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194 Cards in this Set
- Front
- Back
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Composition of GIC
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powder = fluoroaluminosilicate glass with particle size of 4-50um
Liquid = makes up 40-50%, polyalkenoic acid (may also include acrylic, tartaric, itaconic, maleic acid) |
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what are the classifications for GIC
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Type I = luting cements
type II = traditional and high density restoratives Type III = lining cements Type IV = fissure sealants |
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what are Type 1 GIC's and give
examples |
Used for cementation of bridges, crowns and inlays.
fast set with early resistance to water uptake best film thickness= <25um Ketac cement fuji plus vitremer luting |
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what are type II.1 GIC's and give examples
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traditional restorative cements that can be auto cure or resin modified.
prolonged setting reaction causing them to be prone to water uptake and loss for at least 24hrs. good asthetics but not good for undue occlusal load Ketac fil (AC) Fuji II (AC) Fuji VII (AC) Fuji IX (AC) Fuji II LC (RM) vitremer (RM) Photac fil (RM) |
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what are type II.2 GIC's and give examples
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high density reinforced cements all AC
used where aesthetics not important rapid set with resistance to water uptake but sensitive to dehydration for 2 weeks silver particles make it resistant to abrasion but not fracture. They also inhibit F release Fuji IX Ketac molar Ketac silver |
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What are type III GIC's and give examples
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lining cements
rapid set, lack aesthetic properties Vitrebond - RM photac bond -RM fuji bond LC - RM Ketac Bond - AC |
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what are type IV GIC and give examples
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fissure protection
Fuiji III LC - RM |
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what is added to GIC to make it RM
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15-25% HEMA which is a diluent monomer and a light activated catalyst
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what is the relationship between particle size and type of GIC
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finer particles are used for luting and lining
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what is added to materials to make them radiopaque
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barium, strontium or lanthanum
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what are the main constituents of the glass powder for GIC
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silica 29%
CaF 34% alumina 16% cryolite and aluminium phosphate |
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what is the first stage of the GIC setting reaction
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1. Dissolution (immediate)
Acid attacks surface glass particles with release of Ca, F, and Al ions. |
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what is the second stage of the GIC setting reaction
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2. Precipitation (min-hours)
cations (Ca and Al) bind to anionic polyalkenoic acid to form calcium (1st to form, fragile and highly soluable in water) and aluminium polyacrylate (strong, insoluable and provide major physical properties of the set restoration) chains, forming rigid cross links. |
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what is the third stage of the GIC setting reaction
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3. Hydration (hours – months)
progressive hydration of metallic salts in matrix |
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explain the structure of the set GIC
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particles of unreacted glass surrounded and supported by siliceous hydrogel, embedded in a poly salt matrix of cross linked polyalkenoic acid molecules rich in Ca and Al ions
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what % of the set GIC is water
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24%
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when is GIC most susceptible to water contamination
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stage II before Al ions have been locked in to the resistant gel matrix
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what does early water contamination do to GIC
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results in loss of Ca polyacrylate chains causing absorption of water, loss of transluscency, and reduction in the physical properties leaving it susceptible to errosion
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what does dehydration of the GIC result in
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causes cracking and fissuring, softening of the surface and loss of the matrix forming ions. Loss of translucency
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what are the time frames for water contamination and dehydration of GIC
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water contamination = 24hrs
Dehydration = 2 weeks to 6 months modified GIC's = 5min for water contamination and the 2 weeks for dehydration |
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what are the adhesion / bonding properties of GIC
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diffusion based adhesion resulting in an ion exchange layer and a chemical bond b/t the GIC and the E or D. Polyalkenoic acid releases Phosphate and Ca ions from tooth which diffuse into the cement.
bond strenth = 2-4MPa for D and 4-6 MPa for E RM = 10-14MPa organic bonding can also occur via hydrogen bondingor metalic ion bridging |
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What is dentine Conditioner and what is it used for
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10% polyacrylic acid used to remove the smear layer on the tooth in prepartion for the application of GIC.
It enhances the wettability of the tooth surface and preactivates the tooth ions for ion exchange with the GIC |
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What is the mechanism of F in GIC
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after setting F ions are held within the matrix but are free to within it allowing it to be released without a reduction in the physical properties of the GIC.
