Dental Materials* COPY Flashcards
Types of high speed instruments?
High speed
Speed-increasing
Types of burs - instrument?
Friction grips used in both high speed
Fit into handpiece via friction
How does bearing housing work in the handpiece head?
7-8 ball abrings Run freely inside a ball race Needs lubrication by phenolic resin Race holds shank of bur allowing rotation Ceramics > Stainless steel Prevents bur running eccentrically
Importance of eccentric bur movement - consequences if not?
Needs to run centrally
Judder:
- causes vibrations to material causing cracking and crazing, unpleasant and the bur may break
Eccentric:
- irregular removal of tissue (more removed)
Less control
Water cooling - importance? anatomy? compromise? heat effects?
Frictional heat produced needs to be removed by water
At least 4 holes
Positioning of the instrument can compromise water supply (bad)
Improves vision
Can cause substrate to melt, causing clogging cutting surface reducing efficiency
Illumination - advantages? anatomy?
Improves vision
LEDs - more intense whiter light and longer life
Produce less heat and better compared to halogen and glass fibre rod
Balance - essential for? disadvantages? anatomy affects balance? aim?
Ergonomics and precision of use
Badly balanced handpieces compromise accuracy and increases fatigue
Tube housing, and services arranged in the dental unit contribute to balance
Should be neutral or slightly towards the working position
Size of head - importance?
Smaller heads affords greater access and operator vision
Torque - definition? changes in rpm?
Ability of bur to continue to rotate and cut when pressure is applied to the substrate
Power must be maintained
rpm drops from 400,000 to 200,000 on pressure being applied
Indications for a high-speed handpiece?
Cutting enamel and dentine Remove direct restorative materials Gross shaping and polishing of cured direct restorative materials Tooth prep for indirect Removal of indirect prostheses Sectioning of teeth
Mode of cutting - speed increasing vs high? bur movement? cutting effect? advantages of speed increasing?
Bur in a speed-increasing handpiece runs more smoothly with a turbine
Bur moves axially = pecking motion in a turbine
Causes rippling effect leads to microcrack formation
Speed increasing > High speed as its better at refining tooth prep, tooth hemisections and polishing
Reduces noise and vibrations
High speed vs speed increasing - burs? power? torque? motion of bur? balance?
High speed: - friction grip - compressed air - variable - rotation and pecking - neutral Speed increasing: - friction grip - electric micromotor - constant - rotation only - motor end heavy
Indications for slow-speed handpieces?
Contra-angled:
- removal of caries
- polishing enamel and restorative materials
Straight handpieces:
- oral surgery
- extraoral adjustments and polishing of acrylic and metals
Colour rings and their significance on handpieces?
Internal gearings of handpiece
Red - increase usually 1:5
Blue - 1:1
Green - reduction may be 2:1, 4:1 or 20:1
Indications for speed-decreasing handpieces?
Prophylaxis, reduced heat production and reduced prophy paste use
Decontamination of handpieces - how? when? using what?
All must be cleaned after use
Tubes and spaces create challenge for good cleaning
Vacuum autoclaves recommended
Monobloc so debris can’t penetrate joints
Made from stainless steel
Dental burs - use? motion? materials? shapes and sizes?
Removal of tissue or material Mainly grind or abrade substrate's surface High-speed burs either diamond or TC Stainless steel in slow speed Mainy different shapes and sizes
Anatomy of a bur?
Shank: fits into handpiece
Neck: joins shank to head, tapered to accommodate reduction in size of cutting blades
Head: contains baldes or abrasive materials
Types of burs - basics? how it works? advantages?
Diamond:
- central metal shank, resin with embedded diamond particles
- diamond wears away substrate (several layers)
- stainless steel hank to avoid vibration
- advanced electroplating ensure diamonds deposited to increase diamond density
Tungsten carbide:
- alternative, brittle, snatch substrate (bur shatter), noisey, grind and chip action
- mainly stainless steel and tungsten carbide head
- milling permits adjust to blade angle and rake
- milling also produce cross-cuts
- indicted for cutting metal alloys
- more efficient
Stainless steel
- removes carious dentine
- cavity prep (undercut)
- lower cutting speed
The advantages of bonding?
No mechanical retentive prep necessary Enhanced retention Seals the margins reduces microleakage Shrinkage reduced Reinforces the tooth structure Allows tooth coloured restorative materials
Definitions of adhesion, dental bonding, wettability, surface tension and sealing?
Adhesion is the force which binds 2 different materials with intimate contact
Dental bonding is the process of attaching resin composite to the underlying tooth using an intermediate material
Sealing is an impermeable barrier between cavity and restorative material
Wettability is to achieve an intimate microscopic contact with another
Surface tension is the ability of the surface of liquid to resist and external force
3 types of adhesion: mechanical, physical and chemical - how they adhere?
Mechanical:
- all surfaces are rough microscopically
- irregularities connect with one another
- can become intimately related
- sliding is resisted by friction
Physical:
- dipolar molecule attracted to an opposing charges
- orientated so that oppositely charged ends are adj to each other
- weak bond but greater SA
Chemical:
- chemical interacts with the substrate surface
- failure occurs within on of the substrates rather than the interface
Aims for dental bonding - basics of dental bonding (aims) - (tooth, restorative material and bonding agent)?
Tooth surface is rough and an intervening layer of resin fills these micro- and macroscopic irregularities
Restorative material is also rough due to filler which causes microscopic irregularities on its surface
Bonding agent flows into the irregularities produced by the surface modifications of the enamel
Resin solidifies on polymerisation and the 2 material become mechanically bound
Essential prerequisites of a substrate surface? - cleaning (why not prophy paste)?
Rough High SA Good wetting properties High surface energy Free from debris and organic material (prophylaxis with pumice slurry to remove salivary pellicle, don't use prophy paste as it is oily) Dry
Bonding to enamel - properties? outer layer?
Acellular
Inorganic
Dry
Prismatic structure
Outer layer is amorphous - provides limited retention
Acid etch technique - function? forms? outcomes of etch to enamel (key)? creates appearance?
Partly demineralised the crystalline structure of the enamel Formation of clefts which penetrate between 20-30um Outcomes: - increases SA for bond - increases surface roughness - decreases surface tension - increases wettability - increases surface energy Gives a frosted appearance
Bevelling enamel - what is it? what it creates? alters what?
Etching pattern improved by bevelling the enamel (margins prepared at angle 120 degrees)
Removes the outer amorphous enamel exposing fresh enamel for bonding
Alters the angulation of enamel prisms
Etching time considerations for enamel - older and younger patients (enamel differences)?
Older patients have more fluorapatite which is stronger
Younger patients have a thicker layer of aprismatic enamel
Problems with etching - over etching - consequences?
Greater removal of prisms Less porous Loss of etch pattern as too deep Reduced ability of resin to form tags in enamel Impossible to determine
Problems with etching - re etching - why to re-etch and consequences?
Etching can only be done once on the same surface
Repeating = over-etching
Contamination = re-etching
Etch - acid type? concentration? if in doubt?
Ortho-phosphoric acid
Between 35-37%
If in doubt refer to manufacturers instructions
Pros and cons of liquid and gel etch types? example?
Liquid: - tends to run - easier to remove - applied by brush - more effective (no additives) Gel: - stays in place - must be removed thoroughly due to colloidal silica (decreases strength) - syringe - reduced penetration depth
Scotchbond Etchant (3M)
How to use etchant clinically - agitation critical?
Surface of enamel shouldn’t be scrubbed
Acid should be gently agitated
Movement of acid will introduce fresh acid to surface to enhance efficiency and effectiveness
Bonding material - chemical constituents? function? outcome? form bond how?
