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RPG. Revista de Pós-Graduação

versão impressa ISSN 0104-5695

RPG, Rev. pós-grad. vol.18 no.1 São Paulo Jan./Mar. 2011

 

ORIGINAL ARTICLE

 

Spectrophotometric evaluation of color changes of esthetic brackets stored in potentially staining solutions

 

Avaliação espectrofotométrica das alterações cromáticas de braquetes estéticos armazenados em soluções potencialmente corantes

 

 

Marcos Rogério de MendonçaI; Aubrey Fernando FabreII; Marcelo Coelho GoiattoIII; Osmar Aparecido CuoghiI; Lídia Pimenta MartinsII; Ana Caroline Gonçales VerriII

IAdjunct Professor, Department of Children´s and Community Dentistry, Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP) – Araçatuba/SP, Brazil
IIPostgraduate student, Department of Children´s and Community Dentistry, Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP) – Araçatuba/SP, Brazil
IIIAdjunct Professor, Department of Dental Materials and Prosthetic Dentistry, Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP) – Araçatuba/SP, Brazil

Correspondence

 

 


 

RESUMO

O objetivo deste estudo foi avaliar, in vitro, o comportamento cromático de braquetes estéticos armazenados em soluções potencialmente corantes. As amostras foram divididas em quatro grupos de acordo com a marca comercial e imersas em quatro soluções diferentes (água destilada, refrigerante à base de cola, café e enxaguatório bucal) a 37ºC, por 14 dias. As possíveis alterações de cor foram medidas de acordo com o sistema CIE L*a*b* por meio de um espectrofotômetro em cinco intervalos de tempo após armazenamento. A análise estatística foi conduzida usando ANOVA a 1%, testes de Tukey e decomposição das interações com nível de significância de 5%. As alterações de cores ocorreram conforme solução, tempo de armazenamento e marca dos braquetes. As maiores variações cromáticas foram observadas no G3, seguido por G2, G1/G4. Os braquetes estéticos não apresentam comportamento cromático estável e satisfatório.

Descritores: Cor. Braquetes ortodônticos. Espectrofotometria.


 

ABSTRACT

The purpose of this study was to evaluate, in vitro, the chromatic behavior of esthetic brackets stored in potentially staining solutions. The sample were divided into four groups according to the commercial brand and stored in four different solutions (distilled water, cola soda, coffee and mouthrinse) at 37°C for 14 days. Possible color changes measured according to the CIE L*a*b* color system with a spectrophotometer at five intervals of time after storage. The statistical analysis was carried out using ANOVA to 1%, Tukey's tests and decomposition of interactions with a significance level of 5%.The color changes were dependent on the solution, storage time and the brand of brackets. The largest color changes were observed in the G3, followed by G2, G1/G4. The esthetic brackets do not present satisfactory and stable chromatic behavior.

Descriptors: Color. Orthodontic brackets. Spectrophotometry.


 

 

INTRODUCTION

The increasing demand by the adult population42 for orthodontic treatment has led to the use of esthetic brackets14.The plastic brackets, developed in 196930, still present several problems, such as limited torque control3,36, excessive wear and structural fragility1,3, water absorption16, low bond strength18, high friction with orthodontic wires7, outstandingly high color instability13, and structural deformation53. Thereafter, the original composition was modified with the incorporation of glass fibers or ceramic particles into the polycarbonate polymer matrix, resulting in the so called "composite"36 brackets, as well as the development of new types of polymers. Nevertheless, these problems have not yet been completely resolved3,12,13,36.

In an attempt to eliminate the problems with polymeric accessories, ceramic brackets were developed in 19868,44, used in two forms: monocrystalline or polycrystalline17. The polycrystalline is more widely used, more opaque and presents less optical clarity9,44. However, there are still some limitations, such as staining9,24, frictional resistance8,9,15,17,44, friability2,39, abrasion of antagonist teeth47, and problems with removal27.

The color changes in esthetic brackets are of a multifactorial origin44. Discoloration of dental materials may be the result of intrinsic factors such as water absorption, incomplete polymerization of adhesives or resins, matrix composition of the material, content and size of reinforcement particles5,22,44, brand28, tone45, or extrinsic factors such as ingestion of food dyes containing caffeine (coffee, tea, colas), mouthrinse use, saliva29, nicotine33, lipsticks11,44, heat13, time and polymerization intensity21.

