Spruing And Investing Techniques 2023 PDF

SPRUING and INVESTING Presented by Dr. Mohammed Hosny Professor of Fixed Prosthodontics Collage of Dentistry Taibah University Lab Steps 3 M.Hosny 2/6/2023 SPRUING 4 M.Hosny 2/6/2023 Sprue former: Provides a channel in the investment material.  Through this sprue channel molten wax c...

SPRUING and INVESTING Presented by Dr. Mohammed Hosny Professor of Fixed Prosthodontics Collage of Dentistry Taibah University Lab Steps 3 M.Hosny 2/6/2023 SPRUING 4 M.Hosny 2/6/2023 Sprue former: Provides a channel in the investment material.  Through this sprue channel molten wax can escape during the burnout process.  Molten metal can reach the mold cavity during casting. 2/6/2023 M.Hosny 5 Basic requirements of the sprue former 1. Allow the molten wax to escape from the mold. 2. Enable the molten metal to flow into the mold. 3. The metal within it must remain molten slightly longer than the alloy that has filled the mold. 2/6/2023 M.Hosny 6 Types of sprue former 2/6/2023 M.Hosny 7 1) According to sprue former materials  Wax sprue former (preferred).  Plastic sprue former: 1. Solid 2. Hollow  Metallic sprue former: 1. Solid 2. Hollow 2/6/2023 M.Hosny 8 Wax sprue former 2/6/2023 M.Hosny 9 2/6/2023 M.Hosny 10 Plastic sprue former 2/6/2023 M.Hosny 11 2) According to sprue former diameter 1. Large-diameter sprue is recommended because this improves the flow of molten metal into the mold and ensures a reservoir during solidification. 2. A narrow sprue is essential with air-pressure casting machines where a sudden change in air pressure occurred.  2.5mm for molar and metal ceramic.  2mm for premolar and partial coverage. 2/6/2023 M.Hosny 12 3) According to sprue former length (Average 6 mm) Distance between pattern and ring top Gypsum-bonded investment -------- 6-8 mm Phosphate-bonded investment ----- 3-4 mm 2/6/2023 M.Hosny 13 Thermal zone 2/6/2023 M.Hosny 14 Sprue former location  The sprue should be attached to the bulkiest part of the pattern ( non functional cusp). Anterior teeth ------- mid incisal. The point of attachment should be well flared and avoid any constriction to allow good flow of molten alloy. 2/6/2023 M.Hosny 15 Sprue former location Incorrect sprue placement in the central fossa obliterates occlusal anatomy and may result in poor mold filling. 2/6/2023 M.Hosny 16 4) According to number and shape of sprue former A) Single spruing Straight ------- precious and semi precious alloy i) ii) Zigzag ------------- non precious alloy. 2/6/2023 M.Hosny 17 B) Double spruing i) Direct sprue ( V and Y shapes) ------- precious and semi precious alloy ii) Indirect sprue ( stable shape) ------------- 2/6/2023 non precious alloy. M.Hosny 18 C) Multiple spruing ---------- large restoration 2/6/2023 M.Hosny 19 D) Accessory sprue (venting) The thin auxiliary sprue may help gases escape and ensure the casting solidifies in a critical area and thin wall. 2/6/2023 M.Hosny 20 Crucible Former  The sprue is attached to a crucible former, which constitutes the base of the casting ring during investing.  It provides a funnel to facilitate entrance of molten alloy  Made of rubber, wax and wood but usually made of rubber. 2/6/2023 M.Hosny 21 Casting ring holds investment in place and restricts expansion 2/6/2023 M.Hosny 22  Ring liner allows for hygroscopic expansion, venting, facilitates removal of investment, and directs expansion outwards. Made from ceramic or cellulose paper materials. Asbestos liner not used nowadays because it’s a carcinogenic. 2/6/2023 M.Hosny 23 RINGLESS INVESTMENT TECHNIQUE: - Used with higher-strength, phosphate-bonded investments. - It is designed to allow unrestricted expansion of the alloys of higher melting temperature to compensate for high shrinkage. Plastic ring 2/6/2023 M.Hosny 24 SPRUING TECHNIQUE for a single casting 1. Attach a wax sprue to the bulkiest non functional cusp of the wax pattern, and angled it to facilitates filling of the mold. 2/6/2023 M.Hosny 25 2. Add wax to the point of attachment and smooth it to prevent turbulence during casting. 