Influence of Cusp Inclination on Stress Distribution in Implant-Supported Prostheses. A Three-Dimensional Finite Element Analysis

Purpose: The aim of this study was to assess the influence of cusp inclination on stress distribution in implant-supported prostheses by 3D finite element method.Materials and Methods: Three-dimensional models were created to simulate a mandibular bone section with an implant (3.75 mm diameter x 10 mm length) and crown by means of a 3D scanner and 3D CAD software. A screw-retained single crown was simulated using three cusp inclinations (10 degrees, 20 degrees, 30 degrees). The 3D models (model 10d, model 20d, and model 30d) were transferred to the finite element program NeiNastran 9.0 to generate a mesh and perform the stress analysis. An oblique load of 200 N was applied on the internal vestibular face of the metal ceramic crown.Results: The results were visualized by means of von Mises stress maps. Maximum stress concentration was located at the point of application. The implant showed higher stress values in model 30d (160.68 MPa). Cortical bone showed higher stress values in model 10d (28.23 MPa).Conclusion: Stresses on the implant and implant/abutment interface increased with increasing cusp inclination, and stresses on the cortical bone decreased with increasing cusp inclination.

Clinical Viability of Immediate Loading of Dental Implants: Part I-Factors for Success

Two-stage procedure for dental implants presents corroborated clinical success over 40 years. The evolution of surgical techniques, development of diagnostic methods, knowledge about tissue biology, and quality of implants regarding design and surface supported studies with I surgical stage followed by immediate prosthesis placement. However, several factors influence the treatment success with immediate loading. SO, this Study aimed to evaluate some factors regarding the success and characteristics of implants and patients.

Three-Dimensional Finite Element Analysis of Vertical and Angular Misfit in Implant-Supported Fixed Prostheses

Purpose: Three-dimensional finite element analysis was used to evaluate the effect of vertical and angular misfit in three-piece implant-supported screw-retained fixed prostheses on the biomechanical response in the peri-implant bone, implants, and prosthetic components. Materials and Methods: Four three-dimensional models were fabricated to represent a right posterior mandibular section with one implant in the region of the second premolar (2PM) and another in the region of the second molar (2M). The implants were splinted by a three-piece implant-supported metal-ceramic prosthesis and differed according to the type of misfit, as represented by four different models: Control = prosthesis with complete fit to the implants; UAM (unilateral angular misfit) = prosthesis presenting unilateral angular misfit of 100 pm in the mesial region of the 2M; UVM (unilateral vertical misfit) = prosthesis presenting unilateral vertical misfit of 100 pm in the mesial region of the 2M; and TVM (total vertical misfit) = prosthesis presenting total vertical misfit of 100 pm in the platform of the framework in the 2M. A vertical load of 400 N was distributed and applied on 12 centric points by the software Ansys, ie, a vertical load of 150 N was applied to each molar in the prosthesis and a vertical load of 100 N was applied at the 2PM. Results: The stress values and distribution in peri-implant bone tissue were similar for all groups. The models with misfit exhibited different distribution patterns and increased stress magnitude in comparison to the control. The highest stress values in group UAM were observed in the implant body and retention screw. The groups UVM and TVM exhibited high stress values in the platform of the framework and the implant hexagon, respectively. Conclusions: The three types of misfit influenced the magnitude and distribution of stresses. The influence of misfit on peri-implant bone tissue was modest. Each type of misfit increased the stress values in different regions of the system. INT J ORAL MAXILLOFAC IMPLANTS 2011;26:788-796

Evaluation of Bone Insertion Level of Support Teeth in Class I Mandibular Removable Partial Denture Associated With an Osseointegrated Implant: A Study Using Finite Element Analysis

