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BDS4 > Restorative - DMS > Flashcards

Restorative - DMS Flashcards

1
Q

Irrigants have a central role in endodontic treatment.
Ideal Properties of Irrigants

A

 Facilitate removal of debris
 Give lubrication
 Dissolution of organic and inorganic matter
 Penetration to canal periphery
 Kill bacteria/ yeasts/ viruses
 Biofilm disruption
 Biological compatibility
 Does not weaken tooth structure

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2
Q

Obturation Materials-
Ideal Properties of Obturation Materials

A

 Easily manipulated with ample working time
 Dimensionally stable by tissue fluids
 Seals the canal laterally and apically
 Non-irritant
 Impervious to moisture
 Unaffected by tissue fluids
 Inhibits bacterial growth
 Radiopaque
 Does not discolour tooth
 Sterile
 Easily removed if necessary

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3
Q

Gutta Percha Points what are some of the thigs it is made of?

A
  • 20% GP
  • 65% Zinc Oxide; filler
  • 10% radiopacifiers; so shows up on radiograph
  • 5% plasticizers
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4
Q

Endo Sealer Functions-

A
  1. Seals space between dentinal walls and core
  2. Fills voids and irregularities in canal, lateral canals and between GP points using in lateral condensation
  3. Lubricates during obturation
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5
Q

Ideal Properties of a Sealer-

A

 Exhibits tackiness to provide good adhesion
 Establishes a hermetic seal
 Radiopacity
 Easily mixed
 No shrinkage on setting
 Non-staining
 Bacteriostatic or does not encourage growth
 Slow set
 Insoluble in tissue fluids
 Tissue tolerant
 Soluble on retreatment

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6
Q

How does biodentine work?

A

Biodentine is found to be associated with high pH (12) and releases calcium and silicon ions which stimulates mineralization and create “mineral infiltration zone” along dentin-cement interface imparting a better seal.

Can be used to repair perforations and as a pulp cap

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7
Q

What properties make biodentine better than MTA

A

Biodentine and MTA showed comparable cell biocompatibility.

Biodentine was superior to MTA in terms of sealing ability when used as a root-end filling material.

Biodentine™ does not require a two step restoration procedure as in the case of MTA. Easier to work with.

As the setting is faster, there is a lower risk of bacterial contamination than with MTA.

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8
Q

Composite-
1. How does the clinical presentation of caries compare to the radiograph?

A
  • Caries deeper clinically
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9
Q

Give three advantages of composite over amalgam?

A
  • Minimal preparation- less tooth tissue removal required as no need for undercuts
  • Better aesthetics as tooth coloured and range of shade choices
  • Able to bond to tooth surface
  • On demand set- extended working time
  • Low thermal conductivity
  • Elimination of galvanism
  • Bonding allow better marginal seal
  • Better support for remaining tooth tissue- less likely to get sensitivity on pressure due to better transmission of masticatory forces
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10
Q
  1. What are the components of composite?
A
  • Resin- Bis GMA
  • Glass filler particles- quartz or silica
  • Photoiniatior- camphorquinone
  • Silane coupling agents
  • Low weight dimethacrylate- TEGMA
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11
Q
  1. Name four types of composite?
A
  • Microfiled
  • Macrofilled/ Heavily filled
  • Nanfiled (submicron)
  • Hybrid
  • Flowable
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12
Q
  1. What are the clinical disadvantages of composite and how are they minimised?
A
  • Polymerisation contraction stress- consider configuration factor and ensure it is low on placement of composite by placing in increments. Not joing buccal and palatal walls together with one increment for example.
  • Moisture sensitive- isolate tooth efficiently using dental dam
  • Post-operative sensitivity- ensure correct placement of composite, moisture control and adequate bonding procedure to minimise contraction nd microleakage (warn patient)
  • Under-polymerised base- don’t bulk fill and place in 2mm increments which are cured separately
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13
Q

Amalgam-
1. What is the setting reaction for amalgam?

