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BIOLOGICAL CONSIDERATION OF DENTAL MATERIALS AND
CUTTING MECHANISMS
Introduction
Dental materials share with other of biotechnology the problem of
biocompatibility; that is the interaction of manufactured compounds with body
tissue fluids, biocompatible ace to the Dollands Medical Dictionary id defined
as being harmonious with life and not having toxic or injurious effects on
biologic function Manufacturer and biologic and materials scientists are
endeavoring to
! Develop testing methodology for biocompatibility
" #urvey a variety of appropriate materials for usefulness in
particular biologic context
$ %valuate the materials and devices in a clinical setting
&he first efforts of the 'D' to establish guidelines for dental materials
came in !(") when scientists developed specification for Dental 'malgam *ut
it was only in the early !()+s that a committee develop the testing procedure
for generalied use
&he documents of these tests -ecommended standard practice for
biological evaluation of dental material was published in !(." and
republished in !(.( as document no /!
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' similar document was published by the 0D1 in !(2/ &he draft
was entitled 3reclinical evaluation of *iocompatibility of Medical devices
used in Dentistry test methods
1n general biocompatibility is measured on basis of localied
cytotoxicity, systemic responses, allergenialy and carcenogenicity
*ased on these criteria, the re4uirements for dental material
biocompatibility include
1t should not be harmful to the pulp and soft tissue
1t should not contain toxic diffusable sabs tat can be released and absorbed
into the circulatory system to cause systemic toxic response
1t should be free of potentially sensitiing agents that are li5ely to cause an
allergic response
1t should have no carcinogenic potential a broad sense *iomaterial can be
defined as any substance, other that a drug, that can be used for any period
as a part of a system that treats, augments or replaces any tissues, organ or
function of the body &he host environment for dental biomaterial is
complicated because of the presence of bacteria and debris in the oral cavity
and the corrosive properties of saliva and other fluids
Tests for evauation of Bioco!"ati#iit$
&he purpose of biocompatibility tests is to recognie and eliminate any
potential product or component of a product that can cause harm to oral or
maxillofacial tissues
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6sually these tests are classified on three levels with the most rapid and
economical occurring at the primary level ' product with promising attributes
is subjected to more expensive secondary tests and finally to expensive tests in
animals and humans
Grou" I% &ri!ar$ tests
3rimary consists of cytotoxic evaluation in which dental materials in a
flesh or curved state are placed directly on tissue culture cells or on membrane
overlying tissue culture cells that leach to effects of products or components
that leach through the barriers 3roducts that are 4uite cytotoxic can be
modified by the manufactures
Geneto'icit$ tests
Mammalian or nonmammalian cells, bacteria, yeast or fungi are used to
determine whether gene mutations, changes in chromosomal structure or other
deoxyribonucleic acid or generic changes are caused by the test materials,
devices and extracts from materials
Grou" II% Secondar$ tests
&he product is evaluated for its potential to create systemic toxially,
inhalation toxicity, s5in irritation and sensitiation and implantation responses
#ystemic toxicity test such as the oral medium lethal dose 78D9+: test, the test
sample is administered daily to rats for !/ days either by oral gauge or by
dritary inclusion 1f 9+ of the animals survive the product has passed the test
Dermal toxicity test is important because of the great number of chemical
substances not only dental products, that we contact daily &o stimulate dermal
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toxicity the test material is held in contact with the shaved s5in of albino rats
for a period ranging from "/ to (+ days ' primary irritant id capable of
producing a infl response in most susceptible pts after the first exposure
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"=$mins the agent is considered very toxic, if none of the animals die, the agent
is not li5ely to be haardous to humans
I!"antation tests
0or any in vivo implantation techni4ue animal species are selected
according to the sie of implant test specimen and the intended duration of the
test in relation to the life span of the animal 0or short term tests 7less than !"
wee5s: in subcutaneous tissue of muscle animals such as mice, rats, hamsters,
guinea pigs and rabbits are commonly used for long term tests 7more than !"
