Bone cements and their potential use in a mandibular endoprosthesis

Biological and mechanical performance of calcium phosphate cements modified with phytic acid

Calcium phosphate cements, primarily brushite cements, require the addition of setting retarders to ensure adequate processing time and processability. So far, citric acid has been the primary setting retarder used in this context. Due to the poor biocompatibility, it is crucial to explore alternative options for better processing. In recent years, the setting retarder phytic acid (IP6) has been increasingly investigated. This study investigates the biological behaviour of calcium phosphate cements with varying concentrations of IP6, in addition to their physical properties. Therefore cytocompatibility in vitro testing was performed using osteoblastic (MG-63) and osteoclastic (RAW 264.7 differentiated with RANKL) cells. We could demonstrate that the physical properties like the compressive strength of specimens formed with IP6 (brushite_IP6_5 = 11.2 MPa) were improved compared to the reference (brushite = 9.8 MPa). In osteoblast and osteoclast assays, IP6 exhibited significantly better cytocompatibility in terms of cell activity and cell number for brushite cements up to 11 times compared to the brushite reference. In contrast, the calcium-deficient hydroxyapatite (CDHA) cements produced similar results for IP6 (CDHA_IP6_0.25 = 27.0 MPa) when compared to their reference (CDHA = 21.2 MPa). Interestingly, lower doses of IP6 were found to be more effective than higher doses with up to 3 times higher. Additionally, IP6 significantly increased degradation in both passive and active resorption. For these reasons, IP6 is emerging as a strong new competitor to established setting retarders such as citric acid. These cements have potential applications in bone augmentation, the stabilisation of non-load bearing fractures (craniofacial), or the cementation of metal implants.

Digital light 4D printing of bioresorbable shape memory elastomers for personalized biomedical implantation

Four-dimensional (4D) printing unlocks new potentials for personalized biomedical implantation, but still with hurdles of lacking suitable materials. Herein, we demonstrate a bioresorbable shape memory elastomer (SME) with high elasticity at both below and above its phase transition temperature (Ttrans). This SME can be digital light 3D printed by co-polymerizing glycerol dodecanoate acrylate prepolymer (pre-PGDA) with acrylic acid monomer to form crosslinked Poly(glycerol dodecanoate acrylate) (PGDA)-Polyacrylic acid (PAA), or PGDA-PAA network. The printed complex, free-standing 3D structures with high-resolution features exhibit shape programming properties at a physiological temperature. By tuning the pre-PGDA weight ratios between 55 wt% and 70 wt%, Ttrans varies between 39.2 and 47.2 ℃ while Young's moduli (E) range 40-170 MPa below Ttrans with fractural strain (εf) of 170 %-200 %. Above Ttrans, E drops to 1-1.82 MPa which is close to those of soft tissue. Strikingly, εf of 130-180 % is still maintained. In vitro biocompatibility test on the material shows > 90 % cell proliferation and great cell attachment. In vivo vascular grafting trials underline the geometrical and mechanical adaptability of these 4D printed constructs in regenerating the aorta tissue. Biodegradation of the implants shows the possibility of their full replacement by natural tissue over time. To highlight its potential for personalized medicine, a patient-specific left atrial appendage (LAA) occluder was printed and implanted endovascularly into an in vitro heart model. STATEMENT OF SIGNIFICANCE: 4D printed shape-memory elastomer (SME) implants particularly designed and manufactured for a patient are greatly sought-after in minimally invasive surgery (MIS). Traditional shape-memory polymers used in these implants often suffer from issues like unsuitable transition temperatures, poor biocompatibility, limited 3D design complexity, and low toughness, making them unsuitable for MIS. Our new SME, with an adjustable transition temperature and enhanced toughness, is both biocompatible and naturally degradable, particularly in cardiovascular contexts. This allows implants, like biomedical scaffolds, to be programmed at room temperature and then adapt to the body's physiological conditions post-implantation. Our studies, including in vivo vascular grafts and in vitro device implantation, highlight the SME's effectiveness in aortic tissue regeneration and its promising applications in MIS.

