RESIN BASED MATERIALS

bansal, Dr. Cheena

RESIN BASED MATERIALS

Summary

INTRODUCTION
Esthetic dentistry can be defined as the art and science of dentistry, applied to create or enhance beauty of an individual within functional and physiological limits.
Where as cosmetic dentistry is application of the principles of esthetics and certain illusionary principles, performed to signify or enhance beauty of an individual to suit the role he has to play in his day to day life or otherwise. Appearance is closely linked to social acceptance and professional success. No longer are people satisfied with just looking good, it must be coupled with a complete feeling of total well-being. Newer technologies are being harnessed for this purpose and advanced research is being undertaken. Thus, focus of dentistry in the present times is not only on prevention and treatment of disease but also on meeting the demands for better esthetics. Newer dental materials developed for esthetic enhancement are now chosen for their excellent mechanical as well as esthetic qualities. Esthetic dentistry is emerging as one of the most progressive and challenging branches of this field. Thus dentistry has evolved from a curative to a creative science in a very short span.
The modern history of esthetic restorative materials was started with silicate cement, introduced by Fletcher in 1878, the principle anterior restorative material of those days. But, silicate cements were discouraged later on because of their poor strength, irritation to pulp tissue and brittleness. Even the nature of its setting and structure were but imperfectly understood. Self curing acrylic resin was introduced to the dental profession in the mid- 1950s. Initially used for the construction of denture bases, acrylic resin has also been used for many other purposes, including denture teeth, temporary restorations, intraoral splints and veneering agents for crowns and bridges. Since their introduction, acrylic based materials have continued to play a major role in restorative and prosthetic dentistry. But they too showed poor physical properties like high polymerization, shrinkage and coefficient of thermal expansion, irritation to pulp and dimensional instability.
In attempt to improve their properties, and the potential for greater application of resins came about with the introduction of the bisphenol A and glycidyl methacrylate, or BIS-GMA, system by R Bowen in the early 1960s .

Excerpt

In the realm of restorative materials, Buonocore, in 1955, had advocated an acid-etch

technique for bonding resins to enamel; however, his findings were neglected for many years

probably because of the inadequacy of simple resins as restorative material. But when BIS-GMA

became available, he found it to work best. Somewhat later, the acid-etching of enamel in and

around cavity preparations was found to be beneficial.

Over the past two decades, there has been a substantial progress in the development

and application of resin based tooth colored restorative materials. Consequently, new restorative

materials are now being explored by dentists, materials scientists and patients who are searching

for the so-called `amalgam substitute' or `amalgam alternative'.

The focus of dentistry in the present times is not only on prevention and treatment of disease but

on meeting the demands for better esthetics.From a critical point of view some of the new direct

restorative materials are good with respect to aesthetics, but all material characteristics must be

considered, such as for mechanical properties, biological effects, and long term clinical

behaviour.

Newer technologies are being harnessed for this purpose and advanced research is being

undertaken. Thus dentistry has evolved from a curative to a creative science in a very short span.

The constant desire of dental profession to achieve a natural appearance has led to development of

various resin based tooth colored material.

HISTORY

· Early 19th century silicates were only tooth colored material used. They had fluoride

releasing property but their major disadvantage was they become eroded very easily as

were highly soluble in oral fluid and were irritating to pulp.

· Between 1940's and 1950's acrylic resins (PMMA) replaced silicates due to their

insolubility in oral fluid, ease of manipulation, tooth like apprearance and low cost. They

also had many disadvantages like high polymerise shrinkage, high thermal conductivity.

· Early composites based on Poly Methy Methacrylate were not successful because filler

was not bonded to resin this produced defects between mechanically retained particles

and surrounding resin.

· Dr. Michael Buonocore, 1955 first discovered the effect of phosphoric acid on enamel

which made the surface rough and porous thereby receptive to bonding of polymerisible

resin.

In 1962 Dr.Ray L. Bowen of ADA research unit at the National Bureau of Standards

developed bis-GMA and organic silane coupling agent to form bond between filler and resin.

This was the major advancement made by him in restorative dentistry. . Bis-GMA forms the

basis of present-day resin base restorative materials because of its limited shrinkage and

fracture resistance. It was first used in composite in 1969.

