Conservative Dentistry Flashcards
1
Q
What is a complex restoration?
A
Restorations that require extensive recreation of cusps or important anatomical features of teeth
2
Q
What are the five types of cracked teeth?
A
- Craze lines
- Fractured cusp
- Cracked tooth
- Split tooth
- Vertical root fracture
3
Q
Reasons that complex restorations may be required
A
- Secondary caries
- Complete or incomplete fractures
- Repeated failure/replacement of old restoration
4
Q
Assessing a tooth before restoring, you need to assess;
A
- Pulp health
- Extent of caries
- Is the caries active?
- What is angulation of the tooth
- Opposing teeth
- Adjacent teeth
- Erosion
5
Q
Equation relating deflection, thickness and height.
A
- Deflection is proportional to height^3.
- For every mm increase in height of the wall of the tooth, there is substantial increase in the deflection of the cusp. - Deflection is also proportional to the inverse of thickness^3.
- For every mm increase in thickness, there is a substantial decrease in the deflection of the cusp for a given force.
6
Q
Which maxillary cusps are most at risk to fracture?
A
Buccal and palatal cusps of premolars, and the mesio-buccal and disto-lingual cusps.
7
Q
Which mandibular cusps are at risk of fracture?
A
Lingual cusps on molars and premolars
8
Q
What is a dental cement?
A
A loose term describing a range of materials used in dentistry, either alone or in conjunction with other materials, for the restoration of teeth
9
Q
What are the general properties of dental cements?
A
- Often acid:base setting reactions
- Relatively weak
- Often soluble
- Supplied as two components, e.g. powder + liquid; paste +paste
- Properties are sensitive to the P:L ratio
10
Q
Uses of dental cements
A
- Temporary restoration
- Permanent restoration
- Lining (liner) - as thin barrier to chemical irritation
- Base - thick layer barrier to chemical and thermal irritation, and structural replacement
- Luting agent
- Pulp cap
- Root canal sealer
11
Q
What are water-based cements?
A
Two components: Liquid and powder
Liquid: usually an aqueous solution of an acid
Powder: which is usually a metallic base
12
Q
What are the types of dental cements?
A
- Conventional glass-ionomer cements
- Resin-modified glass ionomer cement
- Compomer
- Resin compite
13
Q
Composition of conventional GIC
A
Powder: Fluoraluminosilicate glass
Liquid: Polyalkenoic acid
14
Q
Composition of modified GIC
A
Powder and/or liquid contain polymerisable resin - which needs to be photocured and/or self cured
15
Q
What is the setting reaction for conventional GIC?
A
- Acid attacks glass
- Releases Ca2+/Sr2+, Al3+, Na+, F- which react with the acid
- Ca2+/Sr2+ react first, Al3+ later - The resultant salts hydrate to give gel matrix
- Cross-linking occurs
16
Q
What is the setting reaction of resin-modified GIC?
A
- Sets as conventional GIC with the addition of
2. Resin polymerisation by light photo-cure or self-cure mechanism
17
Q
What is the bonding mechanism of self-cure GICs?
A
- Wetting of tooth surface by polyacrylic acid
- Ionic bonding between COO- and Ca2+
- Formation of an ion exchange layer
- Potential bonding to collagen
- Bond strength is improved by surface conditioners, polyacrylic acid is preferred
18
Q
What is the bonding mechanisms of resin- modified GICs?
A
- Enamel: resin tags
- Dentine: ion exchange layer?, hybrid layer?, dentine tubule tags?
- Bond strength is also improve by conditions - polyacrylic acid is preferred
19
Q
What are the advantages of resin-modifed glass ionomer?
A
- Higher bond strength
- Immediate set
- Less sensitive to water balance - must be kept wet at all times
- Better aesthetics
20
Q
Important properties of resin-modified GICs
A
- Adhesion to calcified tooth structure
- Fluoride release
- Tooth coloured
- Water sensitive during early setting
- Brittle
21
Q
Differences in binding between conventional GIC and resin-modified GIC
A
Conventional GIC: chemical
Resin-modified GIC: chemical and micro-mechanical
22
Q
Difference in water balance between conventional and resin modified GIC
A
Conventional - must not get wet for 24hr and must not dehydrate (place a layer of bind to protect from dehydration)
Conventional high P:L - keep wet at all times after setting
Resin-modified - keep wet at all times after setting
23
Q
Timing of fluoride release by GIC
A
Glass ionomer has a rapid release of fluoride followed by gradual release of fluoride ions over time.
