## 4 Discussion  
[PERSON] et al., when focusing on the topic of bone tissue engineering, emphasized the significant benefits of introducing scaffolds with a three-dimensional structure, which imitate the extracellular matrix. By design, this promotes the adhesion, proliferation, and differentiation of cells. They also mentioned that the used biomaterials must be compatible with the native environment, and consequently must lead to regeneration, not repair in which scar tissue is formed. The authors describe scaffolds combined with stem cells and/or osteropgenitor cells, which are placed on the prefabricated scaffold or incorporated through encapsulation during the production of the scaffold. This is performed by using a hydrogel polymer matrix and by capturing the cells within a semipermeable membrane. They paid attention to the fact that the regeneration process begins peripherally in the places where biomaterials come into contact with the bone, which emphasizes the essence of the perfect adhesion of the implant to the recipient site [11]. [PERSON] et al. presented a therapeutic method that aimed to regenerate periodontitis using a three-dimensional resolvable polymer scaffold in the course of an aggressive form of periodontitis. Their design included the conducting of perforations to immobilize the scaffold, the internal port for the delivery of recombinant human platelet-derived growth factor-BB (rhPDGF-BB), and the protruding perpendicular elements to produce periodontal ligament. During a 12-month observation, when the scaffold was completely covered with soft tissues, the authors observed a 3 mm improvement in the connective tissue attachment, and also partial coverage of the previously exposed root. However, after 13 months, the scaffold was exposed to the oral environment. Fragments of the scaffold were removed and replaced by amelogenin, and then the pocket was sealed with surgical cyanoacrylate gel. Due to this, the graft was uncovered 3 mm below the gingival margin, which required the removal of the exposed fragment. Afterward, there was an increase in dehiscence, which resulted in the need to completely remove the scaffold. Finally, it was found after 14 months that 75.9% of the scaffold's molecular weight remained and that the healing mainly concerned the connective tissue--with minimal evidence of bone repair. Ultimately, the therapy was not proven to be successful. This procedure also required several preparatory steps, a meticulous three-dimensional design, and involved the use of polymers and a recombinant growth factor. However, the authors confirmed the correctness of using biomaterials with a three-dimensional structure, but at the same time raised doubts about the use of a polycaprolactone scaffold. The failure to achieve the desired effect was also explained by the fact that the used material was high in volume and slowly resorbing [20]. An implant material should not only be easy to use but also be perfectly biocompatible for it to be able to integrate, remodel and provide an appropriate scaffold for osteogenic cells. Allogeneic bone blocks fulfill these criteria [7; 8]. However, the collection of autogenous blocks and the use of allogeneic blocks supplied from tissue banks require shaping and fitting when the traditional intra-procedure approach is used. In turn, the use of CAD/CAM technology significantly improves this process. The use of allogeneic bone is also associated with reduced surgical intervention and blood loss, a lack of donor site complications, and negligible antigenicity [21]. The success of treatments with the use of this type of biomaterial is estimated at about 90% in the literature, but an increased risk of its contamination and, consequently, of infectious complications when compared to autogenous blocks cannot be omitted.