Advances in reparative materials for infectious bone defects and their applications in maxillofacial regions

Infectious bone defects are characterized by the partial loss or destruction of bone tissue resulting from bacterial contaminations subsequent to diseases or external injuries. Traditional bone transplantation and clinical methods are insufficient in meeting the treatment demands for such diseases. As a result, researchers have increasingly focused on the development of more sophisticated biomaterials for improved therapeutic outcomes in recent years. This review endeavors to investigate specific reparative materials utilized for the treatment of infectious bone defects, particularly those present in the maxillofacial region, with a focus on biomaterials capable of releasing therapeutic substances, functional contact biomaterials, and novel physical therapy materials. These biomaterials operate via heightened antibacterial or osteogenic properties in order to eliminate bacteria and/or stimulate bone cells regeneration in the defect, ultimately fostering the reconstitution of maxillofacial bone tissue. Based upon some successful applications of new concept materials in bone repair of other parts, we also explore their future prospects and potential uses in maxillofacial bone repair later in this review. We highlight that the exploration of advanced biomaterials holds promise in establishing a solid foundation for the development of more biocompatible, effective, and personalized treatments for reconstructing infectious maxillofacial defects.

The Use of 3D Technology in the Management of Residual Asymmetry following Orthognathic Surgery: A Case Report

The purpose of this case report was to present the aesthetic result of the reconstruction of facial residual asymmetry after orthognathic surgery using a patient-specific three-dimensional (3D) mold and a custom-made polymethyl methacrylate implant. Through computer-aided design (CAD), the healthy contralateral side of the mandible was superimposed onto the side with the defect. Exocad Gallway (exocad GmbH, Darmstadt, Germany) was used to design the patient-specific implants (PSIs) of the right mandibular angle. Next, the implant mold was created using the Meshmixer software (Version 3.5, Autodesk Inc., San Rafael, CA, USA) and fabricated using additive manufacturing. During the surgical procedure, the patient-specific implant (PSI) was cast inside the resin mold using Simplex P bone cement (Stryker, Mahwah, NJ, USA). The implant was fixed using three screws. Combining both indirect (involving the dental laboratory) and direct (with surgical intervention) approaches, this innovative hybrid method, which incorporates both computer-aided design and additive manufacturing (AM), not only enhanced facial aesthetics, functional rehabilitation, and patient quality of life but also mitigated the potential risks linked to conventional grafting methods.

An experimental study on the impact of prosthesis temperature on the biomechanical properties of bone cement fixation

PURPOSE

To investigate the effect of the femoral component and tibial plateau component temperature on the strength of cement fixation during total knee arthroplasty (TKA).

METHODS

Femoral prosthesis, tibial plateau prosthesis, and polypropylene mold base were used to simulate TKA for bone cement fixation. Pre-cooling or pre-warming of femoral and tibial plateau components at different temperatures (4 °C, 15 °C, 25 °C, 37 °C, 45 °C), followed by mixing and stirring of bone cement at laboratory room temperature (22 °C), were performed during research. The prosthesis and the base adhered together, and the bone cement was solidified for 24 h at a constant temperature of 37 °C to verify the hardness of the bone cement with a push-out test.

RESULTS

The push-out force of the femoral prosthesis after fixation was higher than that of the tibial plateau prosthesis, and with the increase of the prosthesis temperature, the push-out force after fixation of the bone cement also increased linearly and the porosity of the prosthetic cement in the tibia and femur decreased as the temperature increased.

CONCLUSION

Without changing the mixing temperature and solidification temperature, the fixation strength of the femoral prosthesis is higher than that of the tibial plateau prosthesis. Properly increasing the temperature of the prosthesis can increase the push-out force of the fixation strength.

Fabrication and characterization of a bioactive polymethylmethacrylate-based porous cement loaded with strontium/calcium apatite nanoparticles

Polymethylmethacrylate (PMMA)-based cements are used for bone reparation due to their biocompatibility, suitable mechanical properties, and mouldability. However, these materials suffer from high exothermic polymerization and poor bioactivity, which can cause the formation of fibrous tissue around the implant and aseptic loosening. Herein, we tackled these problems by adding Sr²⁺ -substituted hydroxyapatite nanoparticles (NPs) and a porogenic compound to the formulations, thus creating a microenvironment suitable for the proliferation of osteoblasts. The NPs resembled the structure of the bone's apatite and enabled the controlled release of Sr²⁺ . Trends in the X-ray patterns and infrared spectra confirmed that Sr²⁺ replaced Ca²⁺ in the whole composition range of the NPs. The inclusion of an effervescent additive reduced the polymerization temperature and lead to the formation of highly porous cement exhibiting mechanical properties comparable to the trabecular bone. The formation of an opened and interconnected matrix allowed osteoblasts to penetrate the cement structure. Most importantly, the gas formation confined the NPs at the surface of the pores, guaranteeing the controlled delivery of Sr²⁺ within a concentration sufficient to maintain osteoblast viability. Additionally, the cement was able to form apatite when immersed into simulated body fluids, further increasing its bioactivity. Therefore, we offer a formulation of PMMA cement with improved in vitro performance supported by enhanced bioactivity, increased osteoblast viability and deposition of mineralized matrix assigned to the loading with Sr²⁺ -substituted hydroxyapatite NPs and the creation of an interconnected porous structure. Altogether, our results hold promise for enhanced bone reparation guided by PMMA cements.

