2. Tooth Morphology Flashcards
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)
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
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
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
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)
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)
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
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
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
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
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
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
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
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
15
Q
Upper molars have … roots. Which cusp is largest?
A
- 3 roots (2 buccal, 1 palatal)
- mesiopalatal
