Bone attachment to glass-fibre-reinforced composite implant with porous surface

A method has recently been developed for producing fibre-reinforced composites (FRC) with porous surfaces, intended for use as load-bearing orthopaedic implants. This study focuses on evaluation of the bone-bonding behaviour of FRC implants. Three types of cylindrical implants, i.e. FRC implants with a porous surface, solid polymethyl methacrylate (PMMA) implants and titanium (Ti) implants, were inserted in a transverse direction into the intercondular trabeculous bone area of distal femurs and proximal tibias of New Zealand White rabbits. Animals were sacrificed at 3, 6 and 12 weeks post operation, and push-out tests (n = 5–6 per implant type per time point) were then carried out. At 12 weeks the shear force at the porous FRC–bone interface was significantly higher (283.3 ± 55.3 N) than the shear force at interfaces of solid PMMA/bone (14.4 ± 11.0 N; p < 0.001) and Ti/bone (130.6 ± 22.2 N; p = 0.001). Histological observation revealed new bone growth into the porous surface structure of FRC implants. Solid PMMA and Ti implants were encapsulated mostly with fibrous connective tissue. Finite element analysis (FEA) revealed that porous FRC implants had mechanical properties which could be tailored to smooth the shear stress distribution at the bone–implant interface and reduce the stress-shielding effect.     

Alkali- and heat-treated porous titanium for orthopedic implants

This study was carried out to investigate the effects of the alkali and heat treatments on the bone-bonding behavior of porous titanium implants. Porous titanium implants had a 4.6 mm solid core and a 0.7 mm thick porous outer layer using pure titanium plasma-spray technique. Three types of porous implants were prepared from these pieces: 1.control implant (CL implant) as manufactured 2.AW-glass ceramic bottom-coated implant (AW implant) in which AW-glass ceramic was coated on only the bottom of the pore of the implant 3.alkali- and heat-treated implant (AH implant), where implants were immersed in 5 mol/L NaOH solution at 60 degrees C for 24 h and subsequently heated at 600 degrees C for 1 h. The implants were inserted into bilateral femora of six dogs hemi-transcortically in a randomized manner. At 4 weeks, push-out tests revealed that the mean shear strengths of the CL, AW, and AH implants were about 10.8, 12.7, and 15.0 MPa, respectively. At 12 weeks there was no significant difference between the bonding strengths of the three types of the porous implants (16.0-16.7 MPa). Histologically and histomorphologically, direct bone contact with the implant surface was significantly higher in the AH implants than the CL and AW implants both at 4 and 12 weeks. Thus, the higher bonding strength between bone and alkali- and heat-treated titanium implants was attributed to the direct bonding between bone and titanium surface. In conclusion, alkali and heat treatments can provide porous titanium implants with earlier stable fixation.     

Electrical stimulation of bone growth into porous A12O3.

Porous, cylindrical, high alumina, ceramic structures were fabricated for implantation in the superior third of canine femoral medullary canals. Implant durations of one, two, four, and eight weeks using three animals per time period were studied. A constant current (10 muA) power supply was used to attempt to stimulate bone growth into the porous ceramic structures. Osseous tissue in-growth was evaluated using a mechanical push-out test, microadiography, and histological thin sectioning. The interfacial shear strength and tissue micro-structure was studied as a function of implant residence site and implant residence site and implant residence time. The results indicate that initially the proximal implants have a higher interfacial shear strength, however, after eight weeks of implantation the distal implants have a shear strength about twice that of the proximal implants. This trend is observed for both the electrically stimulated and nonstimulated specimens. The 10 muA current level used in this investigation was found to have a small but significant effect on shear strength increasing it at implantation times of less than eight weeks.     

Bone compaction enhances fixation of hydroxyapatite-coated implants in a canine gap model

Primary cementless joint replacement depends partly on the ability of bone to heal into those areas of an inserted implant where a gap to surrounding bone initially exists. A new bone preparation technique, compaction, has enhanced gap-healing around grit-blasted implants without osteo-conductive properties. However, hydroxyapatite (HA) porous-coated implants with osteo-conductive properties are often inserted clinically to enhance gap healing and implant fixation. It is unknown whether the osteo-conductive properties of HA porous-coated implants might overwhelm the beneficial effects of compaction on gap healing. Therefore, we compared the compaction technique with the conventional bone-removing technique, drilling, using HA porous-coated implants in a canine gap model. HA porous-coated titanium implants were bilaterally inserted into oversized cavities of the proximal humeri of seven dogs. Each dog served as its own control. Thus, one humerus had the implant cavity prepared with compaction, the other with drilling. Two weeks after surgery push-out test and histomorphometry was performed. Compaction significantly increased ultimate shear strength, energy absorption, apparent shear stiffness, bone implant contact, and peri-implant bone density. The results of this study suggest that compaction may enhance gap healing when osteo-conductive HA porous coated implants are inserted in joint replacements.     

