Efficiency of different polyacrylic acid concentrations on the smear layer, after ART technique, by Scanning Electron Microscopy (SEM).
Abstract: AIM: To assess the efficiency of different polyacrylic acid concentrations on the removal of the smear layer after caries removal with hand and rotary instruments in affected dentine of primary teeth. STUDY DESIGN: In vitro study. METHODS: Six exfoliated primary molars with carious lesions were divided into two groups for caries removal: (1) hand instrument or (2) low speed bur. Each tooth was cut into four pieces. One piece assigned as control surface and the other three surfaces were actively treated with either 40% Fuji IXGP Liquid (GC America), or 40% Fuji IXGP Liquid diluted with water, and 25% Ketac Molar[TM] Conditioner (3M-ESPE). Surfaces were prepared for scanning electron microscopy (SEM). All images were submitted to an analysis by an experienced SEM professional, regarding presence or absence of smear layer and dentinal demineralization pattern. Chi-squared test was carried out (5% significance). RESULTS: There was no difference concerning the presence of a smear layer in relation to the method of caries removal, and 40% Fuji IXGP diluted with water causes a higher demineralization when compared with the control group of teeth (p=0.01). CONCLUSION: Treatments with polyacrylic acid are indicated prior to glass ionomer cement application in primary teeth.

Key words: Scanning electron microscopy, glass ionomer cements, primary teeth. Paediatric Dentistry
Article Type: Report
Subject: Dental caries (Care and treatment)
Electron microscopy (Usage)
Polyacrylamide (Usage)
Authors: Raggio, D.P.
Sonego, F.G.
Camargo, L.B.
Marquezan, M.
Imparato, J.C.
Pub Date: 10/01/2010
Publication: Name: European Archives of Paediatric Dentistry Publisher: European Academy of Paediatric Dentistry Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2010 European Academy of Paediatric Dentistry ISSN: 1818-6300
Issue: Date: Oct, 2010 Source Volume: 11 Source Issue: 5
Geographic: Geographic Scope: Brazil Geographic Code: 3BRAZ Brazil
Accession Number: 276898053
Full Text: Introduction

During the past few decades, Restorative Dentistry underwent many conceptual transformations. What used to be a standard procedure, such as complete caries removal and extension for preventive during cavity preparation, as proposed by Black [Kidd 2004], has now changed due to the use of adhesive restorative materials. This shift in philosophy is focused on carious tissue removal. Nowadays there is no need for a classic cavity preparation, as adhesive materials can be maintained inside the cavity by bonding properties.

Recent studies have focused on partial caries removal, consisting of removal of the outer infected dentine, which has a greater number of microorganisms and cannot be remineralised, because collagen fibers are disrupted. Therefore, the next layer of affected dentine, which has a lower number of microorganisms, but where the collagen fibers are intact, is left in the cavity as it can be repaired through remineralisation [Fusayama, 1979; Massara et al., 2002].

During the 1980s, the Atraumatic Restorative Treatment (ART) was developed in Tanzania and incorporated in clinical practice during the early 1990s. ART is one procedure based on a minimal intervention concept, which adopts the partial caries removal philosophy as an alternative treatment [Frencken et al., 1994; Ercan et al., 2009]. Although the technique was developed for permanent teeth, nowadays there are some recent studies reporting the use of ART on primary teeth. As they have different histology and composition compared with permanent teeth [Sumikawa et al., 1999], more research is indicated on the adhesive ability of ART materials on primary teeth.

The restorative material of choice for ART is a high viscous glass ionomer cement (GIC), due to its biocompatibility, chemical setting reaction, adhesion and fluoride releasing properties [Gaskin et al., 2007; Bonifacio et al., 2009]. There are many discrepancies between manufacturers' instructions in relation to handling and use of GIC. Some suggest that dentine surfaces should be conditioned with polyacrylic acid, prior to cement placing [El-Askary et al., 2008; Hajizadeh et al., 2009], while others, such as the World Health Organization (WHO), recommend the dilution of the acid with water in order to remove the dentine smear layer [Frencken et al., 1997].

The smear layer, when present on the surface of the dentine, may influence the adhesion of restorative materials [Meryon et al., 1987]. Moreover, it may be argued as to whether a smear layer is actually formed when hand instruments are used. In addition, the number of published papers on the use of polyacrylic acid on affected dentine is limited

Because of the above arguments, the aim of this study was to assess the efficiency of different polyacrylic acid concentrations, by SEM, on smear layer removal in primary teeth.

