05 June 2019

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Which preparation do you have to choose for the best marginal adaptation for lithium disilicate CAD/CAM crowns?

Simona Chirico

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The increased aesthetic demand, without sacrificing the preservation of biological structures, has led to the development and use, in recent years, new generations of ceramics. These include lithium disilicate (LGD).
LDG restorations can be manufactured making use of either lost-wax hot-pressing techniques or computer-aided-design/computer-aided manufacturing (CAD/CAM) milling procedures. Among the several CAD/CAM ceramic materials, IPS e.max CAD exhibited superior mechanical properties and better internal fit than that of the other ceramic blocks used for all ceramic restorations.
Different factors play a significant role in determining the success of a restoration: luting technique, adhesive system, thickness of the ceramic restoration, the preparation design.
The study published in the Journal of Esthetic Restorative Dentistry by Angerame et al., evaluate the fracture resistance and marginal quality of maxillary molars restored using LDG occlusal veneers with two preparations designs: 90° rounded shoulder and chamfer.

MATERIALS AND METHODS
Sixteen extracted maxillary molars were assigned to two groups (n = 8). In group 1 (G1), the teeth received a preparation for a conservative full-coverage occlusal veneer restora- tion with a 90 rounded shoulder margin. In group 2 (G2), the teeth underwent a 1-mm cusp reduction with a marginal chamfer. LDG restorations (IPS e.max CAD) were obtained with the Cerec 3 CAD/CAM system and luted with Variolink II cement. After thermomechanical aging (1 250 000 cycles), the specimens were loaded to fracture. A semiquantitative marginal seal evaluation was performed observing resin replicas of the specimens at the scanning electron microscope. Cement thickness was assessed at the stereomicroscope on sectioned specimens. Collected data were statistically analyzed by parametric and nonparametric tests.

RESULTS
The maximum load to fracture was 2395.01 ± 150.96 N in G1 and 2408.39 ± 112.66 N in G2. The fracture pattern was also similar in the two groups, with cracks above the CEJ and it was the most predominant type of restoration failure.
Cement thickness was 132 ± 38 μm in G1 and 150 ± 41 μm in G2.  
As to margin quality assessment, G1 exhibited continuous margins with 96,9% both at the baseline than after aging; instead for G2 at the baseline was 100% and after aging was 93,8%.

CONCLUSIONS
This study demonstrated similar satisfactory performance of the two considered preparations designs for occlusal veneer with LDG. Further in vivo studies are needed to validate the clinical performance of the more conservative preparation design.

(Photo Credit: Dr. Cristian Coraini)

For additional informations:
Influence of preparation designs on marginal adaptation and failure load of full-coverage occlusal veneers after thermomechanical aging simulation