Faculty Bibliography

Background/Purpose: b-Tricalcium phosphate (b-TCP), the most common synthetic bone replacement product, is frequently used in craniofacial reconstruction. Although solid b-TCP can be absorbed over time, the slow degradation rate (1%-3%/year) predisposes this product to exposure, infection, and fracture, limiting its use in the growing face where implants are required to grow and remodel with the patient. Our tissue engineering laboratory has successfully leveraged 3D printers to manufacture 3D-printed bioactive ceramic (3DPBC) scaffolds composed of b-TCP in an architecture which optimizes the needs of rigidity with efficient vascular ingrowth, osteogenesis, and degradation kinetics. The latter qualities are further optimized when the osteogenic agent dipyridamole (DIPY) is used. This long-term animal study reports on the new degradation kinetics profile achievable through this novel manufacturing and tissue engineering protocol. Methods/Description: Twenty-two 1-month-old (immature) New Zealand white rabbits underwent creation of unilateral 10 mm calvarial defects with ipsilateral 3.5 +/- 3.5 mm alveolar defects. Each defect was repaired with b-TCP 3DPBC scaffolds coated with 1000 mM DIPY. Rabbits were killed at 8 weeks (n = 6), 6 months (n = 8), and 18 months (n = 8). Bone regeneration and scaffold degradation were calculated using micro-CT images and analyzed in Amira software. Cranial and maxillary suture patency and bone growth were qualitatively analyzed using histologic analysis.
Result(s): Results are reported as a percentage of volumetric space occupied by either scaffold or bone. When comparing time points 8 weeks, 6 months, and 18 months, scaffolds showed significant decreased defect occupancy in calvaria (23.6% +/- 3.6%, 15.2% +/- 1.7%, 5.1% +/- 3.4%; P < .001) and in alveoli (21.5% +/- 3.9%, 6.7% +/- 2.7%, 0.1% +/- 0.2%; P < .001), with annual degradation rates 55.9% and 94.2%, respectively. Between 8 weeks and 18 months, significantly more bone regenerated in calvarial defects (25.8% +/- 6.3% vs 55.7% +/- 10.3%, P < .001) and no difference was found in alveolar defects (28.4% +/- 6.8% vs 32.4% +/- 8.0%, P = .33). Histology showed vascularized, organized bone without suture fusion.
Conclusion(s): The degradation kinetics of b-TCP can be altered through 3D printing and addition of an osteogenic agent. Our study demonstrates an acceleration of b-TCP degradation from 1% to 3% a year to 55% to 95% a year. Absorbed b-TCP is replaced by vascularized bone and there is no damage noted to the growing suture. This additive manufacturing and tissue engineering protocol has implication to future reconstruction of the craniofacial skeleton

BACKGROUND:Three-dimensionally-printed bioceramic scaffolds composed of β-tricalcium phosphate delivering the osteogenic agent dipyridamole can heal critically sized calvarial defects in skeletally mature translational models. However, this construct has yet to be applied to growing craniofacial models. In this study, the authors implanted three-dimensionally-printed bioceramic/dipyridamole scaffolds in a growing calvaria animal model and evaluated bone growth as a function of geometric scaffold design and dipyridamole concentration. Potential adverse effects on the growing suture were also evaluated. METHODS:Bilateral calvarial defects (10 mm) were created in 5-week-old (approximately 1.1 kg) New Zealand White rabbits (n = 16 analyzed). Three-dimensionally-printed bioceramic scaffolds were constructed in quadrant form composed of varying pore dimensions (220, 330, and 500 μm). Each scaffold was coated with collagen and soaked in varying concentrations of dipyridamole (100, 1000, and 10,000 μM). Controls consisted of empty defects. Animals were killed 8 weeks postoperatively. Calvariae were analyzed using micro-computed tomography, three-dimensional reconstruction, and nondecalcified histologic sectioning. RESULTS:Scaffold-induced bone growth was statistically greater than bone growth in empty defects (p = 0.02). Large scaffold pores, 500 μm, coated in 1000 μM dipyridamole yielded the most bone growth and lowest degree of scaffold presence within the defect. Histology showed vascularized woven and lamellar bone along with initial formation of vascular canals within the scaffold lattice. Micro-computed tomographic and histologic analysis revealed patent calvarial sutures without evidence of ectopic bone formation across all dipyridamole concentrations. CONCLUSION/CONCLUSIONS:The authors present an effective pediatric bone tissue-engineering scaffold design and dipyridamole concentration that is effective in augmentation of calvarial bone generation while preserving cranial suture patency.

