Effects of injecting massive amounts of bioactive ceramics in mice

The effects of massive administration of bioactive ceramic powder (Bioglass (45S5), Ceravital (KGS), apatite-wollastnite containing glass ceramics (A-W GC), and hydroxyapatite (HA], by intraperitoneal (IP), intramuscular (IM), or subcutaneous (SC) injection in Balb/c mice were examined in this investigation. Alumina, Silica Glass (SG), and A-W-Al (containing the same amount of crystal as A-W GC and 6.3% Alumina) were used as nonbioactive controls. The particle size of each material injected was smaller than 44 microns. In addition to the above, two more sizes (smaller than 105 microns and smaller than 255 microns) of A-W GC powder, and a 1 x 1 x 0.2 cm plate of the A-W GC were also evaluated. When the particle size was smaller than 44 microns, intraperitoneal injections of 5 mg per g of body weight of BG, KGS, A-W GC, and A-W-Al were lethal to the mice. Ceramics in fine powder form, which are generally believed to have higher bioactivity, are associated with higher mortality except A-W-Al. On the other hand, when the particle size of the ceramic was increased, the fatal effects of ceramic powders in mice decreased. Plate form of ceramics implanted I.P. had no systemic effects. Intramuscular or SC injections of bioactive ceramic powder with a particle size smaller than 44 microns had almost no systemic effects. Both the particle size of the ceramic powder and the route of administration influenced the reactivity of the bioactive ceramics in the mice. In conclusion, regardless of particle size, neither SC nor IM injection of large doses of highly bioactive ceramics had an adverse effect on the host (mouse).     

Repair of segmental bone defects using bioactive bone cement: comparison with PMMA bone cement.

We developed a bioactive bone cement (BABC) that consists of apatite and wollastonite containing glass ceramic (AW-GC) powder and bisphenol-A-glycidyl dimethacrylate (Bis-GMA) based resin. In the present study, the effectiveness of the BABC for repair of segmental bone defects under load-bearing conditions was examined using a rabbit tibia model. Polymethylmethacrylate (PMMA) bone cement was used as a control. A 15-mm length of bone was resected from the middle of the shaft of the tibia, and the tibia was fixed by two Kirschner wires. The defects were replaced by cement. Each cement was used in 12 rabbits; six rabbits were sacrificed at 12 and 25 weeks after surgery, and the tibia containing the bone cement was excised and tension tested. At both the intervals studied, the failure loads of the BABC were significantly higher than those of the PMMA cement. The BABC was in direct contact with bone, whereas soft tissue was observed between the cement and bone in all PMMA cement specimens. Results indicated that the BABC was useful as a bone substitute under load-bearing conditions.     

Mechanism and strength of bonding between two bioactive ceramics in vivo.

A study was conducted to examine the mechanism and strength of bonding between two bioactive ceramic plates in vivo. Rectangular plates (15 mm X 10 mm X 2 mm) of Bioglass, apatite-wollastonite-containing glass ceramic (designated A-W.GC), and two types of hydroxyapatite sintered at 900 degrees C and 1200 degrees C (designated HA900 and HA1200) were prepared. Two plates of the same materials tied together with silk thread were implanted subcutaneously into rats. The force required to detach the mutually bonded bioactive ceramic plates was measured 4, 8, 12, and 24 weeks after implantation. The interface between the two bonded plates was examined by SEM-EPMA and thin-film x-ray diffraction analysis. At 24 weeks after implantation, the mutual bonding of Bioglass and A-W.GC was stronger than that of the two HA types. SEM-EPMA and thin-film x-ray diffraction analysis of the bonded area of Bioglass and A-W.GC plates showed bonding zones with apatite in the margins, and a bonding zone with calcite in the center. The greater strength of bonding of Bioglass and A-W.GC plates compared with the two types of HA plate 24 weeks after implantation is explained by the wider bonding zone provided by the calcite layer formed in the center of the plates, which is considered to have been perfused with PO4-poor body fluids resulting from PO4 consumption for apatite formation in the margins.     

