Transcript RESD 2313 lecture 2

Clasps

Functional requirements of a clasp:
– Retention. Resist removal of R.P.D. occlusally.
– Reciprocation. Resist lateral forces exerted on an
abutment tooth as the retentive tip flexes in and
out of the undercut.
– Bracing. Resist anteroposterior and lateral
shifting of the entire R.P.D.
– Encirclement. Surround more than 180 degrees
of an abutment’s circumference so that the tooth
does not drift.
Clasp Assembly
 The clasp assembly includes rest and minor
connectors
 The functional requirements of the clasp
assembly also includes Support
 Support is achieved through the rest
component
Major clasp classifications
 Circumferential clasps (Suprabulge or
Akers)
 Bar clasps (infrabulge or Roach)
Circumferential clasps
(Suprabulge or Akers )
 Body, retentive arm, retentive tip, reciprocal
arm, and shoulder.
 Approaches the undercut from the occlusal
portion of the tooth.
 Examples: simple circlet (circumferential),
back action ,embrasure etc .
Bar clasps (infrabulge or Roach)
 Body, approach arm, retentive tip, bracing
tip, reciprocal arm, and shoulder.
 Approaches the undercut from the gingival
portion of the tooth.
 Examples: I-bar, T-bar, Modified T
 The clasp arm is tapered to increase
flexibility
 A continuous clasp needs bracing on all
teeth that it contacts.
Block-out
1. Bulk block out major undercuts
2. Block out undercuts around abutment
teeth.
3. Relief wax on saddle areas. 24gauge.
– a. Internal finish lines- provide a definite joint
between the metal and resin portion of the
appliance.
– b. Tissue stop are placed on the ridge of distal
extension by cutting a 2 x 2mm square in the
relief wax
Duplication
1 Soak stone cast for 30 minutes in SDS
water, 90 degrees F, to eliminate air from
the casts and replace it with water so casts
will not draw moisture from hydrocolloid
and adhere to the cast.
Duplication
 Dupli-All duplicating material is an Agar
Hydrocolloid.
 The pouring temperature is 50 degrees
Celsius.
 Melt down temperature is 90 degrees
Celsius.
Duplication
 Duplicating material must cool
 Red-stripe investment is a phosphate-
bonded investment
 The liquid used with Red-stripe investment
is water.
Wax dip
 Dehydrate the refractory cast to prepare for
wax dipping
 Place in dehydration oven for 1 hour
 Wax dipping ensures a smooth dense cast
Wax-up
 Use combination of pre-formed pattern and
free flown wax.
Sprue and Invest
 A sprue provides a passageway for molten
metal during casting
 Auxillary sprues are used to ensure
complete casting to thicker areas
 The ratio for outer investment is 60 cc of
30% Begosol solution to 400 grams of
investment
Burnout
 Thermal expansion of investment occurs
during burnout.
Casting
 Induction casting machine uses 220 volts of
electricity.
 The electric casting machine also uses water
 Bego casting machine used positive
pressure from above and vacuum from
below
Casting
 A dark shadow will disappear when metal is
ready to cast.
Casting
 Acetylene and oxygen can be used to melt
Cobalt-chromium metal.
 50% new chrome cobalt should be added to
an existing button to make a casting