Working casts and dies Flashcards
Working Cast is
the replica of the prepared teeth, ridge area ,and other parts
Requirements of working casts
1-It must reproduce both prepared and un prepared tooth surfaces. 2-The unprepared teeth immediately adjacent to the preparation must
be free of voids
3-all surface of any teeth involved in anterior in anterior guidance and The occlusal surface of all unprepared teeth must allow for precise
articulation of the opposing casts
4- all relevant soft tissues should be reproduced
DIE is
the positive reproduction of the prepared tooth and consists of a suitable hard substance of sufficient accuracy (improved stone, resin, or metal)
REQUIREMENT OF THE DIES
1-Reproduce exactly the prepared teeth
2-All surfaces must be free from any defects ex. bubbles, nodules
3-Remaining unprepared tooth structure cervical to finish line (by 0.5-10) Should be clear on the die to facilitate proper cervical contours
Requirement of Die material
1-High mechanical strength properties to withstand handling procedures Without fractured
2-superior stability and dimensional accuracy
3-High surface hardness to resist abrasion while wax pattern construction
4-compatible with the impression materials
5-Good color contrast with the casting wax used, so the preparation margin can be seen
6-Easily wet table by wax
7-Easily section able and easy to trim
Different types of Die materials
1-ADA TYPE IV high strength dental stone (most commonly used), amalgam die
2-Epoxy resin die , Refractory die
3-Electroplated dies
Basic type of working cast& die systems
1-working cast with separate Die (multiple pour technique)
2-working cast with removable Die :According to the method of Die Retention in the Working cast there are two type :Dielok tray& Dowel pin
Dowel pin
According to the time of dowel pin placement in the impression
WET-Pinning Technique Pre –pour Technique
DRY- Pinning Technique Post – pour Technique Or pindex system
Advantages of Working cast with a separate die
-simplest method
-the relationship between abutments is kept fixed
-because the gingival tissue around the prepared teeth are intact , it can be Used as a guide for proper contouring
Disadvantages of working cast with separate die
1-Repated removal and transfer from one to the other would Result in distortion of wax pattern
2-Seating the patterns on working cast might be problematic, because Second pour is slightly larger than the first which might necessitates Slight relieve
Advantages of Working cast with removable die
1-less chance of wax pattern distortion due to elimination of repeated Removal from its die
2-omits the possible discrepancies between the separate die and working Cast that might have been due to
Disadvantages of Working cast with removable die
1-If the die not reseat accurately in its position in the working cast, defective Wax pattern would result
2-Inter proximal margins might be damaged during die sawing
Basic requirement of removable die system
1-The dies must return to there original position in the working cast smoothly
2-The dies must remain stable
3-The cast containing the dies must be easy mountable on the articulator
Dowel pins are Characterized by :
1-Knurled head of retention of the poured die material
2-An extension for retention of the die on the working cast which having one Flat surface to :
-provide resistance against rotation
-to insert and remove the die only in one path
