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If you have seen the marketing propaganda for the latest whiz-bang curing lights, you’ve no doubt found claims of superfast
performance and incredible depths of cure. A leading manufacturer of curing lights even goes so far as to state
that its light will cure many popular hybrid composites to depths of 5.5–7.4 mm—in five seconds!
That would be great, if only it were true. This article will give you information that should make you stop and think
before following this misleading claim.
First, to understand how these claims can even be stated at all, you need to know something about how depth of cure
(DOC) is measured. Although there are various ways to accomplish this task, a simple International Standards Organization
(ISO) scrape test may be the most popular, since it is quick and expedient. 1 In this test, a stainless steel cylinder is
essentially filled with composite and cured from one of the open ends. The uncured material on the bottom is scraped
away and the height of the resulting cured material is measured. The DOC is stated as 50 percent of this height.
Contrast that method to the way DOC is measured in the REALITY Research Lab (RRL). We use a modified Class II preparation
in a real extracted human tooth. The tooth is secured in an Ultradent bond strength testing jig (Ultradent Products,
Inc., South Jordan, UT) that has been modified for this purpose. A section of stainless steel matrix, similar to those
used clinically by most dentists, provides the surface against which the composite is cured in this Class II preparation.
“
Despite its snooze-inducing potential, curing 2 mm increments of
composite for 40 seconds remains the gold standard, especially when
your light is not in direct contact with the restorative material. ”
After filling the preparation and curing the material, the restored tooth is removed from the jig and the DOC is measured
using a sophisticated digital hardness testing device. Hardness is the parameter we use to determine how well a
composite has cured deep into the preparation. A similar test is used to gauge how well flowable composites are cured
on the gingival wall of Class II proximal boxes.
The results from the RRL are definitive and categorically reject the 5-second and even 10-second curing claims coming
from light manufacturers. Unfortunately, in clinical situations, undercured composite is very difficult—if not impossible—to
diagnose, even years after the restoration has been placed. Who is to say that the gradual yellowing of a restoration
was caused by undercuring? It might have happened even had the restoration been cured properly. What about a
fractured marginal ridge in a Class II restoration? Would it have fractured if the material’s strength had been maximized
by thorough curing?
It’s my position that clinicians should do anything and everything within their power to increase the probability that
their restorations will be as durable and long-lasting as possible. Longer curing will skew the success rate in your favor.
Why do you think indirect restorations are blasted with intense light for extended periods?
Despite its snooze-inducing potential, curing 2 mm increments of composite for 40 seconds remains the gold standard,
especially when your light is not in direct contact with the restorative material. This would be the situation when you
are incrementally restoring a Class II preparation. Once you have built up the restoration and the restorative material is
very close to the light tip, you can reduce your curing time to 20 seconds, assuming that you are using a relatively translucent
hybrid composite. Reducing curing time does not work with microfills, which are notoriously difficult to cure.
The allure of curing restorations for only 5-10 seconds may be hard to resist, but our data clearly and definitively indicates
that you will be shortchanging your patients if you allow this primrose path. In the final analysis, how long would
you want a restoration to be cured if you were the patient?
To contact Dr. Michael Miller, visit www.realityesthetics.com or e-mail mmiller@realityesthetics.com.
References
1. Fan PL, Schumacher RM, Azzolin K, Geary R, Eichmiller FC. Curing-light intensity and depth of cure of resin-based composites tested according to international
standards. J Am Dent Assoc 2002;133(4):429-434.
Reprinted with permission of the Academy of General Dentistry. Copyright ©2009 Academy of General Dentistry. All rights reserved.
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