Faculty Bibliography

WE43 Mg alloy, composed of Mg, Yttrium, Rare Earth elements, and Zirconium, has proved to be a suitable candidate for production of resorbable osteosynthesis implants in both clinical and experimental settings. In a previous study we tested biocompatibility and degradation properties of untreated (as-cast) and artificially aged (T-5) WE43 Mg-alloys as subperiosteal implants on a maxillofacial sheep model. Both the alloy compositions showed excellent biocompatibility, however, with respect to degradation rate, the as-cast form showed increased degradability compared with the T-5. In the present study, we tested the same alloy composition (i.e. as-cast and T-5) to assess their biological behavior and degradation pattern when implanted as endosteal implants on a calvarial bone sheep model. Six implants in form of cylindrical discs were tested in 6 sheep, one per composition of each disc was placed in two monocortical cranial defect created with high speed trephine bur in the parietal bone. After euthanasia at 6 weeks histomorphological analysis of the bone/implant specimens was performed. WE43-as cast showed higher degradation rate, increased bone remodeling, gas pockets formation and osteolysis compared with the T5 alloy. WE43-T5 showed greater bone/implant interface stability, and seemed to be more suitable for fabrication of endosteal bone screws.

BACKGROUND:Vascularized bone tissue transfer, commonly used to reconstruct large mandibular defects, is challenged by long operative times, extended hospital stay, donor-site morbidity, and resulting health care. 3D-printed osseoconductive tissue-engineered scaffolds may provide an alternative solution for reconstruction of significant mandibular defects. This pilot study presents a novel 3D-printed bioactive ceramic scaffold with osseoconductive properties to treat segmental mandibular defects in a rabbit model. METHODS:Full-thickness mandibulectomy defects (12 mm) were created at the mandibular body of eight adult rabbits and replaced by 3D-printed ceramic scaffold made of 100% β-tricalcium phosphate, fit to defect based on computed tomography imaging. After 8 weeks, animals were euthanized, the mandibles were retrieved, and bone regeneration was assessed. Bone growth was qualitatively assessed with histology and backscatter scanning electron microscopy, quantified both histologically and with micro computed tomography and advanced 3D image reconstruction software, and compared to unoperated mandible sections (UMSs). RESULTS:Histology quantified scaffold with newly formed bone area occupancy at 54.3 ± 11.7%, compared to UMS baseline bone area occupancy at 55.8 ± 4.4%, and bone area occupancy as a function of scaffold free space at 52.8 ± 13.9%. 3D volume occupancy quantified newly formed bone volume occupancy was 36.3 ± 5.9%, compared to UMS baseline bone volume occupancy at 33.4 ± 3.8%, and bone volume occupancy as a function of scaffold free space at 38.0 ± 15.4%. CONCLUSIONS:3D-printed bioactive ceramic scaffolds can restore critical mandibular segmental defects to levels similar to native bone after 8 weeks in an adult rabbit, critical sized, mandibular defect model.

OBJECTIVE:To evaluate the residual stress (nanoindentation based on hardness) of fatigued porcelain-fused to zirconia 3-unit fixed dental prostheses (FDP) with different framework designs. METHODS:Twenty maxillary 3-unit FDP replacing second-premolar (pontic) were fabricated with conventional framework-design (even-thickness of 0.5mm and 9mm2 connector area) and modified framework-design (thickness of 0.5mm presenting lingual collar connected to proximal struts and 12mm2 connector area). Connector marginal ridges were loaded and the fractured and suspended FDPs were divided (n=3/each) into: (1) Fractured zirconia even-thickness (ZrEvenF); (2) Suspended zirconia even-thickness (ZrEvenS); (3) Fractured zirconia with modified framework (ZrModF); (4) Suspended zirconia with modified framework (ZrModS); (5) Non-fatigued FDP with conventional framework design (Control). The FDPs were nanoindented at 0.03mm (Region of Interest (ROI) 1), 0.35mm (ROI 2) and 1.05mm (ROI 3) distances from porcelain veneer outer surface with peak load 4000μN. The Linear Mixed Analysis of Variance (ANOVA) Model on ranks and Least Significant Difference Test on ranks (95%) were used. RESULTS:Highest rank hardness values were found for Control group and ZrModS, whereas the lowest values were found in ZrModF. Statistical differences (p=0.000) were found among all groups except for comparison between ZrModS and Control group (p=0.371). Hardness between ROIs were statistically significant different (p<0.001) where ROI 1 presented the lowest values. SIGNIFICANCE/CONCLUSIONS:Framework-design modification did not influence the residual stress of porcelain-fused to zirconia fatigued 3-unit FDP. Whereas fractured FDPs showed the highest residual stress compared to suspended and control FDPs. Residual stress increased as nanoindented away from framework.