F release is initially high but declines rapidly to a stable level at around 2-3 months GIC also acts as a F reservoir and take up F from topical applications |
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What is the Biocompatibility of GIC
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gingival tissues are tolerant and pulpal response is also favourable if >05mm of dentine otherwise use spot treatment of ledermix
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what dimensional changes occur in GIC
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3% contraction on setting but this is compensated by flow of the material during setting which results in stress relaxation
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what is the fracture resistance of GIC
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weak, lack rigidity and are susceptible to brittle fracture
addition of silver doesn't improve fracture resistance |
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what is the wear resistance of GIC
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limited because full properties can take weeks to months to develop. GIC is also sensitive to acid environments which will lead to greater wear
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what is the co-efficient of thermal expnsion of GIC
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similar to tooth = 11.4 x 10to the -6 / degrees C
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what can effect the colour and transluscency of GIC's
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takes several days to develop
cna be affected by water contam of dehydration RM are particularly susceptible to darkening over time |
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what are the advantages of GIC
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biocompatible
chemical bond F release adequate aesthetics multi-purpose |
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what are the disadvantages of GIC
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water balance issues
prolonged setting time setting contraction 3% weak physical properties |
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An increase in what, increases the bonding of GIC to the tooth structure
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the higher the mineral content the better the bond
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what are the components of CR
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1. Organic Resin Matrix
2. Inorganic filler particles 3. coupling agent 4. photosensitive agent |
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what is the organic matrix component of CR
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base monomers such as Bis-GMA and UDMA and Diluent monomers such as TEGDMA and HEMA
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what makes up the inorganic filler particles in CR
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macrofiller = glass, quartz, ceramic
microfiller = amorphous silica |
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the incorporation of filler particles into the resin matrix serves to
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reinforce material
improve hardness, stiffness, strength and toughness reduce polymerisation shrinkage reduce the coefficient of thermal expansion |
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how are filler particles decribed
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in terms of their distribution (proportion of diff sized particles), the volume (proportion of weight of the material) and their size (average of all the particle sizes)
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what are some different types of filler particles
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nanofilled 5-75nm - Filtek supreme XT
nanohybrid = nanofiller + ground particles 1um - Gradia, premise microfilled = only 40nm - heliomolar microhybrid - herculite course hybrid- microfiller and ground particles of 5um - z100 |
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what is the coupling agent for CR
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silane coupling agent
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what does the coupling agent do in CR
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1. each filler particle is pre-treated with it to promote adhesion between the matrix and the filler particle
2. acts as a flexible stress-breaking layer around each particle |
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what makes up the photosensitive component of CR and what does it do
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camphorquinone which is a di-ketone that absorbs radiant energy of 470nm
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what occurs in the setting reaction of CR
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1. photosensitive di-ketone (camphorquinone) absorbes light energy and enters an excited state then it combines with a tertiary amine reducing agent to form free reactive radical which initiate polymerisation
2. free R's break c=c bonds and adjacent monomers begin to bond together to form the polymer |
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what is the conversion of CR
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conversion is the extent of polymerisation that occurs in the CR
25-55% of resin groups remain unreacted ideal conversion is around 75% |
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what are the critical factors for optimising conversion of CR
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1. thickness (>2mm increments is unreliable)
2. composition (microfinehave lower cure depth and less converted bonds 3. shade (dar or very light shades take longer to cure) 4. light efficiency 5. exposure time |
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what is the air inhibited layer
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layer of resin exposed to O that results in a composition similar to uncured resin.
can be avoided with use of matrix but is usful for bonding increments |
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explain Young's modulus of elasticity
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stress strain relationship.
