Op Tech Flashcards
Why would it be difficult to bond to carious dentine?
Carious dentine has a lower hardness and presence of mineral deposits in tubules
This makes it difficult to produce the hybrid layer as there are denatured collagen fibres
Without a sufficient hybrid layer in place, bond strength will be significantly weaker
What are the reasons why a bond to dentine may fail?
Over etch: collagen fibres collapse therefore the resin cannot penetrate
Over etch: too deep an etch and the primer cannot penetrate the full depth of etch
Too dry: dentine surface collapses
Too wet: primer is diluted and strength is reduced
How do we overcome the problems of bonding to the smear layer?
Use self-etching technique to penetrate and incorporate the smear layer
RMGIC - remineralisation through fluoride release
Outline the creation of the hybrid layer.
Hybrid layer consists of a collagen network exposed by etching and embedded in adhesive resin (resin tags)
Smear layer is first removed using a 35% phosphoric acid conditioner - this opens dentinal tubules by removing smear plugs, decalcifies the uppermost layer - the collagen network in this top 10um of dentine is then exposed and penetrated by the primer and adhesive
Hydrophilic monomer (HEMA) penetrates the hydrophilic dentine surface (preferably primary, well-structured dentine as it has open tubules) and embeds the collagen fibres forming the hybrid layer
What is the definition of flowable composite?
Lower filler content, therefore less viscous than conventional composite.
Used for filling pit/fissure systems, small fractures and luting agent
Higher polymerisation shrinkage
Lower fracture strength
Place with fibre ribbons
Describe the process of light curing a composite resin and its advantages.
Light cured composite requires a blue light source to initiate the polymerisation process. This gives the dentist control over the starting of the material curing and so how much time is available to place material in cavity (extended working time)
This means the material is more likely to make intimate contact with tooth surface and so prevent microleakage
Other restorative materials (e.g. Amalgam) undergo a chemical setting reaction on mixing, and begin to set while being placed - so these are not as easy to work with
Less waste, less finishing
What is the criticism for using flowable composite?
Reduced mechanical properties, lower availability of shades, more difficult to sculpt due to decreased viscosity, discolouration over time
If a dentist uses one 6mm increment, will this suffice?
No - 20 seconds to cure 2mm increment
Larger than 2mm increment will result in an under polymerised base (soft bottom, early fracture, microleakage)
What are the consequences of polymerisation shrinkage?
Dependent on filler particle volume
Affects bond to tooth - stresses develop at hard tissue (high configuration factor a problem)
Potential for cuspal fracture and microleakage
Hinders good marginal ridge adaptation
What properties make RMGIC superior to GIC?
Stronger, better aesthetics, easier to use
What properties make composite superior to GIC?
Better aesthetics, higher compressive strength, higher hardness, higher wear resistance (GIC subject to abrasion), lower solubility (GIC has long term erosion by acids, dissolution of unprotected material during gelation phase)
What is work hardening?
Also known as cold working.
Strengthening of a metal by plastic deformation which occurs because of dislocation movement.
Describe the properties that make CoCr a suitable alloy for use in partial dentures.
High hardness (high abrasion resistance)- very resistant to indentations/scratching/abrasion of the surface - highly desirable as it must withstand wear caused by foodstuffs as if scratched, these sites act as plaque traps High rigidity - high Young's modulus - withstands large stresses while experiencing only a small amount of strain - copes with masticatory loads without changing shape High ultimate tensile strength (fracture strength) - withstands large stresses before it fractures therefore longer lifetime
What are the possible clinical and pathological consequences of leaving caries untreated in an adult lower molar tooth?
enamel: caries spread will start in enamel in pit and fissure system.
chronic reversible pulpitis: once caries has spread through enamel to reach ADJ, it will progress rapidly along ADJ and spread through dentinal tubules. At this stage there s bacterial invasion and pulp becomes irritated.
chronic irreversible pulpitis: caries reaches the pulp chamber and patient experiences pain caused by hydrostatic pressure of dentinal fluid and inflammation of blood vessels within pulp
pulp necrosis: infection has spread to pulp chamber and down root and irreversible damage is done. At this stage an abscess may be seen as inflammation spreads to gingiva. Treatment options are RCT or extraction.
Describe Blacks cavity classification.
Class I: pit and fissure systems
Class II: approximal caries (posterior teeth)
Class III: approximal caries (anterior teeth)
Class IV: approximal caries involving incisal angle
Class V: caries affecting cervical surfaces
Class VI: caries affecting cusp tips
