Past Paper Questions Flashcards
List the constituents of Gutta percha?
- 20% gutta percha- 65% zinc oxide- 10% radiopacifiers- 5% plasticisers
What are some reasons for obturating a canal?
- Promote heamatic sealing- Seal canal laterally and apically- Prevent bacteria from entering canal and periapical tissues to potentially cause perio-endontic lesion
What properties make calcium hydroxide a suitable pulp capping material?
- Promotes tooth remineralisation- Anti-microbial properties- Anti-endotoxin properties
How can you test for irreversible pulpitis?
- Pulp sensitivity test- TTP test- Electric pulp test- Always test contralateral adjacent teeth so pt knows normal response- Normal test show healthy pulp/reversible pulpitis
What is the purpose of sealer when obturating canal?
- Seals space between wall and core- Lubricates GP cones- Fills voids and irregularities between GP cone tips, from lateral condensation
What are the main differences in composition between decorative and dental ceramic?
- Kaolin 50% in decorative and Kaolin <5% dental- Feldspar/silica added to about 15-25% in dental ceramic- Glass 0% in decorative but 15% in dental- Kaolin removed as this is opaque which is bad for dental aesthetics
Definition of translucency?
- Physical property meaning light can pass through material without significant scattering, we need different materials to be different levels of translucent to be able to imitate dentin and enamel for better aesthetics
Definition of Opalescence?
- Material that reflects light and changes its colour, typically light refracted back is white/pale/colourless
How can you modify ceramic surface to make it more retentive prior to using silane?
- Acid etch with hydrofluoric acid
Functions of a provisional crown?
- Protection of prepared tooth from further damage, sensitivity and bacterial invasion- Comfort for pt by reduce sensitivity and discomfort when biting down- Aesthetics which can help with confidence and self esteem- Function like normal chewing, speech, oral hygiene- Evaluation of crown for fit, function, aesthetics and dentist can make any necessary adjustments for final restoration
Name types of prefabricated crowns
- Stainless steel crowns- Zirconia crowns- Polycarbonate crowns- Resin crowns- Ceramic crowns like procelain
Disadvantages and advantages of prefabricated crown
Advantages- Very convenient as only need one visit to be placed- Cost effective as they are cheaper than custom made crowns- Time saving and are useful for children or anxious pt who find long appointments stressful- Dentist can anticipate final result with high degree of accuracy due to standard sizes and shapesDisadvantages- Limited customisation as come in standard shapes and sizes- Limited durability compared to custom made- Limited longevity compared to custom made esp if pt have history of grinding teeth or decay- Aesthetics aren’t as good as custom made esp important in anterior teeth where aesthetics main want
Name constituents of SS and their proportions
- Iron 72%- Carbon <2%- Chromium 17-19%- Nickel 7-9%
What is work hardening?
- Material subjected to cycles of deformation (stress or strain)- Atoms displaced from orig positions - Create defects or dislocations in crystal structure- Dislocations hinder motion of atoms and create and create barriers to slip- Makes metal harder and stronger- Excessive can make metal brittle and prone to fracture
What is meant by springiness?
- Ability of material to undergo large deflections (to form an arc) without permanent deformation (return to original shape)- Calculated as EL/YM
How to decontaminate the impression?
- Gloves- Rinse in water- Place in perform for 10mins- Clean gloves remove imp and rinse under cold water- Wrap slightly damp tissue around and place in bag- Send to lab with prescription
How is porcelain surface prepped in lab for bonding?
- Surface is cleaned using solvent like alcohol- Acid etch with 10% hydrofluoric acid to create surface irregularities- Silane coupling agent to etched surface to promote adhesion between porcelain and bonding agent- Dryed and light cured
What do you use to bond porcelain to composite luting resin?
- Silane coupling agent
How does silane coupling agent act chemically?
- Forms covalent bond between silicone atom in silane and oxygen atoms in porcelain which provides strong and stable attachment- Methacrylate group on other end of silane coupling agent form C=C covalent bond with composite luting agent to help bond porcelain to tooth structure
When would you use dual cured? Why would you still light cure a dual cured?
- Fibre post- Zirconia cure- Composite inlay- Porcelain inlay- Light curing done to ensure complete curing of luting agent - If contains HEMA this is cytotoxic if not completely polymerised and can lead to postoperative sensitivity - Can also improve mechanical properties of luting agent like strength and hardness and wear resistance
What do you do to metal in lab to prepare ?
- Sandblasted to roughen surface to give retention- MDP and 4-META to bond
What metal can be used for acid-etch retained bridge?
- CoCr- NiCr
What is the function of silane in composite restorative material?
- Promote adhesion between composite material and tooth structure- Forms covalent bond between silicone atom in silane and oxygen atoms in porcelain which provides strong and stable attachment- Methacrylate group on other end of silane coupling agent form C=C covalent bond with composite luting agent to help bond porcelain to tooth structure
