construction of metal framework for partial denture

1. LAB PROCEDURES
FOR
FRAMEWORK CONSTRUCTION
Removable partial denture

2. LAB PROCEDURES
FOR
FRAMEWORK CONSTRUCTION
Removable partial denture

3. • Framework fabrication delegated to a technician
located outside the dental office.
• Therefore, effective communication between the
dentist and the technician is essential.
Removable partial denture
Lap Procedures

4. • For successful construction of a removable partial
denture, the dentist must provide dental laboratory
with the following:
• (1) a written work authorization describing the
desired Prosthesis
• (2) a properly articulated and surveyed diagnostic
cast with appropriate partial denture design
• (3) a properly master cast that provides an accurate
reproduction of hard and soft tissue.
Removable partial denture
Lap Procedures

5. LAB WORK STEPS
• First laboratory steps
• Making a diagnostic cast (pouring a cast)
• Surveying the diagnostic cast
• Articulate the casts and drawing design
• Making special trays to be used for taking the final impressions
• Second laboratory steps
• Pouring a master cast using the final impression
• Surveying of the Master Cast and transfer design
• Third laboratory steps
• Investing refractory cast (duplicating master cast)
• Wax elimination and Casting of metal framework
• finishing, polishing
Removable partial denture
Lap Procedures

6. PRIMARY
IMPRESSIONS
STUDY MODELS
SPECIAL TRAYS
Removable partial denture
Lap Procedures

7. SURVEYING
DENTURE DESIGN
Removable partial denture
Lap Procedures

8. TOOTH PREPARATION
FINAL IMPRESSION
Removable partial denture
Lap Procedures

9. FINAL IMPRESSIONS
MASTER CASTS
Removable partial denture
Lap Procedures

10. RETRIPODING THE MASTER CAST
• During the survey and design process, the clinician determines a
specific path of insertion and removal for the partial denture.
• This path is recorded by placing tripod marks on the diagnostic
cast.
Removable partial denture
Lap Procedures

11. RETRIPODING THE MASTER CAST
Removable partial denture
Lap Procedures

12. RETRIPODING THE MASTER CAST
• Placing three easily identifiable marks on the same
horizontal plane.
• These marks must be widely separated and must be
positioned on anatomic portions of the diagnostic cast
• they allow rapid reorientation of the diagnostic cast.
• permits orientation of the master cast and reproducing the
prescribed path of insertion
Removable partial denture
Lap Procedures

13. DESIGN TRANSFER
• Without removing the master cast from the survey
table or changing the tilt, the technician transfers the
design from the diagnostic
cast to the master cast with
extreme care and clearly
marked to avoid confusion.
Removable partial denture
Lap Procedures

14. •Block out is the act of placing
wax and other materials into
undesirable undercuts on the
master cast.
Removable partial denture
Lap Procedures

15. CAST PREPARATION
Removable partial denture
Lap Procedures
Before the addition of the blockout wax,
• maxillary cast is beaded to ensures positive contact of the major
connector with the palatal tissues.
• master cast treated with a surface sealer to provides a film protects
design through blockout and duplication processes.

16. BLOCKOUT TECHNIQUE
• Wax is placed apical to the height of contour and is not applied
in areas where intimate metal contact is desired.
Removable partial denture
Lap Procedures

17. BLOCKOUT TECHNIQUE
• Blockout wax is contoured with a metallic blockout instrument
mounted in the dental surveyor this results in
0-degree blockout (parallel to the path of insertion).
• Other blades are available and offer blockouts that range from 2
to 6 degrees from the path of insertion.
Removable partial denture
Lap ProceduresParallel

18. BLOCKOUT TECHNIQUE
• All tooth-supported removable partial dentures should be
blocked out parallel to the path of insertion.
• Tooth-tissue–supported removable partial dentures may be
given a tapered blockout to allow increased freedom of
movement in function.
Removable partial denture
Lap ProceduresParallel

19. BLOCKOUT TECHNIQUE
• wax shaped with hand instruments on buccal and lingual surface
to provide a slight ledge just apical to the clasp terminus
This guides the placement of the wax pattern accurately.
Removable partial denture
Lap Proceduresshaped

20. BLOCKOUT TECHNIQUE
• Areas of undercut that are not directly involved with framework
fabrication also must be addressed to minimize distortions
during cast duplication.
Removable partial denture
Lap ProceduresArbitrary

21. BLOCKOUT TECHNIQUE
• Wax is used to create a space between the framework and soft
tissue in edentulous area to provide for attachment of acrylic
denture bases
• Wax is also used beneath lingual bars and in other area such as
maxillary and mandibular tori.
Removable partial denture
Lap ProceduresRelief

