ORE Part 1 Oral Biology & Pathology 1 — Questions and Answers
Question 1: What is the major inorganic component of dental enamel?
- Hydroxyapatite [Ca10(PO4)6(OH)2] — approximately 96% by weight (Correct answer)
- Calcium phosphate only
- Collagen
- Fluorapatite
Correct answer: Hydroxyapatite [Ca10(PO4)6(OH)2] — approximately 96% by weight
Dental enamel is approximately 96% inorganic by weight, primarily hydroxyapatite (calcium hydroxyapatite). The remaining 4% is water and organic matrix. This makes enamel the hardest biological substance in the human body.
Question 2: What is the aetiology of dental caries according to the Keyes Circle?
- Interaction of three factors: susceptible host (tooth), cariogenic microorganisms (Streptococcus mutans, Lactobacilli), and fermentable substrate (sugars) — all three must be present (Correct answer)
- Single bacterial infection without diet involvement
- Fluoride deficiency alone
- Genetic susceptibility alone
Correct answer: Interaction of three factors: susceptible host (tooth), cariogenic microorganisms (Streptococcus mutans, Lactobacilli), and fermentable substrate (sugars) — all three must be present
The Keyes model (later expanded to include time) describes caries as arising from the interaction of susceptible tooth surfaces, cariogenic bacteria, and dietary fermentable carbohydrates over time.
Question 3: What is the histological appearance of the 'resting line' in cementum?
- Dark lines (incremental lines) representing periods of reduced cementogenesis, similar to von Ebner lines in dentine (Correct answer)
- The CEJ between enamel and cementum
- Cracks caused by occlusal loading
- Areas of secondary cementum deposition
Correct answer: Dark lines (incremental lines) representing periods of reduced cementogenesis, similar to von Ebner lines in dentine
Resting lines in cementum represent periods of reduced or absent cementum deposition during tooth development. They appear as distinct basophilic lines histologically, marking cyclical growth phases.
Question 4: Which cells are responsible for dentine formation?
- Odontoblasts (Correct answer)
- Ameloblasts
- Cementoblasts
- Osteoblasts
Correct answer: Odontoblasts
Odontoblasts are the dentine-forming cells derived from neural crest cells. They line the pulp chamber and extend processes into dentinal tubules (Tomes' fibres), producing predentine which mineralises to become dentine.
Question 5: What is 'scalloped' basement membrane in the gingival epithelium?
- The undulating interface between the epithelium and underlying connective tissue, formed by rete ridges and connective tissue papillae (Correct answer)
- The CEJ morphology
- The scalloped gingival margin shape
- The attachment of junctional epithelium to enamel
Correct answer: The undulating interface between the epithelium and underlying connective tissue, formed by rete ridges and connective tissue papillae
The gingival epithelium has a scalloped (rete ridge) interface with the lamina propria. Rete ridges interdigitate with connective tissue papillae, increasing surface area and enhancing mechanical attachment.
Question 6: What is the role of salivary immunoglobulin A (IgA) in oral defence?
- Provides mucosal immunity by binding antigens and preventing bacterial adherence to oral surfaces without invoking complement (Correct answer)
- Acts as an opsonin for phagocytosis
- Neutralises bacterial endotoxins in the bloodstream
- Forms antibody-antigen complexes that trigger inflammation
Correct answer: Provides mucosal immunity by binding antigens and preventing bacterial adherence to oral surfaces without invoking complement
Secretory IgA (sIgA) is the predominant antibody in saliva. It agglutinates bacteria and blocks their adhesion to mucosal surfaces, providing non-inflammatory first-line immune defence without complement activation.
ORE Part 1 Oral Biology & Pathology 1
What is the major inorganic component of dental enamel?