# Effect of Osteoporosis on Well-Integrated Bone Implants
## 4 Discussion  
The current in vivo experiment intended to test the effect of an OVX-induced osteoporo-porotic condition on the bone tissue surrounding already-osseointegrated implants. Using a 14-week implantation period with osteopororotic induction at 8 weeks, the evaluation of histological images recorded for osteopororotic animals showed an obvious alteration in the quantity and quality of trabecular bone around implants compared to healthy animals. Our results showed that peri-implant bone characteristics in terms of BA% and BIC% were significantly lower in osteopororotic versus healthy animals. The osseointegration of implants involves a cascade of cellular and extracellular biological events that take place at and around the bone-implant interface [19]. Peri-implant healing is regulated by growth and differentiation factors released by the activated blood cells in the created implant bed, finally reaching an equilibrium status between bone resorption and formation around the implant [20]. This process is initiated within the site of implant osteotomy, immediately after implant placement. The sequence begins with the formation of a blood clot, which organizes and gives rise to woven bone and, finally, leads to lamellar bone formation [21]. Therefore, it is widely believed that bone health and quality are crucial requirements for the success of an implant [22]. A major systemic condition, which adversely affects osseointegration and implant survival, is osteoporosis [23]. Ovariectomized (OVX) rats represent an accepted animal model for simulating osteopororotic conditions [24]. However, histological and radiological studies have presented conflicting results. This can be related to the variation in the age of the animals, different anatomical sites, diverse assessment methods and regions of interest. For instance, previous studies have reported that long bones and the spine are more affected by osteoporosis than jaw bones [25]. In contrast, [PERSON] et al. showed a loose trabecular bone structure in the femoral necks and mandibles of ovariectomized rats while cortical bone morphology remained unchanged [26]. Moreover, earlier studies have confirmed that trabecular bone characteristics in femoral condyles change within 6-12 weeks after OVX surgery, bearing similarity to osteopororotic changes in postmenopausal women [25; 27; 28]. An osteopororotic condition was also achieved in the currently used ovariectomized rats, as confirmed by our histological analysis. In the literature, it has already been postulated that placing implants in a well-established osteopororotic animal model might negatively affect the bone-implant response. For instance, a recent systematic review investigated whether implant osseointegration is compromised in experimental osteopororotic conditions [29]. Despite the large heterogeneity in data, several in vivo studies suggested lower osseointegration in osteopororotic animals. This corroborates with [PERSON] et al. [30] and [PERSON] et al. [31], who also observed lower bone values around implants placed in well-established osteopororotic animals compared to sham-operated rats. The present study was designed in such a way to replicate the effects of late-induced osteoporosis after the osseointegration of implants was established. At 14 weeks after implantation, the amount of bone around implants was significantly decreased in the osteopororotic rats. This result indicates that the osseointegration of implants may be compromised in an osteopororotic bone condition induced postimplantation. Our findings corroborate those of [PERSON] et al. [32], who used a similar experimental design. After 12-week postimplant placement, the radiographic assessment revealed a significantly low bone density in OVX rats compared to SHAM [32]. However, several differences with the present study exist: (i) [PERSON] et al.