Effect of post space preparation on the sealing ability of mineral trioxide aggregate and Gutta-percha: A bacterial leakage study.

AIM: The purpose of this study was to evaluate the effect of post space preparation on the sealing ability of teeth obturated with mineral trioxide aggregate (MTA) and Gutta-percha.
MATERIALS AND METHODS: Fifty intact human mandibular premolars, after decoronation and biomechanical preparation, were randomly divided into three experimental groups. In Group A (n = 10), the canals were obturated with Gutta-percha using cold lateral compaction technique, followed by immediate post space preparation. In Group B (n = 10), the canals were obturated with 8 mm of MTA and in Group C (n = 10), sectional obturation with 4 mm of MTA was done, followed by delayed post space preparation. All specimens were subjected to bacterial leakage analysis, and the occurrence of turbidity was checked.
RESULTS: All specimens in the lateral compaction group leaked. The mean number of days at which leakage was observed in Groups A, B and C were 18.5 days, 93.6 days and 95.5 days.
CONCLUSIONS: MTA can be considered as an alternative to Gutta-percha as an apical third restorative material for teeth indicated for post and core, as it demonstrates better-sealing ability compared with Gutta-percha. Further, the removal of set MTA for post space preparation does not disrupt the integrity of the remaining apical MTA.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

Aesthetic and functional management of mutilated teeth have always been a challenge to the dentist. There are various treatment modalities in managing the mutilated teeth,[1234] one of the standard care for tooth with insufficient coronal structure requires the placement of a radicular post to assist in restoring the tooth to function.[5] Although several obturating materials are available, none of them are able to provide a fluid tight seal.[678] This also holds true for Gutta-percha, especially when it is subjected to removal for preparing dowel space.

Mineral trioxide aggregate (MTA) has also been suggested as a root canal obturating material in permanent teeth with fully developed roots.[789] However, the coronal tooth structure may be lost in teeth obturated with MTA by recurrent decay, fracture of the coronal restoration or fracture of tooth crown,[10] requiring the post space preparation in these root canals prior to the potential placement of a post and core.

Sufficient literature regarding MTA as an apical third restorative material for post and core indicated tooth is not available.[11] Thus, the aim of this study was to evaluate the effect of post space preparation on the apical seal, in teeth obturated with MTA and Gutta-percha using a bacterial leakage system.

MATERIALS AND METHODS

Fifty intact human mandibular premolars, extracted for orthodontic reasons, were selected for this in vitro study. A no. 10 K-file was inserted in the root canal, and the length was noted at which the tip of the file was just visible at the apex. One mm was subtracted from this length and was used as the working length. The roots were instrumented to a no. 40 K-file and shaped using the step-back technique. Gates glidden drills (Dentsply Maillefer, Ballaigues, Switzerland) were used to enlarge the middle and coronal portions of the root canals. Irrigation of the root canals was done using 5.25% sodium hypochlorite (Vishal Dentocare, India) and 17% ethylenediaminetetraacetic acid (Canalarge, Ammdent, India), followed by final irrigation with saline (Axaline, India). Following instrumentation, the canals were dried with absorbent paper points (Dentsply Maillefer, Switzerland), and were divided into four experimental groups and two control groups.

Group A: (n = 10) cold lateral Gutta-percha compaction, followed by immediate post space preparation.

Group B: (n = 10) 8 mm MTA apical plug as obturation, followed by removal of 4 mm MTA for post space preparation.

Group C: (n = 10) 4 mm MTA apical plug only, followed by delayed post space preparation.

Positive control: (n = 10) did not receive any filling material after instrumentation.

Negative control: (n = 10) were not instrumented, but were completely sealed with cyanoacrylate glue (Pidilite, India) and fingernail varnish at the apical portion.

Group A: Cold lateral compaction followed by post space preparation

Canals were obturated with Gutta-percha and AH plus sealer (Dentsply Maillefer, Switzerland) using the lateral compaction technique. After completion of the canal obturation, post space was prepared immediately using Peeso reamers (Mani Inc., Japan) sequentially in a contra-angled handpiece running at 4000 rpm until 4 mm root canal filling was left. The remaining root canal filling was then vertically compacted using a cold plugger. A radiograph was taken to confirm the adequacy.

