Yamaguchi et al.

Asian Pac J Dent 2012; 12: 11-16.

The manufacturing characterization of zirconia core copings ofCAD/CAM systems
Hiroaki Yamaguchi, DDS, Naho Hamano, DDS, PhD, Yuki Katsumata, DDS, PhD, andSatoshi Ino, DDS, PhD
Division of Removable Prosthetics, Department of Oral and Maxillofacial Rehabilitation, Kanagawa
Dental College, Japan
Purpose: The purpose of the present study was to investigate the manufacturing characterization of zirconia
copings for abutments. Comparative evaluation was made using five different CAD/CAM systems.
Materials and Methods: The abutment model was fabricated. Five zirconia copings were produced using
Procera, Katana, Cercon, and Lava 0.5 and 0.6 by CAD/CAM system dealers. Silicone impression material wasplaced between the abutment model and a coping to observe the manufacturing characteristics and pressed. The
abutment model with impression material was embedded in epoxy resin. The embedded model was cut
buccolingually using an automatic precision cutter, and the thickness of silicone impression material wasobserved using an optical microscope with a scale.
Results: A significant difference was observed in the gap average between Procera and Lava 0.5 (p<0.01), andProcera and Lava 0.6 (p<0.05) in the buccal margin. For the buccal corner and occlusal chamfer, the gap was
significantly larger in Procera compared with the other copings (p<0.01). In the palatal margin, the gap was
significantly smaller in Lava 0.6 compared with Procera, Katana, and Cercon (p<0.01).
Conclusion: Marginal lines were smooth and coincided with abutments for all CAD/CAM systems. Although
the gap size varied among the manufacturers, the thickness of impression material was smaller, and theprocessing quality was even in Lava compared with the other copings. These characteristics are considered to berelated to the shape and size of drilling tools of each CAD/CAM system. (Asian Pac J Dent 2012; 12: 11-16.)
Key Words: CAD/CAM system, gap, manufacturing characteristics, zirconia copings

Introduction
Zirconia ceramics have been widely applied for crown restoration due to their esthetic appearance, as well as
favorable biocompatibility, elastic coefficient, and breaking strength.1-7 All ceramic restorations vary frommolar crowns to bridges. Zirconia ceramics are difficult to handle. Since the mechanical stability and size
precision are often affected during the manufacturing processes, such as sintering and molding, it is difficult toproduce stable-quality products.

In recent years, computer-aided design and manufacturing (CAD/CAM)

systems have been introduced in daily practice from designing to processing, to produce stable-quality products.
Processing accuracy is considered important to achieve a satisfactory long-term prognosis with prosthetics.
Although many reports are available regarding the fit of crowns, the fabrication of zirconia copings requires
treatment according to abutment preparation suggested by manufacturers. This fact limits the application inclinical practice. The present study investigated the manufacturing characteristics of zirconia copings that are
not based on abutment preparation suggested by manufacturers, but based on the abutment model with minimum
preparation. Five CAD/CAM systems were compared, and interesting findings were observed.

Materials and Methods
Fabrication of a zirconia coping
Abutment preparation of the all ceramic crown was performed on the tooth model (Nissin Dental Products Inc.
Kyoto, Japan) maxillary right first molar on an assumption that the tooth was vital. The cervical margin of anabutment was chamfer. The axial plane taper was 6°, and the basal plane was 9.0 mm in diameter and 5.5 mm inheight. An impression of the prepared abutment was taken using silicone impression material (Duplicone, Shofu,11Yamaguchi et al.

Asian Pac J Dent 2012; 12: 11-16.

Kyoto, Japan), followed by the fabrication of a working model with improved hard plaster (Fuji Lock, GC,Tokyo, Japan). Fabrications of zirconia copings were assigned to each CAD/CAM system dealer. The types ofcoping fabricated were Procera (Nobel Biocare, Zurich, Switzerland), Katana (Noritake, Nagoya, Japan), Cercon(Dentsply-Sankin, Tokyo, Japan), and Lava (3M Espe, Seefeld, Germany). There were two types of Lava,
including a 0.5-mm framework (Lava 0.5) and 0.6-mm framework (Lava 0.6). Therefore, the total number ofzirconia coping types was five. Thickness of coping was 0.5 mm and 0.6 mm for Lava, 0.6 mm for Procera, 0.5mm for Cercon, and 0.5 mm for Katana.
Fabrication of abutment model made of resin
Impression-taking of an abutment model was performed again using silicone impression material, and 30
abutment models was fabricated using resin. The surface of the resin abutment model was formed using
flowable resin (Filtek Supreme XT Flow, 3M Espe), and cured with a light-curing unit (Optilux 400, Sybron
Dental Specialties, Washington DC, USA) for 20 s. The multilayer-packing method with 2-mm-layer compositeresin (Filtek Supreme DL Universal Restorative, 3M Espe) was performed inside, and every layer was cured
using a light-curing unit for 20 s. Each abutment model was further cured with light for 5 minutes using dental
polymerization equipment to complete polymerization.
Fit test
Figure 1 shows experimental design.

