PEDIATRIC DENTISTRY/Copyright © 1982 by

Relationship of the macroscopic,histological, and radiographic appearanceof interproximal lesions in human teeth: invitro study using artificial caries techniqueLeon M. Silverstone, DDSc, PhD, BChD, LDS, RCS (Eng)

IntroductionIt is well accepted that the use of bitewing ra-

diography is an important adjunct in the diagnosis ofinterproximal caries. However, the relationships be-tween the macroscopic, clinical, and radiographic ap-pearance of a carious lesion and its true extent in thetissues may not be fully realized by the clinician, espe-cially since there is both confusion and controversy inthe literature.

In a detailed in ~itro investigation on 580 extractedteeth, Marthaler and Germann1 found that when ra-diolucencies were limited to the outer enamel, frankcavities were present in 34 percent of the teeth. Whenthe bitewing radiolucencies extended into the inneraspects of the enamel, cavities were present in 66 per-cent of the teeth. This demonstrates just how ad-vanced lesions really are in spite of what can appear tobe "early" detection by radiography. These workersalso showed that when a radiolucency was visible inthe outer half of the dentin, small cavities werepresent in 87 percent of the surfaces. All of the ra-diographs in the above study were taken withoutusing a soft tissue simulator and therefore representeda greater degree of sensitivity than could be achievedclinically.

It was also reported by Leijon~ that a greater num-ber of carious lesions could be detected by extraoralinspection with the unaided eye compared with dentalradiographs taken extraorally, even without using asoft tissue simulator. When radiographs were takenclinically, an additional number of radiolucencies weremasked by soft tissues. Of 169 approximal surfacesdiagnosed as sound enamel by in ~4tro radiography,macroscopic inspection revealed 50 white spot lesions.3

When these teeth were radiographed again, takingseven different exposures by rotating each tootharound its axis, 27 of the 50 lesions were made visibleradiographically. This procedure could not, of course,be carried out under clinical conditions. Even at-tempting to change the radiographic angle slightly in~ivo would result in overlap of approximal surfaces.

Backer Dirks4 tins shown that proximal enamel le-sions may remain limited to the enamel on ra-diographs for four years or more. If a correspondinglyslow development of small lesions not yet observable

American Academy of PedodonticsSpecial Issue/Radiology Conference

on radiographs is assumed, a large number of initial le-sions may accumulate within a few years without be-coming perceptible on radiographs.1

Darling~ obtained a series of teeth having lesions ofvarying sizes and radiographed them in ~tro. He con-cluded that bitewing radiographs were unlikely toshow the lesion before the dentin was involved. Gwin-nett 6 showed that caries frequently involved morethan half the depth of the enamel before any ra-diographic change was detected on a bitewing ra-diograph. This was found to be the case irrespective ofKVP value, exposure time, or processing procedure. Inmany cases, lesions involved the full thickness of theenamel and extended into the dentin while only asmall area of radiolucency was seen on the radiograph.This study, therefore, emphasized the relative insensi-tivity of the clinical radiographic teclmique. In a simi-lar study Buchholz7 concluded that when the ra-diograph demonstrated the smallest perceptable indi-cation of a lesion, histological examination showed ex-tensive demineralization in the dentin.

Of all radiographic methods, bitewing radiographyappears to be the technique of choice for the detectionof interproximal lesions. Hurlbert and Wuehrmann8

carried out a study comparing the detection of inter-proximal carious lesions using panoramic and stan-dard radiography. They concluded that panoramic ra-diographs alone were ineffective diagnostic aids in thedetection of small interproxirnal lesions. They foundthat the best radiographic survey, in terms of numbersof radiographic enamel lesions detected, was the com-bination of periapical plus bitewing radiographs. Forlesions extending into the dentin radiographically, allcombinations except panoramic radiographs usedalone showed comparable results.

