From the Royal College of Dental Surgeons of Ontario's PEAK article program:
In a retrospective study of uncrowned
endodontically treated teeth, the overall survival rates of
molars without crowns at 1, 2, and 5 years were 96%, 88%
and 36% respectively.
Yikes! So no matter how conservative the access for the root canal is and the lack of any significant caries, you should crown these teeth within two years and preferably one.
Source: McComb D, Restoration of the Endodontically Treated Tooth, (PEAK article), Practice Enhancement and Knowledge, Supplement to Feb/Mar 2008 Dispatch. Royal College of Dental Surgeons of Ontario.
Hans Skariah, B.Sc., DMD
Promenade Court Dental
2233 Hurontario St., Mississauga, ON, Canada (905) 273-7100
Plattsville Dental
43 Albert St. West, Unit 8, Plattsville, ON, Canada (226) 656-1000