it provides an impervious seal , fills the irregularities and minor discrepancies between the root canal wall and core filling material , and assists in microbial control if microorganisms were left on the root canal walls or in the tubules.[15 ] ideally , a thin layer of the sealer should be evenly applied to canal walls prior to the placement of the core filling material . the thickness of the endodontic sealer layer is very influential in the quality of the root canal filling.[612 ] an inadequate sealer coating may result in voids and permit bacterial microleakage which leads to endodontic failure . on the other hand , excess placement of the sealer can result in its extrusion beyond the apical foramen which can prevent or delay healing . moreover , most sealers dissolve over time and the dissolution is probably responsible for the increase in leakage along the root fillings over time.[1720 ] therefore , the amount of sealer should be kept to a minimum and should only be found in a thin layer between the gutta - percha and the wall of the canal . several techniques of sealer placement have been described in the literature , such as the use of a file , lentulo spiral , absorbent paper point , gutta - percha cone , and an ultrasonic file . each technique may produce different distribution of the sealer onto the canal walls , which may affect the sealing . at present , there is no evidence to suggest that one method is better and reliable than others . hence , the purpose of this study was to evaluate the influence of three most commonly used methods of sealer placement on the sealing ability of the sealer . one hundred and nineteen ( 119 ) human permanent central incisors teeth that had no caries , restorations , or any other noticeable defects were collected , stored in 0.9% isotonic saline , and used in this in vitro study . the crowns of the teeth were removed at the cementoenamel junction by using a hard tissue cutter ( exact , germany ) under water cooling . the working length was determined by introducing a size 10 k file into the canal until it could be seen at the apical foramen . this length was measured and the working length was set 1 mm short of the resultant measurement . all the teeth were instrumented to a size f3 protaper ( dentsply maillefer , switzerland ) following the full sequence recommended by the manufacturer . during preparation and between each protaper file , the canals were irrigated with 2 ml of 5.25% naocl by using a disposable syringe and a 25-gauge needle . also a size 10 hand file was introduced to remove any debris and to ensure the patency of the apical foramen . all root canals were then irrigated with 5 ml of 17% ethylene diamine tetra acetic acid ( edta ) followed by 5 ml of 5.25% naocl . finally , the root canals were flushed with distilled water and dried with absorbent paper points . the instrumented teeth were divided randomly into 3 experimental groups of 33 teeth each in addition to 2 groups which served as positive and negative control groups of 10 teeth each [ table 1 ] . groups , number of specimens , and sealer placement techniques root canal obturation was performed by using the cold lateral condensation technique . after sealer application according to the groups as shown in table 1 , the prefitted size 30 master gutta - percha cone was placed . the process was repeated until the spreader penetrated only into the coronal one - third of the root canal space . excess gutta - percha was removed with a heated instrument and the remainder was condensed vertically with a cold plugger . the teeth were stored in 100% humidity at 37c for 7 days to allow the sealer to set completely . after 7 days the external root surfaces were coated by two layers of nail polish except the coronal orifices . in the positive control group , no sealer was used and the nail polish was applied as the experimental group . while in the negative control group , the instrumented canals were filled with the sealer using rotary lentulo spiral and cold lateral compaction . then , the external root surfaces were entirely coated with two layers of nail polish , including the coronal orifices . each tooth was subsequently immersed in an aqueous solution of 2% methylene blue dye with ph 7.0 in an individual container and kept in the incubator at 37c for 3 days . the specimens were then decalcified in 5% nitric acid for 72 h and dehydrated gradually in ascending concentrations of alcohol to 100% . methyl salicylate was used overnight to clear the teeth . for linear dye penetration assessment , each tooth was sectioned longitudinally by using a hard tissue cutter ( exakt , japan ) . measurements were done by a blinded assessor under a light microscope ( leica , germany ) at x20 magnification . the coronal leakage was measured to the nearest 0.01 mm , from the coronal end of gutta - percha , to the most apical extent of dye , taking into consideration the region of highest penetration . this was completed using leica image analyzer software ( leica , germany ) , connected to the microscope . ten teeth of each experimental group were randomly selected and dye penetration was measured again after 1 week by the same investigator to determine examiner reliability . the data of the first and second measurements were tested using a single - measured intraclass correlation statistic ( icc ) . the difference in the amount of linear dye penetration between groups was compared using anova . the icc was 0.99 ( 95% ci : 0.991.00 ) suggestive of a high examiner reliability . due to technical problems during the experiment , one specimen was lost in group g1 , resulting in 32 samples for this group . the positive controls