Oral pathology and oral microbiology

In short

Oral pathology studies the nature, causes, structural changes and clinical course of diseases affecting the teeth, jaws, oral mucosa and salivary glands; oral microbiology studies the resident and pathogenic micro-organisms of the mouth and how they cause caries, periodontal disease and oral infections. Together they explain *why* a lesion looks the way it does, linking plaque biofilm and host response to the histology seen on a biopsy slide. The subject is central to the BDS curriculum of the Dental Council of India (whose regulatory role now passes to the National Dental Commission under the National Dental Commission Act, 2023) — examined in the third-year university paper (theory, slide and specimen viva) and again in NEET-MDS, AIIMS/PGI, INI-CET and state PG entrances. It matters clinically in India because tobacco, areca nut and gutkha give the country one of the world's highest burdens of oral cancer and oral submucous fibrosis, and a dentist is often the first to detect it.

Explained

Oral microbiology: ecology and the plaque biofilm

• The mouth hosts over 700 bacterial taxa (the oral microbiome); only a fraction are cultivable. Habitats differ: tooth surface, gingival crevice, tongue dorsum, buccal mucosa, saliva, dentures.
• Acquired pellicle: a 0.1–1 µm glycoprotein film from saliva adsorbed onto enamel within minutes — the substratum for bacterial attachment.
• Plaque formation (4 stages): (1) pellicle formation; (2) reversible adhesion of early colonisers — *Streptococcus sanguinis*, *S. oralis*, *S. mitis*, *Actinomyces*; (3) co-aggregation, bridged chiefly by *Fusobacterium nucleatum*; (4) maturation into a biofilm with extracellular polymeric substance (glucans, fructans) and late colonisers — *P. gingivalis*, *T. forsythia*, *Treponema denticola*, *A. actinomycetemcomitans*.
• Why biofilms matter: 10–1,000 times more resistant to antimicrobials than planktonic cells; quorum sensing (competence-stimulating peptide in streptococci), nutrient gradients, horizontal gene transfer. Therefore mechanical plaque removal, not antibiotics, is the primary control.
• Calculus: mineralised plaque (hydroxyapatite, whitlockite, octacalcium phosphate). Supragingival calculus takes minerals from saliva, subgingival from serum exudate. Calculus itself is not the irritant — its rough surface harbours living plaque.
• Caries microbiology: *Streptococcus mutans* and *S. sobrinus* are acidogenic, aciduric and acidophilic, make insoluble glucans through glucosyltransferase (GTF) and intracellular polysaccharide stores. *Lactobacillus* numbers rise in established lesions; *Actinomyces* in root caries. Transmission is mainly vertical (mother → infant) around the "window of infectivity" (19–31 months).
• Ecological plaque hypothesis (Marsh) now supersedes the specific and non-specific hypotheses: repeated sugar challenge lowers plaque pH, selecting an acidogenic flora — disease results from an ecological shift, not one organism.
• Periodontal microbiology: Socransky's complexes — red (*P. gingivalis*, *T. forsythia*, *T. denticola*) most associated with deep pockets and bleeding; orange bridging; yellow/green/purple early and health-associated. *A. actinomycetemcomitans* serotype b (JP2 clone) with leukotoxin is linked to aggressive (now "grade C") periodontitis.
• Oral fungi and viruses: *Candida albicans* (also *C. glabrata*, *C. tropicalis*) — germ tube, hyphal invasion, SAP proteinases; HSV-1 (primary herpetic gingivostomatitis, recurrent herpes labialis), VZV, coxsackie A (herpangina, hand-foot-and-mouth), EBV (hairy leukoplakia, Burkitt), HPV 16/18 (oropharyngeal carcinoma), measles (Koplik spots).
• Specific infections of oral relevance: tuberculous ulcer (painful, undermined margins — acid-fast bacilli, Ziehl-Neelsen), syphilis (primary chancre, secondary mucous patch, tertiary gumma and interstitial glossitis; Hutchinson's incisors and Moon/mulberry molars in congenital), actinomycosis (*A. israelii*, "sulphur granules", board-like swelling, long-course penicillin), ANUG (fusospirochaetal — *Fusobacterium* + *Treponema*, punched-out papillae, foetor oris, pseudomembrane).
• Laboratory methods: Gram stain, culture on blood/chocolate/Mitis-salivarius (for *S. mutans*)/Rogosa SL (*Lactobacillus*)/Sabouraud dextrose (fungi), anaerobic jars, dark-field microscopy for spirochaetes, KOH mount and PAS for *Candida*, PCR/16S rRNA sequencing and checkerboard DNA-DNA hybridisation for non-cultivables, antibiotic sensitivity by disc diffusion. Snyder and Alban tests estimate caries activity by acid production; Dentocult SM/LB are chair-side kits.

