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ORIGINAL ARTICLE
Year : 2021  |  Volume : 24  |  Issue : 5  |  Page : 660-666

Evaluating the effect of subcrestal placement on platform switched short dental implants and von mises stress in D3 bone–A 3D FEM study


1 Department of Periodontics, College of Dentistry, Gulf Medical University, Ajman, UAE
2 Department of Periodontics, Rajah Muthiah Dental College and Hospital, Annamalai, Chidambaram, Tamil Nadu, India

Date of Submission18-Jun-2020
Date of Acceptance02-Aug-2020
Date of Web Publication20-May-2021

Correspondence Address:
Dr. M S Reddy
Lecturer, Department of Periodontics, College of Dentistry, Gulf Medical University, Ajman, 4184
UAE
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_362_20

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   Abstract 


Aim: To investigate the effect of platform switched short dental implants and subcrestal placement on von Mises stress in the maxillary anterior region (D3 bone) by using three-dimensional finite element model analyses (3D FEM). Materials and Methods: Biomechanical behaviour of von Mises stress in maxillary anterior region (D3) bone were stimulated with the help of 3D FEM with the help of ANSYS WORKBENCH version 17.5. The bone model had a cortical core of (1 mm) surrounding the inner cancellous core, which represents D3 bone. Two models were designed model 1 (6 x 4.6 mm), (7.5 x 4.6 mm) and model 2 (6 x 5.8 mm), (7.5 x 5.8 mm). Loads of 100, 200 N were applied at an angle of 0°, 15°, 30° along the long axis of the tooth model. Results: In all model's cortical bone exhibited greater stress than cancellous bone. Greater stress was reported in axial direction at 30° then 15° and least at 0° irrespective of load applied. An increase in implant length (7.5 mm) did not exhibit any stress reduction in both the model but implant diameter (5.8 mm) led to reduction in von Mises stress in both the groups. Greater the force applied greater was stress in both bones irrespective of direction of force applied (200N). Lastly subcrestal (0.5 mm) placement has slight reduction in stress compared to equicrestal placement in both the groups. Conclusion: Numerical results from the current study suggest that, for short implants, implant diameter is considered more effective design parameter than implant length. Current findings state that platform switch short subcrestal implants results in conservation of marginal bone loss along with better stress distribution around peri-implant regions in D3 bone. However, all models analyzed in this study showed development of von Mesies stresses within physiological limits for human cortical bone.

Keywords: D3 bone, equicrestal, FEM, platform switched implants, short implants, subcrestal


How to cite this article:
Reddy M S, Rajasekar S, Eid Abdelmagyd H A. Evaluating the effect of subcrestal placement on platform switched short dental implants and von mises stress in D3 bone–A 3D FEM study. Niger J Clin Pract 2021;24:660-6

How to cite this URL:
Reddy M S, Rajasekar S, Eid Abdelmagyd H A. Evaluating the effect of subcrestal placement on platform switched short dental implants and von mises stress in D3 bone–A 3D FEM study. Niger J Clin Pract [serial online] 2021 [cited 2022 Dec 3];24:660-6. Available from: https://www.njcponline.com/text.asp?2021/24/5/660/316466




   Introduction Top


One of the major concerns for the long-term success of any dental implants lies in the preservation of crestal bone. The new normal is marginal bone loss up to 1.5 mm in the first year and 0.1–0.2 mm in the following years.[1],[2] Various factors do play a vital role in marginal bone loss categorized broadly into local and biomechanical factors.[3],[4] Thus resulted in search for new techniques and methods in order to preserve marginal bone. Alongside with modified implant designs and techniques, bone density is one such factor that needs considerable attention with regards to quality and quantity. Higher stress around dental implants noticed in low density cancellous bone. Under mechanical load, crestal bone loss is seen more in anterior maxilla due to reduced bone-implant interface as it is composed of D3 bone.[5],[6] D3 bone is composed of thinner porous cortical bone at the crest and fine trabecular bone within the ridge.[7] High failure rate reported in regions of poor bone quality.[8] Various alterations in implant designs and surgical procedures carried out in order to reduce implant failure. One such attempt is subcrestal placement of platform switch short dental implants.

3D FEM is a useful tool not only in analyzing implant biomechanics but also used to predict clinical success. Researchers have reviewed its application in implant dentistry and its impactions in clinical research.[9],[10] Clinicians can extrapolate FEM results by better understanding principles of FEM and interpret the results to clinical conditions. 3D FEM is a theoretical model used to analyze stress and strain with the help of complex geometry models. Nevertheless, it also assesses biomechanical problems before they occur.[11] In the recent past, FEM gradually becomes a valuable tool in medicine and dentistry.

