Wednesday, 25 January 2012

Zinc-oxide-eugenol and composite

For a little while I have been keeping a secret. I had read that eugenol was a pretty effective antibacterial agent and it had been suggested by a specialist endodontist that we place it in the coronal portion of the root canal as an antibacterial plug.

So I place IRM as a plug. What do I then do when I want to place a composite? Well, I place a composite.

That's the secret and I'm ashamed. But why? Because when I was an undergraduate student I seemed to remember being told Zinc oxide eugenol stopped composite from.....what? Setting? Bonding? I couldn't remember but I figured all that eugenol was far enough away from where I was bonding so what did it matter.

But there was always a niggling doubt.

Anyway, it all came out when a student on clinic needed to place a restoration in a tooth that had had IRM placed as a temporary, and which plugged the root canal. I suggested she leave the IRM plug and suddenly I heard this voice saying "that's wrong - very wrong" and I hastily said to the student that it was likely the materials lecturers would lynch me if she ever told them.

But then I thought, what is the science that underpins this doubt I have about using zinc-oxide eugenol? And what about leaving it as a sedative base in those deeply-cavitated pulpitic teeth?

I did a search in pubmed:
(composite OR bonding*agent*) AND (eugenol OR IRM OR kalzinol OR ZnO) AND (strength OR hard*)

There were 116 hits. There were conflicting results on the whether zinc oxide eugenol (rather than just eugenol) significantly affected the bond strength of resins to enamel and dentine. It certainly wasn't as clear cut as I had thought.

I was only able to find one paper that looked at how the composite itself (rather than the bonding agent) was affected. In this paper, whilst composite hardness was affected by the presence of IRM, it was only to a depth of 100 microns - 0.1mm. (He LH, Purton DG, Swain MV: A suitable base material for composite resin restorations: Zinc oxide eugenol. J Dent 2010;38:290-295.) The authors suggested this wouldn't have an affect on bonding elsewhere.

This is in no way a good systematic appraisal of the literature and I hope to soon get round to doing one but  for the moment I'm feeling like I might have a defence should anyone from the materials team coming looking for me... ;-)

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