Irreversible Pulpitis: Etiology, Anatomy, Clinical Picture, and Treatment

Irreversible pulpitis is an inflammation of the dental pulp that does not disappear when its cause is eliminated.

Etiology

The main cause of pulpitis development is the penetration of the carious process into the pulp. It can also be caused by tooth trauma (mechanical injury, occlusal trauma, orthodontic tooth movement), iatrogenic factors (preparation without cooling, poor isolation of the working field, accidental pulp exposure, use of toxic lining and restorative materials).

Mechanism of Pulp Damage in Irreversible Pulpitis

During microbial invasion of the pulp, inflammatory defense mechanisms are activated, neutrophils accumulate, and immune cells gather. Neutrophils migrate from the pulp to the adjacent openings of dentinal tubules and release oxygen radicals, lysosomal enzymes, and nitric oxide, contributing to tissue destruction. The release of pro-inflammatory neuropeptides causes vasodilation and increased permeability of vessel walls. This leads to fluid exiting from the vessel lumen into the tissues.

The exudate is initially serous, then sero-purulent and purulent. Pressure increases in the tissues, and a pulp necrosis focus develops. The necrosis zone is surrounded by an accumulation of neutrophilic granulocytes that phagocytize bacteria, and acellular tissue with signs of partial decay. In the surrounding tissues, a picture of chronic inflammation is observed: macrophages, fibroblasts, mast cells, and foam cells. Even a limited necrosis zone is a sign of reversible pulpitis transitioning to irreversible. The initial necrosis area slowly spreads deeper in the apical direction.

As a result of inflammation, purulent melting of the pulp and its necrosis may occur, or the acute process may transition to chronic if spontaneous evacuation of the exudate has occurred.

In chronic pulpitis, proliferative changes are dominant: inflammatory edema disappears, and fibrous elements grow extensively.

Mechanism of Pain Development

Inflammatory mediators, such as bradykinin and histamine, activate type C nerve fibers. C-fibers are unmyelinated, have low conduction velocity, smaller diameter, and a higher excitation threshold than A𝛅 fibers. They are located deeper and are mainly activated by heat, causing dull, aching, excruciating, prolonged, sometimes diffuse pain. Cold exposure in patients with symptomatic irreversible pulpitis can cause vasoconstriction and a drop in pulp pressure, which may provide temporary pain relief. C-fibers also differ from A fibers in their ability to maintain functional integrity during tissue hypoxia and continue to function for a longer time as inflammation progresses. The reaction of C-fibers indicates that pulp damage is irreversible.

Anatomy

Depending on the etiologic factor, the affected tooth may exhibit:

• A carious cavity that penetrates the pulp of a tooth;
• A tooth restoration close to the pulp chamber or directly adjacent to the pulp tissue;
• Restoration of a tooth with signs of impaired seal (defects, cracks in the restoration, pigmentation on the margin, secondary caries);
• Signs of trauma (cracks, chips in enamel, dentin, partial pulp exposure).

In an acute process, the pulp is edematous, hyperemic, and bright red in color. Small hemorrhages may be found around the vessels. Purulent exudate is initially found as a local accumulation, then spreads to the entire crown and root pulp. The pulp takes on a gray-red or gray color.

In a chronic process, the pulp is replaced by granulation tissue, and then by dense, coarse fibrous scar tissue of a whitish color.

Classification

• Acute irreversible pulpitis;
• Chronic irreversible pulpitis.

Diagnosis

• It is very important to collect complaints and history (presence, nature, and localization of pain, duration of pain episodes, presence/absence of ‘light’ intervals, factors provoking and alleviating pain, recent dental treatment, trauma);
• Tooth percussion — painless or questionable;
• Palpation along the mucobuccal fold — painless;
• Temperature test — exposure to cold and/or heat stimulus causes a pain attack that continues after the stimulus is removed. With extensive pulp involvement, the reaction to cold stimulus may be absent, while the reaction to heat persists;
• Electric pulp test — teeth with irreversible pulpitis have a higher threshold for electrical stimulation compared to teeth with healthy pulp or reversible pulpitis;
• Bite test — negative;
• Selective anesthesia — used to determine the causative tooth in cases of pain irradiation, as well as in differentiating non-odontogenic pain;
• Radiography (intraoral contact radiography, radiovisiography, orthopantomography, cone-beam computed tomography): carious cavity, restoration, or traumatic defect adjacent to/penetrating the pulp chamber, usually no changes in the periapical area. As the process progresses, thickening of the periodontal ligament space may be noticeable.

Clinical manifestations

In acute pulpitis, the patient complains of ‘spontaneous’ paroxysmal pain – a sensation that occurs spontaneously regardless of external stimuli. The frequency and duration of pain attacks and ‘light’ pain-free intervals change over time. In the initial stages, short pain attacks (minutes-hours) alternate with long pain-free intervals (hours-days). As the process progresses, the frequency and duration of pain attacks increase. Pain often occurs at night. The nature of the pain is dull, aching, excruciating, prolonged, sometimes sharp and throbbing, can reach considerable intensity and become unbearable. The pain often radiates to neighboring teeth, antagonist teeth, and may migrate.

Exposure to thermal, mechanical, and chemical irritants leads to a prolonged pain attack that persists after the irritant is removed.

Chronic pulpitis is characterized by a discrepancy between the weak expression of the pain symptom and the significant degree of tooth destruction. The patient complains of prolonged pain arising from the action of irritants, while spontaneous and nocturnal pain are usually absent.

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Treatment

Acute irreversible pulpitis with spontaneous pain is a condition requiring urgent care.

Endodontic treatment: involves complete removal of the pulp, mechanical and medicinal treatment of root canals, and their hermetic obturation followed by tooth restoration.

In permanent teeth with incomplete root formation, revascularization and apexogenesis techniques may be possible.

If the prognosis of endodontic treatment is unsatisfactory, the tooth should be extracted.