the linear part is the linear elastic region and represents the range where elastic deformation occurs and the material returns back to its original shape. The deviation of the curve at higher stess and strain is where the material has exceeded its elastic limit and is the region of plastic deformity |
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what is compressive strength
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measure of the load required to break a specimen in a crushing mode
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what is hardness of a material
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measure of the penetration made in a specimen by a diamond indenter and is measured as force per unit areaof indentation
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what is the compressive strength of CR
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234-350MPa
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what is the hardness of CR
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93-160 VHN
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what is the compressive strength of Dentine and Enamel
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D= 300MPa
E = 380MPa |
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what is the hardness of Dentine and Enamel
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D = 74VHN
E = 400VHN |
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what is the polymerisation shrinkage of CR
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2-3%
creates tensile stress at interface which may lead to marginal leakage, post operative sensitivity and fracture |
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what are the thermal properties of CR
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resins with lower resin content exhibit lower thermal coefficient of expansion but is generally around 50 x 10-6 /c
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what is the thermal coefficient of expansion for Dentine and Enamel
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D = 8.3 x 10-6/c
E = 11.4 x 10-6/c |
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what are the pulpal effects of CR
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potential irritants can can be prevented with the use of lining
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why is bond used for CR
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unfilled resin bonding agents are used to seal the interface b/t acid etched enamel and the CR. Bond penetrates the microporosities created by the etch leading to the development of resin tags
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what is etch and what does it do
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37% orthophosphoric acid used to selectively dissolve mineral components to create microporosities up to 30um in depth that will allow micromechanical retention between CR and E
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what factors can cause poor marginal seal at the CR / tooth interface
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1. polymerisation shrinkage
2. large diff in the thermal coefficient of expansion 3. premature finishing of the CR causing marginal fractures |
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how is CR adequately cured
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> than 400 mW/cm squared for 40 secs per increment
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how much copper do low and hi alloys containgh copper
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low = <6%
high = >12% |
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what are the main components and their percentages of the high copper alloy
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Ag = 41-61%
Sn = 28-31% minor elements |
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what is the advantage of high Cu alloys over low Cu alloys
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High Cu alloys don't have the Sn-Hg (gamma 2 phase) in its final product. the absence of this phase reduces corrosion and creep
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what is the difference between zinc containing and zinc free alloys
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zinc containing = > 0.01% zinc
zinc free = < 0.01% zinc alloys with zinc have decreased rate of marginal fracture but can also exhibit an excessive delayed expansion if contaminated by moisture |
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what is the gamma 2 phase
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Sn-Hg phase found as a product of low Cu alloys. Is susceptible to corrosion and creep
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what is the epsilon phase (E)
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Cu3Sn
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what is the gamma 1 phase of alloy
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Ag2Hg3
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what is the gamma phase of alloy
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Ag3Sn
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what is the setting reaction of amalgum
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y + E + Hg -> Y1 + unreacted alloy (35-50%)
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what are the 6 different types of amalgams
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1. low Cu - lathe cut
2. low Cu - spherical cut 3. High Cu - lathe 4. high Cu spherical 5. high Cu blend Ag-Sn, Cu 6. High Cu blend Ag-Cu |
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when mercury comes in contact with the alloy approximately how much of the surface undergoes a reaction
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3-5 um
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what is the initial mercury content
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40-53%
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what is the final mercury content
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37-48%
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what if there is excess retention of mercury in the final product
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causes decrease in the physical properties of the amalgam
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what is the structure of the set amalgam
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35-50% unreacted portions of alloy held together by Y1 phase matrix
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what is corrosion
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electrochemical destruction of a metal by reaction with its environment
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what is tarnishing of amalgam
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surface corrosion caused by oxi of Sn-Hg phase in low Cu alloys or the Cu containing phases in high Cu alloys
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what is crevice corrosion
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corrosion at the tooth/restoration interface due to the tooth surface being anodic in comparison to the amalgam.
