An in vitro assessment of type,position and incidence of isthmus in human permanent molars

Root canal anatomical complexities, such as isthmus, may limit the action of theendodontic instruments, irrigant solutions and intracanal medications, leading toendodontic treatment failure.

Objectives

This in vitro study assessed the type, position and incidence ofisthmus in human permanent molars.

Material and Methods

One hundred and twenty eight upper and lower first and second permanent molarswere analyzed. The roots were embedded in transparent resin, and then split atdifferent distances from the apex (1.0-2.5-4.0-5.5-7.0 mm). Following the sampleexamination in stereomicroscope, the data were submitted to chi-square statisticaltest at a 5% significance level.

Results

The highest isthmus incidence was at 7.0 mm from the root apex in all samples,except the distal root of lower molars (at 5.5 mm). In upper and lower molars,type V (complete isthmus with a continuous opening between the two main rootcanals) was the most common classification of isthmus (28.8%). In the mesial rootof first and second mandibular molars, type IV had the highest incidence (36% and23.9%, respectively).

Conclusion

It was concluded that isthmus was widely found in flat roots, with a lowpercentage in areas close to the apex. In upper and lower molars, these structureswere most frequently found at 7 mm from the apex.