In 1978, WB Johnson described a

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1 How to use Thermafil successfully Wilhelm Pertot DCD, DEA, PhD graduated from St Joseph University Dental School, Lebanon, in In 1991, he earned a master in endodontics from Marseille Dental School and obtained his PhD in He was nominated assistant professor in 1991, promoted to senior lecturer in 1994 and served as co-director for the postgraduate programme in endodontics in Marseille Dental School from 1992 to Wilhelm has been actively involved in clinical research in different fields of endodontics and has lectured and run hands-on courses extensively, both nationally and internationally Clinical Wilhelm Pertot advises practitioners on how to maximise their results when using the Thermafil obturation technique In 1978, WB Johnson described a technique for the obturation of root canals with thermoplasticised gutta percha. A few years later, the T h e rm a fi l d evice was introduced by Tulsa Dental. In its current version, the T h e rm a fil obturator, which is ava i l a ble in the UK from Dentsply - Maillefer ( ), features a f l ex i ble plastic carrier coated with alpha phase gutta percha. The obturator is carr i e d into a special oven with a temperature and time control. The heated gutta percha becomes therm o p l a s t i c i s e d and the obturator is then i n s e rted into the root canal to the working length. O ver the years, this fa s t obturation system, wh i c h combines a short learn i n g c u rve with a short wo r k i n g time, length control and s e a l a b i l i t y, has proven to be ve ry popular among general practitioners, as well as among specialists. Advantages of the T h e rm a f i l technique L i ke all filling techniques, the T h e rm a fil technique requires good canal shape with a consistent and continuous taper from the apical constriction to the coronal orifi c e. The T h e rm a fil technique o ffers many adva n t a g e s, i n c l u d i n g : Shortness of learning curve Speed of clinical a p p l i c a t i o n Apical control of fi l l Conserva t ive enlarg e m e n t of root canal (wh e n Figure 1: (top to bottom) The Thermafil obturator, the corresponding nickel titanium Verifier and the plastic carrrier from which gutta percha has been removed Figure 2: Thermafil plastic carrier from which gutta percha has been removed. Note the longitudinal groove which facilitates retreatment if needed compared to other wa rm gutta percha compaction techniques) Three-dimensional obturation and apical sealing ability. Description of the material and the technique The T h e rm a fil Plus system features seve r a l c o m p o n e n t s : The T h e rm a fil obturator. This is 25mm in length, and is a tapered, highly flex i bl e, plastic carrier coated with a low molecular weight alpha phase gutta percha, from size 20 to size 140 (Figure 1). The plastic c a rrier features a longitudinal gr o ove along its complete length to facilitate retreatment ( Figure 2) The T h e rm a fil ve r i fiers. These are.04 taper nickel titanium hand instru m e n t s, which are used to check the taper of the canal and select the proper obturator ( Figure 1) The T h e rmaprep oven. This allow s u n i f o rm, predictable and controlled heating

