**1. Introduction**

Modern times bring many challenges in different life spheres, and medical treatment is not an exception. As dentists, we encounter constant scientific as well as technological developments, and it is with great eagerness that we strive to be active users of these benefits, thereby actively advocating for patients' best care. It is not with ease that a modern man would come to peace with the information that they are not eligible for a particular treatment; in dentistry, for instance, that may be the case when one does not have enough available bone for implants to be placed. This further motivates dentists to replace lost tissues by utilizing regenerative procedures. The principle of regenerative medicine and dentistry is founded on its interdisciplinarity as well as on the application of bioengineering techniques that enable the replacement of any lost tissue. In the field of oral surgery, a branch of dentistry, the most interesting tissue replacement is bone and soft (gingival) tissue replacement [1].

Of great help in regenerative procedures is the application of platelet concentrates that originate from the patient's blood [2]. The role of platelet concentrates in regenerative dentistry is based on the fact that they contain growth factors and scaffolds.

In this chapter, we will be discussing platelet-rich fibrin (PRF) and sticky bone, their preparation techniques, and usage indications. We will hereby also comment on other platelet concentrates.

### **2. A brief review of platelets and their role in the body**

Blood is a liquid tissue that consists of plasma (55%), red blood cells (or erythrocytes 45%), platelets (thrombocytes), and white blood cells (leukocytes) that together account for less than 1%. In the organism, blood acts as a transporting medium, participates in coagulation, and serves as a medium for information transduction (e.g., hormones) [3].

In regenerative processes, the focus is placed on platelets. They originate from megakaryocytes in the blood marrow. Platelets are small, discoid-shaped plate-like cells that have no nucleus and have a lifespan of 8–12 days in a resting state. Apart from their role in hemostasis, they also have a role in inflammatory reactions, wound healing, host defense, and tumor biology [4].

Platelets contain three types of granules (alpha, dense, and lysosomes) that dictate platelets' function. Among the three types of granules, the alpha granules are the most abundant and have an important role in regenerative and wound healing processes [4–6]. They contain adhesive proteins, growth factors, and clot-forming factors. The regenerative function of the alpha granules is based on mitogenic factors such as vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), epidermal growth factor (EGF), hepatocyte growth factor (HGF), and insulin-like growth factor (IGF)) [5–7].

In order for the granule release from a cell to occur, platelet activation is required. This process is mediated by platelet activating molecules and some of these molecules are produced by platelets (e.g., collagen, thrombin, thromboxane A, adenosine phosphate, P-selectin, and protease activator receptor–related molecules). On contrary, there are so-called inhibitors that act as platelet receptors' inhibiting molecules, thereby preventing platelet activation (e.g., coagulation factors, aspirin, ADP receptor inhibitors).

Once a blood vessel is injured and there is a rupture at the level of the endothelial layer, platelets start releasing molecules, such as collagen, that activate them. Activated platelets bind to the injured site of the blood vessel with collagen. This is known as adhesion. In addition, activated platelets secrete great amounts of ADP and, at the same time, thromboxane A2 is being synthesized, which then initiates granule (alpha and dense) release, which, in return, results in platelet aggregation. In other words, white platelet clot formation, that is, a result of the processes we explained beforehand, has three stages: platelet adhesion, granule release, and platelet aggregation. Simultaneously with platelet activation, blood vessel injury initiates a coagulation cascade. It starts when blood interacts with tissue factors. This process entails a series of biochemical reactions that convert inactive blood plasma proteins to active proteolytic enzymes. In this way, the coagulation process—that starts with thrombin activation upon blood vessel injury ends with the conversion of fibrinogen to fibrin. As a result, fibrin fibers permeate and secure the thrombus. In this way, the process of hemostasis is accomplished [4, 5, 7].

### **3. Platelet concentrates**

Platelets are not limited to hemostatic processes, but they also influence tissue regeneration, enhance collagen synthesis, and trigger angiogenesis as well as the

#### *PRF and Sticky Bone as Regenerative Materials in Oral Surgery DOI: http://dx.doi.org/10.5772/intechopen.108807*

immune response by releasing growth factors and cytokines [6]. The concept of platelet concentrate preparation is based on the fact that manipulation of normal physiologic processes, such as hemostasis, enables us to obtain concentrated platelets together with a greater amount of growth factors that play a crucial role in wound healing. They do that by stimulating tissue regeneration and proliferation, initiating extracellular matrix deposition, and supporting cell differentiation. By obtaining platelet concentrates, we obtain autologous biomaterials that have an important role in regenerative procedures. To date, there are numerous patents related to platelet concentrates [6]. The first one to be invented was, however, the fibrin glue, and it serves as the precursor of platelet concentrates afterward. Later, PRF (platelet-rich fibrin), sticky bone, and plasma gel were invented. The preparation process is simple. In outline, it is required to draw an adequate amount of blood from a patient in vacuum test tubes with or without anticoagulants and centrifuge them according to a protocol of choice. The point is that with every novel method of platelet concentrate preparation, scientists have struggled to improve the earlier one. The main objective was to increase the number of growth factors and prolong their release time. Novel methods made easier the preparation process by eliminating anticoagulants and simplifying centrifuge protocols.

Further in this chapter, we discuss a brief review of the most important platelet concentrates.
