Effect of Additive and Subtractive Coping Production Techniques on Retention and Marginal Fit of Implant Supported Crowns
This study investigated the marginal and internal fit and retention of crowns fabricated using 4 different castable pattern production methods, namely plastic burn out coping, computer-aided design and computer-aided manufacturing (CAD-CAM) milled (CAD-CAM-M), CAD-CAM additive (CAD-CAM-A), and conventional. This study consisted of 5 groups including 2 different brands of burn out coping groups (Burn out-Straumann [Burn out-S] group and Burn out-Implance [Burn out-I] group), the CAD-CAM-M group, the CAD-CAM-A group, and the conventional group. A total of 50 metal crown copings were produced in each group with 10 metal crown copings. The marginal gap of the specimens was measured twice—both before and after the cementation and thermocycling processes using a stereomicroscope. A total of 5 specimens were selected randomly—1 from each group for scanning electron microscopy analysis and sectioned longitudinally. The pull-out test was performed on the remaining 45 specimens. The lowest marginal gap value was observed in the Burn out-S group before and after cementation with 88.54–97.48 μm, respectively, while the highest marginal gap was observed in the conventional group (186.27–200.58 μm). Implant systems did not significantly affect the marginal gap values (P > .05). Marginal gap values increased significantly after cementation and thermal cycling in all the groups (P < .0001). The highest retention value was measured in the Burn out-S group while the lowest in the CAD-CAM-A group. The highest occlusal cement gap values were observed in the coping groups (Burn out-S and Burn out-I groups), and the lowest in the conventional group in the scanning electron microscopy analysis. The marginal fit and retention values of the prefabricated plastic burn out coping technique was superior when compared with the other techniques, providing that internal fit was superior with the conventional technique.

(a)–(e) Mold design and fabrication process of the specimens.

(a)–(b) Castable pattern production using plastic burn out copping.

(a)–(e) Computer-aided design (CAD) phases of specimens.

(a)–(b) Production of polymethyl methacrylate (PMMA) castable patterns in computer-aided design and computer-aided manufacturing (CAD-CAM) milling group.

(a)–(c) Production of resin models in computer-aided design and computer-aided manufacturing (CAD-CAM) additive group and final metal coping.

Measurement of marginal gap values using stereomicroscope.

Retention values in Newton (N) for the experimental groups.

(a) Scanning electron microscope (SEM) views of occlusal marginal and axial surfaces of Burn out-S group. The implant was separated during the sectioning process in Burn out-S group. (b) SEM views of occlusal marginal and axial surfaces of Burn out-I group.

(a) Scanning electron microscope (SEM) views of occlusal, marginal, and axial surfaces of computer-aided design and computer-aided manufacturing (CAD-CAM) milling (CAD-CAM-M), and (b) occlusal, marginal, and axial surfaces of CAD-CAM additive (CAD-CAM-A).

Scanning electron microscope (SEM) views of occlusal, marginal, and axial surfaces of conventional group.
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