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 »  Home  »  Endodontic Articles 9  »  Temperature change within gutta-percha induced by the System-B Heat Source
Temperature change within gutta-percha induced by the System-B Heat Source
Introduction - Materials and methods.



M.Venturi, G. Pasquantonio, M. Falconi & L. Breschi.
Private Practice, Bologna, Italy,Private Practice, Rome, Italy.
Department of S.A.U. & F.A.L., University of Bologna, Bologna,  Italy.
Department of Science and Society, University of Cassino, Cassino (FR), Italy.


Introduction.
Complete filling of the root-canal system is a fundamental prerequisite for success in root-canal treatment (Schilder 1967). Several studies have revealed that an inadequate sealing of the apex is one of the most important causes of failure (Nguyen 1987, Ingle & Bakland 1994).
The combination of gutta-percha with sealer is the most common method of filling the root-canal system (Canalda-Sahli et al.1992). Several techniques have been proposed to obtain the best adaptation of the guttapercha to the canal walls. In particular, vertical condensation of warm gutta-percha is considered to be one of the most useful techniques to achieve complete filling (Dulac et al.1999) and to ensure success of the treatment (Schilder1967).This technique involves the use of a heat source to soften the gutta-percha cones so as to adapt them to the canal system (Schilder1967). Different endodontic heating systems have been proposed to ensure correct heating of the gutta-percha cones after their placement within instrumented root canals. In particular, one of these systems combines the heating procedure with vertical condensation, in order to obtain the correct pressure of the warm and soft gutta-percha and to allow the homogenous distribution of the filling into the apical third of the endodontic system. This device is called System- B Heat Source (Analytic Technology, Redmond,WA, USA) and its clinical application is related to a modified vertical condensation technique called‘continuous wave of condensation’ (Buchanan 1996, Analytic Technology Corp. 1997b). The correct use of this device simplifies the vertical condensation technique allowing an easier clinical approach. Evident limitations to this technique can be found when a minimal root-canal preparation is performed as it may be very difficult to reach the apical third of the root canal with the heat carrier and to transfer adequate heat to soften the apical gutta-percha. It must be emphasized that in a great number of roots the thickness of the dentine walls is minimal and thus, great effort shave to be taken to obtain minimal endodontic preparations to prevent fracture of the restored teeth.
The aim of this study was to evaluate in vitro thermal changes induced by the System-B Heat Source on the gutta-percha of the apical third of narrow root canals. The null hypothesis tested was that the use of this instrument, in accordance with the manufactures’ instructions, would allow sufficient heat and soften the apical gutta-percha.

