Evaluation of the biocompatibility of a nonceramic hydroxyapatite

Biomimetic Approaches in Clinical Endodontics

In the last few decades, biomimetic concepts have been widely adopted in various biomedical fields, including clinical dentistry. Endodontics is an important sub-branch of dentistry which deals with the different conditions of pulp to prevent tooth loss. Traditionally, common procedures, namely pulp capping, root canal treatment, apexification, and apexigonesis, have been considered for the treatment of different pulp conditions using selected materials. However, clinically to regenerate dental pulp, tissue engineering has been advocated as a feasible approach. Currently, new trends are emerging in terms of regenerative endodontics which have led to the replacement of diseased and non-vital teeth into the functional and healthy dentine-pulp complex. Root- canal therapy is the standard management option when dental pulp is damaged irreversibly. This treatment modality involves soft-tissue removal and then filling that gap through the obturation technique with a synthetic material. The formation of tubular dentine and pulp-like tissue formation occurs when stem cells are transplanted into the root canal with an appropriate scaffold material. To sum up tissue engineering approach includes three components: (1) scaffold, (2) differentiation, growth, and factors, and (3) the recruitment of stem cells within the pulp or from the periapical region. The aim of this paper is to thoroughly review and discuss various pulp-regenerative approaches and materials used in regenerative endodontics which may highlight the current trends and future research prospects in this particular area.

Synergistic Effect of Toceranib and Nanohydroxyapatite as a Drug Delivery Platform-Physicochemical Properties and In Vitro Studies on Mastocytoma Cells

A new combination of Toceranib (Toc; 5-[(5Z)-(5-Fluoro-2-oxo-1,2-dihydro-3H-indol-3-ylidene)methyl]-2,4-dimethyl-N-[2-(pyrrolidin-1-yl)ethyl]-1H-pyrrole-3-carboxamide) with nanohydroxyapatite (nHAp) was proposed as an antineoplastic drug delivery system. Its physicochemical properties were determined as crystallinity, grain size, morphology, zeta potential and hydrodynamic diameter as well as Toceranib release. The crystalline nanorods of nHAp were synthesised by the co-precipitation method, while the amorphous Toceranib was obtained by its conversion from the crystalline form during nHAp–Toc preparation. The surface interaction between both compounds was confirmed using Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV–Vis) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). The nHAp–Toc showed a slower and prolonged release of Toceranib. The release behaviour was affected by hydrodynamic size, surface interaction and the medium used (pH). The effectiveness of the proposed platform was tested by comparing the cytotoxicity of the drug combined with nHAp against the drug itself. The compounds were tested on NI-1 mastocytoma cells using the Alamar blue colorimetric technique. The obtained results suggest that the proposed platform shows high efficiency (the calculated IC50 is 4.29 nM), while maintaining the specificity of the drug alone. Performed analyses confirmed that nanohydroxyapatite is a prospective drug carrier and, when Toceranib-loaded, may be an idea worth developing with further research into therapeutic application in the treatment of canine mast cell tumour.

The Antioxidant Supplementation with Filipendula ulmaria Extract Attenuates the Systemic Adverse Effects of Nanosized Calcium Phosphates in Rats

The aim of this study was to investigate and compare the systemic toxicity of three nanosized calcium phosphates (CaPs): hydroxyapatite (HA), tricalcium phosphate (TCP), and amorphous calcium phosphate (ACP) in rats. Since those metallic compounds are widely used as bone replacement materials, including their use in oral surgery, CaPs were applied (per os) equimollary (17.8 mg/kg, 11 mg/kg, and 9.65 mg/kg b.w., respectively) for 30 days in order to mimic the previously described release rate from dental composites. Also, we employed antioxidant supplementation with Filipendula ulmaria (FU) extract. All the applied CaPs significantly increased serum calcium, triglycerides, LDL, and LDH, while serum levels of testosterone and LH declined, with no alterations in the liver enzymes. The evaluation of oxidative stress markers (in the liver, kidney, and testicle) showed an increase in TBARS values, while SOD and CAT activities and GSH levels were significantly reduced. The relative gene expression of Bax and Bcl-2 was shifted to proapoptotic action, accompanied by intense characteristic histological changes in architecture in all investigated organs. The toxic effects were most prominent in groups treated by ACP. FU administration attenuated the majority of nanosized CaP-induced adverse effects, thus recommending this therapeutic approach to minimize nano-CaP systemic toxicities.

