José Henrique Rubo

Finite‐Element Analysis of Stress on Dental Implant Prosthesis

BACKGROUND Understanding how clinical variables affect stress distribution facilitates optimal prosthesis design and fabrication and may lead to a decrease in mechanical failures as well as improve implant longevity. PURPOSE In this study, the many clinical variations present in implant-supported prosthesis were analyzed by 3-D finite element method. MATERIALS AND METHOD A geometrical model representing the anterior segment of a human mandible treated with 5 implants supporting a framework was created to perform the tests. The variables introduced in the computer model were cantilever length, elastic modulus of cancellous bone, abutment length, implant length, and framework alloy (AgPd or CoCr). The computer was programmed with physical properties of the materials as derived from the literature, and a 100N vertical load was used to simulate the occlusal force. Images with the fringes of stress were obtained and the maximum stress at each site was plotted in graphs for comparison. RESULTS Stresses clustered at the elements closest to the loading point. Stress increase was found to be proportional to the increase in cantilever length and inversely proportional to the increase in the elastic modulus of cancellous bone. Increasing the abutment length resulted in a decrease of stress on implants and framework. Stress decrease could not be demonstrated with implants longer than 13 mm. A stiffer framework may allow better stress distribution. CONCLUSION The relative physical properties of the many materials involved in an implant-supported prosthesis system affect the way stresses are distributed.

Finite Element Analysis of Stress in Bone Adjacent to Dental Implants

Understanding how clinical variables affect stress distribution facilitates optimal prosthesis design and fabrication and may lead to a decrease in mechanical failures as well as improve implant longevity. In this study, the many clinical variations present in an implant-supported prosthesis were analyzed by a 3-dimensional finite-element method. The anterior segment of a human mandible treated with 5 implants supporting a curved beam was created to perform the tests. The variables introduced in the computer model were cantilever length, elastic modulus of cancellous bone, abutment length, implant length, and framework alloy (AgPd or CoCr). The computer was programmed with physical properties of the materials as derived from the literature, and a 100-N vertical load was used to simulate the occlusal force. Images with fringes of stress were obtained, and the maximum stress at each site was plotted in graphs for comparison. Stresses tended to be concentrated at the cortical bone around the neck of the implant closest to the load, whereas stresses in cancellous bone were considered low. In general, the stress distribution was better with stiffer cancellous bone, longer abutments and implants, and shorter cantilevers. The use of a CoCr alloy framework appears to contribute to a better stress distribution.

Tensile bond strength of a composite resin cement for bonded prosthesis to various dental alloys

The development of composite resin cements that chemically bond to dental alloys has improved the construction of resin-bonded prostheses. Composite resins can be selected for various situations, but specific clinical situations may require different alloys. This study evaluated the ability of a composite resin cement to bond to various dental alloys of different compositions. Ten pairs of disks for each alloy (two NiCr, two NiCrBe, one CuAl, one gold type IV, and one gold for metal ceramic) were bonded to a composite resin cement after air abrasion was performed with aluminum oxide. The disks were then rinsed in tap water and were ultrasonically cleaned in distilled water for 2 minutes. The tensile tests exhibited greater values for alloys ultrasonically cleaned, and the best results were recorded by NiCr and NiCrBe alloys.

Effect of cantilever length and framework alloy on the stress distribution of mandibular-cantilevered implant-supported prostheses.

OBJECTIVES The purpose of this in vitro study was to analyze the stress distribution on components of a mandibular-cantilevered implant-supported prosthesis with frameworks cast in cobalt-chromium (Co-Cr) or palladium-silver (Pd-Ag) alloys, according to the cantilever length. MATERIAL AND METHODS Frameworks were fabricated on (Co-Cr) and (Pd-Ag) alloys and screwed into standard abutments positioned on a master-cast containing five implant replicas. Two linear strain gauges were fixed on the mesial and distal aspects of each abutment to capture deformation. A vertical static load of 100 N was applied to the cantilever arm at the distances of 10, 15, and 20 mm from the center of the distal abutment and the absolute values of specific deformation were recorded. RESULTS Different patterns of abutment deformation were observed according to the framework alloy. The Co-Cr alloy framework resulted in higher levels of abutment deformation than the silver-palladium alloy framework. Abutment deformation was higher with longer cantilever extensions. CONCLUSION Physical properties of the alloys used for framework interfere with abutment deformations patterns. Excessively long cantilever extensions must be avoided.