Low viscous dilute dimethacrylate resin system
bis-GMA diluted with TEGDMA
Applied to enamel after etch and flows into crevices
Resin monomer polymerised to form solid polymer
Resin tags impregnate enamel surface?
Bonding to dentine - properties? problematic for bonding? smear layer? contaminants? special bonding characteristics? removal of smear layer?
Living tissue and Heterogenous
Always wet, surface hard to clean and freq contaminated
Layer is debris
Dentinal fluid flows out of tubules = contaminant
Material needs to be miscible with water when bonding dentine
Smear layer removed by phosphoric or nitric acid
Bonding to dentine - 3 chemical processes - priming? coupling agent? sealer? (process of each)
Priming is removal of smear layer and etching the dentine
Coupling agent is impregnation of dentine by a water-miscible fluid
Sealer is the application of a fluid which will bond impregnated material to restoration
Dentine priming (etching) - function? exposes and its function? over-etching consequences?
Modifies or removes the dentine smear layer
Demineralises the intertubular dentine and the periphery of the dentinal tubules
Exposes the collagen matrix, acts as a scaffold that may be impregnated with the primer
Over-etching can cause collagen collapse, same with over-drying
Dentine coupling agent - properties? basic structure?
Bifunctional monomer is amphiphilic, as it bonds to the hydrophobic restorative material and the hydrophilic hydroxyapatite
M-R-X
Bonding agent carriers - function?
Solvents displace water in dentine and are removed by evaporation
Rapidly passess into dentinal tubules
Pros and cons of alcohol, acetone and water-based carriers?
Alcohol: - evaps slower - less sense to dentinal moisture - worse water chaser - reduced postOP sensitivity - increased shelf-life Acetone: - fast evap - more sense to dentinal moisture (technique sense) - good water chaser - highly volatile - bad odour and many coats Water: - hydrophilic - longer drying time - rehydrated demineral collagen - non-sense to dentinal moisture - interfere with adhesion - had to remove
Hybridisation - when does it occur? forms? failure causes?
During infiltration of the partly demineralised dentine with the bonding agent
Forms a hybrid layer
Failure results in voids leading to microleakage
Wet bonding - consequences if over-dried? dentine ideal appearance?
Reduced bond strength
Collagen can be rehydrated but will not revert to normal
Dentine should have a glassy appearance
Reasons to air thin the bonding agent? and consequences?
Evaporate residual solvent Give agent an even spread Incomplete spread Voids Failure PostOP sensitivity
Bonding agent and changes in viscosity - ideal conditions and consequences?
Lower viscosity = better penetration
Air entrapment can lead to an oxygen inhibition layer
Functions for the following chemicals - 1. PENTA, 2. polyalkenoate methacrylates. 3. Bis-GMA, 4. HEMA, 5. Vitrebond, 6. 10-MDP, 7. silicon dioxide, 8. solvents, 9. bifunctional acrylic amides, 10. phosphoric esters, 11. acrylic acid, 12. glycerol methacrylate, 13. maleic acid, 14. camphorquinone, 15. benzoyl peroxide, 16. butylated benzenediol, 17. glutaraldehyde, 18. potassium fluoride and 19. antibacs?
Adhesive promoter Difunctional monomer Regulates strength Wetting agent Moisture tolerance Bonds to metals and hydroxyapatite Increases strength Carrier for resin Etchant/wetting agent Etchant/adhesion promoter Dentine conditioner Wetting agent Dentine conditioner Photo-initiator Dual-cure system Shelf life Collagen fixation Fluoride release Antibacterial
Total etch technique - process? pros?
Etch enamel and dentine together Less time-consuming Higher bond strength Etch with MI Wash and dry Apply bond and dry Light cure and apply resin
Selective etch technique - differences?
Etch enamel and dentine separately
Reduces potential to over-etch
Advantages and disadvantages of etch techniques? example?
Adv: higher bond strength and easier to do
Dis: over-dry, more consuming, techn sense, more steps more failure and nanoleakage
Adper Scotchbond Multi-purpose adhesive
Self-etching systems - definition? pros? application? example?
Attempt to combine conditioning, priming and bonding
Reducing work, less techn sensitive, less sensitive to wetness of dentine, consistent and stable, reduced leakage, impossible to over-etch
Act material and apply to tooth
dry and apply bond
dry and cure
apply composite and cure
Adper Prompt L-Pop
Universal bonding agents - definition? chemical composition? technique used? example? Bond strength (MPa)
Capable of being used as total etch, self-etch or selective etch for direct or indirect restorations
Contains 10-MDP
Move towards selective etch to avoid over-etching
Scotchbond Universal
20MPa
Stresses on the bonding system - stresses? weaker initial bonds why?
Thermocycling Load Chemical degradation Shrinkage Weaker bonds due to shrinkage
Bond failures - adhesive and cohesive?
Adhesive: failure at interface between 2 different materials
Cohesive; failure within substrate or adhesive
Mixed: both
Bonding success is dependent on? - factors?
Procedure and marginal seal gained
Wetting properties of composite
Shrinkage (polymerisation and stress)
Adhesion level
Process of the polymerisation reaction? - monomer definition? - Curing?
Process of reacting monomer molecules together in a chemical reaction to form a 3D network or polymer chains
A monomer is a small molecule that has the potential of chemically bonding to other monomers of the same species to form a polymer
Light-cured mainly
Advantages of light curing - work time? polymerisation? chemical? tertiary amine? time? cure? conversion? unconverted monomer? optimum conditions for conversion?
Extended working time as it is command set
More consistent means of polymerisation
More even distribution of chemicals within paste (blending optimised)
Amount and concentration of tertiary amine required in the material can be lowered
Saving clinic time
Improved cure quality
Higher level of conversion of the monomeric component to the polymer (most light activated materials convert between 50% and 70% monomer to polymer) and unconverted monomer lead to leaching and degradation of restoration with time
Requires heat, light and Pa which increases mechanical properties
Disadvantages of light curing - price? compatibility? energy? attenuation?
Expensive hardware
Compatible systems (wavelength of chems and light)
Adequate energy and correct wavelength or suboptimal restorations
Problems with light attenuation
Mechanism of photo-polymerisation - initiator? products? react? free radicals?
Initiation relies on the use of a photo-initiator (activated by light of specific wavelength)
Light breaks down the photo-initiator to produce molecules (photolytic reaction)
Act chems react with an amine
Free radicals produced initiate the polymerisation reaction
Once initiated the reaction goes to completion
Creates a chain reaction (products continue the reaction)
Mechanism of cure - energy? monomer formation? linking? increased speed? reduced propagation?
Sufficient amount of light energy at the correct wavelength of light required
Monomers polymerise to form a rigid cross-linked polymers
Chains linking via methacrylate groups
Accelerate polymerisation reaction by increasing conc of photo-initiator
Materials sets quicker but propagation phase has shortened and so shorter chains and weaker
Chemical conversion of a photo-initator - wavelength? chemical process?
Specific wavelength
Activated diketone + amine –> free radical
Free radical + monomer + copolymer
Forms a polymer
Photo-initiators - example? colour? disadvantages? example?
Alpha-diketone: yellow, problematic when lighter shade of composite is being manufactured and influences final shade
Camphorquinone: can be used with bleach shades (Ivocerin and PPD)
Absorption of photo-initiators - example, range and peak? peak absorption definition?
Camphorquinone: most sensitive between 390 and 510nm with a peak at 470nm
Peak absorption is a wavelength at which the maximum excitation of a photolytic chemical reaction occurs
PPD and Lucirin TPO most effective between 380-430nm
Spectral band - compatibility? definition? better bulb?