causes self sealing interface |
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what is corrosion fatigue
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fine branch like penetrations that occur around margins and extend along the grain boundaries of the Y1 matrix in regions subjected to occlusal load
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what is galvanic corrosion
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caused by dissimilar metals and an electrolyte (saliva). may cause sharp pain shortly after placement of new amalgam sufficient to require its urgent removal. Also potential for long term corrosion with pitting and roughening of adjacent metal restorations. For this reason crown prep on amalgam core should be placed on tooth structure beyond the gingival extent of the amalgam
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what is creep
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progressive permanent deformation of an amalgam under load
Y2 phase enhances the ability for y1 phase grains to slide under load thereby increasing the chance of creep The main resistance to creep in high Cu A's comes from lack of Y2 phase and the presence of n1 precipitates in the matrix |
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what type of amalgam has the highest physical properties
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high Cu spherical
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what is the thermal expansion of GIC, CR amalgam and tooth
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1. GIC = 10-11
2. CR = 30-60 3. Amalgam = 25 4 tooth = 11.4 |
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what is the modulus of elasticity for GIC, CR amalgam and tooth
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1. GIC = 3-5 GPa
2. CR = 4-16 GPa 3. Amalgam = 55 GPa 4. dentine = 18 GPa 5. Enamel = 82.5 GPa |
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what are the stages of Amalgam placement
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1. placement - small increments and condense rapidly onto cavity walls
2. 1st burnish - 15secs large burnisher 3. carving 4. final burnish 5. finishing to matt finish at later appointment |
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what are the two components required for chemical initiation of polymerisation of CR
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1. tertiary amine accelerator
2.thermochemical initiator (benzoyl peroxide) |
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What is a compomer
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CR's that contain the components of GIC but at levels insufficient to promote the acid/base reaction or the ion exchange adhesion. The acid is activated when water is absorbed into the restoration. However the delayed reaction doesn't allow for the ion exchange or prolonged fluoride release
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what is a Giomer
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the basic glass filler is reacted with acidic polymers in water prior to inclusion into a silica filled resin. Claim that it has fluoride release and storage but this has not been fully substantiated. No ion exchange
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What would a CR with combined chemical and light activation systems be used for?
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Core build ups and luting purposes
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what are the two components required for chemical initiation of polymerisation of CR
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1. tertiary amine accelerator
2.thermochemical initiator (benzoyl peroxide) |
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How does the size of the filler particle effect the CR?
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Fine filler's are more easily polished, retain surface shape and resist wear better.
More heavily filled are harder and stronger and resist occlusal loads. the ideal is a combination of two or more to allow for more efficient packing |
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what are flowable CR
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reduced filler content down to 44-54% thus reducing the viscosity of the material allowing for better flow but also has reduced machanical properties . They have a lower modulus of elasticity and better wettability and are best used as an intermediate layer between the adhesive layer and the overlying resin to reduce contraction stress and improve the seal of the restoration
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what may occur if curing of CR is inadequate
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gap formation, marginal leakage, recurrent caries, pulpal sensitivity and ultimate restoration failure
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what are key points related to curing CR
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increments no > than 2mm
light tip held within 4mm of surface |
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How does filler volume % effect the mechanical properties of CR
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Increased filler loading will increase hardness, stiffness, strength and fracture toughness however decreased modulus of elasticity found in lower filler % is good for cervical lesions where it is desirable for the restoration to be able to flex
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what methods are available for reducing polymerisation shrinkage of CR?
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- incremental placement, shrinkage is generally toward the light source
- GIC base to reduce volume of CR and to deal dentine - GIC liner to act as shock absorber - development of stronger bonding agents - use of 'soft start' 'pulse cure' methods of light curing - the smaller the filler content the greater the shrinkage |
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what factors can reduce CR bonding to enamel
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- poor clinical technique like not using bond
- contamination of surface after etching - microcracks caused during cavity prep - presence of unsupported or fractured enamel margins |
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what methods of CR placement reduce the risk of marginal seal
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- use of etch and bonding agents
- cavity design; flat or shallow better than box - incremental placement - thorough curing - correct selection of material for use |
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what methods of CR placement reduce the risk of marginal seal
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- use of etch and bonding agents
- cavity design; flat or shallow better than box - incremental placement - thorough curing - correct selection of material for use |
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what is the purpose of a matrix
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- to enhance adaption of the restoration to the gingival margin
- provide some degree of contour to the proximal surface |
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what is the purpose of wedging
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- assist in maintaining good contact
- protect interproximal gingiva - improve shape and proximal contour |
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what causes increased corrosion in low Cu amalgams
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in depth corrosion extends by way of the Y2 phase voids and between the Y1 phase grains in low Cu Amalgams where as in high Cu A's it occurs onl between the Y1 phase grains making it progress at a much slower pace
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What type of amalgams require the highest and lowest Hg content?
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Highest = low Cu lathe cut
Lowest = High Cu Sperical |
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What is microstructural evidence of corrosion in Amalgam
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- Increased voids
- presence of 2nd matrix - transformation of E phase into n1 phase - Absense of SnHg phase in low Cu - presence of Sn and Cl containing corrosion product |
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What is the self sealing interface and what products are produced.
