CHAPTER 4 Implant histology

Histologic studies substantiate and authenticate clinical experiences in dentistry as well as in medicine. Studies in implantology should include bone block sections and the soft tissues directly in contact with and completely encircling the implant.

Most of the opportunities for studying the effects of a dental implant on living human tissues have been provided by failing implants; only a few studies have been done on sites bearing successful implants. The reason for this is obvious: a patient enjoying a successful prosthesis is not likely to volunteer his implant for histopathologic studies. Implant failures do not represent the morphology of a successful site, because a failure is usually caused by or accompanied by a large-scale invagination of soft tissues. These tissues are much more loosely organized and much thicker than the narrow band of soft tissues visible in radiographs of successful implant sites. Furthermore, the instability or mobility of a failing implant does not permit the healthy and normal regeneration of bone, and it intensifies the inflammatory reaction. Despite these drawbacks, sections made through failing implant sites do provide valuable information on the kind of tissue found in the area.

This chapter reports studies done on failed implants, implants in experimental animals, and a few successful implants from human donors. The reports range from early studies on now-discarded implant designs to current studies on the most modern types of implants.

ENDOSSEOUS IMPLANTS

Both soft and bony tissues should be included in histologic studies of an endosseous implant site. Soft tissue sections are not too difficult to obtain, and a fairly generous area should be cut away for examination. This may be done by removing with a scalpel

or by electrosurgery all the tissue encircling the implant from the free margin of the gingiva to its mechanical, or gingival, attachment down apically about 2 to 3 mm. more (Fig. 4-1) . In this manner the pathologist has a good section with which to work. The only difficulty in obtaining the section is in removing the tissue that exists interproximally. If this is not done carefully, the ring of tissue can be torn.

All implants that are failing can be removed with very little resistance and very little adherent tissue. In these cases, any time a bone fragment appears in the area of the removed tissue, it is usually an alveolar fragment carried away with the very thin ridge of the external table or a sequestrum, rather than osseous repair.

Bone blocks are more difficult to obtain because a good portion of the osseous structure must be re-moved. Although it is rare to obtain a bone block from a patient, studies with dogs and other animals have provided valuable information. Implants are placed in the animals and are removed at monthly intervals with a good portion of the surrounding bone, with many of the animals having to be sacrificed.

For both soft tissue biopsies and bone block section biopsies, the specimens should immediately be placed in 10% formalin solution for preservation.

Strock and Strock on an early screw implant

One of the earliest histologic studies of inert metal screws protruding into the oral cavity was reported in 1949 by Alvin Strock and Moses Strock of the Surgical Laboratory of the Harvard Medical School and the Dental Service of the Peter Bent Brigham Hospital in Boston. The Strock brothers reported the insertion of a %-in. Vitallium screw in the left maxillary bicuspid area of a dog. The screw

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