Silicone impression material (Tosicon Pastel Injection, Dentsply-Sankin) was placed between the resin abutment model and coping and pressed with the fingers for 5 minutes.
After the impression material was set, copings were removed, and the resin abutment model was embedded withimpression materials using epoxy resin (Epofix, Struers, Pederstrupvej, Denmark) (n=6). The embedded model
was left at room temperature for 2 days, and cut buccolingually using an automatic precision cutter (Isomet,Buehler, Lake Bluff, IL, USA). Five parts inside the cutting surface (1, Buccal margin; 2, Buccal corner; 3,Occlusal chamfer; 4, Palatal corner; and 5, Palatal margin) were measured using an optical microscope with ascale (reading microscope, Nippon Optical Works Co., Ltd., Tokyo, Japan) to examine the thickness of silicone
impression material. Figure 2 shows the measured parts. The average and standard deviation of the obtainedvalues were calculated, followed by one-way analysis of variance and Tukey’s multiple comparison.

Fig. 1.

Experimental design

Fig. 2.

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Measured points in the silicone-abutment modelYamaguchi et al.

Asian Pac J Dent 2012; 12: 11-16.

Observation of inner surface of copings
Silicone impression material (Tosicon Pastel Injection) was applied inside each coping (Cercon, Katana,Procera, Lava 0.5 and 0.6). The coping was placed on the improved hard plaster abutment model that was used
to fabricate each coping, and pressed with the fingers for 5 minutes. After the impression material was set, only
the coping was removed. Next, oxidized titanium power (Cerec Powder, Vita, Bad Säckingen, Germany) wassprayed on the abutment model with impression materials as a pretreatment for optical impression taking tocreate a stable reflection ratio. The inner surface morphology was observed by CAD/CAM (Cerec, Sirona,Bensheim, Germany) optical impression taking.

Results
Fitness
Figure 3 shows the results of fitness tests using a reading microscope. The gap of Procera was 247 µm in thebuccal margin, 278 µm on the buccal corner, 270 µm in the occlusal chamfer, 177 µm on the palatal corner, and238 µm in the palatal margin on average. The gap of Katana was 178 µm in the buccal margin, 138 µm on thebuccal corner, 147 µm in the occlusal chamfer, 163 µm on the palatal corner, and 240 µm in the palatal margin
on average. The gap of Cercon was 162 µm in the buccal margin, 153 µm on the buccal corner, 80 µm in theocclusal chamfer, 96 µm on the palatal corner, and 252 µm in the palatal margin on average. The gap of Lava
0.5 was 133 µm in the buccal margin, 110 µm on the buccal corner, 88 µm in the occlusal chamfer, 100 µm on
the palatal corner, and 168 µm in the palatal margin on average. The gap of Lava 0.6 was 140 µm in the buccal
margin, 123 µm on the buccal corner, 73 µm in the occlusal chamfer, 100 µm on the palatal corner, and 103 µmin the palatal margin on average. One-way analysis of variance was performed to analyze the gap in each part of
the five different copings. Since the results showed a significant difference, a multiple comparison test wasperformed using the Tukey method. The results are shown in Table 1. A significant difference in the gap
average was observed only between Procera and Lava 0.6 (p<0.05). The gap on the buccal corner and in theocclusal chamfer was significantly larger in Procera compared with the other copings (p<0.01). The gap in thepalatal margin was significantly smaller in Lava 0.6 compared with Procera, Katana, and Cercon (p<0.01).

Fig. 3.

Means of gap dimensions at five different measurement parts.

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Yamaguchi et al.
Table 1.

Asian Pac J Dent 2012; 12: 11-16.

