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Table of Contents   
ORIGINAL RESEARCH  
Year : 2013  |  Volume : 24  |  Issue : 1  |  Page : 8-13
Comparison of strain generated in bone by "platform-switched" and "non-platform-switched" implants with straight and angulated abutments under vertical and angulated load: A finite element analysis study


Department of Prosthodontics and Implantology, Faculty of Dental Sciences, Sri Ramachandra University, Porur, Chennai, Tamil Nadu, India

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Date of Submission16-Nov-2011
Date of Decision21-May-2012
Date of Acceptance13-Jul-2012
Date of Web Publication12-Jul-2013
 

   Abstract 

Purpose: The aim of this study was to evaluate the microstrain exhibited by bone around immediately loaded, platform-switched, and non-platform-switched implants under vertical and angled loading using a finite element analysis (FEA) and also to evaluate whether platform-switched implants evoke a better response than non-platform-switched implants on a mechanical basis.
Materials and Methods: Three-dimensional finite element study was undertaken to model and analyze an immediate loaded situation. FEA was chosen for this study since it is useful in determining the stress and strain around the dental implant. Bone responses to vertical and angulated loads on straight and angulated abutments (platform-switched and non-platform-switched abutments) were evaluated.
Results: Non-platform-switched abutments tend to exhibit a lower tensile stress and compressive stress but higher microstrain value (conducive to higher chance of bone resorption) than platform-switched abutments. Ideal bone remodeling values of microstrain (50-3000 μϵ) were exhibited by platform-switched straight abutments under vertical load and angled load (with an abutment-implant diameter difference of 1 mm).
Conclusion: In spite of the obvious advantages, the practice of immediate loading is limited due to apprehension associated with compromised bone response and a higher rate of bone loss around an immediately loaded implant. The mechanical basis for the concept of "platform switching" in immediately loaded situation is analyzed in this context. The results of this limited investigation indicated that the ideal values of microstrain (50-3000 microstrain) can be exhibited by platform switching of dental implants (with an abutment-implant diameter difference of 1 mm) and can be considered as a better alternative for prevention of crestal bone loss when compared to non-platform-switched implants.

Keywords: Bone response, finite element analysis, immediate loading, platform-switched dental implants

How to cite this article:
Paul S, Padmanabhan T V, Swarup S. Comparison of strain generated in bone by "platform-switched" and "non-platform-switched" implants with straight and angulated abutments under vertical and angulated load: A finite element analysis study. Indian J Dent Res 2013;24:8-13

How to cite this URL:
Paul S, Padmanabhan T V, Swarup S. Comparison of strain generated in bone by "platform-switched" and "non-platform-switched" implants with straight and angulated abutments under vertical and angulated load: A finite element analysis study. Indian J Dent Res [serial online] 2013 [cited 2020 Oct 29];24:8-13. Available from: https://www.ijdr.in/text.asp?2013/24/1/8/114913
The introduction of immediately loaded implants has enhanced the image of implant dentistry to the common man with advantages such as single surgical intervention, immediate functionability, and esthetics, when compared to the traditional two-stage implant placement protocol. But the high amount of bone loss and early failures associated with some immediately loaded situations have caused apprehension toward the routine use of this concept. Hence, techniques to control crestal bone loss around immediate loaded implants have been sought for.

It is in this context that the concept of "platform switching" has been introduced. Following the loading of dental implants, bone stabilization beneath the implant collar depends on several factors like respecting biological space, location of an area of inflammatory connective tissue (ICT) zone, and the state of implant surface. The presence of bacterial infiltration at the implant-abutment interface results in the permanent presence of an area of ICT, which contributes to apicalization of the first contact point between the implant and the bone. The concept of platform switching consists of using prosthetic components that are undersized in relation to the diameter of the implant collar in order to limit peri-implant bone resorption.

It increases the distance separating the bony rim from the abutment-implant interface, thereby limiting the area of ICT to a more coronal and medial level. Consequently, crestal bone is stabilized at the level of the implant collar.

Since the biological basis of the limiting effect of platform-switched implants on crestal bone loss has been proven as being able to limit the apical extent of ICT zone and the medialization of the implant-abutment junction, the present study has been undertaken to evaluate the mechanical basis of platform switching and the bone response toward it.


