A basic study on the fitness of a zirconia keeper coping fabricated by CAM
systemH. HAMASAKA, M. SONE, Y. OKAWA, S. SOMEKAWA, M. MASUDA, A. MATUI, Y. TOYOTA, F.
OKUTSU, T. MATSUKAWA, K. OKAMOTO and S. OHKAWA
Division of Removable Prosthodontics, Department of Restorative and Biomaterials Sciences, Meikai
University School of Dentistry
Abstract
The purpose of this study was to evaluate the fitness of a zirconia keeper coping fabricated by CAM
system (Cercon® brain, DeguDent).
Specimens made of a semi-sintered zirconia block (Cercon® base, DeguDent). Fitting accuracy wasevaluated by a cement-replica technique with silicone materials. For the keeper coping specimens, themean fitting gaps were 0.23±0.08 ㎜ at the finish line of coping, 0.26±0.04 ㎜ at the interface between thecoping and post, and 0.32±0.06 ㎜ at the tip of the post. This study found that the adaptation of a zirconia
keeper coping fabricated by this system was not recommended.

Introduction
The dental CAM system and CAD/CAM system has been used generally to fabricate a various prosthesis
in clinical dentistry. However, the keeper coping of magnetic attachment was still cast by a lost wax
method used in dental casting. In the past, although manufacturing method of keeper coping using thedental CAD/CAM system by “scanning probe” has been reported1), it has not been usually used.
Recently, the dental CAM system and CAD/CAM system by “laser scanning” has been primarily usedbecause of high-precision performance, and zirconia ceramics has become popular materials in a clinicaldentistry. Zirconia ceramics has excellent mechanical strength for prosthetic appliances andbiocompatibility with a significant reduction in plaque2). Those facts suggest that zirconia ceramics wereclinically useful for keeper coping of magnetic attachment.
The purpose of this study was to evaluate the fitness of a zirconia keeper coping fabricated by the dental
CAM system by laser scanning.

Materials and Methods
Materials: The prepared epoxy resin tooth at lower canine (338: NISSIN) was selected as the abutment
tooth of keeper coping with a root canal length of 5 mm. The keeper coping was fabricated using the dental
CAM system (Cercon® brain, DeguDent), and a semi-sintered zirconia block (Cercon® base, DeguDent)
was employed for the keeper coping material (Table.1).
Fig.1 shows the wax pattern used for scanning and the zirconia keeper coping fabricated by this CAM
system.

Table.1 Material composition in this study

Fig.1 Keeper coping specimens in this study(a: Wax pattern b: Zirconia keeper coping)Methods (Cement-replica technique): The fitting accuracy was evaluated using a cement-replica technique.
Each keeper coping was placed in the master die with a white silicone material (FIT CHECKER
ADVANCED, GC). After curing a white silicone material, the keeper coping with a white silicone material
is removed from the master die. Then, the keeper coping with it was embedded in a blue silicone material(EXAMIXFINE Regular Type, GC). The keeper coping was demounted from the cured silicone material,
and a blue silicone material filled in the space (Fig.3).

Fig.3 Fabrication procedure of specimens (Cement-replica technique)

Determination of fitting accuracy: Each silicone replica specimens were sectioned in the buccolingual
direction through the center of the coronal root (Fig.4). The measuring points of the white silicone layers
are shown in Fig.5. The maximum value was picked up from the range of each part.

Fig.4 Section of silicone replica specimen in
the buccolingual direction

Fig.5 Measuring points(a: Finish line of coping b: Interface between
coping and post c: Tip of post)

Results
The mean thicknesses of the white silicone layers, namely the mean fitting gaps, were 0.23±0.08 ㎜ at thefinish line, 0.26±0.04 1㎜ at the interface between the coping and post, and 0.32±0.06 ㎜ at the tip of thepost (Fig. 6). There was
0.9 no significant difference in the mean thicknesses of the white silicone layers
between 3 measuring points by one way ANOVA and Tukey–Kramer method (p<0.05).
0.8
0.7

0.6
0.5
0.4

0.23± 0.08

0.26± 0.04

Finish	  line	  of	  coping(a)Interface	  between
coping	  and	  post(b)0.32± 0.06

0.3
0.2
0.1
0Tip	  of	  post(c)Fig. 6 The mean thicknesses of the white silicone layers at 3 measuring points

Conclusion
It was concluded that the fitness of a zirconia keeper coping fabricated by this system was more poor than
the fitness of other prosthesis reported in the past (Permissible fitting gap: 0.1~0.15 ㎜). So the adaptationof a zirconia keeper coping fabricated by this system was not clinically recommended. We will makefurther refinements to manufacturing method by laser scanning.

References
1.
2.

K. Tsuda, Y. Tanaka, T. Kanazawa, M. Sakane, and K. Kumano: Fabrication of a Keeper Coping by
use of the CAD/CAM System, J J Mag Dent, 13(1), 9–17, 2004.
T. Miyazaki, T. Nakamura, H. Matsumura, S. Ban, and T. Kobayashi: Current status of zirconia
restoration, J Prosthodont Res, 57, 236–261, 2013.