|Year : 2013 | Volume
| Issue : 3 | Page : 125-131
Transportation of apical root canal after removal of calcium hydroxide when used as an intracanal medicament: An in vitro evaluation
Nurul-Ameen Inamdar1, Salma H Mulla2
1 Department of Conservative Dentistry & Endodontics, Al-Ameen Dental College and Hospital, Bijapur, Karnataka, India
2 Department of Public Health Dentistry, Al-Ameen Dental College and Hospital, Bijapur, Karnataka, India
|Date of Web Publication||20-Nov-2013|
Department of Conservative Dentistry and Endodontics, Al Ameen Dental College and Hospital, Bijapur, Karnataka
Source of Support: None, Conflict of Interest: None
Aim: To evaluate the incidence of apical root canal transportation after the removal of calcium hydroxide in straight and curved canals. Materials and Methods: Twenty maxillary central incisors (Group A) and twenty mandibular molars (Group B, mesiobuccal canal) were instrumented to the working length using #15 to #45 K-file and # 15 to #30 K-file, respectively. Post instrumentation digital images were taken with the corresponding final file inserted into the canal to the working length. The root canals were then filled with Calcium hydroxide paste using Lentulo spirals and the teeth incubated at 37°C for seven days. The calcium hydroxide paste was then removed up to the working length using a #45 file for group A and a pre curved #30 file for group B. Final digital images were taken with the file inserted into the canal to the working length. Post instrumentation and final digital images were superimposed to evaluate the incidence of transportation. Result: In Group A, no transportation was detected, whereas in Group B, 8 out of 20 canals showed apical transportation. Statistically significant differences were observed between Groups A and B ( P <0.05). Conclusion: Care should be taken when removing the calcium hydroxide paste from curved root canals to avoid transportation.
Keywords: Apical transportation, calcium hydroxide, image analysis software
|How to cite this article:|
Inamdar NA, Mulla SH. Transportation of apical root canal after removal of calcium hydroxide when used as an intracanal medicament: An in vitro evaluation. Saudi Endod J 2013;3:125-31
|How to cite this URL:|
Inamdar NA, Mulla SH. Transportation of apical root canal after removal of calcium hydroxide when used as an intracanal medicament: An in vitro evaluation. Saudi Endod J [serial online] 2013 [cited 2020 Jan 26];3:125-31. Available from: http://www.saudiendodj.com/text.asp?2013/3/3/125/121505
| Introduction|| |
Clinical Endodontics encompasses a number of treatments, but perhaps the most important is treating pulp and root canal system (with or without periradicular pathosis of pulpal origin) so that patients can retain their natural teeth in function and esthetics. Endodontic therapy, essentially is directed towards one specific set of aims to cure or prevent periradicular periodontitis.  The persistence of necrotic tissue and microorganisms in the root canal are considered major etiologic factor for endodontic failure. , It has been established beyond doubt that bacteria play a decisive role in the development of apical periodontitis and elimination of these is accomplished by mechanical instrumentation supported by various irrigating solutions and antibacterial dressing of the canal between appointments. Root canal cleaning and shaping plays a crucial role in the success of endodontic treatment. 
Unfortunately, canal preparation is adversely influenced by the highly variable root canal anatomy and the relative inability of the operator to visualize this anatomy from the radiographs. 
The three main issues presently considered most challenging and controversial in root canal shaping are:
- Identification, accessing and enlargement of the main canals without procedural errors
- Establishing and maintaining adequate working lengths throughout the shaping procedures
- Selection of preparation sizes and overall geometries that allow adequate disinfection and subsequent obturation.