Significant difference of the gap

Buccal margin

Buccal corner

Occlusal chamfer

Palatal margin**(p<0.01), *(p<0.05)

Observation of coping internal surface
Figure 4 shows the results of optical impression taking. A distinctive cutting mark was observed on thebuccal and palatal corners of Katana. Although other copings showed a difference in the gap, no significant
change was found in the optical impression, and the inner surface showed a consistent quality.

Fig. 4.

Optical impressions of coping internal surface were provided by CAD/CAM system.

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Asian Pac J Dent 2012; 12: 11-16.

Discussion
A number of studies have been performed regarding the fit of crown restorations since the marginal and innergap is key to successful treatment results. The marginal fit markedly influences the prognosis following crownbridge treatment since the poor fit may result in periodontitis, secondary caries, and the dissolution of cement.8However, there are no clear criteria to determine the allowance range in clinical application. McLean et al.
reported that a marginal gap of less than 120 µm achieves a favorable clinical result.9,10 Nakamura et al. reported
that a marginal gap of less than 100 µm does not affect the treatment results if there is little marginal leak andresistant resin cement is used for crown placement.11 Beuer et al. reported that cervical marginal fitting was lessthan 50 µm in the abutment model with a 12° taper during the cementation of a zirconia crown to the model.12
These reports revealed that the clinical allowance range differs depending on researchers. The results of thepresent study showed that the biggest gap in Procera compared with the other copings except for the palatalmargin. The thickness of silicone impression material was relatively constant, and the obtained values werelarger than previously reported results for all copings.
In the present study, abutment preparation was performed not according to the manufacturers’ instruction, butaccording to the clinical procedure to minimize the preparation on the assumption that the abutment tooth wasvital. The fit of crowns was examined using rubber-type silicone impression material in the present study since
the clinically used fit-checker is not resilient enough. Although relatively high-flowable impression materialwas selected, the viscosity of silicone impression material was high compared with the high-flowable fit-checker
and cement. Therefore, it is considered that silicone impression material with high viscosity tends to clog evenin the cement space created in the coping inner surface, resulting in an increase in the gap. Although the average
gap was large in Procera, Boening et al. reported that the marginal gap in the molar area of Procera was 90-145µm on average, and 115-245 µm at maximum.13 Manufacturer of Procera reported that the fit of Procera isintentionally loose so that the amount of final seating is minimal regardless of the skill of dentists andtechnicians. This is considered to be the reason for the relatively large gap compared with other manufacturers.
In contrast, the gap was smaller in Lava 0.5 and 0.6 compared with the other products, and there was no
significant difference in the marginal gap. The gap was significantly smaller in the palatal margin of Lava 0.6
compared with the other copings.

There are three types of milling bur in Lava processing machinery.

Specifically, the apical diameter of an inner surface processing bur was the smallest compared with the othermanufacturers’ burs. This is considered to be very beneficial in milling the inner surface of a zirconia coping.
Although cutting burs are accessible from any direction in the outer processing of a coping by CAD/CAM, buraccess is restricted depending on the abutment taper in the inner processing. Therefore, a smaller apical
diameter of a bur is beneficial to fabricate high-precision copings.
Scanning of the inner surface of a coping by optical impression taking revealed that the gap in the Lava series
is relatively small and consistent. Considering a distinctive cutting mark in Katana, the drive system of thecutting machine and type and fatigue condition of cutting tools are considered to influence the processing
precision during cutting work. Due to these CAD / CAM characteristics, it is necessary to increase the cutting
amount of an abutment and the taper of the axial surface of the abutment to simplify optical scanning of anabutment and the coping cutting procedure. These principles are contrary to “minimal intervention treatment”,
the basic policy of modern dental treatment proposed by the World Dental Federation in 2000. Althoughzirconia all ceramic treatment has been widely used as a metal-free treatment, and CAD/CAM performance has15

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Asian Pac J Dent 2012; 12: 11-16.

markedly improved, further improvement of CAD/CAM is necessary to achieve low-invasive tooth treatment.

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Correspondence to:Dr. Satoshi Ino
Division of Removable Prosthetics, Department of Oral and Maxillofacial Rehabilitation,
Kanagawa Dental College
82 Inaoka-cho, Yokosuka, Kanagawa 238-8580, Japan
Fax: +81-46-822-8861 E-mail: inosatos@kdcnet.ac.jp
Accepted March 14, 2012.
Copyright ©2012 by the Asian Pacific Journal of Dentistry.
Online ISSN 2185-3487, Print ISSN 2185-3479

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