Insight 88 — Scanning Provisional Crowns over Uncemented Posts: Why It Works for Provisionals and Not for the Final Impression

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Clinical Explanation

Point one: scanning provisional crowns over uncemented posts

In this patient we are going to increase the VD, and I made post and cores for six anterior teeth. The problem was that until we have posterior support, I cannot deliver the posts. My original plan was to first place provisional crowns on the posterior teeth at the correct VD, cement the posts at the next visit, and only then scan for the provisionals.

Instead, I placed the posts in position without cement and made sure they were seated, made a resin pattern for the one tooth that had no post, and then scanned everything together with the posterior teeth in one pass for the provisional crowns.

I never do this for the final impression, because the definitive crown must be scanned on a tooth whose dimensions are final and will not change even by microns. A post that has not yet been cemented may shift by a few microns after cementation, and a post and core that is still in resin may seat differently after casting. But for a provisional crown, the accuracy we need is on the order of millimetres, not microns.

At the next visit I will first cement the post and cores, refine the preparations, try in the provisional crowns, reline and adjust them if needed, and deliver the anterior and posterior segments together.

Point two: the upper left 4 and 5

Teeth 4 and 5 had been prepared very poorly by the previous dentist, who had placed a fiber post and composite that could not be removed. Here I preferred not to touch their structure, and I discussed with the patient that we would make two crowns splinted together, and if they fail later for any reason, we would place an implant.

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