Material and Methods

Sample selection. Six primary human primary teeth were selected using the following criteria that all teeth had to have an occlusal caries lesion involving up to two thirds of the dentine, verified using x-rays. The exclusions criteria were: carious lesions only in enamel or reaching the pulp cavity, no evidence of a crown fracture, no internal crown resorption or any other condition which would affect inclusion in the study.

Sample preparation. The teeth were cleaned with pumice slurry (SS White, Rio de Janeiro, Brazil) using a brush in a low speed rotary motor, for 15 secs, and then air-dried for 5 secs. Later, they were randomly assigned into two groups for partial removal of the carious dentine. The infected dentine was removed as it came out in scales or chips, indicating that affected dentine had been left in the cavity [Tomes, 1968; Massara et al., 2002]. In the first group (G1), carious dentine was manually removed using an excavator, and in the second group (G2), using low speed rotary motor. Teeth were then sectioned into four pieces, through the middle of the cavity, in the mesial-distal and buccal-lingual directions. This was made using a double-surfaced diamond disk (0.20X22mm) (BesQual-USA) in a water cooled low speed saw.

Immediately after cutting, the surfaces were washed with distilled water and dried using air from a syringe. Three of the surfaces were treated for 15 seconds using: Fuji IXGP liquid at 40% (GC America inc. Chicago), the Fuji IXGP liquid at 40% diluted in a 1:1 ratio with water, or the Ketac Molar[TM] Conditioner at 25% (3M-ESPE[TM], USA). The remaining surface was not treated and served as the control. Subsequently, the surfaces were washed with water, air-dried and separately placed into flasks containing 2% gluteraldehyde and a phosphate buffer. Then, the surfaces were dehydrated using ethanol in increasing concentrations and immersed in hexamethyldisilazane for 10 minutes at room temperature. After dehydration, the surfaces were placed into aluminum stubs and covered with gold in a sputtering process (Balzers Union FL 9646- Liechtenstein) at 10mA for 1 minute. The SEM, model LEO430i [version V2.04 / Cambridge--England (Cooperation Zeiss--Leica)], was regulated for 20KV with a working distance of approximately 20 to 30 mm with augmentations of 1,000X to 10,000X.

Scanning electron microscopy. The images were subjected to a descriptive and quantitative analysis by a trained professional who was blinded regarding the groups (MM). The examiner assessed the presence or absence of any smear layer, exposition of collagen fibers, peritubular and intertubular dentine demineralization with a scale developed for this study. SPSS, version 13.0, was used for the statistics (Fisher's Exact Test and Chi-squared test, p<0.05).


Descriptive Analysis. The first set of SEM figures show the surface of the affected dentine that was subjected to partial caries removal using the manual instrument G1 (A) and round bur G2 (B). As it was not subjected to any kind of smear layer removal, it served as a control. The presence of smear layer (indicated by a star), unorganised tissue, collagen fibers (indicated by an arrow) and the reduced presence of bacteria can be observed (Figure 1).


Figure 2 shows the surface when etched for 15 seconds using polyacrylic acid at 40% (Fuji XI liquid part, GC America inc., Chicago, USA), and partial caries removal carried out using hand instrument or round bur in low speed rotary motor. There is little peritubular and intertubular demineralization (indicated by a circle), presence of collagen fibers (arrow) and residues of smear layer (star) were all observed (Figs 2A). In Figure 2B, it was observed that the smear layer was removed, no collagen fibers were seen, and peritubular and intertubular demineralization was detected with widened tubule orifices (circle).


When affected dentine was etched using the Fuji IX liquid diluted in water, it was observed that the orifices of the dentinal tubules were widened (arrow). This was due to peritubular and intertubular demineralization. Presence of collagen fibers (arrow) and the absence of smear layer were also observed (Fig 3(A)). In Figure 3(B), a remaining smear layer (star) and the presence of peritubular and intertubular demineralization (circle) were seen.

The images of the affected dentine treated for 15 seconds with Ketac Molar[TM] Conditioner (3M[TM] ESPE, USA) at 25% showed the presence of a smear layer (star), intertubular demineralization (circle) and collagen fibers (arrow) (Figure 4A ad B). In Figure 4B, little demineralization of the dentine surface was observed.



Statistical analysis. When the smear layer formation was compared after using the different methods of caries removal, no difference was observed between both methods (Fisher Exact test, p=1.00). After using a Chi-squared test, the use of different acids to clean the dentine showed no influence on the presence of smear layer (p=0.49). In addition, the type of acid did not influence the exposition of collagen fibers (p=0.10), nor the demineralization of peritubular dentine (p=0.05). The acid treatment, however, did influence the intertubular demineralization (p=0.01) and the widening of the tubule orifices (p=0.01).

