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. 

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 ;-)

References

1. Hurst D. Indirect or direct restorations for heavily restored posterior adult teeth? Evid Based Dent. 2010;11(4):116-7.

2. Mannocci F, Bertelli E, Sherriff M, Watson TF, Ford TR. Three-year clinical comparison of survival of endodontically treated teeth restored with either full cast coverage or with direct composite restoration. Journal of Prosthetic Dentistry 2002;88(3):297-301.

3.  Fedorowicz Z, Carter B, de Souza RF, de Andrade Lima Chaves C, Nasser M, Sequeira-Byron P. Single crowns versus conventional fillings for the restoration of root filled teeth. Cochrane Database Syst Rev. 2012 May 16;5:CD009109.