Endodontics

Evaluation of temperature rise on the outer snrface of teeth during rootcanal obturation techniquesRahmat A, Barkhordar* / Harold E- Goodis** / Larry Watanabe*** / Jack

The heat generated at the apical 2 mm of the outer root surface of e.\traded humancanine teeth during three obturation procedures was measured. The rise in temperaturewas found to be less when a sealer was used in all obturation teclini(¡ues. Températuresas high as 44.02 "C were recorded with warm gutta-percha with no sealer, and thelowest temperature rise occurred wilh a thermopla.slivized gutta-percha technique witha sealer. The thickness of the remaining dentin and cementum after cleaning and shap-ing were found to have no effect in reducing temperature rise. The results of this inves-tigation indicated that temperature rise on the outer surface of the root as a result ofheat-generating obturation procedures is negligible and will not have an effect on thesupporting attachment apparatus. (Quinlessence Int 1990:21:585-588.)

Introduction

Theuseof gutta-percha in clinical dentistry dates backto 1847, Hill developed his "HiU's Stopping"' whilesearching for an alternative plastic filling material toamalgam. The material consisted of bleached gutta-percha mixed with carbonate, lime, and quartz. In1865 Clark was the first to use warm gutta-percha forroot canal obturation,- and, as early as 1887, the SSWhite Company started to manufacture gutta-perchapoints.^ In 1893 Rolhns modified the use of gutta-percha by adding vermilion." This development wascriticized because of possible toxic effects from themercuric sulflde that was present in vermilion.

During the first half of this century gutta-percharemained the root canal obturation material of choice,but many alterations, in the form of filling pastes, were

Associate Professor, Section of Endodontics, Deparlment ofRestorative Deiitistrj', University of Caiifornia, San Fran-cisco, School of Dentistry, San Franciico, California 94143-0758.Assistant Professor, Section of Endodoniics, Department ofRestorative Dentistry, University of California, San Fran-cisco,Research Associate, Department of Restorative Dentislry,University of California, San Francisco.Assistant Professor. Department of RestoraUve Denlistry,Universitv of California, San Francisco,

introduced. The use of gutta-percha had -d resurgencein 1960, and since then a considerable amount of datahas been accumulated on its efficacy as a root canalobturation material. Its biocompatibility and adap-tation to root canal walls have been well document-ed,^'' and other advantages are listed below':

1, It is compatible and adapts excellently to the irreg-ularities and contour of the canal by the lateral andvertical condensation method,

2, It can be softened and made plastic by heat or bycommon solvents (eucalyptol, chloroform, xylol).

3, It is inert,4, It has dimensional stability: when unaltered by or-

ganic solvents, it will nol shrink,5, It is tissue tolerant (nonallergenic),6, It will not discolor the tooth structure,7, it is radiopaque,8, It can easily be removed from the canal when nec-

essary.

The following are disadvantages of gutta-percha:

1, It lacks rigidity.2, It lacks adhesive quality.3, It can be easily displaced by pressure.

Gutta-percha is presently used as a root canal res-torative materiai in a variety of techniques*: (1) single-cone; (2) lateral condensation; (3) lateral and vertical

ouiniessenee miêrrmsm mnmffiîoNumber 7/1990 585

Endodontics

Fig 1 Test tootti in position for obturation. Fig 2 Test tooth m position lor temperature reeording andattached to recorder.

condensation; (4) sectional; (5) vertical condensa-tion, warm gutta-percha; (6) chloropercha (modifiedJohnston or modified Nygaard-Ostby); (7) gutta-per-cha-euc a percha; (8) thermomechanical condensa-tion; (9) thermoplastic injection-molded,^ Recently, anew method of injection of a thermoplasticized gutta-percha was introduced by Yee and coworkcrs,^

Heat transferred to the pulp tissue through cavitypreparation and restoration procedures may be harm-ful to the pulp,""' Once the pulp tissue has been re-moved, any heat applied to the clinical crown is rel-atively unimportant. However, heat transfer that oc-curs through the dentin and cementum of the root tothe periodontal ligament and bone is important. If thetechnique and material used in filling the root canalspace transfers a great amount of heat to the sup-porting sttnctures around the root, tissue damage mayoccur,'-'' With the advent of thermoplastidzed gutta-pereha root canal obturation techniques and associ-ated high temperatures, there is concern about damageto the supporting structures through heat transfer.This study compared heat transfer from the root canalspace to the periodontal ligament resulting from ver-tically condensed warm gutta-percha and two ther-moplasticized gutta-percha obturation techniques.

