Partial Veneer Crowns - Posting #7

One can expect partial veneer crown preparations on some school practical examinations - notably USC, for their case-based exam it is sometimes most appropriate to do this type of crown preparation.

There are many times in dental practice that, even if you start off thinking that you are going to do a full gold crown on a patient, you end up doing a partial veneer crown, for example a 3/4 crown, without even knowing it!

For example - and I use this example in my classes all the time - you are doing a FGC on #18 and it is the most distal tooth in the arch, and the gingival level is very high on the distal side. The patient may be in their 20s and they have had very little attachment loss and the tissue is high on that side. Now, you proceed as normal to do the occlusal reduction for the FGC and the occlusal surface of the preparation is, on the distal side, already at the gingival level, and you haven't done the axial reduction on that side of the tooth! So you have no retentive wall on the distal. Presuming that you have three retentive axial walls out of a possible four, you are doing a 3/4 crown, like it or not. Now, how do we get some resistance form for mesial tipping? Place grooves on the buccal and lingual. Then make sure that the margins are smooth and continuous gingival to the grooves, and up onto the distal margin which is just outside the marginal ridge, insure that the gold at the distal margin will not be too thin, and you have a 90 degree rotated 3/4 crown!

The main thing about partial veneer crowns, including the 3/4 and the 7/8 is that they allow, many times, a much more conservative preparation than would be necessary for the PFM. The PFM will allow retention, in principle, more easily, since we are preparing the entire facial surface and extending deep subgingivally - but often we should be thinking about the wisdom of this when a lot of the lingual part of the tooth is broken off - does it make sense to cut off most of the buccal part of the tooth?

In general, we need to keep in mind that a 3/4 or 7/8 crown can be done, and many times can be done more easily than a PFM or full ceramic crown, and certainly more conservatively, and with less hazard to the opposing teeth and with much better margins. Then, for an individual patient, we can decide what makes the most sense, esthetically and otherwise. If all you know how to do is a PFM your practice will be limited, to be sure. We have a variety of model typodonts that are available, and one does have a 7/8 crown on a maxillary premolar! Even this can be the most appropriate restoration in certain circumstances.

If you have any questions about how grooves and flares are made, or whether the standard textbook groove design is really necessary for retention, or if other, easier methods may work, just post a comment on this section and I'll be happy to discuss these things.

We are close to having our Fundamental Restorative Techniques course on-line! This will enable you to see exactly how many of the restorative preparations are done and hear a lot of discussion of the use of different designs.