24
Q
Does GIC prevent secondary caries?
A
In a study by Mickenautsch et al (2009),
At 6 years less caries was found around GICs than amalgam.
There was no difference in deciduous teeth.
More research is needed.
25
Fluoride in restorative materials
In a study by Wiegand et al (2007) they collated information from papers and reviews (1980-2004)
- clinical studies exhibited conflicting data regarding prevention/inhibition of secondary caries
- In the lab, fluoride-releasing materials did show cariostatic properties
- Clinically, not proven whether secondary caries can be significantly reduced
26
What provides the potential anti-cariogenic effect to GIC?
Most-likely due to fluoride;
1. Unfavourable environment for bacteria - prevents bacterial metabolism
2. Decreases enamel and dentine solubility
3. However, not proven in randomised clinical trials.
27
What are the main classifications of Glass Ionomer cements
1. Type IIA - Restorative aesthetic cements
- includes conventional, high P:L and resin-modified
2. Type IIB - restorative reinforced cements
3. Type III - lining cements
28
Type IIA GlC's
Conventional
- relatively low reactivity glass
- medium rapid clinical set (minutes) - Ca2+/Sr2+
- slow maturation (weeks/months) - Al3+
- highly translucency
- mainly superseded by resin-modified GICs
Conventional high P:L ratio
- relatively high reactivity glass
- rapid clinical set
- rapid maturation (minutes)
- medium translucency
29
What are the clinical uses of GICs?
1. Fissure sealant
2. Anterior approximal restoration
3. Cervical restoration
4. Deciduous tooth restoration
5. Lining cement
6. Luting cement
7. Orthodontic bracket cement
30
Atraumatic restorative treatment (ART) technique
1. GIC used as material in developing countries
2. Hand rather than rotary instruments
3. Caries-affected enamel and dentine sealed with high viscosity
4, Success rate is around 90%
5. No LA required, good for children
31
Type IIB GIC
Restorative 'reinforced' cements
- silver or amalgam alloy powder incorporated
- strength is not different from conventional GICs
- maybe increased abrasion resistance
- Use of Type IIB is reduced due to introduction of high P:L materials
32
Type III GICs - Lining cements
In complex restorations, GIC is used to replace dentine, while composite resin is used to fill in the enamel.
33
Silicate cements
Powder component: Si02 + Al2O3, metal fluorides, calcium slats, buffer salts
Liquid component: phosphoric acid
34
Setting reaction of silicate cements
1. Phosphoric acid attacks glass
2. Ca2+, Al3+, F- released
3. Metal phosphate precipitated
35
Properties of silicate cements
1. Strong in compression
2. Weak in tension
3. Soluble in the oral environment
4. Low pH, pulpal toxicity
5. Not adhesive
6. Releases F-
36
Reasons for pulpal vulnerability to insult
1. Dentine permeability
| 2. Unusual features of pulpal blood supply
37
The role of dentine permeability
1. Dentine contains dentine tubules
2. The dentine tubules become wider with increased depth.
3. Within 0.5-1.0mm of the pulp, dentine is a highly permeable tissue.
4. Tubules contain odontoblast processes, which can be injured by deep cutting
5. Tubules permit the influx of bacterial toxins or toxic components of restorative materials
6. Bacteria can directly invade tubules
7. Rapid outward dentinal fluid may be damaging to pulp
38
Reasons for indirect pulp exposure
1. Thermal insult - from cutting dentine
2. Microleakage
3. Material toxicity
39
Why is the pulp vulnerable to insult?
1. No collateral circulation
2. Low compliance environment
3. Rich blood supply
40
Mechanisms of pulpal protection
1. Immune/inflammatory response
2. Outward fluid flow
3. Tubule sclerosis
4. Reactionary dentine deposition
The pulp can response very effectively to slow, progressive insult, but less well to acute injury.
