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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 4  »  Penetration of propylene glycol into dentine
Penetration of propylene glycol into dentine
Introduction - Materials and methods.

E. V. Cruz, K. Kota, J. Huque, M. Iwaku & E. Hoshino
Departments of Operative Dentistry and Endodontics and Oral Microbiology, Cariology Research Unit, Niigata University School of Dentistry, Niigata, Japan.

Previous studies have shown that bacteria in infected root canals and periradicular tissues are capable of invading and residing deeply within dentine and in cementum around the periapex (Ando & Hoshino 1990, Kiryu et al. 1994, Peters et al. 2001). Furthermore, it has been demonstrated that although bacteria in artificial smear layers and prepared reservoir channels in deeper layers of root dentine could be eliminated by procedures such as ultrasonic irrigation with NaOCl (Huque et al. 1998), microorganisms within fins and isthmuses could still remain viable (Sato et al. 1996). Such microorganisms may cause root canal treatment to fail. Thus, the placement of medicaments between appointments may be necessary to disinfect root canals and to reduce periapical pathosis, thus preventing bacteraemia and other local or systemic immunological reactions (Debelian et al. 1994, Walton & Rivera 1996, Murray & Saunders 2000).
Studies have been conducted on the efficacy of a mixture of antibiotics against various forms of oral infections, including those of endodontic origin (Hoshino et al. 1992, Sato et al. 1993, Hoshino et al. 1996, Sato et al. 1996). These were based on the concept of Lesion Sterilization and Tissue Repair (LSTR) therapy. Results of these studies proved to be highly promising as the drug mixture, consisting of metronidazole, ciprofloxacin and minocycline, known as 3Mix, was found to be effective against various oral bacteria from different sources. However, a suitable vehicle to deliver the drug mixture into infected root canals would be helpful. In choosing the appropriate vehicle, one factor that needs to be considered is its ability to facilitate better diffusion of medicaments through root dentine and possibly cementum even in the presence of anatomical aberrations such as fins, isthmuses and blocked canals. Diffusion into the surrounding periradicular tissues may also be an advantage.
Propylene glycol (1,2-propanediol), a dihydric alcohol, is a vehicle that has potential for use in root canal treatment. Its chemical formula is CH 3 CH(OH)CH 2 OH and it has a molecular weight of 76.09 (United States Pharmacopeia 1989). Seidenfeld & Hanzlik (1932) described propylene glycol and conducted studies on its use as a vehicle and pharmaceutical solvent for preparations in medicine. It has been reported to be a widely used vehicle for various pharmaceutical and commercial products such as drugs, cosmetics and foods (Morshed et al. 1988). In addition, it has also been used extensively for caries detection as a constituent of Caries Detector® (Fusayama 1988). In endodontics, it had been used as a vehicle for calcium hydroxide (Saiijo 1957, Laws 1962, Laws 1971, Simon et al. 1995). Unfortunately, no studies have been conducted to determine the extent of penetration of propylene glycol in dentinal tubules or the time required for propylene glycol to diffuse through the root canal system.
The purpose of this study was therefore to determine the efficiency of propylene glycol to diffuse into dentine and through the root canal system using a dye diffusion protocol.

Materials and methods.

Experimental procedure 1: Movement and amount of dye in propylene glycol or distilled water across open dentinal tubules with and without smear layer.

Preparation of specimens.
Ten extracted maxillary central incisors that were not root filled, were free of caries and cracks and stored in 70% alcohol, were used in this study. The histories of the teeth were not known. The crowns of the teeth were removed at the level of the cemento-enamel junction with a high speed bur under water coolant spray. Cementum covering the coronal one-third of roots was removed parallel to the root canal. To ensure an even removal of cementum and to make parallel the remaining root dentine, a 15-mm orthodontic wire attached to the head of an air turbine handpiece and parallel to the diamond bur (SF-13 Dia-Burs, Mani Inc, Tochigi, Japan) was inserted into the root canal. This served as a pivot which the bur followed during cementum removal. The root canals were enlarged using a no. 3 Peeso reamer to a depth of 7 mm.

Removal of smear layer.
To remove smear layer, dentinal debris and soft tissue adherent to the cementum surface of roots, teeth were placed in a Sono Cleaner 50Z ultrasonic bath (Kaijo, Tokyo, Japan) with 5% NaOCl (Wako Pure Chemical, Osaka, Japan). The root canals were further irrigated ultrasonically with 5% NaOCl using an utrasonic unit (Solfy, Morita, Osaka, Japan).

