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Table of Contents
ORIGINAL ARTICLE
Year : 2021  |  Volume : 11  |  Issue : 1  |  Page : 44-52

The analysis of the stress distribution around angulated and parallelly placed implants based on “all on 4 concept” and four implants placed parallel within the interforaminal distance in an edentulous mandible – An in vitro three-dimensional finite element analysis


1 Private Practitioner, Rajarajeswari Dental College and Hospital, Bengaluru, Karnataka, India
2 Private Practitioner & Professor and Head of Department of Oro-facial Pain Clinic, Rajarajeswari Dental College and Hospital, Bengaluru, Karnataka, India
3 Department of Prosthodontics, Rajarajeswari Dental College and Hospital, Bengaluru, Karnataka, India

Date of Submission26-Oct-2020
Date of Decision07-May-2021
Date of Acceptance07-May-2021
Date of Web Publication10-Jun-2021

Correspondence Address:
Dr. Mounika Ayinala
Department of Prosthodontics, Rajarajeswari Dental College and Hospital, No. 14, Ramohalli Cross, Mysore Road, Kumbalgodu, Bengaluru - 560 074, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jdi.jdi_28_20

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   Abstract 

Purpose: The purpose of the study was to analyze and compare the stress distribution in the so-called All-on-Four concept where two anterior implants were placed parallel to each other and two posterior implants were tilted at 45° angle against the four parallelly placed implants within the interforaminal distance in an edentulous mandible.
Materials and Methods: The three-dimensional finite element analysis models consisted of cancellous bone surrounded by the cortical bone, four dental implants positioned in two different designs – i.e., four parallelly placed implants (Model 1) and All-on-Four concept (Model 2) with hybrid superstructures comprising of a Hader bar. The vertical (60N, 130N, and 300N) and lateral (20N, 45N, and 100N) loading protocols were considered and von Mises stress values were determined.
Results: On vertical and lateral loading, lower stress concentrations were observed in the peri-implant region in Model 2. However, there was higher stress concentration noticed on cortical, cancellous bone and bar attachment due to the tilting of implants in every condition.
Conclusion: Within the limitations of the study, All-on-Four concept is an optimal and viable treatment option if executed accurately as it reduces the cantilever length, reduces stress concentrations in the peri-implant region, and is cost-effective.

Keywords: All-on-Four concept, dental implants, edentulous mandible, finite element analysis


How to cite this article:
Mahantshetty M, Thumati P, Ayinala M. The analysis of the stress distribution around angulated and parallelly placed implants based on “all on 4 concept” and four implants placed parallel within the interforaminal distance in an edentulous mandible – An in vitro three-dimensional finite element analysis. J Dent Implant 2021;11:44-52

How to cite this URL:
Mahantshetty M, Thumati P, Ayinala M. The analysis of the stress distribution around angulated and parallelly placed implants based on “all on 4 concept” and four implants placed parallel within the interforaminal distance in an edentulous mandible – An in vitro three-dimensional finite element analysis. J Dent Implant [serial online] 2021 [cited 2021 Jun 13];11:44-52. Available from: https://www.jdionline.org/text.asp?2021/11/1/44/318069




   Introduction Top


Edentulism is a common condition noticed in the elderly population which can be the result of many factors such as poor oral hygiene, dental caries, and periodontal disease. The edentulous condition has been shown to have a negative impact on the quality of life.[1] Due to the increase in life expectancy, there is a greater need for clinicians to provide solutions to the edentulous populations with a prosthesis that could replace the lost natural teeth allowing optimum satisfaction and improving their quality of life.[2]

During 300 BC, Egyptians employed a variety of methods to restore the missing teeth. Conventional dentures have been the routine treatment plan for edentulism. The need for one or two dentures among the adult population would increase from 35.4 million adults in 2000 to 37.0 million adults in 2020 according to an epidemiological survey carried out in the United States. In addition, patients with dentures have presented only a marginal improvement in the quality of life when compared with implant therapy.[3]

Patients using conventional dentures often complain of pain, areas of discomfort, poor denture stability, and difficulties in eating as well as lack of or compromised retention capability.[4] Apart from these, complete dentures account for diminished oral sensory function, poor masticatory performance, reduced bite force, decreased motor control of the tongue, and loss of function.[5],[6],[7] Literature showed that the prostheses retained by osseointegrated implants significantly improved the quality of life for edentulous patients when compared with conventional complete dentures.[3],[8],[9]