Diseases of the teeth and periapex

• Dental caries: microbial, multifactorial, sugar-dependent demineralisation. Enamel caries zones (from inner to outer): translucent, dark, body of lesion, surface. Dentinal caries zones: zone of fatty degeneration of Tomes' fibres, sclerosis (hypermineralised, defensive), demineralisation, bacterial invasion, decomposed dentine. Classifications: G.V. Black's (Class I–VI by site), ICDAS/WHO by severity, acute (rampant) vs chronic, pit-and-fissure vs smooth surface vs root caries.
• Pulpitis: reversible (short, provoked pain) vs irreversible (spontaneous, lingering, worse on lying down). Histology: hyperaemia → acute inflammatory infiltrate → abscess → total necrosis. Low compliance of the pulp chamber makes inflammation strangulating.
• Periapical sequelae: acute apical periodontitis → acute apical abscess → chronic abscess with sinus → periapical granuloma (granulation tissue, chronic infiltrate) → radicular cyst (epithelial lining from rests of Malassez; cholesterol clefts, Rushton bodies, foamy macrophages). Condensing osteitis is the sclerotic variant.
• Developmental anomalies: number (anodontia, supernumerary, mesiodens), size (micro/macrodontia), shape (gemination, fusion, concrescence, dilaceration, dens invaginatus, dens evaginatus, taurodontism), structure — amelogenesis imperfecta (hypoplastic, hypomaturation, hypocalcified), dentinogenesis imperfecta (opalescent teeth, obliterated pulp; type I with osteogenesis imperfecta), dentin dysplasia, enamel hypoplasia (Turner's tooth, congenital syphilis), dental fluorosis — relevant across Rajasthan, Gujarat, Andhra Pradesh, Telangana and Karnataka where groundwater fluoride exceeds the IS 10500 drinking-water limit for fluoride (acceptable 1.0 mg/L, permissible up to 1.5 mg/L in the absence of an alternate source).
• Regressive changes: attrition, abrasion, erosion, abfraction, hypercementosis, resorption (internal/external), pulp stones, secondary and tertiary dentine.

