2. Tooth Morphology Flashcards

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1
Q

Features of all premolars

A
  • labial surface of buccal cusp is similar to canines
  • all have 2 main cusps (buccal and lingual) seperated by central fissure (mesio-distal occlusal fissure)
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2
Q

How to distinguish upper and lower premolars?

A
  • shape of crown (uppers are angular, oval, flattened mesio-distally or hexagonal for 1sts - lowers are more circular)
  • relative size of buccal and lingual cusps (in lower, buccal inclines lingually and has a prominent buccal cusp and small lingual cusp)
  • uppers are wider bucco-lingually but lowers are wider mesio-distally
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3
Q

Features of upper first premolar
- roots?
- cusps?
- grooves?

A
  • two roots
  • buccal cusp higher and carries buccal ridge on labial surface
  • if no wear in buccal cusp, mesial slope is straight and longer than distal slope (opposite of canines)
  • buccal and palatal cusp seperated by central fissure which can cross mesial marginal ridge and extend onto mesial surface (canine groove)
  • palatal cusp is lower than buccal cusp and tip is more mesial than than buccal cusp tip, crown appears asymmetrical
  • crown wider on buccal than palatal
  • occlusal surface contains - buccal and palatal triangular fossa, central fissure, mesio-buccal groove, disto-buccal groove - grooves all join in mesial and distal pits
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4
Q

Features of upper second premolar

A
  • similar to 1st
  • crown smaller and rounder rather than angular
  • buccal and palatal cusps are lower and more equal in size
  • buccal cusp is shorter than upper 1st so compressed occlusal surface and wider marginal ridges
  • mesial slope of buccal cusp is usually shorter than distal slope like canines (diff to 1st premolar)
  • root is single but deeply grooved on mesial and distal surfaces (2 root canals joining at apical foramen)
  • no canine groove or canine fossa on mesial surface
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5
Q

Features of lower first premolar

A
  • smallest premolar more like a canine
  • circular crown with dominant buccal cusp and small lingual cusp
  • from mesial occlusal pit, groove goes onto mesial marginal ridge (canine groove)
  • root is single, conical and slightly flattened mesio-distally (single root canal)
  • disto-lingual accessory cusp is frequent and almost as large as lingual cusp (3-cusp type)
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6
Q

Features of the lower second premolar

A
  • crown larger than first and circular
  • lingual cusp better developed but smaller than buccal cusp (smaller than upper) buccal cusp not as centered over root
  • 2 cusps have a well defined central fissure ending in mesial and distal pits (distal fissure is deeper)
  • mesial slope of buccal cusp shorter than distal (like canines)
  • mesial marginal ridge higher than distal
  • no canine groove or fossa
  • single root, conical and nearly round
  • single root canal
  • disto-lingual accessory cusp is almost always well formed and nearly size of lingual (3 cusp more common than 2)
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7
Q

Differences between upper and lower premolars

A
  • upper crowns have larger lingual cusps than lowers
  • lower crowns are rounder and rotate between fingers - upper are more angular/oval
  • upper crowns have strong median grooves between cusps - lower is weaker
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8
Q

How to compare upper 1st and 2nd premolar

A
  • 1st has smaller palatal cusp relative to buccal whereas in 2nd they’re pretty equal
  • in occlusal, 1st crowns are less symmetrical and more angular than 2nd
  • 1stmore deeply indented mesial occlusal outline than 2nd
  • palatal cusp tip skewed mesially in uppers
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9
Q

Differences between lower 1st and 2nd premolars

A
  • 1st smaller lingual cusp than buccal, 2nds have larger lingual cusp
  • 1st less sym than 2nds
  • 2nds have small second distal lingual cusp
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10
Q

How to differentiate upper and lower molars?

