor,Department of Operative Dentistry. 171
172
Denehy
Fig. 1. Etched x2,000.)
J. Prosthet. Dent. August, 1976
and Torney
internal
enamel
showing
inner
surface
irregularity.
Fig. 2. Unetched internal enamel surface showing grinding of surface irregularity. (Original magnification X2,000.)
Fig. 3. Unetched enamel magnification X500.) Fig. 4. Etched enamel tion X500.)
(UE).
Resin
(R) interface
(E) . Resin (R) interface
(Original
magnification
rills from the bur, but no evidence
shows a space or opening.
shows a close adaptation.
(Original
(Original magnifica-
MATERIALS AND METHODS An autopolymerizing unfilled/filled composite resin acid-etch system* was used in a pilot program to qualitatively study the effects of etching the internal aspects of enamel. Samples of enamel with the dentinal support removed by use of a No. 8 round bur in a slow-speed handpiece were etched internally with 50 per cent phosphoric acid. After etching, rinsing with tap water, and drying with air, the enamel was coated with the unfilled resin and then overlaid with the filled resin. Control samples were also prepared without etching the internal enamel surface. The interface between the enamel and the resin was then examined under the scanning electron microscope. Fig. 1 shows the internal enamel surface after etching for 1 minute. When com*Concise,
3M Manufacturing
Company,
St. Paul, Minn.
Volume 36 Number 2
Enamel
reinforced
by micromecltanical
bond
173
Fig. 5. Diagram of a completed Class III preparation with undermined labial wall.
pared with a nonetched sample (Fig. 2), it can be seen that the grinding rills were removed and the internal surface presented the irregularities caused by etching. The interface between the composite resin and the normal internal enamel surface of the control sample is seen in Fig. 3. A space or opening exists between the resin and the enamel. In contrast, the interface junction seen in Fig. 4, typical of specimens with etched internal enamel surfaces, is closely adapted. It would appear from these interface scannings by electron microscope that micromechanical bonding does occur between the resin system and the internally etched surface of enamel, much the same as it does between the resin system and externally etched surface of enamel. CLINICAL
TECHNIQUE
Unsupported enamel is commonly encountered by the dentist when restoring anterior teeth. It may result from several causes: gross dentinal caries and/or preexisting restorations; incisal attrition where the dentin is exposed and worn away leaving a surrounding collar of enamel; or traumatic fractures leaving an enamel shelf. Class III, IV, or VI cavities may be involved. If enamel support is to be achieved through the internal acid-etch procedure, certain conditions must prevail and certain procedures must be followed. Dentinal support must be lost to the degree that enamel is exposed on the internal aspects of the tooth. No effective micromechanical bonding occurs between the unfilled resins and etched dentin.“, 7 If the composite resin restoration is to properly support the undermined enamel through the internal acid-etch techniqre, the dentist must design the cavity preparation to be sure the resin restoration itself is firmly retained by the tooth. Conventional retention and resistance form in the cavity preparation are often necessary. However, if sufficient bulk of tooth structure is left, an excellent way to retain the restoration is through a combination of the internal and external acid-etch tech-
174
Denehy
J. I’roathct. Dent.
and Torney
Auqut,
Fig. 6. Class VI lesions exhibiting
undermined
Fig. 7. Class VI
with
lesions restored
niques. This is best accomplished
l!lili
enamel walls.
the internal
by beveling
acid-etch
technique.
all enamel
cavosurface
margins
(Fig.
5). Usually, when the enamel has been extensively undermined, the axial and pulpal walls are deeper than ideal. Although the effect of acid penetration through dentinal tubules has been shown not to have a direct effect on the pulp,+1° it is best to place a protective, sealing calcium hydroxide base in the deep areas before etching. The acid is then applied to the enamel cavosurface margins and internal undermined enamel areas. It is allowed to remain on the enamel for 90 seconds, then it is thoroughly rinsed with water and air dried. A white hazy or chalky appearance to the enamel indicates proper etching. If this is not evident, etching should be repeated. Either an ultraviolet light-polymerized or self-curing composite resin may be used with internal acid etching. The unfilled resin is painted over the internally etched enamel and over the etched bevel on the cavosurface margin. The filled resin is then added to build the restoration to the approximate contour and allowed to overlap the unfilled resin on the cavosurface margins (Figs. 6 and 7). These overlapped margins not only achieve added retention but also provide an excellent interfacial seal for the restoration.ll After the resin has properly polymerized, the restoration may be finished in a conventional manner. Proper contour and function should be established in the finished restoration. Care should be taken to maintain the featheredge of composite resin over the beveled cavosurface areas. The internal acid-etch technique also offers interesting possibilities for posterior undermined enamel. The greater masticatory forces and the wear associated with composite resin in posterior teeth, however, pose problems which must be answered before its use is advocated. Research is currently in progress at the University of Iowa which hopefully will answer some of these questions.12 SUMMARY The internal acid-etch technique is not proposed relating to unsupported enamel. It is, however, one treatment when the proper situation arises. Rather undermined enamel in anterior restorations, interior acid-etch bonding deserves consideration.
