21 and 28: mandibular 1st PM

Question 1

occlusion - where is force/stress directed

Answer 1

down the long axis of tooth to protect tooth itself and the underlying structures

Question 2

stamp vs shearing cusp

Answer 2

stamp = fxnal cusp (MAX LINGUAL)

shearing = non-fxnal

Question 3

stamp cusps

Answer 3

functional

• max lingual
• mand buccal

Question 4

shearing cusps

Answer 4

non fxnal

• mand lingual
• max buccal

Question 5

when do 21-28 erupt

Answer 5

10-12 yo

Question 6

bell shape tooth

Answer 6

mand 1st PM, 21/28

• cervical constriction
• flip tooth upside down to see bell

Question 7

shark tooth

Answer 7

21 and 28 – buccal cusp way taller than lingual adn also buccal cusp tip is half way between B/L

Question 8

occlusal view of 21 and 28

Answer 8

• diamond outline
• mesial outline narrower than distal, distal bulges out
• cusp tips mesial
• facial cusp slopes = half way B/L divider

Question 9

F and L HOC on 21/28

Answer 9

mesial to center from occlusal view

Question 10

21/28 proximal contacts

Answer 10

• -from occlusal view, in middle third, almost centered B/L
• -M contact is narrower than D
• -from buccal, you see that M contact is MORE CERVICAL than D, which is unique

Question 11

why are 21/28 unique in terms of proximal contacts

Answer 11

M is more cervical than D

Question 12

transverse ridge

Answer 12

on 21/28, unique -feature

• triangular ridge of facial adn lingual togetehr make the transverse ridge
• each ridge goes from cusp point down to center of occlusal table and there they meet to form one big groove

Question 13

unique features of 21/28

Answer 13

• transverse ridge
• snake eyes
• ML devo groove
• shark tooth
• 45 tilted occ.table

Question 14

ML devo groove

Answer 14

on 21/28, from M pit on occlusal surface to ML surface of crown adn even onto root

Question 15

buccal view of 21/28

Answer 15

• UNIQUE proximal contacts, M is more cervical
• cusp tips M to center
• D slope longer
• CEJ getting flat

Question 16

lingual view of 21/28

Answer 16

• crown/root taper to lingual
• occlusal table visible bc of 45 tilt to lingual
• can see facial part of transverse ridge
• B adn L cusp tips M to center

Question 17

proximal view 21/28 – how do you tell M from D?

Answer 17

• -M has ML devo groove peeking over side

- -MMR parallels occlusal table

Question 18

proximal view 21/28

Answer 18

• B cusp is centered B/L over long axis of root
• ML devo groove on mesial surface
• HOC: buccal, cervical 1/3 & mesial, middle 1/3
• 45 tilt of occlusal table to lingual
• MMR parallel to oclusal tilt

Question 19

notable about 21/28 occlusal tilt

Answer 19

internal anatomy mirrors external anatomy – danger because pulp very close to occlusal surface especially in kids