Spruing of partial denture

1. Spruing of partial denture
By: DR Sara Bahaa Mohamed

2. Spruing of partial denture
Sprue:
It’s a channel through which molten alloy can reach
the mold in an invested ring after the wax has been
eliminated.

3. 3
Function of sprues
1-Direct the molten metal from the Crucible to the
mold Cavity.
2-provide reservoir of the molten metal during
casting So decrease Porosity.

4. Spruing
It is the process by which wax, metal or plastic form
sprues are attached to the wax pattern, to provide an
entrance or pathway channel to the mold space and to
serve as a reservoir of metal during casting procedure.

5. Rule for spruing design
5

6. 6
1- should be Large to Prevent Solidification of the molted Metal and
keep it Liquid till the frame Casting
2-Directly lead to the Cavity as Possible to decrees the Turbulence
molten Metal
3-Leave crucible from common point with no thin part in the sprue
between two bulky parts.
4- No short angles to Prevent gas entrapment and premature
solidification
5- Attached to the bulky points, of the pattern
6- No local Constrictions

7. Principles of spruing
A)Location of attachment
B) angulation of sprue
C) Attachment morphology

8. a) Location of attachment
The ideal location for attachment
of sprue is the thickest portion of wax pattern
The sprue should not be located where it can obliterate
centric occlusal contacts and centric cusp tips and margins

9. b)Angle of sprue attachment
The sprue should be attached to pattern such that it
makes 45° to the walls of mold, which decreases the
turbulence of molten alloy.

10. If the sprue is placed perpendicular to the mold
wall, it induces high turbulence in molten alloy,
leading to creation of a hot spot on mold wall. This
results in localized shrinkage porosity

11. C)Attachment morphology
The attachment of sprue former to the wax pattern should be
such that the transition is smooth and do not posses pits /
irregularities into which investment can flow. Irregularities
produces tags of investment which is prone for fracture by
molten alloy leading to casting failure.

12. Sprues made of different materials
1. Wax: used for casting of small and large
casting, which use single stage burn out.

13. 2.Plastic/Resin:
used for castings of alloys which use 2 stage burn
out with Po4 bonded investment.
3. Metal sprues

14. Sprue length
Very short sprue : porosity in casting at the
junction of sprue and pattern.
Very long sprue : sprue solidifies first leading to
casting shrinkage and incomplete casting

15. 2.Sprue gauge/size
A-diameter
Large diameter sprue this improves the flow of
molten metal into the mould.
less diameter sprue :causes localized shrinkage
porosity.

17. Types of spruing

18. Single Spruing (horizontal Spruing):it has a
limited application, it is used in small castings
Multiple Spruing: Is used in big
castings and has three forms:
a- Top Spruing.
b- Inverted Spruing.
c- Horizontal Spruing.

19. Top Spruing
The sprue has a diameter of a pencil
It consists of a main wide central sprue from which
narrower auxiliary sprues run to each corner of the
wax pattern.

20. Inverted Spruing
In which the base of the refractory cast should have a hole
in its center.
A cone-shaped metal sprue of suitable size is placed into
the hole.
Auxiliary sprues are then placed between the main sprue
and the thick sections of the wax pattern.

22. Investing the refractory cast

23. Complete RPD frame work casting with
sprues

24. FINISHED AND POLISHED R.P.D

25. Thanks