Evidence on effects of early loading on enhanced osseointegration

Evidence on effects of early loading on enhanced osseointegration
Implant Dentistry: Volume 12(1) March 2003 pp 102-103
Ko, Ching-Chang
Lippincott Williams & Wilkins, Inc.
Abstract:
Studies have shown that immediate loading (loading the dental implant within 1 week after implant insertion) can result in a similar success rate to the conventional delayed loading (the implant rests in the bone for 2-8 months before function). However, mechanisms of how length of time before loading the implant affects interfacial bone morphogenesis are not known. This study hypothesizes that early loading can significantly enhance osseointegration via a synergistic interaction between functional loading and sensitized healing bone cells. Three healing stages were investigated using a controlled-load pig model.
Twelve minipigs (Sinclair) were used and equally divided into three groups of immobile healing periods: 1 month, 2 months, and 4 months. For each pig, one experimental implant was placed in one side of the mandible. The implants were rested for the specified healing periods and then loaded in an axial direction for an additional 5 months. The force 6.5 N exerted on the implants was controlled using an intraoral hydraulic device previously used by Ko et al (2002). Radiography and microcomputer tomography were used to assess osseointegration at the end of the experiments. In the contralateral side of each pig, one condition implant was inserted. The condition implant was not subjected to any loading and was logistically scheduled such that the implant tissues harvested were at the above-specified healing stages. The tissues surrounding the condition implants were used to assess cell appearances and percent osteoid to reflect the cellular activities at the time the experimental implant (contralateral side) started to carry loads. Simplified 2D finite element models of the present loading system were constructed to estimate local tissue strains with the input of the mineral contents and material properties of the conditional implants. Cell appearances, percent osteoid, and tissue strains were compared with the final osseointegration of the experimental implants (eg, cervical bone loss and bone density).
The preliminary results showed that two types of bone loss were associated with delayed loading: cervical bone loss and bone loss at the deep implant-bone interface, rather like the reverse of osseointegration. Early loading (1-month) significantly (P < 0.05) reduced both types of bone loss by promoting osteogenesis. Osteoblastic cells with high productivity of osteoid in the early healing stage respond to low strains (< 70 me) effectively. The regenerated dense trabeculae aligned predominantly parallel to the direction of maximum principal stress (tensile), suggesting that early daily loading activated cellular response to elicit an adaptive remodeling. The delayed loading, however, did not show such adaptation patterns. Further studies to incorporate molecular probes will explore and clarify the critical role for implant healing time in early bone response to functional loading. (This study is supported in part by the Whitaker Foundation and MDRCBB.)