demonstrated complete dye penetration throughout the length of the canal in all teeth . in contrast , the negative controls showed no evidence of leakage in any of the samples . means of linear dye penetration and standard deviations for all groups are summarized in table 2 . there was no significant difference ( p = 0.305 ) of dye penetration among all groups . one of the objectives of root canal treatment is to provide a hermetic seal of root canal space . this seal is usually produced by using a semisolid or solid core material in a combination with the endodontic sealer . a solid core can not produce the desired hermetic seal ; thus , the endodontic sealer is required to provide three - dimensional obturation . the experimental system of this study was tested by using both positive and negative control groups . the positive control specimens showed total dye penetration throughout the root canal , which indicated that it is absolutely necessary to use a sealer to fill voids and gaps between the core material and the root canal walls and further confirmed the fact that filling the root canal with only the core obturating material without a sealer resulted in an increased leakage . however , the negative control specimens demonstrated no dye penetration , which indicated that two coatings of nail polish were an effective means of preventing dye penetration . the results of this study showed no statistically significant difference ( p = 0.305 ) in microleakage among the three different tested techniques of sealer placement . however , the rotary lentulo spiral group produced the highest value of microleakage and the master gutta - percha coating group had the smallest mean microleakage value . it was expected that the rotary lentulo spiral group will produce a better adaptation of the sealer onto the canal walls with even thickness which in turn leads to a better seal but the results of this study did not support our assumption . first , more amount of sealer was introduced into the canal as compared with other techniques , and as the sealer shrunk during setting , more gaps and voids might had been created that had contributed to the highest value of microleakage . second , a high volume of the sealer material may also interfere with the placement of additional accessory points which leads to less gutta - percha volume percentage compared to the amount of sealer . third , the use of rotary lentulo spiral during sealer placement may force some air bubbles into the material that will lead to void formation and microleakage , whereas , the endodontic sealer coating of master gutta - percha cone produced less sealer thickness with less potential void formation compared to the other techniques that eventually might have contributed to the smallest microleakage value obtained by this group . our results are in accordance with wiemann et al . 's , who compared the influence of four methods , file , lentulo spiral , ultrasonic files , and master gutta - percha , of sealer placement on the sealer sealing ability . in addition , they reported that less sealer was present in the apical third compared to the coronal and middle thirds of the root canal . kahn et al . investigated the efficacy of six methods of sealer placement using clear plastic blocks with simulated curved canals . they concluded that the lentulo spiral and the max - i - probe delivery system were the most effective means of sealer placement , followed by ultrasonic and sonic files , and the least effective methods were the paper point and the k file . in this study , the three methods of sealer placement showed comparable results and could be used in clinical practice . however , as the master gutta - percha coating technique had produced the lowest microleakage values , it would be suggested to be used for better results . the master gutta - percha coating technique is the simplest method among the three methods tested and it requires no additional instruments and procedures . further research perhaps is needed to study the effect of different sealer placement methods with different obturation techniques . within its limitations , this study showed that the three tested techniques of sealer placement provided a comparable seal . however , the master gutta - percha coating technique could be preferable as it produced the least leakage value , and no extra instrumentation and procedures are needed in its application .
aim : the aim of this in vitro study was to evaluate the sealing ability of an endodontic sealer following different techniques of its placement.materials and methods : a total of 119 permanent human anterior teeth were prepared by using manual protaper and randomly divided into three equal groups of 33 teeth each . 
 the teeth were obturated with the cold lateral condensation technique and ah26 sealer which was placed by using the following : g1 : rotary lentulo spiral ; g2 : manual lentulo spiral ; and g3 : master gutta - percha coating . the remaining 20 teeth served as positive and negative controls . the samples were immersed in the methylene blue solution for 3 days and longitudinally sectioned for dye penetration assessment and analyzed using a stereomicroscope.results:there was no statistically significant difference ( p = 0.305 ) among the three groups . 
 however , the rotary lentulo spiral technique and the master gutta - percha coating technique showed the highest ( 4.5 mm ) and the lowest ( 3.8 mm ) microleakage values , respectively.conclusion:different techniques of sealer placement used in this study provided a comparable seal . 
 however , the master gutta - percha coating technique might be preferable because of its ease of use .