Osseointegration of a hydroxyapatite-coated multilayered mesh stem

A new type of porous coating for hip prostheses called "multilayered mesh" was tested under weight-bearing conditions. The surface of the stem is constructed of titanium mesh produced by etching. The hip stems of hydroxyapatite (HA)-coated multilayered mesh and conventional beads were implanted into canine right hips, and animals were killed 3, 6 and 10 weeks and 6 and 12 months after implantation. Shear strength between the implant and the bone was evaluated by the push-out test. Bone ingrowth was calculated from backscattered electron imaging-scanning electron microscopy (BEI-SEM) images of transverse sections. Toluidine blue stained sections and the BEI-SEM images were evaluated histologically. The break sites of the specimens after the push-out test were evaluated on BEI-SEM images of longitudinal sections. The mean push-out strength of the HA-coated multilayered mesh samples was greater than that of the beads-coated samples every time tested, and the HA-coated multilayered mesh implants had significantly stronger push-out strength at 3 and 6 weeks (p<0.05). The strength of the HA-coated multilayered mesh implants was even greater at 6 and 12 months, whereas the strength of the beads-coated samples decreased. The HA-coated multilayered mesh implants showed significantly higher percentages of bone ingrowth than the beads-coated implants every time tested, except at 6 months (p<0.05). At 6 and 12 months, the bone ingrowth data for the HA-coated multilayered mesh implants increased, whereas it decreased for the beads-coated implants. The new bone formation had reached the bottom of the porous area of the HA-coated multilayered mesh surface by 3 weeks, but not had reached the bottom of the conventional beads surface. At 6 and 12 months, the smaller pores of the bead surface stopped the thickening of trabecular bone, and at 12 months, the break sites were at the bone-implant interface of the bead surface, whereas they were on the bone side of the HA-coated multilayered mesh surface. The difference between the break sites was significant at 12 months (p<0.05). The HA-coated multilayered mesh stem provided faster, stronger, and more durable osseointegration than the conventional bead stem.     

Enhancing the mechanical integrity of the implant-bone interface with BoneWelding technology: determination of quasi-static interfacial strength and fatigue resistance

The BoneWelding technology is an innovative bonding method, which offers new alternatives in the treatment of fractures and other degenerative disorders of the musculoskeletal system. The BoneWelding process employs ultrasonic energy to liquefy a polymeric interface between orthopaedic implants and the host bone. Polymer penetrates the pores of the surrounding bone and, following a rapid solidification, forms a strong and uniform bond between implant and bone. Biomechanical testing was performed to determine the quasi-static push-out strength and fatigue performance of 3.5-mm-diameter polymeric dowels bonded to a bone surrogate material (Sawbones solid and cellular polyurethane foam) using the BoneWelding process. Fatigue tests were conducted over 100,000 cycles of 20-100 N loading. Mechanical test results were compared with those obtained with a comparably-sized, commercial metallic fracture fixation screw. Tests in surrogate bone material of varying density demonstrated significantly superior mechanical performance of the bonded dowels in comparison to conventional bone screws (p < 0.01), with holding strengths approaching 700 N. Even in extremely porous host material, the performance of the bonded dowels was equivalent to that of the bone screws. For both cellular and solid bone analog materials, failure always occurred within the bone analog material surrounding and distant to the implant; the infiltrated interface was stronger than the surrounding bone analog material. No significant decrease in interfacial strength was observed following conditioning in a physiological saline solution for a period of 1 month prior to testing. Ultrasonically inserted implants migrated, on average, less than 20 microm over, and interfacial stiffness remained constant the full duration of fatigue testing. With further refinement, the BoneWelding technology may offer a quicker, simpler, and more effective method for achieving strong fixation and primary stability for fracture fixation or other orthopaedic and dental implant applications.     