Wavelength of light from curing lamp and peak absorption of photo-initiator must be compatible
Spectral band part of spectrum at which light polymerisation unit mat produce chemical excitation
Halogen > LEDs
Types of curing lights - examples? range? intensity? filtres? cooling? deterioration? Poly Wave differences?
Halogen: - broad spectral range - intensity can vary across band - filtres required - cooling fans essential - overtime filament ages and reduces efficiency? Plasma: - N/A LED: - effective polymerisation - very powerful - narrow spectral band - consistent output of wavelength over time - cooling unnecessary - Poly Wave - increased compatibility and more than 1 LED
Consequences of incomplete curing - examples and explanation?
Pulpal inflammation (chemical trauma)
Discolouration and marginal staining (oral fluids can diffuse into the material)
Decreased wear, compressive and flexure strength
Formation of marginal gaps (debonding) - leading to microleakage
Factors affecting cure - Manufacturers - refractive index? shade? opacity? variable diketone/amine chem? particle size? Clinicians - thickness? follow? exit portal? light distance? curing programs? total energy concept?
Manufacturer’s:
- refractive index of resin/glass; needs to be matched, mismatch can lead to light attenuation and reduced polymerisation efficiency
- shade of material; darker loger curing times and reduced light passage
- opacity; longer curing times, attentiationis reduced
- variable diketone/amine chem; altered concentrations influence polymerisation reaction, ambient light susceptibility, shorter polymers and reduced mechanical props
- particle size; light attenuated slower through bulk of fine particles causing reduced penetration
Clinician:
- follow the instructions
- reduced thickness of increments of composite
- exit portal of light guide should be parallel to surface being cured
- distance of light; as close as possible
- curing programs; pick the correct one reduces shrinkage and improve mechanics
- total energy concept; dose = maximum curing time x intensity
Irradiance - safety net? over-cure? pulp? tip size?
Better to increase curing time slight to ensure full cure
Can’t over-cure but increased energy leads to more heat generated - thermal trauma to pulp
Tip size:
- small tips are used for tacking restorations, wider tips irradiate a larger area when working with larger restoration
- tapered (turbo)
CUring light maintenance and care - cleaning? checking? integrity process? black spots? orange shield?
Clean immediately after use
Inspect for damage
Check light output regularly
Cure a 3mm deep cylinder, if soggy bottom = not functioning adequately
Black spots = damaged fibres (replaced >10%)
Orange shield for eye care - reduces retinal damage
Types of curing programs - slow? ramp? soft start and boost? benefits?
Slow cure: light energy remains at intermediate levels and curing time is increased
Ramp cure: light energy increases linearly with respect to time over a period of cure
Soft start: light energy starts at low level and then reverts to maximum output
Boots: constant emission of light energy at maximum output
Aim to improve degree of monomer conversion, reduce polymerisation shrinkage and stresses and improve mechanical properties
What is dental amalgam - definition?
An alloy (containing silver, tin and copper) + mercury
Alloy constituents and their functions - silver, tin, copper (results in?), zinc, mercury
Silver - combines with tin
Tin - combines with silver
Copper - increases mechanical props, decreases creep, increases corrosion resistance and decreases the amount of y2 phase (greater mechanical prop and faster set
Zinc - scavenger of oxygen (good moisture control)
Mercury - catalyst (needs to be pure)
Amalgamation reaction equation - outer layer? y2 phase (constituent? physical properties? comparison to y and y1?)
y + m = y1 + y2 (and unreacted y)
y1 - silver/mercury
y2 - tin/mercury
y - silver/tin
Outer layer reacts, bulk stays unreacted (core within matrix)
y2 phase is tin-mercury, most chemically and electrically active component, inferior physical to y and y1, more prone to corrosion, more mercury released, prone to creeping, ditching and poor tensile strength
Definition of tensile and compressive strength?
Ability of a material to withstand pulling forces in an axial direction
Ability of a material to withstand axially loaded pushing forces
Higher copper amalgam alloy - equation? types (dispersed phase and ternary)? problems with copper alloys?
y2 +silver-copper = copper-tin + y1)
Dispersed phase: silver, tin and copper (poss zinc)
- dispersed
- contain silver-tin or silver-copper
- increased compressive and tensile strength
Ternary: uncompositional
- 3 elements silver, tin and copper in one particle
Problems: overcome by bonding
- greater microleakage
- increased post OP sense, recurrent caries
Types of alloy - difference? types (lathe cut - activity, spherical - production process and admixed)
Differ via particle size and shape
Lathe cut:
- irregular, affects mercury reactivity, different sizes and reactivity needs to be reduced
Spherical:
- heated until molten, sprayed into an inert atmosphere and particles coalesce forming spheres
Admixed:
- combo called blended
Properties of dental amalgam - brittle? y2? thermal cycling? dimensional change? working time?
Brittle - high complessive but weak in tension
More y2 = weaker
Thermal cycling - microleakage, facture and pulpal trauma
Dimensional change affected by particle size and shape, alloy type and quality of condensation
Working time influenced by chem composition, particle size and ageing treatments
(fast, regular or slow-set)
Indications for amalgam restoration?
Class I and II (poss III and V cavities)
Amalgam cavity design - depth? line angles? cavosurface angles? enamel? retention?
Cavity depth of 2mm Rounded internal line angles Cavo-surface angles between 90-110 Remove unsupported enamel Retention - undercuts, slots or grooves and dentine pin
Bonding dental amalgam - how and benefits? material used and clinical examples?
Conservation of tooth tissue
Benefits:
- increased retention and fracture resistance
- decreased microleakage, pulpal trauma, post OP sense, recurrent caries, cuspal deflection
Material - polycarboxylate and zinc phosphate cement or resin based composite adhesive
Dual cure - Nexus 3
Resin modified glass ionomer - Vitrebond Plus
Cavity varnishes - what are they? application? function? advantages? disadvantages?
Are natural rosins or synthetic resins dissolved in a solvent (COpal Varnish)
Applied on walls and floor of cavity, evaporates and leaves a thin film (fills gap between dentine and amalgam)
Decreases post OP sense and inhibits microorganism growth (some dentine can be unprotected)
Amalgam packaging - encapsulated advantages? optimal mixing? amalgamators? over and under mixing properties?
Optimum conditions
Precise proportions
Consistent mixing
Reduced mercury spillage
Reduced risk of contamination and mercury vapour release
Trituration - correct time, speed, motion and force
Amalgamators - compatibility with material, lined with aluminum foil (retains mercury) and mercury vapour nullified
Overtrituration - amalgam too hot and wet leading to excessive expansion and reduced strength
Undertrituration - dry and crumbly leading to low strength and poor corrosion resistance
Condensation of amalgam - placement technique? function? mercury? method? poor method?
Incrementally placed without delay (packed separately)
Removes voids and ensure proper adaption to cavity walls
Expels excess mercury bring to surface leaving a surface rich layer
Failure to remove = weak
Hand instrument or mechanical condenser
Overpack - axially and laterally
Poor method causes poorly adapted walls and inferior physical properties
Carving amalgam - method? aim? burnishing function? polishing function?
Probe around the matrix and prior to removal to remove thin edges of amalgam at the marginal ridge
Equalise marginal ridge heights
Morphology - use tooth to guid instrument
Occlusion
Finish
Burnishing - plastic deformation of a surface due to sliding contact creating a rough surface rendering it shiny
Polishing - reduces corrosion, increases marginal adaptation, more aesthetic and easier to clean (releases mercury vapour)
Amalgam disposal - how? mercury spillage content? aspiration contraindication?
