Introduction: To increase our understanding of the root canal system, we examined the mesiobuccal (MB) roots of maxillary first and second molars, which are considered to be one of the most complex root canal systems. Methods: Uninstrumented MB roots from 153 teeth were imbedded, sectioned, and observed at 8× using a stereomicroscope for main canal numbers, isthmus presence, and dimensional size of canals and dentin walls. Results: The number of canals observed in maxillary first and second molars was 20% and 38.1% for one canal, 79.8% and 60.3% for two canals, and 1.1% and 1.6% for three canals, respectively. The buccal canal was larger than lingual or middle canals at all levels of the root. The average distance between the two main canals was 1.2 ± 0.6 mm in first molars and 1.78 ± 0.6 mm in second molars. Isthmus tissue increased greatly at 3.6 mm from the apex, suggesting optimal root resection at this level. Little differences in thickness between mesial and distal canal walls were seen until reaching the coronal sections of the root where the average canal wall thickness was found to be thinner (33%) on the distal, suggesting a "danger zone" for maxillary molars at a level where the root joins the crown of the tooth. Conclusions: The observations made here provide a more precise understanding of the maxillary MB root system. Orthograde and retrograde root canal therapy might be improved with a comprehensive understanding of pulpal morphology throughout the entire MB root.
- Canal anatomy
- danger zone