Mechanical weakening of devitalized teeth: three-dimensional Finite Element Analysis and prediction of tooth fracture.

AIM: To determine to which extent cavity preparation and each step of dentine removal in the process of root canal treatment (access cavity preparation and root canal enlargement) both individually and jointly contribute to the weakening of the tooth. METHODS: Numerical analysis using finite element method (FEM) of separate and combined influence of two-surface Class II preparation and root canal treatment was undertaken to evaluate the decrease in tooth strength. The influence of the two stages in root canal treatment, access cavity preparation and root canal enlargement, was also analysed separately and jointly. After each of these phases, the crown was restored with composite resin, and the FEA was performed only on restored teeth. To estimate the influence of all these procedures on tooth fracture resistance numerically, a Failure Index based on the maximum principal stress criterion (MPCS) was applied. Compressive and tensile stresses were analysed separately and corresponding Failure Indices were calculated. RESULTS: A two-surface resin composite restoration weakened the tooth by 23.25%. Nevertheless, the Failure Indices showed that this tooth was not likely to fracture even under high occlusal stress (710N). However, after access cavity preparation, the Failure Indices reached the point where, under high occlusal force that may occur in the posterior area, a tooth fracture occurred. The enlargement of root canals had an additional, but relatively small impact on tooth weakening, making the tooth even more susceptible to fracture. The combined influence of both cavity preparation and root canal enlargement led to weakening of 62.6% under a load of 710N, ultimately causing tooth fracture. CONCLUSION: The combined finite element method and the maximum principal stress analysis gave insight into the fracture mechanisms of teeth with two-surface composite restorations followed by root canal preparation. Removal of tooth tissue, despite its subsequent restoration with dental materials, weakened the tooth by changing the stress intensity and distribution through tooth structures. Access cavity preparation had the greatest influence on tooth strength whilst canal enlargement did not contribute to this process substantially.

[Cystic renal tumours in children]. / Cisticni tumori bubrega kod dece.

AIM: To present clinico-pathological features of cystic renal tumours of childhood and to discuss criteria for their diagnosis and classification. MATERIAL AND METHOD: Renal tumours of childhood diagnosed at the Department of Pathology, Mother and Child Health Institute, New Belgrade, in the 1976-1990 period. In the analysys and classification of these tumours criteria of the International Society for Paediatric Oncology and the National Wilms' Tumor Study were used. RESULTS: There were 133 renal tumours diagnosed, and five of them were cystic. Further histological examination revealed that 3 of them were cystic partially differentiated nephroblastomas (CPDN), one cystic nephroma (CN), and one Wilms' tumour (WT) with cystic areas. All children were treated according to the SIOP protocol and showed no evidence of the tumour at follow-up (at least 6 years). CONCLUSION: Cystic renal tumours of childhood represent the spectrum of lesions that include CN, CPDN and WT with multicystic areas. CN is a bening multilocular tumour composed of non-communicating cysts separated by septa containing mature elements only. CPDN is a low risk malignant tumour characterised by the presence of the poorly differentiated elements (blastema) within the septa. WT with multicystic areas contains both cystic and solid areas composed of the same elements as classical WT. CN and CPDN follow a favourable course and they are treated with surgery only while WT with multicystic areas requires the same therapy as the classical WT including surgery, hemio- and radiotherapy. Since other renal tumours in children, such as clear cell sarcoma of kidney and mesoblastic nephroma, can be cystic too, the precise diagnosis of the cystic renal lesions is mandatory for their appropriate treatment.

Aggressive inflammatory pseudotumor of the abdomen 9 years after therapy for Wilms tumor. A complication, coincidence, or association?

BACKGROUND: Inflammatory pseudotumor (IPT) is a benign lesion that occurs in various organs and tissues. It is usually sharply demarcated from the surrounding tissue and surgery is considered to be the best treatment. METHODS: This article discusses a 15-year-old boy with an aggressive IPT of the abdomen occurring 9 years after therapy for Wilms tumor. RESULTS: IPT widely involved the esophagus, stomach, and liver, producing severe dysphagia. Histologically, it showed classic features of IPT and, also, areas of metaplastic bone, a new feature recently described in the same lesion of the kidney. It mimicked malignant tumor clinically and led to extensive surgery, but early follow-up has shown no recurrence. CONCLUSION: Although many complications of surgery and chemotherapy are well known, the authors believe that it is unlikely to be the cause of IPT in the case presented. Therefore, the possibility of coincidence or association of Wilms tumor and IPT remains open.

[Clear cell sarcoma of the kidney in children]. / Sarkom "svelih celija" (clear cell) bubrega kod dece.

Clear cell sarcoma of the kidney (CCSK) is a distinct, highly malignant renal tumour of childhood which was diagnosed in 5 (3.9%) of 133 primary renal tumours in children under 15 years of age in the period from 1976 to 1990. The clinical and pathological features of these patients are presented. The most common clinical features were abdominal mass and haematuria. The male to female ratio was 1: 1.5 and there was predilection for the left side (4:1). The age of patients varied from 5 months to 4 years (average age 23 months). In four children the tumour was in Stage I, and in one child in Stage II. Three tumours showed classical microscopic pattern of CCSK. The treatment for all patients consisted of preoperative chemotherapy, radical surgery and additional aggressive chemotherapy. Four patients developed metastases: three of them to bones and one to the liver. Three patients died of the tumour, one is alive but with the tumour (3 years follow-up), and one child is alive and without any evidence of disease (3-years follow-up). Although relatively uncommon, these tumours are responsible for 50% of all children's deaths from renal tumours and, so, their precise classification is essential for proper treatment.

[Anaplastic type of Wilms' tumour]. / Anaplazicni tip Wilmsovog tumora.

Wilms' tumour, one of the most common solid tumours in children, is classified in groups with favourable, unfavourable and standard risk histology. Anaplastic Wilms' tumour is a representative of the tumours with unfavourable histology. Anaplasia (focal or diffuse) can involve ony component of the tumour but it has no influence on prognosis. Anaplastic Wilms' tumour usually occurs in older children and requires more aggressive therapy. However, if the correct diagnosis is established and adequate treatment applied the prognosis for these children is the same as for Wilms' tumour of standard risk histology.

[Mesoblastic nephroma: morphologic and clinical characteristics]. / Mezoblastni nefrom: morfoloske i klinicke karakteristike.

MN is a rare benign mesenchymal tumour of the kidney which occurs most commonly in the newborn period or early infancy. Tumour is successfully treated by surgery only and local recurrence and metastases are extremely rare. There are presented morphological and clinical features of 6 cases diagnosed among 123 tumours of the kidney. Histologically, mesoblastic nephroma is classified in leiomyomatous and cellular type, but distinction between the two types has no implication for survival. It is important to distinguish cellular type of mesoblastic nephroma from clear cell type of Wilms' tumour as their prognosis and treatment are so different.

[Treatment of acute lymphocytic leukemia in children with combination chemotherapy and irradiation of the central nervous system]. / Akutna limfocitna leukemija u dece lecene hemioterapijom i zracenjem centralnog nervnog sistema

From July 1972 until April 1975 51 children with acute lymphocytic leukemia had been treated with combination chemotherapy and central nervous system irradiation. First remission was induced in 46 patients. 13 patients died during the first and second year of treatment. Central nervous system leukemia developed only in 3 patients. In 9 patients chemotherapy had been stopped after 30 months of treatment. These results are very encouraging and we hope that majority of our patients will survive 5 years without relapse.