**3.1. L-PRF in the treatment of periodontal intrabony defects (IBDs)**

Periodontal tissue regeneration has been defined as the formation of new cementum, alveolar bone, and a functional periodontal ligament on a previously-diseased tooth-supporting root surface. Due to limited intrinsic regenerative potential, IBDs are a common and challenging sequel of periodontal disease. Meta-analyses demonstrated that, treatment with conservative open flap debridement, produces an Average Clinical Attachment (CAL) gain of 2.0 mm [9]. While about 1.5 mm may be attributed to newly formed bone; bone-fill does not implicate the regeneration of new attachment to the root [9]. In this context, L-PRF appears promising for regeneration of the whole periodontal attachment system (**Figure 3A** and **B**). Five RCTs addressing the prospective application of L-PRF in the treatment of Periodontal IBD were found. The identified studies allowed for the following comparisons: (a) L-PRF/Open flap surgery vs. Open flap surgery [10–12], (b) L-PRF/Bio-Oss® constructs (Bio-Oss®, Geistlich Pharma North America, Inc.) vs. L-PRF [13] and (c) L-PRF/DFDBA constructs vs. DFDBA (Demineralized Freeze-Dried Bone Allograft) [14]. All patients included in those studies were periodontally stable and systemically healthy individuals who presented: similar bilateral IBD of at least 5 mm probing depth, located in vital asymptomatic teeth with no furcation involvement. Studies evaluating the addition of L-PRF to conventional open flap procedure reported the biomaterial notably improving both, clinical and radiographic parameters of IBDs, after 9 [11, 12] and 12 months [10]. A significant increase in probing depth (PD) reduction, CAL gain, post-treatment.

Gingival Margin Stability [(GMS) *less post-treatment gingival recession*], bone defect fill and percentage bone defect fill were noticed in all L-PRF-treated sites vs. controls [10–12]. Interestingly, higher patient acceptance was also associated with use of L-PRF. Most probably, this is attributed to the accelerated wound healing and pain-inhibitory properties [10, 11]. The presented PD reduction and CAL gain values were superior to previously-reported values in meta-analysis performed for open flap surgery [9], suggesting the additional benefits of L-PRF over the conventional approach. Treatment with L-PRF/particulate bone-graft substitutes (Bio-Oss® [13] and DFDBA [14]) provided additional statistically-significant benefits, in terms of PD reduction, CAL gain and bone defect fill vs. graft substitutes, after 6 months. Nonetheless, the absence of "simultaneously-run" L-PRF-alone control renders it difficult to

66.7% of L-PRF-treated sites. Severity within residual defects was reduced in 5/6 sites (degree I), whereas one defect remained in degree II. Significantly greater PD reduction, CAL gain and radiographic vertical defect fill was reported on experimental sites vs. controls. L-PRF use

