DENTAL MATERIALS + NATS Flashcards
1
Q
- What can fibre reinforcement be used in?
A
To improve fatigue resistance and impact strength of acrylic dentures, post construction, temp bridges, periodontal splinting, eliminating of metal in PFM restorations
2
Q
- What is the historical significance of fibre reinforcement?
A
Glass → fine glass fibres, ancient phoenicians and egyptians, 1932 Dale Kleis
3
Q
- What are the different fibre types?
- Which are the more commonly used and why?
A
Carbon, Kevlar, Polyethylene, Glass
Polyethylene and glass; used as shade matches for teeth
4
Q
- What are the properties of Kevlar fibres?
A
Aromatic polyamide, pleated structure - atoms radially arranged in sheets, weak flexural, compression and low abrasion resistance; yellow, thermal and mechanically stable, chemically resistant
5
Q
- What are the properties of polyethylene fibres?
A
Shade match, natural crystalline polymers, drawn at lower temp then mp into filamentous fibres, ductile, low density, translucent
6
Q
- What are the properties of glass fibres?
* What are the components?
A
Shade match, melts of mixtures of oxides, cool w/o crystallisation, translucent, high modulus of elasticity
SiO2, Al2O3, CaO, MgO etc.
7
Q
- What are the orientation options of fibre orientation?
A
Unidirectional, bidirectional, random
8
Q
- What physical properties does fibre orientation affect?
A
Type of matrix, type of fibre, quantity of fibres, length of fibres
9
Q
- What is the best orientation of fibres?
A
Perpendicular to point of lod
10
Q
- Why are fibre reinforced composites relatively short-lived?
A
Because surrounding resin absorbs water and degrades the bond between fibres and resin matrix over time
11
Q
- How does moisture in fibre reinforced composites lead to failure?
A
Water absorbed into material by diffusion and enters voids producing expansion of resin → strain resin fibre interface, decreased flexural properties → failure
12
Q
- What are luting cement used for? And name the two types
A
Material used for retention of indirect restoration. It seals the space between restoration and tooth.
Active and passive
13
Q
- What are precious alloys?
A
Gold baby
14
Q
How can fibre reinforced materials be used clinically?
A
Improve fatigue resistance + impact strength of acrylic dentures, approximate dentine characteristics for post construction, temp bridges, periodontal splinting, elimination of metal in PFM restorations, improved aesthetics, better biological tolerance
15
Q
- What can be used to accommodate for luting cement thickness?
A
Die relief
16
Q
- In a Cochrane database systematic review, what is said to have greater risk of failure?
A
Cast metal compared to carbon fibre posts, however evidence is unreliable
17
Q
- What are alloys with noble metal content of at least 25% but less than 75%?
A
Low gold casting alloys, silver palladium alloys
18
Q
- What does the selection of luting cement depend on?
A
Type of restoration being cemented eg; veneer, resin retained bridge, conventional crown bridge
19
Q
- What are the steps for a cohesive gold restoration (gold fillings)?
A
Line cavity with oxiphosphate material then small pieces of gold foil are placed in the cavity and it is incrementally filled up, apply pressure with a spring loaded plunger mellot that is cold welded into position
20
Q
- Why do you line a cavity with oxiphosphate material before doing a gold restoration?
A
Allows the first piece of gold to be effectively kept in the cavity
21
Q
- What is active luting material best suited for?
A
Bonding to tooth and restoration, role in retention and marginal seal
22
Q
- What is passive luting material best suited for?
A
Fills gap between tooth and restoration but no bond between the resto and tooth.
23
Q
- When was the first use of ceramics in dentistry?
A
1770-1774 by Duchateau and Dubois de Clemant making the first porcelain dentures
24
Q
- In passive luting cement what provides the retention of prep?
A
Taper, height of prep, surface roughness and mechanical locking
25
1. What are the ideal properties of luting cement?
_Biocompatible_ - contact with tooth and perio tissue
_Retention_ - active: additional bonding, passive: prep morpho and mechanical interlocking of surface irregularities.