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crevice corrosion releases Cu, Sn, O, OH, Cl.
These products become lodged in the crevice and seal the interface |
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What are the essential requirements for correct A placement?
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- proper plasticity
- minimal Hg content |
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What is condensation of Amalgam?
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incremental placement and compression of each increment into the others to form a continuous homogenous mass
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What are the aims of condensation?
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- adapt A to margins, walls and line angles
- minimise voids and layering between increments - develop maximum physical properties - remove excess Hg |
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What occurs when A is contaminated with moisture during placement?
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- increased tarnishing and corrosion
- excessive delayed expansion of zinc containing A's |
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What are the main causes of A replacement 5 years after placement.
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1. Bulk fracture
2. tooth fracture |
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What is marginal fracture?
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Ditching, crevice formation, marginal breakdown.
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what is the clinical process of marginal fracture?
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repeated occlusal loading -> stress -> creep and corrosion fatigue -> weaker marginal A -> fracture -> ditching and crevice formation which becomes progressively worse and eventually leads to sensitivity and caries
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What factors have been shown to significantly influence the marginal fracture of A?
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- Cu content
- operator factors - pt factors - cavity design and carving - zinc content |
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What factors in the cavity design can efect the longevity of A?
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- failure to remove peripheral caries
- failure to remove fractured enamel - inadequate bulk - failure to extend A to a site where it can be adequately finished |
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What factors relating to the manipulation of A can reduce its longevity?
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- inadequate base
- inadequate wedge and matrix - inadequate trituration, condensation or pre-carve burnishing - moisture contamination - inadequate contouring and finishing |
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What is the failure rate of posterior CR restorations compared to A's?
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2-3 x
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What are the reasons for using lining
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- Seal the dentinal tubules
- replaces dentine body to reduce amount of CR used -> reduced polymerisation shrinkage - fluoride release - protect from irritating CR products |
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How is the amount of GIC lining to be used determined.
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C ratio which is the ratio of the number of bonded surfaces to unbonded surfaces.
in high C ratio situation like class 1 more lining should be used to reduce the stresses of shrinkage. in low c ratio enough lining to seal the dentinal tubules is sufficient |
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What are some pulp therapy agents
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- calcium hydroxide (dycal, life, alkaliner, VLC)
- Corticosteroid-antibiotic preparations (ledermix cement) |
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how should pulp therapy agents be used
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as a spot application for either indirect or direct pulp therapy
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what are the properties of Calcium hydroxide
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- high pH
- control of bleeding - anti microbial properties - stimulation / irritation of the the pulp - solubility |
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Pulp protective measures during restoration placement?
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- Don't excessively dehydrate dentine
- control the generation and vibration via light intermittent cutting and reduction of heat by use of water - protect and seal against microleakage - place a lining - be aware of chemical toxicity particularly flowables under deep resto's - no excessive force when placing restoration - patient recall to monitor |
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When subject to irritation what are typical regressive changes in the pulp?
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- increased fibrous tissue
- decreased cellular, vascular content - decreased pulp space due to reparative dentine |
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Dentine?
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vital part of tooth formed by odontoblasts that secreted collagen matrix as they retreated towards the pulp. Matrix is subsequently mineralised except for predentine adjacent to pulp.
Odontoblasts have cytoplasmic processes that extend variable distances into the dentinal tubules |
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Dential tubules Diameter at the pulp and at the EDJ
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EDJ = 0.5-0.9 um
pulp = 2-3 um |
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What is the permeability of Dentine related to?
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number and diameter of tubules in a given part of the tooth. Permeation will increase with increased surface area and increased depth
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relationship between structure of dentine and bonding of adhesive materials
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deeper dentine his more suface area occupied by tubules but is also moister which may effect the bonding of hydrophobic materials.
In superficial dentine resin tags will contribute less to total bond strength while the greater area of intertubular dentine provids a larger surface area for hybrid layer formation |
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What is the pressure of pulpal interstitial fluid? what is it's rate of flow if tubules are cut (normal and inflammed)? What is resistance to fluid movement proportional to?
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- +ve pressure of 10-14 mm Hg
- 1-2 um per second and up to 2-3 um per second - tubule length (gets more narrow with length) |
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How does the % of tubules with nerve terminals vary with position of dentine?