A
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14
Q
  1. What changes have been made to modern amalgam to improve it?
A
  • Y2 phase has poor strength and corrosion resistance
  • Modern amalgam has high copper content to reduce this
  • The copper reacts with time to reduce the availability of tin for formation of the Y2 phase
  • Zin is also no longer used at it interacts with water causing a poor marginal seal
  • Use of spherical cut (less mercury required, higher tensile strength, less sensitive to condensation, higher early compressive strength)
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15
Q
  1. What are the advantages of amalgam?
A
  • Durable/Strong/High mechanical strength- higher compressive and tensile strength than composite
  • Long term resistance to surface corrosion- harder and higher abrasion resistance than composite
  • Radiopaque
  • Low creep and microleakage (in modern form)
  • Shorter placement time than composite
  • Easy to hand and fast setting time
  • Less finishing required
  • Colour contrast allows secondary caries to be easily sported
  • Economical- relatively cheap
  • High elastic modulus that composite
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16
Q
  1. What are the disadvantages of amalgam?
A
  • Poor aesthetics
  • Does not bond to tooth
  • Thermal diffusivity is high (much higher than amalgam)
  • High thermal conductivity and expansion (coefficient)
  • Cavity preparation may require destruction of sound tooth tissue
  • Marginal breakdown may be an issue
  • Long term corrosion at restoration interface may resulting in ditching (leading to need for replacement or repair)
  • Weak in thin sections
  • Local sensitivity (lichenoid tissue) reaction may occur
  • Galvanic response can occur if two amalgam restoration next to each other
  • Tooth and soft tissue discolouration (amalgam tattoo) possible
  • Mercury is not environmentally friendly (concern about toxicity)
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17
Q
  1. What are the advantages of using non-y2 amalgam? (2) (with copper)
A
  • Higher early strength
  • Less creep
  • Higher corrosion resistance
  • Increase durability of margins
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18
Q
  1. How to remove y2 from amalgam? (2)
A
  • Use copper enriched amalgams
  • To make copper enriched amalgams either use dispersion modified method or single composition
  • Dispersion method- initial reaction as for conventional amalgam but y2 is then removed by its reaction with silver-copper; copper preferentially reacts with tin displacing the mercury which then forms more y1
  • Single composition- use of silver, copper, tin powder which is then missed with conventional liquid mercury forming unreacted silver-copper-tin, y1 and copper tin
  • Can also help to polish margins and avoid galvanic cells
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19
Q
  1. Why was zinc added to amalgam? (2)
A
  • Act as a scavenger (chemical which removes or de-activates unwanted reaction products and impurities) to preferentially oxidise and remove slag
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20
Q
  1. What occurs as a result of zinc being added to amalgam? (1)
A
  • (Delayed) Expansion of amalgam
  • Patients can experience pulpal pain as a result of downward pressure on the pulp

  • Zinc interacts with water particles in saliva/blood to form zinc oxide and hydrogen gas
  • This results in the formation of bubble within the amalgam leading to pressure build up and expansion
  • The restoration will then sit proud of the surface due to upwards pressure and there will be a poor marginal seal
  • This an lead to occlusal interference, greater susceptibility to corrosion and expansion over the cavity margins which can increase fracture risk
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21
Q

A 23 year old woman who is a science teach arrives at the surgery for a regular check-up. She is an NHS patient. Although she has no existing restorations, you discover that she requires a minimal disto-occlusal restoration in a lower molar. When you tell her this, she expresses concern at the possibility that you will use amalgam and asks you about alternative treatments.
1. What concerns do patient commonly have about the safety of amalgam? (6)