Three-dimensional printing and porous metallic surfaces: a new orthopedic application

As-cast, porous surfaced CoCr implants were tested for bone interfacial shear strength in a canine transcortical model. Three-dimensional printing (3DP) was used to create complex molds with a dimensional resolution of 175 microm. 3DP is a solid freeform fabrication technique that can generate ceramic pieces by printing binder onto a bed of ceramic powder. A printhead is rastered across the powder, building a monolithic mold, layer by layer. Using these 3DP molds, surfaces can be textured "as-cast," eliminating the need for additional processing as with commercially available sintered beads or wire mesh surfaces. Three experimental textures were fabricated, each consisting of a surface layer and deep layer with distinct individual porosities. The surface layer ranged from a porosity of 38% (Surface Y) to 67% (Surface Z), whereas the deep layer ranged from 39% (Surface Z) to 63% (Surface Y). An intermediate texture was fabricated that consisted of 43% porosity in both surface and deep layers (Surface X). Control surfaces were commercial sintered beaded coatings with a nominal porosity of 37%. A well-documented canine transcortical implant model was utilized to evaluate these experimental surfaces. In this model, five cylindrical implants were placed in transverse bicortical defects in each femur of purpose bred coonhounds. A Latin Square technique was used to randomize the experimental implants left to right and proximal to distal within a given animal and among animals. Each experimental site was paired with a porous coated control site located at the same level in the contralateral limb. Thus, for each of the three time periods (6, 12, and 26 weeks) five dogs were utilized, yielding a total of 24 experimental sites and 24 matched pair control sites. At each time period, mechanical push-out tests were used to evaluate interfacial shear strength. Other specimens were subjected to histomorphometric analysis. Macrotexture Z, with the highest surface porosity, failed at a significantly higher shear stress (p = 0.05) than the porous coated controls at 26 weeks. It is postulated that an increased volume of ingrown bone, resulting from a combination of high surface porosity and a high percentage of ingrowth, was responsible for the observed improvement in strength. Macrotextures X and Y also had significantly greater bone ingrowth than the controls (p = 0.05 at 26 weeks), and displayed, on average, greater interfacial shear strengths than controls, although they were not statistically significant.     

Preliminary observations of bone ingrowth into porous materials.

A preliminary investigation has been performed (a) to determine the kinetics of bone ingrowth into porous materials and to determine if this ingrowth could be catalyzed by the presence of a foreign substrate; and (b) to measure the bonding capability of bone with a porous-surfaced metallic implant. Tests on porous-surfaced implants corroborate the work of other investigators in showing that bony tissue will grow into a porous substance that has pores large enough to support tissue nourishment. The shear strength of the bone-implant interface appears to increase with pore size and time of healing. Furthermore, it may be possible to catalyze this tissue ingrowth by the introduction into the fracture site of a foreign substance; in this experiment, glass beads 200-290mu in diameter were used.     

The structure of the bond between bone and porous silicon-substituted hydroxyapatite bioceramic implants

The significance of micrometer-sized strut porosity in promoting bone ingrowth into porous hydroxyapatite (HA) scaffolds has only recently been noted. In this study, silicon-substituted HA (0.8 wt % Si-HA) with approximately 8.5% of the total porosity present as microporosity within the struts of the implant was prepared for high-resolution transmission electron microscopy (HR-TEM) via both ultramicrotomy and focused ion beam milling. Between the struts of the porous Si-HA, pores with varying shapes and sizes (1-10 microm in diameter) were characterized. Within the struts, the Si-HA contained features such as grain boundaries and triple-junction grain boundaries. Bone ingrowth and dissolution from a Si-HA implant were studied using HR-TEM after 6 weeks in vivo. Minor local dissolution occurred within several pores within the struts. Organized, mineralized collagen fibrils had grown into the strut porosity at the interface between the porous Si-HA implant and the surface of the surrounding bone. In comparison, deeper within the implant, disorganized and poorly mineralized fibers were observed within the strut porosity. These findings provide valuable insight into the development of bone around porous Si-HA implants.     