Avian Skull Orthopedics

Because the avian skull is the reflection of the wide biodiversity of birds, many anatomic, morphologic, and functional variations are encountered. The main objectives of this article are to review the surgical considerations associated with the functional anatomy of the avian jaw apparatus and its variation among species, and to describe the general medical and surgical management of head traumatic and developmental disorders in birds.

Bone Response to Porous Poly(methyl methacrylate) Cement Loaded with Hydroxyapatite Particles in a Rabbit Mandibular Model

The aim of the current study was to evaluate bone formation and tissue response to porous poly(methyl methacrylate) (PMMA) cement with or without hydroxyapatite (HA) in a rabbit mandibular model. Therefore, 14 New Zealand White rabbits were randomly divided into two groups of seven according to the designed study end points of 4 and 12 weeks. For each rabbit, two decorticated defects (6 mm in height and 10 mm in width for each) were prepared at both sides of the mandible. Subsequently, the defects were filled with, respectively, porous PMMA and porous PMMA-HA cement. After reaching the designated implantation period, the rabbits were euthanized and the mandibles were retrieved for histological analysis. Results showed that both porous PMMA and porous PMMA-HA supported bone repair. Neither of the bone cements caused significant inflammation to nerve or other surrounding tissues. After implantation of 12 weeks, majority of the porosity was filled with newly formed bone for both cements, which supports the concept that a porous structure within PMMA can enhance bone ingrowth. Histomorphometrical evaluation, using histological grading scales, demonstrated that, at both implantation times, the presence of HA in the PMMA enhanced bone formation. Bone was always in direct contact with the HA particles, while intervening fibrous tissue was present at the PMMA-bone interface. On the basis of results, it was concluded that injectable porous PMMA-HA cement might be a good candidate for craniofacial bone repair, which should be further evaluated in a more clinically relevant large animal model.

Synthesis and characterization of an injectable and self-curing poly(methyl methacrylate) cement functionalized with a biomimetic chitosan–poly(vinyl alcohol)/nano-sized hydroxyapatite/silver hydrogel

Preparation and characterizations of injectable p-PMMA/CS–PVA/Nano-HA/Ag⁺ cements.

Osseous vitality in single photon emission computed tomography/computed tomography (SPECT/CT) after balloon tibioplasty of the tibial plateau: a case series

Background

The minimally invasive, balloon-assisted reduction and cement-augmented internal fixation of the tibial plateau is an innovative surgical procedure for tibial plateau fractures. The close proximity of balloons and cement to the knee joint poses a potential risk for osteonecrosis; especially in the case of thin bone lamellae. However, there are no studies about the vitality of the cement-surrounding tissue after these tibioplasties. Therefore, our goal was to assess the osseous vitality after cement-augmented balloon tibioplasty using single photon emission computed tomography/computed tomography (SPECT/CT) in a series of patients.

Methods

This case series evaluated available consecutive patients, whose tibial plateau fractures were treated with balloon-assisted, cement-augmented tibioplasty and received a SPECT/CT. Primary outcome variables were osseous vitality on SPECT/CTs according to the semiquantitative tracer activity analysis. The mean uptake of eight tibial regions of interest was referenced to the mean uptake count on the same region of the contralateral leg to obtain a count ratio. Osteonecrosis was defined as a photopenic area or cold defect. Secondary variables included clinical and radiological follow-up data. Statistics were carried out in a descriptive pattern.

Results

Ten patients with a mean age of 59 years and a mean follow up of 18 months were included. Calcium phosphate (CaP) substitute bone cement was used in 60 % and polymethyl methacrylate mixed with hydroxyapatite (PMMA/HA) bone cement in 40 %. Normal to high SPECT/CT activity without photopenic areas were observed in all patients and the mean tracer activity ratio was four, indicating vital bone in all patients. There were no postoperative infections and only one 57 year old patient with hemineglect and CaP cement showed failed osseous consolidation. The mean Tegner and Lysholm as well as the Lysholm scores were three and 80, respectively.

