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laboratory Procedure for Makinng a Conventional RPD

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by

hanan aldryhim

on 16 December 2013

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Transcript of laboratory Procedure for Makinng a Conventional RPD

5.Waxing up:

To contour wax and performed wax
patterns to form a pattern for RPD framework.

4.Duplication of the
master cast and pouring the refractory cast:

*By means of duplicating flask and reversible hydrocollid material (agar) to prepare a mold of
master cast.

6.Spruing:

2.Beading of the master cast

Beading is scribing the maxillary cast with a sharp instrument or bur in desired area to provide seal between the finished prosthesis and the soft tissues.


3.Wax blockout procedure

It is the elimination of the undesirable
undercut areas on the cast to be used
in the fabrication of a RPD.


1-Transfer the design to the master cast

a.Transfer the orientation of the diagnostic cast to the master cast.


laboratory Procedure for Making a Conventional RPD
Use spoon excavator or suitable bur
depth not more than 0.5 mm.
a.Parallel blockout:
*It is the placement of a small amount of wax, under the survey line of the proximal surface of an abutment tooth. It should be extended to the gingival margin.
*Also in the deep interproximal spaces that may be crossed by minor connector.

*To attach wax performed forms to the framework wax pattern to provide a
channel or hole through which molten metal flow into the mold of the framework wax pattern.



b.Draw the survey line.

c.Indicate and measure the
retentive undercut( 0.01 inch).

d.Draw the design on
the master cast.

B.Shaped blockut:

It is prepared on buccal and lingual surfaces to facilitate accurate placement of wax patterns of clasp arm.

C.Arbitrary blockout:

It is used in the areas of the cast that
is not engaged by the metal framework
such as the labial surfaces of mandibular
anterior teeth.

d.Relief:

*It is the procedure of placing wax sheet
in certain areas of master cast to be
duplicated in the refractory cast.
*To provide space between certain parts
of metal framework and the oral
structures.

7.Investing:

The process of covering or enveloping the RPD
framework wax pattern with a suitable investing
material before casting.
Type of investing material used for cobalt chromium
alloy is
phosphate bonded
investment.

8.Burn out:

*It drives off moister in the mold.
*It vaporizes and thus eliminates the wax
pattern.
*It expands the mold to
compensate
for
contraction of metal on cooling.

9.Casting:

Injection the molten metal quickly
into the mold using force by two
ways:
*Centrifugal force( commonly used).
*Air pressure.

10.Finishing and polishing:

*It is the procedure of smoothening the metal framework with progressively finer abrasive agents to remove scratches and
rough areas and to give a high luster.
*High speed lathe, curbid bur, carborundum disc, rubber wheels,
cones, polishing whee, rag wheel and high gloss compound.

*The cast should be immersed in slurry water
before duplication gently remove the
master cast from the duplicating flask
after complete setting of
agar agar.

*Pour the investment material
in the mould cavity, and allow it
to set.
*Remove the refractory cast from the
mold cavity after setting by cutting
the agar away. Allow the cast to
dry in oven.

Immediately after removal from the
oven, immerse the cast in molten
beeswax. This makes the refractory
cast surface smooth and dense.

*Sprues should attached
to the bulky points of the mold
pattern.
*The point of attachment should be
flared out.
*Use few sprues of large diameter
rather than several smaller sprues.
*Keep all sprues as short
and direct as possible.
Full transcript