Effect of increased strut porosity of calcium phosphate bone graft substitute biomaterials on osteoinduction

The effect of increasing strut porosity on the osteoinductivity of porous calcium phosphate (CaP) and silicate-substituted calcium phosphate (SiCaP) bone substitute materials was investigated in an ovine ectopic model. One to two millimeter-sized granules or block implants with strut porosities of 10, 20, or 30% were inserted into the left and right paraspinalis muscle. At 12 weeks, histological sections were prepared through the center of each implant and bone contact, bone area and implant area quantified. Backscattered scanning electron microscopy (bSEM) was used to visualize bone within small pores in the struts of the scaffolds. Increased bone formation was measured in the SiCaP with 30% strut porosity (5.482% ± 1.546%) when compared with the nonsilicate CaP with the same morphology (1.160% ± 0.502%, p = 0.02), indicating that silicate substitution may increase osteoinduction. Greater bone formation was seen in scaffolds with increased strut porosity. No bone growth was found in any of the SiCaP scaffold with 10% porosity. There was no significant difference between block and granule specimens. Scanning electron microscopy and EDX in combination with histology demonstrated bone formation within pores <5 μm in size. The use of silicate-substituted CaP material with increased strut porosity may further augment repair and regeneration in bony sites.     

新型羟基磷灰石多孔支架的制备与性状

背景：目前几种钙羟磷灰石作为骨的替代品已经在临床上使用,但是由于缺少内部交互的连通孔,使得骨形成过程中经常发生病理性的骨折。 目的：采用改良的技术制备互联多孔羟磷灰石陶瓷支架材料,并对其物理化学特征进行检测。 方法：将羟基磷灰石(质量分数60%)与聚乙烯亚胺质量分数40%混合,采用改良的泡沫凝胶技术技术(聚氧乙烯十二烷基醚质量分数1%)制备多孔羟磷灰石陶瓷。扫面电镜检测材料内部结构,将制备的材料移植动物体骨缺损区观察成骨情况。 结果与结论：多孔羟磷灰石陶瓷具有三维结构,内部充满大小较均一的球形孔隙,直径平均为150 μm,孔隙率75%,孔隙上充满窗孔样相互交通的小洞,平均40 μm, 具有足够的抗压度(10~12 MPa)。动物实验表明,多孔羟磷灰石陶瓷表现出较好的成骨诱导性,可见孔隙里形成了新生骨。结果提示改良的羟基磷灰石支架能够在骨组织工程上应用,有望成为新型的改良品。     

In vivo evaluation of plasma-sprayed titanium coating after alkali modification

In this paper, plasma-sprayed titanium coatings were modified by alkali treatment. The changes in chemical composition and structure of coatings were examined by SEM and AES. The results obtained indicated that a net-like microscopic texture feature, which was full of the interconnected fine porosity, appeared on the surface of alkali-modified titanium coatings. The surface chemical composition was also altered by alkali modification. A sodium titanate compound was formed on the surface of the titanium coating and replaced the native passivating oxide layer. Its thickness was measured as about 150 nm which was about 10 times of that of the as-sprayed coating. The bone bonding ability of titanium coatings were investigated using a canine model. The histological examination and SEM observation demonstrated that more new bone was formed on the surface of alkali-modified implants and grew more rapidly into the porosity. The alkali-modified implants were found to appose directly to the surrounding bone. In contrast, a gap was observed at the interface between the as-sprayed implants and bone. The push-out test showed that alkali-modified implants had a higher shear strength than as-sprayed implants after 1 month of implantation. An interfacial layer, containing Ti, Ca and P, was found to form at the interface between bone and the alkali-modified implant by EDS analysis.     

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.     

Titanium metals form direct bonding to bone after alkali and heat treatments

In this article we evaluated the bone-bonding strengths of titanium and titanium alloy implants with and without alkali and heat treatments using the conventional canine femur push-out model. Four kinds of smooth cylindrical implants, made of pure titanium or three titanium alloys, were prepared with and without alkali and heat treatments. The implants were inserted hemitranscortically into canine femora. The bone-bonding shear strengths of the implants were measured using push-out test. At 4 weeks all types of the alkali- and heat-treated implants showed significantly higher bonding strength (2.4-4.5 MPa) than their untreated counterparts (0.3-0.6 MPa). At 12 weeks the bonding strengths of the treated implants showed no further increase, while those of the untreated implants had increased to 0.6-1.2MPa. Histologically, alkali- and heat-treated implants showed direct bonding to bony tissue without intervening fibrous tissue. On the other hand, untreated implants usually had intervening fibrous tissue at the interface between bone and the implant. The early and strong bonding to bone of alkali- and heat-treated titanium and its alloys without intervening fibrous tissue may be useful in establishing cementless stable fixation of orthopedic implants.     