Waste amalgam box - capsules and contaminated materials
Mercury spillage - microfine sulphur, calcium hydroxide, washing up liquid and 2L of water
Don’t aspirate mercury spillage = re-released vapour
Adverse effects of dental amalgam use (how they occur) - enamel discolour? amalgam tattoo? galvanic cell? contraindications?
Enamel discolour: - dentine permeability - time of restoration - corrosion and migrate into dentinal tubules Amalgam tattoo: - amalgam particles migrate into soft tissue Lichenoid reaction: - electrochemical reaction and a type IV hypersensitivity reaction (replace restoration) Galvanic cell: - 2 different metals + saliva - electric shock - sulphur helps? - replace? Contraindications: - pregnant people - allergy - aesthetics - objection
Zinc oxide eugenol (ZOE) cement - chemical equation? zinc oxide formation? formulations? constituents (powder and liquid + functions)? indications? reinforcing chemicals (name, formulation, function and product?)
Zinc oxide + eugenol –> Zin eugenolate
Formed by thermal decomposition of zinc salts (350-400)
Powder and liquid or 2 pastes
Powder:
- zinc oxide, rosin (reduces brittleness), zinc acetate (accelerator) and zinc stearate (plasticiser)
Liquid:
- eugenol, olive oil (modifies viscosity and taste) and acetic acid (accelerator)
Indicated as a temporary restoration
Reinforcing chemicals:
- polymethylmethacrylate (increases strength and IRM)
- polystyrene (liquid, increases strength, Kalzinol)
- hydrogenated rosin (powder, reinforcing agent, SuperEBA)
EBA-reinforced ZOE cement - chemical addition and function? structure? ratio difference? hydrogenated rosin advantages? disadvantages? formation in practice? reaction type? product formation? water? setting rate factors? indication?
Ortho-ethoxybenzoic acid added to ZOE cements which increases mechanical properties
EBA forms a crystalline form of zinc eugenolate
Higher powder to liquid ratio(7:1) enhances strength
Hydrogenated rosins reduce brittleness, film thickness and facilitates mixing
Affected by moisture
Mix on a glass slab with powder incorp quickly in large increment into liquid (consistency not sticking to glove, rolled into a cylinder and packed with a plunger then clean instruments)
Chelation reaction
Eugenol forms a salt with zinc oxide and zinc 2-ethoxybenzoate also formed
Water needed for initiator and catalyst for setting
Setting rate:
- powder particle size
- conc of accelerator
- powder:liquid ratio (more powder faster set)
Thickness of more than 2 mm for function as a cavity base
Biocompatibility - pH? cement functions? contraindications? insulator? indications cement? reduced practice factors? retention? solubility? interactions? disadvantages ZOE? indications ZOE?
Neutral pH
Function as a bland sedative to dental tissues, bactericidal by inhibiting bacterial meta and reduces bacterial leakage and pulpal inflammation
Contraindicated to be directly placed on vital pulp tissue (cytotoxic)
Good insulator with low thermal and electrical diffusivity due to high filler content
Used under metallic restorations
Decreased use as it is not minimally invasive (cut more tissue) and microleakage prevention is tubule occlusion (cement no)
Mechanically retentive
High sol in water, eugenol constantly released and gradually breaks down by hydrolysis
Interact adversely with resin composites
Difficult to mix, opaque, no bonding and sol in mouth
Indications such as root end fillings, long-term temporisation (high risk) and endodontic sealer
Zinc Polycarboxylate Cement - chemical equations? constituents of powder and liquid + functions? optimising liquid and powder packaging? powder manufacturing process? setting reaction and structure formation? mechanical properties?
Zinc oxide powder + poly(acrylic acid) liquid forming zinc polycarboxylate (polyalkenoate) cement
Powder:
- stannousF (improves set, anti-cariogenic, enhances strength and aids mixing)
- MgO2 (densifier and white
- silica (improves sintering)
- alumina (complex with acid)
Liquid:
- itaconic acid (prevent gelation via stabilisation)
- maleic acid (more reactive + substitute)
Need to be completely dry
Optimising powder:
- desiccant in bottle cap
Optimising liquid:
- loss of water in aq form
- thicker material
- harder to mix
- alters conc of acid sol
Powder manufacturing process:
- heating 2 main ingredients for 9 hours (sinter)
- sintered mass rounded to reduce particle size and reheated (8hr)
- pigment added for colour
- other constituents added
Setting reaction and structure:
- Polyacrylic acid forms chained cross-lin via zinc ions
- set material have zinc oxide cores within zinc polyacrylate binding unreacted cores
- becomes rubbery as setting
Less likely to fracture
Biocompatibility - poly(acrylic acid) characteristics? pH? pulp?
Viscosity - mixing? mixture ratio impact? disadvantages?
Solubility and erosion - fluoride? MgO2? pH?
Aesthetic - bad?
Adhesion - reaction type? bonding? indication? moisture control? instrument cleaning?
Biocompatibility:
Weak acid and high Mr, not diffuse along dentinal tubules and becomes immobilsed
Returns to neutral after mixing
Good compatibility
Viscosity:
Difficult to mix as viscous
Less powder into mix than recommended (due to hard mixing) causing inferior props
Viscosity increases when setting starts and material stretches if disturbed before set complete
F increases dissolution
Sol increases with more MgO2
Erosion due to acidic pH of mouth
Aesthetic
Opaque due to zinc oxide
Adhesion
Chelation reaction with Ca ions
Collagen bonding and better to enamel than dentine due to Ca conc
Used in non-retentive cavities
Good moisture control as water reduces bond strength
Bonds to stainless steel and so instruments need to be cleaned immediately (alcohol good)
ZPC - powder:liquid ratio? advantages and disadvantages? indications? product example? mixing technique (glass vs paper)? clinical tip?
More powder stronger cement but ability to bond is reduced (less liquid) Adv: - long-term durability - acceptable mechanical props Dis: - hard to mix - opaque - sol in mouth - hard to manipulate - ill defined set Indications: - temp restorations (sedative for pulpal pain and chem bond) - future resin composite - bases (seals dentine) - luting of metal restorations Example: - Poly F Plus - Dentsply Mixing: - glass better (stability, extend work and larger SA)7 - paper loses powder - correct amount of powder, half and mix into liquid Clinical tip: prevent sticking - alcohol as a separator - dappen dish handy - surface becomes smooth
Resin modified glass ionomer cement - composition?
Composition:
- GIC + water-sol resin and modified poly(acrylic acid)
- mod polyacrylic acid have pendant methacrylate groups grafted onto polyacid chain (copolymers)
What is HEMA - name? description? water relation? disadv? biocompatibility (toxicity? contraindication? lining? sealing adv?)
Hydroxyethylmethacrylate
Description:
- small and high reactive monomer
Water:
- hydrophilic swelling
- absorb between 10-600% of its own dry weight
- miscible with water
Disadv:
- cytotoxic
Biocompatibility:
- cause chemical dermatitis
- freed monomer can be toxic to pulp and osteoblasts
- not on vital pulp
- lining to protect pulp and rom high exothermic reaction
- RMGIC seals tubules and decreases microleakage
Chemical constituents - Powder - barium/strontium? dried polyacrylic acid? K persulphate? pigments? (reasons for inclusion?) Liquid - polyacrylic acid? HEMA? copolymer? tartaric acid? water? photo-initiator?