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Gingival recessions are characterized by the apical migration of the gingival margin with subsequent root surface exposure. If left untreated, the condition may lead to other problems including: deficient esthetics, dentine hypersensitivity and higher risk of dental caries [17]. Available treatment options include the use of: (a) Coronally Advanced Flaps (CAF); (b) Connective Tissue Grafts (CTG); and (c) Sub-epithelial Connective Tissue Grafts (SCTG). On their own, the aforementioned techniques have important limitations such as (a) unpredictable long-term root coverage (i.e. CAF decreases from 89% to 58.8% after 6 months), (b) limited gain of keratinized tissue width (KTW); important to prevent recurrence, and (c) adverse post-surgical effects such as pain/discomfort, swelling, flap necrosis, etc. [17]. In this review, five RCTs evaluating the application of L-PRF in the treatment of gingival recessions were identified and included. The studies allowed for the following comparisons: (a) L-PRF/CAF vs. CAF [18–19]; (b) L-PRF/CAF vs. EMD (Enamel Matrix Derivate)/CAF [20]; (c) L-PRF/CAF vs. CTG [21]; and (d) L-PRF/CAF vs. SCTG [22]. Similar to previous RCTs, all patients included herein were periodontally-stable and systemically healthy; presented with: similar bi-lateral Miller Class I or II gingival recessions (>2 mm depth) localized on vital teeth, without restorations. According to Padma et al., the addition of L-PRF to CAF improved both, clinical outcomes and post-treatment stability of CAF [18]. After 6 months, the authors reported (significantly) more Recession Depth (RD) reduction, CAL gain and KTW increase in all L-PRF-treated sites vs. controls. Interestingly, post-treatment GMS was also higher in the test group with 100% root coverage after 6 months vs. 64.88% in controls [18]. However, in contrary with this RCT, Aroca et al. reported limited clinical benefits when using the L-PRF/ CAF approach [19]. Herein, CAL gain and Gingival Tissue Thickness (GTH) were the only benefiters of the combination; whereas percentage root coverage, full root coverage, GMS and Recession Width (RW) reduction were significantly higher in CAF-alone controls than the test group [19]. Such "*contradictory*" results may be partially explained by deficient study design, which, not only failed to adequately include blind examiners (leading to potential bias in favor of the "traditional" approach), yet also included: multiple adjacent gingival recessions (with poorer prognosis than single/localized recessions); heavy smokers (in which healing response is usually altered); and the L-PRF were stored in a 4°C refrigerator until use (L-PRF protocols often recommend immediate/fresh use). Indeed, emerging evidence states that growth factor release from L-PRF initiates as early as 5 min from preparation/centrifugation. Hence, storage could have altered its properties and thereby diminished or deteriorated its clinical potential. When compared to other root coverage procedures (EMD/CAF, CTG and SCTG), the L-PRF/ CAF approach showed similar clinical outcomes regarding RD reduction, CAL gain, mean root coverage (%) and complete root coverage (%). KTW increase was the only exception, with both EMD/CAF and CTG controls showing higher KTW than L-PRF-treated groups [20–22]. Interestingly, all studies reported significantly faster healing and fewer complications (pain and discomfort) when L-PRF was used [20–22]. Findings are notable, especially when

was also associated with a greater post-treatment GMS [16].

**3.3. L-PRF in the treatment of miller class I and II gingival recessions**

**Figure 3.** Clinical illustration of L-PRF application in Oro-Maxillo-facial surgery defect regeneration: Natural guided tissue bioengineering using L-PRF as a "bio-scaffold". (A) L-PRF membrane preparation. (B) Clinical application in IBD. (C) Clinical application under CAF. (D) Clinical application in PAOO.

distinguish between the effects of L-PRF and other potential variables in the study. Thus, while promising, additional studies are deemed essential in order to appropriately determine (quantifiably) the effectiveness and advantages of L-PRF application over particulate bonegrafts use.

#### **3.2. L-PRF in the treatment of periodontal furcation defects (PFDs)**

Molars with furcation involvement (resulting from periodontitis) have higher rates of periodontal breakdown and poorer prognosis, than single-rooted teeth [15]. Contemporary treatment options often include the use of regenerative materials and bone grafts; however, the introduction of L-PRF seems promising for better therapeutic outcomes. In our analyses, 1 RCT addressing the therapeutic use of L-PRF in PFDs was found [16]. The study compared L-PRF/open flap vs. open flap debridement alone, in the treatment of grade II mandibular defects. Included patients were periodontally-stable and systemically healthy, with similar bi-lateral grade II buccal furcation defects (at least 5 mm probing depth and ≥ 3 mm horizontal probing depth), in vital asymptomatic mandibular first molars.

L-PRF use significantly improved clinical and radiographic parameters of conventional open flap debridement. After 9 months, complete clinical closure of the defect was achieved in 66.7% of L-PRF-treated sites. Severity within residual defects was reduced in 5/6 sites (degree I), whereas one defect remained in degree II. Significantly greater PD reduction, CAL gain and radiographic vertical defect fill was reported on experimental sites vs. controls. L-PRF use was also associated with a greater post-treatment GMS [16].

