A basic study on accuracy of a zirconia coping fabricated by CAD/CAM
system -Application for post for scanningS. UEDA, M. SONE, M. HAMASAKA, Y. OKAWA, S. SOMEKAWA, M. MASUDA, A. MATUI, Y.
TOYOTA, F. NARUMI, 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 fitting accuracy of zirconia keeper copings manufactured bycomputer-aided design and manufacturing using scan posts.
The keeper copings, made from a zirconia block, were fabricated with four different cement spaces asspecimens (n=3 for each). The fitting accuracy of the specimens was evaluated using the cement replicatechnique. Each silicone replica specimen was sectioned in the buccolingual direction through the center ofthe coronal aspect of the root. The thickness of the white silicone layer was examined at five measuring
points (A: canal orifice of the lingual wall, B: center of the lingual wall, C: apical part of the post, D: centerof the labial wall, E: canal orifice of the labial wall).
The mean thickness of the white silicone layer at the five measuring points was 81±22, 239±39, 574±68,
223±43 and 67±19 µm for points A, B, C, D and E, respectively. There was no significant difference
between the results for each cement space (P<0.05).
Within the limitations of this study, it was suggested that the fitting accuracy of zirconia keeper copings
manufactured with this CAD/CAM system using scan posts was within the clinically acceptable range,excluding marginal gaps.

Introduction
Advancements in computer-aided design/computer-aided manufacturing (CAD/CAM) techniques have
improved prosthetic devices milled in the dental clinic and laboratory. With CAD/CAM techniques,
copings and frameworks for all-ceramic restorations can be made from zirconia, because of its highstability and toughness. Digital impression systems are generally composed of a three-dimensional scannerrecording the object and CAD software that uses the scanned image to design the prosthesis.
Although a method for manufacturing CAD/CAM keeper copings using a scanning probe has beenreported1), the keeper coping of the magnetic attachment was still manufactured using the lost-wax casting
method.
Recently, laser scanning using a dental CAD/CAM system has been primarily used for producing zirconia
prostheses because of its high-precision performance. However, there is greater distortion of the digital
impression when scanning a prepared root canal, possibly because of the limitations of the specificscanning technology. Although applying a scan post could enable digital images of the prepared root canal
to be obtained, there have not been any studies investigating this method.
The purpose of this study was to evaluate the fitting accuracy of zirconia keeper copings manufactured byCAD/CAM using scan posts.

Materials and Methods
Keeper coping fabrication
Prepared epoxy resin mandibular canine teeth (338; Nissin) with a root canal length of 5.0 mm wereselected as the abutment teeth for the keeper copings. Impressions were taken of the prepared teeth using
silicone impression material (Examixfine Regular Type, GC). The working casts were made of type IV
gypsum (New Fujirock, GC). A scan post (Scan Posts, 3Shape) was placed into the prepared post space oneach working cast (Fig. 1). The keeper copings were designed using CAD software (Dental Designer,3Shape) after digitalization of the die was performed using a laser scanner (Aadva Scan D850, GC).
The keeper copings, made from a zirconia block (Aadva Zirconia Disk, GC), were fabricated with four

different cement spaces as specimens (Fig. 2). Each cement space for the zirconia copings was fabricatedusing a milling machine (GM-1000, GC).
A

B

Fig. 1 Scan post placed into the prepared root canal on the master die(A. Scan posts, B. Insert into the master die)Fig. 2 Four different cement spaces

Cement replica technique
The fitting accuracy was evaluated using a cement replica technique. The post space was filled with awhite silicone material (Fit Checker Advanced, GC) and the keeper coping was seated on the master die
using finger pressure. After curing the white silicone, the keeper coping and white silicone material wereremoved from the master die. These keeper copings were then embedded in a blue silicone material(Examixfine Regular Type, GC) and the space created by demounting the keeper copings from the cured
silicone material was filled by the blue silicone (Fig. 3).

Fig. 3 Fabrication of the specimens (cement replica technique)Fitting accuracy
The silicone replica specimens were sectioned in the buccolingual direction through the center of thecoronal aspect of the root (Fig. 4). The thickness of the white silicone was determined as a measure of thediscrepancy between the die and the restoration. The distances were recorded at five different measuring
points. The measuring points are defined in Fig. 5.

Fig. 4 Silicone replica specimen sectioned inthe buccolingual direction

Fig. 5 Measuring points(A: canal orifice of the lingual wall, B: centerof the lingual wall, C: apical part of the post,
D: center of the labial wall, E: canal orifice ofthe labial wall)
Statistical analysis
The fitting accuracy at the different measuring points was analyzed statistically using one-way analysis ofvariance and post hoc Scheffé test (P<0.05).

Results
The mean thicknesses of the white silicone were 81±22, 239±39, 574±68, 223±43 and 67±19 µm forpoints A, B, C, D and E, respectively. C point had significantly higher values when compared with theother measuring points (Fig. 6).
There were no statistically significant differences among the different cement spaces.
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Fig. 6 Thicknesses of the white silicone layers at five measuring points

Discussion
Suto et al. reported that the clinically acceptable limit for the fitting accuracy of CAD/CAM restorations isa discrepancy up to 100 µm.2)
The gaps at B, C and D points had higher values when compared with the clinically acceptable range.
However, there was a possibility that the fitting accuracy achieved was within the clinically acceptable
range because of modifications to the spacer setting on the CAD software.
The mean of the internal gaps at A and E points in this study were within 100 µm. The fitting accuracy ofthe zirconia copings fabricated using the scan posts method was within the clinically acceptable range whenexcluding marginal gaps.
The fitting accuracy of the marginal gaps in the keeper copings manufactured with this CAD/CAM systemshould be examined in future studies.

Conclusion
Within the limitations of this study, it was suggested that the fitting accuracy of zirconia keeper copings
manufactured with this CAD/CAM system using scan posts was within the clinically acceptable range,excluding marginal gaps.

References
1. K. Tsuda, Y. Tanaka, T. Kanazawa, M. Sakane, and K. Kumano: Fabrication of a Keeper Coping by useof the CAD/CAM System, J J Mag Dent, 13(1), 9–17, 2004.
2. N. Suto, S. Miura, R. Inagaki, M. Yoda, and K. Kimura: A Basic Study on Fitness of All-ceramic Crown
fabricated by CAD/CAM system, Ann Jpn Prosthodont Soc, 1, 21–28, 2009.