Quantitative study on osteoconduction of apatite-wollastonite containing glass ceramic granules, hydroxyapatite granules, and alumina granules

The osteoconductive potential of apatite-wollastonite containing glass ceramic (A-W.GC), hydroxyapatite (HA), and alumina (AL) was quantitatively evaluated by implanting them as granules into rat tibiae. The amount of mature bone formed in contact with the ceramics varied depending on the ceramic materials; it reached a plateau earliest in A-W.GC and latest in AL. The bone mass at the interface showed the same results. The osteoconductive potential was suggested to be higher in bioactive ceramics than in bioinert ceramics, and to be related to the formation rate of the surface apatite layer of the bioactive ceramics.     

Characteristics and mechanical properties of acrylolpamidronate-treated strontium containing bioactive bone cement

The aim of the present study was to determine the influence of surface treatment on the mechanical properties of strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement. Previously we developed an injectable bioactive cement (SrHAC) system composed of Sr-HA powders and bisphenol A diglycidylether dimethacrylate (Bis-GMA). In this study, the Sr-HA powder was subjected to surface treatment using acrylolpamidronate, a bisphosphonate derivative, which has a polymerizable group, to improve the interface between inorganic filler and organic matrix by binding Sr-HA and copolymerizing into the matrix. After surface treatment, the compression strength, bending strength, and stiffness of the resulting composites were defined by using a material testing machine (MTS) according to ISO 5833. The fracture surface of the bone cement specimen was observed with a scanning electron microscope. Invitro cytotoxicity of surface-treated SrHAC was also studied using a tetrazolium-based cell viability assay (MTS/pms) on human osteoblast-like cells, the SaOS-2 cell line. Cells were seeded at a density of 10(4)/mL and allowed to grow in an incubator for 48 h at 37 degrees C. Results indicated that after surface treatment, the compression strength and stiffness significantly improved by 22.68 and 14.51%, respectively. The bending strength and stiffness of the bioactive bone cement also showed 19.06 and 8.91% improvements via three-point bending test. The fracture surface micromorphology after compression and bending revealed that the bonding between the resin to surface-treated filler considerably improved. The cell viability indicated that the treated particles were nontoxic and did not inhibit cell growth. This study demonstrated a new surface chemistry route to enhance the covalent bonds between inorganic fillers and polymer matrix for improving the mechanical properties of bone cement. This method not only improves the overall mechanical performance but also increases osteoblastic activity.     

Mechanical properties of bone after implantation of apatite-wollastonite containing glass ceramic-fibrin mixture

Mechanical properties of bone implanted with a mixture of apatite-wollastonite containing glass ceramic (A-W.GC) granules and fibrin were examined by compression testing. A 1:1 mixture of A-W.GC granules and fibrin (Group 1), 1:4 mixture of A-W.GC granules and fibrin (Group 2), and 1:1 mixture of hydroxyapatite (HA) granules and fibrin (Group 3) were implanted in the distal femoral metaphyses of rabbits. Histomorphometric analysis suggested that A-W.GC has a greater osteoconductive potential than HA. Trabeculalike structures were observed 24 weeks after the operation in all groups but were most notable in Group 2. Twenty-four weeks after the operation, in Groups 1 and 3, the compressive strength and compressive stiffness were higher than that of normal cancellous bone, and the fracture toughness was comparable with that of normal cancellous bone. In Group 2, all three values were similar to those of normal cancellous bone. Implantation of A-W.GC granules at a low density induces the formation of bone tissue which is similar to normal bone in both mechanical properties and morphology.     

Transmission electron microscopic study of interface between bioactive bone cement and bone: comparison of apatite and wollastonite containing glass-ceramic filler with hydroxyapatite and beta-tricalcium phosphate fillers.

We developed a bioactive bone cement that consists of apatite and wollastonite containing glass-ceramic (AW-GC) powder and bisphenol-a-glycidyl methacrylate (Bis-GMA) based resin. In this study, we made three types of cement (designated AWC, HAC, and TCPC) consisting of either AW-GC, hydroxyapatite (HA), or beta-tricalcium phosphate (beta-TCP) powder as the inorganic filler and Bis-GMA based resin as the organic matrix. These cements were implanted into rat tibiae and cured in situ. Specimens were prepared 1, 2, 4, and 8 weeks after the operation and observed using transmission electron microscopy. Each of the bone cements was in direct contact with the bone. In AWC-implanted tibiae, the uncured surface layer of Bis-GMA based resin was completely filled with newly formed bone-like tissue 2 weeks after implantation. The AW-GC particles were surrounded by bone and were in contact with bone through an apatite layer. No intervening soft tissue was seen. In HAC-implanted tibiae, it took 4 weeks for the uncured layer to completely fill with newly formed bonelike tissue. The HA particles were also in contact with bone through an apatite layer. In TCPC-implanted tibiae, it took 8 weeks for the uncured layer to fill with newly formed bone-like tissue. The new bone that formed on the TCPC was not as dense as that on the AWC or HAC, and an intervening apatite layer was not evident. Results indicated that AWC had higher bioactivity than either HAC or TCPC.     