Thus, many workers have shown that under clinicalconditions, small approximal lesions are more likely tobe detected on bitewing radiographs than upon clini-cal examination using a mirror and an explorer. How-ever, if approximal tooth surfaces are examinedmacroscopically on extracted teeth, more lesions willbe detected with the unaided eye than on bitewingradiographs. Thus, it appears that for the in vivo orclinical situation where teeth are in approximal con-

414 INTERPROXIMAL LESIONS: Silverstone

Figure la. A molar and pre-molar tooth painted with anacid resistant varnish and setup in interproximal contact ina silicone block at commence-ment of the study. Windowregions of enamel have beenleft exposed on the mesial anddistal proximal surfaces forthe creation of artificialcaries-like lesions.

tact, a bitewing radiograph is the most sensitivemethod of diagnosing interstitial carious lesions. If, onthe other hand, the approximal surface of a tooth canbe viewed directly due to loss of its neighbor, then thisis a more sensitive method of diagnosing the presenceof a lesion. Although these facts have been known formany years, they do not by themselves indicate atwhat stage a small lesion must be at before it can bediagnosed on a radiograph, or how extensive a lesionmust be before it produces the characteristic "whitespot" appearance macroscopically. The aim of this invitro study was to attempt to correlate factors such aslesion size, macroscopic, and radiographic appearance.Since baselines using sound enamel surfaces were re-quired prior to investigating lesion initiation and pro-gression, an artificial caries technique was employed.This acidified gel technique has been described previ-ously by Silverstone9 and is the only one capable ofcreating lesions in human enamel which appear indis-tinguishable from natural lesions when examined his-tologically and by ultra-structural techniques. The re-sults presented in this paper are part of a larger seriesof experiments.

Methods and MaterialsHuman molar and premolar teeth which appeared

caries-free upon macroscopic examination were se-lected for these studies. After cleaning the teeth withpumice powder and a soft brush using a slow-speedhandpiece with a conventional dental engine, proximalsurfaces were examined with incident illuminationusing a stereo-zoom dissecting microscope. Only teethhaving intact proximal surfaces which appeared freefrom caries or stain were used. Teeth were thengrouped together into pairs in such a manner that agood interproximal contact resulted. Each pair ofteeth was then set up into a silicone block such thatthe tooth crowns were in contact while the roots wereretained within the silicone block. Thus, a simple rep-lica of the clinical situation was achieved with each

Figure Ib. View of the dis-tal surface of the premolartooth in Figure la showingthe window region left ex-posed. Each tooth has com-parable mesial and distalareas left exposed for lesionformation.

pair of teeth (Figure la). Due to the elastic nature ofthe silicone material, either or both of the teeth fromeach silicone block could be removed, and returned toits original position. In this way the identical contactregion was maintained for each tooth pair.

After this, the teeth were painted with an acid-pro-tective varnish (Figure la) covering the roots andcrown with the exception of the area of interproximalcontact (Figure Ib). A corresponding window of en-amel was left unpainted on the opposite noncontactproximal surface of each tooth pair. Therefore eachtooth had a mesial and distal window region of enamelexposed for the production of artificial caries-likelesions.

Tooth pairs were photographed and baseline bite-wing radiographs taken (Figure 2) at 90, 70 and 50KVP, 10 ma, and with exposure times of 0.30, 0.36,0.41 and 1.00 seconds. No soft tissue simulator wasemployed in the in vitro radiographic technique.

After removal from their respective silicone blocks,teeth were then exposed to an artificial caries tech-nique consisting of acidified gelatin gels.910 A series of10 percent gelatin gels were employed, acidified to pH4.0 with lactic acid. Teeth were removed for examina-tion after exposure periods of 4, 8,10,12 and 14 weeks.On removal from the artificial caries medium, teethwere washed, dried, and inserted into their respective

PEDIATRIC DENTISTRY: Volume 3, Special Issue 2 415

silicone blocks. Bitewing radiographs were then re-taken using the same series of parameters employedpreviously. On removing teeth from their siliconeblocks, each proximal surface was photographed afterremoval of the varnish. In order to continue with

Figure 2. A bitewing radiograph of the pair of teethshown in Figure la. This is a baseline radiograph taken atthe commencement of the study.lesion progression, teeth were carefully revarnishedwhere necessary and replaced into a fresh aliquot ofthe artificial caries medium. At various exposuretimes, undemineralized longitudinal sections wereobtained so as to examine the histological features oflesions.

