Brazilian gutta-percha points . Part I : chemical composition and X-ray diffraction analysis

Eight nonstandardized gutta-percha points commercially available in Brazil (Konne, Tanari, Endopoint, Odous, Dentsply 0.04, Dentsply 0.06, Dentsply TP and Dentsply FM) were analysed chemically and by X-ray diffraction, and their chemical compositions were compared. The organic fraction (gutta-percha polymer and wax/resin) of the gutta-percha points was separated from the inorganic fraction (ZnO and BaSO4) by dissolving them in chloroform. The gutta-percha polymer was precipitated with acetone. The inorganic fraction was analysed by elemental microanalysis. Energy-dispersive X-ray microanalysis (EDX) and X-ray diffraction were employed to identify the chemical elements and compounds (barium sulfate and zinc oxide). The barium sulfate content was calculated based on the percentage of sulfur found in the elemental microanalysis. All analyses were repeated three times. The means and standard deviations of the percentage by weight of gutta-percha in the points were: Konne (17.6 +/- 0.30), Tanari (15.2 +/- 0.30), Endopoint (16.7 +/- 0.23), Odous (18.8 +/- 0.20), Dentsply 0.04 (15.7 +/- 0.17), Dentsply 0.06 (16.6 +/- 0.17), Dentsply TP (21.6 +/- 0.15) and Dentsply FM (16.3 +/- 0.23). The means and standard deviations of the zinc oxide content were: Konne (79.9 +/- 0.10), Tanari (81.9 +/- 0.07), Endopoint (81.3 +/- 0.40), Odous (79.7 +/- 0.26), Dentsply 0.04 (77.9 +/- 0.03), Dentsply 0.06 (78.2 +/- 0.07), Dentsply TP (69.8 +/- 0.19) and Dentsply FM (72.6 +/- 0.70). The method utilized was appropriate to quantify gutta-percha, wax/resin, zinc oxide and barium sulfate. Cone brands without barium sulfate were found. An unusual high wax/resin percentage was detected in Dentsply FM (p = 0.0003). Dentsply TP showed the highest gutta-percha percentage.


INTRODUCTION
The final objective of endodontic procedures should be total cleaning, shaping and obturation of the root canal system 13,14 .According to Schilder 13 (1967), Gutmann, Witherspoon 6 (2002) and de Deus et al. 3 (2002), gutta-percha is considered the best material for root canal filling, regardless of the technique applied.
Gutta-percha polymer is a trans-1,4-polyisoprene, obtained from the coagulation of latex produced by trees of the Sapotaceae family and mainly derived from Palaquium gutta bail 6,9 .It was first introduced to the Royal Asiatic Society of England in 1843 by Sir Jose d'Almeida and was introduced into dentistry in the late 1800s.It occurs naturally and is harder, more brittle, and less elastic than natural rubber 15 .
Gutta-percha is rigid at room temperature, becomes pliable at 25-30°C, softens at 60°C, and melts at 100°C with partial decomposition 1 .It is a hydrocarbon and is soluble in chloroform, eucalyptone, carbon disulphide, benzene and xylem.When exposed to light and air, gutta-percha undergoes degrading oxidation and becomes brittle 4 .The crystalline phase appears in two forms: 1) the alpha phase and 2) the beta phase.The forms differ only in the molecular repeat distance and single carbon-bond configuration 13,14,15 .
Brittleness, stiffness, tensile strength, and radiopacity have been shown to depend primarily on the proportions of organic (gutta-percha polymer and wax/resins) and inorganic (zinc oxide and metal sulfates) components 2 .Zinc oxide is also responsible for the antibacterial activity of gutta-percha points 11 .The particular percentages of components vary according to the manufacturer.It is evident that since the cones differ in their composition, they may differ in their physical properties and even in their biological effect 17 .
Friedman et al. 4 (1977) have found that the composition of the points is approximately 18 to 22% in gutta-percha polymer, 59 to 75% in zinc oxide and 1.1 to 17.2% in barium sulfate.Marciano, Michailesco 8 (1989) have reported lower ZnO content (36.6%) and higher BaSO 4 content (31.2%).Recently, Gurgel-Filho et al. 5 (2003) reported the absence of barium sulfate in the composition of three dental gutta-percha brands manufactured in Brazil (Konne, Tanari and Dentsply FM), which had never been reported in the literature.
The purpose of the present study was to determine the chemical composition of eight Brazilian commercially available nonstandardized guttapercha cones: Konne, Tanari, Endopoint, Odous, Dentsply 0.04, Dentsply 0.06, Dentsply TP and Dentsply FM.