41
1. Pulpal immune response
1. Pulpal cells detect bacterial antigens that penetrate dentinal tubules
2. B cells produce antibodies in response to bacterial toxins
3, If the insult is not removed, chronic pulpitis may progress to pulp necrosis
42
2. Outwards fluid flow
Loss of enamel leads to capillary leakage
43
3. Dentinal sclerosis
When it is a slow process of cavitation into the enamel, then the odontoblasts can produce calcium phosphate along the walls of tubule to block further irritation.
Prevents bacterial penetration
44
4. Reactionary dentine
Reactionary dentine and reparative dentine are two strategies used by the dentine–pulp complex to respond to injury. The reactionary dentine is secreted by original odontoblasts, while the reparative dentine is formed by odontoblast-like cells.
45
What are some restorative measures used to protect the pulp?
1. Conservative preparations
2. Bases and liners
3. Pulp capping
46
1. Conservatie preparations
- Careful removal of caries-affected dentine with minimal extension into unaffected dentine
- May need to leave remaining thickness
47
Explain the concept of "remaining dentine thickness"
1. Mature human dentine approximately 3mm thick
2. Odontoblast processes extend 0.1-1.0mm into dentine
3. Beneath caries or exposed dentine, tubule sclerosis reduces dentine permeability
4. Freshly cut intact dentine is much more permeable than dentine beneath a lesion
48
What is the critical depth for cutting dentine without injury to odontoblasts?
1. Safe cutting - 0.5-1.0mm
2. Serious injury - 0.3-0.5mm
Deep caries or deep cutting requires a protective lining over the highly permeable dentine or protect against high permeability
49
2. What are the objectives of liners/bases?
1. Seal against micro-leakage
2. Promote tubule sclerosis and reactionary dentine
3. Thermal insulation
50
What are the types of lining materials?
1. Resin modified GIC
- used when >0.5 mm dentine remaining
- Excellent biocompatibility
- Minimal pulpal damage
- Chemical bonding to dentine
2. Ca(OH)2
- used when <0.5mm remaining dentine
- High pH, antibacterial
- Must be a hard setting material
- Needs to be covered with a base
- Stimulates reactionary dentine formation
51
Explain pulp capping
1. Direct pulp capping
2. Indirect pulp capping
- one-step and step-wise
52
What is MTA?
1. MTA is a direct pulp capping material - like calcium hydroxide
2. Unset MTA contains tricalcium silicate, dicalcium silicate and tricalcium aluminate
3. The primary products of MTS reacting with water is calcium hydroxide
52
What are the advantages of MTA?
1. Biocompatible
2. Antibacterial
3. High pH
4. Radioopaque
5, Aids in release of bioactive dentine matrix proteins
53
What are the disadvantages of MTA?
1. High solubility
2. Presence of iron in grey MTA may discolour tooth
3. Setting time of 2 hours and 45 minutes
4. Two-step clinical procedure
5. Handling properties
6. Expensive
54
What is Biodentine?
1. A commercial pulp capping material
2. Powder is in a capsule and liquid is in a pipette
3. Powder contains tricalcium and dicalcium silicate opacifier
4. Liquid contains calcium chloride
5. The material sets in 12-15min
Indicated for root perforations, direct and indirect pulp capping, pulpotomy, internal and external resorption
6, Handles better and sets faster than MTA
55
Process of enamel etching
1. Application of 37% orthophosphoric acid removes the smear layer, surface contaminants, and 10um of enamel, differentially exposing enamel prisms to create honeycomb-like surface irregularities.
2. Increases surface area and surface energy, increasing wetability and allowing greater resin infiltration
3. 15seconds is usually sufficient to create a white 'frosted' appearance, but fluorapatite and more aprismatic primary dentition enamel may require longer etching times.
4. Must be rinsed with oil-free water and kept free of contamination
5. If contamination occurs, etch for a further 10s and rinse
56
What is a smear layer?
A layer of grinding debris and organic film left on the enamel and dentine surfaces, after mechanical cutting.
