CASTING PROCEDURE INTRODUCTION CASTING IS THE PROCESS BY

CASTING PROCEDURE

INTRODUCTION CASTING IS THE PROCESS BY WHICH A WAX PATTERN OF A RESTORATION IS CONVERTED TO A REPLICATE IN DENTAL ALLOY. THE CASTING PROCESS IS USED TO MAKE DENTAL RESTORATIONS SUCH AS INLAYS, ONLAYS, CROWNS, BRIDGES, AND REMOVABLE PARTIAL DENTURES. BECAUSE CASTINGS MUST MEET STRINGENT DIMENSIONAL REQUIREMENTS, THE CASTING PROCESS IS EXTREMELY DEMANDING. IN DENTISTRY, VIRTUALLY ALL CASTING IS DONE USING SOME FORM OR ADAPTATION OF THE LOST-WAX TECHNIQUE HAS BEEN USED FOR CENTURIES, BUT ITS USE IN DENTISTRY WAS NOT COMMON UNTIL 1907, WHEN W. H. TAGGART INTRODUCED HIS TECHNIQUE WITH THE CASTING MACHINE. CASTING CAN BE DEFINED AS THE ACT OF FORMING AN OBJECT IN A MOULD. THE OBJECT THUS FORMED IS ALSO CALLED AS A CASTING.

OBJECTIVES OF CASTING 1) TO HEAT THE ALLOY AS QUICKLY AS POSSIBLE TO A COMPLETELY MOLTEN CONDITION. 2) TO PREVENT OXIDATION BY HEATING THE METAL WITH A WELL ADJUSTED TORCH . 3) TO PRODUCE A CASTING WITH SHARP DETAILS BY HAVING ADEQUATE PRESSURE TO THE WELL MELTED METAL TO FORCE INTO THE MOULD. .

STEPS IN MAKING A CAST RESTORATION 1. TOOTH PREPARATION. 2. IMPRESSION. 3. DIE PREPARATION. 4. WAX PATTERN FABRICATION. - THERE ARE 4 METHODS FOR MAKING WAX PATTERNS FOR A CAST RESTORATION. 5. SPRUING. A) SPRUE FORMER. (SPRUE PIN ). -PROVIDES CHANNEL FOR THE MOLTEN METAL. -MADE OF WAX , PLASTIC OR METAL. -RESERVOIR IS ATTACHED TO THE SPRUE. -IDEALLY LENGTH OF SPRUE IS 3/8 TH” TO ½”

LOST WAX PROCESS THE LOST WAX CASTING PROCESS IS WIDELY USED AS IT OFFERS ASYMMETRICAL CASTING WITHNVERY FINE DETAILS TO BE MANUFACTURED RELATIVELY INEXPENSIVELY. THE PROCESS INVOLVES PRODUCING A METAL CASTING USING A REFRACTORY MOULD MADE FROM A WAX REPLICA PATTERN.

THE STEPS INVOLVED IN THE PROCESS OR THE LOST WAX CASTING ARE: 1. CREATE A WAX PATTERN OF THE MISSING TOOTH / RIM 2. SPRUE THE WAX PATTERN 3. INVEST THE WAX PATTERN 4. ELIMINATE THE WAX PATTERN BY BURNING IT (INSIDE THE FURNACE OR IN HOT WATER). THIS WILL CREATE A MOULD. 5. FORCE MOLTEN METAL INTO THE MOULD CASTING. 6. CLEAN THE CAST. 7. REMOVE SPRUE FROM THE CAST 8. FINISH AND POLISH THE CASTING ON THE DIE.

THE LOST-WAX TECHNIQUE IS SO NAMED BECAUSE A WAX PATTERN OF A RESTORATION IS INVESTED IN A CERAMIC MATERIAL, THEN THE PATTERN IS BURNED OUT ("LOST") TO CREATE A SPACE INTO WHICH MOLTEN METAL IS PLACED OR CAST. THE ENTIRE LOST-WAX CASTING PROCESS. A WAX PATTERN IS FIRST FORMED ON A DIE OF THE TOOTH TO BE RESTORED OR, OCCASIONALLY, DIRECTLY ON THE TOOTH. ALL ASPECTS OF THE FINAL RESTORATION AREINCORPORATED INTO THE WAX PATTERN, INCLUDING THE OCCLUSION, PROXIMAL CONTACTS, AND MARGINAL FIT. ONCE THE WAX PATTERN IS COMPLETED, A SPRUE IS ATTACHED, WHICH SERVES AS A CHANNEL FOR THE MOLTEN METAL TO PASS FROM THE CRUCIBLE INTO THE RESTORATION. NEXT, THE PATTERN AND SPRUE ARE INVESTED IN A CERAMIC MATERIAL, AND THE INVESTED PATTERN IS HEATED UNTIL ALL REMNANTS OF THE WAX ARE BURNED AWAY. AFTER BURNOUT, MOLTEN METAL IS CAST INTO THE VOID CREATED BY THE WAX PATTERN AND SPRUE. ONCE THE INVESTMENT IS BROKEN AWAY, THE ROUGH CASTINGIS PICKLED TO REMOVED OXIDES. FINALLY, THE SPRUE IS REMOVED AND THE CASTING IS POLISHED AND DELIVERED TO THE PATIENT. IF ALL STEPS HAVE BEEN DONE WELL, THE FINAL RESTORATION WILL REQUIRE MINIMAL MODIFICATION DURING CEMENTATION INTO THE PATIENT'S MOUTH.

