Class II Cavity Preperation

8/13/2019 Class II Cavity Preperation

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A lesion developing on the proximal

surface of posterior teeth

Develops under the contact area because

it is a protected area.


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The lesion is covered on the occlusal side

by sound enamel

Proximally it is protected by the adjacent

tooth


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The least destructive path to make a cavity

in this tooth is through the occlusal enamel


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Class II cavity has two parts

1. Occlusal dovetail

2. Proximal box

Called as MO (mesio-occlusal) or

DO (disto-occlusal) depending on

involved side


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Mark the primary grooves and fossa on the

involved (proximal) half of occlusal

surface

Continue the marking to the marginal ridge

just beyond the contact area into the

buccal and lingual embrassure


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3.0 mm

Width of bur #245 is 0.8 mm


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To make a uniform cutting

To give an idea about the required cutting

1.5 mm


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This gives you the desired shape of the

walls and floors of the cavity preparation

(retention form and resistance form)


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Insert the bur 1.5mm into the tooth in the

central fossa/pit

This gives a sense about the desired depth

It has to be maintained


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Move the bur along the cusps and into the

marked pits and fissuresApply light intermittent pressure to prevent

burning of tooth.

Always keep the bur perpendicular toocclusal table


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The bur is moved at the desired depth up

to mesial fossa or distal fossa(involved

side) and into the buccal and lingual

grooves.

Dont cross the centre unless involved

Dont make the cavity wider than 1-1.5bur thickness.


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With triple syringe(three in one)

Should be done intermittently

To have an idea about the cavity features


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From the class I, extend the bur at the

same depth towards the marginal ridge to

the edge of the proximal contact(dont go

all the way to the proximal surface)

Same should be done for both the buccal

and lingual embrassure(already marked)


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The thin layer of structure is fractured and

removed using a chisel or hatchet(can be done after the next step)

The buccal and lingual wall should clearthe adjacent tooth by 0.5mm( probe just

entering between the two)


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Inside the involved proximal margin (1-1.5

bur thickness) the cavity is extendedgingivally to clear the gingival contact area

by 0.5mm

Keep the bur slanting in the opposite

direction

The gingival floor should follow externalsurface


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Buccal wall(side of 245 bur)

Lingual wall(side of 245 bur)

Gingival floor( base of 245 bur)

Axial wall (side of 245 bur)


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Axial wall

Pulpal floor

gingival floor


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The part joining the proximal box and the

occlusal dove tailIsthmus


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It is an external angle

Should be rounded with hatchet or bur

Can create stresses in restoration which

result in fracture of filling at the isthmus

Axiopulpal line angle


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Axial wall is slanting away from theproximal side ( to provide thick amalgam)

Made by moving the bur gingivally in anarc form

Keep the bur at an angle away from the

involved side


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The gingival floor should not be more than

1-1.5 bur thick

The margin of the gingival floor is alsobeveled with GMT


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Smooth curves all around (free from any

loose, short, or sharp margin)

Definite walls and angles

All pits and fissures be removed(marked)Preparation centered on central

developmental groove

Walls of the proximal box just clearing thecontact area


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Maintain uniform depth(1.50 mm)

The flat pulpal and gingival walls

Definite but round internal and external

anglesEnamel margin( 90-CSA) including the

walls of the proximal box

Smooth curves


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Maintain minimal width

Not more than two bur thickness

Keep a minimal width of gingival floor(1-

1.5 bur thickness)

Beveling of the margin of gingival floor


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1-1.5 bur thickness


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Macro mechanical retention

Slight convergence of the side of bur gives

the required occlusal convergence.

Proximal dislodgement is prevented by

occlusal dovetail and proximal grooves


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The cavity has to be wide enough for easy

manipulation

Make the cavity according to the size of

condensors


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To remove

any minute irregularities in the walls

unsupported enamel from the buccal and

lingual and proximal walls.Bevel the margin of gingival floor

Bevel the axiopulpal line angle

Hold the instrument parallel to the wall or abevel will develop


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I. Outline form:


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Out e o

Extension Properly extended Over extended Under extended

Width 1 -1.5 mm Wide Narrow

Proximal outline 0.5 mm of the contact area Wide Narrow (closed contact)

II. Resistance form:

Pulpal floor 0.5 mm below DEJ Flat Parallel to the occlusal plane

Deep Irregular

Shallow Not parallel to the occlusal plane

Marginal ridge Preserved Undermined

Mesial / distal wall Divergent Convergent

Line angles Rounded Sharp

Axial wall 0.5 mm below DEJ Deep Shallow

Isthmus Properly extended Wide Narrow

III. Retention form:

Buccal & lingual walls Slightly converge Over converge Diverge

Dovetail

Prepared

absent


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Thank you

Class II Cavity Preperation

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