Medical

Communication

Biosci. Biotech. Res. Comm. 10(3): 455-462 (2017)

Comparison of stress distribution around implants with

three different attachments in overdenture supported by

four maxillary implants using  nite element analysis method

Asadallah Ahmadzadeh

and Ahmad Teimouri

Assistant Professor, Department of Prosthodontics, School of Dental Medicine, Ahvaz Jundishapur

University of Medical Sciences Ahvaz Iran

Assistant Resident, Department of Prosthodontics, School of Dental Medicine, Ahvaz Jundishapur University

of Medical Sciences Ahvaz Iran

ABSTRACT

As a general rule, the purpose of treatment planning should be minimization and evenly distribution of mechanical stress in the

adjacent implant and bone system. Various experimental studies have examined the distribution of stress in the implant supporting

bones, thus avoiding the dangers involved. But there is still controversy about biomechanical effects and stress distribution in differ-

ent attachment designs. The purpose of this study was to compare the distribution of stress around the implant with three different

attachments in overdenture based on four maxillary implants using  nite element analysis method (FEA). In this experimental study,

using the FEA method, a 3D model of maxilla, implant, attachment components and overdenture was  rst prepared and then, using

the ANSYS  nite element software, the components of the model were superimposed on each other so that it can act as a component

integrated with different materials. Implants are located in the anterior and posterior parts of the maxilla, with two implants placed in

the two sides of the canine, one in the left central position and the other in the right second premolar. These implants were attached

to the overdenture using three bar-clip, ball, and locator attachment designs. The 100N force used in this study and imposed verti-

cally to the tooth 6 unilaterally and bilaterally and the stress level was investigated in each design. Among the three different designs

examined, the highest stress was observed in the vertical force (22.87 MPa) imposed on the implant in the right second premolar

on the right overdenture supported by the locator implant. In the second place, the highest stress was observed on the Ball-retained

overdenture in the right side force, imposed on the implant in the right second premolar corresponding to 12.88 MPa. The least stress

among these three designs was observed in the bar-clip-retained overdenture design, the maximum stress on which is in the vertical

force imposed on the right side to the right second premolar implant at the size of 7.486MPa. Bar-clip-retained overdenture with the

lowest stress caused by the 100 N force is the most appropriate design in the present study.

KEY WORDS: FINITE ELEMENT METHOD; STRESS TEST; BAR-CLIP ATTACHMENT; BALL ATTACHMENT; LOCATOR ATTACHMENT; OVERDENTURE

455

ARTICLE INFORMATION:

*Corresponding Author: Dr.ahmad2013@yahoo.com

Received 12

July, 2017

Accepted after revision 22

Sep, 2017

BBRC Print ISSN: 0974-6455

Online ISSN: 2321-4007 CODEN: USA BBRCBA

Thomson Reuters ISI ESC and Crossref Indexed Journal

NAAS Journal Score 2017: 4.31 Cosmos IF: 4.006

reserved.

Online Contents Available at:

http//www.bbrc.in/

DOI: 10.21786/bbrc/10.3/19

456 COMPARISON OF STRESS DISTRIBUTION AROUND IMPLANTS BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS

Ahmadzadeh and Teimouri

INTRODUCTION

Considering the aging of people in communities and

consequently the increase in complete edentulousness,

today edentulousness has become a public health prob-

lem. Unfortunately, in Iran, edentulousness is not seen

only in the elderly and many young people also suf-

fer from complete edentulousness for a variety of rea-

sons, including systemic diseases, non-compliance with

oral and dental care, and absence of periodic visit to

the dentist. Edentulousness can reduce the quality of

life of patients both physically and psychologically.

Recent studies have shown that tooth loss can affect the

intake and absorption of nutrients due to reduced chew-

ing ability, and increase the risk of multiple diseases.

