MEASUREMENT OF THE RISE IN TEMPERATURE ON THE EXTERNAL ROOT SURFACE DURING OBTURATION-AN IN VITRO STUDY

Research

Dr. Ashwini. S. Colaco (Assistant Professor), Department of Conservative Dentistry and Endodontics, A.J. Institute of Dental Sciences, Mangalore, KAR. INDIA

ABSTRACT

A successful endodontic therapy involves adequate obturation of the root canal system. Heat has often been applied to enhance better packing of the obturation material. However, the use of heat above the threshold level can cause damage to the periodontal system. The objective of this in vitro study was to measure the temperature rise on the external root surface during obturation on using two different systems.

Material and Methods: Twenty extracted human premolars with a single canal and complete root formation were selected for this study. The study was conducted in the department of conservative dentistry and endodontics at A J Institute of dental sciences, after receiving ethical approval from the institute research ethics committee. The root lengths were standardized, working length was determined, shaping and cleaning was completed and the teeth were divided into two groups. In group A the teeth were filled with warm vertical compaction method using System B. while group B were obturated by thermoplasticized gutta-percha technique using Obtura II. A thermocouple device connected to a digital thermometer was used to measure the rise in temperature on the external root surface. Data was analyzed using student t test

Results: The findings of this study suggest there was a rise in temperature in both groups. The critical level of heat that can cause irreversible bone damage is believed to be > 10°C. Group B caused greater rise in root surface temperature than group A nevertheless, the rise in temperature is significantly less than the critical temperature.

Conclusion: The obturation techniques used in this study may not have any damaging effect on the tooth structure. However, caution should taken and further clinical studies would be encouraged.

Key words: Root canal obturation, warm vertical compaction, critical temperature, thermoplasticized gutta-percha, periodontal ligament.

Running title: Rise in external root surface temperature during Obturation

INTRODUCTION

The aim of successful endodontic therapy of the necrotic or irreversibly diseased pulp is complete debridement of the infected tissue followed by obturation of the root canal system with an inert filling material and the creation of a hermetic apical seal.1 Gutta-Percha is the most commonly used root canal obturation material. It is used in several obturation techniques due to its chemical and physical properties such as inertness, biocompatibility, plasticity when warmed, and ease of removal for post or retreatment. Many Gutta-Percha obturation techniques are used to fill root canals amongst which cold lateral compaction is a often used due to its simplicity, however it has certain disadvantages such as risk of void formation, inadequate adaptation of root filling material to the root canal walls and inability to effectively seal lateral canals.2 Studies have also indicated overzealous compaction of gutta-percha cones in order to attain a homogenous mass may predispose the tooth to vertical root fracture due to excessive wedging force.3 Hence in order to improve the obturation quality, Schilder introduced warm vertical compaction technique. In this technique heat is used to soften and enhance better packing of the obturation material.

The main advantages of such techniques include dense obturation with lower risk of void formation and better adaptation to the root canal complexities.4 Amongst the various thermoplasticised techniques, System B Heat Source (SybronEndo), and the Obtura II (Obtura Spartan) are commonly used. System B was developed by Buchanan. It consists of a heating device that is used for warm vertical compaction. System B provides continuous wave of heat which promotes down-packing of gutta percha core material and sealer into the root canal.5 Another recent advance is the use of thermoplasticized gutta-percha technique that utilizes heat along with gutta percha to obturate the root canals.6 Thermoplasticized guttapercha with obtura II is used in difficult cases such as internal resorptions, curved canals, open apex and perforations. This technique demonstrates superior adaptation to the three-dimensional root-canal system.7 However, one of the potential shortcomings associated with the use of heat during obturation is the rise in temperature on the external root surface.8 Temperature elevations of 10°C above body temperature, of duration >1 min, may be sufficient to cause bone tissue injury. Studies have shown that a rise in temperature above critical 45°C causes surface resorption of the cementum, bone remodelling and fat cell necrosis.9 The aim of this in vitro study was to measure the rise in temperature on the external root surface of teeth which are obturated using two different obturating systems.

