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Dentinal wall adaptation of thermoplasticized gutta-percha in the absence or presence of smear layer: A scanning electron microscopic study
0099-2399/93/1911-0558/$03.00/0 JOURNALOF ENDODONTICS Copyngt~ © 1993 by The American Association of Endodontists
Printed in U.S.A.
VOL. 19, No. 11, NOVEMBER1993
Dentinal Wall Adaptation of Thermoplasticized Guttapercha in the Absence or Presence of Smear Layer: A Scanning Electron Microscopic Study Nimet Gengoglu, DOS, PhD, Sami Samani, DDS, MS, and Mahir Gimday, DDS, PhD
The dentinal adaptation of injected thermoplasticized gutta-percha and thermoplasticized guttapercha resulting from Ultrafil and Thermafil systems was evaluated by scanning electron microscopy and compared with adaptation obtained with the lateral condensation of gutta-percha. Each method was evaluated with and without the smear layer removed. Scanning electron microscopic observations showed the thermoplasticized gutta-percha resulting from either system to have better dentinal wall adaptation than lateral condensation of guttapercha in either the absence or presence of the smear layer. In the absence of smear layer, the adaptation of gutta-percha was improved in all groups. Although sealer was used, removing the smear layer was found to enhance the ability of the thermoplasticized gutta-percha to enter the patent tubules.
A new thermoplasticized gutta-percha technique, Thermafil, was introduced by Johnson (7). Beatty et al. (8) found that Thermafil produced a better apical seal than lateral condensation. McComb and Smith (9) observed prepared root surfaces to be covered by an amorphous layer of debris, referred to as the smear layer. Some consider that it is desirable to remove this layer because it covers prepared areas and prevents filling material from penetrating the dentinal tubules or even contacting the canal wall (9, 10). In theory, a good seal should be obtainable with sealer that adheres well to the core material. Thus, removing the smear layer prior to fiUing may actually increase the adhesive strength of the filling to dentin and improve the sealing ability of the filling. The purpose of this study was to investigate the dentinal wall adaptation of three different gutta-percha formulations in the absence or presence of smear layer. MATERIALS AND METHODS Sixty-four single-rooted teeth were used in this study. The teeth were stored in 5.25% sodium hypochlorite for 24 h to remove any organic debris. Pulp tissue remnants were removed with a barbed broach. The teeth were instrumented using the "step-back" technique. Gates Glidden burs were used to prepare the coronal thirds of the canals. The teeth were irrigated with 5.25% sodium hypochlorite before and after recapitulation with a size 60 master apical file. Thirtytwo teeth were randomly chosen and their smear layers removed by final rinses of 10 ml of Calcinase (17% EDTA) followed by 10 ml of 5.25% sodium hypochiorite, as recommended by Yamada et al. (11). The other 32 teeth were irrigated with final rinses of 5.25 % sodium hypochlorite alone. All canals were dried with paper points. Teeth with or without smear layers were randomly assigned to six groups (Table 1). Four teeth were used as control groups (two with and two without smear layer) and not obturated. A gutta-percha master cone (Hygenic Corp., Akron, OH) was fitted to within 0.5 mm of working length in the lateral condensation groups. Freshly mixed Grossman's sealer was placed into the root canal. A DI 1 spreader was inserted 1 to 2 mm shorter than the working length. The spreader was kept in the canal until a fine gutta-percha accessory cone was
The ultimate objective of nonsurgical root canal therapy is complete obturation of the root canal system (1). Since the most common cause ofendodontic failure has been attributed to incomplete obturation (1), many different obturation techniques have been developed in order to increase the success of root canal treatment. Lateral condensation has proven to be a very popular gutta-percha technique. However, Schilder (2) and Brayton et al. (3) noted that with lateral condensation of gutta-percha at no time did a homogeneous mass form nor did the gutta-percha adapt to the root canal walls. Yee et al. (4) introduced the injection of thermoplasticized gutta-percha in 1977. They reported injected gutta-percha to be superior to lateral condensation and capable of filling multiple foramina and other raminifaction. Based on this concept, a low-temperature injection-molded thermoplasticized gutta-percha delivery system has recently been developed. Favorable results for the sealing ability of the low-temperature thermoplasticized gutta-percha technique (Ultrafil) and close adaptation to canal walls have been reported (5, 6).
