Effect of Acidic pH on CAD-CAM Materials and Enamel Wear

Objectives: The aim of this in vitro study was to evaluate the effect of different acidic mediums on wear rate and pattern of CAD-CAM monolithic materials and enamel. The null hypothesis was that different pH do not influence the wear of neither CAD-CAM materials (1) neither sound enamel (2).
Methods: Forty rectangular specimens were prepared using different CAD-CAM monolithic materials: nanohybrid composite (Grandio Blocks, Voco), resin-infiltrated ceramic (Cerasmart, GC), lithium disilicate (E-Max, Ivoclar), cubic zirconia (Katana STML, Noritake) . After storage in distilled water at 37°C for 24 hours, the specimens were tested with a chewing machine with a stainless steel ball as well as a sound intact upper premolar as antagonist (80N loads, 1200000 cycles). Testing was performed using water, Coca-cola, Red Bull as abrasive medium. Wear analysis of the CAD-CAM materials and the sound enamel was performed using a 3D profilometer and analysed with two-way analysis of variance and post-hoc pairwise comparison procedures. Worn surfaces were examined with scanning electron microscopy.
Results: Statistical analysis of the sound enamel wear loss after simulated chewing cycles identified a significant influence of either the different acidic environment (p=0.0001) either the opposing CAD-CAM materials (p=0.001). The most severe wear loss was observed with e-Max in Red Bull environment. CAD-CAM monolithic materials showed a wear rate significantly worst with both acidic environment tested (p=0.0001). Wear loss was in the order: nanohybrid composite = resin-infiltrated ceramic > cubic zirconia > lithium disilicate. A correlation between enamel and cubic zirconia wear pattern was observed on SEM images.
Conclusions: The acidic environment significantly increase the enamel wear when opposing to lithium disilicate, while polymers showed the highest wear rate independently of the medium pH. Thus, both the initial null hypothesis were rejected. The wear pattern of cubic zirconia was similar to sound enamel.