Mandibular First Molar Anatomy

Study Notes

The lingual cusps are pointed and separated by the lingual groove.
The mesiolingual cusp is the widest mesiodistally, with its cusp tip higher than the distolingual cusp.
The cervical line lingually is irregular.
The roots are about 1 mm longer lingually than buccally.

Two cusps and one root are visible from the mesial aspect.
The buccolingual measurement is greater at the mesial portion than at the distal portion.
The contact area is located at the occlusal third and is almost centered buccolingually.
The buccal outline of the crown is convex above the cervical line.
The lingual outline is straight in the lingual direction above the cervical line to the middle third and then becomes convex.

The distal contact area is placed just below the distal cusp ridge and is slightly higher than the mesial contact area.
The cervical line distally usually extends straight across buccolingually and may be irregular.

The mandibular first molar is hexagonal in shape from the occlusal aspect.
The crown measurement is 1 mm or greater mesiodistally than buccolingually.
The buccolingual measurement of the crown is greater on the mesial than on the distal.
The crown converges lingually from the contact areas.
There is a major fossa (central fossa) and two minor fossae (mesial triangular fossa and distal triangular fossa).

The second molar is smaller than the first molar by a fraction of a millimeter in all dimensions.
The roots are not as broad as those of the first molar, nor are they as widely separated.
There is only one developmental groove buccally (buccal groove).
There are four well-developed cusps of nearly equal size, with no fifth cusp or distal cusp.
The DB developmental groove is absent.
The crown and root converge lingually to a lesser degree than the first molar.
The cervical ridge buccally is less pronounced than the first molar.
The B and L developmental grooves meet the central developmental groove at right angles at the CP, forming a cross that divides the occlusal surface into four nearly equal parts.

The mandibular third molar varies considerably in different individuals and presents many anomalies in form and position.
It supplements the second molar in function, but is seldom as well developed as the second molar.
The crown portion or roots may be irregularly developed, with 5 or more cusps, or undersized roots that are more or less malformed.
The roots are generally two in number, shorter in length, and tend to be fused together.
The roots may show a distinct distal curve.
Mandibular third molars are most likely to be impacted, partially or completely within the jaw due to insufficient space for eruption.
They may be horizontally directed and sometimes congenitally absent.