57
Process of enamel bonding
1. Etched enamel does not require a primer for bonding, unlike dentine
2. Bonding is achieved via micro-mechanical interlocking of the resin component into the porosities of the etch pattern
3. Enamel bonding systems have been largely supplanted with dentine bonding systems which can bond to both structures.
58
Structure of dentine
Superficial dentine surface
- 96% intertubular dentine
- 1% fluid from tubules
- 3% peritubular dentine
Deep dentine surface
- 22% made up of water
- 25% comprised of tubules
- decreased surface area of peritubular and intertubular dentine
1. The number and diameter of dentinal tubules increases towards the pulp
2. Dentine mineral content decreases close to the pulp
3. Dentine is constantly moist, and wetness increases closer to the pulp
4. The dentinal tubules become occluded by smear plugs following instrumentation, extending 1-10um into tubules and reducing permeability by 86%
5. The smear layer limits access to the dentine surface
59
Process of dentine bonding
To bond dentine, the smear layer must be;
1. Removed (etch and rinse) or
2. Penetrated/Modified (self-rinse)
Dentine is a wet substrate, but resin composite materials are hydrophobic.
Therefore an interface between the hydrophilic dentine and the hydrophobic resin is required.
60
Types of bonding interfaces
1. HEMA
- A bifunctional coupling agent
a) a hydrophilic functional group
b) a methacrylate group - bonds to resin
- However, a disadvantage is that HEMA continues to be hydrophilic after curing
2. MDP
- An acidic functional monomer - also etches
- phosphate functional group can form ionic bonds with hydroxyapatite
61
What is the classification of dentine bonding agents?
1. Chronological development
2. Number of steps involved
3. Etch and rinse/self-etching
62
4th generation
3 step etch and rinse
1. Acid etch (phosphoric acid) to remove the smear layer, open dentine tubules and demineralise intertubular and peritubular dentine while exposing collagen network.
2. Must be rinsed but not dehydrated as this may lead to collapse of the collagen network
3. The primer containing amphiphilic monomer (HEMA) and solvent is applied to infiltrate the collagen network and enter the dentinal tubules. Solvent evaporates by air drying
4. The bonding resin is applied, linking the methacrylate end of the HEMA.
5. The resin is air thinned and light cured
63
What is the hybrid layer?
The hybrid layer consists of demineralized collagen that is intertwined with cured adhesive monomer.
Etching the enamel and dentine exposes the collagen network. Resin is then able to impregnante into the demineralised collagen.
However, too much etching can collapse the collagen network, which doesn't allow impregnation into the collagen - leading to sensitivity and poor binding.
64
What is the function of primer solvents?
1. Function is to allow the monomer to penetrate the demineralised dentine and collagen network
2, Must be evaporated to prevent monomer dilution and void formation
65
What are the types of primer solvents?
1. Alcohol
- good penetration into moist collagen
- may not reconstitute dry collagen
2. Acetone
- excellent penetration into moist collagen
- won't reconstitute dry collagen
- rapid chairside evaporation
3. Water
- fair penetration into moist collagen
- will constitute dry collagen
- evaporation takes longer
66
5th generation
2 step etch and rinse
1. Initial etching and rinsing steps as per the 3 step system
2. The 2nd bottle contains both primer and adhesive
66
5th generation
2 step etch and rinse
1. Initial etching and rinsing steps as per the 3 step system
2. The 2nd bottle contains both primer and adhesive
67
5th generation
2 step etch and rinse
1. Initial etching and rinsing steps as per the 3 step system
2. The 2nd bottle contains both primer and adhesive
68
6th generation
2 step self-etch
1. Etching and priming performed together in 1st bottle containing a functional acidic monomer such as MDP or 4-META
2. Smear layer is not removed, but penetrated and incorporated into the bonding layer
3. Shorter resin tags and thinner hybrid layer is formed
4. Potential for chemical binding to hydroxyapatite
69
7th generation
1 step (all-in-one) self etch
1. Simplification of technique in one bottle
2. More acidic and hydrophillic than 2 steps SE systems
3. Prior selective etching may produce better results on enamel
69
8th generation
1 step (all-in-one) self etch
1. A one-bottle approach
2. May contain 'adhesive' molecules for bonding to HA and other materials
70
Why do we selective etch?
1. It is thought that the milder pH of SE systems lead to poorer enamel bond than that of E&R systems
2. SE and universal systems can be applied following seperate etching steps
3. It has been suggested that the deeper demineralisation zone in dentine created by seperate etching is less able to be penetrated by the SE primer systems, which generally develop a thinner hybrid layer
4. It has also been suggested that some of the benefits of shallow demineralisation with SE systems allows binding to HA
5. Therefore, selective enamel etching, not dentine etching, is recommended prior to placement of SE system
71
Why does dentine bonding fail?