Implant dentistry is often the treatment of choice to replace missing teeth in partially and completely edentulous patients. A dental implant system consists of a structure connecting a prosthesis to the jaw such that a force due to biting or chewing is distributed over the bone. While detailed knowledge of the loading condition of the implants and the surrounding bone is very important for the design and evaluation of dental implant systems, only limited data are available.[10]

In an edentulous condition, desiring to have implant-supported overdenture with multiple implants may not be feasible in many cases because of expense and the amount of bone left. In such a condition, the All-on-Four treatment concept provides edentulous arches and immediate/postextraction subjects with an immediately loaded, fixed prosthesis using four implants: two axially oriented implants in the anterior region and two tilted implants posteriorly.

The principle involves the use of four implants restored with straight and angled multiunit abutments, which support a provisional, fixed, immediately loaded, full-arch prosthesis. The All-on-Four treatment has been developed to maximize the use of available bone and allows immediate function. Studies showed that the survival rates for All-on-Four concept were between 92.2% and 100%.[11],[12],[13],[14]

Here in this study, the denture is fixed and supported on four implants – two anterior implants are parallel and two posterior implants are at an angle; hence, it is called “All On 4 Concept” and in another case, all four implants are placed parallel and compared for stress distribution. For the successful outcome of a treatment, it is important to analyze the stress distribution around these dental implants. A few experimental approaches have been carried out for stress analyses, the most recent being finite element analysis (FEA). This study is designed to analyze the influence of stress distribution in two different models based on – “All on 4 concept” and four implants placed parallelly within the interforaminal distance in the edentulous mandible using three-dimensional (3D) FEA.

Stress around dental implant systems can be evaluated using mechanical stress analysis, photoelasticity, and strain measurement on bone surfaces. However, these techniques have certain limitations such as difficulties in modifications after modeling. To predict the effects of stress on implant and surrounding bone, FEA can be used as it has become increasingly popular in the past two decades.[15]

The finite element method offers several advantages such as the representation of complex geometries accurately, easy model modifications, and representation of the internal state of stress and other mechanical quantities.[16] FEA has been an efficient computational tool that has been adapted from the engineering arena to dental implant biomechanics.[17]

Thus, to determine the stress distribution in the contact area of implants with bone, FEA can be used. This study analyzes the force transfer and stress distribution of an implant-supported overdenture with a Hader bar attachment. It further desires to optimize the stress distribution to the implant and surrounding bone.

The objective of this study is to present results using a 3D finite element model to assess and evaluate:

  • The stress distribution around four implants placed parallelly in the edentulous mandible
  • The stress distribution around four implants placed on All-on-Four concept, two anterior implants placed parallelly and two posterior implants placed at an angle of 45° in the edentulous mandible.



  •    Materials and Methods Top


    Method of collection of data

    • Threaded tapered implants are taken on two mandibular models, the first model will have implants placed on “All On 4 Concept” and the second model will have four implants placed parallelly.


    Procedure for modeling

    Stress distribution will be evaluated in each situation

    1. Construction of the geometric model
    2. Preparing of finite element mesh
    3. Material properties
    4. Application of boundary conditions
    5. Application of different loads
    6. Analysis of stress pattern.


    Sample collection

    • Four implants of length and diameter of 10/4 mm with a tapered and threaded design will be placed parallelly on the mandible, this will be created in the geometrical model [Figure 1]
    • Two implants of length and diameter of 10/4 mm with a tapered and threaded design will be placed parallel anteriorly and two implants of length and diameter of 12/4 mm with a tapered and threaded design will be placed at an angle of 45° posteriorly, this will be created in the geometrical model [Figure 2].
    Figure 1: Four implants of tapered and threaded design placed on the geometric model parallel to each other

    Click here to view
    Figure 2: Four implants of tapered and threaded design placed on the geometric model based on “all on 4 concept”

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    Laboratory analysis

    • Part I – Two mandibular edentulous geometrical models and mandibular overdenture were created using Nimax software. The geometrical models were simplified using HyperMesh software [Figure 3]


    • Part II – Two anterior implants were placed 3 mm away from the midline of the mandible and two posterior implants were placed 3 mm away from the distal border of the anterior implant, within the interforaminal distance


    • Part III


      • First edentulous mandibular model had all four implants of length and diameter of 10/4 mm with tapered and threaded design, which were placed parallelly in a geometrically created model
      • Second edentulous mandibular model had two anterior implants with length and diameter of 10/4 mm, placed parallel, and two posterior implants of length and diameter 12/4 mm, with a threaded and tapered design, placed at an angle of 45° in the geometrically created model.