Short and wide diameter implant usage has gained popularity over recent years due to various reasons. As a result, used in patients with reduced bone volume, density, or requiring additional bone grafting. As per current terminology, any implant less than 8 mm is considered short.[12] The success of short dental implants in the posterior maxilla and mandibular region exhibited a mixed view. In terms of patient and clinical point of view, short dental implants offer certain advantages to their contrary.[13]

Platform switching concept introduced way back in 1991 to effectively reduce circumferential bone loss with an added advantage of better acceptance by both adjacent hard and soft tissues.[14] As a result, used in the esthetic zone. Currently, we do not have enough data with regards to the short platform switch and subcrestal dental implant placement, which lead us to carry out to this study.

Till date research concerning FEM in the maxillary anterior region (D3 bone) using short and wide platform switched implants to evaluate stress at the bone-implant interface is not ample. Thus, we planned a study to comparatively evaluate the effect of platform switched short implants and subcrestal placement over stress distribution at the bone-implant interface using a vertical load of 100N and 200N three different angles. The null hypothesis tested is that there was no difference in stress distribution among subcrestal and equicrestal placement of platform switched implants. A meticulous anterior maxilla model, implant, and other components modelled to obtain reliable results. And then this 3D FEM model is transferred to ANSYS for evaluating stress distributions at the bone implant interface.


   Materials and Methods Top


Maxillary anterior central incisor region modelled with a cortical bone of uniformly thick 1 mm and an inner core of cancellous bone by 3D FEM. A total of four models created and categorized into two groups. Stress was evaluated at the bone implant interface with two different forces (100N, 200N) in D3 bone. By using Ansys software, von Mises stress evaluated with the help of color-coded bands. Each band of color signified a unique range of stress value, represented in Mega Pascal (MPa). Two different lengths, diameter, and abutments used are model 1 (6 x 4.6 x 3.5 mm), (7.5 x 4.6 x 3.5 mm), model 2 (6 x 5.8 x 4.5 mm), (7.5 x 5.8 x 4.5 mm). The applied force was 100N, 200N in an axial direction of (0°, 15°, 30°) for realistic simulation.[15] All models created by ANSYS WORKBENCH. von Mises stress is evaluation in both cancellous and cortical bone at various depths. [Table 1] and [Table 2]. Mesh generation with 3D FEM geometric models using Hypermesh software [ANSYS software]. Translations interpreted on x, y, and z-axis with ten-noded tetrahedron elements with 3° of freedom per node. All the nodes at the base of the model were fixed so as not to move when subjected to force systems. The boundary condition is an important factor in the FEM reflecting the manner of movements occurring at the nodes and their relationship. Each model comprised of approximately 144786 elements and 218725 nodes. Material properties considered as isotropic, homogeneous, and linearly elastic materials used in the model construction. The Poisson's ratio and young's modulus for different materials used were assigned from the data available in the literature. Elastic properties used in this study is listed in the table [Table 3].[16] These FEA boundary conditions studies include fixed boundary conditions for modelling of the maxillary anterior region. The boundary condition is the application of force and constraint. The FEM assumed a state of optimal osseointegration resulting in an ideal fit between bones and implant interface.[17] All models represent a state of osseointegration and ready to load.
Table 1: Model 1 von Misses stress in cortical and cancellous bone

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Table 2: Model 2 von Misses stress in cortical and cancellous bone

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Table 3: Mechanical properties as well as materials used in FEM model analysis

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   Results Top


A total of four models created and categorized into two groups. Stress was evaluated at the bone implant interface with two different forces (100N, 200N) in D3 bone. By using Ansys software, von Mises stress evaluated with the help of color-coded bands. Each band of color signified a unique range of stress value, represented in Mega Pascal (MPa). In all models, cortical bone exhibited maximum stress greater than cancellous bone. [Figure 1] With regards to angulations of load, greater stress observed in the axial direction of 30°, 15° and least at 0° irrespective of load applied. [Figure 2] and [Figure 3] An increase in implant length did not exhibit stress reduction at equicrestal position but subcrestal placement exhibited maximum stress in model 1. However, an increase in implant diameter led to a reduction in von Mises stress in both models l and 2 with least seen in 5.8 mm diameter implants. [Figure 4] With the force of 200N in the axial direction, both cortical and cancellous bone exhibited maximum stress. [Figure 2] and [Figure 3] Greater the force applied greater was stress in both bones irrespective of the direction of force applied. However, 200N forces exhibited great stress in an axial direction (30°). [Figure 2] and [Figure 3] Lastly, subcrestal placement has a slight reduction in stress compared to equicrestal placement in both groups [Figure 5].
Figure 1: Maximum and minimum von Mises stress in cortical and cancellous