Diseases of the oral mucosa

• White lesions: leukoedema, frictional keratosis, nicotine stomatitis, white sponge nevus, lichen planus (Wickham's striae; histology — hyperkeratosis, saw-tooth rete pegs, band-like lymphocytic infiltrate, Civatte bodies, basal cell degeneration), lupus, candidiasis (pseudomembranous, erythematous, hyperplastic, denture stomatitis, angular cheilitis, median rhomboid glossitis).
• Red/vesiculobullous and ulcerative: geographic tongue, pemphigus vulgaris (suprabasal split, Tzanck cells, "row of tombstones", intercellular IgG "fishnet" on DIF, Nikolsky positive), mucous membrane pemphigoid (subepithelial split, linear IgG/C3 at basement membrane), erythema multiforme/Stevens-Johnson, recurrent aphthous stomatitis (minor, major, herpetiform), Behçet's syndrome, traumatic ulcer.
• Oral potentially malignant disorders (OPMDs) — WHO terminology: leukoplakia (homogeneous and non-homogeneous/speckled/verrucous; proliferative verrucous leukoplakia), erythroplakia (highest malignant transformation), oral submucous fibrosis, oral lichen planus, actinic keratosis, palatal lesions of reverse smoking, oral lupus, dyskeratosis congenita, oral graft-versus-host disease. Approximate annual transformation: leukoplakia ~1%, erythroplakia much higher, OSMF ~7–13% reported in Indian cohorts (figures vary widely by cohort — quote as a range).
• Oral submucous fibrosis (OSMF): areca-nut (arecoline) driven juxta-epithelial fibrosis — burning, intolerance to spice, blanching, vertical fibrous bands, loss of tongue papillae, progressive trismus. Histology stages: very early (oedema, fine fibrillar collagen), early (juxta-epithelial hyalinisation), moderately advanced, advanced (dense hyalinised avascular collagen, muscle atrophy, epithelial atrophy with dysplasia). Clinical/functional staging commonly uses interincisal opening (e.g. >35 mm, 26–35, 15–25, <15 mm) — several systems exist (Khanna & Andrade, Pindborg, More), so name the system used.
• Epithelial dysplasia: architectural plus cytological atypia — drop-shaped rete, loss of polarity, basal cell hyperplasia, increased/abnormal mitoses, nuclear hyperchromatism, increased N:C ratio, dyskeratosis, keratin pearls. Graded mild / moderate / severe (WHO), or as a two-tier low- vs high-grade system; carcinoma in situ = full-thickness change with intact basement membrane.
• Oral squamous cell carcinoma (OSCC): ~90% of oral malignancy. Risk: smokeless tobacco (khaini, gutkha, zarda, mishri), areca nut, bidi/cigarette, alcohol (synergistic), chronic trauma, HPV (more oropharyngeal), poor oral hygiene, nutritional deficiency. In India, buccal mucosa and gingivobuccal sulcus ("Indian oral cancer") dominate because of quid placement, unlike the Western tongue/floor predominance. Histology: invasive nests breaching basement membrane, keratin pearls, individual cell keratinisation; Broders' grading I–IV by differentiation; TNM (AJCC 8th edition) added depth of invasion to T and extranodal extension to N. Variants: verrucous carcinoma (Ackerman's, pushing margins, good prognosis), basaloid, spindle cell, adenosquamous, papillary.
• Pigmented lesions: amalgam tattoo, racial/physiologic melanosis, smoker's melanosis, melanotic macule, nevus, melanoma, Addison's, Peutz-Jeghers, heavy-metal lines.

Cysts, odontogenic tumours and jaw lesions

• Odontogenic cysts (developmental): dentigerous (pericoronal, around unerupted crown), odontogenic keratocyst (OKC — parakeratinised corrugated lining, flat basal interface, palisaded basal cells, satellite cysts; *PTCH1* mutation; recurs; multiple in Gorlin-Goltz / naevoid basal cell carcinoma syndrome), eruption cyst, lateral periodontal/botryoid, gingival cyst, glandular odontogenic cyst, calcifying odontogenic cyst (now "calcifying odontogenic cyst" with ghost cells).
• Inflammatory: radicular/residual, paradental.
• Non-odontogenic and pseudocysts: nasopalatine duct, nasolabial, aneurysmal bone cyst, solitary (simple) bone cyst, Stafne's defect, mucocele/mucus retention, ranula, dermoid.
• Odontogenic tumours (WHO classification, current 5th-edition Head and Neck tumour volume): epithelial — ameloblastoma (conventional/multicystic: follicular, plexiform, acanthomatous, granular cell, desmoplastic, basal cell; unicystic; peripheral; metastasising; *BRAF V600E* common), adenomatoid odontogenic tumour, squamous odontogenic tumour, calcifying epithelial odontogenic tumour (Pindborg tumour, amyloid + calcification); mixed — ameloblastic fibroma, odontoma (compound and complex); mesenchymal — odontogenic myxoma, cementoblastoma, odontogenic fibroma; malignant — ameloblastic carcinoma, clear cell odontogenic carcinoma, sclerosing odontogenic carcinoma. The old "keratocystic odontogenic tumour" has returned to being classified a cyst (OKC).
• Fibro-osseous and giant cell lesions: fibrous dysplasia (ground-glass, *GNAS* mutation, "Chinese-letter" trabeculae, blends with normal bone), cemento-osseous dysplasias (periapical, focal, florid), ossifying fibroma (well-demarcated), central giant cell granuloma vs brown tumour of hyperparathyroidism (identical histology — must check serum calcium, phosphate and PTH), cherubism (*SH3BP2*), aneurysmal bone cyst, Paget's disease of bone (mosaic bone, raised alkaline phosphatase, hypercementosis), osteomyelitis (acute, chronic, Garrè's proliferative periostitis, chronic diffuse sclerosing), MRONJ (medication-related osteonecrosis of the jaw — bisphosphonates, denosumab, antiangiogenics), osteoradionecrosis.
• Salivary gland pathology: sialadenitis, sialolithiasis (submandibular commonest), xerostomia, Sjögren's syndrome (anti-SS-A/Ro, anti-SS-B/La, focal lymphocytic sialadenitis with focus score, risk of MALT lymphoma), necrotising sialometaplasia. Tumours: pleomorphic adenoma (commonest, *PLAG1*, chondromyxoid + epithelial, capsular pseudopodia → recurrence if enucleated), Warthin's tumour, basal cell adenoma; malignant — mucoepidermoid carcinoma (commonest malignant; *CRTC1-MAML2*), adenoid cystic carcinoma (cribriform, perineural invasion, long slow course), acinic cell, polymorphous adenocarcinoma, carcinoma ex-pleomorphic adenoma. Rule of thumb: the smaller the gland, the higher the chance a tumour is malignant.

