Comparative Evaluation of Thermal Alterations on External Root Surface during Mechanical Instrumentation and Thermoplasticized Gutta-percha Obturation: An Ex Vivo Study

INTRODUCTION

Various procedures during endodontic treatment and restoration of endodontically treated teeth like mechanical root canal preparations, obturations with high-temperature gutta-percha techniques can be associated with the rise of temperature in radicular and periodontal tissue¹ which might be detrimental to the tissues around.² However, heat transfer to the periodontium is a multifactorial process and its quantum is affected by the configuration of the root canal, the amount of remaining dentine thickness, cross-section and design of instrument used, the extent of contact between instrument and canal wall, intermittent or continuous instrument usage, number of revolution per minute and the operator force.³ During instrumentation, heat is generated along the canal walls due to variable frictional forces, also high rotational speed could increase temperature locally.⁴

However, the velocity of a mechanical instrument within the root canal might also create thermal stress on the outer root surface as heat is directly proportional to velocity. The heat produced during canal instrumentation has been reported in various in vitro studies done in past by Ozkocak et al. They evaluated temperature changes in the middle portion of the outer radicular surface using a non-contact type infrared thermometer.⁵

Heat-based obturation systems might also contribute to an increase in temperature on the external root surface and surrounding periodontal apparatus because of the higher temperature of the gutta-percha mass achieved at or around 200°C.⁶ Also, transfer of the heated gutta-percha to the root canal is immediate till the entire canal is filled, the transfer of heat can be more widespread and efficient, thus leading to a higher change in temperature. Extreme temperature increase above the normal body temperature (37°C) may cause any insult to the periapical or periodontal tissues. It has been observed that temperature rise above 10°C in the root canal can cause injury to periapical tissue.⁷

So, as to evaluate heat generation with two of the most commonly used mechanical instrumentation endodontic file systems, ProTaper Gold and WaveOne Gold and common representatives of heat-based obturation techniques Thermafil system and EandQ injection obturation system, the present study was undertaken.

MATERIALS AND METHODS

This experimental ex vivo study was conducted in the Department of Conservative Dentistry and Endodontics at Teerthanker Mahaveer Dental College and Research Centre, Moradabad. The clearance for this study was acquired from the Ethical Committee of Teerthanker Mahaveer University and the study was performed in the Department of Cons. Dentistry and Endodontics, TMDC and RC, Moradabad, Uttar Pradesh.

Freshly extracted intact human mandibular premolar teeth extracted for orthodontic and periodontal reasons were collected. Teeth were cleaned of debris, tissue, and blood clots under running water and subsequently with an ultrasonic scaler and were disinfected by insertion in 3% hydrogen peroxide for 7 days stored in normal saline.

The collected teeth were clinically examined under an operating stereomicroscope (Techno Scientific Instruments, LYZER) and radiographs were taken to rule out the inclusion and exclusion criteria.

The sample size for the study was statistically decided as 72 which were divided randomly into two groups with 36 teeth in each:

Group I—Instrumentation with ProTaperGold (PTG; Dentsply Maillefer, Ballaigues, Switzerland).

Group II—Instrumentation with WaveOneGold (WOG; Dentsply Maillefer, Ballaigues, Switzerland).

Both the groups were further subdivided into two subgroups with 18 teeth in each respective subgroup.

Subgroup IA—Thermafil Plus Obturation System (Dentsply Maillefer).

Subgroup IB—EandQ Master Obturation (Meta Biomed EandQ Master Obturation System Cordless).

Subgroup IIA—Thermafil Plus Obturation System (Dentsply Maillefer).

Subgroup IIB—EandQ Master Obturation (Meta Biomed EandQ Master Obturation System Cordless).

The experimental models for recording the temperature during mechanical instrumentation and thermoplasticized obturation were prepared by placing the tooth in the modeling wax, within a 5 mL syringe, after access opening and determination of working length with #10K file radiographically. Three holes were drilled at three different levels, in the plastic syringe wall, so that probes could contact the external root surface at the coronal, middle, and apical third. The recording of temperature was done after maintaining the baseline ambient temperature at 27 ± 1°C.