#### **3.3. L-PRF in the treatment of miller class I and II gingival recessions**

Gingival recessions are characterized by the apical migration of the gingival margin with subsequent root surface exposure. If left untreated, the condition may lead to other problems including: deficient esthetics, dentine hypersensitivity and higher risk of dental caries [17]. Available treatment options include the use of: (a) Coronally Advanced Flaps (CAF); (b) Connective Tissue Grafts (CTG); and (c) Sub-epithelial Connective Tissue Grafts (SCTG). On their own, the aforementioned techniques have important limitations such as (a) unpredictable long-term root coverage (i.e. CAF decreases from 89% to 58.8% after 6 months), (b) limited gain of keratinized tissue width (KTW); important to prevent recurrence, and (c) adverse post-surgical effects such as pain/discomfort, swelling, flap necrosis, etc. [17]. In this review, five RCTs evaluating the application of L-PRF in the treatment of gingival recessions were identified and included. The studies allowed for the following comparisons: (a) L-PRF/CAF vs. CAF [18–19]; (b) L-PRF/CAF vs. EMD (Enamel Matrix Derivate)/CAF [20]; (c) L-PRF/CAF vs. CTG [21]; and (d) L-PRF/CAF vs. SCTG [22]. Similar to previous RCTs, all patients included herein were periodontally-stable and systemically healthy; presented with: similar bi-lateral Miller Class I or II gingival recessions (>2 mm depth) localized on vital teeth, without restorations. According to Padma et al., the addition of L-PRF to CAF improved both, clinical outcomes and post-treatment stability of CAF [18]. After 6 months, the authors reported (significantly) more Recession Depth (RD) reduction, CAL gain and KTW increase in all L-PRF-treated sites vs. controls. Interestingly, post-treatment GMS was also higher in the test group with 100% root coverage after 6 months vs. 64.88% in controls [18]. However, in contrary with this RCT, Aroca et al. reported limited clinical benefits when using the L-PRF/ CAF approach [19]. Herein, CAL gain and Gingival Tissue Thickness (GTH) were the only benefiters of the combination; whereas percentage root coverage, full root coverage, GMS and Recession Width (RW) reduction were significantly higher in CAF-alone controls than the test group [19]. Such "*contradictory*" results may be partially explained by deficient study design, which, not only failed to adequately include blind examiners (leading to potential bias in favor of the "traditional" approach), yet also included: multiple adjacent gingival recessions (with poorer prognosis than single/localized recessions); heavy smokers (in which healing response is usually altered); and the L-PRF were stored in a 4°C refrigerator until use (L-PRF protocols often recommend immediate/fresh use). Indeed, emerging evidence states that growth factor release from L-PRF initiates as early as 5 min from preparation/centrifugation. Hence, storage could have altered its properties and thereby diminished or deteriorated its clinical potential. When compared to other root coverage procedures (EMD/CAF, CTG and SCTG), the L-PRF/ CAF approach showed similar clinical outcomes regarding RD reduction, CAL gain, mean root coverage (%) and complete root coverage (%). KTW increase was the only exception, with both EMD/CAF and CTG controls showing higher KTW than L-PRF-treated groups [20–22]. Interestingly, all studies reported significantly faster healing and fewer complications (pain and discomfort) when L-PRF was used [20–22]. Findings are notable, especially when

distinguish between the effects of L-PRF and other potential variables in the study. Thus, while promising, additional studies are deemed essential in order to appropriately determine (quantifiably) the effectiveness and advantages of L-PRF application over particulate bone-

**Figure 3.** Clinical illustration of L-PRF application in Oro-Maxillo-facial surgery defect regeneration: Natural guided tissue bioengineering using L-PRF as a "bio-scaffold". (A) L-PRF membrane preparation. (B) Clinical application in IBD.

Molars with furcation involvement (resulting from periodontitis) have higher rates of periodontal breakdown and poorer prognosis, than single-rooted teeth [15]. Contemporary treatment options often include the use of regenerative materials and bone grafts; however, the introduction of L-PRF seems promising for better therapeutic outcomes. In our analyses, 1 RCT addressing the therapeutic use of L-PRF in PFDs was found [16]. The study compared L-PRF/open flap vs. open flap debridement alone, in the treatment of grade II mandibular defects. Included patients were periodontally-stable and systemically healthy, with similar bi-lateral grade II buccal furcation defects (at least 5 mm probing depth and ≥ 3 mm horizontal

L-PRF use significantly improved clinical and radiographic parameters of conventional open flap debridement. After 9 months, complete clinical closure of the defect was achieved in

**3.2. L-PRF in the treatment of periodontal furcation defects (PFDs)**

(C) Clinical application under CAF. (D) Clinical application in PAOO.

