Assalamu-alaikum
DR. TAJAMMUL AHMED
a.tajammul@gmail.com
Wax-up procedure, cut back and
framework design
for metal ceramic restoration.
SPECIFIC LEARNING OBJECTIVES;
• At the end of the class student should be able;
• To brief about wax patterns.
•
•
•
•
– Prerequisites
– Marking the margins
– Wax material science
To classify the techniques of wax pattern.
To enumerate direct and indirect techniques of wax pattern.
To enumerate in brief the procedural steps involved in wax-up for
FPDs.
To enumerate about cut-back and framework design for metal
ceramic restorations.
INTRODUCTION
Why wax patterns ?
From this wax pattern, the finished cast restoration is duplicated using
the lost wax process as a part of the indirect procedure.
PREREQUISITES
• Die preparation
Trim the die apical to finish line with
a pear shaped bur.
Sharply undercutting or ditching the die
below the finish line is not advisable
Below the finish line the die smoothened with
the discoid end of a carver.
The die contours should be similar to
that of a natural tooth
MARKING THE PREPARATION MARGIN
The finish line should be highlighted with the side of a sharp red pencil,
A black graphite pencil should not be used because
• Graphite is an anti flux & can prevent casting of the margins.
• The color should be in contrast with that of the green or blue inlay wax so
red can be used.
• Graphite is hard ,can abrade the die.
CEMENT SPACE
Enamels & lacquers should be
applied to
provide space
for cement.
[relief of 20
to 40
micrometers]
It ensures
proper seating
of the casting.
painted to
within 0.5
mm of the
finish line.
A die
hardening
agent i.e.
cyanoacrylate
is applied to
the finish line
area to
Lubricate the
die for
prevent
abrasion of
the die by
waxing
instruments.
easy removal
& seating of
the pattern
MATERIAL SCIENCE
Inlay casting wax is used for forming wax pattern for cast restorations.
Types:
• Type I- direct technique, higher melting point
• Type II- indirect technique, lower melting point
Properties of Inlay casting wax;
• Flow –The wax must flow well at forming temperature{90 % at
45 C} but during carving and burnishing flow should be
minimum.
• The wax should burn out cleanly with no residual ash.
• Wax must be capable of being carved without chipping and
distorting
INSTRUMENTS USED
Dr. Peter K. Thomas designed waxing carving instruments.
PKT no.1&2 for wax
addition and burnishing
PKT no.3 for
occlusal burnishing
PKT no.4 for wax
carving
PKT no.5 for
refining ridges
Apart from 5 PKT instrument there are DPT (Darby –Perry
Trimmer)no. 6 & no. 7
DPT no. 6 wax burnisher
No. 7 wax spatula for large wax additions
SEQUENCE OF WAXING
INTERNAL SURFACE.
WAX PATTERN REMOVAL & EVALUATION.
PROXIMAL SURFACES.
AXIAL SURFACES.[facial and lingual surface].
OCCLUSAL SURFACES.
MARGIN FINISHING.
INTERNAL SURFACE OR WAX COPING
two methods for forming internal surface(coping).
1. Wax addition method.
2. Dipping method.
1. WAX ADDITION METHOD
Flow wax on die from well heated no. 7 wax spatula.
For smaller additions no.1 & no.2 PKT are used.
Wax is added by heating the instrument, touching it to the
wax and quickly reheating its shank in the flame.
2. DIPPING METHOD
This is accomplished by dipping the lubricated die
in a pot of melted wax.
This is particularly used for complete-coverage
restorations.
WAX PATTERN REMOVAL
Wax pattern removal is necessary to evaluate the adapted reproduction
of the prepared tooth surface.
Well adapted pattern
Poor adaptation with folds & creases
which indicate that the wax was not
hot enough when applied.
The fingers of the left hand holds the die.
The right hand holds the pattern. The die is
pulled from the pattern by bending the
fingers of left hand.
PROXIMAL SURFACES
Proximal surfaces gingival to the contact area are normally flat or
concave therefore the embrasures are triangular in shape.