A
  • Aesthetics- poor due to silver colour
  • Mercury poisoning and toxicity
  • Discolouration of teeth and surrounding tissues. LTR and amalgam tattoos
  • Environmental impact
  • Metal allergies
  • Affect on foetal development in pregnancy
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22
Q
  1. State what reassurance you could give her about the safety of amalgam? (4)
A
  • 490 amalgam restoration would be required in the mouth to exceed exposure limits to mercury as set by WHO- evidence suggests the quantities releases from one restoration are very small (0.5microgram/surface/day) and therefore do not cause verifiable effects on human beings (only 15% of this is absorbed- 0.08micrograms)
  • Organic mercury in food is absorbed must more easily (90% compared to 15%)
  • It is a historical dental material which has been used for 150 years with no evidence-based problems
  • Amalgam on the environment is less problematic than many other industries- 50% of that in the environment is natural from rock erosion etc., the consumption of fish and seafood contaminated with methylmercury, in the USA 80% of mercury pollution is from fossil fuels for energy and less than 1% from dentistry. Also have a specific safe disposal of amalgam.
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23
Q
  1. You have successful reassured her and she agrees to have an amalgam placed. You proceed to prepare the disto-occlusal cavity. What aspects of cavity preparation ensure that the caries is adequately removed? (2)
A
  • Systematic approach to caries removal as follows
  • Initially identify and remove carious enamel
  • Then remove enamel to identify maximal extent of the lesion and the amelodentinal junction and smooth enamel margins
  • Progressively remove peripheral caries in dentine- from the ADJ first then circumferentially deeper and then remove deeper caries over the pulp
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24
Q
  1. What aspects of cavity preparation ensure the finished margins are cleansable? (3) (finished amalgam)
A
  • Ensure no overhangs
  • Smooth margins
  • Smooth cavo-surface angles
  • Smooth occlusal surface
  • Contact points removed (clear the contact points with floss make sure can clean around this area)
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25
Q
  1. If the patient insisted on a restoration with a tooth coloured material and you elected to use a direct resin composite. Describe the mechanism by which resin composite is bonded to dentine? (5)
A
  • Use of a dentine conditioner- usually acid etch 35% phosphoric acid for 20 seconds; this removes smear layer, open dentinal tubules by removing smear plugs, delacifies the uppermost layer of dentine and exposes the collagen network in the top 10µm of dentine which is then penetrated by the next two components
  • Primer is then applied- usually HEMA; bifunctional molecule with a hydrophilic end (hydroxyl group) which bonds to the hydrophilic dentine via amine groups on the collagen proteins, (a spacer grow to make it flexible when bonding) and a hydrophobic methacrylate end which contains a carbon-cabon double bonds which opens to form a bond with the next resin layer
  • Adhesive is then added- mixture of resins usually Bis-GMA and HEMA; penetrates the primed dentine which now has a hydrophobic surface and not only impregates down into the dentine tubules but also flows into the small holes in the etched surface and forms a micromechanical bond with the tubules and exposed collagen
  • This forms the hybrid layer of dental collagen plus resin
  • Subsequent layers of composite resin can then be added and bond
26
Q

Denture Base Materials-
1. What are the ideal properties of a denture base?

A
  • Dimensionally accurate nad stable in use
  • High softening temperature
  • Unaffected by oral fluids
  • Low thermal expansion (similar to that of prosthetic teeth)
  • High thermal conductivity (so can feel temp of food and not burn themselves)
  • Nontoxic or irritant / biocompatible
  • High hardness/abrasion resistance
  • Easy to repair
  • Easy and inexpensive to manufacture
  • Ideal colour/translucency
  • Radiopaque
27
Q
  1. What are the constituents of PMMA?
A
  • Powder- benzyl peroxide (initiator), PMMA particles, plasticiser, pigments, co-polymers
  • Liquid- methacrylate monomer, hydroquinone (inhibitor), co-polymers
28
Q
  1. Give 4 possible faults which can occur during production and explain why they occur? For PMMA
A
  • Gaseous porosity- occurs where there is excess monomer boiling in bulkier parts of the denture, often as a result of fast curing or heating the PMMA too quickly
  • Contraction porosity- occurs due to excess monomer or sometimes insufficient pressure
  • Granulation porosity- occurs due to wrong liquid to powder ration- not enough monomer
  • Crazing- occurs due to internal stresses from differences in thermal expansion of base, acrylic teeth and mould and/or as a result of fast cooling rate
  • Free monomer units which act as irritants- occurs due to under curing
29
Q
  1. Give 4 advantages of Co-Cr as a denture base?
A
  • Higher dimensional stability compared with acrylic- will not change shape easily or deform over time
  • High thermal conductivity which allow patient o perceive temperature (of food, drink etc.) better
  • Radiopaque
  • High softening temperature- won’t melt in mouth
  • High YM so rigid and can be cast much thinner due to increased strength which means often less bulky and more comfortable for the patient
  • More hygienic as is less porous which decreases food, plaque and calculus accumulation
30
Q
  1. Give 2 disadvantages of Co/Cr as a denture base?
A
  • More expensive than acrylic
  • More difficult to add teeth to compared with acrylic- use of two different materials can add internal stresses to the material
  • Less aesthetically pleasing as not same colour as mucosa
  • Adjustment is difficult
  • Manufacturer is difficult
31
Q
  1. What undercuts are required for clasps of stainless steel, gold and cobalt chrome?
A
  • SS- 0.75mm
  • Gold- 0.5mm
  • CoCr- 0.25 mm (for 15mm undercut)
32
Q

