Increasing demand for esthetic dental restorations has led to the popularity of ceramic restoration systems. Among these the most used is lithium disilicate, which can be produced either in the laboratory with a hot-press technique, or with CAD/CAM system.
The quality of lithium disilicate crowns produced by the CAD/CAM system has always been discussed. From what emerges in literature, there are no differences between the two methods from the structural point of view and the mechanical characteristics. But for clinical success and longevity?
In the study published in The Journal of Prosthetic Dentistry in 2019, Dolev et al. took this aspect into consideration, evaluating the marginal fit by calculating the marginal discrepancy (MD) (the perpendicular measurement from the cervical margin of the casting to the preparation margin) and the absolute marginal discrepancy (AMD) (angular combination of the MD and the extension error - overextension or underextension-) of lithium disilicate crowns produced by the hot-press and CAD-CAM techniques. Acceptable MD values are included between 50 e 120 mm.
MATERIALS AND METHODS
Thirty typodont teeth were divided into 2 groups. Fifteen teeth were scanned with the CEREC Omnicam intraoral scanner, and crowns were fabricated with the CEREC MC XL chairside CAD-CAM milling unit from IPS e.max CAD blocks. Fifteen typodont teeth were sent to a dental laboratory, and lithium disilicate crowns were fabricated from IPS e.max press ingots using the hot-press technique. The 30 crowns were cemented with a self-adhesive cement (RelyX Unicem) and then sectioned with a precision saw. The MD and AMD were measured for each crown with a light microscope.
Mean MD and AMD values were evaluated by analyzing 8 specific points of the crowns: disto-buccal (DB), disto-lingual (DL), mesio-buccal (MB), mesio-lingual (ML), mid-buccal location ( Mid-B), mid-lingual location (Mid-L), mid-mesial localtion (Mid-M), mid-distal location (Mid-L).
As expected, the MD values were lower than the AMD values because the AMD is an angular combination of the MD and the extension error. The mean AMD values were lower for the crowns fabricated using the CAD-CAM technique, except at the Mid-L/ML and Mid-D/DL locations.
The CAD-CAM technique produced an overall mean ±standard error (SE) AMD width of 115 ±4 mm, whereas the hot-press technique produced an overall mean ±SE AMD width of 130 ±5 mm.
The overall mean ±SE MD values were similar: 87 ±3 mm for the crowns fabricated by CAD-CAM and 90 ±4 mm for the crowns fabricated by the hot-press technique.
Even if the study concludes that there isn’t a statistically significant differences in MD and AMD between the CAD-CAM and hot-press fabrication methods, we can see how the best results are recorded by the lithium disilicate produced with CAD/CAM method.
For additional informations:
Comparison of marginal fit between CAD-CAM and hot-press lithium disilicate crowns
Digital Dentistry 08 May 2019
Author: Rafi Romano
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