Overseas Registration Exam (ORE) Oral Biology, Anatomy and Dental Materials Science Syllabus

Give the dental formula for the permanent and primary human dentitions.

Permanent: $\frac{2\,1\,2\,3}{2\,1\,2\,3}$ per side (I, C, PM, M) = 32 teeth. Primary: $\frac{2\,1\,0\,2}{2\,1\,0\,2}$ per side (I, C, M) = 20 teeth (no premolars).

Which permanent tooth typically has three roots, and how are they arranged?

The maxillary first molar usually has three roots: two buccal (mesiobuccal and distobuccal) and one palatine (lingual). The mesiobuccal root commonly has two canals (MB1 and MB2).

How does the FDI two-digit tooth notation work?

The first digit is the quadrant (1–4 permanent, 5–8 primary; numbered clockwise from upper-right) and the second digit is the tooth (1 central incisor to 8 third molar). For example, tooth 36 is the lower-left permanent first molar.

List the stages of tooth development.

Initiation (bud stage), proliferation (cap stage), histodifferentiation and morphodifferentiation (bell stage), apposition, and maturation/eruption. The enamel organ, dental papilla, and dental follicle form the tooth and its supporting tissues.

What is reciprocal induction in odontogenesis?

Reciprocal signalling between the oral epithelium (enamel organ) and the underlying neural-crest-derived ectomesenchyme (dental papilla). The epithelium induces odontoblast differentiation (forming dentine), and dentine then induces ameloblasts to form enamel.

State the typical eruption sequence and age of the first primary and first permanent teeth.

First primary tooth: mandibular central incisor at about 6 months. First permanent tooth: mandibular first molar (the '6-year molar') at about 6 years. Eruption is generally mandibular before maxillary.

State the major inorganic and organic components of saliva and its daily volume.

Mainly water (about $99\%$); ions include $\ce{Na+}$, $\ce{K+}$, $\ce{Cl-}$, $\ce{HCO3-}$, $\ce{Ca^2+}$, $\ce{PO4^3-}$; organics include amylase, lysozyme, lactoferrin, IgA, and mucins. About $0.5\text{–}1.5\,\text{L}$ is produced per day.

Name the three major salivary glands and their relative secretory contributions and secretion types.

Parotid (about $25\%$, serous), submandibular (about $60\text{–}70\%$, mixed seromucous), and sublingual (about $5\%$, predominantly mucous). At rest the submandibular gland contributes most saliva.

List four protective functions of saliva.

Buffering acids (bicarbonate/phosphate systems), remineralisation (supplying $\ce{Ca^2+}$ and $\ce{PO4^3-}$), antimicrobial action (lysozyme, lactoferrin, IgA), and lubrication/digestion (mucins and amylase). It also aids taste and clearance of debris.

Describe the three phases of deglutition (swallowing).

1) Oral phase (voluntary): bolus pushed posteriorly by the tongue. 2) Pharyngeal phase (involuntary): soft palate elevates, larynx rises, epiglottis closes the airway. 3) Oesophageal phase: peristalsis carries the bolus to the stomach.

Name the five basic tastes and the receptor type for each.

Sweet, umami, and bitter act via G-protein-coupled receptors (taste type 1 and type 2 receptors); salty and sour act via ion channels ($\ce{Na+}$ channels for salty, $\ce{H+}$ for sour). Taste is carried by CN VII, IX, and X.

Give the chemical formula of hydroxyapatite and its acid-dissolution behaviour.

Hydroxyapatite is $\ce{Ca10(PO4)6(OH)2}$. It dissolves when oral pH falls below the critical value of about $5.5$: $\ce{Ca10(PO4)6(OH)2 + 8H+ -> 10Ca^2+ + 6HPO4^2- + 2H2O}$.

How does fluoride convert hydroxyapatite to a more acid-resistant form?

Fluoride replaces the hydroxyl group to form fluorapatite, $\ce{Ca10(PO4)6F2}$, which has a lower critical pH (about $4.5$), making enamel more resistant to acid dissolution and promoting remineralisation.

Explain the de/remineralisation balance and the critical pH concept.

Enamel demineralises when the surrounding fluid is undersaturated with respect to hydroxyapatite (pH below about $5.5$) and remineralises when supersaturated. Caries results when demineralisation persistently exceeds remineralisation.

Define the dental plaque biofilm and describe its matrix.

Dental plaque is a structured microbial biofilm of bacteria embedded in an extracellular polymeric matrix of polysaccharides (e.g. glucans from sucrose), proteins, and DNA, adherent to the acquired pellicle on the tooth surface.

Outline the stages of dental plaque formation.

1) Acquired pellicle forms from salivary glycoproteins. 2) Initial reversible adhesion of early colonisers (e.g. Streptococci). 3) Irreversible attachment and co-aggregation. 4) Maturation into a climax community with increasing anaerobes and species diversity.