In some cases a single, thin, undemineralized sec-tion was removed from the tooth for histological ex-amination. The cut faces of the remaining toothhalves were then varnished so that only the surface ofthe lesion was once again exposed. Specimens werethen replaced into the artificial caries medium for le-sion progression. On removal of the tooth halves afterthis further exposure, they were inserted into thesilicone blocks and photographs and bitewing ra-diographs taken as before. By taking another singlesection from the specimen, the degree of lesion pro-

gression could be ascertained histologically and com-pared to the radiographic findings. This technique wasmade possible by employing a special microtome, TheSilverstone-Taylor Hard Tissue Microtome," which isable to remove single or multiple undemineralized sec-tions at 70-80 fim thickness with no damage to thelesion (Figure 3).

Histological examination of ground sections wascarried out using a polarizing microscope. A series ofaqueous media and a range of alcoholic imhibitionfluids was employed so as to calculate the pore volumeof lesions and the presence and distribution of the var-ious histological zones of the enamel lesion.12 Micro-radiographs were also taken of sections using Cu Ka radiation on Kodak High Resolution Film.

ResultsFigure 4 shows the results of one series of experi-

ments carried out on the pair of teeth shown previ-ously at baseline in Figures 1 and 2. Figure 4a showsthe teeth at the completion of the experiment after atotal of 14 weeks in the artificial caries medium. Thevarnish has been removed from the teeth and theyhave been replaced into their silicone block. Figure 4bshows the bitewing radiograph of the tooth pair atcompletion, taken at 70 KVP with an exposure time of0.36 seconds. These conditions produced the mostsensitive results with the in vitro radiographic tech-nique. With the exception of a small area of radiolu-cency on the distal surface of the molar tooth, there isno radiographic evidence of caries. This radiographshould be compared with the baseline result shown inFigure 2. Figure 4c is a diagram of the two teeth asseen on the radiograph highlighting the two proximalsurfaces that are to be examined in more detail; themesial and distal surfaces of the molar tooth. Figure

Figure 3. The Silverstone-Taylor Hard Tissue Micro-tome. With this apparatus itis possible to remove thinundemineralized unembeddedsections from the window re-gions. Since the sections arecut 70-80 p(m in thicknesswith no damage to the lesionarea, it is possible to examinethe progression of lesions byremoving sections after var-ious exposures to the artificialcaries medium.

416 INTERPROXIMAL LESIONS: Silverstone

Figure 4. Results of one series of experiments carried out on the pair of teeth shown previously at baseline in Figure la.4a. This shows the teeth at the completion of the experiment after a total of 14 weeks in the artificial caries medium. Thevarnish has been removed from the teeth and they have been replaced into their silicone blocks. 4b. This shows the bite-wing radiograph of the tooth pair at the completion of the experiment. With the exception of a small area of radiolucencyconfined to the outer enamel on the distal surface of the molar tooth, there is no radiographic evidence of caries. Thisshould be compared with the baseline radiograph shown in Figure 2. 4c, Diagram showing the two proximal surfaceswhich are to be examined in more detail; the mesial and distal surfaces of the molar tooth. 4d. The distal surface of themolar tooth showing the artificial "white spot" lesion. This lesion was visible as a small radiolucent area on the bitewingradiograph. 4e. The mesial surface of the molar tooth showing the presence of a "white spot" lesion. This lesion was notdetected on the radiograph. 4£ Longitudinal ground section through the distal surface of the molar tooth examined withthe polarizing microscope after imbibition of the section with water (x50). The lesion is extensive, extending the fullthickness of the enamel and passing into the dentin. 4g. Longitudinal ground section showing the mesial surface of themolar tooth after imbibition with water and examined in polarized light (x50). This lesion is not as extensive as the one ofthe distal surface of the same tooth. However, the advancing front of the body of the lesion extends two-thirds throughthe enamel thickness. The advancing front of this lesion as seen after imbibition with quinoline extended a further 100pm. This lesion has a mineral loss in excess of 25 percent and yet there was no indication of its presence on the bitewingradiograph.

