According to OALD, toothache means "a pain in your teeth or one tooth" while Longman and Cambridge say that it refers to pain "in one tooth". If this is the case, what is the condition of having pain in more than one tooth called?
Short answer to your question: toothaches.
Longer answer to your question: When one dictionary defines the scope of a word to be broader than another, it's usually the broader definition that's more accurate. It's very hard to capture all the English language in a single opus (I believe the OED uses a 20+ volume set in their attempt, yet even the OED adds new entries every year as the language evolves.)
Lastly, a toothache might be a misdiagnosis. I suppose someone might initially believe they have a toothache when in fact they are suffering from something else, such as TMJ. My point is that some words (such as medical terms) have both layperson uses and technical uses. There's nothing wrong with someone with an unknown malady from saying:
I have a toothache; I'm going to make a dentist appointment.
Whether the pain is in one tooth, or along the whole row. If TMJ is determined to be the culprit, no one will chastise that person for making a grammatical faux pas. It's the mouth that has the problem, not the grammar or the vocabulary.
That said, my ELL diagnosis is that Longman and Cambridge have abridged definitions that don't fully cover the scope of the word.
When a person has a toothache, it is normal for the person to not be sure which tooth (or teeth) are involved. The pain can seem to move along a side of a jaw, or even switch between the upper and lower jaws. It is possible for multiple nearby teeth to ache at the same time, for several possible reasons:
- Multiple teeth are growing in at the same time.
- A second tooth gets a bad cavity before the first tooth is fixed.
- A tooth is growing in crookedly, and shoving other teeth around.
- An injury affects multiple teeth.
- Multiple teeth are temperature sensitive. Eating something hot or cold can cause several of them to hurt at the same time. (Many dental fillings do not insulate as well as natural tooth-material does.)
- Grinding one's teeth at night and (as J.R. points out) disorders of the temporo-mandibular joint (TMJ) can cause pain in multiple jaw-tooth ligaments simultaneously.
For these reasons, it does not make much sense to distinguish between a "toothache" and multiple "toothaches" during a single episode of mouth pain.
- "I have a toothache" means "I have pain in my jaw(s), close to one or more teeth. I cannot clearly distinguish two separate pains from teeth."
- "I have toothaches" means either "Two very different parts of my jaw(s) hurt. Each pain is close to one or more teeth." or "I sometimes have a toothache. Either I get it taken care of by a dentist, or the pain goes away on its own. Later on, I get another toothache." A person is especially likely to say "I have toothaches" during one of the times the person has a toothache.
Safety note: If a toothache is caused by a cavity, it can go away on its own. This situation is dangerous, and should be treated. The pain goes away after the cavity kills the nerve in the root of the tooth. The cavity can keep growing inside the jaw or skull (at which point it is called an abscess) and do serious damage to the jaw, nerves, and/or brain.
So you are looking to find what the plural of "toothache" might be; or if the word "toothache" can mean multiple teeth at the same time.
Obviously the plural of "tooth" is "teeth", but you should never hear "teethache". There is no such word.
"Ache" is singular, but it is synonymous with "pain", and while we do use these in the plural as in "aches and pains" we also speak of "being in pain", which can describe a complete experience of all-over pain. A person cannot always tell exactly where a pain is coming from, especially when the pain is internal, so it could be said that both ache and pain may describe multiple sources of pain that are occurring simultaneously.
It has been suggested in another answer that the plural of toothache would be "toothaches" - but I have personally never heard this used to describe pain occurring in multiple teeth simultaneously, as in your question.
Consider the word "headache" for example. You only have one head, so if someone spoke of "suffering from headaches" you would rightly conclude that they meant they suffer from recurring instances of pain in their head. So if someone similarly used the word "toothaches" you would understandably conclude they meant a recurring ache, possibly in just the one tooth.
If you speak of your teeth in the plural, there is no need to pluralise the aches. If I had aches in multiple teeth I would still likely say:
I have toothache.
If I really wanted to specify that it was in several teeth:
Several of my teeth ache.
I have toothache in several teeth.
Or if all of my teeth were aching:
My teeth ache.
I don't believe it is helpful to say, for example "I have toothaches in several teeth". For comparison consider: "I keep glasses in several cupboards". Does this mean that you keep just one glass in each of your several cupboards? No - it sound more like you have multiple glasses in multiple cupboards! You cannot have multiple pains in each tooth (at least I don't know how you would discern that you have) and so it is ambiguous at best to use the word "toothaches".