Vertical bone augmentation with 3D-synthetic monetite blocks in the rabbit calvaria

Introduction: Long-term success of osteointegrated dental implants requires sufficient volume of healthy bone at the recipient sites. However, this is frequently lacking as a result of trauma, tooth loss, or infection. Onlay autografting is amongst the most predictable techniques for craniofacial vertical bone augmentation, however, complications related to donor site morbidity are common and alternatives to onlay autografts are desirable. Aim: To develop and evaluate a new synthetic onlay block for vertical bone augmentation. Material and methods: Sixteen synthetic monetite monolithic discs-shaped blocks were prepared using a 3D-printing technique. The blocks were computer-designed, and had a diameter of 9.0 mm, a thickness of either 4.0 mm (n = 8) or 3.0 mm (n = 8) and one 0.5-mm wide central hole that enabled their surgical fixation with osteosynthesis screws. The blocks were randomly allocated to each side of the calvaria (right or left) of eight New Zealand rabbits and fixed with screws to achieve vertical bone augmentation. Eight weeks after the surgical intervention, the animals were sacrificed and the calvaria were retrieved for histological analysis. The following parameters were analysed: the interaction between the graft and the original bone surface, the amount of bone ingrowth within the graft and the gain in bone height achieved by the procedure. Wilcoxon t-test was used to evaluate significant differences between the two types of monetite bone block grafts. Results: The blocks were easy to handle and no damage or fracture was registered while being screw-fixated to the calvarial bone. As a result, the surgical procedure was easy and quick. After a healing of 8 weeks, the synthetic blocks were strongly fused to the calvarial bone surface. Upon histological observation, the monetite blocks appeared to be infiltrated by newly formed bone, without histological signs of necrosis, osteolysis or foreign body reaction. Histomorphometry revealed that bone augmentation occurred within and over the monetite block. The 4.0- and 3.0-mm high blocks were filled with newly formed bone with 35% and 41% of their respective volumes. These observations indicated that craniofacial bone augmentations of at least 4 mm could be achieved with synthetic monetite blocks. Conclusion: Within the limits of our study, this novel material may be able to eliminate the need for autologous bone transplantation for the augmentation of large vertical bone defects.