Intracanal medication, because of their antimicrobial properties, minimizes re-infection or re-growth of bacteria in the canal. , Calcium hydroxide (Ca(OH) 2 ) has been shown to be an effective intracanal medicament during endodontic therapy. First introduced to dentistry by Hermann in Germany in 1920, it has been used for a number of procedures, such as direct and indirect pulp capping, apexogenesis, apexification, treatment of; root resorption, iatrogenic root perforations, root fractures, replanted teeth and interappointment intracanal dressing. ,, It is classified as a strong base and its main action comes from the ionic dissociation of Ca 2+ and OH - ions when contact an aqueous fluids. The hydroxyl ions are believed to be responsible for the highly alkaline nature of calcium hydroxide, which is bactericidal.  They are highly oxidant, free radicals that show extreme reactivity, reacting with several biomolecules and rarely diffuse away from the site of generation. 
Ideally, Ca(OH) 2 should be placed deep and densely in the root canal space so that its biological effect can be exerted in close proximity to the appropriate tissues. The use of dry Ca(OH) 2 powder alone is technically difficult in small and curved canals. Therefore, it is better to mix it with a vehicle such as distilled water, saline, dental anesthetics and Ringer's solution, to facilitate placement. 
The use of viscous vehicles such as Glycerin, polyethylene glycol and propylene glycol will promote the lower solubility of the paste when compared with aqueous vehicles, probably because of their higher molecular weights. In the other hand, oily vehicles such as olive oil, silicone oil, camphor, and metacresyl acetate will promote the lowest solubility and diffusion of the paste within the tissues. , The dissociation of Ca(OH) 2 into OH - and Ca 2+ depends on the vehicle used to prepare the paste. 
Transportation refers to the excessive dentin removal in a single direction within the canal rather than in all directions equidistantly from the main tooth axis. Transportation of the canals may leave some areas un-instrumented, whereas other areas are excessively enlarged, removing valuable dentin instead of the contents of the canal. 
Calcium hydroxide removal before final obturation is routinely accomplished by irrigation with Sodium hypochlorite or Normal saline and/or instrumentation with a small endodontic instrument. 
Furthermore, it is possible that residual paste at the apical portion of the root canal could affect the apical patency during further instrumentation and obturation. ,,,
Thus, the aim of this study is to assess the incidence of apical transportation of straight and curved root canals during the removal of calcium hydroxide when used as an intracanal medicament.
| Materials and Methods|| |
Forty freshly extracted human teeth, 20 maxillary central incisor and 20 mandibular molar teeth with completely formed roots were used for the study. The collected teeth were cleaned of all blood stains, soft tissue tags and calculus by scaling and the teeth stored in 10% formalin solution until used. The selection of the teeth was based on visual examination under bright light, the use of sharp explorer and after access preparation, negotiating the root canal. Fractured root, calcified canals, pulp stones and caries teeth were excluded. The specimens were separated into 2 groups of 20 each:
- Group A - 20 Maxillary central incisors
- Group B - 20 Mandibular molars with moderate mesial root curvature (Degree of curvature 10 to 30° by Schneider method).  The mesiobuccal canal was used for this study.
In both groups, standard endodontic access was performed using round bur (Dentsply, Maillefer, ballaigues, Switzerland) in high speed air Turbine handpiece (NSK Japan). The coronal and middle thirds of the root canals were flared using #1, #2 and #3 Gates Glidden drills (Dentsply, Maillefer, ballaigues, Switzerland) in a slow speed Micro Motor handpiece (SDE-H37s - Marathon, Korea) for group A, and #1 and #2 Gates Glidden drills for group B.
The canal length was visually established by placing a No. 10 file (Mani, INC, Japan) in each root canal until it is seen emerging through apical foramen. The working length was determined by subtracting 1 mm from the total length. The root canals were then instrumented to the working length up to K-file No. 45 (Mani, INC, Japan) in group A and to a precurved K-file No. 30 in group B using step back technique and the use of R C Prep chelating agent (MicroDose, Germany), 3 ml of 2.5% sodium hypochlorite (NaOCl) solution was used for irrigation between each instrument and at the completion of instrumentation. The canals were then dried with paper points (Dentsply, Maillefer, ballaigues, Switzerland).
