Stereo imaging and cytocompatibility of a model dental implant surface formed by direct laser fabrication

Direct laser fabrication (DLF) allows solids with complex geometry to be produced by sintering metal powder particles in a focused laser beam. In this study, 10 Ti6Al4V alloy model dental root implants were obtained by DLF, and surface characterization was carried out using stereo scanning electron microscopy to produce 3D reconstructions. The surfaces were extremely irregular, with approximately 100 microm deep, narrow intercommunicating crevices, shallow depressions and deep, rounded pits of widely variable shape and size, showing ample scope for interlocking with the host bone. Roughness parameters were as follows: R(t), 360.8 microm; R(z), 358.4 microm; R(a), 67.4 microm; and R(q), 78.0 microm. Disc specimens produced by DLF with an identically prepared surface were used for biocompatibility studies with rat calvarial osteoblasts: After 9 days, cells had attached and spread on the DLF surface, spanning across the crevices, and voids. Cell density was similar to that on a commercial rough microtextured surface but lower than on commercial smooth machined and smooth-textured grit-blasted, acid-etched surfaces. Human fibrin clot extension on the DLF surface was slightly improved by inorganic acid etching to increase the microroughness. With further refinements, DLF could be an economical means of manufacturing implants from titanium alloys.     

Interfacial shear strength of titanium implants in bone is significantly improved by surface topographies with high pit density and microroughness

Surface structure of implants influences bone response and interfacial shear strength between implants and bone. The aim of this study was to find topographical parameters that correlate with the interfacial shear strength. Two groups of sand-blasted titanium screws were implanted in 17 sheep tibia, each for 2-52 weeks: (A) acid pickled with HF/HNO(3); (B) acid etched with HCl/H(2)SO(4). Screw removal torque was measured and surface topography of both implant groups was studied by scanning electron microscopy, optical profilometry, and scanning probe microscopy. The roughness as well as the surface area of type A surface was higher in the scan region of 100 microm, but the microroughness and surface area of type B surface was higher in the scan region of 10 microm. A significantly higher removal torque (interfacial shear strength) of the surface treatment type B (412 +/- 60 Ncm) compared to surface treatment type A (157 +/- 33 Ncm) was found after 52 weeks of implantation in sheep due to differences in microroughness of both types of screws. It was also shown that the specification of the parameters Delta(a), R(a) and R(q) was not sufficient to characterize the properties of the implant surfaces. The analysis of R(q) parameter over wavelengths was required to characterize the size, shape and distribution of the implant surface structures.     

Influence of press-fit parameters on the primary stability of uncemented femoral resurfacing implants

Primary stability is essential to the success of uncemented prostheses. It is strongly influenced by implantation technique, implant design and bone quality. The goal of this study was to investigate the effect of press-fit parameters on the primary stability of uncemented femoral head resurfacing prostheses. An in vitro study with human specimens and prototype implants (nominal radial interference 170 and 420 microm) was used to investigate the effect of interference on primary stability. A finite element model was used to assess the influence of interference, friction between implant and bone, and bone quality. Primary stability was represented by the torque capacity of the implant. The model predicted increasing stability with actual interference, bone quality and friction coefficient; plastic deformation of the bone began at interferences of less than 100 microm. Experimentally, however, stability was not related to interference. This may be due to abrasion or the collapse of trabecular bone structures at higher interferences, which could not be captured by the model. High nominal interferences as tested experimentally appear unlikely to result in improved stability clinically. An implantation force of about 2,500 N was estimated to be sufficient to achieve a torque capacity of about 30 N m with a small interference (70 microm).     

An evaluation of ion-textured aluminum oxide dental implants

A study was undertaken to evaluate the ion-beam texturing of aluminum oxide as a means of providing a surface which will produce a biological prosthetic attachment. A wafflelike pattern of surface contours 150 x 75 x 35 microm deep was produced on cylindrical dental implants. The textured surfaces were compared to the as received surfaces in adult mongrel dogs. Implants were inserted into surgically modified healed extraction sites and were left in place for six months. Post-sacrifice mechanical testing was used to quantify the displacement response of the implants. The clinical, radiographic and mechanical testing evaluations did not reveal any statistically significant differences in the performance of the dental implants. However, it was observed that anatomical site and mandibular geometry with respect to implant size play a significant role in affecting implant retention.     