Method and materials

A total of 60 human anterior teeth (maxillary andmandibular canines) were used in this in vitro inves-tigation. The teeth were divided into six groups of tenteeth, and each group was used for one obturation

technique: vertical condensation with warm gutta-per-cha. Obtura (United Corp) thermoplastieized system,or Ultrafil (Hygenic Corp) thermoplasticized system.

Access openings were prepared and the root canalsystems of ail teeth cleaned and shaped using theSehilder" teehnique to facilitate placement of the rootcanal restorative material, A thermocouple was placedon the outer surface of the root 2 mm from the apicalforamen and attached using a cyanoacrylate adhesive.The probe was attached in sueh a manner that theteeth could be held in the hand during the obturationprocedure (Fig 1), The thermocouples were construct-ed of two dissimilar metals, iron and constantain, sol-dered at one end to form the temperature device, andthen connected to a Linseis flat bed recorder (Linseis,Inc), series L55, with a LS 05.80 measuring range of0,5 to 5,0 mV (Fig 2), The probe was used with anomega reference junction to compensate for roomtemperature. Each tooth was held in the hand andobturated according to manufacturer's specificationsusing the different techniques. Group 1 was obturatedwith the warm gutta-percha, vertical condensationteehnique and AH26 root canal sealer (Dentsply In-ternational), Group 2 was obturated by the same tech-nique but without the use of a sealer. Group 3 wasobturated with the Obtura system and a sealer. Group4 was restored with the Obtura system, but the sealerwas omitted. Group 5 was obturated using the Ultrafilsystem and the sealer, while gronp 6 was filled withUltrafil, but no sealer. The starting temperature foreach tooth was 37,00 "C (+ 0.20), Temperatures wererecorded for each tooth for each obturating sequence

586 Qu mtesse n 7/1990

Endodonties

for each technique. After completion of the tempera-tnre recordings, the teeth were sectioned, and the den-tinal-cementum thickness from the inner canal wall tothe onter surface was measured.

Results

The lower temperatures were recorded for all threetechniques when a root canal sealer was used withgutta-percha. The results are summarized in Table 1.The lowest temperatures were recorded with the Ul-trafil system, with a mean temperature increase to38.98 ''C. A mean temperature increase to 39.83 "Cwas recorded with the Obtura system. Temperaturerise with warm gutta-percha techniques was 42.78 ^C.When a sealer was not used, the temperature increaserecorded was greater for all three systems. The Ultrafilsystem again resulted in the smallest increase in tem-perature, with a mean increase to 40.02 "C, followedby the Obtura system, with mean increase to 41.72 "C.The warm gutta-percha system had the greatest in-crease, with a mean increase to 44.42 "C. A one-wayanalysis of variance (ANOVA) and Student-Newman-Keuls test showed that the warni gutta-percha verticalcondensation teehnique without sealer resulted in sig-nificantly higher temperatures than did all othergroups (P < .05).

The mean dentinal and cementum thicknesses aftercleaning and shaping of the thermoplasticized groupsare presented in Table 2. A one-way ANOV̂ A testshowed that there was no correlation between dentinalthickness and temperature rise between the two sys-tems.

Discussiou

The final objective of successful endodontic treatment tis three-dimensional obturation of the root canal sys-tem. The current material of choice used to aceom-plish this objective is gutta-percha. Gutta-percha iscommonly used with a sealer to obturate the root can-al walls. Historically, the placement of gutta-perchawas accomplished by lateral condensation or by a ver-tical condensation of warm gutta-percha. Recently,two systems have been developed that deliver ther-moplasticized gutta-percha material to the preparedroot canal space; with these systems, heat generationoccurs during obturation procedures.

