DM - fibre reinforced composites (FRC)

Question 1

what is fibre reinforced composite composed of?

Answer 1

synthetic material (polymer and fibres)

fibres - glass

the fibres support the composite

Question 2

what types of glass fibres are used in the dental industry?

Answer 2

E-glasses
R-glasses
S-glasses

Question 3

how is E-glass modified to make it more resistant to acid attacks?

Answer 3

Addeding Boron Oxide and reducing CaO

Question 4

addition of what can compromise the strength of fibres?

Answer 4

fillers

Question 5

what types of polymers can be in FRC?

Answer 5

linear (MMA/PMMA)
cross-linked (EDGMA, bis-GMA, epoxi resins)

semi interpenetrating polymer network (comb of both)

Question 6

difference between linear polymers and cross-linked polymers?

Answer 6

linear - thermoplastic
cross-linked - thermoset

Question 7

what type of polymer is ideal for FRC and why?

Answer 7

semi-IPN

better clinical handling property
better bonding to indirect restorations
higher toughness

Question 8

what is resin impregnaton?

Answer 8

surface wetting properties of fibres by the resin, distance of the individual fibres from each other and viscosity of resin material

Question 9

describe the reimpregnation method

Answer 9

PMMA is dissolves in a high evaporative solvent
the solvent evaporates and the fibres stay impregnated with PMMA

Question 10

What is silanation?

Answer 10

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

Question 11

what will affect the mechanical properties of the FRC?

Answer 11

direction of fibres

Question 12

what are the types of directions of fibres?

Answer 12

continuous undirectional
continuous bidirectional
continuous random orientated
discontinuous random orintated (short)

Question 13

describe unidirectional fibres and their uses?

Answer 13

all fibres in one single direction embedded on the resin
uses; posts, fixed pros (improved tensile strength)

Question 14

describe bidirectional fibres and their uses?

Answer 14

fibres aligned in 2 directions

uses: dental bridge frameworks, splints, removable dentures (flexural and tensile strength, increased fracture resistance)

Question 15

describe random orientation fibres and their uses?

Answer 15

fibres randomly dispersed

uses: provisional restorations
(anisotropic properties, cost effective)

Question 16

describe woven fabric fibres and their uses?

Answer 16

interlacing fibres in specific pattern

uses: orthodontic appliances, indirect restorations
(enhanced mechanical properties)

Question 17

list 3 properties of FRC?

Answer 17

biocompatible
radioopaque
high modulus of elasticity (reduce stress, load distribution, minimised risk of fracture)

Question 18

list 4 factors affecting the success of FRC?

Answer 18

fibre alignment
restoration design
volume fibre fraction
fiber length
interfacial bonding
curing and polymerisation
clinical application

Question 19

explain how volume fibre fraction affects the success of FRC?

Answer 19

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

Question 20

explain how fibre length affects the success of FRC?

Answer 20

longer fibres transfer stress more efficiently, decreasing mechanical properties

shorter fibres help with material handling, less risk of fibre agglomeration

Question 21

explain how interfacial bonding affects the success of FRC?

Answer 21

the bond between fibres and matrix is crucial for mechanical properties - silane is used to secure the bond.

Question 22

list the types of bonding mechanism between fibres and matrix

Answer 22

mechanical interlocking
chemical bonding
wetting and capillary action
interdiffusion
hybrid layer formation

Question 23

how does mechanical interlocking improve the success of FRC?

Answer 23

improves stress distribution and load transfer

Question 24

how does chemical bonding affect the success of FRC?

Answer 24

improved composite strength and resistance to debonding

Question 25

how does wetting and capillary action improve the success of FRC?

Answer 25

better load transfer and stress distribution

Question 26

how does interdiffusion affect the success of FRC?

Answer 26

reduces risk of debonding

Question 27

how does hybrid layer formation improve the success of FRC?

Answer 27

improves mechanical properties

Question 28

how does correct curing and polymerisation affect the success of FRC?

Answer 28

avoids internal voids or defects within the composite

Question 29

list advantages of FRC restorations

Answer 29

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

Question 30

list the limitations of FRC

Answer 30

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

Question 31

list the clinical uses of FRC

Answer 31

removable dentures
fixed dental prosthesis
root canal posts
splints
direct restorations

Question 32

are dentures made of FRC?

Answer 32

only partially reinforcing the weakest part

Question 33

how is FRC used for fixed dental pros?

Answer 33

provisional restorations
permanent restorations (framework with FRC, veneered afterwards with composite)

Question 34

advantages of prefabricated root canal posts?

Answer 34

suitable elastic modulus
good aesthetics
direct technique

Question 35

disadvantages of prefabricated root canal posts?

Answer 35

a lot of dentine removal
adhesion issues
interfacial propagation (inadequate support from post)
delamination of composite
delamination of post

Question 36

advantages of individually formed root canal posts?

Answer 36

greater resistance under loading
higher bond strength
higher fatigue resistance
less amount of cement/ canal filled with FRC