   Materials and Methods Top


A three-dimensional finite element study was undertaken to model and analyze the immediate loaded situation. Finite element analysis (FEA) was chosen for this study since it is useful in determining the stress and strain around the dental implant. It provides extensive opportunity for examining the mechanical behavior of complex biological structures. [1]

Bone model

Maxillary bone was modeled as a section of bone approximating the frontal region of maxilla with a cortical bone thickness of 1.5 mm enclosing a trabecular bone core. [2] Properties approximating those of D3 bone were used since 65% of those found in anterior maxilla are of this kind. [3]

Woven bone of approximately 1.5 mm thickness was modeled around the implant with a bone-implant contact of 65% to simulate the immediate loaded situation. [4] The bone block was modeled to be of 18 mm length and buccolingually 8 mm wide to incorporate the implant dimensions in it.

Implant model

A solid tapered implant of 13 mm length and 4.3 mm diameter is modeled and simulated to be placed in the section of bone [Figure 1]. Straight abutments and angulated abutments (15°) of 3.3, 3.7, and 4.3 mm diameter are used along with this implant fixture of standard dimension 4.3 mm diameter. Length of the abutment is kept as 7 mm.
Figure 1: Model

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Three-dimensional tetrahedral structural models of the implant, bone, and abutments have been fabricated using Pro/Engineer Wildfire 2.0 software. All the materials used in the models were considered to be isotropic, homogenous, and linearly elastic. Since there are no universally accepted properties of the biologic materials available in the literature, a mean value of the material properties has been used in the present study.

Material properties

Elastic modulus

It is the mechanical property that determines the load deflection rate of a material (cortical bone - 15.5 GPa, cancellous bone - 6 GPa, woven bone - 3.11 GPa, Ti implant and abutment - 110 GPa). [5]

Poisson's ratio

It is the ratio of transverse strain to longitudinal strain of a given material (Ti implant and abutment - 0.35, bone - 0.3).

Load

Vertical and angulated (45° to the long axis of the implant) loads were applied. Since the average masticatory forces range from 100 to 300 N, [6] similar loading values of 50, 150, and 250 N were used in this study.

An FEA of the implant models was carried out using ANSYS Workbench 10.0 software (ANSYS Inc., Canonsburg, PA, USA). The numbers of nodes and elements used in the study were approximately 50,000 and 35,000, respectively.

Variables/parameters used in the study were: Angulations of the abutment (0°, 15°), diameter of the abutment (3.3 mm, 3.7 mm, 4.3 mm), direction of load application (vertical, 45° angulated), and amount/quantity of load application (50 N, 150 N, 250 N).

On stressing with vertical and off-axis load of 50-250 N, tensile stress, compressive stress, and the microstrain values around the implant were recorded. The microstrain values obtained around platform-switched and non-platform-switched implants were compared and evaluated to see whether they were within an ideal bone remodeling range.


   Results Top


Comparisons of the variables were carried out by grouping them under four categories:



Statistical analyses of the results were carried out using one-way analysis of variance (ANOVA), post-hoc study, and t-test comparison. The results obtained from the study are as follows:

The compressive stress, tensile stress, and microstrain for all the three diameters within each group did not reveal any statistically significant difference (one-way ANOVA).

Significant differences were seen in the tensile and compressive stress among all the four groups for 3.3 and 3.7 mm. Significant difference was seen in tensile stress among all the four groups for 4.3 mm diameter.

Highest tensile stress was exhibited by straight abutment under angled loading and lowest tensile stress was exhibited by straight abutment under vertical loading, when all the four groups were compared.

Highest compressive stress was exhibited by straight abutment under angled loading and lowest compressive stress was exhibited by angled abutment under angled loading, when all the four groups were compared.

Highest strain was exhibited by angled abutment under vertical loading and lowest strain was exhibited by angled abutment under angled loading, when all the four groups were compared.

With an increase in the load, corresponding increase was seen in the tensile stress, compressive stress, and the strain values for a particular abutment.

In a particular group, as the diameter of the implant increases, compressive stress and tensile stress decreases.

In a particular group, as the diameter of the implant increases, the strain value increases.

Under vertical load, angled abutment exhibited higher tensile stress, compressive stress, and strain values for a particular load and abutment, when compared with straight abutment.

