internal anatomy of the mesiobuccal ( mb ) root of the maxillary first molar has been studied extensively for the past three decades because this is the root that exhibited the maximum number of variations not only in the presence of extra canals but also in their canal configuration . the literature showed 73.2% to 93% incidence of two canals and only 1.1% occurrence of three canals . three canals in the mb root with a configuration of vertucci type 8 ( 3 - 3 ) , sert and bairily type xv , or type xviii ( 3 - 2/3 - 1 ) have been reported . however , complex configurations of 3 - 2 - 1 and 2 - 3 - 2 - 1 - 2 canal types in the mb root have rarely been described in studies either in vitro or in vivo . the present case report describes one such atypical configuration of 3 - 2 - 1 in the mb root of maxillary first molar . a young indian male patient reported with the chief complaint of spontaneous pain of moderate intensity in the upper left back tooth region for the past two weeks . he gave a history of localized , mild , intermittent pain in the same region one month back that had increased in intensity in the past three days . on intraoral examination of the second quadrant , the first molar had a deep carious lesion and was mildly tender on vertical percussion . on radiographic examination , there was pulpal involvement with widening of periodontal ligament space [ figure 1a ] . based on these findings , the tooth was diagnosed as a nonvital tooth with chronic apical periodontitis , and the patient was planned for endodontic therapy . the maxillary left first molar was first isolated using rubber dam and then access cavity preparation was initiated . after deroofing the pulp chamber , the mb , distobuccal ( db ) , and palatal canals were located . following along the dentinal map and slowly removing a shelf of dentin covering the dentinal map , a small groove connecting the mb and the palatal canal orifices was identified . access cavity was further widened toward the mesial marginal ridge to facilitate easy exploration along this subpulpal groove , and by probing with dg 16 explorer two additional sticky canal entrances were identified . these extra canals were then negotiated using no . 08 k files . based on their anatomic location on the pulpal groove , the canal orifice nearer to the palatal orifice was named as palatal mesiobuccal ( p - mb ) whereas the one nearer to the mb canal orifice was named as middle mesiobuccal ( m - mb ) [ figure 1b ] the three canals in the mb root and their working length were confirmed with multiple angled periapical radiographs using ingle 's method as well as electronic apex locator ( root zx ; morita , tokyo , japan ) [ figure 1c ] . a careful interpretation of working length radiograph revealed a complex canal configuration of 3 - 2 - 1 in the mb roots . a single canal with a single apical foramen was noted in both the distobuccal and palatal roots and the access was closed with a temporary restoration . ( a ) preoperative radiograph , ( b ) access opening showing three distinct orifices in the mb root , ( c ) working length radiograph , ( d ) postobturation radiograph the presence of this unusual 3 - 2 - 1 canal configuration in the mb root was confirmed using a three - dimensional imaging technique sct - dentascan ( ge healthcare , usa ) after explaining to the patient . the sct images showed buccolingually wide and bulbous mesiobuccal root with three separate canals at coronal third that merged into two canals in the middle and exited as a single canal at the apex [ figure 2c ] . spiral ct images ( a ) coronal third , ( b ) middle third , ( c ) apical third at the next visit , shaping of the mb , db , and the palatal canals was done using ni - ti protaper rotary files ( dentsply , maillefer , switzerland ) in a passive crown - down manner under copious irrigation with 3% sodium hypochlorite solution . m - mb and p - mb canals were cautiously prepared to avoid stripping of the mb root using only hand instrumentation in step back technique . the canals were then obturated with gutta - percha in conventional lateral condensation technique followed by core build up with silver amalgam . after a week , the tooth was prepared for full veneer crown . at six month recall and evaluation , the tooth was functional and completely asymptomatic [ figure 1d ] . a clinician should always remember that the occurrence of a single canal with single exit is not always a rule because there is every possibility for the anatomic complexities to exist in any tooth and in any of the roots . having the knowledge of anatomic variations and the clinician 's skill helps in locating and negotiating these complexities . endodontic success depends on thorough debridement and complete obturation of the entire root canal system . the present case is one such example of the presence of three canals in the mb root of maxillary first molar with unusual internal anatomy . the anatomic configuration of three canals as 3 - 2 - 1 was identified by scouting the canals with hand files . among the three canals , the major canal was the mb ; the second major canal , m - mb , joined the mb canal in the apical third , whereas p - mb is the smallest canal that joined mb canal in the middle third . this same configuration is also confirmed using multiple medially angulated radiographs taken with files in the mb root and further confirmed using three - dimensional imaging technique , sct . although sct has the disadvantage of more radiation exposure than cone beam computed tomography ( cbct ) , it is used due to the lack of availability of cbct . the axial scans in apical third showed buccopalatally elongated bean - seed shaped mb root , being wider buccally and with concavity toward the furcation that is on its distal side . taking this shape into consideration , m - mb and p - mb were conservatively prepared so as to prevent stripping on the distal side . a literature search was conducted on pubmed data base to note the reported cases for the presence of three canals in the mb root of maxillary first molar and the results are tabulated in table 1 . the possible canal configurations reported were vertucci 's type viii ( 3 - 3 ; 3 separate canals with separate foramina ) , sert and bairley 's xv-3 - 2 configuration , xviii-3 - 1 configuration , and xxi-4 - 1 configuration . case reports of three mesio buccal canals of maxillary first molar sert , in his in vitro study on turkish population , first reported the occurrence of 3 - 2 - 1 canal configuration in the mb root of maxillary first molar . later , similar configuration was reported by arora et al . in the mb root of the maxillary second molar . based on this literature review , the present article is one of the rarest configurations to be reported in the mb root of the first molar . an increased awareness of incidence of extra canals in the mb root of maxillary first molar with a better understanding of the complex canal configurations and use of advanced diagnostic aids , such as sct , helps the clinician in proper diagnosis and correct endodontic management of the rarest variations to achieve a successful endodontic outcome .
this case report discusses the identification and management of complex canal configuration of 3 - 2 - 1 in the mesiobuccal ( mb ) root of the maxillary left first molar . 
 careful attention to details of the pulpal floor and applying the knowledge of the laws of orifice location along with deepening the subpulpal groove with ultrasonic tips helped in identifying the three mb canals . 
 manual scouting helped in understanding the anatomic configuration ; the use of three - dimensional imaging technique and spiral computed tomography ( sct ) confirmed the same . 
 sct images showed buccolingually wide and bulbous mesiobuccal root with three separate canals at coronal third that merged into two canals in the middle and exited as a single canal at the apex . 
 this article highlights the role of sct in three - dimensionally analyzing the unseen rarest canal configurations that ultimately enabled the clinician to thoroughly explore , debride , and obturate the entire root canal system .