4d is a photograph of the distal surface of the molartooth showing the artificial "white spot" lesion. Boththis lesion, and the one produced on the mesial surfaceof the molar (Figure 4e), are typical of the macro-scopic appearance of a "white spot" lesion and areseen in contrast to the sound enamel. While the lesionon the distal surface (Figure 4d) showed as a small ra-diolucent area in the outer enamel on the bite-wing ra-diograph, there was no radiographic indication of thepresence of the lesion on the mesial surface (Figure 4e)of the same tooth. (See cover illustrations)

Histologically, the lesion on the distal surface ap-pears extensive (Figure 4f), extending through the fullthickness of the enamel and passing into the dentin.The dark (positively birefringent) region is the bodyof the lesion which has in excess of 25 percent mineralloss. The lesion on the mesial surface of the sametooth is also extensive histologically (Figure 4g) but toa lesser extent than the one on the distal surface.However, the advancing front of the body of the lesionas seen on the photomicrograph extends two-thirds ofthe distance through the depth of the enamel. The ad-vancing front of this lesion, as seen after imbibitionwith quinoline, extended a further 100 /^m approach-ing the enamel-dentin junction but not reaching it.This lesion too has a mineral loss in excess of 25 per-cent and yet there was no radiographic evidence of thelesion on the bitewing radiograph.

Figure 5 shows a pair of premolar teeth used in theexperiments. The bitewing radiograph taken at thecompletion of the experiment (Figure 5a) shows threeproximal areas'of radiolucency. The two proximal sur-faces in contact each show a small radiolucency whichappears to be confined to the outer half of the enamel.The diagram in Figure 5b shows that it is these twoapproximal lesions that are to be examined in moredetail. Figure 5c shows a photograph of the respective

Figure 5a (Top). Bitewing radiograph of a pair of premolar teethtaken after the formation of artificial caries-like lesions. Radiolucentregions can be seen on both the mesial and distal proximal surfaces ofthe larger premolar tooth whereas its neighbor shows a radiolucentlesion on the mesial surface only. 5b (Line drawing). Diagram show-ing the areas of interest to be examined in more detail with this pairof teeth. These are the lesions contained within the two surfaces incontact. 5c (Teeth on fabric). This shows the macroscopic appear-ance of the two "white spot" lesions after removing the varnish fromthe teeth. Both lesions are readily visible by naked eye. 5d (Lowerleft). This is a microradiograph taken from a longitudinal ground sec-tion of the lesion on the mesial surface of the small premolar tooth.The body of the lesion is seen to have penetrated into the dentin andthe enamel has been demineralized considerably. The radiographicevidence of the lesion showed it to be limited to the outer half of theenamel thickness. 5e (Lower right). Microradiograph of the lesionon the distal surface of the large premolar tooth demonstrating thepresence of an extensive lesion. This lesion too has penetrated intoand demineralized the dentin. This lesion appeared to be confined tothe outer half of the depth of the enamel on the bitewing radiograph.

418 INTERPROXIMAL LESIONS: Silverstone

mesial and distal surfaces of the two teeth illustratingwell marked "white spot" lesions. Both lesions have awhite opaque border zone with a more darkly stainedinternal area. Figures 5d and 5e show microra-diographs taken of longitudinal ground sections fromthese lesions. In both cases the enamel has been

6a. Diagram to show the correlation between the macro-icopic appearance of a proximal surface of a premolar tooth and itsippearance on a bitewing radiograph.

figure 6b. Macroscopic appearance of the mesial surface of a man-libular first premolar tooth showing the appearance of an artificial'white spot" lesion. The varnish has been removed from the crown so;hat the lesion is seen in contrast to the sound enamel.

Figure 6c. Microradiograph of the same premolar tooth showing nojvidence of radiolucency on the mesial surface containing the lesionseen in b.

