Evaluation of the marginal integrity of ceramic copings with different marginal angles using two different CAD/CAM systems

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Abstract
To investigate and compare the marginal integrity of ceramic copings constructed with the CEREC3 and the EVEREST system employing three different margin angle designs and explore to what extent these CAD/CAM machines can produce acute marginal angles creating restorations with acceptable margins. Three brass models were prepared with a different marginal finish line, namely a 0° bevel (or 90° shoulder), a 30° bevel and a 60° bevel. Ten restorations were produced for each finishing line and CAD/CAM system, respectively. The copings were milled from lithium disilicate glass ceramic blocks (IPS e.max(®) CAD). An impression was taken for each model to fabricate a series of 10 replica dies for each marginal design. Quantitative analysis of the margins of each coping was performed using digital photography and image analysis software. The marginal integrity of the restorations was evaluated by detecting and measuring any signs of marginal chipping and the Chipping Factor (CF) was calculated. Statistical analysis was performed using Univariate Analysis of Variance and multiple comparisons (Tukey HSD). The average Chipping Factor (CF) of the CEREC copings was: 2.8% for the 0° bevel angle, 3.5% for the 30° bevel angle and 10% for the 60° bevel angle. For the EVEREST copings the average CF was: 0.6% for the 0° bevel angle, 3.2% for the 30° bevel angle and 2.0% for the 60° bevel angle. Univariate Analysis of Variance and multiple comparisons showed that there was a statistically significant difference in the quality of margins between the two systems for the 0° and 60° bevel finishing line. The results of this study indicated that the introduction of a marginal angle of the restoration increases the potential for marginal chipping. Different CAD/CAM systems which employ different milling processes produce restorations with different amount of marginal chipping, although this only became apparent for a marginal angle of a 60°.