Effect of different framework materials on stresses induced at the implant/bone interface in all-on-four implant treatment concept: three-dimensional finite element analysis :Ahmed M Sayed, Ibrahim A Abdelazim, Tanta Dental Journal

ORIGINAL ARTICLE
Year : 2022 | Volume : 19 | Issue : 3 | Page : 105--109

Effect of different framework materials on stresses induced at the implant/bone interface in all-on-four implant treatment concept: three-dimensional finite element analysis

Ahmed M Sayed¹, Ibrahim A Abdelazim²,
¹ Department of Dental Biomaterials, Modern University for Technology and Information, Cairo, Egypt
² Department of Mechanics, Giza Systems, Cairo, Egypt

Correspondence Address:
Ahmed M Sayed
PhD, Modern University for Technology and Information, Al Gamea Al Haditha Street, 5^th District, El.Hadaba El.Wosta, Mokatam, Cairo
Egypt

Abstract

Background and aim Treatment of mandibular edentulous ridge with all-on-four treatment concept is a reliable choice. However, the framework material may affect the stresses transmitted to the implant and bone. The aim of the study was to compare stresses transferred to implant–bone interface on using glass fiber-reinforced composite (GFRC), zirconia (Zr), titanium (Ti) and poly-ether-ether-ketone (PEEK) as framework materials. Patients and methods Three-dimensional finite element model of completely edentulous mandible restored with four implants (two axial anterior implants and two posterior implants 30° distally tilted) connected with a framework of different materials (Zr, Ti, GFRC, and PEEK) was constructed. A unilateral axial load of 250 N was applied at the distal end of the cantilever and the resultant von Mises stresses at implant–bone interface were calculated. Results The lowest von Mises stresses at implant/crestal bone area was recorded with Zr framework followed by Ti then GFRC while the highest von Mises stresses were recorded with PEEK framework. Conclusions Within the limitations of this study, it could be concluded that the stiffer framework material transmits more stresses to the implants. The stress distribution of GFRC, as a framework material, is better than PEEK.

How to cite this article:
Sayed AM, Abdelazim IA. Effect of different framework materials on stresses induced at the implant/bone interface in all-on-four implant treatment concept: three-dimensional finite element analysis.Tanta Dent J 2022;19:105-109

How to cite this URL:
Sayed AM, Abdelazim IA. Effect of different framework materials on stresses induced at the implant/bone interface in all-on-four implant treatment concept: three-dimensional finite element analysis. Tanta Dent J [serial online] 2022 [cited 2023 Mar 29 ];19:105-109
Available from: http://www.tmj.eg.net/text.asp?2022/19/3/105/356076

Full Text

Introduction

After restoring the edentulous patients, especially with atrophied residual ridges, with a complete denture, they reported suffering from many complications related to complete denture such as function, retention, phonetics, pain and excessive salivation [1],[2]. However, implant supported restorations improved this unpleasant condition as they reported a significantly more patient satisfaction as a result of their better function, esthetics, phonetics, retention, and comfort [3],[4],[5].

Unfortunately, alveolar bone resorption limits the placement of dental implants on the posterior regions due to presence of vital structure such as mandibular canal that contains inferior alveolar nerve. Therefore, in 2003, Malo and his colleagues proposed the all-on-four treatment concept to avoid insertion of the posterior implants. This concept involves using of four implants in the anterior region of the jaws; the two most anterior implants are straight while the most posterior implants are angulated with 30–45° [6],[7],[8].

The definite restoration of the all-on-four treatment concept could be a removable overdenture or a fixed bridge over a framework. The framework may be fabricated from different alloys as gold alloy, cobalt–chromium, titanium (Ti) or non-metallic materials as zirconia (Zr), poly-ether-ether-ketone (PEEK) and poly-ether-ketone-ketone [9]. Due to difference in the modulus of elasticity of these materials, different stress distribution patterns had been obtained at the peri-implant–bone and at the framework [10],[11],[12],[13]. Stress distribution may be assessed in-vitro by photo-elastic models, strain gauges and virtually by finite element analysis (FEA) [10],[11],[12],[13],[14],[15].

Glass fiber-reinforced composites (GFRC) showed promising mechanical, optical and biological properties that allowed their uses in the field of dentistry. They used for fabrication of fixed partial prothesis, temporary fixed crown and bridges, endodontic posts, orthodontic retainers, and periodontal splints [16].

Many manufacturers supplied the GFRC in machinable CAD-CAM disks which give a possibility for machining a framework for all-on-four restoration. However, the stress distribution patterns still a question.

Stress distribution pattern within complex structures as implant supported prostheses is a complicated process. Due to the difference in the geometry of jaw bones, implants, abutments and definitive prosthesis in addition to the difference in material properties of the entire system and complex masticatory force, FEA can be a consistent analyzing tool of the stress distribution patterns [17].

Consequently, this study was conducted to evaluate the stress distribution pattern at peri-implant–bone due to load application over the GFRC framework and compare them with the stresses developed with Zr, Ti and PEEK material.

Material and methods

Modeling of the mandible

A three-dimensional geometrical model of a completely edentulous mandible was created from a cone beam computed tomography scan of a completely edentulous patient with the aid of Mimics 21.0 software (Materialise, Belgium). The bone segments were modeled as an outer shell of cortical bone with 2 mm thickness and an inner volume of cancellous bone.

Modeling of implants and frameworks

The implants and the denture frameworks were created using SOLIDWORKS CAD software (DS Solidworks Crop., USA). The implants were designed as a threaded with a diameter of 4 mm and length 16 mm. The implants were inserted in edentulous mandible and distributed according to all-on-four concept. The two most anterior implants are placed axially, whereas the two posterior implants were placed tilted 30° distally to the crest of the ridge and multi-unit abutments were connected to implants.