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- over pulp horn = 50%
- middle coronal dentine = 5% - Cervical root dentine = 1% |
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What nerve fibres make up the dentine/pulp nerve complex?
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- large myelinated A fibres ( sharp, well localised dentine sensitivity)
- unmyelinated C fibres (dull and poorly localised pain of pulpitis) |
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Sensitivity mechanism of Dentine?
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hydrodynamic theory: rate of firing of intradental nerves increases with increased fluid flow
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what is the smear layer comprised of?
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- ground components of enamel and dentine
- contents of dentinal tubules - water and dentinal fluid - saliva and bacteria |
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what is the thickness of the smear layer?
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<2 um
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how does pumice, DC and etch all effect the smear layer?
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- pumice removes SL but not plugs
- DC removes SL and leaves plugs - etch removes SL, plugs and demineralises dentine leaving tubules wide open |
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What are the advantages and disadvantages of smear layer
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- Pros = decreases permeability of tubules and may impede entry of bacteria
- cons = may contain bacteria and interferes with bonding of some materials |
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What are the factors involved in pulp irritation?
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- bacterial
- iatrogenic (cav prep) - trauma (fractured crown) - idiopathic |
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what are the main iatrogenic irritants to the pulp?
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- LA (via vasoconstriction)
- cav prep - thermal and vibration - dessication - bac contamination - |
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How is pulpal irritation cumulative?
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capacity of pulp to respond favourably to a new irritant will assoc. partly with the # and severity of past irritants
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What is Viscostat and what is the active ingredients?
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Heamostatic agent containing 20% ferric sulfate solution
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When is viscostat indicated
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For restorative and prosthodontic dentistry to control bleeding and sulcular fluid
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How is viscostat used?
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Applicator is rubbed with moderate pressure onto the cut tissue at the same time a small amount of the viscostat is slowly expressed. Continue until the syringe application is finished (10mm of the 1.2 ml syringe is enough). Clean area with firm air/water spray if there is further bleeding repeat application for further 15 sec. There may be temp staining of tissue so clean the area well after use.
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How does viscostat work
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Forms a coagulum that seals the orifices of the cut capillaries
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What are the objectives of restoration placement?
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Accurate diagnosis of caries risk
arrest active caries remineralise early lesions conserve existing tooth structure restore deep lesions assess management outcomes |
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What are the resons for restoration replacement?
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- secondary caries
- bulk fracture - margin degradation - fracture - other reasons - tooth fracture |
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What is the approximate longevity of small and large restorations placed in Amalgam vs CR
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Amalgam = small -10yrs, large-8yrs
Cr = small- 7 yrs, large - 4yrs |
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When should RMGI restorations be finished.
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At least 24hrs after placement to allow water absorption to compensate for curing cotnraction and improve marginal adaption and it also allows the acid base reaction to proceed to more complete setting leading to increased cohesive strength.
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Whar is enamel microabrasion and what is it used for?
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conservative method for removing or improving the appearance of intrinsic, superficial, discoloured emamel defects.
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What are the advantages of enamel microabrasion
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enamel develops a shiny glass-like texture within a few months of treatment. These surfaces have been shown to accumulate less plaque. LA not required and no significant post op sensitivity has been recorded
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What are the disadvantages of enamel microabrasion?
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Can't penetrate deep stains or hypoplastic lesions
- also need to consider the inherent danger of using strong acid and soft tissue damage. |
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What effect does microabrasion have on enamel surfaces?
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mild surface abrasion of enamel prisms while there is also acid erosion causes mineralised tissue to compact within the organic area. This replaces the prism rich layer with compacted prism free enamel layer. Light reflected off and refracted through from the treated area gives the different appearance
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Briefly outline the technique for enamel microabrasion?
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- Clean teeth with pumice, wash and dry
- isolate with RD - mix compound (18% HC acid) pumice. - apply with polishing cup or wooden stick for 5 secs then wash for 5secs - repeat to a max of 10x - polish with soflex discs - apply desensitising paste (f- or CPP-ACP - review |
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What are the concerns associated with PPR
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- debris at base of the pit or fissure
- fate of MO's - resin tag length - longevity - regular check ups |
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indications for ppr?
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- small occlusal lesion in the fissure system
- potentially carious fissure |
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What are the indications for CR facing on amalgams?
