Incidence of Isthmus and Dimensions in Mesiobuccal and Mesial Roots of First Molars

Abstract

The aim of this study was to evaluate the incidence of isthmus and dimensions of mesiobuccal (MB) roots from maxillary first molars and mesial (M) roots from mandibular first molars in order to elucidate their anatomy. Twenty-eight maxillary first molars and thirty-one mandibular first molars were evaluated regardless of sex or age. The MB roots of the maxillary first molars and the M roots of the mandibular first molars were cleaned with an ultrasonic instrument to remove calculus; and placed in a 5.25% sodium hypochlorite solution for one hour to remove remnants of the periodontal ligament. Each root was separately embedded in clear resin and the embedded roots were cut perpendicular to the long axis of the root at 1, 2, 3, 4 and 5 mm from the anatomic apex with a low speed diamond saw. The resected surfaces were stained with 2% methylene blue dye for 60 seconds and photographs were taken using a digital camera attached to a stereomicroscope at 30x magnification. The incidence of isthmus and dimensions in MB and M roots in the first molars were evaluated. The findings are as followings, 1. In MB roots of the maxillary first molars, type I isthmus was the most prevalent near the apex. Type II isthmus was the most prevalent at apical the 2, 3 and 4 mm, while type V isthmus was most prevalent at apical 5 mm. 2. The incidence of isthmus of MB roots of the maxillary first molar was 10.7 to 89.3%, and it was observed more than 70% at all levels except 1 mm. The highest incidence of isthmus was seen at the apical 3 mm with 89.3%. Partial and complete isthmuses were 75% and 14.3%, respectively. 3. In M roots of the mandibular first molars, type I isthmus was the most prevalent near the apex. Type V isthmus was the most prevalent at apical 2, 3, 4 and 5 mm. 4. The incidence of isthmus in M roots of the mandibular first molars was 16.1 to 100% and it was observed more than 70% at all levels except 1 mm. The highest incidence of isthmus was seen at the apical 3 mm with 100%. Partial and complete isthmuses were 58.1% and 41.9%, respectively. 5. There were no statistically significant differences in the mesio-distal dimensions (MBM, MBD, MLM, MLD, IM and ID) among 3, 4 and 5 mm from MB root apex of the maxillary first molar (p > 0.05). Based on the root resection at apical 3 mm, the thinnest dimension was 0.78 mm in MLD. The means of MLD and ID at apical 3, 4 and 5 mm were 0.85 mm and 0.95 mm, which were less than 1 mm. 6. There were no statistically significant differences in the mesio-distal dimensions (MBM, MBD, MLM, MLD, IM and ID) at 3, 4 and 5 mm from M root apex of the mandibular first molars (p > 0.05). Based on the root resection level at apical 3 mm, the thinnest dimension was 0.86 mm in MLD. The mean of MLD and ID at apical 3, 4 and 5 mm was 0.96 mm and 0.91 mm, which were less than 1 mm.