Powder: B/S: - improved strength (radiopacity) DP: - reacts with glass forming poly salt matrix PP: - redox catalysts to provide methacrylate cure P: - shades Liquid: PA: - reacts with glass forming poly salt matrix HEMA: - resin CP: - undergo acid-base and polymerisation reactions (interpenetrating network) TA: - sharpens acid-base reaction set W: - react polyacid and glass PI: - light curing
Effect of particle size - cements? restorations? setting reaction influence? translucency?
Cement: - finner glass Restore: - larger size Setting: - smaller particles allow faster setting Trans: - loss of translucency as size reduced
Setting reaction - process (form matrix? add resin why? resin benefit? resin slow reaction?) polymerisation component (light reaction type? no thicker than? compensate for poor penetration?)
Process:
- polyacrylic acid reacts with glass to form poly salt matrix
- add HEMA to act polymerisation reaction (needs to bo sol in water as cement is water based, and without water no reaction between polyacid and glass)
- polymerised resin phase forms scaffold while ionomer cement matrix if formed
- resin increases acid-base reaction slows
Polymerisation component:
- light act free-radical methacrylate reaction (command cure)
- no thicker than 0.5mm
- no problem with lining
- compensate for penetration dark-cure initiator is incorporated but mech reduced (tri-cure: achieve adequate free-radical methacrylate polymerisation)
Stages of RMGIC setting reaction - dual cured stages (acid base composition? light act formation?) tri-cured stages (same as tri + dark cure?)
Dual cured:
- acid-base reaction (6hrs) but water susceptible (polyacrylic acid mixed with HEMA)
- light activation completed within 10s of curing but also water susceptible (methacrylate group on HEMA reacts with other HEMA and with pendant methacrylate on side of polyacrylic acid chain)
Tri-cured:
- dark cure is a redox reaction (5 mins)
Polymerisation shrinkage - why? comparison to resin composite? when? disadv? thin section problems? Exothermic setting reaction (component? dependent on? temperature? contraindications?)
Why: - resin phase Comparison: - greater than resin composites (3-4% but resin 2.2%) When: - onset of the light-act polymerisation reaction Thin: - margins of cement layer may curl up Exothermic setting reaction: - HEMA - dependent on bulk of material - 12C - may have pulpal implications
Adhesion - mechanism? factors limiting adhesion success (acid base? carboxyl group? shrinkage? micromechanical? water uptake? repair?) adhesion to other materials (extend RMGIC layer why? RMGIC’s surface allows? HEMA allows?)
Mechanism:
- Ca chelation
- collagen bonding
Limiting factors:
- limited acid-base reaction (less acid present)
- carboxyl group necessary for adhesion not available at tooth-restoration interface
- shrinkage resin will stress interface between cement and tooth, pulling it away from tooth surface
- micromechanical interlocking disturbed during polymerisation
- water uptake readapting the cement
- repair unlikely (due to fewer carboxyl)
Adhesion:
- no interaction between RMGICs and setting CaOH
- RMGIC layer extended beyond CaOH cement to gain adhesion to surrounding dentine forming a seal
- RMGIC surface is rough allowing micromechanical retention for materials placed above it
- HEMA allows chemical bonding to other resin materials via crosslinking of reactive groups
RMGIC - mechanical properties? fluoride release (disadv? GIC comparison?) staining (how? depth?)
Mechanical properties:
- resin improves mech, but polyHEMA absorbs water and reduced mech
- better lining as no contact with saliva
Fluoride release:
- restoration starts to degrade as F is released
- releases more F than GIC
Staining:
- prone with time
- due to oral fluid uptake (intrinsic and can’t be removed)
RMGIC - advantages (physical, chemical and clinical)? disadvantages (physical, chemical and clinical)? moisture control importance? mixing importance?
Advantages:
- F
- early strength
- adhesion via molecular bonding
- long working time
- not moisture sensitive
- low erosion of cement margins
- simple to use
- command set
- finishing after light cure
- seal dentinal tubules
- release benzoyl iodides/bromides (antibacterial) (but cytotoxic)
Disadvantages:
- exothermic/shrinkage on curing
- monomer leach
- swelling due to moisture uptake (phase separation)
- command set reduces rate of acid-base reaction
- material weaker where redox setting of resin is used
Moisture control:
- important
- reduce binding, mech prop and longevity
Mixing:
- need to break microcapsules to allow mixing of their content (allowing dark-cure)
RMGIC - indications? core build up prerequisites? dressing prerequisites? deciduous prerequisites? lining prerequisites?
Indications:
- small CI cavities
- CIII and V cavities
- non-carious tooth surface loss lesions
- core buildups (need >50% and must be kept moist to prevent chemical curing)
- dressing (occlude dentinal tubules and reduce sensitivity)
- luting
- restore deciduous (minimally invasive and F)
- linings (seal dentinal tubules to reduce microleakage and post OP sensitivity with similar radiodensity to dentine) (more powder increases strength but decreases retention and vice versa)
- blocking undercuts for indirect restorations
- bonding dental amalgam
Presentations of RMGICs - 3 different types? placement into the cavity (adv and disadv)? Paste/paste presentation (nanotechnology?) Finishing (when? with what?)
Types: - powder/liquid - encapsulated - paste/paste systems Cavity: - directly into cavity but difficult to manipulate - minimises voids Paste/paste: - nanotechnology enhances polishability Finishing: - straight away - sharp or rotary - use finishing burs or polishing with discs
Compomers - definition? composition?
Definition:
- combination of fluoride release with advnatges of resin composites
Composition:
- dimethacrylate and difunctional resin monomer containing carboxyl and methacrylate groups
Difunctional resin monomers - filler (main component? function? source of? forms a with? how radiopacity?) resin type and function? source of? hydrophilic monomer example and role? photo-activators examples?
Filler:
- fluoro-alumino-silicate glass which imparts strength
- source of F ions forming a salt matrix with carboxylate
- contains lithium or strontium for radiopacity
Resin:
- TCB resin allows cross-linking
- source of carboxyl group
- glycerol dimethacrylate enhances water diffusion within matrix
- camphorquinone and a tertiary amine
Compomer - setting reaction (stage 1 - initiation? polymerisation type? chemical bonding via? and stage 2 - between chemicals? taken up? fluoride release? matrix formation)
Stage 1:
- initiated by light allowing free radical polymerisation reaction leads to cross-linking of edn group EDMA and methacrylate groups on difunctional resin forming polymer matrix in which glass is trapped
Stage 2:
- between carboxylate of difunctional and glass
- water taken up by resin
- acid side groups start to dissolve outer surface of glass releasing fluoride ions (water in and F out)
- polysalt matric if formed around glass
Compomer - physical properties (shrinkage? curing?) adhesion (system?) fluoride release (reliant on? release comparison to GIC/RMGIC? conc gradient?) watersoprtion?
Physical:
- polymerisation shrinkage seen between 2-3.5%
Adhesion:
- micromechanical
- etch necessary
F release:
- reliant on secondary setting reaction (carboxyl and glass reaction)
- slower release than GIC and RMGIC
- dependent on conc gradient
Watersorption:
- can lead to the excessive expansion of the material causing tooth damage
Compomer - stain resistance? wear resistance?
Stain: - uptake of oral fluids leads to discolouration Wear: - wear occurs quickly - but less wear than resin composites
Comparison of compomer to composite - wear? shrinkage? opacity? cure depth? polish? fluoride? water sorption? stain resist?
Compomer: - wear lower - shrink greater - opacity higher - cure smaller - polish same - fluoride slight - water high - stain lower Composite: - vice versa
Compomer - indications? contraindications?