_Mechanical properties_ : high tensile strength, fracture toughness, fatigue strength, wear resistance
_Marginal seal_ : low solubility, this leads to active luting advantageous and reduced hypersensitivity
_Low film thickness_ : allows full seating of restoration with good marginal adaptation
_Ease of use_ : powder:liquid ratio and working/setting time
_Pseudoplastic_ : coat fit surface of restoration without slumping but flows readily under pressure on fitting
_Radiopacity
Aesthetics_ : ceramic restoration
_Inhibition of plaque accumulation_: easy to polish and elimination of air inhibition layer - resin composite
_Antibacterial
Clear up of excess
Shelf life_
26
1. What is the high fusing temperature of traditional dental porcelain?
1300-1400C
27
1. What is the low fusing temperature of traditional dental porcelain?
850-1100C
28
1. What happens to glass when it is repeatedly heated?
It gains new crystalline component and becomes leucite
29
1. What is cold welding?
When using pure gold for a resto, pressure is applied using a spring loaded plunger mellot to compress goid foil down the cavity and form metallic bonds at point of contact. Prior to placement the gold needs to be heated to 250 degree celsius.
30
1. Why do you need to heat pure gold foil up to 250 degree celsius?
To drive off any grease
31
1. What is the thickness of pure gold foil used?
1 μm
32
1. What is the manufacturer’s goal of leucite inclusions?
To have slightly higher expansion/contraction than the underlying alloy to put porcelain in slight tangential compression to prevent crack propagation within ceramic
33
1. When building up a ceramic crown why shouldn’t you heat it up too rapidly?
Too rapid = steam, crumbling, explode
34
1. How can you limit crack propagation?
A glaze of low mp can help by tensioning surface
35
1. What are the chemical constituents of ceramics?
Kaolin, feldspar
36
* What is Kaolin?
Better known as clay, hydrated aluminosilicate
37
* What is Feldspar?
Mixture of aluminosilicates - potassium aluminosilicates, sodium aluminosilicates
38
* What happens at room temperature?
Forms colloidal suspension in water, surface tension effects provide coherence + plasticity to porcelain powder permitting manipulation by the tech
39
* What happens at 450C?
* Al2O3 2SiO2 2H2O → Al2O3 2SiO2 + 2H2O
Unstable metakaolinite
40
1. What happens at 1000C?
Metakaolinite decomposes to form 3Al2O3 2SiO2
41
1. What happens at 1150C?
Feldspar melts and decomposes
42
1. Why is porcelain chosen for a PFM? (idk how to phrase this q ok)
Porcelain has increased coefficient thermal expansion by addition of leucite, reduces stress concentrations that could have led to crack propagation
43
1. What are the desirable properties of PFMs?
Not melt when firing porcelain, rigid to support thin porcelain veneer, bond to porcelain, similar coefficient of thermal expansion to porcelain
44
1. What are the available PFM alloys?
High gold, low gold
45
1. Why isn’t Cu used in high gold PFM alloys?
It risks porcelain greening
46
1. What does Pd in low gold alloys do in PFM alloys?
Increase melting temp, decrease coefficient thermal expansion
47
1. What are the available PFM metals?
Silver palladium, nickel chromium
48
* What are the advantages of silver palladium?
Higher modulus value + melting range compared to high gold, cost saving
49
* What are the advantages of nickel chromium?
High modulus + melting temp
50
* What are the disadvantages of nickel chromium?
Prone to high casting shrinkage w/ voids, poorer bond strength to porcelain than other alloys, poor biocompatibility due to Be + Ni
51
1. What are the alternatives to PFM alloys?
Captek, CAD-CAM
52
* How does Captek work?
Wax strip adapted to refractory die, fixed, 2nd wax strip adapted to network, fired, gold infiltrates network → metal substructure for porcelain build-up
53
1. How can you overcome shrinkage?
1. Pressed ceramic powder expands and crystallises to fill lost wax mould
Casting of special glass into lost wax mould followed by heat treating e.g. DICOR
Pressing solid ingots of filled glass into lost wax mould e.g. empress
Lightly sintered aluminium oxide to form touching necks between touching particles + infiltrate w/ glass e.g. In-ceram
CAM
54
1. What are the purposes of added filler particles?
To improve mechanical properties, improve opalescence, colour, opacity
55
1. What are the properties of polycrystalline ceramics?
Atoms packed in dense arrays, inhibits crack propagation, tougher and stronger than glass ceramics, relatively opaque
56
1. What is the firing temp of zirconia in tetragonal form?
2370-1170C
57
This thing???? Just learn it - memorise the lines or smth
58
1. What are the properties of ceramics?
Potentially aesthetic, prone to crack propagation, brittle
59
* Why are ceramics brittle?
