Impact Fracture Behavior of  a New Resin Nanoceramic for CAD/CAM

Objectives: 

Determine impact fracture resistance, flexural strength (FS) and modulus (FM), and fracture toughness (K_Ic) of a new Resin Nanoceramic material, compared with feldspathic porcelain and “hybrid ceramic” materials.

Methods: 

1.5mm thick tiles were subjected to a single impact load via a 6.33mm diameter stainless steel sphere on a rod attached to a crosshead that slides down two guides, dropped from 3.2cm height; survival or failure was recorded, along with failure mode.  Weight of rod and crosshead was 160g, yielding impact energy of 50mJ.  The tile was supported by a small ring 8.5mm outer diameter, which served to concentrate the impact load.

Three-point FS, FM, and single-edge V-notched beam (SEVNB) K_Ic  were measured per ISO-6872, modified to accommodate bar sizes obtainable from commercially available blocks. FS & FM: polished 1x4x14 mm bars, 3-point fixture, 10mm span, crosshead speed 1.0mm/min.  K_Ic:  3x4x14mm bars with V-notch, same 3-point fixture, 0.5mm/min.  Modulus of resilience (MR) was calculated from MR=FS²/2FM.

Impact survival data were analyzed via pairwise Chi-Square tests (p<0.05), and other data via ANOVA with Tukey's t-test (p<0.05). 

Results: 

Table shows results, and groups that are statistically not different (SND).

Conclusions:  

At the impact energy tested, LVU displayed statistically significantly superior impact fracture resistance than VM2 and VEN, while VM2 and VEN were statistically not different.  FS and K_Ic of LVU are statistically significantly higher than VEN and VM2.  The combination of high strength and lower modulus give LVU a statistically significantly higher MR than VEN and VM2.  LVU can absorb significantly more stress than other materials without suffering permanent deformation or failure. The high strength and toughness of LVU helps support its use in demanding single-unit restorations, including posterior crowns and implant crowns.  High fracture resistance may provide additional protection against sudden impact loads, such as from accidents or other trauma.