Influence of Bone and Dental Implant Parameters on Stress Distribution in the Mandible: A Finite Element Study

Full text

(1)

D

evelopment of an ideal substitute for missing teeth has been a major aim of dental practition-ers for millennia.1Dental implants are biocompatible

screwlike titanium objects that are surgically placed into the mandible or maxilla to replace missing teeth. The mechanism by which an implant is biomechani-cally accepted by the jawbone is called osseointegra-tion.2,3Stimulus of the bone through applied stresses

has been well documented to influence the success or failure of an implant.4,5Furthermore, primary

sta-bility is especially critical because the bone is still in a state of repair and necessitates applied stresses that promote bone growth.

Himmlova et al,6Iplikçioglu and Akça,7and

Pierris-nard et al8recognized the fact that the dimensions of

an implant influence the magnitude and profile of stresses within the bone. It is commonly understood that increasing the implant length and/or diameter reduces the stresses within the bone. Furthermore, based on clinical experience, practitioners are aware that if the bone is weak, then a larger-diameter implant is required. However, these decisions are based primarily on clinical judgment rather than being supported by any theoretical data. It is critical for the practitioner to fully grasp the relationship

Influence of Bone and Dental Implant Parameters

on Stress Distribution in the Mandible:

A Finite Element Study

Hong Guan, PhD1/Rudi van Staden, BEng2/Yew-Chaye Loo, PhD3/

Newell Johnson, PhD4/Saso Ivanovski, PhD5/Neil Meredith, PhD6

Purpose: The complicated relationships between mandibular bone components and dental implants

have attracted the attention of structural mechanics researchers as well as dental practitioners. Using the finite element method, the present study evaluated various bone and implant parameters for their influence on the distribution of von Mises stresses within the mandible. Materials and Methods: Various parameters were considered, including Young’s modulus of cancellous bone, which varies from 1 to 4 GPa, and that of cortical bone, which is between 7 and 20 GPa. Implant length (7, 9, 11, 13, and 15 mm), implant diameter (3.5, 4.0, 4.5, and 5.5 mm), and cortical bone thickness (0.3 to 2.1 mm) were also considered as parameters. Assumptions made in the analysis were: modeling of the complex mater-ial and geometric properties of the bone and implant using two-dimensional triangular and quadrilateral plane strain elements, 50% osseointegration between bone and implant, and linear relationships between the stress value and Young’s modulus of both cancellous and cortical bone at any specific point. Results:An increase in Young’s modulus and a decrease in the cortical bone thickness resulted in elevated stresses within both cancellous and cortical bone. Increases in the implant length led to greater surface contact between the bone and implant, thereby reducing the magnitude of stress. Conclusions: The applied masticatory force was demonstrated to be the most influential, in terms of differences between minimum and maximum stress values, versus all other parameters. Therefore loading should be considered of vital importance when planning implant placement. INTJ ORALMAXILLOFACIMPLANTS

2009;24:866–876

Key words:cancellous bone, cortical bone, dental implants, finite element technique, stress distribution characteristics

1Associate Professor in Structural Engineering and Mechanics,

Griffith School of Engineering, Griffith University Gold Coast Campus, Queensland, Australia.

2PhD Student, Griffith School of Engineering, Griffith University

Gold Coast Campus, Queensland, Australia.

3Professor and Foundation Chair of Civil Engineering, Director of

Internationalisation, and Professional Liaison, Science, Environ-ment, Engineering and Technology Group, Griffith University Gold Coast Campus, Queensland, Australia.

4Professor of Dental Research and Foundation Dean, School of

Dentistry and Oral Health, Griffith University Gold Coast Campus, Queensland, Australia.

5Listerine Chair Professor of Periodontology, School of Dentistry

and Oral Health, Griffith University Gold Coast Campus, Queens-land, Australia.

6Chief Executive Officer, Neoss Ltd, Harrogate, United Kingdom. Correspondence to:Associate Professor Hong Guan, Griffith School of Engineering, Griffith University, Gold Coast Campus, Queensland 4222, Australia. Fax: +61-(0)7-5552-8065. Email: h.guan@griffith.edu.au

(2)

between various combinations of bone and implant parameters and the resulting stresses on the bone from a wide range of masticatory forces.