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good amalgam resto's but with aesthetic concerns
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What is the procedure for placing CR facing over amalgam restorations
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Remove a thin layer of amalgam (enough to provide bulk of CR)
Bevel existing enamel margin cut mechanical retention into amalgam Place masking agent over the exposed amalgam Bonding to enamel then incremental build up |
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What are tunnel restorations and what do they involve.
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approaching small interproximal lesions from the occlusal but preserving the marginal ridge. the proximal portion is restored with GIC and the occlusal portion is restored with CR.
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What are the main concerns associated with tunnel restorations
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- compromised marginal ridge
- difficulty with access - possibility of leaving caries - damage to aproximal tooth - inability to adequately finish proximal margin |
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What are the three different methods for Posterior Composite placement?
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total bonding (resin to dentine bond), open sandwich, closed sandwich
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What are the advantages of indirect composite restorations
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no polymerisation shrinkage, max polymerisation of the CR leading to increased rigidity and colour stability, minimum porosity of the surface.
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What are the disadvantages of indirect CR restorations
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lack long term research, relys on cementation for bond, takes time
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What are the princples of the open sandwich technique and what are the pros and cons?
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GI restores the gingival protion of the box to just gingival of the contact and esures good bond to the dentine or thin enamel at the margin. It also has the benefit of being less moisture sensitive in an area that is at most risk of mositure contamination. composite forms the contact and occlusal for strength. The postential disadvantage of this type of restoration is that there can be more marginal discolouration on proximal buccal and lingual margins and some studies have reported slight concavity (loss of GI) near the gingival margin possibly due to degradation/dissolution/mechanical wear.
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What are the most common problems for placing posterior CR restorations
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open contacts, difficulty finishing (difficult to determine tooth/resto interface), too long to place.
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What occlusal considerations are important for posterior CR's
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avoid contact with the opposing functional cusp, CR wear will be greater in pt's with group function rather than canine guidance, reduction of opposing must be done b4 the placement of the resto and it is important to discuss this with the pt. If possible avoid all contact of CR with opposing tooth.
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What CR properties cause the greatest wear to opposing enamel structures
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Quartz filled especially if larger particle sizes
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what are the different types of marginal defects that can happen in CR
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wear = exposure of the cavity prep wall, crevice fracture = evidence of chiiping away of CR from the margin, Surface fracture = chipping of excess CR beyond the cavity margin, Void = defect with smooth outline
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What can happen when there is not enough bulk of CR?
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grey area due to microcracks leading to defects
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What are the main problems for obtaining adaption of CR to Dentine and enamel?
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polymerisation shrinkage and difference in co-efficient of thermal expansion
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What are the differences in polymerisation shrinkage of light activated and chemically cured CR's
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VLA = faster leading to increased stress 20secs compared to 15-20mins to achieve max polymerisation. this lead to incremental placement
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What are the factors of hydrodynamic transmission that are most likely to elicit pain
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outward and rapid movement
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What are the two main types of post restoration sensitivity reported?
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1. sensitivity to osmotic and thermal stimuli (cold and sweet - amalgam and CR)
2.sensitive to pressure (more related to CR - pain improves when the margin fails then likely to get sensitivity to cold) |
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What are the three possible conditions leading to post restoration sensitivity
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1. margin and dentine tubules sealed = no problem
2: margin and tubules not sealed = pain to thermal and osmotic stimuli (common with amalgams until the self sealing interface develops 3: Sealed margin but unsealed tubules = fluid filled space under the resto = bending and flexing causing pain via a pumping action but if the resto is rigid they may not experience any symptoms |
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What is the scale of rigidness for CR, Enamel, Dentine, Amalgam
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CR<Dentine<amalgam<enamel
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What ratio of CR have post resto sensitivity
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1 in 6
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How should post resto sensitivity be managed?
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if sensitive to thermal and osmotic stimuli - CR then attempt to seal or replace it f amalgam then try to leave it for a while to settle.
If sensitive to pressure then the resto needs to be replaced |
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What ways can risk of post resto sensitivity be minimised?
