Crown and Bridge III: Main Exam, 13 December 2018

Mount Kenya University · Department of Dental Sciences · Diploma in Dental Technology · BDS3102

Crown and Bridge III past exam, BDS3102, Mount Kenya University, 2018-2019, includes model answers.

Section A (ANSWER ALL QUESTIONS)

1.

  1. a) Write short notes on connector design.
    Model answer
    • Connector design: small, rounded, and smooth to minimise stress concentration.
    • Should be the narrowest part of the bridge to reduce cantilever forces.
    • Provides mechanical retention between pontic and abutment crowns.
    • Should be contoured to match the gingival margin for esthetics.
  2. b) Write short notes on mechanical bonding.
    Model answer
    • Mechanical bonding
    • Roughening of the metal surface increases surface area.
    • Application of a metal primer or bonding agent.
    • Use of a high‑strength resin cement.
    • Proper isolation to avoid contamination.
    • Light curing or chemical curing to set the cement.
    • The resulting bond resists micromovement and improves fracture resistance.
  3. c) State for uses of a solder.
    Model answer
    • Uses of a solder
    • Joining metal components in the substructure.
    • Filling gaps between alloy parts.
    • Providing a smooth surface for ceramic layering.
    • Adjusting the fit of the metal framework.
    • Enhancing the strength of the substructure.
  4. d) Outline five soldering defects.
  5. e) State the requirements of a filler material.
  6. f) Briefly explain chemical bonding in metal ceramic fabrication.
    Model answer
    • Chemical bonding in metal‑ceramic fabrication
    • Oxide layer forms on metal surface.
    • Ceramic glaze reacts with the oxide.
    • Formation of a strong chemical bond at the interface.
    • This bond resists micromovement and improves longevity.

Section B

2. Discuss the causes, presentation and possible solutions for defects for metal substructure for crown and bridge. (20 marks)

Model answer
  • Causes of defects in metal substructure
  • Poor alloy composition.
  • Inadequate alloying or casting technique.
  • Improper cleaning or surface preparation.
  • Excessive or uneven soldering.
  • Inadequate curing of resin cement.
  • Presentation
  • Porosity, cracks, warping, or misfit.
  • Possible solutions
  • Use correct alloy specifications.
  • Refine casting protocols.
  • Thorough cleaning and surface treatment.
  • Controlled soldering with proper temperature.
  • Accurate cementation procedures.
  • Regular quality checks and adjustments.

3. Discuss general principles in metal ceramic fabrication. (20 marks)

Model answer
  • General principles in metal‑ceramic fabrication
  • Selection of compatible materials – alloy and ceramic.
  • Proper cleaning and isolation of the metal.
  • Controlled firing schedules to avoid thermal shock.
  • Layering technique – correct thickness and sequence.
  • Use of bonding agents for chemical adhesion.
  • Quality inspection at each stage.
  • Documentation of procedures for reproducibility.

4. Discuss factors affecting body strength. (20 marks)

Model answer
  • Factors affecting body strength
  • Alloy composition – high strength alloys improve resistance.
  • Casting technique – proper gating and cooling reduce defects.
  • Soldering quality – complete fusion and minimal porosity.
  • Ceramic layering – uniform thickness and proper firing.
  • Cementation method – adequate bonding and fit.
  • Thermal cycling – repeated expansion/contraction can weaken.
  • Occlusal forces – high loads increase stress.
  • Moisture control – prevents corrosion and degradation.

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