Ask Dr. Christensen

Sept. 1, 2002
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].

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 a general practitioner who has accomplished a considerable number of surgical procedures over my career, but I have not yet incorporated implant surgery into my practice. I have read several articles and advertisements about the "mini" implants. Are they a good way to get started in implant surgery?

Answer from Dr. Christensen …

I became involved with the "mini" implants several years ago when they were considered to be acceptable only for transitional use, while the conventional implants were "integrating" into bone. In several heroic cases, I used the mini-implants to "salvage" conventional fixed prostheses for a few years. To my amazement, they served very well, and saved the patients considerable cost and pain. Later, a brand of mini-implant came on the market and was promoted as a long-term implant. It immediately caught my eye.

There are many cases where adequate bone for conventional-sized implants is not present. Some of the smallest, conventional-sized implants are about 3.25 mm in diameter. To have noncomplicated placement of that size of implant, at least 1 to 11/2 millimeters of bone should be present on both the facial and lingual surfaces of the implant. The necessary presence of 6 mm of bone, measuring from facial to lingual of the ridge, is often not present.

How about placing a 1.8 mm-diameter implant, which works much like a screw placed in a shallow, small hole in hardwood, forcing the bone facial and lingual as the screw is placed? Such is the implant from IMTEC Corporation, (800) 879-9799. It can be placed in a minimal amount of bone. I have successfully placed these implants in ridges that were as thin as 4 mm from facial to lingual. They can be placed under dentures, used as fixed partial denture repairs, or in other situations where there is minimal bone. The mini-implants cause minimal soft-tissue trauma and can be easily removed if failure occurs.

Carefully considered, adequate placement of mini-implants in locations where conventional implants are not possible without bone grafting is a good starting place for someone who has surgical background and is willing to learn how to place implants. Of course, I recommend attending an implant surgery course first.

A recent Practical Clinical Courses video on this topic has been very popular and useful: C900A, "The 'Mini' Implant for General Practitioners." We also have a two-day, hands-on implant surgery course throughout the year that has been well-received. Contact us at (800) 223-6569, fax (801) 226-8637, or visit our Web site at

Question …

I have noticed that most dentists place full crowns instead of tooth-colored onlays and inlays. My third-party payment companies favor porcelain-fused-to-metal crowns instead of tooth-colored inlays and onlays. When should I consider conservative indirect restorations instead of crowns?

Answer from Dr. Christensen …

You have seen and read in some of the aesthetic/cosmetic journals much information about the desirability of tooth-colored inlays and onlays. But, judging from the small number of these conservative restorations being accomplished in the United States, one might conclude that the full crown still must be the best restoration.

As you know, it is much easier to prepare and seat a full-crown restoration than it is to prepare and seat an onlay or inlay, but that reason is self-serving. However, it is also well-known that full crowns are stronger and longer-lasting than inlays or onlays in areas of high stress.

When is a tooth-colored onlay/inlay better than a full-crown restoration? In my opinion, the conservative restorations may be better in the following situations:

•The patient has a broad smile and a need for large restorations in maxillary 1st and 2nd premolars or 1st molars; the facial surfaces of the teeth are free of discoloration or cracks; and the gingival relationship to the tooth cervical areas is good. I believe that full crowns are placed too frequently on such teeth.

•The patient has a need for large, tooth-colored restorations, but demands minimal removal of tooth structure. These patients often will accept onlays or inlays when they won't accept full crowns. They should be cautioned about the reduced strength and potential fracture of the conservative restorations.

•The patient's mouth has been restored primarily with crowns, but a few teeth have need of restorations that are not large enough for crowns and are too large for direct restorations.

I have been convinced of the following conclusions from treating my own patients and from research on both conservative and crown restorations: Full crowns have better potential for long service. I also feel that a typical dentist in a busy practice can place full crowns with more predictability than tooth-colored inlays or onlays. Further, I have no reservation in saying that cast gold alloy indirect restorations will outlast tooth-colored restorations. Nevertheless, I encourage dentists to learn to place tooth-colored indirect restorations when they are indicated. Empress (Ivoclar) and its many clones are by far the most popular and predictable types available today.

Our Practical Clinical Courses video - C101B, "Predictable Ceramic Inlays and Onlays" - demonstrates my own conclusions and a simple, predictable technique on this important subject. Contact us at (800) 223-6569, fax (801) 226-8637, 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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