knowledge of the anatomy of root canal systems is an essential prerequisite for endodontic treatment .
many of the problems encountered during and after root canal treatment occur because of inadequate understanding of the pulp space anatomy .
studies on the internal and external anatomy of teeth have shown that anatomic variations can occur in all groups of teeth and can be extremely complex .
this applies to mandibular incisor teeth as well , as many dentists fail to recognize the presence of a second canal .
current knowledge of pulp space anatomy is based on research findings and individual case reports .
there is a lack of consistency in the reported prevalence of second canals in mandibular incisors.[15 ] the differences may be related to study design ( in vivo versus ex vivo ) , technique of canal identification ( radiographic examination , sectioning and clearing ) or to racial divergence .
it is important to be familiar with variations in tooth anatomy and characteristic features in various racial groups , since such knowledge can aid location and negotiation of canals , as well as their subsequent management .
additionally , a number of studies have shown different trends in shape and number of roots and canals amongst the different races.[1368 ] these variations appear to be genetically determined and are important in tracing the racial origins of populations .
descriptions of the frequently occurring root canal systems of permanent teeth are based largely on studies conducted in europe and north america , and relate to teeth of mainly caucasian origin .
these descriptions may not be fully applicable to teeth of non- caucasian origin . there are no published reports on the root canal anatomy of mandibular incisors in north east indian population .
however , some studies have examined an indian population . the north - eastern population in india is mostly comprised of indo - aryans ( caucasoid ) mongoloids ( tibeto - burman and paleo - mangoloid sub race ) and dravidian sub populations .
the population of north - east india is nearly 38 million , out of which tribal mongoloid population accounts for almost 42 - 45% of the total population .
a total of five hundred and thirty six extracted mandibular incisors were randomly collected from general dental clinics within north - eastern india.out of the collected teeth , fifty six teeth were excluded because of immature or resorbed apices and four hundred and eighty teeth were selected for the present study . the gender and age of patients was not known , and no attempt was made to differentiate between central and lateral incisors .
the samples were stored in 5.25% sodium hypochlorite ( organo bio tech laboratories pvt ltd new delhi , india ) for 30 minutes for the removal of organic debris , and then in 10% formaldehyde until use .
the teeth were cleaned under running water , access cavities were prepared and the coronal pulp tissue extirpated in the canal orifices .
the samples were stored in 5% nitric acid solution ( aries laboratories , india ) for 5 days .
demineralization was assessed by the insertion of a paper pin in the crown and with the help of radiographs .
the samples were then rinsed under running water for 4 hours and placed in 70 , 80 and 95% ethyl alcohol successively , for 1 day . at the end of this period ,
the clearing procedure was completed by placing the samples in methyl salicylate ( regent chemicals , mumbai ) ) . at the end of the third day , complete transparency was achieved .
india ink ( united ink and varnishes pvt ltd , mumbai , india ) was injected into the root canals of the transparent teeth using syringes with 27 gauge needle ( shree uniya surgical , india ) . after the ink had dried , root canal morphology was examined by a magnifying glass of 5x magnification [ figure 1 ] , and the following observations were made : transparent specimen showing canal bifurcation 
 number and type of root canals , presence and location of lateral canals and intercanal communications , location of apical foramina , andbifurcation of canals.canals were categorized into the first five types of vertucci 's classification as follows : 
 type i : a single canal is present from the pulp chamber to the apex.type ii : two separate canals leave the pulp chamber , but join to form one canal to the site of exiting.type iii : one canal leaves the pulp chamber , divides into two within the root , and then merges to exit in one canal.type iv : two separate and distinct canals are present from the pulp chamber to the apex.type v : single canal leaving the pulp chamber but dividing into two separate canals with two separate apical foramina . 