Other studies have evaluated temperature rise dur-ing thcrmomechanieal compaction of gutta-percha.Hardie'^ measured the temperature rise to the outer

Table I Mean temperature ("C) of different groupswith and without sealer*

Experimentalgroup

Ultrafil

Obtura

Warmgutta-perchatechnique

With

±38.9fi

39.83

42.78

sealerSD

± 1.41

+ 1.64

+ 3.14

Without sealer

±40.02

41.72

44.02

SD

+ 1.74

+ 1.96

+ 5.45* Startitig temperature for each looth was 37.00 X .

Table 2 Mean denfinal and cementum thickness(mm) for experimental teeth for Ohtura and Ultrafilsystems

Experimentalgroup

With sealer+ SD

Without sealer± SD

Obtura

UltraOl

2.40 ± 0.18

1.50 -i- 0.15

1.35 ± 0.11

1.30 -I- 0.20

surface of the tooth with the rise of thermomechanicalcompaction of warm gutta-percha. Those results arein agreement with the results in this study Marlin andSchilder'^ showed only a 4 °C increase in gutta-perchatemperature when the vertical condensation techniqueis used. The results of this study showed a higher tem-perature increase (4 to 7 ^C). While it is assumed thatthe temperature rise should he the same if the teeh-nique used to obturate the root canal space is thesame, it is possihle that the heat instrument nsed inthis study may, in fact, have been heated to a highertemperature. The heat instrument used in this studywas warmed in a bunsen hurner to the point that itglowed with an orange-white color, and that may ac-count for the differences in the two studies. It is alsopossible that the preparation of the root eanal spaceover narrowed the remaining dentin, thereby eausinga greater temperature increase on the outer surface.Gutmann et al/ ' in an in vivo study, did not find anydeleterious effect on periodontal tissue of dog's teethobturated with the therm op i as tic i zed technique.

Goodman,'^ et ai had previously delineated the pa-rameters and temperatures incurred during the use ofa warm gutta-percha, vertical condensation, canal ob-turation technique. The temperatures recorded werejudged to be well within the physiological range of

uinJeSSenôe International 951 [ Number 7/1990 587

Endodontics

tolerance and would cause no tissue damage. Appar-ently, no one has quantitaled the temperature rise nec-essary to cause irreparable damage to the periodontalligament. In the studies cited,"'' temperatures wereraised to the point that ankylosis oeeurred. But thetemperature rise was not determined. Poison et al'''studied the result of temperature increase on progres-sion of periodonlilis, hut did nol quanlify the tem-peratnre ri.se. The present investigation showed thaimaximal heat was generated by a warm gulta-perchatechnique without sealer (44.02 "C). and, with the useof root canal sealer, the temperature rise was smaller(to 42.78 X) . The temperature rise of 5,98 C to7.02 'C above normal body range should not have adeleterious effect on the periodontal ligament.

The temperatures reeorded were elose to tho.se tem-peratures that cause proteins to coagulate,-" killing theperiodontal ligament, resulting in ankylosis and sub-sequent résorption. However, the data support the useof sealer m all obturation techniques te.sted. becausethe lower temperatures were reeorded when sealer wasused. Obturation techniques require sealer to be usedfor successful obturation.' The investigators in thisstudy have a combined clinieal practice experience of38 years using vertieal compaction of warm gutta-percha with no evidence of either ankylosis or résorp-tion at recall. While this study is in vitro, and in vivoconclusions cannot be drawn from it. the temperaturerise on the root surface would be buffered by the peri-radicular tissues, whieh would cause a reduction intemperature rise in vivo.

Summary

Successful endodontie treatment is predicated on thethree-dimensional obturation ofthe root canal space.While no one restorative material is ideal, gutta-per-cha, through its various delivery systems, is the ma-terial of choice. The placement of gulta-pereha in theroot canal space, depending on the technique used forplacement, involves heat transfer through the materialand surrounding dentinal walls to the outer surfaceof the tooth and the periodontal ligament space.

