Debonding of Resin Ceramic Crowns on CAD/CAM-milled Human Third Molars

Objectives: Previous studies analyzed debonding by using manually prepared teeth. In order to increase the reproducibility of the results, it was the aim of this in vitro study, to create highly standardized dentin dies by CAD/CAM-milling to investigate debonding.
Methods: To manufacture standardized human dentin dies, a virtual die was constructed and a STL-file generated which was used to mill eighteen human third molars into identical dies in a CNC-milling-machine. Following the full crowns were also computer aided designed and manufactured (6 IPS-e.max-CAD (EX), Ivoclar Vivadent; 2x6 Lava-Ultimate-Restorative (LU), 3MEspe). Adhesive cementation was separated into chemical curing and light curing. EX was luted using Multilink (Ivoclar Vivadent) and represented the reference material for chemical curing. LU was luted with Scotchbond-Universal and RelyX-Ultimate (3M Espe). Half of the specimens were chemical cured and the others were additionally light cured. A dye penetration test was performed to detect microleakage (debonding). For inspection, digital microscope (Zeiss) was used. Specimens were aged by cyclic loading (prematec F1000) for 1,000,000 cycles (5-500N, 2Hz, 37°C). Furthermore the abrasion of stainless-steel antagonists was investigated by weighing (Mettler Toledo) before and after cyclic loading.
Results: The chemical cured LU-crowns showed the highest leakage (Mean, Interquartil Range: 8.76%, 5.11-12.94%) followed by the chemical cured EX-crowns (2.3%, 0.54-4.41%). The light cured LU-crowns showed the lowest leakage (0.02%, 0.00-0.05%) with a very good reproducibility. None of the LU antagonists showed abrasion. However the EX antagonists showed a material loss with a mean of 258µg (95% Cl: 140–473µg).
Conclusions: Overall the results (especially for LU-light-cured) demonstrate the high potential of standardized dies to increase reproducibility. Within the limitation of this in vitro study, light curing is necessary for the luting of CAD/CAM crowns to prevent debonding and microleakage. Furthermore the resin-ceramic-material shows antagonist-friendly properties.