A transmission electron microscope study of Néel skyrmion magnetic textures in multilayer thin film systems with large interfacial chiral interaction

Skyrmions in ultrathin ferromagnetic metal (FM)/heavy metal (HM) multilayer systems produced by conventional sputtering methods have recently generated huge interest due to their applications in the field of spintronics. The sandwich structure with two correctly-chosen heavy metal layers provides an additive interfacial exchange interaction which promotes domain wall or skyrmion spin textures that are Néel in character and with a fixed chirality. Lorentz transmission electron microscopy (TEM) is a high resolution method ideally suited to quantitatively image such chiral magnetic configurations. When allied with physical and chemical TEM analysis of both planar and cross-sectional samples, key length scales such as grain size and the chiral variation of the magnetisation variation have been identified and measured. We present data showing the importance of the grain size (mostly < 10 nm) measured from direct imaging and its potential role in describing observed behaviour of isolated skyrmions (diameter < 100 nm). In the latter the region in which the magnetization rotates is measured to be around 30 nm. Such quantitative information on the multiscale magnetisation variations in the system is key to understanding and exploiting the behaviour of skyrmions for future applications in information storage and logic devices.

[Recurrent maxillo-mandibular odontogenic keratocysts: prevention and treatment]

Keratocyst is an odontogenic cyst with an aggressive clinical behavior and a high recurrence rate. Our work describes a 62 year-old patient with Gorlin's syndrome presenting advanced recurrent maxillo-mandibular keratocysts. He already had multiple resections of these lesions. Early diagnosis and treatment of keratocysts is crucial to reduce the extension of the cysts and minimize their malignant transformation especially when they are part of a Gorlin's syndrome.

[Avascular mandibular necrosis]

INTRODUCTION

Jaw osteonecrosis is, in most cases, caused by external irradiation. It is otherwise a rare occurrence.

OBSERVATION

A 52-year-old patient was referred to this hospital for several tooth extractions. In the procedure follow-up, the external aspect of the mandible was more and more exposed. This led to the spontaneous loss of a voluminous bone fragment. The patient had never undergone radiotherapy or a course of bisphosphonates but had a long-term cardio-vascular history. He had undergone endarterectomy of both carotids, an ilio-femoral by-pass, and a coronary dilatation. The diagnosis of bone infarction on a chronic osteomyelitis was made.

DISCUSSION

Blood coagulation disorders are responsible for most cases of bone infarction. Other risk factors include local trauma, chemotherapy, corticoids, and bisphosphonates. Necrosis of the jawbones is rare even though these are prone to trauma and infections. Symptoms are not specific and imaging is contributive late in the evolution. The results of medical treatment (antibiotherapy, vasodilators, and hyperbaric oxygenotherapy) and surgical debridement are very inconsistent.

Bisphosphonates et ostéo(chimio)nécrose maxillo-mandibulaire

INTRODUCTION

Maxillo-mandibular osteonecrosis is exceptional outside a context of cervico-facial radiotherapy. Bisphosphonates are non-metabolized pyrophosphate analogues which inhibit osteoclastic activity. Bisphosphonates are prescribed for the treatment of malignant hypercalcemia, osteolysis associated with metastatic bone disease, Paget's disease and osteoporosis. Maxillomandibular osteonecrosis with bisphosphonates can be observed in 1/10000 patients, but is probably underestimated due to lack of dental examination.

MATERIAL AND METHODS

We describe six cases of mandibular necrosis associated with bisphosphonates: five of them as part of their treatment regimen for a neoplastic condition and one for osteoporosis.

RESULTS

Two patients developed spontaneous bone necrosis. In two others, tooth extraction preceded the onset of osteonecrosis. In the last two patients, we noted a preexisting dental infection. All the histopathological examinations showed necrotic bone colonized by Actinomyces.

DISCUSSION

Bisphosphonate-induced osteonecrosis is only found in the maxillomandibular area because the jaws are the only bone in the skeleton exposed to the external environment. The mandible is rendered particularly prone to necrosis even after minor trauma because of its terminal vascularization. Careful oral examination is recommended before prescribing bisphosphonate therapy.

[Prevention of postoperative bleeding in patients taking oral anticoagulants. Effects of tranexamic acid]

INTRODUCTION

We present a prospective clinical study on use of tranexamic acid mouthwashes in patients taking oral anticoagulants and who have to undergo minor ambulatory oral surgery, without modifying their anticoagulant therapy.

MATERIAL AND METHODS

Forty patients (18 men and 22 females) aged from 42 to 81 were studied from April 2000 to December 2002. All patients were under the same anticoagulant, vitamin K antagonist, (Sintrom) for different pathologies. The anticoagulant therapy was not modified neither before nor after surgery. More than 70 oral procedures were carried out under local anesthesia. The International Normalized Ratio of prothrombin time (INR) was<=4. Tranexamic acid 5% (Exacyl) mouthwashes were prescribed during and after surgery.

RESULTS

All the patients were followed up during 2 weeks after surgery. There were no postoperative bleedings.

DISCUSSION

Use of tranexamic acid mouthwashes under a specific protocol is an efficient, reliable and economic method in preventing postoperative bleeding in patients under oral anticoagulant therapy.

[Central reparative giant cell granuloma of the maxilla. Apropos of a case]

Central giant cell granulomas are uncommon, locally aggressive and benign tumors of the maxillofacial skeleton. The authors report a case of tumor arising from the maxilla and present a review of essential characteristics of the lesion.