This study investigates a comprehensive model of bone regeneration capacity of dypiridamole-loaded 3D-printed bioceramic (DIPY-3DPBC) scaffolds composed of 100% beta-tricalcium phosphate (β -TCP) in an immature rabbit model through the time of facial maturity. The efficacy of this construct was compared to autologous bone graft, the clinical standard of care in pediatric craniofacial reconstruction, with attention paid to volume of regenerated bone by 3D reconstruction, histologic and mechanical properties of regenerated bone, and long-term safety regarding potential craniofacial growth restriction. Additionally, long-term degradation of scaffold constructs was evaluated. At 24 weeks in vivo, DIPY-3DPBC scaffolds demonstrated volumetrically significant osteogenic regeneration of calvarial and alveolar defects comparable to autogenous bone graft with favorable biodegradation of the bioactive ceramic component in vivo. Characterization of regenerated bone reveals osteogenesis of organized, vascularized bone with histologic and mechanical characteristics comparable to native bone. Radiographic and histologic analyses were consistent with patent craniofacial sutures. Lastly, through application of 3D morphometric facial surface analysis, our results support that DIPY-3DPBC scaffolds do not cause premature closure of sutures and preserve normal craniofacial growth. Based on this novel evaluation model, this DIPY-3DPBC scaffold strategy is a promising candidate as a safe, efficacious pediatric bone tissue engineering strategy.

This paper is aimed to present a biomaterials perspective in implant therapy that fosters improved bone response and long-term biomechanical competence from surgical instrumentation to final prosthetic rehabilitation. Strategies to develop implant surface texturing will be presented and their role as an ad hoc treatment discussed in light of the interplay between surgical instrumentation and implant macrogeometric configuration. Evidence from human retrieved implants in service for several years and from in vivo studies will be used to show how the interplay between surgical instrumentation and implant macrogeometry design affect osseointegration healing pathways, and bone morphologic and long-term mechanical properties. Also, the planning of implant-supported prosthetic rehabilitations targeted at long-term performance will be appraised from a standpoint where personal preferences (eg, cementing or screwing a prosthesis) can very often fail to deliver the best patient care. Lastly, the acknowledgement that every rehabilitation will have its strength degraded over time once in function will be highlighted, since the potential occurrence of even minor failures is rarely presented to patients prior to treatment.

BACKGROUND:Alveolar clefts are traditionally treated with secondary bone grafting, but this is associated with morbidity and graft resorption. Although recombinant human bone morphogenetic protein-2 (rhBMP-2) is under investigation for alveolar cleft repair, safety concerns remain. Dipyridamole is an adenosine receptor indirect agonist with known osteogenic potential. This study compared dipyridamole to rhBMP-2 at alveolar cleft defects delivered using bioceramic scaffolds. METHODS:Skeletally immature New Zealand White rabbits underwent unilateral, 3.5 × 3.5-mm alveolar resection adjacent to the growing suture. Five served as negative controls. The remaining defects were reconstructed with three-dimensionally printed bioceramic scaffolds coated with 1000 μm of dipyridamole (n = 6), 10,000 μm of dipyridamole (n = 7), or 0.2 mg/ml of rhBMP-2 (n = 5). At 8 weeks, new bone was quantified. Nondecalcified histologic evaluation was performed, and new bone was evaluated mechanically. Statistical analysis was performed using a generalized linear mixed model and the Wilcoxon rank sum test. RESULTS:Negative controls did not heal, whereas new bone formation bridged all three-dimensionally printed bioceramic treatment groups. The 1000-μm dipyridamole scaffolds regenerated 28.03 ± 7.38 percent, 10,000-μm dipyridamole scaffolds regenerated 36.18 ± 6.83 percent (1000 μm versus 10,000 μm dipyridamole; p = 0.104), and rhBMP-2-coated scaffolds regenerated 37.17 ± 16.69 percent bone (p = 0.124 versus 1000 μm dipyridamole, and p = 0.938 versus 10,000 μm dipyridamole). On histology/electron microscopy, no changes in suture biology were evident for dipyridamole, whereas rhBMP-2 demonstrated early signs of suture fusion. Healing was highly cellular and vascularized across all groups. No statistical differences in mechanical properties were observed between either dipyridamole or rhBMP-2 compared with native bone. CONCLUSION/CONCLUSIONS:Dipyridamole generates new bone without osteolysis and early suture fusion associated with rhBMP-2 in skeletally immature bone defects.