In early 1970's eight curing was introduced as an option for clinician in form of UV

light. Because of its limitations, light cure was later using the visible light cure systems.

With the advent of visible light a great evolution came in the composite system.

Camphorquinone was added as a photoinitiator in conjunction to an amine in the resin.

After this, another major advancement came with the invention of the dentin bonding

agents. Fusayama (1980) have made significant contribution to the research literature in the

area of adhesive bonding agents.

In 1976 microfilled composites

Early 1980s posterior composites

Mid 1980s hybrid composites; I generation indirect composites

Early 1990s II generation indirect composites

In 1991 Beta quartz inserts

1995 Compomer was introduced to improve the handling and fluoride release.

1996 Flowable composite; ceromer

1997 Packable composite

1998 Ormocers; ion-releasing composites; fiber reinforced composites

1999 Single crystal-modified composites

Anu

Com

part

inte

Den

disp

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form

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cho

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ticles in a m

ermediate to

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persion of a

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omposite m

med by blen

rdevant

composite is

sen with th

perties.

Definitions

n material s

metal phase

o those of th

site is defin

amorphous

nded to the

material is a

nding togeth

s a physica

he purpose o

COMPOSI

of compos

science, a s

) that have

he individua

ned as a hig

silica, glass

matrix by a

product wh

her compon

l mixture o

of averagin

ITE RESIN

site resins

solid forme

been comb

al constituen

ghly cross-li

s, crystallin

a coupling a

hich consist

ents having

of the mater

ng the prope

d from two

bined to pro

nts

inked polym

ne, or organ

agent.

ts of at leas

g different st

rials the par

erties of the

o or more d

oduce prope

meric mater

nic resin fil

st two distin

tructure and

rts of the m

e parts to ac

distinct pha

erties superi

rial reinforc

ller particle

nct phases n

d properties

mixture gen

chieve inter

ses (e.g.

ior to or

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s and/or

normally

erally is

rmediate

DCNA 2007; Dental materials; vol. 51; July

Composite is a multiphase material that exhibits the properties of both phases where the

phases are complimentary, resulting in a material with enhanced properties.

Classification of composite

ADA specification No. 27 (JADA Vol. 94, Jun 1977)

· Type I unfilled and filled resins (noncomposite)

· Type II composite resin materials to which a filler has been added

Skinner's classification (10

edition)

· Traditional composites (Macrofilled) 8-12m

· Small particle filled composite 1-5m

· Microfilled composite 0.04 0.4 m

· Hybrid composite 0.6 1 m

According to Craig

Type I: polymer-based materials suitable for restorations involving occlusal surfaces

Type II: other polymer-based materials

Class 1: self-cured materials

Class 2: light cured materials

Group 1: energy applied intra-orally

Group 2: energy applied extra-orally

Class 3: Dual-cured materials

Acc

two ma

materia

a. The

reac

cording to A

cording to M

Prior to dis

ain phases p

als with :

A continuo

An interrup

e continuou

ction produc

Anusavice

Marzouk

scussing the

present in a

ous (dispersi

pted (disper

us phase

ct of Bisphe

(11

editio

e generation

composite r

ion/reinforc

sed/reinforc

Consists o

enol A and g

on)

ns elucidate

resin as stat

ced) phase.

cing) phase

of the synt

glycidyl me

ed by Marzo

ted by him.

thetic resin

ethacrylate.

ouk it is im

Composite

macromol

mportant to

es are all re

lecules, i.e.

note the

inforced

. it is a

Other substitutes for BIS-GMA are :

Modified BIS-GMA by elimination of OH group.

ii.

Urethane diacrylate.

iii.

TEG-DMA.

The interrupted phase :

This may consist of either one or combination of the following :

MACRO- CERAMICS.

ii.

COLLOIDAL and MICRO-CERAMICS.

iii.

Fabricated macro reinforcing macro-reinforcing phases with colloidal micro-

ceramic component bases.

Macro-Ceramics Consists of silicate based materials (SiO

), e.g. quartz, fused silica,

silicate glasses, crystalline lithium aluminium silicate, (Radio-opaque) Ba-Al-boro-Si

etc.

ii.

