Faculty Bibliography

Statement of the Problem: Repair of bone lost to trauma, disease, or birth defect requires regeneration of large volumes of structurally complex bone. Current bone repair methods, like bone grafts or particulate materials, are imperfect for repair of complex craniofacial defects which require formation of large amounts of natural, mechanically strong bone. 3D-printed, Direct Write (DW), scaffolds composed of tricalcium phosphate (TCP) with temporary calcium sulfate filler can serve as a better option to repair large complex bone defects. Such scaffolds are mechanically stable and can be custom printed to match the exact defect shape and size. Current literature debates scaffold pore sizes for optimal bone repair, stating scaffold pore size should be from 100-400mm. The objective of this study is to determine how pore size dictates the quality of ingrowing bone. Thiswill allow the design of scaffolds that can regenerate the natural architecture and mechanical properties of bone in complex craniofacial defects. Methods: Scaffold pores (spaces defined by struts) varied in all dimensions. Two 11mm diameter disk scaffold designs were DW printed of 15:85 HAP/b-TCP ink and filled with temporary calcium sulfate(CS) cement. These two designs allowed the study of pores from ~0-940 mm. The two scaffolds were placed symmetrically in bilateral trephine defects in the calvarias of 8 New Zealand white rabbits. Animals were sacrificed after 8 weeks (n=7) and 16 weeks (n=1). Bone ingrowth and remodeling rates of resected implants were quantified by microCT and hard tissue histology. Results: Contrary to previous literature findings, significant bone ingrowth occurred in pores ranging from 20mm to 940mm. Larger pore sizes allowed more bone ingrowth than smaller pore sizes. As pore size decreased, bone as a fraction of available space increased from 55%-85% and scaffold remodeling decreased from 32%-5%. Conclusions: This study demonstrated precision scaffold production where variable porosity scaffolds were used !

Abstract Regeneration and preservation of bone after the extraction of a tooth is necessary for the placement of a dental implant. The goal is to regenerate alveolar bone with minimal postoperative pain. Medical grade calcium sulfate hemihydrate (MGCSH) can be used alone or in combination with other bone grafts; it improves graft handling characteristics and particle containment of particle-based bone grafts. In this case series a 1:1 ratio mix of MGCSH and mineralized irradiated cancellous bone allograft (MICBA) was mixed with saline and grafted into an extraction socket in an effort to maintain alveolar height and width for future implant placement. MGCSH can be used in combination with other bone grafts and can improve handling characteristics and graft particle containment of particle-based bone grafts. Based on the following cases, it was found that a MGCSH:MICBA graft can potentially be an effective bone graft composite. It has the ability to act as a space maintainer and as an osteoconductive trellis for bone cells, promoting bone regeneration in the extraction socket. MGCSH, a cost-effective option, successfully improved MICBA handling characteristics, prevented soft tissue ingrowth and assisted in the regeneration of bone

Since bone repair and regeneration depend on vasculogenesis and osteogenesis, both of these processes are essential for successful vascularized bone engineering. Using adipose-derived stem cells (ASCs), we investigated temporal gene expression profiles, as well as bone nodule and endothelial tubule formation capacities, during osteogenic and vasculogenic ASC lineage commitment. Osteoprogenitor-enriched cell populations were found to express RUNX2, MSX2, SP7 (osterix), BGLAP (osteocalcin), SPARC (osteonectin), and SPP1 (osteopontin) in a temporally specific sequence. Irreversible commitment of ASCs to the osteogenic lineage occurred between days 6 and 9 of differentiation. Endothelioprogenitor-enriched cell populations expressed CD34, PECAM1 (CD31), ENG (CD105), FLT1 (Vascular endothelial growth factor [VEGFR1]), and KDR (VEGFR2). Capacity for microtubule formation was evident in as early as 3 days. Functional capacity was assessed in eight coculture combinations for both bone nodule and endothelial tubule formation, and the greatest expression of these end-differentiation phenotypes was observed in the combination of well-differentiated endothelial cells with less-differentiated osteoblastic cells. Taken together, our results demonstrate vascularized bone engineering utilizing ASCs is a promising enterprise, and that coculture strategies should focus on developing a more mature vascular network in combination with a less mature osteoblastic stromal cell.

