Dental Materials V: Supplementary Exam, August 2018
Mount Kenya University · Department of Dental Sciences · Diploma in Dental Technology · BDS3103
Dental Materials V (BDS3103) past exam 2017-2018 from Mount Kenya University with model answers.
Instructions: ANSWER ALL QUESTIONS IN SECTION A.
1.
- a) Outline six ideal requirements of a dental flux.Model answer
- Ideal requirements of a dental flux
- Good wetting of metal surfaces
- Low viscosity for easy application
- Non‑toxic and non‑irritating
- Stable at high temperatures
- No residual film after firing
- Compatible with both enamel and metal
- More answers: good adhesion, easy removal, non‑corrosive
- b) Explain the function of antiflux.Model answer
- Function of antiflux
- Prevents oxidation of metal surfaces during firing
- Reduces porosity in the final restoration
- Enhances bond strength between metal and ceramic
- Protects against contamination by airborne particles
- More answers: improves aesthetics, maintains dimensional stability
- c) Outline five types of corrosion in dentistry.Model answer
- Types of corrosion in dentistry
- Galvanic corrosion
- Pitting corrosion
- Crevice corrosion
- Stress corrosion cracking
- Intergranular corrosion
- d) Explain four variables which may affect corrosion.Model answer
- Variables affecting corrosion
- Electrolyte composition (saliva, food acids)
- pH level of the environment
- Presence of metal ions and galvanic couples
- Temperature and humidity
- More answers: mechanical stress, surface roughness
- e) Outline three classifications of stainless steel.Model answer
- Classifications of stainless steel
- Austenitic (e.g., 304, 316)
- Ferritic (e.g., 430)
- Martensitic (e.g., 410, 420)
- Duplex (e.g., 2205)
- More answers: precipitation‑hardening, high‑entropy
- f) Give four uses of stainless steel in dentistry.Model answer
- Uses of stainless steel in dentistry
- Dental handpieces and burs
- Orthodontic brackets and wires
- Surgical instruments (scalpels, forceps)
- Prosthetic components (abutments, screws)
- More answers: impression trays, orthodontic bands
- g) Describe the composition of Cobalt Chromium alloy.Model answer
- Composition of Cobalt Chromium alloy
- 15–25 % Co
- 10–20 % Cr
- 0.5–2 % Mo
- 0.5–1 % Mn
- 0.5–1 % Si
- 0.5–1 % Al
- 0.5–1 % Ni (optional)
- Balance Fe and trace elements
Section B (ANSWER ANY TWO QUESTIONS) (20 marks)
2. Explain how to prevent corrosion in dental restorations.
Model answer
- Preventing corrosion in dental restorations
- Use corrosion‑resistant alloys (e.g., noble metals, stainless steel)
- Apply protective coatings (e.g., porcelain, resin cements)
- Maintain neutral pH in the oral cavity (diet, fluoride)
- Avoid galvanic couples by matching metal types
- Ensure proper polishing and surface finish
- More answers: regular check‑ups, use of antioxidants
3. Describe how to extract Titanium using magnesium reduction method. (20 marks)
Model answer
- Magnesium reduction of titanium dioxide
- Mix TiO₂ powder with excess Mg powder in a crucible.
- Heat to ~1200 °C under inert atmosphere (Ar or N₂) to prevent oxidation.
- Mg reduces TiO₂ to Ti metal, forming MgO as by‑product.
- Cool, then leach MgO with dilute HCl or water to recover pure Ti.
- Final product is sponge‑like Ti, which can be further processed.
4. Appraise use of Titanium and its alloys in dentistry. (20 marks)
Model answer
- High strength‑to‑weight ratio – ideal for implants.
- Excellent corrosion resistance in oral fluids.
- Biocompatibility – minimal allergic reactions.
- Osseointegration – promotes bone bonding.
- Low modulus of elasticity – reduces stress shielding.
- Alloying options (Ti‑6Al‑4V, Ti‑6Al‑7Nb) tailor mechanical properties.
- Surface modifications (hydroxyapatite coating) enhance integration.
- More answers: long‑term stability, cost, and fabrication techniques.