Cavitation-resistant intergranular precipitates enhance creep performance of θ'-strengthened Al-Cu based alloys.

Tensile and compressive creep properties of a quaternary Al-Cu-Mn-Zr (ACMZ) alloy and its commercial counterpart (Al-Cu-Mn-Zr with Ni, Co and Sb additions, RR350) are investigated at 300° C. At low stresses up to 30 MPa where diffusional creep dominates, creep resistance is the same in tension and compression and RR350 deforms more slowly than ACMZ, consistent with RR350 alloy's larger linear fraction of intergranular precipitates (Al7 Cu2 (NiFe) and Al9 FeNi for RR350 vs. θ-Al2 Cu for ACMZ) and a reduced fraction of precipitate-free zones near grain boundaries. At stresses between 30 and 80 MPa, dislocation creep with a stress exponent n ~ 3 becomes rate-limiting in compression, which is expected to be controlled by θ'precipitates within the grain bulk. By contrast, in tension, enhanced creep rate and higher apparent stress exponents are measured, consistent with cavitation at intergranular precipitates becoming increasingly dominant as the stress increases. In the dislocation creep regime, RR350 alloy is again more creep resistant than ACMZ alloy, which is related to three mechanisms (i) a reduced fraction of softer precipitate-free zones, (ii) more effective load transfer to intergranular precipitates, and (iii) reduced cavitation. A model for cavitation is applied to calculate tensile creep rates from compressive creep rates and the model successfully predicts the improved tensile creep resistance of the RR350 alloy. The present investigation underscores the importance of intergranular grain boundary precipitates, in addition to strengthening θ' precipitates, in enhancing the creep resistance of Al-Cu alloys.

Enhanced biomechanical performance of additively manufactured Ti-6Al-4V bone plates.

As the global trauma fixation devices market expands rapidly, it is imperative to improve the production of fixation devices through enhanced design accuracy and fit for best performance and maximum patient comfort. Selective laser melting (SLM) is one of the mature additive manufacturing methods, which provides a viable route for the rapid production of such devices. In this work, the ability of SLM to produce near-net-shape parts, as desired for medical implants, was utilized for the fabrication of bone plates from Ti-6Al-4V alloy powder. Martensitic microstructure obtained after the printing of alloy resulted in poor ductility, limiting its application in the field of orthopedics. A specially designed repeated cyclic heating and cooling close to but below the ß-transus was used to transform from acicular to a bimodal microstructure without the need for plastic deformation prior to heat treatment for improving the ductility. Bone plates subjected to this heat treatment were mechanically tested by means of tensile and 3-point bend tests and demonstrated large improvement in ductility, and the values were comparable to those similar plates prepared from wrought alloy. Other important properties required for implants were assessed, such as corrosion resistance in simulated body fluid and cytocompatibility in vitro using MC3T3-E1 cells. These results for the bone plate after heat treatment were excellent and similar to those of the additively manufactured and wrought plates. Taken together, the performance of the additively manufactured bone plates after subjecting to heat treatment was similar to those of bone plate manufactured using wrought alloy. These results have important implications for the fabrication of patient-specific metallic orthopedic devices using SLM without compromising their biomechanical performance by subjecting them to a tailored heat treatment.

Role of aging induced α precipitation on the mechanical and tribocorrosive performance of a ß Ti-Nb-Ta-O orthopedic alloy.

A low modulus ß Ti-Nb-Ta-O alloy was subjected to heat treatment to investigate its phase stability upon aging. The resultant effect on the mechanical and functional properties was systematically evaluated. The aging of the ß-only microstructure, obtained by solutionizing and quenching, resulted in the formation of ultrafine α-precipitates with increasing order of size as the aging temperature increased from 400 °C to 600 °C. The variation in the size of α-precipitates effected the mechanical properties at the three different aging temperature. The highest hardening observed at 400 °C was associated with macroscopic embrittlement, whereas age softening was observed in samples aged at 600 °C due to coarsening of precipitates and softening of the ß-matrix. In contrast, aging at 500 °C resulted in about 32% increase in tensile strength from the ß-solutionized condition. As the samples aged at 500 °C showed optimum combination of mechanical properties among the aged samples, these were further characterized for their electrochemical, tribological and biological responses. The fretting wear studies showed that the wear rate of the solution-treated samples increased after aging due to the higher corrosion rate leading to a higher rate of tribocorrosive dissolution and formation of a transfer layer harder than that of solution treated sample. The Ti-Nb-Ta-O alloy supported the attachment and proliferation of osteoblasts similar to that on commercially pure Ti. Taken together, this work provides new insights into the preparation of next-generation Ti alloys for biomedical applications with high strength and low modulus through microstructural control induced by heat treatment.