Colloidal and Micro-Ceramics : Originally these consisted of colloidal silicate forms

but have now been replaced by larger sized pyrogenic silica.

Classified in order of their chronological development

1. First generation composites

Consists of macroceramic reinforcing phase in an appropriate resin matrix

Enjoys the broadest clinical experience

Highest mechanical properties in lab testing

Highest proportion of destructive wear clinically due to dislodging of large

ceramic fillers.

High surface roughness

2. Second generation composites

Consists of colloidal and micro-ceramic phases in a continuous resin phase

Exhibit best surface texture of all composite resins

Properties of strength and COTE are unfavorable

Wear resistance is better than that of first generation due to dispersion matrix

macromolecules and difficulty of engaging these minute ceramic particles in

abrading element.

3. Third generation composites

Is a hybrid composite in which there is a combination of macro- and micro

(colloidal) ceramics as reinforces

They exists in ratio of 75:25 in a suitable continous resin phase

The properties are somewhat of a compromised between first and second

generation composites

4. Fourth generation composites

Are hybrid types, but instead of macroceramics fillers they contain heat-cured,

irregularly shaped highly reinforced composite macroparticles, with reinforcing

phase of micro (colloidal) ceramics

Produce superior restorations but they are very technique sensitive

These exhibit maximum shrinkage of all composites

Texture and esthetic capacity only slightly less satisfactory than 2

generation

materials

Physical and mechanical properties between those of the first and second

generation

5. Fifth generation composite

Hybrid system in which the continuous phase is reinforced with microceramics

and macroceramics, highly reinforced heat cured composite particles

The spherical shape of the macrocomposite particles will improve their

wettability and consequently their chemical bonding to continuous phase of the

final composite

Packing factor of final composite is improved

Workability is improved because of specific shape of macromolecules. This

results from easy `slip' that occurs among the particles in spite of high viscosity

of highly reinforced matrix

Surfa

Physi

comp

Sixth gener

Are h

micro

ceram

Exhib

Of all

Its w

comp

According

a. Bas

b. Bas

size

ce texture a

eneration co

ical and me

osites

ration comp

hybrid in w

o (colloid)

mics

bits the high

l composite

ear and sur

osite.

to sturdev

sed on filler

sed on rang

Megafill-

Macrofill

Midfill 1-

Minifill 0

and wear of

omposite

echanical p

posites

hich the co

ceramics

hest percent

s, it has bes

rface textur

vant (4

edi

content (w

ge of filler

quartz , larg

10-100

-10

0.1-1

f these mate

properties a

ontinuous ph

and agglo

tage of reinf

st mechanic

re character

ition)

eight/volum

r particle

ge size

erials would

are similar

hase is rein

omerates o

forcing part

al propertie

ristics are v

me%)

d be compa

to those of

nforced with

of sintered

icles

very simila

arable to tha

f fourth ge

h a combin

micro (co

ar to 4

at of the

neration

nation of

olloidal)

neration

¾ Microfill 0.01-0.1 m

¾ Nanofill 0.005-0.01 m

c. Composites with mixed range of particles sizes are called hybrid and the

largest particle size range is used to define the hybrid type

¾ Midifill hybrid

¾ Minifill hybrid

d. According to whether composite is a homogenous mixture of resin and filler

or includes the pre-cured composite

¾ Homogeneous if composite consists of filler and uncured matrix

material

¾ Heterogeneous if it includes pre-cured composites or other

unusual filler

e. Modified composites- if it includes novel filler modifications in addition to

conventional fillers, it is called modified composites. E.g. fibre-reinforced

composites.

Based on area of application

posterior composites

Based on method of curing

· Chemical curing

· Light curing

UV light

Visible light

Plasma arc

Laser curing

· Dual cure

· Light body Flowable composite

· Medium body Homogeneous microfills, macrofills and midifills

· Heavy body Packable hybrid minifills

INDICATIONS OF COMPOSITES

Class I, II, III, IV, V, VI

Core buildups

Sealants and preventive resin restorations

Esthetic enhancement procedures

Cements

Veneering metal crowns/bridges

Temporary restorations

Periodontal splinting

Non-carious lesions

Enamel hypoplasia

Composite inlays and onlays

Repair of old composite restorations

Patients allergic to metals

CONTRAINDICATIONS OF THE COMPOSITE RESIN RESTORATIONS

· Isolation for a restoration to be susccesful it must be bonded to tooth structure. Bonding

to tooth requires an environment isolated from contamination by oral fluids or other,

which may prohibits bond development. Therefore the ability to isolate the operating area

is a major factor in selecting a composite material for restoration. If the operating area

cannot be totally isolated, a non-bonded amalgam restoration is material of choice.