Diagnostic methods, biopsy and laboratory technique

• Biopsy types: incisional (large or suspected malignant lesion — include the most suspicious area and a margin of normal tissue, avoid necrotic centre), excisional (small, benign-looking <1 cm), punch, aspiration (cyst vs solid; straw-coloured fluid with cholesterol in radicular cyst, "cheesy" keratin aspirate in OKC), FNAC (salivary and nodal), exfoliative cytology and brush biopsy (screening only — never a substitute for biopsy), core needle.
• Pitfalls: do not infiltrate anaesthetic into the lesion (use a block or peripheral infiltration), avoid crushing with forceps or electrocautery at the margin, do not use cautery for the specimen edge, orient and suture-mark margins, fix immediately in 10% neutral buffered formalin, 10:1 volume ratio.
• Tissue processing: fixation → decalcification for hard tissue (formic acid, EDTA) → dehydration (graded alcohol) → clearing (xylene) → impregnation and embedding (paraffin) → microtomy (4–6 µm) → staining → mounting (DPX). Ground sections are used for undecalcified enamel study.
• Stains: H&E (routine); PAS (fungi, glycogen, basement membrane); Gram; Ziehl-Neelsen (AFB); Congo red (amyloid, apple-green birefringence); van Gieson and Masson's trichrome (collagen — used in OSMF); toluidine blue (metachromasia for mast cells; also as a clinical mucosal stain); Papanicolaou (cytology); Giemsa; silver (reticulin, GMS for fungi).
• Advanced: immunohistochemistry (cytokeratins for epithelium, S-100 and SOX10 for neural/melanocytic, HMB-45 and Melan-A for melanoma, CD markers for lymphoma, Ki-67 proliferation index, p16 as HPV surrogate, p53), immunofluorescence (direct on perilesional tissue for pemphigus/pemphigoid), molecular tests (PCR, FISH, next-generation sequencing for *BRAF V600E*, *GNAS*, *CRTC1-MAML2*), frozen section for intra-operative margins, flow cytometry.
• Indian practice and law: biomedical waste segregation under the Bio-Medical Waste Management Rules, 2016 (as amended) — yellow bag for human anatomical/biopsy tissue and soiled waste, red for contaminated recyclable plastics, white puncture-proof for sharps, blue for glassware; laboratories are governed by the Clinical Establishments (Registration and Regulation) Act, 2010 in adopting states, with NABL accreditation (ISO 15189) for quality. Tobacco control rests on COTPA, 2003 (and the Prohibition of Electronic Cigarettes Act, 2019); several states ban gutkha and flavoured chewing tobacco under the Food Safety and Standards Act, 2006 regulations. Cancer registration runs through ICMR's National Cancer Registry Programme (NCRP/NCDIR); oral cancer screening is part of the NP-NCD population-based screening (oral, breast, cervical) delivered at Ayushman Arogya Mandirs.

