Maxillary 2nd Premolar - Important Points

General Identification

• Universal number: #4 (right), #13 (left) - FDI: 15 (right), 25 (left)
• Succeeds: maxillary 2nd deciduous molar
• Eruption: 10-12 years
• Calcification complete: ~14 years

Crown Morphology

Occlusal Surface

• Oval outline with the long axis buccopalatal (same as 1st premolar)
• Mesiodistal fissure separates buccal and palatal cusps
• Key difference from 1st PM: the buccal and palatal cusps are nearly equal in height - this is the hallmark distinguishing feature
• Supplemental grooves radiate from the central groove, giving a more complex occlusal surface than the 1st premolar
• No mesial marginal groove (unlike the maxillary 1st premolar which has a distinct mesial marginal groove/notch)

Buccal Surface

• Single buccal cusp, slightly shorter and more rounded than in the 1st premolar
• No mesial developmental groove on the buccal surface (present on max 1st PM)
• Buccal ridge is prominent
• Crown appears more symmetric (less trapezoidal) than the 1st PM

Palatal Surface

• Palatal cusp is slightly shorter than buccal cusp (but much closer in height than in the 1st PM)
• Palatal surface is smooth and convex
• Smoother than the 1st premolar overall

Proximal (Mesial/Distal) Surfaces

• Mesial contact area: at the junction of middle and occlusal thirds
• Distal contact area: slightly more cervical than mesial
• No mesial concavity (unlike the max 1st premolar, which has a prominent mesial root concavity)

Root and Root Canal Anatomy

Key Distinguishing Features from Maxillary 1st Premolar

Clinical and Endodontic Importance

1. Access cavity: Oval-shaped in a single-rooted tooth; if 2 canals, two separate orifices are found
2. Root proximity to maxillary sinus: The roots of upper 2nd PM are in close proximity to the floor of the maxillary sinus - clinically significant in extractions and sinus lifts
3. During extraction: Buccal bone is thin; palatal movement used (buccal-then-palatal luxation)
4. Local anesthesia: Posterior superior alveolar (PSA) nerve block covers it; supplemented by greater palatine block for palatal soft tissue
5. Nerve supply: PSA nerve (branch of maxillary/V2), palatal soft tissues by greater palatine nerve
6. Missing tooth pattern: The 2nd PM is one of the more commonly congenitally absent teeth (along with mandibular 2nd PM and maxillary lateral incisors)
7. Furcation: No furcation in single-rooted form; when 2 canals exist, can have apical split

Vertucci Root Canal Classification (Endodontics Exam Favorite)

• Type I (1 canal throughout): Most common in max 2nd PM
• Type II (2 canals join into 1 apically): Seen
• Type IV (2 separate canals, 2 apical foramina): ~24-30% of cases
• Always check for additional canal with CBCT or careful probing

Quick Exam Summary

• Only permanent tooth in the maxilla to replace a deciduous molar while being a premolar (bicuspid) in function
• Buccal and palatal cusps nearly equal in height - most reliable crown identification point
• Usually single-rooted and single-canaled - contrast with 1st PM
• No mesial developmental groove on buccal surface
• Proximity to maxillary sinus is clinically important
• Congenital absence is relatively common

• Scott-Brown's Otorhinolaryngology Head & Neck Surgery, p. 688 (permanent teeth section)