premolars revision - dentition
TRANSCRIPT
Lecturer
Oral biology department
BY
Dr. Rehab Ali
Maxillary first premolar
It has 5 aspects:
Buccal Lingual Mesial Distal
occlusal
Maxillary second premolar
It has 5 aspects:
Buccal Lingual MesialDistal
occlusal
Beginning of calc.
(month)
Crown completed
EruptionRoot completed
4
45
53
3
1.5-2y
11-12
2-2.5y
10-11
94-5m 11
10-12
10-12 +3 ye
ars
-5 ye
ars
Geometric outline of the crown
• Facial and lingual aspects have trapezoidal out line.
The smallest uneven side cervically.
Facial Outlines and surface anatomy of the crown
4 5
B cusp is long and pointed B cusp is short and blunt
Longer M slope than D Shorter M slope than D
Mesial contact area in the M1/3 while distally more occlusal.
Mesial contact area at the jun. of O and M1/3 while distally more cervically.
MD D M
Cervical line curved root wise. Cervical line less curved.
4 5MD D M
Prominent B ridge Less prominent B ridge
Short root. Longer root.
Lingual outline and surface anatomy of the crown
The L cusp is shorter by 1 mm than the B cusp.
The L and B cusps are nearly of same height (0.5 mm shorter)
80%, 2 roots
L root is shorter than B root.
Rare to have 2 roots(20%)In case of two roots the L root is shorter.
4 5
Do you like to be a real dentist
or…..?
Geometric outline of the proximal aspect
Trapezoidal in shape
Smallest uneven sides occlusaly
Mesial aspectDistal aspect
Mesial aspect
B cusp is longer than L cusp by 1mm
4
The cusps are nearly at the same level.
The occlusal table is wide.
5
Mesial DG and canine fossa.
The crown surface is smooth and convex while root has shallow developmental depression.
The occlusal table is wide,but narrower than 4.
Root trunk about half the root length.
4 5
Contact area:
At the middle third (OC dimension) and slightly buccal to midline (BL dimension)
At the jun. of O and M 1/3 (OC dimension) and slightly buccal to midline (BL dimension)
Mesial aspect
MMR at the M1/3 MMR positioned more occlusal.
Distal aspect
4 5
DMR more occlusal than MMR DMR more cervical than MMR
CA occlusally positioned and more buccally than MCA.
CA cervically positioned and more buccally than MCA.
Root trunk is long as the bifurcation is near apical 1/3
Surface is smooth and convex except shallower DD on the root trunk than mesially.
Distal aspect
54
One root and if 2 the bifurcation will be more apically.
Surface is smooth and convex except deeper DD in the middle of the root than mesially.
I hope you are better now,
MD MD
Occlusal aspect54
It’s hexagonal It’s oval
B & L triangular ridges.
M & D marginal ridges
B & L triangular ridges.
Thicker M & D MRs
Long Central DG
M and D fossae.
M developmental groove
54
Shorter Central DG.
Not found.
M and D fossae.
Not found. Supplemental grooves could be found (wrinkled)
Pulp cavity.
MD section BL section
Pulp chamberNarrow Wide
Root canals
2 root canals (B&L) but rare 3 canals
L canal is larger &more accessible
In 5 one centralized large canal is present, but may two canals could be exist.
Mandibular first premolar
Buccal Lingual Mesial
occlusal
It has 5 aspects:
Distal
Mandibular second premolar
Buccal Lingual Mesial
occlusal
It has 5 aspects:
Distal
Geometric outline of the crown
• Facial and lingual aspects have somewhat wider trapezoidal shape due to wider cervical third than 4.
54
Facial Outlines and surface anatomy
B cusp
pointed and long
Well prominent B ridge Less prominent B ridge
B cusp
short and less pointed
Lingual outline and surface anatomy
54
The lingual surface is convex with maximum convexity at M 1/3
The L cusp is short and small reaching 2/3 the crown length and has a pointed tip .
ML developmental groove at the ML line angle.
Two cusp type
L cusp is shorter and smaller than B cusp but larger than of 4
The surface convex with maximum convexity at O1/3.
No MLDG
5Three cusp type:
ML cusp is longer and larger than DL cusp. They both shorter than B
cusp and less pointed .
DM
The surface convex with maximum convixty at O1/3.
The L developmental groove between the 2 cusps
N.B. Very little or no lingual convergancy.
Proximal outlines
54
Lingual inclination well prominent
Lingual inclination less prominent
Rhomboidal in shape with narrow occlusal table.
54
Maximum convexity at M1/3 Maximum convexity at O1/3
B cusp tip on line with junction
of B & M 1/3 of the root.
The mesial and distal marginal ridges are straight
L cusp is shorter and smaller than B cusp but larger than of 4
The B cusp centered over the root.
The L cusp is short and small reaching 2/3 the crown length
The mesial MR is oblique while distally is straight
.
ML developmental groove present at the junction of L
and M surfaces .
Proximal surface anatomy
Mesial aspectDistal aspect
Contact area is broader, MCA is directly situated cervically and lingually below the B cusp
positioned.
Contact area nearly at same level
Three cusp type:
ML cusp is longer and larger than DL cusp .
DL cusp is shorter and smaller than ML cusp .
Mesial aspect Distal aspect
Both lingual cusps are shorter than the buccal cusp and less pointed
Surface anatomy is simillar to that of 4
Geometric outline of the occlusal aspect
54Two cusp type:
It’s diamond-shaped.
Lingual convergence is sharp.
The outline is oval
Slight lingual convergence
Three cusp type:
The outline is square
Surface anatomy of occlusal aspect:
Elevations:
B triangular ridge.
L triangular ridge.
M & D marginal ridges
Transverse ridge
54
Depressions:
Central developmental groove
Mesiolingual developmental groove
54
Central developmental groove
)H or U shaped(.
M and D triangular fossae.
)both r circular,but D is deeper(
M and D triangular fossae (M fossa is oval while D fossa is circular,larger & deeper) snake eyes
Elevations:B triangular ridge.
L triangular ridges (ML &DL) .
M & D marginal ridges
Depressions:
Developmental groove (Y shape formed of MB,DB & L grooves).
M and D triangular fossae.
Central fossa with central pit.
Remember the supplemental grooves!!!
Three cusp type: