PEDIATRIC DENTISTRY/Copyright (~ 1979 by The AmericanAcademy of Pedodontics/Vol. 1, No. 4/Printed in U.S.A.

Acid Etching Patterns on Buccal Surfaces

of Permanent Teeth

Khadry A. Galil, D.D.S., D. Oral Surg., Ph.D.Gerald Z. Wright, D.D.S., M.S.D., F.R.C.D. (C)

AbstractRetention difficulties have been encountered whenbrackets are bonded to buccal tooth surfaces with resin.Crucial to these procedures is the quality of the enameletch. The purpose of this study was to investigate acidetching patterns on the buccal surfaces of human posteriorteeth, and to determine if mechanical pretreatment affectsacid etching patterns. One hundred human posterior teethwere prepared for study. The crowns were pumiced,sectioned mesiodistally with a Gillings and Bronwellsectioning machine, washed, and dried. The buccal sur-faces were etched for either 60 or 90 seconds with fivedifferent acids. An additional 25 specimens were pre-treated mechanically, prepared similarly, and were etchedfor 90 seconds. Using standard techniques, specimenswere examined with the scanning electron microscope.Regardless of etching time or acid type, 5 distinct etchingpatterns were observed with a recognizable geographicdistribution. Types 1, 2 and 3 etch patterns paralleled thefindings of Silverstone et al., but were mainly found in thecoronal and middle thirds of the buccal surfaces. Types 4and 5 etch patterns, which were porous and smoothrespectively, were mainly located in the cervical third ofthe buccal surfaces. Mechanical pretreatment by grindingproduced a more favorable etch pattern.

IntroductionRetention of dental resin materials is enhanced

greatly by pretreatment of the enamel surfaces withcertain inorganic acids or chelators. 1 The acid solu-tions act by partially decalcifying the enamel, creat-ing microirregularities on the surface of the teeth. Theprocedure, referred to as acid etching, has receivedmuch attention from investigators, since the qualityof the acid etch is a crucial factor in the retention ofmaterials.

Silverstone et al. ~ recently described and classifiedthree types of etching patterns. Type 1 had enamel

Accepted August 1, 1979

prism cores preferentially removed. Type 2 was thereverse pattern where the peripheral regions of theprisms were removed leaving relatively unaffectedprism cores. Type 3 had areas corresponding to bothTypes 1 and 9.. These observations were made usingsmooth surface and occlusal surface tooth areas.

The present study was initiated to determine whichacid treatments would yield the most consistently fa-vorable etching patterns on buccal tooth surfaces. Pre-liminary observations, however, revealed a deficiencyin the current classification of etching patterns. Ac-cordingly, the purpose of this paper is to describeetching patterns on the buccal enamel surfaces of hu-man teeth which were acid preconditioned and exam-ined with scanning electron microscopy. Failures havebeen encountered when direct bonding brackets arewired to buccal surfaces.3,4 Therefore, a second aimof the study was to determine if mechanical pretreat-ment (light grinding) of buccal surfaces modifiesetching patterns.

Methods and Materials

To investigate buccal surface etching patterns, 100human premolar and molar permanent teeth were col-lected and stored in formalin at -4°C. Specimenswere prepared by lightly polishing the crowns of theteeth with pumice and a soft bristle brush. Teeth weresectioned at the cemento-enamel iunction using aGillings and Bronwell sectioning machine, and theroots were discarded. The crowns of the teeth werecut on a mesiodistal line and the buccal surfaces wereretained for experiments. The buccal surfaces werewashed thoroughly in water and dried. Specimenswere acid etched individually for 60 or 90 seconds us-ing a sable brush (00). The five acids used were (a)37% phosphoric acid,* (b) 50% phosphoric acid,** (c)

* (a) Concise-brand Orthokit-3M

** (b) Caulk Solo Tach--L. D. Caulk

230

505 phosphoric acid,~ (d) 505 phosphoric acid buf-fered with 7g zinc oxide by weight,~ and (e) phosphoric acid (W/W) solution prepared in the lab-oratory. All etched surfaces were carefully rinsed withwater and dried with a clean air spray free from oilcontamination.