Time dependent strength decrease → static fatigue. Alkaline hydrolysis of SiO from solubilisation of Na2O and K2O in feldspathic component
60
1. What are monolithic ceramics used for?
Single-unit anterior prostheses, veneer, inlays, onlays adhesively cemented, ceramic coverage of a metal framework or ceramic substructure
61
1. What are the properties of porcelain?
Hard, relatively resistant to chemical attack, good thermal insulator
62
1. How can you maximise clinical durability of ceramics?
Use max occlusal thickness, use highest elastic modulus substrate possible for core, bond the restoration, develop broad NOT pinpoint occlusal contacts
63
1. What are the challenges of cementation?
Aesthetics, brittle nature of ceramics
64
1. What are the general guidances on cementation of ceramics?
Use of trial paste essential; if resin cementation, silanation just prior to cementation; generally conventional acid base cements must not be used EXCEPT in the case of zirconium oxide based ceramics, use dual cured resin composite
65
1. Which ceramics have high translucency?
Empress esthetic, eMax Press Empress CAD, In-Ceram spinell
66
1. Which ceramics have moderate translucency?
Vita Y-Z zirconia, eMax press-moderate opacity, vita alumina, Lava zirconia
67
1. Which ceramics have low translucency?
eMax press-high opacity, In-Ceram zirconia
68
1. What are the 4 types of traditional casting gold alloys?
* Type 1 - low strength
* Casting subjects to slight stress
* eg// inlays
* Type 2 - medium strength
* Castyings subject to moderate stress
* eg// inlays & onlays
* Type 3 - high strength
* High stress situations
* eg// onlays, thin casting backings, pontics, full crowns
* Type 4 - extra high strength
* Casting thin in cross sections
* eg// saddles, bars, clasps, crowns, bridges, partial denture framework
69
1. Disadvantages of using pure gold as a resto material?
Its time consuming, you dont use any luting cement, its usually only good in protected cavities eg// class 1, buccal pit. The rigidity and elasticity of pure gold is insufficient in high stress situations and there is potential for overworking the pure gold during placement which can lead to work harden (which can be beneficial to some degree)
70
1. How do you express gold content by?
* Carat : parts by weight of gold in 24 parts of alloy
* Fineness : parts by weight of gold in 1000 parts of alloy
71
1. An alloy with 75% gold content in them is expressed by?
18 carat, 750 fine
72
73
1. Based on the % composition summary of traditional casting gold alloys, why is it that when the gold content decreases, the hardness increases?
Due to solution hardening - formation of solid solutions with gold
74
1. As we move from 1-4 on the % composition summary of traditional casting gold alloys table, what **increases?**
Hardness, proportional unit, strength
75
1. As we move from 1-4 on the % composition summary of traditional casting gold alloys table, what **decreases?**
Ductility and corrosion resistance
76
1. All passive luting cements are water based as aqueous acid. Give examples of this:
Zinc phosphate - good compressive strength, low tensile strength and high solubility
Zinc polycarboxylate - antibacterial properties, adhesive to enamel and dentine
GI luting cement
RMGI luting cement
77
1. Zinc phosphate luting cement is the oldest and routinely used by 30% dentists. How is it presented?
Powder and liquid
_Powder_: zinc oxide, up to 10% magnesium oxide as it improves compressive strength, adds colour
_Liquid_: aqueous phosphoric acid 45-64%
78
1. How is zinc phosphate luting cement mixed?
Working time - 3 to 6 mins. Gradual incorporation of powder over a large area of mixing slab.
Slacking the fluid - this is when a small amount of powder is added to fluid approx minute before. This extends setting time
Using a chilled glass slab will increase working time, powder incorporation and strength and decreases solubility
79
1. What is the setting reaction of zinc phosphate luting cement ?
Sets with acid base reaction. Dissolution of surface of ZnO powder (insoluble hydrated zinc phosphate matrix crystals, effectively binding unreacted ZnO particles). Slightly exothermic. Viscosity increases rapidly, 50% in strength in 10 mins and 100% in 24hours. Shrink slightly on setting. No antibacterial effect
80
1. pH of zinc phosphate depends on the thickness of the mix. What is the pH?