Purpose: This study evaluated the influence of distal extension removable partial denture associated with implant in cases of different bone level of abutment tooth, using 2D finite element analysis.Materials and Methods: Eight hemiarch models were simulated: model A-presenting tooth 33 and distal extension removable partial denture replacing others teeth, using distal rest connection and no bone lost; model B-similar to model A but presenting distal guide plate connection; model C-similar to model A but presenting osseointegrated implant with ERA retention system associated under prosthetic base; model D-similar to model B but presenting osseointegrated implant as described in model C; models E, F, G, and H were similar to models A, B, C, and D but presenting reduced periodontal support around tooth 33. Using ANSYS 9.0 software, the models were loaded vertically with 50 N on each cusp tip. For results, von Mises Stress Maps were plotted.Results: Maximum stress value was encountered in model G (201.023 MPa). Stress distribution was concentrated on implant and retention system. The implant/removable partial denture association decreases stress levels on alveolar mucosa for all models.Conclusions: Use of implant and ERA system decreased stress concentrations on supporting structures in all models. Use of distal guide plate decreased stress levels on abutment tooth and cortical and trabecular bone. Tooth apex of models with reduced periodontal support presented increased stress when using distal rest. (Implant Dent 2011;20:192-201)

Evaluation of Different Retention Systems on a Distal Extension Removable Partial Denture Associated With an Osseointegrated Implant

The aim of this study was to evaluate the biomechanical behavior of a mandibular distal extension removable partial denture (DERPD) associated with an implant and different retention system, by bidimensional finite element method. Five hemimandible models with a canine and external hexagon implant at second molar region associated with DERPD were simulated: model A, hemimandible with a canine and a DERPD; model B, hemimandible with a canine and implant with a healing abutment associated to a DERPD; model C, hemimandible with a canine and implant with an ERA attachment associated to a DERPD; model D, hemimandible with a canine and implant with an O'ring attachment associated to a DERPD; and model E, hemimandible with a canine and implant-supported prosthesis associated to a DERPD. Cusp tips were loaded with 50 N of axial or oblique force (45 degrees). Finite element analysis was performed in ANSYS 9.0. model E showed the higher displacement and overload in the supporting tissues; the patterns of stress distribution around the dental apex of models B, C, and D were similar. The association between a DERPD and an osseointegrated implant using the ERA or O'ring systems shows lower stress values. Oblique forces showed higher stress values and displacement. Oblique forces increased the displacement and stress levels in all models; model C displayed the best stress distribution in the supporting structures; healing abutment, ERA, and O'ring systems were viable with RPD, but DERPD association with a single implant-supported prosthesis was nonviable.

Biomechanical Evaluation of Platform Switching in Different Implant Protocols: Computed Tomography-Based Three-Dimensional Finite Element Analysis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of Implant Connection Type on the Biomechanical Environment of Immediately Placed Implants - CT-Based Nonlinear, Three-Dimensional Finite Element Analysis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Fatigue strength: effect of welding type and joint design executed in Ti-6Al-4V structures

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The Effect of Splint Material Rigidity in Implant Impression Techniques

Purpose This in vitro study compared the dimensional accuracy of two impression techniques Duralay splinted impression copings (D) and metal splinted impression copings (M) for implant supported pros theses Materials and Methods A master cast with four parallel implant abutment analogs and a passive framework were fabricated Vinyl polysiloxane impression material was used for all impressions with a metal stock tray Two groups (D and M) were tested (n = 5) The measurement method employed was just one titanium screw tightened to the framework Each group s measurements were analyzed using software that received the images of a video camera coupled to a stereomicroscope at X100 magnification The results were analyzed statistically (t test) Results The mean values of abutment/framework interface gaps were master cast = 32 mu m (SD 2), group D = 165 mu m (SD 60), and group M = 69 mu m (SD 36) There was a statistically significant difference between the D and M groups (P <= 001) Conclusion Under the limitations of this study, it could be suggested that a more accurate working cast can be fabricated using metal splinted impression copings INT J ORAL MAXILLOFAC IMPLANTS 2010 25 1153-1158

