Class II cavity preparations in primary molars p y

Class II cavity preparations
in primary molars
Dr. Aly Sharaf

• Until eruption of the first permanent molar,
the second primary molar is in contact only
on its mesial surface which has an incidence
of caries ten times greater than that of the
distal surface of the same tooth.
• After the tooth’s distal contact is established
little difference in susceptibility remain
between the two surfaces.
Dr. Aly Sharaf

• The susceptibility of caries on distal of the
first primary molar is similar to mesial
surface of the 2 nd primary molar. However,
the mesial surface of 1 st primary molar is less
caries prone. This is due to firm contact
between first and second primary molar
whereas a space is frequently present
between the first molar and canine.
Dr. Aly Sharaf

• Caries on proximal surface most
often begins just below the
contact area and initially spreads
lt lateral lthen gingivally.
i Dr. Aly Sharaf

• Radiograph examination is particularly
important to detect proximal caries. One
study showed that as many as 75% of the
proximal lesions affects the primary molars
would have gone undetected without the aid
of radiographs.
Dr. Aly Sharaf

Armamentarium
• Mirror
• Explorer
• Enamel Hatchet 13‐14
• Contra‐angle
• No. 330 bur
Dr. Aly Sharaf

Check the occlusion:
Use articulating ribbon and tap the jaw of the
manikins. Remember the location of the
marks and use them as an aid in carving the
restoration.
Dr. Aly Sharaf

Class II Amalgam OM #65
Preparation
Dr. Aly Sharaf

Establish Depth
1. Use a #330 pear sharp bur.
2. Start preparation by penetrating the occlusal
surface from the central fossa and extend
toward the mesial and terminate in the
mesial lesion.
3. Use the periodontal probe or (330) to check
the depth of preparation.
Dr. Aly Sharaf

Criteria
Depth
1. Plastic tooth 1.25‐1.5 mm from the
cavosurface. Measured at the mesial ilid ridge
area.
2.Natural tooth penetrate 0.25mm into dentin.
Dr. Aly Sharaf

Width
• At the Isthmus area, about 1/3 to 1/4 the
distance between cusp tip
Note: Isthmus width on this second primary
molar is slightly greater than on the first
primary molar.
Dr. Aly Sharaf

Extended into the Grooves
1. Et Extend dinto grooves using #330 bur and the high h speed
handpiece.
2. Maintain the depth as you extend into the grooves.
3. Tilt the bur toward the oblique ridge as you approach it to
avoid undermine the ridge.
4. As you approach the oblique ridge create a dovetail il(do
not undermine the oblique ridge).
5. Extend the buccal groove approximately equal to the
width of the bur and create a dovetail.
6. Extend mesially and create dovetail leaving only thin wall
of enamel so as to protect tthe adjacent tooth thfrom
abrasion.
7. Use #330 bur or slow speed finish and smooth the walls.
Dr. Aly Sharaf

Criteria
1. 1.25 – 1.5 mm depth must be maintained
i throughout.
2. Buccal and lingual walls should converge slightly
in occlusal direction.
3. Distal wall should be vertical in minimal. In
maximum model it diverge slightly.
4. The oblique ridge must not be undermined.
5. Only thin wall of enamel should be left mesially.
6. All line angles should be rounded.
Dr. Aly Sharaf

Prepare the Proximal Box
1. Place #330 bur inside id the cavity against tthe
wall of tooth structure and move the bur in a
gingival direction, move the bur bucco‐lingually
with a pendulum motion. This will provide the
slight convergence of the buccal and lingual
walls toward the occlusal (broader at gingival
than occlusal surface).
2. Extend proximal box gingivally to break contact
with the adjacent tooth so that tip of an
explorer can be passed through.
Dr. Aly Sharaf

1. Extend buccal and lingual l walls of the
proximal box to self‐cleansing area. This can
be determined by the clearance of an
explorer tip.
2. If necessary use a Hatchet to plan the lingual
and buccal walls of the proximal box
3. The axial wall follow the contour of tooth
(mesial surface of the tooth).
Dr. Aly Sharaf

Criteria
1. The proper depth of proximal lbox is approximately
2.5 –3 mm depending on the clearance.
2. Proximal lbox wall extend so as explorer tip can pass
through the embrasure.
3. The proximal box should be wider gingivally than
occlusally for retention of the restoration.
4. Width of the gingival seat is approximately 1 mm.
5. Proximal box extends gingivally so that the tip of an
explorer can pass through. The depth of the proximal
box from the pulpo‐axial line angle to the gingival seat
approximately 1.25‐1.50 mm.
Dr. Aly Sharaf

6. Rounded daxio‐pulpal lline angles, as are all lines.
7. Sharp cavosurface angle in the buccal lingual
walls/ a ninety degree is desirable.
8. There is a slight extension into the fissured
mesio‐buccal groove (sometimes familiarly
referred to as a dovetail).
9. The axial wall of the proximal box is at the same
depth as the pulpal wall 1.0 to 1.25 mm.
10. The gingival wall on the minimum model is just
at the level of the gingiva: on the maximum, it is
0.5 mm below the gingiva.
g
Dr. Aly Sharaf

Occluso‐distal # 74
Extend into grooves
Terminate your dovetail at central pit.
The transverse ridge which is not undermined
is lfi left intact. The mesial ilwall at the
transverse ridge is slightly undercut on the
minimum model or vertical on the maximum.
This isthmus is 1.25 to 1.5 mm wide.
Dr. Aly Sharaf

Prepare the proximal box
• As mentioned before the pulpal and axial
depth are 1.0 to 1.25 mm. Gingival wall is level
with ihthe gingiva i in minimal i model. dl0.5 mm
below gingiva on the maximum model.
Dr. Aly Sharaf

Two class II “ back‐to‐back” b k” cavities ii can be prepared as
essentially one procedure rather than separately.
Prepare the occlusal portion of each tooth then form
the proximal boxes vertically simultaneously by moving
the burs back and forth between the 2 proximal
surfaces establishing first the buccal walls then the
lingual or (vice verse).
It must be remembered that the axial wall on a first
primary molar will be slightly deep than on the
adjacent second primary molar. Etblihb Establish both gingival
i walls by perpendicularly the bur to round them.
Dr. Aly Sharaf

Dr. Aly Sharaf

Dr. Aly Sharaf