PURPOSE/OBJECTIVE:The objective of this study was to test the osteogenic capacity of dipyridamole-loaded, three-dimensionally printed, bioactive ceramic (3DPBC) scaffolds using a translational, skeletally mature, large-animal calvarial defect model. MATERIALS AND METHODS/METHODS:Custom 3DPBC scaffolds designed to present lattice-based porosity only towards the dural surface were either coated with collagen (control) or coated with collagen and immersed in a 100 μM concentration dipyridamole (DIPY) solution. Sheep (n = 5) were subjected to 2 ipsilateral trephine-induced (11-mm diameter) calvarial defects. Either a control or a DIPY scaffold was placed in each defect, and the surgery was repeated on the contralateral side 3 weeks later. Following sacrifice, defects were evaluated through microcomputed tomography and histologic analysis for bone, scaffold, and soft tissue quantification throughout the defect. Parametric and non-parametric methods were used to determine statistical significance based on data distribution. RESULTS:No exuberant or ectopic bone formation was observed, and no histologic evidence of inflammation was noted within the defects. Osteogenesis was higher in DIPY-coated scaffolds compared to controls at 3 weeks (p = 0.013) and 6 weeks (p = 0.046) in vivo. When bone formation was evaluated as a function of defect radius, average bone formation was higher for DIPY relative to control scaffolds at both time points (significant at defect central regions at 3 weeks and at margins at 6 weeks, p = 0.046 and p = 0.031, respectively). CONCLUSION/CONCLUSIONS:Dipyridamole significantly improves the calvarial bone regeneration capacity of 3DPBC scaffolds. The most significant difference in bone regeneration was observed centrally within the interface between the 3DPBC scaffold and the dura mater.

BACKGROUND:The subcrestal placement of implant platform has been considered a key factor in the preservation of crestal bone, but the influence of implant placement depth on bone remodeling combined with peri-implantitis is not fully understood. The aim of this study was to assess the effect of the crestal or subcrestal placement of implants on peri-implant bone defects of ligature-induced peri-implantitis in dogs. MATERIAL AND METHODS/METHODS:Eight weeks after tooth extraction in six beagle dogs, two different types of implants (A: OsseoSpeed(TM), Astra, Molndal, Sweden; B: Integra-CP(TM), Bicon, Boston, USA) were placed at either crestal or subcrestal (-1.5 mm) positions on one side of the mandible. Ligature-induced peri-implantitis was initiated four weeks after the installation of the healing abutment connections. After 12 weeks, tissue biopsies were processed for histological analyses. RESULTS:Supra-alveolar bone loss combined with a shallow infrabony defect was observed in crestal level implants while deep and wide infrabony defects were present in subcrestal level groups. Subcrestal groups showed significantly greater ridge loss, depths and widths of infrabony defects when compared to crestal groups (P <0.001). CONCLUSIONS:Within the limitations of the animal study, it can be stated that the implants at subcrestal position displayed greater infra-osseous defect than implants at crestal position under an experimental ligature-induced peri-implantitis.