Oral manifestations of systemic disease

• Haematological: anaemia (atrophic glossitis, angular cheilitis, Plummer-Vinson), leukaemia (gingival enlargement, bleeding, necrosis), thrombocytopenia (petechiae), sickle cell and thalassaemia (stepladder trabeculae, hair-on-end skull).
• Endocrine/metabolic: diabetes (periodontitis, candidiasis, sialosis, delayed healing — bidirectional link), hyperparathyroidism (brown tumour, loss of lamina dura), hypophosphatasia (premature tooth loss), acromegaly (macroglossia, prognathism), amyloidosis (macroglossia).
• Nutritional: vitamin C (scurvy — spongy bleeding gingiva), B-complex (glossitis, cheilosis), vitamin D (rickets, enamel hypoplasia), vitamin A (keratinisation changes).
• Immune/infective: HIV (candidiasis, hairy leukoplakia, Kaposi sarcoma, linear gingival erythema, necrotising periodontitis, aphthous-like ulcers), tuberculosis, syphilis, measles.
• Drug effects: gingival enlargement (phenytoin, cyclosporine, nifedipine), lichenoid reactions, xerostomia (anticholinergics, antidepressants), MRONJ, mucositis from chemo/radiotherapy, tetracycline staining.

Key points

• Acquired pellicle - salivary glycoprotein film on enamel; the base layer on which plaque forms.
• Dental plaque - a structured microbial biofilm in an exopolysaccharide matrix; mechanically removed, not antibiotic-treated.
• Ecological plaque hypothesis - caries results from a sugar-driven ecological shift to acidogenic flora, not a single pathogen.
• Critical pH - about 5.5 for enamel and 6.2–6.7 for dentine/cementum; below it hydroxyapatite dissolves.
• Socransky's red complex - *P. gingivalis*, *T. forsythia*, *T. denticola*; the flora of deep, bleeding pockets.
• Caries zones - enamel: translucent, dark, body, surface; dentine includes a defensive sclerotic zone.
• Radicular cyst - commonest jaw cyst; lining from rests of Malassez; cholesterol clefts and Rushton bodies.
• Odontogenic keratocyst - parakeratinised corrugated lining, palisaded basal cells, *PTCH1*, high recurrence; multiple in Gorlin-Goltz syndrome.
• Ameloblastoma - benign but locally aggressive; multilocular soap-bubble radiolucency; resection with margin, not curettage; *BRAF V600E* frequent.
• Pleomorphic adenoma - commonest salivary tumour; enucleation recurs because of capsular pseudopodia.
• OSMF - areca-nut-driven juxta-epithelial fibrosis with trismus; a potentially malignant disorder, largely an Indian disease.
• Epithelial dysplasia - architectural + cytological atypia; graded mild/moderate/severe or low/high grade; predicts transformation risk.
• OSCC in India - gingivobuccal sulcus/buccal mucosa predominance from quid habit; AJCC 8th edition includes depth of invasion and extranodal extension.
• Erythroplakia - velvety red patch with the highest malignant transformation rate of all OPMDs.
• Pemphigus vs pemphigoid - suprabasal vs subepithelial split; fishnet intercellular IgG vs linear basement-membrane IgG/C3.
• CGCG vs brown tumour - histologically identical; distinguished only by serum calcium, phosphate and PTH.
• Biopsy rule - include the lesion edge with adjacent normal tissue, avoid the necrotic centre, fix in 10% neutral buffered formalin at a 10:1 ratio.
• Biomedical waste - biopsy tissue goes in the yellow category under the Bio-Medical Waste Management Rules, 2016.

Formulas and examples

Example 1 — plaque pH and demineralisation. A plaque sample after a sugar rinse contains lactate 8 mmol/L and undissociated lactic acid 0.6 mmol/L.

• Ratio [A⁻]/[HA] = 8/0.6 = 13.33; log₁₀(13.33) = 1.125.
• pH = 3.86 + 1.125 = 4.99 ≈ 5.0.
• 5.0 < 5.5, so enamel is demineralising. It is also below the dentinal critical pH of ~6.2, so an exposed root surface would dissolve faster still — this is why root caries progresses rapidly in elderly patients with recession.

