wax_pattern by huangyuarong

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									Wax pattern
    Wax patterns
   The wax pattern is precursor of the finished
    cast restoration that will be placed on the
    prepared tooth , as the wax pattern will be
    duplicated exactly through the investing and
    casting technique, the final restoration can be
    no better than its wax pattern, A few extra
    minutes spent on the wax pattern can often
    save hours that might be spent correcting the
    casting.
    Wax pattern
   Casting of wax pattern can be summarized in
    producing mold around wax pattern with
    refractory material (investment) and when set
    the wax pattern is heated to vaporize, the
    produced space (mold) is filled with molten
    metal through an empty channel (sprue).
Properties of casting wax
Different type of wax are used to form a good
  pattern, soft wax is used to maximize the
  fitness between wax pattern and die while for
  obtaining accurate shape with enough strength
  to resist any deformation as will as to protect
  and support the fine details of wax pattern
  another type of wax is used ( medium or hard
  wax).
Stresses occur in the inlay wax as a result of the
  heating and manipulation of the wax during
  fabrication of the pattern. Wax. a thermoplastic
  material, "relaxes" as these stresses are
  released. The result is distortion, which is
  exhibited as a poor fit. To minimize this
  distortion, patterns should never be left off the
  die, and they should be invested as soon as
  possible after fabrication
The casting wax has several requirement:
   It must flow readily when heated, without
    distorting or loosing its smoothness.
   It must be capable of being carved without
    chipping, distorting.
   Evaporate without leaving any debris or
    residual ashes, which can contaminate the
    produced cast restoration.
   Take the fine and sharp details of pattern and
    preserve it till investing without any distortion.
   Has acceptable strength and rigidity after
    cooling.
Casting wax
Inlay casting wax is actually composed of several
waxes. Paraffin is usually the main constituent
(40% to 60%). The remaining balance consists of
dammar resin (to reduce flaking) plus carnauba,
ceresin, or candelilla wax (to raise the melting
temperature), or beeswax. Dyes are added to
    provide color contrasts.
 armamentarium

• Bunsen burner (A)
• Inlay wax (B)
• Waxing instruments,
 PKT (no. 1, no. 2, no.
3, no. 4, no. 5, no. 7
 spatula)
• Cotton cleaning cloth (D)
•Sharp colored pencil (contrasting color
  to wax)
• Separating liquid (E)
• Occlusal indicator powder
 (zinc stearate* or powdered wax) (F)
*NOTE: Zinc stearate may present health
  hazard if it is inhaled.
armamentarium
Waxing instruments can be categorized by the
 intent of their design: wax addition, carving,
 or burnishing. Of the popular PKTs (designed
 by Dr. Peter K. Thomas.
specifically for the additive waxing instrument
  no. 1and no. 2 are wax addition instruments,
  no. 3 is a burnisher for refining occlusal
  anatomy, and nos. 4 and 5 are wax carvers.
armamentarium
The PKT no. 1 instrument is used for large
  increments ;the smaller no. 2 is used for
  lesser additions.
   A no. 7 waxing spatula is useful for adding
  large amounts of wax, particularly in forming
  the initial coping or thimblelike layer of wax
  that covers all prepared surfaces.
  Wax carvers should be kept sharp and should
  never be heated
When carving wax, light pressure should be
 used to obtain the desired smooth
 surface.
 Burnishing is an alternative to carving for
 obtaining a smooth wax pattern of the
 desired contour, Burnishing consists of
 slightly warming a blunt instrument and
 rubbing the wax.
The instrument should not be so hot that it melts
  the wax surface. The PKT no. 3 instrument is
  useful for burnishing the occlusal surfaces. The
  PKT nos. 1 and 2 can be used for burnishing as
  well as for wax addition.
.    For removing wax, burnishing is less
    effective than carving, but probably easier
    to control and leaves a smoother surface,
    which can particularly important when
    trimming excess wax near the margin.
    Careless (excessive) carving in this area
    can result in abrasion of the die, creating
    a ledge around
    The finished casting
Wax is added by heating the instrument in the bunsen
flame, touching it to the wax, and quickly reheating
its shank in the flame. Wax flow away from the hottest
part of the instrument.
so that if the shank is heated, a bead of wax will flow
off the tip, However if the tip is heated, the wax will
flow up the shank of the instrument (to the
considerable annoyance of inexperienced operators).
