Johan Malmström

Electron Beam-Melted, Free-Form-Fabricated Titanium Alloy Implants: Material Surface Characterization and Early Bone Response in Rabbits

Titanium-6aluminum-4vanadium implants (Ti6Al4V) were prepared by free-form-fabrication (FFF) and were used either as produced or after machining and compared with wrought machined Ti6Al4V. Auger electron spectroscopy (AES), depth profiles, and interferometry were used to analyze the surface properties. The tissue response after 6-weeks in rabbit femur and tibia was evaluated using light microscopy and histomorphometry. The results revealed that the bulk chemical and mechanical properties of the reference material and the electron beam-melted (EBM) material were within the ASTM F136 specifications. The as-produced EBM Ti6Al4V implants had increased surface roughness, thicker surface oxide and, with the exception of a higher content of Fe, a similar surface chemical composition compared with machined EBM Ti6Al4V and machined, wrought Ti6Al4V implants. The two latter implants did not differ with respect to surface properties. The general tissue response was similar for all three implant types. Histomorphometry revealed a high degree of bone-to-implant contact (no statistically significant differences) for all the three implant types. The present results show that the surface properties of EBM Ti6Al4V display biological short-term behavior in bone equal to that of conventional wrought titanium alloy. The opportunity to engineer geometric properties provides new and additional benefits which justify further studies.

Bone response to free form‐fabricated hydroxyapatite and zirconia scaffolds: a histological study in the human maxilla

OBJECTIVES Synthetic and biological materials are increasingly used to provide temporary or permanent scaffolds for bone regeneration. This study evaluated the effect of material chemistry and microporosity on bone ingrowth and osseointegration of zirconia (ZrO(2)) and hydroxyapatite (HA) scaffolds in the human maxilla. MATERIAL AND METHODS Twelve patients subjected to dental implant placement were enrolled in the study. Scaffolds of ZrO(2) and HA were placed in the maxilla of each subject, using a randomization protocol. After 3 months of healing, biopsies were harvested comprising the scaffolds and surrounding bone tissue. The biopsies were processed for histological evaluation and morphometric analysis (bone ingrowth and bone-to-scaffold contact). RESULTS Healing was uneventful in all cases. All scaffolds demonstrated a measurable bone response using light microscopy and scanning electron microscopy. Microporous HA scaffolds revealed four times larger bone ingrowth and seven times larger bone contact as compared with ZrO(2) scaffolds. CONCLUSION The results show that chemistry and microporosity of HA promote bone ingrowth and bone contact of ceramic scaffolds in human maxilla.

Bone response to free form fabricated hydroxyapatite and zirconia scaffolds : a transmission electron microscopy study in the human maxilla

BACKGROUND Understanding the interfacial reactions to synthetic bone regenerative scaffolds in vivo is fundamental for improving osseointegration and osteogenesis. Using transmission electron microscopy, it is possible to study the biological response of hydroxyapatite (HA) and zirconia (ZrO(2) ) scaffolds at the nanometer scale. PURPOSE In this study, the bone-bonding abilities of HA and ZrO(2) scaffolds produced by free-form fabrication were evaluated in the human maxilla at 3 months and 7 months. MATERIALS AND METHODS HA and ZrO(2) scaffolds (ø: 3 mm) were implanted in the human maxilla, removed with surrounding bone, embedded in resin, and sectioned. A novel focused ion beam (FIB) sample preparation technique enabled the production of thin lamellae for study by scanning transmission electron microscopy. RESULTS Interface regions were investigated using high-angle annular dark-field imaging and energy-dispersive X-ray spectroscopy analysis. Interfacial apatite layers of 80 nm and 50 nm thickness were noted in the 3- and 7-month HA samples, respectively, and bone growth was discovered in micropores up to 10 µm into the samples. CONCLUSIONS The absence of an interfacial layer in the ZrO(2) samples suggest the formation of a direct contact with bone, while HA, which bonds through an apatite layer, shows indications of resorption with increasing implantation time. This study demonstrates the potential of HA and ZrO(2) scaffolds for use as bone regenerative materials.

