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