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seal the tubules, good placement technique, limit polymerisation shrinkage - increments
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What are the prinicples to control polymerisation contraction of CR restorations
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1 = first increment on one surface only 2= apply first increment to the weakest interface 3 = direct contraction toward the walls via light placement
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Optimised adaption of CR relies on what 3 factors
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- reduce total volume of CR with GIC
- incremental placement - Direction of the light |
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Bacterial growth under failed CR restorations in comparison to failed amalgam restorations?
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3.5 x greater caries effect because caries progression is faster under CR, more species of anaerobic bacteria under CR, 8x the amount of bateria.
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What are the four main reasons that care needs to be taken with post comp.
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1. reduce incidence of sensitivity by sealing the tubules
2. Reduce incidence of tooth fracture at margins by removing any unsound enamel during the preparation 3. reduce the incidence of recurrent caries via meticulaous and thoughtful incremental placement to optimise adaption 4. reduce frequency of replacement becuase loss of tooth structure at each replacement |
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Main problems with posterior composites.
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- polymerisation shrinkage leading to sensitivity and leakage at the margins
- achieving a proximal contact/contour - removal of failed resto's leading to loss of further tooth structure |
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What are the requiredments for placing a post CR
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adequate access, adequate isolation, protected occlusal relationship (always assess occlusion prior to cutting the cavity)
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How can wedging technique be utilised to get the best occlusal contact in CR
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pre-wedging provides slightly more separation to compensate for the thickness of the matrix, provide a guide to level gingival wall
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When should a gingival retention groove be placed for Post CR
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proximal box on ginigval wall if <0.5mm of enamel. Place grove just inside the CEJ and fill with GIC lining
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what is the C factor?
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Ratio of bonded sufaces to unbonded sufaces
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Berglund 1990 study on Hg released from amalgams found that.
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People with around 10 amalgams recieved on average 2.5ug Hg from their amalgams the average for people without amalgams is 10-20ug and the allowable occupational exposure is 300-500ug per day.
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What was the study and what did it find regarding the amount of mercury vapour released during dental procedures
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Engle et al 1992 found that removal of amalgam without extended evacuation = 16ug, removal with = 2ug. Dry finishing of amalgam = 44ug vs wet finishing =4ug
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How long to do extended evacuation for the removal of amalgam vapour?
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20-30secs
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A study of urinary mercury levels in dentists found that
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1.3% of dentists exceeded the 100ug/L where the first symptoms and signs appear. Important factors were: type of practice, type of capsule, removal of excess, type of flooring, age of the dental office
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What are the important recommedations for the safe use of amalgams in the dental practice?
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1. good ventilation (replace filters) 2. pre-portioned single use capsules 3. check seal on reusable capsules if used 4. select amalgams that require less Hg 5. store scrap under radiographic fixed solution 6. avoid ultrasonic amalgam condensers 7. remove or finish amalgams under water spray
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What are the indications for an amalgam with CR facing?
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Large restoration. A will provide best proximal contacts, best resistance to occlusal forces, is more conservative than indirect procedure. Still allows for good aesthetics and the facing can be replaced when neccessary
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What is the rationale for using an indirect CR or ceramic inlay?
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polymerization shrinkage occurs out of the mouth and max polymerisation of the CR increase rigidity and colour stability of the material. Great reduction in the interface stress between luting agent and enamel. Ensures good contact points and resistance to opposing loading.
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What do you understand about the CAD/CAM type of restoration?
For example CeRec. |
Indirect Restoration placed in one appointment. Prefabricated block of ceramic material. Mechanically machined. Minimal adjustment out of mouth. Final occlusal contouring after luting.
Limited shade selection. |
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Briefly indicate the steps in placing material into the proximal part of the restoration for an open sandwhich technique
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Polyacrylic acid, glass ionomer to satisfactory level, etch/bond, incremental design of CR
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Discuss in detail the ‘key principles’ that will influence the successful placement of a posterior composite restoration. Where appropriate, use an example of composite resin into resin-bonded ‘proximal only’ class II cavity which has enamel present at all the margins.
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Understand the generation of stresses associated with polymerisation contraction
i) Light activated vs non light activated ii) C factor iii) Stress generation with: a) Greater volume of CR b) Bulk vs incremental placement c) VLA CR II. Minimise the total bulk of CR by: i) Use GI lining ii) Indirect restoration III. Selected incremental placement. IV. Carefully directed application of light to favour adaptation to tooth structure. |
