Liners & Bases

Purposes of liners & bases Protect the pulp from: chemical insult leakage electrical insult thermal insult

Hydrodynamic theory of dentinal pain: Cause of pain: Hydrodynamic theory of dentinal pain: flow of fluids within the dentinal tubules is the cause of pain. Key point: changes in temperature change the volume of the fluid: the fluid flows

Stopping fluid flow: Completely seal the dentinal tubules Completely seal the path to the external surface of the restoration

Thermal properties of dental materials Conductors: metals (amalgam, cast alloys) Insulators: enamel dentin (except tubules) all luting cements, resin composites, porcelains

How insulators affect thermal expansion: Slow the rate at which dentinal fluid is heated or cooled - fluid changing volume slowly will move more slowly - less pain? Reduce the heat conducted to or from the dentinal fluid; some of the heat will be conducted away by the surrounding tooth structure.

Therapeutic effects of liners & bases: neutralizes acids slows or stops increase in the number of bacteria dulls pain (obtundent) increases the resistance of adjacent tooth structure to dissolution in acids stimulates the formation of reparative dentin

Classification of liners & bases: thin liners (< 0.20 mm) liners (0.20 - 0.75 mm) bases (> 0.75 mm)

Cavity Varnish

Thin liners – cavity varnishes uses: reduce leakage of amalgam restorations protect cements from exposure to oral fluid while setting coating to reduce electrical shock from freshly placed metallic restorations

Thin liners – cavity varnishes natural gum: copal or rosin solvent: acetone, chloroform, ether, benzene, polystyrene

Thin liners – cavity varnishes manipulation: avoid evaporation – do not use thickened varnish apply with a cotton ball remove excess from the ball apply two layers, wait 15 – 20 s between layers

Dentin permeability: effect of a varnish Two layers are more effective. Note: the end result is less leakage, not no leakage D. Pashley, 1983

One Day - Leakage in Class III Restorations - Dispersalloy Leakage into axial wall Initially, some products work better than others. No leakage Murray, G. A., J. L. Yates, et al. (1983). Oper Dent 8: 148-51.

Seven Day - Leakage in Class III Restorations - Dispersalloy Murray, G. A., J. L. Yates, et al. (1983). Oper Dent 8: 148-51.

Six Months - Leakage in Class III Restorations - Dispersalloy After 6 months, the liners make no difference. Corrosion has sealed the margins. Murray, G. A., J. L. Yates, et al. (1983). Oper Dent 8: 148-51.

filled cavity varnishes dentin bonding systems adhesive resin cements Thin liners (< 0.20 mm): cavity varnishes filled cavity varnishes dentin bonding systems adhesive resin cements

Thin liners - filled cavity varnishes Not recommended: Fillers dissolve, leading to accelerated dissolution of the liner.

filled cavity varnishes dentin bonding systems adhesive resin cements Thin liners (< 0.20 mm): cavity varnishes filled cavity varnishes dentin bonding systems adhesive resin cements discussed earlier in the bonding and luting cement slides

Classification of liners & bases: thin liners (< 0.20 mm) liners (0.20 - 0.75 mm) bases (> 0.75 mm)

Hard-setting calcium hydroxide Liners (0.20 - 0.75 mm): Hard-setting calcium hydroxide calcium hydroxide-containing resin composites hard setting zinc oxide - eugenol glass-ionomer cements resin-modified glass-ionomer cements

Hard-setting Calcium Hydroxide Cements Wt. % Paste 1 Paste 2 calcium hydroxide 49% salicylate esters 44% ethylene toluene sufonamides 37% tricalcium ortho phosphate 30% zinc oxide 9% calcium tungstate 14% titanium dioxide 4% zinc stearate 0.5% hydrophilic & dissolves in in H2O – accelerates dissolution of Ca hydroxide weak acids that attacks Ca hydroxide & zinc oxide chelates with Ca++ & Zn++ ions: gels

Hard-setting Calcium Hydroxide Cements : Advantages: easy manipulation rapid hardening – accelerated by water vapor good sealing stimulates reparative dentin recommended for direct pulp capping recommended for indirect pulp capping when close to the pulp

Hard-setting Calcium Hydroxide Cements: Disadvantages: low strength weakened when exposed to moisture dissolves, especially under acidic conditions Hard-setting calcium hydroxide washed out under an amalgam restoration

Hard-setting calcium hydroxide Liners (0.20 - 0.75 mm): Hard-setting calcium hydroxide calcium hydroxide-containing resin composites hard setting zinc oxide - eugenol glass-ionomer cements resin-modified glass-ionomer cements

calcium hydroxide direct pulp capping agent: current product: DYCAL® Radiopaque Calcium Hydroxide Composition Caulk / Dentsply

Calcium Hydroxide-Containing Composite Liners barium sulfate fillers urethane diacrylate diluents polymer matrix activators & photoinitator curable by light Makes the cement radiopaque Essentially a resin composite with a calcium hydroxide replacing glass as the filler.

