Working cast and die-Impression=> diagnostic cast => preparation on a patient=>2nd imperession=>working cast -cast is appositive replica of the arch. -Diagnostic cast to make special tray and temporary bridge -Requirments of a good cast: a. accurate( accuracy of the impression =>accuracy of the cast) reproduce all details captured in the impression c. dimensional stability. surface of tooth. b.

D. Include the prepared and unprepared e. hard. g. no voids, bubbles or nodules in

f. can be casted easily. critical areas. H.trimming

-Die is a ppositive replica of the prepared tooth alone (prepared single tooth). -You have to make impression for the whole arches not only the prepared tooth. -Requirements of a die: a.Accurate. b. dimensional stable (or have slight expansion ). hard,resistant to abrasion. d. No voids, bubles or nodules. ( concavity below the finishing line ), e. Discernible finishing line c.

-Die materials: a. Gypsum. copper ). b. Resin. c. electroplating die ( silver or

d. flexible die materials ( resemble heavy bodied silicon and polyether impression materials. ).

Gypsumaccording to ADA ( American dental association ) the gypsum products are classified to five classes. We cant use except class 4 and 5. They have slight expansion which compensates metal casting contraction ( so it is not considered a disadvantage.) -Dont depend on the color because every company have a special color.

Type IV: -Advantage: 1-accuracy. 2-straight forward technique.

-disadv.: If not handled carefully and it is scratched => can be damaged Type V: Advantage: Harder than type IV. expansion. Disadvantage: slight increase

Epoxy Resin -it is mainly epoxy resin. -Advantage: 1)high strength. 2)good abrasion resistance. -disadvantage: 1)polymerization shrinkage. 3)time consuming and complex procedure. -Base and catalyst. 2)will fit more tightly. 4)high cost.

Electroplating

-. -adv.: 1-high strength and good abrasion resistance. -disadv.: 1-the material that will precipitate is toxic and its vapor is very dagerous. 2-time consuming(can use only one material which is polyaddition silicone). 3- needs special equipment. 4-not suitable for all impression

-electroplating die: impression material should withstand immersion in solution for long time to be used in this technique ( addition silicon ). We electroplate just the prepared teeth. Flexible die material 3rd pour.

b. removable die system, require: 1-die return to exact position. 3-easily mounted cast on an articulator.

2-die is stable. Techniques:

1-dowel pin. : put pins under the prepared teeth and edentulous area in the impression material, and they are fixed by bobby pins. Then pour the ridge, apply separating medium and pour the base. After that saw the ridge to get the removable die.

2-Pindex system. pour the ridge. Special drill is used to make holes in the cast below the prepared teeth and edentulous area. Using glue, fix pins to the cast. Apply separating medium then pour the base. Finally, saw the cast to get the removable die. -there are two types of pindex drill according to the pointer: a. laser pointer, b. normal pointer. -there are two types of pins used in the pindex system technique: a. two pins ( one long pin under buccal cusp, one short pin under lingual cusp), for better access cementation. b. one pin ( with two extensions, one long and one short ).

-the vacuum mixing machine makes the mix dense and free of voids. -selection of the cast fabrication technique is according to the availability of equipment and what the technician prefer. advantage: 1-less cost. .disadvantage: 1-bulky2-removable die-

3-alternatives c. alternative techniques: * di-lock technique (plastic). *dva model system (just name). *zeiser model system.