Dentine Flashcards
What is the composition of dentine?
70% hydroxyapatite
20% organic material, mainly collagen
10% water
Tubules around 1-5μm width
Why resin bond to dentine?
- Eliminate marginal and internal gaps
- Seal dentinal tubules
- Enhance retention
- Enhance strength
What are the problems of bonding to dentine?
- Formation of a smear layer
- Complex substrate (dentine)
- Hydrophobic resins, hydrophilic dentine
- Fluid flow into tubules
How can we fix the smear layer?
- use of dentine conditioner, usually 37% phosphoric acid but not always. This creates a demineralised surface layer approx 4um thick
How can we bond hydrophobic resins to hydrophilic dentine?
with the use of Hydroxyl groups -OH Carboxyl groups -COOH phosphate groups -P-(OH)3 - these bond with the amino groups in the collagen and the hydroxyl groupss in hydroxyapatite
- bond to hydrophobic resins with methacrylate groups?
- use a space to stick them together, long enough to prevent rigidity and allow both ends to bond freely
- bifunctional monomer = polar group, spacer, methacrylate group
What are dentine primers made of?
A bifunctional monomer:
A polar group
A spacer
A methacrylate group
-A solvent or water to carry the monomer deep into the demineralised collagen
How to prevent fluid flow in tubules?
We now have a surface of hydrophobic methacrylate groups
Bond directly using methacrylate based resin
What is dentine sealer?
Methacrylate based
- Bis-GMA (Bis-GMA bisphenol A-glycidyl methacrylate)
- UDMA (urethane dimethacrylate)
Either light cured or chemically cured
Can contain some bifunctional monomer to aid bonding with the primer
What are the 3 stages to dentine bonding?
- Apply conditioner (removes smear layer and opens tubules)
- Apply primer - bonds to hydrophilic collagen and hydroxyapatite
- Apply sealer - seals tubules and bonds to the primer
What are the concerns with dentine bonding?
Eliminate the marginal gap (due to polymerisation shrinkage)
wet dentine bonding
What happens if you thoroughly dry dentine?
collagen collapses
volatile solvent in primer chases water out of collagen and brings in the bifunctional monomer
What are the 4 types of dentine bonding agents?
Type 1 - etch, prime, seal
Type 2 - etch, prime and seal
Type 3 - etch and prime, seal
type 4 - etch and prime and seal
What is the prime and bond NT?
- Uses acetone to carry primer and sealer into dentine
- Acetone chases water out of the dentine
- Needs time and possibly air to evaporate the acetone
Give an example of a prime and bond NT
- scotchbond 1 XT
- water and ethanol carry primer and sealer
- needs agitation to ensure primer and sealer get into the dentine
What do self etching primers do? (type 3)
Acidic monomers that etch and prime
The smear layer is dissolved, but not removed, collagen demineralised and infiltrates the collagen network
What are the benefits of self etching primers?
- no need to rinse or dry (more consistent results)
- can prevent marginal staining (caused by weak etching of enamel) by pre-etching enamel with phosphoric acid
Which type of bonding agent has the weakest bonds?
Type 4 - all in one
How do all in one systems work?
..
Which type of dentine bonding agent to use?
Type 1’s are the most difficult to use and require excellent technique
Type 2’s are almost equally difficult and the bond strength is (generally) worse
Type 3’s are quite simple to use and have good bond strength
Type 4’s are currently unpredictable as they are still quite new
What is usually used as a dentine conditioner?
EDTA, Maleic acid, oxalis acid, phosphoric acid, nitric acid
What ideal properties should a direct aesthetic restorative material have?
Safe for dental team and patient Aesthetic Durable, chemically stable and tasteless Poor conductor of heat Minimal tooth preparation Easy to use Cost effective
What is the composition of dental composite resins?
The matrix component is typically a mixture of methacrylate resins (most commonly bis glycidyl methacrylate or bisGMA formed by the reaction of glycidyl methacrylate with bis-phenol A).
The filler is typically a silica (SiO2) powder.
Modern dental composites usually contain a photoinitiator (most commonly camphorquinone).
What can dental composites be set by?
Chemical cure or light cure
How does the chemical cure happen?
In chemical cure, two pastes are mixed (an activator with a free-radical initiator) but this approach is effectively obsolete in restorative materials.
How does light cure happen?