1.6-3.6 pH which is relevant to vital pulp
81
1. How is zinc polycarboxylate presented?
_Powder_: zinc oxide, up to 10% magnesium oxide
_Liquid_: aqueous copolymer acid 30-40% (high viscosity)
Alternative presentation: acid freeze dried and added to powder. For liquid: distilled water
82
1. What is the setting reaction for zinc polycarboxylate luting cement?
Acid dissolves in zinc oxide. The zinc ions cross link between carboxyl groups on polyacrylic acid chains. Unreacted powder bound in matrix of zinc polyacrylate
83
1. What is the working time of zinc polycarboxylate luting cement?
Short working time of 30-40s. Can be extended by adding tartaric acid. This is mixed on cold glass slab
84
1. What is the outcome of higher powder:liquid ratio?
Shorter working time. Ratio can be altered. Impacting on physical properties as it appears viscous but pseudoplastic
85
1. pH of zinc polycarboxylate luting cement
pH 3-4 this results in less injuries to pulp, rapid increase in pH and polyacid too large to penetrate dentine
86
1. What are some of the properties of zinc polycarboxylate?
Lower compressive strength, higher tensile strength, reaches 80% full strength in 1 hour. Soluble in acid, cleans up messy
87
1. How is GI luting cement presented?
_Powder_: fluoro-alumino-silicate glass
_Liquid_: aqueous poly alkenoic acid
Alternative presentation: acid freeze dried and added to powder. For liquid: distilled water
88
1. What is the setting reaction of GI luting cement?
Chemical set:
- Dissolution - Ca2+ ions released first then Al3+
- Gelation
- Hardening: Al3+ trivalen, slower to be released from glass, Al3+ ensures strong cross linking of polymer chains
Slow setting:
- Dissolution and initial set 3-6mins
- Viscosity increases rapidly
- Hardening can take 7 days
- Needs protecting - prevent dissolution/contamination
89
1. What are the properties of GI luting cement?
- fluoride release
- bond to enamel and dentine - seal, retention
- initial acidity - can cause pulpal inflammation
- compared with ZnO cements: better compressive strength, low tensile strength and fracture toughness and less soluble
90
1. What are the constituents of RMGI luting cement?
Components of GI polymonomer eg HEMA, Bis-GMA. No photo initiator - chemical cure only
91
1. Why is RMGI better than GI?
- lower solubility
- improved biocompatibility, fluid release, physical properties (tensile strength) and adhesion to tooth tissue
92
1. Why is RMGI less desired than GI?
- can undergo hygroscopic expansion
- avoid under conventional all ceramic crowns
- suitable under zirconia core/CAD CAM crown
93
1. Give example of RMGI:
RelyX luting and RelyX luting plus (3M ESPE)
94
1. Constituents of Resin-based luting cements resins
1. - silanated filter
- resin eg. Bis-GMA
Lower filler content, hence lower viscosity
Most dual cured - chemical and light
95
1. What are the 2 types of resin-based luting cements?
- conventional resin luting cements
- chemically adhesive resin luting cements
96
1. Conventional resin luting cements:
What are they used for?
All ceramic resto, indirect composite and quartz fibre posts eg. veneers, dentine bonded crowns
How is it bonded? Conventional way - etch, rinse, dry, dentine bonding agent
Bonding to fitting surface of ceramic: etched with hydrofluoric acid and just before cementing. Silane coupling agent applied and air dried. Micromechanical and chemical bond respectively
97
1. What is hydrofluoric acid?
- very toxic (only used in lab)
- must be neutralised - if not may leach out leading to tissue damage later
- tends to slump - periphery of veneer may not etch as well
- can cause damage to periphery of ceramic
98
1. Chemically adhesive resin luting cement
What is it used for?