Materials and methods.
Twenty-eight noncarious human teeth (27 maxillary incisors and one maxillar first molar, for a total of 30 canals) were selected for the study. The teeth had no restorations and apical foramen a between 0.20 and 0.35 mm in diameter. Rootswi th resorption, fractures or open apices were discarded. Immediately after extraction the teeth were stored in 0.5% chloramine (Ogna, Milan, Italy) at 4 8C up to1month.
Specimens were prepared by the same operator under 3.5x magnification (Designs for Vision, Ronkonkoma, NY, USA). A conventional endodontic access to the pulp chamber was made using a tapered diamond bur (no. 845.314.012 Komet Brasseler, Lemgo, Germany) mounted on a contra-angle hand piece (Kavo Intramatic 25C, Kavo GmbH & Co, Biberach, Germany), and a Batt bur No. 4 (Dentsply Maillefer, Ballaigues, Switzerland) mounted on a low-speed hand piece (Kavo 20 LH Intra Lux 3 hand piece with a Kavo 68 LH Intra Lux head 1:1, Kavo GmbH & Co, Biberach, Germany). All preparations were performed under copious air/water spray.
Each canal was measured and the working length was calculated with a size 06 stainless steel K-file (F.K.G.Dentaire, La Chaux-de-Fonds, Switzerland) placed into the canal until it was just visible at the apical foramen. Root canals were divided in two equal groups on the basis of their apical diameter: in group 1, a size 20 or 25 K-file engaged the apex in D1; in group 2, a size 30 or 35 K-file engaged the apex in D1. The canals were instrumented at working length with a combination of step-back and coronal a ring instrumentation technique using K-files size 06-70 with a watch-winding and pull motion, and with linear filing. A size 20 or 25 K-file in group 1, and 30 or 35 in group 2 were controlled to engage in D1 at working length, and successively larger flles were inserted at 1.0 mm steps short of each other until the mid canal area was instrumented to a size 70 file.
During the first phases of the instrumentation, Hedstrom files size 08-20 (Micro-Mega, Besancon, France)were also employed, and in the coronal and middle third of the canals a ring was obtained with Gates- Glidden burs size1, 2 and 3 (Dentsply Maillefer). All root canals were prepared in order to obtain a continuous, tapered funnel, and without any apical stop. Apical patency was maintained by recapitulation with a size 10 K-file.
The canals were irrigated with 5% sodium hypochlorite between each file size, and were lubricated with RCPrep (Hawe Neos Dental, Bioggio, Switzerland). After canal preparation, specimens were rinsed with water, then with 5% NaOCl, and finallydried with absorbent paper points.
Size F nonstandardized gutta-percha cones (Kerr Co., Romulus, MI, USA)) were placed in the canals 1mm shorter than working length in anticipation of the apical movement of the gutta-percha during vertical condensation (Schilder 1967). No endodontic cement was used. Two small holes were then cut on the root surface of each tooth using a round size10 bur mounted on a low speed hand piece: the first cavity (coronal, point C) was placed 2 mm apically from the cement-enamel junction (CEJ) andwas0.25 mm in depth; the second one (apical cavity, point A) was placed 1.5 mm from the apex and in direct contact with the gutta-percha in the canal. Two Cromel- Alumel type K (AG, Sunnyvale, California, USA) thermo couples equipped with a fine tip (diameter, 0.2) were secured at points A and C with a light-cured composite resin to fully seal the preparations (Z-250Restorative System,3M, Minneapolis, MN, USA).
The two thermo couples were then connected to a type K digital thermometer (range: _60-1200 8C; estimated error: _0.1 8C below 200 8C and _1 8C over 200 8C). A small amount of composite resin was used to cover and insulate the apical foramen.
Teeth were then connected to a metallic grid with epoxy resin, in a vertical position so that each root could be immersed in deionized water, whilst the coronal part of the teeth remained above the liquid surface (Fig. 1). The metallic grid with the attached teeth were then immersed in a thermostatic bath of deionized water (at constant temperature of 37 8C). Specimens had the access of the root canal above the water level (Fig.1).

Figure 1. Image of the specimens preparation. The roots were connected to a metallic grid and immersed in a thermostatic bath (at constant temperature of 37 8C); the coronal part of the teeth remained above the liquid surface. The thermocouples were connected at points A and C.

The roots were connected to a metallic grid and immersed in a thermostatic bath

Prior to down packing, the temperature of the tip of the System-B Heat Source used for the study was recorded by means of a thermocouple in order to compare the real temperature with the value indicated by the manufacturer. Temperatures were recorded in air on direct contact with the insert tip of the System-B Heat Source; measurements were performed at the tip of the instrument, and at 2, 4 and 20 mm from its tip. Four different System-B Heat Source devices with four different F tips were tested, but no statistical differences were found between the units.
Considering that no exact correlation was found between the temperature set on the display and the temperature recorded by the thermocouple on the tip, the System-BHeat Source was set to 250 8C, thus,at a higher temperature than the one suggested (200 8C on display during apical condensation, i.e. down-pack; Buchanan 1998).
Gutta-percha cones were then submitted to warm vertical compaction using the System-B Heat Source with a F plugger (Analytic Technology, Redmond, WA, USA, mod.1005 Serial number #1532515) and following the System-B technique recommended by the manufacture (Analytic Technology Corp. (1997b). The heat carrier was left in the canal for 10 s (Buchanan 1996). The tip of the instrument was taken as deep as possible inside the canals: depending on the curves in some canals it approached at 1mm from the apex, in others it stopped at 5 mm.
Temperature values were recorded at points C and A throughout the whole process of vertical compaction of the gutta-percha and the highest recorded value was taken as representative for each specimen.
Statistical analysis was performed in order to evaluate the distribution of the differences of temperatures recorded at points A and C of each of the two groups. A Kolmogorov-Smirne test was applied to evaluate the distribution of the data within the groups and means and standard deviations of each group were calculated. A  two-way anova was used to compare the two groups.