Development of Cement-bonded Keeper Used with Carbon
Lead-Part3 A Trial for Ready-made Pattern
H. Matsubara＊, H. Mizutani, H. Hideshima＊＊, T. Ando, K. Nakamura, H. Sasakiand Y, Igarashi
Removable Partial Denture Prosthodontics, Graduate School,＊ Dental Laboratory, Clinical Facilities Dental Hospital,＊＊Clinic for Conservation Of Oral and Maxillofacial Function, Dental Hospital ,Tokyo Medical and Dental University
Introduction
To fabricate magnetic attachment keeper housings for cementation method,
ready-made plastic patterns have been usually used.
But the outer diameters of the plastic patterns often limit the shape of the casting
patterns of keeper components.
We have already made presentations on the new method for fabricating keeper
component at the previous 18th and 19th meetings.
In the first presentation, we reported a new method for fabricating them with trial
graphite patterns made with rod-shaped graphite for writing.
This method was proved to be very useful because of the good casting performanceowing to the high thermal stability and mechanical strength of the graphite material
and good compatibility of the graphite with investing materials.
In the second presentation, we reported the pattern fabrication with carbon material(#2191) widely used in the industrial field to develop ready-made carbon patterns,
which had a problem on the thermal stability of the material.
This time, we are going to present a new trial carbon pattern which improved thermalstability for casting.
Objectives
The purpose of this study was to assess the efficacy of a newly developed carbon
material for developing ready-made carbon patterns for fabricating keeper housings.

Materials and Methods
1. Materials
Newly developed carbon material (Aichi Steel Co. Japan) was used in thisexperiment. This material has higher heat resistance property than the carbon
material #2191 (Aichi Steel Co. Japan) used in the previous study.
Carbon patterns for fabricating keeper housings were made with this material.
The keeper without holder (PHYSIOMAGNET

Aichi Steel Co. Japan) wasused in this study. Carbon patterns were fabricated so as to confirm the positionof carbon pattern in the investing material.
2. Experiment 1
Six carbon part of the casting patterns were fabricated with newly developed
carbon material.
They were heated and stored under six heat conditions (450℃, 500℃, 550℃, 600℃,650℃, 700℃, 30 minutes) in the furnace respectively. After heating and storing,the diameters of carbon patterns were measured to assess the thermostabilities ofthe pattern sizes.
And changes of the surface textures of them were observed by visual comparison.
(fig3-１,3-2 fig4)
3. Experiment 2
On the basis of experiment 1, casting patterns of keeper components in which thecarbon part were incorporated were fabricated by the usual method in twoconditions (stored 690℃ furnace for 30 minute,stored 700℃ furnace for 20minute) .
After casting, the diameter of keeper space were measured and evaluate

Fig1

Fig2

Fig3

Fig4
Fig4

Fig5

Fig6

Fig7

Fig.1 Trial graphite pattern made from carbon rod
Fig.2 Improved trial product for ready-madeFig.3 The state after heating (450℃, 30 minute)Fig.4 The state after heating (650℃, 30 minute)Fig.5 The measurement of diameter (650℃, 30 minute)
Fig.6 As cast after heating and storing 700℃, 20 minuteFig.7 700℃, 20 minute, after casting and then keeper cemented to the root cap

Results and Discussions
There is little difference of the diameter for keeper space among the samples derived
from 450℃ to 650℃ of furnace heating conditions, though the surface textures of thecarbon patterns showed a little change.
It is concluded that the new carbon material showed great improvement in terms of thethermal stability for fabricating keeper components. However, considering theaccuracy of casting or fitness, further improvement of heat resistance of the materials
will be needed.