wee5s: in muscle or bone animals such as rabbits, dogs, sheep, goats with a
relatively long life expectancy are used
0or subcutaneous and muscle implementation the test materials is pac5ed
into various types of plastic tubes
0or bone implants, holes are drilled using low speed intermittent cutting
under profuse irrigation, the cylinders of the test implant material are
inserted into the drilled holes using finger pressure &he diameter of the
implant and drilled hole should correspond to prevent the ingrowth of
fibrous tissue >istopathologically, the formation of new bone on to the
surface of the test implant material without intervening ?& is evaluated
Grou" III% &recinica usa(e test
&u" and dentin usa(e test
&he test is designed to assess the biocompatibility of dental materials
placed in dentin adjacent to the dental pulp Dogs, miniature pigs with dentition
recently erupted and intact permanent teeth are selected
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?lass @ cavity on labial = buccal surfaces of teeth using sharp burs with
ade4uate air water spray to leave !mm of tabular dentin between the floor
of the cavity preparation and pulp
&he cavities are restored some are retained as control specimens
's a negative control, some form of "+% is used
0or a positive control a restorative material that consistently induces
moderate to secure pulp response is selected
&he animals are scarified after . days, "2 days, and .+ days &he
specimens are graded for a degree of inflammatory response, prevalence of
reparative dentin formation and the number of microorganisms entrapped in the
surrounding cavity walls and cut dentinal tubules
&est materials that induced least inflammatory response in pulp were
considered promising
8ess reparative dentin better the material, because more bul5 of the
dental vital pulp is available to deal with future episodes of caries and dental
treatment
&u" ca""in( and "u"oto!$ usa(e tests
#imilar to those described earlier except that the pulp is mere exposed
for pulp capping evaluation and is partially removed for the pulpotomy
assessment ' calcium hydroxide product is used as a negative control
'nimals are sacrificed at . and .+ days
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*ut there has been increasing concern regarding the physical insertion of
an amalgam being a major contributing factor responsible for greater responses
rather than chemical, toxic or thermal properties of amalgam
1t has been reported that a common histophathologic feature of amalgam
restored teeth is a dense accumulator of nutrophils between the predentin
and odontoblastic lager
#ome other authors have shown that radioactive mercury reached the pulp
in humans after ) days if no cavity liner was used C they also found that the
rate of diffusion of mercury into enamel and dentin was inversely to the
degree of mineraliation
&his implies that in old pts the penetration of mercury ions in less 7owever if the practitioner places a conventional amalgam restoration after
cutting a cavity preparation at high speed, the pressure of condensation will
intensify the initial minimal inflammatory response and it will subse4uently
increase the formation of reparative dentin to level comparable with thatformed after use of low speed air water techni4ue
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+isi#e i()t cure co!"osite resins
&he level of pulp response to resin composite restoration depends on the
degree of curing
*ecause an incomplete curing of the resin permits an even higher
concentration or residual unpolymeried monomer to reach the pulp
o matter what types of lamps 76@ or visible light: are developed for
dental profession, insufficient energy is available to cure a large volume or
thic5ness in one application hence curing should be done in incremental layers
Eenerally an increase in the sie of a tooth preparation and the mass of
the restoration are associated with greater shrin5age of the restoration
@olumetric shrin5age F polymeriation shrin5age is still the overwhelming
obstacle in maintaining adhesion and minimiing microlea5age
>ence a more conservative cavity preparation incremental placement of
resin composite is highly recommended for posterior restorations
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'ce to *DG composite resins have been found to produce an
inflammatory response in the pulp when placed in test cavity in animals,
strongly allergenic inhibit -' cele synthesis
3eroxides used to generate free radicals in the polymeriation of
composite resins are 5nown to be promoters of s5in tumors
0ree radicals may be involved in development of some cancers and it is
5nown that these chemicals leach out of set composites from both the resin and
filler
*isphenol a has been reported to leach out and been claimed that this
