Table 1.
Overview of the types of isthmus based on the Hus & Kim5 classification and the incidence of isthmus based on the Teixeira12 NI; no isthmus (no canal + one canal + type I isthmus), PI; partial isthmus (type II + III + IV isthmus), CI; complete isthmus (type V isthmus).
| Distance from apex | n | No canal | One canal | Type I | Type II | Type III | Type IV | Type V | NI | PI | CI | PI + CI | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| n (%) | n (%) | n (%) | n (%) | ||||||||||
| MB root of maxillary first molar | 1 mm | 28 | 4 | 11 | 10 | 2 | 1 | — | — | 25 (89.3%) | 3 (10.7%) | — | 3 (10.7%) |
| 2 mm | 28 | — | 4 | 4 | 9 | 6 | 2 | 3 | 8 (28.6%) | 17 (60.7%) | 3 (10.7%) | 20 (71.4%) | |
| 3 mm | 28 | — | 3 | — | 10 | 5 | 6 | 4 | 3 (10.7%) | 21 (75.0%) | 4 (14.3%) | 25 (89.3%) | |
| 4 mm | 28 | — | 4 | 4 | 7 | 4 | 4 | 5 | 8 (28.6%) | 15 (53.5%) | 5 (17.9%) | 20 (71.4%) | |
| 5 mm | 28 | — | 1 | 3 | 5 | 3 | 5 | 11 | 4 (14.3%) | 13 (46.4%) | 11 (39.3%) | 24 (85.7%) | |
| M root of mandibular first molar | 1 mm | 31 | 7 | 9 | 10 | 2 | 3 | — | — | 26 (83.9%) | 5 (16.1%) | — | 5 (16.1%) |
| 2 mm | 31 | — | 7 | 2 | 4 | 3 | 5 | 10 | 9 (29.0%) | 12 (38.7%) | 10 (32.3%) | 22 (71.0%) | |
| 3 mm | 31 | — | — | — | 7 | 2 | 9 | 13 | — | 18 (58.1%) | 13 (41.9%) | 31 (100%) | |
| 4 mm | 31 | — | — | 1 | 11 | 2 | 5 | 12 | 1 (3.2%) | 18 (58.1%) | 12 (38.7%) | 30 (96.8%) | |
| 5 mm | 31 | — | — | 2 | 6 | 8 | 6 | 9 | 2 (6.5%) | 20 (64.5%) | 9 (29.0%) | 29 (93.5%) |