A
  • upper have 3-4 major cusps, lower have 4-5
  • upper are rhomboid shape occlusally, lowe are square or rectangular
  • upper cusps are asym mesiodistally, lower are more so
  • upper have 3 roots, lower have 2 usually
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11
Q

Features of the upper first molar

A
  • rhomboid shaped crown
  • 4 main cusps seperated by H-shaped occlusal fissure
  • mesio-palatal cusp largest - connected to buccal cusp by mesial marginal ridge and disto-buccal cusp by oblique ridge enclosing central fossa
  • accesory cusp of varying size called tubercle of Carabelli on palatal surface of mesio-palatal cusp
  • 2 buccal cusps (almost equal in size) separated by buccal fissure
  • disto-palatal cusp (smallest) separated from mesio-palatal by palatal fissure curving distally to end in distal pit
  • 3 roots, 2 buccal and 1 palatal
  • palatal root is longest and thickest, 3 or 4 root canals, one occupying mesio-buccal root divides into 2
  • palatal root canal is wider than buccal
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12
Q

Features of upper second molar

A
  • 3 types
  • first type (most frequent) like the 1st molar but smaller and disto-palatal cusp is smaller - 4 cusps
  • type 2 is heart shaped and has 3 cusps (no disto-palatal). palatal seperated from buccal by T-shaped fissure
  • type 3 (least frequent) is produced by fusion of mesio-palatal and disto-buccal, makes oval crown possessing 3 cusps in a straight line
  • no cusp of Carabelli
  • 3 roots - 2 buccal 1 palatal
  • less divergent than 1st and can be fused. root canals similar to 1st but division in mesio-buccal canal in infrequent
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13
Q

Features of upper 3rd molar

A
  • most variable
  • most commonly like a Type 2 2nd molar (heart shaped)
  • roots smaller, vary in numbers and are fused
  • reduced type can resemble 2nd premolar but usually larger and irregular root of fused rootlets
  • retains basic triangular shape in upper but lower can retain square shaoe or reduce to circle
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14
Q

Differences in upper 1st and 2nd molars

A
  • 1st have 4 cusps in rhomboid (mesiopalatal, mesiobuccal, distobuccal and distopalatal), 2nd have 3 in simple triangle without distopalatal
  • 1st have Carabelli’s tubercle
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15
Q

Upper molars have … roots. Which cusp is largest?

A
  • 3 roots (2 buccal, 1 palatal)
  • mesiopalatal
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16
Q

Features of lower first molar

A
  • 5 cusps
  • central fissure from central fossa dividing crown into buccal and lingual half
  • distal part has distal cusp
  • mesial terminates in mesial pit
  • fissure from central fossa divides lingual into mesio-lingual and disto-lingual
  • buccal cusps are rounder and lower than steeper lingual and tips displaced lingually
  • 2 roots (1 mesial, 1 distal) curving distally
  • mesial root deeply grooved
  • 3 root canals - 2 in mesial, 1 in distal (larger)
17
Q

Features of lower second molar

A
  • regular rectangular shape of crown
  • 4 cusps with cross shaped occlusal fissure
  • 2 buccal and 2 lingual cusps with central fissure. - buccal cusps lower and rounder than lingual
  • wider mesially than distally
  • 1 mesial and 1 distal root smaller and less divergent than 1st - may be fused
  • 3 root canals, 2 mesial 1 distal
18
Q

Features of lower third molar

A
  • variable but less than upper 3rd
  • 4 cusps but can be 5 - irregular branching occlusal fissure pattern
  • crown reduced it retains regular shape - rectangular or circular
  • 1 mesial and 1 distal root which are partly fused - one is sub-divided looking like an upper
  • 2 or 3 root canals
19
Q

Compare lower 1st and 2nd molar

A
  • 1st have 5 cusps, 2nd have 4
  • little cusp stuck on behind in 1st is bucally displaced - buccal side has 3 cusps and lingual has 2 in upper
  • mesio-buccal cusp is largest but most worn in lower
20
Q

Explain functional cusps

A
  • the cusp that bites into central fossa of opposing posterior tooth in intercuspal position
  • usually palatal cusps on upper teeth and buccal of lower
  • e.g in lower 2nd is buccal
  • non-functional cusp is guiding cusp