Finite element analysis (FEA) is becoming a com-mon method to advance dental technologies.9,10Areas

of application in implant dentistry include studies of jawbone and implant properties as well as the bone-implant interface.11–17In the past, extensive research

has been undertaken on the characteristics of stress distribution in bone surrounding implants.18–21

How-ever, no published work appears to have investigated the stress distribution in the bone when various bone and implant parameters are considered. Ultimately the outcome of this study will help dental practitioners to identify the stimulus state of the bone; hence, clinicians would be able to predict success or failure for all com-binations of implant lengths and diameters with a given cortical bone thickness, as well as the material properties of cancellous and cortical bone, under a range of masticatory forces.

METHODS

Model Construction

A two-dimensional (2D) representation of the bone and implant was analyzed using the Strand7 FEA sys-tem.22This is considered to be equally accurate and

more efficient in terms of computation time, as com-pared to a three-dimensional (3D) equivalent. Data

for the bone dimensions were based on computer-ized tomographic scans. The different types of bone, ie, cancellous and cortical, were distinguished and the boundaries were identified to assign different mater-ial properties within the finite element model. Figure 1a shows a mandible section and implant with the loading and restraint conditions. Also shown are the detailed parameters considered in this study. The modeled implant was conical with 2 degrees of taper and a helical thread. For a particular finite element model with dimension (D) = 4.5 mm, length (L) = 11 mm, and cortical bone thickness (Tcor) = 1.2 mm, the total numbers of plane strain elements were 2,870 for the implant, 5,956 for cancellous bone, and 1,094 for cortical bone. The total number of nodal points in the entire model was 9,969.

As indicated in Fig 1b, the von Mises stresses along the lines VV for cancellous bone and HH for cortical bone were measured for all possible parameter com-binations. The relative locations of these lines are con-sidered by clinicians to be critical for examining the stress levels and helping to understand the stimulus response of bone. Both lines VV and HH were chosen on the buccal side of the implant, where the stress level is higher than on the lingual because of the load-ing characteristics. The stress contour plots will be presented for the buccal side of the model only. The lengths of VV and HH were dependent on the implant dimensions and Tcor. Because of the irregularity of the mesh, a straight line (VV) of nodes used for measuring

Fig 1 Finite element model of the mandible and dental implant. (Left) Cross section in distal direction. (Right) Locations for stress reporting. D = implant diameter; L = implant length; FH= horizontal load; FV= vertical load; M = moment; Tcor = cortical bone thickness; Ecor = Young’s modulus of cortical bone; Ecan = Young’s modulus of cancellous bone; VV = length in cancellous bone used to determine von Mises stresses; HH = length in cortical bone used to measure von Mises stresses. Ranges of values used are reported in the text.

Tcor L Taper D Fv M FH Loading condition Fixed constraint Dental implant Cancellous bone Cortical bone Tcor/2 0.2 mm HH VV

(3)

stress was only approximated.The distance of VV away from the thread tip was not a varying parameter affected by the implant diameter; it was fixed at 0.2 mm (see Fig 1b) in an attempt to capture the stresses at the most critical location.23

Bone and Implant Parameters

An extensive literature review by van Staden et al18

indicated that the commonly assumed Young’s mod-ulus for cancellous bone ranges from 0.08 to 7.93 GPa. Cortical bone is normally assumed to vary from 5.57 to 22.8 GPa. The present study adopted a range of Young’s modulus for cancellous bone (Ecan) from 1 to 14 GPa and for cortical bone (Ecor) from 7 to 20 GPa, both at 1-GPa intervals (see Fig 1a). The selection of such a range was based on the understanding that in some exceptional cases Young’s modulus of cancel-lous bone can reach 14 GPa when that of cortical bone is also at a high range.

With such a large range of material parameters to be considered, the corresponding densities of cancel-lous and cortical bone needed to be determined. Fig-ures 2a and 2b show the relationships between Young’s modulus and the density of cancellous (␳can) and cortical (␳cor) bone, respectively, as per published clinical data of several authors.24–28Note in Fig 2a

that Ciarelli et al28suggested two different

relation-ships for the cancellous bone in different regions. Based on these data, the following equations are pro-posed to determine the mean relationships between Young’s modulus and the density of cancellous and cortical bone, respectively.