Preparation and application of smear layer.
In order to standardize the presence of smear layer experimentally, decalcified and pulverized dentine with dental plaque was closely adapted to the root canal walls using a finger spreader, in accordance with the method developed previously (Huque et al. 1998).

Figure 1. Schematic illustration of specimen preparation for experimental procedure 1. Dotted lines represent area of the root removed and exposed, whilst the heavy line surrounding the lower two-thirds represents the area covered with inlay wax.

root removed and exposed, whilst the heavy line surrounding the lower two-thirds represents the area covered with inlay wax

Application of dye.
The specimens were dried and the remaining apical twothirds of each root were covered with inlay wax (Fig. 1). Ten microliters of 0.1 mol L −1 safranin O (Schmid GmbH, Köngen, Germany) was introduced into the root canals and sealed with inlay wax. The prepared root samples were placed in individual vials, each containing 2 mL of propylene glycol (Wako Pure Chemical, Osaka, Japan) for the propylene glycol group or distilled water for the distilled water groups.

Measurement of dye released through the dentinal tubules.
The amount of dye released through the dentinal tubules from the root canals was measured using a U-3200 spectrophotometer (Hitachi, Tokyo, Japan) at different times. The procedure was repeated four times on each of the 10 samples after changing the conditions of the root canals, i.e. with or without smear layer, as well as the vehicle used for safranin O, i.e. distilled water or propylene glycol. Thus, these conditions were propylene glycol without smear layers, distilled water without smear layer, propylene glycol with smear layer and distilled water with smear layer.

Experimental procedure 2: Time and depth of dye penetration through the root canal system and beneath fin areas.
Sixty extracted human teeth, consisting mostly of maxillary premolars and mandibular incisors, were used. After crown removal, pulp tissue and debris from the root canals were removed. Canal patency was established by inserting a smooth broach into the root canals 1 mm short of the apical foramen. The presence of fins in root canals were confirmed with the aid of a SMZ-10 stereomicroscope (Nikon, Tokyo, Japan). The orifices of canals were enlarged to a diameter of 2 mm. The root canals were irrigated ultrasonically with 5% NaOCl to remove smear layer and pulp debris. After ultrasonic irrigation, outer root surfaces were covered with inlay wax leaving the apical foramina open. This was confirmed by inserting a smooth broach through the root canal. The specimens were separated randomly into equal groups of 30 roots each: group I for application of safranin O in propylene glycol, and group II for application of safranin O in distilled water. After introducing 10 L of 0.1 mol L −1 safranin O solution into each canal, the orifices of roots were sealed with inlay wax. To avoid contamination by dye exiting through the apical foramen, coronal ends of roots were suspended from the cover of a container. This container also served to provide a moist environment by the placement of wet tissue papers. All samples were maintained at 37 C, and the time for the exit of dye through the apical foramen was noted with the appearance of dye solution at the periapex. After 24 h, the roots were split into two using a pair of straight crown scissors and the depth of dye penetration through the dentinal tubules was measured by directly scanning the samples with the use of Canon IX-4025 scanner (Canon, Tokyo, Japan). The scanned images were viewed using Adobe Photoshop 4.0 J (Adobe Systems, California, USA). These were subsequently treated to delineate the split surfaces of the root from the root canal wall and its background. RGB images of the specimens were subsequently produced for analysis. Image analysis was performed to determine the area of dye penetration using a MacIntosh G3 computer and the public domain NIH Image program (developed at the U. S. National Institutes of Health and available from the Internet by anonymous FTP from or on floppy disk from the National Technical Information Service, Springfield, Virginia, part number PB95–500195GEI) as shown in Figure 2.
An additional 24 maxillary premolar roots were used to observe the extent of dye penetration through the root canal system. These specimens were separated randomly into two groups and treated in a similar manner as described above, except that the roots were not covered with inlay wax.
Readings from the samples were compared using the paired t -test.

Figure 2. NIH Image analysis of specimen showing percentage of surface area penetrated by dye (indicated by dark gray areas) when propylene glycol (a) and distilled water (b) were used as vehicles.

Image analysis of specimen showing percentage of surface area penetrated by dye (indicated by dark gray areas) when propylene glycol