 

OBJECTIVE

Therefore, the objective of this study was to evaluate the color changes of esthetic brackets after storage in potentially staining solutions. The null hypothesis to be tested was that the esthetic brackets did not change color after contact with dye solutions.

 

MATERIAL AND METHODS

 

Brackets

For this study, 160 esthetic brackets for central incisors on the right side were used, of the Roth type, slot 0.022" x 0.028", of different brands (Table 1).

 

Solutions

Four different solutions were used: (1) distilled water; (2) cola soda (Coca-Cola®, produced by Spaipa, Marília, SP, Brazil); (3) soluble coffee (Nescafé®, produced by Nestlé of Brazil Ltda, Araras, SP, Brazil), prepared according to the manufacturer's recommendations; (4) mouthrinse containing alcohol (Listerine® Tartar Control, produced by Altana Pharma Ltda, Jaguariúna, SP, Brazil, Custom Johnson & Johnson Industrial Ltda).

 

Study groups

Four groups were formed with 40 brackets for group and ten brackets for solution (Table 1).

 

 

 

Storage

Each bracket was stored in a polypropylene microtube with cover, enumerated, and stored at 37°C. All solutions and microtubes were regularly renewed after every 24 hours of storage. The total storage period was 14 days.

 

Spectrophotometric analysis

The color change readings were made using a reflectance spectrophotometer (Un-Visible Spectrophotometer UV-2450®, manufactured by Shimadzu, Kyoto, Japan) with wavelength range 380-780 nm and standard illumination D654. To allow the standard positioning of the brackets during the reading, four individual polyvinyl chloride (PVC) matrices, black color were fabricated, one for each brand of bracket, with a standard fitting and precise positioning of the bracket-matrix set for later reading the bracket color (Figure 1). Before the readings, each bracket was washed by ultrasound for one minute, and properly dried on paper towels. The color changes to be calculated by the CIE L*a*b*system10, and the total color difference (ΔE*) was calculated by the following equation: ΔE* = [(ΔL*)² + (Δa*)² + (Δb*)²]½. The L* parameter corresponds to the value or degree of lightness or brightness and a*b* values of chroma, where +a* is red and -a* is green, +b* is yellow and -b* is blue.

 

 

 

Data collection

The color change reading was taken by means of the software attached to a computer with a previously established configuration, and the value of ΔE* was automatically obtained for each bracket in each experimental period, generating a mean ΔE* for each experimental time, bracket brand and solution. The experimental times were: T0 (before the initial immersion), T1 (1 day after the initial immersion), T3 (3 days), T7 (7 days), T10 (10 days) and T14 (14 days after immersion).

 

Measurement of pH change

The pH of the solutions was measured before and after 24 hours of initial immersion and storage in polypropylene microtubes (Table 2), using ion analyzer (Orion Research 720A, Orion, USA) coupled to a magnetic stirrer (NT 101, Nova Técnica, Piracicaba, SP, Brazil).

 

 

Statistical analysis

Statistical analysis was performed using the SAS System™ and Microsoft Excel® programs. According to the Kolmogorov-Smirnov test, data distribution was normal with p=0.0539. Next, an arcsine transformation was performed and the three-factor analysis of variance (brand, solution and time) was applied (Table 3). Since there were no significant differences between any of the sources of variation, the Tukey's test was applied and the decomposition of the interactions brand*solution*time was performed. The level of significance was 1% for analysis of variance and 5% for the decompositions.

 

 

RESULTS

The mean color change values and their standard deviations (sd) during the experiment are shown in Table 3. Tests were also performed for comparisons between brands, solutions and time (Tables 4 to 6).

 

Group 1

In the distilled water solution, when chronologically compared, ΔE* values were statistically significant. In the soda, the values from ΔE* showing a gradual increase over time, with statistically significant differences. Similarly, the brackets stored in coffee showed a gradual increase in the value of ΔE*, statistically significant. When stored in the mouthrinse, only the value of ΔE*3 was found to be statistically significant when compared with the other values. (Figure 2)

 

 

Group 2

In distilled water the values not showing statistically significant difference. In the soda, showed a gradual increase over time, with statistically significant difference. The brackets stored in coffee also showed a gradual increase in the value of ΔE* with over time, and were statistically significant. In the mouthrinse only the value of ΔE*7 was found to be statistically significant when compared with the other values. (Figure 3).