      • Part IV – This was converted into FEA by Ansys software


    • Part V – Computations of stress arising in the implant bed were made with FEA, using 3D computer models
    • Type II bone quality was approximated and complete osseointegration was assumed
    • The masticatory load was stimulated on the mandibular overdenture under a static load (lateral component – 20N, 45N, and 100N and vertical intrusive component – 60N, 130N, and 300N) values of von Mises equivalent stress at the implant–bone interface which was computed using FEA [Figure 4] and [Figure 5].
    • Digital images were taken for each specimen and stress values were measured using Ansys software. [Figure 6] and [Figure 7] show the stress distribution on cortical, cancellous bone, implants, and Hader bar in Models 1 and 2.
    Figure 3: Geometric model of cortical, cancellous bone and mandibular overdenture created with Nimax software

    Click here to view
    Figure 4: Static load with vertical and lateral components applied on the mandibular overdenture supported by four parallelly placed implants

    Click here to view
    Figure 5: Static load with vertical and lateral components applied on the mandibular overdenture in an All-on-Four concept

    Click here to view
    Figure 6: Stress distribution on cortical, cancellous, implants and Hader bar in Model 1

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    Figure 7: Stress distribution on cortical, cancellous, implants and Hader bar in Model 2

    Click here to view



       Results Top


    The stress distribution in various areas such as cortical, cancellous bone, implant, and bar attachment in Models 1 and 2 was recorded. Vertical load of 60, 130, and 300N was applied and the values were recorded. The stress distribution in various areas was noticed on the application of a lateral load of 20, 45, and 100N. [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6] show the tabulated data.
    Table 1: Stress distribution in model 1 and 2 at various areas at a vertical load of 60 N

    Click here to view
    Table 2: Stress distribution in model 1 and 2 at various areas at a vertical load of 130 N

    Click here to view
    Table 3: Stress distribution in model 1 and 2 at various areas at a vertical load of 300 N

    Click here to view
    Table 4: Stress distribution in model 1 and 2 at various areas at a lateral load of 20 N

    Click here to view
    Table 5: Stress distribution in model 1 and 2 at various areas at a lateral load of 45 N

    Click here to view
    Table 6: Stress distribution in model 1 and 2 at various areas at a lateral load of 100 N

    Click here to view


    Stress distribution in Models 1 and 2 at various areas at a vertical load of 60 N

    In Model 1, on the application of 60 N vertical forces, the stress found at cortical bone was 4.2 MPa, at cancellous bone, it was 0.7 MPa, at implant area, it was 8.1 Mpa, and bar attachment, it was 20.2 MPa.

    In Model 2, on the application of 60 N vertical forces, the stress found at cortical bone was 7.6 MPa, at cancellous bone, it was 0.7 MPa, at implant area, it was 5.2 Mpa, and bar attachment, it was 30.2 Mpa [Table 1].

    Stress distribution in Models 1 and 2 at various areas at a vertical load of 130 N

    In Model 1, on the application of 130 N vertical forces, the stress found at cortical bone was 9.2 MPa, at cancellous bone, it was 1.5 MPa, at implant area, it was 17.6 MPa, and bar attachment, it was 43.8 MPa.

    In Model 2, on the application of 130 N vertical forces, the stress found at cortical bone was 16.5 MPa, at cancellous bone, it was 1.5 MPa, at implant area, it was 11.4 Mpa, and bar attachment, it was 65.5 Mpa [Table 2].

    Stress distribution in Models 1 and 2 at various areas at a vertical load of 300 N

    In Model 1, on the application of 300 N vertical forces, the stress found at cortical bone was 21.3 MPa, at cancellous bone, it was 3.5 MPa, at implant area, it was 40.7 Mpa, and bar attachment, it was 101.1 MPa.

    In Model 2, on the application of 300 N vertical forces, the stress found at cortical bone was 38.2 MPa, at cancellous bone, it was 3.6 MPa, at implant area, it was 26.3 Mpa, and bar attachment, it was 151.2 Mpa [Table 3].

    Stress distribution in Models 1 and 2 at various areas at a lateral load of 20 N

    In Model 1, on the application of 20 N lateral forces, the stress found at cortical bone was 1.4 MPa, at cancellous bone, it was 0.24 MPa, at implant area, it was 3.5 Mpa, and bar attachment, it was 5.6 MPa.

