Ask Dr. Christensen

Feb. 1, 2002

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].

Question ...
I am still having a problem achieving tight contact areas when placing Class II resin-based composite restorations. I have been using a Tofflemeyer matrix and thin (0.001") stainless-steel matrix bands, with small Premier sycamore wedges placed tightly. Occasionally the contact areas are tight, but often they are flat instead of contoured.

Answer from Dr. Christensen ...
You are using almost exactly the same technique I used for several years, with the same results. May I suggest some changes?

The technique you suggested is acceptable for situations in which the proximal box forms are small and extend minimally facially, lingually, and apically. In fact, for those situations, it is one of the preferable methods. In minimal small box forms, the Tofflemeyer technique produces tight, flat contact areas, which are similar to those that the tooth had originally. Another technique I prefer for small proximal box forms is the short tine Composi-Tight [Garrison Dental Solutions — (888) 437-0032]. When the box forms and extensions are larger, other matrix applications are preferable.

The wedge brand you are using [Premier Dental Products — (888) 773-6872] is one of the best. You may not know that recently Premier introduced a very small, thin sycamore wood wedge, called the "Mini," which adapts well to the sectional matrices I am describing. Sycamore wood expands when saturated with fluid, making the matrix adapt better.

For the medium-sized box forms, I suggest the Palodent Sectional Matrix System [Dentsply — (877) 725-6336], or the longer tine version of the Garrison Composi-Tight matrix system. For the largest box forms, I suggest the Danville Contact Matrix System [Danville — (800) 827-7940]. The Contact Matrix System has larger and longer tines that do not fall into the box forms when the matrix is applied to the tooth.

Contrary to the problem you have expressed, the sectional matrices can produce excellent, tight contact areas, or contact areas that are slightly too tight, requiring stripping for optimum tightness.

A recently made Practical Clinical Courses video presentation that shows proper clinical use of sectional matrices is tape C501B — "Predictable Long-Lasting Class 2 Resin Restorations." Please call (800) 223-6569 for more information.

Question ...
I am confused about placement of resin-reinforced glass ionomer onto tooth surfaces. This category of material is sold as luting cement, restorative material, liner, and base. Some speakers have told me that placement of these materials does not require acid conditioning of tooth surfaces before the material is placed; others say that acid is required before placement. Additionally, I have been told that the materials do not bond to tooth structure as well as resin bonding systems, and that restorative resin should be placed without resin-modified glass ionomer first. Please advise me on these questions.

Answer from Dr. Christensen ...
This topic is confusing for many reasons. The most important one is the variety of uses for resin-reinforced glass ionomer. Additionally, this category of materials has had many names over its short history. Some of them are resin-reinforced glass ionomer, resin-modified glass ionomer, glass ionomer resin, and just glass ionomer.

I prefer resin-reinforced glass ionomer (RRGI). The materials are about 80 percent glass ionomer and 20 percent resin. Combining the characteristics of both materials has been excellent, providing fluoride release, relative seal of tooth surfaces, moderate bond to tooth structure, good expansion-contraction properties, and reduced dissolution when compared with conventional glass ionomers.

Another reason for the confusion has been the varied curing methods of the different categories. They vary from chemical set for cements, to light-cure for liners, to tri-cure for restorative materials. Regardless of the curing characteristics, the materials are basically the same.

Some manufacturers have marketed RRGI with a conditioning liquid to be placed on the tooth and washed off before using the RRGI material. These weak polyacrylic acid solutions remove a small amount of the smear layer, or debris, and somewhat improve the bond of the material to tooth structure. However, various research projects have shown that the acid conditioning is not necessary and may be omitted.

You are right in your comment that resin bonding systems provide a better bond to dentin than RRGI. However, that bond must be qualified. Resin materials usually placed over resin bonding agents expand and contract significantly, providing a potentially transient bond to tooth structure, while RRGI materials expand and contract similarly to tooth structure, providing a longer bond potential. In either case, I do not think the difference in bond is clinically significant. Nevertheless, the subject provides good speculative discussion. As usual "the proof is in the pudding" — RRGI has provided strong, nonsensitive cementation of crowns and fixed prostheses, prevention of sensitivity in resin-based composites when placed on virgin cut tooth structure, cariostatic moderate longevity restoration of pediatric molars, and excellent moderate longevity restoration of carious lesions in mature adults.

A recently made Practical Clinical Courses video presentation that shows proper clinical use of RRGI and other cements is tape C102A "Cements — A Critical Choice." Call (800) 223-6569 for details.

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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