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Year : 2011  |  Volume : 14  |  Issue : 2  |  Page : 156-159
Influence of different organic solvents on degree of swelling of poly (dimethyl siloxane)-based sealer

Department of Conservative Dentistry and Endodontics, Faculty of Dental Sciences, Sri Ramachandra University, Chennai, India

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Date of Submission25-Jan-2010
Date of Decision13-May-2010
Date of Acceptance21-Jul-2010
Date of Web Publication7-Jul-2011


The study evaluated the compatibility of chloroform, ether, and xylene with poly(dimethyl siloxane) (PDMS) based sealer. Freshly mixed sealer was placed in 90 glass molds with 5 mm diameter and 2 mm thickness. All samples were stored in 75% relative humidity at 37ºC for 2 weeks. All the samples were divided into three groups: group A - chloroform; group B - ether, and group C - xylene and immersed in fresh solvent at room temperature. The specimens were weighed before and after immersion for each group at the end of 2, 5, and 10 min. The swelling ratio was calculated for all the groups. Intergroup comparison revealed no difference in the mean swelling ratio for 2, 5, and 10 min (P > 0.001; Tukey HSD Post Hoc). Intragroup comparison revealed significant difference in swelling ratio between 2 and 5 min for group B and group C (P < 0.001; Paired t test). Ether has the highest compatibility with PDMS-based sealer after 2 min followed by xylene after 5 min.

Keywords: Chloroform; degree of swelling; ether; poly (dimethyl siloxane) based sealer; swelling ratio; xylene

How to cite this article:
Vinothkumar TS, Kandaswamy D, Arathi G, Dinesh K. Influence of different organic solvents on degree of swelling of poly (dimethyl siloxane)-based sealer. J Conserv Dent 2011;14:156-9

How to cite this URL:
Vinothkumar TS, Kandaswamy D, Arathi G, Dinesh K. Influence of different organic solvents on degree of swelling of poly (dimethyl siloxane)-based sealer. J Conserv Dent [serial online] 2011 [cited 2023 Oct 1];14:156-9. Available from:

   Introduction Top

Retreatment can be ascribed largely to microbial infection due either to technical inadequacies in primary treatment, or orthograde reinfection of the canal system. Retreating previously filled root canal systems demands that antimicrobial irrigants and medicaments gain access to all ramifications of the system which may be harboring organic matter and microorganisms. [1] Several techniques for removing the root canal filling materials including the use of solvents, heat, hand files, rotary files, and ultrasonic instruments used either alone or in combination. [2] However, root canal sealers are more difficult to remove from anatomical ramifications where they may be inaccessible to mechanical methods of removal. In these circumstances, solvents become essential if canals are to be thoroughly cleared of residual materials for effective disinfection and resealing. [1]

Roekoseal (Colténe/Whaledent, Altstatten, Switzerland), a poly(dimethylsiloxane) (PDMS) based root canal sealer, is considerably less cytotoxic than epoxy resin based root canal sealers and has little apoptotic effect on cells exposed to it and it expands by 0.2% during the first 4 weeks and remains stable thereafter. [3]

Cross-linked polymers that do not dissolve, such as PDMS, swell in contact with nonpolar solvents. The solubility of a solvent in PDMS influences the degree of swelling, which is measured by the ratio of the mass of the swollen network and solvent combined to the mass of dry extracted solid. However, the swelling ratio (SR) has not been considered in the literature pertaining to solvent compatibility of PDMS-based sealer. [4]

High-solubility solvents such as chloroform, xylene, and ether are preferred during retreatment procedure as they imbibe PDMS in short time. [4] Many studies have suggested chloroform as the most effective solvent for most filling materials. [5],[6],[7],[8],[9] A slowly evaporating softening solvent such as xylene that may allow more working time and a cleaner procedure is desired. [10] However, chloroform and xylene have caused concern as putative hazardous materials and even as suspected carcinogens. [11] Proper handling may minimize a patient's exposure to these solvents; nevertheless, the staff of an endodontic office is repeatedly exposed to the vapors of these materials and, therefore, they may constitute an occupational hazard. [8]

The purpose of this study was to evaluate the compatibility of chloroform, ether, and xylene with PDMS-based sealer for three immersion periods of 2, 5, and 10 min. The null hypothesis tested was there is no difference in compatibility of the sealer with different solvents for all the immersion periods.

