Measurements and numerical experiments are reported for a sub-set of the problems defined as the Ultrasonic Benchmark 2002 by the World Federation of Nondestructive Evaluation Centers. The backscatter from cylindrical voids of 0.125, 0.5, 1.0, 2.0, and 4 mm radii in an Aluminum block for an incident plane longitudinal elastic wave has been numerically evaluated using one exact and one approximate solution and compared. The exact solution is based on the separation of variables method. The approximate solution is based on Kirchoff's approximation. Within the Thomson-Gray measurement model and the paraxial approximation for the transducer beam, the peak-to-peak voltage is computed as a function of void radius using the exact and approximate backscatter solutions. Using a prescribed reference RF signal waveform, the backscattered RF flaw signals are predicted. Within the Kirchoff's approximation, the backscatter from partially illuminated cylindrical voids is evaluated as a function of the fractional area illuminated. RF signal waveforms were measured for cylindrical voids of 0.5, 1.0, 2.0 and 4.0 mm radii in an Aluminum block under a normal incidence immersion method. The RF signals were also measured, as the transducer was scanned perpendicular to the cylindrical void axis. Measurements were also carried out to obtain the backscatter from solid cylinders of various radii immersed in water. Comparisons between predicted peak-to-peak voltages and measurements are made. Attention is drawn to the transition from 2D backscatter to 3D backscatter encountered when seeking comparisons between predictions and measurements.

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Aim: The primary aim of this study is to analyse the stress distribution between an ALL ON FOUR implant supported prosthesis and the TREFOIL implant supported prosthesis with 3D finite element models. Settings and Design: An in vitro perspective Materials and Methods: Two mandibular three-dimensional Finite Element Models were constructed by the CREO version 5 software, in which Model A depicts a mandible with ALL ON FOUR implant supported prost hesis and Model B will depict TREFOIL implant supported prosthesis. Model A contains four implants, two anterior straight and posterior tilted implants (30°), a bar and denture containing acrylic teeth. In Model B, it contains three straight implants and a prefabricated compensatory bar with standardised dimensions. To evaluate and compare the stress distribution between the bone and implant interface, one deleterious cantilever load of upto 300 N is applied on the second molar bilaterally and simultaneously. Another full bite biting load of 150 N is given bilaterally and simultaneously on the central groove of premolars and molars. Statistical Analysis Used: The results of the simulations obtained were analysed in terms of Von Mises equivalent stress levels at the bone -implant interface. Results: The results of loading 1 showed that the maximum Von Mises stress was recorded in the anterior implant region of the Trefoil system (Model B) when compared to All on four concept. The results of loading 2 showed that the maximum Von Mises stress were recorded in the anterior implant region Trefoil system (Model B) when compared to All on four concept. Conclusion: This invitro study concludes that All on Four implant supported prosthesis showed better stress distribution when compared to the Trefoil concept.