Participation of the Periosteum, Endosteum, and Hematogenous Marrow in the Early Osseointegration of a Titanium Implant Inserted in Contact with the Hematogenous Marrow

<i>Background and Objectives</i>: Implant osseointegration has been widely studied over the past few decades, particularly focusing on surface modifications that aim to improve integration. However, the literature includes few studies regarding the role of the endosteum in early osteointegration. Therefore, the aim of the present work is to approach the technique of implant insertion into bones with marrow, with an emphasis on the use of implants that are long enough to achieve marrow penetration. <i>Materials and Methods</i>: Titanium implants were inserted into the femurs of eight eleven-month-old rabbits. Fourteen days later, the animals were euthanized in accordance with the current legal and ethical guidelines. The histological processes that occur at the bone-implant interface were investigated. Histological sections of the bone-implant interface were colored using the Trichrome's Goldner method, and were further analyzed and photographed using an Olympus microscope. <i>Results</i>: The histological analysis showed that during the initial osteointegration phases, the newly formed bone originated from the endosteal-medular zone. Periostal proliferation was observed only during the early stages. The bone that proliferated on the implant's endosteal/medullary interface exhibited a surface area approximately 6 times larger than that of the bone formed on the osteal surface. Also, its length was approximately 25% longer. <i>Conclusions</i>: The bone tissue that proliferates on the endosteal and marrow surface of the implant increases significantly the bone-implant interface, and creates the setting for a good secondary stability. The findings suggest several clinical implications, as follows: penetrating the bone marrow during the insertion of short implants allows for increasing the bone-implant interface; the flap should be carefully managed; the integrity of the periosteum must be kept, as this is a key anatomical structure in cases of deficient bone marrow (i.e., severe mandible atrophy or vertical ridge augmentations).