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Year : 2020  |  Volume : 10  |  Issue : 1  |  Page : 51-55

External root surface temperature changes during high-temperature injectable thermoplasticized root canal obturation in simulated immature teeth

1 Department of Conservative Dentistry and Endodontics, SGT Dental College, Gurgaon, Haryana, India
2 Department of Conservative Dentistry and Endodontics, Faculty of Dentistry, Jamia Millia Islamia, New Delhi, India
3 Private Practitioner, Dentsitry Redefined, New Delhi, India

Date of Submission16-Apr-2019
Date of Decision19-May-2019
Date of Acceptance31-May-2019
Date of Web Publication27-Dec-2019

Correspondence Address:
Dr. Vivek Aggarwal
Department of Conservative Dentistry and Endodontics, Faculty of Dentistry, Jamia Millia Islamia, New Delhi - 110 024
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/sej.sej_61_19

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Introduction: The present study evaluated the change in the temperature of the external root surface of simulated immature teeth obturated with high-temperature injectable thermoplasticized gutta-percha.
Materials and Methods: Root canals of 60 mandibular premolars were enlarged till size # 6 peeso freely passed through the apex. After placement of an apical barrier of 4 mm of mineral trioxide aggregate (MTA), two K-type thermocouples were attached at middle and apical thirds. The canals were obturated using high-temperature injectable thermoplasticized gutta-percha with either no sealer; AH plus sealer; or MTA Fillapex sealer. Maximum temperature rise was measured and evaluated. The data were analyzed using two-way ANOVA test.
Results: The temperature increased after 4 s of placement of heated gutta-percha. There was no significant effect of sealer placement on the peak rise in temperature at the middle third (P < 0.05). There was no difference between the AH plus and MTA Fillapex groups (P = 0.42).
Conclusions: The use of thermoplasticized gutta-percha can significantly increase the temperatures on the external root surface.

Keywords: Immature apex, mineral trioxide aggregate, obturation, sealer, temperature changes, thermocouple

How to cite this article:
Singla M, Aggarwal V, Sinha N. External root surface temperature changes during high-temperature injectable thermoplasticized root canal obturation in simulated immature teeth. Saudi Endod J 2020;10:51-5

How to cite this URL:
Singla M, Aggarwal V, Sinha N. External root surface temperature changes during high-temperature injectable thermoplasticized root canal obturation in simulated immature teeth. Saudi Endod J [serial online] 2020 [cited 2020 Apr 1];10:51-5. Available from: http://www.saudiendodj.com/text.asp?2020/10/1/51/274192

  Introduction Top

Management of an immature tooth with open apex presents a challenge for the clinician. The criterion to categorize an apical area as open apex varies with different authors. Radiographic evidence of thin walls along with apical diameter ranging from sizes ISO 40 to 100 have been suggested to categorize the open/immature apex.[1],[2],[3],[4],[5],[6] It is difficult to achieve an apical stop in open apex cases.[1],[2] The traditional treatment involves long-term placement of calcium hydroxide in the root canal space to induce hard-tissue barrier formation at the apex.[1],[2],[5],[6] However, this method may alter the mechanical strength of the dentin and make the tooth susceptible to fracture.[1],[7] This method is being gradually replaced by the one-step placement of mineral trioxide aggregate (MTA) barrier in the apical one-third of the root canal.[7] The remaining canal space is filled by thermoplasticized gutta-percha.

The temperature of the contemporary thermoplasticized gutta-percha can range from 160°C to 240°C.[8],[9] Root canal obturation with high temperature can cause a transient increase in the root surface temperature.[10] This transient increase in temperature may damage the supporting structures, including the periodontal ligament and the alveolar bone. A 10°C increase has shown to damage the bone in rabbits.[11] Molyvdas et al.[12] reported that the use of high-temperature thermoplasticized technique resulted in inflammation and destruction of collagen fibers. Other reports have suggested that temperatures ranging from 50°C to 60°C results in damage to the alveolar bone.[12],[13],[14]

