Papers by Author: Paulo Guilherme Coelho

Abstract: This study evaluated the in vitro degradation of pellet, powder and plates of poly-L-DL-lactic acid (PLDLLA) after two processing methods. Part of the material was reduced to powder by cryogenic milling and part of it molded injected in plate form. The crystallinity was evaluated by Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), and Gel Permeation Chromatography (GPC) before and after immersion in simulated body fluid for 30, 60, and 90 days. The glass transition temperature (T_g) of the pellets and the powder were 61.5°C, 66°C. The T_gs of the plates ranged from 59.55°C to 63.06°C. Their endothermic peaks were observed at 125°C and 120°C, which was not identified to the plates samples. The FTIR spectrum showed bands of amorphous and crystalline content. The XRD results showed a peak related to the crystalline content, and a wide reflection related to the amorphous content. The milling process increased the crystallinity and the molding injection decreased it.

Abstract: The objective of this series of experiments was to evaluate the effect of bioceramic coatings/ incorporations on implant surfaces as a function of implant and surgical drilling design. Methods: A series of four in vivo studies were conducted utilizing the dog proximal tibia model. The models provided implants that remained from 2 to 5 weeks implantation time. The different studies comprised the placement of implants with intimate contact with bone following placement and implant designs that resulted in healing chambers. The various implant types presented surfaces with and without Ca- and P-based bioceramic incorporations. Biomechanical and histomorphometric measurements along with qualitative bone-implant interface morphology evaluation were performed. For all studies, one-way ANOVA at 95% level of significance was employed along with Tukey's post-hoc multiple comparisons. Results: Close contact between cortical and trabecular bone and all the different implant surfaces irrespective of implant fit (with and without healing chambers) showed that all surfaces were biocompatible and osteoconductive. In general, appositional bone healing was observed at all implant regions that were in intimate contact with bone immediately after placement, and an intramembranous-like healing occurred throughout the whole volume of the healing chambers. Irrespective of implant + surgical drilling design, the presence of Ca and P resulted in a bone morphology that showed primary osteonic structures at earlier times than uncoated surfaces. Conclusion: Irrespective of implant design and surgical drilling combination, the presence of Ca and P on the implant surface positively modulated early healing around endosseous implants.

Abstract: Among surface modifications commercially available for dental implants, the incorporation of bioceramic coatings is one of the most popular. However, concerns regarding the effectiveness of the bond between the metallic surface and the coating have led to the development of thin-film Ca- and P- based bioceramic coatings. The purpose of this study was to evaluate the early bone response to a thin ion bean deposited (Test) bioceramic implant surface compared to an alumina-blasted/acid-etched (Control) surface in a canine model. Results showed that although no difference in bone-to-implant (BIC) could be noted between the two different surfaces, more organized bone architecture was present around the Test implants in 4 weeks. Based on this observation, the incorporation of a thin- film bioceramic coating positively influenced bone healing around dental implants at early times.

Abstract: Incorporation of bioceramics on the surface of dental implants has been utilized in an attempt to increase biological response of bone to materials. This paper reports the in vitro biological evaluation of Ca/P-based nanothickness bioceramic coated alumina-blasted/acid-etched titanium implants (AB/AE nanotite implant) and compare its performance to the untreated and uncoated implants, Ca/P-based nanothickness bioceramic coated untreated implants (untreated nanotite implant), alumina-blasted/acid-etched titanium implants (AB/AE implant) and hydroxyapatite plasma-sprayed implants (PSHA Implant). Balb/c 3T3 fibroblasts were used to asses the cytocompatibility of implant materials according to ISO-10993-5 protocols. Osteoblasts from Balb/c femurs seeded onto different implant surfaces showed the effect of surface topography and chemistry on cell adhesion. The results showed that all implants were not cytotoxic and that PSHA and AB/AE nanotite implants favored osteoblasts adhesion.

