20 and 29: mand 2nd PM Flashcards
3 basic traits of 20 and 29
- more variable (can have 2 or 3 cusps)
- 4 or 5 devo lobes form it
- Y, H, U types; Y is most common (aka 3 cusps most common)
coronal outline of 20/29
- 3 cusp variant DIVERGES (opposite of taper) toward the lingual, this means smaller lingual embrasures and prominent F HOC
- broad M and D contact area
Y type, specific traits
- buccal cusp is M
- ML cusp M and DL cusp D
- B>ML>DL
- 3 named grooves = Mesial (between buccal adn ML) , distal (btwen B and DL), lingual between the 2 lingual cusps
3 grooves of Y types
- distal is between DL adn B
- mesial is between ML adn B
- lingual between ML adn DL
U and H types
- 2 cusp/4 lobe 20/29
- lingual cusp M
- buccal cusp M
- tapers slightly to lingual
- still have large B cusp and broad contact areas
from buccal view, how can you tell left from right in 20/29
MMR is higher/more occlusal than DMR (so this means the top corner when you look at buccal surface is higher, closer to occ.surface on M)
distal slope is longer than mesial, B cusp to mesial
promixal contacts, 20/29, from buccal view
M adn D contacts near jxn of occlusal and middle thirds of crown
CEJ of 20,29
still curves
buccal view of 20/29–contacts and ridges and slopes
contacts: both at jxn of occlusal and middle thirds
marginal ridges: MMR higher…more occlusal **you can tell left from right
slopes: distal slope is longer because cusp is mesial
20/29 vs 21/28 length
total length of 1st mand.PM is longer (21/28)
-crown of 20/29 is shorter
20/19 lingual view
- you can see ALL cusps
- ML is larger than DL
- CEJ flat
- crown tapers to lingual if 2 cusps but diverges if 3
- root usually tapers to lingual
proximal views of 20/29
- buccal cusp position is more to the buccal than on 21/28
- flat CEJ
- HOC: buccal is at jxn of cervical and middle 1/3 & lingual is middle third
