As in all infections, the body answers with increased circulation (hyperaemia): the supplying blood vessels expand. Hyperaemia can transform into an acute or chronic pulpitis. A tooth with acute pulpitis is extremely sensitive to temperature. Cool air is sufficient to trigger the pain. In pulpitis acuta serosa, extended capillary vessels cause the excretion of granulocytes and serum. Activated enzymes, causing the breakdown of proteins, create pus, leading to severe pain in pulpitis acuta purulenta.

Chronic pulpitis on the other hand is often completely without symptoms. It is usually caused by caries. White blood cells (leucocytes) accumulate in the pulpa to combat inflammation. The bacteria cause the blood vessels of the pulpa to become permeable to serum (pulpitis serosa) and the number of infection combating cells increases (e.g., lymphocytes). Bacteria aggravate the infection. Pus-forming granulocytes supervene and the pain intensifies.

In reversible, acute pulpitis, the tooth reacts to sweetness, cold and heat. The pain lasts for a short while only. The sensitivity test is positive. If caries can be removed without opening the pulpa, the tooth loses its symptoms. The pulpa can be kept vital. This acute form of pulpitis is therefore reversible.

In irreversible pulpitis, which may be acute or chronic, the tooth is permanently painful. The dentin is frequently destroyed up to the pulpal cavity and cariously altered. Pain continues even after caries removal and medicamentous filling. The tooth's sensitivity to touch and biting is joined by decreasing or lacking reaction to a sensitivity test. The damaged pulpa cannot be reversed to its original healthy state, it is irreversible.

Vitality loss of the tooth marrow leads to pulpal necrosis which initially shows no symptoms. This may occur through a bacterial infection such as gangrene or after trauma without the participation of bacteria. If infection occurs in the jaw bone via the foramen apicale, it results in acute or chronic apical parodontitis. Diagnosis is confirmed with a negative sensitivity test. Therapy consists of trepanation with subsequent root canal preparation and filling.

If the disease is left untreated, anaerobic putrefactive bacteria decompose the dead tissue and result in gangrene. Putrefactive bacteria create a gas. This gas creates pressure in the tooth which in turn causes severe pain. Dental trepanation often alleviates the pain, as these putrefactive gases, pus and secretion can escape, whereby the root canals are massively infested with bacteria, which can be recognised in a foul odour and taste. In pulpal gangrene, the result of a sensitivity test is negative. If the tooth is knock-sensitive, bacteria have entered the jaw bone through the foramen apicale. The body is trying to defend itself by forming defensive tissue, an apical granuloma. This can be recognised as a dark apical spot on the X-ray. Cysts and abscesses may form later under certain conditions.

A chronic apical parodontitis often displays no pain. The treatment principle in irreversible pulpitis and pulpal gangrene consists of the removal (extirpation) of the painful and infected or devital pulpa and the antibacterial filling of root canals with tissue compatible pastes and gutta-percha pins.

This diagnosis displays an inflammation of the periodontium near the root tip. This acute or chronic periapical infection is caused by

• Infected or necrotic pulpa
• Incomplete or overfull root fillings
• Drugs
• Disinfectants,
• Apical trauma
• Grinding and parafunctions

When viewing X-rays we often discover a pea-sized, encapsulated centre of inflammation, Parodontitis apicalis chronica. The previously healthy bone is replaced by inflammatory soft tissue near the root tip. The soft tissue at the root tip is also called a granuloma.

Chronic parodontitis apicalis can become acute if bacteria are involved. The chronic infection flares up. The tooth becomes sensitive to biting. Therapy consists in trepanation of the tooth and subsequent root canal treatment. A successful therapy results in the gradual abatement of the inflammation.

In parodontitis apicalis, bacteria in the root canal are responsible for the inflammation. If a fistula forms, the acute pain subsides. Successful canal preparation and disinfection leads to a regression of the fistula after only a few days.

The principle of root canal treatment consists in removing infected or devital tissue from the inside of the tooth and to seal the cavity with filling material. Treatment takes place under local anaesthetic if the pulpa is not devital.

Root canal treatment can be divided into:

1. Removal of pulpal tissue
2. Determination of root canal length
3. Preparation of root canals
4. Filling of root canals

First the canal portals have to be found and expanded. Once the portal is found, the diseased tissue is removed from the root canal. If the roots are strongly arched, are very fine or calcified, it may be impossible to reach the apex with the preparation instruments. The result is insufficient root canal treatment, which does not allow the inflammation to abate.

The determination of the root canal length specifies the operational length of the root canal instruments by displaying the length to the foramen apicale. A decisive factor for the correct filling of the canals is its length, previously determined by X-ray. The X-ray displays how far the instrument is away from the root tip and which length the instruments in the canal may have. Determination of canal length can also be performed electrically, whereby a probe is inserted into the canal and the end of the root canals is indicated by a measurement device.

Root canal preparation serves to prepare the root canal for root filling. The canals are extended and planed with flexible, mechanically or manually driven drills and files, which adjust even to arched or bent roots. Canal preparation is also possible with ultrasound.

Canal preparation should be performed up to the foramen apicale.

Unintended lateral penetration of the root is called “via falsa” (the “wrong way” in Latin). The objective of root canal filling is to fill the prepared root canal with special, bacteria-proof paste and matching gutta-percha tips and thus ensure sustainable treatment success. Root canal filling is performed with endogenous substances, which should be tissue-compatible, hardening, fluid, dimensionally stable, parietal, bacteria-proof, non-resorbable and visible on X-ray. A disinfecting effect is also expedient in order to render remaining or newly introduced bacteria harmless.

In thermoplastic root canal filling, heated and formable gutta-percha is injected into the prepared root canal or inserted as gutta-percha pins. The insertion of several gutta-percha pins with hardening pastes is preferred. While the orthograde root canal filling is normally positioned from the crown, the retrograde root canal filling is performed at the tip of the root (e.g., in root tip resection).

A final X-ray is performed to control whether the canals were filled completely and bubble- free. A cavity may not be created, as bacteria could settle there and cause an infection (parodontitis apicalis). The cavity is then either provisionally or terminally closed. Root canal treated teeth have often lost their form and stability die to the disease and its treatment. This indicates the necessity of crowns for their protection.