Abstract
Computer-aided design/computer-aided manufacturing (CAD/CAM) systems are widely used for the fabrication of porcelain-fused-to-metal (PFM) crowns. This study was conducted to compare PFM crowns through triple scanning in terms of marginal discrepancy between the CAD/CAM and lost-wax fabrication techniques. Twenty uniform resin dies of a prepared maxillary first molar were randomly divided into 2 groups: conventional lost-wax; and milling. Marginal discrepancy was evaluated at the framework and porcelain steps through triple scanning and direct visualization under a stereomicroscope. Then, the crowns were cemented to the related die and the marginal gap was measured with triple scanning, direct visualization under a stereomicroscope and scanning electron microscopy (SEM). The data was analyzed using the independent t test and the one-way analysis of variance (ANOVA). The significance level was set at 0.05. Differences in the mean marginal gap were measured by the various evaluation methods. Triple scanning and stereomicroscopy identified increasing discrepancy during the fabrication process. According to the results of the independent t test, stereomicroscopy showed no difference after cementation between the CAD/CAM and lost-wax groups (p > 0.05), triple scanning showed higher fitness in the CAD/CAM group (p < 0.05), and SEM showed better adaptation in the lost-wax group (p < 0.05); however, there was a positive correlation between the findings of stereomicroscopy and SEM (p < 0.05). The cobalt-chromium crowns had clinically acceptable marginal fitness from both the CAD/CAM and lost-wax techniques; however, the lost-wax group showed lower marginal discrepancy after cementation according to SEM.
Highlights
The clinical durability of porcelain-fused-to-metal (PFM) restorations stems from their exact adaptation to the abutment teeth.[1]
According to the results of the independent t test, stereomicroscopy showed no difference after cementation between the computer-aided design/ computer-aided manufacturing (CAD/CAM) and lost-wax groups (p > 0.05), triple scanning showed higher fitness in the CAD/CAM group (p < 0.05), and scanning electron microscopy (SEM) showed better adaptation in the lost-wax group (p < 0.05); there was a positive correlation between the findings of stereomicroscopy and SEM (p < 0.05)
Conclusions.The cobalt-chromium crowns had clinically acceptable marginal fitness from both the CAD/CAM and lost-wax techniques; the lost-wax group showed lower marginal discrepancy after cementation according to SEM
Summary
The clinical durability of porcelain-fused-to-metal (PFM) restorations stems from their exact adaptation to the abutment teeth.[1]. In the case of a misfit, some complications would occur, such as dental caries,[1] periodontal disease,[2–5] dental pulpitis,[3] reduced long-term success of the PFM crown,[3] and cement loss.[4]. Nickel-chromium and cobalt-chromium are popular alloys in PFM restorations. Due to nickel allergy and the toxicity of beryllium, cobalt-chromium alloys are consi dered the better alternative.[4]. They have some characteristics, such as a relatively low cost,[5,6] stability in biological environments, corrosion resistance,[4–6] and the ease of use in computerized milling methods.[5]. Cobalt-chromium alloys are used in the lost-wax and computer-aided design/ computer-aided manufacturing (CAD/CAM) methods.[4–6]. Computer-aided design/computer-aided manufacturing (CAD/CAM) systems are widely used for the fabrication of porcelain-fused-to-metal (PFM) crowns
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