␳can =(3.54 ⫻Ecan) + 0.16 (Equation 1) 5

␳cor =(0.25 ⫻Ecor) + 3.09 (Equation 2) 3

Tcor is another parameter to be evaluated. Mellal et al29assumed a thickness of 1 mm, whereas Natali

et al30assumed 0.8 and 1.9 mm. For the present

study, a more extensive range of Tcor (0.3, 0.6, 0.9, 1.2, 1.5, 1.8, and 2.1 mm) was selected (Fig 1a). The Pois-son’s ratios (␯) for the implant (grade 4 commercially pure titanium), cancellous bone, and cortical bone were 0.3, 0.3, and 0.35, respectively. Note that the cor-tical bone was constrained along the lingual and buc-cal faces of the cross section in the distal direction (see Fig 1a), thus representing a realistic function of the mandible surrounding an implant.

Various dimensions based on the Neoss31implant

system were employed: lengths of 7, 9, 11, 13, and 15 mm and diameters of 3.5, 4.0, 4.5, and 5.5 mm.

Loading Conditions

The present study focused only on the stresses within cancellous and cortical bone; therefore, the implant system was simplified, and such components as the abutment, abutment screw, and crown were not included. In reality, masticatory forces act on the top of the crown. Neglect of the implant components means that the masticatory force is transferred to the head of the implant. This requires the introduction of a moment (M) around the z-axis, together with the forces acting in the horizontal (x-axis) (FH) and verti-cal (y-axis) (FV) directions. Note that M was applied around the negative z-axis and is based on the hori-zontal load laterally transferred at a distance (crown height) of 6.5 mm.

The range of loading was considered as FH= 25 to 250 N, FV= 50 to 500 N, and M = 162.5 to 1,625 Nmm. Based on a theoretical study by Choi et al,32these

loading conditions are regarded as comprehensive. The present study included an extensive range of loading magnitudes to analyze the effect of traumatic

Fig 2 Relationship between Young’s modulus and density in the mandible. (Left) Cancellous bone. (Right) Cortical bone. 0.8 0.6 0.4 0.2 0 Appar ent density (g/cm 3) 0 0.2 0.4 0.6 0.8 1.0 1.2 Carter et al27 Lotz et al26 Ciarelli et al28 Ciarelli et al28 Proposed, Eq (1) Ecan (GPa) 2.5 2.0 1.5 1.0 0 Appar ent density (g/cm 3) 0 5 10 15 20 25

Abendschein and Hyatt24 Lotz et al26

Lotz et al25 Proposed, Eq (2)

Ecor (GPa) 0.5

(4)

loading. Because of the linearly elastic behavior of the implant-bone system, only the maximum forces were applied in the analysis. The results upon application of the minimum and half maximum forces can be readily calculated.

Assumption Strategies

In addition to the assumption of a 2D representation of the bone and implant, other assumptions made in the model were:(1)50% osseointegration between the bone and implant, and(2)linear relationships between the stress value and Young’s modulus of both cancellous and cortical bone at any specific point.

Bone-Implant Interface.The interface surrounding

the implant includes both blood and bone fragments. This interface is considered clinically ideal for osseoin-tegration, although it is mechanically unfavorable. The stage after insertion and before full osseointegration is critical for the surrounding bone because it exhibits the most distinct stress concentrations. In the pos-tosseointegration stage, however, the lamina dura has been formed and the implant stability drastically increases.

Previous finite element studies10,29,33,34assumed

that immediately loaded implants are in direct contact with cancellous bone, without a blood interface. Borchers and Reichart35suggested two typical stages

of lamina dura interface formation:(1)immediately after implantation the cancellous bone is in direct con-tact with the implant, and (2)a layer of the lamina dura (cortical like) of approximately 1.5 mm in thickness forms. In a study by Natali et al,30the two formation

stages of the lamina dura were modeled with Young’s moduli of 0.3 GPa and 1.5 GPa, respectively. The forma-tion of lamina dura improves the stress distribuforma-tion and represents a clinically favorable course of healing. A study by Berglundh et al36provided an overview of

the various phases of blood and hard (bone) tissue for-mation during the bone healing stages at the bone-implant interface, sampled 2 hours after bone-implant placement.The blood interface extended 0.13 mm into the thread chamber.

Based on these findings, the present study assumed 50% osseointegration between the bone and the implant. The voids between the bone and implant were modeled as blood (Fig 3). Young’s mod-ulus and the Poisson’s ratio of the blood were taken as 0.7 GPa and 0.3, respectively.