Different technique used for fabrication of
    wax pattern
1) Direct technique
 Pattern is constructed inside the mouth. It is
   indicated in an enclosed cavities inlay and
   posts. In this method hard or medium wax,
   the melting temperature of that type of wax
   is 37.
2) Indirect technique
 pattern is constructed outside the patient
 mouth. It is most popular method for wax
 pattern construction during cast restoration due
 to its good access and visualization beside time
 saving to the dentist and the patient. The wax
 has a melting temperature 25.
3) Indirect-direct technique
 Pattern constructed by indirect method and fine
  adjustment is carried out directly inside the
  patient mouth before its casting.
Different method of wax pattern
    construction
1) Dipping method
To develop a thin , uniform
and adapted layer of thin
wax on the die. This is done
by dipping the die into wax
that has been thoroughly
melted (using wax dipping pot).
2) Addition method
To obtain a bulk of the wax pattern, then carving is
  carried out this is done by melting the wax and
  dropping it on the die until complete building of the
  pattern and then carved by sharp carver. The main
  drawback of this technique is due to strain collected
  from multiple addition of wax tend to release with time
  and subsequently distort the wax pattern.
3) Molten press method
It is the most suitable method to construct accurate and
   adapted wax pattern. This is method is done by adding
   a molten wax and pressure is applied with fingers at
   each application, this procedure assure that the wax is
   closely adapted and free of irregularities , this method
   overcomes the most drawback of addition method.
4) Injection method
This method used in producing wax pattern with fixed
  and accurate dimension. This method is summarized
  as injection the molten wax through metallic syringe
  (heated) into enclosed mold which is relieved by a
  hole opposed to the feeding hole. The wax feeding is
  continuing under pressure until complete hardening
  of the wax .
Step of wax pattern
The following sequence is recommended for waxing
posterior teeth:
1.Internal surface
2.Wax pattern removal and evaluation
3.Proximal surfaces
4.Axial surfaces
5.Occlusal surfaces
6.Margin finishing
Coping Fabrication
The first step in making a wax pattern is the
fabrication of a thin coping, or thimble on the
die. The coping is usually made of wax, but
heated resin sheets also can be used for this
purpose, This type of coping also can be used
with partial veneer crowns, and even pin-
retained castings.
To prevent the wax from sticking to the die stone, coat
the die thoroughly with die lubricant and allow it to
soak in for several minutes. If the surface of the die
appears dry after this period of time, repeat the
application Remove any excess lubricant with a
gentle stream of compressed air. Flow wax over the
surface of the preparation on the die, using quick
strokes of a hot no 7 wax spatula Overlap and remelt
the margins of wax already placed on the die
Dipping the die into a small metal container filled with
molten wax is yet another method that can be used
for developing a uniform, thin initial coping of wax on
the die.
Wax Pattern Removal
The wax should be allowed to cool thoroughly
before the coping is removed from the die. A
constant light grip is maintained on the pattern
by the thumb and forefinger of one hand while
pressure is applied against them with the thumb
and forefinger of the other hand, which also
holds the die a small square of rubber dam will
increase friction between the fingers and the
pattern. If the pattern fails to move, there may
be excess wax gingival to the margin.
Proximal Surfaces
 the part of the proximal surface that
extended from the base
of sulcus to the free margin
of the free gingiva has been
described as the emergence
profile the profile natural
teeth are not convex.
They tend to be flat or slightly concave from the contact
  area to the cemento enamel junction, any restoration
  must reproduce this feature.
  Overcontouring often makes maintaining periodontal
  health difficult, Excessively concave or under contoured
  proximal surfaces make flossing ineffective and must be
  avoided.
  Experimental data indicate that over contoured produce
  gingival inflammation and hyperplastic change in 4week
  while under contouring produced no significant change,
  so its better to under contour than over contour.
Contact Areas:
The size and location of the contact areas should be established
  before waxing the remainder of the proximal surfaces. Abnormally
  large proximal contact areas make plaque control more difficult
  and can lead to periodontal disease. Very small (point) contacts
  may be unstable and cause drifting. Deficient contacts can also
  lead to food impaction; although this is not a direct cause of
  chronic periodontal disease, it can be very uncomfortable and
  painful to the patient.
