Ali Eskandarizadeh - Associate Professor, Oral and Dental Disease Research Center, Kerman University of Medical Sciences, Kerman, Iran.
Nafiseh Elm-Amooz - Assistant Professor, Oral and Dental Disease Research Center, Kerman University of Medical Sciences, Kerman, Iran.
Faranak Rahimi - Resident of Restorative Dentistry, Department of Restorative Dentistry, School of Dentistry, Kerman University of Medical Sciences, Kerman, Iran.
Kheyzaran Baharlooyi - Specialist of Restorative Dentistry, Private Practice.

Introduction: Resin composites are an important part of restorative treatment in modern dentistry. There are many trademarks available in Iran market and physico-chemical properties of many of these resin composites are not evaluated yet. This study was carried out to evaluate the physico-chemical properties of four available resin composites and also to assess the effect of aging on their properties. The findings of this study help clinicians to choose the best materials available. Methods: Four types of resin composites available in Iran market including Filtek Z350 XT, Filtek Z250, Herculite XRV Ultra and Herculite XRV were evaluated. Five samples were made of each composite using a metal mold (2* 10 * 10 mm). Two areas of each sample were light cured for 40 seconds. Samples were kept in saline for 24h and then underwent polishing process. Samples of each group were randomly allocated to five groups held in different conditions as follows: room temperature, distilled water in 37˚C, Distilled water plus hydrochloric acid, distilled water and thermocycling (5000 rounds of 5-55˚C), distilled water, thermocycling, and hydrochloric acid. At the end of one month, indentation was applied on each sample using nano-indentation technology (TriboIndenter, Hysitron, Minneapolis,MN). Results: The results of this study revealed that the type of composite and the environmental conditions affect elasticity and nano-hardness. Conclusion: storage conditions affected the elasticity of Filtek Z350XT, Herculite XRV Ultra and Herculite XRV and the hardness of Filtek Z350 XT and Herculite XRV Ultra

resin composite aging, nanoindentation, nano-hardness, modulus of elasticity