METHODOLOGY

Firstly, ethical review was done and approval was attained by the institute research ethics committee. This was an in vitro research study was conducted in the department of conservative dentistry and endodontics at A J Institute of dental sciences, for duration of three months. The study was conducted after receiving ethical approval from the institute research ethics committee. Informed consent and confidentiality was not applicable since it was an in vitro study.

20 single rooted human anterior and premolar teeth were selected for this study. The inclusion criteria for the selection of the tooth sample included that all the selected extracted teeth should have completely formed apices with no abnormal root morphology or noticeable defects. Radiographs were used to evaluate single canal teeth with no resorption or calcification, along with confirmation of the type I root canal anatomy and patency of the canals. Any tooth that did not fit in the inclusion criteria was excluded from the study. Soft tissues and the calculus were removed from the selected teeth. Next, All samples were then decoronated to obtain a standardized root length of 15 mm from the apex using 898 (213) flame diamond bur (NTI-Kahla GmbH). The working length was determined 1 mm shorter from the apical foramen using a size 15 k file (Dentsply/Maillefer, Ballaigues, Switzerland). The shaping and cleaning of root canals was done using rotary protaper Ni-Ti file system (Dentsply/Maillefer).

All teeth were enlarged upto ProTaper F3 file (Dentsply/Maillefer). Copious irrigation with 5% sodium hypochlorite and ethylenediaminetetraacetic acid (EDTA) of approximately 20 mL per root canal was done before, during, and after preparation. Before the obturation, passive ultrasonic irrigation was applied with an Irrisonic tip (Helse Dental Technology, S~ao Paulo, SP, Brazil), which was activated by an ultrasonic EMS device (Hu-Friedy, Chicago, IL). Then, the root canals were dried with absorbent paper points, and AH Plus sealer (Dentsply, York, PA) was manipulated according to the manufacturer’s instructions, and the canal walls were thinly coated with sealer. In sequence, the samples were divided into 2 experimental groups (group A and group B). Each group consisted of 10 teeth. Following which, the root canals were obturated.

Group A:

In this group canals were obturated using warm vertical compaction method using System B (Sybron Endo, Sybron Dental Specialities, USA). The technique employed was as recommended by the manufacturer and followed the Buchanan technique. A medium-large insert tip, which bound in the canal 3 mm from the working length, was selected following which an appropriate sized gutta-percha cone was selected and placed 0.5 mm short of the working length. The System B unit was preset to 200â—¦C as recommended by the manufacturer. The gutta-percha cone was thermo softened and apically condensed.

Group B:

The teeth in this group were obturated by thermoplasticized gutta-percha technique using Obtura II technique. A 23-gauge Obtura (Obtura Spartan, Fenton, MI, USA) needle tip was selected. The control unit of Obtura II was turned on, and the display showed the required temperature of 200°C after couple of minutes (according to the instruction manual). The gun was loaded with a fresh pellet of gutta- percha and plunger was pushed forward. The needle was then positioned in the canal so that it reached 3 to 5 mm short of the working length. The trigger was pressed so that the molten gutta-percha flowed, and the tip was withdrawn slowly out of the canal. An apical plug was created in this manner. A segmental technique was used in which 3 to 4 mm of gutta-percha were sequentially injected and uniformly compacted with pluggers without any apical pressure. Backfilling was achieved by the application of thermoplasticized gutta-percha in 3–4 increments until gutta-percha reached up to the top orifice level, and then compaction was done with a plugger.

Measurement of the rise in temperature on the external root surface

The temperature measurement was carried out using a thermocouple device which in turn is connected to a digital thermometer to produce an accurate reading. The root lengths of all teeth were standardized at 15 mm and the measurement of the rise in temperature was carried out at the apical 5mm of the root for all teeth. The rise in temperature on the external root surface of teeth during obturation in group A and group B was measured in Ëšc and recorded.

Statistical analysis:

The mean rise in temperature in both the groups was measured. Subsequently students t test was used to test the significant difference in the rise in temperature between group A: teeth that we obturated with warm vertical compaction method using system B and group B: thermoplasticized gutta-percha method using Obtura II technique.