Conclusions

This novel study about cement-augmented balloon tibioplasties showed that osseous vitality remains intact according to SPECT/CT analysis; irrespective of the type of cement and even in the presence of thin bone lamellae. This procedure was safe and well-suited for lateral tibial plateau fractures in particular. Surgeons may consider using PMMA/HA bone cement for void filling in elderly fracture patients without concern about bone viability.

Beneficial effects of biomimetic nano-sized hydroxyapatite/antibiotic gentamicin enriched chitosan–glycerophosphate hydrogel on the performance of injectable polymethylmethacrylate

Preparation and characterization and injectable p-PMMA/CS-GP/nano-HA/GM cements.

Development of calcium phosphate/sulfate biphasic cement for vital pulp therapy

OBJECTIVES

Bioactive calcium phosphate cement (CPC) has been used widely to repair bone defects because of its excellent biocompatibility and bioactivity. However, the poor handling properties, low initial mechanical strength, and long setting time of CPC limit its application in vital pulp therapy (VPT). The aim of this study was to synthesize biphasic calcium phosphate/sulfate cements and evaluate the feasibility of applying these cements in VPT.

METHODS

The physical, chemical, and mechanical properties of CPC were improved by mixing the cement with various amounts of α-calcium sulfate hemihydrate (CSH). The hydration products and crystalline phases of the materials were characterized using scanning electron microscopy and X-ray diffraction analysis. In addition, the physical properties, such as the setting time, compressive strength, viscosity, and pH were determined. Water-soluble tetrazolium salt-1 and lactase dehydrogenase were used to evaluate cell viability and cytotoxicity.

RESULTS

The developed CPC (CPC/CSH cement), which contains 50wt% CSH cement, exhibited no obvious temperature increase or pH change during setting when it was used as a paste. The initial setting time of the CPC/CSH biphasic cement was substantially shorter than that of CPC, and the initial mechanical strength was 23.7±5.6MPa. The CPC/CSH cement exhibited higher viscosity than CPC and, thus, featured acceptable handling properties. X-ray diffraction analysis revealed that the relative peak intensity for hydroxyapatite increased, and the intensity for calcium sulfate dehydrate decreased as the amount of CPC was increased. The cell viability and cytotoxicity test results indicated that the CPC/CSH cement did not harm dental pulp cells.

SIGNIFICANCE

The developed CPC/CSH biphasic cement exhibits substantial potential for application in VPT.

Enhanced dentin-like mineralized tissue formation by AdShh-transfected human dental pulp cells and porous calcium phosphate cement

The aim of the present study was to investigate the effect of Sonic hedgehog (Shh) on human dental pulp cells (hDPCs) and the potential of complexes with Shh gene modified hDPCs and porous calcium phosphate cement (CPC) for mineralized tissue formation. hDPCs were cultured and transfected with adenoviral mediated human Shh gene (AdShh). Overexpression of Shh and cell proliferation was tested by real-time PCR analysis, western blotting analysis, and MTT analysis, respectively. The odontoblastic differentiation was assessed by alkaline phosphatase (ALP) activity and real-time PCR analysis on markers of Patched-1 (Ptc-1), Smoothened (Smo), Gli 1, Gli 2, Gli 3, osteocalcin (OCN), dentin matrix protein-1 (DMP-1), and dentin sialophosphoprotein (DSPP). Finally, AdShh-transfected hDPCs were combined with porous CPC and placed subcutaneously in nude mice for 8 and 12 weeks, while AdEGFP-transfected and untransfected hDPCs were treated as control groups. Results indicated that Shh could promote proliferation and odontoblastic differentiation of hDPCs, while Shh/Gli 1 signaling pathway played a key role in this process. Importantly, more mineralized tissue formation was observed in combination with AdShh transfected hDPCs and porous CPC, moreover, the mineralized tissue exhibited dentin-like features such as structures similar to dentin-pulp complex and the positive staining for DSPP protein similar to the tooth tissue. These results suggested that the constructs with AdShh-transfected hDPCs and porous CPC might be a better alternative for dental tissue regeneration.

Biocompatibility and bone formation with porous modified PMMA in normal and irradiated mandibular tissue

A cemented mandibular endoprosthesis is a potentially viable option for mandibular reconstruction after ablative surgery. The commonly used PMMA cement has the inherent weakness of a lack of bioactivity. Improvement by the addition of porosities and bioactive compounds like calcium phosphates may resolve this issue.

OBJECTIVE

The objective of this study was to assess the bone and tissue response to two modified PMMA cements with post-operative radiation as an additional influencing factor.

