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 »  Home  »  Endodontic Articles 4  »  Penetration of propylene glycol into dentine
Penetration of propylene glycol into dentine
Discussion - References.



Discussion.
Propylene glycol is a colourless liquid with a mildly acrid smell and somewhat sweet taste. It has been reported to offer all the advantages of ethylene glycol, with low toxicity and no demonstrable cumulative effects in experimental animals (Seidenfeld & Hanzlik 1932). Its antimicrobial activity for general use has also been documented. Olitzky (1965) has reported that concentrated solutions of propylene glycol have a marked germicidal efficiency and that its use as a vehicle may provide a potential for preventing or treating microbial infections. It is considered by the Council on Pharmacy and Chemistry of the American Medical Association as a harmless constituent for pharmaceutical products, particularly when administered for a limited period and within acceptable daily intake as prescribed by the World Health Organization, that is, 25 mg kg –1 body weight (Kollöffel et al. 1996). Glover & Reed (1996) reported adverse effects associated with propylene glycol, but it is interesting to note that this occurred following excessive ingestion of a propylene glycol-containing product. Based on chronic toxicity data, the use of propylene glycol when given in small amounts does not produce any deleterious effects (Ruddick 1972). Aside from the fact that it is a well-recognized vehicle for drugs, propylene glycol has also been found to be less cytotoxic than other commonly used vehicles for intracanal medicaments and possesses antibacterial properties that are highly beneficial in endodontic treatment (Bhat & Walkevar 1975, Thomas et al. 1980). It possesses hygroscopic properties that allow absorption of water, resulting in a sustained release of intracanal medicaments for prolonged periods (Fava & Saunders 1999).
Distilled water is one of the commonest vehicles used in delivering medicaments into the root canal. It is an aqueous substance having a high viscosity and surface tension (Ho 1983) that causes a high degree of solubility when the paste that it forms with the medicament comes in direct contact with tissue and tissue fluids, resulting in its rapid solubilization and resorption by tissue macrophages (Fava & Saunders 1999). When used as a vehicle for calcium hydroxide, there is the possibility of rapid carbonation of calcium hydroxide from the atmospheric carbon dioxide or that generated by tissue decomposition resulting into the formation of carbonates that do not possess any therapeutic value (Simon et al. 1995). This is not favourable clinically, because it may delay the resolution of infection (Esberard 1992).
Bacteria on the surfaces of root canals may be easily removed and killed by various endodontic procedures, such as ultrasonic irrigation with NaOCl (Huque et al. 1998). However, bacteria which invade and reside deeply within dentinal tubules (Ando & Hoshino 1990) may survive such irrigation procedures (Huque et al. 1998) if the medicaments introduced into the root canal are not delivered efficiently. These remaining bacteria may be capable of causing infections once they reach the periradicular tissues.
Sodium hypochlorite, the most commonly used irrigant in endodontic therapy (West & Roane 1998), in conjunction with ultrasonics, is capable of eliminating bacteria in smear layer and artificially prepared reservoir channels in root dentine (Huque et al. 1998). In order to closely simulate clinical situations, sodium hypochlorite was used as irrigant in this study. However, since sodium hypochlorite alone may not effectively remove smear layer, the use of ultrasonics was employed to enhance the cleansing effect of sodium hypochlorite and improve its ability to remove smear layer as demonstrated by Huque et al. (1998).
Some of the root canal medicaments commonly used, such as formocresol, are volatile, protein-denaturing agents in liquid form and thus, do not require the use of vehicles to exert their bactericidal effect. However, rather high concentrations are necessary to kill bacteria in infected canals. Thus, use of these agents not only leads to elimination of microorganisms but to damage of   periradicular tissues, as well. The antibacterial efficacy of 3Mix had been confirmed against oral infections both in vitro and in vivo (Hoshino et al. 1988, Hoshino et al. 1989, Sato et al. 1992, Sato et al. 1993, Hoshino et al. 1996, Sato et al. 1996). Thus 3Mix could effectively eliminate microorganisms remaining in infected canals, particularly those residing in areas that could not be reached by root canal irrigants. However, an efficient vehicle may be helpful to allow this medicament to more effectively penetrate such areas and thus kill the remaining bacteria. It has been demonstrated that when propylene glycol was used to deliver the dye into the root canal, greater amounts of solute were allowed to penetrate through the dentinal tubules. The results obtained with this method were much higher than when distilled water was used as vehicle. Smear layer delayed the release of dye, even when propylene glycol was used as the carrier. This underlines the need to remove smear layer before introducing medicaments into the root canal if the maximum effect is to be achieved.
Results of the present study also indicated that dye in propylene glycol passed through the main canal of the root and out of the apical foramen with relative ease. In contrast, the dye in distilled water was slow, or even failed, to exit through the apical foramen. Before splitting the tooth, it was noted that in samples where dye in distilled water was used, the solution remained in the orifice. The high surface tension of distilled water may have delayed the efficient penetration of dentinal tubules significantly (Tasman et al. 2000). This accounts for the limited staining, as well as the much reduced area and depth of dye penetration of these samples which was confined mainly in the coronal end of the roots. Propylene glycol, although viscous as compared with distilled water, has a low surface tension. This gives it an advantage of being able to penetrate through dentinal tubules that was not observed when distilled water was used as a vehicle.
In observing the time and depth of dye penetration through the root canal system, including dentinal tubules, the root specimens were either covered entirely with inlay wax (except for the apical foramen) or left uncovered (except for the coronal opening). The results of the present study showed that there was no difference in the results obtained whether the roots were covered or not. In both instances, propylene glycol managed to penetrate deeply into the deeper layers of root dentine.
Another aim of the present study was to develop a standardized procedure that would allow testing of the efficiency of vehicles for intracanal medicaments to diffuse through dentinal tubules. A part of the study used the same set of specimens that were subjected to different vehicles and different experimental conditions. This allowed for a more accurate observation and comparison of the results that would not have been possible if different sets of teeth, whose histories and physical condition varied greatly, were used. Analysis of the split halves of the specimen was done using Adobe Photoshop and NIH Image Program. This enabled a uniform, efficient and bias-free observation of the actual depth of dye penetration in the individual specimens. In addition, the procedure permitted the actual measurement of the total surface area that was penetrated by the dye. This method would therefore be a very useful tool to visualize and measure the areas and extent of microleakage in dye penetration studies.

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