Primary fixation is one of the most important factor in establishing adequate osseointegration between implant and bone.

To evaluate the initial healing response of bone around implants without primary bone contact, this study was designed to create considerable space between implant and bone in 5 mongrel dogs, about l-year old. After 3 holes of 6 . h in diameter were prepared at the femur neck of the dogs, commercially pure titanium thread type implants(STERI-OSS®), 8mm in length and 3.8mm, 5.0mm and 6 .0mm in diameter, were inserted. Implants were supported by only nonresorbable membrane(Teflon®), and the penetration of upper soft tissue into the gap was inhibited by it. The each implant was positioned in the center of the drilled hole. 9 implants with different diameters were inserted in 3 dogs for histologic observation, and 12 were inserted in 2 dogs for mobility test and removal torque test. Fluorescent dyes were injected in order of Doxycycline, Arizarin Red S, and Calcein at intervals of 2 weeks. At 4-,8-, and 12-week after placement, 3 dogs were sacrificed for histologic observation, and at 8- and 12-week after placement, 2 dogs were sacrificed for mobility test using Periotest® (Simens AG, Bensheim, Germany) and torque test using Autograph AGS-1000D series®(Japan).

The result were as follows:

1. The wider the gap between bone and implant was, the less bone maturity was, and the later osseointegration was occurred. Trabecular direction of new bone around implant was changed from parallel to perpendicular to the implant, and the gap was filled with new bone, over time.

2. There was a decreasing tendency over time in the mobility of all implants, but the wider gap between bone and implant was, the smaller decrease of the mobility was.

3. There was a increasing tendency over time in the removal torque gauge of all implants, and the wider gap was, the smaller increase of the removal torque gauge was.

The results suggest that osseointegration in case of implant without primary bone contact may be obtained by guided bone regeneration technique with prolonged healing period, but the time of second surgery should be considered carefully.