Finite element modelling of the formation of pre-load damage in cement mantles of orthopaedic joint replacements

Finite element modeling of the formation of pre-loaded damage in cement mantles of orthopaedic joint replacements was presented. The existence of cracking suggested a high level of residual stress. The direction of maximum principal stress vectors corresponded well with the observed crack orientation. Results suggested that cracking depends upon a combination of residual stress, porosity and temperature rise during polymerization.

Modelling fatigue of bone cement

Accurate models of cement and interface fatigue are essential if computationally assessing risk of aseptic loosening of cemented joint replacements is to become clinically relevant. A series of approaches will be presented that attempt to model several aspects of bone cement fatigue relevant to predicting cemented joint replacement failure. Failure models for homogeneous (bulk) bone cement and its interface with implant and host tissue are reviewed. Variability introduced by porosity and interaction between fatigue and creep are also considered. Finally, some current and potential future developments are discussed.

Effect of Nanosilica on Rheology, Fresh Properties, and Strength of Cement-Based Grouts

The effect of colloidal nanosilica on the fresh and rheological parameters, plastic shrinkage, heat of hydration, and compressive strength of cement-based grouts is investigated in this paper. The fresh and rheological properties were evaluated by the minislump flow, Marsh cone flow time, Lombardi plate cohesion meter, yield value, and plastic viscosity. The key parameters investigated were the dosages of nanosilica and superplasticizer and temperature of mixing water. Statistical models and isoresponse curves were developed to capture the significant trends. The dosage of nanosilica had a significant effect on the results. The increase in the dosage of nanosilica led to increasing the values of flow time, plate cohesion meter, yield stress, plastic viscosity, heat of hydration at 1 day and 3 days, and compressive strength at 1 day, while reducing the minislump, plastic shrinkage up 24 h, and compressive strength at 3, 7, and 28 days. Conversely, the increase in the dosage of superplasticizer led to decreasing the values of flow time, plate cohesion meter, yield stress, plastic viscosity, heat of hydration at 1 day and 3 days, and compressive strength at 1 day, while increasing the minislump, plastic shrinkage, and compressive strength at 3 and 7 days. Increasing the temperature of mixing water led to a notable increase in the results of minislump, flow time, plastic viscosity, heat of hydration at 3 days, and compressive strength at 1 day, while it reduced the plate cohesion, compressive strength at 3, 7, and 28 days. The statistical models developed in this study can facilitate optimizing the mixture proportions of grouts for target performance by reducing the number of trial batches needed.

Conductivity/activation energy relationships for cement-based materials undergoing cyclic thermal excursions

The electrical conductivity of a range of concrete mixes, with and without supplementary cementitious materials (SCM), is studied through multiple cycles of heating and cooling over the extended temperature range −30/+70 °C. When presented in an Arrhenius format, the experimental results display hysteresis effects at the low-temperature end of the thermal cycle and, in those concretes containing supplementary cementitious materials at higher water/binder ratios, hysteresis effects were evident over the entire temperature range becoming more discernible with increasing number of thermal cycles. The depression in both the freezing and thawing point could be clearly identified and was used to estimate pore-neck and pore-cavity radii. A simplified approach is presented to evaluate the volumetric ratio of frozen pore water in terms of conductivity measurements. The results also show that the conductivity and activation energy of the concrete specimens were related to the water/binder ratio, type of SCM, physical state of the pore water and the thermal cycling regime.

Biocompatibility of Calcium Phosphate Bone Cement with Optimised Mechanical Properties

The broad aim of this work was to investigate and optimise the properties of calcium phosphate bone cements (CPCs) for use in vertebroplasty to achieve effective primary fixation of spinal fractures. The incorporation of collagen, both bovine and from a marine sponge (Chondrosia reniformis), into a CPC was investigated. The biological properties of the CPC and collagen-CPC composites were assessed in vitro through the use of human bone marrow stromal cells. Cytotoxicity, proliferation and osteoblastic differentiation were evaluated using lactate dehydrogenase, PicoGreen and alkaline phosphatase activity assays respectively. The addition of both types of collagen resulted in an increase in cytotoxicity, albeit not to a clinically relevant level. Cellular proliferation after 1, 7 and 14 days was unchanged. The osteogenic potential of the CPC was reduced through the addition of bovine collagen but remained unchanged in the case of the marine collagen. These findings, coupled with previous work showing that incorporation of marine collagen in this way can improve the physical properties of CPCs, suggest that such a composite may offer an alternative to CPCs in applications where low setting times and higher mechanical stability are important.

Provision of resin bonded bridgework for a patient with microstomia secondary to scleroderma

Scleroderma is a connective tissue disorder that can present with orofacial involvement. A 48 year-old patient presented to Cork University Dental Hospital with concerns about the appearance of her upper central incisor teeth, which had become progressively mobile in recent years. A diagnosis of localised scleroderma had been made a number of years previously by her medical practitioner and the patient reported that her scleroderma-associated microstomia had progressed significantly in recent years. Most reports of this condition advocate the use of sectional impression trays and sectional dentures to replace missing teeth. This report describes the use of resin-bonded bridgework (RBB) and discusses the possible advantages of this treatment option over those already presented in the literature.