Faculty Bibliography

The aim of this study was to evaluate the in vivo performance of two different deproteinized bovine bone (DBB) grafting materials: DBBB (Bio-Oss®) and DBBL (Laddec®), for the regeneration of critically sized (8 mm) defects in rabbit's calvaria. Three round-shaped defects were surgically created in the calvaria of 13 New Zealand White rabbits proximal to the coronal suture in the parietal bone. Two of the defects were filled with one of the grafting materials while a third was left empty to serve as a negative control. Bone regeneration properties were evaluated at 4- and 8-weeks after implantation by means of histological and histomorphometrical analyses. Statistical analyses were performed through a mixed model analysis with fixed factors of time and material. Histological evaluation of the control group evidenced a lack of bridging bone formation across the defect sites at both evaluation time points. For the experimental groups, new bone formation was observed around the defect periphery and to progress radially inwards to the center of the defect site, regardless of the grafting material. Histomorphometric analyses at 4 weeks demonstrated higher amount of bone formation through the defect for DBBB group. However, at 8 weeks, DBBL and DBBB demonstrated osteoconductivity and low resorption rates with evidence of statistically similar bone regeneration through the complete boney defect. Finally, DBBB presented lower soft tissue migration within the defect when compared to DBBL at both evaluation time points. DBBB and DBBL presented similar bone regeneration performance and slow resorption rates. Although both materials promoted bone regeneration through the complete defect, DBBB presented lower soft tissue migration within the defects at 4- and 8-weeks.

To evaluate the effect of fatigue and aging on the crystalline content and reliability of a zirconia-toughened-alumina (ZTA) composite compared to its individual counterpart materials (3Y-TZP and Al₂O₃). Thirty-six disc-shaped specimens per group were obtained to comply with ISO 6872:2015. Crystalline content, microstructure and reliability of experimental groups were evaluated in four stages: 1) immediate; 2) aged; 3) fatigued; 4) aged + fatigue. Aging was performed in autoclave and Step-Stress-Accelerated-Life-Testing (SSALT) was performed using three stress profiles. Weibull statistics were used to determine Weibull parameters and life-expectancy. A significant increase in monoclinic phase in 3Y-TZP was observed after aging (19.31%), fatigue (17.88%) and aging + fatigue (55.81%), while ZTA evidenced minimal variation among all conditions (<5.69%). 3Y-TZP presented higher reliability than ZTA at 300 and 500 MPa, and ZTA outperformed Al₂O₃ at the same stress missions. None of the ceramics yielded acceptable reliability at 800 MPa. A higher characteristic strength was observed for 3Y-TZP, followed by ZTA and Al₂O₃. While after aging ZTA and Al₂O₃ remained stable, 3Y-TZP exhibited a significant increase in the characteristic stress. Aging did not affect the reliability of ZTA and Al₂O₃. 3Y-TZP demonstrated an increase in monoclinic content and characteristic strength after aging.

PURPOSE/OBJECTIVE:This study evaluated the probability of survival and failure mode of endodontically treated incisors without ferrule restored with CAD/CAM FRC post-cores. METHODS:Root canals of bovine incisors were treated, leaving post preparations of ∼10 mm. Teeth were allocated into three groups: (i) cast metal post-core, (ii) FRC prefabricated post with a direct resin core build-up, and (iii) CAD/CAM FRC post-core. Posts and zirconia crowns were cemented using resin cement. Specimens were subjected to step-stress accelerated-life fatigue testing in water. Use level probability Weibull curves, probability of survival for a mission of 100,000 cycles at 25, 50, and 100 N, Weibull modulus, and characteristic strength were calculated and plotted. Failure mode was examined under a stereomicroscope. RESULTS:Restored incisors demonstrated high probability of survival (93-100%) for missions estimated at 25 and 50 N, irrespective of post-core foundation. At 100 N, incisors restored with metal posts presented significantly higher probability of survival (99%) relative to CAD/CAM posts (79%), whereas FRC groups demonstrated no significant difference. Weibull analysis indicated no significant difference on the Weibull modulus (m = 3.38-5.92). Incisors reconstructed with metal post-cores (431 N) presented significantly higher characteristic strength relative to prefabricated (200 N) and CAD/CAM (202 N) FRC post-cores. While post fracture was the chief failure mode for prefabricated and CAD/CAM FRC post-cores, post and/or root fracture were the main event for metal post-cores. CONCLUSION/CONCLUSIONS:Endodontically treated incisors without ferrule restored with CAD/CAM FRC post-cores presented promising probability of survival for loads compatible with anterior masticatory forces and favorable failure modes.

