Presentation on theme: "Single die Single copper band impression may be done using either impression compound or rubber base. The type of single die material depends on the type."— Presentation transcript:
Single die Single copper band impression may be done using either impression compound or rubber base. The type of single die material depends on the type of the impression material used. Classification of the single die according to the die materials 1- Stone die. 2- Amalgam die. 3- Acrylic die. 4- Refractory die. 5- Electroplated die. a) Silver plated die b) Copper plated.
1) Stone die: It can be either with impression compound or rubber base. The stone used as a die material should have minimum amount of setting and thermal expansion and maximum amount of surface hardness and smoothness.
Technique 1) Warp the impression band by molding wax extending 10mm beyond the cervical margin. 2) Following the manufactures instruction, the stone is mixed at a proper water/powder ratio. 3) Pour the mixed stone into the waxed band, increment, maintaining proper vibration to avoid air bubbles. 4) Insert a dowel pin after the impression has been filled with stone. 5) After complete setting of the stone, remove the die from the rubber impression material, while incase of impression compound, the band is placed in hot water bath till the compound is softened and the die is carefully removed
2) Amalgam die: It is indicated only for copper with impression compound, because the elastic property of the rubber base impression cannot withstand the forces of amalgam condensation. - Advantages : It can produce a harder die than the stone die. - Disadvantage: 1) Done only with impression compound. 2) Long setting time. 3) Much setting expansion.
Technique: 1- Warp the impression band by modeling wax extending 10mm beyond the cervical margin of the root portion. 2- The waxed band is centralized inside a casting ring and investment material is poured around and in between the band and the casting ring this is to give better handling and condensation of amalgam. 3- Trituration amalgam according to the manufactures instruction and packed properly to fill the impression and the root portion.
4- After complete setting of amalgam, remove the die and trim the root portion so it can be seated in the working cast. 3) Acrylic and epoxy resin dies: Pour either self-curing acrylic resin or epoxy into the copper band with impression compressive strength than that the stone die.
4) Refractory die (ceramic die): A special type of ceramic material can be used for the construction of the single die. It is supplied as a powder and liquid that mixed and fired according to the manufacture’s instruction “fired after the condensed porcelain is removed from the impression.
Preparation of the die 1.Trimming the die If the die represent free gingiva at higher level than the finish line trimming away must done to define the margin. 2. Correction the defect If small defect present on die result from caries or previous restoration that are under cut to path of withdrawal of the new restoration, its convenient to block the out on the die with zinc phosphate cement.
3. Shaping the die handle Shaping of the die handle by using an acrylic bur, then ditching the die below the finish line by 0,3 mm using inverted cone bur, this circumferential groove act as guide during wax pattern construction and help during finishing of the cast restoration.
4. Marking the margin: The finish line of the preparation should be colored with bright red pencil (color should be contrast with that of the wax will be used) without any pressure to preserve the preparation
without any scratches and to facilitate carving of wax at the margin, a lead pencil is not recommended because it can abrade the die it darker color can interfere with effort to verify with efforts to verify the wax was properly adapted at margin, and traces of graphite (antiflux) can prevent complete casting on margin
5. Provision of an adequate cement space: Die spacer is used to maintain constant thickness space between the internal surface of the casting and prepared surface of the tooth except immediately adjacent to margin
each The space provide room for luting agent and allow complete seating of the restoration at the preparation margin there should be aband of close adaptation (about 1 mm wide) to prevent dissolution of luting agents, The ideal dimension for cement space has been suggested at 20 to 40 microns for wall If the cement space is too narrow, the casting will not seat properly during cementation because of hydraulic pressure that develops when the viscous mass of luting agent cannot escape through the narrow gap between crown and preparation as the restoration is seated.
Conversely, if the cement space is too wide, the casting will be loose on the tooth, resistance form will be reduced, and the position of the casting will be difficult to maintain accurately during evaluation and occlusal adjustment. In addition, the risk of the crown loosening during function increases.
Marginal integrity ( finish line) Ending of tooth preparation should terminate at a definite position and configuration being termed as finish line.
Basic guidelines for establishing finish line 1.It should be easily prepared without being over extended cervically when ever possible. 2.Easily identified in both impression and die. 3.Facilitates a distinct boundary (edge) to which the wax pattern could be easily adapted and finished. 4.Allow producing sufficient bulk of material to: - enable handling wax pattern without being distorted.
allow s producing sufficient strength of restoration. - enhance esthetic properties when porcelain is used. 5. Conservation of tooth structure should be considered.
1. Chamfer finish line Its mainly used in the cast metal crowns and the metal (only) portion of metal ceramic restoration. 2. Shoulder finish line This type of finish line is usually recommended for the all ceramic crown and facial part of metal-ceramic crowns It should form a 90 degree angle with unprepared tooth surface. 3. Rounded (radial) shoulder It is a modified form of shoulder finish line characterized by a rounded internal angle (gingivo –axial) its indicated for all ceramic crown preparation.
4. Sloped shoulder finish line it is a modification of the classic shoulder finish line being characterized by a 120 degree as an alternative to 90 degree. 5. Bevel finish line This type is frequently indicated for cast metal restoration, especially if a ledge or shoulder already exists due to caries, cervical erosion or previous restoration. Its shape forms an obtuse angle with the unprepared axial tooth surface.
6. Shoulder with bevel finish line This type is recommended for facial surface of metal ceramic restorations in those situations where gingival esthetic are not critical and a shoulder is already present either because of destruction by caries or previous restorations. 7. Feather edge margin 8. Knife edge (chisel edge) margins