The Antioxidant Supplementation with Filipendula ulmaria Extract Attenuates the Systemic Adverse Effects of Nanosized Calcium Phosphates in Rats

The aim of this study was to investigate and compare the systemic toxicity of three nanosized calcium phosphates (CaPs): hydroxyapatite (HA), tricalcium phosphate (TCP), and amorphous calcium phosphate (ACP) in rats. Since those metallic compounds are widely used as bone replacement materials, including their use in oral surgery, CaPs were applied (per os) equimollary (17.8 mg/kg, 11 mg/kg, and 9.65 mg/kg b.w., respectively) for 30 days in order to mimic the previously described release rate from dental composites. Also, we employed antioxidant supplementation with Filipendula ulmaria (FU) extract. All the applied CaPs significantly increased serum calcium, triglycerides, LDL, and LDH, while serum levels of testosterone and LH declined, with no alterations in the liver enzymes. The evaluation of oxidative stress markers (in the liver, kidney, and testicle) showed an increase in TBARS values, while SOD and CAT activities and GSH levels were significantly reduced. The relative gene expression of Bax and Bcl-2 was shifted to proapoptotic action, accompanied by intense characteristic histological changes in architecture in all investigated organs. The toxic effects were most prominent in groups treated by ACP. FU administration attenuated the majority of nanosized CaP-induced adverse effects, thus recommending this therapeutic approach to minimize nano-CaP systemic toxicities.

Buffering capacity and antibacterial properties among bioactive glass-containing orthodontic adhesives

This study was to evaluate the acid-buffering capacity and antibacterial properties of orthodontic adhesives containing bioactive glasses (BAGs) (45S5, 45S5F, S53P4), Hydroxyapatite, beta-tricalcium phosphate, and Canasite. Fillers comprising 15 wt% bioactive glasses, HAp, β-TCP, and Canasite incorporated with 55 wt% silanated glass were added to a mixture of UDMA/TEGDMA. Acid-buffering capacity was tested by exposing disc-shaped samples of each adhesive to medium of bacteria-produced acids, and pH changes were recorded at 24 and 48 h. Antibacterial properties were assessed by indirect testing by exposing polymerized adhesive samples to a medium and direct testing by immersing the specimens in solutions containing S. mutans and S. sanguinis. A significant buffering capacity was shown by the 45S5, 45S5F and S53P4 BAG adhesives. The antibacterial properties were not significant in all experimental adhesives. Therefore, the experimental orthodontic adhesives containing BAGs demonstrated a significant buffering capacity but did not show significant antibacterial properties against S. mutans and S. sanguinis.

Zn-doping of silicate and hydroxyapatite-based cements: Dentin mechanobiology and bioactivity

The objective was to state zinc contribution in the effectiveness of novel zinc-doped dentin cements to achieve dentin remineralization, throughout a literature or narrative exploratory review. Literature search was conducted using electronic databases, such as PubMed, MEDLINE, DIMDI, Embase, Scopus and Web of Science. Both zinc-doping silicate and hydroxyapatite-based cements provoked an increase of both bioactivity and intrafibrillar mineralization of dentin. Zinc-doped hydroxyapatite-based cements (oxipatite) also induced an increase in values of dentin nano-hardness, Young's modulus and dentin resistance to deformation. From Raman analyses, it was stated higher intensity of phosphate peaks and crystallinity as markers of dentin calcification, in the presence of zinc. Zinc-based salt formations produced low microleakage and permeability values with hermetically sealed tubules at radicular dentin. Dentin treated with oxipatite attained preferred crystal grain orientation with polycrystalline lattices. Thereby, oxipatite mechanically reinforced dentin structure, by remineralization. Dentin treated with oxipatite produced immature crystallites formations, accounting for high hydroxyapatite solubility, instability and enhanced remineralizing activity.

