Prosthodontips – should I place a crown or an onlay?
In this month’s Prosthodontips column, Josh Sharpling discusses how to make the right choice between crowns and onlays.
In this column I am going to talk about a question I am asked a lot – should I be placing a crown or an onlay?
I run courses teaching both posterior crowns and onlays. The question that most commonly comes up is: should I place a crown or an onlay?
A tricky choice
The choice between these two restorations can be a tricky clinical situation to navigate. However, I have come up with some rules that point me in the right direction.
Both crowns and onlays are cuspal coverage restorations. These restoration types are used for a number of clinical reasons, some of which are listed below:
- Large cavity size
- Cracked tooth syndrome
- Fractured cusps
- Unsupported cusps
- Endodontically treated tooth.
These can be grouped together by situations where a tooth is likely to fracture.
Protect the tooth
In these clinical situations my default restoration is an onlay rather than a crown.
This is because an onlay is less destructive to the remaining tooth structure.
In an already compromised tooth, I think we must aim to retain as much tooth as possible. There is no doubt that a crown prep is more destructive than an onlay prep.
With the big benefit of less tooth preparation, what are the drawbacks of onlays?
I can think of the following:
- The preparation can be more technically demanding
- Dentists are more comfortable with conventional crown preparations
- Tooth restoration margin lines can be more visible with onlays (although margins can be hidden by extending the preparation into a veneerlay type restoration)
- Retention is via adhesive means, and adhesive dentistry is very technique sensitive.
Despite these, I still chose an onlay as my restoration of choice in most clinical situations.
My rules for posterior cuspal coverage
Every posterior tooth which needs cuspal coverage receives an onlay, unless:
- I cannot isolate the tooth with rubber dam (compromising my moisture control and potential success of adhesive dentistry)
- The majority of the prepared margin is in dentine (I am more comfortable with a long term bond to enamel than to dentine)
- I am replacing a failing crown.
I hope you found this column helpful, and if you have any questions, please don’t hesitate to get in touch at [email protected].
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- Occlusion revisited: part one.
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