Example 2 — malignant transformation in an OSMF cohort. A dental college in Maharashtra follows 480 OSMF patients for 5 years; 36 develop OSCC.

• Crude transformation = 36/480 × 100 = 7.5% over 5 years.
• Annualised (simple division) = 7.5/5 = 1.5% per year.
• Interpretation: roughly 1 in 13 patients transformed in 5 years, far above the ~1% lifetime-order risk quoted for homogeneous leukoplakia — so OSMF warrants 6-monthly review and absolute areca-nut cessation. (Published Indian figures range widely, commonly 7–13% cumulative; cohort selection matters.)

Example 3 — caries-activity test interpretation. Two children are tested on Mitis-salivarius agar; saliva is diluted 1:100 and 0.1 mL plated. Child A yields 180 *S. mutans* colonies, Child B yields 9.

• CFU/mL = colonies × dilution factor ÷ volume plated = 180 × 100 ÷ 0.1 = 1.8 × 10⁵ CFU/mL for A.
• Child B = 9 × 100 ÷ 0.1 = 9 × 10³ CFU/mL.
• Counts above about 10⁵ CFU/mL are conventionally taken as high caries risk; A is high risk (needs diet counselling, fluoride varnish, sealants), B is low risk. Chair-side kits report the same thresholds as score classes rather than raw counts.

Example 4 — depth of invasion and T staging (AJCC 8th edition). A buccal mucosa OSCC measures 28 mm greatest surface dimension with a measured depth of invasion of 7 mm, no bone involvement.

• Size 2–4 cm alone would be T2; DOI >5 mm but ≤10 mm also places it at T2 — tumour is T2.
• Had DOI been 12 mm with the same 28 mm size, DOI >10 mm would upstage it to T3. This is why the pathology report must state DOI (measured from the basement membrane of adjacent normal mucosa) and not just thickness.

Example 5 — Sjögren labial gland biopsy. A biopsy yields 12 mm² of glandular area containing 9 lymphocytic foci.

• Focus score = 9 ÷ (12/4) = 9 ÷ 3 = 3 foci per 4 mm².
• Score ≥1 is positive, so the histopathology item is satisfied; it is combined with anti-SS-A/Ro, ocular staining, Schirmer and unstimulated salivary flow (≤0.1 mL/min) in the classification criteria.

Where it is used

• Oral pathology laboratories and histopathology reporting in dental colleges and hospitals — slide reading, grading dysplasia, margin and depth-of-invasion reporting; roles as tutor/lecturer in Oral and Maxillofacial Pathology after MDS.
• Head-and-neck oncology units (Tata Memorial Hospital, AIIMS, Regional Cancer Centres, Kidwai, Cachar Cancer Hospital) — biopsy correlation, frozen sections, multidisciplinary tumour boards, p16 and molecular testing.
• Public-health oral cancer screening under NP-NCD at Ayushman Arogya Mandirs, tobacco-cessation centres and COTPA enforcement; ICMR/NCDIR cancer registry data entry and field screening studies.
• Diagnostic labs and NABL-accredited histopathology/microbiology services (SRL, Metropolis, Dr Lal PathLabs, hospital labs) — FNAC, IHC panels, culture and sensitivity, molecular diagnostics.
• Pharmaceutical and oral-care industry — clinical and microbiological trials of toothpastes, mouthrinses (chlorhexidine, fluoride, herbal), probiotics and antifungals for firms such as Colgate-Palmolive India, HUL, Dabur, ICPA; medical-affairs and clinical-research-associate roles.
• Clinical practice — deciding which white patch to biopsy, managing OSMF and candidiasis, diagnosing periapical lesions, recognising oral signs of diabetes, HIV and leukaemia, and referring suspected malignancy early.

