Bone autografts & allografts placed simultaneously with dental implants in rabbits

Efficacy of bone ring grafts for the reconstruction of alveolar ridge deficiencies: A systematic review. Part I: Clinical trials

BACKGROUND

Bone ring (BR) grafts have been introduced to reconstruct alveolar ridge defects with simultaneous implant placement, but its clinical effectiveness remains undetermined. This systematic review aimed to comprehensively investigate BR grafts in diverse scenarios of ridge defect with simultaneous or staged implant placement.

METHODS

Electronic retrieval of MEDLINE, Embase, Cochrane Library(CENTRAL), Web of Science, Scopus, and citation search until August 3, 2023, was used to identify relevant clinical articles that utilized BR grafts for ridge defect reconstruction. The quality of evidence in the studies reviewed was assessed with the Joanna Briggs Institute Critical Appraisal tool. The protocol was registered in Prospective Register of Systematic Reviews (CRD42023453943).

RESULTS

Fourteen studies with 251 BRs were identified, of which 8 studies were for alveolar ridge augmentation, 4 studies were for extraction socket augmentation, and 2 studies were for sinus floor elevation. Reported sources of BRs included autografts, allografts, and xenografts. The follow-up period ranged from 4 months to 4.7 years. Regarding the primary outcomes, the utilization of BR grafts demonstrated favorable bone gain along with acceptable graft absorption and marginal bone loss. Regarding the secondary outcomes, satisfactory bone mineral density and implant stability were confirmed, accompanied by a recorded incidence of postoperative complications (20 cases) and an implant failure rate of 5.58%.

CONCLUSIONS

BR grafting with simultaneous or staged implant insertion is an effective approach for reconstructing alveolar ridge deficiencies. The BR grafts demonstrate favorable bone remodeling and osteointegration with the alveolar bone and implant; however, its success may be compromised by complications. Future studies should further investigate the clinical efficacy of BR grafting comparing to other bone augmentation techniques in diverse scenarios.

Fresh-frozen allogeneic bone blocks grafts for alveolar ridge augmentation: Biological and clinical aspects

The possibilities for oral bone regeneration procedures vary depending on the type of bone defect to be treated, which in turn dictate the type of graft to be used. Atrophic alveolar ridges are non-contained defects and pose a challenging defect morphology for bone regeneration/augmentation. Successful results are regularly obtained with the use of particulate grafts in combination with barrier membranes. In cases of very narrow ridges with need of larger amount of bone augmentation, block grafts are often used. Fresh-frozen allogeneic bone block grafts have been proposed as an alternative to autogenous (AT) bone blocks. Based on a systematic appraisal of pre-clinical in vivo studies and clinical trials including a direct comparison of fresh-frozen bone (FFB) blocks versus AT bone blocks it can be concluded that a FFB block graft: (a) cannot be considered as a reliable replacement of a AT bone block, and (b) should only be considered in cases where the amount of necessary augmentation-in a lateral direction-is relatively limited, so that the main portion of the body of the implant lies within the inner (i.e., the vital) aspect of the block.

Evaluation of Two Configurations of Hydroxyapatite and Beta-Tricalcium Phosphate in Sinus Grafts with Simultaneous Implant Installation: An Experimental Study in Rabbits

BACKGROUND

This study aimed to evaluate peri-implant bone formation in rabbits after sinus grafting mediated by hydroxyapatite and beta-tricalcium phosphate (HA + β-TCP) in granule or paste configurations, concomitant with immediate implant installation.

MATERIAL & METHODS

Thirty-four rabbit maxillary sinuses were grafted with HA + β-TCP, half of which were applied in a granule and half in a paste composition. Implant placement was performed simultaneously. At 7 and 40 days postoperatively, the animals were euthanized, and samples were prepared for tomographic, microtomographic, histological, histometric (hematoxylin and eosin staining, HE), and immunohistochemical (labeling of transcription factor Runx-2 [RUNX2], vascular endothelial growth factor [VEGF], osteocalcin [OCN], and tartrate-resistant acid phosphatase [TRAP]) analysis. Implant removal torque was also measured.

