Ring aorund the Lateral

[sndmn2]

Pressed two Maryland bridges yesterday. One I sprued from the inc. edge the other from the labial . Wouldn't you know it. The labial one one pressed with what looks like a "bulls eye" right where the sprue was attached. So the bridge looked translucent,ring of "MO" and then translucent right in the center of that.A couple of thoughts crossed my mind.
1. This was the first time I pressed a HT pellet. Do you guys press HT at a higher temp? I think the Ivoclar oven has differant firing temps for differant pellets.
2. Since it was like pressing a pontic is a larger than normal sprue needed?
3. Stuff like this just happens so don't drive myself nuts thinking about it?
Thanks, Rick

 

[Al.]

NO that happens on all of them.
Sixonice gave a scientific explanation of why a while back.

Its not an issue if you are going to layer. If you press and stain you need to sprue on the incisal edge or on the lingual.

On bridges when you only sprue the abuttments you will also get a trans line in the middle of the pontic where the material form both sprues meet in the midddle of the pontic. Sometimes this can be mistaken for a crack in the middle of the pontic.
Now I sprue all three, both abutments and the pontic with 3 10 ga sprues rather than with 2 8 ga sprues on the abutments only.

 

[sndmn2]

O.K That's good to know. I"m pressing two more this weekend.
Thanks, Rick

 

[dentor2010]

NO that happens on all of them.
Sixonice gave a scientific explanation of why a while back.

Its not an issue if you are going to layer. If you press and stain you need to sprue on the incisal edge or on the lingual.

On bridges when you only sprue the abuttments you will also get a trans line in the middle of the pontic where the material form both sprues meet in the midddle of the pontic. Sometimes this can be mistaken for a crack in the middle of the pontic.
Now I sprue all three, both abutments and the pontic with 3 10 ga sprues rather than with 2 8 ga sprues on the abutments only.

a guy from Ivoclar said that a 3 sprue method makes the meeting point be at the junction which will create a weak point for your bridges. be careful.

 

[sixonice]

Pressed two Maryland bridges yesterday. One I sprued from the inc. edge the other from the labial . Wouldn't you know it. The labial one one pressed with what looks like a "bulls eye" right where the sprue was attached. So the bridge looked translucent,ring of "MO" and then translucent right in the center of that.A couple of thoughts crossed my mind.
1. This was the first time I pressed a HT pellet. Do you guys press HT at a higher temp? I think the Ivoclar oven has differant firing temps for differant pellets.
2. Since it was like pressing a pontic is a larger than normal sprue needed?
3. Stuff like this just happens so don't drive myself nuts thinking about it?
Thanks, Rick

let me jump in here. i have experienced this myself and can explain what happened and how to prevent it. first off, always sprue off the long axis of the restoration (on anteriors go off the incisal, posteriors choose the largest cusp, consider the easiest flow of the ceramic). The reason you got that little low value spot is because the lithium disilicate hit an axial wall and turned over on itself. imagine logs floating down a river (if you were looking from above). the logs all point down the river in a pattern. now imagine a spot where the logs turned sideways - the pattern would be different in the area where the logs turned sideways & jammed up. the reason i use this analogy is because e.max get pressed in a semi-liquidous form. the lithium disilicate crystals all line up with each other and form a "pattern". by spruing to the labial you more or less created a break in the pattern. the material is fine, same strength, just that little low value halo that you can stain or layer on. just sprue them more off the incisal on anteriors and your all set. maryland bridges are not endorsed for lithium disilicate, but i sprue to both abutments and the pontic if the dentist wants to move forward with it. same with a splinted e.max, i sprue to each unit. finally, yes, if your pressing with a ivoclar press they do have separate press paramters for HT, LT & MO ingots. hope this helps you understand what happened and how to avoid it in the future.