PURPOSE: Based on the current evidence, the effect of implant macrogeometry has a significant influence on osseointegration. Thus, this study evaluated histomorphometrically and histologically the bone response to acid-etched in comparison to grit-blasted/acid-etched (GB) and machined control (C) surfaced implants possessing identical macrogeometry placed in high-density bone. MATERIALS AND METHODS: Implant surface topography of the 3 different surfaced implants has previously been characterized. The macrogeometry of the implants were conical, and healing chambers were created in the cortical regions. The 3 groups were placed in the external mandibular body of adult male sheep (n = 5). After 6 weeks in vivo, all samples were retrieved for histologic observation and histomorphometry (eg, bone-to-implant contact [BIC] and bone area fraction occupancy [BAFO]). RESULTS: No statistical difference was observed for BIC and for BAFO, although there was a tendency that the mean values for BAFO was higher for the textured surface groups. CONCLUSIONS: It is suggested that the effect of surface topography is minimal in high-density bone and osseointegration seemed to be macrogeometry dependent.

PURPOSE: Orthopedic and maxillofacial bone fractures are routinely treated by titanium internal fixation, which may be prone to exposure, infection or intolerance. Magnesium (Mg) and its alloys represent promising alternatives to produce biodegradable osteosynthesis devices, with biocompatibility and, specifically, hydrogen gas production during the degradation process, being the main drawback. Aim of this study is to test and compare biocompatibility, degradation rate and physiscochemical properties of two Mg-alloys to identify which one possesses the most suitable characteristics to be used as resorbable hardware in load-bearing fracture sites. MATERIALS AND METHODS: As-cast (WE43) and T5 Mg-alloys were tested for biocompatibility, physical, mechanical and degradation properties. Microstructure was assessed by optical microscopy, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS); mechanical properties were tested utilizing quasi-static compression and failure analysis. Locoregional biocompatibility was tested by sub-periosteal implantation on the fronto-nasal region of large-animal model (sheep): regional immunoreaction and metal accumulation was analyzed by LA-ICP of tributary lymph-nodes, local reactions were analyzed through histological preparation including bone, implant and surrounding soft tissue. RESULTS: Mechanically, T5 alloy showed improvement in strength compared to the as-cast. Lymph-node Mg accumulation depicted no differences between control (no implant) and study animals. Both alloys showed good biocompatibility and osteogenesis-promoting properties. CONCLUSION: This study demonstrated excellent biocompatibility and osteogenesis-promoting capabilities of the tested alloys, providing a platform for further studies to test them in a maxillofacial fracture setting. T-5 alloy displayed more stability and decreased degradation rate than the as-cast.

This paper characterizes in an in vitro setting the release of calcium (Ca) and phosphate (PO4) of 3D printed bioactive ceramic scaffold prepared from extrudable paste containing hydroxyapatite and beta-tricalcium phosphate (beta-TCP). Hydroxyapatite and beta-TCP were calcined at 800 degrees C for 11 h, fabricated into four experimental groups (100% HA, 100% beta-TCP, 15%/85% HA/beta-TCP, and 15%/85% HA/beta-TCP (design)), sintered to 1100 degrees C for 4 h. Calcium and phosphorus concentrations were evaluated using ICP spectroscopy, and the release of Ca and PO4 ions during dissolution of the CaP-based scaffolds was measured by submerging in 0.05 mol/L Tris(hydroxymethyl) aminomethane-HCl and maintaining a temperature of 37 degrees C. The Ca and PO4 concentrations of the solutions were measured with the utilization of a calcium assay kit and a phosphate assay kit and read in a UV-visible spectrophotometer. The 100% HA scaffold group showed the greatest concentration of Ca ions (similar to 1.9 mg/dL), but ultimately released at a lower amount as time increased; the 100% HA scaffold also showed the lowest total amount of calcium ions released over the course of evaluation. The results for the 100% beta-TCP were on the opposite of the HA with the highest amount of calcium ion release over the study. While the PO4 ion release showed a similar trend as those observed with Ca ions with an apparent difference in the 100% HA scaffold group. There was nearly 0 mg/dL of the phosphate ions released in the first 24 h, in comparison to the amount of Ca ions released during the same time frame. Since various formulations can lead to different properties of these bioactive ceramic scaffolds, it is important to understand how the tailoring of this important biphasic material can impact the long-term outcome of an ever-important in vivo clinical trial in the future.

