In this article, I’ll explain why you shouldn’t air dry your dental adhesive (“bonding agent”) prior to curing it. In order to explain why these adhesives shouldn’t be air-dried, I’ll also describe the oxygen inhibited layer (OIL). Please note, this article is written with regard to fourth and sixth generation gold-standard adhesives (like Optibond FL, Clearfil SE and Clearfil SE protect). Universal adhesives have a solvent in them which require you to air dry it. That being said, even if you are not using a fourth or sixth generation adhesive, this article is still highly relevant. Ready to nerd out with me?
To begin lets first acknowledge that dental composite is cured through a radical polymerization reaction.
However, free radicals, like the oxygen found in room air, prevent a thorough polymerization reaction from taking place. This means that the top-most layer of dental composites have a layer of uncured monomers. The literature reports this layer is anywhere from 4 μm- 53 μm thick.
Just to put that into perspective, the OIL is about half the thickness of a sheet of paper – its hard to believe something that thin is so impactful.
Moving along. Grossman found that the average adhesive thickness for Optibond FL is 221 μm. When an adhesive is air thinned, it can easily be thinned to the extent that it is only 10-50 μm thick.
Why is an adhesive thickness of 10-50 μm so problematic? Because that means the only thing left of the adhesive layer is the air inhibited layer, which will not adequately cure.
Now, Rueggeberg and Margeson reported that the OIL has some limited capability to undergo polymerization (aka cure), but its unsatisfactory for dental bonding.
So, in effect, air thinning the adhesive layer will cause an inadequate bond between the dentin and adhesive layer and may result in failure.
What should you do in the event you have excessive pooling of the bonding agent? Next time you’re thinking of air drying your dental adhesive, simply wick it away with a micro-brush.
P.S. I hope this article was helpful! I love geeking out and I’m glad you could join me. Do you need dental continuing education hours? Dental Digest would like to help! Did you know we made it possible for you to earn dental continuing education through our dental podcast? Click here to get started!
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This article was written by Dr. Melissa Seibert who unabashedly identified as a big dental nerd. Click here to learn more.
Resources and References:
Bijelic-Donova J, Garoushi S, Lassila LV, Vallittu PK. Oxygen inhibition layer of composite resins: effects of layer thickness and surface layer treatment on the interlayer bond strength. Eur J Oral Sci. 2015 Feb;123(1):53-60. doi: 10.1111/eos.12167. Epub 2014 Dec 31. PMID: 25556290.