The teeth were then mounted in square pieces of silicone with special marks to ensure repositioning of the specimens supported on a fixed platform to allow successive digital radiovisiography (RVG) digital images to be taken with reproducible angulations. For the purpose of standardization during imaging procedure, an apparatus was designed similar to the positioning and angle device used by Forsberg  [Figure 1]. This system consisted of a platform, sensor holder and a central carrier stand made up of wax block. The distance between the cone and the specimen and between the specimen and the sensor (Sopix, Dental Focus, NJ) was kept constant throughout the study. Post instrumentation RVG digital images were taken in a buccolingual direction with the corresponding file inserted into the canal to the working length and exposure time (0.12 s; 70 kV, 7mA) kept same for all radiographs [Figure 2]. This was done to confirm that there was no apical transportation in the beginning of the canal preparation before placing calcium hydroxide.
Each root canal was filled with Ca(OH) 2 paste (1 gm of calcium hydroxide powder mixed with 1 ml of Normal Saline). Lentulo spirals (Dentsply, Maillefer, ballaigues, Switzerland), #3 for group A and #1 for group B in a slow speed handpiece run at moderate speed were used to place the paste in the root canal until the dressing is detected through the apex. The Ca(OH) 2 paste was then condensed using hand plugger and quality of filling checked with radiograph.
The access cavities were temporarily sealed with a dry cotton pellet and Cavit G (3M, ESPE Germany). The specimens were stored in an incubator at 37°C in 100% humidity for seven days. Then the temporary seal was removed and the Ca(OH) 2 paste cleaned from the canals up to the working length by using K-files #20 to #45 for Group A and precurved K-files #15 to #30 for Group B to the working length with subsequent irrigation with NaOCl solution. Calcium hydroxide was considered to be totally removed when no paste was recovered from the root canal either from the orifice or from the apical foramen that confirmed with a radiograph.
Twenty milliliters of 2.5% NaOCl solution was used for irrigation performed using a disposable plastic syringe with 27 gauge needle tip inserted till middle to apical third of the root canal. The canals were dried with paper points and each tooth was repositioned on its square piece of silicone.
A final RVG digital image with the corresponding file inserted into the root canal to the working length was taken under the same condition as the post instrumentation radiograph images.
The post instrumentation and the final radiograph were analyzed using the computerized image analysis software (Magnus Pro. 3.0, Olympus and Adobe Photoshop 6.0,) [Figure 3]. The images were analyzed for divergence of the files in the apical 2 mm.
| Specimen Evaluation|| |
The Magnus Pro software works by measuring the linear distance between two points. This can be done by selecting a point, left clicking on the mouse and dragging it to the second reference point. On completion of the selection, the software automatically calculates the length of the selected points and projects it on the screen. Hence, in our study we calculated the distance from the tip of the file to the outer curvature (mesial) of the root in microns. In cases where the outer border of the root was not very clear, a pseudo color imaging option was used which imparted different colors to the root based on the density. Thus, the outer border of the root became more distinct eliminating the variations associated with operator variable.
After this, the digital images were transferred to Adobe photoshop 6.0 software. To detect the root canal wall differences between both images, the final image was superimposed over the post instrumentation image until their external contours coincided. The overlapping of the files was checked in the apical 2 mm. The preparation was considered acceptable (no transportation) when there was a contact between the superimposed files in the apical 2 mm. The preparation was considered unacceptable (transportation) when there was a divergence between the superimposed files in the apical 2 mm [Figure 4] and [Figure 5].
|Figure 4: Superimposition of images in adobe photoshop software (no transportation)|
Click here to view
|Figure 5: Superimposition of image in adobe photoshop software (transportation seen)|
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The data obtained in microns and that obtained after superimposition was statistically analyzed using Fishers Exact test and Mann Whitney test.
| Results|| |
The results of Superimposition of post instrumentation and final radiograph using the Adobe Photoshop 6 software was summarized in [Table 1] and [Table 2] and [Figure 6].
|Figure 6: Comparison of apical transportation between maxillary central incisors and mandibular molars|
Click here to view
In all straight root canals (group A), the comparison between post-instrumentation and final radiographs showed an acceptable preparations without any sign of transportation. On the contrary, in curved root canals (group B), 8 of 20 canals showed unacceptable preparations.