Dentine bonding is more susceptible to failure than enamel bonding.
1. Failure to ensure contamination-free environment
2. Poor bonding substrate - sclerosed or caries-altered dentine
3. Hydrolysis of bond later due to dentine's inherent wet nature and marginal leakage. Hydrophillic components can lead to water sorption and degradation of the hydrophillic phase and breaking of polymer bonds
4. Molecules (MMPs and cysteine cathepsins) that break down collagen - they lie dormant in dentine, once you remove the dentine and expose collagen network - they breakdown the collagen in the hybrid layer. It is thought that inhibitors as part of the bonding protocol can retard this process. This is still being researched.
72
Resin composite components
1. A highly cross-linked resin matrix
- polymerisable methacrylate monomers
- colouring pigments
- photo-initiator and accelerator
- stabilisers
2. Filler particles
3. A coupling agent coating the filler surface, which acts as an interfacial bond between the resin matrix and filler particles (allows the materials to integrate)
- y-methacryloxypropyltrimethoxysilicane ('silane')
73
What are the general properties of resin composite materials?
1. Reasonable fracture toughness
2. Low water sorption
3. Aesthetics and polish-ability
4. Reasonable modulus of elasticity
5. Polymerisation shrinkage
6. Radiopacity
74
Properties of resin in resin composite
1. Allows manipulation at ambient temperature
2. Shrinks on setting - polymerisation of unbound monomer particles reduces the volumetric space between particles leading to shrinkage
3. Various different methacrylates
75
Properties of the photo-initiator in resin composite
Usually camphorquinone - which is excited by blue light and then reacts with an amine accelerator, creating free radicals.
The free radicals react with monomer molecules, disrupting the carbon double bond and creating free radical molecules, which in turn reacts with other monomer molecules resulting in propagation and cross-linking of the resin monomer.
76
Properties of stabiliser in resin composite
1. Stabilisers (inhibitors) are present in resin composite to extend shelf-life and to ensure that the working times are sufficient
77
Properties of filler in resin composite
1. Provides reinforcement, rigidity, hardness, toughness, reduction in polymerisation shrinkage, control of handling
2. Ideally has a refractive index closely matching that of the resin composite for aesthetics and translucency
3. Usually a glass filler
4. Filler surface is 'silanated' with the coupling agent to allow adhesion to the resin matrix
78
What are the advantages of resin composite material?
1. Allows for the conservative preparation in teeth
2. Good adhesive marginal seal
3. Good aesthetics possible
4. Easy to repair/refurbish
79
What are the disadvantages of resin composite?
1. Moisture sensitive
2. Polymerisation shrinkage
3. Wear resistance
4. Fracture toughness not ideal in thin sections
5. Correct placement can be time consuming, laborious and challenging
6. Potential for staining
80
What are the properties of different filler sizes for resin composite?
1. Smaller filler particle size and increased density allows for lower monomer content and improved physical properties such as wear, polymerisation shrinkage and polish-ability
2. However, there is a limit to the amount of filler by weight achievable. Smaller filler particles have increase SA:V which affects viscosity and handling properties, increasing water sorption
81
What is the oxygen inhibition later?
The oxygen-inhibited layer is the sticky, resin-rich uncured layer that is left on the surface.
This superficial layer contains un-polymerised monomer and is depleted of free radicals, but does allow further addition of resin composite increments.
The oxygen inhibition layer is highly susceptible to staining and must be removed on finishing and polishing.
82
What is polymerisation shrinkage?
Polymerisation shrinkage is in the order of 1-4% higher than flowable materials.
Shrinkage is volumetric and proportional to the size of the increment placed.
This can lead to marginal gap formation and internal stresses that lead to cracks in the tooth.
In more severe cases it can leak to leakage resulting in pain.
83
What is c factor?
A ratio of a restoration's bonded to un-bonded surfaces
84
What are the limiting factors of light curing?
1. Curing time
2. Intensity of curing unity
3. Distance and angulation
4. Depth of increment
5. Shade, filler type, accelerator
85
What is degree of conversion?
