OBSERVATIONS ON ETCHED ENAMEL IN NON-ERUPTED DECIDUOUS MOLARS: A SCANNING ELECTRON MICROSCOPIC STUDY

OBSERVAÇÕES EM ESMALTE CONDICIONADO DE MOLARES DECÍDUOS NÃO ERUPCIONADOS: ESTUDO AO MICROSCÓPIO ELETRÔNICO DE VARREDURA

OBSERVATIONS ON ETCHED ENAMEL IN NON-ERUPTED DECIDUOUS MOLARS:

A SCANNING ELECTRON MICROSCOPIC STUDY^*

OBSERVAÇÕES EM ESMALTE CONDICIONADO DE MOLARES DECÍDUOS NÃO ERUPCIONADOS: ESTUDO AO MICROSCÓPIO ELETRÔNICO DE VARREDURA

Marcelo FAVA^**

Ii-Sei WATANABE^***

Flávio FAVA DE MORAES^***

Luciane RIBEIRO DE REZENDE SUCASAS DA COSTA^****

FAVA, M. et al. Observations on etched enamel in non-erupted deciduous molars: a scanning electron microscopic study. Rev Odontol Univ São Paulo, v. 11, n. 3, p. 157-160, jul./set. 1997.

Under the scanning electron microscope, the characteristics of the buccal surface enamel of human non-erupted deciduous molars were evaluated after using 15, 30, and 45 seconds of phosphoric acid etching time. The teeth were extracted, kept in a 70% alcohol solution and later dehydrated and metallized for analysis with the scanning electron microscope JEOL, JSM-6.100. The in vitro experiment with 35% phosphoric acid revealed that there is a tendency of predominance of interprismatic enamel dissolution or type II pattern with 15 and 45 seconds etching time. The dissolution of the interprismatic enamel was more pronounced when an acid etching time of 45 seconds was used. The enamel surface demonstrated type I and type II patterns when acid etching time was 30 seconds.

UNITERMS: Dental enamel; Acid etching, dental; Microscopy, electron, scanning.

INTRODUCTION

The acid etching process promotes the formation of cavities of variable depths on the enamel surface. The etched enamel has been studied and classified according to patterns (SILVERSTONE et al.¹⁰, 1975; NATHANSON et al.⁶, 1982). There are also a great number of variables which may affect the obtained results, such as: tooth morphology, surface and type of tooth, method of application, and time and type of acid etching (NORDENVALL et al.⁷, 1980; REDFORD et al.⁸, 1986). One of the factors which could possibly interfere with the acid etching technique in deciduous teeth is the existence of "prismless" enamel which has been described by several authors (GWINNET⁴, 1973; TINANOFF; MUELLER¹¹, 1977; CARRASSI et al.¹, 1985; SEBELLI et al.⁹, 1993).

In the present study we have examined the surface of enamel of non-erupted deciduous molars, after treatment with phosphoric acid using different etching times, by means of a scanning electron microscope (SEM).

MATERIALS AND METHODS

Twenty non-erupted human deciduous molars having completely formed crowns were extracted from deceased children with ages varying from 12 to 18 months, whose autopsies were conducted at the obituary service of the School of Medicine, University of São Paulo. Then, all teeth were fractured in buccolingual sections using a vise.

Subsequently, the buccal surface of 15 teeth were conditioned with 35% phosphoric acid gel (Esticid® , Kulzer). The acid was applied with a brush for 15, 30 or 45 seconds (five teeth for each group) employing routine clinical procedures. Additionally, five teeth were selected for the control group. All these specimens were rinsed in distilled water and dehydrated in an increasing series of alcohols. After air drying, the specimens were mounted on metal stubs and coated with gold using a Balzers "Ions Sputter" SCD-040. The specimens were examined under the scanning electron microscope, JEOL, JSM-6.100, at 15 kV. A total of 90 selected scanning electronmicrographs were examined in three groups.

RESULTS

Scanning electron microscope observations of the buccal region of normal non-erupted deciduous molars showed a surface presenting some small round depressions (Figure 1).

Figure 1
- General view of the enamel surface of human normal non-erupted deciduous molar. Small round depressions are noted (arrows) (X4,500).