Group B: Mineral trioxide aggregate obturation followed by post space preparation

White ProRoot MTA (Dentsply Maillefer, Switzerland) was mixed as recommended by the manufacturer. The MTA was compacted in increments using no. 3 and no. 4 endodontic finger pluggers (Dentsply Maillefer, Switzerland). An apical plug of 1-2 mm was first placed and checked radiographically to ensure optimal positioning. Further increments were similarly added under light hand pressure and the canals were obturated with 8 mm of MTA in the orthograde manner. Standard radiographs were taken to evaluate the quality of the obturation. Moist cotton pellet was placed over the MTA filling to facilitate setting of the material.

Each specimen was placed into a moistened oasis (Oasis Choice, India) for 24 h. The cotton pellet was then removed, and setting of the material was confirmed with an endodontic probe. Subsequently, 4 mm of MTA was removed, using a high-speed long shank diamond round no. 2 bur (Mani Inc., Japan) and water coolant spray, simulating post space preparation. The bur was placed on the surface of the MTA for 1 s, followed by irrigation with saline and drying with an air syringe. The process was repeated until an apical plug of 4 mm MTA retained in the canals and was confirmed radiographically.

Group C: 4 mm mineral trioxide aggregate apical plug only

All the teeth in this experimental group received an apical plug of 4 mm white ProRoot MTA, similar to the method described for Group C. Delayed post space preparation was done till the MTA apical plug using Peeso reamers.

All specimens were placed in an incubator (Accumax, India) at 37°C for 7 days, for the materials to set. Later the external surfaces of all the specimens, except 2 mm of the apical area were coated with two layers of nail varnish to ensure seal. The teeth in the negative control group were completely coated with nail varnish and cyanoacrylate. All specimens from the four experimental groups and the two control groups were subjected to microleakage analysis using bacterial leakage model.

Bacterial leakage model

The apparatus used to evaluate microbial leakage [Figure 1] was modified from the apparatus previously described by Siqueira et al.[12] and Gomes et al.[13] Enterococcus faecalis MTCC 439 (Institute of Microbial Technology, Chandigarh, India) was used for the bacterial leakage test and the strain was sub-cultured weekly. The apparatus was designed so that there would be a single pathway between the upper chamber (bacterial reservoir) and the lower chamber (brain heart infusion [BHI] broth), which would allow access only through the root canal.

Figure 1

Diagrammatic representation and photograph of the dual-chamber model used to assess bacterial leakage

Polyethylene tubes with rubber stoppers were modified for use. 1 mm diameter circular entry was made through the center of each rubber stopper using a high speed air rotor handpiece into which the tooth was inserted in such a way that only the apical end was in the BHI broth in the polyethylene tube. The tips of 5 ml disposable plastic syringes were cut and modified to adapt to the outer surface of the stoppers so as to create a chamber around the coronal end of the tooth.

The components of the bacterial leakage model were subjected to ethylene oxide sterilization and then assembled under laminar flow hood. Two layers of cyanoacrylate glue were applied to the interface between the tooth and the stopper to avoid direct bacterial penetration into the broth.[14] Each assembly was labeled and incubated at 37°C for 4 days in order to confirm the sterility of the assembly. Once the samples were deemed sterile, the upper chamber of the split-model was filled with 500 μL aliquots of E. faecalis. After every 7 days, this BHI inoculated with E. faecalis was replaced with a new 500 μL aliquots.

The whole apparatus was incubated at 37°C. Over the experimental period of 120 days, the lower chamber was examined daily for the presence of turbidity, which indicated that bacteria had penetrated through the residual filling in the root canals and had reached the broth. When the turbidity of the BHI was observed, bacterial confirmation was carried out by gram staining. The number of leaking samples for each group at different time intervals were observed and noted. The absence of turbidity in the BHI medium indicated no bacterial leakage. Data were subjected to the independent Student's t-test at 5% significance.

RESULTS

Table 1 demonstrates the number of samples in each group that exhibited turbidity and the days at which turbidity was observed. All 10 samples of Group A demonstrated turbidity. Five samples of Group B and 6 samples of Group C did not leak during the study. All the samples in the positive control group leaked within the first 2 days, whereas none leaked in the negative control group.