Various studies have evaluated the increase in surface temperatures during root canal obturation with thermoplasticized gutta-percha techniques.[10],[15],[16] Lipski [10] used Obtura II system and injected gutta-percha at 160°C. The increase in surface temperature ranged from 8.5°C to 22.1°C. Another study by Lipski [17] evaluated continuous wave compaction technique using a System B Heat Source and reported a rise of 11.7°C in the root temperatures. This rise is very less as compared with intra-canal temperatures during obturation. This can be attributed to the poor thermal conductivity of the dentin.[18] This prevents excessive heat transfer to the periodontal and adjacent structures. However, this protective effect is directly proportional to the thickness of dentin.[19] In cases of thin walls, the heat can be rapidly transmitted to the external root surfaces. The purpose of this study was to measure the change in the root surface temperature in simulated immature teeth obturated with high-temperature injectable thermoplasticized gutta-percha technique combined with different sealers.

  Materials and Methods Top

Sixty freshly extracted, uniradicular, human mandibular premolars were used in this study. An approval was taken from the Institutional Research Review Committee (FTS/2016/IEC/12/JMI). The selected teeth were without cracks, root resorption, or extensive caries; and had approximately similar dimensions with a mesiodistal width of 5.0–5.5 mm and buccolingual width of 7–8 mm. To rule out any aberrant canal morphology and to confirm a single straight root canal, the samples were radiographed. The samples were stored in distilled water till use. Coronal endodontic access was prepared using round diamond burs in a high-speed water cooled handpiece. An ISO size # 10 file was introduced in the canal till it emerged from the apical foramen. Working length was estimated by subtracting 0.5 mm from the length. The root canals were enlarged till ISO size # 40 using a balanced force technique. To simulate immature apex, the canal diameter was gradually enlarged by passing increasing sizes of peeso reamers beyond the apex. The apex size was enlarged till size # 6 peeso drill freely passed through the apex. To confirm the thinning of root canal walls, the samples were radiographed in a buccolingual direction. The radiographs were fed into Image J software (Image J 1.48 v, Wayne Rasband, NIH, USA). The root canal wall thickness was determined using measuring tool of the software keeping the apical diameter as a reference. The canal wall thickness was kept at a maximum of 2 mm by filling the root canal walls using ISO size # 40 H files. The canals were copiously irrigated between the change of file and peeso reamer, with 5.25% sodium hypochlorite and 17% ethylenediaminetetraacetic acid solution with a 27G needle, followed by a final rinse with 10 mL of distilled water. To simulate clinical conditions, the samples received 4 mm of white MTA (ProRoot, Dentsply/Tulsa Dental, Tulsa, OK, USA) apical barrier. The samples were embedded in a saline-soaked sponge to prevent extrusion of the MTA. The MTA powder was mixed with the manufacturer's supplied liquid till a thick consistency was obtained. The material was packed apically using hand pluggers without any ultrasonic activation. A wet cotton pellet was placed in the root canal space and the canal entrance was sealed with the temporary restorative material (Cavit-G 3M ESPE). The specimens were stored at 100% humidity at 37°C. After 7 days, the entrance filling was removed and the root surfaces were dried with a blotting paper. Two K-type thermocouples (HI766 series K-type thermocouple, Hanna Instruments, Mumbai, India) were attached at the middle (5 mm from apex) and coronal (9 mm from apex) thirds using a sticky wax [Figure 1]. The wires of the thermocouples were coated with hot glue. The thermocouples were attached to a digital thermometer (Thermometer with RS232 Output-HI93531R, Hanna Instruments, Mumbai, India). Before placing on to the root surfaces, the thermocouples were tested on ice and boiling water. To simulate the heat dissipation by body tissues at body temperature, the samples were fixed on the lid of a perforated plastic container containing normal saline in a manner that the roots were submerged. The assembly was kept in a laboratory water bath, with the temperature set at 37°C.
Figure 1: Placement of thermocouples at middle and coronal thirds of the root

