comparison of wear resistance of hawley and vacuum formed retainers: an in-vitro study

statement of problem: as a physical property, wear resistance of the materials used in the fabrication of orthodontic retainers play a significant role in the stability and long term use of the appliances. objectives: to evaluate the wear resistance of two commonly used materials for orthodontic retainers: acropars op, i.e. a polymethyl methacrylate based material, and 3a-gs060, i.e. a polyethylene based material. materials and methods: for each material, 30 orthodontic retainers were made according to the manufacturers’ instructions and a 30×30×2 mm block was cut out from the mid- palatal area of each retainer. each specimen underwent 1000 cycles of wear stimulation in a pin on disc machine. the depth of wear of each specimen was measured using a nano wizard ii atomic force microscope in 3 random points of each specimen’s wear trough. the average of these three measurements was calculated and considered as mean value wear depth of each specimen (µm). results: the mean wear depth was 6.10µm and 2.15µm for 3a-gs060 and acropars op groups respectively. independent t-test showed a significant difference between the two groups ( p < 0.001). the results show polymethyl methacrylate base (acropars) is more wear resistance than the polyethylene based material (3a-gs060). conclusions: as the higher wear resistance of the fabrication material can improve the retainers’ survival time and its cost-effectiveness, vfrs should be avoided in situations that the appliance needs high wear resistance such as bite blocks opposing occlusal forces.