|Year : 2012 | Volume
| Issue : 3 | Page : 163-167
Influence of a base on coronal microleakage of post-prepared teeth: A scanning Electron Microscopic - In vitro study
K Sudha, T Murali Mohan, Y Malleswar, DL Malini
Department of Conservative Dentistry and Endodontics, Government Dental College and Hospital, Vijayawada, Andhra Pradesh, India
|Date of Web Publication||15-Oct-2012|
Department of Conservative Dentistry and Endodontics, Govt. Dental College and Hospital, Vijayawada, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
Objective: The aim of the present study was to evaluate the influence of a base on coronal microleakage of post-prepared teeth. The objectives are to compare the degree of coronal microleakage of apical fill of post-prepared teeth with and without the use of zinc oxide eugenol (ZOE) cement base, using scanning electron microscope.
Materials and Methods: Sixty maxillary teeth were divided into three groups, post-space was prepared, and coronal micro-leakage checked by using methylene blue dye in three groups: (1) with ZOE, (2) without ZOE, (3) sticky wax.
Results: The leakage of methylene blue dye observed was minimum in Group A (both linear and lateral), moderate to severe in Group B, and least in Group C.
Conclusion: The leakage of methylene blue dye was minimum with 2 mm of ZOE base. Hence, it is always advisable to have some sealing between the post- and gutta-percha.
Keywords: Microleakage, sticky wax, zinc oxide eugenol
|How to cite this article:|
Sudha K, Mohan T M, Malleswar Y, Malini D L. Influence of a base on coronal microleakage of post-prepared teeth: A scanning Electron Microscopic - In vitro study. J NTR Univ Health Sci 2012;1:163-7
|How to cite this URL:|
Sudha K, Mohan T M, Malleswar Y, Malini D L. Influence of a base on coronal microleakage of post-prepared teeth: A scanning Electron Microscopic - In vitro study. J NTR Univ Health Sci [serial online] 2012 [cited 2019 Nov 19];1:163-7. Available from: http://www.jdrntruhs.org/text.asp?2012/1/3/163/102442
| Introduction|| |
Success of endodontic treatment depends on the proper cleaning and shaping of the root canal and removal of bacteria, which results in the reduction or elimination of microorganisms. Finally a properly placed coronal restoration should complete the task. Complete coronal restoration of endodontically treated teeth is indicated when structural or esthetic requirements cannot be met by remaining tooth structure (i.e. loss of excessive tooth structure or badly broken teeth). Where clinical crown is lost due to caries or traumatic injury, intra-radicular pins or posts are frequently used to provide mechanical support and attachment for a complete crown. After obturation of the root canal until cementation of the post, there exists numerous opportunities in which the root canal may become contaminated. The preliminary step in post-preparation is the removal of a portion of the gutta-percha from the root canal and retaining the remaining filling inside without disturbance. According to Imura et al.  microleakage in the canal is considered to be a major factor influencing the longevity of the endodontic treatment. It may lead to passage of bacteria from the root canal into the periapical area and the development of pulpal pathology. Coronal leakage of the root canal filling is now considered as an important cause of failure in root canal therapy.  The coronal seal plays a significant role in successful root canal therapy and protects the root canal from contamination. The loss or absence of coronal seal has been considered as one of the common frequent causes of root canal treatment failure. Coronal microleakage due to the breakdown of temporary restorations placed to seal occlusal preparation is considered a clinically significant etiology of root canal failure. In the present study, zinc oxide eugenol (ZOE) is used as a base in post-prepared teeth, which is placed coronal to gutta-percha to prevent the coronal microleakage.
| Materials and Methods|| |
Sixty maxillary incisors, physiologic saline solution, 2.5% sodium hypochlorite, absorbent paper points, gutta-percha points, surgical spirit, intraoral periapical radiographs, zinc oxide powder, eugenol, sticky wax, varnish, and methylene blue dye were used.
