Let me walk you through it:
Demineralisation is occurring more than remineralisation and caries (bacteria) is making in-roads on your tooth.
Dental caries progresses slowly through your enamel, (enamel caries) due to its strength and the protection of saliva, until it hits the border with the dentine (ADJ) where it is sent off on a bit of a wild goose chase in an attempt by your tooth to protect the nerve. The caries spreads out along the border for a while, before eventually overcoming this barrier and making its way through and into the dentine.
Dentine is not as hard as enamel and because it is made of tubes, the caries progresses quicker than before (dentine caries). Whilst being weaker, dentine is a living a tissue and reacts by laying down more and more tubes, shrinking the nerve away from the harmful caries. This is called 'secondary dentine' or 'reactionary dentine' and occurs in response to a deep attack.
Once in dentine, it is likely that you will begin to experience some symptoms, as the nerve in your tooth begins to be affected and the nerve inside swells slightly (pulpitis
). This small amount of inflammation is known as 'reversible pulpitis'. The caries will continue towards the nerve- unless stopped with a filling- and the closer it gets the more irreversible the swelling of the nerve will become, 'irreversible pulpitis'.
Soon the swelling will be so great, that the blood vessels supplying the tooth through the small entrance at the base of the root called the 'apical foramina', are strangled, causing the nerve to die off. We call this 'pulpal necrosis' and so ends the life of your tooth.
The sooner we catch the caries, the easier it is to stop and reverse it- yet another reason for frequent dental visits! The deeper it progresses, the more extensive and expensive your treatment will become.
Eventually the bacteria will infect the root canal system causing 'periapical periodontitis'. 'Peri', meaning around, 'apical' meaning the end of your tooth. Also 'perio' short for 'periodonitum' (or the supporting structure of your teeth; the bone/ligaments etc.) and 'itis' meaning inflammation. Put it all together and you have an 'inflammation in the periodontal tissues around the end of your tooth'. Not to be confused with Periodontal disease
which is something completely separate.
This can be an acute inflammation accompanied by pain and swelling, redness and heat, or a chronic inflammation, where a longer-term balance between your body and the bacteria is set up. Acute periodontitis is painful. The tooth more often than not is very sore to bite on and some times even sensitive to touch. Chronic periodontitis isn't painful and often discovered incidentally on an X-ray. However, just to make it extra confusing for you, 'chronic' can quite easily become 'acute' and vice versa- it just depends on the virilant (how nasty) the bacteria are and of course, your immune system's ability to keep them at bay.
Acute or chronic periodontitis can lead to a dental abcess (collection of pus) which you will surely know about. The tooth at this point will definitely become very painful, because there are so many nerve endings in the ligament surrounding the tooth. That is, unless the infection has a place to drain- a 'sinus'. This is where the infection from the end of the tooth makes it way out onto your gum somewhere near the offending tooth. A little boil or blip, through which pus and infection can escape is often seen, felt and commonly tasted (not very nice). As long as this tract remains open, pain is unlikely as there is no build up of pressure. If it gets blocked- Boom = Pain.
An abcess can be so small and hardly noticeable but very painful, often just pushing the tooth up in its socket only a millimetre, or your face can swell to the size of a football and make you look as if you'd gone 5 rounds with Mike Tyson.
Spreading infection is a serious consequence that is quite rare, but it can occur. This 'dental cellulitis' means the infection is no-longer confined to the tissues around the problem tooth and begins spreading through your facisal planes entering other tissues. It requires immediate antibiotics and sometimes even hospitalization.