Light cure composite materials have produced a radical shift in dentistry over the past 40 years; it's a shift I have lived in while graduating in 1980. One of the constants I believed in, like the speed of light, was that it was not possible to provide too much light to a light cured material. As it turns out, I might have been wrong.

In researching composite curing I came across a 2006 study that looked at the thickness of the oxygen inhibited layer with varying amounts of light applied to the adhesive layer resin (the bonding resin) under direct fill composites.

In this study, curing the adhesive resin layer longer than recommended by the manufacturer actually resulted in a higher degree of conversion and a thinner oxygen inhibited layer.

Curing the adhesive layer for 30 seconds or more (curing time was tested to 60 seconds) thinned the oxygen inhibited layer enough that defects were observed between the adhesive layer and the composite resin. A thick oxygen inhibited layer produced better bond to the curing composite.

So what's the take home argument? On an adhesive layer of bonding resin under a direct composite, a lot of light might be too much. Cure the bonding resin under your composites for the amount of time recommended by the manufacturer, not more.

Reference:
J Biomed Mater Res B Appl Biomater. 2006 Jul;78(1):115-23.
Effect of light-cure time of adhesive resin on the thickness of the oxygen-inhibited layer and the microtensile bond strength to dentin. Kim JS1, Choi YH, Cho BH, Son HH, Lee IB, Um CM, Kim CK.

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Comments

Commenter's Profile Image Costin
April 9th, 2014
So true Gary! We did a tiny study in our practice together with Prof. Bluck from Charité University in Berlin and it clearly showed the difference between insufficient curing time and extended curing time. Just as a precaution though, for curing times over 5 seconds (pretty much all of them) we cooled the lamp's tip with aer. Even with LED lights, the superficial temperature of the composite is increasing considerably. Also, when the composite surface is contaminated with a small traces of blood, the temperature build-up rate is increasing exponentially.
Commenter's Profile Image Gerald Benjamin
April 10th, 2014
Of all the things in dentistry to worry about, over curing resin is not one of them. Dentists are notorious for not spending an adequate amount of time curing resin. In addition, dentists are notoriously cheap and are buy lights from China that are not consistent in their light output. I have been placing direct posterior resins for almost a quarter of a century using bilateral, transenamel illumination with two powerful lights simultaneously. You can't over cure the resin and you will not overheat the pulp. One tooth a YEAR requires endo in the year that place a posterior resin.