558
Vol. 19, No. 11, November 1993
Thennoplasticized Gutta-percha
559
TABLE 1. Operated groups Smear Layer Present Group la Group 2a
Group 3a
Smear Layer Absent Group 1b (lateral condensation with Grossman's sealer) Group 2b (injected thermoplasticized gutta-percha with Grossman's sealer) Group 3b (thermoplasticized guttapercha with Grossman's sealer)
FIG 2. A scanning electron micrograph of laterally condensed guttapercha in the absence of smear layer showing close adaptation in the middle third of the canal (original magnification x1500). Notice the sealer in the dental tubules. D, dentin; S, sealer.
FIG 3. A scanning electron micrograph of injected thermoplasticized gutta-percha showing close adaptation in the presence of smear layer in the middle third of the canal (original magnification x350). D, dentin; G, gutta-percha.
FIG 1. A, A scanning electron micrograph of root filling showing the laterally condensed gutta-percha not to be in a homogeneous mass in the presence of smear layer (original magnification x35). Sealer is seen between the gutta-percha and canal walls and between the gutta-percha cones but voids are present elsewhere. B, Notice the voids between the canal wall and laterally condensed gutta-percha and the voids between sealer and gutta-percha in the middle third of the canal (original magnification x350). G, gutta-percha; D, dentin; S, sealer.
placed. The canal was considered to be adequately obturated when enough points were placed that the spreader could no longer penetrate beyond the coronal third of the canal. After complete canal obturation the coronal gutta-percha was remove with a hot instrument. In the groups obturated with Thermafil, size 60 Thermafil devices were used because the apical preparations were en-
larged to a size 60. The roots were coated with Grossman's sealer and then Thermafil obturators were passed through a flame and inserted into each root canal to a level at which the central carrier extended to a full working length distance yet the carrier stayed in place. An inverted cone bur was used to cut through the shank of each carrier at the coronal level of each root canal. Following obturation, the teeth were stored for 7 days at room temperature and 100% humidity to allow the materials to set. Then single longitudinal grooves were cut on the labial and lingual root surfaces, first with a round bur and then with a diamond disc. Later, pliers were used to fracture the teeth. No distortion occurred during the fracturing process. The specimens were coated with gold for a Scanning Coating System (Bio-Rad SC 502) and examined with a scanning electron microscope (JEOL JSM 5200; JEOL, Tokyo, Japan) for density and homogeneity of the fillings, conformity to the
560
Gen~oglu et al.
Journal of Endodontics
FJa 4. A, Injected thermoplasticized gutta-percha showing stippled appearance due to projection into the tubules in the absence of smear layer in the middle third of the canal (original magnification x350). B, Patent tubules are plugged with gutta-percha and sealer (original magnification x1500). D, dentin; G, gutta-percha; S, sealer.
prepared canal, and adaptation of the materials to the dentinal walls. RESULTS Scanning electron microscopic examination of the control teeth, which were irrigated with sodium hypochlorite alone, showed the presence of an intact smear layer. However, the teeth that were irrigated with the Calcinase (EDTA) and sodium hypochlorite combination showed smear layer removal with clean walls. In the presence of smear layer, the root canal filling by lateral condensation did not form a homogeneous mass (Fig. 1A) and although the sealer was observed to fill many of the voids between the gutta-percha and canal walls, poor adaptation could be seen in higher magnification (Fig. 1B). It was observed that removing the smear layer enhanced the wall adaptation of the laterally condensed gutta-percha. Although the patent tubules were filled with sealer in the coronal and middle third of the canal (Fig. 2), poor adaptation was found in the apical third of the canal. In the presence of smear layer, the root canal filling from injected thermoplasticized gutta-percha was homogeneous
FtG 5. A, Thermoplasticized gutta-percha resulting from Thermafil showing good adaptation to the dentin in the presence of smear layer. Notice the cracks on the surface of the filling (original magnification x35). B, In this specimen, gutta-percha adhered to the other half and the metal carrier is seen (original magnification x35). C, Close adaptation of Thermafil can be seen in the middle third of the canal (original magnification x350). G, gutta-percha; S, sealer.
