If there is no pain ,no hot and cold sensation then you should visit your dentist and get the filling done . It looks like it is not exposed though that will be confirmed by the dentist. If it is not exposed and you do not go for fillig now then with time the pain and sensation can be there and then you have to go for the root canal treatment with crown which will be quite an expensive treatment. At this stage only filling will serve the purose and it will not be very costly. For more info on fillings you can visit the following link on our website....www.identalhub.com/article_average-cost-of-dental-filling-449.aspx