Adhesively bonding to metals eg. RRB, metal veneers and poorly retained indirect restoration
99
1. What properties are conferred by the constituents?
* Ag (silver)
* Slight strengthening effect
* Counteracts reddish copper tint
* Cu (copper)
* Increases strength
* Lowers melting point
* If content has more than 16% alloy will tarnish (copper oxidises - will tarnish)
* Pt/Pd (platinum/palladium)
* Increases both strength and melting point
* Zn (zinc)
* Acts as a scavenger
* When used up, this function is taken over by (AB)Cu…later
* Undesirable as it impairs physical properties of the casting if Cu is used up in this way
* So always have soome fresh alloy in the button to avoid having deficit in Zn and subsequent substitution of zinc to oxygen as a scavenger
100
1. Which types are possible for heat treatments?
Type 3 and 4 - results in further hardening i/e : precipitation hardening of Ag/Cu and Au/Cu systems
101
1. Which types are **NOT** possible for heat treatment?
Type 1 and 2 - due to lack of silver and copper that is required for the necessary atomic diffusions
102
1. How are heat treatments achieved?
* Melting and cooling and alloy results in a new crystal structure
* Takes time
* Length of time influences the structure - if you allow it to cool slowly to room temperature, premature precipitation and order hardening will happen
103
1. How do you avoid premature hardening?
* Cool the casting rapidly from excess of 600 degrees celsius
* Red colour of sprue region of casting indicates above 600 degrees celsius
* Once the red colour lost through cooling - cold water plunge
* Result in fine grain structure
* Disintegrates investment
104
1. What happens if an alloy contains Pt/Pd?
* Cold water cooling risks coring which is undesirable from a corrosion perspective
* To prevent corrosion, alloy must be heated to 700 degrees celsius for 10mins (called quenching - aka. Homogenisation heat treatment… aim is to eliminate coring and improve corrosion resistance)
105
1. Why do we usually NOT use gold?
* Expensive sia
* Volatility of stock market
* Developed to use less gold - low gold alloys
106
1. What are low gold alloys?
* Low gold content alloys
* Normally have gold of 45-50% but could be down to 10%
* High in palladium
* White in color
107
1. What does silver palladium alloy contain?
Primarily Ag and Pd, little to no Au
108
1. Benefits of low gold alloys?
Classified into 4 types, it utilises the same casting equipment, low cost and good clinical performance
109
1. What are the properties of silver palladium alloys?
Lower density compared to gold alloys
* Affects castability due to low density requiring casting equipment to exert greater force than normal traditional casting alloy
* May dissolve oxygen which is NOT good cause it can cause porosity
* Displays lower ductility than conventional gold alloys
* Care must be taken when in use
110
1. How does the try-in luting cement paste work?
If there is no try-in paste, more light is reflected
If there is try-in paste, more light is transmitted and therefore looks more realistic
111
In respect to the tooth and restoration where is resin luting cement placed?
Between veneers and etched tooth surface & denting bonding agent
112
Using the luting cement to bond metal
1. _Base metal alloy (Ni-Cr)_:
- roughen fitting surface w/50um alumina grit: micromechanical retention
- chemically adhesive resin luting cement: modified Bis-GMA resin. **Carboxylic monomer**, 4 META eg. C&B superbond. **Phosphate monomer**, MDPeg. Panavia 21,F
_Precious metal alloy_:
- chemically adhesive resin luting cement has low affinity
- modify fitting surface:
**Tin plate - irregular surface, attracted to tin oxide on alloy surface
Silica coating to metal - then use silane coupling agent
Metal primers - bifunctional monomer - one end methacryl group, other mercapto or thiol group**
113
1. Caldicott guardian consent
What is principle 1?
Justify the purpose for using confidential information
114
1. Caldicott guardian consent
* What is principle 1?
* What is principle 2?
* What is principle 3?
* What is principle 4?
* What is principle 5?
* What is principle 6?
* What is principle 7?
1. Justify the purpose for using confidential information
2. Don’t use personal confidential data unless absolutely necessary
3. Use the minimum necessary personal confidential data
4. Access to personal confidential data should be on a strict need-to-kno basis
5. Everyone w/ access to personal confidential data should beware of their responsibilities
6. Understand + comply w/ the law
7. The duty to share info can be as important as the duty to protect pt confidentiality
115
What is this graph?
What data is required?
What must be looked at? (i also dk how to phrase this q ok)
Kaplan-Meier survival analysis
Date of placement, last date of follow up, outcome - survival/failure
The confidence intervals - difference between the upper and lower dotted lines
116
If the graph looks like this, what happens?
There are no confidence intervals shown therefore judgement cannot be made
117
1. How can the lab predict the durability of materials?
* What happens if it survives?
* What happens if it fails?