The acid conditioning of enamel surfaces using 35% phosphoric acid for different times (15, 30 or 45 seconds), promoted variable dissolution patterns. Based on the classification described by SILVERSTONE et al.¹⁰ (1975), two types of effects were observed (types I and II).

After fifteen seconds, the type II etching pattern was more prevalent (Figure 2). At high magnification, the SEM image showed details of the intact prism cores and loss of prism periphery (Figure 3).

Figure 2
- Shows type II etching pattern after 15 seconds of acid etching. The periphery of enamel prisms is dissolved (arrows) (X4,500).

Figure 3
- At high magnification, details of interprismatic enamel dissolution are showed after acid etching (arrows) (X9,000).

In general view, the enamel surface conditioned for 30 seconds showed type I pattern, which had lost essentially the prism cores. These characteristics are noted in some areas (Figure 4). In adjacent areas, the type II pattern was found showing etched interprismatic enamel (Figure 5).

Figure 4
-Shows type I etching pattern after 30 seconds of acid etching. The cores of the prism are dissolved (arrows) (X4,500).

Figure 5
- At high magnification, details of interprismatic enamel dissolution can be observed (arrows) (X9,000).

The buccal surface conditioned for 45 seconds revealed predominantly dissolution of the interprismatic substances (Figure 6). At high magnification, as in Figure 7, characteristics of type II patterns were clearly observed. The distribution of those structures are observed in three-dimensional SEM images.

Figure 6
- View of type II etching pattern after 45 seconds of acid etching. The periphery of enamel prisms is more pronounced tham in that after 15 second acid etching (arrows) (X4,500).

Figure 7
- At high magnification, interprismatic enamel dissolution can be noted more clearly in the 45 second acid etching (arrows) (X9,000).

DISCUSSION

Our results clearly reveal data on acid conditioning of human non-erupted deciduous molars, examined under the scanning electron microscope.

Acid conditioning of buccal enamel of non-erupted deciduous molars using 35% phosphoric acid gel for 15, 30 or 45 seconds showed type I and type II patterns as reported by SILVERSTONE et al.¹⁰ (1975).

Our results demonstrated that there was a tendency towards the predominance of interprismatic enamel dissolution or type II pattern (SILVERSTONE et al.¹⁰, 1975) when etching time was 15 and 45 seconds. HOSOYA⁵ (1991) observed that the type II pattern was the most prevalent in deciduous teeth, regardless of time employed, region etched, and depth of the enamel. However, the use of 10 and 20 seconds of acid etching may produce unsatisfactory alterations in some cases.

The results demonstrated that between 15 and 45 seconds of application the different characteristics are clearly observed. When 45 seconds time was used, etching promoted a more pronounced dissolution of the interprismatic enamel. REDFORD et al.⁸ (1986), GARCIA-GODOY; GWINNET³ (1991), HOSOYA⁵ (1991) confirmed that the acid induced patterns became more pronounced when the application time increased.

With 30 seconds acid etching time, the enamel surface demonstrated pattern type I in some areas and pattern type II in the adjacent areas. This great variation may be attributed to the fact that dental enamel does not present a specific conditioning pattern, varying from tooth to tooth, from surface to surface and in different areas of the same surface (SILVERSTONE et al.¹⁰, 1975; CARSTENSEN², 1992).

CONCLUSIONS

Based on our data we may conclude that:

1. The in vitro experiment with 35% phosphoric acid revealed that there is a tendency towards the predominance of interprismatic enamel dissolution or type II pattern with 15 and 45 seconds etching time.

2. The dissolution of interprismatic enamel is more pronounced when the 45 seconds acid etching time was used.

3. The enamel surface demonstrated pattern type I and type II when the 30 seconds acid etching time was used.

ACKNOWLEDGEMENT

We gratefully acknowledge the assistance of Mrs. Laura Fusaro in the preparation of the manuscript, and the Service of Obituary Verification of the School of Medicine of the University of São Paulo for providing the teeth used in this study. This work was supported by CNPq (Process 150033-94-0 (nv)).

FAVA, M. et al. Observações em esmalte condicionado de molares decíduos não erupcionados: estudo ao microscópio eletrônico de varredura. Rev Odontol Univ São Paulo, v. 11, n. 3, p. 157-160, jul./set. 1997.