For this reason, dental implants are used to improve the

chewing ef cacy in complete edentulous patients and

have improved the quality of life of these patients to an

optimum level, (MacEntee etal 2003, Abnet etal., 2005,

Semba etal 2006, Goiato et al 2008, Pennington etal

2012, Cunha etal 2013 Cakir etal 2014, Dezhdar etal

2017 and Geerts 2017).

The treatment that is predominantly performed for

edentulous patients is the use of complete denture hands.

From a public health perspective, although this treat-

ment is a simple and inexpensive treatment, it cannot,

be a general remedy for all patients. One of the main

problems in edentulousness patients is their low satisfac-

tion in denture use. The main reason for this discontent

is poor compliance, inadequate collision, ulceration and

pain (Zarb etal 2004). Considering the problems men-

tioned for ordinary complete dentures, a rational solu-

tion must be sought to the problems. Two types of treat-

ment are widely used for these patients: there are  xed

implant supported prostheses and implant-dependent

overdenture that are widely used for complete edentu-

lous patients (Dias et al 2013) and the use of any of

these treatments depends on the patient’s characteristics

and conditions, including the amount of bone remain-

ing, intervertebral space, oral hygiene, cost, and patient

satisfaction (Za ropoulos etal 2010).

Fixed implant-based prostheses may be one of the

best ways to treat edentulousness and are implemented

in case of suf cient bone and mandibular space (Chee

etal 2006). More implants are usually needed to support

a  xed prosthesis than an overdenture (Payne etal 2009).

Since it is sometimes impossible to use a large number of

implants for the patient, this issue limits the use of  xed

prostheses (Chee et al 2006). Other constraints on the

use of  xed prostheses is the loss of facial beauty due to

the lack of lip support and soft tissue face, lack of access

to hygiene, multiple and high cost surgical procedures

(Vogel 2007). Using overdentures has greatly resolved

the problems associated with the use of  xed prosthe-

sis. Implant-based overdenture is a moving prosthesis

that is placed on smaller number of implants per jaw,

and has excellent attachment and stability. Overdenture

is a simple, cost-effective, durable, less invasive treat-

ment and a successful treatment option for edentulous

patients and its use has recently become very common

(Assunção et al 2008). Implant-based overdenture has

improved the function of implant therapy (Awad et al

2003) due to the bene ts of physical and natural beauty,

and is superior to conventional dentures in many cases

(Sadowsky 2001). Different studies have shown that this

type of treatment has improved general health and qual-

ity of life of patients (Awad et al 2003). So, although

the patient wants a  xed implant-based prosthesis, (s)

he tends to use overdenture. Implant-based overdentures

are connected to the implant by an interstitial part called

attachment, which allows the prosthesis to resist against

displacement forces (Locker 1998).

Many attachments such as rods, buttons, and mag-

nets, are used to support implant-dependent overden-

tures (Machado etal 2011). Clinical success and longev-

ity of dental implants are affected by the distribution of

stress transferred to the implant and surrounding bones

(Jacques et al 2009). Also, the lack of suf cient bio-

compatibility between the implant and the surrounding

bone can lead to implant failure (Berglundh etal 2002).

Different attachment systems used in overdentures show

different biomechanical characteristics and can be dan-

gerous to implant supporting bones (Sadowsky 2007).

Various experimental studies have examined the distri-

bution of stress in the implant supporting bones, thus

avoiding the dangers involved. But there is still contro-

versy about biomechanical effects of stress distribution

in different attachment designs (CHUN etal 2005) and

(Baumeister 1978). Paying attention to the principles of

biomechanics in implant-based prosthesis can provide

a suitable treatment design for each patient and reduce

the probability of functional problems or implant fail-

ure (Baumeister 1978). Different methods are used to

evaluate the stress and strain in the bone around the

implant, which can be used for photoelastic analysis,

strain gauge, and  nite element analysis.

Fine Element Analysis (FEA) is a precise method for

evaluating the amount and pattern of stress distribu-

tion in dental structures which has many advantages

over other methods. Precise geometric reconstruction of

the structures involved in stresses acceptance and dis-

tribution, ability to accept and receive different simply,

showing the procedure of internal stresses and other

mechanical quantities, rapid and simple repeatability of

the tests are among the bene ts of this study method.