Accuracy of Impression Techniques for an Implant-Supported Prosthesis

Purpose: This in vitro study compared the dimensional accuracy of a stone index and of two impression techniques (squared impression copings and modified squared impression copings) for implant-supported prostheses. Materials and Methods: A master cast with four parallel implant-abutment analogs and a passive framework were fabricated. Vinyl polysiloxane impression material was used for all impressions with a metal stock tray. Three groups of impressions were tested (n = 5): index (1), squared (S), and modified squared (MS). The measurement method employed was just one titanium screw tightened to the framework. The measurements (60 gap values) were analyzed using software that received the images from a video camera coupled to a stereomicroscope at x 100 magnification. The results were evaluated statistically (analysis of variance, Holm-Sidak method, alpha = .05). Results: The mean abutment/framework interface gaps were: master cast = 31.63 mu m; group I = 45.25 mu m; group S = 96.14 mu m; group MS = 51.20 mu m. No significant difference was detected among the index and modified squared techniques (P = .05). Conclusion: Under the limitations of this study, the techniques modified squared and index generated more accurate casts than the squared technique. INT J ORAL MAXILLOFAC IMPLANTS 2010;25:715-721

Comparison of impression techniques and materials for implant-supported prosthesis

Purpose: To investigate, in vitro, the dimensional accuracy of two impression techniques (squared impression copings and squared impression copings sandblasted and coated with impression adhesive) made of vinyl polysiloxane and polyether impression materials. Materials and Methods: A master cast (control group) with four parallel implant abutment analogs, a passive framework, and a custom aluminum tray was fabricated. Four groups (n = 5 each group) were tested: squared Impregum (SI), squared Express (SE), sandblasted adhesive squared Impregum (ASI), and sandblasted adhesive squared Express (ASE). The measurement method employed was just one titanium screw tightened to the framework. A stereomicroscope was used to evaluate the fit of the framework by measuring the size of the gap between the abutment and the framework. The results were analyzed statistically. Results: The mean values for the abutment/framework interface gaps were: master cast, 31.63 mu m (SD 2.16); SI, 38.03 mu m (SD 9.29); ASI, 46.80 mu m (SD 8.47); SE, 151.21 mu m (SD 22.79); and ASE, 136.59 mu m (SD 29.80). No significant difference was detected between the SI or ASI techniques and the master cast. No significant difference was detected between the SE and ASE techniques. Conclusion: Within the limitations of this study, it can be concluded that Impregum Soft medium consistency was the best impression material and the impression technique did not influence the accuracy of the stone casts. INT J ORAL MAXILLOFAC IMPLANTS 2010;25:771-776

Accuracy of impression and pouring techniques for an implant-supported prosthesis

Purpose: The purpose of this in vitro study was to compare the dimensional accuracy of a stone index and of 3 impression techniques (tapered impression copings, squared impression copings, and squared impression copings splinted with acrylic resin) associated with 3 pouring techniques (conventional, pouring using latex tubes fitted onto analogs, and pouring after joining the analogs with acrylic resin) for implant-supported prostheses. Materials and Methods: A mandibular brass cast with 4 stainless steel implant-abutment analogs, a framework, and 2 aluminum custom trays were fabricated. Polyether impression material was used for all impressions. Ten groups were formed (a control group and 9 test groups formed by combining each pouring technique and impression technique). Five casts were made per group for a total of 50 casts and 200 gap values (1 gap value for each implant-abutment analog). Results: The mean gap value with the index technique was 27.07 mu m. With the conventional pouring technique, the mean gap values were 116.97 mu m for the tapered group, 5784 mu m for the squared group, and 73.17 mu m for the squared splinted group. With pouring using latex tubes, the mean gap values were 65.69 mu m for the tapered group, 38.03 mu m for the squared group, and 82.47 mu m for the squared splinted group. With pouring after joining the analogs with acrylic resin, the mean gap values were 141.12 jum for the tapered group, 74.19 mu m for the squared group, and 104.67 mu m for the squared splinted group. No significant difference was detected among Index, squarellatex techniques, and master cast (P > .05). Conclusions: The most accurate impression technique utilized squared copings. The most accurate pouring technique for making the impression with tapered or squared copings utilized latex tubes. The pouring did not influence the accuracy of the stone casts when using splinted squared impression copings. Either the index technique or the use of squared coping combined with the latex-tube pouring technique are preferred methods for making implant-supported fixed restorations with dimensional accuracy.