The purpose of this study was to assess vital bone formation at 4 to 5 months and 7 to 9 months following sinus augmentation with anorganic bovine bone matrix (ABBM) with and without recombinant human platelet-derived growth factor (rhPDGF). Twenty-four subjects received bilateral sinus elevation surgery with ABBM on one side and ABBM and rhPDGF on the contralateral side. Twelve patients had core sampling at 4 to 5 months and 12 patients at 7 to 9 months postoperatively. In subjects with cores taken at 4 to 5 months, mean vital bone, connective tissue, and residual graft were 11.8%, 54.1%, and 33.6%, respectively, with ABBM alone. Cores of sinuses filled with ABBM and rhPDGF showed mean 21.1% vital bone, 51.4% connective tissue, and 24.8% residual graft. Paired t test showed a statistically significant difference in vital bone. In cores taken at 7 to 9 months, the values for ABBM alone and ABBM + rhPDGF were 21.4% vs 19.5% vital bone, 28.4% vs 44.2% connective tissue, and 40.3% residual graft vs 35.5%. There was no statistically significant difference in vital bone at 7 to 9 months after surgery. Test and control groups showed clinically acceptable levels of vital bone both at 4 to 5 months and 7 to 9 months postsurgery. However, vital bone formation was significantly greater in the 4- to 5-month sections of ABBM + rhPDGF vs the Bio-Oss alone. In the 7- to 9-month specimens, this difference disappeared. More rapid formation of vital bone with the addition of rhPDGF may allow for earlier implant placement.

PURPOSE: The purpose of this experiment was to analyze the mechanics of the ceramic abutment-implant joint and the dimensional changes in the abutment screws from cyclic loading. MATERIALS AND METHODS: Two groups of experimental assemblies were used, one with zirconia abutments and the other with titanium abutments (n = 10). Each specimen consisted of an implant, an abutment, and a metal crown affixed in an acrylic resin base. The specimens were subjected to cyclic loading of 200 N for 1 million cycles at 10 Hz. After loading, a torque-angle signature analysis was done, the dimensions of the screws were measured, and the implant-abutment interfaces were examined with scanning electron microscopy. RESULTS: There was a statistically significant increase in the total length of the screws: 121 mum in the titanium group versus 88 mum in the zirconia group (P < .004). Microscopic analysis showed collected debris on the zirconia abutment undersurface and the screws. A statistically similar decrease in torque was observed: 18% for zirconia versus 13.5% for titanium. Radiographic microanalysis revealed that the debris collected in the zirconia assemblies was essentially a collection of titanium, vanadium, and aluminum, with traces of zirconium. CONCLUSIONS: While there was a loss of torque in both types of abutments, the stability of the zirconia abutment-implant joint was not affected by the loading. The study provides a better understanding of zirconia abutments, screw designs, and the mechanism holding together the implant-abutment assembly.

ABSTRACT: Microporous scaffolds designed to improve bony repair have had limited success; therefore, we sought to evaluate whether time-released porous scaffolds with or without recombinant bone morphogenetic protein 2 (rhBMP-2) could enhance stem cell osteoinduction. Custom-made 15/85 hydroxyapatite/beta-tricalcium phosphate scaffolds were left empty (E) or filled with rhBMP-2 (E+), calcium sulfate (CS), or CS and rhBMP-2 (CS+). All scaffolds were placed in media and weighed daily. Conditioned supernatant was analyzed for rhBMP-2 and then used to feed human adipose-derived mesenchymal stem cells (ASCs). Adipose-derived mesenchymal stem cell ALP activity, OSTERIX expression, and bone nodule formation were determined. E scaffolds retained 97% (SD, 2%) of the initial weight, whereas CS scaffolds had a near-linear 30% (SD, 3%) decrease over 60 days. E+ scaffolds released 155 (SD, 5) ng of rhBMP-2 (77%) by day 2. In contrast, CS+ scaffolds released only 30 (SD, 2) ng (10%) by day 2, and the remaining rhBMP-2 was released over 20 days. Conditioned media from E+ scaffolds stimulated the highest ALP activity and OSTERIX expression in ACSs on day 2. However, after day 6, media from CS+ scaffolds stimulated the highest ALP activity and OSTERIX expression in ASCs. Adipose-derived mesenchymal stem cells exposed to day 8 CS+-conditioned media produced significantly more bone nodules (10.1 [SD, 1.7] nodules per high-power field) than all other scaffolds. Interestingly, day 8 conditioned media from CS scaffolds simulated significantly more bone nodules than either E or E+ scaffold (P < 0.05 for both). Time-released hydroxyapatite/beta-tricalcium phosphate porosity provides sustained growth factor release, enhances ASC osteoinduction, and may result in better in vivo bone formation.