Restorations subject to on and off loading in function; define in advance survival number of cycles and cross head speed, apply cyclical force 2N to test upper load limit; initial test upper load limit is 60% of applied load equivalent for mean flexural strength, record number of cycles to failure or survival
Increase upper applied load limit by set increment
Lower the upper applied load limit by set increment and start again
118
1. How do you calculate fatigue limit?
Fatigue Limit (MPa) = Lowest stress + increment \* (A/N _+_0.5) failure data, use -, survival data use
119
How do you interpret this graph?
Sample A fails with less stress than sample B, so A is less dependable than B as B has a lower probability of failing at an applied stress of 200MPa
120
1. How can you assess dependability?
Using the Weibull statistical distribution
121
* How might the low values of strength be explained?
Specimen faults, porosities
122
What does a low Weibull modulus mean?
A wide distribution of fracture stress values and a long tail at low values of stress - possible unreliability
123
* What does a high Weibull modulus mean?
A close grouping of fracture stress values - better dependability
124
1. According to Davidge et al. what does a prolonged application of stress show?
It shows stress insufficient to induce short term failure will ultimately fail in time due to the subcritical growth existing defect of flaws i.e. static fatigue
125
1. Whats digital workflow?
* Combination of technologies employed by the dental team to primarily provide pts w restorative care Converting analogues, eg// cast to digital stuff
* Data acquisition (using diff devices to acquire info)
* CAD Design stage ( using design software specific to virtually manipulate plan and design)
* CAM manufacturing phase ( where diff machining and processing tools are employed to create physical devices like crown, bridge)
* Final processing and tx delivery
126
1. What are the advantages of digital workflow?
streamline info exchange chairside to lab. Lan to chairside
- optimise productivity
- archive design for repeat manufacture eg lost denture
- use established and novel materials, avoiding lost wax technique
127
1. How is digital impression recorded?
Introral scanner. Digitised in lab conventional imps, model cast from imps
128
1. How does the CAD/CAM scanner work? Eg Leitz
- all contact surface
- works best with flat profile shapes
- some can rotate probe to reach into crevasses and anterior spaces and so needs complex maths to define shape as an x,y,z, coordinate system
129
1. What are the two main methods of data acquisition?
Clinical and Laboratory
130
1. What is under clinical method of data acquisition?
*
* Intraoral scanning (IOS)
* Impression wand (handheld device used for intraoral scanning)
* Systems :
* iTero, Trios - confocal macroscopy, white light)
* Direct scan (sterioscopic vision)
* Lava COS (active wavefront sampling, blue light)
* CEREC AC
* Same working practices & principles remain in digital just like conventional eg// tissue retractions, clear margins
* Output - output screen provides real time & 3D film type (DIACOM/DCM - digital imaging and communications in medicine)
131
1. What is under laboratory method of data acquisition?
*
* Benchtop scanning
* Desktop optical scanner
* Surface scan
* Dental model scan
* Conventional impression scan
* Standard triangle language output - describes only the surface geometry of a 3D object, no present color/texture attributes, only elevation & distance
* Early scanning technique - laser light to scan (ben over the contours on model, sensor detects lines to determine the shape), not rly accurate, prone to produce flawed restorations
* Therefore, nowadays structured light eg// series of light patterns projected onto surface of model and recorded by sensor and has a higher accuracy
* Bench top scanner - texture scanning (high res. Cameras capturing pictures of gypsum model/impressions then itll overlay on a 3D model which enhances the visualisation & surface detail which increases the realism of 3D models), color, texture, life-like
132
1. General principles for non contacting scanner work?
- emits some radiation (laser source → passes thru projection lens → hits object → reflects back to collecting lens → camera captures; has a charge coupled device)
- distance between outwards and return path
- detect the reflection from surface of radiation
- time the round tip (scanner - surface - scanner)
- determines elevation of only one point
133
1. What is the time of the flight scanner of non contacting scanner used for?
To measure more than one point. Rotatable mirrors added to move and measure points. Can yield from 10,000 to 100,000points per second