The term 'degree of conversion' applied to resin composites, refers to the conversion of monomeric carbon-carbon double bonds into polymeric carbon-carbon single bonds. Increasing the conversion results in higher surface hardness, flexural strength, flexural modulus, fracture toughness, and diametral tensile strength.
Conventional resin composites may reach 75% conversion at initial cure, but can continue to polymerise further.
86
What is biodegradation of resin composites?
1. Hydrolytic degradation is related to the absorption of water by the polymeric network and may cause swelling and softening of the polymer network - due to hydrolysis of polar groups.
2. Enzymatic degradation may involve the action of external and intrinsic enzymes. These enzymes degrade monomers/polymers
87
What are finishing and polishing?
Finishing: gross remodelling of the restoration to the final shape with coarse instruments
Polishing: removed and refines surface irregularities using fine instruments.
88
What are cervical lesions?
Lesions found at the neck of the tooth, near the CEJ.
89
What are the types of tooth wear?
1. Attrition
2. Abrasion
3. Erosion
4. Abfraction - loss of tooth structure due to micro-fracture in areas of stress concentration
90
Sources of abrasion
1 .Food
2. Toothbrushing
3. Denture clasps
4. Environmental particles
5. Oral habits
91
Sources of erosion
1. Intrinsic
- gastric acid
2. Extrinsic
- dietary or environmental acids
92
What is abfraction?
Abfraction refers to microfractures in tooth structure that can occur due to stress concentration caused by occlusal loading (parafunction)
93
Types of abfraction
1. Centric occlusion - 'barrelling' deformation
2. Eccentric occlusion - 'bending' deformation
However, the theory of abfraction is controversial and not universally accepted. There is no clinical evidence.
94
Treatment of dentine hypersensitivity. What to do?
Patients commonly attend dental practices complaining of sensitivity to cold.
1. Diagnostic tests are imperative to establish a correct diagnosis
2. Non-carious cervical lesions can be treated with various medicaments, sealed or restored. However, often identification of the underlying aetiology may permit resolution without restorative intervention
95
Treatment protocol for carious cervical lesions
White spot lesion
- remineralise with topical fluoride
- CPP-ACP
- Improve oral hygiene
- Diet assessment
Cavitated lesion
- modify to be non-plaque retentive
- restore as required (if it cannot be cleaned by patient or is plaque retentive
96
Treatment protocol of non-carious cervical lesions
1. No treatment/restoration
2. Desensitising treatment
3. Restoration may be required if;
- pain or sensitivity is not resolve by local desensitising agents
- protecting against further progression
- plaque retentive
- an aesthetic requirement
- retention required for denture component
97
Restorative material requirements for carious lesion
1. Fluoride release
2. Moisture tolerance
3. Aesthetic
4. Durable
5. Adhesive
98
Restorative material requirements for non-carious lesions
1. Moisture tolerant
2. Aesthetic
3. Adhesive
99
Material available for carious lesion restorations
1. Restorative glass ionomer (GIC, or RMGIC)
2. Lining glass-ionomer (Vitrebond and resin comp)
3. Dentine bonding agent and resin composite
4. Amalgam
100
Contemporary clinical descriptions of carious dentine
1. Hard
2. Firm
3. Leathery (affected dentine)
4. Soft (infected dentine)
Previous classification was a histological description which used the terms 'affected' and 'infected' dentine
101
What is amalgam?
1. Direct restorative material
2. A mixture of two or more metals - Silver-tin alloy powder mixed with mercury
3. The reaction between the mercury and alloy is known as 'amalgamation'
102
Methods used to produce amalgam alloy particles
1. Lathe cut: from pre-homogenized ingot of alloy
2. Spherical/spheroidal: molten allow is sprayed into a column of inert gas. These droplets solidify as they fall down the column forming spherical particles
103
What are the difference between admixed and spheroidal amalgam?
1. Admixed
- slower set
- greater resistance to condensation
2. Spheroidal
- faster set
- initial strength gained earlier
- requires less condensation force
104
Why is moisture contamination bad for amalgam?
