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1

BASES AND LINERS Definition and terminology

Materials permanently applied onto the dentine before the application of the permanent restorative materials (e.g. GIC, RMGIC, RBC, dental amalgam)
•Bases= viscous materialsapplied in a thick layerinto the cavity. Their roleis to reduce the amount of the restorative material or to “cover-up”the retentions and the irregularities of the cavity.
•Liners= fluid materialsapplied in a thin layer(under 0.5mm) onto the exposed dentine. Their roleis to assure the well-being of the dental pulp through adhesion to the dental tissues with or without antibacterial action.

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Bases and liners-Role

Protective
•Palliative
•Therapeutical
over the vital dentine

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Pulpal Responses

Physical-Thermal, electrical

Mechanical-Handpiece, traumatic occlusion

Chemical-Acid from dental materials

Biologic-Bacteria from saliva

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hydrodynamic effect

through exposure of the dentinal tubules may appear a flux of dentinal fluid towards or from the dental pulp

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when there is a superficialamalgam filling

a slightly late pain after application of a thermal stimulus (when the base material wasn’t used or when there is a percolation of the filling = lack of marginal adaptation)
3.It results the necessity of application of a thin layer of varnish or liner , even for the superficial amalgam filled cavities, which are able to prevent the flux of dentinal fluids and not to action as a thermal isolator (as was thought in the past) 5

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Possible pulp irritation sources
•Chemical stimuli

–many of the restorative materials release possible toxic compounds for the dental pulp (through their composition–e.g.RBC or pH–e.g.dental cements) –recent studies show that the most of the dental pulp reactions,which were thought to be of the toxic chemical origin,occur due to the bacterial contaminations(microleakage) –it’s better not to eliminate the possible toxic factor of the different compounds of the restorative materials

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Possible pulp irritation sources
•Bacteriaandendotoxins

–microleakage–through marginal percolation of the salivary fluids loaded with bacteria=pulp irritation
–NOW–the important role of the dental liners and bases is to protect the pulp from the bacterial toxins much more than from the toxic compounds of the dental materials

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Bases and liners–Main role

blocking of the microleakageusing adhesive techniques, so that to eliminate the possible gaps between the filling material and the dental structures

1.=>a barrier against bacterial marginal percolation, thus, protecting the dental pulp from the bacterial toxins’ effects and

2.=>preventing the hydrodynamic flux towards the dental pulp.

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Bases, liners and varnishes variants

1. Varnishes
2. Cahydroxide cements 3. Zinc –oxide–eugenolcements
4. Glass ionomers cements
5. Resin modified glass ionomers
6. Light-cured RBCs

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1.Varnishes
Delivery form
Application:
Indications

Yellow, clear liquid with a content of natural or synthetic resins : •Copal •Colophony •Sandarac •Polystirene(synthetic) dissolved into alcohol or acetone

Application: –onto the base of the cavity through brushing using an applicator (2-3 coats) –after the solvent’s evaporation, it will remain a thin layer of resins


Indications: –Used as a barrier against the external chemical factors or against those resulted from the dissolution of the compounds from the filling material

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2. Ca hydroxide cements
delivery form
setting reaction

2 pastes, which have:
•The white paste: Cahydroxide(50%), Znoxide(10%), sulphonamide (40%)
•The yellow paste: buthyleneglycol disalicylate(40%), Tidioxide, Casulphate

•Setting reaction: –Mixing of equal volumes of pastes (30sec) –It seems to be a chelation reaction between the Zn oxide and buthyleneglycol disalicylate (aprox.2 min)

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2. Ca hydroxide cements
properties
indications

Properties: -very reduced mechanical prop, but it resists at the condensation forces of the amalgam -pH 11-12 = dentino-genetic effects

Indications: -Big cavities or over the exposed dental pulpin order to stimulate the production of reparative or secondary dentine

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3. Zinc oxide–eugenolcements
•Properties:

pH 6.6-8 = without toxic effects(or minimum ones) over the dental pulp, if it is applied in big cavities –

The eugenol = painkiller and antibacterial effects –

Disadvantage= high solubility in the oral cavity, through hydrolysis of the eugenol –Very reduced mechanical prop.(15 MPa)

–THE EUGENOL INHIBITS THE POLYMERIZATION REACTION OF THE RESINS!!!!!