Transportation cross tabulation with Fishers Exact Test showed 100% of group A samples with no transportation whereas 40% of group B showing transportation.
The Fishers exact test determined P = 0.003 (<0.0005). This value is statistically significant. Thus, there is significant statistical association between Groups and Apical Transportation (P = 0.003).
The values in micrometer measured by Magnus Pro Software for Group A and Group B were evaluated with Mann Whitney test. The calculation of difference between post instrumentation and final images showed mean transportation of 6.35 microns with a standard deviation of 5.071 in Group A whereas Group B showed mean transportation of 61.25 microns and a standard deviation of 73.733, confirming that there is significant difference in the transportation of the canals between Group A and Group B (P < 0.005).
| Discussion|| |
The control of microorganisms in infected root canals with apical periodontitis is a frequent concern and if it is necessary to perform an endodontic treatment in several sessions, an intra canal medicament has to be used. It is proposed that both growth and multiplication of micro-organism, persisting inspite of careful shaping and irrigation of the root canal system should be suppressed. Therefore, the selected intra canal medicament should be an excellent antimicrobial agent that is capable of controlling the infection of the root canal system. 
Calcium hydroxide is the most frequently used endodontic material and pulp capping agent.  It is also a short- or long-term intracanal dressing material and may be included in some root canal sealer as well. , Although a number of other root canal medicaments have been advocated, Ca(OH) 2 remains the material of choice because of its superior activity and reduced cytotoxicity to the periradicular tissues. 
The routine application of Ca(OH) 2 products in dentistry has resulted in considerable degrees of success in the treatment of various pathological conditions of the tooth. These include: Assisting in the production of reparative dentin to bridge a pulp exposure, induction of apical closure in incompletely developed pulpless teeth, healing of large periradicular lesions, to prevent or arrest root resorption and to repair perforation resulting from internal root resorption. 
Calcium hydroxide is a white odorless powder with a molecular weight of 74.08. It has low solubility in water (about 1.2 gm/l at 25°C), which decreases as the temperature rises; it has a high pH (12.5 to 12.8) and is insoluble in alcohol. The low solubility is a good clinical characteristic as a long period is necessary before it becomes soluble in tissue fluids when in direct contact with vital tissues. Calcium ions play an important role in the initiation of the remineralization process and although hydroxyl ions play an important role in these effects, it is difficult to accept that, by producing an alkaline pH, they are the sole initiator of the healing process. 
Maxillary central incisors, owing to their large and near straight canal morphology pose less difficulty during instrumentation and irrigation and thus showed no incidence of transportation in the study. Whereas the instrumentation of the narrow and curved mesiobuccal canal of the mandibular molars constitutes a challenge for the clinician because of the need to keep the instrumentation centered within the original anatomy of the canal.
In the current study, 8 out of 20 mandibular teeth showed apical transportation with an incidence rate of 40% and none of the maxillary central incisors showed transportation. (P <0.005).
The cervical flaring of the root canal in this study was done with Gates Glidden drill before estimation of working length. The use of these drills for widening the cervical third and the more coronal portion of the middle third might reduce the incidence of excessive thinning of the root canal walls, thus minimizing the negative influence of canal shape on the outcomes of endodontic instrumentation by obtaining a straight line access. 
