Change in working length following instrumentation of molar canals

A study was undertaken to determine the reduction in working length following instrumentation of molar canals. A sample of forty maxillary and forty mandibular extracted teeth was used. The canals were measured before and after instrumentation. The greatest changes were observed in the mesiobuccal canal of the maxillary molars, which showed a mean reduction of 0.35 mm. with a range of 0.8 mm. The smallest changes were observed in the palatal canal of the maxillary molars and the distal canal of the mandibular molars. These canals showed a mean change of less than 0.1 mm. None of the changes were statistically significant.