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Mandibular Trapezoidal

# Mandibular First Molar

[Previous tooth Mandibular Second Premolar FDI 35 · 45](https://endo-guide.app/access-cavities/mand-second-premolar)[Next tooth Mandibular Second Molar FDI 37 · 47](https://endo-guide.app/access-cavities/mand-second-molar)

![Mandibular first molar — occlusal access with three orifices: mesiobuccal, mesiolingual and distal](https://endo-guide.app/images/access-cavities/atlas/mandibular-molar-3canal.webp)

Mandibular first molar — occlusal access with three orifices: mesiobuccal, mesiolingual and distal

 Average Length 21.0 mm

 Root Development 9-10 years

 Universal # 19, 30

 FDI # 36, 46

### Access Cavity Design

Shape Trapezoidal / Rectangular

OrientationBase faces mesial, shorter side faces distal

Entry PointMesial two-thirds of occlusal surface

Do Not Invade

- Mesial marginal ridge

### Canal Anatomy

#### Configurations

2 roots, 3 canals (MB, ML, D)~67%

2 roots, 4 canals (MB, ML, DB, DL)~28-30%

3 roots (Radix Entomolaris)3-6% globally; 5-30% in East Asian populations

#### Canal Positions

 MB Mesiobuccal

Slightly buccal to mesiobuccal cusp tip

 ML Mesiolingual

Slightly lingual, connected to MB by isthmus

 D Distal

Central when single (oval), or DB + DL when two

 MM Middle MesialUp to 46.2% with magnification

Between MB and ML, often below pulp floor level

 RE Radix Entomolaris3-6% globally; 5-30% in East Asian populations

Extra distolingual root with sharp buccal curvature

#### Danger Zones

- ⚠Mesial furcation perforation
- ⚠Stay within mesial two-thirds of occlusal surface

### Clinical Tips

Warning

Access shape is TRAPEZOIDAL/RECTANGULAR, NOT triangular — wider mesially

Technique

Middle mesial canal (MMC): anatomical prevalence 5-15%; detection up to 46.2% with microscope + troughing

Tip

Microscope increases MMC detection from ~7% (naked eye) to ~46% — magnification transforms outcomes

Technique

For Radix Entomolaris: Extend access distolingually; flexible NiTi files essential for sharp buccal curvature

Technique

SLOB technique + 20-30 degree mesial or distal angulation reveals superimposed RE on PA

### Anatomical Variations

#### Middle Mesial Canal (MMC)

Up to 46.2% with magnification

Between MB and ML canals, often only accessible below pulp floor

Access Modification: Trough along developmental groove connecting mesial canals

#### Radix Entomolaris

3-6% globally; 5-30% in East Asian

Extra distolingual root with sharp buccal curvature and apical 'kick'

Access Modification: Extend distolingually, trapezoidal shape with distal base

 Ethnic Variation

East Asian (Chinese, Korean, Eskimo)5-30%

Caucasian, African, Indian<5%

### Other teeth in the atlas

Maxillary

[Maxillary Central Incisor](https://endo-guide.app/access-cavities/max-central-incisor)[Maxillary Lateral Incisor](https://endo-guide.app/access-cavities/max-lateral-incisor)[Maxillary Canine](https://endo-guide.app/access-cavities/max-canine)[Maxillary First Premolar](https://endo-guide.app/access-cavities/max-first-premolar)[Maxillary Second Premolar](https://endo-guide.app/access-cavities/max-second-premolar)[Maxillary First Molar](https://endo-guide.app/access-cavities/max-first-molar)[Maxillary Second Molar](https://endo-guide.app/access-cavities/max-second-molar)

Mandibular

[Mandibular Central Incisor](https://endo-guide.app/access-cavities/mand-central-incisor)[Mandibular Lateral Incisor](https://endo-guide.app/access-cavities/mand-lateral-incisor)[Mandibular Canine](https://endo-guide.app/access-cavities/mand-canine)[Mandibular First Premolar](https://endo-guide.app/access-cavities/mand-first-premolar)[Mandibular Second Premolar](https://endo-guide.app/access-cavities/mand-second-premolar)[Mandibular Second Molar](https://endo-guide.app/access-cavities/mand-second-molar)

For Educational Purposes Only

Access cavity designs based on established endodontic principles. Always refer to current literature and clinical guidelines.

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