    In Model 2, on the application of 20 N lateral forces, the stress found at cortical bone was 2.8 MPa, at cancellous bone, it was 0.35 MPa, at implant area, it was 3.05 Mpa, and bar attachment, it was 8.7 Mpa [Table 4].

    Stress distribution in Models 1 and 2 at various areas at a lateral load of 45 N

    In Model 1, on the application of 45 N lateral forces, the stress found at cortical bone was 3.5 MPa, at cancellous bone, it was 0.62 MPa, at implant area, it was 8.9 Mpa, and bar attachment, it was 14.1 MPa.

    In Model 2, on the application of 45 N lateral forces, the stress found at cortical bone was 7.01 MPa, at cancellous bone, it was 0.89 MPa, at implant area, it was 7.6 Mpa, and bar attachment, it was 21.9 Mpa [Table 5].

    Stress distribution in Model 1s and 2 at various areas at a lateral load of 100 N

    In Model 1, on the application of 100 N lateral forces, the stress found at cortical bone was 7.1 MPa, at cancellous bone, it was 1.2 MPa, at implant area, it was 17.8 Mpa, and bar attachment, it was 28.3 MPa.

    In Model 2, on the application of 100 N lateral forces, the stress found at cortical bone was 14.02 MPa, at cancellous bone, it was 1.7 MPa, at implant area, it was 15.2 Mpa, and bar attachment, it was 43.8 Mpa [Table 6].


       Discussion Top


    The All-on-Four concept is a highly successful treatment option for the edentulous patient with excellent clinical outcomes. This is achieved without major grafting and its associated costs and surgical morbidity.[18],[19] The reduced number of implants and componentry also enables the reduction of the cost compared to traditional implant reconstructions. The All-on-Four concept is a paradigm shift in how implants are placed and angulated compared to traditional concepts with axial placement in a vertical manner. The angulations allow placement that avoids anatomical structures and also allows the use of longer implants, enabling increased bone-to-implant contact and placement of the implant into better-quality bone anteriorly.[17],[20]

    This has led to many innovations in the implant designs, number of implants, and different angles they are placed which attempts to minimize the stress of the masticatory loads, and hence, function to increase the longevity of the implant-supported overdenture. Also in most of the resorbed ridges where implant placement is difficult due to anatomic structures or maxillary sinus in the vicinity, different angulations can be used to overcome these problems. Often, patients cannot afford the high cost of implants for restoring complete ridges; in such cases, minimizing the number of implants by using newer techniques such as “All on 4 concept” can help reduce cost.

    The use of Non Rigid attachments like bars, studs, magnetic attachments, etc., help in better distribution of stress on the implants.[15]

    This study is for the most part directed toward determining the stress patterns generated around implants that is in a situation where all four implant-supported overdenture is placed parallel and other situation where “All on 4 concept” (that is two anterior implants are placed parallel and two posterior implants are placed at an angle of 45°) is followed with bar attachments and also to find the optimal stress distribution around the bone, implant, and attachment system. The factors which influence the distribution of stresses around the implant-supported overdenture and the alveolar bone include the implant design, implant number, implant angulation, implant length and diameter, type of attachment, and the type of load. This study also undertakes to explore the effect of these factors on the stress distribution and endeavors to rationalize the cause–effect relationship between them.

    In a 2D method, it is not possible to study horizontal or oblique bite forces. Therefore, it is not a valid representation of a clinical situation.[21],[22] To suit the aims of this study, a 3D finite element model was generated, which is well suited to study the true biomechanical behavior in localized regions of major supporting hard tissues of the mandible. Certain assumptions were made in geometric considerations, material properties, boundary conditions, and bone–implant interface to make the modeling and solving process possible. It is apparent that the presented model was only an approximation of the clinical situation; therefore, it is advisable to focus on qualitative comparison rather than quantitative data from these analyses.

    Model considerations

    To get the exact bony contours of cancellous and cortical bone, a mechanical model of an edentulous mandible was generated from computerized tomography (CT scan). Some parameters were not considered in this study, with the complexity of the geometry during meshing the number of elements may exceed the operating capacity of the software and hence may require substructuring or other alternatives to conduct an analysis. A comparatively simple 3D model was used to evaluate these parameters. The stress found on mucosa and overdenture was not found to be significant and it did not affect the purpose of this study. To save the computer memory, modeling time, processing time, and ease for analysis, the ramus and condyles of the mandible were also not modeled. The boundary conditions were applied at the distal end of the mandible to simulate muscle forces.

