Dye Leakage Study: Comparing Conventional and New Techniques

The purpose of this study was to compare the degree of dye penetration of Thermofil and Simplifill to standard lateral condensation using AH26 plus. Forty-five human maxillary incisors were instrumented and obturated with three different methods: Rotary Profile with the Thermofil method and AH-26 Plus sealer, Rotary Lightspeed with the Simplifill method and AH-26 Plus sealer, and hand file with lateral condensation and AH-26 Plus. An additional 45 teeth were used as positive controls in three separate but corresponding groups, and another 15 were in a negative control group. Apical leakage was measured and evaluated on both the internal canal surfaces and the obturation material itself. The results showed that there was a significant difference between the control and obturated groups but no significant difference between any obturation groups.

Root canal obturation consists of placing an inert filling material in the space previously occupied by pulp tissue. To achieve successful endodontic therapy, it is important to obturate the root canal system completely.

Gutta-percha is used with various techniques for obturation of the root canal system. Chemically pure gutta-percha exists in two crystalline forms: alpha and beta. The forms are interchangeable depending on the temperature of the material. When heated, the initial beta form changes to the alpha form. When cooled, it can change back into the beta form.¹ The alpha form has adhesives and a low viscosity. This type is found in Thermofil. The beta form has no adhesion characteristics but has a higher viscosity. This type is typically found in standard gutta-percha points.

Throughout the years, a variety of techniques using gutta-percha have been developed for root canal fillings. These techniques include lateral condensation, Kloroperka, Chloropercha, warm vertical condensation, injectable thermoplasticized, Ultrafill, and Thermofil. Investigators have evaluated the apical seals obtained by these various gutta-percha filling techniques.

Lateral condensation remains the most widely accepted and used obturation technique.² As a result, all other techniques are compared to it to evaluate success.

In 1978, Johnson³ demonstrated a simple method of carrying thermoplasticized gutta-percha to the extent of a prepared canal. A flexible metal carrier the same size as the final apical instrument is coated with alpha form gutta-percha. The carrier is used to transport the gutta-percha to the working length, then to compact it using a single insertion motion. This method of obturation was marketed under the name of Thermofil Endodontic Obturation System (Tulsa/Dentsply Dental Products). The newer system uses a plastic rather than metal carrier.

In 1999, Lightspeed Technologies introduced the Simplifill Obturation System. It utilizes a metal carrier, which has an apical gutta-percha plug that is 3 to 4 mm at the end. The carrier is removed during the obturation process. This technique is used in conjunction with the Lightspeed Rotary Nickel Titanium Reamer.⁴ This is the most recently introduced obturation product on the market.

Studies have shown that Thermofil has shown less apical dye penetration than the single-cone obturation and laterally condensed gutta-percha.⁵ Other studies have shown significantly less leakage with lateral condensation than Thermofil.⁶ In a more recent study, there was no significant difference in the leakage between lateral condensation and the sectional Simplifill method⁷ (Figure 1).

The sealer recommended by both manufacturers is the new AH-26 Plus. This new sealer does not form paraformaldehyde when mixed, as did the original AH-26 sealer. Another modification is the increased amount of barium sulfate introduced into the sealer to give it a more radiopaque appearance.^8,9

A review of the literature failed to reveal any studies comparing lateral condensation, Thermofil, and Simplifill obturation techniques directly.

The purpose of this study was to determine if Thermofil or Simplifill, and the techniques recommended by each manufacturer to prepare the canals, result in significantly less leakage penetration than the standard of hand filing and lateral condensation using AH-26 Plus. To do this, the Thermofil and Simplifill methods were used in accordance with manufacturer instructions in two groups containing 15 teeth each. The third comparison group, also with 15 teeth, used the traditional lateral condensation. Four additional groups, each also containing 15 teeth, were used for three corresponding positive controls and one negative control.

