In addition, the morphology of the hard rutile scale grown on the implant surface increases nanoroughness (Fig. 4). Studies carried out by Webster et al. [29] have pointed out the importance of the surface roughness at the nanometre range in the connectivity to bone. It has been discussed that the increase of micro- and submicro-scale surface roughness, with feature sizes comparable to those of resorption pits of bone and cell dimensions, leads to enhanced osteoblasts differentiation and increased bone-to-implant contact in vivo [33].

In the specific case of osteoporotic rabbits, the results showed that the modification of the surface by the thermal treatment gives rise to a better bone response in BMD and BIC values at longer time of implantation, i.e., 30 days (Figs. 5 and 6). These results seem to indicate that the crystallography and the chemical composition given by the rutile enhance the interaction between osteoblasts and surface improving the bone regeneration around the Ti6Al4V implants.

With respect to local administration of GH to the osteoporotic rabbits, significant results have not been obtained, although a slight improvement was observed. In our study, densitometric results related to those animals in the GH treated group that were sacrificed after 15 days showed a tendency towards increased bone mineral density (BMD) that did not reach statistical significance. Our results emphasize the idea of the variability in the response to GH because, by itself, topical administration gives rise to very different results probably due to additional characteristics that affect to variables such as the host, the methodology of administration of GH or the implant itself. These results are in agreement with the authors’ previous data [11] and other authors [34]. For example, Calvo-Guirado et al. [14] found topical application of 4 IU of GH like biomimetic agent at the moment of implant placement has no significant effects on the BIC at 5 and 8 weeks, although bone formation and inter-thread bone values did increase significantly. However, controversial about the efficiency of the topical administration of GH is found in the literature. Munoz et al. [35] found that topical application of growth hormone GH and melatonin synergistically enhance new bone formation around titanium implants in early stages of healing.