and the filling reproduced the shape and irregularities of the canals well. With higher magnification gutta-percha showed close adaptation to the dentinal walls in every part of the roots (Fig. 3). In the absence of smear layer, even though sealer was being used, the injected thermoplasticized gutta-
Vol. 19, No. 11, November 1993
FiG 6. A, In the absence of smear layer patent tubules were filled with gutta-percha and thermoplasticized gutta-percha has a stippled appearance due to projection into the tubules in the middle third of the canal (original magnification x1500). B, Despite the cracks, thermoplasticized gutta-percha resulting from Thermafil maintained contact with the dentinal wall in the apical third of the canal (original magnification x350). D, dentin; G, gutta-percha; S, sealer.
percha was stippled in appearance due to projections into the patent tubules (Fig. 4.4) and the patent tubules were plugged with filling (Fig. 4B) in all parts of the roots. In the presence of smear layer, root filling from the thermoplasticized gutta-percha resulting from Thermafil showed close adaptation to the dentinal wall in all parts of the root. Some specimens showed cracks (Fig. 5A); in other specimens, the metal carrier could be seen as the gutta-percha adhered to the other half of the teeth (Fig. 5B). Despite these cracks the filling resulting from Thermafil maintained contact with the dentinal wall in all parts of the roots. In the absence of smear layer, Thermafil was stippled in appearance (Fig. 5C) and the patent tubules were plugged with filling (Fig. 6A). Again, the cracks did not effect the adaptation of the filling (Fig. 6B). DISCUSSION The result of this study indicated that the thermoplasticized gutta-percha resulting from Therrnafil and Ultrafil systems showed close adaptation to the dentinal walls and better replicated the irregularities of the canals than did lateral
Thermoplasticized Gutta-percha
561
condensation of gutta-percha. The results of this study concerning laterally condensed gutta-percha corroborate those of Brayton et al. (3), Larder et al. (12), Wollard et al. (13), and Coviello et al. (14). Scanning electron microscopic findings of Torabinejad et al. (15) also indicated injection-molded guttapercha to be superior to laterally condensed gutta-percha. Michanowicz et al. (6) investigated the dentinal wall adaptation of injected thermoplasticized gutta-percha with or without sealer and compared this with the lateral condensation technique. They concluded that the root canal system can be obturated as well or better with the injected thermoplasticized gutta-percha system with sealer, as with laterally condensed gutta-percha. Although they observed that injected guttapercha flowed into the dentinal tubules when used without sealer, they still advised using sealer to produce better apical seal. In the present study, it was seen that removing the smear layer enhanced the adaptation of gutta-percha in all groups. Although better results were observed in the coronal and middle thirds of the canals for the laterally condensed guttapercha in the absence of smear layer, still poor adaptation was seen in the apical areas. The effect of removing smear layer was more pronounced for thermoplasticized gutta-percha than for laterally condensed gutta-percha. Even though sealer was used, the entry of the thermoplasticized guttapercha into tubules was observed. White et al. (10) also observed tubular penetration in the absence of smear layer and also indicated that such tubular penetration increased the interface between the filling material and the dentinal wall and thus may decrease the apical leakage. This was supported by Kennedy et al. (16) and Cergneux et al. (17), although not by Evans and Simons (18). It was also observed that the cracks which were seen on the surface of Thermafil specimens did not effect adherence to the dentinal walls. According to the results of this study, the thermoplasticized gutta-percha resulting from Thermafil or Ultrafil techniques proved to be superior to laterally condensed gutta-percha in regard to dentinal wall adaptation in the absence or presence of smear layer. Dr. Gen~o01uis a lecturer, Department of Endodontics, Marmara University, Faculty of Dentistry, Istanbul, Turkey. Dr. Samani is professor, Department of Endodontics, University of Medicine and Dentistry, New Jersey Dental School, Newark, NJ. Dr. Gunday is associate professor, Department of Endodontics, Marmara University, Faculty of Dentistry, Istanbul, Turkey. Address requests for reprints to Dr. Nimet Gen~o~lu,Anafartalar Sokak, Fulya Apt. 3/1, Yesilk6y, Istanbul, Turkey.