The influence of Young's modulus of loaded implants on bone remodeling: an experimental and numerical study in the goat knee

The aim of this study was to examine the influence of the Young's modulus of the implant material on the bone remodeling in a loaded condition. A combined animal experimental and computational study was set up. The animal experimental group comprised of 16 Saanen goats, each receiving one titanium implant (Young's modulus 110 GPa) and one high-density polyethylene (HDPE) implant (Young's modulus 1 GPa) in the left femoral condyle. Both types of implants received a titanium coating of 100 nm thickness. The implants protruded in the knee joint space and were directly weight bearing. The first group of eight goats was sacrificed after 6 weeks of loading and the second group of eight goats after 6 months of loading. The 16 femoral condyles with the 32 implants were prepared for microfocus computed tomography (micro-CT) scanning and histological sectioning. Three-dimensional trabecular bone parameters were calculated on the micro-CT images for the zones neck, middle, and apex of the implant. The percent of bone contact with the implant was measured on longitudinal histological sections. An axisymmetric finite element (FE) model was created to compare peri-implant bone strains and relative motion between a titanium and a HDPE implant for the experimental loading condition, and to assess the influence of different bone-implant interface (contact) conditions. From the statistical analysis of the 3D bone parameters, the difference between the titanium and HDPE implants was not significantly different (p > 0.05) between the zones (neck, middle, and apex) for both groups of goats. The implants could be considered in their entirety. After 6 weeks of loading, the PE implant presented lower connectivity and smaller marrow spaces in the circular region of 0-500 microm. In the region 500-1500 microm more bone volume was present for the PE implant. After 6 months, the PE implants showed more bone volume and thicker trabeculae than the titanium implants for the entire length of the implant. This effect was already present in the smallest region of interest, 0-500 microm. After 6 months more fibrous encapsulation was found around titanium implants. FE results demonstrated a substantial influence of the interface conditions on peri-implant strains and relative motion. For interface conditions that were representative for the early postoperative situation (involving press-fit and friction), differences in peri-implant bone strain distributions between titanium and HDPE could be related to the experimentally observed differences in amounts of bone and fibrous encapsulation. In contrast, differences in relative motion did not seem to play a role. Both the experimental and computational results suggest that implant stiffness can affect the peri-implant tissue response, which may be related to differences in peri-implant strains.     

Surface characterization of microtextured silicone.

A set of microtextured silicone surfaces was manufactured using the technique of photolithography. The textures consist of a uniform array that imparts anisotropy to the surfaces. Processing the material required multiple steps which may have altered the surface characteristics. This project aimed to determine if a surface texture on implant grade silicone would affect the material characteristics. ESCA and contact angle studies revealed no measurable alteration of the surface chemistry or surface energy due to the texturing procedure or the presence of the texture. Both analytical techniques confirmed the material was silicone. The actual dimensions of the surface textures, size, spacing, depth and orientation of the textures were found to be close to the design values, using SEM and quantitative two- and three-dimensional profilometry. Standard 2D profilometry was not sufficient to characterize the surfaces, as a direct result of the uniformity of the arrays. A method of characterizing regular surface periodic structures is presented.     

Residual aluminum oxide on the surface of titanium implants has no effect on osseointegration