A new resin matrix for dental composite having low volumetric shrinkage

The applications of dental restorative composite resins containing 2,2 bis [4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane (Bis-GMA), as a base resin, and triethylene glycol dimethacrylate (TEGDMA), as a diluent, are often limited in dentistry due to the relatively large amount of volumetric shrinkage that occurs during the curing reaction. In this study, various new resin matrices were examined for use as dental composites in order to reduce the amount of volumetric shrinkage that occurs in dental composites as a result of curing. Bis-GMA derivatives were synthesized by substituting methyl groups for hydrogen on the phenyl ring. The derivatives of TEGDMA with different chain lengths or reactive groups were also examined. The molecular structural changes in the TEGDMA derivatives were not effective in reducing the level of volumetric shrinkage. The resin matrix containing a Bis-GMA derivative and TEGDMA showed a reduced amount of volumetric shrinkage in proportion to the number of methyl groups on the phenyl rings. Polymerization with a mixture of Bis-GMA, its derivatives and a diluent is a promising strategy for obtaining a polymer with a low amount of volumetric shrinkage. A comparison of the volumetric shrinkage of dental composites containing Bis-GMA, TMBis-GMA (2,2-bis[3,5-dimethyl, 4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane)), and TEGDMA with that prepared from a Bis-GMA and TEGDMA mixture showed that the volumetric shrinkage reduction in the new resin was approximately 50%. Furthermore, the mechanical strength of the former was higher than that of the latter.     

Effect of ZnO addition on bioactive CaO-SiO2-P2O5-CaF2 glass-ceramics containing apatite and wollastonite

Some ceramics show bone-bonding ability, i.e. bioactivity. Apatite formation on ceramics is an essential condition to bring about direct bonding to living bone when implanted into bony defects. A controlled surface reaction of the ceramic is an important factor governing the bioactivity and biodegradation of the implanted ceramic. Among bioactive ceramics, glass-ceramic A-W containing apatite and wollastonite shows high bioactivity, as well as high mechanical strength. In this study, glass-ceramics containing zinc oxide were prepared by modification of the composition of the glass-ceramic A-W. Zinc oxide was selected to control the reactivity of the glass-ceramics since zinc is a trace element that shows stimulatory effects on bone formation. Glass-ceramics were prepared by heat treatment of glasses with the general composition: xZnOx(57.0-x)CaOx35.4SiO(2)x7.2P(2)O(5)x0.4CaF(2) (where x=0-14.2mol.%). Addition of ZnO increased the chemical durability of the glass-ceramics, resulting in a decrease in the rate of apatite formation in a simulated body fluid. On the other hand, the release of zinc from the glass-ceramics increased with increasing ZnO content. Addition of ZnO may provide bioactive CaO-SiO(2)-P(2)O(5)-CaF(2) glass-ceramics with the capacity for appropriate biodegradation, as well as enhancement of bone formation.     

Effect of bioactive filler content on mechanical properties and osteoconductivity of bioactive bone cement.