Methods and Materials

One hundred and five extracted straight central incisors were selected and distributed randomly in seven equal groups denoted by numbers 1 through 7. The selected teeth were radiographed from buccolingual and mesiodistal views. The radiographs were used to determine the canal shape and patency. Teeth that had any curvature or calcification were eliminated from the study and replaced.

Group 1

This group was prepared using the Thermofil system and Tulsa rotary instrumentation files (.04 taper ISO series). Lengths were determined by introducing a #10 K-type stainless steel file to the apex of the tooth. The file was observed visually as it exited the canal, and a measurement was recorded at that time. Then 1 mm was subtracted from that measurement. This was the working length measurement.

The canals were serially filed to size 15 with stainless steel K-type files to the working length. Then, in a crown-down fashion as described by the manufacturer, the Orifice Shaper instruments were introduced into the canal to flare the coronal area of the tooth. The crown down technique was continued with the ISO .04 series of instruments to the apex. The NiTi hand files were then used to ream the apex to adequate size as determined by the operator. The range of apical sizes was from 50 to 60. After preparation was finished, the taper and size of the canal was verified using the plastic verifying tools as described by the manufacturer. The canals were irrigated and dried with paper points to allow for obturation.

At this point, the corresponding Thermofil was heated in the oven provided by the manufacturer. AH-26 Plus, as recommended by the manufacturer, was applied to the walls of the preparation using the master file. After adequate heating, as indicated by the automatic oven, the carrier was delivered into the orifice of the canal to the working length. The handle was cut using a high-speed round bur and the remainder reduced to 2 mm below the orifice to allow space for temporary material. Cavit was placed into the orifice to ensure a good seal.

Group 2

This group consisted of 15 teeth used as positive controls for Group 1. This group was prepared in the same manner as Group 1 but was not filled with any obturation material.

Each group had its own positive control because the canal preparation techniques for each obturation material were unique. Therefore, a group prepared with the Lightspeed technique had to be compared to a positive control prepared in a similar fashion. A group prepared with the Tulsa rotaries that was to receive the Thermofil obturators could not be compared with a positive control group that was not prepared in a similar fashion, i.e., a hand file group.

Group 3

This group was prepared with the Lightspeed system and filled with the Simplifill obturation technique. The teeth were accessed and working lengths determined in the same manner as for Group 1. The preparation was performed as demonstrated in the video directions provided by the manufacturer. The technique is as follows. After the working lengths were determined, the canals were serially enlarged with a stainless-steel file to a size 15. The coronal one-third was preflared using Gates-Glidden burs. Nos. 3, 2, and 1 were introduced sequentially in a crown-down fashion until one-third of the measurement had been reached. Then the smallest Lightspeed to bind was introduced into the canal by hand. This instrument was inserted into the battery-operated handpiece and turned on to rotate at the maximum speed of 2,000 rpm as recommended by the manufacturer. With adequate lubrication (NaOCl), the instruments were inserted into the canal and forwarded to the working length. Subsequent larger instruments (the next instrument in the series) were introduced into the canal to the working length and continued until 12 pecks of motion was reached as described by the manufacturer. The instrument used to acquire the 12 pecks is known as the master apical rotary. This was the last file to be used in the canal, and an X-ray was taken to ensure adequate maintenance of the working length. The apical preparation size ranged from 40 to 80. The average size was 55. Then the next larger rotary was introduced into the canal to 5 mm short of the working length. The preparation was completed at this point, and the canal was ready to be filled with the Simplifill system. AH-26 Plus cement sealer was mixed and used as recommended by the manufacturer. The Simplifill size was the same size as the master apical rotary used. The Simplifill was coated with sealer and introduced to the working length. The handle was then separated from the gutta-percha plug by a counter-clockwise twisting action of the handle. The rest of the canal was filled with sealer using a centrix syringe tip to deliver it into the canal until reaching 2 mm short of the orifice, again allowing space for future placement of the temporary material. Subsequently, the largest size gutta-percha point that would reach the Simplifill plug was placed into the canal. Accessory cones were placed as space provided but without any spreading, as directed by manufacturer. Cavit was placed into the orifice for sealing.

