biologic 1 / orthodontic courses by indian dental academy

8/12/2019 Biologic 1 / orthodontic courses by Indian dental academy

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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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biologic 1 / orthodontic courses by indian dental academy

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