Effects of ZnO/TiO2 nanoparticle and TiO2 nanotube additions to dense polycrystalline hydroxyapatite bioceramic from bovine bones

OBJECTIVES

A bovine dense hydroxyapatite ceramic (HA) was produced as new biomaterial, however, the production of a material with consistently high flexural strength remains challenging. The objective of this study was to evaluate the effects of ZnO nanoparticles, TiO₂ nanoparticles, and TiO₂ nanotubes (1%, 2%, and 5% by weight) on the microstructure and flexural strength of a bovine dense hydroxyapatite ceramic (HA).

METHODS

Discs (Ø=12.5mm; thickness=1.3mm) were prepared and subjected to X-ray diffraction (XRD), and observation with a field emission scanning electron microscope (FE-SEM), biaxial flexural strength (BFS) testing, and Vickers hardness (VH) testing. The BFS and VH data were subjected to ANOVA and Tukey post-hoc tests (α=0.05) and Weibull analysis.

RESULTS

The XRD showed that the addition of nanomaterials caused the formation of a secondary phase when 5% of the ZnO nanoparticles was used, or when all percentages of the TiO₂ nanoparticles/nanotubes were used, and the HA crystallographic planes were maintained. Differences were not observed between the higher BFS values obtained with pure HA and those obtained with the 5% addition of TiO₂ nanoparticles. However, the results were different compared with the other groups (α=0.05). The results obtained by Weibull analysis revealed that the 1%, 2%, and 5% addition of TiO₂ nanotubes, and the 1% and 2% addition of TiO₂ nanoparticles decreased the HA characteristic strength (σ₀), while the Weibull modulus (m) increased when 5% of TiO₂ nanoparticles, 1% and 2% of ZnO nanoparticles, and 2% of TiO₂ nanoparticles were added, but with no statistical difference from the pure HA. The 5% addition of ZnO₂ nanoparticles decreased the σ₀ without changing m. Moreover, the 5% addition of TiO₂ nanoparticles resulted in an m closest to that of pure HA. Regarding the VH results, the blend of HA with 1% and 2% addition of TiO₂ nanoparticles exhibited the higher values, which were similar between the different addition ratios (p=0.102). Moreover, the addition of 5% TiO₂ nanoparticles resulted in higher value compared with pure HA.

SIGNIFICANCE

This study demonstrated that the HA blend with 5% of TiO₂ nanoparticles has the greatest potential as a bovine HA dense bioceramic reinforcement.

Current perspectives of bio-ceramic technology in endodontics: calcium enriched mixture cement - review of its composition, properties and applications

Advancements in bio-ceramic technology has revolutionised endodontic material science by enhancing the treatment outcome for patients. This class of dental materials conciliates excellent biocompatibility with high osseoconductivity that render them ideal for endodontic care. Few recently introduced bio-ceramic materials have shown considerable clinical success over their early generations in terms of good handling characteristics. Calcium enriched mixture (CEM) cement, Endosequence sealer, and root repair materials, Biodentine and BioAggregate are the new classes of bio-ceramic materials. The aim of this literature review is to present investigations regarding properties and applications of CEM cement in endodontics. A review of the existing literature was performed by using electronic and hand searching methods for CEM cement from January 2006 to December 2013. CEM cement has a different chemical composition from that of mineral trioxide aggregate (MTA) but has similar clinical applications. It combines the biocompatibility of MTA with more efficient characteristics, such as significantly shorter setting time, good handling characteristics, no staining of tooth and effective seal against bacterial leakage.

Direct Manufacture of Hydroxyapatite Scaffolds Using Blue Laser

The study deals with the direct manufacturing of hydroxyapatite scaffolds using selective polymerization of the slurry liquid phase. The bovine hydroxyapatite has great similarity with the human bone structure, making it able for a direct connection with the bone tissues. This study aims to obtain scaffolds using a new technique of rapid prototyping, obtained by polymerization of acrylic resin (liquid phase of slurry) by ultraviolet light present in a range of the band spectrum emitted by the blue laser light. Sub-micrometer hydroxyapatite was obtained by the calcination and grinding of bovine bone in a vibratory mill. Mixtures of hydroxyapatite and resin were prototyped in three-dimensional pieces and sintered afterword and subjected to blue laser emission path directed in a CNC equipment. Grounded particles obtained in the grinding vibratory mill, with equivalent diameter of 0.35 microns, were reactive enough to compensate the low green densification bellow 50 vol%. Polymerization tests realized indicated that the incidence of the laser with fluency of 170 mW.s/mm2promoted the curing of the 0.5 mm diameter pieces in depth about 0.5 mm, which allowed the prototyping of the scaffolds with sufficient mechanical strength for handling.