Abstract: The objective of this study was to physico/chemically characterize a commercially available and a newly developed Bioglass and also to evaluate their degradation properties. Materials and Method: Two bioresorbable glasses were utilized, a bioglass synthesized at Chemical Engineering College (University of São Paulo, Lorena, São Paulo) (BG1), and the other bioglass utilized was Biogran (BG2) (3i Implant Innovations, Brazil). Particles size distribution histograms were developed for both materials, and then they were characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) before and after immersion in simulated body fluid (SBF) for 30, 60, and 90 days. Results: The particle size distribution showed that the mean particle diameters at 10%, 50%, and 90% of the total volume were 17.65, 66.18, and 114.71 µm for BG1, and 354.54, 437.5, 525.00 µm for BG2. SEM images of BG1 showed that the as-received material had a rough surface and as the time of degradation elapsed, this surface became smooth. The images of BG2 showed that the as-received material also had a rough surface, and after immersion in SBF, the material’s crystalline content/morphology could be observed. The X-ray diffraction recorded that BG1 showed a silica peak, not seen at BG2. FTIR revealed that both bioglasses were of similar composition, except for the CO3-carbonate minor peak, present at the BG2 sample. Conclusions: 1. The particle size distribution showed a polydispersed pattern for both materials. 2. The material suffered degradation, and the decomposition increased as a function of immersion in SBF. 3. Both bioglasses had similar composition.

Abstract: Objective: This series of laboratorial and in-vivo studies describe the characterization, evolution, and in-vivo performance of various Ca- and P-based nanothicknesses and microstructures ion beam assisted depositions (IBAD) onto Ti-6Al-4V implants. Materials and Methods: Characterization- The 4 mm in diameter and 10 mm in length implant rods (Ti-6Al-4V) with IBAD I, IBAD II, and control (alumina-blasted/acid-etched, AB/AE) surfaces were provided by an implant manufacturer. The in-vitro characterization comprised the following techniques: (1) SEM/EDS, (2) XPS/Depth Profiling (3) Thin-film XRD (4) AFM + ToF-SIMS for coating thickness determination (5) AFM- Ra determination. In-vivo- Three animal experiments were carried out for evaluation of the nanothickness bioceramic coatings. All experiments comprised a proximal tibia model with 4-6 implants placed along the bones. Times in-vivo ranged from 2-5 weeks. Static (bioactivity, bone to implant contact) and dynamic (mineral apposition rates- MAR) histomorphometric measurements were recorded. Biomechanical testing was performed by pullout and torque to interfacial failure testing. Results: Combination of the characterization techniques showed that all bioceramic coatings were Ca- and P-based bioceramics of amorphous microstructure. AFM +ToF-SIMS showed that IBAD II coatings were thicker (300-500 nm) compared to IBAD I coatings (30-50 nm). Surface roughness did not change significantly for the IBAD implant groups compared to control. The in-vivo results showed higher degrees of osseoactivity, torque to failure, and MAR for the coated implants at different times in-vivo. IBAD II had higher biomechanical fixation at early implantation times compared to other groups. Conclusions: The results obtained in the in-vitro part this study support that both IBAD I and IBAD II coatings are Ca- and P- based amorphous bioceramics in the nanothickness range with theoretical high dissolution rates. The increased osseoactivity observed for IBAD coated and the high MAR values observed for IBAD coated compared to AB/AE implants support the effect of the bioceramic coating presence in the overall bone healing. A thickness effect was reveled through biomechanical testing where IBAD II (300-500nm thickness) presented higher performance.

Abstract: The shear bond strength between a ceramic material (Titankeramik®, Vita Zahnfabrik, Germany) and two biocompatible titanium alloys was investigated. Ti-13%Nb-13%Zr (TNZ) and Ti-35%Nb-7%Zr-5%Ta (TNZT) alloys were obtained based on the blended elemental technique followed by a sequence of cold uniaxial and isostatic pressing and sintering. Characterization involved microstructural analysis (SEM) and crystalline phase identification (XRD). Subsequently, samples were machined to 4 x 4 mm with a base of 5 x 1 mm. The base metals were blasted with Al2O3 particles followed by the application of a coupling agent and opaque ceramic. After ceramic firing, the specimens were loaded in a universal testing machine (0,5mm/min). XRD revealed the presence of α and β-phases for TNZ, and peaks related to β phases and Nb and Ta for the TNZT alloy. SEM evaluation (TNZ) depicted remaining pores and biphasic microstructure formation. SEM micrographs of the TNZT alloy revealed good densification and a homogeneous β structure. Shear bond strength data (MPa) were statistically analyzed (one-way ANOVA and Tukey test, α=.05) revealing that TNZT (37.6 ± 2.91) presented significant higher values (p=0.0002) compared to TNZ (26.03 ± 2.92). In conclusion, it seems that Ti alloy composition plays a significant role on ceramic bonding.