EVALUATION OF THE APICAL SEAL AFTER POST SPACE PREPARATION : IN VITRO STUDY

Introduction: Large crown destruction often leads to restoring endodontically treated teeth using post and core. As a result of post space preparation the integrity of the apical seal can be affect, thus increasing the chances of microleakage occurring. Aim: The goal of the study is to observe and evaluate the quality of the apical seal after post space preparation. Materials and Methods: 27 extracted single-rooted teeth were used. The coronal part was removed, and the root length was standardized to 15mm. The canals were prepared with Revo-S rotary system, irrigated with 5ml 5.25% sodium hypochlorite, saline, and 2ml 40% citric acid. The canals were filled with Adseal and gutta-percha using cold lateral condensation technique. The teeth were divided into two groups depending on post space preparation speed and one control group: first group (n=9) 2800 rpm; second group (n=10) 4700 rpm; control group (n=8) – with no preparation. Nail varnish was applied on the external root surface of the teeth except the apical 2mm, afterwards the teeth were insert in 2% methylene blue for 24 hours and then washed under running water for the same time. The teeth were cut longitudinally in a buccal-lingual direction so that the level of dye penetration between the root canal wall and the filling material could be visualized. The measurement was done in mm. Results: The highest average value of apical penetration was observed in the second group (4700 rpm) 1.10 mm. The difference of the apical penetration between group 2 (1.10 mm) and control group (0.25mm) is significant, while the average value of Group 1 (2800 rpm) does not differ statistically from the other two groups. Concusion: Post space preparation combined with the higher speed of the drill can increase the risk of damage the apical seal.


INTRODUCTION
Endodontically treated teeth with high destruction of the crown need to be restored with post and core.The purpose of the post is retention of the core and prevention of bacterial contamination caused by coronal leakage [1][2][3].A common negative side effect during post space preparation is affecting the apical seal which can lead to microleakage.Post space preparation requires the removal of gutta-percha and sealer, or other filling material, from the coronal and middle part of the root canal and can damage the apical seal [6,7].The length of the remaining apical filling material is directly linked to the resistance of microleakage of the apical seal.It is widely accepted that a length of 3 to 5 mm of the remaining filling material is adequate for the apical seal [8,9].It is shown that the optimal apical seal is achieved when at least 6 mm of filling material is retained [9].If the fillings are reduced to 3mm or lower then the quality of the seal depends on the type and qualities of the filling material [8].
The sealing properties of root canal sealers can be directly linked to their physical characteristics.Even in contemporary dentistry, no material fulfills all required properties for a hermetic seal of the root canals [10].However, that does not decrease their role in eliminating the interface between the gutta-percha and the dentin walls of the filled root canal [ Barros 10].One of the main functions of the sealers is to create an environment in which bacteria cannot survive, thus preventing re-infection [2,3].
There are many different methods of removing guttapercha.The thermal method is one of the main methods for gutta-percha removal [11].The chemical solvent method (using solvents as chloroform or xylene) is followed by many problems regarding its toxicity and difficulty in manipulation [6].Another widespread method for post space preparation is mechanical -the usage of Gates Glidden drills, Peeso reamers, ProTaper Retreatment files (D1, D2, D3) however it is harder to control the amount of gutta-percha being removed and cause overheating in the root canal.The root canal filling material may be dislo-https://doi.org/10.5272/jimab.2019251.2327cated creating holes in the obturation or twisted or vibrated affecting the apical seal [12].
The goal of the current study is to assess the state of the apical seal after post space preparation using peeso reamers with different speed.

MATERIALS AND METHODS
Twenty-seven extracted single-rooted teeth were stored in saline at room temperature, and used for the research.The coronal part of the teeth removed with a diamond bur and the roots were measured at 15mm each.All of the canals were prepared with Revo-S Ni-Ti rotary system as far as AS35 in the zone of apical constriction.The final irrigation was done with 5 ml 5.25% sodium hypochlorite, saline, and 2ml 40% citric acid.The root canal filling was done with epoxy resin-based sealer (Adseal) and gutta-percha using cold lateral condensation technique.The teeth were divided into 3 groups: Group 1 (n=9) -the post space preparation was performed at 2800 rpm with Peeso reamer; Group 2 (n=10) -post space preparation was performed at 4700 rpm with Peeso reamer; Group 3 (n=8) -Control group.The root canals were prepared and filled (without post preparation).
After processing, the teeth have been covered with two layers of waterresistant nail varnish.Only the apical 2 mm of the root surfaces were left uncovered.The coronal parts of the samples were sealed with light curing resin composite.
The teeth were placed in 2% methylene blue solution for 24 hours and then washed under running water for the same time.After that, they were left to dry for dye fixation.The teeth were cut longitudinally in a buccal-lingual direction so that the level of dye penetration between the root canal wall and the filling material could be visualized.The measurement was done in mm.
The data was entered and processed with the statistical package IBM SPSS Statistics 23.0.The significance level for rejecting the null hypothesis was p<0.05.We applied the following statistical methods: Variation analysis, Graphical analysis, One Sample nonparametric test of Shapiro-Wilk, ANOVA, Tamhane's T2 Post Hoc test.

