Journal of Endodontics Research -
Temperature change within gutta-percha induced by the System-B Heat Source
By JofER editor
Published on 09/8/2008
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.

This study evaluated the temperature change within gutta-percha during the vertical compaction technique performed with a System-B Heat Source.

This study demonstrated the thermal changes in guttapercha that occur during the vertical compaction technique by means of a System-B Heat Source. The use of a thermostatic bath distinguished this study from previous reports. The null hypothesis was rejected as the use of the System- B Heat Source (set at 250 8C) in thin canals revealed that the heating of the apical gutta-percha was inconsistent and that the compaction was performed usually at body temperature. Moreover, at the CEJ, the use of the heating device revealed that increases of outer surface temperature on the root was compatible with the periradicular tissues.

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.

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.

Temperatures recorded in air and on direct contact with the insert tip of the System-B Heat Source are shown in Table 1. It must be emphasized that 2 mm from the end of the insert tip (thus, where the higher temperature is recorded), data obtained by means of a thermocouple revealed lower temperatures than the ones shown on the display. In particular, by setting the instrument at 250 8C the temperature reached by the instrument was 123 8C at the tip, and 160, 158 and 66 8C, respectively, at 2, 4 and 20 mm from the tip (Table 1).
The distance between the apex and the deepest point reached by the insert tip was also recorded (Tables 2 and 3); mean values obtained revealed a deeper penetration in group 2 (2.86 mm) thangroup1 (3.26 mm) owing to the differences of the apex diameter (respectively, 0.30-0.35 and 0.20-0.25 mm).
Values of increments in temperature (DT) of the guttapercha of the tested specimens revealed by the thermocouple at points A and C are shown in Tables 2 and 3 (respectively for specimens of groups 1 and 2). DT recorded in point A revealed a mean value of 0.5 _0.5 8C for group 1 and 0.9 _1.1 8C for group 2 (Table 4). It must be emphasized that point A was set 1.5 mm from the apex, and thus in the specimens in which the insert tip arrived at 1mm from the foramen, the thermocouple was very close to the surface of the insert tip. DT values recorded at point C gave a mean value of 4.1 _1.7 8C for group 1 and 3.9 _1.81 8C in group 2 (Table 4).
Statistical analysis revealed that the data were normally distributed (Kolmogorov-Smirne Test). Lower and upper 95% were determined for each group (Table 4). The statistical analysis revealed that 95% of DT values at point A of group 1 were between 0.2 and 0.8 8C, whilst in group 2 were between 0.3 and 1.6 8C. Similarly,95% of the data at point C of group1were distributed between 3.1 and 5.1 8C, and in group 2 were between 2.9 and 4.9 8C (Table 4).
The two-way anova revealed a statistical difference between DT recorded at points A and C at both groups (P < 0.05), but no difference could be determined between the two groups as no relationship with the different apex diameter was found.

Table 1. Temperature recorded in air with a thermocouple in direct contact with the tip of the System-B-Heat Source.

Temperature recorded in air with a thermocouple in direct contact with the tip of the System-B-Heat Source

Table 2. Increments of temperature in (DT) recorded at point A (1.5 mm from the apex) and C (2 mm from the CEJ) of specimens of group1 (apical diameter 0.20-0.25 mm).

Increments of temperature

Table 3. Increments of temperature (DT) recorded at point A (1.5 mm from the apex) and C (2 mm from the CEJ) of specimens of group 2 (apical diameter 0.30-0.35 mm).

recorded at point

Table 4. Statistical analysis of the increments of temperature (DT) recorded at points A and C of the two groups considered in the study.

Statistical analysis of the increments of temperature recorded at points A and C of the two groups considered in the study

