Is there any article discussing this issue and which technique is preferred, to redo the final impression, reline the crown or take pick up impression ?
Identiify the type of open margin; whether its a (positive or negative) vertical or a (positive or negative) horizontal deficiency, do some basic diagnostics on master cast, a sceond pour and try and identify the cause of the discrepancy to avoid similar problems. Once etiology is identified, proceed to a remake.A reline or pick-up impression has no place in fixed (only) prosthodontics.
Thanks for your valuable answer, but regardless what the technical reason was, nothing but redo is a scientific to manage such cases? To save patient time, material and based on evidence as well? And can you kindly share something to read about the type of open margin? Thanks again
An acceptable clinical marginal gap for allceramic/CADCAM restorions are 100-120 microns. That is the recommendation supported and suggested by a large body of scientific literature. A significant open margin wil be regarded as a failed restoration. You have to decide whether it is acceptable marginal gap. Saving patient time should not be part of the diagnostic process. Good luck.
Hi. Marginal gaps in the range of 60-100 microns are considered acceptable but cannot be identified clinically.therefore, if a margin is identified in the mouth , a new impression is mandatory.
I do agree with George, if the open margins are clinically identified then the gap is more than 100 microns which is not excepted and will sooner or later results in sensitivity problems and caries hence it best advised to remake the impression and redo the crown
So the technique that we use to do by adding porcelain to all cream margin is not appropriate ?
In general, I agree. A crown with an insufficient margin should be remade completely. If you want to transfer the insufficiency to the dental technician for adaption, you can use the following approach:
1. Cut back the margin of the crown in the area of the gap 1.0 mm superior to the margin of the preparation. Make sure that there is a pronounced chamfer.
2. Take an impression (e.g. polyether) with the positioned crown.
3. The dental technician should cast the impression with a special resin.
Because of the shrinkage of the ceramics during the firing process, the marginal fit will be tolerable at best. Because of the limited strength of the veneering ceramic (approx. 80 MPa) it should be implemented only in case of small areas with margin insufficiencies, using a special margin ceramics (available e.g. by Vita Zahnfabrik, Bad Saeckingen, Germany).
....or simply accept that old fashioned gold crowns perform by far better (accuracy of fitting below 50 microns) and are much longer lasting....!
If margin shows deficiency this will negativ reflect in in the cement and either way periclitate the success of the restoration.
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