Linear Relationship Between Stress and Young’s

Modulus.The total number of parameter

combina-tions was 27,440, based on 5 implant lengths, 4 implant diameters, 7 cortical thicknesses, and 14 Young’s moduli each for cancellous and cortical bone, respectively. Because the completion of such a huge

number of simulations would be unviable, further assumptions were made to reduce the number of sim-ulations to a manageable level. The feasibility of a lin-ear relationship for the stress variation for all combinations of Ecan and Ecor was exploited. For the purpose of validation, an FEA was carried out to obtain the actual von Mises stress values for D = 4.5 mm, L = 11 mm, and Tcor = 1.2 mm. Varying Ecan from 1 to 14 GPa for every possible value of Ecor resulted in little variation from linearity. An example of this is shown in Figs 4a and 4b, where the actual stress at the midpoint of line VV is measured for all combinations of Ecan and Ecor and compared to the respective linear prediction. For Figs 4a and 4b, Ecan = 7 GPa and Ecor = 13 GPa, respectively. For Ecan and Ecor, the predicted stresses varied from the actual ones by an average of 5.7% and 4.3%, respectively. Note that the stresses recorded at the midpoint of line HH produced a similar percentage error (4.9% and 6.5% for Ecan and Ecor, respectively) for VV. With linear relationships between the stress and Ecan or Ecor assumed, only the minimum and maxi-mum values of Young’s modulus were considered for each type of bone instead of the initial data set of 14. This reduced the total number of analyses to 560.

RESULTS

To demonstrate the overall behavior of the implant-bone system, the stresses measured along the lines VV and HH were presented for three load levels: mini-mum, half maximini-mum, and maximum.

Fig 3 Proposed modeling of blood and hard tissue. Implant Hard tissue (cancellous bone) Blood 0.13 mm

(5)

Influence of Varying Implant Diameter

Figure 5 presents the von Mises stresses measured along the lines VV and HH for all possible implant diameters. The other parameters were set to their average values (L = 11 mm, Tcor = 1.2 mm, Ecan = 7 GPa, Ecor = 13 GPa). When D increased, the stress along the line VV oscillated more significantly, follow-ing the thread profile (Fig 5a). The increased oscilla-tion was a result of reduced distance (IC) between the implant thread and cortical bone and the subsequent reduced volume of cancellous bone (Fig 5b). This reduced the capacity of cancellous bone to distribute the stress more evenly. The stresses along the line HH exhibited a reduction when D was increased (Fig 5c). This reduction was caused by the larger-diameter implant supporting an increased portion of the load; hence, less stress was induced in the cortical bone. Generally, higher stresses were found at the implant neck for all diameters. When D = 5.5 mm, stress was

concentrated at H1because of the different shape of the implant head as compared to other implant diameters (Fig 5d). The stress levels along the lines VV and HH increased as FH, FV, and M increased, which is evident in Fig 5 and subsequent figures.

Influence of Varying Implant Length

The von Mises stresses measured along the lines VV and HH, for all possible implant lengths, are shown in Fig 6. Average values were assigned for all other para-meters (D = 4.5 mm, Tcor = 1.2 mm, Ecan = 7 GPa, Ecor = 13 GPa). The stresses decreased within both cancellous and cortical bone (Figs 6a and 6c, respec-tively) as L increased. This is because the surface area contact between the bone and implant also increased, leading to the implant absorbing more of the load. Figures 6b and 6d show that, for all implant lengths, stress was concentrated at the implant neck within the cancellous and cortical bone.

Fig 4 Actual and predicted stresses at the mid-point of line VV. (Top) Cancellous bone. (Bottom) Cortical bone. Linear prediciton Predicted Actual –2.8 –4.9 6.9 2.6 9.4 9.0 –4.7 –3.5 –2.8 8.8 6.1 7.9 2.9 7.4 40 35 30 25 20 15 10 5 0 von Mises str ess (MP a) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Ecan (GPa) Linear prediciton Predicted Actual 2.7 3.5 3.2 –7.5 –4.3 –8.2 –7.1 1.9 5.3 1.5 4.6 –6.1 –3.2 1.7 40 35 30 25 20 15 10 5 0 von Mises str ess (MP a) 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Ecor (GPa)

(6)

Influence of Varying Cortical Bone Thickness

Figure 7 presents the von Mises stresses measured along the lines VV and HH for all possible values of Tcor. Average values were used for all other parame-ters (D = 4.5 mm, L = 11 mm, Ecan = 7 GPa, Ecor = 13 GPa). As Tcor decreased, the ability of the cortical bone to support the load also decreased, leading to a slight increase in the magnitude of stresses along the line VV (Fig 7a). A nondistinctive trend was found for the stress profiles along the line HH (Fig 7c). Figures 7b and 7d, respectively, show that, for all cortical bone thicknesses, stresswas concentrated at the implant neck within the cancellous and cortical bone.