Injectable foams for regenerative medicine

The design of injectable biomaterials has attracted considerable attention in recent years. Many injectable biomaterials, such as hydrogels and calcium phosphate cements (CPCs), have nanoscale pores that limit the rate of cellular migration and proliferation. While introduction of macroporosity has been suggested to increase cellular infiltration and tissue healing, many conventional methods for generating macropores often require harsh processing conditions that preclude their use in injectable foams. In recent years, processes such as porogen leaching, gas foaming, and emulsion-templating have been adapted to generate macroporosity in injectable CPCs, hydrogels, and hydrophobic polymers. While some of the more mature injectable foam technologies have been evaluated in clinical trials, there are challenges remaining to be addressed, such as the biocompatibility and ultimate fate of the sacrificial phase used to generate pores within the foam after it sets in situ. Furthermore, while implantable scaffolds can be washed extensively to remove undesirable impurities, all of the components required to synthesize injectable foams must be injected into the defect. Thus, every compound in the foam must be biocompatible and noncytotoxic at the concentrations utilized. As future research addresses these critical challenges, injectable macroporous foams are anticipated to have an increasingly significant impact on improving patient outcomes for a number of clinical procedures.

Application of calcium phosphate materials in dentistry

Calcium phosphate materials are similar to bone in composition and in having bioactive and osteoconductive properties. Calcium phosphate materials in different forms, as cements, composites, and coatings, are used in many medical and dental applications. This paper reviews the applications of these materials in dentistry. It presents a brief history, dental applications, and methods for improving their mechanical properties. Notable research is highlighted regarding (1) application of calcium phosphate into various fields in dentistry; (2) improving mechanical properties of calcium phosphate; (3) biomimetic process and functionally graded materials. This paper deals with most common types of the calcium phosphate materials such as hydroxyapatite and tricalcium phosphate which are currently used in dental and medical fields.

Integrated risk assessment of a hydroxyapatite-protein-composite for use in oral care products: a weight-of-evidence case study

Risk assessment of cosmetic ingredients represents a regulatory standard requirement in Europe and other regions. An integrated approach was designed to assess the safety of HPC, a particulate composite of hydroxyapatite and protein (gelatin) for use in oral care products, employing a weight-of-evidence assessment and considering specific physico-chemical properties and exposure conditions. An initial evaluation of the constituents suggested that their chemical nature does not represent a particular health hazard per se. Hydroxyapatite is the main component of teeth and bones in mammals; gelatin is used in food and assumed to be safe once a BSE/TSE risk has been excluded. In vitro screening tests were chosen to further evaluate the biocompatibility: Hen's egg test-chorioallantoic membrane (HET-CAM) to assess irritating effects towards mucous membranes; MTT cytotoxicity test with 3T3 fibroblasts; human corneal epithelial models to investigate inflammatory mediators and cytotoxicity; macrophage assays to measure cytotoxicity, inflammatory mediators and oxidative stress. Together with results from clinical studies, exposure estimates and analyses of kinetic properties, the presented information provides sound evidence to support the safe use of HPC. This is an example of a risk assessment for cosmetic use of small particles without the need for additional animal studies.

Calcium phosphate-based composites as injectable bone substitute materials

A major weakness of current orthopedic implant materials, for instance sintered hydroxyapatite (HA), is that they exist as a hardened form, requiring the surgeon to fit the surgical site around an implant to the desired shape. This can cause an increase in bone loss, trauma to the surrounding tissue, and longer surgical time. A convenient alternative to harden bone filling materials are injectable bone substitutes (IBS). In this article, recent progress in the development and application of calcium phosphate (CP)-based composites use as IBS is reviewed. CP materials have been used widely for bone replacement because of their similarity to the mineral component of bone. The main limitation of bulk CP materials is their brittle nature and poor mechanical properties. There is significant effort to reinforce or improve the mechanical properties and injectability of calcium phosphate cement (CPC) and this review resumes different alternatives presented in this specialized literature.

