title: An in vitro investigation of wear resistance and hardness of composite resins.
abstract: OBJECTIVE
  The aim of the present study was to investigate the wear resistance and hardness of five kinds of composite resins.
  
  
  METHODS
  Sixty-five specimens were fabricated with one nano-hybrid (Charisma Diamond), two micro-hybrid (3MZ250, Clearfil AP-X) and two packable (3MP60, Surefil) composite resins, according to a randomized complete block design (n=13, 8 for wear test; 5 for hardness test). The composites were filled in a rectangular mold, and light polymerization. After storage in 37°C deionized water for 24h, all specimens were tested with a custom-made toothbrush machine with a stainless-steel ball as antagonist (3N loads, 1Hz, 6×10(5) cycles) immersed in calcium fluoride slurry. Wear volume, hardness and surface structure of each tested material was examined by a three-dimensional non-contact optical profilometer, Vickers indentation technique and scanning electron microscope.
  
  
  RESULTS
  The volume loss ranked from least to most as follows: Charisma Diamond, P60, Z250, Clearfil AP-X and Surefil. Regarding hardness, the rank from highest to lowest as follows: Clearfil AP-X, P60, Surefil, Z250, Charisma Diamond. The interactions between wear resistance and microhardness were not significant.
  
  
  CONCLUSIONS
  The custom-made machine is considered suitable to simulate sliding of an antagonist cusp on an opposing occlusal composite restoration. Nanofilled composite may have superior wear compared to other composite resins.
authors.affiliation: School of Stomatology, Tongji University Shanghai 200072, China.
authors.forename: Liqun
authors.initials: L
authors.lastname: Cao
authors.forename: Xinyi
authors.initials: X
authors.lastname: Zhao
authors.forename: Xu
authors.initials: X
authors.lastname: Gong
authors.forename: Shouliang
authors.initials: S
authors.lastname: Zhao
keywords: Composite resins; hardness; wear resistance