Odontogenic myxoma: A causality dilemma - Report of a nonpareil case and review of literature.

Odontogenic myxoma is a benign locally aggressive neoplasm with a sparse prevalence and incertitude histogenesis. They constitute 3%-6% of odontogenic tumors in gnathic bones. It is ubiquitously seen between vicenarian to early quadragenarian group with female proclivity and fondness to the mandibular jaws. They are silent lesions clinically and show myxoid stroma amidst fibrous background. This report highlights central odontogenic myxoma in a 43-year-old male patient and focuses on concepts, differential diagnosis, molecular concepts and treatment aspect.

Surface Severe Plastic Deformation of an Orthopedic Ti-Nb-Sn Alloy Induces Unusual Precipitate Remodeling and Supports Stem Cell Osteogenesis through Akt Signaling.

This work presents a strategy to augment the bioactivity of a new-generation metastable ß-Ti-Nb-Sn alloy through surface severe plastic deformation. Foremost, the alloy was strengthened by precipitation of α phase using a well-designed thermo-mechanical processing route. Subsequently, the surface of the aged alloy was subjected to severe plastic deformation via surface mechanical attrition treatment (SMAT). Upon SMAT, a unique phenomenon of strain-induced precipitate coarsening was observed. A possible mechanism is proposed wherein the precipitates first dissolve due to significant slip transfer across the α/ß-interface followed by reprecipitation along the other precipitates thereby leading to coarsening. Coarsening of the precipitates abrogated the strengthening caused by plastic deformation as a result of which the hardness did not increase significantly after SMAT in sharp contrast to other alloys. SMAT led to a decrease in the attachment of human mesenchymal stem cells because of an increase in the roughness-mediated surface hydrophobicity. On the other hand, an increase in the roughness led to the formation of more number of focal adhesions. This in turn enhanced the proliferation rate and more importantly, osteogenic differentiation of stem cells. Detailed investigation into the underlying mechanism revealed that an increase in focal adhesions activated the Akt-mediated mechano-transduction signaling pathway that enhanced the osteogenic differentiation. In summary, the potential of surface severe plastic deformation to impart bioactivity to the next-generation of orthopedic ß-Ti alloys is underscored in this work.

Engineering the next-generation tin containing ß titanium alloys with high strength and low modulus for orthopedic applications.

Metastable ß Ti alloys are the new emerging class of biomaterial for load bearing orthopedic applications. However, these alloys in the single ß phase microstructure have insufficient strength for use in load bearing applications. It is imperative to strengthen these alloys by carefully designed thermo-mechanical processing routes that typically involve aging treatment. In this investigation two newly designed Sn based ß Ti alloys of composition Ti-32Nb-(2, 4) Sn are evaluated. The effects of Sn content on the mechanical properties and biological performance of these alloys processed through designed thermo-mechanical processing route are investigated. The increase in the Sn content led to a reduction in the elastic modulus of the alloy. An increase in the Sn content increased the aspect ratio of the α precipitates, which led to a significant strengthening in the alloy while keeping the elastic modulus low. In addition, the corrosion behavior of the alloy was evaluated in simulated body fluid. The Sn containing ß alloys have an excellent corrosion resistance as desired for an implant material. The corrosion resistance improved with an increase in Sn content. These alloys were also observed to have excellent cytocompatibility as they not only supported the attachment and proliferation of human mesenchymal stem cells but also their osteogenic differentiation in vitro. The combination of high strength, low elastic modulus, superior corrosion resistance and biocompatibility underscores the promise of Sn containing ß Ti alloys for use in orthopedic applications.