    The accuracy of the results decreases with the increase in element size. However, for this study, the gradual increase in element size protected the area of interest from being affected by the inaccuracies of the stresses in large elements. The acceptable percentage of error for the FEA model should be <3% and here it is 0.3%. The results of this analysis concur with the findings of other studies that have used different investigation methods.[23],[24],[25],[26] Therefore, the model employed in this study is considered to satisfactorily simulate reality.

    Material properties

    Materials properties and their structural basis help us to understand the bone quality type. The stress and strain distribution in the structure is greatly influenced by the material properties. The implant with the superstructure, acrylic resin, and all the vital structures such as cortical, cancellous bone, and mucosa were assumed to be linearly elastic, homogenous, and isotropic.

    Loading conditions

    In this study, two different models were used for stress analysis, on each model, masticatory forces were applied, i.e., vertical load of 60 N, 130 N, and 300 N from the occlusal aspect and oblique load of 20 N, 45 N, and 100 N to the occlusal plane from the buccolingual direction. The muscle forces were used as a static force in the model. These forces simulated different situations that had been found in vivo to which an overdenture wearer has been subjected.

    Stress distribution

    To summarize the overall stress at a point, the von Mises stresses were most commonly reported in FEA studies. Both compressive and tensile stresses were calculated.

    Implants

    The titanium–aluminum–vanadium (Ti 6A1-4V) implants used in this study were of a tapered threaded design, 10 and 12 mm in length and 4 mm in diameter. Rieger concluded that a cylindrical implant design directed most of the applied axial load to the apical bone, while the tapered design provided better stress distribution.[27] Therefore, a tapered design was designed for this study. The ideal distance between the implants was as follows: the two anterior implants were 3 mm away from the midline and two posterior implants were 3 mm away from the distal surface of anterior implants. The bar attachment was 2 mm in breadth, 2 mm in height, and 2 mm in width.

    In this present study using FEA, it is clearly seen that the stress distribution around cortical bone during the vertical and lateral loading in Model 1 is less than Model 2, this is because of the angulation of implants in Model 2 and the more complex structure of the implant and bar attachment system in Model 2. The stress distribution around the cancellous bone during vertical and lateral loading in both Model 1 and Model 2 is almost the same. The stress distribution around the implants during vertical and lateral loading is more in Model 1 than in Model 2, this is because of the angulation of posterior implants given in Model 2 we can use longer implants which helps in better stress distribution, also in Model 1, the cantilever length is longer, whereas in Model 2, the cantilever length is shorter, thus reducing the stress around implants in Model 2 compared to Model 1. The stress around the bar attachment during vertical and lateral loading in Model 1 is less when compared to Model 2, this is because Model 2 has a more complex attachment system with angulated abutment, so stress concentration is more in Model 2 when compared with Model 1 and also the direction of lateral forces increases the stress.

    Within the limitations of the 3D virtual analysis, the results of this study demonstrated that the loading and tilting of a single implant increased the stresses when compared to the stress around a single vertical implant. In contrast, when analyzing the stress around four implant-supported prosthesis/overdenture in completely edentulous mandible, the tilting of the distal implants supporting decreased cantilevered segments showed decreased peri-implant stresses when compared to all four vertically placed implants supporting cantilevered segment. The cantilever length reduction and longer posterior implants distally tilted associated with “All on 4 Concept” played a key role in decreasing the peri-implant stresses seen around the implants.

    Limitations of finite element modeling

    The present study has certain limitations: first, the vital anisotropic tissues were considered isotropic. Next, the loads applied were static loads that were different from the dynamic loading seen during the function. The finite element method is an extremely accurate and precise method for analyzing structures. However, living structures are more than mere objects. FEA is based on mathematical calculations which are based on simulation of the structure in its environment. However, living tissues are beyond the confines of set parameters and values since biology is not a compatible entity. Hence even though FEA provides a sound theoretical basis of understanding the behavior of a structure in a given environment, it should not be considered alone. Actual experimental techniques and clinical trials should follow FEA to establish the true nature of the biological system.