BACKGROUND:Autologous bone grafts remain a standard of care for the reconstruction of large bony defects, but limitations persist. The authors explored the bone regenerative capacity of customized, three-dimensionally printed bioactive ceramic scaffolds with dipyridamole, an adenosine A2A receptor indirect agonist known to enhance bone formation. METHODS:Critical-size bony defects (10-mm height, 10-mm length, full-thickness) were created at the mandibular rami of rabbits (n = 15). Defects were replaced by a custom-to-defect, three-dimensionally printed bioactive ceramic scaffold composed of β-tricalcium phosphate. Scaffolds were uncoated (control), collagen-coated, or immersed in 100 μM dipyridamole. At 8 weeks, animals were euthanized and the rami retrieved. Bone growth was assessed exclusively within scaffold pores, and evaluated by micro-computed tomography/advanced reconstruction software. Micro-computed tomographic quantification was calculated. Nondecalcified histology was performed. A general linear mixed model was performed to compare group means and 95 percent confidence intervals. RESULTS:Qualitative analysis did not show an inflammatory response. The control and collagen groups (12.3 ± 8.3 percent and 6.9 ± 8.3 percent bone occupancy of free space, respectively) had less bone growth, whereas the most bone growth was in the dipyridamole group (26.9 ± 10.7 percent); the difference was statistically significant (dipyridamole versus control, p < 0.03; dipyridamole versus collagen, p < 0.01 ). There was significantly more residual scaffold material for the collagen group relative to the dipyridamole group (p < 0.015), whereas the control group presented intermediate values (nonsignificant relative to both collagen and dipyridamole). Highly cellular and vascularized intramembranous-like bone healing was observed in all groups. CONCLUSION:Dipyridamole significantly increased the three-dimensionally printed bioactive ceramic scaffold's ability to regenerate bone in a thin bone defect environment.

Background/Purpose: Alveolar cleft surgery is the most common bone reconstruction performed in patients with a cleft. Osteogenic agents such as BMP-2 have been used to restore the bony cleft without the morbidity of bone graft, but concerns remain regarding premature fusion of sutures, exuberant bone formation, and malignant degeneration. We have recently demonstrated that dipyridamole-coated, 3D printed bio-ceramic (3DPBC) scaffolds generate comparable bone amounts to BMP2 and significantly greater bone compared to negative controls in short-term growing animal model studies. No detrimental effects to growth sutures were noted in any animals. This study investigates the long-term osteogenic properties, degradation kinetics, and effects on facial growth of these tissue engineering constructs in growing animal models. Methods/Description: Twenty-two 1-month-old (immature) New Zealand white rabbits underwent creation of unilateral 3.5 x 3.5 mm alveolar defects. Each alveolar defect was repaired with either 3DPBC scaffolds coated with 1000 muM dipyridamole (n = 14) or with autogenous bone graft from the radius (n = 8). Six rabbits from the 3DPBC scaffold group were sacrificed at 8 weeks. The remaining rabbits (n = 8 each group) were euthanized following completion of craniofacial growth (6 months). Bone regeneration, scaffold degradation, and maxillary suture patency were calculated using CT images reconstructed and analyzed in Amira software. Facial symmetry was evaluated using dense-surface 3D modeling and validated with bilateral cephalometric measurements of maxillary projection. Bone growth and suture patency were qualitatively evaluated through histologic analysis.
Result(s): After 6 months, animals with defects repaired with 3DPBC scaffolds regenerated an average of 52.9% +/- 3.3% bone (mean +/- SEM), compared to 40.7%+/-4.0% in defects repaired with bone graft (P = .02). This is compared to unoperated alveolus occupied by 39.3% +/- 1.6% bone. Scaffolds showed significant degradation at 6 months (6.7% +/- 1.6%) compared to at 8 weeks (27.1% +/- 1.9%; P >= .001). Morphometric analysis using dense surface modeling showed similar symmetry indices of 55.0 +/- 3.3 for scaffold animals and 61.7% +/- 1.6% for bone graft animals (P = .10). Comparative measurements of operated and unoperated sides showed no significant differences in asymmetry between scaffold and bone graft animals (P = .86). Histologic analysis of scaffold samples revealed vascularized, organized bone within scaffold interstices without evidence of ectopic bone, excess inflammatory cells, or suture fusion.
Conclusion(s): In a growing animal model, dipyridamole-coated 3DPBC scaffolds can regenerate bone comparable to autogenous bone graft by radiographic and histologic analysis. Over 6 months, scaffolds show significant, favorable degradation and do not result in premature suture fusion or disruption of facial growth compared to bone graft. These results support long-term safety and efficacy of this tissue engineering strategy in the repair of alveolar cleft defects