 

 

Group 3

For distilled water, statistically significant difference was found only between the values of ΔE*1. In the soda, showed a gradual increase over time, with no statistically significant difference, except between the values of ΔE*1 and ΔE*3. For coffee, no statistically significant difference were found between the values of ΔE*3, ΔE*7 and ΔE*10, despite showing a tendency towards a gradual increase in the value of ΔE*. In the mouthrinse, the values indicating that there was no statistically significant difference, except between the values of ΔE*3 and ΔE*7 (Figures 4 and 5).

 

 

 

Group 4

For the distilled water solution the values of ΔE* were not statistically significant. In the soda, the values no showed statistically significant difference. In coffee, despite the trend towards gradual increase over time, there was no statistically significant difference between the values of ΔE*7 and ΔE*10. In the mouthrinse, only the value of ΔE*1 was found to be statistically significant, despite the gradual reduction in the values of ΔE* over time. (Figure 6)

 

 

Considering the solutions used and the period of time of the trial as an overall treatment for the studied brands, the mean values of ΔE*, in ascending order, were found for the G3 and G1, followed by G2 and G4 (Table 4). When comparing the means of the solutions, it was possible to prove that coffee caused the greatest color change, followed by soda, mouthrinse and distilled water (Table 5). When comparing the values of ΔE* versus time, it was observed that higher color change values were recorded in T14, indicating that the longer the storage period, the greater the trend towards change color (Table 6).

 

 

 

 

DISCUSSION

As esthetics is their main advantage over metal brackets39, the stability and color match of esthetic brackets is a cause for concern. Some authors have attempted to correlate the numerical values of color changes with visual perception, by means of spectrophotometry23 of esthetic brackets12,13,25,26,51 and composite resin or prosthetic restorations11,35,38,40,41,43,48. However, these thresholds of reference for the ΔE* cannot be compared with those in this study because the results are dependent on the methodology, moreover, the brackets tested were different.

It has been shown that the brand, the solution and storage time influence the degree of color change of the materials49, which can also be observed in this experiment (Tables 4 to 6), since all bracket brands tested underwent color change in all solutions over time. The storage period was taken with the purpose of exposing the brackets to extreme conditions to assess the degree of staining, since after this period, there is a trend towards saturation6. Moreover, a period of 24 hours of artificial treatment is considered very short to investigate the color change of the composites43. The choice of solutions was based on the literature11-13,20,31,38,43,51 and the products routinely used by orthodontic patients.

Among the evaluated groups, color changes were observed in the G1 and G3 in distilled water, resulting from the loss of brightness (L*) caused by water absorption, since the value of L* was decreased in relation to baseline (T0). Water absorption by dental materials can be explained by differences in composition, size, quantity and distribution of particles within the matrix38,48. Water absorption into the G2 and G4 brackets was lower, with no statistically significant difference between them.

In the soda, only G4 underwent no statistically significant change in color, although the mean ΔE* value over time was relatively high. In the pH measurement of the solutions, it was found that the soda had the lowest initial pH Tabela 2, which possibly affected the surface integrity of the specimens5,6, favoring color change probably due to the absorption of pigments from the solution by the brackets.

For all groups stored in coffee there was statistically significant difference, with higher ΔE* values, whichshows the greatest potential of this staining solution Tabela 5, in agreement with previous studies38,49. This color change was due to the large amount of yellow pigments in the solution, by adsorption and absorption11,46, which could be corroborated the increase in the values of the coordinate b*.

In mouthrinse, all groups suffered color change, and the highest ΔE* values were observed for G3. According to a previous study20, 12 hours of immersion is equivalent to a period of one year under clinical conditions, that corresponding at only one daily rinse with duration of two minutes, with great compatibility with the values found from T1 to T3. Some authors34,37 reported that alcohol tends to alter the surface properties of composites, increasing the area of adsorption of pigments. Since the color of the mouthrinse was blue, the coordinate values L* and b* decreased gradually, which contributed to the higher ΔE* values for the G3, particularly in T1, possibly due to some type of specific reaction with some constituent of the ceramic matrix, since no other group showed similar behavior. According to literature20,32 whether or not mouthrinses contain alcohol in their composition, they affect the microhardness of restorative materials. Other authors19,52 reported no effect, saying that the behavior of this solution is no different from that of distilled water that also was observed in this study.