Comparison of plasma-sprayed hydroxyapatite coatings and hydroxyapatite/tricalcium phosphate composite coatings: in vivo study

This study aimed to compare biological properties, including osteoconduction, osseointegration, and shear strength, between plasma-sprayed hydroxyapatite (HA) and HA/tricalcium phosphate (TCP) coatings, using a transcortical implant model in the femora of canines. After 3 and 12 weeks of implantation, the implants with surrounding bone were assessed histologically in undecalcified sections in backscattered electron images (BEIs) under a scanning electron microscope (SEM). After short-term (3 week) follow-up, both coatings conducted new bone formation and revealed direct bone-to-coating contact. The HA/TCP coating could not enhance early host-to-coating responses. At 12 weeks, serious dissolution of the HA/TCP coatings evidently occurred. By the new bone healing index (NBHI) and apposition index (AI), we found no significant difference between HA/TCP-coated implants and HA-coated implants throughout all implant periods. At 12 weeks of implantation, some particles dissociated from the HA/TCP coating were found within the remodeling canal. After push-out measurements, the shear strength and failure mode of HA/TCP-coated implants were similar to those of HA-coated implants, and no statistical differences were found between either coating. Consequently, this study indicates that HA/TCP coatings have excellent biological response and may be considered suitable bioactive ceramic coatings for short-term clinical use.     

The effect of surface macrotexture and hydroxylapatite coating on the mechanical strengths and histologic profiles of titanium implant materials

A mechanical and histological evaluation of uncoated and hydroxylapatite-coated titanium implant materials was performed. Cylindrical implants of uncoated commercially pure (CP) titanium and hydroxylapatite-coated Ti-6Al-4V alloy were studied using a transcortical model, with implants evaluated after periods of 3, 5, 10, and 32 weeks. All implants had a surface macrotexture consisting of a series of semicircular annular grooves, approximately 750 micron in maximum depth. The attachment characteristics of interface shear stiffness and interface shear strength were determined by mechanical push-out testing. Nondecalcified histologic and microradiographic techniques, with implants in situ, were used to evaluate the response to the implant materials and the presence of the surface macrotexture. Mechanical testing results indicated that the hydroxylapatite-coated implants exhibited significantly greater values of maximum interface shear strength than the uncoated implants after all time periods. Interface shear stiffness was also significantly greater at all time periods for the hydroxylapatite-coated implants as compared to the uncoated implants. Histological evaluation after 3 weeks revealed an osteoid layer covering on all areas coated with the hydroxylapatite material; mineralization of this layer appeared to be complete after 10 weeks. In all cases, longer-term implants demonstrated mineralization of interface bone directly onto the hydroxylapatite coating, and in no case was a fibrous layer observed between the hydroxylapatite coating and the interface bone. Sections from the uncoated CP titanium implants revealed a thin fibrous layer present in nearly all areas. Only isolated regions of direct bone-implant apposition were observed for the uncoated implants. The presence of this fibrous tissue layer, however, apparently did not adversely affect the development of considerable attachment strength. The results from this study indicate that the hydroxylapatite coating can significantly increase the attachment strength of implants which rely upon bone apposition for fixation. In addition, the hydroxylapatite coating provides an osteophilic surface for bone deposition, and allows for a more rapid development of implant-bone attachment.     

Effect of porosity on the osteointegration and bone ingrowth of a weight-bearing nickel-titanium bone graft substitute

Porous nickel-titanium (NiTi) alloy is a promising new material for a bone graft substitute with good strength properties and an elastic modulus closer to that of bone than any other metallic material. The purpose of this study was to evaluate the effect of porosity on the osteointegration of NiTi implants in rat bone. The porosities (average void volume) and the mean pore size (MPS) were 66.1% and 259+/-30 microm (group 1, n=14), 59.2% and 272+/-17 microm (group 2, n=4) and 46.6% and 505+/-136 microm (group 3, n=15), respectively. The implants were implanted in the distal femoral metaphysis of the rats for 30 weeks. The proportional bone-implant contact was best in group 1 (51%) without a significant difference compared to group 3 (39%). Group 2 had lower contact values (29%) than group 1 (p=0.038). Fibrotic tissue within the porous implant was found more often in group 1 than in group 3 (p=0.021), in which 12 samples out of 15 showed no signs of fibrosis. In conclusion, porosity of 66.1% (MPS 259+/-30 microm) showed best bone contact (51%) of the porosities tested here. However, the porosity of 46.6% (MPS 505+/-136 microm) with bone contact of 39% was not significantly inferior in this respect and showed lower incidence of fibrosis within the porous implant.     

