DUPLICATION OF CASTS AND CROSS MOUNTING

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DUPLICATION OF CASTS AND CROSS MOUNTING

• TIM VAN

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INTRODUCTION

• Encompasses an overview of cast duplication and
  ability to critique both master and processing
  casts.
• Cast duplication is an obligatory step.
• Accurate clinical information is vital!
• Face-Bow Recording
• Charting of centric stops at RCP/ICP
• Interocclusal Record / BITE

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BEFORE DUPLICATION

• What steps are done before duplication?
• Obviously, past the stage of pouring up master
  cast.
• Indexing/Mounting
• Pindex
• Split Cast Mounting Technique
• Surveying
• Tripodising
• Outline height contour
• Undercuts

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BEFORE DUPLICATION (2)

• Blockout
• Defined as a number of areas that may be
  eliminated by blockout material.
• Different types of blockout material.
• Different classifications of blockout
• Paralleled
• Shaped
• Arbitrary
• Relief
• Avoid tissue impingement.
• Difference to Blockout?

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CAST DUPLICATION

• Allows preservation of original master cast.
• Processing/working cast is used instead to fit
  the RPD framework.
• Duplicating Materials and Flasks
• Silicone vs Agar
• Different properties

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DUPLICATION PROCEDURE

• Moistening of the master cast.
• Placed at the bottom of a suitable duplicating
  flask. Check Orientation
• Use of a Gelovit MP machine to heat and monitor
  the temperature of agar.

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DUPLICATION PROCEDURE (2)

• Agar dispensed, ideally flowed at the posterior
  end of cast.
• Then guided around teeth and other critical
  areas.
• Filled to brim of flask.
• Top and feeder are then fitted feeder ring
  filled.
• Flask placed in cold water bath and allowed to
  set.

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DUPLICATION PROCEDURE (3)

• Flask inverted and bottom of flask is removed.
  Excess agar then removed.
• Master cast separated from the agar.
• Inspect mold for any defects. Re-take if
  necessary.
• Once checked, a positive duplicate is created.
  Investment material is added incrementally.
• Fill mold completely.
• Ensure no dehydration to ensure no dimensional
  changes.

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CROSS MOUNTING

• Used to assess accuracy of mounting of casts and
  the actual duplicate casts themselves.
• Split cast technique allows mounting of any pair
  of casts together.
• Involves mounting original master casts with
  duplicate processing casts.
• Assess accuracy of cross mount with
• Centric stops at RCP/ICP using articulating
  paper.
• Shimstock tolerance.
• Any combination of casts with exactly the same
  articulator setup should be identical in terms of
  both centric stops and shimstock tolerance.

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CONCLUSION

• Shows importance of cast duplication and cross
  mounting.
• Thus, it is a mandatory procedure to minimise any
  introduced errors, which would lead to the
  ultimate failure of the treatment.