References 1. Nguyen NT. Obturation of the root canal system. In: Cohen S, Bums RC, eds. Pathways of the pulp. 3rd ed. St. Louis: CV Mosby Co., 1984:20595. 2. Schilder H. Filling root canals in three dimensions. Dent Clin North Am 1967;11:723-44. 3. Brayton SM, Davis SR, Goldman M. Gutta-percha root canal fillings. Oral Surg 1973;35:226-31. 4. Yee FS, Marlin J, Krakow AA, Gron D. Three-dimensional obturation of the root canal using injection-molded, thermoplasticized dental gutta-percha. J Endodon 1977;3:168-74. 5. Michanowicz A, Czonstkowosky M. Sealing of an injection thermoplasticized low-temperature (70°C) gutta-percha: a preliminary study. J Endodon' 1984;10:563-6. 6. Michanowicz AE, Czonstkowosky M, Piesco NP. Low-temperature (70°C) injection gutta-percha: a scanning electron microscopic investigation. J Endodon 1986;12:64-7.
562
Gen;oglu et al.
7. Johnson WB. A new gutta-percha technique. J Endodon 1978;4:184-8. 8, Beatty RG, Baker PS, Haddix J, Hart F. The efficacy of four root canal obturation techniques in preventing apical dye penetration. J Am Dent Assoc 1989;119:633-7. 9. McComb D, Smith D. A preliminaryscanning electron microscopicstudy of root canals after endodontic procedures. J Endedon 1975;1:238-42. 10. White RR, Goldman M, Un PS. The influence of the smeared layer upon dentinal tubule penatration by plastic filling materials. J Endodon 1984;10:558-62. 11. Yamada RS, Armas A, Goldman M, Lin PS. A scanning electron microscopic comparison of a high volume final flush with several irrigating solutions. Part 3. J Endedon 1983;9:137-42. 12. Larder TC, Prescott AJ, Brayton SM. Gutta-percha: a comparative study of three methods of obtuaration. J Endodon 1976;2:289-94. 13. Wollard RR, Brough SO, Maggio J, Seltzer S. Scanningelectron micro-
Journal of Endodontics scopic examinationof root canal filling materials. J Endodon 1976;2:98-110. 14. Coviello J, Brillant JD, Wright J. Preliminary scanning electron microscopic study of the chlororosin lateral condensation technique, J Endedon 1977;3:54-62. 15. Torabinejad M, Soobe Z, Trombly PL, Krakow AA, Gron P, Marlin J. Scanning electron microscopic study of root canal obturation using thermo•plasticizedgutta-percha. J Endedon 1978;4:245-50. 16. KennedyWA, Walter WA, Gough RW. Smear layer removal effects on apical leakage.J Endodon 1986;12:21-7. 17. Cemgneux M, Ciucchi B, Dietschi BB, Holz J. The influence of the smear layer on the sealing ability of canalobturation. Int Ended J 1987;20:22832. 18. EvansJT, Simon JHS. Evaluationof the apicalseal produced by injected thermoplasticizedgutta-percha in the absence of smear layer and root canal sealer. J Endodon 1986;12:101-7.
