MICROLEAKAGE

Introduction :

The goal of operative dentistry, undoubtedly is to restore the tooth to

its form and functions. One of the requisite of a restorative material is to

adapt itself to cavity walls. Inspite of tremendous improvements in means

and technologies, none of the material could actually join chemically with

the tooth surface. The gap left between cavity walls and the restorative

materials plays important role in the prognosis of the restorative treatments.

Previously pulpal reactions to dental procedures were thought to be induced

by mechanical irritations but bacterial leakage is a greater threat to pulp than

the toxicity of restorative materials. Different authors have termed it as

marginal predation liquid diffusion, fluid exchange, capillary penetration

and etc.

Definition :

Microleakage is defined as “The clinically undetectable passage of

bacteria and bacterial products, fluids, molecular or ions from the oral

environment along the various gaps present in the cavity restoration

interface”.

Possible Routes of Microleakage :

1) Within/via the smear layer.

2) Between the smear layer and cavity varnish/cement.

3) Between the cavity varnish/cement and the restoration.

It has been found that minimum of 1.0 m space is left at tooth

restoration interface even after employing the adhesive liners and materials.

Clinical implications :

1) Post-operative sensitivity :

Due to direct communication between oral fluids and pul and it.

Leads to change into local ionic concentrations.

These acids/basic materials and other substances produce movement

of fluids in tubules.

Lead to pain in pulp.

Mostly noticed in

o Proximal cavities

o Cervical cavities

o In resin restorations due to polymergation

shrinkage

2) Secondary Caries/Recurrent Caries :

Bacteria with average diameter less than 1.0 m can easily

penetrate the gaps.

If the gap is 50 m it this space can produce nutrients for the

bacteria hence inviting recurrent caries.

3) Pulpal pathology :

Marginal gaps allow bacteria.

And produce a number of inflammatory components

Which penetrate dentinal tubules

And affect pulp leading to pulpal diseases

At gingival wall

4) Marginal discolouration :

Evident in esthetic restorations

It leads to accumulation of subsurface interfacial staining

5) Dissolution of the certain materials like cements.

Factors that Influence Microleakage :

a) Properties of restor materials that contribute

microleakage :

Major :

1) Coefficient of thermal expansion

2) Plymerization shrinkage

3) Adhesion.

Minor :

Creep

Elasticity

Resistance to fatigue failures

Solubility

1) Coefficient of thermal expansion (CTE) :

It is the change in length per with length of a material per degree

change in temperature.

With increase in temperature expansion

With decrease in temperature contraction

Ideally rest material should be closely to tooth

C.T.E/contracting

If C.T.E of 2 very

o 1 may expand/contract more than other during

change in temperature.

o Leads to leaky rest margins.

(Table 23.1 Sikri page 551)

2) Polymerization Shrinkage :

Occurs with polymeric materials

Monomer chains are polymerized to form polymer

chain

o There occurs a decrease in volume and increase in

density

o This shrinkage pulls material away from cavity

walls.

If intermediate adhesive resin used

o Contraction stresses are high

o Occur a break in adhesive bond

o Leads to microleakage

(Table 23.2 Page 551)

3) Adhesion :

Adhesion is the attraction of molecular of two different substances to

each other when they are brought in close contact.

Lack of adhesion – microleakage

Adhesion influences by –

o Wetting capabilities

o Surface energies

o Presence of water

o Swear layer

o Composition of enamel and dentin

o Surface roughness etc.

b) Influence by operator :

Improper isolatory

Poor consternation

Improper insertion

Poor cavity designs

Poor burnishing

Exposing cement live to the oral cavity.

c) Role of smear layer in microleakage :

Subsequent to instrumentatory of the tooth, the natural deposits

composed of microcrystalline cutting debris embedded within the

denatured collagen is formed on the cut surfaces known as “smear layer”.

It is 1-2 m thick

Consists of blood, saliva, bacteria, enamel and dentin particles.

Initial cutting debris – may be pushed into tubules

o 1-5 m-smear plays

Weather of decrease M.L. – Not clear

o 1 opinion – leave smear layer intact to act as barrier but when

pH level drops – it dissolves

o 2- opinion – remove smear layer

Because smear layer itself contain bacteria and also

smear layer can present bacterial entry but not bacterial

products and good adaptation of adhesive material.

Best way – remove natural smear layer but not smear plugs

Replace with sterile, inert and non toxic synthetic smear layer.