Impression Materials-
1. What are the ideal properties of an impression material?

A
  • Low thermal expansion/contraction
  • Adequate working and setting time
  • High surface reproduction- 10-70µm for accurate
  • Low setting shrinkage or dimension change
  • Non-toxic or non-irritant (biocompatible)

  • Low viscosity (should flow readily)
  • High surface wetting ability- makes intimate contact with teeth and mucosa (small contact angle- no spaces between globules of material and so all surface is replicated)
  • High tear strength
  • 100% elastic recovery
  • Compatible with cast materials
  • Acceptable taste
  • Can be decontaminated with dimension changes
33
Q
  1. Name 2 non-elastic impression materials?
A
  • Impression compound
  • Impression paste
  • Zinc oxide eugenol
34
Q
  1. Name 4 elastomers?
A
  • Polyether- impregum
  • Polysulphides
  • Addition curing silicone- polyvinyl siloxane (PVS)
  • Condensation curing silicone- lab putty
35
Q
  1. Name 2 hydrocolloids?
A
  • Alginate (irreversible)
  • Agar (reversible)
36
Q
  1. What are the constituents of alginate?
A
  • Salt of alginic acid- e.g. sodium alginate
  • Calcium sulphate
  • Trisodium phosphate
  • Fillers
  • Modifiers, flavouring and chemical indicators
37
Q
  1. What is the setting reaction of alginate?
A
  • Sodium alginate and calcium sulphate > calcium alginate and sodium sulfate
38
Q
  1. Give 2 advantages of alginate?
A
  • Relatively easy to use
  • Adequate setting time
  • Okay surface detail- ok accuracy
  • Nontoxic and non-irritant
  • Cheap
39
Q
  1. Give 2 disadvantages of alginate?
A
  • Poor tear strength- avoid deep undercuts
  • Must be poured as soon as possible due to dimensional change as a result of moisture inhibition and syneresis (can’t be stored)
40
Q
  1. Give 2 uses of alginate?
A
  • Primary impression for denture
  • Impression for study models
    Impression for retainers
41
Q
  1. Give 3 advantages of elastomeric materials over alginate?
A
  • Higher tear strength- reduce risk of tearing on removal from mouth
  • Lower rigidity for ease removal from undercuts
  • Greater surface reproduction than alginate (more accurate)

  • Greater elastic recovery
  • Good dimensional stability
42
Q

What is luting cement used for?

A

1 A dental cement used to attach indirect restorations to prepared teeth is called a luting agent. 2 A luting agent’s primary function is to fill the void at restoration-tooth interface and mechanically lock the restoration in place to prevent its dislodgement during mastication.

43
Q

Glass Ionomer-
1. What is the constituants of glass ionomer?