The cleanliness of titanium dental implants surfaces is considered to be an important requirement for achieving osseointegration, and it has been hypothesized that the presence of inorganic contaminants could lead to lack of clinical success. Aluminum ions are suspected to impair bone formation by a possible competitive action to calcium. The objective of the present study was to describe the effects of residual aluminum oxide particles on the implant surface on the integration of titanium dental implants as compared to decontaminated implants in a rabbit experimental model. Threaded screw-shaped machined grade 3 c.p. titanium dental implants, produced with high-precision equipment, were used in this study. The implants were sandblasted with 100-120 microm Al2O3 particles at a 5atm pressure for 1min, then 24 implants (control implants) underwent ASTM F 86-68 decontamination process in an ultrasonic bath. The other 24 implants (test implants) were washed in saline solution for 15min. Both test and control implants were air-dried and sterilized at 120 degrees C for 30min. After sterilization the implants were inserted into the tibiae (two test and two control implants in each rabbit). Twelve New Zealand white mature male rabbits were used in this study. The protocol of the study was approved by the Ethical Committee of our University. No complications or deaths occurred in the postoperative period. All animals were euthanized, with an overdose of intravenous pentobarbital, after 4 weeks. A total of 48 implants were retrieved. The images were analyzed for quantitation of percentage of surface covered by inorganic particles, bone-implant contact, multinucleated cells or osteoclasts in contact with the implant surface and multinucleated cells or osteoclasts found 3mm from the implant surface. The differences in the percentages between the two groups have been evaluated with the analysis of variance. The implant surface covered by inorganic particles on test implants was significantly higher than that of control implants (p=0.0000). No statistically significant differences were found in the bone-implant contact percentages of test and control implants (p=0.377). No statistically significant differences were found in the number of multinucleated cells and osteoclasts in contact with the implant surface (p=0.304), and at a distance of 3mm from the implant surface (p=0.362). In conclusion, our histological results do not provide evidence to support the hypothesis that residual aluminum oxide particles on the implant surface could affect the osseointegration of titanium dental implants.     

Immunohistochemical in situ characterization of orthopedic implants on polymethyl metacrylate embedded cutting and grinding sections

When investigating the tissue reaction on orthopedic implants, the cellular activity at the bone-implant interface is of special interest. Preparation of undecalcified bone sections with methylmetacrylate (MMA)-based resins allows evaluation of the host tissue reactions with the implant in situ. However, the technical workup is demanding and few reports exist on the immunohistochemical characterization of these sections. Rat (R), sheep (S), and human (H) samples were investigated. R specimens contained intramedullary rods in the rat tibia. S specimens were sheep tibiae with an external fixator. H specimens were obtained from deceased patients. Specimens were embedded in MMA-based Technovit 9100N using cold polymerization. Sections of 10-15 microm thickness were obtained and prepared for immunohistochemical staining. Good morphological detail was preserved in all specimens providing information about mineralization, recent bone formation, and bone-implant contact. The following antibodies could reproducibly be detected specifically: Osteopontin (R, S, H), Osteonectin, Cathepsin D (R, S), von Willebrand factor (R, H), Osteocalcin, ED 1 (R), CD 3, CD 68, Keratin (H). Control procedures without adding primary antibodies showed no unspecific staining. Reliable detection of immunohistochemical markers of bone resorption, bone formation, inflammation, and angiogenesis at undecalcified sections with the implant in situ appears promising in enhancing our understanding of the cellular activity and cell-matrix interactions at the bone-implant interface.     

Femtosecond laser microstructuring of zirconia dental implants

This study evaluated the suitability of femtosecond laser for microtexturizing cylindrical zirconia dental implants surface. Sixty-six cylindrical zirconia implants were used and divided into three groups: Control group (with no laser modification), Group A (microgropored texture), and Group B (microgrooved texture). Scanning electron microscopy observation of microgeometries revealed minimal collateral damage of the original surface surrounding the treated areas. Optical interferometric profilometry showed that ultrafast laser ablation increased surface roughness (R(a), R(q), R(z), and R(t)) significantly for both textured patterns from 1.2 x to 6 x-fold when compared with the control group (p < 0.005). With regard to chemical composition, microanalysis revealed a significant decrease of the relative content of contaminants like carbon (Control 19.7% ± 0.8% > Group B 8.4% ± 0.42% > Group A 1.6% ± 0.35%) and aluminum (Control 4.3% ± 0.9% > Group B 2.3% ± 0.3% > Group A 1.16% ± 0.2%) in the laser-treated surfaces (p < 0.005). X-ray diffraction and Raman spectra analysis were carried out to investigate any change in the crystalline structure induced by laser processing. The original predominant tetragonal phase of zirconia was preserved, whereas the traces of monoclinic phase present in the treated surfaces were reduced (Control 4.32% > Group A 1.94% > Group B 1.72%) as the surfaces were processed with ultrashort laser pulses. We concluded that femtosecond laser microstructuring offers an interesting alternative to conventional surface treatments of zirconia implants as a result of its precision and minimal damage of the surrounding areas.     

