Dental Anatomy of Lower Premolars and Mandibular Growth
Classified in Biology
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Lower First Premolar
Prominent Elevations & Depressions/Snake-Snail Eye Lingually
Chronology
- Enamel: 5-6 years old
- Eruption: 10-11 years old
- Root: 12-13 years old
Geometry
- Lingual/Buccal: Trapezoid; short side cervical
- Mesio-Distal: Rhomboidal
- Occlusal: Diamond
Buccally
- Cervical Ridge
- Buccal Ridge
- Mesio-Distal Buccal Developmental Groove
Lingually
- Mesio-lingual Developmental Groove
Mesially
- Mesio-lingual Developmental Groove
Mesial Contact Area
- Junction between buccal and middle thirds
Distal Contact Area
- Middle third
Occlusally
- 2 well-developed cusps
- Each cusp: triangular ridge
- Mesial/Distal Marginal Ridges
- Triangular Fossae
- Developmental Pits
- Central Developmental Groove
- Transverse Ridge
- Mesio-lingual Developmental Groove
Lower Second Premolar
3-Cusp Type has 5 Lobes of Calcification/No Lingual Convergence
Chronology
- Enamel: 6-7 years old
- Eruption: 11-12 years old
- Root: 13-15 years old
Geometry
- Lingual/Buccal: Trapezoid; short side cervical
- Mesio-Distal: Rhomboidal
- Occlusal: Square (3-cusp), Round (2-cusp)
Buccally
- Cervical Ridge
- Buccal Ridge
- Mesio-Distal Buccal Developmental Groove
Lingually
- Disto-lingual Developmental Depression
Mesial Contact Area
- Junction between buccal & middle thirds
Distal Contact Area
- Middle third
Occlusally
- 2 or 3 well-developed cusps
- Each cusp has a triangular ridge
- Mesial/Distal Marginal Ridges
- Triangular Fossae
- Developmental Pits
- Central Developmental Groove
- Central Pit Fossa (3-cusp only)
- Supplemental Grooves
- Lingual Ridge (3-cusp only)
Mandibular Growth Stages
At Birth
- Size: Too small; no teeth erupted; deciduous teeth enclosed in crypts
- 2 Halves of Mandible: 2 separate halves still not united
- Mental Foramen: Below crypt of deciduous canine
- Mandibular Canal: Near lower border of mandible
- Angle: 170 degrees
- Condylar Head: Lower than coronoid process
- Sigmoid Notch: Shallow
Childhood
- Size: Increased a bit in height; deciduous teeth erupted
- 2 Halves of the Mandible: Joined at symphysis
- Mental Foramen: Below socket of deciduous canine
- Mandibular Canal: Higher than mylohyoid line
- Angle: 140 degrees
- Condylar Head: Lower than coronoid process
- Sigmoid Notch: Deeper than at birth
Adult
- Size: Increase in height; permanent teeth eruption; growth of alveolar process
- 2 Halves Mandible: Appearance of mental protuberance
- Mental Foramen: Socket of lower 1st premolar; midway between upper & lower border
- Mandibular Canal: Parallel to mylohyoid line
- Mandible Angle: 110-120 degrees
- Condylar Head: Higher than coronoid process
- Sigmoid Notch: Deep