Casting failure M.Hosny 2023.pdf

CASTING FAILURE Presented by Dr. Mohammed Hosny Professor of Fixed Prosthodontics Collage of Dentistry Taibah University 2/11/2023 M.Hosny 2 I. No Casting 2/11/2023 M.Hosny 3 I. No Casting Possible causes A. Gate ( sprue) obstruction  Presence of investment fragments  Metallic sprue...

CASTING FAILURE Presented by Dr. Mohammed Hosny Professor of Fixed Prosthodontics Collage of Dentistry Taibah University 2/11/2023 M.Hosny 2 I. No Casting 2/11/2023 M.Hosny 3 I. No Casting Possible causes A. Gate ( sprue) obstruction  Presence of investment fragments  Metallic sprue former wasn’t removed B. Molten alloy was not directed into the mold cavity C. Premature solidification of alloy during casting  Low casting pressure  Cold ring  Incompletely heated or melted alloy 2/11/2023 M.Hosny 4 II. Incomplete casting  Possible causes: A. At the margins Rough margins: mainly due to presence of foreign material inside mold cavity e.g. piece of investment Round and convex margin: due to insufficient casting pressure, cold ring , insufficient alloy heating Round and concave margin: air entrapment preventing molten alloy to enter the mold freely  Less venting  Incomplete wax burnout  Carbon residues from wax  Thick margin 2/11/2023 M.Hosny 5 2/11/2023 M.Hosny 6 Incomplete casting B. Perforated castings 1. Perforation at thin areas: due to lack of accessory sprues 2. Perforation at the sprue attachment due to insufficient alloy. 2/11/2023 M.Hosny 7 III. Casting Defects By Addition 1. Frayed margins “fins” 2. Bubbles or nodules 3. Rough casting surface 2/11/2023 M.Hosny 8 III. Casting Defects By Addition 1. Frayed Margin (Fins) Possible causes: 1. Premature or rough ring handling after investing 2. Weak investment mix (High W/P ratio) 3. Too rapid heating during burnout 4. Improperly situated pattern (too close to ring periphery resulting in a very thin investment bridge) 2/11/2023 M.Hosny 9 FINS 2/11/2023 M.Hosny 10 III. Casting Defects By Addition 2. Bubbles or nodules a. Large Nodule Possible causes: Air entrapment during investing 2/11/2023 M.Hosny 11 III. Casting Defects By Addition 2. Bubbles or nodules b. Multiple Nodules Possible causes:  Inadequate vacuum during investing  Improper brush technique  Lack of surfactant c. Nodules on the Occlusal surface Possible causes  Excessive vibration 2/11/2023 M.Hosny 12 III. Casting Defects By Addition 3. Rough Casting surface Possible causes: 1. Presence of multiple bubbles on the surface of wax pattern 2.Rough surface of wax pattern 3. Increased w/p ratio of the mix. 4. Excess surfactant 5. Over heating of investment ring 6. Over heating of metal 7. Using investment material with large grain size 2/11/2023 M.Hosny 13 IV. Porosity A-Back pressure porosity Due to inability of air to escape through the pores of investment To reduce it’s occurrence: 1- Use of a porous investment 2- Proper burnout 3- Adequate mold and casting temperature 4- High casting pressure 5- Casting under vacuum 6- Proper wax pattern placement 7- Proper water powder ratio 2/11/2023 M.Hosny 14 IV. Porosity B-Gas inclusion porosity Occurs due to gas entrapment during casting. The gas source may be one of: 1- Blow torch if reducing zone not used. 2- Affinity of some alloys to absorb oxygen 3- Vapor resulting from heating of investment 4- Oxides entrapment inside the molten alloy → 2/11/2023 M.Hosny 15 IV. Porosity C-Suck-back porosity Results when the metal in the sprue solidifies before the metal in the mold, due to use of too long or too narrow sprue or improper location of the sprue. → D-Micro porosity  This type of porosity is not detectable by the naked eye.  A rough restoration may produce a galvanic cell that facilities tarnish and corrosion. 2/11/2023 M.Hosny 16 V. Dark discolored casting that resists pickling Due to decomposition of calcium sulphate binder in gypsum bonded investment due to overheating  Sulphur acts with cupper or silver in gold alloys resultant compound resists pickling of casting. 2/11/2023 M.Hosny 17 VI. Oversized or undersized restoration  Either tooo…… large or toooo…….. small  Due to expansion of investment To reduce it:  Proper water powder ratio  Ring liner  Amount of liquid added  Mold heating 2/11/2023 M.Hosny 18 VII. Warped or distorted restoration Possible causes:  Incorrect impression or die construction  Incorrect handling of wax pattern  Incorrect position of wax pattern in the casting ring  Under estimation of wax relaxation due to induced stresses  Using force during removal of restoration from ring 2/11/2023 M.Hosny 19 References Contemporary of Fixed Prosthodontics. 5th edition. P. 618 2/11/2023 M.Hosny 20 2/11/2023 M.Hosny 21