12 - morphology of the lower premolars

whats in the essay?

• function + general

• buccal morphology

• lingual

• proximal view

• occlusal morphology

• shape of 3 cusp and 2 cusp type

function + general

inital mastication

canine assistance in chewing

vertical dimension maintenance (between nose and chin)

1st mand premolar has 2 cusps and 1 root, 2nd mand premolar has 3 cusps and 1 root

buccal morphology (+ roots)

• mand 1st premolars = slightly longer than 2nd (longer crown but shorter root)

• mand 1st premolar has sharper buccal cusp (110. degrees) bc of steeper angle of cusp ridges of buccal cusp

• contact areas are more cervical on cusp tip in mand 1st premolars than 2nd

• mesial contact areas are near junction of middle and occlusal thirds

• distal contact area is an EXCEPTION → more occlusal than the mesial contact (its usually more cervical) bc dist marg ridge = more horizonal

• crown shape = pentagon

• mand 1st = 1 B cusp, 1 L cusp

• mand 2nd pm = 1 b, 2 lingual

roots:

• each tooth has one root

• roots tend to taper apically

• apical third bends distally

• mandibular 1st roots are thinner and slightly shorter than mand 2nd premolar roots

lingual morphology

• mand 1st premolar is narrower mesiodistally on the lingual side

• SOMETIMES if 2nd mand premolar has only one lingual cusp (aka only 2 cusps, its narrower lingually)

• ONLY 3 cusp mand 2nd premolars have wider crowns lingually

• mand 1st prem lingual cusp is pointed on the tip and shorter

• mand 2nd molars with ONE lingual cusp - the lingual cusp is smaller than the buccal cusp but still longer than the lingual cusp of the 1st premolar

• single lingual cusp tip is more mesial to the centre line of the root. in the 2 lingual cusp variation, there is one large buccal and 2 lingual cusps

GROOVES:

• MAND 1ST mesiolingual groove separates the mesial slope of the lingual cusp from the mesial marginal ridge (adloff notch)

• on MAND 2ND: LINGUAL groove between mesiolingual and distolingual cusps

proximal view; + root depression mention

• mand molars shaped like rhomboid from proximal view (upper = trap, lower = rhomb)

• distal marginal ridge of mand 1st is more horizontal which is what makes it (uniquely) more occuslal than the mesial marge groove

• in 2nd mand, mesial marge groove = more occlusal like normal

• mesiolingual groove is not present on 2nd mand, only first

• more prominent root depression on distal surface of root in ALL premolars apart from max 1st molar

occlusal morphology

• not symmetirical = more bulk in distal half

  Tooth	Cusp Number	Shape from occlusal view
  Mandibular 1st premolar	2	Diamond-shaped (mesiolingual pushed in)
  Mandibular 2nd premolar	2	Rounded / oval
  Mandibular 2nd premolar	3	Square or rectangular (wider)

3 cusp type - what shape?

Y shape bc of developmental gtooves

occlusla surface contains:

• central pit

• mesial developmental groove

• mesial triangular fossa

• distal developmental groove

• distal triangular fossa

• lingual developmental groove

• supplemental grooves

2 cusp type

• -  one buccal cusp and one well developed lingual cusp is present

• -  a central groove travels in a mesiodistal direction and end in mesial and

  distal fossa (forming ‘H’ shape)