Clinical effect of platelet rich fibrin in the treatment of periodontal intrabony defects. Systematic review and meta-analysis.

Introduction: One of the consequences of periodontitis is periodontal intrabony defects (PID). Various biomaterials have been used for its treatment, but there is still no biomaterial considered as the gold standard. Current research is focused on the use of platelet-rich plasma (PRP) for the treatment of PID. Objective: To determine the clinical effect of PRP in the treatment of PID through a systematic review with meta-analysis. Materials and Methods: A literature search was conducted until February 2017 in the biomedical databases: Pubmed, Embase, Scielo, Science Direct, SIGLE, LILACS, IBECS, and the Cochrane Central Register of Clinical Trials. The criteria for the selection of the studies, which were randomized clinical trials, were the following: articles or papers published in the last 5 years, reporting clinical effects, with a follow-up time equal to or greater than 6 months, and a sample size equal to or greater than 10 patients reporting the use of PRP as a treatment for PID. The methodological quality of the studies was analyzed using the Cochrane Handbook of Systematic Reviews of Interventions as a reference. Results: The search strategy yielded nine articles reporting a reduction in probing depth and gingival recession, and an increase in clinical insertion level when using PRP alone or in combination with another biomaterial. Conclusion: The reviewed literature suggests that the use of PRP in the treatment of PID has a positive clinical effect.


INTRODUCTION.
Periodontal disease is characterized by clinical attachment loss with subsequent destruction of periodontal tissues. 1-3 If left untreated, the condition will lead to a premature loss of teeth. 2,4 Periodontal treatment aims to eliminate the inflammatory process, prevent the progression of periodontal disease, maintain natural dentition in optimal health and function, and regenerate lost periodontal tissues. 3,5, 6 Therapeutic modalities for restoring the diseased periodontium have shown limited potential for good results because they fail to completely regenerate periodontal tissues. 4, 5 One of the consequences of periodontal disease is the appearance of periodontal intrabony defects (PIDs). Several biomaterials, such as autogenous and allogeneic bone grafts, have been used to treat PIDs. However, there is no single graft material to date considered as the gold standard for the treatment of DIP. 3,5, 7 The key to regeneration is to stimulate a sequence of curative events that result in the formation of an integrated tissue. Such modulators include the use of growth factors (GFs), the application of extracellular matrix proteins and binding factors, and the use of bone morphogenetic proteins. 2,8,9 There is evidence demonstrating the effectiveness of GFs in periodontal regeneration. 2,4,10, 11 GFs play a key role in the multiplication and development of vascular endothelial cells, smooth muscle cells and fibroblasts. GFs have multiple effects on cellular remodeling phenomena and modulate the inflammatory reaction in the healing and tissue regeneration processes. 2,3,5,9,12- 15 Platelet-rich fibrin (PRF) as described by Choukroun et al. 16 is a second-generation platelet concentrate containing platelets and GFs in the form of fibrin membranes prepared from the patient's own blood, free of any anticoagulant or other artificial biochemical modifications. 3, 6 PRF improves regeneration and wound healing and is superior to other platelet concentrates because of its ease of use and inexpensive preparation method, as no exogenous compounds such as bovine thrombin or calcium chloride are needed. PRF has emerged as one of the most promising regenerative materials in the field of periodontics. 3 Although some studies have evaluated the effect of PRF in the treatment of PID, the diverse nature among them makes it difficult to obtain clear interpretations. The aim of this article was to evaluate the clinical effect of PRF in the treatment of periodontal intrabony defects

MATERIALS AND METHODS.
This review was carried out according to a previously designed research protocol following the guidelines established in the PRISMA standards. 17 Search methodology A broad search strategy was conducted in the biomedical databases Pubmed, Embase, Scielo, Science Direct, SIGLE (System of Information on Grey Literature in Europe), LILACS, IBECS, and in the Cochrane Central Register of Clinical Trials. A manual search was also conducted in higher impact journals of periodontology such as: Periodontology 2000, Journal of Clinical Periodontology and Journal of Periodontology from the 2 nd of January, 2012 until the 28 th of February, 2017; using a combination of topic or thematic headings with the following keywords: ("fibrina rica en plaquetas" OR "platelet-rich fibrin" OR "PRF" OR "plasma rich in growth factors") AND ("defecto intraóseo" OR "defecto periodontal" OR "infrabony defect" OR "periodontal defect").

Selection criteria
The following inclusion criteria were considered: articles reporting the use of PRF in the treatment of PID; reporting clinical effects (reduction in probing depth, increase in clinical insertion level and reduction in gingival recession) when using in the treatment of PID; articles published in the last 5 years, reporting a follow-up time equal to or greater than 6 months, with sample sizes equal to or greater than 10 patients.Articles reporting the use of PRF in the control group, and articles published in non-indexed journals were excluded from the study.

