Basic Medical and Dental Sciences: Applied Oral Anatomy, Histology, Physiology, Microbiology, Pathology and Pharmacology
Basic Medical and Dental Sciences
This domain tests the science the practical domains rest on: tooth morphology and eruption, histology of enamel, dentine, cementum and pulp, oral physiology and occlusion, oral microbiology, pathology, and pharmacology. Questions are usually applied - a clinical or laboratory situation is described and you choose the principle that explains it.
Morphology and eruption points examiners reuse
- Primary molars are narrower mesiodistally than the premolars that replace them; the resulting leeway (primate spaces) lets the permanent first molar drift mesially during the mixed dentition.
- Eruption chronology to memorise: first molars ~6 years, central incisors 6–7, laterals 7–8, first premolars 9–10, second premolars 10–12, canines 11–12, second molars 12–13.
- The mandibular first premolar has a small, often non-functional lingual cusp; mandibular second premolars vary most in cusp number (2-, 3- and Y-patterns).
- Enamel rods run from the dentino-enamel junction outward, deviating occlusally in permanent teeth and gingivally in primary teeth - hence the different bevel direction for primary crowns.
Microbiology, pathology and pharmacology core
Caries is a biofilm and sugar-driven process; Streptococcus mutans and Lactobacillus are the acidogenic, aciduric organisms associated with advancing lesions. Pulpal and periapical disease is polymicrobial and largely anaerobic, progressing from reversible pulpitis through irreversible pulpitis and necrosis to periapical periodontitis and granuloma or cyst. For local anaesthetics, only the uncharged base form crosses the nerve membrane, and vasoconstrictors prolong duration by slowing systemic absorption.
Worked example
A stem states that 2% lidocaine with 1:100,000 epinephrine gives a longer, deeper mandibular block than plain 2% lidocaine. Reasoning: pKa and onset in healthy tissue are identical; the vasoconstrictor constricts local vessels, less drug is carried away, more stays near the nerve, duration extends from roughly 1–1.5 hours to 2–3 hours, and peak plasma concentration falls. Then add the caveat the examiner wants: in acutely inflamed, acidotic tissue the base fraction drops, so onset is slow and depth poor regardless of the vasoconstrictor.
Traps that cost marks
Mixing primary and permanent eruption years; assuming primary crowns are scaled-down permanent crowns (they are flatter and markedly constricted cervically); and forgetting that the uncharged base, not the hydrochloride salt, penetrates the nerve sheath.