Which of the following is correct?
(A) Retention is increased with increased taper
(B) Resistance is increased with decreased height
(C) Retention is increased with decreased width
(D) Resistance is increased with increased height
D)
Name four contraindications for a PFM?
- More conservative method available
- Poor oral hygiene
- Uncontrolled caries or periodontal disease
- Age → Pulpal considerations (more space required for material)
- Insufficient tooth structure
Which of the following is correct in regard to impression material
(A) Alginate has excellent long term stability
(B) PVS is hydrophillic
(C) Polyether has poor taste
(D) Agar is irreversible hydrocolloid
(C)
What are 5 ideal characteristics of impression materials?
o Biocompatible o Elastic o Prevents tearing during removal o Good flow o Fluid enough to adapt to tissue but viscous enough to remain in tray o Easy manipulation o Dimensionally stable after setting o Cheap and available o Quick setting time (<5min) o Long shelf life
Which of the following is false about PVS?
(A) Has the least polymerisation shrinkage compared to other elastomers
(B) Allows for second and third pours
(C) Setting is inhibited by latex gloves and rubber dam
(D) Cold decreases setting time
(D) Cold increases setting time (heat decreases the setting time)
What are three advantages of polyether compared to PVS?
- Hydrophillic (to an extent - moderate)
- Snap-set mechanicm
- Setting not affected by latex
In regard to impression taking techniques:
(A) Dual phase does not require a special tray and therefore popular in private practice
(B) Monophase can be used with polyethers and polysulphides
(C) Putty wash involves light body PVS and condensation silicone putty
(D) Metal stock tray can be used for monophase technique
(B)
(A) Requires special tray
(C) Use addition silicone putty
(D) Special tray only
Briefly explain what you aim to capture in an ideal impression?
o Record all surfaces of prepared tooth
Axial and proximal walls
Occlusal surface
Entire margin
Emergence profile: Impression penetration into the sulcus to capture tooth surface apical to margin
o All teeth in arch and appropriate soft tissue adjacent to prepared tooth
o Free of air bubbles, tears, thin spots, and drag marks
What are the biological requirements of provisionalisation? Name five.
- Protect pulp from chemical and thermal irritants (primarily of the provisional material)
- Protect exposed dentinal tubules
- Maintain occlusal and positional stability (ie. maintain inter and intraarch stability)
- Prevent fracturing of tooth
- Maintain periodontal health
Which of the following is false in regard to provisionalisation materials?
(A) PMMA has the greatest exothermic heat
(B) PRMA is radiolucent
(C) Microfilled resin composites are commonly used as they are cost-effective
(D) Light-cured materials have low aesthetic qualities
(C) They are expensive but generally used due to other advantageous characteristics:
- Good aesthetics
- High polishability, trimming and contouring
- Less exothermic reaction
- Less shrinkage
- Minimal odour
- Radiopaque
Why is the indirect-direct technique used?
- Multiple provisional restorations – reduces chair-side time
- Avoid exposure of patient to adverse properties of acrylic resin (e.g., toxic and heat)
- Optimise material properties
- Use materials that don’t polymerize intraorally
- Make significant contour or occlusal changes
What is considered “ideal lighting” when shade matching
Diffuse, comfortable for eyes, controlled, stable and constant
Daylight at 10am and 2pm on sunny day
OR
Colour-corrected fluorescent lighting (5000-6500K; CRI = 90-98)
What factors affect corrosion of a metal alloy in dental prosthetics?
- Phase structure –> Multiple phases increase
- Low pH in oral cavity (e..g caries)
- High atomic weight percentage = More atoms available to be released –> React and therefore corrosion
- Nickel and copper generally corrode more
- High percentage of NON noble metals generally increase corrosion
List five ideal properties of luting agent
o High resistance to microleakage and erosion
o Low solubility with intraoral fluids
o Biocompatible (non-toxic and anticariogenic)
Low pH of luting agents can irritate pulp
If >1mm dentine thickness, pH is buffered
Provide insulation for metal crowns
o Low viscosity and film thickness
Flow required to cover surface roughness and displace during seating
- Intermediate modulus of elasticity
- High strength and toughness
- High resistance to plastic deformation
- Working and setting time appropriate for clinical needs
- Easy manipulation
- Colour stable
- Radio-opaque
Which luting agent possesses the following characteristics:
- Film thickness of 25 microns
- Chemical bonding for retention
- Good biocompatability
- High solubility
- Low compressive strength
(A) Zinc phosphate
(B) Zinc polycarboxylate cement
(C) GIC
(D) Resin-based cement
(C)
(A) Biocompatibility low as toxic (although clinically acceptable) and not chemical bonding
(B) Does not have high solubility and film thickness is higher (high viscosity)
(D) Not chemical bonding, has low solubility, high compressive strength and film thickness is higher
Briefly explain pretreatment of restorations - metal, glass ceramic and zirconia
Pre-treatment of restoration
Metal → Rinse with water/alcohol + air dry
Glass ceramic → Hydrofluoric etch + wash + air dry +silane
Zirconia → Sandblast + wash/alcohol + air dry + primer
OR Zirconia cleaner + wash + air dry + primer
Briefly explain five considerations when selecting an abutment tooth for a bridge?
• Assess: o Vitality o Remaining tooth structure fore resistance and retention o Mobility o Periodontal health
• Crown:Root ratio
o Resistance to lateral forces
o Ideal 2:3
o Maximum acceptable 1:1
• Root configuration
o Size
o Shape
o Number – E.g. Multirooted splayed roots more support than single conical root
• Abutments to pontic
o Ante’s Law: Root surface area of abutment teeth must be greater than or equal to the teeth being replaced
o Tylman: Need at least one abutment for each pontic
What are ideal properties of core materials?
o High compressive strength o Sufficient flexural strength to prevent flexure of core o Biocompatible with oral tissues o Resistant to leakage o Easily manipulated o Ability to bond to tooth structure o Dimensionally stable o Minimal potential to absorb water o Bactericidal/static
What is the purpose of posts and what are ideal properties of a post?
Purpose
- Retains cores
- Stabilises root
- DOES NOT retain the crown
Ideal properties: As long as practical Minimise width of post → Maintain as much dentine as possible Conform to the root shape Centered within the root Parallel as possible Have no sharp line angles Be a separate post-core from the crown Be anti-rotational Contain a cementation groove to reduce the pressures that occur on cementation