It should be noted, however, that Fuji IXGP at 40% diluted in a drop of water, as recommended by WHO, created greater intertubular demineralization when compared with the control, un-etched, surface (p=0.01).


Comparing dentine from primary and permanent teeth, variations in depth, permeability and hardness are found. Because of these differences the clinical treatment for primary teeth should be different [Meryon et al., 1987; Sumikawa et al., 1999]. Bond strength differences between primary and permanent dentine are due to morphogenesis.

One other important factor that may affect bonding of dental materials to dentine is the age of a tooth. Older teeth usually have obstructed dentine tubules due to crystal deposits, therefore becoming less prone to acid etching. In the present study, age of teeth must be carefully considered when analyzing the results. Only exfoliated primary teeth were included in this study, which means that they were old in terms of primary molars' natural age span in the mouth. This may suggest that the kind of acid treatment used in this experiment could have different demineralization pattern if applied to younger teeth.

When dentine is removed during cavity preparation, either with rotary or manual instruments, mineralized matrix is lost and debris from the preparation is left behind. This debris is the smear layer [Pashley, 1984; Gwinnett, 1984]. This is in accordance with the results presented herein, as there was no difference (p=1.00) of smear layer formation between low speed bur or hand instruments.

GICs have a physical-chemical bonding to dentine, providing a cariostatic effect and thoroughly sealing the cavity [Kidd, 1978; Aboush, 1986]. However, in order to achieve better bonding, it is desirable that a tooth surface is clean, without a thick smear layer. Bonding occurs even when the tooth surface is not cleaned, but it is significantly strengthened when cleaning is carried out prior to GIC application [Kidd, 1978; Powis, 1982; Aboush, 1986]. For dentine surface cleaning prior to GIC application, dentists are advised to use one of the available cleaning solutions. Polyacrilic acid is indicated [Hajizadeh et al., 2009], as it has a decalcifying action and high molecular weight, which does not allow its infiltration into the dentinal tubules. This decreases the risk of further demineralization [Wilson and McLean, 1988].

The previous dilution of the polyacrilic acid in water, as recommended by World Health Organization manual, has not been described in detail. In the present study, before the dilution, each drop of the acid and water were weighed in an analytical balance, and later, the final concentration of the dilution was calculated to be around 23.5%. The Fuji IXGP dilution caused greater intertubular demineralization compared with the control group (p=0.01). This is probably due to the decreased molecular weight and viscosity of the acid, causing a greater penetrability into the dentine.

The concentration of an acid and how it is applied onto a surface, as well as the time for such application, all influence cleaning. In agreement to other studies [Long et al, 1986; Hewlett et al., 1991], our results show that a 15 sec. application was efficient in removing any smear layer. Also, the conditioning influenced intertubular demineralization (p=0.01) and widening of the tubule orifices (p=0.01), compared with the control group.

In addition, the type of dentine tissue onto which the acid is applied should also be analysed. Due to the demineralization caused by acid etching, greater care for the affected dentine is necessary, as this tissue already presents some mineral loss. Calcium is essential in the ion exchange between the tooth and the restorative material promoting the physical-chemical bond. The effect of phosphoric acid etching on primary teeth is lower, although the tubules also widen when dentine is etched [Hosoya, 1988].

Carious tissue removal using hand instrument or low speed bur does not differ in smear layer formation. Treatment of the affected dentine with pure (40% and 25%) or diluted (40% diluted in water) polyacrylic acid was efficient in smear layer removal, therefore such procedure is indicated prior to GIC cement application in primary teeth during ART.


Further studies should be carried out investigating the ideal polyacrylic acid concentration, and therefore, the acid dilution step during ART may be skipped. In vitro studies on the GIC bond strength to affected dentine, previously etched with either pure or diluted polyacrylic acid, should be carried out, in order to compare to the present study.


The present study was independently evaluated and approved by a Committee of Ethics in Research at the Sao Leopoldo Medical Dental Faculty.


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D.P. Raggio *, F.G. Sonego **, L.B. Camargo *, M. Marquezan **, * J.C. Imparato *,

Depts. of * Orthodontics and Paediatric Dentistry, Univesity of Sao Paulo, SP; ** Paediatric Densirty Sao Leopollo Medical Dental Faculty SP; ** Restorative dentistry, Federal University of Santa Maria, Sao Paulo, Brazil.

Postal address: Dr. D.P. Raggio, Av Lineu Prestes, 2227-05508-000 Sao Paulo SP, Brazil.

Email: danielar@usp.br
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