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Departamento de Odontologia Restauradora, Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo

Softening time of gutta-percha cones was studied in vitro using five chemical solvents: xylol, chloroform, turpentine, eucalyptql, and orange oil. An apparatus which reproduces the penetration force of an endodontic file was used on the sectioned roots of previously filled teeth. The most rapid chemical solvent of gutta-percha cones was chloroform and the slowest was eucalyptol.

Key Words: chemical solvent, gutta-percha.

Introduction

Even with the most modern techniques, endodontic treatment is not free of failures, and it is often necesary to retreat root canals. Thus, it may be necessary to remove an old obturation; this fundamental step is often difficult.

Currently root canals are filled with endodontic cement and gutta-percha cones.

These cones are composed mainly of a vegetable resin, from which comes their name, and are softened using chemical solvents.

Since 1833 when Bowman proposed the use of gutta-percha in Dentistry and chloroform as an excellent solvent, much has been written concerning the use of chemical solvents for the softening of gutta-percha cones. Callahan (1894) recommended a technique of filling root canals which used gutta-percha dissolved in chloroform, known as Chloropercha. Buckley (1910) recommended the use of chloroform and eucalyptol as solvents for gutta-percha. However, more recently, Sommer and Ostrander (1956) and Grossman (1978) recommended the use of xylol as the best solvent. Figueiras et al. (1962) emphasized the use of the combination of two chemical solvents, chloroform and eucalyptol, for the softening of gutta-percha.

In an investigation designed to clarify which solvent was the best to soften gutta-percha cones, Della Nina et al. (1980) concluded that xylol was the most effective. Kaplowitz (1991) compared the effect of 18 essential oils in relation to gutta-percha. He observed that only chloroform and purified oil of turpentine completely dissolved gutta-percha and proposed the use of this oil to remove root canal fillings, since it was biocompatible and non-carcinogenic.

Pécora et al. (1992) presented an oil obtained from the exocarp of the sweet orange as a dissolving agent of zinc oxide-eugenol cement. This oil is obtained by soaking the exocarp in hexane and distilling at low pressure in a double-boiler.

Biagini and Pécora (unpublished results) studied gutta-percha solvents and verified that mixtures of eucalyptol + xylol and eucalyptol + chloroform (1:1) were very effective.

A review ofthe literature shows a small number of investigations with the objective of determining which chemical solvent has the best effect in softening gutta-percha. Thus, the choice of a solvent depends on each professional without scientific basis. Thus, the objective of this study is to investigate which chemical solvent softens gutta-percha in previously filled root canals in the shortest time.

Material and methods

An apparatus called Penetrometer-PVBS was developed to perform this study. It consisted of a no. 30 endodontic file connected to a comparison dial with micrometric precision, with a mecanism of vertical movement of the dial-file system and a screw on its base for fixation and movement of the samples in two orthogonal directions. The penetration force of the file was generated by the spring of the comparison dial, being set at 70g, since the dimension of spring deformation is constant

(Figure 1).

The samples were the roots of extracted human maxillary central incisors, previously filled with gutta-percha cones (Maillefer) and Grossman cement (FORP-USP, 1992), sectioned at the middle third by a carbide disk coupled to a micromotor. The samples were conditioned at 37°C and 95% relative humidity for one week.

The file was centered over the principal cone by moving the samples. Then, using vertical movement, the dial-file system was lowered so the spring of the comparison dial, using an endodontic instrurnent, could exert a force on the principal cone, with the deformity of the spring set at 200 mm, standardizing the force exerted on the cone.

One of the solvents to be tested (chloroform, xylol, orange oil, turpentine, or eucalyptol) was then placed on the surface of the sample using a 10 mm pipette. Using a chronometer, the time interval from the placement of the solvent to when the file penetrated the gutta-percha 20 mm was measured.

Results

The results of the tests of softening of gutta-percha by chemical solvents are shown in Table 1. Statistical analysis was carded out using the Kruskal-Wallis test and the results are shown in Table 2.

Discussion

Because retreatment is a common practice we are aware that with a certain frequency the professional and the patient come in contact with substances which may be harmful to their health. According to the Merck Index, if inhaled, chloroform can cause intense hypotension, respiratory and cardiac depression and can lead to death. It is also listed as carcinogenic and is banned from use in cosmetics and food containers. Xylol causes irritation to the mucosa by contact and by inhalation causes convulsions, insomnia, excitement and depression of the CNS, and can lead to death by respiratory depression.

The chronic use of these substances causes depression of bone marrow, aplasia and rarely leukemia; it can be harmful when absorbed by the epithelium and is listed as a carcinogenic substance.

Orange oil does not present any harmful effects, has low solubility in water, is soluble in alcohol, is used in pharmaceuticals for fragrance and flavor and also has an expectorant action. Turpentine is used as an expectorant, antiseptic, rubefacient, contra-irritant and anti-flatulence. Eucalyptol, the principal component of eucalyptus oil, is used in pharmaceuticals for flavoring and fragrance, to increase appetite (refreshing flavor) and also is used to increase flavor and aroma.

There was no statistically significant difference between chloroform and xylol and between xylol and orange oil. Thus, we can conclude that the action of orange oil on gutta-percha is the same as xylol, but without presenting the harmful effects of xylol.

Turpentine requires more time to soften gutta-percha than orange oil and less than eucalyptol and also has anti-microbial properties, is non-carcinogenic and biocompatible.

Conclusions

1. The most rapid solvent of gutta-percha was chloroform, followed by xylol, orange oil, turpentine and eucalyptol. 2. Orange oil presents the same softening action on gutta-percha as xylol. 3. Turpentine acts on gutta-percha. 4. Xylol and chloroform are toxic and may be substituted by essential oils.

References

Bowrnan 1833 apud Grossrran LI: Tratamento dos canais radiculares. Atheneu, Rio de Janeiro 1954

Buckley JP: Is it necessary lo use secret formula preparations in tile practice of Dentistry? D Cosmos 52: 429-435,1910

Calallan JR: Sulfuric acid for opening root-canals- D Cosmos 26: 957-959, 1894

Della Nina S: Avaliação das propriedades dos solventes de guta-percha. Quintessência 7 : 27-32, 1980

Figueiras J, Bevilacqua S, Melo C: Endodontia clinica. Cientifica, Rio de Janeiro 1962

Grossrnar LI: Endodontics practice. 7tl1ed. Lea & Febiger, Philadelphia 1978

Kaplowitz GJ: Evaluation of the ability of essential oils to dissolve gutta-porcha. J Endod 17: 448-449, 1991

Pécora JD: Apresentação de um óleo essencial obtido do Citrus Arantium, eficaz na desintegração do cimento de óxido de zinco-eugenol do interior do canal radicular. Odonto 1: 130-132, 1992

Sommer RF, Ostrander D: Clinical endodontics. WB Saunders, Philadelphia 1956