Ask Dr. Christensen

Aug. 1, 2004
Many of my potential implant patients do not want to have bone grafting when placing implants. If an implant is planned in the maxillary sinus area, how much bone is...

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 ...

Many of my potential implant patients do not want to have bone grafting when placing implants. If an implant is planned in the maxillary sinus area, how much bone is necessary for the implant without grafting? I have heard several suggestions.

Answer from Dr. Christensen ...

Using a dental radiograph, you can easily determine the amount of bone present from the crest of the boney ridge to the floor of the sinus. Periapical radiographs produce images that are equal to actual bone present. You will remember that most panoramic radiographs produce images that show about 25 percent more bone structure than is actually present. If there is at least 10 mm of bone from the crest of the ridge to the floor of the sinus, there is a minimum amount of bone needed from that perspective. However, you must now determine if there is enough bone present in the facial-lingual location. You may do this by making a tomographic radiograph showing the bone in the facial-lingual dimension, but general dentists do not commonly order such radiographs, and they can be expensive for the patient. An alternative method is to anesthetize the patient and use a caliper that penetrates soft tissue on the facial and lingual at the same time, providing a measurement of the facial lingual bone. An example of such an instrument is the Ridge Mapping Caliper from Salvin. A reasonable amount of facial lingual bone into which to place an implant without grafting is about 6 mm or more. Typical root form implants are nearly 4 mm in diameter.

The measurements I have suggested are minimums, and more bone would be highly desirable. If there is less bone than I have indicated, grafting into the sinus with crestal or lateral bone augmentation is possible, but it is expensive, time consuming, and somewhat painful as it heals. Another alternative for minimal bone in the facial-lingual dimension is the placement of "mini" implants, which are 1.8 mm in diameter.

One of our recent videos, V2300 "Making Decisions about Successful Use of Implants," shows the bone characteristics necessary for successful placement of implants. It is a great guide for both restorative and surgical dentists. For more information, contact Practical Clinical Courses at (800) 223-6569, fax (801) 226-8637, or visit our Web site at

Question ...

I am seeing many advertisements for new resin cements. In what situations should resin cement be used in preference to resin-modified glass ionomer cement?

Answer from Dr. Christensen ...

Yes, there are many advertisements for resin cements. The recent introduction of numerous resin cements, and the advertising associated with them could make you think you should abandon previous cements. There are several types of resin cement available, and you probably need more than one type.

Light-curing, multi-color resin cement is indicated for indirect veneers. Light-curing resin cements allow color modification for indirect veneers without the disagreeable subsequent color change associated with dual cure resin cements. They provide strong attachment of veneers to acid-etched enamel or bonded dentin.

Dual-curing, multi-color resin cements are indicated for ceramic or polymer inlays and onlays or all-ceramic crowns. The thickness or opacity of these restorations, and their light-blocking nature require dual-cure cement for proper curing. The presence of multi-colors allows coordination of the color of the cement with the restoration and the tooth. Also, these cements can be used as universal cements.

Auto-curing resin cement is indicated for cementing any non-color sensitive indirect restoration that needs significant strength and filling of defective margins with a relatively insoluble substance. An example is when salvaging a crown that has become loose and has questionable margins. These cements can also be used as universal cements.

Should resin cement be used as your universal cement? Resin-modified glass ionomer cement, currently the most popular of the universal cements, has one major positive characteristic that resin cements do not have, cariostatic potential from its fluoride release. Further, resin cement is almost too strong for routine universal cementation, since future removal of defective crowns cemented with resin is difficult. Although the currently available resin cements are excellent, in my opinion, resin-modified glass ionomer is a better universal use cement.

Our newest video, C504A "RelyX Unicem — A Unique Self-Etching Cement" shows the first predictably non-sensitivity producing resin cement. RelyX Unicem combines the constituents of a self-etching primer with resin cement. For more information, contact Practical Clinical Courses at (800) 223-6569, fax (801) 226-8637, or visit our Web site at

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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