2 of the gutta percha, by allowing precise temperature and time control (Figure 3) The T h e rmacut burs. These feature a smooth non-cutting round head, which is used to sever the plastic carrier without a ny risk of perforation. These burs are ava i l a ble in 4 sizes:.010,.012,.014 and.016 (Figure 4) The post-space burs. These are long special non-cutting burs, which are used to prepare the space for the dowel post. T h e s e burs are ava i l a ble in two sizes (005 and 007), and two lengths (25mm and 31mm) I m p o rtance of the canal s h a p e The T h e rm a fil technique is a combination of different filling techniques. On insert i o n of the obturator, the tapered plastic carr i e r a l l ows the practitioner to exe rt both lateral and ve rtical compaction forces on heated gutta percha. The shape of the prepared root canal is c l e a r ly of paramount importance. A tapered funnel-form preparation is i n d i s p e n s a ble, not only to achieve a we l l cleaned root canal system but also to allow its three-dimensional obturation. The use of rotary nickel titanium instruments is recommended (ProFile or Greater Ta p e r r o t a ry files), because they ideally prepare a c o n t i n u o u s ly tapered shape, with a controlled apical diameter. N e rve rtheless, it should be noted that less coronal enlargement is needed with the T h e rm a fil technique than with other wa rm ve rtical gutta percha compaction techniques (ve rtical compaction or System B), which require more elimination of coronal dentine structure to allow p r e fitting of the pluggers. This is eve n more obvious in seve r e ly curved and long canals, in which the high flexibility of the plastic carrier enables the T h e rm a fi l obturator to fit easily at the working length ( Figure 5). Figure 3: The Thermaprep oven, is used to warm Thermafil obturators Gauging the canal p re p a r a t i o n After cleaning and shaping have been c o m p l e t e d, a ve r i fier corresponding in size to the last instrument used to the wo r k i n g length is used to gauge the canal. T h e ve r i fier should slide easily, without any contact with the canal walls, and should fi t p a s s ive ly in its last 1mm, with soft friction at the working length. If the ve r i fier is blocking betwe e n 0.5mm and 1mm from the working length, it may be used in a rotary motion to e n l a rge this portion of the canal. A l t e rn a t ive ly, a smaller ve r i fier may be tested and should usually fit easily to the working length. The corr e s p o n d i n g T h e rm a fil obturator is then used to achieve obturation of the canal. This method relies on the adjustment of the obturator silicone stop at the working length to control penetration and avoid ove r extension of the plastic carrier into the periapical tissues. Another interesting and reliable method, is based on the use of a T h e rm a fil plastic c a rrier from which the gutta percha has been removed (Figure 1). As the gutta percha extends 1mm beyond the tip of the c a rr i e r, the T h e rm a fil obturator to be used would be the one corresponding in size to the plastic carrier that blocks at wo r k i n g length or between 0.5mm and 1mm from the working length (Figure 6). In order to Figure 4: The Thermacut bur, which is used to sever the Thermafil obturator, features a smooth non-cutting round head and is available in 4 sizes (.010,.012,.014 and.016)

3 Figure 5: The flexibility of the plastic carrier allows insertion of the Thermafil obturator to the apical terminus of severely curved canals. The canals were shaped using ProFile instruments avoid direct contact between the carr i e r and the canal walls during obturation, the test carrier should only bind at its tip, without any lateral contacts. T h i s l e aves enough room laterally for the gutta percha and sealer. In this instance, ove r extension of the plastic carrier is h i g h ly unlike ly, if not impossibl e. Filling pro c e d u re The T h e rm a fil obturator should be dipped in a sodium hy p o c h l o r i t e solution for at least one minute to ensure its decontamination (Glickman, 1992). In the mean time, the canal is dried with paper points and root canal sealer is prepared. The manufa c t u r e r recommends the use of the paste-paste e p oxy resin-based root canal sealer ( Topseal, Dentsply-Maillefer; AH plus, D e n t s p ly). Because of its relative ly fluid c o n s i s t e n cy, this sealer should be used c a r e f u l ly and only in ve ry small amounts. Thus, to avoid ex t rusion of excess sealer in the periapical tissues, o n ly the coronal third of the canal is coated with a small amount of sealer using a paper point. Other sealers, such as Ke rr s Root Canal Sealer, may also be used (Ke rr UK). In that case, care should be taken to avoid a ve ry thick mix which could prevent the obturator being inserted to the desired length. The obturator is placed into the ove n, which allows homogenous heating of the gutta percha at the ex a c t temperature. Heating time varies from 15 to 45 seconds, depending on obturator size, and is reg u l a t e d a u t o m a t i c a l ly. No prewa rming of the oven is required. When the obturator is ready for use, it is pulled out from the oven and i n s e rted directly into the canal using a s l ow, fi rm and continuous apical m ovement (Figure 7). As it moves apically, the diameter of the tapered plastic carriers increase, t h e r e by exe rting more hydraulic lateral pressure (wedging effect) on t h e rmoplasticised gutta percha and sealer (Figures 8a and 8b). The obturator is stabilised using light finger pressure to limit shrinkage of the gutta percha while cooling. At that point, an X-ray might be taken to ensure placement of the T h e rm a fil obturator at the correct working length (Figures 6d and 10c). The coronal gutta percha around the plastic carrier is compacted using hand pluggers. The shaft of the obturator is then cut o ff at the canal orifice using a T h e rmacut bur (Figures 9 and 10).

