Monday, 21 May 2012

Crowns or not for root-filled teeth?

Some time ago I wrote a paper for the EBD journal looking at whether there was high level evidence (i.e. systematic reviews or randomised controlled trials) for restoring heavily-filled vital posterior teeth with crowns (1). I was unable to find a single RCT let alone a systematic review of RCTs. At the time, though, I came across a study that compared crowns versus no crown on root-filled premolars (2). It was as small study with 117 participants and a fairly low failure rate in both groups (root-filling plus composite versus root-filling plus crown) and no statistical difference between the two. My search strategy would have allowed for other trials involving root-filled teeth but there appeared to be none. 

And so, since that time, I have been discussing with students that the evidence for placing crowns on root-filled posterior teeth is poor, and that there is therefore a reasonable degree of uncertainty over whether we should place them or not. I raise this because there are known negative consequences of placing crowns: cost, time, removal of sound tooth tissue, possibly increased risk of caries due to poor margins and poor OH, and probably some more. Do the positives of preventing tooth fracture and maintaining coronal seal outweigh these?

By coincidence, this morning I have just extracted a root-filled and crowned lower left 2nd molar with the students because it was grossly carious beneath the crown, causing it to fail (only roots retained). And that was in a well-motivated patient with good OH and low sugar intake. 

The Cochrane Library - Independent high-quality evidence for health care decision making

A systematic review has just been published (3) that, funnily enough, identified just one RCT comparing crowns to no crowns on root-filled teeth - the one I described above. What was the conclusion? 

"There is insufficient evidence to support or refute the effectiveness of conventional fillings over crowns for the restoration of root filled teeth. Until more evidence becomes available clinicians should continue to base decisions on how to restore root filled teeth on their own clinical experience, whilst taking into consideration the individual circumstances and preferences of their patients."

I think I might have worded this differently and suggest that, equally, there is insufficient evidence to support or refute the effectiveness of crowns over conventional fillings but the point is still the same - we are left with personal experience and patient values to guide us (2 of the 3 components for evidence-based decision-making) but are left bereft of good research to inform this.

Given the number of crowns placed in practice and the cost of these to individuals and society, plus the cost of root-canal fillings in the first place, it seems ludicrous that those who pay for these services (the NHS, private insurance groups, patients) do not demand an RCT or two to be done. If anyone's got an idea of where to get the funding and if there's anyone in practice who wants to participate, I'm ready to run one!

Happy decision-making ;-)



  1. Dr Hurst, really interesting thoughts on restoring root filled teeth.

    Now that I'm nearly half way through VT, I am slowly developing a serious lack of faith in patients to keep their dentition caries free after the restorative work I do (even though I still try hard with OHI).

    I do wonder whether it is worth crowning a tooth when I can predict that there will be caries around the margins in a few months.

    It would be great to hear more about this subject.


    1. Hi Vincent, it's great to hear from you. I think the only way we are going to be able to make more objective and realistic decisions is to run trials in general practice on patients like the ones you are treating. An interesting dilemma is, if we don't think the patient's risk of caries is getting lower should we be intervening at all other than stabilising caries and extracting teeth?

      Within a randomised controlled trial we might try and improve our prognostic powers by stratifying patients into, say, good and bad oral hygiene groups so that the crown and no crown groups have equal numbers of each. Then we'd need to ensure we had enough patients to detect a statistical difference, if it's there, between patients with good and bad oral hygiene and the risk of caries in each group.

      A great trial for general practice!