Fracture resistance of endodontically treated teeth restored with glass fiber posts of different lengths.

STATEMENT OF PROBLEM Endodontically treated teeth are known to have reduced structural strength. Glass fiber posts may influence fracture resistance and should be evaluated. PURPOSE The purpose of this study was to evaluate the influence of glass fiber post length on the fracture resistance of endodontically treated teeth. MATERIAL AND METHODS Forty intact human maxillary canines were selected and divided into 4 groups, the control group consisting of teeth restored with a custom gold cast post and core, with a length of two-thirds of the root. Other groups received prefabricated glass fiber posts in different lengths: group 1/3, removal of one-third of the sealing material (5 mm); group 1/2, removal of one-half of the sealing material (7.5 mm); and group 2/3, removal of two-thirds of the sealing material (10 mm). All the posts were cemented with resin cement, and the specimens with glass fiber posts received a composite resin core. All the specimens were restored with a metal crown and submitted to a compressive load until failure occurred. The results were evaluated by 1-way ANOVA, and the all pairwise multiple comparison procedures (Tukey honestly significantly difference test) (α=.05). RESULTS The ANOVA showed significant differences among the groups (P<.002). The Tukey test showed that the control group presented significantly higher resistance to static load than the other groups (control group, 634.94 N; group 1/3, 200.01 N; group 1/2, 212.17 N; and group 2/3, 236.08 N). Although teeth restored with a cast post and core supported a higher compressive load, all of them fractured in a catastrophic manner. For teeth restored with glass fiber posts, the failure occurred at the junction between the composite resin core and the root. CONCLUSION The length of glass fiber posts did not influence fracture load, but cast post and cores that extended two-thirds of the root length had significantly greater fracture resistance than glass fiber posts.

Validation of an experimental polyurethane model for biomechanical studies on implant-supported prosthesis: compression tests

Objectives The complexity and heterogeneity of human bone, as well as ethical issues, frequently hinder the development of clinical trials. The purpose of this in vitro study was to determine the modulus of elasticity of a polyurethane isotropic experimental model via tension tests, comparing the results to those reported in the literature for mandibular bone, in order to validate the use of such a model in lieu of mandibular bone in biomechanical studies. Material and Methods Forty-five polyurethane test specimens were divided into 3 groups of 15 specimens each, according to the ratio (A/B) of polyurethane reagents (PU-1: 1/0.5, PU-2: 1/1, PU-3: 1/1.5). Results Tension tests were performed in each experimental group and the modulus of elasticity values found were 192.98 MPa (SD=57.20) for PU-1, 347.90 MPa (SD=109.54) for PU-2 and 304.64 MPa (SD=25.48) for PU-3. Conclusion The concentration of choice for building the experimental model was 1/1.

Tensile bond strength of a resinous cement to a nickel-chromium alloy modified with five surface treatments

A problem associated with resin-bonded fixed partial dentures is inadvertent dislodgment at the metal/cement interface. It has been suggested that Panavia Ex resinous cement requires only air abrasion of the alloy with 50 microns aluminum oxide particles to record reliable bond strength values. The purpose of this study was to discuss the consequences of changes in the type of air abrasion and surface oxidation of the alloy. Fifty pairs of disks of a Ni-Cr alloy were treated by five methods: (1) air abrasion with 50 microns aluminum oxide (control), (2) air abrasion with 50 microns glass beads, (3) air abrasion with a mixture of aluminum oxide and glass beads (ratio 1:1), (4) air abrasion with aluminum oxide and immersion in acid solution of potassium permanganate, and (5) air abrasion with aluminum oxide and immersion in aqueous solution of potassium permanganate. The disks were cemented to each other with Panavia Ex composite resinous cement and tensile tests were conducted at a crosshead speed of 0.5 mm/ minute. No statistically significant differences were recorded among the treatments for the alloys used in this study except air abrasion with glass beads, which exhibited the lowest bond strength values.

