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 »  Home  »  Endodontic Articles 7  »  A preliminary study of the percentage of gutta-percha-filled area in the apical canal filled with vertically compacted warm gutta-percha
A preliminary study of the percentage of gutta-percha-filled area in the apical canal filled with vertically compacted warm gutta-percha
Methods and materials.



Instrumentation.
A total of 60 maxillary and mandibular canines were used. The width of the apical root canal of the maxillary canines has been found to be similar to that of the mandibular canines (Wu et al. 2000c). Access to the root canal system was made in each tooth. A size-10 ¢le was inserted in to the canal until the tip of the ¢file was just visible at the apical foramen (AF). The length to the AF was used as the working length (West & Roane 1998). The coronal aspect of each canal was £ared, using Gates Glidden drills (Dentsply Maillefer, Ballaigues, Switzerland); sizes 50-90 (nos. 1-3) were taken to a depth of 6 mm from the AF, and sizes 110 (no. 4) and 130 (no. 5) to 8 and10 mm from the AF, respectively.
The average canal diameter has been found to be 0.3 mm in maxillary canines, but wider in mandibular canines1mmfromthe apex (Wu et al.2000c), where root canals have the smallest diameter (Dummer et al. 1984). In order to standardize material extrusion and in most cases not enlarge the narrowest part of root canal, all canals were prepared using K-¢les (Dentsply Maillefer )and a size 30 was taken to the AF using circumferential ¢ling until the ¢le was loose. Sizes 40, 50, 60 and 70 were then taken to 1, 2, 3 and 4 mm from the AF, respectively. Finally, the canal was smoothened by again applying the size 30 master ¢le to the AF. Each canal was irrigated between each instrument with 2 mL of a freshly prepared 2% solution of sodiumhypochlorite, using a syringe and a 27-gauge needle. After completion of the preparation, the canal was irrigated with10 mL of 2% NaOCl.
The prepared canals were divided into two equal groups (n ј 30).

Obturation.
All canals were obturated by two operators using warm vertical compaction (Ruddle 1994). The two operators had similar experience of using this technique. Each operator obturated15 root canals in each group. Because it was difficult to standardize the amount of sealer and because the amount could be an influencing factor on the percentage of gutta-percha, no sealer was used. The tip of a medium-sized, nonstandardized gutta-percha cone (Auto¢t, Analytic, Glendora, CA, USA) was trimmed back until tug-back was achieved 0.5 mm short of the AF. The trimmed gutta-percha cone was placed in the canal 0.5 mm short of the AF.
The heat source was standardized by the use of Touch’n Heat (Model 5004, Analytic Technology, Redmond, WA, USA) at a power setting of 10. Each time it took approximately 5 s to place the instrument at the desired depth; the gutta-percha was then heated for 4 s. Ina pilot experiment, a thermocouple was ¢fixed to the tip of the instrument, and between 5 and 9 s after activating the heater at a power setting of 10, a temperature elevation of180 to 230 8C was recorded. The temperature reached a maximum of 270 8C at15 s.
The heat carrier was inserted into each canal three times, to different depths, in order to heat the gutta-percha before vertically compacting it, using prefitted pluggers (Dentsply Maillefer). During the last heating, the heat carrier was inserted to a level 4 mm from the AF in one group and 2 mm from the AF in the other group. A sustained push was performed fora few seconds with the last plugger. In order to assure that the heat carrier could penetrate to the proper depth, the heat carrier was prefitted in each canal.
The number of teeth with gutta-percha extrusion was recorded for each group. The extruded gutta-percha was cut at the AF using a sharp blade and placed on a piece of gauze. For each tooth, the weight of extruded gutta-percha was determined by weighing the gauze before and after collecting the extruded materials, using a sensitiv e scale (1601A, MP8-1, Sartorius AG, Gottingen, Germany).
The ¢filled teeth were stored in100%humidity at 37 8C for 2 weeks.

Sectioning and image analysis.
Using a low-speed saw (Sagemikrotom1600, Leitz, Wetzlar, Germany) all roots were horizontally sectioned 1.5 mm from the AF. As compared to the commonly used Isomet 11-1180 low-speed saw (Buehler Ltd, Evanston, IL, USA), this saw prevents smearing gutta-percha. Because the pressure that pushes the specimen toward the rotating saw disc is controllable, a very light pressure was selected. Smearing gutta-percha was prevented by an improved cooling system; constant fresh cooling water ejected directly towards the interface between the saw disc and the tooth. It had previously been found that under such conditions no smearing of gutta-percha was seen under a microscope at a magnification 50_ (Wu & Wesselink 2001,Wu et al. 2001, 2001a). Colour slides of the sections were taken using a Photomakroskop M400 microscope (Wild, Heerbrugg, Switzerland) at a magnification of 50_. The slides were scanned as tagged image ¢le format (TIFF) images. Using a KS100 Imagening system 3.0 (Carl Zeiss Vision GmbH, Hallbergmoos, Germany) the area of the canal and the gutta-percha was recorded and the percentage of PGFA was calculated. The image analysis was performed blindly by two investigators.

Statistics.
At-test was used to compare the average canal area of the two groups. To investigate the factors associated with either the PGFA in root canals or the occurrence of gutta-percha extrusion, Multiple linear regression models (SPSS/PCюStatistics 4.0software, SPSS International BV, Gorinchem, the Netherlands) were used. When PGFA was the dependent factor, the covariates were the area of the root canal, the depth of heat application (2 or 4 mm), and the operator (1 or 2).When the occurrence of gutta-percha extrusion was the dependent factor, the covariates were the area of the root canal, the depth of heat application (2 or 4 mm), the operator (1 or 2), and the PGFA. The level of significance in all tests was set at P < 0.05.