   Materials and Methods Top

The root canal sealer tested in this study was RoekoSeal (Colténe/Whaledent, Altstatten, Switzerland) and it was mixed according to the manufacturer's instructions. Freshly mixed sealer was placed in 90 standard cylindrical glass molds (5 mm diameter × 2 mm thick). A glass microscope slide was then pressed onto the upper surface to make the surface flat. All the 90 samples stored in a chamber with 75% relative humidity at 37°C for 2 weeks to allow the materials to set completely. The excess material was trimmed level with the surface of the mold with a sharp scalpel, and the samples were taken out of the molds. The samples were then weighed in grams three times with a digital scale (XB 220A; Precisa, Dietikon, Switzerland). The mean values were calculated.

Samples were then divided into three groups: group A - chloroform (Merck, Darmstadt, Germany), group B - ether (Fisher Scientific, Pittsburgh, PA), and group C - xylene (p-xylene, Puris, Fluka, Switzerland). Each sample was then immersed in 10 ml aliquots of fresh solvent in glass petri caps at room temperature in such a way that both surfaces of the samples were accessible to the solvent. The specimens were then weighed for each group at the end of 2, 5, and 10 min. After the designated immersion period, specimens were removed with tweezers and blot dried. All samples were weighed in triplicate and the mean values were calculated.

SR was determined for each sample by calculating the ratio of mass of swollen sealer and solvent combined to the mass of the set sealer before exposure to the solvent. SR values for all the groups after immersion in solvent for 2, 5, and 10 min were designated as T2 , T5 , and T10 , respectively.

Statistical analysis

One-way ANOVA followed by Tukey HSD post hoc test was used for intergroup comparison and paired t test was used for intragroup comparison at a significance level of P < 0.001. Statistical analysis was performed using SPSS 15.0 software (for Windows version 15.0; SPSS Inc, Chicago, IL).

   Results Top

Solvents compatibility of PDMS with different solvents for all exposure times are summarized in [Table 1]. Intergroup comparison revealed no difference in the mean swelling ratio at T2, T5 , and T 10 (P > 0.001). Intragroup comparison revealed statistically significant difference in SR between T2 (1.112500± 0.0886501) and T5 (1.105213± 0.0882627) for group B (P < 0.001) and between T2 (1.091625± 0.1375252) and T5 (1.108100± 0.1357226) for group C (P < 0.001). Hence, the null hypothesis was rejected.
Table 1: Results of SR of PDMS-based sealer in different solvents

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Although the mean SR at T10 was low when compared to T2 and T5 in both group B and group C, the difference was not significant (P > 0.001).

   Discussion Top

Occasionally, the need arises to re-treat an endodontically treated tooth during which it is necessary to remove the sealer and obturating materials. Generally, endodontic instruments in combination with solvents are used to completely eliminate filling materials from the root canals, [9],[12],[13],[14] because the dangers of using purely mechanical means to remove root canal filling materials are root perforation, canal straightening, or altering the original shape. [9],[12],[15] When an organic solvent is used during retreatment, extrusion of the solvent into periapical tissue should be prevented. [9],[12],[13],[14],[15]

PDMS has repeating units of -OSi(CH 3 ) 2 - groups. This chemical structure leads to a hydrophobic surface. [4] Exposing this surface to an air or oxygen plasma introduces silanol groups, destroys methyl groups, and makes the surface hydrophilic. [4] PDMS that has been treated with plasma can be kept hydrophilic indefinitely by keeping the surfaces in contact with water or polar organic solvents; otherwise, if the surface is left in contact with air, surface rearrangements occur that bring new hydrophobic groups to the surface to lower the surface free energy. [16],[17]

Among the commonly used solvents, chloroform, ether, and xylene are highly compatible with PDMS. They have a solubility parameter (SP, d) in the range of 7.3-9.5 cal 1/2 cm -3/2 . PDMS will absorb these solvents from a microchannel, and the polymer will saturate with the solvent over time. [4] However, prediction of swelling of PDMS by a solvent is important when considering which solvents to use in removing PDMS-based sealer from the root canal walls.

