[ finite-element analysis of stress distribution around dental implant in different bar-attachment systems]

When implants are used to support an over denture, the optimal stress distribution is desirable to minimize the forces on the implants. The purpose of this study was to compare stress patterns generated around implant supported over denture with two different bar attachment systems ITI [Dolder] and OT with finite element method. In this descriptive study, the stress distribution around dental implants in an edentulous mandible with two different bar attachment systems [OT without spacer and ITI [Dolder] with spacerl was calculated by means of three-dimensional, finite-element model of an entire lower jaw. This model was provided with two endosseous implants in the canine region. The implants were connected to a 2 mm bar height and a vertical force was applied to the first left molar and gradually increased from 0 to 50N. Then, resultant stress distribution was evaluated. In OT and ITI [Dolder] bar attachments, the maximum von Mises stress values were observed in the cortical bone adjacent to the implant neck and this value was higher for OT bar [6.114Mpa] than ITI [Dolder] bar attachment [3.896 Mpa]. This 3-D FE study suggested that the use of ITI [Dolder] bar attachment with spacer is more advantageous than OT bar attachment for implant-supported overdenture with regard to optimizing stress distribution

comparison of the accuracy and dimensional stability between two silicon impression materials [Speedex and Irasil]

Condensation silicons are more commonly used in fixed Prosthodontics than other elastomers. The aim of this study was to compare the accuracy and dimensional stability of two condensation silicons: Speedex and Irasil. A metal master model containing two abutments representing two prepared teeth with definite dimensions was prepared and a metal tray was made. 40 impressions were taken [20 of each impression material] and 10 of them were poured with die stone [Prevest] after 30 minutes and the other IC were poured after 120 minutes, according to the manufacturer's instructions. Using a steriomicroscope M6c-l 0 and Digital camera motican-480 the following dimensions were measured three times on the metal and stone models: [1] x = distance between the center of the abutments [2] y1 = height of the abutment with an undercut [3] y2 = height of the abutment without an undercut [4] z1 width of the abutment with an undercut, and [5] z2 = width of the abutment without an undercut. The difference between the dimensions of the main and stone models was assessed, Multivariance and T-tests were used for statistical analysis. There was no significant difference in dimensional stability between groups I and 4 [Speedex, 30' and Speedex, 120'] and between groups 2 and 3 [Irasil, 30'-120']. A significant difference was observed between Speedex and Irasil in both time periods [30 and 120 minutes]. The difference between the die stone and the master model was significant in mesiodistal [x] and buccolingual [H] dimensions for both materials. A significant difference was also found between Irasil and the main model in occlusogingival [y1] and buccolingual [z2] dimensions in both time periods, but Speedex failed to show a significant difference in the same dimensions and time periods. In the y2 dimension in contrast to Irasil, Speedex demonstrated a significant decrease of dimensional stability. Timing did not affect the dimensions of the two impression materials. The mesiodistal dimensions [x] of both Speedex and Irasil increased on the casts. A significant difference was found in dimensional stability between Speedex and Irasil impression materials

[Comparison of occlusal plane in edentulous patients to natural dentition]

It is Important to make occlusal plane in complete dentures as closely as possible to occlusal plane in natural dentition. In this study it was tried to show the relationship between the occlusal plane in natural dentition to points porion-Nasion PN. ANS+Frakfort plane and compare occlusal plane in denture teeth to the same points [Porion/Nasion/PNANS+Frakfort plane]. 35 edentulous patients with class I occlusion: 21 male and 14 female, were randomly selected from Isfahan Dental school, Department of prosthetic Dentistry. Complete upper and lower denture was constructed for these patients following standard procedure. After completion of upper and lower prosthesis occlusal plane was marked and Lateral Cephalometry Radiographs was made for them. At the same time 35 adult patients with normal class I occlusion with no history of ortho treatment were selected and Lateral Cephalometry Radio graphs were done for them. The angle between occlusal plane, frankfort plane and PN. ANS was measured for all seventy patients on radiographs. The results were compared to each other. In this study it was determined that there is an inverse linear relationship between the angle PN.ANS and occlusal plane, frakfort plane. In patients with natural dentition coefficient of correlation was 0.989. This relation did not exist in edentulous patients. Coefficient Correlation between two angles was 0.45. Since the only variable between edentulous and edentulous state is occlusal plane, we can conclude that the routine procedure for determining occlusal plane, for all the patients, does not restore the natural state