We took three types of bioactive bone cement (designated AWC, HAC, and TCPC), each with a different bioactive filler, and evaluated the influence of each filler on the mechanical properties and osteoconductivity of the cement. The cements consisted of bisphenol-a-glycidyl methacrylate-based (Bis-GMA based) monomers as an organic matrix, with a bioactive filler of apatite/wollastonite containing glass-ceramic (AW-GC) or sintered hydroxyapatite (HA) or beta-tricalcium phosphate (beta-TCP) powder. Each filler was mixed with the monomers in proportions of 50, 70, and 80% (w/w), giving a total of nine cement subgroups. The nine subgroups were designated AWC50, AWC70, AWC80, HAC50, HAC70, HAC80, TCPC50, TCPC70, and TCPC80. The compressive and bending strengths of AWC were found to be higher than those of HAC and TCPC for all bioactive filler contents. We also evaluated the cements in vivo by packing them into the intramedullary canals of rat tibiae. To compare the osteoconductivity of the cements, an affinity index was calculated for each cement; it equaled the length of bone in direct apposition to the cement, expressed as a percentage of the total length of the cement surface. Microradiographic examination up to 26 weeks after implantation revealed that AWC showed a higher affinity index than HAC and TCPC for each filler content although the affinity indices of all nine subgroups (especially the AWC and HAC subgroups) increased with time. New bone had formed along the AWC surface within 4 weeks, even in the cement containing AW-GC filler at only 50% (w/w); observation of the cement-bone interfaces using a scanning electron microscope showed that all the cements had directly contacted the bone. At 4 weeks the AWC had bonded to the bone via a 10 micron-thick reactive layer; the width of the layer, in which partly degraded AW-GC particles were seen, became slightly thicker with time. On the other hand, in the HAC- and TCPC-implanted tibiae, some particles on the cement surface were surrounded by new bone and partly absorbed or degraded. The results suggest that the stronger bonding between the inorganic filler and the organic matrix in the AWC cements gave them better mechanical properties. The results also indicate that the higher osteoconductivity of AWC was caused by the higher reactivity of the AW-GC powder on the cement surface.     

Gentamicin-loaded strontium-containing hydroxyapatite bioactive bone cement--an efficient bioactive antibiotic drug delivery system

Modified strontium-containing hydroxyapatite (Sr-HA) bone cement was loaded with gentamicin sulfate to generate an efficient bioactive antibiotic drug delivery system for treatment of bone defects. Gentamicin release and its antibacterial property were determined by fluorometric method and inhibition of Staphylococcus aureus (S. aureus) growth. Gentamicin was released from Sr-HA bone cement during the entire period of study and reached around 38% (w/w) cumulatively after 30 days. Antibacterial activity of the gentamicin loaded in the cements is clearly confirmed by the growth inhibition of S. aureus. The results of the amount and duration of gentamicin release suggest a better drug delivery efficiency in Sr-HA bone cement over polymethylmethacrylate bone cement. Bioactivity of the gentamicin-loaded Sr-HA bone cement was confirmed with the formation of apatite layer with 1.836 ± 0.037 μm thick on day 1 and 5.177 ± 1.355 μm thick on day 7 after immersion in simulated body fluid. Compressive strengths of the gentamicin-loaded Sr-HA cement reached 132.60 ± 10.08 MPa, with a slight decrease from the unloaded groups by 4-9%. Bending moduli of Sr-HA cements with and without gentamicin were 1.782 ± 0.072 GPa and 1.681 ± 0.208 GPa, respectively. On the contrary, unloaded Sr-HA cement obtained slightly larger bending strength of 35.48 ± 2.63 MPa comparing with 33.00 ± 1.65 MPa for loaded cement. No statistical difference was found on the bending strengths and modulus of gentamicin-loaded and -unloaded Sr-HA cements. Sr-HA bone cement loaded with gentamicin was proven to be an efficient drug delivery system with uncompromised mechanical properties and bioactivity.     

Differences in ceramic-bone interface between surface-active ceramics and resorbable ceramics: a study by scanning and transmission electron microscopy.

The interface between bioactive ceramics and bone was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The materials were apatite-wollastonite-containing glass ceramic (A-W.GC) as a representative surface-active ceramic, and calcite and beta-tricalcium phosphate (beta-TCP) as resorbable ceramics. Particles of these materials, ranging between about 100 microns and 300 microns in diameter, were implanted into rat tibiae, and specimens were prepared for observation at 8 weeks after implantation. Both SEM and TEM demonstrated that A-W.GC was bonded to bone through a thin Ca-P-rich layer consisting of fine apatite crystals apparently different from those of bone in shape, size, and orientation. Collagen fibers of the bone reached the surface of this layer, and chemical bonding between A-W.GC and the bone was speculated. Calcite and beta-TCP, on the other hand, made direct contact with the bone, and no apatite layer was present at the interface. The surfaces of the implants became rough due to degradation, and bone grew into the finest surface irregularities. However, we were unable to demonstrate any continuity of crystals between the resorbable implants and bone by high-resolution TEM. Accordingly, the bonding strength was considered to be mainly attributable to mechanical interlocking.     

