The following references need to be added

Microsoft.SqlServer.Smo
Microsoft.SqlServer.SmoEnum
Microsoft.SqlServer.ConnectionInfo

ServerConnection oCon = new ServerConnection(server, DBUserID, DBPassword);

Server oServer = new Server(oCon);
Restore oRestore = new Restore();

//sFileName - File Physical Location

if (File.Exists(sFileName))
{           
    oRestore.Database = DbName;
    oRestore.Action = RestoreActionType.Database;
    oRestore.Devices.AddDevice(sFileName, DeviceType.File);
    oRestore.NoRecovery = false;
    oRestore.ReplaceDatabase = true;
    oRestore.PercentCompleteNotification = 10;
    oRestore.PercentComplete +=
    new PercentCompleteEventHandler(bkp_percentComplete);
    oRestore.SqlRestore(oServer);
}

protected void bkp_percentComplete(object sender, PercentCompleteEventArgs e)
{
     lblStatus.Text = e.Percent.ToString() + "% restored";
}