Mandibular First Premolar: Tooth Morphology

The mandibular first premolar is the first posterior tooth in the mandibular dental arch. It is smaller in size as compared to the mandibular second premolar. It appears similar to the mandibular canine because of the large buccal cusp and small lingual cusp.  In some specimens, the lingual cusp is similar in shape to a cingulum.

Development and Eruption of Mandibular First Premolar

Following is the summary of the development and eruption of the mandibular first premolar.

• Initiation of calcification of premolar: 1-2 years
• Completion of the crown of premolar: 5 – 6 years
• Eruption of premolar: 10-12 years
• Completion of the root of premolar: 12- 13 years

Buccal Aspect

• A well-developed buccal ridge is present.
• The buccal cusp is large and pointed, and it is the only cusp in occlusion.
• Two cuspal slopes are associated with the buccal cusp; among them, the mesial cuspal slope is larger than the distal cuspal slope.
• The root of the mandibular first premolar is identical to the mandibular canine except that it is slightly shorter in length.

Lingual Aspect

• The crown and root of the mandibular first premolar taper towards the lingual aspect.
• Lingual cusp is always smaller as compared to the buccal cusp. Due to this difference, the occlusal surface, buccal cusp, and cuspal slopes are visible from the lingual aspect.
• The premolar inclines the lingual aspect, and this inclination is another reason for the visibility of the occlusal surface of the tooth.
•  Another important identification feature of the mandibular first premolar is the presence of the lingual developmental groove. The lingual developmental groove is closely associated with the lingual cusp towards the mesial aspect and is known as the mesiolingual developmental groove.
• It has a single root, and on the lingual aspect, the root tapers and forms a ridge. 

Mesial Aspect

• The buccal surface is more convex. As the result of this convexity, the tip of the buccal cusp of the mandibular first premolar is centered over the root.
• The lingual cusp of the tooth is in line with the lingual outline of the root.
• Mesial marginal ridge inclines towards the lingual aspect.
• Due to the inclination of the mesial marginal ridge, part of the occlusal surface is visible from the mesial aspect.
• The mesiolingual developmental groove is visible from the mesial aspect.

Distal Aspect

• Distal marginal ridge is slightly higher as compared to the mesial marginal ridge.
• The distal marginal ridge is smooth with no developmental groove or depression.
• The distal surface of the root is convex.

Occlusal Aspect

• The mandibular first premolar occlusal outline is a roughly diamond shape.
• A prominent buccal ridge is visible from the occlusal aspect.
• The mesial and the distal marginal ridges are well developed.
• From the buccal cusp tip, a ridge descends to the center of the occlusal surface. This ridge is known as the buccal triangular ridge.
• Similarly, from the tip of the lingual cusp, a ridge descends to the center of the occlusal surface. The lingual triangular ridge is small and less developed.
• There are two triangular depressions adjacent to the ridges. These depressions are named the mesial and the distal triangular fossae.

Video lecture of Mandibular First Premolar Dental Morphology

Demonstration of Mandibular First Premolar Morphology on tooth models