Horizontal Alveolar Ridge Augmentation in the Mandibular Posterior Region Using Biphasic Calcium Phosphate and Leukocyte-and Platelet rich fibrin (L-PRF): A case report.

In bone defects caused by tooth loss, tissue reconstructions are necessary to enable prosthetic rehabilitation with dental implants. Diverse techniques and materials of different origins are used for this purpose. Leukocyte-and Platelet-Rich Fibrin (L-PRF) has been used in association with osteoconductive biomaterials in procedures of bone regeneration and for covering grafted areas. The aim of this article was to demonstrate a clinical case of bone grafting in the posterior region of the mandible, performed with the use of synthetic biomaterial composed of biphasic calcium phosphate associated with Leukocyte-and Platelet-Rich Fibrin for performing bone augmentation in an alveolar ridge with a horizontal defect, thereby enabling later installation of dental implants and prosthetic rehabilitation in the region.


Introduction
Tooth loss due to trauma, extractions or periodontal disease, leads to resorption of the alveolar ridge, resulting in vertical or horizontal bone defects or a combination of these. These often make it impossible to install osseointegrated implants [1,2].
In regions of resorbed alveolar ridges, reconstruction of defects with bone grafts are required. These may be performed prior to or simultaneously with installation of the implants. Diverse techniques described in the literature have been successfully performed by clinicians, with the use of materials of different origins and types [3,4]. In horizontal bone defects, reconstructions may be performed by means of fixation of bone blocks, techniques for division and expansion of the crest or by means of the guided bone regeneration (GBR) technique [1,[5][6][7].
Osteoconductive materials of synthetic origin have been widely used in bone regeneration procedures, particularly biphasic calcium phosphate, composed by the association of hydroxyapatite with tricalcium β-phosphate. They have characteristics of resorption to allow bone growth and maintain the volume of the graft area. Studies have shown high success and survival rates of implants installed in areas regenerated with this material [8][9][10][11].
Leukocyte-and platelet-rich fibrin (L-PRF), initially described by Choukroun in 2001 [12], is an autologous material that has been used in different regenerative procedures involving hard and soft tissues [13]. It is obtained by centrifugation of venous blood, leading to the occurrence of a natural and gradual process of polymerization. This results in a dense fibrin matrix, with a large number of platelets and leukocytes trapped within it. This product slowly releases cytokines and growth factors involved in angiogenesis and in the process of tissue regeneration in a period lasting from 7 to 14 days [14][15][16] .
The aim of this study was to describe a clinical case of lateral augmentation of the alveolar ridge bone by means of the guided bone regeneration technique, with the use of biphasic calcium phosphate and L-PRF.

Case Report
The patient, a 61-year-old woman presented to the clinic of the were requested. In addition, intra and extraoral photographs were taken for planning the case. The laboratory blood exams showed no alteration. In the computed tomography assessment, loss of bone thickness in the region of tooth 35 was verified ( Figure 2), which required tissue regeneration therapy to enable implant installation. In addition, the need for extracting tooth 35 was shown. The patient was informed of the diagnosis and the treatment proposed for resolving the case.
These were promptly accepted by the patient, who then signed the Term of Free and Informed Consent. Pre-operative medications were prescribed (2 g Amoxicillin, one hour before surgery; 4 mg Dexamethasone, 1 tablet 1 hour before surgery) [17].       covered with two L-PRF membranes. Subsequently, suturing was performed in the region (Figure 10).  Four months after implants were placed, the sites were reopened, and healing caps were inserted (Figures 10B and C). Two months after the reopening procedure, the patient received a fixed splinted dental prosthesis relative to teeth 35 and 36.

Discussion
Guided bone regeneration, a procedure widely used for alveolar bone ridge augmentation, is a technique that has been well-documented in the literature.
Moreover a high survival rate has been shown for implants installed in the areas of defects treated with this safe and predictable therapy. In GBR, the role played by resorbable or non-resorbable membranes used as a barrier, refers to creating and maintaining space, preventing soft tissue growth, and providing the graft with stability [4,5,18,19].
In the present report, alveolar preservation and horizontal augmentation were performed with the use of a particulate biphasic calcium phosphate graft associated with leukocyte-and platelet-rich fibrin (L-PRF) in the liquid phase. The entire grafted area was covered with L-PRF membranes, without association of resorbable or non-resorbable membrane barriers as described in the GBR technique [20]. One of the advantages of using L-PRF membranes was that, due to their highly dense structure, they can be sutured onto the soft tissues, thereby promoting enhanced stability in the region. Furthermore, in case of suture dehiscence in the operated area, the L-PRF membrane does not cause problems, as it remains exposed to the oral environment, and continues with its function of to volume [21].
Another in vivo study evaluated the effect of resorbable membranes and platelet-rich fibrin membrane (PRF) on bone healing in critical defects in rat tibiae.
The rats were divided into three experimental groups using one layer of collagen membrane, two layers of collagen membranes and platelet-rich fibrin (PRF) membranes and a control group without any covering membrane. After 7 and 28 days, the histomorphometric analysis showed that the group that received PRF membranes had higher level of bone neoformation and a lower level of fibrosis when compared with the other groups [22].
Clinical studies with humans, with the use of L-PRF membrane for covering grafted areas have been published in the literature. These have shown positive results in several situations, and may be an alternative material for use in the bone regeneration process [23][24][25][26].
By means of a modification made in the centrifugation protocol to obtain leukocyte-and platelet-rich fibrin clots, it was possible to develop leukocyte-and platelet-rich fibrin in the liquid phase. This concerned platelet concentrate shows an abundant quantity of activated fibrinogen in the liquid phase containing growth factors responsible for tissue regeneration [27]. One of the clinical applications in bone regeneration is the possibility of agglutinating particulate biomaterials [2,28].
In the present clinical case, the use of leukocyte-and platelet rich fibrin in the liquid phase, associated with particulate synthetic biomaterial, made it possible to agglutinate the biomaterial particles, thereby favoring their accommodation and stability in the bone defect of the grafted region. This was also applied on the L-PRF membranes, promoting better adhesion between them in the surgical bed. This characteristic of agglutination and adhesiveness was advantageous when the grafting technique was being performed.
In the second surgical stage of the implants placement, it could be noted that the regenerated area had a bone density that allowed good primary stability of the implants at the time of their placement.

Conclusion
In the present case report, the use of L-PRF membranes for covering the biphasic calcium phosphate particulate graft proved to be an effective therapeutic approach to guided bone regeneration for the purpose of horizontal bone augmentation. However, further controlled studies are necessary to evaluate the success of this therapeutic approach.

Consent
Written informed consent was obtained from the patient for publication of his clinical details and clinical images.

Conflicts of Interest
The author(s) declare(s) that they have no conflicts of interest.