Oral Pathology and Oral Microbiology: Cysts, Tumours and Biofilm Pathogens
Oral Pathology and Oral Microbiology
INI-CET tests pattern recognition of odontogenic lesions, the biology of potentially malignant disorders, and the specific organisms driving caries and periodontal disease.
Core rules
- Radicular cyst is the most common odontogenic cyst, always associated with a non-vital tooth; dentigerous cyst is second and encloses the crown of an impacted tooth; odontogenic keratocyst is characterised by parakeratinised corrugated epithelium with palisaded, hyperchromatic basal cells, satellite cysts and PTCH1 mutation, and is associated with naevoid basal cell carcinoma syndrome.
- Ameloblastoma: mandibular posterior region, follicular or plexiform pattern, reverse polarity of peripheral cells, 'soap bubble' radiolucency, locally aggressive, BRAF V600E mutation in many cases.
- Oral submucous fibrosis follows areca nut use: juxtaepithelial hyalinisation with collagen cross-linking by arecoline, progressive restriction of mouth opening, high malignant transformation risk.
- Leukoplakia is a clinical diagnosis of exclusion; erythroplakia carries a higher transformation rate. Squamous cell carcinoma is the commonest oral malignancy, with buccal mucosa predominating in the Indian subcontinent and tobacco/areca as principal risks.
- Microbiology: Streptococcus mutans initiates caries via glucosyltransferase and insoluble glucan; lactobacilli dominate advancing lesions; Actinomyces is linked to root caries. Red complex - Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola - drives chronic periodontitis; Aggregatibacter actinomycetemcomitans is linked to aggressive periodontitis; Fusobacterium nucleatum acts as a bridge organism.
Worked example
A unilocular radiolucency in the posterior mandible shows a thin lining of parakeratinised, corrugated epithelium with hyperchromatic palisaded basal cells and a daughter cyst in the wall. Ameloblastoma would show odontogenic epithelium islands with reverse polarity and stellate reticulum-like centres. The parakeratin, corrugation and satellite cysts identify an odontogenic keratocyst, which predicts a high recurrence rate and justifies long-term radiographic follow-up.
Traps
- Naming ameloblastoma as malignant: it is benign but locally aggressive.
- Calling leukoplakia a histological diagnosis - it is clinical and requires biopsy to grade dysplasia.
- Equating the most common odontogenic tumour with the most common odontogenic cyst.