FEA is a numerical and quantitative method for analyz-

ing stress in complex structures. In this method, sepa-

rate structural elements are connected through points

BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS COMPARISON OF STRESS DISTRIBUTION AROUND IMPLANTS 457

Ahmadzadeh and Teimouri

or nodes. These components are created by dividing the

primary structure into units of the proper shape. For

each element, the physical properties are considered

proportional to the simulated material (Powers 2006).

This method is also used in dental studies as an ideal

method for preparing the correct tooth model and it’s

supporting structures in three dimensional form. This

method can provide measurement of partial mechanical

responses towards the difference in mechanical param-

eters and the evaluation of stress in dental materials and

tissues at different levels (Motta etal 2006). Various stud-

ies, using the FEA method, have shown that stress dis-

tribution in maxillary and mandibular implant systems

is signi cantly affected by various attachment designs

(CHUN et al 2005). The maxillary implant supported-

overdentures are less predictable than mandibular over-

dentures, and there is controversy over the use of dif-

ferent designs and the number of implants used (Dudley

2014). One of the overdenture treatments in maxilla is

the use of four implants, which has been studied in few

studies. There are also few studies on maxillary over-

denture than the mandibular one (Raghoebar etal 2014).

Some studies have shown that 4 or more than 4 max-

illary implant-dependent overdentures are more stable

and more durable than less than 4 implant-dependent

overdentures (Raghoebar etal 2014). These implants can

hold the overdenture with various attachments. Results

of studies on the acceptance and use of various attach-

ments showed that the bar and button attachments that

have a good stability as well as locators that are newer,

are at a higher level in terms of general acceptance and

enjoy more clinical use (Büttel etal 2009) and (Lonc˘ar

2015). For this reason, these attachments will be used in

a four-implant design to measure stress in the present

study. The present study uses a FEA method to simulate

the structure of various overdenture designs based on

four maxillary implants, to investigate the distribution

of Von Mises stress in the surface of all attachments and

implant supporting bones so that the most suitable solu-

tion for the treatment is identi ed.

MATERIAL AND METHODS

The present study is an experimental study in which the

distribution of stress is investigated and compared in

4 maxillary implant-dependent overdentures by FEA

method. In this study, the CBCT-Scan (NewTom VGi;

Finland) of a 30-year-old patient that was available in

the radiology department of Ahwaz Dental Faculty was

used to prepare the Maxilla model. Maxilla data were

imported to the Mimics ver. 8.1.1 for digitalization of

images. After transferring CBCT-Scan data to the Mim-

ics software, other changes were made to this data,

which included deleting the patient’s tooth data from

the initial data. The entire maxilla structure and root

site of the teeth was reconstructed with cortical bone

and 2 mm soft gum tissue was considered on it. The

maxillary bone structure was considered isotopic and

homogeneous, while the elasticity coef cient was lin-

early assumed. The overdenture was constructed on the

maxilla model that was obtained by a 3D printer of the

existing model. It is essential to accurately measuring

the implant for implant modeling. Hence, one specimen

of SPI implant (Thommen Medical, Element, Switzer-

land) with a diameter of 4x12.5 mm was measured by

the Coordinate Measuring Machine (CMM; Mitutoyo-

America Corporation) and the dimensions required for

modeling were used in solid works 2014. In this study,

Ball, Bar-clip, Locator (ThommenMedical, Switzerland)

attachments were used. Overdenture and attachments

were initially measured by CMM and turned into digi-

tal images. The output  le of the Mimics software was

imported to the modeling software called Solid Works

(SolidWorks® Of ce Premium 2007 SP, Corporation,

Concord, MA, USA) to turn into a geometric model. Geo-

metric modeling in Solid Work software was performed

automatically based on the surface detail speci ed by

the user. In the above model, implants were placed in

the right second premolar, left and right canine and left

central regions. One 4-mm long locator with housing

with a diameter of 3.6 mm and a height of 2.3 mm was

modeled. Also, ball with a width of 2.2 and a height of

4.3 mm and bar-clip with width and height of 2.2 and

3 mm respectively were modeled. In the Bar design, the

abutment pattern was used and the outside part of the

implant had height of 5.5 mm.