· Occlusion composite materials exhibit less wear resistance than amalagem. For patients

with heavy occlusion, bruxism, or restorations that provide all of a tooth's occlusal

contacts, amalgam rather than composite is usually indicated. Factors that affect the wear

resistance of composite include tooth location, width of the tooth preparation, type of the

contact from opponent tooth on composite surface

10. Based on consistency

· Subgingival area/root surface composite restorations extending on root surface may

exhibit gap formation at junction of composite and root. So, a lining of GIC is

recommended.

· Poor oral hygiene

· High caries index

· Habits (bruxism)

· Operator's ability and commitment factors the ability to isolate, placement of etchant,

primer and adhesive on tooth structure, insertion, finishing and polishing of composite

restoration are more difficult. These requires both technical ability and knowledge of

material's use and limitations

ADVANTAGES OF THE COMPOSITE RESIN

¾ Esthetics

¾ Conservation of tooth structure less extension, uniform depth not necessary,

mechanical retention usually not necessary.

¾ Less complex when preparing the tooth

¾ Insulative

¾ Used almost universally

¾ Strengthening

¾ Bonded to tooth structure resulting in good retention, low microleakage,

minimal interfacial staining and increased strength of remaining tooth

structure.

¾ Repairable

¾ No corrosion

¾ Polymerization shrinkage

¾ Technique sensitive

¾ Higher coefficient of thermal expansion

¾ Difficult, time consuming

¾ Increased occlusal wear

¾ Low modulus of elasticity

¾ Bio-compatibility

¾ Staining

¾ Costly

COMPOSITION AND FUNCTION OF COMPONENTS:-

Tooth enamel and dentin are two examples of the many composite materials found in nature.

Enamel contains approx. 95 wt% inorganic structure, 90 to 92% of which is hydroxyapatite.

The other components 1 wt% is of organic enamelin structure and 4 wt% of water. Dentin

contains 75 wt% of inorganic, 20 wt% organic matters and 5 wt% water. In both enamel and

dentin reinforcing filler particles are hydroxyapatite crystals. The difference in the properties

of these two tissues is associated in part with differences in the matrix-to-filler ratios.

There are 3 main structural components in composite resin

1. Matrix a plastic resin material that forms a continuous phase and binds the filler

particles.

2. Filler reinforcing particles and/or fibers that are dispersed in the matrix.

3. Coupling agent bonding agent that promotes adhesion between the fillers and the

matrix.

RESIN MATRIX:-

Most dental composite use a blend of aromatic or aliphatic dimethacryalytes monomers

such as Bis-GMA (most commonly used); Triethylene glycol (TEGDMA); Urethane

methacrylate (UDMA). These three monomers form highly crossed linked polymer

structure.

DISADVANTAGES OF THE COMPOSITE RESIN RESTORATIONS

Som

produce

short co

1. Hig

2. Gen

3. Vol

4. Hig

5. Use

dete

The

three fe

hydroxy

me early co

e materials

omings of m

gh shrinkage

neration of h

latility.

ghly irritant

e of high

erioration of

e breakthrou

eatures

1. The bis

polycar

2. Termin

radical

3. Hydrox

of high

water b

The Bis-GM

yl groups th

omposites w

that were

methyl meth

e during pol

heat.

to pulp and

quantity o

f the mecha

ugh came w

s-phenol A

rbonates and

al methacry

system.

xyl groups

viscosity

by the resin.