Response of articular cartilage and subchondral bone to internal fixation devices made of poly-L-lactide: a histomorphometric and microradiographic study on rabbits

To study the tissue response of articular cartilage and subchondral bone to biodegradable fixation devices, pins and rods made of poly-L-lactide with a fibers-in-matrix texture were implanted through the articular surface of the intercondylar portion of the distal rabbit femur. The initial raw material viscosity average molecular weight of the polymer was 660,000. One pin or screw was implanted per animal. The pins were cylindrical and measured 4.5 mm in transverse diameter. The screws had a core diameter of 3.2 mm and an outer diameter of 4.5 mm. At insertion, the implants were cut flush with the articular surface. After follow-up times of 36 and 48 weeks, the specimens were examined histomorphometrically and microradiographically. The intact contralateral femur served as a control for comparison. No signs of erosion or degradation of the polymer could be seen in the specimens. A brim of reparative tissue was formed at the entrance of the implant channel. The width of the reparative tissue from the tissue-implant boundary towards the center of the entrance hole varied greatly between the specimens, from 30 to 950 microm. In most specimens this bridging tissue consisted of undifferentiated mesenchymal tissue. Only two out of 24 specimens showed a near-normal metachromatic toluidine-blue staining of the matrix. Degenerative chondrocyte clustering occurred in the pre-existing cartilage within a 400 microm wide zone from the tissue-implant interface into the recipient tissues. Some new-bone formation was seen to envelop the implant in all specimens, but the fractional osteoid formation surface of the trabeculae showed a value significantly higher than that of the intact control side only in the screw-implanted 36-week specimens. Because of the long degradation time of poly-L-lactide, the restoration process of the articular cartilage was slow, and with regard to the quality and quantity of the reparative tissue, very variable. Large implants made of poly-L-lactide may not be suitable for insertion through intra-articular surfaces.     

An evaluation of variables influencing implant fixation by direct bone apposition

A systematic mechanical and histologic evaluation of design variables affecting bone apposition to various biocompatible materials was undertaken. The variables investigated included material elastic modulus, material surface texture, as well as material surface composition. The implant materials included polymethylmethacrylate (PMMA), low-temperature isotropic (LTI) pyrolytic carbon, commercially pure (C.P.) titanium, and aluminum oxide (Al2O3). Implant surface texture was varied by either polishing or grit-blasting the various materials. Implant surface composition was varied by applying a coating of ultra-low temperature isotropic (ULTI) pyrolytic carbon to the various implants. A total of 12 types of implants were evaluated in vivo by placement transcortically in the femora of adult mongrel dogs for a period of 32 weeks. Following sacrifice, mechanical push-out testing was performed to determine interface shear strength and interface shear stiffness. The results obtained from mechanical testing indicate that for implants fixed by direct bone apposition, interface stiffness and interface shear strength are not significantly affected by either implant elastic modulus or implant surface composition. Varying surface texture, however, significantly affected the interface response to the implants. For each elastic modulus group the roughened surfaced implants exhibited greater strengths than the corresponding smooth surfaced implants. Undecalcified histologic evaluation of the implants demonstrated that the roughened implants exhibited direct bone apposition, whereas the smooth implants exhibited various degrees of fibrous tissue encasement. Thus, for implants utilizing direct bone apposition fixation, it appears that of the parameters investigated, implant surface texture is the most significant.     

Effect of Nd: YAG laser on titanium dental implants studied by AFM

Bacterial contamination of dental implants is considered the main cause of implant failure. Recently, the laser treatment of the implant surface has been proposed as an useful method for decontamination. In such a view, the present study was conducted to investigate the effects of a Nd:YAG laser on the surface morphology of a titanium dental implant by means of an atomic force microscope. We demonstrated that, when the pulse energy of the laser was kept below 30 mJ, independently from the pulse rate, the laser-treated specimens exhibited a qualitatively similar surface morphology when compared to the untreated titanium implants, suggesting that the implant surface was unaffected by the treatment, in these particular conditions. We also found that, by cooling the implant surface with an air flow? during laser irradiation, the mean temperature of the implant was maintained under 37 degrees C. All these data taken together suggest the possibility to use Nd:YAG laser for the treatment of failing dental implants.     