Influence of Varying Young’s Modulus for Cancellous Bone

In Fig 8 all other parameters were set to average val-ues (D = 4.5 mm, L = 11 mm, Tcor = 1.2 mm, Ecor = 13 GPa). As shown in Fig 8a, as Ecan increased, the stress magnitude increased as a result of the cancellous bone’s ability to support a greater portion of the load. The stress within the cortical bone (Fig 8b) increased as Ecan decreased. This was because the cancellous bone was supporting less load and therefore an increased portion of the load was supported by the cortical bone.

Fig 5 Stress profiles with varying D. (Top)Cancellous bone. (Bottom)Cortical bone. 20 15 10 5 0 von Mises str ess (MP a) 0 2 4 6 8 10 VV (mm) 3.5 mm 4.0 mm 4.5 mm 5.5 mm 4.5 mm 4.5 mm FH= 250 N, FV= 500N, M = 1,625 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm 40 30 20 10 0 von Mises str ess (MP a) 0 0.25 0.50 0.75 1.00 1.25 1.50 HH (mm) 3.5 mm 4.0 mm 4.5 mm 5.5 mm 4.5 mm 4.5 mm FH= 250 N, FV= 500N, M = 1,625 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm Implant Cortical bone Cancellous bone D = 3.5 mm D = 5.5 mm Cancellous bone Cortical bone Implant D = 3.5 mm D = 5.5 mm HH HH H1 VV IC IC

(7)

Influence of Varying Young’s Modulus for Cortical Bone

In Fig 9 all other parameters were set to average val-ues (D = 4.5 mm, L = 11 mm, Tcor = 1.2 mm, Ecan = 7 GPa). Figure 9a indicates that as Ecor decreased, the stress magnitude increased slightly in cancellous bone—a result of the cancellous bone having to sup-port an increased sup-portion of the load. However, the stress within the cortical bone (Fig 9b) increased as Ecor increased. This is the result of the increased resis-tance of the cortical bone to the applied load.

DISCUSSION

FEA has been used extensively to predict the biome-chanical performance of jawbone surrounding a den-tal implant. Previous research investigated the stresses in the surrounding bone, which were influ-enced by both the implant dimensions7,8,37–43and

the biomechanical bond formed between the bone and the implant.23However, to date no research has

been conducted to evaluate the stress characteristics influenced by all combinations of the various bone and implant parameters.

Fig 6 Stress profiles with varying L. (Top) Cancellous bone. (Bottom) Cortical bone. 20 15 10 5 0 40 30 20 10 0 von Mises str ess (MP a) 0 5 10 15 VV (mm) 7 mm 9 mm 11 mm 13 mm 15 mm 11 mm 11 mm FH= 250 N, FV= 500N, M = 1,625 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm von Mises str ess (MP a) 0 0.25 0.50 0.75 1.00 1.25 1.50 HH (mm) Implant Cortical bone Cancellous bone L = 7 mm L = 15 mm Implant Cortical bone Cancellous bone L = 7 mm L = 15 mm HH HH FH= 125 N, FV= 250N, M = 812.5 Nmm 7 mm 9 mm 11 mm 13 mm 15 mm 11 mm 11 mm FH= 250 N, FV= 500N, M = 1,625 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm VV

(8)

The present analysis considered various combina-tions of bone, implant, and loading parameters, including D, L, Tcor, Ecan, Ecor, FH, FV, and M. In general, good agreement was found with previous research7,8,37–41in that an increase in implant length

and diameter was associated with reductions in stress within the cancellous bone. However, this study also demonstrated that when D increased, the stress along the line VV oscillated more significantly, follow-ing the thread profile (Fig 5a).

Himmlova et al6and Tawil et al40indicated that

implant diameter was more important for improved stress distribution than implant length. However, this study shows that an increase in implant length reduces stress within both cancellous and cortical bone for a wider range of parameters. This is more obvious than the influence of varying diameter. The finding is also in contrast with that of Pierrisnard et al,8who concluded that the stress within the bone

was virtually constant, independent of implant length and bicortical anchorage.

