Stress distribution patterns of implant supported overdentures-analog versus finite element analysis: A comparative in-vitro study

Assessment of peri-implant bone stress distribution with the effect of attachment type and implant location using finite element analysis

Background

The objective of the current research was to evaluate how stress is distributed in the peri-implant bone of a mandibular overdenture with implants placed asymmetrically to the midline.

Methods

A 26-year-old male's mandible, with missing teeth, was examined using computed tomography (CT) scanning. Two implants were inserted at right angles to the occlusal plane, in the positions of the right canine and left lateral incisor of the mandible, with an internal connection. Two types of attachments (bar and ball) were designed. To simulate the clinical condition, anterior (on central incisors) and bilateral posterior (on premolars and molars) loadings were applied. The stress distribution was assessed using finite element analysis (FEA).

Results

The lateral incisor level implant was found to have the highest maximum principal stress (about 33 MPa) in both models in the anterior loading condition. However, in both models, the canine-level implant revealed more stress values (about 22 MPa) in the posterior loading condition.

Conclusion

In mandibular implant-supported overdentures, when implants were placed asymmetrically to the midline, one acted as a fulcrum and sustained more occlusal load. The bar attachment system did not reveal superior results in terms of stress distribution compared to the ball attachment.

Mandibular Flexure and Crestal Bone Stress Distribution on an Implant-Supported Fixed Full Arch Mandibular Prosthesis: Finite Element Analysis in Three Dimensions

Aim This study's objective was to assess and analyze, using 3D Finite Element Analysis, the impact of four mandibular complete arch superstructures on the distribution of stress in the crestal bone during mandibular flexure. Materials and methods Four Finite element models of the mandible with different implant-retained framework designs have been developed. Three of these models had six axial implants placed at intervals of 11.8 mm, 18.8 mm and 25.8 mm from the midline, respectively. One model had two tilted implants and four axial implants splinted with a single piece of framework at intervals of 8.4 mm, 13.4 mm and 18.4 mm from the midline. For analyzing the stress distribution, the finished product was transferred to ANSYS R 18.1 software (Sirsa, Haryana, India) for finite element simulation, the models were constructed, the ends were restrained, and bilateral vertical loads of 50N, 100N and 150N were applied to the distal part of the framework. Results Bilateral loads were applied to each of the four 3D FEM and after assessment of Von Mises Stress and Total Deformation, a finding was made that the model with six axial implants supported by a single piece of framework underwent the highest total deformation and the model with four axial implants and two implants with distal tilts displayed most significant Von Mises stress. Conclusion Within the constraints of this 3D FEA, it was determined that mandibular flexure and peri-implant bone stress were affected by the way the framework is divided and the nature of mandibular movement. The three types of frames with the least bone stress are demonstrated by the mandibular deformation that results from two-piece frameworks on axial implants. Regardless of the number of implants, the single framework splinted with six implants shows a flexure in mandible with the highest bone stress around the implant irrespective of the angulation of the implant. Clinical significance When it comes to edentulous jaws, reducing stress in implant-supported restorative systems at varying degrees of the bone and implant interfaces and superstructures of prosthetics is one of the fundamental goals of implant treatment. A framework with proper design and a low modulus of elasticity reduces mechanical risk. Additionally, a larger number of implants helps to prevent cantilevers and spacing between the implants.

Peri-implant stress distribution assessment of various attachment systems for implant supported overdenture prosthesis by finite element analysis - A systematic review

Background

Various attachments like ball, bar-clip, magnetic attachments are used in implant supported overdentures. Finite Element Analysis (FEA) a newly innovated technology has been used in dental implantology to evaluate stress distribution patterns. There is little evidence available regarding the stress distribution in peri-implant region for implant supported overdentures. The purpose of the review was to generate scientific evidence on peri-implant stress distribution in FEA model with different types of attachments employed in implant supported overdentures.

Materials and methods

Systematic review was conducted as per the Preferred Reporting Items for Systematic Reviews Guidelines and Meta-Analyses statement (PRISMA). A comprehensive search was undertaken by two reviewers from January 2020 to June 2020 with no year limits to published articles. Only in-vitro FEA studies were included. Following electronic databases were searched for published studies- PubMed, Web of Science. Characteristics of the studies tabulated and analysis of articles was done to compare different attachment systems.