Exposure of the murine RAW 264.7 macrophage cell line to hydroxyapatite dispersions of various composition and morphology: assessment of cytotoxicity, activation and stress response

Cellular stress responses leading to the release of cytotoxic mediators are discussed as indicators of the hazard presented by particles, and in particular ultrafine particles or nanomaterials. The present study was designed to investigate effects of the following materials on RAW 264.7 macrophages: three hydroxyapatite materials of various morphologies, i.e., nano-sized with rod-like (HA-NR), plate-like (HA-NP) or needle-shaped (HA-NN) morphology, and an irregularly shaped composite of hydroxyapatite and protein (HPC) in the low micrometer range. Concentrations of 50, 100, 500, 1000 and 5000 microg/ml were applied and cells were analyzed for viability (XTT-test), cytokine production (TNF-alpha) and induction of nitric oxide (NO) after 18 and 42 h. DQ12 quartz and lipopolysaccharide (LPS) served as positive controls. Up to concentrations of 500 microg/ml, cell viability was not considerably impaired by the test samples at both timepoints. Overall, viability was about one order of magnitude higher than with comparable concentrations of quartz. TNF-alpha release was induced in all samples after 18 h, with HA-NR showing the most pronounced induction at 100 microg/ml, still clearly below the LPS signal. No or little induction was observed after 42 h. NO production was low after 18 and 42 h. The results support the conclusion that the tested materials exhibit good biocompatibility and are safe to use.

Bioactive materials in endodontics

Endodontic treatment in dentistry is a delicate procedure and many treatment attempts fail. Despite constant development of new root canal filling techniques, the clinician is confronted with both a complex root canal system and the use of filling materials that are harmful for periapical tissues. This paper evaluates reported studies on biomaterials used in endodontics, including calcium hydroxide, mineral trioxide aggregate, calcium phosphate ceramics and calcium phosphate cements. Special emphasis is made on promising new biomaterials, such as injectable bone substitute and injectable calcium phosphate cements. These materials, which combine biocompatibility, bioactivity and rheological properties, could be good alternatives in endodontics as root canal fillers. They could also be used as drug-delivery vehicles (e.g., for antibiotics and growth factors) or as scaffolds in pulp tissue engineering.

Novel low temperature setting nanocrystalline calcium phosphate cements for bone repair: osteoblast cellular response and gene expression studies

Low temperature setting calcium phosphate cements (CPC) formed from reactive calcium phosphate precursors are receiving great attention in the fields of orthopaedics and tissue engineering. The purpose of this study was to evaluate the mechanical properties and osteocompatibility of a novel calcium deficient hydroxyapatite (CDSHA) with a Ca/P ratio of 1.6 developed in our laboratories and compare it to a previously developed calcium deficient hydroxyapatite (CDHA) with a Ca/P ratio of 1.5. The results demonstrated that the calcium-deficient hydroxyapatites (HA) formed from the CPCs were similar to biological HA at physiological temperature and the elastic moduli of CDHA and CDSHA were found to be 174.42 +/- 20.41 MPa (p < 0.05) and 115.86 +/- 24.8 MPa (p < 0.05), respectively. The surface morphologies of the two calcium deficient HA's formed were identical with a micro/nano porous structure as evidenced from SEM. The cellular proliferation on CDHA, and CDSHA, was comparable to the control, tissue culture polystyrene (TCPS) (p < 0.05). Alkaline phosphatase activity was significantly elevated on CDHA and CDSHA matrices at early time points when compared with the control (TCPS) (p < 0.05). Osteoblast cells gene expression on CDHA, and CDSHA showed type I collagen, alkaline phosphatase, osteocalcin, and osteopontin activity at both 7 and 14 days of culture. Thus, novel calcium-deficient HAs, CDHA, and CDSHA formed at low temperature are promising candidates for orthopaedic applications based on their ability to promote osteoblast cell adhesion and gene expression in vitro.

