Anatomy MB2 first molar – How often is there an MB2

Anatomy MB2 first molar study data ranges from 50%-95% MB3 is 1-3% (source) My opinion is there are 7 main reasons these stats vary.  One is how we define an isthmus versus canal, two is the technique we use to study the teeth, three is experience and bias of examiner, and four is inclusion exclusion criteria like number or roots. Age of patient base, ethnicity of patient base, and amount of dentistry the teeth have had impact the results as well. Failing teeth that we extract and teeth we treat (especially retreat) in an endo office will be more likely to have complex anatomy since that is likely why we did the extraction or sent the tooth to the endo office in the first place, Wolcott 2005 shows this.  Second year endo students find more than first year, so experience matters Palazzolo Endodontic Practice 2015 and Corcoron 2007.

µCT image of maxillary first molar

Lit Review of 8400 teeth 2 canals in 57% – (61% in lab studies and 55% clinical studies) Cleghorn 2006 JOE

µCT MB2 studies – Are most accurate

Interesting classification system used in µCT study on 179 Egyptian teeth (some exuding criteria) that were extracted without dental work. Not sure how that selection criteria impacts the results, could be older patients with perio or younger patients with decay that can not afford dental work. Briseño-Marroquín JOE 2015 64% had MB2 or MB3 at some point along path 38% had 2 foramina 2% had 3 foramina 14% start as 2 but join back

Verma 2011 IEJ µCT 20 teeth MB2 90%. Communications in 55%. 1 apical foramen 15%, 2 foramina 20%, 3+ foramina 65%. Accessory canals 85%. About 1/3 could not be classified by Vertucci or Weine (Prob why above study was done)

Somma 2009 IEJ 30 teeth µCT – MB2 80% (42% of these were independent). Communications between the two canals were found in all specimens, with isthmuses in 71% of the cases. 1 apical foramen 37%, 2 apical foramina 23%, 3+ 40%.  So good luck!!!

What is an isthmus vs what is a canal?

Sometimes the difference is obvious and sometimes it is highly subjective. This video shows an isthmus between the MB2 and the MB1. However, what if the canal ends where this isthmus is? Is that then an MB2 that joins?

First molar MB2 study CBCT

5250 teeth in multicenter study 74% with different offices ranging from 48% in Venezula to 98% in Belgium. 3 roots (94% of teeth are), males and younger patients increased likelihood of MB2, again I feel this is simply because easier to see on bigger males and less calcified in youth. Martins 2018 JOE

85% of teeth with 3 roots, which 99% had in their study, have an MB2. .6% have MB3 and males had more MB2 (89%), possibly because bigger and thus easier to see? Zhang JOE 2017

25% one canal and 27% have 2 POE. 75% have 2 at some point. Ghobashy JOE 2017

Normal position of the MB2 and one of very rare times we utilize dental pins.

Anatomy studies MB2 non-µCT

Palazzolo Endodontic Practice 2015  64% MB2, more in men (bigger?), more in younger=less calcified (70% drop to 39% both first and second though), more in those without crown=less calcified and maybe better access, and more in older endo residents

Silva JOE 2014 – Brazil CBCT  314 teeth 3 roots 3 canals 53%,  3 roots 2 MB canals 43%, 2 roots with 1 canal in mesial and 2 canals in distal 3% and 1% reverse of that.  Interestingly, .65% 3 separate 2 canals in palatal

Brazil CBCT study May 13 – 86-91% MB2 PROVIDED dealing with a three rooted molar Reis JOE 2013

Table 1. The Total Number of Teeth, Teeth with 3 Roots, and the Presence/Absence of MB2 Canals in 3-rooted First and Second Maxillary Molars

Table 2. The Prevalence of MB2 Canals According to Root Third Assuming have an MB2 (obviously)

Korean Population CBCT study 2012     64% MB2 1.25% DB2   .25% single root and fused .73%  Kim JOE 2012

Jordan study 2007 Smadi 63% under 3.5x and 57% naked eye.  They also state in this study that max first molars have highest failure rate.  I am of opinion this is low as 3.5x is not a high mag.  I use 6x for everything and have used 2.5, 3.5.4.5, and 6.0 in my career and can say that the jump from 3.5 to 4.5 made a difference for me.  Studies have shown increase in mag increases ability to locate MB2.