Using X-Smart endo motor, ProTaper Gold rotary (PTG; Dentsply Maillefer, Ballaigues, Switzerland) files were used at 300 rpm and 150 torque (g × cm) in the root canal whereas WaveOne Gold rotary (WOG; Dentsply Maillefer, Ballaigues, Switzerland) files were used at 350 rpm in the root canal according to the manufacturer’s instructions. The three temperature probes were placed on the external root surface at the coronal, middle, and apical third which were attached to digital temperature indicators to measure temperature rise. After completion of the biomechanical preparation in both the groups, the final used file was kept running in the root canal for 60 seconds and the highest temperature change across the canal at each of the three-thirds was recorded in both the instrumentation groups.

After biomechanical preparation, samples in group I and II were further subdivided into two subgroups: A and B and were brought to room temperature to obtain the baseline temperature, following which thermoplasticized obturation was carried out with Thermafil Plus Obturation System (Dentsply Maillefer) and EandQ Master System (Meta Biomed EandQ Master Obturation System Cordless), in the respectively assigned subgroups.

In subgroup IA and IIA, specimens were obturated with Thermafil Plus Obturation System (Dentsply Maillefer). The selected Thermafil Plus gutta-percha obturator was then placed in the ThermaprepPlus oven and heated according to the manufacturer’s directions. The resistance temperature probes were placed at the level of drilled holes and the highest temperature was recorded once the heated carrier was placed till the working length.

In subgroup IB and IIB, specimens were obturated with EandQ™ Master System (Meta Biomed EandQ Master Obturation System Cordless). The temperature probes were placed in such a way that they were in contact with the coronal, middle, and apical third of the external root surface through drilled holes in the plastic syringe wall, and the tip was placed inside the root canal space of the prepared tooth without binding. The highest temperature rise was recorded, once the heated gutta-percha spread freely from the tip of the hand-held gun in the canal by keeping it 3–5 mm shorter than the working length, after preheating to 200°C.

The collected data were tabulated and statistically analyzed using multiway ANOVA for intergroup comparison and post hoc analysis for intragroup comparison at different levels.

RESULTS

In group I (PTG), the highest temperature rise was found in the middle third ranging from a maximum of 31.60°C to a minimum of 28.60°C with the mean being 29.71°C followed by an apical third which ranged from a maximum of 30.50°C to a minimum of 28.60°C with the mean being 29.63°C and least in coronal third ranging from a maximum of 30.26°C to a minimum of 28.40°C with the mean being 29.37°C.

In group II (WOG), the highest temperature rise was found in the middle third ranging from a maximum of 30.60°C to a minimum of 28.10°C with the mean being 29.36°C followed by apical third ranging from a maximum of 30.33°C to a minimum of 28.10°C with the mean being 29.4°C and least in coronal third with a maximum of 30.20°C to a minimum of 28.10°C with the mean being 29.0°C.

Thus, temperature rise in the ProTaper Gold group was significantly higher at the coronal, middle, and apical third with p %3C; 0.05 while comparing temperature rise in WaveOne Gold group (Fig. 1).

In subgroup IA and IB (Thermafil Plus Obturation System), the highest mean temperature rise was found in the apical third ranging from a maximum of 28.50°C to a minimum of 27.60°C with the mean being 27.97°C followed by middle third ranging from a maximum of 28.10°C to a minimum of 27.40°C with the mean being 27.74°C and least in coronal third with a maximum of 28.10°C and a minimum of 27.20°C with the mean being 27.64°C (Fig. 2).

In subgroup IIA and IIB (EandQ Master Obturation System), the highest mean temperature rise was at apical third ranging from a maximum of 32.00°C to a minimum of 29.00°C with the mean being 30.02°C followed by middle third ranging from a maximum of 31.70°C to a minimum of 28.70°C with the mean being 29.80°C and least in coronal third with a maximum of 31.50°C to a minimum of 28.60°C with the mean being 29.54°C (Fig. 3).

Thus, temperature rise in EandQ Master Obturation System was found to be significantly higher at the coronal, middle, and apical third with p < 0.05 while comparing temperature rise in Thermafil Obturation System at the coronal, middle, and apical third.