compound may mimic the effects of natural estrogens and may attach to
oestrogen receptors on cells and their possible contributory role in breast and
testicular cancer has also been claimed
,inc &)os")ate Ce!ent
Hinc phosphate has been widely used to cement all sorts of castings and
applications from crown to orthodontic bands
&hey have been used in deep cavities to build up dentin since the
thermal consecutively of the cement is approximately e4ual to that of enamel
&he fluid component of inc phosphate cement consists of
orthophosphoric acid and small amounts of aluminium F inc &he powder
contains inc oxide &he set product is integrated amorphous inc phosphate
containing unreacted inc oxide particles
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&he usage tests with deep cavities suggest that there could be a moderate
to sense localied pulpal damage produced within the first $ days since it has a
very low ph 7/" at $min: initially and gradually neutralies at /2 hrs any free
orthophosphoric acid functions to irritate the pulp particularly in deep cavities
with open tubules
&here is a mar5ed pulp tissue response when inc phosphate cement is
used for luting purpose &his may be, because the orthophosphoric acid is
forced into the dentinal tubules when the pt bites on a tongue blade to seat the
restoration
Gass Iono!er Ce!ents
&he pulp responses to E1? are considered moderate and less irritating
&his is attributed to the absence of strong acids and toxic monomers &he
polymers used possess higher molecular weighs that limit their diffusion
through the dentinal tubules of the pulp
,inc &o$acr$cate Ce!ents
&he cement was developed to combine the properties of strength of Hn
phosphate with the adhesiveness and biocompatibility of inc oxide eugenol
&he acrylic acid ions bind to the metallic ions so tightly that they are
not easily reached from the set cement &he freshly set and completely set
cements show a low degree of cytotoxicity
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&oxicity can be reversed by cherating inc with %D&' 7Hn polyacrylate
are not bacteriostatic: subcutaneous, bone implants have not indicated toxicity
of the cement
,inc O'ide Eu(eno Ce!ent
Hinc oxide eugenol cements are least injurious to the dental pulp ot
only there is no irritation produced by the material but actually it exerts a mild
palliative and sedative effect on the pulp 1t seems to be much a bland
substances that it may even lac5 necessary irritating products to stimulated the
formation of secondary dentin formation
Siicate Ce!ent
#ilicate in set form consist of glass particles covered with a layer of
aluminoAsilica get and a matrix of amorphous insoluble phosphates and
fluorides
Most in intro screening tests have shown that silicate cements are
mar5edly cytotoxic, due to the retention of phosphoric acid even after "/ hrs
and to some extent fluoride ions in concentrations of !9="9mg = ml reduce cell
growth
#ilicates implanted into subcutaneous tissue inhibit cell enyme activity,
elicit severe inflammatory response and cause necrosis of tissue with fibrous
capsule formation &here has been noticeable degree of acute inflammatory cell
infiltration with disruption of odontoblastic cell layer within ! to $ days of
placement -esponse shifts from moderate to severe after 9 C 2 wee5s
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-ecent studies have demonstrated that microlea5age around the silicate
may be important in promoting pulp response as is reaching of the material
Conditionin( A(ents
%tching agents are used with both resin composite systems and E1?s
%tching agents remove the surface contaminants to permit the micro
mechanical attachment or the ionic exchange of dental material with the tooth
*eannstrom showed that conditioning of dentin and removal of the
smear unit allows the ingress of bacteria and the outward flow of dentinal fluid
within the tooth material interfacial region and possibly contributes to
formation of a biofilm that interfaces with adhesion
?onse4uently it is recommended that the smear layer should remain, but
in a modified form #o only the surface layer of dentin 7!+mm depth: needs to
be modified and not its deeper layers
>ence conditioning techni4ues that are associated with wea5er acids,
shorter periods of application and the elimination of rubbing and scrubbing
procedure produce a minimal pulp response and satisfactory bonding
Bondin( A(ents
*onding agents are used to reduce the expected pulp responses induced
by the subse4uent placement of more toxic resin based composite materials
*onding agents do not appear to be toxic #pecimens from subhuman primates
revealed low to average inflammatory cellular response values at all time
intervals
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ALLERGIC RES&ONSES TO DENTAL MATERIALS
