A new technique for good fitness of dental magnetic attachment on the magno-telescopic crown system

Eri Makihara¹, Shin-ichi Masumi¹, Masahiro Arita¹, Takumi Ogawa², Yuko Shigeta², and Shunji Fukushima²

¹ Division of Occlusion & Maxillofacial Reconstruction, Department of Oral Functional Reconstruction, Kyushu Dental College, Kitakyushu, Japan

² Department Fixed Prosthodontics, School of Dental Medicine, Tsurumi University, Yokohama, Japan

Introduction

A magno-telescopic (MT) crown is a telescopic crown that is applied dental magnetic attachment for its retention. Usually, a keeper is fixed into the occlusal surface of an inner crown with a cementing material, and a magnetic assembly is fixed into the internal occlusal surface of an outer crown with the same cementing material.

Although MT crown is useful, there are some problems about fitness among an abutment tooth, an inner crown, and an outer croun.

The purpose of this study is to introduce a new method we designed for fabricating of MT crown.

Methods

1. Conventional method for fabricating a MT inner crown

a. After tooth preparation for a residual cap, a keeper housing pattern is selected (Fig.1, 2).

b. After putting the pattern on an occlusal surface of an abutment tooth of a working cast, wax-up is done (Fig.3).

c. Investing, casting, and polishing are done according to the conventional method (Fig.4).

d. After painting a metal primer, a keeper is fixed with a cementing material (Panavia, Kurare, Japan) (Fig.5 -8) .

2. Problem of conventional method

Fitness between an abutment tooth and an inner crown is sometimes bad.

3. A new method for fabricating a MT inner crown

a. After tooth preparation for a residual cap, a keeper housing pattern is selected and make a hole in the center of it (Fig.9,10).

b. After putting the pattern on an occlusal surface of an abutment tooth of a working cast, wax-up is done (Fig.11).

c. Investing, casting, and polishing are done according to the conventional method (Fig.12).

d. After fixing an inner crown with a cementing material (super bond, Sun Medical, Japan), a keeper is fixed with a cementing material (Panavia, Kurare, Japan) (Fig.13 -16) . These procedures are done in a patientÕs oral cavity.

4. Flow chart for fabricating of an inner crown

5. Conventional method for fabricating a MT outer crown

a. After putting a magnetic assembly on an inner crown, impression is taken and a working cast is made (Fig.17, 18).

b. After waxing-up of an outer crown, investing, casting, and polishing are done according to the conventional method (Fig.19,20).

c. After sand blasting and painting a metal primer, the assembly is fixed with a cementing material (Panavia, Kurare, Japan) (Fig.21 -24) .

6. Problem of conventional method

A cementing material fixing a magnetic assembly into an outer crown makes the reduction of retentive force by existing it between an inner crown and an outer crown.

7. A new method for fabricating a MT inner crown

a. An outer crown consists of two pieces. After waxing-up of an outer crown, investing, casting, and polishing are done according to the conventional method (Fig.25 -28).

b. After sand blasting and painting a metal primer, put the assembly on an inner crown.

c. After pouring a cementing material in an outer crown and fixed the assembly. Press the assembly until finishing the polymerization of a cementing material (Fig.29, 30) .

d. Fix an inlay with a cementing material (Fig.31, 32)

8. Flow chart for fabricating of an inner crown

Conclusion

In this study, we introduced a new method for fabricating a magno-telescopic crown.

We designed a new inner crown which has a pin-hole on the occlusal surface to get a good fitness between an abutment tooth and an inner crown. This hole is covered with a keeper after fixing an inner crown on an abutment tooth.

We also designed a new outer crown that has a hole on the occlusal surface to get a good fitness between an inner crown and an outer crown. Furthermore, there is no reduction of the attractive force of dental magnetic attachments.

We hope that many dentists and dental technicians will apply this useful method.

Discussion Board