The study surfaces were mounted to aluminumstubs and a 200 A layer of gold palladium was evap-orated onto the enamel surface to prevent a chargebuild-up on the specimen during electron bombard-ment. Following preparation, specimens were exam-ined with an Hitachi HHS 2R scanning electron mic-roscope which was operated on an accelerating po-tential of 20 k.v. All specimens were scanned on thebuccal surfaces from occlusal to the cemento-enamelareas.

Using an additional 25 permanent teeth consistingof 10 molars, 10 premolars and five incisors, the effectsof grinding on buccal surfaces were studied. Speci-mens were prepared in the manner previously de-scribed. The right side of each buccal surface waslightly ground with a green stone. In the initial stagesof the experiment, the ground and unground sectionswere divided by a line of nail polish. This demarca-tion was found to be unnecessary, and was deleted asthe study progressed. For this portion of the experi-ment, etching was accomplished using 37g (W/W)H,PO4 solution applied for 90 seconds.

ResultsFive acids and two etching times were used to ex-

amine etching patterns. Each of the 10 study groupscontained 10 specimens; a realistic sample size whenconsidering the variable enamel quality between teethand between areas of the same tooth. Regardless ofthe types of acid used, the 90-second acid applicationyielded the most consistently favorable etch. The 60-second etching time allowed identification of the etch-ing patterns; however, these specimens containedmore area of unetched enamel.

Five etching patterns were distinguished on thebuccal surfaces. Figure 1 shows a typical Type 1 etch-ing pattern where prism cores were preferentially re-moved, leaving prism peripheries intact. The Type 2etching pattern is shown in Figure 2: the prism coresremain relatively intact while the prism peripheriesare demineralized selectively. Figure 3 exhibits a Type3 etching pattern, which is a mixture of Type 1 andType 2 configurations. A pitted enamel surface hasbeen classified as a Type 4 pattern, and is shown in

Caulk Auto Taeh-L. D. CaulkCaulk Nuva System for orthodontic braekets-L. D.Caulk

Figure 4. A Type 5 pattern is characterized in Figure5, which has a fiat, smooth surface after etching. Theetching patterns were observed in all acid groupsafter either 60 or 90 seconds of acid application.

An interesting finding was the distribution of theetching patterns shown in Table 1. Type 1 and Type2 etches predominated on the coronal areas of thebuccal surfaces. The Type 3 etch, a combination ofTypes 1 and 2, was primarily located in the middlethird. The Type 4 and 5 etches, which were less welldefined patterns, were observed mostly in the cervi-cal regions of the buccal surfaces.

The study sample contained some bicuspids re-moved for orthodontic purposes. It was observed thatthese younger teeth which often contained periky-mata and imbrication lines displayed a slightly dif-ferent etching pattern on the cervical regions. It wasobserved that the perikymata had a Type 1 patternand ,appeared to etch better than the imbrication lines,which exhibited a Type 4 pattern.

The mechanical pretreatment portion of the studyrevealed that grinding the enamel surface enhancedthe quality of the etch, (see Figure 6). Using highermagnification, the enamel ,surfaces displayedType 1 and 2 etching patterns over .entire :groundareas. Moreover, regions which etched as Type ~t or 5on the unground left side demonstrated on!ly ’Type 1and 9. patterns on the ground right side.

The amount of enamel removed by grinding wasmeasured in the ,range of 140-150 ~tm. At the ground-unground enamel junction, where grinding was shal-lower and less :uniform, the etching lacked uniformity.In these areas patches of Type ,~l ~and 5 etch patternswere evident.

DiscussionA significant finding of this study is the observa-

tion and description of 2 types of etching patterns notincluded in existing classifications. They were presentto varying extents in all specimens examined, regard-less of the acid treatment. Although the two patternsreferred to as ~T, ypes 4 and 5 have been observed in thepast, they appeared to have a random distribution andlittle importance was accorded to them. This studyfound them to have a more systematic distribution.Consequently, when examining etching patterns ofbuccal surface enamel, their existence merits consid-eration by both researchers and clinicians.