The teeth were then cleaned off debris with a hand scaler and stored in physiologic saline to prevent dehydration until further use. The coronal two-thirds of the clinical crown of each specimen were removed to facilitate instrumentation of the canal. The root canal opening was done and pulpal tissue was removed with barbed broach. The coronal one-third of each canal was instrumented with pressure-less rotary instruments #4 through #2 Gates Glidden burs. The root canal was then instrumented to working length determined at 0.5 mm from the apical foramen. Cleaning and shaping of each root canal was done. Periodic recapitulation and irrigation of the canals with 2.5% sodium hypochlorite solution was repeated between file sizes. All the specimens were randomly divided into three groups namely Group A, Group B, and Group C. The teeth were dried with absorbent paper points. A master gutta-percha cone was fitted to tug back at the working length and a radiograph was taken to check the apical seal. ZOE sealer was mixed according to the manufacturer's direction. Uniform application of sealer to the root canal walls is obtained with the lentulospiral. Obturation was done with gutta-percha points and ZOE sealer using lateral condensation technique. Radiographs were taken to check the lateral and apical seal. In all the specimens the sealer was allowed to set for 48 h. Post-space preparation was done in Groups A, B, and C by removing gutta-percha with peeso reamers.
In Group A, post-space was prepared with peeso reamers leaving 4 mm of apical gutta-percha remaining. The zinc oxide powder and liquid were mixed according to the manufacturer's direction. The plugger that would reach the coronal surface of the remaining gutta-percha was selected and premeasured with silicone stop to allow a 2-3 mm space to the apical gutta-percha. 2 mm of ZOE mix was tacked on to the condensing end of the premeasured plugger. The ZOE was inserted coronal to the gutta-percha and was twisted a half turn and removed depositing the ZOE cement. The next large size plugger was used to vertically condense the ZOE cement against the gutta-percha. Any excess ZOE was removed with a pre-measured K-file.
In Group B, the post-space was prepared leaving 6 mm of gutta-percha remaining and the post-space was left without zinc oxide base.
In Group C (negative control), the post-space was prepared leaving 4 mm of apical gutta-percha remaining and 2 mm of sticky wax was filled in the coronal space.
Except for the access cavity, the external surface of each tooth in Groups A, B, and C were coated with two layers of nail varnish and two layers of sticky wax. All the specimens were submerged in methylene blue dye for 1 week. The excess dye was removed with running tap water. Post-operative radiographs were taken to check the lateral and apical seal. All the specimens were sectioned half longitudinally with diamond disks at low speed. The specimens were subjected to scanning electron microscopic examination under a magnification of 50×.
| Results|| |
Group A with ZOE cement as a base shows the mean and standard deviation of 0.4750 ± 0.5085, respectively [Figure 1]. In this group, the deepest dye penetration was 1.5 mm. None of the roots had shown the dye penetration of the entire canal and the 12 roots had shown the low penetration.
Group B laterally condensed gutta-percha without ZOE cement had a mean penetration and SD of 3.1250 ± 1.0745, respectively. In this group, the dye penetration measured from 0.5 to 5 mm, the roots had some penetration, and six roots had total penetration [Figure 2].
The apical fillings of all of the negative controls (Group C) exhibited no dye penetration [Figure 3]. The mean and the SD were 0.300+0.4216, respectively [Figure 4].
| Discussion|| |
Endodontic treatment removes the vital contents of the canal which subsequently leads to the reduction in elasticity, desiccation, and increases brittleness of remaining tooth structure. The objective will be returning them to full occlusal and cosmetic function. It is the manipulation of the pulp chamber that leads to the greatest weakness of a treated tooth. When the roof of the chamber is removed for endodontic access, the inherent resistance of the treated tooth is greatly reduced. This weakening leads to the need for strong internal as well as external support which is achieved by post-core systems. Restoration of endodontically treated teeth often requires the placement of an intracanal post. After obturation of the root canal and until the cementation of the post, there exist numerous opportunities in which the root canal may become contaminated. This may be pronounced when only a small volume of obturating material remains in the canal such as after post-space preparation,  Taintor and Ross  conducted a survey of endodontists and found that the majority preferred lateral condensation of gutta-percha as a method of obturation. Advantages are predictability, relative ease of use, conservative preparation, and controlled placement of materials. Madison and Zakariasen  stated that rotary instruments specifically peeso reamers are popular. They are relatively easy to manipulate, time efficient, and result in canal enlargement. As per Hiltner et al.  no statistically significant difference was found in linear dye leakage when gutta-percha was removed by flame-heated endodontic pluggers and peeso reamers with 4 mm of apical gutta-percha remaining. In the present study, also the post-space is prepared by peeso reamer leaving a minimum of 4 mm of gutta-percha. Camp and Todd  studied the effect of immediate and delayed post-space preparation on the apical seal. They had concluded that no significant difference in the amount of leakage (linear or volumetric) was found among gutta-percha removal techniques regardless of the time of removal (immediate or delayed).
