Ask Dr. Christensen

In this new monthly feature, Dr. Gordon Christensen answers frequently asked questions from readers. This month, he discusses curing lights and hybrid restorations.

by Gordon J. Christensen, DDS, MSD, PhD

Question ...

There appears to be controversy over the subject of resin curing lights. What type of light should I buy for the fastest and most adequate curing of resin?

Answer from Dr. Christensen ...

Do you remember in the 1970s that all restorative resins were auto-cured? You would place the restorative resin in the tooth preparation and wait for a significant time until the resin cured by itself. Since then, you and I have become accustomed to using halogen lights that cure resin in about 30-45 seconds. The change from auto-cure to halogen light-cure was a great relief, because of the decreased curing time and the command set.

Some positive differences can be achieved again by changing to fast halogen lights or plasma arc curing lights. Fast halogen curing lights reduce curing time by 60 percent or more, while plasma arc curing lights reduce curing time by over 90 percent.

What is the significance of reducing curing time by 60 percent to 90 percent? Clinical Research Associates (CRA) measured the amount of time consumed in one year curing restorative resins in typical dental offices. It was found that when average per-minute gross income for U.S. dentists was applied to the total curing time, the average U.S. dentist was spending about $43,000 worth of clinical time light-curing resin in one year. A conservative estimate shows that a change to a fast halogen light reduced curing-time overhead by about $28,000 per year, while changing to a plasma arc light reduced the overhead cost by about $38,000 per year.

But what if the restorative resin or the tooth preparation are compromised by fast resin curing? For 21/2 years, CRA has studied the influence of fast curing lights on teeth and restorative resins. Clinically significant negative influences on tooth preparations or on the physical properties of the restorative resin have not been found. Please see CRA's Web site (www.cranews.com) for research details on this subject.

At this time, I suggest three viable alternatives for dentists wanting to decrease resin curing time:

1. Purchase a Turbo Tip for your older Demetron/Kerr halogen light. This simple $187 to $230 purchase reduces curing time by up to 50 percent.

2. Purchase a fast halogen curing light - Hilux 250 TA (First Medica), Optilux 501 (Demetron/Kerr), or Virtuoso Phase 2 (Den-Mat) - and reduce curing time up to 60 percent. This change costs about $600 to $1,700.

3. Purchase a plasma arc light - Arc Light IIM (Air Techniques), Power Pac (American Dental Technologies), or Virtuoso Xenon Power Arc Light (Den-Mat) - and reduce curing time about 90 percent. These plasma arc lights range in cost from $ 2,900 to $4,600.

I suggest waiting awhile before considering the purchase of an LED (Light Emitting Diode) curing light. These lights are being developed further, and I predict they will eventually be perfected.

Question ...

Some new brands of hybrid resin are advertised as replacements for both typical hybrids and mircofills. Is there one that satisfies both strength and smoothness needs?

Answer from Dr. Christensen ...

Microfills - such as A110 (previously Silux) (3M/ESPE); Durafill (Heraeus Kulzer); and Renamel (Cosmedent) - have become well-known for their increased smoothness over a period of service, as well as their beautiful translucence. However, they are also known for their brittleness and breakage during service. Conversely, conventional hybrid resins - such as Herculite (Kerr), TPH Spectrum (DENTSPLY Caulk), Tetric Ceram (Ivoclar North America), and others - are well-known for their ease of placement, high strength, and for the dentist's ability to differentiate the materials from tooth structure while finishing. However, conventional hybrids do not retain the smoothness of microfills during service, and they do not have the translucence necessary for some Class 3 and Class 4 applications.

Some of the new-generation hybrids have significantly different properties. The following products have some characteristics that are superior to the previous generations of hybrids: Esthet*X (DENTSPLY Caulk), Renamel Hybrid (Cosmedent), Renew (Bisco), Point 4 (Kerr), and Vitalescence (Ultradent).

These hybrids have the translucence of microfills, if desired, as well as the strength of previous hybrids. In numerous clinical studies, they have been shown to rival microfills for surface smoothness when placed, but they have a slight roughening that occurs over a brief service period. This roughness is not as severe as the conventional hybrids named earlier, but the new hybrids are not quite as smooth as microfills.

It appears that the new generation of hybrids provides improvements over the older generation. The most popular new brands are DENTSPLY Caulk's Esthet*X and Ultradent's Vitalescence.

These new hybrids are very useful because of their translucence, color-matching properties, superior smoothness, and high strength. I have been using them for many of the situations in which I previously used microfill, conventional hybrid, or combinations of the two.

Dr. Christensen is a practicing prosthodontist in Provo, Utah. He is the founder and director of Practical Clinical Courses, an international continuing-education organization for dental professionals initiated in 1981. Dr. Christensen is a co-founder (with his wife, Rella) and senior consultant of Clinical Research Associates, which, since 1976, has conducted research in all areas of dentistry and publishes its findings to the dental profession in the well-known CRA Newsletter. He is an adjunct professor at Brigham Young University and the University of Utah. Dr. Christensen has educational videos and hands-on courses on the above topics available through Practical Clinical Courses. Call (800) 223-6569 or (801) 226-6569.

Dr. Christensen's views do not necessarily reflect the opinions of the editorial staff at Dental Economics.

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