It has been traditional for the properties of prismcores and peripheries following acid treatment to pro-vide the basis for classification of etching patterns.This is the basis of classification of Silverstone et al.~

Types 1, 2 and 3 etching patterns are classified this

PEDIATRIC DENTISTRYVol. I, No. 4 231

Figure 1. Scanning electron micrograph showing Type 1 etch-ing pattern after applying phosphoric acid for 1 minute.(Magnification X 1750).

Figure 3. Scanning electron micrograph showing Type 3 etch-ing pattern after applying phosphoric acid for 1 minute.(Magnification X 1750).

Figure 2. Scanning electron micrograph showing Type 2 etch-ing pattern after applying phosphoric acid for 1 minute.(Magnification X 1750).

Figure 4. Scanning electron micrograph showing Type 4 etch-ing pattern after applying phosphoric acid for 1 minute.(Magnification X 1750).

way and are in agreement with previous observations.The Type 4 pattern differed. It displayed only a ran-dom distribution of depressions with no preferentialdestruction of either cores or peripheries. These pittedareas occasionally occurred in little patches over theenamel surface. As shown in Table 1, Type 4 etchingwas commonly found in the cervical areas and has adiminished frequency in the occlusal areas.

It is difficult to account for the findings of the Type4 etch pattern. The distribution suggests an underly-ing difference in enamel morphology. Ripa et al.

found a layer of prismless enamel on 70% of the perma-nent teeth they scanned.5 Gwinnett6 demonstratedthat etched prismless enamel displays no rod or prismpatterns. It is similar to the Type 4 etch pattern.Therefore, it is plausible that Type 4 etching may re-sult when regions of prismless enamel are present.

It is important to point out that most investigatorsare in agreement on the presence of prismless enamel,but they differ in opinion on its frequency and loca-tion.7'11 These studies were not limited to studyingthe buccal surfaces of human posterior teeth. It could

ENAMEL ETCHING232 Galil and Wright

TABLE 1. Distribution of Etching Typeson the Buccal Surfaces

Figure 5. Scanning electron micrograph showing Type 5 etch-ing pattern after applying phosphoric acid for 1 minute.(Magnification X 1750).

Figure 6. Scanning electron micrograph (low mag.) illustra-ting the difference between ground enamel (G) on the rightside and unground enamel (U) on the left side. 90 secondetching with phosphoric acid. (Magnification X 300).

be fallacious to extrapolate findings from one tootharea to another.

Similar to Type 4 patterns, Type 5 etching showsno evidence of prism outlines. Indeed, the regions ofenamel classified as Type 5 are extremely flat andsmooth, and they lack microirregularities for penetra-tion and retention of resins. The same type of patternwas noted by Wei in a S.E.M. study of acid etchingon fluoride treated teeth.12 Therefore, it is possiblethat Type 5 etching patterns occur on teeth which

% Frequency of Observation

Types ofEtch Pattern

12345

Coronal

75751055

LocationMiddle

2020802020

Cervical

55

107575

have previously received fluoride treatment or possrbly from patients who resided in high fluoride areas.The finding could account for the retention problemsencountered when clinicians attempt to etch and sealfluoride treated teeth. However, a Type 5 patternwould be expected over the entire enamel surface iffluoridation were responsible, and this study foundonly a scattered distribution of Type 5 areas in theocclusal region. Obviously, chemical analysis of teethsubject to Type 5 etching is required to resolve thisquestion.

Although the underlying causes of Types 4 and 5etching remain academically debatable, these etchingpatterns do exist. They may be responsible for someretention problems encountered in research and clin-ical practice. For these reasons, the authors of thispaper consider it essential that Type 4 and 5 etch pat-terns be included in future etch classifications.

The photomicrographs of the mechanically pre-treated specimens showed that removal of a thin layerof surface enamel leads to more consistently superioretching patterns for primary and permanent teeth. Itis suggested that grinding removes superficial areas ofprismless enamel, thus exposing underlying prismaticenamel that is more prone to acid etching.

The mechanical pretreatment effects differed fromthose of Brannstrom et al. who found little changewhen grinding with a diamond point or aluminum ox-ide disc.13 These authors, however, had not indicatedthe amount of superficial enamel removed. In thepresent study, the most consistently favorable etcheswere seen when 140 to 150 um of enamel were re-moved. The transitional areas, which had shallowerand uneven grinding, had less uniform etch patterns.Apparently, the amount of "buccal correction" neces-sary for optimum etching, particularly in the cervicalregion of buccal surfaces, should be established in fu-ture studies.