Process of selection and extraction of data
Titles and abstracts of all the articles complying with the aforementioned inclusion and exclusion criteria were reviewed. Full texts of the articles that seemed to meet the selection criteria were obtained in order to assess the bias risk. A checklist was made in duplicate to evaluate the studies and to extract the information of interest. Two reviewers (LG and EI) independently performed the evaluation of the articles regarding title, author, year of publication, type of study, number of patients, ages of patients, follow-up time, country where it was conducted, number of areas treated per group, number of patients per group, type of PID treated, reduction in probing depth, increase in clinical insertion level, reduction in gingival recession, number of centrifugations, primers used, post-surgical medication and risk of bias. For the resolution of any discrepancy between the reviewers, they met and discussed with a third reviewer (SR) in order to reach an agreement.

Assessment of the methodological quality and risk of bias of the studies
For the assessment of the methodological quality and risk of bias, each study was analyzed according to the Cochrane Handbook of Systematic Reviews of Interventions. 18 Each study was evaluated in seven domains: selection bias (random sequence generation and concealment of allocation), performance bias (blinding of participants and research staff), detection bias (blinding of outcome assessors), attrition bias (incomplete outcome data), reporting bias (selective reporting of results), and other biases. Each domain was assessed as high, low, or unclear risk.

Analysis of results
Data from each study were placed and analyzed with RevMan 5.3 (Cochrane Group, UK). For performing the meta-analysis, results of the studies were combined independent of the follow-up period length.

RESULTS.
The initial search in the biomedical databases yield-ed107 titles; Figure 1 shows the article selection flowchart. Table 1 also shows the characteristics and variables considered in the 20 selected articles. Figure 2 presents the analysis of the methodological quality and the risk of bias of the studies. Articles identified in electronic searches (database) and journals. n=107 Articles excluded for being repeated. n=12 Articles excluded after evaluating their titles. n=49 Articles excluded after evaluating their abstracts. n=26 Studies conducted on animals (n=4) Bibliographic Reviews (n=6) Systematic Reviews (n=3) Case reports (n=12) Articles included in meta-analysis. n=19 Articles identified to read their titles n=95 Articles identified to read their abstracts. n=46 Articles identified in the systematic review n=20 Random sequence generation (selection blas).
Blinding of outcome assessment (detection blas).
Other blas.     Figure 3 shows the forest plot for the reduction in probing depth when using PRF in the treatment of periodontal intrabony defects. Figure 4 shows the forest plot for the increase in clinical insertion level when using PRF in the treatment of periodontal intrabony defects. Figure 5 presents the forest plot for the reduction in gingival recession when using PRF in the treatment of periodontal intrabony defects.

DISCUSSION.
Results revealed that the use of PRF in the treatment of PID produced an increase in the clinical insertion level, a reduction in probing depth, and a reduction in gingival recession significantly greater than the control treatment.
Subgroup analysis showed that all these clinical effects were similarly beneficial if PRF was used alone, or if PRF was used in combination with another biomaterial or substance that stimulates tissue regeneration.
In this study, a random effects model for the meta-analysis was used. In addition, it was found that there was no difference if the RCT had a parallel 21-23,26-28,32,34,37,38 or cross- over design 19,24,25,29-31,33,35,36 . The studies showed positive clinical effects for the use of PRF in the treatment of PID. This is similar to the findings reported by Smail et al., 39 who performed a study that did not provide sufficient evidence for the systematic differences in estimates of the effect of interventions between split-mouth and paral-  lel-arm RCTs for continuous or binary data. This review also demonstrates that PRF does not have a clear standard protocol because the type of centrifuge and configuration also differ from one study to another. Therefore more standardized protocols are needed to allow for a better comparison and homogenize the results.
One strength of this systematic review was the selection of the studies, because an exhaustive search was performed in the most important databases and strict inclusion criteria were followed. However, there are also limitations such as the presence of many RCTs that presented a high and unclear risk of bias. Another positive aspect is the comparison of these results with other sys-tematic reviews on this subject. 40,41 These reviews confirm that using PRF produces a positive and beneficial clinical effect in the treatment of PIDs. It is important to consider that these reviews included RCTs published in years prior to those included in this study.
However, the promising effect of PRF for the treatment of PIDs cannot yet fully accepted. Most of the RCTs show a high heterogeneity and were conducted primarily in European and Asian countries, with only two from North America and one from Africa. As each continent and country has its own culture and diet, these factors can influence the clinical effects of PRF. It is advisable to carry out well-designed RCTs dealing with this issue in countries in oth-er continents, especially in Latin America, because Latin American countries have the greatest genetic diversification, culture, food and a wide range of climates.

CONCLUSION.
The clinical effect of PRF in the treatment of PID is  positive either when used alone or in combination with another biomaterial. Its clinical effect was significant in reducing probing depth, reducing gingival recession, and increasing clinical insertion level, regardless of whether the RCT had a parallel or cross-over design