Shahi J Dent Rest Dent 2007 Iranian 62% have 4 or more canals so likely close to 62% MB2

Corcoran 2007 JOE 37% to 62% from beginning to end of endo residency.  Initial experience helps

Endo program Hartwell 2007 JADA 70% – The results of this study demonstrate that it is imperative for any dentist performing root canal therapy on maxillary first molars to examine carefully the pulpal floor to locate all canals, especially the second mesiobuccal canal.

Jung May 2005 JOE 81% MB2 47 Korean teeth Scope used

Wolcott 2005 JOE Used very strict definition of MB2 (not sure what that means) 3578 teeth but includes retreats so little lower 58% found in untreated teeth  66% in retreats

al Shalabi IEJ 2000 MB2 78% the occurrence of two canals and transverse anastomoses decreased significantly with increasing age

Stropko JOE 1999 Clinical 1096 conventionally treated maxillary molars. MB2 73% separate canal in 55%. However, as the operator became more experienced, scheduled sufficient clinical time, routinely employed the dental operating microscope, and used specific instruments adapted for microendodontics, MB2 canals were located in 93.0% of first molars and 60.4% in second molars.

Thomas IEJ 1993 216 extracted teeth 74% had MB2, calcification beginning in all samples by 10 years old

Kulild 1990 JOE 54% by hand, 86% with bur, and 96% with scope.  Coronal half microscope Shows better techniques and equipment result in more found

Hartwell and Bellizzi in vivo Dec 82 1982 “A discrepancy was observed when 4 canal maxillary molar obturation was compared with the in vitro studies. Access prep should be reevaluated to facilitate the search and location of the 4th canal in maxillary molars.  It is almost axiomatic to accept the fact the root canal system of the MB root of the max molars frequently have more than one canal.”  BINGO!!!

Weine Oral Surg Oral Med Oral Pathol. 1969 Sectioned and magnification found 53% but both molars so lower than just first molars

Study comparing the different methods of MB2 location

Direct access found 78% with a 15 minute time limit to locate MB2, CBCT found only 69%, access and then CBCT found 87%, and root grinding found 92%. The access may have mroe to do with time than with access to CBCT as 15 minutes was max initially and then 5-10 minutes were allowed after CBCT. What helped more, the extra time or the CBCT? Since access found more than CBCT one must wonder. Hiebert JOE 2017 The conclusion says if don’t find MB2 then take CBCT but how can they say that over spend 5-10 more minutes? Need a study that allows 25 minutes searching direct vs. 15 minutes then CBCT then 5-10 more.

Maxillary molar isthmus studies – C shape canal

Degerness JOE 2010 – 8x scope 80% MB2 and 1% MB3 more of an isthmus study

This and the following photo are why I think there is so much variance in % of MB2 “found” in studies. Is it a fin, an isthmus, or an MB2?

von Arx Int Endo J 2005 76% two canals and isthmus, 10% two canals no isthmus, 14% one canal

Weller JOE 1995 Isthmus study.  50 extracted teeth under scope with dye.  60% MB2 40% only one. The incidence of an isthmus was highest in the apical 3- to 5-mm levels. In teeth that had
two canals, the 4-mm sections contained a complete or partial isthmus 100% of the time.

In vivo study Oct 87 Neaverth 1987 77% MB2 and 3% MB3 – Also has great definition of what they consider an MB2

So are the first and third ones MB2? or figure eight shaped single canals?

C Shaped canal

Martins JOE 2016 1% have c shaped canal somewhere

Foramina studies

Briseño-Marroquín JOE 2015 64% had MB2 or MB3 at some point along path 38% had 2 foramina 2% had 3 foramina 14% start as 2 but join back

Multiple methods Filho JOE 2009 March  67% have MB2 and of those 65.30% exhibited 1 foramen    2 foramina, which were found in 12.25%, 9.37%, and 9.10%, respectively, of the teeth of this study’s ex vivo, clinical, and CBTC

Fogel 1994 in vivo 71% found and 32% had separate apical foramina

Marroquín JOE 2004 523 teeth under 40x mag 71% MB roots had 2 apical foramina.  33% MB roots had accessory foramina

Palatal canal studies

Variation in palatal canals is very low, 2%, but can be much higher in certain Asian ethnic groups reaching 33% in first molars. Nosrat JOE 2017

DB root studies

Fogel lit review JOE 2017 shows 1.7% have 2 canals, unsure how first and second molars differ.

Interesting studies

Almeida AGD GD March 2015 case study of 8 POentry and appears to be 6 POE