  number and type of root canals , presence and location of lateral canals and intercanal communications , location of apical foramina , and bifurcation of canals .
canals were categorized into the first five types of vertucci 's classification as follows : 
 type i : a single canal is present from the pulp chamber to the apex.type ii : two separate canals leave the pulp chamber , but join to form one canal to the site of exiting.type iii : one canal leaves the pulp chamber , divides into two within the root , and then merges to exit in one canal.type iv : two separate and distinct canals are present from the pulp chamber to the apex.type v : single canal leaving the pulp chamber but dividing into two separate canals with two separate apical foramina . 
 
type i : a single canal is present from the pulp chamber to the apex .
type ii : two separate canals leave the pulp chamber , but join to form one canal to the site of exiting .
type iii : one canal leaves the pulp chamber , divides into two within the root , and then merges to exit in one canal .
type iv : two separate and distinct canals are present from the pulp chamber to the apex .
type v : single canal leaving the pulp chamber but dividing into two separate canals with two separate apical foramina .
results of this investigation indicate that one third of the teeth exhibit two canal system ( 36% ) . of the teeth with two canals ,
type iii configuration was most common followed by type ii and type v [ figure 2 ] .
although two canals were found in 36% of teeth , only 6.25% of canals exited in two separate foramina ( type v ) [ table 1 ] . out of all the canals showing two canal configuration , around 83% joined and exited in single foramen ( type ii and iii ) and remaining 17% exited in two separate foramina ( type v ) [ table 1].the apical foramen was found to coincide with the apical root tip in 47.2% of teeth [ table 2 ] . in the present study
, lateral canals were observed in around 13% of the cases [ figure 3 ] [ table 3 ] .
anastomosis were found only in type iii canals which accounts for 2.5% of all the teeth [ table 4 ] .
apical ramifications were seen in around 7.42% of the teeth , out of which 75.7% were with two rami , 24.3%with three rami , and none with four rami [ table 4 ] [ figure 4 ] . in teeth with two canals ,
bifurcations were seen maximum in middle third ( 64% ) followed by in cervical third 23.3% and in apical third 1.25 % [ table 5 ] .
intercanal communications were observed in 28.4% of all teeth and in 70.2% of teeth with two canals [ table 6 ] .
canal configuration ( from left to right ) types i , ii , iii and v number and percentage of canal system types in mandibular incisors ( n=480 ) in the study distribution of apical foramen in mandibular incisors ( n=480 ) in the study curvatures in type i canal configurations- straight , s shaped and j shaped distribution of lateral canals in mandibular incisors in the study distribution of apical ramification in mandibular incisors in the study type i variations- apical ramification , reticular structure and lateral canals distribution of position of canal bifurcation in mandibular incisors in the study distribution of intercanal communications in mandibular incisors in the study
various methods have been used to study root canal morphology including radiographic examination , root sectioning , staining and clearing techniques , direct observation with microscope , sectioning and macroscopic observation , stereo microscope , spiral computed tomography , and cone beam computed tomography .
vertucci used the clearing technique to study the root canal morphology of extracted mandibular anterior teeth .
it has been reported that fine details of the root canal system can be visualized by staining and clearing[figure 1 ] .
this technique also makes canal negotiation with instruments unnecessary , thereby maintaining the original form and relation of canals , and provides a three - dimensional view of root canal .
the process of changing the tooth into a transparent object involves many physical and chemical changes .
the inorganic constituents of the tooth are first dissolved by decalcification , and further water , air , and lipid components are removed by dehydration and by subsequent immersion in the clearing agents , th and this method was used in the present study as well .
the literature on mandibular incisors reveals that 1168% of mandibular incisors possess two canals , although in many of these cases , the canals merge into one in the apical 13 mm of the root .
vertucci examined the root canal morphology of 300 mandibular anterior teeth and reported a second canal in 27.5% of mandibular incisors .
miyashita et al . , reported that 12.4% of mandibular incisors contained two canals ; however , only 3% had two foramina .
sert et al . , noted that two canals were present in 68% of mandibular central incisors .
mauger et al . , evaluated the canal morphology at different root levels in one hundred mandibular incisors , and reported that 98100% of the teeth had one canal in the area 13 mm from the apex .
