class i [lecture by dr.wedad etman @amcofam]
TRANSCRIPT
Class I lesion affects
�The pit and fissures of posterior teeth Surfaces involved are:Surfaces involved are:
–Occlusal surfaces of premolars & molars
–Occlusal 2/3 of the facial & lingual surfaces of molars
� Palatal surfaces of maxillary incisors
Spread of pit &fissure caries in
enamel & dentin
In enamelCone shape
Base towards DEJ
& apex toward the surface& apex toward the surface
In dentin (Spreads more rapidly than enamel)
Cone shape
Base towards DEJ
& apex towards the pulp
Class I could be :• Simple occlusal cavity S.O.C
• Compound class I (two surfaces)
* Occluso buccal O.B.C
* Occluso lingual or palatal O.L.C /O.P.C
• Complex class I (more than two surfaces)
* occluso bucco lingual O.B.L.C
• Buccal pit
• Paltal pit in anterior
CLASS I SIMPLE OCCLUSAL CAVITY
(OCCLUSAL SURFACE ONLY)
Outline form
Varies in shape according to theVaries in shape according to the
number of cusps
and orientation of pits ad fissures
Resistance form is obtained by
• Outline placed equidistance from the defective pits ,fissures on smooth ,soundtooth structure
• Sufficient width to include the defects, • Sufficient width to include the defects,
pits & fissures and permit insertion of small condenser for placement of amalgam
But otherwise as narrow as possible
(preservation of tooth structure)
Extension for prevention
Black suggested that it was necessary to
• remove additional tooth structure to gain access
Resistance
• remove additional tooth structure to gain access
& visibility
• extend the cavity to self-cleansing areas to
AVOID RECURENT CARIES
Black’s cavity width
1/3 intercuspal distance
CONSERVATIVE APPROACHE
Introduction of amalgams with better properties
& the use of smaller instruments
Resistance
� Cavity width (faciolingual width)
,/- intercuspal distance
(not more than ,-,./ mm)
No extension for prevention
A Conservative cavity preparation
• Saves tooth structure
Minimize pulpal irritation
Resistance
• Minimize pulpal irritation
• Strong tooth structure,
marginal integrity &
restoration longevity
� Outline should consist of smooth
curves on occlusal surface
(no sharp line angles)
Resistance
To avoid stress concentration
• Box form (mortis form)
* flat floor
* definite line & point angles
Resistance
Distribution of force
• Cavosurface margin is 90° butt joint
• Remove any undermined enamel (enamel
supported with dentin)
Resistance
• Depth * 0.5mm below DEJ (cavity in dentin)
* The whole cavity depth is about
1.5 - 2 mm
from cavity margin to pulpal floor
Resistance
from cavity margin to pulpal floor
Pulpal floor
D
�Minimal extension into the marginal ridge (only enough to remove the defect) without removing dentinal support
� Mesial & distal walls
* divergent occlusally(≥≥≥≥ 10°) to follow
Resistance
* divergent occlusally(≥≥≥≥ 10°) to follow
the direction of enamel rods & prevent undermining of the marginal ridge
• Join weekend ridge between two cavities (<0.5 mm apart)
Resistance
Retention form
Is obtained through
• Converging Buccal and lingual walls occlusally (undercut)
• Parallelism of the walls
• Griping action of dentin
Extra means of retention
Grooves
Retention
Prepared at the line angle between floor of the cavity & its walls with
a ¼ round bur
• Establishing RESISTANCE & RETENTION
(depth & width of the cavity)
gives adequate convenience
Convenience form
gives adequate convenience
to instrumentation ,removal of
decay & insertion of the
restoration
If there is spot of caries
remaining in the cavity
Infected carious dentin should be removed by:
• Excavators (spoon or discoid) • Excavators (spoon or discoid)
soft caries
• Large carbide Rose head at low speed
hard caries
* Until the tooth structure feels hard & firm
* lesion is lighter in color
The removal of carious dentin should not affect resistance form
Create a flat floor peripheral
to the excavated area
Compound class I
cavity cavity
It involves two surfaces
• Occlusal surface
• Buccal or Lingual grooves OF molars
Compound class I
• Buccal or Lingual grooves OF molars
� Occlusal box follows the same principles for class I simple occlusal cavity
� After preparing the occlusal cavity
* #245 bur is held ⊥ to the pulpal floor &
parallel to the long axis of the tooth crown
Cavity preparation
parallel to the long axis of the tooth crown
* moved towards the buccal/lingual
direction along the fissure maintaining uniform depth until the bur reaches the buccal/lingual surface
• The step is prepared keeping the bur parallel to the buccal/ lingual surface of the corresponding groove
So The axial wall will follow the contour of
the buccal/lingual surface at a the buccal/lingual surface at a
uniform depth of 0.5mm inside
the DEJ (0.2mm is permissible)
• Axiopulpal line angle is
rounded
Resistance
• Extend the lingual box gingivally to terminate at the buccal/lingual groove creating a flat gingival seat for
…………. Resistance …………. Resistance
• Gingival wall meets the tooth surface at 90°& the axial wall makes an obtuse angle with the pulpal floor ……………..Resistance
• Mesial & distal walls of the B/L BOX are made parallel to each other with slight occlusal convergence ………………………………..Retention
• Mesial & distal walls are butt joint with the cavity margins………………… Resistancecavity margins………………… Resistance
Pit & fissure on facial or lingual surface
only(buccal pit /paltalpit)
• Shape varies (oval –round-oblong) depending
upon the extent of caries
• Walls continually joined & slightly convergent • Walls continually joined & slightly convergent
towards the cavosurface margin
• Axial wall follows the contour of the
buccal/lingual surface