Figure 6d. Microradiograph showing the mesial surface of theongitudinal ground section taken from the premolar tooth. An exten-sive lesion can be seen in which the body of the lesion has penetratedto a depth of 700 /im. In spite of the lesion extending through three-quarters of the enamel depth, with a considerable degree of deminer-ilization, there is no evidence of this lesion on the bitewing ra-diograph. Because it has been possible to vary radiographic parame-ters, it is doubtful whether a clinical bitewing radiograph could ac-complish this degree of "sensitivity."

demineralized extensively and both lesions extend intothe dentin, showing demineralization to a depth of ap-proximately 300 ̂ m in the dentin. Figure 6 shows apremolar tooth from a further experiment in this se-ries. The diagram in Figure 6a orientates the toothsurfaces as seen on macroscopic examination (Figure6b) and by bitewing radiography (Figure 6c).Macroscopically, the "white spot" lesion can be seenvery clearly and there is no difficulty identifying itsperiphery. However, there is no evidence of radiolu-cency of this mesial surface on the bitewing ra-diograph. The microradiograph of the same lesiontaken from a longitudinal ground section (Figure 6d)

.shows a well-defined lesion extending approximately700 ^m into the enamel. The microradiograph showsonly the advancing front of the body of the lesion,which is the region demonstrating the greatest degreeof damage within the lesion. Its true advancing frontis approximately 50 fim deep to this region, consistingof histological zones 1 and 2, the translucent zone andthe dark zone.

DiscussionThis study has shown quite clearly that bitewing

radiographic examination of teeth in proximal contactis a relatively insensitive technique for the diagnosisof intact-surface carious lesions. When a lesion is firstdetected on a bitewing radiograph, appearing to belimited to the outer enamel, the lesion has, in reality,already penetrated several hundred micrometers intothe dentin. Direct vision of the relevant cleaned anddried tooth surface by eye clearly identifies themacroscopic area as a "white spot" lesion. Since a

number of parameters were varied in the radiographictechnique used in this study, and since no soft tissuesimulator was employed in the experiments describedin this report, the radiographs must be regarded as su-perior with respect to sensitivity relative to thosetaken under standard clinical conditions. Thus, it maybe concluded that the detection of a radiolucency onthe proximal surface of a tooth in a bitewing ra-diograph implies that the lesion has alreadypenetrated into the underlying dentin.

This study has also demonstrated that a surface

PEDIATRIC DENTISTRY: Volume 3, Special Issue 2 419

appearing caries-free on a bitewing radiograph canalso have an extensive lesion present. Such lesionsmay have penetrated two-thirds of the depth of theenamel and have greater than 25 percent of mineralloss. Although such lesions are not detected by the ra-diographic technique, they are readily visible as"white spot" lesions if the cleaned and dried surface isexamined by direct vision. While this is possible clini-cally when there is no adjacent tooth present, satisfac-tory macroscopic examination is not possible with nor-mal proximal contact.

The teeth used in these experiments were from thepermanent dentition. How can these results be extra-polated to teeth in the primary dentition? Recentstudies by Harris and Silverstone" comparing rates ofadvance of artificial lesions through primary and per-manent enamel have shown a faster rate of attack inprimary enamel. Progression in primary enamel wasapproximately 20 percent faster than in permanentenamel under identical conditions of attack. In addi-tion, since primary enamel is only about one-half ofthe thickness of permanent enamel, a lesion has totravel a much shorter distance to reach the dentin.With respect to the clinical diagnosis of interproximalcaries, it is more difficult to detect caries occurring be-tween primary molars since their morphology is suchthat flat contact areas exist compared to contact"points" in the permanent dentition. These factorshighlight the difficulties associated with early diag-nosis of interproximal caries in primary molars.

Figure 7 diagrammatically shows the size of a car-ious lesion when viewed by different techniques. Inthe upper three diagrams, the lesion is seen to pene-trate about two-thirds of the depth of the enamelwhen examined histologically. When the same longitu-dinal section is examined by microradiography, the le-sion appears smaller since only the body of the lesionis detected by this technique. Thus, the advancingfront of the lesion seen on a microradiograph coincideswith the deep edge of the body region. Histologically,both the dark zone and the translucent zone are seendeep to the body of the lesion. The third diagramshows the results of bitewing radiography. With a le-sion of this size, no radiolucency will be detected onthe radiograph and such a surface will be diagnosedas caries-free. The lower series of three diagrams showa more extensive lesion. Histologically the lesion haspenetrated into the dentin. Microradiography showsthe lesion to be limited to the enamel whereas bite-wing radiography indicates that the lesion is confinedto the outer half of the enamel.

The in vitro technique described here appears to bea very useful model system since it is possible to corre-late the true size of a lesion with its appearance whenexamined by other techniques. The use of The Silver-stone-Taylor Hard Tissue Microtome to remove very

HISTOLOGY BITE-WINGMICRORADIOGRAPHYRADIOGRAPHY

Figure 7. Diagram to demonstrate the size of an enamellesion as seen by different techniques. The most sensitive isexamination by optical methods, preferably polarized lightmicroscopy, using quinoline as a mounting medium. In thismanner, both the translucent zone (Zone 1) and the darkzone (Zone 2) can be seen, positioned in advance of the bodyof the lesion. The next sensitive is the use of microradiogra-phy which demonstrates the depth of the body of the lesion.This is comparable to examining the lesion in water andviewing the section by optical methods. The least sensitive isthe use of bitewing radiography. In the upper lesion, therewould be no evidence of a lesion using bite~ring radiography.In the lower more extensive lesion, t:he bitewing ra-diographic appearance indicates a lesion ]~sitioned in theouter half of the enamel whereas, in fact, the lesion haspenetrated into the dentin.

thin undermineralized sections has m~my advantagesover other sectioning machines. With conventionalsectioning machines a relatively thick section is re-moved from the tooth crown. In addition to the sec-tion being thick, the amount of tissue lost either sideof the section is also large due to the thickness of thecutting disc and the vibration experienced at its pe-riphery. Thus, it is often only possible to obtain asingle section from a small white spot :lesion. The truedeep edge of the advancing front of the cone-shapedlesion may actually be represented on the section.More likely however, the true advancing front may belost due to the blade passing through this region andeliminating tissue over a width of about 200 pm.Thus,a lesion appearing histologically to have penetratedtwo-thirds of the depth of the enamel :might in realityhave penetrated well into the dentin.

With the hard tissue microtome used in these stud-ies it is possible to remove either a single section ofabout 80 ftm in thickness or serial sections. It is possi-ble to cut about ten serial sections from a single whitespot lesion and examine them histologically without

420 INTERPROXIMAL LESIONS: Silverstone

the necessity for grinding the section in order toreduce its thickness. Examination of a lesion seriallyin this manner will show the true depth of the lesion.Thus, it is important to bear such technical considera-tions in mind if the true extent of a lesion is to be de-termined. It is suggested that this in vitro model sys-tem could be used to test the sensitivity of new ra-diographic systems (e.g., xeroradiography) or newdevelopments in film type or developing techniques.This model system will allow the correlation of lesionsize by the various examining procedures and will alsoprovide a direct comparison between conventional andnew radiographic techniques.

Since the lesion is always more extensive relative toits radiographic appearance, does this imply that theclinician should restore the relevant surface as soon asradiolucencies are detected? The answer is emphati-cally no. Dental caries is not a simple process of con-tinuing demineralization. The production of a lesion isthe result of a dynamic series of events in whichphases of remineralization alternate with phases ofdemineralization. Many clinicians have experiencedthe phenomenon of radiographic reversals. This wasrecorded as early ago as 1938," and since then manyworkers have recorded reversals in diagnosis wherebysmall lesions detected clinically or by radiography ap-parently have disappeared when examined at a laterdate using identical criteria.4

Of the four classical histological zones of enamelcaries, two of them are due to remineralization phe-nomena as shown by Silverstone.121' These two zones,the surface zone (zone 4) and the dark zone (zone 2),are narrow bands occuring at the surface of the lesionand at its advancing front. When such lesions are ex-posed to synthetic calcifying fluids in vitro, a muchgreater degree of remineralization occurs15 and, de-pending on the type of calcifying fluid employed, thelesion can be remineralized throughout its entiredepth." An example of such an experiment can be seen

in Figures 8a and 8b. This does not imply that the le-sion disappears since it is still recognizably differentfrom sound enamel by histological and ultrastructuralexamination. Recent studies have shown that afterremineralization of natural and artificial lesions invitro, there is a significant increase in diameter of theindividual crystals, thousands of which make up eachsingle prism. This increase in crystal diameter, whichcan be 2-4 times greater than that found in the soundenamel," reduces significantly the rate of lesionprogression.18 The presence of fluoride ions is essentialin the remineralization mechanism and recent workhas indicated that only low levels appear to be neces-