Indications: - CIII - strong enough and good aesthetic - CV - matrix flexible retained in abfraction lesions - fissure seal - flowable - luting of metal based restore - restore deciduous Contraindications: - aesthetic (composite better) - core build ups (not strong enough) - luting ceramics (risk fracture) - CI, CII and CIV (not strong enough) - temp root fill (poor seal)
Compomer - presentations? product examples?
Presentations:
- compules (light and moisture tight)
Examples:
- Dyract and F2000
GIC - full name? components? reaction? special release?
Full: - glass polyalkenoate cement Components: - glass and acid Reaction: - acid-base Release: - F
Glass - example? composition (radiopacity? translucent? release?) compounds in glass? manufacturing glass (temp? process?) passivation treat (function and how?)
Example: - fluoro-alumino-silicate Comp: - strontium and lithium for radiopacity - aluminium/silica ratio for leucency - ion release determines solubility Comp: - alumina - silica - CaF - AlF - AlPO4 - NaF Manufacturing: - mix heated to between 1150-1450 - poured onto metal plate then into water - forms glass frit Pass: - to reduce reactivity - washed in acetic acid leads to ion depletion
Acid - examples? combo (why)? facilitate reaction (group?) Mr influence on GIC (props to mech and work time? maleic acid function? tartaric acid function?)
Example: - polyacrylic - polymaleic - copolymers of polyacrylic Combo: - convey diff props Facilitate: - carboxylate group creating a carboxyl and hydrogen ion to facilitate reaction Mr: - higher acid Mr gives better mechanical props - also increases viscosity - maleic allows encapsulation by making it less viscous - higher Mr quicker setting - tartaric accelerates setting phase
Setting reaction - process (glass attacked? pH rises causing? aqueous phase? polyacrylic acid? cations? form?
Glass: - attached by H from acid, liberating Al and Ca. also releasing Na and F pH: - aqueous phase pH rises leading to ionisation of polyacrylic Aq; - mig of Al and Ca into Aq Polyacrylic: - ionisation undwinds the polymer chain increasing viscosity of paste (proportional with cation conc) Cations: - condense on polymer chain Form: - insoluble salt
Condensation and maturation - Ca importance and formation? Al polyacrylate form? F complexes? maturation process (mech props?)
Ca:
- condensation occurs more rapidly with Ca forming Ca polyacrylate gel formed
Al:
- takes longer to form as Al is 3 charged
F:
- complexes of F in the sol
Maturation process:
- further cross-linking of matrix and more cations bound onto the polyanion chain
- mech props increase substantially during maturation
Mech properties - compressive? flexural? solubility? erosion?
Compressive:
- adequate (less than dentine)
Flexural:
- low compared to other restorative materials
Solubility:
- varies with time of exposure to the oral environment
Erosion:
- better resistance if protected from moisture
Adhesion to the tooth - chemical? 2 mechanisms (polyacrylic acid? CaPO4 and AlPO4 interface? and H bond?) bond strength (special and why?) conditioning the tooth (how and why?)
Chemical:
- chemically bonding to the tooth without intermedial materials
Polyacrylic:
- displaces surface PO4 and Ca, enters the hydroxyapatite structure and forming a Ca polyacrylate salt
Interface:
- intermediate layer of CaPO4 and AlPO4 and polyacrylates are formed at the tooth/restore interface
H bonds:
- within dentine col
Strength:
- low but durable
Special:
- can rebond if broken as the polyacrylate and Ca ions are close together
Conditioning:
- by acid conditioner (citric and polyacrylic acids
- removes smear layer and debris
Fluoride release - released how? rate of release factors? changes in F release? longevity? increased longevity factors? F ion conc function?
Released how:
- from the glass during the setting reaction and lie within the matrix and free to migrate
Release factors:
- conc of ions in cement
- conc of ions in surrounding environment
- pH
Changes:
- initial washout assoc with maturation
- then slows down to normal
- lasts for years
Factors:
- can uptake F from environment if conc higher, recharged and can be re-released when external conc is reduced (F sink)
F:
- sufficient to inhibit bacterial growth and plaque build-up
GIC - aesthetics (better after? colour changes?) wear (maturation why? variations in wear? why wear? erosion why?)
Better:
- after maturation of matrix (2-3 days)
Colour:
- more resistant to changes in colour when compared with resin based composites
Wear:
- must be allowed to mature fully protected from washout by saliva
- rapid wear during first 10 days
- wear occurs due to loss of glass particles from matrix when under load-bearing areas
- erosion may occur when pH remains low over long time
GIC - advantages (bond? adhesion? caries? accessories? situations? cavity?) and disadvantages (mech? physical?
Adv: - dynamic bonding which can regenerate (abfraction lesions) - chemical adhesion (non-retentive cavities) - cariostatic - no hardware - home visits and non-ideal situations - no rubber dam - limited cavity prep Dis: - poor aesthetics - weaker (no large cavities) - washout - damaged by early finishing - long setting time - protection from desiccation - early low mech strength
indications (classes? temp? protection?) contraindications (classes? size?support? appearance?)
Indications: - atraumatic restorative tech - deciduous teeth - tunnel prep - CIII and V (non-carious tooth loss) - intervisit endodontic access cavity resto - long-term intermediate resto - core construction (needs sufficient tooth) - PRR - liner/base - dressing - fissure sealant - luting a crown Contraindications: - CI or CII cavities (heavy load) - larger cavities of post - cores with little or no tooth support - aesthetics are primary concern
Cavity preparation - form? main aim? cavity conditioning - example? timing? process? Hand mixing GIC - adv and dis?
Form:
- rounded internal form with no sharp edges
No need to prepare extensively just remove caries
Conditioner:
- Fuji cavity conditioner (20% polyacrylic acid)
- apply for between 15-30s
- rinse of using water and gently dry
Hand mix:
- produces optimum if adhered to precisely
- inferior props result from ratio, dispensing and mixing style
Effect of a higher powder:liquid ratio (mechanical and chemical properties)? Effect of lower powder:liquid ratio (mech property reduction %)?
Higher ratio: - increases compressive strength - setting time decreases - more viscous - reduced chemical bond formation - low mechanical props (glass particles not wetted sufficiently by acid to start setting reaction) Lower ratio: - properties decline - deleterious effects - reduced mech properties of 60% per 25% reduction from standard
Mixing the powder and liquid - (proportions of each? spatulation tech?)
Shake the bottle
1 scoop of powder flattened using the flattener
2 drops of liquid positioned vertically
Vigorous spatulation
No plastic spatula
Use glass slab
Quick wetting of powder with acid necessary
Encapsulated GIC - advantages over hand mixing? disadvantages over hand mixing? Content of encapsulated GIC (outer and inner)?
Adv:
- proportions less than GS
Dis:
- maintain Pa on pillow for at least 2 seconds
- insufficient liquid will make the substance highly viscous
Content:
- outer: nozzle, cap, clip and plunger
- inner: access hole, plunger, powder, pillow and plastic clip
Moisture control - area prerequisites? saliva contamination? water balance?
Area: - needs to be clean and dry Saliva: - decreased props - decreased adherence Water: - not allowed to give up water during setting so the water balance in the material is maintained
Placement - instruments? manipulation problems and tips? aid structure and setting? Class V accessory?
Instruments: - flat plastic Manipulation: - due to its sticky consistency - use water as separating medium Structure: - matrix strips for placement - apply Pa until set leaves smooth surface V: - cervical matrices - use tweezers
Finishing - when? average time? failure to follow? inferior to? least damage process?
When: - after manufacturer's recommended time Average: - at least 3m and some up to 6m Failure; - will lead to surface damage Inferior: - to matrix strips whatever method of finishing Least damage: - under fine water spray
GIC - protection from water contamination - susceptible when? problem caused? timing? consequence? examples?
