Background: the present in vitro study has been undertaken to evaluate the significance of time in placement of composite over calcium silicate based materials i.e. MTA, Biodentine and TheraCal LC with and without bonding agent application. Materials & Methods: 105 plastic tubes were cut from plastic pipes for taking internal diameter of 4 mm. 30 blocks for each experimental group were made, i.e. MTA, Biodentine and TheraCal LC  (4 X 5mm) in dimension. And similarly, 15 blocks for control groups (n=5 for MTA, Biodentine and TheraCal LC) were made of similar dimensions. These blocks were divided on the basis of timing of placement of composite (10 minutes, 1 day and 7 days) into experimental group (MTA, Biodentine and TheraCal LC) and control groups and marked accordingly. Each experimental group was subdivided depending on the use of bonding agent (Adper single bond 2, 3M ESPE), i.e. with and without bonding agent. The groups were divided into various subgroups. All the samples were viewed under scanning electron microscopy were gold plated using vacuum evaporator (JEOL JFC 1600, Japan). All the samples were then subjected to statistical analysis. The mean microhardness value of each specimen was calculated, and the values were expressed as the mean ± standard deviation. The microhardness measurements were performed with a Vickers microhardness tester.  The data obtained was tabulated and subjected to statistical analysis. Results: Maximum amount of gap was shown by Biodentine 7 day subgroup without bonding agent (B5). MTA 10 minutes subgroup with and without bonding agent (A1, A2), Biodentine 10 minutes with bonding agent (B2), Biodentine 7 day with bonding agent (B6), TheraCal LC 10 minute and 1 day subgroup with and without bonding agent (C1, C2, C3, C4) showed no gap (0 µm) between the calcium silicate material and composite resin or bonding agent interface. In case of Vickers microhardness number, duncan’s test parameters attains value from A (minimum microhardness number) to G (maximum microhardness number), with B, C, D, E, F having intermediate values in increasing order. Conclusion:  The composite restoration can be placed immediately over the calcium silicate based materials if proper manufacturer’s instructions are followed while manipulation of calcium silicate based materials.
Key words: Biodentin , Composite,  Esthetic, MTA, TheraCal LC