Factors controlling bacterial penetration :

a) Size and nature of the gap :

Varies with different rest materials – 10-50

ms

But 10 m is enough for lactobacillus entry.

Self sealing capability of rest materials

reduce bacterial penetration

Self sealing may also occur because of

o Deposition of mineral salts of low solutility

o Accumulation of corrosion products

o Calcification of plaque like debris around margins etc.

d) Host defence factors :

Sclerotic dentin/reparative dentine

Hydrostatic pressure of pulp increase than

outside pressure of oral cavity

Plasma proteins in dentinal fluid – act as

natimicrobial agents

Large molecular weight proteins like

fibrinogen

Make dentin less permeable to bacteria

Presence of smear plugs – increase M.L.

Alteration of chemical structure of dentin by

o Leaching of tin/Mercury ions from amalgan

o Leaching of fluoride from GIC and

silicaticement

e) Restorations

Alters dentin permeability

GIC, silicates, compromise – release fluoride into gaps

Have antimicrobial effect

Silver, tin, mercury – antimicrobial effects.

Restorative materials and microleakage :

I. Fresh mix condensed – does

not adapt closely

10-15 m gap

but it is self sealing restorative mat with time

Due to corrosive products

In low copper – corrosive products formation and accumalation takes

place on gaps.

o Corrosive products like oxides and chlorides often

In high copper – greater resistance to corrosion

o So slower rate of formatting of corrosive products

o So microleakage for longer period

Due to dimensional changes :

Quite minimal

During setting – small contraction initially (when misery

in consumed)

Followed by small expansion (as crystal matrix is formed)

High Cu alloys – dimens change very little 0.2% by volume.

According to ADA No. 1 – dimechange of 20 m/cm is allowable for

set amalgam.

Coefficient of thermal expansion of Amalagm = 25x10-6/0 C so not

much different between them – do due to C.T.E Moderate leakage.

Measures to reduce :

Amalgam microleakage :

1) Types of alloys :

Different types have different leakage

Spherical alloy – more leakage and postoperative sensitivity.

Because not closely adapted

And more shrinkage after it sets

So lateral condensation done

Better to select lathe cut/advised alloys

2) Condensation of amalgam :

Condense immediately – as time lapse

Loss of plasticity/increase in internal voids

Incremental insertion – so proper condensation

Adequate condensation pressure – 10 pounds with 2 mm condenser

tip

(c pressure varies with alloys)

Condensation from center to periphery (stepping process)

Removes air spaces

Pushes material against cavity walls

Decreases microleakage

Mechanical condensation better.

(Quint Int.23(7)-495-1992)

3) Burnishing :

Adapt material to margins – (so decrease microleakage)

Spherical alloys – no reduction in micreleakage.

Because during condensation particles may be pushed

aside.

4) Alloys with lesser creep values :

Less creep – less M.L.

According to ADA no.1 creep less than 3% is considered acceptable

o Low copper alloys – 0.8 –8%

o High copper alloys – 0.1 – 1% (decrease M..L)

5) Sealing the cavity wall with varnish

Presents microleakage (until concision products form)

But do not exist as long as life of rest.

Limited to six months

6 months enough for corrosion products fill gaps.

Use of GIC liners – decrease microleakage

6) Sealed amalgam restorations

A coating of unfilled resin is placed over rest margins and adjacent enamel

after etching enamel surface

Resin may wear away

But covers until corrosion products fills gap.

7) Bonded amalgams

Have shown to over come microleakage

8) Use of gallium alloys

It has high wetting ability

II. Microleakage around GIC

:

Adheres to tooth with chemical bond

But cartoxyl groups of cement and Ca+ of tooth

Hydrophilic so can bond even in wet surfaces

C.T.E – closely match tooth

Fluoride releasing property

Has ability to renew broken ionic bonds

Highly technique sensitive

1st 30 min – moisture – ions are leached out

1st 24 hours – more solubility

1st 24 hours excess dehydration/dessication

Chalky /crazed/cracked appearance

Which of extends to margins

Leads to microleakage

So coated with varnish/unfilled resins

Using of sharp hand instruments for finishing before material has

completely set.