Name the key cariogenic bacteria and explain why they cause caries.

Streptococcus mutans and Lactobacillus species. They are acidogenic (ferment sugars to acid) and aciduric (survive at low pH), and S. mutans synthesises adhesive glucans from sucrose, promoting biofilm accumulation and enamel demineralisation.

State the ecological plaque hypothesis of caries.

Disease results from a shift in the balance of the resident plaque microbiota driven by environmental change. Frequent sugar intake and low pH select for acidogenic/aciduric species (e.g. S. mutans), causing caries rather than a single specific pathogen.

Name the bacteria associated with periodontal disease ('red complex').

The red complex of Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola. These are Gram-negative anaerobes associated with mature subgingival plaque and chronic periodontitis.

Differentiate the innate and adaptive immune defences of the oral cavity.

Innate (immediate, non-specific): saliva (lysozyme, lactoferrin), epithelial barrier, neutrophils, complement, and gingival crevicular fluid. Adaptive (specific, slower): T and B lymphocytes producing antibodies, including secretory IgA in saliva.

List the five cardinal signs of acute inflammation and their Latin names.

Redness (rubor), heat (calor), swelling (tumor), pain (dolor), and loss of function (functio laesa). These result from vasodilation, increased vascular permeability, and leukocyte infiltration.

Define stress, strain, and Young's modulus as applied to dental materials.

Stress is force per unit area, $\sigma = \frac{F}{A}$; strain is fractional deformation, $\varepsilon = \frac{\Delta L}{L_0}$; Young's modulus (stiffness) is $E = \frac{\sigma}{\varepsilon}$. A high modulus means a rigid material; a low modulus means a flexible one.

Define the coefficient of thermal expansion and its relevance to restorations.

It quantifies dimensional change per degree of temperature change. A mismatch between a restoration and tooth structure causes percolation (marginal gap opening/closing with temperature changes), leading to microleakage. Composite ideally matches tooth thermal expansion.

What is the difference between a thermoplastic and a thermosetting polymer in dentistry?

Thermoplastics (e.g. some denture liners) soften repeatedly on heating and are not cross-linked. Thermosets (e.g. set acrylic, composite resin) form irreversible cross-links on curing and cannot be re-melted. Most denture bases are heat-cured thermoset PMMA.

Classify dental impression materials into elastic and non-elastic groups.

Elastic: hydrocolloids (reversible agar, irreversible alginate) and elastomers (polysulphide, condensation silicone, addition silicone/PVS, polyether). Non-elastic (rigid): impression plaster, impression compound, zinc oxide eugenol, and waxes.

Compare addition silicone (PVS) and polyether impression materials.

PVS (addition silicone) is hydrophobic, highly accurate, dimensionally stable, releases no by-product, and is very elastic. Polyether is hydrophilic (works in moisture), very accurate, but stiff (hard to remove) and absorbs water if stored in humidity, distorting the impression.

State the setting reaction of gypsum products and how W:P ratio affects strength.

$\ce{(CaSO4)2 \cdot H2O + 3H2O -> 2CaSO4 \cdot 2H2O}$ (calcium sulphate hemihydrate to dihydrate), an exothermic reaction. A lower water:powder ratio gives a denser, stronger model. Dental stone needs less water than plaster because its particles are denser and less porous.

Compare the key properties of dental amalgam and resin composite as restorative materials.

Amalgam: high compressive strength, durable, cheap, non-adhesive (needs mechanical retention), non-aesthetic, contains mercury. Composite: tooth-coloured, bonds via acid-etch/adhesive, but undergoes polymerisation shrinkage and is more technique-sensitive and wear-prone in load-bearing areas.

Explain the setting and adhesion mechanism of glass ionomer cement (GIC).

GIC sets by an acid-base reaction between fluoroaluminosilicate glass powder and polyacrylic acid liquid, forming a salt/hydrogel matrix. It bonds chemically to tooth structure (ionic exchange with $\ce{Ca^2+}$) and releases fluoride, but is brittle and has low fracture toughness.

Name common luting (cementing) materials and a key feature of each.

Zinc phosphate (high strength, no adhesion, low pH initially), glass ionomer (chemical bond, fluoride release), resin-modified GIC (combines fluoride release with improved strength), and resin cements (highest strength and bond, used for ceramics/veneers but technique-sensitive).

Compare the general properties of metals, ceramics, and polymers used in dentistry.

Metals (e.g. cobalt-chromium, gold alloys, titanium): strong, ductile, tough, good thermal/electrical conductors, but non-aesthetic. Ceramics (e.g. porcelain, zirconia, lithium disilicate): hard, aesthetic, biocompatible, but brittle (low tensile strength). Polymers (e.g. PMMA, composite resin): light, flexible, easily processed, but lower strength and wear resistance.