Although the literature49 reports that the low pH and high concentration of alcohol tend to increase the potential for staining of certain products, this study showed that the factor most responsible for color changes in the brackets was the amount and type of pigment in the solution, which is in agreement with previous studies38,48. It was also reported that changes in optical properties (opacity/translucency) of the polymeric matrix5 may be responsible for clinically observed color change.

Due to these complications, a number of variables (intrinsic and/or extrinsic) should be considered in the inference clinic50. The complex interaction of factors in the oral environment such as temperature, humidity, biofilm, salivary pellicle, food, and beverage consumption can affect dental materials. Furthermore, the combination and the simultaneous effects of different foods or beverages, mouthwash, saliva, and brushing were not evaluated.

Although ceramic brackets present better performance chromatic than the polycarbonate type8, this laboratory study showed that this superiority is not always true and the association between laboratory results and clinical experience should guide the choice of the best accessories.

This study also showed that solutions used in everyday life are able to cause color changes in esthetic brackets, which may help to clear the frequent concern regarding the necessary minimum time required for the solutions to cause color change. In this study, the experimental times used were overestimated when compared to the times prevalent in the patients' life. Nevertheless, the influence of cosmetic color enhancements in patients who make excessive use of these solutions can have a strong correlation with the results shown.

CONCLUSION

The results presented led to the rejection of the null hypotheses, and all groups tested underwent color changes when immersed in the studied solutions. Therefore, the esthetic brackets do not present satisfactory and stable chromatic behavior.

 

ACKNOWLEDGMENTS

The authors thank Morelli Orthodontics for the donation of the Composite® brackets.

 

REFERENCES

1. Aird JC, Durning P. Fracture of polycarbonate edgewise brackets: a clinical and SEM study. Br J Orthod 1987;14(3):191-5.         [ Links ]

2. Aknin PC, Nanda RS, Duncanson MG, Currier F, Sinha PK. Fracture strength of ceramic brackets during arch wire torsion. Am J Orthod Dentofacial Orthop 1996;109(1):22-7.         [ Links ]

3. Alkire RG, Bagby MD, Gladwin MA, Kim H. Torsional creep of polycarbonate orthodontic brackets. Dent Mater 1997;13(1):2-6.         [ Links ]

4. Al-Wahadni A, Ajlouni R, Al-Omari Q, Cobb D, Dawson D. Shade-match perception of porcelain-fused-to-metal restorations: a comparison between dentist and patient. J Am Dent Assoc 2002;133(9):1220-5.         [ Links ]

5. Sham AS, Chu FC, Chai J, Chow TW.. Color stability of provisional prosthodontic materials. J Prosthet Dent 2004;91(5):447-52.         [ Links ]

6. Asmussen E. Factors affecting the color stability of restorative resins. Acta Odontol Scand 1983;41(1):11-8.         [ Links ]

7. Bazakidou E, Nanda RS, Duncanson MG, Sinha P. Evaluation of frictional resistance in esthetic brackets. Am J Orthod Dentofacial Orthop 1997;112(2):138-44.         [ Links ]

8. Birnie D. Ceramic brackets. Br J Orthod 1990;17(1):71-4.         [ Links ]

9. Bishara SE, Fehr DE. Ceramic brackets: something old, something new, a review. Sem Orthod 1997;3(3):178-88.         [ Links ]

10. Commission Internationale de l'Eclairage (CIE). Recommendations on uniform color spaces, color difference equations, psychometric color terms. Supplement nº. 2 of publication CIE nº. 15 (E-1.3.1) ed. Paris: Bureau Central de la CIE; 1978.         [ Links ]

11. Dietschi D, Campanile G, Holz J, Meyer JM. Comparison of the color stability of ten new generation composites: an in vitro study. Dent Mater 1994;10(6):353-62.         [ Links ]

12. Faltermeier A, Behr M, Müssig D. Esthetic brackets: the influence of filler level on color stability. Am J Orthod Dentofacial Orthop 2007;132(1):5 e13-6.         [ Links ]