112 Bone Grafting - Recent Advances with Special References to Cranio-Maxillofacial Surgery

probing depth), in vital asymptomatic mandibular first molars.

grafts use.

comparing with SCTG (the current "*gold standard*" technique for treating Miller Class I and II gingival recessions); indicating that L-PRF/CAF could be a safer and less invasive alternative to current grafting techniques, and a more cost-effective strategy or approach than EMD is in treating Miller Class I and II gingival recessions (**Figure 3C**).

RCT evaluating the use of L-PRF in ARP was identified, according to the inclusion criteria set herein [32]. This sole study compared the application of L-PRF vs. natural blood clots in post-extraction sockets of third molars. Patients were systemically healthy and non-smoking adults requiring bi-lateral mandibular third molar removal. The use of L-PRF significantly improved post-extraction soft tissue healing after 7 days [32]. Early and significantly-higher radiographic bone formation/maturation was noticed in the L-PRF treated sites vs. controls, at 8 weeks. By 12 weeks, inter-group differences were non-significant. Radiographic bone density (measured by gray scale value) at 12 weeks increased in the biomaterial group compared to controls, nonetheless, the differences were not significant [32]. Similar to other studies, L-PRF reduced early post-surgical pain (VAS scale) on day 1; however inter-group differences

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**3.6. Personal expertise: L-PRF in periodontally accelerated osteogenic orthodontics**

alleviating the need for analgesics and anti-inflammatory medications [30].

Tissue regeneration and anatomical reconstruction in defects of the oro-maxillo-facial complex have been always a critical and controversial issue. Both, quality and quantity of the regenerated tissues are important to consider, esthetically and functionally. Practically, the surgeon is faced with an ample collection of regenerative techniques and materials to choose from. *How can one select the "ideal" or "best-fit" strategy and procedure for an optimal clinical outcome? Evidence-based studies? Level of evidence?* To the best of our knowledge, this is the first review of Randomized Controlled Clinical Trials on L-PRF use and application in Oral

**4. Conclusions and closing remarks**

In our own pilot prospective observational study [30] involving a cohort of 11 patients (with informed consent) receiving a Wilcko's modified **PAOO** (Periodontally Accelerated Osteogenic Orthodontics—*a somewhat new surgical procedure which allows faster tooth movement via combining orthodontic forces with corticotomy and grafting of alveolar bone plates*) technique with L-PRF (incorporated into the graft and as covering membrane), accelerated wound healing with no signs of infection or adverse reactions was evident (**Figure 3D**). Post-surgical pain, inflammation and infection were recorded for 10 days post-operatively, while the overall orthodontic treatment and post-treatment stability were followed up to 2 years. In our data analysis, post-surgical pain was found to be either "mild" (45.5%) or "moderate" (54.5%); immediate post-surgical inflammation was recorded as either "mild" (89.9%) or "moderate" (9.1%); and, resolution was marked to begin on day 4 where most patients experienced either "mild" or no inflammation (72.7 and 9.1%, respectively). Interestingly, complete resolution was achieved in all patients by day 8, the average orthodontic treatment time was calculated at 9.3 months and all cases were stable throughout. Thus, we concluded that combining L-PRF with traditional bone grafts (L-PRF plug or block) potentially accelerates wound healing and reduces post-surgical pain, inflammation and infection without interfering with tooth movement and/or post-orthodontic stability, over an extended 2-year observational period; thereby

were not significant by day 7 [32].

