Accessory mesial canal=Middle Mesial Canal
Middle Mesial Canal is a canal in-between the mesial buccal and mesial lingual canals of a lower molar. The occurrence rate ranges from .3-46% (Kim v Azim) depending on your source but the number with own POE is possibly under 3% or as high as 46%.
What is the middle mesial canal?
One can think of the Middle Mesial Canal or Accessory mesial canal as a component of the isthmus space between the mesiobuccal (MB) and mesiolingual (ML) canals that is both cleansable and shapable. There is no consensus of a definition between canal and isthmus.
Middle mesial canal has been known about for a long time. It has been proposed that the mesial roots of mandibular molars develop as 1 RCS and compress with age in the middle to form two. Hess 1925
- Mesial roots of first and second molars mostly had one large canal until 11 and 15 years of age, respectively. Pieris 2008
- Aging could explain lower incidence of MMC in first versus second molars
- Age is a large factor in likelihood of middle mesial canal existing. Nosrat JOE 2015
We can hypothesize that the space between the mesiobuccal (MB) and mesiolingual (ML) canals is an isthmus that can we clean and shape.
Research on percentages of teeth with mid mesial canal
Lit Review 13% MMC Navarro Med Oral Path Oral Cir Buccal 2007
36% had three canals at some point along root and 100% had isthmus Harris JOE 2013
12% but only 2% with separate canal but unsure if second or first molar 1981 Pomeranz JOE
8% increase in number canals found with DOM 8-13x from naked eye Carvalho 2000 JOE Sept
micro-CT study of middle mesial canals
As ususall the micor Ct study shows why root canals are impossible to treat 100% successfully. Versiani Arch Oral Biol 2016 shows 54% have 3 orifices and 44% have 3 foramina!
CBCT research on middle mesial canals
16% true mid mesials canals however only 2.4% had own POE. 25% and 8% of 1st and 2nd respectively and 65% and isthmus BUT excluded “calcified canals” whatever that means. Tahmasbi JOE 2017
Research on aspects of the mid mesial such as fins and isthmus
Azim JOE Feb 2015 38% had MMC
- Magnification from 6-11x
- To be included canal had to be negotiable to within 5mm of apex
- Age was a big factor
- 10% had own apical foramina unknown if first or second
- 12% were fin unknown if first or second
de Pablo JOE 2010 Systemic review 41 studies
- Isthmus communications = 55% on mesial and 20% on distal root. What is an isthmus and what is a canal? Depends on age likely. In the young it is a canal in the elderly an isthmus.
Isthmus are common (50% in 20-39) but decrease with age 24% in 60 and over (Gu 2009 JOE Chinese micro CT study)
Tend to be close to ML canal JOE Aug 2010 Kazandag also shows from 4.5x to DOM percentage found went from 16%-18% Pomeranz 81 and Nosrat 15 showed same
X-rays of middle mesial canal
Mesial roots of first and second molars mostly had one large canal until 11 and 15 years of age, respectively. Pieris 2008
Tend to be close to ML canal JOE Aug 2010 Kazandag also shows from 4.5x to DOM percentage found went from 16%-22%
1% separate canal but unsure if second or first molar 1981 Pomeranz JOE