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The samples were divided into three groups on the basis of root canal sealer. Group 1 received no sealer. In Group 2, AH plus sealer (Dentsply DeTrey GmbH, Konstanz, Germany) was used. Group 3 received MTA Fillapex sealer (Angelus MTA fillapex handy mix tubes, Londrina, Brazil). The sealers were prepared according to the manufacturer's instructions. The sealer was carried into root canal space with the help of ISO size # 80 paper points and was evenly spread on the root canal walls. After application of sealer, the canals were obturated using high-temperature injectable thermoplasticized gutta-percha (Elements obturation system, sybron endo). The extruder handpiece of the system was activated and the temperature was set at 200°C. The gutta-percha was extruded in the canal using 23G needle. The needle was inserted in the canal till 1 mm from the set MTA. The gutta-percha was extruded and compacted using finger pluggers in 4 mm increments. A total of two increments were used to fill the root canal space. The temperature readings from both the thermocouples were recorded every second. The measurements were started 30 s before the obturation and were carried out after 3 min of compacting the gutta-percha in the coronal space. Maximum temperature increase was calculated by subtracting 37°C from the peak temperature obtained. The temperature readings were recorded for statistical evaluation, using SPSS software version 15 for Windows (SPSS Inc., Chicago, IL, USA). The data were statistically analyzed using two-way ANOVA and post hoc Holm Sidak tests, and the level of statistical significance was kept as 5%.

  Results Top

The temperatures were recorded at two locations: middle and coronal third of the root. Two-way ANOVA was used to analyze the data, keeping sealer and location of the thermocouple as variables. The maximum increase in the temperature in the group with no sealer was 9.2°C ± 1.4°C at the middle third and 9.7°C ± 1.2°C at the coronal third. The AH plus group presented with a peak rise of 8.5°C ± 1.6°C and 8°C ± 1°C at the middle and coronal thirds, respectively. The MTA Fillapex sealer group showed a maximum temperature rise of 8.7°C ± 1.1°C at the middle and 7.4°C ± 0.9°C at the coronal thirds [Table 1]. There was no significant effect of sealer placement on the peak rise in temperature at the middle third [Table 2]. However, the changes were significant at the coronal thirds. Both AH plus and MTA Fillapex presented with significantly lower peak values at the coronal thirds compared with the group with no sealer (P < 0.05). There was no difference between the AH plus and MTA Fillapex groups (P = 0.42). The distribution of peak rise in temperature has been displayed as box-and-whisker plot in [Figure 2].
Table 1: Maximum rise in temperature (°C) obtained in all groups

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Table 2: Statistical analysis of effect of location of thermocouple and effect of sealer placement using two-way ANOVA calculations

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Figure 2: The box-and-whisker plot of peak rise in temperature in all groups

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In all groups, the temperatures started to increase within 4 s of first gutta-percha increment. The temperature in the middle thirds increased to maximum within 14–22 s. Similarly, when the second increment was placed near the coronal thermocouple, the temperature started to increase with 2 s and attained its peak within 10 s of second increment [Figure 3]a, [Figure 3]b, [Figure 3]c.
Figure 3: Temperature change during root canal obturation

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  Discussion Top

The present study evaluated the effect of high-temperature injectable thermoplasticized gutta-percha obturation on the root surface temperature in simulated immature teeth. It was found that temperature on the external surface increased within a few seconds of the introduction of high-temperature gutta-percha in the canal. Many dental procedures such as tooth cutting, ultrasonic preparations, post space preparations, root canal obturations, and diode laser application can increase the temperature of the dentoalveolar tissues.[14],[15],[16],[17],[18],[19],[20],[21] These procedures can be divided into two depending on the source of heat: procedure that releases heat due to friction or tooth preparations and procedures that involve the use of heated dental materials. The traditional method of root canal obturation involved cold lateral compaction of gutta-percha in the root canal space.[8],[9] This method has a high clinical success rate. However, in cases of canal complexities, thermal compaction of gutta-percha is advised. The gutta-percha softens at high temperatures, and it can be flowed into the relatively in accessible areas.[9] The thermoplasticized gutta-percha method heats the gutta-percha at temperatures >160°C and the molten gutta-percha is injected into the root canal space.[9] This high temperature inside the root canal space can be transmitted to the external root surface and can damage the supporting dentoalveolar tissues.[14],[15],[16],[17] The critical temperature, which causes irreversible damage to the bone, is believed to be 56°C. The reason for this belief is that the alkaline phosphatase gets denatured at this temperature.[22] However, this has been refuted by many studies. Lundskog [23] reported that an application of 50°C for 30 s produced bone damage. Eriksson and Albrektsson [11] utilized a thermal chamber for “intravital microscopy” of the heated bone tissue to determine the temperature threshold for bone injury. The authors found that application of 47°C for 1 min resulted in resorption of bone without subsequent regeneration. The results of these studies have suggested that critical temperature for bone injury can be as low as 47°C (10°C rise from normal body temperature). Moreover, the damage to the vital tissues is also dependent on the duration for which the vital tissues are subjected to the high temperatures.[11],[20]