MA has two

hat provide

were based

as satisfact

hacrylate are

lymerization

d soft tissue.

f methacry

anical prope

with the int

A nucleus:

d polysulph

ylate group

these indu

about 12,0

o phenyl gro

intermolecu

on methyl

tory as thos

ylic acid re

erties.

troduction o

found in t

hones.

ps these

uce hydroge

000 poise an

oups, which

ular bonding

l methacryl

se produced

esulted in

of Bis-GMA

thermoplast

are polyme

n bonding a

nd undoubte

h provide ri

ate but this

d by the lat

high absor

A in 1962.

ics of high

erizable by

and thereby

edly enhanc

gidity to the

s monomer

ter monome

rption of w

The molec

h strength

convention

y result in a

ce the absor

e molecule

did not

ers. The

water

cule has

such as

nal free-

material

rption of

and two

The advantage of using this monomer appear to be

1. Because Bis-GMA and UDMA have almost five times the molecular weight of the

methylmethacrylate, the density of the methacrylate double- bond groups is approx.

one-fifth as high as in these monomers, which reduces the polymerization shrinkage

proportionately. The use of the dimethacrylate also results in extensive cross-linking

which increases the strength and rigidity of the polymer.

2. It is non-volatile.

3. It produces less heat during polymerization.

4. It is a large molecule hence less diffusion into pulp and subsequent toxicity

A defect pointed out by Bowen himself is that this monomer is impossible to

crystallize and hence to purify. Also the stability of its color is questionable. Owing to its

high viscosity, it requires low molecular weight thinning monomers such as the glycol

methacrylates. The addition of low molecular weight monomer or the diluents is needed to

attain the high filler content and also to attain consistencies of the paste suitable for clinical

manipulation. These diluent monomers can be any fluid methacrylate, but are usually

dimethacrylates such as TEGDMA.

The mixture of TEGDMA and Bis-GMA provides appropriate viscosity needed for

binding of filler particles. Bis-GMA and TEGDMA in ratio of 3 :1 and 1:1 have been tried.

The function of the diluent can be listed as follows

1. Attains a consistency that is suitable for manipulation i.e. to reduce the viscosity

2. Results in higher filler loading.

3. Results in higher degree of conversion.

4. Increase the number of cross-linking reactions during setting of the resin matrix.

5. Increase the time before gelation of the matrix occurs and subsequently reduce

marginal polymerization contraction stress.

Disadvantages of the increased concentration of the diluent

1. Greater polymerization shrinkage.

2. Increased flexibility.

The dim

among

softenin

Bis-GM

between

with a

(triethy

characte

viscous

with Bi

and ben

elongat

Decreased

methacrylate

the polyme

ng and/or de

MA has a ve

n the hydro

a more flu

leneglycold

eristics, and

s Bis- GMA

is-GMA. O

nzyl metha

ion and deg

abrasion res

e monomer

er chains. T

egradation b

ery high vis

oxyl groups

uid resin i

dimethacryl

d it is mos

A. Optimal p

Other diluen

acrylate, a

gree of cure

sistance.

rs also have

This results

by heat and

scosity beca

on the mo

in order t

ate) has

t often use

properties a

nts include

monofunct

e the advant

s in a rigid

solvents su

ause of the

onomer mol

to be use

excellen

ed as the di

are produce

ethylene-

tional mon

tage of prod

d resin mat

uch as water

hydrogen b

ecules. Thu

ful for de

nt viscosi

iluent mono

ed when TE

and hexam

omer adde

ducing exte

trix that is

r and alcoho

bonding inte

us, Bis- GM

ental comp

ity and

omer for U

EGDMA is

methylene-gl

d to enhan

ensive cross

highly resi

ol.

eractions th

MA must be

posites. TE

copolyme

UDMA or th

used in a 1

lycoldimeth

nce polyme

s-linking

istant to

hat occur

e diluted

EGDMA

erization

he more

1:1 ratio

hacrylate

er chain

Bis-GM

is maxi

polyme

thus en

monom

in the p

spectrop

polyme

Incorp

the

Benefit

reduce t

Resin stren

MA molecul

mized. The

er backbone

nhancing the

mer to polym

polymer ma

photometry

erization.

poration of

filler partic

ts of the fill

The primar

the amount

Reinforcem

wear.

