intermediary liners and bases Flashcards
What are cavity liners and insulating bases?
materials placed between dentin (sometimes pulp) and restorative material to provide pulpal protection or pulpal response
What forms the restorative system?
intermediate materials + restorative material + tooth structure
What is the best barrier between the restorative
material and the pulp?
sound dentin
What do restorative materials always suffer from?
micro-gap at the tooth/restoration interface –> microleakage
What will microleakage cause?
- hypersensitivity through dentinal fluid flow after applying restoration
- marginal discoloration
- recurrent caries
- adverse pulp reaction
- failure of restoration
What is dentin bridge?
the amount of remaining dentin thickness between the pulp and the restoration (ideal barrier)
What are the types of pulpal protection?
- chemical
- mechanical
- electrical
- thermal
- biological
What is chemical protection?
- sealing of dentinal tubules is essential against the penetration of
- metallic ions, corrosion products, acids and chemicals from the restorative material
- bacterial toxins, salivary ions and various irritants
What is thermal protection?
protection from thermally conductive metallic restorations such as amalgam and cast gold
What is electrical protection?
against galvanism due to use of dissimilar metals e.g., amalgam and cast gold restorations
What is mechanical protection?
against condensation of amalgam and cementation of inlays as well as the stresses during masticatory function
What is biological protection (pulpal medication)
through the use of calcium hydroxide that facilitates reparative dentin formation
What are the ideal requirements for intermediary materials?
- should provide a sedative action to the pulp
- should be compatible with pulp-dentin organ and stimulate
reparative dentin formation - should improve the marginal sealing and the adaptation to the
cavity walls (bonded to tooth structure) - should possess thermal and electrical insulating capacity at minimal film thickness
- should have sufficient strength to resist fracture during condensation of the permanent restoration
- should have minimal effective film thickness without affecting the bulk of the restoration
- should be compatible with overlying restorative material
- should resist degradation in the oral fluids
- should have adequate workability and be easy to apply
What are liners?
thin film materials that are used mainly for sealing of dentinal tubules to provide chemical protectio
What are the functions of varnish?
- forms a barrier against chemical irritations
- seals dentinal tubules –> decreases hypersensitivity
- decrease microleakage
What are the indications of varnish?
- under amalgam restoration: it prevents penetration of metallic ions and corrosion products into dentinal tubules, tooth discoloration (amalgam blues)
- inder zinc phosphate cement: it was irritant cement that used to
cement metallic crowns and cast gold restorations
What are the contraindications of varnish?
- under resin composite restorations (will not be retained)
- under glass ionomer, resin modified glass ionomer and Zn polycarboxylate cement (varnish will not allow formation of chemical bond)
How can calcium hydroxide be supplied?
- two pastes (chemical-cured)
- one paste (light-cured)
What are the proprties and indications of calcium hydroxide?
- applied for pulpal medication (when the remaining dentin bridge is < 0.5mm or in direct contact with exposed pulpal tissue) –> indirect capping
- t will stimulate odontoblasts –> form reparative dentin at the exposure site
- relieves pulpal inflammation
- used in direct pulp capping (calcium hydroxide is added directly on pulp)
- porous and soluble; it is not used as electric or chemical insulators (disadvantage)
What is flowable composite?
- low-filled composite with low viscosity
- used as a liner/base under composites to absorb stresses and increase the adaptability
- applied in 0.5-1mm thickness
What are base materials?
materials with thick consistency to substitute lost dentin and provide thermal, electrical and mechanical pulpal protection
What are the types ofbases?
- reinforced zinc oxide and eugenol (RZOE)
- zinc phosphate cement (ZPC)
- zinc polycarboxylate cement (PCC)
- resin modified glass ionomer (RMGI)
What are the characteristics of RZOE?
- eugenol produces palliative, sedative and obtundent action on the pulp when used in very low concentrations
- ZOE has an antiseptic and anti-inflammatory effect.
- an excellent thermal insulator in a film thickness as low as 0.25mm
- an excellent electrical insulator and has a good sealing ability
- used as a temporary filling material and temporary cement or base material
What are the characteristics of ZPC?
- has high compressive strength –> most rigid, tough and durable base material (highest mecanical protection) –> advantage
- excellent thermal and electrical insulator in thickness of 1mm or more
- the most irritating base material (its acidic pH is 2 after mixing and reach neutrality after 48 hours) –> disadvantage
- has an exothermic setting reaction –> thermal irritation
- mixing is done on a glass slab to distribute heat (exothermic reaction) –> powder is separated to quadrants (total is 6 portions) –> this decreases mixing which decreases heat generation
What are thecharacteristics of PCC?
- it bonds chemically to tooth structure –> decreased microleakage
- it produces minimal irritation to pulp-dentin organ
- good thermal insulator in thickness not less than 1.5 mm (high thickness)
- an electrical insulator
- compatible with all restorative materials except ZOE and
varnish
What are the characteristics of RMGI?
- it has an excellent sealing ability due to chemical adhesion to tooth structure
- it has an anti-cariogenic property due to fluoride release
- biocompatible with dentin pulp organ and all permanent restorative materials
- provides adequate thermal, chemical and mechanical protection
- an excellent material to be used as dentin substitute.
What are the indications of RMGI?
they can be used as liners, bases, luting cements as well as restorations
What are the factors affecting selection of intermediary materials?
- remaining dentin thickness (RDT); increased depth of the cavity –> RDT decreases –> need for intermediary materials
- adhesive properties of liner or base
- type of restorative material (metallic or esthetic restoration, a direct or indirect one)
What should be done in shallow cavities (RDT > 2mm)?
- there is no need for pulpal protection, only chemical protection (sealing) is needed
- amalgam restoration –> only a solution liner (varnish)
- resin composite –> only its bonding system is needed
- GIC restoration –> does not need any pulpal protection in this case
- Indirect restoration –> only its bonding system and resin cement is needed
What should be done in moderately-deep cavities (RDT=0.5-2mm)?
- amalgam –> varnish + base (chemical protection of pulp)
- resin composite –> bonding system + flowable composite
- GIC restoration –> does not need placement of any intermediary material
- indirect restorations –> only its bonding system & resin cement is needed
What should be done in very deep cavities (RDT < 0.5mm)?
- there is strong need for pulpal protection
- in this case, pulpal medication with Ca(OH)2 is essential in case of frank pulp exposure to induce secondary dentin formation and relief pulpal inflammation
- sealing is also essential by (varnish + strong base) with amalgam or by (adhesive + flowable composite) with composite
What do intermediary materials do at micro-gaps?
act as sealant
Why is intermediary material added beforerstoration?
to protect pulp or stimulate pulp to produce reparatuive dentin
What happens if there are micro-gaps present?
leakage of oral fluids
What type of sensation do irritants cause?
pain
Do liners provide mechanical protection?
no as they are placed as thin film
Where is varnishing done in the tooth?
floor and walls
On which restoration is varnish used?
amalgam