RESULTS
In the current study, apical microleakage was seen in all experimental groups but at different levels.The results in table 1 show that: • The apical microleakage has the highest average value in Group 2 (4700 rpm); • The difference between the value in Group 2 and the Control Group is significant, while the average value of the apical microleakage in Group 1 (2800 rpm) does not statistically differ from that in the other two groups (fig.1-2).* -the same letters mean lack of significant difference between the mean values and the different -significant difference (p<0,05)  The results in Figure 1 show that the apical penetration has the highest average value in Group 2 (4700 rpm) -1.10 mm.The difference in the apical penetration levels between Group 2 (1.10 mm) and Group 3 (0.25mm) is significant, while the average value of Group 1 (2800 rpm) does not differ statistically from the other two groups.

Fig. 2. Apical microleakage was seen in all experimental groups
sation technique is widely used and considered to be very effective [21], the vertical condensation technique using warm gutta-percha was created to offer a more dense and stable filling [22] and the single cone technique provides void-free obturation along with a minimal sealer thickness and is all used in the present [23].There are various studies that compare the efficiency of these obturation techniques [24,25].
In the current study, we used Adseal, which is an epoxy-based resin.The studies have shown that epoxybased resin sealer is more reliable when it comes to preventing apical microleakage and reinfection, due to its long setting time, good flow and penetration into the dentinal tubules during the obturation, it forms a good mechanical adhesion to the dentin, though it can not bind to the guttapercha.The epoxy-based materials show some expansion after setting -up to 1.2% during the 4-week period, and these dimensional changes could be the possible reason for minimal apical leakage [26].Other authors use different filling materials such as Resilon-Epiphany, due to the better adhesion to the dentine and resistance to the rotational forces [27].Thermafil, which demonstrates a better hermetic seal and has a limited use due to manipulation difficulties [28].Mittal [29] et al. find that for Resilon-AH plus, the apical microleakage is minimal due to the better adhesion of AH plus to the root canal walls.
The quality of the root canal filling is important for the integrity of the apical seal during post space preparation Maintaining the apical seal is crucial for a successful endodontic treatment, and it should not be broken during the post space preparation.The optimal amount of gutta-percha that should remain apically is 5mm.Maintaining a length of 5 mm is important for prevention of reinfection and microbial leakage.Though there have been studies carried out to determine the impact on the apical seal and the possibility of reinfection depending on the amount of residual root canal filling material apically [9,30]we have decided to leave at least 5 mm of filling material, a length that is considered optimal.
During post space preparation the integrity of the apical seal can be disrupted which creates a pathway for bacterial invasion and reinfection of the root canal system.In our study, the apical microleakage has the highest average value in Group 2 (4700 rpm).

CONCLUSION:
The post space preparation itself, as well as the higher speed of drill, increase the risk of damaging the apical seal.

DISCUSSION
In the limitation of this study, the post space preparation was performed using Peeso reamers at a different speed, for Group 1 -2800rpm and for Group 2 -4700 rpm leaving 5mm of material apically.Some studies reported that the mechanical removal of gutta-percha with a Peeso drill was the most desirable method of post space preparation compared with chemical solvent or heated instrument [2,7,12].Post space preparation with Peeso reamers is more efficient but has the highest potential for creating ledge, lateral root perforation, canal transportation, over enlargement of the canal, which results in weakened remaining root structure.
The negative sides of using Peeso reamers are the increase of temperature in the root canal, which may lead to damage of the organic tissue.Increasing the temperature by 10ºC might cause damage to the alveolar bone and periodontal ligament [13][14][15].Another possible complication is breaking of the apical seal during post space preparation and creating voids in the seal [12].
Dye penetration technique was used in this study to evaluate the degree of apical microleakage.The samples were immersed in 2% methylene blue for 24 hours.This is a commonly used method in many studies [6,7,16].Longitudinal sectioning of the samples is widely used to asses dye leakage [17].The advantage of this method is the ability to measure the leakage from a single section.We chose to use this method in the current study due to its reliability and easy to assess results.There are other dye methods that include 0.5% eozine, 1% black India ink, 0,5% rhodamine B, 0,5% fuchsin and others [17].
There are still contradictions about whether the post space preparation should be done immediately after root canal obturation or after 3-7 days.There are many studies that compare the positive and negative sides of immediate and delayed post space preparation and its effect on the stability of the apical seal [6,[18][19][20].
Nagas et al. [19] evaluated the effects of immediate and delayed post space preparation on apical leakage using different filling material and obturation technique.They establish that significantly better sealing was achieved at the apical end using delayed post space preparation (24 hours, 7 days) than with immediate.
Aidemir et al. [18] investigated the effect of immediate and delayed post space preparation on the integrity of the apical seal, and their results suggested that there was no significant difference between both methods.In the present study, we chose to conduct post space preparation 7 days after obturation.
The types of obturation techniques can influence over hermetical seal of the root canal The lateral conden-

Table 1 .
Comparative analysis of the apical microleakage (mm) in the investigated groups