some observations of tooth enamel surfaces

Arch. oral Bid. Vol.1, pp.21 1-217, 1959. Pergamon Press Ltd. hinted in Gt. Britain.

SOME OBSERVATIONS OF TOOTH ENAMEL SURFACES

L. S. FOSDICK, L. MCMILLAN and R. Q. BLACKWELL

Chemistry Department, Northwestern University Dental School, Chicago, Illinois, U.S.A.

Abstract-The relatively flat portions of the labial surfaces of human central incisor teeth were polished with various abrasives, in an attempt to produce consistently reproducible surfaces for the comparison of the effects of various treatments. The natural tooth surfaces were so masked by irregularity that the effects of these treatments were difficult to interpret. It was found that when these surfaces were polished by high lustre-producing abrasives, such as tin oxide or levigated alumina, a reproducible surface was formed. These abrasives obliterated all traces of the rod ends, producing the appearance of a Bielby layer. This surface resisted the action of weak acids and did not respond normally to the application of fluorides. When chalk was used as the abrasive another characteristic and reproducible surface was formed. The rod ends and inter-rod areas of the tooth were clearly visible and the surface responded evenly and reproducibly with weak acids and fluorides. Portions of such surfaces were treated with fluorides and oxalates and the entire surface then etched with 0.1 M lactate buffer of pH 45, and the boundary zone between the treated and untreated areas was examined. The protected areas of the surface were clearly visible.

Attempts were made to produce replicas of carious lesions in the enamel at various increments of depth. It was found that replicas could be obtained near the depth of maximum penetration. These replicas showed each rod protruding, with the inter-rod substance decalcified.

INTRODUCTION

THE enamel of teeth is the hardest substance in the body. It has a very definite structure, a composition which is constant within narrow limits, and it resists most substances that are normally found in the mouth, with the exception of acids. When clean and dry it may be rather dull but it can be polished to varying degrees of brilliance depending upon the polishing agent used. Chalk produces a sort of velvet finish without lustre. Tin oxide, levigated alumina and insoluble sodium metaphosphate produce a brilliant lustre. The various calcium phosphates produce a lustre somewhere between that produced by the chalk and the brilliant lustre of the levigated alumina. When the polished tooth surface is wet with saliva, the differences in degree of polish obtained from the various polishing agents generally diminish and the clean wet surface appears highly polished.

The enamel of the natural tooth surface under high magnification may appear smooth, gnarled or corroded, but when polished with any of the abrasives mentioned above will generally yield a smooth surface. This surface must first be penetrated for the formation of a carious lesion. Under ordinary circumstances, when an extracted tooth is etched with pure dilute acids the initial etch indicates a more rapid solution of the rods. Further exposure to acids destroys all traces of structure. In the development of a smooth-surface carious lesion, it would appear that the cementing substance dissolves first.

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212 L. S. FOSDICK, L. MCMILLAN AND R. Q. BLACKWELL

When powdered enamel is treated with fluorides, it resists the attack of acids. This action should, presumably, be detectable on intact teeth.

In view of the importance of the enamel surface, it was thought that an electron microscopic study of it and its response to various treatments would be of interest. There have been a number of publications depicting enamel surfaces and acid-etched surfaces, but none has shown the comparative effect of various polishing agents, nor have any demonstrated the early stages of enamel caries by the methods herein shown (SCOTT and WYCKOFF, 1946; SCOTT, USSING, SOGNNAES and WYCKOFF, 1952;

KENNEDY, TEUSCHER and FOSDICK, 1953; LENZ, 1956; SCOTT and ALBRIGHT, 1954;

MATSUMIYA, TAKUMA, TSHUCHIKURA and OKADA, 1956). This papers deals with the

effect of polishing agents, acids and fluorides on the enamel surface. In addition,

the appearance of early caries of the enamel is presented.

MATERIALS AND METHODS

The preparation of replicas In these experiments only the relatively flat labial surfaces of central incisors were

used. In each case a replica of the surface was taken by means of polyvinyl alcohol.

The alcohol was applied to the surface and allowed to set for approximately 4 hr. When it had attained a suitable consistency, it was stripped from the surface. The replica surface was then covered with a thin film of Formvar and allowed to dry. It was then floated on water with the polyvinyl alcohol portion in contact with the water. The polyvinyl alcohol dissolved, leaving the thin Formvar replica floating on the surface. The replica was placed on a steel grid, allowed to dry and shadowed with chromium, after which it was examined in the electron microscope. The advantage of this indirect replication is that the thick, pliable, polyvinyl alcohol film may be stripped from undercuts without tearing.

