Crowns are tighten in insertion

[Tayebdental]

Why my crowns are tight now in insertion in the pt. mouth , i haven’t changed anything as far as I know,. cement spacer is the same ,shrink rate is dialed in as indicated on the puck , sintering is the same. any idea?

 

[rkm rdt]

Why my crowns are tight now in insertion in the pt. mouth , i haven’t changed anything as far as I know,. cement spacer is the same ,shrink rate is dialed in as indicated on the puck , sintering is the same. any idea?

From a pvs model or an intra oral scan?

 

[Tayebdental]

From a pvs model or an intra oral scan?

all from scans,

 

[rkm rdt]

all from scans,

Different drs or just one?

 

[tuyere]

Have you tried with all-new tooling? Is your spindle due for replacement? Any head crashes or improper collet maintenance that might have damaged the collet?

 

[Tayebdental]

Different drs or just one?

One dentist in particular and another sometime

 

[Tayebdental]

Have you tried with all-new tooling? Is your spindle due for replacement? Any head crashes or improper collet maintenance that might have damaged the collet?

I change tools according to tooling schedule in CNC, the spindle seems to be fine with no vibration or abnormal sounding, I clean collet weekly and lightly grease sense I don’t use the mill everyday . I am changing all tools anyway and do a calibration and touch point surfacing

 

[rkm rdt]

Ok I assume everything fits fine on your models.
What IOS are they using?

 

[Affinity]

models? we dont need no stinkin models!

 

[RileyS]

models? we dont need no stinkin models!

Nooo! I miss stone models

 

[TheLabGuy]

Might have to go out to the office and see what they are seeing. Tight at margin area? Tight proximals? Tight because they have undercuts you ain't blocking out? Tight because the shrinkage rates ain't right...bad oven, or element going? Tight at occlusal intaglio? Tight because of sharp edges of preps getting rounded digitally? Tons of reasons and causes is my point.

 

[Tayebdental]

Ok I assume everything fits fine on your models.
What IOS are they using?

The issue of tightness is not all time, modeless always. Issue with prime scan/Cerec and iTero

Might have to go out to the office and see what they are seeing. Tight at margin area? Tight proximals? Tight because they have undercuts you ain't blocking out? Tight because the shrinkage rates ain't right...bad oven, or element going? Tight at occlusal intaglio? Tight because of sharp edges of preps getting rounded digitally? Tons of reasons and causes is my point.

Many variables I agree.They remotely checked the mill, the numbers seem within limits.( milled cubic wax shape and measurement was fine) I am changing new all cutting toolings and surfacing touch plate with calibration, the sintering furnace calibration is within 3*c, blocking is automatically done by Exocad (I have to recheck that). I am pouring an imp. scanning / designing /milling two crowns with different thickness and starting point of cement spacer for comparison on the die.

I had a a discussion with the dentist on a particular prep, for a remake where the abutment in scan prep seems boxy in shape and in relation to adjacent teeth, which makes it difficult for insertion, and I suggested to taper prep to ease insertion.

Tightness seems internally and hi occlusion , and not on all cases which makes me wonder, I even suspected the shrink rate numbers on the puck!, I bring opposing .6 mm between adjusting antagonist and cutting crown occasionally. Never had this issue before.

 

[Affinity]

Nooo! I miss stone models

Yeah, I still do 99% of my work on stone models. Once you sell them on the cool toxic plastic, theres no going back. Im biding my time.

 

[Affinity]

I even suspected the shrink rate numbers on the puck!,

This is a variable that you really have no control over. I think its an approximate at best depending on what zr youre using. If you think about it, youre dialing in the mill for a crown that is 20% larger and hoping when it fires that it matches the same exact tolerances as your mill made it. Try sending along a milled PMMA crown and ask if there is a difference between the two. My .02

 

[rkm rdt]

I would outsource the milling of a few crowns and see if there is any difference.
With so many variables, I would want to eliminate all possibilities one at a time.

 

[Sda36]

Why my crowns are tight now in insertion in the pt. mouth , i haven’t changed anything as far as I know,. cement spacer is the same ,shrink rate is dialed in as indicated on the puck , sintering is the same. any idea?

It's acting like an impression pulled to early and not timed, had that nightmare enough times. Stretches and then sets leaving an undersized prep with crazy vertical limits. Just adding this as it may help you to access your current headache. Hope it helps.
Merry Christmas to you and yours as well, you'll figure this out but it's still a pain for sure.

 

[Sda36]

It's acting like an impression pulled to early and not timed, had that nightmare enough times. Stretches and then sets leaving an undersized prep with crazy vertical limits. Just adding this as it may help you to access your current headache. Hope it helps.
Merry Christmas to you and yours as well, you'll figure this out but it's still a pain for sure.

Z axis is likely the issue.

 

[Flipperlady]

I would be temped to ask the dentist to watch a couple of cases from start to finish. I would especially watch what kind of temporaries they use, are they falling out between appointments? Things shift, a slight movement can throw everything off. Might not be on your side.

 

[Sda36]

I would be temped to ask the dentist to watch a couple of cases from start to finish. I would especially watch what kind of temporaries they use, are they falling out between appointments? Things shift, a slight movement can throw everything off. Might not be on your side.

I always ask them to make provisionals using shimstock as a guide, pulls through tight but doesn't tear. That way what we deliver is the same contact pressure ~ 10 microns or so. Some shimstock is 8 microns, another is 12.

 

[Affinity]

I pull shimstock through on my contacts, but I get complaints its too tight and that they want floss to snap through, if floss snaps, then shimstock wont hold, not to mention that theres barely any contact at all.