Ask Dr. Christensen

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

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 info@pccdental.com.

Question ...

Recently, I have used two brands of the new resin cements that have a self-etching primer incorporated within them. I have been pleased with their ease of use and especially with the lack of tooth sensitivity after cementation. Should these cements be used as primary cements, or should the more popular resin-modified glass ionomer cements be used?

Answer from Dr. Christensen ...

There have been three of these cements introduced in recent months.They are RelyX Unicem (3M ESPE), MaxCem (Kerr), and Embrace WetBond Universal Resin Cement (Pulpdent). Acceptance of these products by the profession has been excellent. They are simple to use, strong, insoluble - and of high importance - nonsensitivity-producing. Their dual-cure characteristics make them as easy to use as any cement in the history of dentistry. Slight light exposure at the time of seating allows immediate removal of the majority of the excess cement, including the contact areas, followed by a longer cure of the microscopic margin areas. The cement within the internal surfaces of the restoration requires a few minutes to cure by chemical methods.

What are the potential negative characteristics of these cements? Although fluoride release is possible from resin, the amount of fluoride release is negligible because of the insolubility of the resin material. Usually, indirect restorations are placed because of the presence of dental caries. In such situations, in my opinion, use of resin cements is contraindicated. Conversely, often the reasons for placement of indirect restorations are occlusal wear or tooth breakage. In these situations, use of resin cements is indicated, since cariostatic activity is not as important as in caries-active situations. Based on research and experience, caries-active mouths are better served by using resin-modified glass ionomer (RelyX Luting Plus Cement - 3M ESPE, or FujiCEM - GC). These cements have proven fluoride release, which research has shown to inhibit dental caries around margins of restorations.

Usually, high strength of a material indicates its superiority. However, in the case of crowns, sometimes the strength provided by the cement is too high. Every dentist has had the experience of taking off a crown that has been cemented with resin cement. Often, the crown removal is nearly impossible without totally cutting the crown from the tooth preparation. Resin cements are the strongest of all cements, while resin-modified glass ionomers are somewhat weaker. As most dentists know, removal of a crown cemented with resin-modified cement is moderately difficult. But usually, when a slot is cut in the crown and leverage is applied with a screwdriver-like instrument, the crown releases from the tooth preparation. Such is not the case with resin cement.

The new dual-cure, self-etch containing resin cements are highly useful when the high strength of resin is needed. However, they do not meet the needs for cementation of ceramic veneers. Light-cured translucent resin cements are more suitable for seating veneers.

In summary, it is my opinion that resin-modified glass ionomer cements are the most suitable cements for routine cementation of most crowns and fixed prostheses, and the new resin-self-etch containing cements are best suited for only specific high-strength requiring situations.

Some of our videos that will help answer this question are: C504A “RelyX Unicem - A Unique Self-Etching Cement,” C102A “Cement - A Critical Choice,” V19-99 “Successful All-Ceramic Crowns and Fixed Prostheses.” For more information, contact Practical Clinical Courses at (800) 223-6569, or visit our Web site at www.pccdental.com.

Question ...

The varieties of resin filler formulations are frustrating me. For anterior visible restorations, should I use microfill, nanohybrid, or nanofilled resin-based composite?

Answer from Dr. Christensen ...

You listed three excellent, but very different, types of materials. Microfill is one of my long-time favorites as a thin superficial layer over tooth structure or an underlying hybrid resin. Microfill can be polished to an extremely smooth surface, and the surface becomes even smoother with tooth brushing. However, I suggest only 1 or 1.5 millimeters of microfill thickness because of its weakness if placed thicker. The most popular brands of microfill are Durafill VS (Heraeus Kulzer) and Renamel Microfill (Cosmedent).

Nanohybrids are becoming more popular. They are much stronger than microfill and can be placed in thicker amounts. They are relatively smooth on placement, but over a period of time, a slightly frosty appearance will be observed. This condition is not noticeable to typical patients and would be a negative factor only for the most discriminating patients.

Nanofilled resin-based composites, the most well-known of which is Filtek Supreme (3M ESPE), have been received very well by the profession and are excellent in both their appearance and strength. This category of resin is for nearly universal use. Slight modification of translucency is currently being made to allow better blockage of light transmission in tooth preparations that do not have a lingual wall of tooth structure.

For most patients, the following concepts could be used for visible anterior tooth restorations:

• Nanofiller alone

• Nanohybrid alone

• Hybrid resin with a coating of microfill

Most patients would not recognize the clinical differences between the three resin types. I have a personal preference for placing either hybrid first on the lingual surface - followed by a microfill - or using Nanofill alone.

Further information on this topic is available in the following PCC videos: C501B “Predictable Long-Lasting Class 2 Resin Restorations,” and V1502 “The New Generation of Tooth-Colored Inlays and Onlays.” 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 above topics available through Practical Clinical Courses. Call (800) 223-6569 or (801) 226-6569.

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