Effects marginal integrity

Prevention :

1) Proper manipulation

Liquid/powder ratio-if lower – increase solubility

Placed only after proper cleaning of the surfaces

2) Conditioning of tooth surface before insertion

Agents – tanic acid

o Poly acrylic acid

o Citric acid etc

Prior conditionring – increase bonding – decrease microlieakage

Rapid initial setting – decrease moisture containnation

But increase microleakage

Due to poly shrinkage

In light airing GIC

Less water, les carboxylic acid

Decreased wetting

But water uptake – function f resin component

Reduces microleakage

Use of compomer as lining /flourable lining reduces microleakage

3) Finishing

After 24hours

Use rotary instrument to finish than menual cutting inst.

As they tear away material at margin – marginal ditching

4) Protection from moisture

During fonishing – apply Vaseline /petroleum jelly

Final protection – 2 coats of varnish/unfilled resin

Varnish semipermiable

Unfilled resin-more resist water

But varnish preffered –as at adheres closely

III. Microleakage around

composite restorations :

Unable to bond on their own to tooth (so acid etch, prime, adhesive

area)

If insufficient enamel thickness – increase M.L.

It bonds dentin but not completely decrease M.L.

o Due To clinical composition of dentin

o Dentinal fluids

o Smear layer etc

Polymerization shrinkage

o Range 1.67 – 5.68% light activated (lesser shrinkage than

others)

o If DB agents used

It bonds composite to tooth structure

But shrinkage results in tensile/shear stresses at tooth rest interface

Within limits of can with stand its bond strength

In exceeded plastic/elastic deformation

Separation of interface

Masticatory forces

Repeated plastic/elastic deformation of rest

Enhance M.L

C.T.E.

22-55X10-6/0 C Higher than tooth

so debonding

so microleakage

Water absorbtion

Absorb water

Cause rest of expand

Compensate poly. Shrinkage – but mechanical prop impaired

Technique sensitive : in class II :

Placement in gingival areas difficult

Entarapment of air

Difficult during condensation (sticky)

Inadequate bonding to ging – polymerization shrinkage.

Measures to Reduce Marginal Leakage :

1) Choice of material

Microfilled :

Better marginal adaptation (than macrofilled)

Greater flexibility during shrinkage decreases contracting forces

It has larger water absorption capability

So decrease M.L.

2) Cavity design :

Conservative :

So decrease polymerization shrinkage

Decrease wear

Modified cavity designs :

Placement of bevels

Reduced depths

Rounded internal angles

Shape :

According to shape size varies

V-shaped has less M.L. than box shaped cavities

Fig. 23.7, Page 55.7

Decrease ratio of decrease microleakage

Bevels :

Bevels on carosurface margins controvetsial

Some say – bevel – increase surface area

M.L.

Some say – occlusal bevel – not needed

Because of enamel rod directions and rest may be extended to load bearing

areas

Cervical bevel – removes remaining enamel

Increase M.L.

Decrease M.L.

Good marginal adaptation

Volume Bond area

Facial and lingual bevels in proximal box

Increases M.L. (75%)

(1998 (48))

3) Acid etching technique and bonding :

a) Enamel etching :

Etching : Removes surface continuants

Raise surface energy

Increase surface for bonding

Bonding agent drawn by capillary attraction into microporosities

Polymer tags are formed

Provide micromechanical interlocking

Etching depends on :

Thickness of enamel

Cervical enamel

Thin

Irregular prism structure

Devoid of characteristic prism markings

So bonding not intimate near cervical regin

So increase microleakage

Dentin etching :

Earlier – discouraged because of

hydrophobic resin it opens and widens tubules

Result in increase permeability

So bacterial ingress

Recently hydrophilic resins – create open tubules and porous intertubular

layer

So close adhesion

Prevents penetration of bacterial / toxins

Even then- non uniform bonding due to :

Thickness of smear layer

Degrees of etching

Wetting capacity

Forces of polymerization contraction etc

Another types of leakage :

NANO LEAKAGE by sano et al 1995

Occurs within nano metrisized spaces around collagen fibres within fhydrid

layer

Can occur at bottom or along whole width of hybrid layer

Reduced by using the self etching/self priming systems

Cause for nanoleakage :

Inability of adhesive resin to infiltrate into demineralized dentin

Leaves pores /spaces /voids

Predispose to accumulation of water/oral fluids

Degrades the bond If resin fully infiltrated into deminalized dentins - high modulus of

elasticity

If resin fails infiltrated into deminalized dentins - low modulus of

elasticity

Contact with water oral fluids deminalized dentin – low modulus of

elasticity

Glass Ionomer bonding agents

So new boding agents based glass ionomer technology or glass ionomer

boding agents

Eg : Scotch bodn multipropose pertac universal bond and

They have carboxylic acid groups which attach to dentin and attach

composite to glass ionomer.