Gish et al. studied and stated that coronal leakage of bacteria from saliva into the root canal filling material is also a potential cause of failure. This problem may be more pronounced when only a small volume of obturating material remains in the canal such as after the post-space preparation. Hence, in the present study, ZOE is used as a base to prevent coronal microleakage . Imura et al. stated that invasion of microorganisms into root canal space during endodontic therapy reduces the rate of success of endodontic treatment. Therefore, sealing ability of temporary filling material is important for the success of root canal treatment. Dickey et al. stated that ZOE does not stain tooth and is extremely lubricating. ZOE sets because of combination of chemical and physical reactions yielding a hardened mass of zinc oxide embedded in a matrix of long, sheath-like crystals of zinc eugenolate. Hardening of mixture is due to zinc eugenolate formation, which is a prostaglandin inhibitor. Cox et al.  studied bacterial and isotope microleakage of dental restorations comparing the sealability of various permanent and temporary restorative materials. ZOE exhibited a better seal.
In the present study, the ZOE base was placed coronal to gutta-percha of post-prepared teeth. If retreatment of the apical fill of greater post-depth is required, the removal of 2 mm of the ZOE can be easily accomplished with the use of any gutta-percha solvent and files.
The present study used the methylene blue dye to assess coronal microleakage. A great penetration of dye was recorded after longitudinal splitting and clearing of the specimens. The pH of methylene blue used in this study was buffered to 7. This was done in order to avoid dissolution of the inorganic portion of the tooth as reported by Antoniazzi et al.  The advantages of dye penetration studies are that they are non-destructive and can demonstrate leakage without the need for a chemical reaction or exposure to hazardous radiation.  Several methods for accessing leakage of root canal filling were compared and the results showed that methylene blue dye penetrated further into the canal than isotope tracers, thus giving a better representation of coronal or apical leakage. For this reason, methylene blue dye penetration was used in this study to evaluate coronal leakage of root canals after post-space preparation. The dye penetration was observed under scanning electron microscope (SEM). SEM allows the observation of dye penetration at micron level and the marginal adaptability of ZOE base to the tooth can be evaluated at the same time. The results of the present study suggest that contamination of the root canal of post-prepared teeth can be effectively prevented during a testing period of 1 week with ZOE placed coronal to apical gutta-percha. In Group A, microscopic evaluation of the apical fill revealed that the coronal surfaces of ZOE always appeared to be uneven, with imprints of the pluggers and thin slithers of ZOE on the canal walls. Penetration of the dye in this group was frequently seen at the level of these thin slithers. The results of the finding in Group A are in agreement with other studies in which ZOE allows none to minimal leakage. Pashley et al.  compared t he sealing property of temporary filling materials and stated the importance of materials and the powder to liquid ratio in achieving good seal between the filling materials (ZOE, cavit, polycarboxylate cement) and the cavity walls.
The findings in Group B are in agreement with those of Madison and Zakariasen where the coronal linear dye measurements of the methylene blue dye penetration averaged over 3 mm during a 2-week period of immediate post-prepared teeth. In Group B, the penetration of the dye was often seen on the sealer gutta-percha surfaces, extending laterally into the dentin.
The results of this study clearly indicates that the placement of a 2-mm thickness of ZOE cement coronal to the gutta-percha after the preparation of the post-space can significantly reduce the amount of coronal microleakage as compared with the gutta-percha without ZOE base. It may be subjected that after obturation and compaction of the root canal, the canal orifice should be sealed with 2 mm thickness of the ZOE cement to prevent coronal leakage.
| Conclusion|| |
By this study, it was observed that there is minimal microleakage in post-prepared teeth with ZOE base. Hence, it is always advisable to have some sealing between the post and gutta-percha.
| References|| |
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]