MATERIAL AND METHODS
The gutta-percha contained in eight different dental gutta-percha cones commercially available was analysed.Gutta-percha brands, expiration date and lot number were, respectively: Konne (Belo Horizonte, Brazil), Dec In order to separate gutta-percha point components, the procedure described by Gurgel-Filho et al. 5 (2003) was followed: 1 g of commercial guttapercha points was dissolved in 10 ml of chloroform (Synth, Diadema, SP, Brazil) (24 hours/300 rpm).The resulting solution was then centrifuged (Andreas Hettich GmbH & Co. KG, Tuttlingen, Germany) for 15 minutes at 6,000 rpm.This permits the separation of a solid phase (inorganic components -zinc oxide and metal sulfates) from the supernatant (organic components -gutta-percha, resins and waxes) remaining in the solution.
Since gutta-percha has a low dissolving rate and, in general, undergoes a slow dissolving process 16 , the samples were placed in contact with 10 ml of chloroform for 24 h prior to centrifuging.The gutta-percha polymer, insoluble in acetone (Synth, Diadema, SP, Brazil), was coagulated by adding this solvent and weighing after total solvent evaporation.The mass of soluble material in acetone (wax/resin) was determined after the solvent's evaporation.
The organic fraction (gutta-percha polymer and wax/resin) was determined using the procedure described by Gurgel-Filho et al. 5 (2003).The barium sulfate content was determined according to the sulfur percentage (elemental microanalysis) obtained, using equation 1.The zinc oxide content was calculated using equation 2 when the specimen contained sulfur, or by equation 3 if it did not.Energy-dispersive X-ray microanalysis (EDX) was utilised to establish qualitatively the presence of chemical elements in the samples.The analysis was carried out on sections of all eight brands mounted on aluminum stubs (Carlo Erba, Rodano, Italy) and carbon coated.A DSM-940A scanning electron microscope (Carl Zeiss, Jena, Germany) with Link System 3.34 Series 300 (Koninklijke Philips Electronics N.V., Eindhoven, Netherlands) with Si(Li) detector was used for the analysis.The sections were analysed at 1,000 X magnification.
The apparatus used for the X-ray diffraction analysis was a Philips MDR Pro (Eindhoven, Holland) operating at 40 kV and 20 mA, using a copper tube.The equipment was calibrated to produce 10 2 cps.Each specimen was observed separately and compared with the X-ray diffraction pattern of zinc oxide and barium sulfate to verify the presence of these two compounds.
The quantitative determination of carbon, hydrogen, nitrogen and sulfur chemical elements in the samples was carried out in a CHNS/O Carlo Erba microanalyser, model 1110 (Rodano, Italy) with combustion at 1,000°C in oxygen atmosphere.A thermal conductivity detector (Carlo Erba, Rodano, Italy) was employed.All the analyses were repeated three times for each material.

RESULTS
The results of the chemical assay according to the organic and inorganic fractions of the eight nonstandardized gutta-percha cones are shown in Table 1.The data obtained were statistically evaluated using the Kruskal-Wallis test (SPSS 12.0, SPSS Inc., Chicago, USA) at the significance level of p = 0.05.
Dentsply FM showed the highest percentage of wax/resin (10.4%) (p = 0.0003).Between the other gutta-percha cones, no statistically differences were found for wax/resin percentage.
The qualitative presence of BaSO 4 and ZnO was determined by means of X-ray diffraction, according to the presence and absence of BaSO 4 , respectively.The energy-dispersive X-ray micro-analysis showed all the elements present, such as barium, in all gutta-percha cones studied.
Elemental microanalysis showed the presence of carbon, hydrogen and nitrogen in all specimens.This analysis quantifies these components.The final composition of the eight gutta-percha cones is shown in Table 2.In Table 3, the data obtained from the present study are compared with results of Friedman et al. 4 (1977), Marciano, Michailesco 8 (1989) and Gurgel-Filho et al. 5 (2003).