Fig 7 Stress profiles with varying Tcor.(Top) Cancellous bone.(Bottom) Cortical bone. 20 15 10 5 0 von Mises str ess (MP a) 0 5 10 15 VV (mm) 0.3 mm 0.6 mm 0.9 mm 1.2 mm 1.5 mm 1.8 mm 2.1 mm 1.2 mm 1.2 mm FH= 250 N, FV= 500N, M = 1,625 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm 0.3 mm 0.6 mm 0.9 mm 1.2 mm 1.5 mm 1.8 mm 2.1 mm 1.2 mm 1.2 mm FH= 250 N, FV= 500N, M = 1,625 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm 60 50 40 30 20 10 0 von Mises str ess (MP a) 0 0.25 0.50 0.75 1.00 1.25 1.50 HH (mm) Implant Cortical bone Cancellous bone Tcor = 0.3 mm Tcor = 2.1 mm VV Implant Cortical bone Cancellous bone Tcor = 0.3 mm Tcor = 2.1 mm HH HH FH= 125 N, FV= 250N, M = 812.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm

(9)

No research to date has considered the influence of the cortical bone thickness on the stresses in cancel-lous and cortical bone. The present study concluded that decreased Tcor led to cortical bone supporting less load, which in turn caused a slight increase in the magnitude of stress in cancellous bone.

Generally, as the strength of either cancellous or cortical bone increased, their ability to carry the load increased. When Ecan increased, the stress magnitude increased because the cancellous bone was able to support a greater load. When Ecor decreased, the stress magnitude increased within the cancellous

bone because the cancellous bone had to support a greater portion of the load. On the other hand, the stress within the cortical bone increased as Ecor increased, because the cortical bone offered more resistance to the load.

It was consistently found in the present study that elevated stress levels were located at the implant neck for all combinations of the different parameters. This phenomenon is supported by Meijer et al,13who

con-cluded that the regions of bone exposed to maximum stresses are located around the implant neck.

Fig 8 Stress profiles with varying Ecan. (Left) Cancellous bone. (Right) Cortical bone.

Fig 9 Stress profiles with varying Ecor.(Left) Cancellous bone. (Right) Cortical bone. 20 15 10 5 0 von Mises str ess (MP a) 0 2 4 6 8 10 VV (mm) 1 GPa 7 GPa 14 GPa 7 GPa 7 GPa FH= 250 N, FV= 500N, M = 1,625 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm 60 50 40 30 20 10 0 von Mises str ess (MP a) 0 0.25 0.50 0.75 1.00 1.25 1.50 HH (mm) 1 GPa 7 GPa 14 GPa 7 GPa 7 GPa FH= 250 N, FV= 500N, M = 1,625 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm 20 15 10 5 0 von Mises str ess (MP a) 0 2 4 6 8 10 VV (mm) 7 GPa 13 GPa 20 GPa 13 GPa 13 GPa FH= 250 N, FV= 500N, M = 1,625 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm 40 30 20 10 0 von Mises str ess (MP a) 0 0.25 0.50 0.75 1.00 1.25 1.50 HH (mm) 7 GPa 13 GPa 20 GPa 13 GPa 13 GPa FH= 250 N, FV= 500N, M = 1,625 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 25 N, FV= 50N, M = 162.5 Nmm FH= 125 N, FV= 250N, M = 812.5 Nmm

(10)

CONCLUSION

This research is a pilot study aimed at offering an ini-tial understanding of the complicated stress distribu-tion characteristics in the bone resulting from variations in bone and implant parameters. Realistic geometries, material properties, loading, and support conditions for the jawbone and implant were consid-ered in the present study. Modeling assumptions were validated and a vast range of parameters was studied. The majority of stress characteristics corre-lated well with previous research, with some new findings. In general, it was found that the implant length had a noteworthy characteristic relationship with the stress in the bone. Implant length was more influential than implant diameter in terms of the stress variation in cancellous bone. However, implant diameter was more influential in the stress variation in cortical bone. Overall, in both cancellous and corti-cal bone, the applied load and moment were the most influential and should therefore be given prior-ity when planning implant placement.

Evaluating the influence of other parameters that affect the stresses governing osseointegration and bone growth can constitute future work. These para-meters include implant taper, pitch and thread design, implant neck offset, different percentages of osseointegration, and implant orientation within the bone.

