Casts, models and dies

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1 Casts, models and dies Dr. Judit Borbély 2017

3 Information

Study cast -made according to a study impression made previously -should be mounted on an articuator Besides revealing the shape of the hard and soft tissues, the

18 Study cast -made according to a study impression made previously -should be mounted on an articuator Besides revealing the shape of the hard and soft tissues, the mounted casts permit the cast s relation to each other and occlusion to be studied in detail, even from lingual aspect. It helps to decide the patient s treatment plan.

19 MASTER CAST It is the cast what is first poured out with stone after taking impression at the dental office. Ready appliances are also transported on it.

20 WORKING CAST -a copy what is made from the master cast with the help of duplicating material -used for making the wax pattern for the metal framework of a removable partial denture on its surface with prefabricated wax elements

21 SECTIONAL MODEL The dies of the prepared teeth or roots can be removed separately from the cast to make a very accurate or precise wax pattern for making a fixed dental appliance. Several methods are used for making sectional casts: Pindex method Kiefer method Crystal method

22 MODEL OR CAST and DIE CAST: the positive likeness of a patient s upper or lower jaw DIE: small model of prepared teeth

23 DIES I. DIE: small model or cast with a base Produced from an impression (mainly elastomeric types) of the crown or root surface of the tooth Used in construction of fixed appliances (inlays, crowns, bridges) Essential function of the die is to allow a restoration to be constructed in the laboratory which has an accurate internal or fitting surface.

28 DIES II. the base of the die provides a means of locating the die within a larger localizing model which includes the other teeth on the arch adjacent to the prepared tooth. the die can be removed and replaced in its original position Materials for preparing dies: 1.die stone: most widely used 2. Acrylic 3. Polyurethan

29 The desirable properties of model and die materials I. accurate reproduction of all the details of the impression sufficient strength and hardness to withstand work done upon them ease of manipulation and production of model or die in a reasonable time

30 The desirable properties of model and die materials II. good colour contrast with other materials suitable for use with all types of impression materials The most widely used model material is STONE ( derived from gypsum ).

Manufacturing CaSO4 2 H2O CaSO4 ½ H2O + 1 ½ H2O Dihydrate hemihydrate Mineral gypsum: CaSO4 2 H2O - When the dihydrate is heated (110 and 130 o C), water of crystallization is removed dry

31 Manufacturing CaSO4 2 H2O CaSO4 ½ H2O + 1 ½ H2O Dihydrate hemihydrate Mineral gypsum: CaSO4 2 H2O - When the dihydrate is heated (110 and 130 o C), water of crystallization is removed dry β-hemihydrate - irregular particles plaster of Paris, model stone autoclave α-hemihydrate - more perfect crystals model stone, die stone When calcium sulphate hemihydrate particles are mixed with water, the reverse of the above reaction occurs CaSO4. 1/2H2O + water CaSO4. 2H2O

32 β-hemihydrate α-hemihydrate

34 CASTING OF IMPRESSIONS I. during casting all impressions must be handled with great care to avoid damage and weakening of the cast impressions taken in compound, zinc oxide paste, alginate or elastomers do not require treating with separating medium, stone does not stick to them plaster impressions must be painted with with a soap or detergent solution (waterglass) all equipment used for mixing the stone must be clean (any material remaining from the previous mix in the mixing bowl must be removed, as it may impair the surface of the cast as well as accelerating the setting time) the water-stone ratio should be that advised by the makers of the particular stone being used

35 CASTING OF IMPRESSIONS II. the main problem in casting impressions is the exlusion of air from the mix since its presence weakens the cast three methods may be used to eliminate as much air as possible: 1. mechanical spatulation (for at least 30 seconds till consistency is smooth and creamy in a flexible bowl with a stiff bladed spatula) 2. vibration table: during filling up of the impression vibrating is recquired until the stone fills all the deepest parts of the impression 3. vacuum mixer

Disinfection of stone casts or dies Although the impression itself should be disinfected before being handled further by the dental office staff or the laboratory technicians, whenever there is a

36 Disinfection of stone casts or dies Although the impression itself should be disinfected before being handled further by the dental office staff or the laboratory technicians, whenever there is a question about whether or not this has been done, the stone cast or die also can be treated. Soaking the gypsum, iodophor, glutaraldehyde, phenol. In addition, stone materials are available that contain disinfecting agents.

37 Pindex-method

38 Pindex-method

48 Kiefer method Images from: Dr. Peter Hermann, Zoltan Hajdu: Sectional casts

49 Crystal method Images from: Dr. Peter Hermann, Zoltan Hajdu: Sectional casts

50 Gingiva mask Images from Dr. Peter Hermann and Zoltan Hajdu

61 Thank You for Your Attention!

Introduction to the patient and know the chief complain (clinical step). Diagnosis and filling a case sheet with preparation and motivation the

Introduction to the patient and know the chief complain (clinical step). Diagnosis and filling a case sheet with preparation and motivation the patient to the treatment (clinical step). Treatment planning