DISCUSSION

The amount of heat generated during the various endodontic procedures involving root canal preparation, warm obturation techniques using thermoplasticized gutta-percha, preparation for post-space, and its cementation can produce thermal changes on the external root surface.⁸ Higher temperature levels might damage the bone tissue and might cause tooth ankylosis or bone necrosis and resorption of the tooth and the surrounding supportive structure.⁹ With high temperatures around 56°C, the inactivation of bone alkaline phosphatase has been reported.² It has also been assessed, that a 1-minute exposure at 53°C might result in interrupted blood flow in the bone and may result in protein denaturation when exposing the periodontal ligament to a 43°C temperature.¹⁰ However, in general, increase in 10°C is considered as the critical temperature at which damage may occur to tooth support tissues.¹

In this study, to evaluate the temperature change during mechanical instrumentation and thermoplasticized obturation techniques at the coronal, middle, and apical third of the root canal, an attempt was made to simulate in vivo conditions, by using modeling wax as a medium in the experimental model. The recording of temperature change was done by using three sets of resistance temperature detector (RTD) which were in contact with the external root surface at three levels through the drilled holes after maintaining the baseline ambient temperature of 27 ± 1°C.

In the present study, during instrumentation with PTG and WOG, a higher temperature increase was seen in both the groups, at the middle third of the external root surface. However, on comparative evaluation, the temperature rise was significantly lower during reciprocating instrumentation with WOG. The reciprocation instead of the continuous rotary motion can be favorable, especially in cases with minimum dentine thickness as there is alternating contact of the cutting edges, due to variable cross-section throughout the length of the instrument which induces less stress formation on root canal dentine and thus aids in less invasive instrumentation. Further, the single-use of these file system tends to decrease the instrument fatigue and the risk of cross-contamination, when compared with the multiple numbers of files required in rotary system.¹¹ Sarthaj et al. have shown that reciprocating instruments, tend to preserve the original anatomy of the canal, as this approach is less invasive and minimizes canal transportation risk, ledge formation, irregular apical enlargement, and incidence of canal curvature straightening.¹² Patino et al. described that the reciprocation (alternating) motion reduces excessive torsional stresses which are induced during rotary instrumentation.¹³

During thermoplasticized obturation with Thermafil Plus Obturation System and EandQ Master Obturation System, a higher temperature increase was found in both the groups at the apical third of the external root surface. However, on comparative evaluation, the temperature rise was significantly lower during thermoplasticized obturation with Thermafil core-carrier system.

The carrier-based obturation technique is a simple method for the thermoplasticized gutta-percha delivery, in the prepared canal, as the softened gutta-percha mass adapts and easily flows into the irregularities of the root canal system. Hale et al. radiographically showed better results with the Thermafil system when compared with lateral condensation due to insufficient deeper penetration of spreaders after placement of master cone and thus prohibiting accessory cones from reaching the apical 1–3 mm during lateral condensation.¹⁴ Buchanan showed a higher percentage of the gutta-percha filled in apical third with carrier-based obturation than lateral condensation.¹⁵ Thermafil technique is considered as a gold standard technique especially in the case of double curves, narrow canals, long canals, and severe curves.^9,16–18

In our study, during obturation with Thermafil core-carrier system, the temperature rise of 1.30°C was recorded above the maintained 27.0°C ambient temperature, which is in accordance with the finding of Behnia and McDonald, where they found relatively low-temperature rise with Thermafil obturation ranging from 4.26°C (mesiobuccal roots of maxillary molars) to 4.87°C (maxillary incisors).¹⁹ Deboa also found a rise in temperature of 2.1–6.1°C with the Thermafil obturation technique. Core carrier obturation technique results in gutta-percha tag formation within dentinal tubules and also overfilling is reported which can cause thermal trauma and extrusion trauma.²⁰ Heeran and Levitan found more risk of thermal trauma due to overfilling with Thermafil and demonstrated that the likelihood of overfilling was associated with the canal tapering.²¹

On the other hand, injectable obturation techniques involve softening of gutta-percha at temperature %3E;160°C with the help of a hand-held gun. The regulation of heat is done to provide proper extrusion of gutta-percha according to the size of the needle. The technique presents various limitations such as lack of sealing ability which causes extrusion of flowable gutta-percha into the periapical area, creation of voids during final setting, frequent overfilling of the canal, and thermal trauma to periapical tissues.¹⁹ El Deeb et al. showed the extrusion of gutta-percha beyond the apical foramen during the thermoplasticized injectable gutta-percha technique.²⁰ With an EandQ injectable obturation system, the temperature rise of 4°C was recorded above the maintained 27.0°C ambient temperature, which is in accordance with the finding of Horan et al.,²² where temperature change of 4°C was recorded at external root surface during flowable gutta-percha obturation. Similarly, Gutmann et al. also reported alterations in temperature of 3°C with thermoplasticized obturation on the root surface.²¹ Barkhordar et al. reported temperature increase ranging from 5.98 to 7.00°C using thermoplasticized gutta-percha.^23–30