1. Moisture contamination in zinc containing alloys will undergo increased expansion
2. Zn + H2O -> ZnO + H2
3. Liberation of hydrogen causes delayed expansion
4. Although moisture tolerant, adequate moisture control is required
105
Corrosion of amalgam
1. Amalgam is prone to corrosion
| 2. Corrosion products are thought to accumulate at the tooth-restorartion margin and form a seal, reducing microleakage
106
Tarnish and amalgam
1. Formation of a surface coating resulting in a loss of lustre on the amalgam surface
2. Integrity and mechanical properties of the restoration is not affected
107
Contraction and expansion of amalgam
1. Small contraction occurs in the first 30minutes due to diffusion of mercury into alloy particles
2. As the reaction proceeds, the outward thrust of growing crystals results in an expansion of the amalgam
108
Clinical indications for amalgam
1. Not used in anterior teeth
2. Small to moderate posterior approximal cavities in high caries risk patients
3. Moderate to large posterior approximal cavities in moderate-high risk caries patients
4. Extensive multi-surface posterior cavities irrespective of caries risk
5. Core for endodontically treated teeth
109
Advantages of amalgam
1. Low cost
2. Moisture tolerant
3. Less chair-side time
4. Ease of removal
5. Ability to be condensed
6. Reproduction of inter-proximal contact (easier than resin composite)
7. Long history of use
110
Disadvantages of amalgam
1. Unaesthetic
2. More tooth structure removed during cavity prep
3. Mercury concern
4. Higher risk of tooth fracture
5. Stains dentine
6. High thermal conductivity
7. Some patients may be allergic to mercury (rare)
111
What is the median survival rate of amalgam?
Amalgam has the highest median survival rate compared to resin composite, GIC, RMGIC.
Almost close to 10 years.
112
What is the most common cause of restoration failure?
1. Caries
2. Fracture of tooth
3. Endo
4. Restoration loss
5. Insufficient interproximal contact
113
Principles of amalgam prep
1. Minimum occlusal-gingival depth of 2mm for strength of amalgam
2. Rounded internal line angles
3. Cavity walls converging towards the occlusal
4. Width of 2mm of the isthmus
5. Depth of 2mm from the occlusal of the isthmus
6. No unsupported enamel
7. Flat and smooth floors
114
Minimum thickness of resin composite vs amalgam
Resin composite - requires a minimum thickness of 1.5mm in occlusion
Amalgam - requires a minimum thickness of 2-2.5mm
115
Before beginning surgical treatment, what do you need to assess?
1. Remaining tooth structure
2. Cracked tooth syndrome
3. Cuspal flexure - hairline cracks are observed
4. Occlusal forces/parafunctional habits
5. Function in arch
6. Endodontically treated and requiring cuspal protection?
7. Health of the pulp
8. Size of the pulp
9. Size of the existing restoration
10. Angulation/tilting of the tooth
11. Opposing teeth and occlusion
12. Supraeruption
13. Need for radiographs ?
116
What is an amalgam retention form?
A feature of the tooth preparation that resists dislodgement of a crown in a vertical direction or along the path of placement.
117
What is an amalgam resistance form?
The features of a tooth preparation that enhanced the stability of the restoration.
118
How is retention and resistance gained for amalgam restorations?
Through the use of deliberately cut tooth preparations (slots, grooves, boxes), and pins
119
Principles of complex amalgam preparations
1. Cavo-surface margin of 90 degrees - to prevent amalgam and enamel fracture due to unsupported structures
2. Minimum depth of 2-2.5mm
3. Anatomically reduced cusps
4. Grooves or slots for retention
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Dentine pins for amalgam restorations
Self-threading pins are used in dentine today for amalgam - as they are found to be the most retentive compared to cemented pins and friction-lock pin systems.
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Self-threading pins
1. Retentive
2. Induces stress into dentine resulting in micro-fractures and crazing
3. Optimum retentive strength obtained with self threading pins when they are placed 2mm into dentine and 2mm into amalgam
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Criteria for amalgam pin location
1. Pin hope should be prepared 0.5-1mm pulpal to DEJ
2. Ensure at least 2mm amalgam to be condensed occlusally `
3. At least 0.5mm amalgam surrounding the pin
4. 2mm depth of the pin hole into the dentine
5. May have to cut a small cove for the pin
6. The pin hole should be cut parallel with the external surface of the tooth to ensure no damage to pulp or PDL