RESULTS

On tomography, maintenance of sinus membrane integrity was observed in both the groups. Higher values of morphometric parameters evaluated by micro-CT were found in the "paste group" after seven days. At 40 days, there were no significant differences between the groups in most of the microtomographic parameters evaluated. In histological sections stained with HE, a higher percentage of newly formed bone was observed in the "granule group" after 40 days. Similar positive immunolabeling was observed for both RUNX2 and OCN in both the experimental groups. TRAP immunolabeling was similar in both groups as well. VEGF labeling increased in the "granule group", indicating a higher osteoconductive potential in this biomaterial. Similar removal torque values were observed in both groups. Thus, the two HA + β-TCP configurations showed similar healing patterns of simultaneously installed implants adjacent to sinus floor elevation. However, significantly higher bone values were observed for the "granule configuration".

CONCLUSIONS

The HA + β-TCP granules and paste presentations showed favorable long-term healing results, with bone formation in similar quantities and quality adjacent to the implants.

Improvement of Osseointegration by Ultraviolet and/or Simvastatin Treatment on Titanium Implants with or without Bone Graft Materials

We evaluated and compared ultraviolet (UV) treatment and simvastatin (SIM) immersion effects on the osseointegration of sandblasted, large-grit, acid-etched (SLA) titanium dental implants at two different time points in rabbit tibias, with or without xenogenic bone graft materials. The surface alteration on simvastatin treatment titanium discs was analyzed using an infrared spectrometer. Implants were categorized into four groups according to the surface treatment type. Twelve rabbits received two implants per tibia. A tibial defect model was created using a trephine bur, with implants in contact with the bone surface and bovine bone graft materials for gap filling. The rabbits were sacrificed after 2 or 4 weeks. UV treatment or SIM immersion increased the bone-to-implant contact (BIC) on nongrafted sides, and both increased the BIC and bone area (BA) on grafted sides. The application of both treatments did not result in higher BIC or BA than a single treatment. At two different time points, BIC in the nongrafted sides did not differ significantly among the UV and/or SIM treated groups, whereas BA differed significantly. UV or SIM treatment of SLA titanium implants accelerates osseointegration in tibias with or without xenogenic bone graft materials. The combination of both treatments did not show synergy.

Design and evaluation of a novel sub-scaffold dental implant system based on the osteoinduction of micro-nano bioactive glass

Alveolar ridge atrophy brings great challenges for endosteal implantation due to the lack of adequate vertical bone mass to hold the implants. To overcome this limitation, we developed a novel dental implant design: sub-scaffold dental implant system (SDIS), which is composed of a metal implant and a micro-nano bioactive glass scaffold. This implant system can be directly implanted under mucous membranes without adding any biomolecules or destroying the alveolar ridge. To evaluate the performance of the novel implant system in vivo, SDISs were implanted into the sub-epicranial aponeurosis space of Sprague-Dawley rats. After 6 weeks, the SDIS and surrounding tissues were collected and analysed by micro-CT, scanning electron microscopy and histology. Our results showed that SDISs implanted into the sub-epicranial aponeurosis had integrated with the skull without any mobility and could stably support a denture. Moreover, this design achieved alveolar ridge augmentation, as active osteogenesis could be observed outside the cortical bone. Considering that the microenvironment of the sub-epicranial aponeurosis space is similar to that of the alveolar ridge, SDISs have great potential for clinical applications in the treatment of atrophic alveolar ridges. The study was approved by the Animal Care Committee of Guangdong Pharmaceutical University (approval No. 2017370).