As per our findings, it is obvious that rotary instrumentation with both PTG and WOG in reciprocating movement does not lead to a temperature change on the external root surface that could have a deleterious effect on the adjoining periapical tissue. Similarly, the use of carrier-based obturation technique or thermoplasticized gutta-percha technique does not lead to a temperature change that could result in deleterious effects on the surrounding tissue. Since it has been established in previous studies that a temperature rise <10°C on the external root surface is relatively safe and preserves the natural integrity and healthy state of the adjacent tissue.^3,5,12,15,17

There are certain limitations to the present in vitro study as it has been acknowledged that surface temperature rise in vivo remains lower because of the periodontal ligament, bone, and microvasculature. In this study, only single-rooted teeth were evaluated, whereas temperature alteration may vary in a multi-rooted tooth with varying remaining dentine thickness. Also, the simultaneous use of irrigants helps in lowering the temperature.

CONCLUSION

With both the tested biomechanical preparatory systems and heat-based obturation techniques, the temperature rise observed was found to be below the critical level of 10°C above normal body temperature. Thus, based on results obtained in this study, it can be safely advised that for biomechanical preparation of root canal, reciprocating WaveOne Gold system with Thermafil carrier-based obturation system, respectively, should be preferred for biomechanical preparation and obturation during root canal treatment, with respect to safety regarding temperature rise on the root surface.

REFERENCES

1. Chauhan A, Nilker V, Mandke L. Effect of temperature rise on periodontal tissue during endodontic treatment: an in-vitro study. Indian J Oral Health Res 2015;1(2):66–71. DOI: 10.4103/2393-8692.172038.

2. Dimitrov S, Gueorgieva T, Dogandzhiyska V, et al. In vitro investigation of influence of temperature rising on periodontal tissue during endodontic treatment. J Imab 2009;15(2):32–35.

3. Reddy K, Prasad S, Kumar C, et al. Comparison of remaining root dentine thickness after three rotary instrumentation techniques by cone beam computerised tomography-an in vitro study. J Res Adv Dent 2014;3(3):32–39.

4. Sadique KP, Rashid PA, Simon EP, et al. Thermal alteration on the external root surface during endodontic treatment using three different rotary file systems: an in vitro study. Saudi J Oral Dent Res 2017;2(3):63–67.

5. Ozkocak I, Taskan M, Aytac F, et al. Temperature increases on the external root surface during endodontic treatment using single file systems. Niger J Clin Pract 2015;18(5):676–680. DOI: 10.4103/1119-3077.158976.

6. Vijayalakshmi BH, Girija S, Padmaja M. An ex-vivo evaluation of thermal changes in periodontal ligament during the use of thermoplasticised gutta-percha obturating techniques. Int J Res Sci Res 2015;6(5):4056–4060.

7. Eriksson A, Albrektsson T, Grane B, et al. Thermal injury to bone: a vita-microscopic description of heat effects. Int J Oral Surg 1982;11(2):115–121. DOI: 10.1016/s0300-9785(82)80020-3.

8. Kwon S, Park Y, Jun S, et al. Thermal irritation of teeth during dental treatment procedures. Restor Dent Endod 2013;38(3):105–112. DOI: 10.5395/rde.2013.38.3.105.

9. Cen R, Wang R, Cheung G. Periodontal blood flow protects the alveolar bone during thermal injury during thermoplasticised obturation: a Finite element analysis study. J Endodon 2018;44(1):139–144. DOI: 10.1016/j.joen.2017.08.004.

10. Lipski M. In vitro infrared thermographic assessment of root surface temperatures generated by high-temperature thermoplasticised injectable gutta-percha obturation technique. J Endodon 2006;32(5):438–441. DOI: 10.1016/j.joen.2005.10.047.

11. Berutti E, Chiandussi G, Paolino D, et al. Canal shaping with WaveOne primary reciprocating files and ProTaper system: a comparative study. J Endodon 2012;38(4):505–509. DOI: 10.1016/j.joen.2011.12.040.

