Mechanical analysis of implant support in removable partial
denture design applied a magnetic attachment
R. kanbara, H. Kumano, R. Aoyama, W. Fujinami, Y. Nakamura，K. Shoji，H. Nagai, and J. Takebe
Department of Removable Prosthodontics, School of Dentistry, Aichi Gakuin University
Abstract
The purpose of this study was to investigate the effect of implant support on the tissue around theabutment tooth and the behavior of the removable partial denture using three-dimensional finite
element method in the design of the removable partial denture applied a magnetic attachment.
The analysis model was constructed using a mandibular plaster model and a skull model. The
missing teeth were right lower second premolar, first and second molar, left lower second premolar,and first molar. The basic model used a retainer with RPI clasp on both first premolar and themagnetic attachment on left second molar. The analysis items were two types of the basic model andthe implant support model in which implants were embedded in right free end missing of the basicmodel. The analysis conditions were set for these models, and three-dimensional finite element
analysis was performed.
The results of this analysis, the mechanical effect of the implant support in the design of removablepartial denture decreased the displacement of the denture, and showed the relaxation of the stress ofthe tissue around the abutment tooth on the implant side.

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 free end missing.
In such a situation, the application of the magnetic attachment to the posterior molar can change themissing form from the free end missing to an intermediary missing by providing the tissue support atthe 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 defectprosthesis from the crown bridge to the removable denture, although implant treatment has been
established, as another method, as well as the magnetic attachment applied to the posterior molar,
There is also report on the use of implant support in the at the posterior position to stabilize
removable partial denture. However, for the intervention of the implant support in the design ofremovable partial denture, at present, still there are many questions about mechanical effects.

Objective
The purpose of this study was to analyze by using the three-dimensional finite element method, andto examine what kind of mechanical effect of using implant support in the design of removablepartial denture with magnetic attachment.

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 wasscanned using a model and impression scanner(7 series, Dental Wings, Montreal, Canada) tomake model shape data in STL format. Next, askull model was CT photographed and theobtained CT data was prepared in STL format
with mandibular bone data and tooth root
Fig.1 : The mandibularFig.2 : a mandibular plastershape data using three-dimensionalmodel used in this study
model and a skull model
construction soft (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
Angels, USA) and constructed a model. The thickness
Fig.3 : The design of the removable partial dentureof the residual ridge mucosa and periodontal ligament
were set with reference to the literature values and themorphology of the mandible was simple form. 1The design of the removable partial denture is shown inFig.3. The magnetic attachment was designed for themandibular left second molar and the RPI clasp wasapplied on the both sides first premolar as the direct
retainer.The magnetic attachment applied in this research
was GIGAUSS D1000 and accurately reproduced its
high diameter and width for model construction.
2. Analysis Items
Analysis items are shown in Fig.4.
Fig.4 : the analysis items
The analysis items were two types of the basic model and theimplant support model with implant (lemgth 10.0mm φ3.8mm ) embedded in the second molar
equivalent of the right side of the mandible of the basic model. The implant of the implant supportmodel was equipped with a healing abutment (height 4.0 mm) and set as a support area under thedenture base.
Table1 : the mechanical property values Table2 : the material constant
The mechanical property
conversion program
values of the analysis model are
shown in Table 1. About theperiodontal ligament and theresidual 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 atotal of 4 places on the denture occlusal surface and the loading
direction was perpendicular 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 a constraint
condition in the x, y, and z directions. In the contact condition, thecontacting relationship with the tooth and the mucosa in contact
with the denture was added by Coulomb friction and the coefficientof defined Coulomb friction was set at μ = 0.090 for this study. 3Fig.5 : the load conditions

Analysis Results
The stress in this analysis was evaluated by Von Mises stress.
1. Alveolar cavity of the mandibular left second
molar
Fig. 6 shows the stress distribution of the alveolar cavity ofthe mandibular left second molar. Compared to the basicmodel, stress relaxation was confirmed in the implant supportmodel.
2. Alveolar cavity of the mandibular left firstpremolarFig. 7 shows the stress distribution of the alveolar cavity ofthe mandibular right first premolar. Compared with the implant
support model, stress spread was observed at the distal portionof the alveolar cavity in the basic model, but no significant
difference was observed around the alveolar cavity.

Fig.6 : the stress distribution of the alveolar
cavity of the mandibular left second molar

Fig.7 : the stress distribution of the alveolar
cavity of the mandibular left first premolar

3. Alveolar cavity of the mandibular right firstpremolar
Fig. 8 shows the stress distribution of the alveolar cavity of themandibular right first premolar. At the distal portion of thealveolar cavity and around the alveolar cavity, Compared tothe basic model, stress relaxation was confirmed in theimplant support model.
4. Displacement of denture baseFig. 9 shows the amount of displacement of thedenture base. The displacement of the equivalent tomandibular right second molar, first molar, andsecond premolar was reduced in the implant supportmodel compared to the basic model. As for theamount of displacement, the basic model tended toincrease as the distance toward the distal, and theimplant support model tended to increase as thedistance toward the mesial. There was no significant
difference between the two models in thedisplacements of equivalent to mandibular left second
molar, the first molar, and the second premolar. As forthe amount of displacement, both models tended tothe increase as the distance toward the mesial.

Fig.8 : the stress distribution of the alveolar
cavity of the mandibular right first premolar

Fig.9 : The amount of displacement of the denture base

Discussion and Conclusion
The results of this study confirm that the mechanical effects of implant support in the design ofremovable partial denture using magnetic attachment include stress relaxation of the tissue aroundthe abutment tooth using the magnetic attachment and the tissue around the abutment tooth on theimplant support side. It was also confirmed that the use of implant support for the free end missing
reduced mucosal burden zone of the denture and suppressed the amount of the displacement of thedenture base. From the above, in the design of removable partial denture in the free end missing,taking advantage of the implant support the rearmost missing form an intermediate missing
reduction, possibly attained stability of partial denture was suggested.

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