The preparation of the surface The natural tooth surface. The tooth was cleaned with a toothbrush and water,

set in quick-setting acrylic resin for ease of handling, and the surface moisture removed.

The polished tooth surface. The tooth was set in quick-setting acrylic cement for ease in handling. It was then polished or buffed on a metallurgical polishing wheel, using the appropriate abrasive slurry on a velvet pad.

Acid etch. In order to provide a standard surface for comparison, the tooth set in acrylic resin was buffed with heavy chalk. This yielded a surface that could be duplicated at will. It was then immersed in acid or buffer solution for the appropriate time, washed with water and dried. If the tooth was to be treated with a protective agent, one half of the standard surface was covered with polyvinyl pressure-sensitive tape and the uncovered half treated with the agent for the appropriate time. The surface was then washed and the tape stripped off and washed again. Then the whole surface was etched with acid in the usual manner.

SOME OBSERVATIONS OF TOOTH ENAMEL SURFACES 213

Early carious lesions The method used was originally devised by POLARA (1953). The tooth was set

in acrylic resin, as previously described, with the early carious lesion or “white spot” exposed. An attempt was made to obtain a satisfactory replica. In most cases the “holes” corresponding to the cementing substance were so deep that intact Formvar replicas could not be obtained. If the Formvar replicas were not intact, the surface of the lesion was lightly stroked with a fine “gold file” to remove the outer layer. Another replication was attempted, and if not successful the area was again stroked with the file to remove another layer. This procedure was repeated until intact replicas were obtained. By the use of this method several replicas of the deeper regions of early enamel caries may be obtained. In no cases could replicas be made if the empty spaces between the rods were large enough for microbial invasion.

RESULTS AND DISCUSSION

The results are shown in the following micrographs. Figs. 1-3 show various normal tooth surfaces. Actually almost all possible variations from smooth surfaces to microscopic eroded areas may be observed. In most cases these variations may be observed in different areas of the same tooth. In all cases the surface of the teeth appeared normal to the naked eye.

Because of the many variations of normal enamel surfaces it is difficult to interpret the results of various treatments; hence, it is imperative that a standard surface be prepared. Fig. 4 shows such a standard surface. This type of surface may invariably be prepared on a sound tooth by buffing with “heavy” chalk. Each rod end is visible and it appears that the cementing substance’is eroded faster than the rod substance. This surface reacts characteristically to acid etch and to the absorption of tin fluoride or neutral sodium fluoride. When dry, this surface has a dull velvety sheen.

When the tooth is buffed with levigated alumina, tin oxide, insoluble sodium metaphosphate or calcium sulphate, the dry surface takes on a brilliant polish. This type of surface can be prepared on a natural tooth surface or on a chalk-buffed surface. The latter usually requires less buffing. Fig. 5 shows such a surface. All abrasives that produce a high lustre yield such a surface and micrographs of each cannot be differentiated. This type of surface can also be produced at will and hence might be considered a standard surface. However, this surface is not readily etched at pH 4.5. The amorphous surface, with all rod ends obliterated, appears to offer some degree of protection against acids and hence cannot be used as a “standard surface”. When the highly polished, amorphous surface is buffed with chalk, the typical surface (Fig. 4) is produced.

When the chalk-buffed surface is etched with O-1 N hydrochloric acid for 5 set (Fig. 6) a characteristically mild decalcification is produced. This type of surface may be produced with weaker acids or with buffered acid solutions. A 0.1 N lactate buffer of pH 4.5 will ordinarily yield such a surface with a 15 min etch. However, with such mild etching agents there is considerable variation from tooth to tooth. In order to obtain a satisfactory etch, the time of immersion in the acid solution will vary from 10 to 20 min (Fig. 7). A highly polished surface such as is shown


in Fig. 5 may resist etching with O-1 M lactate buffer of pH 4.5 for 30 min. Much of the variation in the pattern of the etched tooth surfaces can be eliminated if the surface is previously prepared by buffing with chalk.

When a portion of the standard surface is treated with neutral 2 % sodium fluoride or a neutral sodium fluoride dentifrice for 24. hr after which the entire surface is etched for 15 min with a lactate buffer, the treated portion is protected against etch (Fig. 8). However, if a surface is treated with acid 2% sodium fluoride of pH 3, calcium fluoride globules always form (Fig. 9). This layer is readily brushed off. When 4% tin fluoride of pH 3 is used, or if a stannous fluoride dentifrice is used as the treatment, the surface is amply protected against 0.1 M lactate buffer of pH 4.5 (Fig. 10). Sodium oxalate also appears to offer a mild protective action (Fig. 11).