A W o r d To T h e W i s e Increasingly at issue is the validity of the peer review system for determining who receives grant funding and whose papers are published. A typical criticism is the following, "The central problem with the peer review approach is that it is only any good for next step research of limited vision. It is totally inappropriate for the exciting big leaps which carry understanding forward" (Lab News 1991:7 Oct.). Sounds like someone whose grant wasn't fundedH But the question is serious. How do we distinguish between proposed "exciting big leaps" which are genius and those which are madness? Wallace Sturr
Printed in U.S.A.
VOL. 19, No. 11, NOVEMBER1993
Dentinal Wall Adaptation of Thermoplasticized Guttapercha in the Absence or Presence of Smear Layer: A Scanning Electron Microscopic Study Nimet Gengoglu, DOS, PhD, Sami Samani, DDS, MS, and Mahir Gimday, DDS, PhD
The dentinal adaptation of injected thermoplasticized gutta-percha and thermoplasticized guttapercha resulting from Ultrafil and Thermafil systems was evaluated by scanning electron microscopy and compared with adaptation obtained with the lateral condensation of gutta-percha. Each method was evaluated with and without the smear layer removed. Scanning electron microscopic observations showed the thermoplasticized gutta-percha resulting from either system to have better dentinal wall adaptation than lateral condensation of guttapercha in either the absence or presence of the smear layer. In the absence of smear layer, the adaptation of gutta-percha was improved in all groups. Although sealer was used, removing the smear layer was found to enhance the ability of the thermoplasticized gutta-percha to enter the patent tubules.
A new thermoplasticized gutta-percha technique, Thermafil, was introduced by Johnson (7). Beatty et al. (8) found that Thermafil produced a better apical seal than lateral condensation. McComb and Smith (9) observed prepared root surfaces to be covered by an amorphous layer of debris, referred to as the smear layer. Some consider that it is desirable to remove this layer because it covers prepared areas and prevents filling material from penetrating the dentinal tubules or even contacting the canal wall (9, 10). In theory, a good seal should be obtainable with sealer that adheres well to the core material. Thus, removing the smear layer prior to fiUing may actually increase the adhesive strength of the filling to dentin and improve the sealing ability of the filling. The purpose of this study was to investigate the dentinal wall adaptation of three different gutta-percha formulations in the absence or presence of smear layer. MATERIALS AND METHODS Sixty-four single-rooted teeth were used in this study. The teeth were stored in 5.25% sodium hypochlorite for 24 h to remove any organic debris. Pulp tissue remnants were removed with a barbed broach. The teeth were instrumented using the "step-back" technique. Gates Glidden burs were used to prepare the coronal thirds of the canals. The teeth were irrigated with 5.25% sodium hypochlorite before and after recapitulation with a size 60 master apical file. Thirtytwo teeth were randomly chosen and their smear layers removed by final rinses of 10 ml of Calcinase (17% EDTA) followed by 10 ml of 5.25% sodium hypochiorite, as recommended by Yamada et al. (11). The other 32 teeth were irrigated with final rinses of 5.25 % sodium hypochlorite alone. All canals were dried with paper points. Teeth with or without smear layers were randomly assigned to six groups (Table 1). Four teeth were used as control groups (two with and two without smear layer) and not obturated. A gutta-percha master cone (Hygenic Corp., Akron, OH) was fitted to within 0.5 mm of working length in the lateral condensation groups. Freshly mixed Grossman's sealer was placed into the root canal. A DI 1 spreader was inserted 1 to 2 mm shorter than the working length. The spreader was kept in the canal until a fine gutta-percha accessory cone was
The ultimate objective of nonsurgical root canal therapy is complete obturation of the root canal system (1). Since the most common cause ofendodontic failure has been attributed to incomplete obturation (1), many different obturation techniques have been developed in order to increase the success of root canal treatment. Lateral condensation has proven to be a very popular gutta-percha technique. However, Schilder (2) and Brayton et al. (3) noted that with lateral condensation of gutta-percha at no time did a homogeneous mass form nor did the gutta-percha adapt to the root canal walls. Yee et al. (4) introduced the injection of thermoplasticized gutta-percha in 1977. They reported injected gutta-percha to be superior to lateral condensation and capable of filling multiple foramina and other raminifaction. Based on this concept, a low-temperature injection-molded thermoplasticized gutta-percha delivery system has recently been developed. Favorable results for the sealing ability of the low-temperature thermoplasticized gutta-percha technique (Ultrafil) and close adaptation to canal walls have been reported (5, 6).