13. Faltermeier A, Behr M, Müssig D. In vitro colour stability of aesthetic brackets. Eur J Orthod 2007;29(4):354-8.         [ Links ]

14. Faltermeier A, Rosentritt M, Reicheneder C, Müssig D. Experimental composite brackets: influence of filler level on the mechanical properties. Am J Orthod Dentofacial Orthop 2006;130(6):699 e9-14.         [ Links ]

15 . Ghafari J. Problems associated with ceramic brackets suggest limiting use to selected teeth. Angle Orthod 1992;62(2):145-52.         [ Links ]

16. Göhring TN, Gallo L, Lüthy H. Effect of water storage, thermocycling, the incorporation and site of placement of glass-fibers on the flexural strength of veneering composite. Dent Mater 2005;21(8):761-72.         [ Links ]

17. Gottlieb EL, Nelson AH, Vogels DS 3rd. 1990 JCO study of orthodontic diagnosis and treatment procedures. 1. Results and Trends. J Clin Orthod 1991;25(3):145-56.

18. Guan G, Takano-Yamamoto T, Miyamoto M, Hattori T, Ishikawa K, Suzuki K. Shear bond strengths of orthodontic plastic brackets. Am J Orthod Dentofacial Orthop 2000;117(4):438-43.         [ Links ]

19. Gürdal P, Akdeniz BG, Hakan Sen B. The effects of mouthrinses on microhardness and color stability of aesthetic restorative materials. J Oral Rehabil 2002;29(9):895-901.         [ Links ]

20. Gürgan S, Oner A, Köprülü H. In vitro effects of alcohol-containing and alcohol free mouthrinses on microhardness of some restorative materials. J Oral Rehabil 1997;24(3):244-6.         [ Links ]

21. Hosoya Y. Five-year color changes of light-cured resin composites: influence of light-curing times. Dent Mater 1999;15(4):268-74.         [ Links ]

22. Johnston WM, Reisbick MH. Color and translucency changes during and after curing of esthetic restorative materials. Dent Mater 1997;13(2):89-97.         [ Links ]

23. Johnston WN, Kao EC. Assessment of appearance match by visual observation and clinical colorimetry. J Dent Res 1989;68(5):819-22.         [ Links ]

24. Karamouzos A, Athanasiou AE, Papadopoulos MA. Clinical characteristics and properties of ceramic brackets: A comprehensive review. Am J Orthod Dentofacial Orthop 1997;112(1):134-40.         [ Links ]

25. Lee YK. Changes in the reflected and transmited color of esthetic brackets after thermal cycling. Am J Orthod Dentofacial Orthop 2008;133(5):641 e1-6.         [ Links ]

26. Lee YK. Colour and translucency of tooth-coloured orthodontic brackets. Eur J Orthod 2008;30(2):205-10.         [ Links ]

27. Liu JK, Chung CH, Chang CY, Shieh DB. Bond strength and debonding characteristics of a new ceramic bracket. Am J Orthod Dentofacial Orthop 2005;128(6):761-5.         [ Links ]

28. Makinson OF. Colour changes on curing light-activated anterior restorative resins. Aust Dent J 1989;34(2):154-9.         [ Links ]

29. Meyer-Lueckel H, Umland N, Hopfenmuller W, Kielbassa AM. Effect of mucina alone in combination with various dentifrices on in vitro remineralization. Caries Res 2004;38(5):478-83.         [ Links ]

30. Newman GV, Snyder WH, Wilson CE Jr. Acrylic adhesive for bonding attachments to tooth surfaces. Angle Orthod 1968;38(1):12-8.         [ Links ]

31. Omata Y, Uno S, Nakaoki Y, Tanaka T, Sano H, Yoshida S, et al. Staining of hibrid composites with coffe, oolong tea, or red wine. Dent Mater J 2006;25(1):125-31.         [ Links ]

32. Penugonda B, Settembrini L, Scherer W, Hittelman E, Strassler H. Alcohol-containing mouthwashes: effect on composite hardness. J Clin Dent 1994;5(2):60-2.         [ Links ]

33. Prayitno S, Addy M. An in vitro study of factors affecting the development of staining associated with the use of chlorhexidine. J Periodontal Res 1979;14(5):397-402.         [ Links ]

