Most of the time, you can use the remaining three implants to help "anchor" your denture in place.Make sure you check with your dentist to ensure that the remaining implants are in good condition and that the denture is fitting properly on your gums and your remaining implants.
From your description, it sounds like you have a failing four unit bridge supported by two teeth and some posts (what you are referring to as metal screws). So the teeth have already gone through root canal treatment, posts, and bridgework. At this point, most likely the teeth cannot be repaired in a predictable fashion for long term success. This is the time to give dental implants serious consideration. This will provide you with a much more predictable long term solution.
From what I can gather on the photo you provided, it looks like you have a chipped central right incisor.I would recommend that have the tooth evaluated by your dentist to rule our further damage to the tooth and surrounding tissue. Once this has been determined, it can be repaired with a simple bonding procedure using tooth colored material. As for costs, this can vary based on your area. In the US, the average cost from this type of restoration is between $200-$350. If done well, the material will hold up for many years. After the repair, you will need to be careful and avoid heaving biting on the tooth. Best of luck!
Implants are not typically used to replace wisdom teeth (third molars). From your description, I would recommend extraction of the wisdom tooth in question and there will be no need to consider an upper implant to oppose it. You will have adequate function without both teeth with no adverse impact on your oral health.
The picture you posted is not very clear and the information provided are not sufficient to provide you with an adequate diagnosis.However, here is what I tell you based on what I think I see on your picture.It appears that you upper right canine (eye tooth) has a lesion at the gum line.A clinical and exam and x-ray are needed to confirmed the diagnosis.This could be tooth decay (dental caries) at the neck of the tooth. Depending on the extent of the decay, the treatment will be do restore the tooth. This can be a simple as putting in a tooth colored filling or it can get more involved if the decay is deep and involving the nerve of the tooth.I would recommend seeing a dentist in your area as soon as possible. Your remaining teeth appear to be in good shape and it is always better to intervene early before the damages are too extensive. As for costs, the depends on where you are. However, if this turns out to be a simple cavity that only requires a filling, your are looking at treatment costs in the 200-500 range.
