Materials used as liners and bases 10 Flashcards
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.
Bases and liners-Role
Protective
•Palliative
•Therapeutical
over the vital dentine
Pulpal Responses
Physical-Thermal, electrical
Mechanical-Handpiece, traumatic occlusion
Chemical-Acid from dental materials
Biologic-Bacteria from saliva
hydrodynamic effect
through exposure of the dentinal tubules may appear a flux of dentinal fluid towards or from the dental pulp
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
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
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
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
- =>a barrier against bacterial marginal percolation, thus, protecting the dental pulp from the bacterial toxins’ effects and
- =>preventing the hydrodynamic flux towards the dental pulp.
Bases, liners and varnishes variants
- Varnishes
- Cahydroxide cements 3. Zinc –oxide–eugenolcements
- Glass ionomers cements
- Resin modified glass ionomers
- Light-cured RBCs
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
- 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)
- 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
- 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!!!!!
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)
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