The framework was designed as a solid bar of 5 mm in thickness, 6 mm in width and following the curvature of the mandible and with 2 mm away from the crest of the ridge. The distance between each two implants was 21 mm and with 16 mm distal cantilever extension [Figure 1] [12].{Figure 1}

Material properties

The used materials were assumed to be isotropic, homogenous and linearly elastic with properties listed in [Table 1].{Table 1}

Defining meshing

The assembly was meshed by tetrahedral mesh element with parabolic edges to produce a high-quality solid mesh that produced a total number of nodes equals 1 238 571 nodes and a total number of elements equals 837 484 element [Figure 2]a.{Figure 2}

Defining contacts and gaps between components

The fixation of the three-dimensional model was performed at the distal part of the assembly to prevent movements in the 6-degrees of freedom.

Load application

An axial static load of (250 N) was applied onto the most distal part of the bar cantilever extension [Figure 2]b.

Resultant stresses

Von Mises' equivalent stresses were selected as they are most commonly reported in FEA studies to summarize the overall stress state at a point [12]. Consequently, von Mises stress distribution pattern was calculated at the implant–bone interface after load application with each framework material. The resultant stresses from FEA calculations were based on Euler–Bernoulli equation and method of weighted residuals.

Results

The highest von Mises stresses at implant–bone interface for both anterior and posterior implants were represented in [Table 2] and [Figure 3].{Table 2}{Figure 3}

For all tested framework materials, the highest stresses were detected at the areas of the two posterior implants than anterior one.

Zr framework material has reported the lowest stresses at both anterior and posterior implants compared to the other three (Ti, GFRC, and PEEK) studied materials 36.758 and 178.207 MPa, respectively.

Slightly higher von Mises stresses were detected in Ti than Zr framework 42.673 and 203.223 MPa, followed by GFRC 58.964 and 277.804 MPa.

On the other hand, PEEK framework had reported the highest stresses at both anterior and posterior implants 77.066 and 409.459 MPa, respectively.

Discussion

The all-on-four dental implant concept provides a reliable treatment option for patients with atrophic residual ridges either by high patient satisfaction or clinical success rate [4],[18]. However, the prosthetic materials play a significant role in the stresses and strains developed at implant–bone interface [10],[11],[12],[13],[19].

The present study had utilized FEA to evaluate the stress distribution pattern in four framework materials with different mechanical properties at the implant/bone interface in mandibular all-on-four implant treatment concept.

FEA had been utilized as a noninvasive preliminary evaluating method that can predict the behavior of the materials without any morbidity to patients [17]. Moreover, FEA is an appropriate technique for measuring complex structures that cannot be standardized clinically [10],[17],[19].

The angulation of the distal abutment was set at 30° with accordance with previous FEA studies [11],[12],[20].

The cantilever length was 16 mm and the load was applied at the most distal part of the cantilever to maximize the stresses over the implant as it was reported the proportional relation between cantilever length and stresses over the implants [21],[22].

The equivalent stresses developed at the cortical bone plates surrounding the anterior straight implant and posterior angled implant were evaluated with four different framework materials.

The results of this study had shown that the least von Mises stresses at implant/crestal bone interface were created with Zr framework followed by Ti then GFRC. However; the highest stresses were noticed on using PEEK as framework material.

This finding may be due to high the modulus of elasticity of the Zr framework material followed by Ti and GFRC. This may be due to the fact that materials with high elastic modulus may induce high internal stresses but better stress dissipation to the adjacent prosthetic structures and less stresses transmitted onto the implant/bone interface.

However, the highest stresses induced at the implant/bone interface with PEEK framework material that having low elastic modulus. This finding agreed with previous studies reported that high stresses were induced at the crestal bone on using framework materials with low elastic modulus as PEEK or poly-ether-ketone-ketone compared to other materials that have higher elastic modulus such as cobalt–chromium, Ti, and Zr [10],[11],[12],[19],[23],[24].

Lee et al. [23], had reported that the framework material with low elastic modulus may induce less internal stresses but has poor stress dissipation and transmit more stresses to adjacent prosthetic structure with subsequent lower long-term safety.

Therefore, the using GFRC with its intermediate modulus of elasticity, between PEEK and Zr, affords a suitable solution for making a framework with appropriate internal stress and stress dissipation ability. Moreover, its lower density, compared with Zr and Ti leading to lower weight which is more favorable criterion for the patient to have a lighter restoration.

Regarding the stress distribution pattern at the anterior and posterior implants, the results of the present study revealed increase in the stresses at the posterior implant. This is in correspondence with other studies [11],[19],[25]. The higher the stresses induced onto bone, the more bone resorption [25].

This finding may agree with Korsch et al. [26] had reported more biological and severe complications in posterior implants compared to anterior implants when they follow up all-on-four success rate.

The limitations of the FEA in the current study include considering the anisotropic tissues, like bone, as isotropic material. The applied load was performed as a unilateral static load while the actual load has a dynamic behavior.

Moreover, the tilting of posterior implant was set at 30° while in clinical situation the angle of the posterior implant may be set up to 45°. Furthermore, the design considered that the contact between implant and bone is 100% which is impossible in the clinical scenario.

Within the limitations of the current study and regarding all-on-four treatment concept, it may be concluded that:

The stiffer framework material, the less stresses transmitted to the implants.GFRC, as a framework material, has better stress distribution than PEEK and lower density than Zr and Ti which enables it as a reliable solution.

Acknowledgements

The authors thank Prof. Azza Farahat for her technical support.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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