Osseointegration of dental implants without primary stability: an experimental study in sheep

* Department of Oral Maxillofacial Surgery, College of Dentistry, Hawler Medical University, Erbil, Iraq. Introduction Primary implant stability is a prerequisite fo r ach iev ing and mainta in ing osseointegration. Primary stability is defined as the absence of mobility in the bone bed after the implant has been placed. There are basic principles to achieve successful osseointegration which includes: the use of biocompatible materials, an implant that precisely adapted to prepared bone (high primary stability), a traumatic surgery to minimize tissue damage and undisturbed healing phase (delay loading). With various advances in implant microtopographic surfaces and design, practitioners have been able to modify and change the original Brånemark protocol to a great extent. Later on one of these principles of delay loading was changed, and now an immediate loading of dental implants become an established technique without affecting the osseointegration. Several studies have shown that single stage surgery with immediate placement of dental implants after extraction and immediate loading of implants has predictable and successful results comparable to those of the traditional 2-stage protocol. Comprehensive reviews of in vivo studies have reported that micromotion at the bone -implant interface in the range of 50 to 150 μm may adversely affect osseointegration and remodeling at bone bone-implant interface. A review of literature found no studies evaluating the fate of dental implants when placed without primary stability. Therefore, this experimental study aimed to evaluate the outcome of implants without primary stability, clinically and radiographically. The study could fill in gaps in knowledge about an important subject concerning dental implantology. Background and objective: Primary implant stability is considered necessary for achieving and maintaining osseointegration. This experimental study aimed to evaluate the outcome of implants without primary stability, clinically and radiographically. Methods: Two adult sheep (3-4 years of age), 70 kg in weight, were included in the study. After sedation and local anesthesia, the lateral side of the basal bone of mandible is exposed by a single long incision. The implant bed performed in the inferior border of the basal bone of mandible drilling to 5 mm in diameter and 10 mm in length. Five implants were inserted into the basal bone of mandible for each side (right and left), but the sizes of inserted implant was 3.8 mm in diameter and 10 mm in length, after 4 months the 2 sheep were sacrificed and the universal torque ratchet was used to measure the stability of the implant by a counter torque 30 N/cm test. Cone Beam Tomography (CBCT) was used to evaluate the implants radiographically. Results: Nineteen (from 20) implants successfully tolerated a 30 N/cm countertorque test comprising (95%). Only one implant failed to osseointegrate (5%). During the healing period, no any adverse clinical signs reported. Conclusion: Dental implants may have a chance to osseointegrate even in the lack of primary stability.