4.2 bent clasps and major connectors

what are the basic instruments for bent clasps + major connector fabrication?

• flat tip wire bending pliers

• curved laboratory pliers

• cutting pliers

• hollow chop laboratory pliers

what are direct retainers?

component of RPD used to retain to prevent dislodgement, consisting of a clasp assembly/precision attachment parts:

• reciprocal arm

• occlusal rest

• retentive arm

what is a precision attachment? (long)

• a retainer consisting of a metal receptacle (matrix) and a closely fitting part (patrix) that are factory made

• matrix contained in the normal or expanded contours of crown on abutment tooth or dental implant

• Patrix attached to pontic or the removable dental prosthesis framework

what is a precision attachment? (short)

• an interlocking device, where one component is fixed to an abutment and the other is integrated into the removable dental prosthesis in order to stabilise and/or retain it

what is a precision rest?

• prefabricated

• rigid metallic extension (patrix) in FDP or RDP that intimately fits into box-type rest seat or keyway (matrix) portion of precision attachment in a restoration

• factory made

• Two types (intracoronal and extracoronal)

what are the two types of precesion rests?

• intracoronal

• extracoronal

what are semi precision attachment?

• laboratory fabricated rigid metallic extension (patrix) of a fixed or removable dental prosthesis that fits into a slot-type keyway (matrix) in a cast restoration

• Allows some movement between the compnents

what are precision rest?

• precision rest is prefabricated, rigid metallic extension (patrix) used in fixed or removable dental prosthesis

• Fits intimately into box-type rest seat or keyway (matrix) portion of a precision attachment in a restoration

what are semi precision rest?

• rigid metallic extension used in fixed and removable dental prostheses

• Fits into an intracoronal preparation in a cast restoration, which is laboratory fabricated

what is a dental surveyor?

• instrument used for analysis, planning and construction of model cast dentures

what does dental surveyor consist of?

• platform

• vertical column with a cross arm

• vertical spindle at the end

The spindle has a chuck where various surveying instruments can be attached, such as a spring loaded attachment for measuring

what is below the vertical attachment of dental surveyors?

• a mobile cast holder connected to a ball joint on top of the platform

what is a good feature of the cast holder of surveyors?

• cast holder can be adjusted to different angles or locked in a horizontal position for convenience during the dental surveying process

how many degrees should the path of insertion be and why shouldn’t it be higher?

• not exceed 35 degrees - high angulation makes placement of denture virtually impossible

• Over 45 degrees will increase pathological forces during mastication and lead to inevitable overloading of abutment teeth

what is suprabulge?

• portion of tooth or crown that converges toward the occlusal surface

what is suprabulge clasp?

• any partial removable dental prosthesis retentive clasp that approaches the retentive undercut from an occlusal or suprabulge direction

what is an infrabulge?

portion of crown of a tooth apical to the survey line

what is infrabulge clasp?

removable partial denture retentive clasp that approaches the retentive undercut from a cervical or infrabulge direction

single shoulder clasp fabrication

double shoulder clasp fabrication

three shoulder clasps

jackson’s clasp fabrication

what are clasps made of wire usually made like?

• made of ovoid steel

• specific diameters for diff teeth

• canines and premolars recquire diameter 0.8-0.9mm

• Molars need 1mm

• Rrare cases, Au-Pt OR Ag-Pd alloys can be used

how should reciprocal clasp arm and occlusal rest be when positioned over suprabulge zone?

rigid and non-elastic

how should the retentive clasp arm be positioned over infrabulge area?

• elastic and passive

how is optimal retention and reciprocation chieved from clasp’s arms?

clasp arms should encircle the tooth from both the vestibular and lingual side

what are the bent major connectors?

connective

reinforcing

what are major connectors like?

• long

• relatively narrow

• rigid without being bulky (for comfort of patient)

• Shouldn’t obstruct frenulum or reach bottom of oral cavity

• Do not require undercut finish lines like maxillary major connectors

• Cross section has a half-pear shape

What are recquirements of major connectors?

• connector should stay in front and under tongue

• During mastication, should follow vertical sinking motion of saddle

• Motion correlate with susceptibility of mucosa

• Avoid trauma by not having the mandibular major connector directly press on mucosa

• Pre-emptive waxing or using lead foil can prevent this

• Gypsum model can be covered with lead foil

• Maintain distance around 0.8-1.2mm between major connector and mucosa

what is the distance that should be maintained between major connector and mucosa?

0.8-1.2mm

what should the major connectors follow during mastication?

vertical sinking motion of saddle

where should major connectors be located?

in front and under tongue