       Summary and Conclusion Top


    From the analysis of this study, the following conclusions were drawn regarding the stress distribution in two different situations:

    1. In Model 1 analysis of stress distribution, the implant-supported overdenture where all the four implants were placed parallel in the edentulous mandible using 3D FEA showed that:

      On application of 60 N vertical forces, the stress found at cortical bone was 4.2 MPa, at cancellous bone, it was 0.7 MPa, at implant area, it was 8.1 MPa, and bar attachment, it was 20.2 MPa; on application of 130 N vertical forces, the stress found at cortical bone was 9.2 MPa, at cancellous bone, it was 1.5 MPa, at implant area, it was 17.6 MPa, and bar attachment, it was 43.8 MPa; on application of 300 N vertical forces, the stress found at cortical bone was 21.3 MPa, at cancellous bone, it was 3.5 MPa, at implant area, it was 40.7 MPa, and bar attachment, it was 101.1 MPa; on application of 20 N lateral forces, the stress found at cortical bone was 1.4 MPa, at cancellous bone, it was 0.24 MPa, at implant area, it was 3.5 MPa, and bar attachment, it was 5.6 MPa; on application of 45 N lateral forces, the stress found at cortical bone was 3.5 MPa, at cancellous bone, it was 0.62 MPa, at implant area, it was 8.9 MPa, and bar attachment, it was 14.1 MPa; and on application of 100 N lateral forces, the stress found at cortical bone was 7.1 MPa, at cancellous bone, it was 1.2 MPa, at implant area, it was 17.8 MPa, and bar attachment, it was 28.3 MPa.
    2. In Model 2 analysis of stress distribution, the implant-supported overdenture where all the four implants are based on “All on 4 Concept” that is two anterior implants were placed parallel and two posterior implants were placed at 45° angle in the edentulous mandible using 3D FEA showed that:

      On application of 60 N vertical forces, the stress found at cortical bone was 7.6 MPa, at cancellous bone, it was 0.7 MPa, at implant area, it was 5.2 MPa, and bar attachment, it was 30.2 MPa; on application of 130 N vertical forces, the stress found at cortical bone was 16.5 MPa, at cancellous bone, it was 1.5 MPa, at implant area, it was 11.4 MPa, and bar attachment, it was 65.5 MP; on application of 300 N vertical forces, the stress found at cortical bone was 38.2 MPa, at cancellous bone, it was 3.6 MPa, at implant area, it was 26.3 MPa, and bar attachment, it was 151.2 MPa; on application of 20 N lateral forces, the stress found at cortical bone was 2.8 MPa, at cancellous bone, it was 0.35 MPa, at implant area, it was 3.05 MPa, and bar attachment, it was 8.7 MPa; on application of 45 N lateral forces, the stress found at cortical bone was 7.01 MPa, at cancellous bone, it was 0.89 MPa, at implant area, it was 7.6 MPa, and bar attachment, it was 21.9 MPa; and on application of 100 N lateral forces, the stress found at cortical bone was 14.02 MPa, at cancellous bone, it was 1.7 MPa, at implant area, it was 15.2 MPa, and bar attachment, it was 43.8 MPa.
    3. The values of stress showed that in Model 1 and Model 2 under both vertical (60 N, 130 N, 300N) and lateral load (20 N, 45 N, 100 N) the stress at cortical bone was increased in Model 2 when compared to Model 1, the stresses at cancellous bone were almost same in Model 1 and Model 2, the stress around the implants increased in Model 1 when compared to Model 2 and at the bar attachment the stresses were increased in Model 2 than in Model 1.


    This study concludes that the “All-on-Four concept” allows the clinicians to plan optimal implant positions and accurately execute the plan. Well-distributed implant positions translate to a biomechanically sound prosthesis supported by the least number of implants. The tilting of the distal implants supporting decreased cantilevered segments showed decreased peri-implant stresses when compared to all four vertically placed implants supporting the cantilevered segment. The cantilever length reduction and distally tilted longer posterior implants associated with “All on 4 Concept” played an important role in decreasing the peri-implant stress around the implants.

    Within the limitation of this study:

    1. Vital anisotropic tissues were considered isotropic
    2. The loads applied were static loads that were different from the dynamic loading seen during the function
    3. Living tissues are confined by set parameters and values.


    It can be said that “All on 4 concept” is a viable treatment modality, with the angled posterior implants allowing longer implants anchored in better quality bone, reduces posterior cantilever, eliminates bone grafts in the edentulous maxilla and mandible in the majority of cases, implants well-spaced, good biomechanics, and reduced cost due to less number of implants, thus increasing the overall survival and success rate of the treatment in edentulous patients.

    Financial support and sponsorship

    Nil.

    Conflicts of interest

    There are no conflicts of interest.



     
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