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Introduction: Aesthetic demands are increasing the popularity of posterior composite restorations. Though multidimensional materials that bond chemically, composites have higher cost and shorter longevity compared to other restorative materials like amalgam and gold. An ideal restorative materials have properties comparable to properties of tooth surface it. An important factor is the surface microhardness of composite. Over years, composites have developed a lot from conventional composites to microhybrid and nanocomposites.

Objective: The purpose of this in vitro study was to investigate the difference in surface microhardness of nanocomposites and microhybrid composites.

Materials and Method: The sample size consisted of 20 disks made of microhydrid (Group 1) and nanocomposites (Group 2).  For testing the surface microhardness 10 disk shaped specimens each of Z350 and Z100, measuring 5 mm in diameter and 2 mm in thickness were prepared and tested using the Vickers hardness tester.

Result: In the intergroup comparison of both top surface and bottom surface microhardness, nanocomposites showed higher microhardness values (96.30 VHN and 74.21 VHN) as compared to the microhybrid composites (93.54 VHN and 72.86 VHN) that were not significant statistically.When intragroup comparisons were done for top and bottom surface microhardness, top surface showed higher value than bottom surface independent of the material used. This was statistically significant (p= 0.001).

Conclusion: Nanocomposite had higher microhardness values than microhybrid composite restorative material and within the groups, the top surface microhardness was higher than bottom surface irrespective of the composite material used. Thus, the microhardness for top surface, which is closer to the light source is significantly higher compared to bottom surface that is away in both the materials used.

Depth of cure; microhardness; microhybrid composite; nanocomposite.