Susceptible: - during the initial phases of the setting reaction Problem: - disrupts matic and damages surface Timing: - at least 1hr after placement Consequence: - mech props substantially reduced Example: - Fuji varnish
Protection against desiccation - isolation? clinical appearance? consequence? example (resto and luting cement)?
Isolation: - area is isolated for won on other teeth Appearance: - extensive cracks and crazing Consequence: - crack never heal and cause potential fracture and failure of resto Example: - Fuji IX GP for restorative - AquaCem for luting cement
Definition of base and lining?
Base:
- functions as barriers against chemical irritation, provides thermal insulation and resist forces applied during condensation of the restorative material (dentine replacement material)
Lining:
- materials are placed as thin coatings, and their main function is to provide a barrier against chemical irritation
Calcium hydroxide cement - base or lining? chemical reaction produced? presentation? constituents (base and catalyst and reason for inclusion? base/catalyst suspension) setting reaction (reaction type? ingredient needed? energy produced?) and structure (complex similar to?)
Base or lining: - lining Chemical: - on reaction between CaOh and salicylate forming a Ca disalucylate complex Presentation: - 2-paste system Constituents: Base: - CaOH; main - ZnOH; filler (radiopacity) - ZN stearate; filler (radiopacity) All suspended in plasticiser (N-ethyl toulene sulphonamide) Catalyst: - TiO2; filler - CaSO4; filler (radiopacity) - Ca tungstate filler (radiopacity) Suspended in 1-methyl trimethylene disalicylate butane-1-3-diol ester Setting reaction: - chelation reaction between Ca and butylene glycol disalicylate - water need - slightly exothermic Structure: - Ca disalicylate complexes surrounding CaOH - zinc oxide eugenol cement
Calcium hydroxide cement - mechanical properties (strength? on loading? sectioning?) solubility (stability? plasticiser addition 2 types? overtime?) biocompatibility (degradation? pH change on release? acidogenic bacteria? hydrophobicity of plasticiser?
Mech:
- poor weakest of all setting cements
- deforms plastically once set upon loading
- thin (air-thinned)
Solubility:
- unstable but soluble, degrades in water presence
- hydrophilic sulphonamide plasticiser included to control viscosity but permits water permeation
- facilitates breakdown of cement and determines degrad
- addition of hydrophobic hydrocarbon plasticisers resist water ingress
- overtime cement degrades and lost due to leakage and moisture
Biocompatibility:
- degradation not desirable but allows CaOH release
- CaOH increases pH (12.5) bactericidal/static
- acidogenic bacteria dormant or die
- hydrophobicity for plasticiser determine CaOH release
Calcium hydroxide cement - mode of action (reactions? alkalinity? removes? neutralise? irritates? formation? cell stim? differentiate? formation of? Ca derivative? calcification of?) retention?
Mode of action:
- causes inflammatory reactions
- alkalinity causes liquefaction necrosis of superficial pulp
- removes inflamed tissue
- neutralisation of toxicity
- irritates adj pulp and causes minor inflamm
- dentine bridge formed
- pluripotent pulpal cells stimulated
- differentiate into odontoblasts
- tertiary (reparative) dentine laid down forming calcified bridge walling off pulp from base of cavity
- Ca derived from the pulp not cement
- calcification of carious dentine also occurs
Retention:
- no adherence to dentine chemically or micromechanically
Light cured CaOH cements - addition of resin (examples)? HEMA? energy released? pulp risk? strength? disadvantages? effective at? pulp capping (contraindication?)
Addition:
- UDMA, bis-GMA and HEMA
HEMA:
- permits water ingress so there will be diffusion of fluid within cement
Energy:
- higher exothermic reaction during polymerisation
pulp:
- when placed close to pulp
Strength:
- slightly enhanced
Brittle:
- less
Disadv:
- periphery of cement can lift away from cavity result from polymerisation shrinkage
Effective:
- sealing dentinal tubules
Pulp capping:
- contraindicated with direct application to exposed pulp
- form physical barrier between exposed pulp and other materials
Adv (stim form? barrier?) and Dis (strength? energy? adhesion? light cured? pH) of setting CaOH cements?
Adv: - stimulates formation of reparative dentine - physical barrier over exposed pulp, allowing dentinal tubules to be sealed Dis: - low compressive strength - soluble - breakdown - no adhesion - High pH causes local irritation - exothermic - light cured shrinkage
Indication for CaOH cements?
Deep cavity over pulpal floor
In/direct pulp capping
Mixing and placement of CaOH (timing? appearance when ready?) (size? setting speed?) - 2 paste? clinical examples?
Mixing: - similar consistency and amount - blend 2 pastes for 30s - ready to apply when only one colour is present (2 pastes are diff colours) Placement: - small thin layer at base - air thin - covered with GIC - setting is rapid Clinical: - Life by Kerr Hawe
Tricalcium silicate cements - what are they? related to? bioactive? better property compared to other? material choices (MTA? Bio-Aggregate? Biodentine? Tri-calcium phosphate?)
What: - group of materials based on calcium silicate chem Related to: - mineral trioxide aggregate Bioactive: - placed in direct contact with living tissues Better: - others calcium silicate have a slow set so newer products are quicker MTA - ProRoot MTA - MTA-Angelus - Neo MTA plus - TheraCal LC Bio-aggregate: - Innovative Bioceramix Biodentine: - septodont Tri-calcium phosphate - Pulpdent
Biodentine Septodont - increased rate of reaction gained by? constituents (liquid and powder? and their function?) setting reaction and structure (reaction? type of reaction? dissolves and forms? precip? porosity? surrounded by a matrix? Ca release?)
Gained by:
- particle size distribution
- inclusion of CaCO3 and CaCl
Liquid:
- hydrosoluble polymer water reducing agent (reduces water content and helps retain workability - surfactant)
- CaCl (accelerator)
Powder:
- tricalcium silicate (core)
- dicalcium silicate (2nd core)
- CaCO3 and CaO (filler)
- FeO (shade_
- zirconium dioxide (radiopacifier)
Setting reaction:
- cement + water = chemical reaction
- hydration reaction
- Ca silicate partially dissolves in liquid
- produces a hydrogel of hydrated silicate
- this precipitates on remaining silicate particle surfaces and spaces between particles
- leads to significant decrease in material’s porosity and increase in compressive strength
- on setting hydrating tricalcium silicate surrounds by matrix of calcium silicate hydrate, CaOH and CaCO3
- Ca release: CaCO3 acts as nucleating site on which Ca silicate hydrates (high Ca release)
Biodentine - physical properties (strength? flex? stability? fluid? washout? colour? radiopacity?) biological properties - placed on? bioactive (induces? hard tissue form? plugs found?) biocompatibility - pulp risk? pH? seal? microleakage? marginal adaptation? bonding?
Similar compressive strength and hardness to dentine
Similar flexure as dentine
High dimensional stability
Low fluid uptake and sorption
High washout
Doesn’t discolour
Similar radiopacity to dentine
biological prop:
- placed on dentine and vital pulp tissue
Bioactive:
- induces pulp cell prolif and cytokine release
- hard tissue formed with interface synth with dentine via dynamic mineral interaction zone similar to hydroxyapatite composition
- plugs of material observed in dentinal tubules
Biocompatibility:
- low risk on pulp
- pH 8.2 (promotes inflamm cell)
- good seal
- better microleakage resistance than RMGIC
- excellent marginal adaptation to cavity
- bnds to affected dentine (treat with NaOCl)
biodentine - indications?
