Effects of Platelet-rich Plasma on Osteoblast and Osteoclast Number in Canine Mandibular Bone Grafts

Statement of the Problem: Platelet-rich plasma (PRP) was first reported as enhancing autologous mandibular bone grafts in 1998. Since then a number of studies have reported contradictory results on the benefits of PRP used in various types of bone grafts. A recent study from our laboratory reported that the use of PRP in conjunction with autologous mandibular bone grafts in canines resulted in an increased volume of new bone in the graft site at 1 and 2 months, but no difference was seen at 3 and 6 months. This increase was not due to an increase in the rate of bone formation. Additionally, removal of non-viable grafted bone was greater at 1 and 2 months with PRP. We report here on the comparative number of osteoblasts (ob) and osteoclasts (oc) in PRP and non-PRP autologous mandibular bone grafts in canines at 1, 2, 3, and 6 months. Materials and Methods: Twelve adult male dogs had bilateral inferior border marginal resections that measured 2cm x 1cm between the mandibular angle and the mental foramen. Corticocancellous bone harvested from the posterior ilium of each animal was particulated in a bone mill, and equal volumes were placed in each defect. Grafts were stabilized with Vicryl mesh secured to the mandible with two 1.5 x 6mm titanium screws. PRP was produced from 20cc of peripheral blood from each animal. The right side graft in each animal had PRP added while the left side had nothing added. All dogs were maintained on soft diets for 2 weeks postoperatively. Three animals were sacrificed at 1, 2, 3, and 6 months, respectively. The grafts along with adjacent bone were harvested at the time of sacrifice, fixed, dehydrated, and embedded in Spurr’s undecalcified. Two median sections were cut, polished and mounted. Sections were stained with Sanderson’s rapid bone stain and Alizarin red, and examined with a Leitz bright-field microscope. Method of Data Analysis: Twenty fields from each section were analyzed at 100x. The total number of osteoblasts/field were counted. The total number of osteoclasts/field were counted along with the visible number of nuclei in each cell. These numbers were compared for PRP and non-PRP grafts for all times. Results: The comparative numbers of ob and oc for the PRP and non-PRP grafts for all times are expressed as ratios. At 1 month the ratio of ob in the PRP grafts compared to the non-PRP grafts was significantly greater at 1.65:1. The ratio of oc in the PRP grafts compared with the non-PRP grafts is also significantly greater at 2.01:1. At 2 months the ratio of ob in the PRP grafts compared to the non-PRP grafts is 1.02:1, and the ratio of oc in the PRP grafts compared to the non-PRP grafts is 1.21:1. The ratio of ob in the PRP grafts compared to the non-PRP grafts at 3 months is 1:1.1, and the ratio of oc in the PRP grafts compared to the non-PRP grafts is 1.2:1. At 6 months, the ratio of ob in the PRP grafts compared to the non-PRP grafts is 1:1.12, and the ratio of oc in the PRP grafts compared to the non-PRP grafts is 1:1.02. The differences in the number of ob and oc at 2, 3, and 6 months are not statistically significant. The number of oc nuclei seen at the different times, with or without PRP ranged from 3 to 16. There was no statistically significant difference in the number of nuclei in oc with or without PRP at any time. Conclusion: The enhanced healing of autologous bone grafts using PRP that has been reported in previous studies may be due to an increased number of both ob and oc in the graft site. This may be due to increased recruitment and differentiation of ob and oc precursor cells in the PRP graft sites. In the study reported here this effect appears early in the healing process, and is no longer evident after 1 month.