Wolcott J, Ishley D et al. J Endodon 2005; 31: 262–264

This study extends by 3 yrs an earlier report on 1,873 consecutive maxillary molars either treated or retreated over a 2 yr period, and a total of 5,616 teeth were examined clinically and radiographically by 6 experienced endodontists.

MB2 canals were found in 58% of 2,814 initially treated first molars, and 66% of 764 retreated ones (P < 0.0001). For second molars, respective figures were: 34% of 1,845 and 40% of 193 (P = 0.13). After controlling for molar type, the overall incidence of MB2 was associated with type of treatment (Mantel Haenszel test: P < 0.0001).

The authors note that it is not possible to prove experimentally that an untreated MB2 canal may cause treatment failure, but their findings are supportive of this hypothesis.