title: Effect of organic acids in dental biofilm on microhardness of a silorane-based composite.
abstract: OBJECTIVE
  This study evaluated the effect of lactic acid and acetic acid on the microhardness of a silorane-based composite compared to two methacrylate-based composite resins.
  
  
  METHODS
  Thirty disc-shaped specimens each were fabricated of Filtek P90, Filtek Z250 and Filtek Z350XT. After measuring of Vickers microhardness, they were randomly divided into 3 subgroups (n = 10) and immersed in lactic acid, acetic acid or distilled water. Microhardness was measured after 48 hr and 7 day of immersion. Data were analyzed using repeated measures ANOVA (p < 0.05). The surfaces of two additional specimens were evaluated using a scanning electron microscope (SEM) before and after immersion.
  
  
  RESULTS
  All groups showed a reduction in microhardness after 7 day of immersion (p < 0.001). At baseline and 7 day, the microhardness of Z250 was the greatest, followed by Z350 and P90 (p < 0.001). At 48 hr, the microhardness values of Z250 and Z350 were greater than P90 (p < 0.001 for both), but those of Z250 and Z350 were not significantly different (p = 0.095). Also, the effect of storage media on microhardness was not significant at baseline, but significant at 48 hr and after 7 day (p = 0.001 and p < 0.001, respectively). Lactic acid had the greatest effect.
  
  
  CONCLUSIONS
  The microhardness of composites decreased after 7 day of immersion. The microhardness of P90 was lower than that of other composites. Lactic acid caused a greater reduction in microhardness compared to other solutions.
authors: Department of Operative Dentistry, Dental School, Tehran University of Medical Sciences, International Campus, Tehran, Iran.
authors: Sedighe Sadat
authors: SS
authors: Hashemikamangar
authors: Department of Pediatric Dentistry, Dental School, Tehran University of Medical Sciences, International Campus, Tehran, Iran.
authors: Seyed Jalal
authors: SJ
authors: Pourhashemi
authors: Tehran University of Medical Sciences, International Campus, Dental School, Tehran, Iran.
authors: Mohammad
authors: M
authors: Talebi
authors: Department of Operative Dentistry, Dental School, Tehran University of Medical Sciences, International Campus, Tehran, Iran.
authors: Nazanin
authors: N
authors: Kiomarsi
authors: Department of Epidemiology and Biostatistics, Faculty of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors: Mohammad Javad
authors: MJ
authors: Kharazifard
keywords: Dental biofilm; Methacrylate-based composite resin; Microhardness; Organic acids; Silorane-based composite resin