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Zinc oxide–eugenolcements
Indications

It isn’t so good to be used as liner or base
-It isn’t indicated for direct pulp cappingdue to the slightly irritative effects of the eugenol (in these cases there has to be used a Ca hydroxide as a liner and then the ZOE cement as a temporary filling)
-For root canal fillings(slow setting) or periodontal cements(fast setting)

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Reinforced zinc-oxide-eugenolcements (polymer modified

Composition:
–Variant 1: hydrogenated resins within powder –Variant 2: MMA orpolystirenewithin liquid

•Properties and indications: –Increase of compression strength (40MPa) indicates it as base or liner –Temporary filling material

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3.b.EBAzinc-oxid-eugenol cements (with ortho-ethoxybenzoicacid)

Deliveryform: –Bicomponent:white powder/pink liquid

•Composition: –Powder:Zn oxide(75%), quartzoralumina(20%) and hydrogenated resins(5%) –
Liquid:eugenol(37%),EBAacid(63%)
•Properties: –The presence of EBAstimulates the crystalline structure formation=higher mechanical strength (60MPato compression) –The solubility is more reduced

•Indications:
–Liner
–Temporaryfillings

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4. Glass ionomer cements
5. Resin-modified glass ionomer cements
Advantages as bases and liners

•adhesion to hard dental tissues
•F release
•radioopacity
•the working time and the setting time is shorter than GICused for fillings(type II)

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Advantages of theRMGIC compared withGIC used as liners

Adhesion toRBC used as filling material
•To obtain adhesion between GIC andRBC,it is necessary the acid conditioning
•Application of orthophosphoric acid 20sec on enamel, then 20 sec on the dentine andGIC
•Maintaining too much the contact of the acid this will determine: –a depth penetration of the acid, which won’t be able to be removed through rinsing (citotoxiceffect) –there is a risk for GICfracture

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The most indicated as liner or base

light-curedRMGIC (when a RBC is used as a restorative material

–Adhesion to RBC without the necessity of acid etching
–Higher compression strength than conventional GIC

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6. Light-cured RBCs
composition
advantages

A large variety of them on the market, although their role is not concluded very well yet : –Eventuallythe combination of the benefits of setting “on demand” with the therapeutical effects of Ca or F release

•Composition: –Bis-GMA + Cahydroxide –phosphonate resins+ glass which release F –Bis-GMA + Cahydroxide+ glass which release F

•Advantages: –They are under question and aren’t clinically demonstrated till now

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Choosing a liner with or without the base material under fillings of :
•Amalgam

1.Superficial cavities(only to prevent the hydrodynamic flux) •maybe varnish
2.Medium cavities (also as thermal isolator)
•modified ZOE (supplementary antibacterial effect)
3.Deep cavities(also as dentino-geneticeffect) •Cahydroxide(neodentinogenetic) + •ZOE (thermal isolator)

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Choosing a liner with or without the base material under fillings of :
•Composites

Main problem= microleakage (bacterial percolation)
1.Enamel superficial cavities
•Correct application of the adhesive technique, without using a liner or a base
2. Deep cavities -Cahydroxidenear the pulp on a minimum area -Light-cured GIC(RMGI)as base, in those cases where the isolation of the cavity isn’t perfect,and there are some problems with the adhesive technique for the RBC
!!!NEVER use ZOEcementsornatural resin based varnishes(they interfere with the polymerization reaction of the used RBC)

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Choosing a liner with or without the base material under fillings of :
•GICsandRMGICs (type II)

There isn’t necessary a liner, onlyin very deep cavities =>Cahydroxide

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The aim of sealing the pits and fissures

decay prevention -stopping in evolution of the undetectable incipient decays at the macroscopic inspection

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Choosing a sealing material

One has to respect the following properties :
•setting reaction type(chemically= long, light= short) •F release or not(enhancement of the carioprophylactic effect at patients with decay problems) •appearance(translucent, opaque, coloured) •cooperation with the patient

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Sealing materials: variants

Self-curing RBCs
GICs
Light-cured RMGICs
Self-cured RMGICs

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The efficiency of the sealing materials

Self-curedRBCs -longsettingtime
Light-curedRBCs -the most efficient in time,especially in certain conditions when the zones are prepared prophy-jetoracid-etching
GICs Light-curedRMGICs-☺ ☺☺ ☺themostpreferredbetweenGICs
Self-curedRMGICs -quicker abrasion and dissolution,but they are preferred especially for the patients where there isn’t a perfect isolation AND
!!!!Strictly respect and perform all the required stages!!!