ACKNOWLEDGMENTS

Special thanks go to John Divitini and Fredrik Engman from Neoss Limited for their technical advice.

REFERENCES

1. Irish JD. A 5,500-year-old artificial human tooth from Egypt: A historical note. Int J Oral Maxillofac Implants 2004;19:645–647. 2. Brånemark PI, Adell R, Breine U, Hansson BO, Lindstrom J, Ohls-son A. Intra-osseous anchorage of dental prostheses. I. Experi-mental studies. Scand J Plast Reconstr Surg 1969;3:81–100. 3. Brånemark PI, Hansson BO, Adell R, et al. Osseointegrated

implants in the treatment of the edentulous jaw. Experience from a 10-year period. Scand J Plast Reconstr Surg 1977;16: 1–132.

4. Mellal A, Wiskott HW, Botsis J, Scherrer SS, Belser UC. Stimulat-ing effect of implant loadStimulat-ing on surroundStimulat-ing bone. Compari-son of three numerical models and validation by in vivo data. Clin Oral Implants Res 2004;15:239–248.

5. Carter DR, Orr TE, Fyhrie DP, Schurman DJ. Influences of mechanical stress on prenatal and postnatal skeletal develop-ment. Clin Orthop Relat Res 1987:237–250.

6. Himmlova L, Dostalova T, Kacovsky A, Konvickova S. Influence of implant length and diameter on stress distribution: A finite element analysis. J Prosthet Dent 2004;91:20–25.

7. Iplikçioglu H, Akça K. Comparative evaluation of the effect of diameter, length and number of implants supporting three-unit fixed partial prostheses on stress distribution in the bone. J Dent 2002;30:41–46.

8. Pierrisnard L, Renouard F, Renault P, Barquins M. Influence of implant length and bicortical anchorage on implant stress dis-tribution. Clin Implant Dent Relat Res 2003;5:254–262. 9. DeTolla DH, Andreana S, Patra A, Buhite R, Comella B. Role of

the finite element model in dental implants. J Oral Implantol 2000;26:77–81.

10. Geng JP, Ma QS, Xu W, Tan KB, Liu GR. Finite element analysis of four thread-form configurations in a stepped screw implant. J Oral Rehabil 2004;31:233–239.

11. Menicucci G, Mossolov A, Mozzati M, Lorenzetti M, Preti G. Tooth-implant connection: Some biomechanical aspects based on finite element analyses. Clin Oral Implants Res 2002; 13:334–341.

12. Canay S, Hersek N, Akpinar I, Asik Z. Comparison of stress dis-tribution around vertical and angled implants with finite-ele-ment analysis. Quintessence Int 1996;27:591–598.

13. Meijer HJ, Starmans FJ, Steen WH, Bosman F. Loading condi-tions of endosseous implants in an edentulous human mandible: A three-dimensional, finite-element study. J Oral Rehabil 1996;23:757–763.

14. Rieger R, Mayberry M, Brose MO. Finite element analysis of six endosseous implants. J Prosthet Dent 1990;63:671–676. 15. O’Mahony A, Bowles Q, Woolsey G, Robinson SJ, Spencer P.

Stress distribution in the single-unit osseointegrated dental implant: Finite element analyses of axial and off-axial loading. Implant Dent 2000;9:207–218.

16. Zarone F, Apicella A, Nicolais L, Aversa R, Sorrentino R. Mandibular flexure and stress build-up in mandibular full-arch fixed prostheses supported by osseointegrated implants. Clin Oral Implants Res 2003;14:103–114.

17. Patra AK, DePaolo JM, D’Souza KS, DeTolla D, Meenaghan MA. Guidelines for analysis and redesign of dental implants. Implant Dent 1998;7:355–368.

18. van Staden RC, Guan H, Loo YC. Application of the finite ele-ment method in dental implant research. Comput Methods Biomech Biomed Eng 2006;9:257–270.

19. Simsek B, Erkmen E, Yilmaz D, Eser A. Effects of different inter-implant distances on the stress distribution around endosseous implants in posterior mandible: A 3D finite ele-ment analysis. Med Eng Phys 2006;28:199–213.

20. Nomura T, Powers MP, Katz JL, Saito C. Finite element analysis of a transmandibular implant. J Biomed Mater Res B Appl Bio-mater 2007;80:370–376.