The effect of tin-electroplating on the bond of four dental alloys to resin cement: An in vitro study☆☆☆★★★♢♢♢

STATEMENT OF THE PROBLEM Nickel-chromium alloys are indicated for the construction of resin-bonded fixed partial dentures; however, the potential toxicity of nickel has been a source of concern. Composite cements do not develop an adequate bond to air abraded noble alloys, which cannot be electrolytically etched. Tin-electroplating of noble alloys appears to be an alternative treatment for resin bonding. PURPOSE This in vitro study investigated the effect of tin-electroplating on the bond of a composite cement to base and noble alloys. MATERIAL AND METHODS Tensile tests were made with disks of four alloys that were cemented to each other with an adhesive composite cement after (1) air abrasion with 50 microns aluminum oxide and (2) air abrasion plus tin-electroplating. RESULTS Tin-electroplating increased the bond strength of metal-ceramic gold alloy (Au,Pd,Pt) to a level comparable to the nickel-chromium alloy, but had a harmful effect on type IV gold alloy. CONCLUSIONS Despite the recommendation for tin-electroplating of type IV gold alloys, this procedure did not improve bond strength to composite in this study.

Stress Distribution in Single Dental Implant System: Three-Dimensional Finite Element Analysis Based on an In Vitro Experimental Model.

AbstractThis study aimed to analyze the stress distribution in single implant system and to evaluate the compatibility of an in vitro model with finite element (FE) model. The in vitro model consisted of Brånemark implant; multiunit set abutment of 5 mm height; metal–ceramic screw-retained crown, and polyurethane simulating the bone. Deformations were recorded in the peri-implant region in the mesial and distal aspects, after an axial 300 N load application at the center of the occlusal aspect of the crown, using strain gauges. This in vitro model was scanned with micro CT to design a three-dimensional FE model and the strains in the peri-implant bone region were registered to check the compatibility between both models. The FE model was used to evaluate stress distribution in different parts of the system. The values obtained from the in vitro model (20–587 &mgr;&egr;) and the finite element analysis (81–588 &mgr;&egr;) showed agreement among them. The highest stresses because of axial and oblique load, respectively were 5.83 and 40 MPa for the cortical bone, 55 and 1200 MPa for the implant, and 80 and 470 MPa for the abutment screw. The FE method proved to be effective for evaluating the deformation around single implant. Oblique loads lead to higher stress concentrations.

Deformation of Implant Abutments After Framework Connection Using Strain Gauges

When a cylinder is connected to an abutment it is expected that abutment and cylinder will be subjected to compression forces throughout their periphery because of the clamping force exerted by the screw. The deformation resultant of this compression should be measurable and uniform along the periphery of the abutment. Considering that multiple retainers connected to each other can affect the fit of a framework, as well as the use of different alloys, it is expected that the abutments will present different levels of deformation as a result of framework connection. The aim of this study was to evaluate the deformation of implant abutments after frameworks, cast either in cobalt-chromium (CoCr) or silver-palladium (AgPd) alloys, were connected. Samples (n  =  5) simulating a typical mandibular cantilevered implant-supported prosthesis framework were fabricated in cobalt-chromium and silver-palladium alloys and screwed onto standard abutments positioned on a master-cast containing 5 implant replicas. Two linear strain gauges were fixed on the mesial and distal aspects of each abutment to capture deformation as the retention screws were tightened. A combination of compressive and tensile forces was observed on the abutments for both CoCr and AgPd frameworks. There was no evidence of significant differences in median abutment deformation levels for 9 of the 10 abutment aspects. Visually well-fit frameworks do not necessarily transmit load uniformly to abutments. The use of CoCr alloy for implant-supported prostheses frameworks may be as clinically acceptable as AgPd alloy.