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Figure 2: von Mises stress in cortical and cancellous bone different length (6 x 4.6), (7.5 x 4.6)

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Figure 3: von Mises stress in cortical and cancellous bone different length (6 x 5.8), (7.5 x 5.8)

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Figure 4: von Mises stress in cortical and cancellous bone with implant diameter of 5.8 mm

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Figure 5: von Mises stress in cortical and cancellous bone with 0.5 mm subcrestal placement

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   Discussion Top


In comparison to natural teeth, stress destitution in implants will differ due to the absence of periodontal ligament. As a result, dental implants are more at risk due to excessive load leading to peri-implantitis.[18] The present study reports the highest stress in the crestal bone around the implant neck and more on in oblique direction (30°). These results were like other FEM studies. Results from the current study differ with the null hypothesis tested, despite two different forces applied. 2 mm subcrestally placed dental implants displayed better biomechanical behavior than equicrestal placement with (6 x 4.6 mm) implant. These findings agree with other studies.[19],[20]

In the literature, we have a contradictory statement concerning subcrestal implant place. Only a few researchers evaluated the concept of platform switch and short subcrestal implant placement under biomechanical conditions. This study might be the first to do so in D3 bone. In the present study, cortical bone stress reduced significantly at 0.5 mm subcrestal with 5.8 mm diameter and in both lengths (6, 7 mm). Thus, suggesting subcrestal placement results in a reduction of cortical bone stress. This phenomenon attributed to different biomechanical behaviors exhibited by subcrestal implants by not engaging the crestal cortical bone. Besides, cancellous bone exhibited the least stress in subcrestal position attributed to the elastic modulus. As a result, it promotes better stress distribution.[21],[22] Marginal bone at implant neck is vital for implant survival and esthetics as anterior maxilla represents esthetic zone.

Other factors analyzed in this study, are biomechanical behavior of short implants (length and diameter), amount and angulation of force applied. Based on implant diameter, the FEM results of the present study corroborate with previous biomechanical studies that lower stress concentration reported with wide diameter implants (5.8 mm), especially in short implants.[23],[24] This could be because short wider diameter implants have better stress distribution as it improves implant strength and fracture resistance at the bone crest.[25] Also, other studies state that the implant diameter is more important than its length in improving the stress distribution pattern.[26]

Some authors reported a low success rate with short dental implants compared to others.[27] Others expressed good predictability and success, which were similar to our results. They recommended these implants in the atrophic bone as the case with the anterior maxilla.[28] In D3 bone implant success depends on the length and diameter of implants under mechanical load. Current study results are in accord with the stress values, and state that short implants (6 mm) are capable of dissipating stress in cortical bone, which in turn affects marginal bone loss. Thus attributing to the latest concept that is an increase in functional surface area (FSA) will lead to a better distribution of von Mises stress.[29] Another reason is, based on stress principle[30]; lastly masticator load distribution occur initially at first millimeters around the implant neck and implant length do not get better on stress distribution.[31]

Bone if overloaded will lead to crestal bone resorption and can lead to implant failure. Microscopic bone destruction occurs when force is applied, but if this exceeds the permissible limits, it jeopardizes implant success.[32] Based on the results observed in this study were high stress was noticed in cortical bone when axial load of 100N, 200N applied at (30°). These results are consistent with the literature.[33] Reality is that the oblique loading is likely to add von Mises stress concentration in the direction of load.[34] As a result, oblique forces are considered more destructive to bone tissue, which may add to a higher rate of bone resorption over time. Cancellous bone exhibited low stress values as compared to the cortical bone that might be ascribed to low elastic properly of cancellous bone. These findings agree to our current study.[35],[36]


   Conclusion Top


In order to manage the risk of bone overloading and enhancing implant biomechanical stress-based effectiveness, the computed findings from the current study indicate that, for short implants, implant diameter deemed to be more efficient design factor than the length of the implant. Current findings state that platform switch short subcrestal implants model results in conservation of marginal bone loss along with better stress distribution around peri-implant regions in D3 bone. Nevertheless, all the models studied in this research demonstrated a concentration of von Mises stresses within biological limits for a human cortical bone.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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