PEDIATRIC DENTISTRYVol. 1, No. 4 233

ConclusionsThis study examined the acid etching effects on the

buccal surfaces of human posterior teeth with scan-

ning electron microscopy. Based on the findings ofthis investigation, it was concluded that five etchingpatterns are present on the buccal surfaces of humanposterior teeth; the etching patterns appear to have asystematic geographic distribution; and mechanical

pretreatment by grinding enhances etching patternson buccal surface enamel.

Acknowledgments

The valuable technical assistance of Miss Pat Greenhorn isgratefully acknowledged.

This study was supported by the Ontario Ministry of Health,Grant No. PR 687-C.

References1. Buonocore, M. G.: "A Simple Method of Increasing the

Adhesion of Acrylic Filling Material to Enamel Surface,"] Dent Res, 34:849-853, December, 1955.

2. Silverstone, L. M., Saxton, C. A., Dogon, I. L., andFeierskov, O.: "Variation in Pattern of Acid Etching ofHuman Dental Enamel Examined by Scanning ElectronMicroscopy," Caries Res, 9:373-387, 1975.

3. Garn, N. W.: "Direct Bonding: A Clinical Study Using anUltraviolet Sensitive Adhesive System," Am ] Orthod,69:455-463, April, 1976.

4. Swaine, T. G. and Wright, G. Z.: "Direct Bonding Appliedto Space Maintenance," ]Dent Child, 43:401-405, Novem-ber-December, 1976.

5. Ripa, L. W., G~vinnett, A. J., and Buonecore, M. G. : "ThePrismless Outer Layer of Deciduous and PermanentEnamel," Arch Oral Biol, 11:41-48, January, 1966.

6. Gwinnett, A. J.: "Human Prismless Enamel and Its Iiaflu-ence on Sealant Penetration," Arch Oral Biol, 18:441-444,March, 1973.

7. Horsted, M., Fejerskov, O., Larsen, M. J. and Thylstrup,A.: "’The Structure of Surface Enamel with Special Refer-ence to Occlusal Surface of Primary and Permanent Teeth,"Caries Res 10:287-296, 1976.

8. Sheykholeslam, Z., Buonocore, M. G.: "Bonding of Resinsto Phosphoric Acid-Etched Enamel Surfaces of Permanentand Deciduous Teeth," ] Dent Res, 51:1572-1575, Novem-ber-December, 1972.

9. Eidehnan, E.: "The Structure of the Enamel in PrimaryTeeth: Practical Applications in Restorative Techniques,"] Dent Child, 43:172-1 6, May-June, 1976.

10. Theuns, H. M., and Greneveld, A.: "Polarizing Microscopyof Sound Enamel," Caries Res, 11:293-300, 1977.

11. Fuks, A. B., Eidelman, E., and Shapiro, J.: "Mechanicaland Acid Treatment of the Prismless Layer of PrimaryTeeth vs. Acid Etching Only: A S.E.M. Study," J DentChild, 44:222-2’25, May-June, 1978.

12. Wei, S. W.: "Effect of Topical Fluoride Solution onEnamel Surfaces as Studied by Scanning Electron Micro-scopy," Caries Res, 9:445-458, 1975.

13. Br~innstr6m, K., Nordenvall, K. J., and Malmgren, O.: "TheEffects of Various Pretreatment Methods of the Enamelin Bonding Procedures," Am ] Orthod, 74:522-530, 1978.

KHADRY A. GALIL is Associate Professor and memberof the Departments of Anatomy and Oral Surgery, TheUniversity of Western Ontario, Faculty of Dentistry,London, Ontario, Canada.

GERALD Z. WRIGHT is Professor and Chairman ofPedodontics, Department of Pediatric and CommunityDentistry, The University of Western Ontario, Facultyof Dentistry, London, Ontario, Canada.

Requests for reprints may be sent to Khadry A. Galil,Department of Oral Surgery, Faculty of Dentistry, TheUniversity of Western Ontario, London, Ontario, Can-ada N6A 5B7.

ENAMEL ETCHING234 Galil and Wright