Mandibular Molars Root Anatomy and Access Cavities

Dr. Mohammad Hammad

Lower first Molar Internal anatomy

• The earliest permanent tooth to erupt. • Usually has 2 roots and 3 or 4 canals.

MB and ML in the mesial root and D (DB and DL) in the distal root.

• Percentage of a MM canal ranges from 1% to 15%.

• 4 pulp horns; mesiobuccal, mesiolingual, distobuccal and distolingual.

• The pulp chamber cross-section is rhomboid or trapezoid in shape.

• Mesial root is wider than the distal root.

• Roots curves mesially from cervical line to middle third then angles distally to the apex.

• Thin concave distal wall of the mesial root.

• MB canal usually more curved than ML canal.

Mesial curve

Distal curve

Thin concave wall

Number of canals in the Mesial root:

1. One canal 40 (28)%, 43 (29)%.2. Two canals 59 (8)%, 50 (6)%.3. Three canals 1%, 7%.(Vertucci et al., 1984; Gulabivala et

al., 2001)

• Orifices of all canals lie in the mesial 2/3 of the crown.

• MB orifice is usually underneath the MB cusp.

• ML orifice is usually lingual to the central grove.

• MM might be found in the groove between the ML and MB.

MesialDistal

Lingual

Buccal

• If a single distal orifice, usually oval buccolingually and located distal to the buccal groove.

• If two distal canals (DL and DB), they are round from orifice to apex.

• Number of canals in the distal root:1.One canal 85 (15)%, 83.3 (4)%.2.Two canals 15 (8)%, 16 (3)%.3.Three canals 0%, 0.7%.(Vertucci et al., 1984; Gulabivala et al.,

2001)

• Access cavity is usually rhomboid or trapezoid.

• Mesially the access cavity should not invade the mesial marginal ridge.

• Distal extension should allow straight-line access to the distal canal(s).

Access cavity of lower first molar

• Removal of caries and restorations. • Access cavity has mesial and distal

boundary limitations. • Mesial boundary is a line connecting the

mesial cusp tips. • Distal boundary is a line connecting the

buccal and lingual grooves. • Starting location is on the central groove

halfway between the mesial and distal boundaries.

• Round or fissure bur placed perpendicular to occlusal table. Penetration should be directed towards the largest canal, distal canal until drop-in is felt.

• Unroofing is carried out. Number and location of orifices determine shape and location of access cavity.

• Removal of cervical dentine bulge and finishing.

Lower second molar Internal anatomy

• Smaller than the lower first molar and more symmetrical.

• Pulp chamber and canal orifices are smaller than that of the first molar.

• The tooth might have one, two, three or four canals.

• The two mesial canals are closer than that of the lower first molar.

• Number of canals in the mesial root:1. One canal 65 (38)%, 56 (52)%.2. Two canals 35 (9)%, 40%.3. Three canals 0%, 0%.

(Vertucci et al., 1984; Weine et al., 1988)

• Number of canals in the distal root:1. One canal 95 (3)%, 94.6 (9)%.2. Two canals 4 (1)%, 1.3%.3. Three canals 0%, 1.3%.

(Vertucci et al., 1984; Weine et al., 1988)

• Access cavity is similar to that of the first lower molar when three orifices are located.

• When two orifices are located, the orifices would be equal in size and line up in the buccolingual centre of the tooth. Access cavity would be rectangular in shape.

• Access cavity is oval in the presence of only one orifice, and usually lined up in the centre of the occlusal surface.

Lower third molar Internal anatomy

• It has unpredictable anatomy. Careful examination of root morphology before treatment is essential.

• It might have one to four roots and one to six canals.

• Access cavity might be oval, triangle, rhomboid,…etc. Depends on number and location of orifices.

Teeth with C-shaped root canal system

• First reported in 1979.• Usually found in lower second molars

but can be found in any molar tooth.• The pulp chamber is a single ribbon-

shaped orifice with an arc of 180 degrees or more.

• Starts usually at the mesiolingual line angle and sweeps towards the distal aspect of the pulp chamber.

• Below level of orifice either continue as arc shape until apex or divide into canals.

• Incidence of c-shaped molars have great ethnical variation.

• About 32% in Chinese and Japanese, 19% in Lebanese, 33% in Koreans, 10% Jordanians, 2% Sri Lankan.

• Access cavity shape depends on location and size and shape of pulp chamber. Very difficult to treat such teeth.