It has also to be taken into account that several clinically relevant parameters such as contact area, contact time between root canal sealer and solvent, temperature, interaction between irrigant and organic solvent, and dilution of the solvent by biological fluids or irrigants were not considered in the present study.

Although there are no international standards for root canal sealer solubility in organic solvents, an International Organization for Standardization 6876:2001 is available that describes the procedure to determine the solubility of set sealer in water. [18] According to the instructions given by this standard, ring molds should have an internal diameter of 20 mm and a height of 1.5 mm. Furthermore, Whitworth and Boursin reported a simple method for the evaluation of root canal sealer solubility by using sample molds of 4 mm in diameter and 2 mm thickness. [1] The method used in our investigation was oriented, to a great extent, by using these descriptions and in present investigation the samples were 5 mm diameter and 2 mm thick.

Few clinical data are available on the time clinicians typically leave root canal flooded with solvents during endodontic retreatment. The time limit of 10 min employed in this study reflects the mean times of 1.5-10.8 min reported in laboratory-based studies for the retreatment of canals filled with laterally condensed gutta-percha and sealer. [14],[19] Application of this experimental model with incubation times of 2, 5, and 10 min for standardized samples allowed us to demonstrate clear differences in the solubility profiles of major classes of root canal sealer cement in three common volatile solvents.

In general, our results pertaining to the solubility of PDMS-based sealer after immersion in chloroform are in disagreement with the previous results, which evaluated the solubility by comparing the mean percentage change in weight. [20] Since the degree of swelling is a reliable measurement tool for the solvent compatibility of PDMS-based sealers, chloroform was included for comparison in the present study. Moreover, there was no associated ban in its use in dentistry. [21]

When the mean SR of PDMS-based sealer following immersion in chloroform, ether, and xylene at each immersion time was compared, it was found that there was no difference in swelling between the three solvents. PDMS-based sealer exhibited maximum swelling in ether at the end of 2 min when compared to that of 5 min. However, when immersed in xylene, PDMS-based sealer exhibited maximum swelling at the end of 5 min when compared to that of 2 min. This can be attributed to the difference in the individual solubility parameter of the solvents. The solvents that have an SP similar to that of PDMS (d = 7.3 cal 1/2 cm -3/2 ) generally swell PDMS more than solvents that have an SP substantially different from that of PDMS. [4] The SP for ether, xylene, and chloroform are 7.5, 8.9, and 9.2 cal 1/2 cm -3/2, respectively, which address the behavior of these solvents inspite of their high solubility. The deswelling of PDMS-based sealer following the immersion period of 5 min in ether and 10 min in xylene could be due to the variation in vapor pressure of ether (638.8 mmHg) and xylene (8.04 mmHg) at room temperature (30°C). [22] Moreover, the deswelling phenomenon might pose difficulty for the clinician in removing the sealer from the root canal walls. Hence, the net available intraoral time for the efficient removal of PDMS-based sealer from the root canal walls is restricted to 2 min for ether and 5 min for xylene.

Under the limitations of the present study, it can be concluded that ether has the highest compatibility with PDMS-based sealer after 2 min followed by xylene after 5 min. Further investigation is needed to evaluate the influence of other parameters like contact area, contact time between root canal sealer and solvent, temperature, interaction between irrigant and organic solvent, and dilution of the solvent by biological fluids or irrigants on degree of swelling of PDMS-based sealers.

