Development of the extracoronal attachment “GIGAUSS C 600 EC Keeper Tray”

Nakashima H., Kumano H*., Nakamura Y.*, Masuda T.*, Ando A. *, Miyata T.*, Hasegawa A., Tanaka Y.*

GC DENTAL PRODUKTS CORP

*The First Department of Prosthodontics, School of Dentistry, Aichi-Gakuin University

Introduction

GIGAUSS C 600 EC keeper tray was developed as a pre-formed attachment pattern to apply an extra coronal magnetic attachment. This attachment was originally designed for use with a non-vital tooth. The extra-coronal design allows applications with vital teeth. An extra coronal attachment requires strength at the neck part.(Fig1) To provide and maintain adequate strength, sufficient thickness at the neck part and “R” part area is required. However, to allow greater versatility, the maximum thickness imparted is limited. As for R of the neck part, the use of a pre-fabricated housing pattern ( GIGAUSS C 600 housing pattern ) is limited to R 0.1 mm without processing. The use of a pre-formed housing pattern with processing is R 0.4 mm at the maximum.

OBJECTIVE

The purpose of this study was to examine the influence of the difference in R of the neck part in order to determine its effect on the maximum neck part strength of the neck part of the extra coronal attachment design. We compared the strength of a R 0.1mm neck part and a R 0.4mm neck part, which is considered a maximum allowed thickness.

MATERIALS AND METHODS

Measurement of displacement

The base parts fabricated by wax-up method were attached to keeper tray patterns with R 0.1 mm and R 0.4 mm neck parts(Fig2), followed by casting using CASTWELL M.C 12 ( GC corp. Japan )(Fig3). Loads were applied to the center of the cup(Fig4), and the relationship between the displacement and permanent set was investigated. Autograph AGS-500D ( SHIMADU corp. Japan ) was used for the test. (Fig5) Measurement of plastic strain was performed by Digimatic height gage. ( Mitutoyo corp. Japan )

<Procedure >

1. Sample was attached to the Autograph. (initial position)(Fig6-A)

2. Arbitrary amount to the sample was applied by the Autograph. The applied amount was measured as a displacement. (Fig6-B)

3. After load release, the displacement between initial position and spring back condition was measured by Digimatic height gauge. (permanent set) (Fig6-C)

Measurement of breaking load

In the measurement of the breaking load, extra coronal attachment was destroyed by compressive load. Subsequently, the maximum compressive load to break test piece and the load when permanent set occurred were measured. The load was measured by Autograph using a test piece similarly fabricated as the one used in the measurement of displacement.

Analysis of stress by FEM

Stress distribution in the elastic region was investigated under a load of 100N in each model of R 0.1mm neck part and R 0.4mm neck part.

< Analysis condition >

analysis type : elastic analysis

element type : 3D hexahedron and pentahedron

analysis system :MSC.MARC (MSC software)

RSULTS

Measurement of displacement

Both R0.1mm and R0.4mm had the same elastic limit of 0.14mm thrust amount.

Measurement of breaking load

Significant difference was confirmed between R0.1mm and R0.4mm in the measurement of breaking load.(Fig7) Cracks from neck part R caused breaking.(Fig8) The load applied at the elastic limit of 0.14 mm that we measured in the former chapter was 338 N both in R 0.1mm and R 0.4mm.

Analysis of stress by FEM

The stress distribution obtained by FEM showed no difference between R 0.1mm(Fig9) and R 0.4mm(Fig10).

Analysis of stress by FEM

The stress distribution obtained by FEM showed no difference between R 0.1mm(Fig9) and R 0.4mm(Fig10).

DISCUSSION

While there was a significant difference in the breaking strength between R0.1mm and R0.4mm, there was no difference in the elastic limit.

The result of FEM in the elastic region showed no difference in stress distribution between R 0.1mm and R 0.4mm. This result corroborated the fact that the loads applied at the elastic limit were the same between R 0.1mm and R 0.4mm.

CONCLUSIONS

Extra coronal attachment pattern should be used in the elastic region. The result showed no difference in strength between R 0.1mm and R 0.4mm until the permanent set was achieved. Therefore, pre-formed housing pattern with a R 0.1mm neck part was selected.

REFERENCES

1. Jackson,T.R.: The applicaiton of rare earth magnetic retention toosseointegrated implants. Int. J. Oral & Maxill. Imp., 1: 81-92, 1986.

2. Tanaka, Y.: Dental Magnetic Attachment, Q&A, Ishiyaku Publishers, Inc. (Tokyo), 1995.

3. Nakamura, Y.: Stress analysis of overlay denture and a magnetic attachment using finite element method. J Jpn Prosthodont Soc, 42: 234-245, 1998.

Discussion Board