## 4 Discussion  
Third mandibular molar surgery is the most common clinical procedure done by oral and maxillofacial surgeons. It can be associated with several postoperative complications, such as pain, swelling, trismus, alveolar osteitis or surgical site infection. Many studies have been conducted to determine procedures capable of reducing the incidence of these complications. The idea of applying a platelet concentrate in the wound area foresees the synergistic action of various growth factors and the multiplication of their biological significance locally [30]. The production protocol of these products affects their composition and biological characteristics and the clinical effect of their application [53; 54]. The healing time of the extraction alveolus varies significantly among individuals [13]. Various studies show that in the 4 th week of socket healing, about 2/3 of the alveolus is filled with woven bone, and in the 10 th week, it is completely filled. However, after this period, the intensive process of bone tissue remodeling continues with only partial replacement of woven bone with mature lamellar bone type, which lasts up to 6 months [14]. Some authors consider that a period of 2 or 3 months is too short to monitor the effects of these products on the healing of the extraction alveolus. On the other hand, there are authors who believe that a short follow-up period (up to 3 months) is more suitable for monitoring the effects of platelet preparations, because their beneficial effect is expected only in the initial stages of healing [55]. Several studies were published with methodology similar to our study [56; 57]. They reported statistically significant better bone healing of alveoli in which L-PRF was applied. Our results partly coincide with this; the present study results suggest some positive effect of L-PRF application. The volume of new bone tissue and bone density were higher in the experimental group, and the depth of the periodontal pocket distal to the second molar was smaller in this group. Although neither of these differences were statistically significant, they undeniably exist. Several studies evaluated the effect of L-PRF in promoting bone tissue regeneration, but in other clinical applications, such as in maxillary sinus floor elevation and various augmentation procedures [58], function defect treatment [26], endodontic therapy [59] and socket preservation [3]. There is no clear consensus in terms of the required quantity of L-PRF for the optimal effect. The content of platelets in platelet concentrates is 2 to 8.5 times higher than in blood, depending on the method of production. However, it is important for clinicians to note that the initial platelet count is not the same in all patients and that different individuals probably have a different critical concentration of platelets in these products required to achieve a significant biological effect. Further, the significance of the different content of other cellular elements of the blood remains unclear [27]. In the present study, two L-PRF plugs were placed in the experimental alveoli. We can assume that more of L-PRF is probably needed, especially in the alveoli of teeth with more than one root. In 2017, [PERSON] et al. published a systematic review of the literature on soft and hard tissue changes after alveolar ridge preservation interventions. For some studies included in this review, he determined that there was an extremely high degree of heterogeneity, and this could explain why in these studies, the differences between the control and experimental groups were not statistically significant [60]. The inability to bilaterally make defects of the same dimensions and shapes can potentially explain the results of the present study. However, this is a limitation faced by all clinical studies because it is not possible to create two identical defects, as it is possible in vitro studies. A similar conclusion was reached by [PERSON] et al., who published a systematic review in 2018.