DM - fibre reinforced composites (FRC) Flashcards
what is fibre reinforced composite composed of?
synthetic material (polymer and fibres)
fibres - glass
the fibres support the composite
what types of glass fibres are used in the dental industry?
E-glasses
R-glasses
S-glasses
how is E-glass modified to make it more resistant to acid attacks?
Addeding Boron Oxide and reducing CaO
addition of what can compromise the strength of fibres?
fillers
what types of polymers can be in FRC?
linear (MMA/PMMA)
cross-linked (EDGMA, bis-GMA, epoxi resins)
semi interpenetrating polymer network (comb of both)
difference between linear polymers and cross-linked polymers?
linear - thermoplastic
cross-linked - thermoset
what type of polymer is ideal for FRC and why?
semi-IPN
better clinical handling property
better bonding to indirect restorations
higher toughness
what is resin impregnaton?
surface wetting properties of fibres by the resin, distance of the individual fibres from each other and viscosity of resin material
describe the reimpregnation method
PMMA is dissolves in a high evaporative solvent
the solvent evaporates and the fibres stay impregnated with PMMA
What is silanation?
dental glass fibres are always pretreated with coupling agents ‘silanes’
this helps with adhesion, creating bonds
it improves surface wetting of fibres and allows chemical adhesion between fibres and polymer matrix
what will affect the mechanical properties of the FRC?
direction of fibres
what are the types of directions of fibres?
continuous undirectional
continuous bidirectional
continuous random orientated
discontinuous random orintated (short)
describe unidirectional fibres and their uses?
all fibres in one single direction embedded on the resin
uses; posts, fixed pros (improved tensile strength)
describe bidirectional fibres and their uses?
fibres aligned in 2 directions
uses: dental bridge frameworks, splints, removable dentures (flexural and tensile strength, increased fracture resistance)
describe random orientation fibres and their uses?
fibres randomly dispersed
uses: provisional restorations
(anisotropic properties, cost effective)
describe woven fabric fibres and their uses?
interlacing fibres in specific pattern
uses: orthodontic appliances, indirect restorations
(enhanced mechanical properties)
list 3 properties of FRC?
biocompatible
radioopaque
high modulus of elasticity (reduce stress, load distribution, minimised risk of fracture)
list 4 factors affecting the success of FRC?
fibre alignment
restoration design
volume fibre fraction
fiber length
interfacial bonding
curing and polymerisation
clinical application
explain how volume fibre fraction affects the success of FRC?
the more fibres embedded on the composite, the better strength and stiffness
if too many fibres might compromise the flowability and affect placement on cavity
explain how fibre length affects the success of FRC?
longer fibres transfer stress more efficiently, decreasing mechanical properties
shorter fibres help with material handling, less risk of fibre agglomeration
explain how interfacial bonding affects the success of FRC?
the bond between fibres and matrix is crucial for mechanical properties - silane is used to secure the bond.
list the types of bonding mechanism between fibres and matrix
mechanical interlocking
chemical bonding
wetting and capillary action
interdiffusion
hybrid layer formation
how does mechanical interlocking improve the success of FRC?
improves stress distribution and load transfer
how does chemical bonding affect the success of FRC?
improved composite strength and resistance to debonding
how does wetting and capillary action improve the success of FRC?
better load transfer and stress distribution
how does interdiffusion affect the success of FRC?
reduces risk of debonding
how does hybrid layer formation improve the success of FRC?
improves mechanical properties
how does correct curing and polymerisation affect the success of FRC?
avoids internal voids or defects within the composite
list advantages of FRC restorations
easy manipulation
improved flexural strength, fatigue strength, elastic modulus and bond strength
mechanical strength and elastic modulus close to dentine
metal free, possible to use in cases of allergic reactions
high aesthetics
cost effective
minimal lab work needed (no waxing/ casting)
easy repair
list the limitations of FRC
researched still required for long term clinical performance
humidity of the oral cavity may degrade and weaken the interface between matrix and fibres
easy to fracture and delaminate
list the clinical uses of FRC
removable dentures
fixed dental prosthesis
root canal posts
splints
direct restorations
are dentures made of FRC?
only partially reinforcing the weakest part
how is FRC used for fixed dental pros?
provisional restorations
permanent restorations (framework with FRC, veneered afterwards with composite)
advantages of prefabricated root canal posts?
suitable elastic modulus
good aesthetics
direct technique
disadvantages of prefabricated root canal posts?
a lot of dentine removal
adhesion issues
interfacial propagation (inadequate support from post)
delamination of composite
delamination of post
advantages of individually formed root canal posts?
greater resistance under loading
higher bond strength
higher fatigue resistance
less amount of cement/ canal filled with FRC
