Background: Implant design influences primary stability and osseointegration during early healing. However, when primary stability cannot be achieved, the addition of molecules to the implant surface might improve bone to implant contact (BIC) at an early stage. Leucocyte and platelet rich fibrin (L-PRF) has shown to promote the formation of a dense fibrin clot on nano-rough implant surfaces, which seems to be crucial to provide a provisional scaffold for the migration of osteogenic cells. 
Aim/Hypothesis: To evaluate the effect of L-PRF coating on the peri-implant bone formation and angiogenesis at early healing in a pig model. 
Material and Methods: Four implants were placed in the skull of twelve domestic pigs with an oversized preparation (0.4mm): two 4.2x8mm ASTRA EV implants (OsseoSpeed surface), and two 4.0x8mm Blossom implants (Ossean surface). Implants conditions were randomised as control A (ASTRA EV no coating), control B (Blossom no coating), test A (ASTRA EV coated with L-PRF), and test B (Blossom coated with L-PRF). Two follow-up periods were settled to evaluate the early healing: 7 days (6 pigs) and 28 days (6 pigs). To assess the BIC, microCT images were taken from the bone samples at 28-days. Moreover, two peri-implant areas (rings) were analysed. The first ring, close to the implant (0.4mm width), was considered as the “newly formed bone” given the oversized preparation. A second ring, situated around the first ring (0.4 mm width), was considered as an area of bone remodelling. All bone specimens were also processed for histomorphological and immunohistochemical analysis (Masson’s trichrome, CD31 and TRAP).
Results: Forty-eight implants were installed following the randomisation protocol. One pig died immediately after surgery and was used as a control. The oversized preparation was confirmed by the microCT of the control, with a mean BIC value of 27.8 %. The mean BIC after 28 days was 89.3% (± 3.8) and 83.9% (± 5.7) for Blossom coated and non-coated, respectively (p<0.05). For ASTRA EV implants, a mean BIC of 82.1% (± 11.0) was observed for coated implants, and 77.7% (± 8.5) for non-coated (p<0.05). For both implant surfaces, bone trabecular pattern and bone microstructure were not significantly affected by the L-PRF functionalization (p>0.05) (Figure 1). Histological analysis showed inflammatory infiltrate around all implants at day 7. At 28 days, immunohistochemical analysis revealed newly formed microvessels and bone apposition in contact with the implant surface were found in all the conditions.  
Conclusion and Clinical implications: L-PRF implant coating appears to improve BIC in an oversized preparation after 28 days. However, peri-implant bone structure seems not to be affected by L-PRF implant surface functionalization. Microvascularisation and bone apposition around oral implants might be increased by L-PRF coating in oversized preparations after 28 days. When primary stability cannot be achieved or when altered systemic/local conditions are present, L-PRF coating might enhance implant osseointegration.

Peri-implant bone structure and microvessel density after implant functionalization with L-PRF