Comparative Strain Gauge Analysis of External and Internal Hexagon, Morse Taper, and Influence of Straight and Offset Implant Configuration

Purpose: The present study was designed to analyze strain distributions caused by varying the fixture-abutment design and fixture alignment.Materials and Methods: Three implants of external, internal hexagon, and Morse taper were embedded in the center of each polyurethane block in straight placement and offset placement. Four strain gauges (SGs) were bonded on the surface of polyurethane block, which was designated SG1 placed mesially adjacent to implant A, SG2 and SG3 were placed mesially and distally adjacent to the implant B and SG4 was placed distally adjacent to the implant C. The 30 superstructures' occlusal screws were tightened onto the Microunit abutments with a torque of 10 N cm using the manufacturers' manual torque-controlling device.Results: There were statistically significant differences in prosthetic connection (P value = 0.0074 < 0.5). There were no statistically significant differences in placement configuration/alignment (P value = 0.7812 > 0.5).Conclusion: The results showed fundamental differences in both conditions. There was no evidence that there was any advantage to offset implant placement in reducing the strain around implants. The results also revealed that the internal hexagon and Morse taper joints did not reduce the microstrain around implants. (Implant Dent 2011; 20:e24-e32)

Compressive fatigue in titanium dental implants submitted to fluoride ions action

The aim of this study was to assess the influence of a fluoridated medium on the mechanical properties of an internal hexagon implant-abutment set, by means of compression, mechanical cycling and metallographic characterization by scanning electronic microscopy. Five years of regular use of oral hygiene with a sodium fluoride solution content of 1500 ppm were simulated, immersing the samples in this medium for 184 hours, with the solutions being changed every 12 hours. Data were analyzed at a 95% confidence level with Fisher's exact test. After the action of fluoride ions, a negative influence occurred in the mechanical cycling test performed in a servohydraulic machine (Material Test System-810) set to a frequency of 15 Hz with 100,000 cycles and programmed to 60% of the maximum resistance of static compression test. The sets tended to fracture by compression on the screw, characterized by mixed ruptures with predominance of fragile fracture, as observed by microscopy. An evidence of corrosion by pitting on sample surfaces was found after the fluoride ions action. It may be concluded that prolonged contact with fluoride ions is harmful to the mechanical properties of commercially pure titanium structures.

Effect of unilateral misfit on preload of retention screws of implant-supported prostheses submitted to mechanical cycling

Purpose: The aim of this study was to evaluate the effect of different levels of unilateral angular misfit on preload maintenance of retention screws of single implant-supported prostheses submitted to mechanical cycling. Materials and methods: Premachined UCLA abutments were cast with cobalt-chromium alloy to obtain 48 crowns divided into four groups (n=12). The crowns presented no misfit in Group A (control group) and unilateral misfits of 50μm, 100μm and 200μm in the groups B, C and D, respectively. The crowns were attached to external hexagon implants with a titanium retention screw with torque of 30N/cm. Oblique loading of 130N at 2Hz was applied on each replica, totalizing 5×104 and 1×106cycles. Detorque values were measured initially and after each cycling period. Data were evaluated by analysis of variance and Tukey's HSD test (p<0.05). Results: All groups presented reduced initial detorque values (p< 0.05) in comparison to the insertion torque (30. ± 0.5. N/cm) and Group A (25.18. N/cm) exhibited the lowest reduction. After mechanical cycling, all groups presented detorque values from 19.5. N/cm to 22.38. N/cm and the mechanical cycling did not statistically influence the detorque values regardless the misfit level of the replicas. Conclusion: The unilateral misfit influenced the preload maintenance only before mechanical cycling. The mechanical cycling did not influence the torque reduction. © 2010 Japan Prosthodontic Society.