A basic study on accuracy of a hybrid-resin coping fabricated byCAD/CAM system -Using scanning post and evaluation by µCTS. UEDA, M. SONE, M. HAMASAKA, Y. OKAWA, S. SOMEKAWA, D.MATSUMOTO, K.
TAKAHASHI, 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 hybrid resin copings fabricated by thedental CAD/CAM system and manufacturing using a scanning post.
The desktop scanner (Aadva Scan D850,GC) was used in this study, and images were acquired with ascanning post (Scan Posts™,3shape). Designing software (Dental Designer, GC) was employed for creatinga hybrid resin coping design, and a milling machine (Aadva Mill LW-1, GC) was used to fabricate thecoping from hybrid resin blocks (CERASMART 270,GC) as specimens(n=5). Desktop µCT (SkyScan1172,SkyScan) was used to measure the marginal and internal fitting accuracy of a hybrid resin coping and14 measuring points were evolution in this study.
Within limitations, this study suggested that the fitting accuracy of hybrid resin copings fabricated withthis CAD/CAM system using a scanning post was within the clinically acceptable range of 100 ㎛, with theexception of two points (buccal and lingual margins).

Introduction
The progress of dental CAD/CAM systems has made it possible to fabricate various clinical applications
including inlays, onlays, crowns, bridges, all-ceramic frameworks, and more dentures in clinical dentistry
and has made possible the creation of highly accurate products. Several reports introduced the fabricationof root canal copings or posts and cores using CAD/CAM1–3); however, they had scanned the acrylic resin
pattern and milled and sintered it onto another material for a root canal coping or post and core instead ofinvesting and casting the pattern into the metal. The technique used the same initial procedures for creatinga metal cast coping or post and core.
Our present study4) introduced a method of fabricating CAD/CAM keeper copings using a scanning post
Scan Posts™,3shape) and revealed no significant difference in the cement space for internal fitting;however, the marginal fitting accuracies were not clear.
The purpose of this study was to evaluate the fitting accuracy of hybrid resin copings fabricated by theCAD/CAM system with a scanning post.

Materials and Methods
Prepared epoxy resin mandibular canine teeth (338, Nissin) were selected as the abutment teeth for thecopings, and the root canal was recontoured with a drill (ParaPost X Drill, Coltene-Whaledent) to fit thesame form of scan posts and pressed to a depth of 5.0 mm, creating a rotational resistance groove andadditional reduction to gain more clearance (Fig.1).

Fig.1 Abutment tooth form for coping
The copings were made from a hybrid resin block (CERASMART 270, GC). They were designed using
CAD software (Dental Designer, 3Shape) after digitalization of the die was performed using a desktop
scanner (Aadva Scan D850, GC), and they were fabricated by a milling unit (Aadva MILL LW-1, GC) inthis study (Fig.2). The cement space was set based on our study (Fig.3).

Fig.2 Work flow of scanning and designing coping

Fig.3 Cement space (㎛)The hardware device used in this study was a desktop μCT scanner (SkyScan 1172, SkyScan) for theevolution of the fitting accuracy of hybrid resin copings. Images were acquired using 104 kV voltage, 100㎂ current, and a 0.5 mm thick aluminum filter. After being scanned, the images were reconstructed in thesoftware (NRecon, SkyScan), and the space between the hybrid resin coping and the abutment wasmeasured using the instrument (CTAn, SkyScan). Measurement points are shown in Fig.4.

Fig.4 Measurement points in this study. MB: margin of buccal; ML: margin of lingual; MM:margin of mesial; MD: margin of distal

Results
The mean space between the hybrid resin coping and the abutment of each point is shown in Figs.5 and 6.

Fig.5,6 The mean space between hybrid resin coping and abutment
All points except MB and ML had spaces of less than 100 ㎛ between the hybrid resin coping and theabutment.

Discussion
The fitting accuracy of Point MB and Point ML were inferior to the clinically acceptable range of 100µm.5) This fact could be attributed to the setting of the sprue position in the software. Point MB waslocated on the sprue side (Fig.7). This region may be unfavorable for cutting the details of the margin due
to the fact that the milling pathway was inhibited by the sprue. Point ML was located on the opposite sideof the sprue because Point ML was located at the opposite end of a hybrid resin block, and this area wassusceptible to damage during the milling process. The hybrid resin block would be bent in the opposite
direction of the milling load side and would be increased. This fact seems to depend on the characteristicsof the CAD/CAM milling blocks.

Fig.7 Location of point MB and ML after milling

Conclusion
Within the limitations of this study, it was suggested that the fitting accuracy of hybrid resin copings
fabricated with this CAD/CAM system using scan posts was within the clinically acceptable range,
excluding MB and ML.

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