MATERIALS & METHODS

An in vivo animal study was performed using a mandibular rabbit model. A porous PMMA cement (A) and a porous cement incorporated with Beta-tricalcium phosphate particles (b-TCP) (B) were placed in bilateral mandibular defects with exposed roots and mandibular nerve of 20 animals. Half of the animals underwent additional post-operative radiation.

RESULTS

The animals were healthy with only a minor complication in one rabbit. Temperature analysis showed no significant risk of thermal necrosis with the maximal in vivo cement temperature at 37.8°C. Histology demonstrated: (1) good bone ingrowth around the defect as well as within the pores of the cement and defect bridging was achieved in 70% of the specimens after 12-15 weeks of implantation, (2) no pulpal injury with minor secondary cementum response, (3) an intact mandibular nerve with no inflammation, (4) extensive degradation and resorption of the b-TCP particles by 12-15 weeks, and (5) presence of an intervening thin fibrous tissue at the bone-to-cement interface. Histomorphometrical analysis revealed that there was no difference between the different cements and the presence or absence of post-operative radiation. The 12-15 weeks specimens showed significantly more bone ingrowth and bone maturity than the 4-7 weeks specimens.

CONCLUSION

Both modified PMMA cements have good biocompatibility, bioactivity and support bone ingrowth and additional post-operative radiation did not show any negative effects.

Evaluation of soft tissue coverage over porous polymethylmethacrylate space maintainers within nonhealing alveolar bone defects

Current treatment of traumatic craniofacial injuries often involves early free tissue transfer, even if the recipient site is contaminated or lacks soft tissue coverage. There are no current tissue engineering strategies to definitively regenerate tissues in such an environment at an early time point. For a tissue engineering approach to be employed in the treatment of such injuries, a two-stage approach could potentially be used. The present study describes methods for fabrication, characterization, and processing of porous polymethylmethacrylate (PMMA) space maintainers for temporary retention of space in bony craniofacial defects. Carboxymethylcellulose hydrogels were used as a porogen. Implants with controlled porosity and pore interconnectivity were fabricated by varying the ratio of hydrogel:polymer and the amount of carboxymethylcellulose within the hydrogel. The in vivo tissue response to the implants was observed by implanting solid, low-porosity, and high-porosity implants (n = 6) within a nonhealing rabbit mandibular defect that included an oral mucosal defect to allow open communication between the oral cavity and the mandibular defect. Oral mucosal wound healing was observed after 12 weeks and was complete in 3/6 defects filled with solid PMMA implants and 5/6 defects filled with either a low- or high-porosity PMMA implant. The tissue response around and within the pores of the two formulations of porous implants tested in vivo was characterized, with the low-porosity implants surrounded by a minimal but well-formed fibrous capsule in contrast to the high-porosity implants, which were surrounded and invaded by almost exclusively inflammatory tissue. On the basis of these results, PMMA implants with limited porosity hold promise for temporary implantation and space maintenance within clean/contaminated bone defects.

Effect of calcium phosphate cements on growth and odontoblastic differentiation in human dental pulp cells

OBJECTIVE

Calcium phosphate cements (CPCs) are an interesting class of bone substitute materials. However, the biological effects of CPCs have not been well studied in human dental pulp cells (HDPCs). The purpose of this study was to investigate the effects of CPCs on the mechanical properties, growth, and odontoblastic differentiation in HDPCs compared with Portland cement (PC) and mineral trioxide aggregate (MTA).

METHODS

Experimental CPCs either containing chitosan (Ch-CPC) or without chitosan (CPC) were composed from the alpha-tricalcium phosphate powder. Setting time, compressive strength measurements, cell growth, alkaline phosphatase (ALP) activity, the levels of messenger RNA for differentiation-related genes, and mineralization of the HDPCs on various cements were assessed.

RESULTS

The setting time for CPC-Ch was 7.5 minutes, which was significantly less than the 8.6 minutes for the CPC. On the seventh day of immersion, the compressive strength of CPC-CH reached 13.1 MPa, which was higher than 10.8 MPa of CPC. CPC and Ch-CPC-treated cells showed decreased cell proliferation but increased the levels of ALP activity, enhanced mineralized nodule formation, and upregulated odontoblastic markers messenger RNA including osteonectin, osteopontin, bone sialoprotein, dentin matrix protein-1, matrix extracellular phosphoglycoprotein, and dentin sialophosphoprotein (DSPP), compared with untreated control. The response of CPC and CP-CPC were similar to that of PC and MTA. However, the adhesion, growth, and differentiation in Ch-CPC-treated cells were similar to that in the CPC.

CONCLUSION

CPC may be useful for pulp-capping applications based on its abilities to promote HDPC differentiation.