Mechanical consideration of implant support in removable partial
denture design applied by a magnetic attachment using
three-dimensional finite element analysis
Kumano H, Kanbara R, Fujinami W, Matukawa R, Ando A, Hata M, Kojima N, Yoshioka F,Ozawa S, Nakamura Y, Nakamura H, Shoji K and Takebe J.
Department of Removable Prosthodontics, School of Dentistry, Aichi Gakuin University
Abstract
The purpose of this study was to examine the mechanical effects of implant support in removablepartial denture design using three-dimensional finite element analysis. The analysis model was apartial edentulous mandibular where #35, 36, 45, 46 and 47 were missing. For design of the basicmodel, the RPI clasps were designed on #34 and #44 as retainer, and a magnetic attachment wasapplied on #37 as overdenture abutment. The implant support models were created in which two
types of implants with different lengths (6.5 mm and 10.0 mm) were placed in cantilever missing on
the right side of the mandible of the basic model. Stress analysis of these analysis models wasconducted. In the implant support models, there was no significant difference in the analysis results
depending on the length of the implant. Additional support by the implant demonstrated the stress
reducing of the abutment teeth even by the short implant. These results suggest implant supported
removable partial denture would expand its indication on designing removable partial denture.

Introduction
In the design of removable partial dentures in which tooth support and tissue support with different
amount of tissue displacements are complicated, it is very difficult to set appropriate mechanicaldistribution especially for cantilever missing.
In such a situation, the application of the magnetic attachment to the posterior molar can change themissing form from the cantilever missing to an intermediary missing by providing the tissue support
at the posterior position. In addition, it is clinically very useful to acquire the retentive force of thedenture by the attractive force of the magnetic attachment.
In recent years, as a method of prosthetic treatment from the crown bridge to the removable denture,
although implant treatment has been established, as another method, as well as the magneticattachment applied to the posterior molar, There is also report on the use of implant support in the atthe posterior position to stabilize removable partial denture.
However, there are still many questions about the mechanical effects of implant support in thedesign of removable partial denture.

Objective
The purpose of this study was to examine the mechanical effect of implant support in the design ofremovable partial denture applied by a magnetic attachment using three-dimensional finite element
analysis.

Material and Methods
1. Analysis model
The mandibular model used in this study is shown in Fig.1. For model construction, a mandibular
plaster model and a skull model (P10 - SB.1) manufactured by Nissin Co., Ltd. were used (Fig. 2).
Initially, this mandibular plaster model was scanned using a model and impression scanner (7 series,

Dental Wings, Montreal, Canada) to makemodel shape data in STL format. Next, askull model was CT photographed and theobtained CT data was prepared in STL
format with mandibular bone data andtooth root shape data using
three-dimensional construction softFig.1 : The mandibularFig.2 : Mandibular plastermodel used in this studymodel and a skull model(Mimics version l1.0，Materialise，Leuven，Belgium). We imported these data into computer
aided engineering（CAE）pre／post processing software(Patran 2013 windows 64bit, MSC software, Los Angeles,USA) and constructed a model. The thickness of theresidual ridge mucosa and periodontal ligament were set
with reference to the literature values and the morphologyof the mandible was simple form. 1
Fig.3 : The design of the removable partial denture
The design of the removable partial
denture is shown in Fig.3. The
magnetic attachment was applied on#37 as overdenture abutment and theRPI clasp was applied on #34 and #44
as the direct retainer. The magnetic
attachment applied in this research
was GIGAUSS D1000 and accurately
reproduced its high diameter andwidth for model construction.
The analysis model created by the above
method was used as the basic model in this study.

Fig.4 : Analysis items

2. Analysis Items
Table1 : Mechanical property values
Analysis items are shown in
Fig.4. The implant supportmodels were created in which two
types of implants with different
lengths (6.5 mm and 10.0 mm)
were placed in cantilever missing
on the right side of the mandible ofthe basic model. The implant of theimplant support model wasequipped with a healing abutment (height 4.0 mm) and set as a support
area under the denture base.
The mechanical property values of the analysis model are shown in
Table 1. About the periodontal ligament and the residual ridge mucosa,these nonlinear viscoelastic properties were introduced by material
constant conversion program（Table 2）.
3. Analysis Conditions
The load conditions are shown in Fig.5. The
loading site was a total of 4 places on the denture
occlusal surface and the loading direction wasperpendicular to the occlusal plane. Based on theliterature value, the load amount was set to 200 N
in total2. The inferior border of the mandible was defined as aconstraint condition in the x, y, and z directions. In the contact

Table2 : Material constantconversion program

Fig.5 : Load conditions

condition, the contacting relationship with the tooth and the mucosa in contact with the denture wasadded by Coulomb friction and the coefficient of defined Coulomb friction was set at μ = 0.090 for
this study. 3
The evaluation of the analysis results was based on the Von Mises stress and the displacement ofthe denture.

Analysis Results
1. Stress distribution in the alveolar boneFig. 6 shows a stress
distribution in the alveolar bone
in each abutment tooth. In the#37 of the alveolar cavity whichapplied a magnetic attachment,
stress relaxation was confirmedin the implant 10.0 model, theimplant 6.5 model as comparedwith a basic model. Next, in the#34 of the alveolar cavity, no
significant difference wasconfirmed in the alveolar cavity
in any of the models. However, inthe distal alveolar cavity, stressrelaxation was confirmed in theimplant 10.0 model and theimplant 6.5 model compared withthe basic model.
2. Stress distribution in
Fig.6 : Stress distribution in the alveolar bone
the residual mucous
membraneFig. 7 shows the stress
distribution in the residual mucous
membrane. In the residual mucous
membrane of the right side,
significant stress relaxation wasobserved in the implant 10.0 modeland the implant 6.5 model comparedwith the basic model, confirming thatFig.7 : Stress distribution in the residual mucous membrane
the mucosa supporting area of denture
was decreased. Next, comparing the implant 10.0 model with the implant 6.5 model, no significant
difference was observed in stress distribution in the residual mucous membrane.
3. Displacement of denturebaseFig. 8 shows the amount ofdisplacement of the denture base. In
the part corresponding to the # 45,
46 and 47, a decrease in the amountof displacement was observed in theimplant 10.0 model and implant 6.5
model compared with the basic
Fig.8 : A mount of displacement of the denture basemodel. The basic model showed a tendency for the displacement amount to increase toward thedistal side, and the implant 10.0 model and the implant 6.5 model showed a tendency for thedisplacement amount to increase toward the mesial side. In the part corresponding to the # 35, 36
and 37, the difference in the amount of displacement was not observed in all models, and the amountof displacement tended to increase toward the mesial side.

Discussion and Conclusion
From the results of this study, as a mechanical effect of implant support in the design of removablepartial denture,
1: Stress relaxation was observed in the tissue around the abutment tooth, including the magnetic
attachment.
2: In the burden style of denture, it was confirmed that the tissue borne area was reduced and thedisplacement of the denture base was suppressed.
3: In the implant 10.0 model and the implant 6.5 models, significant differences were notobserved in both stress distribution and denture displacement in the alveolar bone.
Therefore, these results suggest implant supported removable partial denture would expand its
indication on designing removable partial denture.

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