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 e-mail to email@example.com.
I have heard that nanofill composite resins are stronger, smoother, and better than microfill composite resins. Should I discontinue using microfill resins and instead use nanofill resins for all of the locations in which I previously used microfills?
Answer from Dr. Christensen ...
This topic is confusing! For more than 20 years, microfill resins have been the smoothest composite resins available. They have retained or increased their smoothness over a period of time in the mouth. They have served well as a superficial layer of restorative resin placed on acid-etched enamel used as direct veneers, as a superficial layer of smooth resin on the surface of a stronger microhybrid resin, or as the total restorative resin in small-cavity preparations. However, in spite of their excellent service, microfill resins do not have as much strength as the commonly used microhybrid resins.
Recently, nanofill resins have been introduced, the best known of which is 3M ESPE’s Filtek™ Supreme. This category of resins has been advertised to be as strong as microhybrids and as smooth as microfills, when observed over time in the mouth.
The advertising is correct. Nanofill composites are stronger than microfills, and they do retain their smoothness in the mouth. Acceptance of nanofill composites by practitioners has been excellent, and numerous new brands of nanofill resins are expected to be marketed soon.
Should you switch to using nanofill resins and eliminate microfills? This is a matter of personal preference. Some of the most discriminating dentists prefer to place microhybrid resin internally in cavity preparations, with a layer of microfill on the external surface of the restoration. This concept provides strength obtained from the microhybrid internally, and smoothness from the microfill externally. The overall acceptability of this type of restoration is difficult for any other concept to rival.
Nevertheless, nanofill, resin-based composites look very promising. Minor clinical differences between the microhybrid/microfill combinations and the nanofill restoration need to be considered before making a decision about which to use.
Microfill resins, best known as Durafill® (Heraeus Kulzer), Renamel Microfill (Cosmedent), and Heliomolar (Ivoclar Vivadent), have extremely smooth surfaces when finished properly. This smooth surface is relatively easy to produce using disks and polishes, and the smooth surface is well known to be retained over a service period. In fact, microfills become smoother as the patient continues to brush and eat foods that also smooth them. The low-wear characteristics of microfills have been proven in many in-vitro and in-vivo research projects.
Why use nanofills? When using a nanofill resin-based composite, there is only one category of material to use for the entire restoration. Nanofill composites are stronger than microfills, and they can be finished to be as smooth as microfills. However, some clinicians state that producing a smooth surface on a nanofill is somewhat more difficult and time-consuming than producing the same smoothness on a microfill. Even if this is true, it is a small difference. Is it time to abandon microfills? I don’t think so. If you are satisfied with microhybrid/microfill combinations, stay with them. If you are not satisfied, change to nanofill and make your own comparison.
Another category of resin, called nanohybrid, uses a combination of glass particles and nanofillers. This classification is further confusing practitioners. Although these resins have good strength and esthetic properties, clinicians are having a difficult time differentiating them from the long-used microhybrids.
In summary, continue to use microfills if you like them. There appears to be no major reason to change as long as you recognize their weaknesses.
As other brands are introduced, I expect this category to gradually take over the universal-use resin marketplace.
Often, patients return to my general practice with gross occlusal prematurities after having completed orthodontic therapy. Shouldn’t orthodontists be responsible for completing occlusal equilibration after they complete orthodontic treatment? It seems that occlusal equilibration should be included in the orthodontic portion of the treatment.
Answer from Dr. Christensen ...
You have asked a question that describes one of my most frustrating pet peeves. When orthodontic therapy is accomplished, the teeth are moved in all directions, including rotation in their sockets. When the therapy is completed - and the brackets or bands and wires are still on the teeth - the teeth remain in the positions the orthodontic treatment was intended to produce. However, when moved by the orthodontic therapy, the teeth occlude on inclined planes, including triangular ridges, oblique ridges, and other areas that place potentially moving forces on the teeth during occlusion. As soon as the orthodontic appliances are removed - and the restraint to movement provided by the fixed appliances is removed - the teeth have a significant tendency to return to their original positions. Of course, removable retainers assist in keeping the teeth relatively well in their desired new positions. But how much more stability would be provided by an occlusal equilibration accomplished at the time the orthodontic appliances are removed? The major prematurities would be removed and the new occlusion would start with more stability.
I suggest you have a discussion with those practitioners who provide orthodontic therapy for your patients. Decide which one of you should accomplish occlusal equilibrations after orthodontic therapy. If the orthodontic practitioner does not want to do the occlusal equilibrations, have the completed orthodontic patients appointed for an occlusal equilibration at your office on the day the orthodontic appliances are removed.
After many years of “completed” orthodontic patients returning to my prosthodontic practice, my feeling is that occlusal equilibration should be accomplished as soon as possible after orthodontic therapy is completed, preferably within a few hours.
Our newest video package concentrates on occlusal concepts. Included are one-hour videos on occlusal splints, occlusal equilibration, and simple TMD therapy. For more information, contact Practical Clinical Courses at (800) 223-6569, or visit our Web site at www.pccdental.com.
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 discussed topics available through Practical Clinical Courses. Call (800) 223-6569 or (801) 226-6569.