The alveolar ridge resorption and soft tissue shrinkage after tooth extraction are the main problems affecting the aesthetics and function of alveolar ridge. In order to achieve successful implantation and long-term effect, sufficient bone volume, keratinized gingiva and appropriate occlusal relationship should be obtained. Therefore, alveolar bone should be preserved as much as possible during tooth extraction to reduce edentulous ridge resorption rate and promote the bone remodeling of alveolar bone [19]. Compared with the natural healing, ARP has significant advantages in preserving the size and contour of alveolar bone, especially in the maxilla [20].
Most studies on the dimensional changes of soft and hard tissues after tooth extraction suggested that the ideal bone graft material should not only have osteoconductive properties but also promote osteoinduction and osteogenesis [21]. Only autologous bone has these three characteristics and is still considered to be the gold standard for bone augmentation surgery [22]. However, due to the additional site and prolonged time of operation, the morbidity of donor side, limited autogenous bone availability and postoperative discomfort, bone substitutes are more commonly used for bone regeneration. Bone graft materials are chosen based on their ability to serve as a scaffold, maintain space for new bone ingrowth and possess osteoconductive activity [23].
DBBM has strong hydrophilicity, high biocompatibility and good plasticity, it can promote the adhesion of osteoblasts to bone, plays important role as a scaffold, and has a very low risk of causing host allergy, inflammation and immune reactions. Twenty-seven patients were randomized into two treatment groups following single tooth extraction in the incisor, canine and premolar area. In the test group, the alveolar socket was grafted with Straumann Bone Ceramic (SBC), while in the control group, Bio-Oss was applied. 8 months later, they found that both materials preserved the mesio-distal bone height of the ridge [24]. In another study, Kim et al. [25] treated the extraction socket sites of 20 first molars in two different ways, filling Bio-oss with gelatin sponge and natural healing respectively. After 3 months, the absorptivity of alveolar ridge width was 14. 3% and 20. 7% (P < 0. 05). Histological studies have found that the rate of new bone formation is about 26.0% ± 23.7% when DBBM was used alone, and it can even reach 48.3% [26, 27]. Although DBBM has been proven to have reliable osteogenesis effect as a bone substitute material [28], DBBM lacks osteogenesis and osteoinduction. Research confirmed that the part where DBBM directly contacts the bone surface will first lead to the formation of new bone, while it takes one year at the peripheral part without direct contact [29]. The use of DBBM alone will delay bone healing and prolong osteogenesis time to a certain extent [30]. Therefore, it is significant to explore a material to promote the osteoinduction of bone substitute materials.
CGF is a new generation of platelet concentrate after PRP and PRF. The production of CGF requires variable speeds to separate blood cells from fibrin-rich blocks, which are denser and contain a higher concentration of growth factors than PRF [16]. This results in a better regenerative capacity and greater versatility. CGF contains a large amount of platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), insulin-like growth factor (IGF), fibroblast growth factor (FGF), bone morphogenetic proteins (BMPs) and metastatic growth factors-β (TGF-β) etc. Among which, FGF can accumulate macrophages, fibroblasts and other cells to the wound site through chemotaxis, thereby promoting wound healing [31, 32]. BMP can mediate osteogenesis alone and promote the formation of bone matrix and form calcified bone tissue when mix with other bone growth factors. TGF-β, as an important regulatory factor in the process of bone formation and remodeling, controls inflammation through synthetic fibrous connective tissue and local vascular proliferation, and also induces regeneration of alveolar bone [33].
In this study, none of the patients experienced rejection or wound infections around the grafting region, which indicated that the deproteinized bovine bone and CGF were safe and biocompatible. Due to the dispersive nature and small particles of DBBM, leakage often occurs, so it is necessary to cover the wound with a collagen membrane, and the gingival flap is tightly sutured to prevent the leakage of bone powder. In this study, CGF was cut into small pieces and fully mixed with DBBM, which was easy to mold. In the meantime, because of the elasticity and adhesion of CGF membrane, leakage rarely occurs even if the tooth extraction wound cannot be closed tightly.
The vertical bone loss of labial buccal bone wall was more obvious than the lingual bone wall due to its thin thickness after tooth extraction [34]. Similar conditions were observed in our study, so the alveolar crest height was divided into labial and palatal plate height, which were measured and compared respectively. Different from the changes in the control group, the height of labial and palatal plate in CGF group did not change significantly 3 months after operation. Although the width of alveolar ridge decreased, the change was much less than control group. During the implantation operation, some bone powder particles at the tooth extraction in CGF group were seen surrounded by new bone. Furthermore, CBCT showed obvious bone trabecular formation in the operation area. It can be concluded that the use of CGF combined with DBBM for ARP can effectively maintain the volume of the alveolar bone, significantly promote the regeneration of the alveolar tissue, and reduce bone resorption effectively. Therefore, when ready to insert dental implant, the CGF group has better alveolar ridge condition, more bone volume, and better surgical environment. Many other studies have shown that CGF can accelerate bone healing [14, 16, 35,36,37]. Among them, Kim et al. [14] applied CGF in sinus augmentation without any graft materials and confirmed respectively that CGF was effective in promoting healing of bone and can induce new bone formation rapidly. Our previous research showed that the application of CGF in recipient site with a small area of chronic periapical lesions can accelerate the regeneration of alveolar bone and the healing of inflammation, greatly shorten the healing period [35]. Fang et al. [36] found that the combinational use of CGFs with DBBM could promote new bone regeneration without adding exogenous stem cells in bilateral maxillary sinus floor augmentation, which yields effects similar to combining BMSCs with DBBM. Furthermore, Durmuş lar et al. [37] found that the combined use of CGF and bone graft enhanced the expression of osteogenic related genes and stem cell marker STRO-1, and promoted bone regeneration of large defects around implants (about 2.37 mm in diameter). Together, these results recommend the use of CGF as a restoration material in bony defects.
Sufficient alveolar ridge dimensions is important for implant placement, it is also necessary that the regenerated bone is of good quality. It is pointed out that the quality and quantity of regenerated bone influence the initial stability of implant and can determine the success of dental implant osseointegration [38, 39]. The new bone density of CGF group was significantly higher than control group. This showed that the osteogenic effect of CGF combined with DBBM in patients with anterior tooth loss is better than using DBBM alone, especially in the early stage. Considering correlation between the bone quality and quantity, future studies about combining platelet concentrates and bone graft materials are needed.
Relaying on the strong soft tissue induction ability of CGF membrane [40], a full and sufficient keratinized gingival could be seen 3 months after the operation. The LWHI in the CGF group was higher than the control group 1 week after the operation, indicating that CGF promoted the rapid growth of soft tissue. It was worth mentioning that the VAS score of CGF group on the 1st day after operation was significantly lower than control group, indicating that CGF may relieve postoperative pain. In addition, we found the extraction sites of the two groups healed well after operation, but the attached gingiva in the CGF group were sufficient and plump, while the alveolar ridge in the control group atrophy in varying degrees and the attached gingiva were relatively narrow. The proportion of patients without bone grafting in the CGF group was significantly higher than the control group, suggesting that CGF combined with DBBM can reduce the proportion of patients with bone increment, reduce the cost of bone grafting, shorten the treatment period and create favorable conditions for implant and postoperative aesthetic effect.