Table 1

Number and average days at which bacterial leakage occurred

The teeth restored with 8 mm of apical MTA, and later subjected to 4 mm apical MTA removal, exhibited leakage after 77 days (mean — 93.6 days), whereas those restored with an apical 4 mm plug of MTA showed turbidity after 68 days (mean — 95.5 days). Statistically significant differences were observed between the groups, except the two MTA groups (P = 0.87) as shown in Table 2.

Table 2

Statistical comparison among the experimental groups as per independent Student t-test

DISCUSSION

Three-dimensional sealing of the root canal space is one of the main goals of endodontic therapy and is an essential requisite for preventing apical and coronal leakage. The teeth indicated for post and core often result in the disturbance of the apical seal during post space preparation, irrespective of the method chosen for Gutta-percha removal.[5151617181920] Thus, the quest for the ideal root canal filling material for teeth indicated for post and core is still debated.

Mineral trioxide aggregate has not been tested conclusively for use as a root canal filling material in teeth requiring post and core. This study was thus aimed at assessing whether MTA can provide an adequate apical seal in teeth indicated for post and core. The positive control group helped to test the hypothesis that when the leakage occurred from the upper chamber to the lower chamber, it caused turbidity of the medium. Conversely, the negative control group confirmed that the test apparatus was efficient and that the BHI broth in the lower chamber was not in contact with any environmental contamination due to improper seals.

Boutsioukis et al.[21] evaluated the use of ultrasonic tips and rotary GT files for removal of set MTA and concluded that both these techniques are inefficient for removing the set MTA from the root canals. Chemical solvents such as 2% carbonic acid and 10% citric acid have also been proposed for the dissolution of MTA.[2223] However, it is difficult to control the depth of penetration of these liquid chemical agents manually. Therefore, for the controlled removal of MTA in this study, long shank rotary diamond points no. 2 were used. In a study conducted by Jalalzadeh et al.,[11] the removal of MTA was achieved efficiently by using long shank rotary diamond points. However, no research is available in the literature that demonstrates an optimum technique for safe removal of MTA for post and core and, therefore, further research is warranted in this field. The risk of root perforation must be considered when selecting the most appropriate instrument for MTA removal. In this study, a diamond bur was used because the teeth were decoronated and teeth with relatively straight roots had been selected. Alternatively, surgical length small round burs, end cutting burs, LN burs (Dentsply Maillefer, Switzerland) and Mueller burs (Meisinger, USA) could also be proposed for MTA removal.

The use of organic dyes has been one of the oldest and most popular techniques for microleakage assessment.[2425] However, the use of bacteria as tracers most closely approximates clinical conditions in terms of leakage,[2627] because it uses a biological marker.[28] Furthermore, the root canal fillings are very susceptible to leakage when attacked coronally by saliva and micro-organisms.[2930] Therefore, coronal bacterial microleakage was the method chosen in this study.

As per the results of this study, all the samples of the lateral compaction and immediate post space preparation group (Group A) exhibited leakage in a short time, which correlated with the results of other similar studies.[3132] Five samples of Group B (MTA obturation, followed by post space preparation) and six samples of Group C (4 mm MTA apical plug only) did not exhibit leakage. This is also in conjunction with the results of a study by Khademi and Shekarchizadeh,[32] in which only 4 out of 15 samples filled with MTA showed bacterial leakage after 120 days.

The current study exhibited results with minimum differences between Groups B and C (P = 0.87) but, performed better than the Gutta-percha Group A, in terms of the number of samples that did not leak, as well as the mean days at which turbidity was observed. These results are also supportive to previous studies[113233] demonstrating similar superiority of MTA over Gutta-percha in terms of sealing ability and therefore preventing bacterial influx.

CONCLUSION

The methodology adapted in this study could help clinicians address cases of badly mutilated coronal tooth structure, requiring post and core restorations, in teeth, which have been previously obturated with MTA. Hence within the scope of this study, it can be concluded that, MTA exhibits superior sealing ability even after the removal of set MTA for the post space preparation.