When a carious lesion is visible to the eye, it has gone too far for replication. However, if the surface layers are removed by a fine “gold file”, the rods are scraped off to the point that the organic and cementing substances will support the replica. Figs. 12 and 13 show such cavities. It will be noted that the cementing substance is completely decalcified, leaving the rods without rigid support. This supports the observations made with the light microscope. It should be noted that such micrographs can be obtained from any enamel caries, providing the process has not penetrated the dentine. The primary difference between such lesions is the depth at which the organic matter in the cementing substance will support the replica.

REFERENCES

KENNEDY, J. J., TEUSCHER, G. W. and FOSDICK, L. S. 1953. The ultramicroscopic structure of enamel and dentin. J. Amer. dent. Ass. 46, 423-431.

LENZ, H. 1956. Elektronenmikroskopische Untersuchungen bei beginnender Schmelzkaries. Zahniirztl. Rdsch. 65, 285-289.

MATSUMIYA, S., TAKUMA, S., TSHUCHIKURA, H. and OKADA, K. 1956. Electron microscope studies on the prophylatic effect of the topical application of sodium fluoride on dental caries. Indonesian dent. J. 7, 19-30.

POLLARA, B. 1953. An electron microscope study of natural and chemically induced dental caries. MS. Thesis, Graduate School, Northwestern University, Chicago.

Scorr, D. and ALBRIGHT, T. T. 1954. Electron microscopy of carious enamel and dentine. Oral Surg. 7, 64-78.

SCOTT, D. B., USSING, M. J., SOGNNAES, R. F. and WYCKOFF, R. W. G. 1952. Electron microscopy of mature human enamel. J. dent. Res. 31, 74-84.

SCOTT, D. B. and WYCKOFF, R. W. G. 1946. Typical structures on replicas of apparently intact tooth surface. Publ. Hlth Rep., Wash., 61, 1397-1400.

Fro. 1. Clean untreated enamel surface. x 9300.

FIG. 2. Clean untreated surface. x 13,600.

FIG. 3. Clean untreated surface. x 9300.

FIG. 4. Clean surface, buffed with Sturges heavy chalk. Note each rod end is clearly visible. x 9300.


PLATE 1

L. S. FOSDICK, L. MCMILLAN AND R. Q. BLAC.KW~LL

PLATE 2


FIG. 5. Surface buffed with levigated alumina. x24.000. Surfaces polished with tin oxide, insoluble metaphosphate or calcium sulphate yield the same type of structure.

FIG. 6. Chalk-buffed surface etched 5 set with @l N HCl. x9300.

FIG. 7. A chalk-polished tooth etched 15 min with 0.1 N lactate buffer of pH 4.5. x9300.

215


FIG. 8. The boundary between a chalk-polished surface (left) and a chalk-polished surface treated with a 2% sodium fluoride dentrifice for 2& hr (right). The whole surface was then etched for 15 min with 0.1 N lactate buffer of pH 4.5. x 13,600.

FIG. 9. Chalk-polished surface treated with 2% sodium fluoride solution of pH 3 for 2 hr. ~20,000. Note globules of calcium fluoride.

FIG. 10. The boundary between a chalk-polished surface (below) and a chalk- polished surface treated with stannous fluoride dentrifice for 2) hr (above). The entire surface was then etched with 0.1 N lactate buffer of pH 4.5 for 15 mm. x 9300.

SOME OBSERVATIONS OF TOOTH ENAMEL. SIJRFAC‘bS

PI.AlF 3

L. S. FOSDICK, L. MCMILLAN AND R. Q. BLACKWELL

PLATE 4


FIG. 11. The boundary between a chalk-polished surface (above) and a chalk- polished surface treated with 2% sodium oxalate solution for 21 hr (below). The entire surface was then etched for 15 min with 0.1 N lactate buffer of pH 4.5. x 9300.

FIG. 12. Natural carious lesion of the enamel, near the bottom of the lesion. Note rods with inter-rod substance dissolved. x 9300.

FIG. 13. Naturalcarious lesion of the enamel, near the bottom of the lesion. x 13,600.

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some observations of tooth enamel surfaces

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