Ask Dr. Christensen

Aug. 1, 2007
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 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 e-mail to [email protected].

Q I do not place implants, but I often refer patients for implant placement by other practitioners. I do not know the exact amount of bone necessary for placement of an implant without grafting. Most of my patients don’t want to have extensive autogenous bone grafting. How can I estimate if an implant can be placed before sending the patient for consultation?A Your question encouraged me to express my strong opinion that general dentists should make significantly more investigative diagnostic evaluations before they send patients to surgically-oriented dentists. The information sent to the dentists who place the implants should specifi cally state:
  1. Your plans for the location of the implants
  2. The required angulation of the implants, as shown by a template, if necessary
  3. The diameter and length of the implants
  4. What type of abutment you want to place on the implants
  5. The type of prosthesis you plan for the implants
  6. Any other useful information for the surgery

To determine this information, you need to know the quantity and quality of the bone present. For an implant of about 4 mm in diameter and at least 10 mm in length, I suggest there should be:

  • Approximately 6 mm of bone in a facial-lingual dimension, as determined by use of a ridge-mapping caliper or a tomographic radiograph made in the area of the planned implant placement.
  • Approximately 10 mm of bone from the bony crest of the ridge to the most apical area in which the implant can be placed, as determined by use of a periapical radiograph or a panoramic radiograph. Keep in mind that your panoramic device shows 20 to 25 percent more bone than is actually present, while a periapical radiograph shows nearly the exact amount of bone that is present.
  • The location of the implant should preferably be no closer than 1 mm from vital structures such as the maxillary sinus, the incisive foramen, and the inferior alveolar canal. The mental foramen is an extremely variable anatomical structure. I recommend staying 5 mm away from it to be safe.

With adequate diagnostic devices, you can determine if the preceding characteristics are present and if an implant is indicated. If these characteristics are not present, you have two choices. You may refer the patient for bone grafting, or you may consider the use of small-diameter implants.

Bone grafting autogenous bone from other sites in the patient’s body such as the chin, ramus of the mandible, iliac crest, rib, or other sites is certainly a possibility for some patients. However, the operation is painful, expensive, and requires signifi cant time for healing. Most patients do not want to consider such grafting. Grafting with one of the many bone-grafting materials available on the market is another alternative. However, it, too, is expensive, timeconsuming, painful, and sometimes disappointing.

Another alternative when adequate bone for conventional-diameter implants is not present is use of “mini” or small-diameter implants. These implants range from about 1.8 mm to nearly 3.0 mm in diameter, and they are the same length as conventional-diameter implants. Currently, two brands are approved by the FDA, IMTEC® and Dentatus ®. These “mini” implants can be placed in much less bone than conventional-diameter implants. For adequate placement of small-diameter implants, at least 3.0 mm or more of bone must be present in a facial-lingual dimension. When minimal bone is present, a fl ap must be raised to see the actual anatomy of the bone and to allow precision placement of the small-diameter implant. In my opinion, when 5 mm or more of bone is present in a facial-lingual dimension, the small-diameter implants may be placed through the gingiva without a flap operation.

I have provided a long answer to your question; however, it is a complex question. There are many variations to the answers I have provided for you.

Our organization, Practical Clinical Courses has several videos that show implant surgery with close-up, detailed clinical video.Two directly related to your question are

V2317, “Mini Implants for Your Practice” (small-diameter implants) and V2301, “Simplified Implant Surgery” (conventional-diameter implants). For more information, call Practical Clinical Courses at (800) 223-6569 or visit our Web site at

Q I have heard many contraindications and rules for placing dental implants, but I have also seen successful implants placed when nearly all of those contraindications or rules have not been observed. When should I advise patients against having implants placed, and what are the current beliefs and evidence about implant placement?A Your observations of the success of implants placed in many contraindicated locations and when the rules have not been observed are correct, yet many of them still integrate and continue to serve. More than 20 years ago, when I was learning implant placement and restoration, there were many rules which have subsequently been disproved.

Among them were edicts against making radiographs before implants are integrated, and the dogma that implants would not integrate if they were not covered with carefully sutured soft tissue while the integration was taking place.

Additionally, waiting four to six months before loading was mandatory. Still present is the rule that you never attach implants to natural teeth. All of the above rules have been shown to be untrue.

What current beliefs or evidence-based conclusions are still incorrect? It is difficult to determine the answers, but the following are opinions of various experts based on both clinical evidence and research.

Drs. D. Hwang and J. L. Wang stated the absolute contraindications for implants to be:

  1. Recent myocardial infarction
  2. Valvular prosthesis surgery
  3. Active treatment of a malignancy
  4. Psychiatric illness
  5. Recent cerebrovascular accident
  6. Immunosuppression bleeding issues
  7. Intravenous bisphosphonate use

I have a few others to add to the list:

• If the patient is healthy, can chew adequately, appears to be esthetically acceptable, but has very minimal bone present, implants are probably not indicated.

• Although there is some disagreement in the literature, if the patient is a long-term smoker, I usually express pessimism about the potential success of implants.

• If the patient has had horrible oral hygiene before extractions, it has been my observation that the same oral hygiene characteristics will prevail after the implants are placed, and these conditions will potentially endanger the gingival health around the implants.

• If the patient is noncommittal about his or her desire for the implants, I do not try to convince him or her to have the procedure done. Implant patients have to be a positive part of the team to make the trauma, time, and changes involved with implants worthwhile.

To summarize, although there are some serious health and psychological contraindications for implants, most healthy people with adequate bone present are excellent candidates for implants.

Dr. Christensen is a practicing prosthodontist in Provo, Utah. He is the founder and director of Practical Clinical Courses, an international continuing-education organization initiated in 1981 for dental professionals.

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

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