This author believes that one of the main mechan-isms whereby fluoride acts in caries prevention (if notthe main mechanism) is in promoting remineraliza-tion. It has long been known that partially deminer-alized enamel takes up fluoride preferentially relativeto sound enamel. Therefore, small lesions in approxi-mal regions, not diagnosed by conventional techniquesof clinical examination and radiography (as shown inthis study), are able to take up significant amounts offluoride, acting as fluoride-ion reservoirs. When condi-tions favoring demineralization occur, fluoride is re-leased in addition to calcium and phosphate ions.Thus, remineralization occurs and mineral is precipi-tated back into the lesion. This is the reason whysome lesions never progress to the stage where theyare diagnosed by conventional techniques.

Silverstone21 has shown recently that in order forthe submicroscopic crystals in enamel to increase insize relative to those of sound enamel, it is first neces-sary that the region is partially demineralized. Thus,remineralization can only occur after a bout ofdemineralization. Therefore, it might be necessary forall proximal surfaces to become carious at the his-tological level so that they can benefit from reminer-alization which, in turn, will give the region a degree

Figure 8a. Longitudi-nal ground section show-ing a lesion which haspenetrated the full en-amel thickness (x50).This section is examinedin water with the polariz-ing microscope. The adja-cent half of the lesionwas exposed to a syn-thetic calcifying fluid invitro (left). Figure 8b. (Right) After exposure to the calcifying fluid the lesion shows a significant degree of

mineralization. This section is examined in an identical manner to the control seen in Figure 8a.The size of the body of the lesion has been reduced dramatically. These results were accomplishedby the addition of 0.05 mM fluoride ions (1 ppm) into the synthetic calcifying fluid.

PEDIATRIC DENTISTRY: Volume 3, Special Issue 2 421

of resistance towards lesion progression. Since smalllesions cannot be diagnosed, their presence remainsundisclosed unless they progress to the stage wherethey are detected by conventional means. The factthat many "caries-free" proximal surfaces may con-taln small lesions is highlighted by the fact that thisauthor, in collecting small natural lesions for his re-search over many years, usually obtains them. by sec-tioning teeth which appear caries-free proximally evenon macroscopic examination.

The phenomenon of remineralization is emphasizedin this manuscript in an effort to prevent the well-meaning clinician from attempting to restore a toothbecause there is a small lesion indicated on a bitewingradiograph. A restorative approach is indicated onlywhen there is definite radiographic evidence of lesionprogression relative to a previous radiograph. Hence,the use of bitewing radiographs is an essential part ofclinical diagnosis, since, in addition to the detection ofinterproximal lesions, they should also form the base-line from which lesion progression can be judged. Nat-urally it is essential that the clinician appreciates thetrue extent of a lesion relative to the size it may ap-pear to be at when examined by the relatively insensi-tive diagnostic techniques available. However, realiz-ing the extent of a lesion, or even the possibility thatlesions exist even if they cannot be diagnosed, shouldin itself encourage the use of a caries-preventiveapproach. Thus, primary prevention at the clinicallevel may well be secondary prevention at the his-tological level.

The use of fluoride is important in enhancingremineralization although it does not appear to benecessary to use high concentrations. Recent findingssupport the frequent Supply of low concentrations offluoride rather than the infrequent application of veryhigh concentrations. The old maxim of "more is bet-ter" does not apply with respect to fluoride levels inenamel and caries susceptibility, as has been thoughtfor many years. Since it can take up to three or fouryears for a smooth surface lesion to progress to thestage where the dentin is invaded, there is adequatetime to intercept the carious process. By employingsuitable preventive methods,~ lesions can be success-fully remineralized such that they never progress tothe stage where they are diagnosed. Hence, such sur-faces will remain "caries-free" at the clinical and ra-diographic levels of diagnosis.

I would like to express my gratitude to Patty M~ Morgando, De-partment of 0ral Pathology and Diagnosis, University of Iowa Den-tal School, for carrying out the bitewing radiography and to MaryJ. Featheratone, Division of Cariology, for technical a~d~mce.

Dr. Silverstone is professor and head, division of cariology, DowsInstitute for Dental Research, and professor of pedodontics, Collegeof Dentistry, University of Iowa, Iowa City, Iowa 52242. Requestsfor reprints should be sent to him.