Study on repairing canine mandibular defect with porous Mg-Sr alloy combined with Mg-Sr alloy membrane

To discuss the feasibility of the application of porous Mg–Sr alloy combined with Mg–Sr alloy membrane in the repair of mandibular defects in dogs. The second and third mandibular premolars on both sides were extracted from six dogs. The model of mandible buccal fenestration bone defects were prepared after the sockets healed. Twelve bone defects were randomly divided into groups A and B, then Mg–Sr alloy was implanted in bone defects of group A and covered by Mg–Sr alloy membrane while Mg–Sr alloy was implanted in bone defects of group B and covered by mineralized collagen membrane. Bone defects observed on cone beam computed tomographic images and comparing the gray value of the two groups after 4, 8 and 12 weeks. After 12 weeks, the healing of bone defects were evaluated by gross observation, X-ray microscopes and histological observation of hard tissue. Bone defects in each group were repaired. At 8 and 12 weeks, the gray value of group A was higher than that of group B (P < 0.05). At 12 weeks, the bone volume fraction of group A was higher than that of group B (P < 0.05). The newly woven bone in group A is thick and arranged staggered, which was better than that of group B. Porous Mg–Sr alloy combined with Mg–Sr alloy membrane could further promote the repair of mandibular defects, and obtain good osteogenic effect.

BMP9 promotes osteogenic differentiation of SMSCs by activating the JNK/Smad2/3 signaling pathway

Synovial mesenchymal stem cells (SMSCs) with high proliferation and multi differentiation ability, and low immunogenicity have attracted research attention for their potential application in tissue engineering. Once their ability of osteogenesis is strengthened, it will be of practical value to apply the SMSCs in the field of bone regeneration. The current study aimed to investigate the osteogenic characteristics of SMSCs induced by bone morphogenetic protein 9 (BMP9) both in vitro and in vivo and to elucidate the mechanism underlying these characteristics. Specifically, different BMPs were assessed to determine the protein that would be the most favorable for stimulating osteogenic differentiation of SMSCs following their separation. The BMP9-enhanced osteogenesis of SMSCs was fully investigated in vitro and in vivo, and the c-Jun N-terminal kinase (JNK)/Smad2/3 signaling pathway stimulated by BMP9 was further explored. Our data suggested that BMP9 could significantly promote gene and protein expression of runt-related transcription factor 2, alkaline phosphatase, osteopontin, and osteocalcin, and SP600125, a JNK-specific inhibitor, could effectively decrease this tendency. Similar results were also confirmed in rats with cranial defects. In conclusion, our study indicated that BMP9 promotes bone formation both in vitro and in vivo possibly by activating the JNK/Smad2/3 signaling pathway.

Acellular mineralized allogenic block bone graft does not remodel during the 10 weeks following concurrent implant placement in a rabbit femoral model

OBJECTIVES

Due to bone loss, endosseous implants often require addition of a bone graft to support adequate primary fixation, bone regeneration, and osseointegration. The aim of this study was to compare effectiveness of autogenic and allogenic bone grafts when used during simultaneous insertion of the implant.

MATERIALS AND METHODS

4-mm-diameter rabbit diaphyseal bone autografts or allografts (n = 16/group) with a 3.2-mm pre-drilled hole in the center were placed into a 4 mm defect in the proximal femur of 3.5 kg male New Zealand White rabbits. Machined 3.2 × 10 mm grit-blasted, acid-etched titanium-aluminum-vanadium (Ti6Al4V) implants were placed. Control implants were placed into progressively drilled 3.2-mm holes in the contralateral limbs. Post-insertion day 70, samples were analyzed by micro-CT and calcified histology, or by mechanical torque and push-out testing followed by decalcified histology.

RESULTS

Both grafts were integrated with the native bone. Micro-CT showed less bone volume (BV) and bone volume/total volume (BV/TV) in the allograft group, but histology showed no differences in BV or BV/TV between groups. Allograft lacked living cells, whereas autograft was cellularized. No difference was found in maximum removal torque between groups. Compressive loading at the graft-to-bone interface was significantly lower in allograft compared with autograft groups.

CONCLUSIONS

There was less bone in contact with the implant and significantly less maximum compressive load in the allograft group compared with autograft. The allograft remained acellular as demonstrated by empty lacunae. Taken together, block allograft implanted simultaneously with an implant produces a poorer quality bone compared with autograft.