4 Figure 6a: Preoperative X-ray of a lower first molar requiring an endodontic treatment Figure 6b: X-ray of the working length control. The canals were shaped using ProFile instruments Figure 6c: X-ray of the plastic carriers used for gauging of the canal and choice of the Thermafil obturator Figure 6d: X-ray upon insertion of the Thermafil obturators. The distal canal was filled using a size.35 obturator, and size.25 was used in the mesial canals. The obturator in the mesio-lingual canal has not been cut-off yet Figure 6e: Postoperative X-ray of the completed case P roblems and solutions Pain upon insertion of the obtura t o r Sometimes, the insertion of the T h e rm a fi l obturator might result in pain for the patient. This is usually due to air compression into the periradicular tissues. S l ow insertion of the obturator and, in some cases, administration of local anesthesia would avoid such a probl e m. O ve r filling and ove rex t e n s i o n As for all obturation techniques that rely on gutta percha compaction, the T h e m a fi l obturation technique might result in ove r filling of the gutta percha and/or the s e a l e r. Ove r filling results from gutta percha or sealer ex t rusion in the periapical tissues. Mixing the sealer at the correct consistency, the use of only a small amounts of sealer and slow i n s e rtion of the T h e rm a fil obturator at the correct working length should avo i d this probl e m. O ve r extension results from the extension of the T h e rm a fil plastic c a rrier in the periapical tissues. This is caused by using a T h e rm a fil obturator with a diameter smaller than the apical diameter of the preparation and not checking the working length. T h i s g e n e r a l ly results in an incomplete apical seal and might be avoided by a perfectly tapered preparation and by the selection of the proper obturator. As ex p l a i n e d e a r l i e r, the proper T h e rm a fil obturator

5 should be chosen according to the carr i e r binding at or between 0.5mm and 1mm from the working length. This would make it impossible for the plastic carrier to be pushed past the binding point. D i rect contact between the plastic carrier and the wall of the canal In some cases, when the canal is long, c u rved and/or improperly shaped, the plastic carrier might come into direct contact with the canal wall without gutta percha or sealer in position. If this phenomenon occurs apically, this might lead to lack in sealability (Barkins & M o n t g o m e ry, 1992; Juhlin et al, 1993). This can be avoided by giving the canal the adequate continuous tapered shape and by choosing the correct T h e rm a fil obturator, as described earlier. O b t u ration of large and elliptic canals Single rooted premolars (upper and lowe r ), l ower incisors, and mesial and distal canals of lower molars often show elliptical or r i b b o n - l i ke coronal shapes, while the crosssection tends to be round towards the apex. Thus, in the coronal areas, the compaction pressure exe rted by the plastic carrier alone might prove to be inadequate to allow complete flow of gutta percha and sealer into the irr egularities. To allow adequate filling of the coronal portion of the root canal system, the gutta percha around the c a rrier is compacted using Pierr e M a c h t o u s hand pluggers (Dentsply - Maillefer). Occlusion of the openings of other canals in mu l t i rooted teeth upon elimination of the carrier and of excess of gutta perc h a The obturator is designed with excess gutta percha to accomodate large canals. T h u s, upon insertion of the obturator in relative ly small canals in multirooted teeth, sealer and gutta percha will usually flow back and accumulate at the orifice. This might lead to obscuring access to other canals. M o r e ove r, severing of the obturator at that point might lead to projection of debris into the other canals. To prevent these phenomena, excess gutta percha should be trimmed off the shaft using a scalpel bl a d e before heating, and a paper point or small cotton pellet might be placed into the orifice of the other canals. P re p a ration of a dowel space Some authors prefer to postpone the dowel space preparation to a l l ow complete setting of the s e a l e r. Neve rtheless, this procedure might prove i n d i s p e n s a ble, especially aesthetics are concerned or when a t e m p o r a ry crown must be adjusted. S everal studies (Rybicki and Zillich, 1994; Saunders et al, 1993) have shown that the apical seal of the T h e rm a fil is undisturbed if the dowel space is prepared immediately after obturation. After trimming the handle of the T h e rm a fil carrier at the orifi c e of the canal, preparation of a d owel space might prove difficult or might lead to the retrieval of the entire plastic carr i e r. This is usually due to the use of a drill that is too small in size, which slides alongside the T h e rm a fi l c a rr i e r. To avoid this problem, the selected drill should be the largest drill fitting inside the coronal portion of the prepared canal. Using the selected drill at high speed is often sufficient to allow r e m oval of excess carrier and gutta percha and preparation of the dowel space. In a recent paper, Cantatore & Cochet (1998) proposed a modification of the tip of the T h e rmacut bur to allow its i n s e rtion deep into the canal. High speed rotation without water spray wo u l d produce enough frictional heat to soften the plastic and the gutta percha, thus e n a bling removal of excess carrier and gutta percha. R e c e n t ly, a new bu r, the Post Space bu r ( D e n t s p ly-maillefer) has become ava i l a ble. This bu r, which features a long non-cutting head is used at high speed without water spray, to produce frictional heat and to soften the plastic and the gutta percha. Once the desired portion of the T h e rm a fil obturator has been e l i m i n a t e d, the shape of the free space is r e fined according to the reconstru c t i o n t e c h n i q u e. Figure 7: The Thermafil obturator is inserted into the root canal to working length, using a slow, firm and continuous apical movement