Preparation of epoxy-SiO2 hybrid sol-gel material for bone cement

An organic-inorganic hybrid material, epoxy-SiO(2), was prepared by incorporating epoxy structure units covalently into a SiO(2) glass network via the sol-gel approach. The precursor was obtained by the reaction of diglycidyl ether of bisphenol A (DGEBA) with 3-aminopropyl trimethoxysilane (APTS). The precursor was then hydrolyzed and co-condensated with tetraethyl orthosilicate (TEOS) in tetrahydrofuran (THF) at room temperature to yield epoxy-SiO(2) hybrid sol-gel material having a 50 wt % SiO(2) content. Thermal properties of the hybrid material were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The hybrid sol-gel material epoxy-SiO(2) was the solid, powder component of bone cement. The liquid component contains bis-phenol-A glycidyl methacrylate (Bis-GMA), triethyleneglycol dimethacrylate (TEGDMA), and methyl methacrylate (MMA) with 25, 55, and 20 vol %, respectively. We discuss the comparison between the new epoxy-SiO(2) bone cement and the commercial Simplex P bone cement. Mechanical properties such as Young's modulus, compressive strength, hardness, and impact strength of the new epoxy-SiO(2) bone cement exceeded those of Simplex P bone cement. The tensile and bending strengths of the new epoxy-SiO(2) bone cement were approximately the same as those of Simplex P bone cement. In order to evaluate the biocompatibility of the new bone cement, an MTT test and optical microscopy were conducted in cell culture. Results indicated that the new epoxy-SiO(2) bone cement exhibits very low cytotoxicity compared with Simplex P bone cement.     

Pressurization of bioactive bone cement in vitro

We have developed a bioactive bone cement consisting of MgO-CaO-SiO2-P2O5-CaF2 glass-ceramic powder (AW glass-ceramic powder), silica glass powder as an inorganic filler, and bisphenol-a-glycidyl methacrylate (bis-GMA) based resin as an organic matrix. The efficacy of this bioactive bone cement was investigated by evaluating its pressurization in a 5-mm hole and small pores using a simulated acetabular cavity. Two types of acetabular components were used (flanged and unflanged sockets) and a commercially available polymethylmethacrylate (PMMA) bone cement (CMW 1 Radiopaque Bone Cement) was selected as a comparative control. Bioactive bone cement exerted greater intrusion volume in 5-mm holes than PMMA bone cement in both the flanged and unflanged sockets 10 minutes after pressurization (p < 0.05). In the small pores the bioactive and PMMA bone cements exerted almost identical intrusion volumes in flanged and unflanged sockets 10 min after pressurization. The intrusion volume in the flanged socket 10 minutes after pressurization was greater than that in the unflanged socket in all groups (p < 0.05). These results show that bioactive bone cement intrudes deeper into anchor holes than PMMA bone cement.     

Ultrastructure of the interface between bioactive composite and bone: comparison of apatite and wollastonite containing glass-ceramic filler with hydroxyapatite and beta-tricalcium phosphate fillers.

We have developed a bioactive bone cement that consists of apatite and wollastonite containing glass-ceramic (AW-GC) powder and bisphenol-a-glycidyl dimethacrylate (Bis-GMA)-based resin. In this study, we made three types of composite (designated AWC, HAC, and TCPC) consisting of AW-GC, hydroxyapatite (HA,) or beta-tricalcium phosphate (beta-TCP) powder as the inorganic filler and Bis-GMA-based resin as the organic matrix. The proportion by weight of the filler mixed into the cement was 70%. Rectangular plates (10 x 15 x 2 mm) of each composite were made and abraded with 2000 alumina powder. These composites were implanted into tibial metaphyses of rabbits. Specimens were prepared 10 and 25 weeks after implantation and examined using transmission electron microscopy (TEM). AWC was in direct contact with bone 10 weeks after implantation, and AW-GC particles were partially absorbed at the surface. HAC was in contact with partially mineralized extracellular matrix 10 weeks after implantation. In TCPC-implanted specimens, randomly oriented mineral was observed 10 weeks after implantation; however, collagenous extracellular matrix rarely was observed. In 25-week specimens, AW-GC particles were completely absorbed and replaced by new bone, and there was no intervening soft tissue. Both HAC and TCPC were in contact with bone at 25 weeks. These results indicate that AWC has higher bioactivity than either HAC or TCPC.     