No presente trabalho, empregando a técnica de microscopia eletrônica de varredura, foram estudadas as características do esmalte da superfície vestibular de molares decíduos humanos não erupcionados, avaliando-os após utilização de ácido fosfórico durante períodos de 15, 30 e 45 segundos. Os dentes foram extraídos e mantidos em solução de álcool a 70% e, posteriormente, desidratados e montados em bases metálicas, para análise em microscópio eletrônico de varredura JEOL, JSM-6.100. A experiência in vitro com ácido fosfórico a 35% revelou que há uma tendência de predominância de dissolução de esmalte interprismático, ou padrão tipo II, com 15 e 45 segundos de tempo de condicionamento. A dissolução do esmalte interprismático é mais pronunciada quando são utilizados 45 segundos de condicionamento ácido. A superfície do esmalte demonstrou padrões tipo I e tipo II no caso de condicionamento ácido de 30 segundos.

UNITERMOS: Esmalte dentário; Ataque ácido dentário; Microscopia eletrônica de varredura.

BIBLIOGRAPHIC REFERENCES

Recebido para publicação em 17/02/97

Aceito para publicação em 08/05/97

• ¹
  CARRASSI, A. et al Morfologia dello smalto e distribuzione dello strato aprismatico nei denti decidui. Dent Cadm, v. 54, n. 2, p. 51-59, Feb. 1986.
• ²
  CARSTENSEN, W. The effect of different phosphoric acid concentrations on surface enamel. Angle Orthod, v. 62, n. 1, p. 51-58, Spring 1992.
• ³
  GARCIA-GODOY, F.; GWINNETT, A. J. Effect of etching times and mechanical pretreatment on the enamel of primary teeth: a SEM study. Am J Dent, v. 4, n. 3, p. 115-118, June 1991.
• ⁴
  GWINNETT, A. J. Human prismless enamel and its influence on sealant penetration. Arch Oral Biol, v. 18, n. 3, p. 441-444, Mar. 1973.
• ⁵
  HOSOYA, Y. The effect of acid etching times on ground primary enamel. J Clin Pediatr Dent, v. 15, n. 3, p. 188-194, Winter 1991.
• ⁶
  NATHANSON, D. et al SEM of etching patterns in surface and subsurface enamel. J Pedod, v. 7, n. 1, p. 11-17, Fall 1982.
• ⁷
  NORDENVALL, K. J. et al Etching of deciduous teeth and young and old permanent teeth. A comparison between 15 and 60 seconds of etching. Am J Orthod, v. 78, n. 1, p. 99-108, July 1980.
• ⁸
  REDFORD, D. A. et al The effect of different etching times on the sealant bond strength, etch depth and pattern in primary teeth. Pediatr Dent, v. 8, n. 1, p. 11-15, Mar. 1986.
• ⁹
  SEBELLI, P. M. et al Sealant adhesion in primary teeth. In: ARGENTINE DIVISION ANNUAL MEETING, 15. Paraná, Oct. 26-31, 1982. Divisional Abstracts. J Dent Res, v. 72, n. 4, p. 659, Apr. 1993.
• ¹⁰
  SILVERSTONE, L. M. et al Variation in the pattern of acid etching of human dental enamel examined by scanning electron microscopy. Caries Res, v. 9, n. 5, p. 373-387, 1975.
• ¹¹
  TINANOFF, N.; MUELLER, B. Acid etch characteristics on prismless enamel. J Int Ass Dent Child, v. 8, n. 1, p. 17-21, July 1977.

*

Part of a post-doctorate research carried out at the School of Dentistry of the University of São Paulo, supported by CNPq (Process 150033-94-0 (nv))

**

Department of Pediatric Dentistry, School of Dentistry, State University of São Paulo (UNESP) - São José dos Campos - SP - Brazil.

***

Department of Anatomy and Histology, Institute of Biomedical Sciences, University of São Paulo (USP) - São Paulo - SP - Brazil.

****

Department of Pediatric Dentistry, School of Dentistry, Federal University of Goiás - GO - Brazil.

Publication Dates

• Publication in this collection
  11 Mar 1999
• Date of issue
  July 1997

History

• Accepted
  08 May 1997
• Received
  17 Feb 1997