Solubility of Calcium Hydroxide Liners (wt. %) hard-setting resin 24 h in H2O 1.0 – 2.0 < 0.5 35% H3PO4 for 60 s 2.0 – 2.5 < 0.18 much more stable in water & acids

Properties of Calcium Hydroxide Liners stronger Properties of Calcium Hydroxide Liners (MPa) hard-setting resin compressive str (MPa) 26 - 32 83 - 104 pH 9 – 10 9 - 10 both are basic; may be important to stimulating formation of reparative dentin.

Hard-setting calcium hydroxide Liners (0.20 - 0.75 mm): Hard-setting calcium hydroxide calcium hydroxide-containing resin composites hard setting zinc oxide - eugenol glass-ionomer cements resin-modified glass-ionomer cements Relatively weak & soluble. Does not stimulate reparative dentin as well as calcium hydroxide

Hard-setting calcium hydroxide Liners (0.20 - 0.75 mm): Hard-setting calcium hydroxide calcium hydroxide-containing resin composites hard setting zinc oxide - eugenol glass-ionomer cements resin-modified glass-ionomer cements Probably like RMGIs – more data is needed

Hard-setting calcium hydroxide Liners (0.20 - 0.75 mm): Hard-setting calcium hydroxide calcium hydroxide-containing resin composites hard setting zinc oxide - eugenol glass-ionomer cements resin-modified glass-ionomer cements Stronger than GIs; like GIs bond to dentin & enamel

Calcium hydroxide is associated with the most reparative dentin. RMGIs are associated with less reparative dentin Tertiary dentin is another term for “reparative dentin.” Murray PE et al. (2001) Restorative pulpal and repair responses J Amer Dent Assoc132(4) 482-491.

Calcium hydroxide liners have the least affect on the density of odontoblasts. Remaining Dentin Thickness of 0.04 to 0.50 mm Remaining Dentin Thickness of 0.501 to 2.993 mm No cavity present. Number of odontoblasts (mm2) RMGIs reduce the odontoblast density Murray PE et al. (2001) Restorative pulpal and repair responses J Am Dent Assoc132(4) 482-491.

Hard-setting calcium hydroxide Liners (0.20 - 0.75 mm): Hard-setting calcium hydroxide calcium hydroxide-containing resin composites hard setting zinc oxide - eugenol glass-ionomer cements resin-modified glass-ionomer cements Less reparative dentin than calcium hydroxide; also reduces the number of odontoblasts

Classification of liners & bases: thin liners (< 0.20 mm) liners (0.20 - 0.75 mm) bases (> 0.75 mm)

zinc phosphate cements zinc polyacrylate cements glass-ionomer cements Bases (> 0.75 mm): zinc phosphate cements zinc polyacrylate cements glass-ionomer cements resin-modified glass-ionomer cements polyacid-modified composite resins In the past, each of the above cements (and other cements too) has been used as a base under various restorative materials.

zinc phosphate cements zinc polyacrylate cements glass-ionomer cements Bases (> 0.75 mm): zinc phosphate cements zinc polyacrylate cements glass-ionomer cements resin-modified glass-ionomer cements polyacid-modified composite resins Bases is rarely used today. Why?

Bases (why use has declined): less need to protect pulp from restorative materials – materials are thought to be more biocompatible than in the past experts now question the wisdom of placing a weaker material (the base) under a stronger material (the restorative material)

Bases (if you are going to use one) – desirable properties strong immediately after placement stronger when aged stiff; does not flex

Compressive Strength at 7 Min 1.2 MPa needed to resist condensation stresses

Elastic Modulus Zinc phosphate is the stiffest of these potential base materials. It is least likely to bend when the restorative material is under load.

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