34. Reis AF, Gianini M, Lovadino JR, Ambrosano GM. Effects of various finishing system on the surface roughness and staining susceptibility of packable composite resins. Dent Mater 2003;19(1):12-8.         [ Links ]

35. Ruyter IE, Nilner K, Moller B. Color stability of dental composite resin materials for crown and bridge veneers. Dent Mater 1987;3(5):246-51.         [ Links ]

36. Sadat-Khonsari R, Moshtaghy A, Schlegel V, Kahl-Nieke B, Möller M, Bauss O. Torque deformation characteristics of plastic brackets: a comparative study. J Orofac Orthop 2004;65(1):26-33.         [ Links ]

37. Sarret DC, Coletti DP, Peluso AR. The effects of alcoholic beverages on composite wear. Dent Mater 2000;16(1):62-7.         [ Links ]

38. Schulze KA, Marshall SJ, Gansky AS, Marshall GW. Color stability and hardness in dental composites after accelerated aging. Dent Mater 2003;19(7):612-9.         [ Links ]

39. Scott GE Jr. Fracture toughness and surface cracks: the key to its understanding ceramic brackets. Angle Orthod 1988;58(1):5-8.         [ Links ]

40. Seghi RR, Hewlett ER, Kim J. Visual and instrumental colourimetric assessments of small colour differences on translucent dental porcelain. J Dent Res 1989;68(12):1760-4.         [ Links ]

41. Seghi RR, Johnston WM, O'Brien WJ. Spectrophotometric analysis of color differences between porcelain systems. J Prosthet Dent 1986;56(1):35-40.         [ Links ]

42. Sinha PK, Nanda RS. Esthetic orthodontic appliances and bonding concerns for adults. Dent Clin North Am 1997;41(1):89-109.         [ Links ]

43. Stober T, Gilde H, Lenz H. Color stability of highly filled composite resin materials for facings. Dent Mater 2001;17(1):87-94.         [ Links ]

44. Swartz ML. Ceramic brackets. J Clin Orthod 1988;22(2):82-8.         [ Links ]

45. Uchida H, Vaidyanathan J, Viswanadhan T, Vaidyanathan TK. Color stability of composites as a function of shade. J Prosthet Dent 1998;79(4):372-7.         [ Links ]

46. Um CM, Ruyter IE. Staining of resin-based veneering materials with coffee and tea. Quintessence Int 1991;22(5):377-86.         [ Links ]

47. Viazis AD, DeLong R, Bevis RR, Rudney JD, Pintado MR. Enamel abrasion from ceramic orthodontic brackets under an artificial oral environment. Am J Orthod Dentofacial Orthop 1990;98(2):103-9.         [ Links ]

48. Vichi A, Ferrari M, Davidson CL. Color and opacity variations in three different resin-based composite products after water aging. Dent Mater 2004;20(6):530-4.         [ Links ]

49. Villalta P, Lu H, Okte Z, Garcia-Godoy F, Powers JM. Effects of staining and bleaching on color change of dental composite resins. J Prosthet Dent 2006;95(2):137-42.         [ Links ]

50. Wiltshire WA, Labuschagne PW. Staining of light-cure aesthetic resin restorative materials by different staining media: an in vitro study. J Dent Assoc S Afr 1990;45(12):561-5.         [ Links ]

51. Wriedt S, Schepke U, Wehrbein H. The discoloring effects of food on the color stability of esthetic brackets – an in vitro study. J Orofac Orthop 2007;68(4):308-20.

52. Yanikoğlu N, Duymuş ZY, Yilmaz B. Effects of different solutions on the surface hardness of composite resin materials. Dent Mater J 2009;28(3):344-51.         [ Links ]

53. Zinelis S, Eliades T, Eliades G, Makou M, Silikas N. Comparative assessment of the roughness, hardness, and wear resistance of aesthetic bracket materials. Dent Mater 2005;21(9):890-4.         [ Links ]

 

 

Correspondence to:
Marcos Rogério de Mendonça
Disciplina de Ortodontia – Faculdade de Odontologia de Araçatuba
Universidade Estadual Paulista Júlio de Mesquita Filho

Rua José Bonifácio, 1.193
CEP 16015-050 – Araçatuba/SP, Brazil
e-mail: rogeriofoa@terra.com.br

Received in: 24/2/11
Accepted in: 31/3/11