Indications:
- deep cavities
- reversible pulpitis (dressing and smoothed for subsequent restorations)
- carious or iatrogenic exposure
- trauma
- pulpotomy in primary molars
- perforation repairs
Evidence which supports pulpal protection (biodentine)
More effective than calcium hydroxide for maintaining long-term pulp vitality after indirect and direct pulp-capping
Higher success rate, less pulpal inflammatory response and more predictable hard dentine bridge formation than calcium hydroxide
Clinical protocol for biodentine? - process of placement and repair? contraindications? other products (NRC and TheraCal LC? properties?)
Rubber dam Prepare cavity Clear margins Remove infected dentine Mix material Place cavity Allow material to set for 12 mins Leave as dressing then smooth Or cover with composite or amalgam Contraindications: - don't layer with GIC or ZoE (reacts) - don't etch with H3PO4 (selective etch) - need >2mm of resin composite to mask opacity - don't desiccate (microleakage) NRC: - compressive strength and pH similar to white MTA - not cytotoxic TheraCal LC: - light cured - resin does not react with cement - no leaching of CaOH so doesn't work
What is the definition of a resin-based composite material?
Composed of a chemically active resin and an inorganic filler bound together by a silane coupling agent
What forms the principal resin bis-GMA?
Bisphenol A and glycidyl methacrylate
(Bisphenol A diglycidyl ether dimethacrylate) - Bis-GMA
Describe the structure if bis-GMA?
Long chain monomer with a methacrylate group at either end of an aromatic spine
Name 4 types of diluent monomers that can be used in composite ti control the viscosity?
Methylmethacrylate (MMA)
Ethylene glycol dimethacrylate (EGDM)
Tri(ethylene glycol) dimethacrylate (TEGDMA)
Urethane dimethacrylate (UDMA)
Name 6 ways in which the filler component of resin-based composite improve the properties?
Increased strength
Increased wear resistance
Reduced polymerisation shrinkage
Improved optical properties such as colour, fluorescence and translucency
Radiopacity conveyed by adding heavy metals such as barium salts
Less heat production during polymerisation (filler acts as a heat sink)
Reduced thermal expansion
Name the 2 filler types?
Glasses
Ceramics
Name the 2 main glass fillers for RBCs?
Crystalline silica
Colloidal silica
What is the definition of a ceramic filler type?
inorganic, non-metallic solid prepared by the action of heat and subsequent cooling
What do ceramic filler types contain?
Zirconia-silica filler
Zirconium oxide
What effect does the filler particle size and shape influence the RBCs?
Properties
Amount of filler that can be added
Describe the properties of a macrofilled composites?
15-35um
Larger particles can support higher loads as they have a lower surface area to volume ratio
Good mechanical properties (high strength)
Wear resistance poor
Difficult to finish and polish to an acceptable level
Describe the properties of a fine particle composite?
Reduces wear to some extent
Means easier finishing and smoother surface
Mechanical properties are enhanced
Better packing of the filler
Describe the properties of a microfilled composite?
Colloidal silica filler as sub-micron particles
Has an affinity for water and if uncoated takes up water leading to hydrolytic degradation
Filler loading substantially lower
Strength of these materials is not as high as that of conventional resin composite
Wear no better than conventional composite
Describe the properties of a hybrid composite?
Ideal distribution of packing to achieve an optimum filler loading is called a trimodal distribution
Pros of microfine and macrofine composite
Describe the properties of a nanofilled composite?
Non-agglomerated and non-aggregated particles of between 20–70 nanometres
Act as a single unit enabling high filler loading and high strength
Strength of a hybrid material but are easier to polish as the individual filler particles are much smaller
Explain how the effect of filler loading can affect the properties of RBCs?
Strength in compression increases but with it brittleness
Resistance to wear is potentially increased but too much filler may lead to surface breakdown as there is inadequate resin to bind the filler together
Paste becomes stiffer as more filler is added so affecting manipulation
Adaptation to the cavity margin and wall may be compromised
What is the role and definition of a silane coupler?
Silane molecule is bifunctional with groups that react with the inorganic filler (hydrophilic groups) and others that react with the organic resin (hydrophobic groups)
What is the disadvantage of using a silane coupler?
Bond between the filler and resin needs to be durable and strong but degraded by water absorbed by the material during clinical function
Leads to creep and wear and then fracture
Name the 3 types of setting mechanisms for RBCs?
Chemically cured (sometimes referred to as self-cured or dark cured) Light cured Dual cured = light + chemically
Describe the formulation for a chemically cured system?
Supplied as a two-paste system
Setting reaction commences when the two pastes are blended
What does every light-cured RBC need? and give 2 examples?
Photo-initiator + Accelerator (tertiary amine)
Diketone (e.g. camphorquinone)
Phenylpropanedione (PPD)
What is used to stop colour change overtime?
2-hydroxy-4-methoxybenzophenone
Works by absorbing electromagnetic radiation
What material is used to increase shelf-life and premature setting?
Monomethyl ether of hydroquinone
How is radiopacity added to RBCs?
Such as barium, zinc, strontium and ytterbium)
Added to the radiolucent filler
How is the tooth colour added to RBCs?
Inorganic oxide compounds such as iron oxides are added to the resin in very small quantities
What consequence of polymerisation shrinkage is the main?
If material shrinks markedly, gap left at the tooth / restoration interface leading to microleakage
Fracture
Debond
Name the 4 ways in which you can start to overcome polymerisation shrinkage?
Material selection
Method of material placement into the cavity
Amount
Position
Use of the correct matrix system when constructing the approximal wall
Employing various curing techniques
How can material selection reduce polymerisation shrinkage? and give an example?
Lower molecular weight monomers that exhibit greatest shrinkage on polymerisation
Many products now have a mix of bis-GMA with bisphenol A polyethylene glycol diether dimethacrylate (bis-EMA) and UDMA as their resin component
No TEGDMA
How can material placement reduce polymerisation shrinkage? and give an example?
Influenced by the shape of the cavity Configuration factor (C factor) - ratio of bonded to unbonded surfaces Higher the ratio the more stress is potentially incorporated into the situation
What is the definition of the C factor?
Minimum number of cavity surfaces are contacted by the material
Incremental build-up
With each cured increment shrinkage is minimised and compensated for to some extent
Why can composite be funny to work with in a dental practice?
Ambient light can start the setting process
What is the solution to the oxygen inhibition layer?
Create an anaerobic environment such as using a matrix strip or cover with glycerine or dentine bonding agent
What is the definition of hygroscopic expansion?
Material swells with water sorption
Starts c15 minutes after initial polymerisation and continues for up to 10 weeks
Expansion offsets the effects of polymerisation shrinkage
How can the coefficient of thermal expansion effect the properties of RBCs?
Tooth and material usually similar
Tooth / restoration interface is stressed during thermal cycling as restoration shrinks (cold) or expands more than the tooth with hot so compressing the tooth tissue with which it is in contact
What material mimics oestrogen?
Bisphenol A
WHy is HEMA dangerous?
Powerful dermatological sensitiser causing chemical dermatitis
When are dual-cured resin composites used?
Mainly core build-up materials or for bonding indirect restorations
Hardness is such that they cut like dentine
May also be used to bond posts in situ as well as being used as the core build-up material
What are the advantages and disadvanatges of RBCs?
Adv: - aesthetic - conservative cavity - command set - bonding to tooth - reduced microleakage - low thermal conductivity Dis: - time consuming - hydrophlilic - photophilic - shrinkage - tech sense - decreased longevity - more bacteria - hard to finish