6 Figure 8a and b: As the Thermafil obturator is pushed apically, the tapered plastic carriers excert more lateral pressure on the heated gutta percha and sealer, thus allowing obturation of lateral canals. Here, the simulated canal was filled using Thermafil without sealer and gutta percha was pushed to the full extent of the lateral canal Figure 9: After insertion, the Thermafil obturator is maintained using finger pressure and cut-off with a Thermacut bur R e t re a t m e n t The conventional method for T h e rm a fi l retreatment relies on the use of a gutta percha solvent which will allow insert i o n of a hand instrument between the plastic c a rrier and the canal wa l l. The presence of the longitudinal gr o ove in the plastic carrier allows easier i n s e rtion of the hand instru m e n t. W h a t ever the solvent, different studies h ave shown that the maximum time needed for T h e rm a fil retreatment neve r exceeds six to seven minutes (Ibarrola et al, 1993; Wi l c ox and Juhlin, 1994; B e rtrand et al, 1997). Howeve r, the best ava i l a ble technique for T h e rm a fi l retreatment today relies on the use of a r o t a ry nickel titanium instrument after using a s o l vent for s o f t e n i n g the gutta percha. T h e use of o r i fi c e shapers size 3 (size 40,.06 taper) or 2 (size 30,.06 taper) would then a l l ow a P r o File size 25,.06 taper to penetrate into the canal alongside the plastic c a rr i e r. The nickel titanium instrument is a d vanced toward the apex using an inand-out pecking motion, and, at one point, will completely pull-out the plastic c a rrier from the canal. C o n c l u s i o n T h e rm a fil is an easy, reliable and e fficient technique, which allow s practitioners to obtain three-dimensional root canal fillings with wa rm gutta percha in a minimum amount of time ( B e c ker & Donnelly, 1997). N eve rtheless, one should bear in mind that excellent results can only be obtained if the root canal system has been thoroughly cleaned and given the proper shape. R e f e re n c e s Barkins W and Montgomery S (1992). E valuation of T h e rm a fil obturation in curve d canals prepared by the Canal Master-U system. J Endo 1 8 : B e c ker TA and Donnelly JC (1997). T h e rm a fi l obturation : a literature rev i ew. Gen Dent 4 5 : B e rtrand MF, Pe l l egrino JC, Rocca JP, K l i n g h o ffer A and Bolla M (1977). Removal of T h e rm a fil root canal filling material. J Endo 2 3 : 5 4-7

7 Figure 10a : Preoperative X-Ray of a mandibular molar adressed for retreatment Figure 10b: X-Ray of the working length control. The canals were shaped using the ProFile instruments Figure 10c: X-Ray upon insertion of the Thermafil obturators Figure 10d: View of the access cavity after sectionning of the obturators Figure 10e and 10f: Postoperative X-Rays of the completed case Cantatore G and Cochet JY (1998). T h e T h e rm a fil System. E n d o 17 : I b a rrola JL, Knowles KI and Ludlow MO (1993). R e t r i evability of T h e rm a fil plastic cores using o rganic solvents. J Endo 19 : Johnson WB (1978). A new gutta-percha technique. J Endo 4 : Saunders W P, Saunders EM, Gutmann JL and Gutmann ML (1993). An assessment of the plastic T h e rm a fil obturation technique. Pa rt 3. The effect of post space preparation on the apical seal. Int Endod J 26 : Rybicki R and Zillich R (1994). Apical sealing with T h e rm a fil following immediate and d e l ayed post space preparation. J Endo 20 : 64-6 Juhlin J, Walton R and Dov gan J (1993). Adaptation of the T h e rm a fil components to canal walls. J Endo 1 9 : Wi l c ox LR and Juhlin JJ (1994). Endodontic retreatment of T h e rm a fil versus laterally condensed gutta percha. J Endo 2 0 :