22. DUPLICATION
• Duplication materials and techniques are alloy specific.
• low heat alloys are use gypsum-bound refractory materials that
use reversible hydrocolloid for duplication .
• high-heat alloys use phosphate-bound investments and glycerin-
based colloids for duplication.
Removable partial denture
Lap Procedures

23. REFRACTORY CAST
• Gypsum-bonded refractory materials (low heat investments) are
used for casting Type IV partial denture gold and Ticonium and
can be heated to 704°C.
• Refractory materials used for Vitallium, chrome cobalt alloys, and
titanium alloys (high-heat investments) can be heated to1037°C
Removable partial denture
Lap Procedures

24. REFRACTORY CAST
• After removal, the refractory cast is placed in a drying oven at
93°C for 30 to 60 minutes .
• The dry refractory cast is dipped into beeswax at138°C to 149°C
for 15 seconds to ensure a smooth, dense surface.
Removable partial denture
Lap Procedures

25. WAXING THE FRAMEWORK
• Before waxing can begin, the design must be transferred from
the master cast to the refractory cast.
• If appropriate ledges were created during blockout procedures,
the placement of retentive clasp tips is much easier and more
precise.
Removable partial denture
Lap Procedures

26. WAXING THE FRAMEWORK
• The plastic patterns are “glued” to the refractory cast with a
mixture of acetone and plastic pattern scraps mixed to a
watery consistency (tacky liquid).
Removable partial denture
Lap Procedures

27. WAXING THE FRAMEWORK
• Some care is required to remove these prefabricated patterns
without distorting them.
• It is important that retentive clasp patterns are not distorted
because the shape of the clasp greatly affects flexibility.
• After the plastic patterns have been placed on the refractory
cast, they must be adapted without distortion.
Removable partial denture
Lap Procedures

28. WAXING THE FRAMEWORK
• At every step, the technician must exercise
extreme care not to stretch the pattern.
• A blade is used to trim pattern material that
extends beyond the outline drawn on the cast.
• these patterns must be joined using wax that
used to seal the margins of the major
connector and to create the minor connectors
and rests.
Removable partial denture
Lap Procedures

29. SPRUING THE FRAMEWORK
• The location and geometry of the sprue former is based upon
recommendations of the alloy manufacturer.
Removable partial denture
Lap Procedures

30. SPRUING THE FRAMEWORK
• Ticonium is cast using a single sprue former that approaches
through the refractory cast.
• Type IV gold and chrome-cobalt alloys are cast using a sprue
that approaches from above and gives rise to a number of
smaller, accessory sprues.
Removable partial denture
Lap Procedures

31. INVESTING THE REFRACTORY CAST
• Some systems require a two-part investment process, the first
part being a 3- to 4-mm “paint-on” layer that is carefully
brushed onto the waxed refractory cast to ensure that no voids
are present.
Removable partial denture
Lap Procedures

32. INVESTING THE REFRACTORY CAST
• An investment ring large enough to accommodate the
refractory cast and its first layer is selected. An appropriate
amount of refractory material is measured, mixed, and placed
into the investment ring.
Removable partial denture
Lap Procedures

33. WAX ELIMINATION
• The burnout has three purposes :
• It drives off moisture in the mold.
• It vaporizes and thus eliminates the
pattern leaving the cavity in the mold.
• It expands the mold to compensate
for contraction of the metal on
cooling.
Removable partial denture
Lap Procedures

34. CASTING
• The metal is melted by heat and forced into the mold cavity by
force.
Removable partial denture
Lap Procedures

35. CASTING
• Heat may be applied by a blowtorch using gas air ,gas and
oxygen, acetylene, electric conduction or induction.
• Force may be Centrifugal or air pressure.
• Induction casting is the method of choice for base metal alloys.
Removable partial denture
Lap Procedures

36. CASTING
Removable partial denture
Lap Procedures

37. CASTING RECOVERY
Removable partial denture
Lap Procedures
• the mold is removed and allowed to cool
• the outer layer of refractory material is removed by tapping it
with a mallet
• The remaining investment is removed by airborne particle
abrasion

38. FINISHING THE FRAMEWORK
Sprue removal
• Using high-speed lathes and large abrasive disks
Removable partial denture
Lap Procedures

39. FINISHING THE FRAMEWORK
Finishing
• Nodules are removed from the surfaces that
will contact the teeth.
• Rubber wheels and points are used to give
the framework a “satin” finish.
• Technician uses coarser disks and stones and
then proceeds to finer grinding agents
Removable partial denture
Lap Procedures

40. FINISHING THE FRAMEWORK
Polishing
• Electro-polishing occurs in a bath of 85%
orthophosphoric acid, which is heated to
60°C.
• The anode is attached to the cast that
immersed in the solution
• Ultrasonic cleaning is used to remove residual
polishing materials.
Removable partial denture
Lap Procedures

41. Removable partial denture
Lap Procedures