Light activated systems contain a photoinitiator; setting is initiated by exposure to an appropriate lamp.
Camphorquinone is the most common. Activated at 470 nm – hence visible blue light is used
what are the properties of dental composite resins?
Tough and relatively wear resistant.
Durable and insoluble.
Aesthetic (tooth coloured and translucent).
Possible to achieve a good bond strength with tooth tissue.
Relatively safe and biocompatible if handled correctly.
BUT hydrophobic so need bonding system to adhere to hydrophilic tooth tissue.
What is composite resin?
A complex material in which two or more distinct, structurally complementary substances, typically ceramics, glasses and polymers, combine to produce structural or functional properties not present in any individual component
How can you classify dental composite
Initiation technique
Heat-cure Self-cure Light-cure Dual-cure
Filler size
Macrofilled Microfilled Nanofilled Hybrid
Viscosity
Flowable Packable
Clinical application
Direct (Anterior/Posterior) Indirect
What are the advantages of dental composite?
Aesthetics • Bonding to tooth structure • Tooth-sparing preparation • Less-costly and more conservative alternative to indirect restorations • Repairability • Reduced quantity of mercury exposure and the environmental release • Lack of corrosion
What are the disadvantages of dental composite?
Composite shrinkage (up to 3%) and microleakage • Post-op sensitivity • Secondary caries • Chipping and lower wear resistance than amalgam • Technique sensitive • Adverse biological reactions
What biological considerations are needed with dental composites?
Direct Composite resins
Oral lichenoid reactions Allergic reactions
Dentine bonding agents
Some pulpal reactions have been reported
Indirect resin-based materials
Allergic reactions in patients
Hand dermatitis in technicians
What are the benefits of adhesion?
Creates a strong attachment to tooth tissue • Resists polymerisation shrinkage and minimises leakage • Tooth preparation limited to damaged/lost tooth tissue – no need for mechanical undercut • Supports weakened tooth structure • Optical integrity at cavity margins
What is required for composite placement?
Access to and removal of diseased tissue
Minimal preparation at all times
Minor enamel bevelling to enhance bonding and aesthetics anteriorly
Clean dry field ESSENTIAL throughout bonding and placement:
• Rubber dam
• High volume suction
• Cotton wool rolls and/or “Dry Guard”
• Lip retractors
• Matrices
What are the indications for use of composite?
Restoration of Caries • Repair of enamel and dentine fractures • Tooth wear rehabilitation • To mask mild discolouration • As a temporary restoration for indirect veneer preparations
What are the contraindications for use of composite?
Where there is insufficient tooth structure and enamel present for bonding • Deep subgingival caries where moisture control is not possible • Indirect restorations may be more appropriate for severely damaged and heavily restored teeth • Allergic reaction to resin-based dental materials
Why is bonding to dentine not as durable as bonding to enamel?
Heterogeneity of structure and composition of dentine
Dentin surface characteristics (after chemical treatment/cutting)
Bond strategy and physicochemical properties of the adhesives
How does polymerisation shrinkage occur?
Monomer molecules bonding into a polymer network lose volume (take up less space ) - creates contraction
They exchange VDW’s in covalent bond spaces
What can stresses from polymerisation lead to?
Shrinkage - bond failure and poor marginal adaptation
Gap formation between cavity and restorative material - bacterial penetration and pulpal damage
Leads to sensitivity, pain, recurrent caries
What happens if you dry the dentine thoroughly?
Collagen collapses
Collagen forms very dense layer and primer cant penetrate and produce molecular entanglement = weak bond strength
What chemical system occurs in type 4 (all in one) systems?
Methacrylate hydrolysed to give phosphoric acid ester groups bonded to methacrylate
Why are nanofilled particles an advantage?
Nano particles can surround the bigger particles to avoid them being exposed and making the surface of the restoration rough
How can you minimise polymerisation shrinkage of composite?
Fill in oblique increments
What does algesic mean?
Pain producing substances
What are intra-pulpal nerves classified by?
myelinated or unmyelinated
function
conduction velocity
Which part of dentine is innervated?
Innner NOT outer
Why are odontoblasts not considered receptors?
Resting membrane potential of OB show values is too low to be receptor and pain still felt after OB damaged
What theory is the most likely mechanism for dentine sensitivity?
Hydrodynamic theory - fluid movement in tubules leads to mechanical distortion of underlying soft tissue