Group 4

This group consisted of 15 teeth that were used as positive controls for Group 3. They were prepared in a similar manner as in Group 3 except that they were not obturated.

Group 5

This group was the lateral condensation group.

The working length was determined as in previous groups. Then preparation began with K-type files introduced to the working length and filed up to size 25. The preflaring was accomplished as in Group 3. The apices were serially prepared up to a size 50, and the apical portions were merged with the middle portion by hand flaring with the last file. Throughout the procedure, NaOCl was used for irrigation. The canals were dried with paper points, and a final radiograph was taken with the final file to length to determine the position of the apical preparation. A D11T spreader was introduced to length to determine the adequacy of flare. The spreader passed to length without any resistance.

Traditional lateral condensation was done by placing a master cone to length using AH-26 Plus for sealer. At least two accessory cones were placed to within 1 mm of length. The rest was filled with cones as the preparation permitted. Radiographs were taken and evaluated by two independent endodontists for adequate condensation. Both agreed as to the adequacy. If not, more cones were placed until agreement was reached as to the radiodensity of the fill. The excess was burned off to 2 mm below the orifice, and cavit was placed in the orifice for seal.

Group 6

This group consisted of 15 teeth used as positive controls for Group 5. The teeth were prepared in a similar manner as Group 5 except that they were not obturated using lateral condensation.

Group 7

This group was the negative control group or no-treatment group. No instrumentation was performed in this group.

Following obturation, the root surfaces of all the samples were coated with two layers of clear nail polish resin up until the apical 2 mm. The apical 2 mm were free of any resin materials. There was an increase in lateral canal presence or delta formation in the apical area, but randomization of the sample distribution should have accounted for this variability. Other studies also utilized this technique for elimination of lateral canal leakage anywhere other than the apical 2 mm area.¹⁰ The teeth were then glued from the incisal edges to a tongue depressor perpendicularly and immersed into a plastic container of India ink, which engulfed two-thirds of the root. The container was covered and allowed to sit for seven days from the time of submersion.^11,12

Results

The teeth were sectioned vertically along their long accesses. To ensure that the sectioning process did not damage the inside of the canal, the operator vertically cut with a diamond disc along the root short of reaching the gutta-percha, thereby creating a stress canal.¹⁰ A chisel was used to wedge and split the teeth. The teeth were then randomly distributed in the group for evaluation. Two observers who were unaware of the research purpose or protocols were asked to use a stereomicroscope to identify any blue dye that may have penetrated into the root canal, including the walls of the preparation or the middle of the filling, which may also leak. The evaluators measured dye leakage with a millimeter-scaled ruler under a 5x stereomicroscope (Global Surgical Corp., St. Louis) from the apical constriction to the longest point of dye penetration along the canal wall or gutta-percha itself. A maximum of 20 mm was recorded due to the variation in lengths of each sample tooth.

Statistics

The analysis of variance was used to compare leakage among the seven groups. Upon finding significance, Bonferroni-adjusted multiple pairwise Mann-Whitney tests were used to determine which treatment groups differed from one another. A pairwise test was considered statistically significant if p<0.005.

The ANOVA results are shown in Figure 2 and Table 1. There was statistically significant difference among the seven groups (p<0.001). Pairwise multiple comparisons showed that the Thermofil (Group 1), Simplifill (Group 3), and lateral compaction (Group 5) techniques differed from the instrumented-but-unfilled groups (Groups 2, 4, and 6) and the no-treatment group (Group 7) but did not differ statistically from one another (Table 3).

