Effect of stiffness of single implant supported crowns on the resultant stresses. a finite element analysis

Objective: In the present study, the 3D finite element method was used to investigate the effect of crown material on stress distribution in the bone surrounding immediately loaded single dental

Materials and Methods: A 3D Finite Element model of mandibular first premolar was constructed to evaluate the performance of seven crown materials with different degree of stiffness [Porcelain, zirconium, Porcelain fused to gold, pure titanium, titanium alloy, Poly methyl methacrylate, and Polyether ether ketone PEEK]. The model was constructed using Solid Works version 2010 software. The model simulated also a cement layer between the implant abutment and the crown [Virolink II, Vivadent]. An axial static occlusal force of 200 N was applied to eight points in each functional cusp. The three-dimensional [3D] FE model was analyzed by ABAQUS/CAE version 6.10 software

Results: The results of this study indicated that among all crown materials the maximum von Mises stress values was observed in porcelain crown design [345.390 MPa].The highest von Mises stresses were found in the abutments for all models. In implants, the greatest stress was concentrated on the cervical region. PMMA and PEEK crown designs transferred less stress to abutment and screw. In all models, von Mises stresses increased in the coronal third of cortical bone in which the maximum von Mises stresses observed in the implant ­ cortical interface

Conclusions: Using more rigid material for the superstructure of an implant supports prosthesis did not have any effect on the stress values and stress distribution at the bone tissue surrounding implant. However, in the abutment, cement and crown structure, stress distributions and localizations were affected by the material's rigidity. More clinical studies are needed to evaluate the survival rate of these materials

Morphogenesis of rabbit kidney pre-and postnatal

Mammalian renal development differs from that of most of the other organs in that it proceeds through a series of three successive phases, each is marked by the formation of a more complex pair of kidneys. These kidneys are called the pronephros, mesonephros, and metanephros. The current study has been conducted to elucidate the developmental changes of rabbit kidneys during their pre- and postnatal life. In the present study we used samples, at different ages, of the rabbit kidneys from embryonic day 15 [E15] till maturity for light and scanning electron microscopical investigation. At E15, large mesonephros, occupied a great part of abdominal cavity of rabbit embryo, and undifferentiated metanephros were noticed. At E19 metanephros became differentiated into cortex and medulla with the initiation of nephron-forming stage. Additionally at this stage, the caudal series of mesonephros still detected but in degenerated and atrophied structure. Just before birth, at E30, the kidney demonstrated well-developed renal corpuscles, differentiated proximal and distal convoluted tubules, with apparently detectable loop of Henle and large collecting ducts. Shortly after birth rabbit kidney showed further morphogenesis and at two-months old, the kidney of rabbit with mature histological structure of the renal parenchyma was documented. In conclusion, the development of rabbit kidneys occurred mainly during the prenatal period while their histological maturity occurred from two to three weeks after birth. The present findings were discussed with previous publications

Experimental functional evaluation of bladder augmentation using demucosulated gastrocystoplasty compared to myotomy and myomyectomy

This study was conducted on 30 dogs divided into three equal groups: Group I underwent vesicomyotomy, group II had vesicomyectomy and group III had vesicomyectomy with demucosulated gastrocystoplasty. All groups were compared pre-and postoperatively as regards bladder capacity, pressure and compliance. The mortality and postoperative complications were recorded. The study concluded that the functional evaluation of various techniques for bladder auto-augmentation showed that bladder capacity increased with a better compliance and without any metabolic complications related to the presence of gastrointestinal mucosa in the augmented unit. The addition of a seromuscular gastric patch to vesicomyectomy improved the functional results and decreased the incidence of complications