Dentin is a poor conductor of heat.[18] It can provide protection to the supporting tissues from the increased temperature inside the tooth. However, the degree of this protection depends on the thickness of dentin. Gluskin et al.[24] reviewed the thermal injuries caused by intraradicular heat transfer and suggested that the dentin thickness should be evaluated before use of intracanal ultrasonics. Other studies have also suggested that the thickness of remaining dentin plays and important role in heat transfer to the external root surface.[10],[14],[19] This effect is accentuated in cases with immature apex. The root canal walls are thin and fragile and can transmit greater amount of heat. In the present study, the peak temperatures obtained in the group without sealer ranged from 7.1°C to 12.8°C. The critical temperature of 10°C was exceeded in 6 out of 20 samples. Placement of sealer had no significant effect on the rise in peak temperatures in the middle third. The peak temperatures in AH plus and MTA Fillapex groups ranged from 5.2°C to 10.9°C and 5.6°C to 10.2°C, respectively. However, the critical temperature of 10°C was exceeded in only three samples out of 20 in both groups.

The changes on the external root surface have been evaluated by two different methods.[10],[15],[17] The thermal imaging camera can capture the whole of the root surface. However, a major drawback of this system is the inability to place a heat sink. In the clinical scenario, the root is surrounded by periodontal tissue and bone. These tissues are at 37°C and can help to rapidly dissipate any temperature change on the external root surface. To clinical simulate body tissues around the root structure, the roots were submerged in normal saline maintained at 37°C. This method allowed the placement of thermocouples on the root surface. However, the use of thermal imaging is not feasible with this method.

The changes in the external root temperature during root canal obturation have been evaluated by different authors. Notably, Lipski has evaluated the effect of different obturation methods on changes in peak temperatures using infrared imaging. Evaluation of continuous wave compaction method of obturation at 160°C, peak temperatures of 8.5°C were obtained in the maxillary anterior teeth.[17] While using the Obtura system at 160°C, the authors reported a mean maximum temperature rise of 9.35°C in premolars.[25] Weller and Koch [15] used thermocouples and reported a maximum increase of 8.9°C using gutta-percha at 200°C. In spite of reduced dentin thickness, the peak temperatures in the present study were similar to the previously reported studies. This can be explained by the use of heat sink model, which could have helped to rapidly dissipate the heat.

There are certain limitations to the present study. The placement of thermocouples allowed taking temperature measurements at selected areas only. This does not represent the temperature changes on the whole of the root surface. However, as explained earlier, it is the only viable method to measure temperature using a heat sink.

The results of the present study show that use of thermoplasticized gutta-percha can increase the temperatures on the external root surface. Caution must be exercised while using high-temperature obturation methods in roots with thin dentinal walls.

  Conclusion Top

The use of high-temperature thermoplasticized gutta-percha can increase the external root surface temperature.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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Molyvdas I, Zervas P, Lambrianidis T, Veis A. Periodontal tissue reactions following root canal obturation with an injection-thermoplasticized gutta-percha technique. Endod Dent Traumatol 1989;5:32-7.  Back to cited text no. 12
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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2]


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