Discussion

A literature review of 15 studies by Beck and Donnelly found no significant difference between the apical leakage of Thermofil and lateral condensation.¹³ This is consistent with the present study. The current study is also consistent with one done by Santos and Walker that compared apical leakage allowed by lateral condensation to that allowed by the Simplifill technique.⁷ The results were similar, although Santos and Walker used different kinds of sealers. The purpose of this study was to evaluate and compare all three techniques since no such study has yet been published to the best knowledge of the authors. The authors also noted that most of the studies reviewed failed to utilize the sealer recommended by the manufacturer: AH-26 Plus. In the current study, the sealers were consistent with manufacturer recommendations and consistent among sample groups.

The current study used seven groups. Group 1 was the Thermofil group and was prepared as recommended by the manufacturer by using the Tulsa/Dentsply rotary NiTi files. Group 2 was its positive control and was separate and distinct due to its preparation requirements. Group 3 was the Simplifill group and was prepared using the Lightspeed rotary NiTi files. Group 4 was its positive control, which had a separate and distinct preparation technique. Group 5 was the hand file and lateral condensation group. Group 6 was its distinct positive control. Group 7 was the no-treatment group. Three distinct positive controls were used to ensure that the statistical analysis would be accurate due to the separate and distinct preparation techniques required for each filling group.

In this study, both the no-treatment control group (Group 7) and the instrumented-but-unfilled groups (Groups 2, 4, and 6) had leakage throughout the canal. Since each tooth was of differing lengths, a maximum of 20 mm was recorded to simplify and standardize analysis calculations. The untreated control group was coated with resin polish in a similar fashion as the other groups, leaving the apical 2.0 mm free of any resin material. It is believed that the dye enters the apical foramen through capillary action.

Although there was no significant difference in the dye penetration between the test groups, there were some interesting observations that should be mentioned. During the obturation using Thermofil, the operator routinely noticed that the thermoplasticized gutta-percha or sealer would be pushed through the apex regardless of the final apical size. In some cases, there seemed to be a large amount of material extruded from the end of the root (Figure 4). This may have severe clinical implications because this technique may, in fact, cause a high number of overfills.

Also, when the authors examined the split sections after evaluation, the plastic carrier often seemed stripped of the gutta-percha that should have surrounded it, and only sealer remained surrounding the core (Figures 5 and 6).

As in the Thermofil cases, the operator found that in the Simplifill cases a high number of samples had overextrusion of the sealer from the apex regardless of the master apical rotary final size. The apical plug itself remained in the canal. This overextrusion may be attributed to the fact that the apical plug corresponds very closely with final apical preparation size and that the snug fit of the plug acts as a plunger, hydraulically forcing the sealer out the apex. It was also noted that the area in the canal above the apical plug had a significant amount of voids. This may be attributed to the backfill technique, which allows passive placement of accessories and does not suggest spreading of the gutta-percha in the coronal area.

In both these cases, the extrusion of the sealer would manifest as a sealer "puff" or "umbrella." This again may have clinical implications that need to be examined, but it should be noted that the release of paraformaldehyde observed from the conventional AH-26 is not seen with the new AH-26 Plus. If this is indeed the case, then the overextrusion may not be as relevant. Whether or not this new formulation has less of an irritating effect needs to be evaluated in future studies. The overextrusion of the material may also have an effect on the leakage. Theoretically, in the Thermofil technique, this overfill of "puff" may compensate for any shrinkage that may occur due to the cooling of the gutta-percha. The cooling may in fact pull some of the sealer or gutta-percha back into the canal, thereby giving a false sense of seal at the apex. Over time, when the sealer or gutta-percha gets resorbed by the body, leakage may continue where the shrinkage has occurred.

Conclusion

In general, the authors believe that the standard lateral technique gave the most consistent results; and it had minimal, if any, overfills that may irritate the periapical tissues. No significant difference was found in leakage amounts. Both new techniques and sealer show promise, but further refinement of each technique and further investigation in vivo must be done to evaluate compatibility in the oral cavity.

Authors

M. Sadegh Namazikhah DMD, MSEd, is a professor of clinical dentistry, acting chairman of the Endodontic Department, and director of the Advanced Endodontic Program at the University of Southern California School of Dentistry.