Cemento-ossifying fibroma of mandible mimicking complex composite odontome.

Cemento-ossifying fibroma (COF) is a fibro-osseous lesion or non-odontogenic tumour that affects craniofacial bones. These lesions are included in the spectrum of fibro-osseous lesions arising from periodontal ligament cells, which can deposit combination of cementum and bone surrounded by fibrous tissue. It clinically, macroscopically and radiologically resembles complex composite odontome and can be differentiated only on the basis of histopathology. They usually occur solitarily as a painless and expansile spherical or ovoid jawbone mass that may displace the roots of adjacent teeth. They predominantly occur in females in third and fourth decades of life. We present a case report of a 20-year-old man, with a mildly painful swelling in the mandible which was successfully treated with enucleation and diagnosed as COF. Its resemblance to complex composite odontome and unique surgical approach are highlighted in this paper.

Central odontogenic fibromyxoma of mandible: an aggressive odontogenic pathology.

Myxoma of the jaws which was first described by Thoma and Goldman in 1947 is a rare neoplasm and its rate of prevalence and incidence is not available. Myxoma term, according to 1992 WHO classification, is used along with odontogenic myxoma (OM) and myxofibroma. There are two forms of myxomas or fibromyxomas that are recognised in head and neck region: one is derived from the facial skeleton and the other is derived from the soft tissue. Most of the OM are located intraosseously, but peripheral ones are also recognised. OM behaves differently from myxomatous tumours of long bones, which recur more often and may transform into malignancy. A majority of these lesions occur between 2nd and 4th decade. In the pathogenesis of OM, dental papilla, dental follicle and periodontal ligament tissues have been implicated as possible 'germ centres'. This case describes an uncommon finding of central odontogenic fibromyxoma, throwing light on its epidemiology, clinical, histopathology, molecular and treatment aspects.

Adult-onset cystic hygroma: A case report of rare entity.

Cystic hygroma is a benign congenital malformation of the lymphatic system that occurs in infant or children younger than 2 years of age. Although cystic hygroma is well recognized in pediatric practice, it seldom presents de novo in adulthood. These are commonly present in head and neck but can be present anywhere. Cystic hygroma is very rare in adults, but it should be considered in the differential diagnosis of adult neck swellings. Patients presenting with a painless, soft, fluctuant, and enlarging neck mass should have a careful history and physical examination along with radiological imaging to assist with diagnosis. Surgical intervention is the treatment of choice for this rare condition. Here, we are reporting a case of cystic hygroma in a 32-year-old male patient in the neck region. The objectives of this case report are to discuss the clinical presentation, diagnosis, histopathological findings and management of this malformation.

Unicystic plexiform ameloblastoma with mural proliferation: a full-blown lesion.

Ameloblastoma is the most common aggressive benign odontogenic tumour of the jaws and has received considerable attention due to its frequency, clinical subtypes and high tendency to infiltrate and recur. There are various types of this tumour and confusion still exists among clinicians as to its correct classification. Multicystic ameloblastoma is the most frequent subtype while unicystic ameloblastoma can be considered a variant of the solid or multicystic subtype. Unicystic ameloblastoma is considered a less aggressive tumour with a variable recurrence rate. However, its frequency is often underestimated. Ameloblastoma is often asymptomatic, presenting as a slowly enlarging facial swelling or an incidental finding on radiograph. It is seen in all age groups but is most commonly diagnosed in the third and fourth decades. We report a case of unusual unicystic ameloblastoma and present its clinical, radiological and full-blown histological changes and treatment modalities, providing new insights into ameloblastomas.

Adenoid basal cell carcinoma: a rare facet of basal cell carcinoma.

