I would recommend going in for a consultation to evaluate your bonding. Over time, boding can pick up stain from food and beverages and from smoking. If the stains on your bonding are superficial and the bonding is still sealed, it may be possible to just buff out the discoloration. If the boding needs replacement, the cost can vary based on the size of the filling. You may plan on spending $250-350. The materials we have now are much better than those from 15 years ago, so this could be a good investment in feeling better about your smile.
After seeing your photos, I would recommend an orthodontic evaluation. I think going purely with bonding or veneers would give you a tooth size that appears too big for your face. After closing much of the space with orthodontics, it is likely that you will still need some bonding on the upper lateral incisors due to the shape of these teeth. In doing this combination, I think you could get a very esthetic result.
I would recommend getting in to your dentist as soon as possible. If there is no pain, it is likely that the abutment screw has come loose from the implant or that the crown has come loose from the abutment. Functioning on a loose screw can put stress on the screw which can eventually cause it to shear off. The movement can also cause gum irritation around the implant. Over time this can damage the bone around the implant.
If the sensitivity resolved and has now returned, I would recommend having it evaluated by your dentist to determine if a root canal is indicated. If the cold sensitivity lingers more than several seconds after removing the cold, this usually indicates that the nerve is dying and a root canal will be necessary. You mentioned that the cold was around the outside of the tooth. Another thing that could be causing the cold sensitivity is if the gum has receded exposing the root surface of the tooth.