Experimental study on low intensity ultrasound and tissue engineering to repair segmental bone defects

In order to evaluate the efficacy of low intensity ultrasound and tissue engineering technique to repair segmental bone defects, the rabbit models of 1.5-cm long rabbit radial segmental osteoperiosteum defects were established and randomly divided into 2 groups. All defects were implanted with the composite of calcium phosphate cement and bone mesenchymal stem cells, and additionally those in experimental group were subjected to low intensity ultrasound exposure, while those in control group to sham exposure. The animals were killed on the postoperative week 4, 8 and 12 respectively, and specimens were harvested. By using radiography and the methods of biomechanics, histomorphology and bone density detection, new bone formation and material degradation were observed. The results showed that with the prolongation of time after operation, serum alkaline phosphatase (AKP) levels in both groups were gradually increased, especially in experimental group, reached the peak at 6th week (experimental group: 1.26 mmol/L; control group: 0.58 mmol/L), suggesting the new bone formation in both two group, but the amount of new bone formation was greater and bone repairing capacity stronger in experimental group than in control group. On the 4th week in experimental group, chondrocytes differentiated into woven bone, and on the 12th week, remodeling of new lamellar bone and absorption of the composite material were observed. The mechanical strength of composite material and new born density in experimental group were significantly higher than in control group, indicating that low intensity ultrasound could not only effectively increase the formation of new bone, but also accelerate the calcification of new bone. It was concluded that low intensity ultrasound could evidently accelerate the healing of bone defects repaired by bone tissue engineering.

Endoscopic Subureteral Urocol Injection for the Treatment of Vesicoureteral Reflux

PURPOSE

We evaluated the effect of Urocol injection for the endoscopic treatment of VUR in children.

MATERIALS AND METHODS

A total of 208 children (62 boys and 146 girls, mean age 4.78 years) with 346 refluxing ureters underwent subureteral injection of Urocol between January 2000 and February 2002. VCUG was performed at 6 months, and ultrasound was performed at 1 week and 3 months postoperatively.

RESULTS

Followup VCUG showed no evidence of reflux in 240 ureters (69%), significant decrease in reflux grade in 62 (18%) and no change in 44 (13%). Ultrasound revealed no obstruction or hydronephrosis.

CONCLUSIONS

The results of this study demonstrate that subureteral injection of Urocol was effective for the treatment of VUR. We conclude that Urocol represents a new, safe, simple, less expensive and repeatable technique in treating VUR.

Calcium phosphate cement reinforced by polypeptide copolymers

Water-based calcium phosphate with bone repairing capability was reinforced by polypeptide graft copolymers and micelles that were formed by polypeptide copolymers. The mechanical studies showed that the compression strength and fracture energy of the calcium phosphate cement (CPC)/polypeptide composites are appreciably higher than those of CPC. The molecular structure of the polypeptide graft copolymers and the association form of the polypeptide copolymers exhibit a marked effect on the mechanical properties of CPC/polypeptide composites. The polypeptide copolymers with more hydrophilic side chains and with core-shell micelle forms have more effective reinforcement effect. The morphological studies based on the scanning electron microscope (SEM) observations revealed that both polypeptide graft copolymers and polypeptide copolymer micelles are well dispersed in CPC matrix. According to the obtained experimental results, reinforcement mechanism was suggested.

The physicochemical properties of the solidification of calcium phosphate cement

In this article, the physicochemical properties of the solidification of calcium phosphate cement (CPC) were investigated, and the components of the solidified body and the characteristics involved in the application were measured. The setting process of CPC was moderate and slightly exothermic, the heat liberation rate was slow, and the temperature increased little. At the initial stage of the hydration, the compressive strength rose linearly with time, and reached the maximum value after 4 hours. The volume was slightly shrunken by 1% during the setting process, and the total heavy metal content was below 2 ppm. The porosity of the solidified body was about 30%, which was mainly the gel pore with size below 0.1 microm. The final product of hydration was low crystalline hydroxyapatite (HAP). Its real density was 2.859 g/cm(3), which was lower than the theoretical value. This may be due to the existence of lattice defects, which will lead to a slight rise in solubility when leached in physiological saline.