558
Vol. 19, No. 11, November 1993
Thennoplasticized Gutta-percha
559
TABLE 1. Operated groups Smear Layer Present Group la Group 2a
Group 3a
Smear Layer Absent Group 1b (lateral condensation with Grossman's sealer) Group 2b (injected thermoplasticized gutta-percha with Grossman's sealer) Group 3b (thermoplasticized guttapercha with Grossman's sealer)
FIG 2. A scanning electron micrograph of laterally condensed guttapercha in the absence of smear layer showing close adaptation in the middle third of the canal (original magnification x1500). Notice the sealer in the dental tubules. D, dentin; S, sealer.
FIG 3. A scanning electron micrograph of injected thermoplasticized gutta-percha showing close adaptation in the presence of smear layer in the middle third of the canal (original magnification x350). D, dentin; G, gutta-percha.
FIG 1. A, A scanning electron micrograph of root filling showing the laterally condensed gutta-percha not to be in a homogeneous mass in the presence of smear layer (original magnification x35). Sealer is seen between the gutta-percha and canal walls and between the gutta-percha cones but voids are present elsewhere. B, Notice the voids between the canal wall and laterally condensed gutta-percha and the voids between sealer and gutta-percha in the middle third of the canal (original magnification x350). G, gutta-percha; D, dentin; S, sealer.
placed. The canal was considered to be adequately obturated when enough points were placed that the spreader could no longer penetrate beyond the coronal third of the canal. After complete canal obturation the coronal gutta-percha was remove with a hot instrument. In the groups obturated with Thermafil, size 60 Thermafil devices were used because the apical preparations were en-
larged to a size 60. The roots were coated with Grossman's sealer and then Thermafil obturators were passed through a flame and inserted into each root canal to a level at which the central carrier extended to a full working length distance yet the carrier stayed in place. An inverted cone bur was used to cut through the shank of each carrier at the coronal level of each root canal. Following obturation, the teeth were stored for 7 days at room temperature and 100% humidity to allow the materials to set. Then single longitudinal grooves were cut on the labial and lingual root surfaces, first with a round bur and then with a diamond disc. Later, pliers were used to fracture the teeth. No distortion occurred during the fracturing process. The specimens were coated with gold for a Scanning Coating System (Bio-Rad SC 502) and examined with a scanning electron microscope (JEOL JSM 5200; JEOL, Tokyo, Japan) for density and homogeneity of the fillings, conformity to the
560
Gen~oglu et al.
Journal of Endodontics
FJa 4. A, Injected thermoplasticized gutta-percha showing stippled appearance due to projection into the tubules in the absence of smear layer in the middle third of the canal (original magnification x350). B, Patent tubules are plugged with gutta-percha and sealer (original magnification x1500). D, dentin; G, gutta-percha; S, sealer.