Fused Filament Fabrication (FFF)-based 3D printing is an efficient technique for developing medical implants, but it is not very useful in developing small yet mechanically robust design-specific fixtures such as dental implants (<15 mm). Specifically, it is challenging to 3D print robust Polyetheretherketone (PEEK) small implants due to PEEK's high melting temperature and melt viscosity. However, in this study, we efficiently utilize high-temperature FFF to develop the first-of-its-kind patient-specific robust PEEK dental implants with high print resolution. Specifically, we explore the effects of critical FFF processing conditions on the mechanical properties of the implants and subsequently determine an optimized set of processing conditions that are essential in developing durable dental implant systems. Our results indicate that the 3D printed dental implants exhibit good fatigue properties and suffice the clinical and industrial requirements for dental implants. Furthermore, we prove that the 3D printed implants exhibit adequate mechanical durability even after simulated (accelerated) aging of 30 years.

Bone defects are associated with trauma, congenital disorders, non-unions, or infections following surgical procedures. Defects which are unable to heal spontaneously are categorized as "critical sized" and are commonly treated using bone grafts in an effort to facilitate bone regeneration and stabilization. Grafting materials can be either natural or synthetic, each having their respective advantages and disadvantages. Synthetic bone grafts are favored due to their ability to be tailored to exhibit desired properties and geometric configurations. β-tricalcium phosphate (β-TCP) is a synthetic grafting material that has been widely utilized for regenerative purposes due to its favorable osteoconductive properties. In combination with 3D printing, grafting materials can be further customized with respect to their macro and micro features. One way to customize devices is by using 3D printing and varying the surface area, by varying the internal component measurements. The objective of this study was to compare the effect of porosity and surface area of 3D printed β-TCP scaffolds with different strut diameters and the effect on cell proliferation in vitro. ß-TCP scaffolds were printed using a custom-built 3D direct-write micro printer with syringes equipped with different extrusion tip diameters (fdiameter: 200 µm, 250 µm and 330 µm). After sintering and post processing, scaffolds were subjected to micro-computed tomography (µCT) and a Scanning Electron Microscope (SEM) to evaluate surface area and porosity, respectively. Compressive strength was assessed using a universal testing machine. Cell proliferation was assessed through cellular viability, using human osteoprogenitor cells. The surface area of the scaffolds was found to increase with smaller strut diameters. Statistically significant differences (p<0.05) were detected for cellular proliferation, between the smallest extrusion diameter, 200 μm, and the largest diameter, 330 μm, after 48-, 72-, and 168-hours. No statistical significances were detected (p>0.05) with regards to the mechanical properties between groups. This study demonstrated that a smaller diameter rod yielded a higher surface area resulting in increased levels of cellular proliferation. Therefore, tailoring rod dimensions has the capacity to enhance cellular adhesion and ultimately, proliferation.

BACKGROUND:Computerized surgical planning (CSP) in osseous reconstruction of head and neck cancer defects has become a mainstay of treatment. However, the consequences of CSP-designed titanium plating systems on planning adjuvant radiation remains unclear. METHODS:Two patients underwent head and neck cancer resection and maxillomandibular free fibula flap reconstruction with CSP-designed plates and immediate placement of osseointegrated dental implants. Surgical treatment was followed by adjuvant intensity modulated radiation therapy (IMRT). RESULTS:Both patients developed osteoradionecrosis (ORN), and one patient had local recurrence. The locations of disease occurred at the areas of highest titanium plate burden, possibly attributed to IMRT dosing inaccuracy caused by the CSP-designed plating system. CONCLUSION/CONCLUSIONS:Despite proven benefits of CSP-designed plates in osseous free flap reconstruction, there may be an underreported risk to adjuvant IMRT treatment planning leading to ORN and/or local recurrence. Future study should investigate alternative plating methods and materials to mitigate this debilitating outcome.