The next step in FEA modeling is to apply appropriate

boundary conditions and loading. For this purpose, the

geometric model was imported to ABAQUS / Standard

software (Version 6.14/1, Pawtucket, IR) for  nite analy-

sis. ANSYS software was used to implement FEA mode-

ling. The elements used in this study included SOLID187,

CONTA174 and TARGE170, the  rst of which was used

to generate the grid in the geometric model components

and the latter two elements for the attachments. In the

loading stage, the 100N static forces were applied ver-

tically to the center of the  rst molar center and the

stress distribution was demonstrated on the surface of

all implant supporting attachments and bones based on

computer graphic forms.

RESULTS AND DISCUSSION

Among the three different designs examined, the high-

est stress was observed in the vertical force (22.87

MPa) imposed on the implant in the right second pre-

molar on the right overdenture supported by the loca-

tor implant. In the second place, the highest stress was

458 COMPARISON OF STRESS DISTRIBUTION AROUND IMPLANTS BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS

Ahmadzadeh and Teimouri

FIGURE 1. Distribution of stress caused by the bilateral force in ball attachment-based

overdenture

FIGURE 2. Distribution of stress caused by the bilateral force in ball attachment-based

overdenture

observed on the Ball-retained overdenture in the right

side force, imposed on the implant in the right second

premolar corresponding to 12.88 MPa. The least stress

among these three designs was observed in the bar-

clip-retained overdenture design, the maximum stress

on which is in the vertical force imposed on the right

side to the right second premolar implant at the size of

7.486MPa. In the working side of the bone, the most

stress was induced to the nearest implant of the same

side. The results for the highest levels of stress in dense

and sponge bones did not reach the  nal bone resorp-

tion in any of the treatment plans (Figures 1 to 4).

Therefore, it can be concluded that overdenture based

on the bar-clip implant with the least stress produced

by the 100 N force, is the most suitable design, and the

ball design has the least stress and is suitable in the

second place (Tables 1 to 6).

In the working side of the bone, the most stress

was imposed to the nearest implant of the same side.

The results for the highest levels of stress in dense and

BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS COMPARISON OF STRESS DISTRIBUTION AROUND IMPLANTS 459

Ahmadzadeh and Teimouri

FIGURE 3. Distribution of stress caused by the bilateral force in bar-clip attachment-based

overdenture

FIGURE 4. Distribution of stress caused by the bilateral force in locator attach-

ment-based overdenture

sponge bones did not reach the ultimate bone resistance

in any of the treatment designs (Figures 1 to 4).

Among the three different attachment designs studied

in this study, the highest bone stress was observed around

the implant of the second right premolar area (working)

where locator attachment was used. In the present study,

the locator attachment was not evaluated using the FEA

method. After the locator attachment, the highest stress

was observed in the bone around the implant of the sec-

ond premolar area (working) using the ball attachment

and the result was consistent with the result of the study

by Chun etal. with the difference that the vertical input

force was 150 N was applied only bilaterally. In the pre-

sent study, vertical forces were applied unilaterally and

bilaterally with the highest concentration of stress in the

working side of the bone near the nearest implant to the

loading site in both cases.

According to the non-uniformity of force distribu-

tion obtained in the study of Mejer et al., the highest

the stress was seen in the working side of the bone and

Ahmadzadeh and Teimouri

460 COMPARISON OF STRESS DISTRIBUTION AROUND IMPLANTS BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS

Table 1. Maximum stress in implants in different treatment designs (Mpa) (bilateral force)