12. Sarthaj A, Johnson P, Samuel A, et al. Evaluation of various kinematics in WaveOne gold reciprocating file system: an in vitro study. Endodontology 2020;32(2):100–103.

13. Patino P, Parraga A, Mundina B, et al. Alternating versus continuous rotation: a comparative study of the effect on instrument life. J Endodon 2010;36(1):157–159. DOI: 10.1016/j.joen.2009.09.023.

14. Hale R, Gatti R, Glickman G, et al. Comparative analysis of carrier-based obturation and lateral compaction: a retrospective clinical outcomes study. Int Endod J 2012;2012:1–9.

15. Buchanan S. Common misconceptions about carrier-based obturation. Endod Prac 2009. 30–34.

16. Michanowicz E, Michanowicz P, Michanowicz M, et al. Clinical evaluation of low-temperature thermoplasticized injectable gutta-percha: a preliminary report. J Endodon 1989;15(12):602–607. DOI: 10.1016/S0099-2399(89)80159-1.

17. Behnia A, McDonald N. In vitro infrared thermographic assessment of root surface temperatures generated by the Thermafil plus system. J Endodon 2001;27(3):203–205. DOI: 10.1097/00004770-200103000-00016.

18. Lipski M. Root surface temperature rises in vitro during root canal obturation with thermoplasticized gutta-percha on a carrier or by injection. J Endodon 2004;30(6):441–443. DOI: 10.1097/00004770-200406000-00016.

19. Weller R, Koch K. In vitro radicular temperatures produced by injectable thermoplasticised gutta-percha. Int Endod J 1995;28(2):86–90. DOI: 10.1111/j.1365-2591.1995.tb00164.x.

20. El Deeb M, Ishley D. An invitro assessment of the quality of apical seal of thermomechanically obturated canals with and without sealers. J Endodon 1983;9(6):242–245. DOI: 10.1016/S0099-2399(86)80021-8.

21. Gutmann J, Saunders W, Saunders E, et al. An assessment of the plastic Thermafil obturation technique part 1 radiographic evaluation of adaptation and placement. Int Endod J 1993;26(3):173–178. DOI: 10.1111/j.1365-2591.1993.tb00789.x.

22. Horan B, Tordik P, Imamura G, et al. Effect of dentin thickness on root surface temperature of teeth undergoing ultrasonic removal of posts. J Endodon 2008;34(4):453–455

23. Barkhordar RA, Goodis HE, Watanabe L, et al. Evaluation of temperature rise on the outer surface of teeth during root canal obturation techniques. Quint Int 1990;21(7):585–588.

24. Jonasson E, Bergquist A, Berg J. Measurements of the root surface temperature during thermo-mechanical root canal filling in vitro. Int Endod J 1985;18(3):199–202. DOI: 10.1111/j.1365-2591.1985.tb00441.x.

25. Rakusin H, Powe R, Bowles W. Evaluation of heat transfer during root canal obturation with thermoplasticized gutta-percha. Part II. In Vivo response to heat levels generated. J Endodon 1987;13(9):441–448. DOI: 10.1016/S0099-2399(87)80062-6.

26. Hardie E. Further studies on heat generation during obturation techniques involving thermally softened gutta-percha. Int Endod J 1987;20(3):122–127. DOI: 10.1111/j.1365-2591.1987.tb00602.x.

27. Romero A, Green D, Wucherpfennig A. Heat transfer to the periodontal ligament during root obturation procedures using an in vitro model. J Endodon 2000;26(2):85–87. DOI: 10.1097/00004770-200002000-00006.

28. Zhou X, Chen Y, Wei X, et al. Heat transfers to periodontal tissues and gutta-percha during thermoplasticized root canal obturation in a finite element analysis model. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010;110(2):257–263. DOI: 10.1016/j.tripleo.2010.04.005.

29. Donnermeyer D, Schäfer E, Bürklein S. Real-time intracanal temperature measurement during different obturation techniques. J Endodon 2018;11(11):1–5.

30. Heeran TJ, Levitan ME. Effect of canal preparation on fill length in straight root canals obturated with real seal 1 and Thermafil plus. J Endodon 2012;38(10):1380–1382. DOI: 10.1016/j.joen.2012.06.021.