Response of normal female human osteoblasts (NHOst) to 17beta-estradiol is modulated by implant surface morphology

Titanium (Ti) surfaces with rough microtopographies enhance osteogenic differentiation, local factor production, and response to osteogenic agents in vitro and increase pullout strength of dental implants in vivo. Estrogens regulate bone formation, resorption, and remodeling in females and may be important in implant success. Here, we tested the hypothesis that estrogen modulates osteoblast response to implant surface morphology. Primary female human osteoblasts were cultured to confluence on three Ti surfaces (pretreatment, PT - R(a) 0.60 microm; sandblasted and acid-etched, SLA - R(a) 3.97 microm; and Ti plasma-sprayed, TPS - R(a) 5.21 microm) and treated for 24 h with 10(-7) or 10(-8) M 17beta-estradiol (E(2)). Cell number decreased with increasing surface roughness, but was not sensitive to E(2). Alkaline phosphatase specific activity of isolated cells and cell layer lysates was lower on rough surfaces. E(2) increased both parameters on smooth surfaces, whereas on rough surfaces, the stimulatory effect of E(2) on alkaline phosphatase was evident only when measuring cell layer lysates. Osteocalcin levels were higher in the conditioned media of cells grown on rough surfaces; E(2) had no effect in cultures on the plastic surfaces, but increased osteocalcin production on all Ti surfaces. TGF-beta1 and PGE(2) production was increased on rough surfaces, and E(2) augmented this effect in a synergistic manner; on smooth surfaces, there was no change in production with E(2). The response of osteoblasts to surface topography was modulated by E(2). On smooth surfaces, E(2) affected only alkaline phosphatase, but on rough surfaces, E(2) increased levels of osteocalcin, TGF-beta1, and PGE(2). These results show that normal adult human female osteoblasts are sensitive to surface microtopography and that E(2) can alter this response.     

Titanium implant surface modification by cathodic reduction in hydrofluoric acid: surface characterization and in vivo performance

Etching is used for the surface modification of titanium to improve the implant performance in bone. In this study, pure titanium implants were surface modified by a cathodic reduction process by using hydrofluoric acid (HF) at various concentrations (0.001, 0.01, and 0.1 vol %) and a constant current of 1 mA/cm(2). The resulting surface microtopographies were analyzed by atomic force microscopy, scanning electron microscopy, and profilometry, while the surface chemical contents were evaluated by time of flight secondary ion mass spectrometry. The competitive forces between ionic surface implementation induced by the current direction and the HF etching effect on titanium were highlighted. The implant performance was evaluated in an in vivo rabbit model by using a pull-out test method. The group of implants modified with 0.01% HF showed the highest retention in bone. Fluoride and hydride amounts measured in the surfaces, as well as surface skewness (S(sk)), kurtosis (S(ku)), and core fluid retention (S(ci)) were positively correlated to the implant's retention in bone in vivo. Frequently used parameters for characterizing the implant, such as oxide content and the average height deviation from the mean plane (S(a)), were not correlated to implant performance, suggesting that these parameters are not the most important in predicting the implant performance.     

The in-vivo wear performance of prosthetic femoral heads with titanium nitride coating

This paper reports the study performed on four titanium nitride (TiN) coated prosthetic femoral heads collected at revision surgery together with patient data. Surface topology has been examined using Scanning Electron Microscopy (SEM) and elemental analysis of both coating and substrate have been evaluated using energy-dispersive X-ray spectrometry. Quantitative assessment of the surface topography is achieved using contacting profilometry. The average Ra roughness value is calculated at five different locations for each femoral head. The UHMWPE counterface worn volume has been measured directly on the acetabular components. TiN fretting and coating breakthrough occurred in two of the four components examined. In the damaged coating areas the surface profile is macroscopically saw-toothed with average tooth height 1.5 microm. The average Ra value is 0.02 microm on the undamaged surfaces and 0.37 microm on the damaged ones. Failure of the coating adhesion resulted in the release of TiN fragments and of metallic particulate from the substrate fretting corrosion and in the increase of the head surface roughness affecting counterface debris production. Our results suggest that TiN-coated titanium alloy femoral heads are inadequate in the task of resisting third body wear mechanisms in vivo.     