Introduction: Low wattage laser use in periodontal therapy is well documented, but effects on bone repair are not understood. We used a low wattage laser to examine the effects of laser treatment on bone healing in a rabbit cranial defect bone-healing model. Materials and Methods: Bone defects were created in rabbit parietal bones using a trephine in 16 rabbits (5mm in diameter, 1/2 skull thickness defects), and 4 were created in the two parietal bones of each rabbit. One defect was untreated (control), and the remaining three were treated for 15, 30 and 45 seconds using a Navigator 810 nm diode laser (Ivoclar Vivadent, Inc) with non-initiated tip at 1.0 watts in continuous mode. Defects were evaluated using micro computed tomo-graphy (microCT) and hard tissue histomorphometry at 2 and 4 weeks. Results: Treatment was observed to increase levels of coagulation at the wound sites. 2-week analysis was inconclusive, but 4-week results were significant. Histomorphometric analysis of the 15, 30, and 45-second treatment groups versus the control group showed a 21% increase in bone formation, which was significant at a p <= 0.05 level. Treated sites showed higher osteoblastic activity than untreated sites. Increase in bone formation may be related to stabilize coagulation and lower amounts of wound contracture at treated sites. Conclusion: Low wattage laser treatment of craniofacial bone defects suggested significant increases in bone formation versus untreated sites

OBJECTIVE: To evaluate a novel method of detecting and comparing the porosity of white Mineral Trioxide Aggregate and Portland cement at two different pH. MATERIALS AND METHODS: Cylindrical specimens (n = 120) were prepared from hydrated ordinary white Portland Cement (WPC) (n = 60) and white Mineral Trioxide Aggregate (WMTA) (n = 60) and exposed to environments with pH of 4.4 (n = 30) or 7.4 (n = 30). The pore size distribution and total pore volume were detected using Mercury Intrusion Porosimetry. Data were analyzed by analysis of variance and post-hoc Tukey or Tamhane test (p = 0.05). RESULTS: The pore volume of WMTA was significantly lesser than WPC at both pH (p < 0.05). The surface tension of mercury was taken as 480 (N/m) and the contact angle 141.3 degrees for both materials. Pores were consistently found in all specimens. Total pore volumes for WPC and WMTA (cubic centimeter/gram) were 0.1954 and 0.1023, respectively, while the diameter of the pores ranged from 50-100 A and 20-50 A, respectively. CONCLUSIONS: Mercury Intrusion Porosimetry technique is a promising and reliable technique for assessing the porosity of endodontic materials

ABSTRACT: Solid freeform fabrication techniques such as direct write technology can be used to fabricate tissue-engineering scaffolds in 3 dimensions with high levels of reproducibility and precision. These can comprise complex structures made of osteoconductive, remodelable lattices to conduct bone ingrowth and solid barriers to prevent soft tissue invasion. As such, they act as a combination of bone graft and barrier membrane. Results from animal studies have shown that these structures fill rapidly with healing bone and can conduct bone across critical-size defects to fill large defects in rabbit skull. Results indicate that this technology can be used to produce both off-the-shelf and custom-fabricated bone graft substitutes. These may initially be used to restore alveolar ridge defects, but could also be used, in the future, to repair or replace complex craniofacial bone defects such as cleft palate defects. In the more distant future, these technologies could be combined with controlledrelease bioactive substances such as growth factors and pharmaceuticals to regenerate complex structures comprising multiple tissue types.

Where does dentistry fit into the field of regenerative medicine? Based on the fact that the goal of regenerative medicine is to restore function to damaged organs and tissues, it is apparent that dentistry, which has long embraced the concept of restoring function of damaged teeth, has embraced this goal from the very beginning. In this brief review we present the opinion that if you take as the primary criterion the restoration of tissue and organ function, dentistry has not only been at the forefront of restorative medicine but actually predates it in practice. We illustrate the depth and breadth of dental regenerative medicine using examples of therapies or potential therapies from our laboratories. These begin with an example from a historical area of strength, dental implant design and fabrication, progress to a more high tech bone scaffold fabrication project, and finish with a stem cell-based soft tissue engineering project. In the final analysis we believe that the restorative nature of dentistry will keep it at the forefront of regenerative medicine.