134
1. What builds up on the time of flight concept?
Triangulation
135
1. Clinically what scanner is used?
Handheld scanner for intraoral that can be moved in different direction
136
1. What are the other non-contacting imaging methods?
_Parallel confocal imaging technique
The moire Effect
Active wavefront sampling_
137
1. What are the patient factors that may be affecting the accuracy of handheld scanners?
ENOUGH
- limited pt mouth opening
- pt movement
- salive
- i/o humidity
138
1. What are the anatomical factors affecting the accuracy of handheld scanner?
Tooth formation and tooth position
139
1. What is XML and why is it used?
eXtensible markup language - software, hardware independent tool for storing and transporting data
It simplifies:
- data sharing and transport
- platform changes, data availability
- expansion/upgrade to new operating system without losing data
- addition/removal of data as the XML application will still work
140
1. What is the aim of material and processing consideration?
Produce a good fitting restoration
141
1. What are the current CAM methods?
Reductive and additive
142
1. What are the rapid prototyping methods for current CAM methods?
- stereolithography (SLA): UV laser beams solidify photosensitive resin layers into 3D polymer
- selective laser melt (SLM): continuous layering build up process
- selective laser sintering (SLS): applied to plastic, glass, ceramic, alloys
143
1. Materials used in CAM
- _zirconia and alumina cerami_c:
- supplied as green.
- on sintering shrink 20-35% by volume
- For accuracy needed to be measured and convey blank density to the milling unit (scan barcode and feed into comp) allows for correct shrinkage for good fit.
- _glass ceramic_:
- correct machining essential
- post machining crystallisation may produce distortions that are not tolerated
- machining when product is crystalised could damage the machine → adversely affecting the materials property
- _types of ceramic blanks_:
- green - powder pressed/cast to form by manufacturer
- partially sintered - blanks subjected to heating by manufacturer
- fully dense - fully sintered and dense
144
1. What can be designed digitally?
Crowns, bridges, veneers, inlays, removable partial denture, complete dentures, fixed and removable ortho
145
1. Benefits of digital design overview?
*
* Constantly improving tech
* Time saving
* Cost efficient
146
1. Benefits of digitally designed fixed prosthesis?
*
* Full complement of resto options
* Adaptive design tools
* Virtual articulator - replicates aesthetics, function, guidance& occlusal relationships
* Realtime digital monolithic crown design
147
1. What is the meaning of benchmark for digital materials?
God fit, functions and aesthetics
148
1. What is the benchmark for digital materials?
All ceramic eg// Emax CAD
149
1. What are the two main fixed restorative materials?
All ceramic and zirconia
150
1. What are the variety of metals that can be created in the digital workflow?
DPM( digital precious metal) crown/inlay, DNP(digital non precious metal) post and core
151
1. What is the downfall of metal restorations that are designed digitally?
They’re still manufactured the same way as conventional methods in terms of casting and finishing
152
1. What are the CAM methods?
- Reductive
- Additive
- Pattern produced in burnout plastic
- Rapid prototyping methods
153
1. What is the reductive CAM method?
- Its cut from block of optimised properties or green stage block w/ post machining txt to optimise properties.
- 3 axis milling machine (x,y,z)
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1. What is the additive CAM method?
3D printing - build up in successive layers to desired shape, pattern produced in burnout plastic and rapid prototyping methods
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1. What are the common machining and performance concerns?
- Machine damage → leaves in the resto as residual stresses → early clinical failure by future crack propagation
- Minimal machined thickness
- Machine tolerance
- Merlon - for quality control. Asking the machine to shape material to specific thickness of Merlons
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1. What possibilities does CAD factor in for?
- Shrinkage factor in all direction
- If blank is composed of many layer, making it complex to model
157
1. What are the new possibilities associated with CAD/CAM?
-
New denture materials
- Frenetic industrial activity
- Potential to provide appliances with greater comfort and improved aesthetics
- Eliminate metal from denture and reducing oral and systemic illness linked with p/p (caries)
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1. Metal free denture in the past:
- 1950’s: Polyamide (Nylon) - crystalline: acrylic flexible, engages greater undercuts without the need of clasps. Excellent aesthetics
- 1986’s: Acetal resin (polymethylene) - crystalline polymer - good clasp material used but needed to be short in length and wide in cross section. This lead to plaque build up
Both materials were high modulus of elasticity, high strength and good heat resistance
159
1. What are the metal free dentures now utilised?
One of them being: Polyarylether Ketone Polymer:
- Polyetheretherketone (PEEK)
- Polyetherketoneketone (PEKK)
- Aryl ketone Polymer (AKP)
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What is the suitable use for materials used for metal free dentures?