Most posterior contact areas are located in the occlusal third of the
  crown. However, contact between the maxillary first and second
  molar occurs in the middle third
 " The contact areas between mandibular teeth and maxillary molars
  are generally centrally located. Between maxillary premolars and
  molars, the contact areas are usually toward the buccal surface
  (making the lingual embrasure larger than the buccall.
buccal and lingual surfaces
should be shaped to follow the contours of the adjacent
  teeth. The location of the height of contour generally
  located in the cervical third of most teeth, except on
  mandibular molars it is usually in the middle third of the
  lingual surface. The facial contours of both maxillary
  and mandibular posterior teeth extend approximately
  0,5 mm beyond the out line of root at the cemento
  enamel junction
the amount of lingual prominence differ between the
  maxillary and mandibular teeth, it is 0.5 mm on
  maxillary and mandibular first premolars, about 0.75
  mm on mandibular second premolars, and nearly 1.0
  mm on mandibular molars.
Occlusal morphology
No discussion of the wax pattern would be complete
  without mention of occlusal theory and effect of
  articulation on the occluasl surface of wax pattern.
 during centric closure in the normal dentition, the lingual
  cusps of the maxillary posterior teeth and the buccal
  cusp of the mandibular posterior teeth make the contact
  with the occlusal fosse or the marginal ridge of the
  opposing teeth. They grind food like mortar during
  mastication and are called functional cusps.
On the other hand, the buccal cusps of the maxillary molar
  and the lingual cusps of the mandibular molars do not
  contact the opposing teeth. These cusps prevent food
  from over flowing, and the protect the buccal mucosa
  and the tongue by keeping them away from the
  functional cusps. Since these cusps do not make direct
  contact with opposing teeth, they are called non
  functional cusps.
The occlusal scheme can be classified by the location of
  the occlusal contact made by the functional cusp on the
  opposing tooth in centric relation. There are tow types:
  cusp fossa and cusp marginal ridge
Cusp marginal ridge arrangement
This relation is a type of occlusal scheme in which
  functional cusp contact the opposing occlusal surface on
  the marginal ridges of the opposing pair of teeth or in
  the fossa, this relation is basically one tooth to two
  tooth arrangement,
since the majority of adult exhibit the cusp-marginal ridge
   type of occlusion, its an occlusal pattern widely utilized
   in daily practice. It can be used for single restoration ,
   the disadvantage of cusp marginal ridge occlusion is
   food impaction and displacement of the teeth may arise
   if the functional cusps wedge into the lingual
   embrasure .
Cusp fossa arrangement
The cusp fossa relation is an occlusal pattern in which
  each functional cusp is nestled in to the occlusal fossa
  of the opposing tooth. It’s a tooth to tooth
  arrangement , its rarely found in its pure form in
  natural teeth.
  Each centric cusp should make contact with the
  occlusal fossa of the opposing tooth at three point are
  in the mesial and distal incline and the inner facing
  incline of the cusp, producing tripod contact.
Since a cusp tip itself never comes in contact with the
   opposing tooth, the cusp tip can be maintained for a
   long time with a minimum of wear.
  the mandibular functional cusp arise opposite the middle
   (buccolingually) of the maxillary tooth. Similarly the
   maxillary functional.
  cusps are positioned halfway between the mandibular
   buccal and lingual cusp tip. There fore , occluasl force
   are transmitted along the long axes of the tooth.
the functional cusps of the maxillary posterior teeth
become slightly shorter as they progress distally
Nonfunctional cusps are made slightly shorter than the
functional cusps to insure clearance in excursive
movement, the nonfunctional cusp also become slightly
shorter from anterior to posterior The resulting antero
posterior curvature of the occlusal plane is called the
curve of spee . Presence of this feature in a reconstructed
mouth help to prevent protrusive interferences
The left right curvature resulting from the non functional
cusp being shorter than the functional cusp is curve of
Wilson. Its prevents interferences in the lateral excursions
Margin Finishing
Remove the pattern from the working cast and place it
back on the freshly lubricated die. Make certain that the
red line on the die finish line is still distinct Smooth any
roughness on the axial surfaces with a slightly warm
Burnisher To optimize the adaptation of the wax pattern
(and the cast restoration) to the die, the margins must
be reflowed and refinished immediately before investing
the wax pattern.
The two principal objectives are
(1) minimizing dissolution of the luting agent and
(2) facilitating plaque control
If a zone of superior adaptation (i.e., marginal gap width)
between the casting and the prepared tooth surface is
created, cement dissolution will reduced
To obtain this superior adaptation minimum the pattern
should be reflowed over a band approximately 1 mm
wide, measured from the margin on to the prepared
surface

								
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