8. Influence of the Angle of Attractive Surface of Root Cap Affect Abutment Tooth for Overdenture

Yuusuke Katakura¹, Tetsuo Ohyama^1,2, Eiichi Nagai^1,2, Tomohiko Ishigami^1,2, Hitoshi Toyoma^1,2, Shigeru Ohno¹, Yoshimasa Takeuchi¹ and Mikage Hasegawa¹

¹⁾ Department of Partial Denture Prosthodontics, Nihon University School of Dentistry

²⁾ Division of Clinical Research, Dental Research Center, Nihon University School of Dentistry

Introduction

The magnetic attachment shows maximum retentive force in the vertical direction on the attractive surface of the keeper and the magnetic assembly. In addition, it can strengthen support of the prosthesis when it is setting the keeper in parallel with occlusal plane. Therefore it is recommended to set it up in parallel to occlusal plane. However the anterior tooth that was inclined of the alveolar bone have possibility of receiving harmful force.

Hence we examined the influence that the angle of inclination of the root cap top surface on the abutment tooth and denture support tissue using three dimensional finite element method.

Materials and Methods

In this study, we built three-dimensional finite element models of a human mandible reconstructed from tomographs of a jaw and tooth. The analytical models were developed cortical bone, cancellous bone, periodontal ligament, alveolar ridge and canine. We set the tooth was inclined 15 degrees from occlusal plane (Fig. 1).

Fig.1

To analyze cases of four type mandibular models with canine were developed. Full overdentures placed on the metal copings, which were selected by four types over the abutment teeth. The height of the model of coping is 2.5 mm from the top of the lingual alveolar ridge, and tapers are six degrees. The top surface set the state that was parallel to occlusal plane with 0 degrees, and the root cap set four kinds of models that 15, 30 and 45 degrees and the surface inclined in the labial side (Fig. 2).

The magnetic assembly and the keeper were not constructed, because the factor of adsorption was not considered. The denture base and artificial tooth were integrated for the model's simplification. A total of four models were evaluated.

This study utilized Rhinoceros version 1.0 (Robert McNeil & Associates, USA) and ANSYS, version 11.0, FEM computer software (Ansys Inc, USA) for the analysis of modeled specimens.

Fig.2

Mechanical analysis by the three dimensional finite element method was solved. The model was completely constraint all degree of freedom on mandibular condyle and the 10 contact points.

Table 1 shows that the analyses were executed the nodes total loads of 9.8 N on masticatory muscles.

Table 1

Table 2 shows the Youngfs modulus and Poissonfs ratio values identified for each material simulated in this study.The results were compared by geometrical nonlinear analysis.

Table 2

Results

The results were displayed as 2D stress contour plots to indicate stress levels and patterns of stress concentration. Stress levels were calculated according to the minimum principal stress. These models demonstrated areas of high stress concentration on abutment teeth.

The 15 degree model showed the distribution of the stress equality in comparison with the other models (Fig.3).

Fig. 3

Discussions

The abutment teeth inclined by the first setting 15 degrees, the root cap top surface and the tooth axis are perpendicular. It is thought that the stress to teeth was equalized for the direction of the tooth axis.

Conclusions

According to our results, it is consequently suggested that the load of the abutment tooth was reduced with the model that set 15 degree inclined tooth.

Acknowledgement

This project was supported by the Sato Fund, Nihon University School of Dentistry.

References

1. Korioth TW, Hannam AG Deformation of the human mandible during simulated tooth clenching. J Dent Res 73:56-66, 1994.

Discussion Board