Interview questions

• Q: Why is mechanical plaque control more effective than antibiotics against plaque? A: Plaque is a biofilm whose matrix, slow-growing phenotype and nutrient gradients make it 10–1,000 times less susceptible to antimicrobials, so physical disruption is the reliable means of removal.
• Q: What makes *Streptococcus mutans* the chief caries pathogen? A: It is acidogenic, aciduric and acidophilic, adheres through glucosyltransferase-made insoluble glucans, and stores intracellular polysaccharide to keep producing acid between meals.
• Q: Why do root surfaces decay faster than enamel? A: Cementum and dentine have a higher critical pH (about 6.2–6.7 versus 5.5), so they demineralise at pH values that leave enamel intact.
• Q: How do you distinguish an odontogenic keratocyst from a dentigerous cyst? A: The OKC has a thin, corrugated parakeratinised lining with palisaded basal cells and a cheesy keratin aspirate and grows antero-posteriorly with little expansion; the dentigerous cyst has a thin non-keratinised lining attached at the CEJ of an unerupted tooth.
• Q: Why is ameloblastoma treated by resection rather than curettage? A: It infiltrates marrow spaces beyond the radiographic margin, so curettage leaves tumour islands and recurrence rates are high; resection with a 1–1.5 cm margin is standard.
• Q: Which oral potentially malignant disorder carries the highest transformation risk, and why is OSMF so important in India? A: Erythroplakia has the highest rate; OSMF matters because areca-nut and gutkha chewing is widespread, it causes progressive trismus and reported cumulative transformation of roughly 7–13%.
• Q: Where should an incisional biopsy be taken in a large ulcerated lesion? A: At the active periphery, including adjacent normal tissue and the full depth of the lesion, avoiding the necrotic slough at the centre, with anaesthesia placed away from the site.
• Q: What changed in oral cancer staging with AJCC 8th edition? A: Depth of invasion was added to the T category and extranodal extension to the N category, so a small but deeply invasive tumour now stages higher.
• Q: How do you tell a central giant cell granuloma from a brown tumour of hyperparathyroidism? A: They are histologically indistinguishable; serum calcium, phosphate, alkaline phosphatase and parathyroid hormone levels make the distinction.
• Q: Which single test best separates pemphigus from pemphigoid? A: Direct immunofluorescence on perilesional tissue — intercellular fishnet IgG in pemphigus, linear basement-membrane IgG/C3 in pemphigoid.
• Q: Why does a pleomorphic adenoma recur after enucleation? A: Its capsule is incomplete with tumour pseudopodia extending beyond it, so enucleation leaves tumour behind; it needs excision with a cuff of normal gland.
• Q: What is the significance of p16 immunostaining in a head-and-neck carcinoma? A: It is a surrogate marker of transcriptionally active high-risk HPV, validated mainly for oropharyngeal carcinoma, where positivity carries a better prognosis and a separate staging system; it is not a reliable HPV marker in conventional oral cavity cancers.
• Q: How is biopsy tissue handled after removal in an Indian dental set-up? A: Fixed immediately in 10% neutral buffered formalin at roughly ten times the specimen volume, labelled with site and orientation, sent with a filled requisition; residual anatomical waste goes into the yellow bag per the Bio-Medical Waste Management Rules, 2016.

Common mistakes

• Treating calculus as the direct cause of periodontal destruction instead of the living plaque biofilm it harbours.
• Quoting one critical pH for the whole tooth — enamel and root surface differ, which changes the caries-risk answer.
• Naming "keratocystic odontogenic tumour" — the current WHO classification lists it again as the odontogenic keratocyst.
• Confusing tumour thickness with depth of invasion, which is measured from the basement membrane of adjacent normal mucosa.
• Writing "leukoplakia is precancerous" without using the current OPMD terminology or giving a transformation estimate with its uncertainty.
• Injecting local anaesthetic directly into the lesion, crushing the specimen with forceps, or taking only the necrotic centre — all give non-diagnostic biopsies.
• Reporting a giant cell lesion of the jaw without excluding hyperparathyroidism biochemically.
• Mixing up pemphigus and pemphigoid split levels, or doing immunofluorescence on frankly ulcerated rather than perilesional tissue.

Related topics

Oral medicine and diagnosis · Periodontics: plaque, pocket and host response · Conservative dentistry and endodontics · Oral and maxillofacial surgery: cysts and tumours · General pathology and immunology · Public health dentistry and tobacco control.