Ultrastructural characterization of the implant/bone interface of immediately loaded dental implants

Primary stability and an optimized load transfer are assumed to account for an undisturbed osseointegration process of implants. Immediate loaded newly designed titanium dental implants inserted in the mandible of minipigs were used for the characterization of the interfacial area between the implant surface and the surrounding bone tissue during the early healing phase. Histological and electron microscopical studies were performed from implant containing bone specimens. Two different load regimens were applied to investigate the load related tissue reaction. Histological and electron microscopical analysis revealed a direct bone apposition on the implant surfaces, as well as the attachment of cells and matrix proteins in the early loading phase. A striking finding of the ultrastructural immunocytochemical investigations was the synthesis and deposition of bone related proteins (osteonectin, fibronectin, fibronectin receptor) by osteoblasts from day one of bone/biomaterial interaction. Calcium-phosphate needle-like crystallites were newly synthesized in a time-related manner directly at the titanium surface. No difference in the ultrastructural appearance of the interface was found between the two loading groups. Our experimental data suggest that loading of specially designed implants can be performed immediately after insertion without disturbing the biological osseointegration process.     

Mechanical stability of two-step chemically deposited hydroxyapatite coating on Ti substrate: effects of various surface pretreatments

The success of implants in orthopaedic and dental load-bearing applications crucially depends on the initial biological fixation of implants in surrounding bone tissues. Using hydroxyapatite (HA) coating on Ti implant as carrier for bone morphogenetic proteins (BMPs) may promote the osteointegration of implants; therefore, reduce the risk of implant failure. The goal of this study was to develop an HA coating method in conditions allowing the incorporation of protein-based drugs into the coating materials, while achieving a mechanical stable coating on Ti implant. HA coatings were deposited on six different groups of Ti surfaces: control (no pretreatment), pretreated with alkali, acid, heat at 800°C, grit blasted with Al?O?, and grit blasted followed by heat treatment. HA coating was prepared using a two-step procedure. First step was the chemical deposition of a monetite coating on Ti substrate in acidic condition at 75°C and the second step was the hydrolysis of the monetite coating to HA. Coatings were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The roughness of substrates and coatings was measured using profilometry technique. The mechanical stability of the coatings deposited on the pretreated substrates was assessed using scratch test. The coatings deposited on the grit-blasted Ti surface demonstrated superior adhesive properties with critical shearing stress 131.6 ± 0.2 MPa.     

Soft-tissue response to silicone and poly-L-lactic acid implants with a periodic or random surface micropattern

Tissue reaction to biomaterials is dependent on properties such as surface topography. The aim of this study was to evaluate the tissue reaction around implants with different surface topographies. We made coin-shaped silicone and poly-L-lactic acid (PLLA) implants with double-sided parallel microgrooves (depth 1.0 microm; width 10.0 microm) and random roughness on a micrometer scale. The control implants were smooth. These implants were inserted into subcutaneous pockets created on the flanks of goats. After 1, 3, or 12 weeks, the goats were sacrificed and the implants retrieved and histologically processed. Light microscopic evaluation revealed the formation of fibrous tissue capsules around all implant materials. The PLLA did not visibly degrade during the study period. Histomorphometric analyses were performed on capsule thickness, capsule quality, and on the implant-tissue interface quality. Compared with the silicone implants, the capsules around the PLLA implants showed significantly better capsule quality. Compared to the smooth implants, the capsules around the microgrooved implants were thicker, but the capsules around the roughened implants were thinner. However, randomly roughened implant surfaces generally elicited a stronger and more prolonged inflammatory reaction compared to smooth and microgrooved implant surfaces. We conclude that the application of microgrooves or random surface roughness to polymer implants apparently does not have beneficial effects on peri-implant tissue healing.