as the answer to all problems useful method of conservative than the extensive removal of enamel reinforcement through
Volume 36 Number 2
Enamel
reinforced
by micromechanical
bond
175
References 1. Almquist, T. C., Cowan, R. D., and Lambert, R. L.: Conservative Amalgam Restorations, J. I’ROSTHET. DENT. 29: 524-528, 1973. 2. Eames, W. B., O’Neal, S., Black, J., and Rodgers, L. B.: The Incisal Edge Repair Bonanza, J. Am. Dent. Assoc. 90: 369-372, 1975. Publishing Company, 3. Black, G. V.: Operative Dentistry, Chicago, 1908, Medico-Dental p. 115. 4. Nelson, S. R., Till, M. J., and Hinding, J. H.: Comparison of Materials and Methods Used in Acid-Etch Restorative Procedures, J. Am. Dent. Assoc. 89: 1123-1127, 1974. 5. Mitcham, J. C., and Turner, L. R.: The Retentive Strengths of Acid-Etched Retained Resins, J. Am. Dent. Assoc. 89: 1107-1110, 1974. 6. Ibsen, R. L., and Neville, K.: Adhesive Restorative Dentistry, Philadelphia, 1974, W. B. Saunders Company, p. 126. 7. Torney, D. L.: The Retentive Value of Dentin in the Acid Etch Technique, Unpublished Master’s Thesis, University of Iowa, 1974. 8. Jennings, R. F., and Ranly, D. M.: Autoradiographic Studies of Pss Penetration Into Enamel and Dentin During Acid Etching, J. Dent. Child. 39: 69-71, 1972. 9. Lee, H. L., Orlowski, J. A., Scheidt, J. C., and Lee, J. R.: Effects of Acid Etchants on Dentin, J. Dent. Res. 52: 1228-1233, 1973. 10. Winson, D. E.: Autoradiographic Studies of the Penetration of Externally Placed Cads and Ps2 Into the Enamel and Dentin, Georgetown Dent. J. 31: 3-7, 1965. 11. Buonocore, M. G., Sheykholeslam, Z., and Glena, R.: Evaluation of an Enamel Adhesive to Prevent Marginal Leakage: An in Vitro Study, J. Dent. Child. 40: 35-40, 1973. 12. Espinosa, H. D.: Resin Supported Enamel Via Internal Acid Etching, Master’s Thesis, University of Iowa, 1976. UNIVERSITY OF IOWA COLLEGE OF DENTISTRY DENTAL SCIENCE BUILDING IOWA CITY, IOWA 52242
ARTICLES TO APPEAR IN FUTURE ISSUES Development
of new polishing
Takao Fusayama, D.D.S., D.D.Sc., D.D.Sc.
Effect of rapid Lawrence son, M.S.
curing
Gettleman,
Constructing Albert
D.D.S., D.M.Sc., Yoshihiro Sakai,
A silicone dentures
rubber
Gary R. Goldstein,
D.D.S.,
Nagata, D.D.Sc.,
on polymer
M.S.D.,
amalgam D.D.S., D.D.Sc., Masaaki and Hisashi Hisamitsu,
implant
Dan Nathanson,
to fit existing M.S.,
attachment D.D.S.
for dental
Naohiro D.D.S.,
procedures
D.M.D.,
cast crowns
T. Goldberg,
agents
materials
D.M.D.,
removable
Iwaku, D.D.S.,
and Richard
partial
L. Myer-
denture
clasps
of removable
partial
and Rex D. Jones, D.D.S.
for primary
retention
