A microcomputed tomography evaluation of the marginal fit of cobalt-chromium alloy copings fabricated by new manufacturing techniques and alloy systems.
BACKGROUND
Although new digital manufacturing techniques are attracting interest in dentistry, few studies have comprehensively investigated the marginal fit of fixed dental prostheses fabricated with such techniques.


OBJECTIVE
The purpose of this in vitro microcomputed tomography (μCT) study was to evaluate the marginal fit of cobalt-chromium (Co-Cr) alloy copings fabricated by casting and 3 different computer-aided design and computer-aided manufacturing (CAD-CAM)-based processing techniques and alloy systems.


METHODS
Single Co-Cr metal crowns were fabricated using 4 different manufacturing techniques: casting (control), milling, selective laser melting, and milling/sintering. Two different commercial alloy systems were used for each fabrication technique (a total of 8 groups; n=10 for each group). The marginal discrepancy and absolute marginal discrepancy of the crowns were determined with μCT. For each specimen, the values were determined from 4 different regions (sagittal buccal, sagittal lingual, coronal mesial, and coronal distal) by using imaging software and recorded as the average of the 4 readings. For each parameter, the results were statistically compared with 2-way analysis of variance and appropriate post hoc analysis (using Tukey or Student t test) (α=.05).


RESULTS
The milling and selective laser melting groups showed significantly larger marginal discrepancies than the control groups (70.4 ±12.0 and 65.3 ±10.1 μm, respectively; P<.001), whereas the milling/sintering groups exhibited significantly smaller values than the controls (P=.004). The milling groups showed significantly larger absolute marginal discrepancy than the control groups (137.4 ±29.0 and 139.2 ±18.9 μm, respectively; P<.05). In the selective laser melting and milling/sintering groups, the absolute marginal discrepancy values were material-specific (P<.05). Nonetheless, the milling/sintering groups yielded statistically comparable (P=.935) or smaller (P<.001) absolute marginal discrepancies to the control groups.


CONCLUSIONS
The findings of this in vitro μCT study showed that the marginal fit values of the Co-Cr alloy greatly depended on the fabrication methods and, occasionally, the alloy systems. Fixed dental prostheses produced by using the milling/sintering technique can be considered clinically acceptable in terms of marginal fit.
Graduate student, Department of Medical and Biological Engineering, Graduate School, Kyungpook National University, Daegu, Republic of Korea.
Eun-Ha
EH
Kim
Assistant Professor, Department of Prosthodontics, School of Dentistry, Kyungpook National University, Daegu, Republic of Korea.
Du-Hyeong
DH
Lee
Graduate student, Department of Dental Science, Graduate School, Kyungpook National University, Daegu, Republic of Korea.
Sung-Min
SM
Kwon
Associate Professor, Department of Dental Biomaterials, School of Dentistry, Kyungpook National University, Daegu, Republic of Korea. Electronic address: tykwon@knu.ac.kr.
Tae-Yub
TY
Kwon
D000704:Analysis of Variance; D002858:Chromium Alloys / Q000737:chemistry*; D017076:Computer-Aided Design; D003442:Crowns; D018772:Dental Marginal Adaptation; D003764:Dental Materials; D017267:Dental Prosthesis Design; D005615:Freezing; D006801:Humans; D007834:Lasers; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry; D013499:Surface Properties; D019231:Tooth Preparation, Prosthodontic; D055114:X-Ray Microtomography / Q000379:methods*; D015040:Zirconium / Q000737:chemistry
D002858:Chromium Alloys; D003764:Dental Materials; D016876:Metal Ceramic Alloys; D015040:Zirconium; C028541:zirconium oxide