BACKGROUND:We aimed to histomorphometrically evaluate the effects of Leucocyte-Platelet-Rich Fibrin (L-PRF), with and without the combination of a bone grafting material, for alveolar ridge preservation using an in vivo canine model. MATERIAL AND METHODS/METHODS:Seven dogs (Female Beagles, ~18-month-old) were acquired for the study. L-PRF was prepared from each individual animal by drawing venous blood and spinning them through a centrifuge at 408 RCF-clot (IntrasSpin, Intra-Lock, Boca Raton, FL). L-PRF membranes were obtained from XPression fabrication kit (Biohorizons Implant Systems, Inc., AL, USA). A split mouth approach was adopted with the first molar mesial and distal socket defects treated in an interpolated fashion of the following study groups: 1) Empty socket (negative control); 2) OSS filled defect 3) L-PRF membrane; and 4) Mix of Bio-Oss® with L-PRF. After six weeks, samples were harvested, histologically processed, and evaluated for bone area fraction occupancy (BAFO), vertical/horizontal ridge dimensions (VRD and HRD, respectively), and area of coronal soft tissue infiltration. RESULTS:BAFO was statistically lower for the control group in comparison to all treatment groups. Defects treated with Bio-Oss® were not statistically different then defects treated solely with L-PRF. Collapsed across all groups, L-PRF exhibited higher degrees of BAFO than groups without L-PRF. Defects filled with Bio-Oss® and Bio-Oss® with L-PRF demonstrated greater maintenance of VRD relative to the control group. Collapsed across all groups, Bio-Oss® maintained the VRD and resulted in less area of coronal soft tissue infiltration compared to the empty defect. Soft tissue infiltration observed at the coronal area was not statistically different among defects filled with L-PRF, Bio-Oss®, and Bio-Oss® with L-PRF. CONCLUSIONS:Inclusion of L-PRF to particulate xenograft did not promote additional bone heading at 6 weeks in vivo. However, we noted that L-PRF alone promoted alveolar socket regeneration to levels comparable to particulate xenografts, suggesting its potential utilization for socket preservation.

PURPOSE/OBJECTIVE:To evaluate the effect of composition, fabrication mode, and thermal cycling on the mechanical properties of different polymeric systems used for temporary dental prostheses. MATERIALS AND METHODS/METHODS:Standard bar-shaped specimens (25 × 2 × 2 mm) were fabricated of six polymeric systems of varying compositions and fabrication modes (n = 10/group): conventional PMMA (Alike, GC) - group CGC; conventional PMMA (Dêncor, Clássico) - group CD; bis-acryl (Tempsmart, GC) - group BGC; bis-acryl (Yprov, Yller) - group BY; milled PMMA (TelioCAD, Ivoclar) - group MI; 3D printed bis-acryl - (Cosmos Temp, Yller) group PY. Half of the specimens were subjected to 5000 thermal cycles (5 °C to 55 °C). Three-point bending tests were performed using a universal testing machine with a crosshead speed set to 0.5 mm/min. Flexural strength and elastic modulus were calculated from the collected data. FTIR spectra were recorded pre and post curing and after thermal cycling to evaluate material composition and degree of conversion. Energy-dispersive spectroscopy (EDS) and scanning electron microscope (SEM) were utilized to examine the composition and micromorphology of the systems, respectively. Data were analyzed using two-analysis of variance and Tukey tests (α = 0.05). RESULTS:FTIR spectra indicated that BGC, BY and PY groups corresponded to urethane dimethacrylate systems (bis-acryl), while CGC, CD, and MI groups corresponded to monomethacrylate systems, polymethyl methacrylate (PMMA). Bis-acryl BGC system yeilded the highest flexural strength (80 MPa), followed by the milled PMMA MI system (71 MPa), both statistically significant different relative to other groups. Bis-acryl BY exhibited the lowest flexural strength (27 MPa). Thermocycling significantly increased the flexural strength of all polymeric systems (∼10-15 MPa), except for the 3D-printed PY group. Bis-acryl BGC (1.89 GPa) and conventional PMMA CGC (1.66 GPa) groups exhibited the highest elastic modulus, followed by milled PMMA MI group (1.51 GPa) and conventional PMMA CD (1.45 GPa) systems, with significant difference detected between BGC group and MI and CD groups. The 3D printed PY (0.78 GPa) and bis-acryl BY (0.47 GPa) systems presented the lowest elastic modulus. Thermocycling did not have a significant influence on the elastic modulus. FTIR spectra indicate water sorption and release of unreacted monomers as well as increased degree of conversion (∼5-12%) after thermal cycling. CONCLUSION/CONCLUSIONS:Composition and fabrication mode and thermal cycling significantly affected the mechanical properties of polymeric systems used for temporary dental prostheses.