#### **3.4. L-PRF in sinus floor augmentation**

Resorption of the upper jaw bone after tooth loss is a frequent problem faced in posterior maxillary implant placement due to lack of sufficient bone mass for anchorage. Common maxillary sinus augmentation techniques provide a solution via increasing the available bone height at the expense of sacrificing volume of the maxillary sinus [23]. Traditionally, autologous bone grafts and resorbable membranes are used to promote osteogenesis and avoid soft tissue in-growth into the surgical site. However, donor site morbidity and size restrictions, latter resorption of the graft and high-cost of membranes, are main disadvantages [24, 25]. In this context, L-PRF appears to provide a promising alternative overcoming such limitations. In this review, two RCTs evaluating the use of L-PRF in lateral window sinus augmentation were found. Applications were performed either as: (a) grafting material (L-PRF/Bio-Oss® constructs vs. Bio-Oss®) [26] or (b) absorbable covering membrane for the lateral osteotomy window (L-PRF vs. Geistlich Bio-Gide®) [27]. In both studies, included subjects were systemically healthy adults with maxillary atrophy (defined as <5 mm residual bone crest height measured in OPG/orthopantomogram). Smoking status was not assessed. The addition of L-PRF to Bio-Oss® bone-substitute revealed neither advantages nor disadvantages over Bio-Oss® alone controls [26]. After 6 months, clinical and radiographic examinations revealed both groups exhibiting similar amounts and density of mineralized tissues, with no signs of material resorption. Histological evaluations also showed non-significant differences regarding: (a) percentage of newly formed bone, (b) percentage of residual Bio-Oss®, (c) bone-to-bonesubstitute contact, and (d) post-treatment inflammatory reactions [26]. Regarding coverage of lateral osteotomy sinus window, L-PRF use resulted in a similar amount of vital bone formation (%) and residual bone-substitute when compared to Bio-Gide® controls (L-PRF: 17.0 and 15.9%, Bio-Gide®: 17.2 and 17.3%, differences are not statistically-significant). Overall, despite a slightly superior to no coverage at all (12.1%), it can be stated that results were similar to those reported using other conventional membranes (collagen: 17.6%; e-PTFE: 16.9%) [27]. Within the presented limitations in both RCTs, evidence suggests that L-PRF is a safe, simple to use and handle, and cost-effective alternative to traditional bone grafts and absorbable membranes; in low-income patients, pursuing maxillary sinus augmentation procedures.

#### **3.5. L-PRF in alveolar ridge preservation**

Post-extraction changes in alveolar bone compromise prosthodontic rehabilitation with fixed, removable and/or implant-supported prosthesis. Alveolar Ridge Preservation (ARP) is a technique which involves the use of grafting and barrier materials in order to significantly reduce post-extraction bone loss [28]. L-PRF has been demonstrated to accelerate/enhance bone repair [29, 30], promote fibroblast proliferation [3, 30] and increase vascularity [31]; thereby potentially favoring the post-extraction healing process and the ARP approach. Yet, a single RCT evaluating the use of L-PRF in ARP was identified, according to the inclusion criteria set herein [32]. This sole study compared the application of L-PRF vs. natural blood clots in post-extraction sockets of third molars. Patients were systemically healthy and non-smoking adults requiring bi-lateral mandibular third molar removal. The use of L-PRF significantly improved post-extraction soft tissue healing after 7 days [32]. Early and significantly-higher radiographic bone formation/maturation was noticed in the L-PRF treated sites vs. controls, at 8 weeks. By 12 weeks, inter-group differences were non-significant. Radiographic bone density (measured by gray scale value) at 12 weeks increased in the biomaterial group compared to controls, nonetheless, the differences were not significant [32]. Similar to other studies, L-PRF reduced early post-surgical pain (VAS scale) on day 1; however inter-group differences were not significant by day 7 [32].

#### **3.6. Personal expertise: L-PRF in periodontally accelerated osteogenic orthodontics**

In our own pilot prospective observational study [30] involving a cohort of 11 patients (with informed consent) receiving a Wilcko's modified **PAOO** (Periodontally Accelerated Osteogenic Orthodontics—*a somewhat new surgical procedure which allows faster tooth movement via combining orthodontic forces with corticotomy and grafting of alveolar bone plates*) technique with L-PRF (incorporated into the graft and as covering membrane), accelerated wound healing with no signs of infection or adverse reactions was evident (**Figure 3D**). Post-surgical pain, inflammation and infection were recorded for 10 days post-operatively, while the overall orthodontic treatment and post-treatment stability were followed up to 2 years. In our data analysis, post-surgical pain was found to be either "mild" (45.5%) or "moderate" (54.5%); immediate post-surgical inflammation was recorded as either "mild" (89.9%) or "moderate" (9.1%); and, resolution was marked to begin on day 4 where most patients experienced either "mild" or no inflammation (72.7 and 9.1%, respectively). Interestingly, complete resolution was achieved in all patients by day 8, the average orthodontic treatment time was calculated at 9.3 months and all cases were stable throughout. Thus, we concluded that combining L-PRF with traditional bone grafts (L-PRF plug or block) potentially accelerates wound healing and reduces post-surgical pain, inflammation and infection without interfering with tooth movement and/or post-orthodontic stability, over an extended 2-year observational period; thereby alleviating the need for analgesics and anti-inflammatory medications [30].