Results

Locator attachments showed better stress distribution than ball attachment system in all the studies but one. Two studies showed results in favour of ball attachment compared to bar-clip attachment system when stress was evaluated distal to the implants. No significant difference in terms of stress concentration could be generated between ball versus magnetic/equator versus locator attachment system due to less number of studies and conflicting results.

Conclusion

Various studies showed different results due to heterogenicity in selected attachment systems and study designs. Locator attachments showed favourable stress distribution around peri-implant bone than other attachments.

Stress Distribution on Various Implant-Retained Bar Overdentures

The purpose of this study was to evaluate the effects of various fabrication techniques and materials used in implant-supported mandibular overdentures with a Hader bar attachment over added stress distribution. Three-dimensional geometric solid models, consisting of two implants (3.3 mm × 12 mm) placed at the bone level on both mandibular canine regions and a Hader bar structure, were prepared. Model 1 simulated a bar retentive system made from Titanium Grade 5 material by Computer Numerical Control (CNC) milling technique without using any converting adapter/multi-unit element on the implants, while Model 2 simulated the same configuration, but with converting adapters on the implants. Model 3 simulated a bar retentive system made from Cobalt-Chromium material, made by using conventional casting technique with converting adapters on the implants. Static loads of 100 Newton were applied on test models from horizontal, vertical and oblique directions. ANSYS R15.0 Workbench Software was used to compare Von Mises stress distribution and minimum/maximum principal stress values, and the results were evaluated by using Finite Element Analysis method. As a result, the highest stress distribution values under static loading in three different directions were obtained in Model 1. Stress was observed intensely around the necks of the implants and the surrounding cortical bone areas in all models. In scope of the results obtained, using converting adapters on implants has been considered to decrease transmission of forces onto implants and surrounding bone structures, thus providing a better stress distribution. It has also been observed that the type of material used for bar fabrication has no significant influence on stress values in those models where converting adapters were used.

3D Finite Element Study on Incomplete Osseointegration: Locator Attachment versus Ball Attachment

BACKGROUND: Incomplete implant osseointegration may affect the choice of the type of attachment to ensure less amount of bone resorption, periods of maintenance, and longer implant/attachment life-time. AIM: The aim of this study was to evaluate, using 3D FE analysis (FEA), the influence of two different types of attachments on the rate of bone resorption, need for maintenance and implant/attachment life time in cases of unpredictable osseointegration in various bone types and using different implant angulations. METHODS: Six finite element models were prepared; three for the locator attachment while the other three for the ball attachment. Each of the three models simulates vertical implant and inclined implants by 10° and 20° degrees. Frictional contact between implant and cortical bone simulated the incomplete osseointegration scenario. RESULTS: Non-linear static analysis results showed that locator attachment and its cap may have longer time life in comparison with the ball attachment and its cap. CONCLUSIONS: Both attachments were safe for cortical and spongy bone, while the cortical bone receives less Von Mises stress by up to 33% with the increased implant angulation.

The importance of correct implants positioning and masticatory load direction on a fixed prosthesis

Background

Through the biomechanical study of dental implants, it is possible to understand the dissipation effects of masticatory loads in different situations and prevent the longevity of osseointegration. Aims: To evaluate the microstrains generated around external hexagon implants, using axial and non-axial loads in a fixed four-element prosthesis with straight implants and implants inclined at 17°.

Material and Methods

Three implants were modeled using CAD software following the manufacturer’s measurements. Then, implants were duplicated and divided into two groups: one with straight implants and respective abutments, and the other with angled implants at 17° and respective abutments. Both groups were arranged inside a block simulating bone tissue. A simplified fixed prosthesis was installed on both groups and the geometries were exported to CAE software. Five loads of 300N were performed at axial and non-axial points on the fixed prosthesis. Stress on the implants and strain on the block were both analyzed. An in vitro experiment was performed following all structures made in FEA in order to validate the model. In each experimental block, 4 strain gauges were linearly placed between the implants and the same loads were repeated with a loading applicator device.

Results

The deformations computed by the gauges were correlated with the FEA results, showing that the group with inclined implants had more damaging biomechanical behavior and was significantly different from the group with straight implants (P<0.005).

Conclusions

The mathematical model used is valid and inclined implants can induce unwanted bone remodeling.

Key words:Finite Element Analysis, Dental Implants, Fixed Prosthesis.