It is concluded that the agreement between the two radiographic examiners and the agreement between either radiographic examiner and the clearing technique were poor to moderate, indicating the limited value of radiographs alone when studying certain aspects of the root-canal system.

Purpose: To evaluate tooth preparation for full veneer cast restorations performed by final year dental students in Sudan. Materials and Methods: 117 stone dies from two different dental institutions were collected and evaluated. Polyvinylsilioxane impression material was used to produce two impressive replicas of which one was sectioned in faciolingual plane and the other in mesiodistal plane. Occlusal clearance was measured using a digital caliper. Amount of axial preparation was also measured. Impression silhouettes that were produced using an overhead projector were used to measure convergence angle. Working casts were examined for smoothness and evenness of the preparations, existence or absence of additional features of retention and the finishing line were evaluated for its position and continuity. All obtained data were statistically analyzed by using T-test, ANO-VA, and Pearson Chi square tests. P-values ≤ 0.05 were considered as statistically significant. Results: Average taper of the examined preparations was 39.98˚, with 44.1˚ in the faciolingual, and 35.8˚ in the mesiodistal dimensions. Preparations for full coverage restorations were over prepared. 38.5% of the total number of preparations were found to have finishing lines in the sub and supra gingival positions. 19.66% were unable to maintain continuity of the finishing line all around the preparation. All preparations were generally smooth with no sharp angles, and 1.7% of the preparations had additional retentive features. Conclusion: Within the limitations of this study, it could be concluded that the convergence angle and finishing line preparations were less than adequate in a sizeable proportion of the preparations examined.

The aim of this investigation was to assess the operative response of a representative sample of Irish General Dental Practitioners of various times since qualification to carious lesions of varying extent in both approximal surfaces of a lower left first molar tooth. 82 General Dental practitioners participated. The dentists were asked to treat 2 manikin teeth for minimal caries on both approximal surfaces extending to the enamel dentine junction, 2 teeth for caries extending approximately to half the thickness of the dentine and 2 teeth for caries extending more than 3/4 of the dentine thickness. Weight measurements were made of the tooth substance cut away. Mean volumes of tooth material removed ranged from 21 mm3 for minimal caries to 76 mm3 for the largest amount of caries. A two-factor analysis of variance revealed that the type of cavity preparation the dentist used had a significant effect on the volume of tooth material removed for all three extents of caries. Time since graduation had a significant effect on the volume of tooth material removed for the least extent of caries, but not for the other categories of carious involvement.

For paired press-stud overdenture attachments from one manufacturer, there was no difference in retention force when the attachments were parallel or tilted (one at vertical angle of 15°), after approximately one year of simulated separating/reuniting cycles by a patient. The parallel attachments showed greater retention after periodic tightening than the tilted attachments. IntroductionThe mandibular two-implant overdenture has become a widely used restoration for edentulous patients, and the success of this type of restoration has been documented [1][2][3][4]. However, there has been a report of high failure rate of the retentive components used in these restorations, which seems to be related to their repeated use [5]. For example, concerns have been expressed about the effect of wear between components of the commonly used Bona-type stud attachments [6]. There have also been concerns that the relative angulation of these components may affect their rate of wear [7][8][9]. The purpose of this in vitro study was to investigate the possible effect of repeated separation and reunion cycles on the retention of paired overdenture stud attachment assemblies set in acrylic resin. The present results are compared to those reported in other studies [9][10][11][12][13][14], providing some insight into these concerns and the major factors involved. Material and Methods Test modelTwo cylindrical blocks of acrylic resin (Vari-Set 20, Met Prep Ltd, Coventry, UK), approximately 36 mm in diameter, were constructed. One end on each block was cut flat and polished (Met Prep PH Machine). For the first set (Group 1) of 10 test specimens, two analogues for stud attachments (ITI ® Straumann) were secured vertically in one acrylic block, 22 mm from the center and along a diameter line, with the aid of a surveyor (Bachman ® Parallelometer, Cendres & Metaux, Switzerland), as shown in Figure 1. A second set (Group 2) of 10 specimens was assembled in the same manner, except one attachment was set vertically and the second was set at a 15° angle toward it, as shown in Figure 2. The attachments for the stud assemblies of both Groups 1 and 2 were secured to the other acrylic block, using the same material. A removable square metal rod was fastened to the second acrylic block and fit into corresponding square tubing in the first block, serving as a guidance rod for seating during the separation and reunion cycling. A nut was incorporated in the upper acrylic AbstractStatement of problem: Loss of retention of implant overdenture stud attachment assemblies presents maintenance problems to both the patient and dentist.Purpose: The purpose of this in vitro study was to investigate effects of repeated separation and reunion cycles on retention of paired overdenture stud attachment assemblies set in acrylic resin. Material and methods:Ten pairs of stud attachments were set vertically and parallel to each other (Group 1). Ten other pairs of stud attachments were set with one vertical and the other at a vertical angle of 15°, so that it converged...