Bridge expansion

[KTR]

We always adjust liquid/ water ratio for bridges. You don't want to adjust single units so max expansion, but bridges will gain length invested with the same mix. Add more water and less liquid for a bridge. We usually add about 5 mil more water and less liquid.

 

[number1]

The reservoir should be filled, but little more. I use 8 gauge (I think) direct sprues. Make sure the reservoir is in the center of the ring, the crown close to the top and little or no button at the bottom. What temp do you burnout at?
I use a rapid burnout, I put the ring into the furnace preheated to 1250 F for 30 minutes, then I turn the oven down to 950 F for 30 minutes. I find it casts nicer at the cooler temp but if you don't heat it above 1200ish, you won't get rid of the carbon.

I also use a rapid burnout, straight into a 1200F oven for 60 minutes

 

[Dimis]

Ok, last idea
If your not sure if the bridge will draw or not before waxing, and you don't own a surveyor ! make a quick coping on each abutment and place a steel mandrel, etc over the abutments and lute together. Now lift off to see if any of the wax
coping crack or break. You may learn you need to make a reduction coping so the bridge will draw...
If you want to learn more about spruing techniques, start a new thread.. or buy a scanner for printing or milling your larger bridges.... lol

What is a surveyor?


Sent from my iPad using Tapatalk

 

[CatamountRob]

What is a surveyor?

 

[rkm rdt]

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[Bumfrey]

instead of normal die spacer i use rubber-sep on bridgework. Gives a little more 'wiggle' room for easier seating, as it can be removed easily. Just have to be careful with space as it can be applied too thick very easily.

 

[SiKBOY]

Or you can just double or triple up on the die spacer.

For Goldie's, I use the pre made sprue was with reservoirs
oven at 850 for half hr. Drop temp to 650 for half hr and cast. Don't need a lot
Of heat to cast Full Goldie's.

If the Goldie's are extra thick, I'll make the reservoir thicker.

I just had to cast a 3 unit full gold bridge with a slot attachment on the distal of the 5. (Lower 5 to 7). With the 2 unit, I used 2 pieces of indirect hard plastic bar joined together (to double the thickness of the reservoir). No porosity when I had to polish.

 

[aqdental]

Good morning.

How do I adjust my investment ratio for better fitting long span bridges? I follow the wax/sprue techniques in some of the forums and use Fast Fire investment. 30 minute bench set with a 60 minute burnout at 1450. After casting, bench cool to touch. I find that the individual units fit ok, but the bridge as a whole does not. It seems to only happen on big bridges with multiple pontics. Simple 3 or 4 unit bridges are no big deal. Is there any merit to adjusting the ratio? And if so, which way?

Thanks

Are they over or under expanded? Is rocking the problem? Please specify.

 

[Darby Hawkes]

Good morning.

How do I adjust my investment ratio for better fitting long span bridges? I follow the wax/sprue techniques in some of the forums and use Fast Fire investment. 30 minute bench set with a 60 minute burnout at 1450. After casting, bench cool to touch. I find that the individual units fit ok, but the bridge as a whole does not. It seems to only happen on big bridges with multiple pontics. Simple 3 or 4 unit bridges are no big deal. Is there any merit to adjusting the ratio? And if so, which way?

Thanks

The alloy makes a huge difference for what you are asking. Are you doing full cast or sub structure for PFM? I have stabilized all bridges for investing by using an 8 gauge plastic sprue rod instead of wax (the rod that comes with artimax articulators). Making this change made a world of difference on bridges fitting without rocking.