Deflection and stress distribution in three different IMZ abutment designs.

PURPOSE: The purpose of this study was to compare the stress distribution in the resin element and the retaining screw for three different IMZ prosthetic systems: 1) original threaded Intra-Mobile Element (IME); 2) Abutment Complete (ABC); and 3) Intra-Mobile Connector (IMC). This stress distribution comparison was then related to variations in deflection of the prosthetic superstructure. MATERIALS AND METHODS: Employing the finite element method, a three-dimensional model simulating a cast gold restoration attached to an osseointegrated IMZ implant fixture was generated for each system. The representation of the implant fixture, the supporting structures, and the external contours of the crown were identical in the three models, while the configuration of the abutment varied to characterize the individual systems. Each model was discretized into axisymmetric finite elements representing the crown, the various implant system components, and supporting structures. A series of harmonic functions was written to define non-axisymmetric loads of 100 N and 500 N evenly distributed over the entire occlusal surface of the crown. Each load was applied individually to the models, first in a vertical direction, and then at a 45 degree angle to the median plane. Predicted deflection and stress distributions were computed and plotted for each loading condition of each model. RESULTS: Deflections measured at the buccal cusp tip ranged from 0.002 mm (100-N load applied vertically to the ABC model) to 0.802 mm (500-N load applied at 45 degrees to the IME model). Maximum effective stresses in the retaining screw ranged from 129 MPa (100-N load applied vertically to the ABC model) to 1,315 MPa (500-N load applied at 45 degrees C to the IMC model). A correlation was observed between the peak stresses in the screw and the deflection of the superstructure. CONCLUSIONS: Deflections and stress concentrations with the IMC were predicted to be in the same range as with the IME, but much greater than with the ABC.

Effects of radiofrequency glow discharge on impression material surface wettability.

STATEMENT OF PROBLEM: Argon radiofrequency glow discharge (RGD) may simultaneously sterilize and improve surface wettability of impression materials. PURPOSE: The purpose of this study was to define RGD technical parameters that influence the surface wettability of impression material (optimization phase). Definition of RGD was followed by an assessment of these optimized RGD parameters on the wettability of four impression materials either uncontaminated or contaminated with saliva, compared with conventional liquid disinfection (application phase). MATERIAL AND METHODS: For the optimization phase, addition silicone samples were cast against glass with 10 samples per group/parameter (n = 210). Parameters evaluated were duration of exposure, sample shape and angle, position within the RGD chamber, and argon gas delivery pressure. Changes in surface wettability were determined with contact angle measurements. For the application phase, standardized RGD parameters (90 degrees to the plasma flow, flat, 60 seconds, 5 psi) were used on four groups of impression materials with (n = 120 samples, 30 per material) or without (n = 120 samples, 30 per material) prior saliva contamination. RESULTS: RGD treatment of a polyvinyl siloxane impression material significantly (p < 0.0001) reduced contact angle measurements from 63 +/- 1 to 13 +/- 4 degrees, regardless of the parameter evaluated. For the application phase, results indicated different responses to RGD relative to nontreated controls. With all materials treated with RGD or disinfectant exposure, the finest 20 microns standard line was reproduced at x10 magnification with the American National Standards Institute/American Dental Association Specification 19 test die (Sabri Enterprise, Downers Grove, Ill.; n = 80, 10 samples per group). CONCLUSION: These results suggest RGD selectively alters impression material surface wettability.

Finite element stress analysis of IMZ abutment designs: development of a model.

PURPOSE: This article describes the development of a model system for use in finite element stress analysis of three different IMZ abutment designs: original threaded Intra-Mobile Element (IME), Abutment Complete (ABC), and Intra-Mobile Connector (IMC). MATERIALS AND METHODS: A three-dimensional model simulating a cast gold crown restoration attached to an osseointegrated IMZ implant fixture was generated for each abutment design. Each model was discretized into axisymmetric finite elements representing the crown, the various implant system components, and supporting structures. A convergence test was performed to optimize the mesh. Convergence test mesh refinement for the IME, the IMC, and the ABC abutment models resulted in 818 elements, 2,566 nodes; 738 elements, 2,362 nodes; and 663 elements, 2,051 nodes, respectively. Progressive tightening of the retaining screw (preload) was simulated; the degree of screw tightening necessary to prevent opening of the crown-abutment interface in extreme loading (500-N occlusal load at 45 degrees) was determined individually for each system. CONCLUSIONS: Models of three IMZ abutment designs have been refined and the appropriate relative screw preloads determined. This model system is to be used subsequently in stress analysis comparison for the three systems.

Management of the clinical curriculum in which students direct rather than perform the laboratory stages of restorations.

At the University of Iowa, senior dental students direct rather than perform laboratory construction of clinical prosthodontic work. This report highlights the fundamentals of a successful curriculum based on this concept. One critical component of the curriculum involves teaching the process of self-evaluation of laboratory work as well as the evaluation of work received from a commercial laboratory. Instructors teach students how to evaluate a product in the sophomore preclinical curriculum. A computerized evaluation form, developed by the prosthodontic faculty, allows assessment of the students' laboratory work in addition to self-evaluation. To incorporate patient care into the appraisal process, a modified preclinical evaluation framework is used during the junior clinical clerkship. This expanded framework takes into consideration patient treatment factors such as degree of difficulty, diagnosis and treatment planning, use of infection control, and students' understanding of patients' comprehensive treatment plan. In the senior clinic, the students' ability to direct the construction of a prosthesis is enhanced by the unique diversity of faculty within the Department of Family Dentistry at the University of Iowa. This department unites private practice dentists with academicians and general practitioners with specialists.

Deflection of superstructure and stress concentrations in the IMZ implant system.

The finite element method was used to model a 4.0 x 13.0-mm IMZ implant restored with a cast gold crown to examine the relationship between deflection of the prosthetic superstructure and stress concentrations in the retaining screw using both the polyoxymethylene intramobile element and the analogous titanium element under various loading conditions. A strong correlation was observed between the peak stresses in the screw and the deflection of the superstructure. Deflections and stress concentrations generally increased with increases of either the load magnitude or the load angle. Greater deflection and stress concentrations within the coronal retaining screw were predicted with the use of the resin IME than with the titanium element.

Odontogenic myxoma of the maxillary sinus: a clinical report.

This report describes the transoral maxillary resection of an odontogenic tumor and prosthetic reconstruction with titanium implants placed horizontally in the residual palate. The treatment provided enabled the removal of the lesion and prosthetic restoration of the missing structures, while maintaining optimal facial esthetics and obtaining support, retention, and stability for the prosthesis (Fig. 5).