Ramiar Shirani, DDS, is a postgraduate endodontic resident at the USC School of Dentistry.

Amir Mohseni, DDS, is a postgraduate endodontic resident at the USC School of Dentistry.

Fariborz Farsio, DMD, is in the International Student Program at USC School of Dentistry.

References

1. Goodman A, Schilder H, et al, The thermomechanical properties of gutta-percha, II: The history and molecular structure of gutta-percha. Oral Surg Oral Med Oral Path Oral Radiol Endod 37:954, 1974.

2. Dummer PMH, Comparison of undergraduate endodontic technique programs in the United Kingdom and in some schools in Europe and the United States. Int Endod J 24:169-77, 1991.

3. Johnson WB, A new gutta-percha filling technique. J Endod 4:184-8, 1978.

4. Widley WL, Senia ES, A new root canal instrument and instrumentation technique: A preliminary report. Oral Surg Oral Med Oral Pathol 67:198-207, 1989.

5. Beaty RG, Baker PS, et al, The efficacy of four root canal obturation technique in preventing apical dye penetration. J Am Dent Assoc 199:633-7, 1989.

6. Lares C, EL Deeb ME, The sealing ability of the Thermofil obturation technique. J Endodon 16:479-9,1990.

7. Santos M, Walker W, et al. Evaluation of apical seal in straight canals after obturation using the Lightspeed Sectional Method. J Endodon 25(9), 1999.

8. Smith MA, Steiman HR, An in vitro evaluation of microleakage of two new and two old root canal sealers. J Endodon 20:18-21,1994.

9. Limkagwalmongkol S, Abbott PV, Sandler AB, Apical dye penetration with four root canal sealers and gutta-percha using longitudinal sectioning. J Endodon 18:535-9,1992.

10. Cohen B, Pagnillo M, et al, The evaluation of apical leakage for three endodontic fill systems. Gen Dent Nov-Dec 618-23, 1998.

11. Delat DM, Spangberg LSW, Comparison of apical leakage in root canals obturated with various gutta percha techniques using a dye vacuum tracing method. J Endodon 29:315-9, 1994.

12. Mann SR, McWalter GM, Evaluation of apical seal and placement control in straight and curved canals obturated by laterally condensed and thermoplasticized gutta percha. J Endodon 12:10-7, 1987.

13. Becker TA, Donnelly JC, Thermofil obturation: literature review. Gen Dent 45:46-55, 1997.

To request a printed copy of this article, please contact/ M. Sadegh Namazikhah, DMD, MSEd, USC School of Dentistry, 925 W. 34th St., Room 124C, Los Angeles, CA 90089-0641.

Legends

Figure 1. From left to right, Light speed rotary file, Simplifill, Tulsa rotary file, Thermofil.

Figure 2. Group 1 -- Thermofil; Group 2 -- Positive control prepared with Tulsa rotary files; Group 3 -- Simplifill; Group 4 -- Positive controls prepared with Lightspeed files; Group 5 -- Lateral compaction; Group 6 -- Positive controls prepared with hand files; Group 7 -- negative controls with no preparation.

Figure 3. Group 1 -- Thermofil; Group 2 -- Positive control prepared with Tulsa rotary files; Group 3 -- Simplifill; Group 4 -- Positive controls prepared with Lightspeed files; Group 5 -- Lateral compaction; Group 6 -- Positive controls prepared with hand files; Group 7 -- negative controls with no preparation.

Figure 4. Example of the overextrusion that occurred in some samples from the apex of the tooth using the Thermofil obturation system.

Figure 5. Example of a new Thermofil carrier size 40 straight from the manufacturer. Note that the plastic carrier is showing through the gutta-percha even in unused samples.

Figure 6. Example of a sectioned sample that had gutta-percha stripping at the apical portion of the penetration. This may have clinical implications.