Page 120 - My FlipBook

116 OPERATIVE DENTISTRY

tern should noAv be removed, preferably by the use of the heated
hollow needle, in such manner as to give the cement an ample grasp
upon the inlay, and should be equal to or more than the amount
of retention of which the cavity in the tooth is capable. The pat-
tern is then ready for investment.
Method of Using Wax Pattern, Pin Attached. This method is
of service when for any reason it is desired to have the maximum
amount of retention. In such cases the tooth Avill generally be non-
vital and a portion of the pulp cavity used for the reception of
the pin.
Placing the Pin. The cavity should be first freed from retentive
form as described above, using either cement, temporary stopping,
modeling compound, or Avax, then the opening made in the root
canal to receive the pin which is placed in position, with a light
coat of sticky Avax on the outer end. The pin should be long enough
to reach Avell into the body of the wax pattern and should be iridio-
platinum, platinized gold or tungsten. These materials Avill stand
the heat of casting the inlay without alloying or losing their rigidit3^
Tungsten Pins. The use of tungsten in casting gold inlays is of
great advantage, as this material is easily cast upon when the wire
has been previously gold-plated. The wire is about six times as
strong as iridio-platinum of the same gauge and three times as strong
as steel. This material does not lose its temper upon being heated.
It therefore gives us a very rigid pin in the completed work. As the
gold will not cast to the end of the pin, which has been cut off and
is not gold-plated, it is very essential that these exposed ends be
well buried in the Avax, which can be accomplished by seeing that
the pin does not come near the surface of the casting, or else that
the end is bent so as to throw the exposed surface uiore deeply into
the Avax pattern. With the pin in position in the cavity the wax
for the pattern is manipulated the same as though no pin had been
used. When the pattern is withdrawn the pin should come aAvay
with the wax. In case it does not, withdraw the pin from the tooth
and seal it into the hole it has left in the Avax pattern and return
to position to insure alignment. Withdraw the pattern after chill-
ing and all is ready for investment.
Method of Using Pure Gold Matrix With Pin Soldered on,
Casting the Contour. This method is advised as most practical in
cavities of Class Four (first plan), when teeth are non-vital, in in-
cisal restorations vital or non-vital, in occlusal restorations, cavities
of class six particularly in vital cases, and in lingual restorations.