Result

The mean temperature rise, and standard deviation (SD) recorded on the apical third of the outer root surfaces during obturation in both groups was analyzed. The mean ±SD of rise in temperature in group A and group B are 3.47 ± 0.77 and 4.38 ±1.56 respectively. Analysis using student t test indicates that there is statistically very high significant difference in the mean temperature rise between the two groups (p < 0.01).The mean rise in temperature in group B (4.38 ±1.56) was significantly higher than group A (3.47 ± 0.77) at 1% level of significance (P< 0.01) as represented in table I.

Table I: Statistical significance in the rise in temperature in group A and group B using student t test analysis

GROUP

E ±SD

t value

Significance

GROUP A

3.47 ± 0.77

1.59

P<0.01

GROUP B

4.38 ±1.56

DISCUSSION

Recent advances in obturation procedures have led to the development of various systems that promote the improvement of the quality of obturation. Techniques such as warm vertical compaction method using System B and thermoplasticized gutta-percha technique using Obtura II helps to attain a more homogenous mass. The heat used in both techniques increases the flow of the material and produces a denser, well‑adapted and dimensionally stable root canal filing.10 This is an in vitro study that investigated the rise in temperature on the external root surface during root canal obturation using two different technique’s which includes warm vertical compaction method using system B and thermoplasticized gutta-percha technique using obtura II technique. The results of this study supported the hypothesis that there was a statistically significant difference in temperature measurements among both the groups. However, when correlated with the clinical situation, the temperature rise is significantly less than the critical temperature of 10°C, indicating that the use of both these obturation techniques does not damage the surrounding tissues. This result may be attributed to poor thermal conductivity of dentine (1.36 × 10−3 cal / s/cm 2 /C/cm) which helps to dissipate the heat and prevent its transfer to the attachment apparatus.11 In addition, gutta-percha is a poor thermal conductor of heat, and does not allow heat transmission.12 In vivo the presence of blood circulation present in the periodontal membrane and the wetness of dentine; brought by the presence of fluids in the dentinal tubules also contribute to limit heat transmission resulting in lower temperature on the root surface.13

The mean temperature rise at the apical third for group A was 3.47 ± 0.77 and group B was 4.38 ±1.56 respectively. At p < 0.01, the mean temperature rise was statistically significant. Analysis using student t test indicates that there is statistically very high significant difference in the mean temperature rise between the two groups and that group B was greater than group A. Consequently, when correlated with the clinical situation, although both the groups showed statistically significant rise in temperature in the apical third at their respective P values and the heat generated within the root dentine could be transmitted to the attachment apparatus. Nevertheless, in this study at no given point of time, the temperature change on the external root surface exceeds the critical temperature.

The critical temperature for injury to the attachment apparatus has been reported to be 10°C above the human body temperature. [14] A sophisticated vital microscopic study conducted by Eriksson and Albrektsson concluded that the temperature for bone injury may be as low as 47°C or 10°C above human body temperature(37°C).15 This critical temperature is associated with denaturation of alkaline phosphatise, thereby bone alkaline phosphatase is rapidly inactivated causing deleterious effects on the alveolar bone, cementum and periodontal ligament.16 In this study since the rise in temperature is significantly less than the critical temperature, the use of warm vertical compaction using system B or thermoplasticized gutta-percha technique using Obtura II for obturation does not damage the surrounding tissues.

CONCLUSION

Within the limitations of this study, it was found that there was a rise in temperature during endodontic obturation on using both methods. Thermoplasticized obturation technique using Obtura II caused greater rise in root surface temperature. However, when correlated with a clinical situation, the temperature rise is significantly less than the critical temperature, indicating that the use of both these obturation techniques may not have any damaging effect on the tooth structure. The present study was conducted in an extra oral environment thus, further clinical studies would be required in this aspect.

Disclosure and conflict of interest: Not applicable.

Acknowledgement: I wish to express my appreciation to Manipal University and staff of A J Institute of Dental Sciences, especially Dr Manjula for the statistical analysis.

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