Polymer--calcium phosphate cement composites for bone substitutes

The use of self-setting calcium phosphate cements (CPCs) as bioresorbable bone-replacement implant materials presently is limited to non-load-bearing applications because of their low compressive strength relative to natural bone. The present study investigated the possibility of strengthening a commercially available CPC, alpha-BSM, by incorporating various water-soluble polymers into the cement paste during setting. Several polyelectrolytes, poly(ethylene oxide), and the protein bovine serum albumin (BSA) were added in solution to the cement paste to create calcium phosphate-polymer composites. Composites formulated with the polycations poly(ethylenimine) and poly(allylamine hydrochloride) exhibited compressive strengths up to six times greater than that of pure alpha-BSM material, with a maximum value reached at intermediate polymer content and for the highest molecular weight studied. Composites containing BSA developed compressive strengths twice that of the original cement at protein concentrations of 13-25% by weight. In each case, XRD studies correlate the improvement in compressive strength with reduced crystallite dimensions, as evidenced by a broadening of the (0,0,2) reflection. This suggests that polycation or BSA adsorption inhibits crystal growth and possibly leads to a larger crystal aspect ratio. SEM results indicate a denser, more interdigitated microstructure. The increased strength was attributed to the polymer's capacity to bridge between multiple crystallites (thus forming a more cohesive composite) and to absorb energy through plastic flow.

Comparison of the biomechanics of hydroxyapatite and polymethylmethacrylate vertebroplasty in a cadaveric spinal compression fracture model

OBJECT

Polymethylmethacrylate (PMMA) has long been used in the stabilization and reconstruction of traumatic and pathological fractures of the spine. Recently, hydroxyapatite (HA), an osteoconductive, biocompatible cement, has been used as an alternative to PMMA. In this study the authors compare the stabilizing effects of the HA product, BoneSource, with PMMA in an experimental compression fracture of L-1.

METHODS

Twenty T9-L3 cadaveric spine specimens were mounted individually on a testing frame. Light-emitting diodes were placed on the neural arches as well as the base. Motion was tracked by two video cameras in response to applied loads of 0 to 6 Nm. The weight-drop technique was used to induce a reproducible compression fracture of T-11 after partially coring out the vertebra. Load testing was performed on the intact spine. postfracture, after unilateral transpedicular vertebroplasty with 7 to 10 ml of PMMA or HA, and after flexion-extension fatiguing to 5000 cycles at +/- 3 Nm. No significant difference between the HA- and PMMA cemented-fixated spines was demonstrated in flexion, extension, left lateral bending, or right and left axial rotation. The only difference between the two cements was encountered before and after fatiguing in right lateral bending (p < or = 0.05).

CONCLUSIONS

The results of this study suggest that the same angular rigidity can be achieved using either HA or PMMA. This is of particular interest because HA is osteoconductive, undergoes remodeling, and is not exothermic.

Biocompatibility of root canal filling materials

Results of in vitro and in vivo studies clearly indicate that some endodontic sealers may cause local and systemic adverse effects. Though occasionally contradictory data has been reported from various authors, it may be concluded that zinc-oxide-eugenol sealers possess a marked cytotoxic and tissue-irritating potency. Most Ca(OH)2-based materials, however, were biocompatible. Genotoxic effects have been observed with sealers releasing paraformaldehyde or containing mutagenic substances, such as bisphenol-A-diglycidyl-ether or its derivatives. It cannot be excluded that these materials may pose a systemic risk because formaldehyde is rapidly distributed systemically following its application into the pulp cavity. Furthermore an increasing number of cases with an aspergillosis of the maxillary sinus have been observed which were mainly caused by zinc-releasing endodontic sealers. Overall, it is recommended that for endodontic practice, sealers that have been found to be biocompatible in a "mixed bag" of various in vitro and in vivo tests, be selected. From this point of view, ZnOE-sealers should no longer be used for root canal fillings. This recommendation applies also to sealers containing paraformaldehyde or generating this substance during their setting reaction. More experimental and clinical studies are necessary to elucidate whether new materials, such as mineral trioxide aggregate (MTA) or calcium phosphate cement, will be biocompatible alternatives in the future.

Dental materials: 1997 literature review

This review of the published literature on dental materials for the year 1997 has been compiled by the Dental Materials Panel of UK. It continues a series of annual reviews started in 1973. Emphasis has been placed upon publications, which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, dentine bonding, dental amalgam, endodontic materials, casting alloys, ceramometallic restorations and resin-bonded bridges, ceramics, denture base resins and soft lining materials, impression materials, dental implant materials, orthodontic materials, biomechanics and image processing, resin composites, and casting investment materials and waxes). Three hundred and thirty three articles have been reviewed.