The thickness of the resin base needed to the top of copings-Examination by the three-dimensional finite element methodM. Obayashi1, T. Ohyama1,2, S. Nakabayashi1,2, S. Tadokoro1, N. Shibuya1, H. Yasuda1, T. Okubo1 andT. Ishigami1,2
1

Department of Partial Denture Prosthodontics, Nihon University School of Dentistry
Division of Clinical Research, Dental Research Center, Nihon University School of Dentistry

2Introduction
Denture fracture is common complication in overdenture because the thickness of denture base is often
not enough above the copings and copings become fulcrum.1) Very few attempts have been made at suchstudy. In this study the correlationship between the thickness of resin base and stress concentration above
copings was assessed using three-dimensional finite element (FE) method addition to model-testing.

Materials and Methods
1. ModelThe outline of plunger, resin plate and coping were modeled using three-dimension data from ANSYS.
(Rel 15.0, ANSYS Inc., U.S.A) and Space Claim Direct Modeler (Space Claim Corp.) The maximum
principal stress and displacement of these models were evaluated using ANSYS. Table1 shows the Young’s
modulus and Poisson’s ratio.2)

Table 1: Material Properties
Figure 1 shows plunger, resin plate and coping models. The plunger as press a resin plate was a column
with radius of 1.6mm according to JIS T6501.3) The resin plate was 10mm in length, 64mm in width, and2.5, 3.0, 3.5mm in height. It makes hollows according to shape of copings. It is diameter of 6.0mm a part ofthrusting it into resin plate is height of 2.0mm.4)
2 types bending test models as modified 3-point bending test (3PB) and modified 4-point bending testmodels (4PB) were constructed for assessing a thick of resin plate. Model A is 3PB of a dome shape copingand 3 different thickness of resin plate. Model B is 3PB of a trapezoidal shape coping and 3 different
thickness of resin plate. Model C is 4PB of a dome shape coping and 3 different thickness of resin plate.
Model D is 4PB of a trapezoidal shape coping and 3 different thickness of resin plate.

Fig.1: analysis model
2. Loading and boundary conditions
Figure 2 shows Loadings and boundary conditions. Loading amount is 110N, according to bending
strength of ACRON. The surface of plunger was loaded each 55N, 110N in total. A complete constraint wasapplied to the bottom of copings in the all degree of freedom.

Fig.2: Loading and constraint conditions
3. Displacement
The measuring point was set on the surface of resin plate and the displacement was analyzed verticaldirection.

ResultFigure 3 shows maximum principal stress of the section of 3BP and 4BP. The stress concentrated resin
plate surface corresponding to top of copings in dome shape. The stress concentrated resin plate surface
corresponding to the corner of copings in trapezoidal shape. An increasing of thickness of resin plate
reduced stress concentration. The fracture part in model-testing was similar to the result of FE method.
.

Fig.3: 3BP and 4BP maximum principal stress
Figure 4 shows the maximum value of maximum principal stress of 3PB and 4 PB. 3 different thickness ofresin plate were investigated the maximum value of maximum principal stress in 4 models. An increasingof thickness of resin plate reduced the maximum value of maximum principal stress. There were nodifference stress between dome shape and trapezoidal shape.

Fig.4: Maximum value of maximum principal stress
Figure 5 shows displacement of resin plate 3PB and 4BP. The arrows are plunger. The figure is coping.
Resin plate was displaced equally on both side starting from coping both model A and B. An increasing ofthickness of resin plate reduced the displacement in all models.

Fig.5: displacement of 3PB and 4BP

Discussions
It found that an increasing of thickness of resin plate reduced the maximum principal stress anddisplacement both 3PB and 4PB.
It found that the stress concentrated the center of resin plate in model A and C. It found that the stressconcentrated the corner of copings in model B and D.
Tendency of denture fracture are suggested by FE method because model-testing by Kanazawa5） has thesame evaluation as that.

Conclusions
Those results suggested that an increasing of thickness of resin plate reduced risk of fracture the same asmodel-test and it showed the effect of coping shape as invisible effect in model test. Further experiment iswarranted to identify the required thickness of denture base.

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