DISCUSSION
The root canal system contains lateral canals that communicate with the periodontal tissue in the furcation or at the apex 2 .Every exit from the root canal is to be regarded as a possible route for decomposition products where there is a necrotic pulp 7 .The tendency of apical/periodontal lesions of endodontic origin to heal depends upon a number of factors, including complete filling of the root canal system in three dimensions.An ideal technique to accomplish this was presented in 1967 by Schilder 13 , showing that it is possible to produce a three-dimensional bioinert root canal filling by heating a gutta-percha point within the canal 13 .
Gutta-percha cones are commercially available and are composed of barium sulfate, zinc oxide, waxes, resins and gutta-percha 8,10 .These different components are combined in various quantities for the different commercial brands 10 .
The constituents of eight Brazilian gutta-percha cones were identified by qualitative chemical analysis and their relative percentages were determined.The chemical structures of resins and/or waxes presented were not analysed.The results obtained from these experiments showed heterogeneity among the different brands of dental gutta-percha cones.X-ray microanalysis and elemental microanalysis provided an overview of the elemental composition of the gutta-percha points.Elemental microanalysis is the most popular technique to quantify Sulfur content.While these methods, as used in the present study, provide qualitative data, assumptions about the quantitative data may be made based on the results.Zinc was universally present in large amounts, reflecting the fact that zinc oxide is the main ingredient in these points, according to many studies 4,5,6,8 .
The composition of Tanari points determined here (gutta-percha 15.2%, wax/resin 2.9%, zinc oxide 81.9%) is very similar to that reported by Gurgel-Filho et al. 5 (2003): 15.6; 2.4 and 82.0%respectively.This indicates that no composition change was introduced by the manufacturer recently.However, the composition of Konne and Dentsply points is different from previous analysis.The content of gutta-percha in Konne points reported in the literature, for example, was 18.9 ± 0.30%, different from that determined (17.6 ± 0.30%).This confirms the change in Konne point composition.Analysis of Dentsply FM point composition showed that barium sulfate is indeed present in its chemical composition.
The range of components in gutta-percha points, according to Gurgel-Filho et al. 5 (2003), Friedman et al. 4 (1977), and Marciano, Michailesco 8 (1989), is 14.5 to 21.8% in gutta-percha, 1.0 to 4.1% in wax/resin, 0 to 31.2% in barium sulfate and 36.6 to 84.3% in zinc oxide (Table 3).The content of gutta-percha, BaSO 4 , and ZnO in the Brazilian brands, determined in the present work, is in the range reported by said authors.The greatest difference observed was in the wax/resin content observed for Dentsply FM points (10.4%), much higher than the highest value determined in previous analyses (4.1%).The unusual absence of BaSO 4 , reported by Gurgel-Filho et al. 5 (2003), in some Brazilian brands is now observed in four brands (Konne, Tanari, Endopoint and Odous).This absence is no longer unusual.
In the early 1970s, the ideal semisolid root canal filling material should possess the proper combination of flexibility and rigidity to permit the negotiation of almost any root canal, regardless of its anatomic characteristics 4 .Later, advanced methods based on three-dimensional data acquisition became available for the description of canal   Schilder 13 (1967) introduced the concept of cleaning and shaping.Most obturation problems are actually problems of cleaning and shaping.Actually, the endodontist can develop a continuously tapering conical form in the root canal preparation within the regular dentine walls.This fact permits the use of gutta-percha cones having an ideal composition, avoiding the high percentage of inorganic fraction to make the cones rigid, making the three dimensional root canal system obturation easy using thermoplastic techniques.
The chemical composition of gutta-percha points varies according to the manufacturer, especially considering the proportions of gutta-percha and zinc oxide.This may lead to variations in brittleness, stiffness, tensile strength, and radiopacity 4,6 , and also in flow, plasticity, elongation, inherent tension force, and thermal behaviour 4,6,17 .
Cones become more rigid with high concentrations of inorganic components and low percentage of gutta-percha 14 , making the conventional filling technique easier (lateral condensation).Gutta-percha cones should present at least 17% of gutta-percha and no more than 3% of wax/resin (Dentsply FM and Dentsply TP, 10.4 ± 0.11 and 4.0 ± 0.36 respectively), enabling a good thermal behaviour during warm root canal filling.Barium sulfate and Zinc oxide provide radiopacity 15 .
Other studies have been carried out, aiming to correlate physical properties, chemical composition and clinical behaviour (microleakage) of the different brands of gutta-percha cones already available to the practitioner.

CONCLUSIONS
This paper showed that the method utilized was appropriate to quantify gutta-percha, wax/ resin, zinc oxide and barium sulfate content.Cone brands without barium sulfate were found (Konne, Tanari, Endopoint and Odous).The gutta-percha and zinc oxide content varied from 15.2% to 21.6% and 69.8% and 81.9%, respectively.An unusual high wax/resin percentage was detected in one brand (Dentsply FM).Dentsply TP showed the highest gutta-percha percentage.

TABLE 1 -
Mean and standard deviation (SD) of percentage weights of organic and inorganic fractions after chemical assay of gutta-percha cones.

TABLE 3 -
Comparison between ranges of component percentage of gutta-percha cones made by different authors using different brands.