Cavity liners and_bases_2


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Cavity liners and_bases_2

  1. 1. Cavity liners and bases Liners and bases are materials placed between dentin (sometimes pulp) and the restoration to provide pulpal protection or pulpal response. Pulp protection against: 1.Chemical protection 2.Electrical protection 3.Thermal protection 4.Mechanical protection 5.Pulpal medication Protective needs for a restoration varies depending on the extent and location of the restoration and the type or restorative material used. LINERS: Are relatively thin layers of materials (140pm) used to provide a barrier to protect the dentin from residual reactants diffusing out of a restoration and/or oral fluids, which may penetrate leaky tooth-restoration interfaces. • May provide pulpal treatment, some thermal and electrical insulation. • The need to liners is greatest with metallic restorations that are not well bonded to the tooth structure such as amalgam , while the composite and resin modified GIC are bonded to the tooth so it eliminates the need to liners UNLESS the cavity is very close to the pulp and pulpal medication is needed.
  2. 2. Types of liners: 1.thin film liners: A . Solution liners: varnishes, 2 - 5 µm thick. B . Suspension liners: 20-25 µm. 2.thicker liners: also known as Cement liners: 200-1000 µm (0.2-1mm) used for thermal protection, pulpal medication. BASES: o Cement bases, typically 1-2 mm. o Used to provide thermal protection for the pulp and supplement mechanical support for the Restoration  by the stress distribution on the underlying dentin surface e.g. forces of amalgam condensation. Objectives of pulpal protection:  Reviewing the anatomy, physiology of dentin – pulp complex.  Structure of dentin.  Reaction o pulp to different stimuli: If the insult is strong and near to the pulp, the odontoblastic processes are retracted rapidly and a thin local bridge of hydroxyapatite crystals is formed at the site.  Smear layer: During cavity preparation with rotary instruments, some of the cutting debris is compacted to the surface that material known as smear layer…this layer is very effective barrier so it is left when using a non-bonding restoration like amalgam. However, it is partially porous 30 %, it can’t prevent slow
  3. 3. long term diffusion…that’s way the smear layer should be sealed with a layer of liner.  Handling of smear layer (according to rest. mat. used): With amalgam => leave it. With composite => must be removed. Traditional liners (varnishes) could be used with recent amalgam restorations, but dentin and bonding systems can produce better effect and replace the liners. Solution liners (varnish)  Copal or natural resin dissolved in non-aqueous volatile solvent, (ether, alcohol and acetone)upon drying it will produce a thin film layer. ADVANTAGES: flexible – dry rapidly. On the other hand, thick films tend to trap solvent during drying and become brittle. LAYERS OF VARNISH:  Single coating covers only 55% of the surface because the smear layer is moist and the varnish is hydrophobic..SO A SECOND LAYER IS NEEDED  Second coat covers 80-85% N.B. use of varnishes decreased since 1990 due to using of DBS, desensitizing agents. Suspension liners: Same effect – dry slowly – give thicker films.  Constituents are suspended or dissolved in water. Thermal protection  thicker layer (20-25 µm)
  4. 4. Functions of Cavity liners: 1. Primary purpose  protective seal of exposed dentin surface. 2. Electrical insulation (with newly placed amalgam restoration) from the electrical circuts with restorations in adjacent teeth. 3. Thermal insulation with metallic restoration  Degree of insulation depends upon  Thickness of remaining dentin  2mm of dentin or equivalent thickness of insulating material should exist to protect the pulp. 4. Pulpal medication (dentin bridging)  -Zno/E liner  Ca (OH)2 liner  Eugenol is slightly acidic, phenoloic compound that have an obtundant action on the pulp at low concentrations with mild to moderate pulpal inflammation. N.B. high conc will be irritating to the pulp.
  5. 5.  ZnO/E  liner, base, cement ZnO/liner  for moderately deep cavities because it is released during setting and over several days. Now a days  resin-modified glass ionomer cement is used.  Ca (OH)2  very deep cavities or microscopic Exposure Ca (OH)2  Caustic (Alkaline, pH 12) Stimulate secondary dentin formation Types - Ca (OH)2 suspension - Chemically set material - Light-cured material  Ca (OH)2  dissolution or degradation overtime  Setting reaction of the ZnO/E and calcium hydroxide  accelerated by moisture.  Eugenol and calcium hydroxide cannot be incorporated is the same formulation because eugenol rapidly chelates with calcium ions in a strong exothermic reaction  the choice of eugenol-based versus Calcium-hydroxide-based liner is based on the relative depth of the tooth preparation.
  6. 6. Historical Background:  Before 1960’s Zn phosphate cement Reinforced ZnO/E  1970 polycarboxylate cement  1985-1994 GlC LCGIC, compomers chemical adhesion, Good mechanical properties, fluoride release, command setting and rapid achievement of strength. Previously Deep cavity: • Ca (OH)2 liner • Base for mechanical support +stress distribution. • Varnish on the base plus walls except when using zinc phosphate cement the varnish must be applied before the cement. • Amalgam Currently • Light cured Ca (OH)2 liner • GIC base For indirect restoration: • A base is used to block undercuts • Preferable to be bondable to dentin to prevent dislodgement during temporization and impression taking. - Composition, structure and properties of different cement bases. - Klaniputation
  7. 7. Clinical consideration with liners and bases  Clinical judgment depends upon: 1) Remaining dentin thickness (RDT) 2) Consideration of adhesive material 3) Type of restorative material use * in amalgam: 1.5 mm depth => 2 layers of varnish + amalgam * in composite: acid itch – primer – bonding agent> THE AIM: to give chemical protection. * eugenol can’t be used under composite because it inhibits polymerization. * in case of very thin RDT use spherical amalgam because it needs less forces of condensation.  Newer liners place less emphasis on pulpal medication and focus more on chemical protection by sealing, adhesion and mechanical protection.  Newer compositions rely on mechanically strong acrylic resin matrices, and that choice makes the release of eugenol or calcium hydroxide more difficult or impossible..
  8. 8. Dr. Mostafa
  9. 9. Dr. Mostafa