Over-contouring makes periodontal health difficult to maintain.
Excessive concave or undercontouring makes flossing ineffective.
CONTACT AREAS
The reference of size and location of contact areas should be established by
contra lateral teeth and the ideal anatomic form.
The position of contact areas changes from anterior to posterior in both the
arches.
On maxillary teeth- more occlusal and buccal when progressing anteriorly.
On mandibular teeth- centrally located
AXIAL SURFACE
The buccal and lingual surfaces should be shaped to
follow the contours of adjacent teeth.
Natural teeth are 1mm wider at their height of
contour than at CEJ, generally located in the
gingival third except for the lingual surface of
mandibular molars it is located in the middle
third
A – correct
B - overcontoured
EMERGENCE PROFILE
The part of the axial contour that extends
from the the base of the gingival sulcus
past the free gingival margin is emergence
profile [Stein and Kuwata DCNA 1977].
It extends to the height of contour
producing a straight profile in the gingival
third of the axial surface which facilitates
access for oral hygiene.
Straight emergence profile allows tooth bristles to
reach into the gingival sulcus
A- proximal surface
B – facial, lingual surface
OCCLUSAL SCHEME
There are two occlusal schemes :
Cusp marginal ridge scheme.
Cusp fossa scheme.
The buccal cusp of the mandibular
premolars and the mesiobuccal
cusp of the mandibular molars
contact the embrasures between
the maxillary teeth.
The mandibular centric cusps
contact farther distally into the
mesial fossa of the maxillary tooth
and contact only one tooth.
In both the occlusal schemes the maxillary centric cusp
contact the fossa of mandibular teeth
OCCLUSAL SURFACE
The occlusal surface of the pattern can be carved by
following carving technique.
The wax addition techniquegiven by Everitt V. Payne.
The functional core techniquegiven by F.S.Meyer.[JADA 1934]
It uses the principles of articulation to
develop a functional occlusal surface
which includes determination of the
height and distribution of cusps, ridge
and groove direction and fossa depth.
The technique uses tracings in the
mouth to capture the pathways traveled
by the opposing cusps in mandibular
function.
WAX ADDITION TECHNIQUE
Cones for buccal
cusp
Buccal ridges and
triangular ridges
Mesial and distal
cusp ridges for
buccal cusps
Cones for lingual
Marginal ridges
Supplemental anatomy
THE FUNCTIONALLY GENERATED PATH TECHNIQUE
The technique was first described by Meyer
The technique uses tracings in the mouth to capture the pathways
traveled by the opposing cusps in mandibular function.
The prerequisite for the use of this technique for the restoration of a
single tooth is the presence of an optimal occlusion.
It involves two steps:
1.Fabrication of functional core/index or counter die
2.Fabrication of wax pattern.
MARGIN FINISHING
To optimize the adaptation of the wax
pattern to the die, the margins must be
reflowed and refinished immediately
before investing the wax pattern .
Well adaptation is
neccesary :
to minimize dissolution
of luting agent.
to facilitate plaque
control.
CUTTING BACK
For metal ceramic restoration, once final contour of the pattern
is completed, the pattern is cut back about 1mm.
This provides :
an even thickness of porcelain
smoothness of metal-ceramic
junction.
TROUGHING THE PATTERN
Depth cuts are used to standardize
the amount of wax to be removed
from the veneering area
For this a cut back instrument
can be made from a damaged
hand instrument
SPRUING OF THE PATTERN
sprue : the channel or hole through which
plastic or metal is poured or cast into a gate
or reservoir and then into a mold .[GPT 8]
sprue former : a wax, plastic, or metal
pattern used to form the channel or channels
allowing molten metal to flow into a mold to
make a casting.[GPT 8]
• The diameter of a sprue former should be approximately of the same
size as the thickest area of the wax pattern.[14 gauge i.e.. 1.7 mm]
a large sprue former--------distort the delicate pattern
a small sprue former --------localized shrinkage porosity