Background/Purpose: Our tissue engineering laboratory has previously demonstrated that dipyridamole-coated, 3D printed bioceramic (3DPBC) scaffolds comprised of B-tricalcium phosphate generate significantly more bone compared to negative controls in short-term growing animal model studies. No detrimental effects to the cranial suture were observed in any experimental animals. The longterm osteogenic efficacy and safety of our 3DPBC scaffold for tissue engineering in growing calvaria was assessed by describing bone regeneration compared to autogenous bone graft, scaffold degradation kinetics, and the effects of the construct on cranial growth over time. Methods/Description: Twenty-two 1-month-old (immature) New Zealand white rabbits underwent unilateral 11-mm craniotomy within 2 mm of the coronal and sagittal sutures. Rabbits' calvarial defects were repaired by 1 of 2 interventions: 3DPBC scaffolds coated with 1000 mM dipyridamole (n = 14) or autogenous calvarial bone graft (n = 8). Six rabbits from the 3DPBC scaffold group were sacrificed at 8 weeks. The remaining rabbits (n = 8 each group) were observed until craniofacial growth was completed (6 months) and then euthanized. Bone regeneration, scaffold degradation, and cranial suture patency were analyzed in Amira software using reconstructed microcomputed tomography (muCT) images. Cranial growth was assessed by comparing bilateral cephalometric measurements based on muCT images. Bone growth and suture patency were qualitatively evaluated through histologic analysis.
Result(s): After 6 months of healing, animals with defects repaired with 3DPBC scaffolds regenerated an average of 53.9% +/- 3.6% (mean +/- SEM) bone, compared to 53.5% +/- 3.6% in defects repaired with bone graft (P = .95). Unoperated calvarial bone porosity was 49.4%+/-2.0%. Scaffolds showed significant degradation at 6 months (15.1% +/-0.7%) compared to 8 weeks (23.2% +/- 0.9%; P<=.001). Comparative measurements of operated and unoperated sides showed no significant differences in asymmetry between scaffold and bone graft animals (P > .24). Analysis of histologic sections revealed well-vascularized, organized bone formation within scaffold interstices with no evidence of ectopic bone formation, excess inflammatory cells, or suture fusion.
Conclusion(s): Dipyridamole-coated 3D-printed bioceramic scaffolds bone regeneration is comparable to autogenous bone graft without showing signs of adverse events such as premature cranial suture fusion, or detrimental effects to facial growth. The scaffold demonstrates favorable absorption kinetics, highlighting the potential for this technology in pediatric bone tissue engineering

OBJECTIVE:The aim of this in vivo study is to compare the osseointegration of endosteal implants placed in atrophic mandibular alveolar ridges with alveolar ridge expansion surgical protocol via an experimental osseodensification drilling versus conventional osteotome technique. METHODS:Twelve endosteal implants, 4 mm × 13 mm, were placed in porcine models in horizontally atrophic mandibular ridges subsequent to prior extraction of premolars. Implants were placed with osseodensification drilling technique as the experimental group (n = 6) and osteotome site preparation as the control group (n = 6). After 4 weeks of healing, samples were retrieved and stained with Stevenel's Blue and Van Gieson's Picro Fuschin for histologic evaluation. Quantitative analysis via bone-to-implant contact (BIC%) and bone area fraction occupancy (BAFO%) were obtained as mean values with corresponding 95% confidence interval. A significant omnibus test, post-hoc comparison of the 2 drilling techniques' mean values was accomplished using a pooled estimate of the standard error with P-value set at 0.05. RESULTS:The mean BIC% value was approximately 62.5% in the osseodensification group, and 31.4% in the regular instrumentation group. Statistical analysis showed a significant effect of the drilling technique (P = 0.018). There was no statistical difference in BAFO as a function of drilling technique (P = 0.198). CONCLUSION/CONCLUSIONS:The combined osseodensification drilling-alveolar ridge expansion technique showed increased evidence of osseointegration and implant primary stability from a histologic and biomechanical standpoint, respectively. Future studies will focus on expanding the sample size as well as the timeline of the study to allow investigation of long-term prognosis of this novel technique.