Dilute resin modified glass ionomer cements :

Diluted version

Fingi bond II LC

Completely replaces commotional boding agents as –

Chemical adhesion

C.T.E. close of tooth

Better sealing ability both with enamel /dentin.

4) Cavity filling technique :

Thick / bulk filling – induce significant shrinkage

High stresses generated

Lead to debonding

Small/multiple increments – Poly. Shrinkage controlled

Mostly preffered in class II

ClassV

Inserts :

(Beta quarts glass inserts – mega fillers)

Insets with modifiers made of lithium aduminosilicate glass

Give tooth appearance

Available in various sizes and shapes

Inserts are controlled by cavity size and shape

Filler content is more than resin

So decreased contraction

C.T.E. is 4x10-6/0 C which is low

No shrinkage/No matresorption.

Prepolymerised composite balls :

Greater M.L. than inserts

Because of high cumulative internal stresses generated during thermal

changes

But it has beta quartz inserts which has C.T.E. close to dentin which

is expected to reduce additional stresses on the interface.

Soft start polymerization :

Procedure involves short polymerization at low intensity followed by

the final cure at high intensity.

At gingival margins

Allows composite resin to flow during initial setting

So minimizes stresses at interface

And also prolonged curing allow greater inversion rate of monomer

component.

5) Direction of light source :

Poly. Shrinkage is directed towards light.

Curing from occlusal aspect.

Gingival increment shrinks occlusally

So curing aids –

o Use – light directing wdges

- Flexible light guides

- Focusing tips

Facilate better curing in poor access areas (like gingival margins)

So shrinkage will be towards gingival margin

Three sited light curing

Buccal, lingual and gingival

Better adaptation.

6) Sealing the marginal gaps :

Unfilled low viscosity resins

Applied overall after finishing and polishing

Eg : pit and fissure sealants can be applied

By Lutz et al (1986)

7) Delaying the Finishing :

Time :

Microleakage depend on time :

Many authors advocati to delay finishing by 24 hours.

Study by Fusayama and Kohno 198925.

Finishing after 3 month of insertion – considerable M.L.

Finishing after1 day – almost no M.L.

But study by Yap et al 1998 :

Finishing after 1 week – more microleakage

Because of stress during finishing effects the already marginal seal.

So finishing should be done immediately.

Variations in finishing techniques :

Increase M.L – dry finishing

High heat on marginal adaptation

Recommendations :

Rotary instruments

Slow speed

Light intermittent strokes

With generous air coolants

Use of soflex discs – good marign adaptation.

8) Use of cavity liners and bases :

Ca(OH)2 GIC – common base materials

Used in deep cavities for pulp protection

Reduces the bulk of composite

So deduces the poly. Shrinkage.

GIC :

Chemical bond

Hydrophilic

C.T.E. close to tooth

Fluoride reservoir

Bilayering technique / sandwich technique.

Light cure GIC better than chemical cure

Because adheres immediately

No ionic leach out

Harden cement resists stresses – so better adaptation

9) Use of composite inlay restorations :

Loting agent :

It bond to tooth using composite cementing medium.

It may be chemically cured/dual cured.

Light curing luting agents should not be preffered.

Because they lead to high conversion (of monomer) rote of inlay and

reduces availability of remaining un converted monomers for

co-polymerization with the luting resin.

Fails to bond chemically with inlay.

Chemically cured preffered than light cured

Because inlay may be 2 mm/more thick

So difficult to cure.

Microfilled preferred than hybrid luting reins.

Because less heavily filled materials (hybrid) tend to lose earlier by wear

mechanism.

Composite inlay :

Better

Because poly. Shrinkage takes place before cementation.

But failure of inlay to bond with luting resin so different methods :

1) Use solvent such as ethyl acetate to soften the cavity side of the

restoration.

2) Sound blasting with aluminium oxide abrasive particles of the cavity

side of rest.

3) Etching cavity side with 10% hydrofluoric acid.

10) Expanding matrix resins for dental composites :

Resins expand slightly during polymerization

Facilitate bulk placement

Decrease M.L.

IV. MICROLEAKAGE

AROUND DIRECT GOLD RESTORATIONS:

Adapt to cavity walls more efficiently

Because :

1) High malleability and ductility

So good burnishing and adapts well to margins.

2) Short bevel on cavosurface margins

Facilitate burnishing /polishing

3) Insoluble in oral fluids

4) Condensation – induce elastic compression

Adapts strong.

