Fracture Resistance of Restorative Materials subjected to Cumulative Impact Load

Objective: The aim of this study was to compare the fracture resistance of indirect restorative materials under repeated impact loads with increasing magnitude.

Method: Disc specimens of 12mm diameter and 4mm thick were prepared using Lava™ Ultimate CAD/CAM Restorative (LVU:  3M™ ESPE™), IPS Empress™ CAD Block (EMP:  Ivoclar™ Vivadent™), and IPS e.max™ CAD (EMX:  Ivoclar™ Vivadent™). The sample size per group was n = 10. A 12g, 28.5mm-diameter steel ball was repeatedly dropped onto each disc from increasing heights (0.05m, 0.08m, 0.13m, 0.25m, 0.48m to 0.61m) until the disc fractured. The cumulative energy required to fracture the disc was calculated as the sum of the impact energy values from each ball drop until fracture, inclusive. The discs were visually inspected for damage using transillumination.

Result: LVU had the highest impact fracture resistance; followed by EMX and then EMP.  The mean cumulative energy required to fracture the disc specimens of the 3 groups were 1004.53, 653.9, and 106.6 mJ, with a standard deviation of 381.6, 232.5, 75.9 mJ respectively.  Differences between the 3 groups were statistically significant (Mann-Whitney U test, p<0.05). Furthermore, EMP and LVU showed fewer cases of complete fracture, as seen in most of the EMX specimens.

Conclusion: The cumulative impact load test could provide quantitative comparison between the fracture resistances of dental restorative materials under repeated impact loading.