- Reductive (milling) by CAD/CAM
- Thermoplastic - injection moulding/extrusion & compression moulding. Requires careful temp control to avoid porosity leading to poor finish
161
1. Babes, tell me about digital removable partial dentures and its benefits
*
* Basically the method is the same as conventional in terms of tx planning, design and design verification… clinical steps are the same too like making a study model and then taking 2nd imps.
* ONCE 2nd imps are scanned, then you start the digital design where you’ve got a 3D cast and a 360 degree view of realtime digital RPD design
* You can check path of insertion and undercuts through virtual surveyor (RED for deep undercuts, YELLOW for shallow undercuts)
* Got diff diff tools for u to use to create the design then do design verification
162
1. What is laser sintering?
Using powdered metal and high strength laser to diffuse them tgt and become one single layer of metal. It builds up over hours and becomes a big framework
163
1. What are the types of metal free framework?
Flexible denture(pink color in lecture slides), acetal denture(cream color in lecture slides)
164
1. How to manufacture and design a digital complete denture?
Impressions and occlusal registration are done conventionally then only scan models to have a 3D version of it then you can combine with digital workflow and work virtually
165
1. What are the major anatomical landmarks?
Sulcus depth, retromolar pad, canine position
166
1. What is Pounds 1971 Triangle Denture Concept
Where the lingual surfaces of the lower molars are situated between two lines projected from buccal and lingual aspect of retromolar pad to mesial aspect of canine
Basically you want the complex software algorithms to present an ideal denture tooth position according to arch and occlusal registration
167
1. What does the virtual articulator provide us with???
Physical motions and responses for each tooth in the denture arch allowing for greater occlusal stability and a defined functional path
168
1. How many files are produced for each denture?
Two - denture base and arch of teeth
169
1. Two main manufacturing protocols that exist are?
Printing - both denture base and denture teeth are printed separately
Milling - base plate and denture teeth can be milled on same block of PMMA
170
1. Tell me about implant restorations?
Digital planning - includes surgical and restorative procedures, helps improve communication and gives you predictable results
171
1. Tell me about data acquisition stage for implants
Scan the oral cavity or scan the cast
Use the scan body to accurately locate the implant in the arch (accurately translate the position of implant in oral cavity into digital file to be utilised into implant software)
172
1. What are the design stages in implant workflow?
Slightly more complex but basically the same principles as other fixed restos: adaptive tools used to create the abutment where the resto sits and then subsequent crown, bridge or bar is designed around that
173
1. What is the leading material used in digital implant manufacture?
Titanium - biocompatibility and its strength to weight ratio
174
1. What are the advantages of additional applications in digital dentistry?
Can help w patient monitoring, dental education and digital dental revolution in which realtime virtual planning could revolutionise the tx planning of pt care … ur clinician and pt and technician can communicate in realtime in virtual environment providing instantaneous discussion and problem solving
175
What is a composite material?
A composite material is a combination of two materials with different physical and chemical properties.
176
What is fibre reinforcement?
Fibre reinforcement is a composite material made of a polymer matrix reinforced with fibres.
177
The stiffness of a material is measured by its?
Modulus of elasticity.
178
What is polymerisation?
Polymerisation, any process in which relatively small molecules, called monomers, combine chemically to produce a very large chainlike or network molecule.
179
What occurs in a free-radical polymerization?
Free-radical polymerization are chain reactions in which the addition of a monomer molecule to an active chain end, regenerates the active site at the chain-end
180
There are 4 types of traditional casting gold allows, which type is for extra high strength used for casting thin in cross sections.
Saddles,
bars,
clasps,
bridges
and partial denture frame works.
181
Gold content is expressed as?
Carat and fineness
182
Why, as gold content decreases, does hardness increase?
More formation of solid solutions with gold.
183
Luting cements are used to cement which type of restorations?
Indirect restorations.
184
What type of cement would be used in a post and crown indirect restoration?
Luting cement
185
What is the purpose of a die relief?
Die relief, by means of a paint-on die spacing material, is the most common method of achieving sufficient space between metal castings and tooth surfaces for cement to flow during seating
186
What is a luting cement?
Material used for retention of indirect restorations and to seal the space between the restoration and the tooth.
187
Die harderner is applied to help prevent?
chipping or flaking of the model when carving the wax.
188
What is the purpose of the die relief?
The die relief creates a space for the luting cement, when the inlay is fitted
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