The evolution of dental implants 153

distance between them, that was important, Perron-Andres fairly consistently fashioned implants that could not be set deeply enough to avoid invagination problems. His skill in fashioning, inserting, and stabilizing an implant can be seen in Fig. 5-33. Even though the uppermost spires are not embedded in bone, the thick condensation of bone around the lower spirals is obvious. At the time of the last x-rays, the implant had been in place 3 years.

One of the most practical and successful modifiers of Formiggini's original design was the French-man Raphael Chercheve. An early Chercheve de-sign, made of cobalt-chrome, is shown in Fig. 5-34. Trying to avoid the fragility of widely spaced spirals, he placed the spirals quite close together. How-ever, even though open spirals are more fragile, they allow freer blood circulation and consequently more

Fig. 5-33. A, Perron-Andres screw inserted into an open socket. B, Thirty-six months later, bone is seen closely adapted to and through the spirals.

Fig. 5-34. Raphael Chercheve's early spiraled implant. Al-though it closely resembled Formiggini's prototype, it had fewer spirals and a longer neck.

Fig. 5-35. Chercheve's early spiral, buried well in bone. Note that the spirals are covered by a bony shelf, which makes exfoliation extremely difficult.