Lentulo spiral was used in the present study to place Ca(OH) 2 in the canal. Care was taken not to engage the instrument in the canal to avoid instrument fracture. Sigurdsson et al.,  compared Lentulo spiral, a paste injection system and a #25 size K-file used in counterclockwise direction to place Ca(OH) 2. They demonstrated that Lentulo spiral is the most effective technique of carrying Ca(OH) 2 paste to working length. The curvature of the root did not have an influence on the Lentulo's performance. The injection technique carried the Ca(OH) 2 paste to the working length in only half of the teeth whereas the counterclockwise rotation of #25 K file was the least effective in getting the paste to the working length. This technique also provided the poorest quality fill.
Difficulty in removing Ca(OH) 2 dressing from the root canal was reported by Lambriandis et al.,  Porkaew et al.,  and Calt and Serper. In the present study also it was seen that transportation occurred in curved canals after the removal of Ca(OH) 2 . This might be due to incomplete removal of Ca(OH) 2 leading to blockage in apical area, decrease in flexural strength of dentin due to high pH of Ca(OH)2 , or due to improper instrumentation leading to straightening of canal.
Calcium hydroxide is usually removed from the root canal by the use of copious irrigation with either NaOCl or saline, combined with instrumentation and a final rinse with 17% ethylene diamine tetraacetic acid (EDTA). However none of the above technique is efficient in removing all the substance from the canal wall, leaving up to 45% of the root canal surface covered with remnants. 
The remnants of Ca(OH) 2 can obstruct the penetration of sealers into the dentinal tubules, hinder the bonding of resin sealer adhesion to the dentin, and markedly increases the apical leakage of root canal treated teeth.  Thus, the complete removal of Ca(OH) 2 from the root canal before obturation becomes mandatory.
Margelos et al., showed that an interaction occurs between Ca(OH) 2 and eugenol based sealer, with the Ca(OH) 2 preferentially engaging the eugenol and preventing a standard zinc oxide eugenol (ZOE) setting reaction, resulting in set ZOE cement that was brittle in consistency and granular in nature. 
Transportation of the root canal is a frequent mishap during the instrumentation of curved root canals. As endodontic instruments are manufactured from straight metal blanks, it results in uneven force distribution in certain contact areas and there is a tendency for the instrument to straighten itself inside the root canals. This excessive dentin removal in a single direction within the apical canal areas causes canal transportation, whereas coronal areas are transported toward the concavity or the furcation in multi-rooted teeth resulting in zipping and elbow formation. ,
During canal instrumentation, dentinal and pulpal debris can block access to the apical third, increasing the possibility of ledge formation, transportation, or perforation. Also, during the removal of Ca(OH) 2 , residual paste could block the apical area of the root canal, affecting the apical patency during endodontic treatment. Buchanan  emphasized the importance of maintaining apical patency during endodontic treatment. He also insisted that the patency file must passively move through the apical constriction without widening it. On the contrary, when there is an apical blockage, the file will go in a straight direction transporting the canal anatomy.
Likewise, White et al., reported a 32% decrease in dentin strength after the use of Ca(OH) 2 and proposed this was caused by breakdown of the protein structure as a result of alkalinity of calcium hydroxide.  Also Anderson et al., theorized that the proteolytic action of Ca(OH) 2 could weaken a tooth by upto 50%. This situation could favor apical transportation when Ca(OH) 2 is used for a long period of time. 
Some authors suggest the enlargement of the canal to next file size to remove Ca(OH) 2 paste.  This procedure could be applicable in straight and large canals but would increase the possibility of transportation in curved canals.
To measure transportation in this study we have superimposed digital images on each other and used Magnus Pro software. Direct digital imaging and measurement of the post instrumentation and final digital image of the canals eliminates any variable that photography or human interpretation would impose.  Although Ca(OH) 2 is widely recommended as an intracanal medicament, the findings of this study showed an important effect to consider when Ca(OH) 2 is selected as a root canal dressing in curved canals. Future research should focus on this aspect to confirm as well as reduce the negative effects and optimize the benefits of calcium hydroxide in endodontic treatment.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2]