21. Stegaroiu R,Watanabe N,Tanaka M, Ejiri S, Nomura S, Miyakawa O. Peri-implant stress analysis in simulation models with or with-out trabecular bone structure. Int J Prosthodont 2006;19:40–42. 22. Strand7 Theoretical Manual. Sydney, Australia: Strand7, 2004. 23. Lai H, Zhang F, Zhang B, Yang C, Xue M. Influence of

percent-age of osseointegration on stress distribution around dental implants. Chin J Dent Res 1998;1:7–11.

24. Abendschein W, Hyatt GW. Ultrasonics and selected physical properties of bone. Clin Orthop Relat Res 1970;69:294–301. 25. Lotz JC, Gerhart TN, Hayes WC. Mechanical properties of tra-becular bone from the proximal femur: A quantitative CT study. J Comput Assist Tomogr 1990;14:107–114.

26. Lotz JC, Gerhart TN, Hayes WC. Mechanical properties of meta-physeal bone in the proximal femur. J Biomech 1991;24: 317–329.

27. Carter DR, Schwab GH, Spengler DM. Tensile fracture of cancel-lous bone. Acta Orthop Scand 1980;51:733–741.

(11)

28. Ciarelli MJ, Goldstein SA, Kuhn JL, Cody DD, Brown MB. Evalua-tion of orthogonal mechanical properties and density of human trabecular bone from the major metaphyseal regions with materials testing and computed tomography. J Orthop Res 1991;9:674–682.

29. Mellal A, Wiskott HW, Botsis J, Scherrer SS, Belser UC. Stimulat-ing effect of implant loadStimulat-ing on surroundStimulat-ing bone. Compari-son of three numerical models and validation by in vivo data. Clin Oral Implants Res 2004;15:239–248.

30. Natali AN, Pavan PG, Ruggero AL. Analysis of bone-implant interaction phenomena by using a numerical approach. Clin Oral Implants Res 2006;17:67–74.

31. Neoss Implant System Surgical Guidelines. Harrogate, UK: Neoss Limited, 2006.

32. Choi AH, Ben-Nissan B, Conway RC. Three-dimensional model-ling and finite element analysis of the human mandible dur-ing clenchdur-ing. Aust Dent J 2005;50:42–48.

33. Gallas MM, Abeleira MT, Fernandez JR, Burguera M. Three-dimensional numerical simulation of dental implants as orthodontic anchorage. Eur J Orthod 2005;27:12–16. 34. Chun HJ, Park DN, Han CH, Heo SJ, Heo MS, Koak JY. Stress

dis-tributions in maxillary bone surrounding overdenture implants with different overdenture attachments. J Oral Reha-bil 2005;32:193–205.

35. Borchers L, Reichart P. Three-dimensional stress distribution around a dental implant at different stages of interface devel-opment. J Dent Res 1983;62:155–159.

36. Berglundh T, Abrahamsson I, Lang NP, Lindhe J. De novo alveo-lar bone formation adjacent to endosseous implants. Clin Oral Implants Res 2003;14:251–262.

37. Yokoyama S, Wakabayashi N, Shiota M, Ohyama T. The influ-ence of implant location and length on stress distribution for three-unit implant-supported posterior cantilever fixed partial dentures. J Prosthet Dent 2004;91:234–240.

38. Ivanoff CJ, Grondahl K, Sennerby L, Bergstrom C, Lekholm U. Influence of variations in implant diameters: A 3- to 5-year ret-rospective clinical report. Int J Oral Maxillofac Implants 1999; 14:173–180.

39. Misch CE. Implant design considerations for the posterior regions of the mouth. Implant Dent 1999;8:376–386. 40. Tawil G, Aboujaoude N, Younan R. Influence of prosthetic

para-meters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21:275–282. 41. Zhang L, Zhou Y, Meng W. A three-dimensional finite element

analysis of the correlation between lengths and diameters of the implants of fixed bridges with proper stress distribution. Hua Xi Kou Qiang Yi Xue Za Zhi 2000;18:229–231.

42. Siegele D, Soltesz U. Numerical investigations of the influence of implant shape on stress distribution in the jaw bone. Int J Oral Maxillofac Implants 1989;4:333–340.

43. Holmgren EP, Seckinger RJ, Kilgren LM, Mante F. Evaluating parameters of osseointegrated dental implants using finite element analysis—A two-dimensional comparative study examining the effects of implant diameter, implant shape, and load direction. J Oral Implantol 1998;24:80–88.

Figure

Updating...

References

Updating...

Related subjects :