Under angled load, angled abutment exhibited lower tensile stress, compressive stress, and strain (except 3.3 abutment) values for a particular load and abutment when compared with straight abutment.

Straight abutment under vertical load exhibited lower tensile stress, compressive stress, and strain (except 4.3 abutment) values for a particular load, when compared with angled abutment.

Angled abutment under angled load exhibited lower tensile stress, compressive stress, and strain (except 3.3 abutment) values for a particular load, when compared with straight abutment.

It was seen that the tensile and compressive stress values were well within the higher limits (100 MPa and 150 MPa, respectively). [6] Only exception was found in case of the tensile stress for straight abutments under 150 N and 250 N angulated loads, which exhibited values above the higher limit.

Non-platform-switched abutments tend to exhibit a lower tensile stress and compressive stress but higher microstrain value (conducive to higher chance of bone resorption) than platform-switched abutments. Ideal bone remodeling values of microstrain (50-3000 μϵ) were exhibited by platform-switched straight abutments (3.3 mm D) under vertical load and angled load (with an abutment-implant diameter differences of 1 mm).


   Discussion Top


Long-term success in implant dentistry requires the evaluation of many dental criteria which are unique to this discipline. The quantity and quality of the available bone in the patient is a primary determining factor in predicting individual patient success. The internal and external architecture of bone controls virtually every facet of the practice of implant dentistry. Therefore, it is essential for the clinician to have a firm grasp over the modern concepts of bone physiology, metabolism, and biomechanics.

Bone as an organ is able to change in relation to a number of factors, including hormones, vitamins, and mechanical influences. Wolff had observed, "every change in the form and function of bone or of its function alone is followed by certain definitive changes in the internal architecture and equally definitive alteration in its external conformation in accordance with mathematical laws." The greater the magnitude of stress applied to the bone, greater the strain observed. Bone modeling and remodeling are primarily controlled by the mechanical environment of strain. The density of alveolar bone evolves as a result of mechanical deformation from microstrain. [3]

In the theory of mechanostat, H. M. Frost proposed that bone mass is the direct result of the mechanical usage of the skeleton. A model of four zones for compact bone as related to mechanical adaptation to strain has been proposed: The pathologic overload zone (greater than 3000 microstrain), mild overload zone (1500-3000), adapted window (50-1500), and acute disuse window (0-50).

Crestal bone loss often evidenced during the early implant loading is a result of bone in the pathologic overload zone (excess stress at the implant-bone interface). Stress is seen to be greatest at the crest, compared with other regions in the implant body. An optimum strain environment exists for each specific anatomic area and the peak strains innate for that area should be maintained to optimize the bone's response. [3]

Following implantation of a biocompatible device into cortical bone, anabolic modeling on bone surfaces is the first osseous healing reaction to take place. Similar to fracture healing, a bridging callus (woven bone) forms at the periosteal and endosteal surfaces. Under optimal conditions (minimal trauma and vascular compromise), the callus originates within a few millimeters from the margin of the implantation site. The mean elastic modulus of the newly formed woven bone was found to be 6.65 ± 3.54 GPa and the hardness was found to be 1.26 ± 1.02 GPa, which is much lower than the mechanical properties of the old bone. It is weaker than lamellar bone and sufficient time is needed for it to be remodeled into a mature lamellar configuration. [7]

Timing for the woven callus is taken to be 6 weeks in humans, but the maturation process may take time up to 18 weeks. Therefore, an unloaded healing phase (two-stage implantation procedure) has been widely used to prevent extensive functional movement during healing. The recommended time between placement and functional loading of machined-surface dental implants has been 3 months for the mandible and 6 months for the maxilla, and early loading of the implant was considered to be a primary cause of implant failure. However, such recommendations are a result of evaluating randomly chosen healing times during the initial phase of implant development and are based on the subsequent clinical outcome of either implant integration or mobility. [3]

The concept of platform switching consists of using prosthetic components that are undersized in relation to the diameter of the implant collar in order to limit peri-implant bone resorption. By using a component that is narrower than the implant collar, the prosthetic connection is displaced toward the center of the implant, and this increases the distance separating the peripheral bone from the base of the abutment. Platform switching is particularly indicated in all cases where an optimal esthetic result is desired. It can take place when an implant is loaded upon placement, using the single-stage surgical protocol, in single cases of immediate placement of a temporary prosthesis in sub-occlusion, and in cases of immediate loading for completely edentulous patients. [8],[9]

An evaluation of the stress-strain response occurring in the bone adjacent to immediately loaded platform-switched implants has been assessed in the present study using FEA.