Antibiotic delivery system using nano-hydroxyapatite/chitosan bone cement consisting of berberine

Different concentrations of berberine were mixed with nano-hydroxyapatite/chitosan (n-HA/CS) bone cement to generate an antibiotic drug delivery system for treatment of bone defects. Properties of the system such as setting time, compressive strength, surface morphology, phase compositions, drug release profiles and antimicrobial activity were also characterized. It was shown that the setting time of the cement ranged from 17.03 +/- 0.50 min to 28.47 +/- 0.96 min and the compressive strength changed from 184.00 +/- 7.94 MPa to 120.33 +/- 9.02 MPa with the increase of berberine. The XRD, IR, and SEM analyses suggested that berberine powders were stable in the bone cement in simulated body fluid (SBF). In vitro release of berberine from the bioactive bone cement pellets in SBF could last more than 4 weeks. The release profiles of 1.0 wt % berberine loaded bone cement followed the Higuchi equation at the infusion stage. The drug loaded pellets can inhibit bacterial growth (Staphylococcus aureus) at the standardized berberine minimum inhibitory concentration of 0.02 mg/mL during berberine release from 1 to 28 days. The n-HA/CS bone cement only with 1.0 wt % berberine proved to be an efficient antibiotic drug delivery system.     

Study of water sorption,solubility and modulus of elasticity of light-cured dimethacrylate-based dental resins

Polydimethacrylate resins were prepared by photopolymerization of Bis-GMA, TEGDMA, UDMA or Bis-EMA (4) monomer, initiated by camphoroquinone/N,N-dimethylaminoethyl methacrylate system. The study of physical properties of these resins showed that TEGDMA seems to create the most dense polymer network, which however is the most flexible (0.74GPa), absorbs the highest amount of water (6.33 wt%) and releases the lowest amount of unreacted monomer (2.41 microg/mm(3)). UDMA and Bis-EMA (4) create more rigid networks, which absorb lower water and release higher unreacted monomer than TEGDMA. Bis-EMA (4) absorbs the lowest water amount (1.79 wt%) and releases the highest amount of unreacted monomer (14.21 microg/mm(3)). Bis-GMA leads to the formation of the most rigid network (1.43 GPa), which absorbs lower water than the resin made by TEGDMA but higher than the resin made by UDMA and Bis-EMA (4). Copolymers of Bis-GMA with the other monomers were also prepared, using various monomer combinations and molar ratios. Copolymers Bis-GMA/TEGDMA (50/50 and 70/30 wt%) showed significantly higher values for Young's modulus (1.83 and 1.78 GPa) than those predicted by the linear dependence of the values on the copolymer composition. Gradual replacement of TEGDMA with UDMA or/and Bis-EMA (4) in copolymerization with Bis-GMA resulted in more flexible resins with lower water sorption and higher solubility values, depending on the TEGDMA content.     

Nano-mechanics of bone and bioactive bone cement interfaces in a load-bearing model

Many bioactive bone cements were developed for total hip replacement and found to bond with bone directly. However, the mechanical properties at the bone/bone cement interface under load bearing are not fully understood. In this study, a bioactive bone cement, which consists of strontium-containing hydroxyapatite (Sr-HA) powder and bisphenol-alpha-glycidyl dimethacrylate (Bis-GMA)-based resin, was evaluated in rabbit hip replacement for 6 months, and the mechanical properties of interfaces of cancellous bone/Sr-HA cement and cortical bone/Sr-HA cement were investigated by nanoindentation. The results showed that Young's modulus (17.6+/-4.2 GPa) and hardness (987.6+/-329.2 MPa) at interface between cancellous bone and Sr-HA cement were significantly higher than those at the cancellous bone (12.7+/-1.7 GPa; 632.7+/-108.4 MPa) and Sr-HA cement (5.2+/-0.5 GPa; 265.5+/-39.2 MPa); whereas Young's modulus (6.3+/-2.8 GPa) and hardness (417.4+/-164.5 MPa) at interface between cortical bone and Sr-HA cement were significantly lower than those at cortical bone (12.9+/-2.2 GPa; 887.9+/-162.0 MPa), but significantly higher than Sr-HA cement (3.6+/-0.3 GPa; 239.1+/-30.4 MPa). The results of the mechanical properties of the interfaces were supported by the histological observation and chemical composition. Osseointegration of Sr-HA cement with cancellous bone was observed. An apatite layer with high content of calcium and phosphorus was found between cancellous bone and Sr-HA cement. However, no such apatite layer was observed at the interface between cortical bone and Sr-HA cement. And the contents of calcium and phosphorus of the interface were lower than those of cortical bone. The mechanical properties indicated that these two interfaces were diffused interfaces, and cancellous bone or cortical bone was grown into Sr-HA cement 6 months after the implantation.     

