Is missing a tooth (or two, or three) really that much of an issue? It can be, although the precise nature and urgency of the problem will depend on which tooth happens to be missing.
1. Missing Incisors or Molars
A missing central incisor poses a rather obvious dilemma if seemingly only an aesthetic one. The missing tooth is going to be immediately evident the moment you open your mouth, so you should see a dentist as soon as possible to discuss your replacement options sooner rather than later. What about when the issue isn't aesthetic? If you should have a missing rear molar, it might not seem like a problem in the slightest. After all, it's going to be practically impossible for anyone to notice. But the health of your teeth is more about how they look.
You can live with missing teeth, but this should not be your ongoing strategy. Tooth loss can contribute to a number of potentially dangerous outcomes. Your teeth are configured to share a fairly even workload. When a tooth is missing, its remaining neighbours have to work that little bit harder, accelerating tooth degradation by wear and tear. If left for an extended period of time, the lack of a placeholder can also pose a problem, in that the surrounding teeth will pivot into the gap, making it harder to fit a prosthetic replacement. Missing teeth can also lead to misalignment of your bite, which can lead to a problematic condition known as temporomandibular joint dysfunction.
2. Extraction or Periodontal Disease
Your missing teeth might have degraded to the point that they were extracted by a dentist, without a prosthetic replacement being discussed at the time. It can also be that the teeth have decayed and broken off, either as a whole or in fragments. This is a complication. The tooth is gone, but fragments of its pulp (the dental nerve) and periodontal ligaments will remain. Infection of the site is possible (and even more likely due to the periodontal disease that caused the decay in the first place). Even if the tooth is no longer there, you could be facing a dental abscess.
3. Replacement Options
If you're missing a tooth, see your dentist to discuss your replacement options. It might not require an urgent solution, but to simply live with the missing tooth is to compromise your overall dental health. Dental implants are a standard form of replacement, but dentures (fixed or detachable) will also be suitable. You might also be a candidate for a dental bridge, which is when the prosthetic tooth is secured by being connected to the teeth on either side.
A missing tooth doesn't require immediate attention, but you shouldn't delay treatment indefinitely. A minor inconvenience now can result in a significant issue in the future.