porosity in full gold bridgework

[emh56]

spruing full gold pontic on full gold bridge to avoid porosity

 

[Affinity]

Use a very large resevoir on a tapering sprue. Like, the size of the pontic.. You can also use a vent and maybe give it an extra turn..

 

[Affinity]

http://www.ijdr.in/article.asp?issn...5;issue=3;spage=340;epage=345;aulast=Baskaran

 

[user name]

Reservoir should be heavier than the intended casting. Low temp, proper torch flame, don't over heat the metal.

Contrary to Affinity, I never give it an extra turn. With more metal, your getting more force in your casting without cranking it up. Too much casting force can cause unwanted turbulence in the metal.

Always make sure your torch is clean and not blowing out oxidized bits from the tip, and clean the crucible.

 

[Affinity]

haha now that I look at that picture, its maybe not the best example, I was trying to find pictures of the resevoir.

My advice is maybe misleading, using more force depends on if youre already winding 3x or 4x and how much gold your throwing .. I usually go 3 for gold, 3.5- 4 for NP or larger frames. The vents should control the added velocity of the metal.

Having said that, Ive cast maybe 2 full gold bridges in my career, one for the cdt test and one a couple years back, so maybe dont listen to me.

 

[user name]

@Affinity Holy smokes brother! Im with you on 3.5-4 on NP, but for FC Gold, Im 1.5.

 

[Affinity]

I cast 1-2 / week, with no issues, no porosity.

 

[ztech]

Porosity in cast alloy cannot be eliminated, you can only control where it is. The last area of a casting to cool will have porosity, as will any areas that cool after the access to a reservoir has cooled. The trick is to keep the reservoir in the heat zone while putting the casting in the first areas to cool. You can do this with larger reservoirs, you can to it with a larger mass of alloy, you can also do it with a lower burnout temp. I caution against the use of chill vents since they will cool first and draw from the pattern alloy as they shrink. I also don't use blind vents since most modern investments allow the casting pressures to escape without using them. The process of casting is important also. Lower the pressure to decrease turbulence as stated above, and lower the flame temp to allow more rapid solidification.

 

[rkm rdt]

mill the gold
cash the cheque

 

[rkm rdt]

haha now that I look at that picture, its maybe not the best example, I was trying to find pictures of the resevoir.

My advice is maybe misleading, using more force depends on if youre already winding 3x or 4x and how much gold your throwing .. I usually go 3 for gold, 3.5- 4 for NP or larger frames. The vents should control the added velocity of the metal.

Having said that, Ive cast maybe 2 full gold bridges in my career, one for the cdt test and one a couple years back, so maybe dont listen to me.

lol, fake sprues !

 

[ps2thtec]

mill the gold
cash the cheque

Agree ! Check this thread .

https://dentallabnetwork.com/forums/threads/old-school-meets-new-technology.25832/#post-248877

 

[larsondental]

short sprues and a runner bar will work also