79 . Principles of construction of model cast RPD. Fulcrum lines. Types of defects of the dental arches:

Constructional principles of model cast dentures with cast clasps and precision attachments:

• Surveying:

  • To identify the most favorable tilt, the retentive undercuts and interferences.

  • To located and delineate the contours and relative positions of abutment teeth and associated structures

  • Path of insertion.

  • Recording the position of the cast.

  • Measuring the retention.

  • Recording the prosthetic equator.

• Planning:

  • Placing by the help of the surveyor.

• Teeth preparation:

  • Fixing the teeth in the wax in the right positions.

• Model cast denture technology:

  • Flasking process

  • High temperature Polymerization cycle (long or short)

  • After cooling, remove the denture from the gypsum

  • Clean and polish

what is fulcrum line

a theoretical line around which a removable dental prosthesis tends to rotate.

what are the fulcrum planes?

• horizontal

• vertical

• saggital

fulcrum on horizontal plane

• Rotation of denture on sagittal plane

• denture base moves away from supporting tissues, counteracted by direct or indirect retainer

• denture bases moved towards supporting tissue, counteracted by occlusal rest ad tissues of supporting ridges

fulcrum on sagittal plane

• rotation around longitudinal axis formed along crest of residual ridge

• less in magnitude but can be damaging

• counteracted by:

  • major and minor connector

  • close adaption of denture base

  • direct retainer design

fulcrum on vertical plane

• rotation around horiozntal plane

• counteracted by:

  • reciprocal arm and minor connector

  • major connector

  • close adaption to denture base

types of defect of dental arch?

• rotation around fulcrum line passing through posterior most abutment when denture base moves vertically towards or away from supporting residual ridges

• rotation around longitudinal axis formed by crest of residual ridge

• rotation around vertical axis located near centre of arch