Setting Calcium Hydroxide Cement Flashcards
What’s the old classification of a Base and Lining?
Base: - Barrier against chemical irritation - Provide thermal insulation and resist forces applied during condensation of the restorative material - Malleable "Dentine replacement material"
e. g.
1. Zinc oxide eugenol
2. Zinc phosphate
3. Glass ionomer cements
Lining:
- Placed as thin coating on the pulpal surface
- Barrier against chemical irriation
- DO NOT FUNCTION as thermal insulators
e. g.
1. Varnish-type materials which calcium hydroxide OR zinc oxide powder are added
What’s Calcium Hydroxide cement?
- Lining material
- Reaction between Calcium hydroxide & Salicylate esters forming a calcium disalicylate complex
- 2 paste system
- Available as light-curing product - BUT calcium hydroxide is not available or any reaction with tooth (bound in resin)
What’s the setting reaction of Calcium Hydroxide cement?
- Chelation reaction between calcium and butylene glycol disalicylate
(Water is required)
- Exothermic reaction but of negligible significance
- End result = calcium disalicylate complexes surrounding unchanged calcium hydroxide
What are the mechanical properties of Calcium Hydroxide cement?
- Poor mechanical strength (weakest of all cements)
- Deforms in shape once you load it with another material on top
- Must be used in thin section (air thinned)
What’s the solubility of Calcium hydroxide cement?
- Unstable and soluble
- Degrades in the presence of water
- Hydrophilic sulphonamide plasticiser included to control viscosity but permits rapid water permeation
- The high solubility facilitates the breakdown of the cement = degradation - that’s why you need to place something on top to minimise moisture
- Cements degrade over & lost lowly due to marginal leakage and presence of moisture from dentine
How biocompatible is Calcium hydroxide?
Chemical Irritant
- Increases the pH of the local environment making it bactericidal or bacteriostatic
- Extent of effect depends on pH of surroundings in which bacteria thrive
What’s the mode of action or Calcium hydroxide?
- Causes series of inflammatory reactions
- High pH (alkalinity) causes liquefaction necrosis of the superficial pulp – removes up to 1.5mm of the inflamed tissue
- Neutralisation of toxicity follows in the deep layers with coagulative necrosis – irritates adjacent pulp and causes minor inflammation
= Dentine bridge formed
- Pleuripotential pulpal cells stimulated and differentiate into odontoblasts
- Reparative (tertiary) dentine laid down forming a calcified bridge so walling off pulp from base of cavity
- Calcium for new dentine derived from pulp cells not cement
Does Calcium Hydroxide bind to the dentine?
No - no adherence either chemically or micromechanically
How does light-cured calcium hydroxide cements differ to regular cement?
- Addition of resin – bis-GMA and HEMA
- Calcium hydroxide plays no part no part in setting reaction – no dissolution of calcium hydroxide
- HEMA allows water ingress
What are the characteristics of Light cured calcium hydroxide cements?
- Higher exothermic reaction during polymerisation process = potential risk when placed close to pulp
- Slightly higher mechanical strength + less brittle
- Can allow microleakage – periphery of cement lifts during polymerisation shrinkage
BUT
- Seals dentinal tubules
What are the advantages of using calcium hydroxide cements?
- Stimulates the formation of reparative dentine
- Forms a physical barrier over exposed pulp + seals dentinal tubules
- Cheap
What are the disadvantages of using calcium hydroxide cements?
- Low compressive strength
- Soluble = breaks down during use
- No adhesion to dentine
- High pH on setting causes local irritation
- Chance of microleakage if using light-cured material due to polymerisation
What are the indications for using Calcium hydroxide?
- Deep cavity over pulpal floor
- Indirect pulp capping
- Direct pulp capping
What is pulp capping?
- A method by which a physical barrier between the (exposed) pulpal tissue and the other material(s) used to restore the cavity
- Many restorative materials are contraindicated to be directly placed on exposed dentine as they are cytotoxic
What is the preferred alternative to Calcium Hydroxide?
Tricalcium Silicate Cement
- Used for indirect or direct pulp caps - forms seal and excellent biocompatability