References

1. Marthaler, T. M. and Germann, M. Radiographic and visual ap-pearance of small smooth surface caries les~ons studied on ex-tracted teeth. Caries Res 4:224, 1970.

2. Leijon, G. Initial approximal primarkaries i rontgenbilden DelII. Svensk Tandlak T 6:239, 1969a.

3. Leijon, G. Initial appro:dmal primarkaries i rontgenbilden Del I.Sveusk Tandlak T 62:227, 1969b.

4. Backer Dirks, O. Posteruptive changes in dental enamel. J dentRes 45:503, 1966.

.5. Darling, A. I. The pathology and prevention of caries. Br Dent J107:287, 1959.

6. Gwinnett, A. J. A comparison of proximal carious lesions a~ seenby clinical radiography, contact microradiography, and fight mi-croecopy. JADA 83:1078, 1971.

7. Bucholz, R. E.Histologic-radiographic relation of proximal ~ur-face carious lesions. J Prey Dent 4:23, 1977.

8. Hurlburt, C. E. and Wuehrmann, A. H. Comparison of inter-proximal carious lesion detection in panoramic and standard in-traoral radiography. JADA 93:1154, 1976.

9. Silverstone, L. M. The primary translucent ~me of enamel carie~and of artificial carie~like lesions. Br Dent J 120:461, 1966.

10.Silverstene, L. M. Observations on the dark zonein early enamelcaries and in artificial caries-like legions. Caries Res 1:261, 1967.

11.Sflverstone, L. M. and Taylor, R. Preparation of thin, un-demineralized, unembedded, ~ections of human enamel: The Sil-verstone, Taylor hard ti~ue microtome. J Dent Res 60(SpecialIesue A.):2, 1981.

12.Silverstone, L. M. The structure of carious enamel, including theearly lesion. In: Oral Sciences Reviews, No. 3 Dental Enamel(Edited by Melcher, A. H. and Zarb, G. A.) pp 100-160. Munks-gaard, Copenhagen, 1973.

13.Harris, A. D. and Silverstone, L. M. Histological .features ofsound human deciduous enamel and lesions produced in vitro. JDent Res 60(Special issue A):815, 1981.

14.Anderson, B. G. Clinical study of arresting dental caries. J DentRes 17:443, 1938.

15~Silverstone, L. M. Remineralization phenomena. In: CariostaticMechanisms of Fluoride. (Edited by W. E. Brown and K. G.Konig). Caries Rea ll(Supp]. 1):59, 1977.

16.Silverstone, L. M., Wefel, J. S., Zimmerman, B. F., Clarkson, B.H., and Featherstone, M. J. Ren~nerallzation of natural and ar-tificial lesions in human dental enamel in vi~o: the effect of cal-cium concentration of the calcifying fluid. Caries Res 15:138,1981.

17.Silverstone, L. M. and Wefel, J. S. The effect of remineralizationon artificial caries-like lesions and their crystal content. In: Bi-logical Mineralization: Edited by G. H. Nancollas. Special Issue.J Crystal Growth 53:148, 1981.

18.Silverstone, L. M. and Featherstone, M. J. The effect of differentremineralisation regimens on lesion progression/n vitro. CariesRes 15:198(59), 1981.

19.Silverstone, L. M. The role of fluorides in remineralization ofenamel. In: Changing Perspect~’ves in Nutrition and Can’es Re-search. (Edited by M. C. Alfano) pp 38-41. American Academyof Pedodon~Acs Monograph, Medcom, Inc., New York, 1979.

20. Featherstone, M. J, Silverstene, L. M., Wefel, J. S., and Clark~son, B. H. The effect on remineralization in vitro of fluoride inthe calcifying fluid. J Dent Res 59(Special Issue A):62, 1980.

21. Silverstone, L. M. Alterations in crystal diameters in humanenamel after demineralization and reminersJization. Caries Res1981 (In pres~).

22. Silverstone, L. M. t~event~ve Den~, Update Books Ltd,London and Boston, p 168, 1978.

422 INTERPROXIMAL LEsIoNS: Silverstone