A
  • Acid- polyacrylic acid and tartaric acid
  • Base- silica, aluminia, calcium fluoride, aluminium fluoride, sodium fluoride
44
Q
  1. Briefly describe the setting reaction of GI?
A
  • Acid base reaction- class + acid > salt and silica gel
  • Phase 1- Dissolution- acid is added to the solution, H+ ions attach glass surface and Ca, Al, NA & F ions are released, silica gel is left around the unreacted glass
  • Phase 2- Gelation- initial set (takes several minutes) due to calcium ions crosslinking with polyacid by chelation with the carboxy groups to form calcium polyacrylate (calcium ions are bivalent- react with two molecules joining them but may also link bond to two groups on same molecules which prevents setting)
  • Phase 3- Hardening- Trivalent aluminium ions ensure much higher degree of crosslinking between acid molecules to form aluminium polyacrylate which gives an increased strength and better mechanical properties (starts about 30 mins after initial set and can take several weeks)
45
Q
  1. Give 4 uses for GIC?
A
  • Definitive restorative material in non-weight bearing cavities e.g. cervical restorations when moisture control is poor
  • Fissure sealants in poorly cooperative children
  • Core build up prior to crown placement
  • Provisional restoration material
  • Luting for cementing indirect restoration
  • Lining material underneath fillings
46
Q
  1. Give 4 properties of GIC?
A
  • Low shrinkage- no contract on setting
  • Good long-term stability with low microleakage
  • Relatively insoluble once fully set with stable chemical bond to enamel and dentine
  • Self-adhesive to tooth substance
  • Releases fluoride
  • Cheap to sue
  • Thermal expansion similar to dentine
47
Q
  1. Give 4 disadvantages of GIC?
A
  • Brittle
  • Poor wear resistance
  • Poor tensile and compressive strength
  • Moisture suspectable when first placed
  • Poorer aesthetics- lack translucency
  • Poor handling characteristics
48
Q
  1. What is differences/advantages of RMGI vs Gi liner? (3)
A
  • On demand set
  • Higher mechanical set initially
  • Lower solubility
  • Better translucency and aesthetics than GI
  • Better handling
49
Q
  1. Why is it a bad idea to use GI luting cement for a filling? (2)
A
  • Low mechanical performance- low fracture strength, toughness and will wear
  • No chemical bond to restoration surface- requires sandblasting of restoration for mechanical adhesion
  • Short working time
50
Q
  1. Why is RMGI not good as a lutting cement?
A
  • It contains HEMA which absorbs water causing it to swell in a wet environment (may cause provisional crowns to crack or posts to split the root)
  • It can also be cytotoxic to the pulp
51
Q
  1. What luting cement would you use for a metal post core? (1)
A
  • GI luting cement
52
Q
  1. What luting cement would you use for a porcelain veneer? (2)
A
  • Resin luting cement (light cure acceptable) with silane couple agent
53
Q
  1. What luting cement would you use for a carbon fibre post? (2)
A
  • Dual cure composite resin cement with dentine bonding agent (etch)
54
Q

Luting Cements-
1. What are the ideal properties of a luting cement?

A
  • Low viscosity to allow seating of restoration
  • Cariostatic
  • Radiopaque
  • Biocompatible
  • Low solubility

  • Thin film thickness- below 25 mircons
  • High compressive and tensile strength
  • Young modulus similar to tooth
  • High hardness
  • Easy to use- easy to mix, working time long enough to allow seta but setting time short
  • Tooth coloured with variation available and non-staining
55
Q
  1. Why is RMGI not good as a luting cement?
A
  • It contains HEMA which absorbs water causing it to swell in a wet environment (may cause provisional crowns to crack or posts to split the root)
  • It can also be cytotoxic to the pulp
56
Q
  1. How do you bond a porcelain veneer?
A
  • Light cure composite cement with silane couple agent (DBA)
57
Q
  1. How do you bond non-precious metal?
A
  • Dual cured composite with metal coupling agent- materials containing MDP or 4-META (molecules with acidic end which reacts with metal oxide and carbon-carbon double bond which bonds to luting agent)
  • Must also be sure cure as light will not penetrate
  • Panavia- contains MDP 9self cured anaerobic resin material which incorporated metal coupling agent into the composite resin
58
Q
  1. What are the components of temp bond?
A
  • Base- zinc oxide, starch, mineral oil
  • Accelerator- EBA, eugenol, canuba wax
    ZOE
59
Q
  1. Can you bond zirconia?
A
  • No, it is inert so it cannot be etched or bonded to
  • Sandblasted for micromechanical retention with cement
60
Q
  1. Why are lithium disilate crowns strong?
A
  • Contain unique needle-like crystals which make crack propagation through the material very difficult giving good flexural stability

BDS4 (24 decks)

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