In vivo study of the effect of RGD treatment on bone ongrowth on press-fit titanium alloy implants

Early bone ongrowth is known to increase primary implant fixation and reduce the risk of early implant failure. Arg-Gly-Asp (RGD) peptide has been identified as playing a key role in osteoblast adhesion and proliferation on various surfaces. The aim for this study is to evaluate the effect of RGD peptide coating on the bony fixation of orthopaedic implants, to justify its further evaluation in clinical applications. Sixteen unloaded cylindrical plasma sprayed Ti6Al4V implants coated with cyclic RGD peptide were inserted as press-fit in the proximal tibia of 8 mongrel dogs for 4 weeks. Uncoated control implants were inserted in the contralateral tibia. Results were evaluated by histomorphometry and mechanical push-out test. A significant two-fold increase was observed in bone ongrowth for RGD-coated implants. Also, fibrous tissue ongrowth was significantly reduced for RGD-coated implants. Bone volume was significantly increased in a 0-100 microm zone around the implant. The increased bony anchorage resulted in moderate increases in mechanical fixation as apparent shear stiffness was significantly higher for RGD-coated implants. Increases in median ultimate shear strength and energy to failure were also observed. This study demonstrates that cyclic RGD coating increases early bony fixation of unloaded press-fit titanium implants.     

Threaded versus porous-surfaced designs for implant stabilization in bone-endodontic implant model

An endodontic implant model system was used to compare the effect of implant design on stabilization in bone. Specifically a porous-surfaced design was compared to conventional threaded and smooth-tapered endodontic implant designs. All implants were placed in immediate function thereby assessing the effect of early limited movement on the fixation achieved. A total of eighty-three endodontic implants were inserted in the mandibles of six adult mongrel dogs. Animals were sacrificed immediately after implantation and after 3, 6, and 12 months. Implants were evaluated by clinical and radiographic examination and after animal sacrifice by pull-out tests of the implant from the tissues, SEM examination of the pulled-out implants and, finally, histology. The pull-out test results indicated increasing shear strength with implantation time for the porous-surfaced implants in contrast to the gradual loss of fixation for the threaded implants and the continuous low shear strength for the smooth implants. Histological studies and SEM examination indicated the reason for these changes. Smooth implants became encapsulated by fibrous connective tissue from early post-implantation time periods. Threaded implants, although initially mechanically interlocked with bone, developed a fibrous connective tissue capsule that gradually thickened with time until, by 6 months, little mechanical interlock of bone and implant was present. It was assumed that this fibrous capsule thickening was caused by implant movement. The porous-surfaced implants, however, became stabilized by bone ingrowth and showed more extensive bone formation within the surface pores with time. It is concluded that for implants that are made functional immediately after implantation, as in this study, porous-surfaced implants can become strongly fixed by bone ingrowth, in contrast to conventional threaded or smooth-surfaced designs, thus presenting a more favourable long term prognosis.     

Hydrothermal and mechanical stresses degrade fiber-matrix interfacial bond strength in dental fiber-reinforced composites

Fiber-reinforced composites (FRCs) show great promise as long-term restorative materials in dentistry and medicine. Recent evidence indicates that these materials degrade in vivo, but the mechanisms are unclear. The objective of this study was to investigate mechanisms of deterioration of glass fiber-polymer matrix bond strengths in dental fiber-reinforced composites during hydrothermal and mechanical aging. Conventional three-point bending tests on dental FRCs were used to assess flexural strengths and moduli. Micro push-out tests were used to measure glass fiber-polymer matrix bond strengths, and nanoindentation tests were used to determine the modulus of elasticity of fiber and polymer matrix phases separately. Bar-shaped specimens of FRCs (EverStick, StickTech, and Vectris Pontic, Ivoclar-Vivadent) were either stored at room temperature, in water (37 and 100 degrees C) or subjected to ageing (10(6) cycles, load: 49 N), then tested by three-point bending. Thin slices were prepared for micro push-out and nanoindentation tests. The ultimate flexural strengths of both FRCs were significantly reduced after aging (p < 0.05). Both water storage and mechanical loading reduced the interfacial bond strengths of glass fibers to polymer matrices. Nanoindentation tests revealed a slight reduction in the elastic modulus of the EverStick and Vectris Pontic polymer matrix after water storage. Mechanical properties of FRC materials degrade primarily by a loss of interfacial bond strength between the glass and resin phases. This degradation is detectable by micro push-out and nanoindentation methods.