prepared canal, and adaptation of the materials to the dentinal walls. RESULTS Scanning electron microscopic examination of the control teeth, which were irrigated with sodium hypochlorite alone, showed the presence of an intact smear layer. However, the teeth that were irrigated with the Calcinase (EDTA) and sodium hypochlorite combination showed smear layer removal with clean walls. In the presence of smear layer, the root canal filling by lateral condensation did not form a homogeneous mass (Fig. 1A) and although the sealer was observed to fill many of the voids between the gutta-percha and canal walls, poor adaptation could be seen in higher magnification (Fig. 1B). It was observed that removing the smear layer enhanced the wall adaptation of the laterally condensed gutta-percha. Although the patent tubules were filled with sealer in the coronal and middle third of the canal (Fig. 2), poor adaptation was found in the apical third of the canal. In the presence of smear layer, the root canal filling from injected thermoplasticized gutta-percha was homogeneous
FtG 5. A, Thermoplasticized gutta-percha resulting from Thermafil showing good adaptation to the dentin in the presence of smear layer. Notice the cracks on the surface of the filling (original magnification x35). B, In this specimen, gutta-percha adhered to the other half and the metal carrier is seen (original magnification x35). C, Close adaptation of Thermafil can be seen in the middle third of the canal (original magnification x350). G, gutta-percha; S, sealer.
and the filling reproduced the shape and irregularities of the canals well. With higher magnification gutta-percha showed close adaptation to the dentinal walls in every part of the roots (Fig. 3). In the absence of smear layer, even though sealer was being used, the injected thermoplasticized gutta-
Vol. 19, No. 11, November 1993
FiG 6. A, In the absence of smear layer patent tubules were filled with gutta-percha and thermoplasticized gutta-percha has a stippled appearance due to projection into the tubules in the middle third of the canal (original magnification x1500). B, Despite the cracks, thermoplasticized gutta-percha resulting from Thermafil maintained contact with the dentinal wall in the apical third of the canal (original magnification x350). D, dentin; G, gutta-percha; S, sealer.
percha was stippled in appearance due to projections into the patent tubules (Fig. 4.4) and the patent tubules were plugged with filling (Fig. 4B) in all parts of the roots. In the presence of smear layer, root filling from the thermoplasticized gutta-percha resulting from Thermafil showed close adaptation to the dentinal wall in all parts of the root. Some specimens showed cracks (Fig. 5A); in other specimens, the metal carrier could be seen as the gutta-percha adhered to the other half of the teeth (Fig. 5B). Despite these cracks the filling resulting from Thermafil maintained contact with the dentinal wall in all parts of the roots. In the absence of smear layer, Thermafil was stippled in appearance (Fig. 5C) and the patent tubules were plugged with filling (Fig. 6A). Again, the cracks did not effect the adaptation of the filling (Fig. 6B). DISCUSSION The result of this study indicated that the thermoplasticized gutta-percha resulting from Therrnafil and Ultrafil systems showed close adaptation to the dentinal walls and better replicated the irregularities of the canals than did lateral
Thermoplasticized Gutta-percha
561
condensation of gutta-percha. The results of this study concerning laterally condensed gutta-percha corroborate those of Brayton et al. (3), Larder et al. (12), Wollard et al. (13), and Coviello et al. (14). Scanning electron microscopic findings of Torabinejad et al. (15) also indicated injection-molded guttapercha to be superior to laterally condensed gutta-percha. Michanowicz et al. (6) investigated the dentinal wall adaptation of injected thermoplasticized gutta-percha with or without sealer and compared this with the lateral condensation technique. They concluded that the root canal system can be obturated as well or better with the injected thermoplasticized gutta-percha system with sealer, as with laterally condensed gutta-percha. Although they observed that injected guttapercha flowed into the dentinal tubules when used without