Ask Dr. Christensen

June 1, 2002
In this monthly feature, Dr. Gordon Christensen addresses the most frequently asked questions from Dental Economics readers.

by Gordon J. Christensen, DDS, MSD, PhD

In this monthly feature, Dr. Gordon Christensen addresses the most frequently asked questions from Dental Economics readers. If you would like to submit a question to Dr. Christensen, please send an email to [email protected].


When curing resin through a mylar strip, the cured resin surface is extremely smooth. This same smooth surface is made on resin where I have used a "Light Tip" on my curing wand or a "Contact Pro 2." Can I bond a new portion of resin to the smooth, nonoxygenated surface of cured resin?

Answer from Dr. Christensen…

Others of us also have asked this question, which has led some dentists to avoid using a "Light Tip" or a "Contact Pro 2."

Try the simple experiment outlined below to determine if there is any problem bonding new resin to smooth resin that has been cured under a mylar strip or similar surface. For the test, you may use either two microscopic slides or two mylar strips. I will use mylar strips in my example.

Place a piece of resin on one of the mylar strips.

  1. Place the other mylar strip on top of the resin resting on the first strip.
  2. Apply pressure to the resin to flatten it out under the strips.
  3. Cure the resin and remove the strip.
  4. Place a thin layer of unfilled bonding agent on the cured resin.
  5. Try to cure new resin onto the smooth, previously cured resin.

You will have no difficulty bonding the new resin to the previously cured resin. However, if you wait a day or two, bonding the new resin to the old resin will not be as successful. It will be even more difficult if the restoration is in the mouth and has been bathed in saliva for a few hours. If the resin has matured for a period of days, attachment of new resin to the old resin surface is not possible because most of the chemical activity of the old resin has been exhausted.

If repair of an old, hybrid, resin restoration is necessary, follow these steps:

  1. Cut a retentive preparation in the old resin.
  2. Sandblast it to remove the residual resin from the glass-filler particles.
  3. Place silane on the resin surface.
  4. Follow with an unfilled bonding agent.
  5. Follow with the resin of your choice.

Mild bonding of the old and new resin will occur, but the main retention is mechanical. Because microfill resin does not have glass filler particles in it, chemical retention should not be expected when the previous repair is attempted.

A recent Practical Clinical Courses video - C901(B), "Curing Resin With Light State-of-the-Art" - discusses related topics and is an excellent aid in teaching staff. Call (800) 223-6569, or visit


What should a typical, moderate-sized, Class 2 MOD restoration cost a patient? Some third-party payment organizations want to pay amalgam fees for Class 2 composite resin restorations, yet these restorations take longer for me to place than amalgams of similar size.

Answer from Dr. Christensen…

Discussing fees without regard to geographic location is difficult, so let's make some assumptions to allow you to relate the example to your own area.

When observing current typical national fees - as reported by Dr. Tom Limoli's Atlanta Dental Consultants - a typical MOD composite restoration costs about $163. An amalgam of similar size costs about $117, or 72 percent of the composite. Comparing further, a typical PFM crown costs over $600 ($480 plus the lab fee).

Some practitioners say that the cumulative time it takes to produce an excellent Class 2, resin-based, composite restoration is similar to the time required for a total crown procedure. It appears that restorative fees are too low when compared to crown fees.

Amalgam fees should be considered carefully in relation to fees for other procedures. Most dentists find that the fees for both amalgam and resin-based composite procedures are too low given the time required for quality service. Dentists should set fees at a moderate level based on the time involved and the difficulty of the procedure. Most would agree that Class 2, resin-based composites are more difficult and somewhat less predictable in service than their well-proven competitor, amalgam. If resin-based composite procedures are performed regularly, I suggest that fees for amalgam and composite be kept about equal so dollars are removed from the patient's decision-making equation.

I recommend a recently released video in the very popular Practical Clinical Courses' Forum Collection. This video discusses the various controversies surrounding Class 2 resin restorations. Call us at (800) 223-6569, or visit

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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