Steven Lipner

-SHAPED MOLARS are named for the morphology of their root canal system. Teeth that exhibit this anatomical feature do not have separate, distinct orifices. Rather, these teeth are composed of a pulp chamber with a single ribbon-shaped orifice. One anatomical variation of the c-shaped canal occurs when the ribbon-shaped opening extends from the pulp chamber to the apex as a single canal. Another anatomical variation is observed when the c-shaped orifice splits into discrete canals.
    In 1991, Melton devised a classification system for c-shaped canals. Category I is designated by an unbroken, continuous c-shaped canal running from the pulp chamber to the apex. Category II comprises pulp chambers that have the appearance of a semicolon. These teeth present with one main c-shaped canal, as well as one distinct mesial canal. Category III encompasses c-shaped molars that have two or more distinct canals. Category IV includes molars that have only one ovoid canal, while Category V comprises C-shaped molars in which no canal is evident.
    C-shaped canals are most often found in mandibular second molars, though they can be found in mandibular first molars, maxillary molars, mandibular premolars, and maxillary laterals. The incidence of c-shaped canals is reported to be in the range of 2.7 percent to 8 percent. The frequency of c-shaped canals varies greatly among different ethnicities. The prevalence of c-shaped canals in Asian populations has been reported to be as high as 30 percent.
    C-shaped canal anatomy presents the clinician with an immense challenge. The high frequency of transverse anastomoses, apical deltas, and lateral canals compels the clinician to use every resource at his disposal to achieve an adequately debrided canal. These resources include the use of copious volumes of sodium hypochlorite, ultrasonic activation of irrigants, and multiple recapitulation and exploration of apical deltas with pre-curved handfiles. Extreme caution should be employed when cleaning and shaping c-shaped molars. The isthmus connecting the canals should not be prepared with greater than a number 25 file, because the risk of a strip perforation is high. In addition, the presence of a lingual developmental groove in the mesiolingual wall makes it another area of narrow root thickness. To prevent strip perforation, take care to avoid overly aggressive instrumentation.
    A patient was referred to our office for the evaluation and treatment of tooth number 31. Root canal therapy had been initiated in another office due to symptoms of pulpal necrosis and acute apical periodontitis. Two days after the initial treatment was performed, the patient was seen by an oral surgeon because a submandibular swelling had developed. The oral surgeon performed an incision and drainage and placed the patient on antibiotics. The patient was seen in our office approximately one week after treatment was initiated. The patient was anesthetized and the tooth was accessed under rubber dam isolation. The canals were cleaned and shaped and irrigated with copious volumes of sodium hypochlorite. Pre-curved handfiles were used to explore the complex apical anatomy present in this tooth, and the sodium hypochlorite was agitated using an ultrasonic file. The canals were dried and calcium hydroxide was placed. When the patient returned two weeks later, the tooth was asymptomatic. The canals were re-instrumented and irrigated under ultrasonic activation. After thoroughly drying the tooth, the canals were obturated. The patient will return for a six-month recall.
 

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