   References Top

1.Whitworth JM, Boursin EM. Dissolution of root canal sealer cements in volatile solvents. Int Endod J 2000;33:19-24.  Back to cited text no. 1
2.Ruddle CJ. Nonsurgical endodontic retreatment. J Calif Dent Assoc 2004;32:474-84.  Back to cited text no. 2
3.Orstavik D, Nordahl I, Tibballs JE. Dimensional change following setting of root canal sealer materials. Dent Mater 2001;17:512-9.  Back to cited text no. 3
4.Lee JN, Park C, Whitesides GM. Solvent compatibility of poly (dimethylsiloxane)-based microfluidic devices. Anal Chem 2003;75:6544- 54.  Back to cited text no. 4
5.Chutich MJ, Kaminski EJ, Miller DA, Lautenschlager EP. Risk assessment of the toxicity of solvents of Gutta-Percha used in endodontic retreatment. J Endod 1998;24:213-6.  Back to cited text no. 5
6.Kaplowitz GJ. Evaluation of gutta-percha solvents. J Endod 1990;16:539- 40.  Back to cited text no. 6
7.Tamse A, Unger U, Metzger Z, Rosenberg M. Gutta-percha solvents: A comparative study. J Endod 1986;12:337-9.  Back to cited text no. 7
8.Wennberg A, Orstavik D. Evaluation of alternatives to chloroform in endodontic practice. Endod Dent Traumatol 1989;5:234-7.  Back to cited text no. 8
9.Wourms DJ, Campbell AD, Hicks ML, Pelleu GB. Alternative solvents to chloroform for gutta-percha removal. J Endod 1990;16:224-6.  Back to cited text no. 9
10.Metzger Z, Ben-Amar A. Removal of overextended gutta-percha root canal fillings in endodontic failure cases. J Endod 1995;21:287-8.  Back to cited text no. 10
11.Squire RA. Ranking animal carcinogens: A proposed regulatory approach. Science 1981;214:877-80.  Back to cited text no. 11
12.Gilbert BO, Rice RT. Retreatment in endodontics. Oral Surg Oral Med Oral Pathol 1987;64:333-8.  Back to cited text no. 12
13.Hansen MG. Relative efficiency of solvents used in endodontics. J Endod 1998;24:38-40.  Back to cited text no. 13
14.Uemura M, Hata G, Toda T, Weine FS. Effectiveness of Eucalyptol and d-Limonene as gutta-percha solvents. J Endod 1997;23:739-41.  Back to cited text no. 14
15.Stabholz A, Friedman S, Tamse A. Pathways of the pulp. 6 th ed. St Louis: Mosby; 1994. p. 690-728.  Back to cited text no. 15
16.McDonald JC, Whitesides GM. Poly(dimethylsiloxane) as a material for fabricating microfluidic devices. Acc Chem Res 2002;35:491-9.  Back to cited text no. 16
17.Ng JM, Gitlin I, Stroock AD, Whitesides GM. Components for integrated poly(dimethylsiloxane) microfluidic systems. Electrophoresis 2002;23:3461-73.  Back to cited text no. 17
18.International Organization for Standardization. International Standard ISO 6876: 2001: Dental root canal sealing materials. International Organization for Standardization: Genf (Switzerland); 2001.  Back to cited text no. 18
19.Moshonov J, Trope M, Freidman S. Retreatment efficacy 3 months after obturation using glass ionomer cement, zinc oxide eugenol, and epoxy resin sealers. J Endod 1994;20:90-2.   Back to cited text no. 19
20.Schafer E, Zandhiglari T. Comparison of the effectiveness of chloroform and eucalyptus oil in dissolving root canal sealers. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;93:611-6.  Back to cited text no. 20
21.McDonald MN, Vire DE. Chloroform in the endodontic operatory. J Endod 1992;18:301-3.  Back to cited text no. 21
22.Liley PE, Thomson GH, Friend DG, Daubert TE, Buck E. Perry's Chemical Engineers' Handbook. 7 th ed. New York: McGraw-Hill; 1997. p. 66-75.  Back to cited text no. 22

Correspondence Address:
Thilla Sekar Vinothkumar
#14/D-1, A.E. Koil Street, New Washermenpet, Chennai, Tamilnadu 600 081
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0972-0707.82621

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