sealer, they still advised using sealer to produce better apical seal. In the present study, it was seen that removing the smear layer enhanced the adaptation of gutta-percha in all groups. Although better results were observed in the coronal and middle thirds of the canals for the laterally condensed guttapercha in the absence of smear layer, still poor adaptation was seen in the apical areas. The effect of removing smear layer was more pronounced for thermoplasticized gutta-percha than for laterally condensed gutta-percha. Even though sealer was used, the entry of the thermoplasticized guttapercha into tubules was observed. White et al. (10) also observed tubular penetration in the absence of smear layer and also indicated that such tubular penetration increased the interface between the filling material and the dentinal wall and thus may decrease the apical leakage. This was supported by Kennedy et al. (16) and Cergneux et al. (17), although not by Evans and Simons (18). It was also observed that the cracks which were seen on the surface of Thermafil specimens did not effect adherence to the dentinal walls. According to the results of this study, the thermoplasticized gutta-percha resulting from Thermafil or Ultrafil techniques proved to be superior to laterally condensed gutta-percha in regard to dentinal wall adaptation in the absence or presence of smear layer. Dr. Gen~o01uis a lecturer, Department of Endodontics, Marmara University, Faculty of Dentistry, Istanbul, Turkey. Dr. Samani is professor, Department of Endodontics, University of Medicine and Dentistry, New Jersey Dental School, Newark, NJ. Dr. Gunday is associate professor, Department of Endodontics, Marmara University, Faculty of Dentistry, Istanbul, Turkey. Address requests for reprints to Dr. Nimet Gen~o~lu,Anafartalar Sokak, Fulya Apt. 3/1, Yesilk6y, Istanbul, Turkey.
References 1. Nguyen NT. Obturation of the root canal system. In: Cohen S, Bums RC, eds. Pathways of the pulp. 3rd ed. St. Louis: CV Mosby Co., 1984:20595. 2. Schilder H. Filling root canals in three dimensions. Dent Clin North Am 1967;11:723-44. 3. Brayton SM, Davis SR, Goldman M. Gutta-percha root canal fillings. Oral Surg 1973;35:226-31. 4. Yee FS, Marlin J, Krakow AA, Gron D. Three-dimensional obturation of the root canal using injection-molded, thermoplasticized dental gutta-percha. J Endodon 1977;3:168-74. 5. Michanowicz A, Czonstkowosky M. Sealing of an injection thermoplasticized low-temperature (70°C) gutta-percha: a preliminary study. J Endodon' 1984;10:563-6. 6. Michanowicz AE, Czonstkowosky M, Piesco NP. Low-temperature (70°C) injection gutta-percha: a scanning electron microscopic investigation. J Endodon 1986;12:64-7.
562
Gen;oglu et al.
7. Johnson WB. A new gutta-percha technique. J Endodon 1978;4:184-8. 8, Beatty RG, Baker PS, Haddix J, Hart F. The efficacy of four root canal obturation techniques in preventing apical dye penetration. J Am Dent Assoc 1989;119:633-7. 9. McComb D, Smith D. A preliminaryscanning electron microscopicstudy of root canals after endodontic procedures. J Endedon 1975;1:238-42. 10. White RR, Goldman M, Un PS. The influence of the smeared layer upon dentinal tubule penatration by plastic filling materials. J Endodon 1984;10:558-62. 11. Yamada RS, Armas A, Goldman M, Lin PS. A scanning electron microscopic comparison of a high volume final flush with several irrigating solutions. Part 3. J Endedon 1983;9:137-42. 12. Larder TC, Prescott AJ, Brayton SM. Gutta-percha: a comparative study of three methods of obtuaration. J Endodon 1976;2:289-94. 13. Wollard RR, Brough SO, Maggio J, Seltzer S. Scanningelectron micro-
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A W o r d To T h e W i s e Increasingly at issue is the validity of the peer review system for determining who receives grant funding and whose papers are published. A typical criticism is the following, "The central problem with the peer review approach is that it is only any good for next step research of limited vision. It is totally inappropriate for the exciting big leaps which carry understanding forward" (Lab News 1991:7 Oct.). Sounds like someone whose grant wasn't fundedH But the question is serious. How do we distinguish between proposed "exciting big leaps" which are genius and those which are madness? Wallace Sturr