ACCURACY OF THE LOST-WAX TECHNIQUE A CASTING SHOULD BE AS ACCURATE AS POSSIBLE, ALTHOUGH A TOLERANCE OF RT 0. 05% FOR AN INLAY CASTING IS ACCEPTABLE IF. THE LINEAR DIMENSION OF AN AVERAGE DENTAL INLAY CASTING IS ASSUMED TO BE 4 MM, +0. 05% OF THIS VALUE IS EQUAL TO ONLY +2 YM, WHICH SUGGESTS THAT IF TWO CASTINGS MADE FOR THE SAME TOOTH HAVE A VARIATION OF 4 YM, THE DIFFERENCE MAY NOT BE NOTICEABLE. TO VISUALIZE THIS DIMENSION, RECALL THAT THE THICKNESS OF AN AVERAGE HUMAN HAIR IS ABOUT 40 YM. THEREFORE THE TOLERANCE LIMITS OF A DENTAL CASTING ARE APPROXIMATELY ONE-TENTH THE THICKNESS OF A HUMAN HAIRT. O OBTAIN CASTINGS WITH SUCH SMALLTOLERANCE LIMITS, RIGID REQUIREMENTS MUST BE PLACED NOT ONLY ON THE INVESTMENT MATERIAL BUT ALSO ON THE IMPRESSION MATERIALS, WAXES, AND DIE MATERIALS. NATURALLY, TECHNICAL PROCEDURES AND THE PROPER HANDLING OF THESE MATERIALS ARE EQUALLY IMPORTANT. THE VALUES FOR THE SETTING, HYGROSCOPIC, AND THERMAL EXPANSIONS OF INVESTMENT MATERIALS MAY VARY FROM ONE PRODUCT TO ANOTHER, AND SLIGHTLY DIFFERENT TECHNIQUES MAY BE USED WITH DIFFERENT INVESTMENTS. IN EACH CASE, THE VALUES OBTAINED FOR ANY ONE PROPERTY SHOULD BE REPRODUCIBLE FROM ONE BATCH TO ANOTHER AND FROM ONE CASTING TO ANOTHER.

CASTING DEFECTS Casting involves large no of steps: Casting design, pattern making, moulding, melting, pouring, shake out, fettling, inspection&finishing Use of defective material/equipment , carelessness of operator or lack of skill result in defective casting

COMMON DEFECTS 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Open Blows & Blow Holes Pin Hole Porosity Entrapped Air & Other Gases Cracked Casting Bent/Twisted Casting Dropped Mold Fusion Swell Run Out Mismatch

COMMON DEFECTS 11. Shrinkage-Faults 12. Rat Tail & Buckles 13. Mis-run & Cold Shut 14. Core Shift 15. Inclusions 16. Cuts & Washes 17. Metal Penetration 18. Hard Spots 19. Scrabs 20. Hot Tears

• Open blows are smooth cavities/voids on surface of casing • Blow holes are bubble of gas entrapped inside casting • Caused by gases carried by hot metal OPEN BLOWS & HOLES

RUN OUT • Occurs when molten metal leaks out of mould during pouring • Avoided by modifying moulding system, providing proper parting line&providing proper gating system

MIS RUN • Caused when section thickness of casting is so small • Minimized by proper design of casting, providing suitable gating & risering

CASTING MACHINE Device force alloy liquid into mould formed in investment in casting ring. From the evolution of single chamber casting system(OROTIG patent)the last innovation in fusion and casting for titanium and dental alloy was form, ie the universal semi-automatic casting machine SPEEDCAST 220 MJ-TI by OROTIG.

SPEED CAST 220 MJ -TI

SPEEDCAST 220 MJ-TI

The single chamber configuration allow metal to fused on specific copper crucible, very close to feed pipe of casting cylinder; significantly shortening the time it taken to transfer cast alloy from crucible to mould, maintaining mass as hot and compact as possible, with much faster mould filling time.

THESE FEATURES MAKE IT POSSIBLE FOR EXTREMILY LOYAL REPRODUCTION TO MOULD MARGIN AS WELL AS USE OF MUCH SIMPLER TECHNIC BY OPERATOR.

THE POSSIBILITY TO FUSE UPTO 26 G OF TITANIUM AND UPTO 40 G OF ALLOY MAKE IT AN INDISPENSIBLE INSTRUMENT FOR ALL DENTAL TECHNICIAN LABORATORIES LOOKING FOR INNOVATION AND AVANT-GRADE PRODUCT.