Basal cell carcinoma (BCC) is a common, locally invasive epithelial malignancy of skin and its appendages. Every year, close to 10 million people get diagnosed with BCC worldwide. While the histology of this lesion is mostly predictable, some of the rare histological variants such as cystic, adenoid, morpheaform, infundibulocystic, pigmented and miscellaneous variants (clear-cell, signet ring cell, granular, giant cell, adamantanoid, schwannoid) are even rarer, accounting for <10% of all BCC's. Adenoid BCC (ADBCC) is a very rare histopathological variant with reported incidence of only approximately 1.3%. The clinical appearance of this lesion can be a pigmented or non-pigmented nodule or ulcer without predilection for any particular site. We share a case report of ADBCC, a rare histological variant of BCC that showed interesting features not only histologically but also by clinically mimicking a benign lesion.

Glandular odontogenic cyst: a rare entity revealed and a review of the literature.

A glandular odontogenic cyst (GOC) is a developmental cyst that is a clinically rare and histopathologically unusual type of odontogenic cyst. GOCs are now relatively well-known entities; their importance relates to the fact that they exhibit a propensity for recurrence rates from 21% to 55%, similar to odontogenic keratocysts, and may be confused microscopically with central mucoepidermoid carcinoma. Furthermore, some microscopic features of GOCs may also be found in dentigerous, botryoid, radicular and surgical ciliated cysts. The present case report aims to describe a typical case of GOC, throwing light on its epidemiology and origin, as well as on its clinical, radiographic and microscopic features, which may be helpful for diagnosis in problematic cases, long-term follow-up and to determine the most appropriate treatment.

Gorlin-Goltz syndrome in twin brothers: an unusual occurrence with review of the literature.

Gorlin-Goltz syndrome, also known as nevoid basal cell carcinoma syndrome, is caused by genetic alteration produced by a mutation in the 'patched' tumour suppressor gene, and is inherited in a dominant autosomal way. Although sporadic cases have been found, this syndrome has rarely been reported in twin patients. The syndrome is characterised by a wide range of developmental abnormalities and has a predisposition to neoplasms such as multiple pigmented basal cell carcinomas and keratocysts in jaws; it also has other features such as palmar and/or plantar pits and calcification of falx cerebri. Owing to the critical oral and maxillofacial manifestations of this syndrome, it is important to recognise its characteristics in order to make a diagnosis, and to plot early preventive treatment and establish the right genetic evidence. Based on a combination of imaging, clinical and histopathological findings, we present a diagnosed case of Gorlin-Goltz syndrome in 18-year-old twin brothers. All cystic lesions were enucleated and 1 year follow-up showed no recurrence.

Enhancing the mechanical and biological performance of a metallic biomaterial for orthopedic applications through changes in the surface oxide layer by nanocrystalline surface modification.

Nanostructured metals are a promising class of biomaterials for application in orthopedics to improve the mechanical performance and biological response for increasing the life of biomedical implants. Surface mechanical attrition treatment (SMAT) is an efficient way of engineering nanocrystalline surfaces on metal substrates. In this work, 316L stainless steel (SS), a widely used orthopedic biomaterial, was subjected to SMAT to generate a nanocrystalline surface. Surface nanocrystallization modified the nature of the oxide layer present on the surface. It increased the corrosion-fatigue strength in saline by 50%. This increase in strength is attributed to a thicker oxide layer, residual compressive stresses, high strength of the surface layer, and lower propensity for intergranular corrosion in the nanocrystalline layer. Nanocrystallization also enhanced osteoblast attachment and proliferation. Intriguingly, wettability and surface roughness, the key parameters widely acknowledged for controlling the cellular response remained unchanged after nanocrystallization. The observed cellular behavior is explained in terms of the changes in electronic properties of the semiconducting passive oxide film present on the surface of 316L SS. Nanocrystallization increased the charge carrier density of the n-type oxide film likely preventing denaturation of the adsorbed cell-adhesive proteins such as fibronectin. In addition, a net positive charge developed on the otherwise neutral oxide layer, which is known to facilitate cellular adhesion. The role of changes in the electronic properties of the oxide films on metal substrates is thus highlighted in this work. This study demonstrates the advantages of nanocrystalline surface modification by SMAT for processing metallic biomaterials used in orthopedic implants.