Discussion - References.
Several parameters influence the heating of guttapercha during vertical compaction, particularly because canal systems are complex and narrow. The main parameter to be considered is the low heat conductive capability of dentine (1.36 _10_3 cal/cm2 8C; Craig & Peyton 1961); other factors influencing the heating of gutta-percha are the dentine thickness (Figdor et al.1983), the dimension of the residual roots (Fors et al. 1985) and the periradicular blood circulation (Hardie1986).
The various influences related to the heating of guttapercha can be classified into mechanical, physical, chemical and biological.
Mechanical factors are related to the fact that guttapercha must be plasticized to become adapted to the canal, however, it should not be too soft in order to allow control of the material. Two aspects influence the degree of softening: the necessity to reach and fill narrow and small spaces that require a soft gutta-percha, and the clinical necessity of precise positioning of the cone at the apex in particular when the patency of the orifice is maintained. Moreover, with very soft gutta-percha, the pluggers would penetrate the material rather than compacting it; this could generate empty spaces inside the mass of the gutta-percha during the removal of the instruments (Jurcak et al.1992).
Chemical-physical aspects are related to the fact that the gutta-percha heating process should remain within the range from 37 to 42-45 8C. Temperatures higher than 45 8C give volumetric changes during the cooling owing to phase changes in the structure of the material (Schilder et al. 1985). Heating gutta-percha over 100 8C gives irreversible modifications to the molecular structure (Marciano & Michailesco1989).
Biological problems relate to possible damage to periradicular tissues when the gutta-percha is heated inside the root and when the residual dentine walls are thin (Lee et al.1998).
Factors affecting heat distribution relate to the compaction technique (Silver et al. 1999) and the use of an endodontic cement, that acts as a heat insulator for the periodontal region. Indeed, it has been reported that an endodontic cement can decrease the temperatures by 1-2 8C on the root surface (Barkhordar et al.1990). Considering this finding and to avoid unpredictable influences in the temperatures of the gutta-percha, the endodontic cement was purposely omitted during the specimen preparation particularly because differences in the thickness of the cement layer within the specimens could have affected the results.
Problems may be encountered during the application of warm vertical compaction techniques in small canals asit can be difficult to obtain real thermal effects on the apical portion of the root-canal filling materials. It has been demonstrated (Goodman et al. 1981) that an increase of 4 8C of the apical gutta-percha (over the body temperature of 37 8C) is the ideal level to obtain the correct softening for excellent compaction and good control of the material in accordance with the Schilder’s technique (Schilder 1967). Moreover, it has been reported that using traditional heat-carriers (heated on flame) in wide canals (Marlin & Schilder 1973) the gutta-percha in the coronal third can reach an average temperature of approximately 50 8C, whilst getting closer to the apex the increase of temperature (DT) dramatically drops; at the apical third of the canal DT ison ly 2-4 8C, thus temperature rise over 42 8Care rare. Other similar data were recorded filling wide canals (Goodman et al. 1981, Marciano &Michailesco1989) and confirmed that minimal increases in temperature of gutta-percha are obtainable when approaching the apex even if the carrier is heated with a flame at very high temperature. In thin root canals, these difficulties in heating gutta-percha at the correct temperature increase dramatically.
The use of an electric heat carrier such as Touch’n Heat (models5 001, 5002 and 5004) produces different thermal phenomena (Analytic Technology Corp. 1993). In fact, the heating source is the tip insert itself that can be continuously heated, moreover very thin and flexible tips a re available allowing them to reach apical regions in curved and thin canals.
The System-BHeat Source (AnalyticTechnology Corp. 1997a), compared to the Touch’nHeat, presents more technological capabilities such as the display for the temperature control of the tip and the advantage of combining heating and compaction allowing the Buchanan’s‘ Continuous Wave’ obturating technique (Buchanan1996).
The suggested working temperature for the device using the smallest tip at a distance of 5-7 mm from the apex is185 8C (Buchanan1998). In the present study, different temperature settings were selected in order to evaluate the effective heating power of the device (Table 1) as previous studies have revealed that at the temperature reading on the unit’s liquid crystal display was in accurate and higher than achieved at the tip (Blum et al. 1997, Silver et al. 1999). These discrepancies have been confirmed in this study, thus a higher temperature (250 8C) than the suggested one (200 8C) was set for the down-pack. In fact by setting the tested System-B Heat Source at the temperature of 250 8C on the display, the highest temperature recorded was 160 8C, 2 mm from the tip (Table 1): this result was obtained by putting the thermocouple indirect contact with the instrument.
Several in vitro studies recorded different values of temperature of the gutta-percha during the warm vertical compaction technique (Blum et al. 1997, DuLac et al. 1999, Silver et al. 1999). The different results probably depend upon three factors: the dimension of canals, the periradicular temperature, and the use of a system of thermo-dispersion that can simulate the periradicular blood circulation by maintaining it at a constant temperature of 37 8C. Overall, in such narrow canals there is a small contact area between the tip of the instrument and the coronal part of the apical gutta-percha, reducing the transfer of heat.
The results of the present study revealed that the use of the System-B Heat Source in root canals immersed in a thermostatic bath of water at a constant temperature of 37 8C induces insignificant temperature increases on the apical gutta-percha (0.5 _0.5 8C for group 1 and 0.9 _1.1 8C for group 2) and in all specimens, this increase was lower than the 4 8C previously identified as optimal for the warm compaction. These findings were not related to insufficient penetration of the insertion tip inside canals as the mean distances from the apex were lower (3.26 mm in group 1 and 2.86 mm in group 2) than the suggested ones under normal clinical conditions( usually up to 5-7 mm from the apex). To obtain changes of 3-4 8C within the apical gutta-percha in narrow canals it would be necessary to use instruments at a higher temperature, which might negatively affect periradicular tissues, particularly at the CEJ where dangerous valuesc an be recorded (Hand et al. 1976,Weller & Koch 1995). An increase of 10 8C in periradicular tissues is considered to be dangerous (Eriksson & Albrektsson1983, Fors et al.1985, Hardie1986, Gutmann et al.1987a, Gutmann et al.1987b, Saunders 1990,Weller & Koch 1995), even if effective bone necrosis was found only after maintaining a constant temperature of 44- 47 8C for at least 1min (Eriksson & Albrektsson 1983). Previous studies revealed that traditional heat carriers and Touch’n Heat can create a10 8C increase on the outer surface of the root (Blum et al. 1997, Silver et al. 1999), whilst the System-B Heat Source usually cannot reach this level (Lee et al.1998, Romero et al.1998). The results of this study also confirmed that the DT at point C was not higher than 10 8C in any of the specimens (mean value of 4 8C forgroup1and 3.8 8C for group 2), thus confirming the safety of the clinical use of the System-BHeat Source. Moreover, under normal clinical conditions the endodontic cement, by increasing thermal insulation of the endodontic canal system, reduces the possibility of creating damage to periradicular tissues using the System-B Heat Source.


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