Adhesive layer properties as a determinant of dentin bond strength

The goal of this study is to evaluate the hypothesis that the properties of the resin adhesive might affect the microtensile bond strength (MTBS) of multibottle dental adhesive system. In order to alter the properties, the experimental resin adhesives containing 2,2-bis (4-2-hydroxy-3-methacryloyloxypropoxyphenyl)propane (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) at various ratios were prepared. Degree of conversion immediately after curing (DC-immed), degree of conversion at 48 h after curing (DC-48h) of a thin coat of the experimental adhesives, the flexural strength (FS) of the bulk specimens made of the experimental adhesives, pH, viscosity at shear rate of 1 S(-1), and the microtensile bond strength (MTBS) values of the adhesives to dentin were investigated. The maximum MTBS and FS values of the resin adhesives were observed when the ratio of Bis-GMA/TEGDMA was 60/40. However, pH and viscosity values increased with increasing Bis-GMA content in the adhesives. When Bis-GMA content was more than 60 wt %, the viscosity increased exponentially and restricted the DC and FS, and accordingly decreased the bond strength. The stronger the resin adhesives were, the higher the bond strength to dentin could be obtained.     

Osteoconductivity and bone-bonding strength of high- and low-viscous bioactive bone cements.

A study was conducted to evaluate the osteoconductivity and bone-bonding ability of two types of bioactive bone cement, both consisting of apatite and wollastonite containing glass-ceramic powder (AW-P), fused silica glass powder (SG-P), submicron fumed silica as an inorganic filler, and bisphenol-a-glycidyl methacrylate (Bis-GMA) based resin as an organic matrix. The cements had two kinds of formulas: one (dough-type cement; designated DTC) composed of 85% (w/w) filler and 15% resin, which was developed for fixation of the acetabular component in total hip arthroplasty and could be handled manually; and one (injection-type cement; designated ITC) composed of 79% (w/w) filler and 21% resin. ITC was developed for fixation of the femoral component and, because it had a lower viscosity than DTC, could be injected. The DTC and ITC both contained 73% AW-P, 25% SG-P, and 2% fumed silica in the weight ratio of the filler component. Two other types of cement, both of which consisted of 83.3% AW-P or SG-P, 1.7% fumed silica, and 15% resin, were used as reference material (designated AWC or SGC) for a detaching test. Following the packing of bone defects in the rat tibiae with either DTC or ITC, histological examination revealed that the DTC and ITC had both directly contacted the bone and were almost completely surrounded by bone by 16 weeks after the surgery and that no marked biodegradation had occurred at 52 weeks postimplantation. Rectangular plates (2 x 10 x 15 mm) of AWC, DTC, ITC, and SGC were implanted into the metaphysis of the tibia of male rabbits and the failure load was measured by a detaching test at 10 and 25 weeks after implantation. The failure loads of AWC, DTC, ITC, and SGC were 3.65, 2.21, 2.44, and 0.04 kgf at 10 weeks and 4.87, 2. 81, 2.82, and 0.13 kgf at 25 weeks, respectively. Observation of the bone-implant interface by scanning electron microscopy and energy dispersive X-ray microanalysis revealed that all the samples except SGC formed direct contact with the bone and that only AWC-implanted tibiae had a layer of a low calcium and phosphorus level at the bone-implant interface. Results showed that DTC and ITC have excellent osteoconductivity and bone-bonding ability under non-weight-bearing conditions.