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# Caries, gingivitis and periodontitis: the lesion view

- Lesion

Plaque bacteria make acid that dissolves enamel (caries) and inflame the gums (gingivitis); unchecked, this destroys the tooth's support (periodontitis).

Updated Nov 12, 2026

## Key points

- Caries: Streptococcus mutans and lactobacilli ferment dietary sugars into acid; fluoride forms acid-resistant fluoroapatite.
- Gingivitis: plaque and calculus (mineralised plaque) cause red, swollen, bleeding gums; reversible with hygiene.
- Periodontitis: shift to anaerobic Gram-negative flora (Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Tannerella); loss of attachment, pockets, bone loss, tooth loss.
- Systemic links: diabetes, HIV, Crohn disease, Down syndrome, neutrophil defects; periodontal bacteria can cause endocarditis and lung or brain abscess.
- Untreated caries reaches the pulp: pulpitis, pulp necrosis, periapical abscess, granuloma or cyst.

## What it is

The mouth holds a complex microbiome; when its balance shifts, plaque biofilm causes the two commonest oral diseases. Caries is focal demineralisation of enamel and dentin by acids from bacterial fermentation of sugars; it is the main cause of tooth loss in young people. Gingivitis is reversible inflammation of the gums from plaque and calculus; periodontitis destroys the periodontal ligament, cementum and alveolar bone.

## Structure

- Caries: chalky white spot in enamel that becomes a brown cavity; dentin softens as tubules fill with bacteria.
- Gingivitis: hyperemic, edematous gingiva with a dense infiltrate of neutrophils, lymphocytes and plasma cells.
- Periodontitis: deepened pockets, apical migration of the junctional epithelium, chronic inflammation, osteoclastic resorption of alveolar bone.
- Periapical lesion: granulation tissue or an epithelium-lined radicular cyst at the root apex.

## Step by step

- Bacteria form a sticky biofilm (plaque) on the teeth when hygiene is poor.
- Frequent dietary sugar is fermented into organic acids that drop the pH at the tooth surface.
- Acid dissolves hydroxyapatite: demineralisation outpaces remineralisation and a cavity forms.
- At the gum margin, plaque toxins trigger inflammation (gingivitis).
- If dysbiosis persists, host neutrophils, cytokines and RANKL-driven osteoclasts destroy ligament and bone (periodontitis).
- The tooth loosens and is lost; bacteria can enter the blood during chewing or procedures.

## Gingivitis vs periodontitis

| Feature | Gingivitis | Periodontitis |
| --- | --- | --- |
| Tissue involved | Gingiva only | Ligament, cementum, alveolar bone |
| [Bone loss](https://durgical.com/en/conditions/periodontitis/) | None | Yes, radiographic |
| Pockets | None or false pockets | True pockets with attachment loss |
| Reversibility | Reversible | Irreversible damage |
| Outcome | Bleeding gums | Tooth mobility and loss |

## Clinical notes

- Caries and periodontitis are largely preventable with fluoride, sugar reduction and daily hygiene.
- Periodontitis is linked with poorly controlled diabetes in both directions.
- Dental caries remains very common in Colombia, including in pregnant women and children.

## Memory aid

Sugar plus bugs equals acid; plaque plus time equals pockets.

## Test yourself

Think of the answer, then tap the question to see it.

## What causes dental caries?

Focal demineralisation of enamel and dentin by acids produced when plaque bacteria such as Streptococcus mutans ferment dietary sugars.

## What separates periodontitis from gingivitis?

Periodontitis destroys the supporting structures (periodontal ligament, cementum, alveolar bone) with attachment loss; gingivitis is limited to the gums and reversible.

## How does fluoride protect teeth?

It is incorporated into enamel as fluoroapatite, which resists acid dissolution better than hydroxyapatite.

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## Elsewhere in DurgiPedia

- [Oral cavity, tongue and teeth](https://durgical.com/en/histology/oral-cavity-tongue-and-teeth/)
- [Teeth](https://durgical.com/en/embryology/teeth/)
- [Salivary secretion](https://durgical.com/en/physiology/salivary-secretion/)

## Connections

## Related 3

- [Aphthous ulcers and reactive oral lesions](https://durgical.com/en/general-pathology/aphthous-ulcers-and-reactive-oral-lesions/)
- [Odontogenic cysts and tumours](https://durgical.com/en/general-pathology/odontogenic-cysts-and-tumours/)
- [Patterns of acute inflammation: serous, fibrinous, purulent, abscess, ulcer](https://durgical.com/en/general-pathology/patterns-of-acute-inflammation-serous-fibrinous-purulent-abscess-ulcer/)

## Related conditions 2

- [Dental caries](https://durgical.com/en/conditions/dental-caries/)
- [Periodontitis](https://durgical.com/en/conditions/periodontitis/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Dental Caries](https://www.ncbi.nlm.nih.gov/books/NBK551699/) (StatPearls (NCBI Bookshelf), 2025); [Periodontitis](https://www.ncbi.nlm.nih.gov/books/NBK541126/) (StatPearls (NCBI Bookshelf), 2025); [Gum Disease](https://medlineplus.gov/gumdisease.html) (MedlinePlus, US National Library of Medicine, 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/caries-gingivitis-and-periodontitis-the-lesion-view/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/caries-gingivitis-and-periodontitis-the-lesion-view/