Implant histology 83

action to the implant material. Even at the mucosal margin the amount of reaction was minimal. The surrounding structures, including the adjacent tooth, were normal.

From their studies the Strocks drew several conclusions:

1. Certain metals completely buried in the body tissues are biologically inert.

2. Similarly, partially embedded implants are equally well tolerated.

3. A "pseudoperiodontal" membrane develops close to and completely encapsulates the em-bedded portion of the implant. It consists of a thin layer of connective tissue.

4. No downgrowth of the gingival epithelium exists, as it does in periodontal pocket formation.

5. The bone and metal implants do not attach with one another, although the implant re-mains firm.

Palazzi on Formiggini's implant

Among the earliest of European histologic studies on endosseous implants were those done on Formiggini's implant. In March, 1955, Professor Palazzi of Pavia University, summarizing an earlier report, reiterated: "We inform you that we have implanted Formiggini's spirals into a dog, and that histological preparations have shown that real osseous trabeculac formation had taken place between the implant spaces as well as fibrous tissue regeneration."

Zepponi on Formiggini's implant

Professor F. Zepponi of Rome University, in collaboration with Professor O. Santoro, submitted a report on a Formiggini open spiral implant from a human donor.

It is interesting to note that Zepponi's first report was on a tantalum implant that had remained in the mouth for 9 months. It was the only implant that Zepponi removed, out of more than forty-eight implantations. Its failure resulted from an initial mistake in the operative technique--the axis of the implant had not been oriented according to the masticatory forces. As a result, it was aggravated by unequal pressures in an acute distal direction.

Even though the implant had been improperly set, a great deal of resistance was encountered upon removal. This was caused by the tenacious binding

*Palazzi, S.: Atti del simposio degli impianti alloplastici, Compte rendu du Congres, March, 1955.

of the fibromucosal tissues in and around the spirals and by the presence of a dense osseous fragment. The implant had to be carefully removed so as not to disturb or modify these surrounding tissues. Zepponi postulated that if the implant had been set along a correct vertical axis, it would have functioned successfully. This was later verified by correctly positioning a second implant in the same site. The replacement was completely satisfactory in every way.

The implant was removed, showing osseous tissues in and around the spirals (Fig. 4-3). The bony growth inside the spirals never could have occurred if osteogenesis had not taken place in the area. (Subsequent studies indicate that bone rarely forms within the spirals of such an implant. This probably results from insufficient space between the spirals, which constricts the development of blood vessels and, consequently, bone in the area. Instead, a thick, dense fibrous connective tissue grows through the spirals and encapsulates them, tenaciously binding them.)

Various histologic sections of the tissues around and within the Formiggini implant removed by Zepponi were studied. The material was fixed in 10(r formalin. Several sections were done in the area of the largest dimension of the bony fragment, perpendicular to the implant axis, so as to get a complete view of the tissues. The sections were pre-pared with hematoxylin and eosin.

The section made at a superficial level corre-

Fig. 4-3. A Formiggini implant with bone growing not only around the spirals but also through them. (From Chercheve, R.: Les implants endo-osseux, Paris, 1962, Librairie Maloine.)