Guided bone augmentation using ceramic space-maintaining devices: the impact of chemistry

The purpose of the study was to evaluate histologically, whether vertical bone augmentation can be achieved using a hollow ceramic space maintaining device in a rabbit calvaria model. Furthermore, the chemistry of microporous hydroxyapatite and zirconia were tested to determine which of these two ceramics are most suitable for guided bone generation. 24 hollow domes in two different ceramic materials were placed subperiosteal on rabbit skull bone. The rabbits were sacrificed after 12 weeks and the histology results were analyzed regarding bone-to-material contact and volume of newly formed bone. The results suggest that the effect of the microporous structure of hydroxyapatite seems to facilitate for the bone cells to adhere to the material and that zirconia enhance a slightly larger volume of newly formed bone. In conclusion, the results of the current study demonstrated that ceramic space maintaining devices permits new bone formation and osteoconduction within the dome.

Guided bone regeneration using individualized ceramic sheets

Guided bone regeneration (GBR) describes the use of membranes to regenerate bony defects. A membrane for GBR needs to be biocompatible, cell-occlusive, non-toxic, and mouldable, and possess space-maintaining properties including stability. The purpose of this pilot study was to describe a new method of GBR using individualized ceramic sheets to perfect bone regeneration prior to implant placement; bone regeneration was assessed using traditional histology and three-dimensional (3D) volumetric changes in the bone and soft tissue. Three patients were included. After full-thickness flap reflection, the individualized ceramic sheets were fixed. The sites were left to heal for 7 months. All patients were evaluated preoperatively and at 7 months postoperative using cone beam computed tomography and 3D optical equipment. Samples of the regenerated bone and soft tissue were collected and analyzed. The bone regenerated in the entire interior volume of all sheets. Bone biopsies revealed newly formed trabecular bone with a lamellar structure. Soft tissue biopsies showed connective tissue with no signs of an inflammatory response. This was considered to be newly formed periosteum. Thus ceramic individualized sheets can be used to regenerate large volumes of bone in both vertical and horizontal directions independent of the bone defect and with good biological acceptance of the material.

Guided bone augmentation using a ceramic space-maintaining device

OBJECTIVE The purpose of this study was to evaluate 3-dimensionally whether vertical bone augmentation can be achieved using a hollow hydroxyapatite space-maintaining device in a rabbit calvarial model. Furthermore, different inner surface topographies, different permeabilities, and different porosities of the ceramic were tested to determine the optimal conditions for bone regeneration. STUDY DESIGN A total of 48 hollow domes made of hydroxyapatite in 4 different designs were placed subperiosteally on rabbit skull bone. The rabbits were humanely killed after 12 weeks, and the results were analyzed 3-dimensionally using micro-computed tomography. RESULTS The results suggest a larger production of bone volume when using an occlusive, dense hydroxyapatite space-maintaining device with a rough inner surface. CONCLUSIONS Hydroxyapatite space-maintaining devices permit new bone formation and osteoconduction within the dome.

Evaluation of Bone Ingrowth in Free Form Fabricated Scaffolds

Colloidal processing was used to cast zirconia and hydroxyapatite materials. The cast materials reached densities around 99% when sintered at 1500°C and 1200°C respectively. By controlling the colloidal process the sintered density of hydroxyapatite was also reduced to around 80% when the same sintering condition was used. The casting process was combined with free form fabrication to prepare designed scaffolds with identical macroporosity. These scaffolds were used to evaluate the early bone tissue response in rabbit femur. After six weeks of implantation the bone area in scaffolds of zirconia and hydroxyapatite were compared. In scaffolds of hydroxyapatite the bone area was roughly three times larger compared to corresponding scaffolds of zirconia. When the scaffolds of hydroxyapatite also contained an open microporosity of around 20% the amount of bone was even more pronounced. The results showed the importance of the material composition and the microstructure on the bone regenerating performance of scaffolds.