The present study aimed to evaluate the effect of parathormone (PTH) administered directly to the implant's surface prior to insertion, using a large translational animal model. Sixty titanium implants were divided into four groups: (i) Collagen, control group, where implants were coated with Type-I Bovine-collagen, and three experimental groups, where implants received varying doses of PTH: (ii) 12.5, (iii) 25, and (iv) 50 μg, prior to placement. Fifteen female sheep (~2 years old, weighing ~65 kg) received four implants in an interpolated fashion in C3, C4 or C5 vertebral bodies. After 3-, 6- and 12-weeks, samples were harvested, histologically processed, qualitatively and quantitatively assessed for bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO). BIC yielded lower values at 6-weeks for 50 μg relative to the control group, with no significant differences, when compared to the 12.5- and 25-μg. No significant differences were detected at 6-weeks between collagen, 12.5- and 25-μg groups. At 3- and 12-weeks, no differences were detected for BIC among PTH groups. With respect to BAFO, no significant differences were observed between the control and experimental groups independent of PTH concentration and time in vivo. Qualitative observations at 3-weeks indicated the presence of a more mature bone near the implant's surface with the application of PTH, however, no significant differences in new bone formation or healing patterns were observed at 6- and 12-weeks. Single local application of different concentrations of PTH on titanium implant's surface did not influence the osseointegration at any time-point evaluation in low-density bone.

OBJECTIVES/OBJECTIVE:To characterize the mechanical and biological properties of three commercially available resins, which are currently used for provisional restorations and to compare them to an experimental resin intended for definitive fixed dental prostheses. MATERIALS AND METHODS/METHODS:Three commercially available resins: Crowntec (CT, Saremco), Temporary C&B (FL, Formlabs), C&B MFH (ND, Nextdent), and the experimental resin: Permanent Bridge (PB, Saremco) were printed and subjected to biaxial flexural strength test, finite element analysis, Weibull analysis, scanning electron microscopy, cell proliferation, immunohistochemistry and cytotoxicity assays. Samples from CT, PB, and ND were provided directly from the manufacturers ensuring ideal workflow. FL was printed using the workflow as recommended by the manufacturer, using a Formlabs 2 printer and their post-processing units Form Wash and Form Cure. RESULTS:From the tested resins, PB yielded the best overall results in terms of mechanical properties. Cell proliferation and cytotoxicity did not show any significant differences among materials. PB showed higher values for probability of survival predictions (35%) when subjected to 250 MPa loads, whereas the other materials did not reach 10%. SIGNIFICANCE/CONCLUSIONS:Despite mechanical differences between the evaluated materials, the outcomes suggest that 3D printed provisional resins may be used in clinical settings, following the manufacturers indications. New materials intended for long-term use, such as the PB resin, yielded higher mechanical properties compared to the other materials. Alternative printing and post-processing methods have not yet been evaluated and should be avoided until further literature is available. CLINICAL SIGNIFICANCE/CONCLUSIONS:3D printed resins for provisional restorations have become popular with the emergence of new technologies. In this study, we evaluated three different commercially available resins for provisional restorations and one new experimental resin. The results from this study indicate that commercially available resins could be used in clinical settings under certain conditions and limited periods of time. Following the manufacturers protocols is of paramount importance to not compromise these properties.