the differences between these morphology studies may be related to variations of examination methods , classification systems , sample sizes and ethnic background of tooth sources . in a study in jordanian population , it was found that 73.8% of the mandibular incisors possessed a single root canal , and 26.2% of teeth were with two canals .
the results of the present study indicate that one third of the teeth exhibit two canal system ( 36% ) [ table 2 ] [ figure 2 ] .
it was found that 63.75% of mandibular incisors possessed a single root canal ( type i ) with straight , j and s shaped curvatures [ figure 3 ] as well as frequent apical ramifications , lateral canals and reticular structures [ figure 4 ] .
only 6.25% of canals exited in two separate foramina ( type v ) . of the teeth with two canals ,
type iii configuration was most common followed by type ii and type v. therefore , the frequency of two canals in the present study was within the range of previous reports .
this is due to failure of the dentist to recognize the presence of the second canal , and the need for access cavities to have appropriate inciso - gingival extension to facilitate the location of lingual canals .
none of the teeth were seen with type iv canal system , which may be due to smaller number of samples examined in the present study and any conclusion drawn needs to be based on study of a larger population .
the apical foramen was found to coincide with the apical root tip in 47.2% of teeth [ table 2 ] .
this is higher than reported in previous studies that demonstrated that the apical foramen coincided with the anatomical apex in 1746% of cases . in the present study , total apical foramen count stands at 510 ( n=480 ) , which is because of type v canal configuration and apical ramifications
this finding may be of significance in working length determination which often depends on the average position of the apical constriction relative to root apex . in the present study , lateral canals were observed in around 13% of teeth and were found most frequently in the middle of the canal [ table 3 ] [ figure 4 ] .
lateral canals in the apical third account for 2.94%.this is consistent with the findings of miyashita et al . ; however , much lower than that reported by vertucci .
anastomoses were found only in type iii canals which accounts for 2.5% of all the teeth .
apical ramifications were seen in around 7.42% of the teeth out of which 75.7% were with two rami , and 24.3% with three rami , and none with four rami [ table 4 ] . in teeth with two canals ,
bifurcations were seen maximum in middle third ( 64% ) followed by the cervical third 23.3% ; and , the apical third 1.25% [ table 5].this requires an individualized procedure for preparation and filling in each of these conditions to obtain the most desirable results .
pulp space anatomy of mandibular incisors in an indian population show high incidence of complexity which includes variations in canal configuration , number of canals and presence of isthmus .
intercanal communications were observed in 28.4% of all teeth , and in 70.2% of teeth with two canals [ table 6 ] .
the high percentage of intercanal communications in teeth with two canals may be of clinical significance , because it may be difficult to debride and fill these communications adequately .
within the limitations of the present study , it can be concluded that overall , 36% of mandibular incisors in this north - east indian population had two canals . in the teeth with two canals ,
the type iii canal system was the most prevalent followed by type ii.type v was the least prevalent .
 aim : to aim of this study is to investigate the root canal characteristics of mandibular incisors in a north east indian population using a canal staining and tooth - clearing technique.materials and methods : four hundred and eighty extracted mandibular incisors , collected from dental clinics within north east india were selected for this study . following pulp tissue removal , 
 the teeth were decalcified with 5% nitric acid , dehydrated with ascending concentrations of alcohol and rendered clear by immersion in methyl salicylate . after staining of the canal systems with india ink , cleared teeth 
 were examined under 5x magnification and the following features were evaluated : ( i ) number and type of root canals ; ( ii ) presence and location of lateral canals and intercanal communications ; ( iii ) location of apical foramina ; and , ( iv ) bifurcation of canals.results:the majority of mandibular incisors had a single canal ( 63.75% of teeth possessed a type i canal system ) . 
 although 36.25% of the roots possessed two canals , only 6.25% had two separate apical foramina.conclusions:the prevalence of two canals in this group ( of north east indians ) of mandibular incisors was 36.25% and is within the range of previous studies performed on populations of different racial origin . 