2/6/2023 M.Hosny 26 3. Remove the pattern from the die, using extreme caution not to distort it by bending the fingers of the left hand. 2/6/2023 M.Hosny 27 4 - Insert the sprue into the hole in the crucible former with forceps and lute with wax which should be smoothed.  Use of a surfactant greatly enhances wetting of the pattern during investing. 2/6/2023 M.Hosny 28 5. Line the casting ring, keeping it flush with the open end, and moisten the liner. 6. Place the ring over the pattern to ensure it is sufficiently long to cover the pattern with about 6 mm of investment. 2/6/2023 M.Hosny 29 SPRUING TECHNIQUE for multiple castings  When more than two units are being cast together, each is joined to a runner bar.  A single sprue is used to feed the runner bar. 2/6/2023 M.Hosny 30 INVESTING DENTAL CASTING INVESTMENTS They are composed of: Refractory material…………….. Silica, responsible for the thermal expansion of the mold during wax elimination. Binder…………………… gypsum, or magnesium oxide and an ammonium phosphate compound. Modifiers……………………… accelerators, retarders and reducing agents e.g. (carbon). 2/6/2023 M.Hosny 32 Ideal requirements of investment materials  Able to control of expansion.  Produce smooth castings.  Accurate surface reproduction.  Chemical stability at high casting temperatures.  Adequate strength to resist casting forces.  Sufficient porosity to allow gas escape.  Easy recovery of the casting. 2/6/2023 M.Hosny 33 Types of investment materials  Gypsum-bonded  Phosphate-bonded  Silicate-bonded 2/6/2023 M.Hosny 34 Gypsum-bonded investments  Binder: gypsum (Calcium sulfate hemi hydrate).  Refractory material : cristobalite or quartz.  Not chemically stable at high temperatures above 1000°(1080°).  More porous.  Long working time.  Mixed with distilled water.  Produce smooth surface casting.  Used for casting of conventional type II,III, and IV gold alloys. 2/6/2023 M.Hosny 35 Phosphate-bonded investments  Binder: Magnesium oxide and ammonium phosphate compound.  Refractory material: Silica.  Mixed with colloidal silica.  Higher strength.  Higher expansion due to the special liquid.  Stable at high temperatures; suitable for base metal alloys. 2/6/2023 M.Hosny 36 Phosphate-bonded investments  Carbon-containing materials (gray in color) are used for high gold or palladium alloys.  Carbon-free investments are used for base metal alloys because carbon if found affect final alloy composition.  Lower porosity.  Rougher surface.  Shorter working time. 2/6/2023 M.Hosny 37 Expansion Setting expansion Occurs during material setting as a result of crystal growth Hygroscopic expansion Extension of setting expansion by adding water to the setting investment by: Wet liner.  Submerging the ring in a water bath at 37°C for 1 hour immediately after investing. Thermal expansion  Solid-state phase transformations of silica.  More controllable. 2/6/2023 M.Hosny 38 2/6/2023 M.Hosny 39 How to increase expansion  Prolonged spatulation  Hygroscopic technique  Use of two ring liners  Storage in 100% humidity  Lower water-powder ratio in gypsum-bonded  Increase special liquid in phosphate-bonded 2/6/2023 M.Hosny 40 Investing techniques  Single investing  Brush technique  Vacuum technique  Double investing 2/6/2023 M.Hosny 41 Application of wetting agent (surfactant) 2/6/2023 M.Hosny 42 Brush technique 2/6/2023 M.Hosny 43 Vacuum technique 2/6/2023 M.Hosny 44 Double investing 2/6/2023 M.Hosny 45 Wax elimination (burnout)  Aims:  Complete elimination of wax to obtain an empty mold.  Obtain adequate thermal expansion.  Elevates the temperature of the investment to prepare it for casting.  Burnout temperatures  Gypsum-bonded: 650-700°c  Phosphate-bonded: 850-900°c 2/6/2023 M.Hosny 46 2/6/2023 M.Hosny 47 References Contemporary of Fixed Prosthodontics. 5th edition. P. 601 2/6/2023 M.Hosny 48 2/6/2023 M.Hosny 49