Aer(ic contact Der!atitis
Dermatitis usually occurs where the body surface ma5es contact with an
allergen 'llergen is defined as a substance that is not primarily irritating on
the first exposure but produces reaction more rapidly in animals of appropriate
genetic constitution on subse4uent exposure to similar concentrations
'n allergic contact dermatitis associated with monomers of bonding
agents fre4uently involves the distal parts of the fingers and palmas aspects of
the fingertips
Aer($ to Late' &roducts
>ypersensitivity to latex may represent a true latex allergy or a reaction
to accelerators and oxidants used in latex processing
&heorem C a chemical used in latex processing may cause allergic
response
'mmonia used to preserve the rubber sap hydrolyes and degrades the
sap to produce allergens 8eaching of the rubber products by soa5ing then in
hot water brings the allergens the surface and places the highest concentration
of allergens next to the s5in of the wearer
-eactions range from localied rashes and swelling to more serious
types such as wheeing and anaphylaxis %cema is the most common adverse
reaction
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1t is also important to 5now from a detailed history if the pt who is being
treated is allergic to latex because the operators glove often ma5es contact with
the s5in of the pt *esides the rubber dam sheet is made from latex
&o avoid these adverse responses to latex products of vinyl gloves or
gloves made from other synthetic polymers may be used
Aer(ic Contact Sto!atitis
1t is by far the most common adverse reaction to dental materials &he
adverse reactions may be obtained as a local or contact type lesions, but the
reaction may be far away from the material site 7itching on the palms of the
hands or soles:
&he most definitive diagnostic test for allergic contact dermatitis =
stomatitis is the patch test &he suspected allergen is applied to the s5in with
the intent to produce as small area of allergic contact dermatitis &he test ta5es
about /2 C () hrs reaction may cause hyperemia, edema, vesicle formation and
itching
Dental materials contain many components 5nown to be common
allergens such as chromium, cobalt mercury eugenol, colophonium,
formaldehyde
Resin Base
&he allergic reactions associated with resin based materials effect not
only pts but also the dental personnel wor5ing with these materials &he
polymeriation of composite materials is never complete &he incomplete
polymeriation of resin restorative material may predispose to material
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degradation Degradation and wear of the materials release components of the
resin based materials, and these may cause reactions locally and systemically
' postmortem study in dental staff and controls using radiochemical
neutron activation analysis &he study stated that a high level of mercury was
found in two hyroid specimens 'ccumulation of mercury in several organs
particularly 5idney pituitary gland occipital lobe of brain was seen
#heep experiments showed the some mercury from amalgam fillings can
pass from the mother to the fetus >owever human experiments appear to
indicate that there is no correlation between the mercury levels in the fetus and
number of amalgam fillings in the mother
Aer($ to Nic-e
'bout !+ of female population is allergic to nic5el &his is attributed
to greater exposure of females to nic5el because all the gold plated jewellary is
made with a nic5el undercoat beneath the gold plating only $+ of those pts
with a 5nown nic5el allergy develop a reaction to an inteaoral nic5el chromium
dental alloy
To'icit$ and Aer(enicit$ of Ber$iu!
*errylliosis is an inflammatory lung disease resulting from inhalation of
beryllium dust or fumes *eryllium controls cast ability and surface oxidation
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MICROLEA.AGE
' microscopic space always exists between the restoration and the
prepared cavity, with the exception of those systems based on polyacrylic acids
and possibly certain dentin bonding agents
1f lea5age is more bacterial growth occurs between the restoration and
the cavity wall and extends upto the dentinal tubules 1t has been concluded that
the toxic products liberated by such microorganisms might produce continuingirritation to the pulp
T)er!a C)an(es
&ooth structure and dental restorations are continually exposed to hot
and cold beverages and food 1nstantaneous temperature changes during the
course of a meal may be as high as )9I? the thermal conductivity andcoefficient of thermal expansion of restorative materials are important
properties to be considered in pressuring the health of the pulp and in
minimiing the increased microlea5age that may occur as a result of
temperature cycling
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Gavanis!
