Investigation of Mechanical Properties of Polymer-Infiltrated Tetrapodal Zinc Oxide Networks

Objectives: The aim of this study was to evaluate hardness, flexural strength, water absorption, and the behavior under the influence of thermal cycling and hydrolysis of a tetrapodal zinc oxide (tZnO)-based polymer infiltrated ceramic network (PICN) with different weight ratios, in comparison to the clinically established PICN Vita Enamic (VE).
Methods: Particles of tZnO were pressed into disc-shaped specimens (diameter=12mm, thickness=1.2mm), sintered to a network, and infiltrated with polymer (mixture of BisGMA and TegDMA (ratio 60:40)). Three materials were investigated (n=37 per group): a tZnO-based PICN with two different weight ratios (60wt.% and 75wt.% tZnO) and VE. Biaxial flexural strength (BFS) was measured using the piston-on-three-balls test, before and after 150 days of water storage with 37,500 thermal cycles (n=10 per subgroup). Vickers-hardness was measured on n=8 specimens per group. Water absorption was measured in certain intervals up to 30 days (n=6 per group).
Results: All three groups showed a degradation of BFS after artificial aging through thermal cycling and hydrolysis. The results for Vickers-hardness und BFS were lower in both specimen groups with tZnO than for VE (as shown in table 1). 60%tZnO showed the greatest water absorption in comparison to the other groups.
Conclusions: By varying the weight fraction of tetrapodal zinc oxide, the mechanical properties of the investigated PICN can be influenced. Compared to VE, the mechanical properties do not fully meet the requirements of dental restorations. The size and shape of the tZnO-particles might also play an important role for further research.