This study compared vertical compaction of gutta-percha with the Obtura and Ultrafil thernioplasticizedsystems. All techniques caused temperature increasesthrough the dentinal wails to the outer surface of thetest teeth, but the lowest temperatures in all techniquesoeeurred when sealer was used. In some cases, thetemperature rise approached the level that could causetemperature damage (vertical compaction without

sealer), but analysis ofthe data found thai the systemsand techniques used and the température mcreasesgenerated would not cause a temperature rise in theperiodonlal ligament high enough to cause damage tothe tooth-supporting tissues.

References

1. History Committee of the Missouri Slaie Denial Association:History of Dentistry in Missouri. Fulton, Missouri, The OvidPress, Inc, 1938, p 16.

2. Noyes E: Fifty years or rool canal filJirgs. J Àm Deni ÀSSOÎ1922;9:785-794.

3. Keane HC: A Century of Serviee w Deiilisiry. Philadelphia. SSWhile Manulaciuring Co, 1944, p S3.Weinberger BW: An Inlroduclion lu the Hislory iif Deiilisiry.Si Louis, CV Mosby Co, 194S. p 353.Feldmiin G, Nyborg H: Tissue reactions ol' rool canal fillingmaterials. 1. Comparison between guita percha and silver amal-gam implanted in rabbils. Odonlot Rev Í962;t3;l.Wolfson E, Seltzer S: Reaction oí rat connective tissue to someË Lit ta-percha formulations. J Endod I975;i.395.Grossmiin L: Endmtonlic Pracliee, ed 9. Philadelphia. Lea &Febiger, 1978. pp 275-285.Nguyen NT: Obluralion of ihe rool canal system, in Cohen S,Burns RC (eds): Pallmays of ihe Pulp. St Louis, CV Mosby Co,1983, pp 205-301.Yee FS, el al: Three-dimensional obturation ol' Ihe root canalusing injeelion-molded, Ihermoplasticized déniai gutla-percha.J Endod iy77;3:)6S-174

Ziich L. Cohen G: Ptilp response to externally applied heal.Orul Siirg Oral Med Oral Palhiil t965:t9:515-530.Nyborg H. Braunbtrom M: Ptilp reactions lo heat. J ProslliclDem l%8;19:605-612.

Atrizadeh F, Kennedy J, Zander H: Ankylosis of teeth followingthermal injury. J Periodom Res 197l:6:159-tí7.Line SE. Poison AM, Zander HA: Relationship belucen peri-odoulal injury, selective cell repopulation, and ankylosis. J Peri-odonlol 1974:45:725-730.

Schilder H: Filhng root canals in three dimensions. Dem Clii'Norlh Am 1967:11:723-744.

Hardie EM: Heat Iransmissiotl lo ihe ouler surface of the tooLhduring the Ihermo-mechanical compaction technique of roolcanal obluraliou. Im Endod J ]986;19:734Marlin J, Schilder H: Physical properties of gutta percha whensubjected lo heat and vertical condensation. Oral Surg Orul MedOral Fmhol 197Î:Î6:872-S79.

Gutmann JL, Ranksin H. Powe R, et al; Evaluation of heattransfer during root canal obturation with the miopías lie izedgulta-pcrcha. Part 11. In vivo response lo heiit levels generated../i-<i,/m/1987:13:441^48.Goodman A, Schilder H. Aldrich W: The thermomechanicalproperties of gutta-percha. Part IV. Oral Surg Oral Med Ural

ly. Poison AM, Kennedy JE, Zander HA: Trauma and progressionof marginal periodonlilis in squirrel monkeys. 1. Co-destructivefactors of periodontitis and thermally-produced injury. J Per-iodonl Res 1974:9:100-107.

20. Sank JJ, Nurris K. Foster JM, et al: Expression of heat stressproteins by human periodonlal ligament cells. / Oral Parhol198S;17:496 498. p

588 -«tujber 7/1990