Microleakage may be due to :

Improper compaction – in spaces / voids

Non uniform stepping

Type of gold selected

Improper lines of force

Inadequate condensation pressure.

Measures to reduce leakage :

1) Cohesive gold foils preffered – good seal because mat and

powdered gold are porous:

- Former should be gold foil – internal bulk

Then used an veneer

Prevent leakage

2) Uniform stepping preffered:

- Half to 1.4th stepping – drive away air spaces

Adapt closely to underlying surface

- Always center to periphery

3) Lines of force:

- 900 to pulpal floor in center

- Then changed to 450 to cavity walls at periphery

4) Condensation force:

10 pounds – average force with 1 mm condenset tip.

Proper adaptation

5) Restoration build up:

Done in convex form

Material should be always be banked on the cavity walls ahead of the

center.

Allows application of force in right direction and thorough adaptation.

6) Surface procedures:

Burnishing, finishing, polishing bring metal closer to tooth surface

Good seal.

V. Microleakage around cast restorations :

No close adaptation – 10-160ms gap¯

so luting agent required ¯

low viscous luting agent preferred ¯

because it penetrate into irregularities of both tooth and rest ¯

so micromechanical retention

Advantages :

Now – adhesive luting agents available ¯and also have chemical retention

intermediate cement layer-promote leakage

¯because of solubility

increase solubility zinc phosphate, silicate, silicophosphate

cement line may be exposed to oral environment¯

as margins are not adequately and beveled and burnis heal¯

because it is difficult to burnisher to reach ging areas in class II inlays¯

when harder gold is used do to burnish

Excessive taper¯

excessive loads¯

rest gives away by rotating on preparation surfaces¯

break in the cement lute

Measures to reduce microleakage :

Adhesive luting agents should be preferred ¯

chemical bonding

In case of gold –

o Bevels placed properly

o Burnishing margins (malleable and ductile) ¯

so close proximity to cement surface, due to permanent deformation

o Good percentage of elongation

Type II and III – 20-35% elongation

o In case of high soluble cements (Zp, ZnSi phosphate, silicole >

0.04 – 0.10% solubility) burnishing should be delayed 24 hrs¯

This allows for superficial few microns of cement to dissolve ¯

Then burnished

o In case of nonsoluble cements ¯

burnishing done immediately

o If rest have close fit within 20ms ¯

degradation of cement is resisted ¯

increase life of restoration

Microleakage around porcelain restorations :

Dental porcelain is a brittle material ¯

low tensile strength ¯

if strain exceeds 0.1%¯

fracture ¯

so bonded properly

Earlier – bonded with luting cements ¯

high rate of failure

Recently – luting resin cements ¯

dual cure

Chemical bond strength

Initially improved ¯

later weakened by hydrolysis ¯

decrease bond strength after 1 year ¯

wear of cement lute at interfaces with inlay and tooth

Interfacial gaps

Varies with diff. systems because of technique sensitivity

Difficult to prepare ceramic inlays that precisely fit cavity.

Fired ceramic inlays – depend on operator skill

Ceramic inlays gaps wider than composite inlays

Measures to reduce microleakage :

Operator skill and patience.

Advances in adhesive technology

Resin luting cements better than luting cements ¯

as bond degrates with time ¯

ceramic inlay surface treated both mechanically and chemically ¯

1st – acid etching done

- Hydrofluoric acid – for fired porcelain

- Ammonium bifluoride – for milled / cast ceramics ¯

give micromechanical retention ¯

etched surface than silanated to increase wetting and so improves

chemical retention.

Resin luting cements should not be applied with one prior tooth bonding

procedures.

Closure fit of restoration

o Operators skill and patience

o Glass ceramic restorations (dicor) – excellent marginal

adaptation.

Methods to detect microleakage :

Invitro tests tries to simulate oral environment by thermocycling. Yet

the dynamic nature of pulpodentinal complex and its defence mechanisms

cannot be easily simulated in-vitro. More so, the accumulation of plaque and

other agents might vary the microleakage results in vivo.

The various methods are described, however none of these method is

considered perfect till now.