Reduction i

Improved w

Reduction i

ngth is depe

les are used

e minimal fl

e. Increased

e stiffness o

mer limits th

atrix. In pre

y that 25-

fillers into r

cles are wel

reinforcing

lers -

ry purposes

of matrix m

ment of matr

in polymeri

in thermal c

workability

in water sor

endent upo

d and the de

lexibility of

d cure result

of the polym

he number o

esent comm

55% of th

FILLERS (

resin matrix

l bonded to

g the matrix

s of the fill

material.

rix resin res

ization shrin

contraction

by increasin

rption, softe

on monome

egree of con

f the Bis-GM

ts in enhan

ymer networ

of unreacted

mercial com

the methac

(DISPERSE

x greatly im

o resin matri

can actuall

ler particles

sulting in in

nkage

and expans

ng the visco

ening and st

r compositi

nversion (D

MA molecu

nced cross-l

rk. In addit

d monomers

mposites, it

crylate gro

ED PHASE

mproves the

ix. If not, th

ly weaken th

s are to stre

ncreased har

sion

osity

taining

ion, being

DC) of the m

ule enhance

inks betwee

tion, the fur

s that may s

has been v

ups remain

material pro

he filler part

he material.

engthen the

rdness, stre

greatest wh

methacrylate

s the rigidit

en polymer

rther conve

serve as pla

verified by

n unreacte

operties, pro

ticles instea

e composite

ength and de

hen stiff

e groups

ty of the

r chains,

ersion of

asticizers

infrared

ed after

ovided

d of

e and to

ecreased

The rou

Materi

Crys

Increased

strontium (

X-rays.

Contribute

utinely use

a. Qua

extr

fine

com

even

b. Silic

pure

pyro

hav

boro

c. Oth

zirc

d. Rec

ytte

e. Ions

alum

als used for

Pure silica

stalline

Crystobalit

Tridymite

Quartz

radiopacity

(Sr) and bar

to esthetics

d fillers 

artz quart

remely hard

er particles

mposites, wh

n abraded th

ca silica h

e silica, fu

ogenic and

e been use

osilicates ar

her fillers

conium diox

cently filler

erbium triflu

s have been

minum silic

r fillers -

y and diag

rium (Ba) g

tz is chemi

d, making it

s. These w

hich were d

he opposing

has been us

fused silica

d precipitat

ed. Glasses

re also used

such as

xide have al

s containin

uoride

n added to s

cate and stro

Pure

gnostic sen

glass and o

ically made

difficult to

were used

difficult to p

g tooth struc

sed as filler

a and collo

ted forms

s as alumi

tricalcium

lso been use

ng fluoride

silica particl

ontium silic

e silica

nsitivity th

ther heavy

e, but was

grind into

in early

polish and

cture.

r in many f

oidal silica

of colloida

inum silica

m phospha

are tried su

les e.g. lithi

ate glass.

hrough the

metal comp

forms as

a. Both

al silica

tes and

ate and

uch as yttri

ium aluminu

non-c

Glass

Modific

- Li, A

- Ba, Zn

e incorpora

mpounds tha

ium trifluor

num silicate,

crystalline

cation by ion

n, St, Y, St,

Pyrogenic s

ation of

at absorb

ride and

, barium

, Zr,

silica

2. Amorphous silica

· Colloidal silica (0.04m)

Pyrolytic/precipitation process

Pyrogenic/fumed silica

· Agglomerated silica (1 - 25 m)

3. Organic filler

4. Fiber fillers

5. Single crystals Sic

6. Crystalline polymers.

7. Fluoride containing fillers

Organic fillers 

Are nothing but heterogenous fillers. This was introduced in order to circumvent the

viscosity problem. Precured microfill composite was blended with uncured material. Precured

particles were generated by grinding cured composites to a 1 20 m sized powder. The

procured particles become chemically bonded to the new material, provide islands with better

properties and can be finely finished.

Another method to overcome the viscosity problems has been to sinter the smaller

filer particles into large but porous filer particles, impregnate them with monomer and add

the new particles to a microfill composite. Within the local region of sintered filler particle,

the material is highly filled and yet capable of being polished. [these two modifications are

for microfill composite to overcome viscosity]. The unmodified microfills are called

homogenous microfills.

Fiber fillers:-

This type of fillers has led to the introduction of fiber-reinforced systems. The main

advantage of fibers is that they have excellent strength in the primary fiber direction.