&he presence of dissimilar metals in the oral cavity creates small
currents &hus producing irritation and on many occasions sensitivity to the
pulp
Bhen any two dissimilar restorations are wet in saliva, an electric
couple exists with a difference in potential between the restorations, when these
restorations are brought in contact, the potential is suddenly short circuited
through the two alloys &he result is sharp pain
' similar effect may be observed by touching the time of a silver for5 to
a gold foil or inlay restoration and at the same time allowing some part of the
for5 to come in contact the oral soft tissue
Bhen the tooth all not in contact a circuit stills exists #aliva forms the
electrolyte and the hard and soft tissues can constitute the external circuit
Roe of Dentin
Dentin is a dynamic structure with constant fluid exchange throughout
the structure 'ny changes in the hydrodynamics can result in pulpal reaction
7'ce to *ranstroms hydrodynamic theory: &his can occur by undue
desiccation of the surface or by pressure exerted in the placement of a
restoration
1nstrumentation involved in cutting a cavity preparation produces a
tenacious layer of debris = particularly on the dentin &his thin layer or the
smear layer provides additional protection to the dentin and the pulp from a
potential irritant
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BIOLOGICAL CONSIDERATIONS TO CUTTING INSTRUMENTS
3ulp reactions to rotary cutting instruments
&he most important single factor in determining pulpal response to a
given stimulus eg ?utting instruments is the -emaining Dentin &hic5ness
7-D&: between the floor of the cavity preparation and the pulp chamber
&he heat generated by the cutting instruments during the removal of
tooth structure has be generally accepted as the cause of pulp injury -3M,
3ressure and #urface area of control
&he factors to be considered when pulp reactions are evaluated are
a/ T$"e of Cuttin( instru!ents
#teel burs produce more heat than carbide burs because of inefficientcutting
*urs and diamond instruments that are dull do not cut efficiently and
results in heat production
#piral fluted burs produce more heat than straight fluted burs
Diamond instruments generate more heat than carbide burs when cutting
at high speeds without coolants
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#/ Met)od of A""ication
1n low speed, high speed era intermittent cutting is the best method of
controlling frictional heat pressure more than and ounces contributed to the
intensity of pulp injury
c/ Cooants
3roper use of efficient instruments coolant are re4uired to control
frictional heat at the cutting site &he three most important coolants are 'ir,
Bater and 'irABater 'ir alone was not found to be a consistently protective
when less than "mm of dentin was remaining between cavity floor and the
pulp &he use of air coolant can cause desiccation of the dentinal tubules which
intensity pulp damage 'ir coolants can be used only when visibility is a
problem in cavity preparation %g JDuring removal of deep caries or finishing
procedures of cavity preparations
d/ 0ater
?opious flow of warm water is effective in controlling temperature
increases 1t is logical to use water to minimie trauma by 5eeping warm tissues
warm and wet tissue wet
e/ Air10ater Cooant
Most popular and effective method and has several advantages over a
water coolant @isibility is not as great a problem since less water is re4uired 7)
to 2cc=min: &he lubricating and cleaning action of the air water spray
increases &he cutting efficiency and instrument life
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'ir water spray is superior to the water stream of subgingival
margination because the spray helps to 5eep the gingival crevice open for better
vision
1n areas of difficult vision hand pieces with fiber optics are an excellent
alternative
&he aerosol created by dry cutting with a air coolant is a health haard at
dentist, pt and the personnel present &he odour is disturbing to pts because
they thin5 that the tooth is being burned
To Concude
1t is imperative for a dentist purchasing a material to 5now if the
material is safe and if it is safe, how safe it is relative to other materials
Dentists, Dental students should 5now the most li5ely side effects of materials,
whether they affect dental pts or the auxillary personnel and laboratory
techni4ues &hey should also invariably recognie mechanisms through which
these effects are produced and efforts should be made to minimie it
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