Limitations of the study

  • The study has been carried out keeping the bone response (principal microstrain in the bone around the immediately loaded implant) as the main determinant for implant success. The tensile stress and compressive stress generated by the implant has not been taken into consideration in the present study.
  • Despite the best efforts to model the structure accurately, the model has several limitations. It does not give insight into the geometric behavior of the bone as a result of chewing forces.
  • The masticatory forces are dynamic in nature, whereas the present study was conducted under static loads.
  • Bone is a viscoelastic, anisotropic, and heterogeneous material, whereas in the present study it was assumed to be linearly elastic and homogenous in nature. The resultant values obtained may not be accurate quantitatively, but are generally accepted qualitatively.
  • The merging of the colors in the model makes it difficult to ascertain the definitive range. So, subjective variation cannot be eliminated.
  • 65% osseointegration was assumed in the present study under immediate loading conditions. This may vary in the actual clinical situation.
  • Narrow platform implants are often associated with difficulties in achieving the required emergence profile.

   Conclusion Top


The mechanical basis of bone response around platform-switched implants has been looked into in the present study. Strain generated in bone by platform-switched and non-platform-witched implants with straight and angulated abutments under vertical and angulated loads has been studied with the help of FEA. Results show that non-platform-switched abutments tend to exhibit a lower tensile stress and compressive stress but higher microstrain value (conducive to higher chance of bone resorption) than platform-switched abutments. Based on the data obtained from the present study, it can be concluded that the ideal bone remodeling values of microstrain (50-3000 microstrain) have been exhibited by platform switching of dental implants (with an abutment-implant diameter difference of 1 mm) and can be considered as a better alternative for preservation of crestal bone loss when compared to non-platform-switched implants.

Nevertheless, clinical studies involving platform-switched implants should be carried out for further research and understanding in this particular area.

 
   References Top

1.Geng JP, Tan KB, Liu GR. Application of finite element analysis in implant dentistry: A review of the literature. J Prosthet Dent 2001;85:585-98.  Back to cited text no. 1
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2.Koca OL, Eskitascioglu G, Usumez A. Three-dimensional finite-element analysis of functional stresses in different bone locations produced by implants placed in the maxillary posterior region of the sinus floor. J Prosthet Dent 2005;93:38-44.  Back to cited text no. 2
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3.Misch CE. Contemporary Implant Dentistry. 2nd ed. St. Louis: Mosby; 1999.   Back to cited text no. 3
    
4.Romanos GE, Testori T, Degidi M, Adriano P. Histologic and histomorphometric findings from retrieved, immediately occlusally loaded implants in humans. J Periodontol 2006;77:326.  Back to cited text no. 4
    
5.Sevimay M, Turhan F, Kilicarslan MA, Eskitascioglu G. Three dimensional finite element analysis of the effect of different bone quality on stress distribution in an implant-supported crown. J Prosthet Dent 2005;93:127-34.  Back to cited text no. 5
    
6.Bozkaya D, Muftu S, Muftu A. Evaluation of load transfer characteristics of five different implants in compact bone at different load levels by finite elements analysis. J Prosthet Dent 2004;92:523-30.  Back to cited text no. 6
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7.Ricks L. The use of nanoindentation in determining regional dependence of material properties in new and old bone. 2005.  Back to cited text no. 7
    
8.Gardner DM. Platform switching as a means to achieving implant esthetics: A case study. N Y State Dent J 2005;71:34-7.  Back to cited text no. 8
    
9.Hartmann HJ, Steup A. Implant-supported anterior tooth restoration. Keio J Med 2006;55:23-8.  Back to cited text no. 9
[PUBMED]    

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Correspondence Address:
T V Padmanabhan
Department of Prosthodontics and Implantology, Faculty of Dental Sciences, Sri Ramachandra University, Porur, Chennai, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.114913

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]

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