Different tests –

1) Dyes

2) Chemical tests

3) Radioactive isotopes

4) Neutron activation analysis

5) Scanning electron microscopy

6) Bacterial studies

7) Electrochemical studies

8) Air pressure

9) Artificial caries

10) Pain perception

11) Reverse diffusion method

1) Dyes :

Coloured agents like organic dyes used

Have contrasting colour

Agents used

o Methylene blue

o India ink

o Crystal violet

o Fluoroscein

o Rhodamine B

o Eosin

o Basic fuschin

o Erythrosine etc

Requirements :

Should not bond to tooth / restoration

Should be color stable under all conditions of investigation

Availability :

Solutions

Particle suspensions of different particle sizes

Technique

Immersion of restored tooth in dye solution for predetermined period ¯

tooth removed, washed and sectioned ¯

examined under microscope for extent of penetration of dye

Limitations :

Diff. conc of two dyes vary penetrations times from 5min-1 hr.

Dyes may bind to tooth / restorations.

Eg : basic fuschin bonds to carious dentin and mistaken for large gap.

Some dyes may be not colour stable

Eg : aniline blue – colourless in alkaline conditions such as in presence

of Ca(OH)2

2) Chemical tracers :

Reaction bt 1 and more chemicals taken plan

Chemical used : 50% silver nitrate solution (or) 1% silver chloride

benzene 1,4-diol (hydroquinone) – photographic developer

Technique

o 2 colourless chemicals react – produce an opaque ppt (usually

silver salt)

o Immerse extracted filled tooth in 50% silver nitrate solutions

which reacts with photographic developer (benzene 1,4 dio) ¯

opaque silver salt produced

Limitations :

Diff. conc of two dyes vary penetrations times from 5min-1 hr.

Dyes may bind to tooth / restorations.

Eg : basic fuschin bonds to carious dentin and mistaken for large gap.

Some dyes may be not colour stable

Eg : aniline blue – colourless in alkaline conditions such as in presence

of Ca(OH)2

3) Radioactive isotopes :

Ca, I, P, C, S, Rb etc used similar to dyes

Technique

Immersed in isotope solutions ¯

Removed, washed, sectioned¯

Autoradiographed to detect tracer

Advantages :

They can detect minute amount of microleakage ¯

Because of their small size – 40nm

Whereas dye smallest size is – 120nm

Limitations :

a) Subjective assessment of results (with using

steriomicroscope – subjectivity minimized)

b) High energy isotopes produce scatter on film –

mistaken for increased leakage.

c) Ca – have affinity to tooth / rest material – may

mislead the results

d) Expensive and technique sensitive

4) Neutron activation analysis :

Technique :

Restored tooth soaked in an aqueous solution of non-radioactive manganese salt ¯

Then tooth placed in core of nuclear reactor ¯

Bombardment with neutrons takesplace ¯

Activates Mn55 to Mn56

¯

Radiation is emitted by tooth is measured to quantify the volume of tracer

present.

Limitations :

a) Inability to identify the points where rest. has leaked

b) Heavy exp costs

c) Effort of nuclear engineers and dentists required

d) Mn may be absorbed by tooth / rest

5) Scanning electron microscope :

It is direct visual observation of rest adaptation to cavity because of high

magnification and depth.

Used in both invivo and invitro.

Earlier – used replicas of tooth

Recently – evaluates rubber base impressions directly ¯

Reduces many steps (in accuracy decreased)

Limitations :

Potential to induce artifacts during specimen preparation.

6) Bacterial studies :

Test the possibility of bacteria penetrating through or around rest.

Technique :

Immersed in the cultured broths ¯

Filling is removed ¯

Dentin sharing from the base of cavity cultured.

Limitations :

Results are qualitative and not quantitative

Marginal gaps of 0.5-1m or larger – allow bacterial penetration ¯

smaller than this gap cannot be detected¯

smaller than this gap allow toxins

7) Electrochemical studies :

Technique :

Insertion of electrode into extracted tooth in a way that it contacts base of

rest¯

Once restored teeth sealed to prevent electrical leakage through natural

tooth structure.

¯Then immersed in a electrolytic bath

¯Potential is applied between tooth and the bath

¯Leakage assessed by measuring current flow across as serial resistor

Drawback :

Unsuitable for metallic rest

Inability in invivo situations

8) Air pressure :

Compressed air was used to test the marginal seal

Technique :

Compressed air is introduced through the root canal and pulp chamber ¯

loss of pressure is measured within static system ¯

microscopic examination of air bubbles at margins is noticed – subjective

view.

Disadvantages :

Inability to use invivo

Drying effect of compressed air

Some air may leak before it enters tooth

Advantage :

Tooth need not be destroyed and result can be quantified

a) Artificial caries :