Unfortunately, it is difficult to efficiently pack the fibers or orient their direction. Small

additions of fibers to regular fillers are effective in improving properties. The limiting factor

is that fibers only may be used with dimension greater than 1 m because of the concern for

cariogenicity of submicron fibers such as asbestos. Most current fibers have diameters of 5 to

10 m and effective length of 20 to 40 m.

Single crystal- Sic:-

Single crystals generally have symmetric shapes and are commonly long plates,

behaving like fibers, their singular advantage is that they are much stronger than non-

crystalline or polycrystalline fibers. The strongest e.g. of a crystal modified composite is an

experimental composition that employs Sic single crystal. Unfortunately, the crystals are

colored and not well suited for esthetic considerations. However, in clinical uses in which

esthetics are not important, these crystals modified composites could be very valuable.

Pure silica:- Pure silica occurs in several crystalline forms and non-crystalline form (glass).

Crystalline forms are stronger and harder, but when used, result in composites that are

difficult to finish and polish. Therefore most composites are now produced using silicate

glasses. Barium, zinc and ytterium-modified silica glasses are currently the most popular

fillers. Non-crystalline glass are sometimes modified with other ions to produce desirable

changes in properties. Lithium (Li) and aluminum (Al) ions make the glass easier to crush to

generate small particles. Barium (Ba), Zinc (Zn), Boron (B), Zirconium (Zr) and Yttrium (Y)

ions have been used to produce radiopacity in filler particles. Excessive modification (by

replacement of silicon in structure) however can reduce the efficacy of silane coupling agent.

Amorphous silica:-

Microfill and hybrid composites utilize microfiller of SiO

that can be produced in

variety

of ways. Two basic forms are usd in dental composites. Colloidal silica is chemically

precipitated from a liquid solution as amorphous silica particles. Pyrogenic silica is

precipitated from a gaseous phase as amorphous particles. The actual properties of each form

are slightly different, but the differences have not yet been shown to produce different

clinical properties for composites.

Crystalline polymer fillers some newer composites include crystalline polymer to

supplement traditional fillers. Crystalline polymer is not nearly as strong as inorganic filler,

but is it is stronger than amorphous polymer material.

II.

Filler size 

A. Sturdevant classified fillers according to particle size as Megafill, macrofill,

midifill, minifill, microfill, and Nanofill. Composites with mixed ranges of particle

sizes are called hybrids and the largest particle sizes are called hybrids and the

largest particle size range is used to define the hybrid type (e.g. minifill hybrid)

· Megafillers

For posterior composite restorations, it is also possible to place one or two

large glass inserts (0.5 to 2 mm Particles) into composites at points of occlusal

contact or high wear. These pieces of glass are referred to as glass inserts ( inserts)

or megafillers. Although they have demonstrated improved wear resistance to

contact area wear, these techniques are more complicated and do not totally

eliminate contact free area (CFA) wear. Furthermore the bonding of composite to

the insert is questionable.

· Macrofillers

Filler particle sizes for the earliest composites averaged 10 to 20m in

diameter, with many of the larger particles as larger as 50m. this was very

difficult to finish, created a rough surface due to unequal wear of the matrix

and filler.

· Nanofillers

Nanofillers are so small that they fit between several polymer chains. These

characteristics permit the opportunity to achieve very high filler loading levels

in composite while still maintaining workable consistencies.

III.

Filler loading :- [filler content] As in Skinners (11

edition), inorganic filler

particles account for between 30 and 70 volume% or 50 to 85 wt% of a composite.

IV.

Filler surface area:- [Anusavice 11

edition]

The potential amount of filler that can be incorporated into a resin is greatly influenced

by total filler surface area, which is a function of particle size, with surface area increasing

Details

Pages
Type of Edition: Originalausgabe
Year: 2014
ISBN (PDF): 9783954899562
File size: 5.5 MB
Language: English
Publication date: 2015 (June)
Keywords: Esthetic dentistry history of esthetic

Author

Dr. Cheena bansal (Author)

RESIN BASED MATERIALS

Summary

Excerpt

Table Of Contents

Details

Author

Dr. Cheena bansal (Author)