Prosthodontips – should I place a crown or an onlay?

Prosthodontips onlayIn 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].

Previous Prosthodontips:

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