PURPOSE: Currently, surgeons approach autogenous microtia repair by creating a two-dimensional (2D) tracing of the unaffected ear to approximate a three-dimensional (3D) construct, a difficult process. To address these shortcomings, this study introduces the fabrication of patient-specific, sterilizable 3D printed auricular model for autogenous auricular reconstruction. METHODS: A high-resolution 3D digital photograph was captured of the patient's unaffected ear and surrounding anatomic structures. The photographs were exported and uploaded into Amira, for transformation into a digital (.stl) model, which was imported into Blender, an open source software platform for digital modification of data. The unaffected auricle as digitally isolated and inverted to render a model for the contralateral side. The depths of the scapha, triangular fossa, and cymba were deepened to accentuate their contours. Extra relief was added to the helical root to further distinguish this structure. The ear was then digitally deconstructed and separated into its individual auricular components for reconstruction. The completed ear and its individual components were 3D printed using polylactic acid filament and sterilized following manufacturer specifications. RESULTS: The sterilized models were brought to the operating room to be utilized by the surgeon. The models allowed for more accurate anatomic measurements compared to 2D tracings, which reduced the degree of estimation required by surgeons. Approximately 20 g of the PLA filament were utilized for the construction of these models, yielding a total material cost of approximately $1. CONCLUSION: Using the methodology detailed in this report, as well as departmentally available resources (3D digital photography and 3D printing), a sterilizable, patient-specific, and inexpensive 3D auricular model was fabricated to be used intraoperatively. This technique of printing customized-to-patient models for surgeons to use as 'guides' shows great promise.

Integration between implant and bone is an essential concept for osseous healing requiring hardware placement. A novel approach to hardware implantation, termed osseodensification, is described here as an effective alternative. 12 sheep averaging 65kg had fixation devices installed in their C2, C3, and C4 vertebral bodies; each device measured 4mm diameterx10mm length. The left-sided vertebral body devices were implanted using regular surgical drilling (R) while the right-sided devices were implanted using osseodensification drilling (OD). The C2 and C4 vertebra provided the t=0 in vivo time point, while the C3 vertebra provided the t=3 and t=6 week time points, in vivo. Structural competence of hardware was measured using biomechanical testing of pullout strength, while the quality and degree of new bone formation and remodeling was assessed via histomorphometry. Pullout strength demonstrated osseodensification drilling to provide superior anchoring when compared to the control group collapsed over time with statistical significance (p<0.01). On Wilcoxon rank signed test, C2 and C4 specimens demonstrated significance when comparing device pullout (p=0.031) for both, and C3 pullout tests at 3 and 6 weeks collapsed over time had significance as well (p=0.027). Percent bone-to-implant contact (%BIC) analysis as a function of drilling technique demonstrated an OD group with significantly higher values relative to the R group (p<0.01). Similarly, percent bone-area-fraction-occupancy (BAFO) analysis presented with significantly higher values for the OD group compared to the R group (p=0.024). As a function of time, between 0 and 3 weeks, a decrease in BAFO was observed, a trend that reversed between 3 and 6 weeks, resulting in a BAFO value roughly equivalent to the t=0 percentage, which was attributed to an initial loss of bone fraction due to remodeling, followed by regaining of bone fraction via production of woven bone. Histomorphological data demonstrated autologous bone chips in the OD group with greater frequency relative to the control, which acted as nucleating surfaces promoting new bone formation around the implants, providing superior stability and greater bone density. This alternative approach to a critical component of hardware implantation encourages assessment of current surgical approaches to hardware implantation.