Calcium Hydroxide Cements
Calcium hydroxide cements are essentially mineral biomaterials for protecting the dental pulp, used to prevent its irritation or promote its healing.
1. Composition:
Calcium hydroxide, also called hydrated lime or slaked lime, is a fine, odorless white powder with the chemical formula Ca(OH) 2
Calcium hydroxide is produced from calcium carbonate through the following chemical reactions:
Calcination of calcium carbonate (CaCO3 ) at high temperature gives calcium oxide or quicklime (CaO), depending on:
CaCO 3 CaO + CO 2 .
– Calcium hydroxide is then obtained by mixing quicklime (CaO) and water (H2O ) .
This hydration reaction releases a lot of heat, according to: CaO + H 2 O Ca(OH) 2 .
2. Presentation:
Calcium hydroxide can be used either as a compound (dry powder) or as a commercial preparation.
2.1. Magistral preparations:
Magistral preparations are made extemporaneously from pure calcium hydroxide powder and a liquid, generally sterile physiological serum. The mixture with the liquid is done until the desired consistency is obtained).
Preparation with sterile water allows for a better effect of the material because the release of Ca² + and OH ions is stronger. Therefore, it better stimulates the induction and formation of the calcified barrier, as well as antimicrobial activity.
2.2. Commercial preparations:
Commercial preparations are ergonomic and practical products to use, packaged in tubes, syringes or cartridges.
Calcium hydroxide is thus available in the form of:
– paste to be mixed with another paste, for example: Life® (Kerr Hawe, Switzerland), Dycal® (Dentsply, USA).
– already mixed preparation, ready to be applied, for example: Multi-Cal® (Pulpdent Corp., USA).
Commercial preparations are numerous and can be differentiated depending on the vector that is associated with calcium hydroxide.
– aqueous vector: allows rapid ionic release
– viscous vector (glycerin, polyethylene glycol): allows a slower release
– oily vector (olive oil, silicone oil, etc.): causes very slow ionic dissolution. They are rarely used.
Conversely, to obtain rapid ionic release from the start of treatment, it is necessary to use a calcium hydroxide paste with an aqueous vector such as Calxyl® or Pulpdent®.
In addition, there are commercial preparations that are more intended for pulp capping because they contain a hardener allowing faster setting: Dycal®, Life®.
3. Properties:
3.1. Physicochemical properties:
3.1.1. PH:
Calcium hydroxide is a very alkaline substance with a pH of around 12.5.
It is chemically classified as a strong base.
This high pH is due to the release of OH ions. It is between 11 and 13 but varies depending on the amount of water. Thus, a magistral preparation using sterile water will have a higher pH than a commercial preparation.
3.1.2. Working time:
Working time is the period during which the cement can be handled without altering its properties. It is 3 to 5 minutes, and depends on humidity and composition.
3.1.3. Setting time:
Setting time is the time required for the cement to acquire its final mechanical properties. When calcium hydroxide is mixed with water, surface crystallization is observed but no real setting of the material. In fact, its transformation into solid phase is found only for hardening pastes, after a setting time of approximately 2.5 to 5.5 minutes.
3.1.4. Solubility:
Calcium hydroxide is sparingly soluble in water (1.2 g/L at 25°C) and tissue fluids. It dissociates into calcium and hydroxyl ions with a dissociation coefficient of 0.17.
The low solubility of calcium hydroxide is an advantage because it counteracts toxic alkaline diffusion.
As the temperature increases, this solubility decreases.
3.1.5. Thermal conductivity:
Calcium hydroxide has low thermal conductivity. Its thickness influences the insulation: the greater the thickness, the better the thermal insulation. It must be between 1.5 and 2 mm to be effective.
3.1.6. Compressive strength:
The compressive strength of calcium hydroxide is very low. It varies from
3.9 MPa at the beginning of the setting reaction to 10.5 MPa after 24 hours, which does not allow calcium hydroxide to be used as a coronal reconstruction material. Therefore, it is necessary to protect it.
This low compressive strength also explains why calcium hydroxide in magistral preparation should not be used alone as pulp-dentin protection under an amalgam.
It would not withstand the forces exerted by the practitioner when he presses the amalgam. If it is then used, it must be protected by a thin layer of another material (Glass Ionomer Cement for example).
3.1.7. Radiopacity:
Calcium hydroxide in magistral preparation is weakly radiopaque. Its radiopacity is close to that of dentine; it is therefore difficult to distinguish on radiographs.
3.1.8. Adhesion and sealing:
Calcium hydroxide has poor adhesion to dentin and poor sealing capacity. Therefore, calcium hydroxide-based materials do not provide a watertight seal against bacteria.
The non-adhesion of calcium hydroxide to dentin and its poor mechanical properties require it to be applied in a layer of limited thickness.
3.2. Biological properties:
3.2.1. Biocompatibility:
In principle, materials brought into contact with living tissues must be biocompatible and free of cytotoxic or mutagenic effects. However, calcium hydroxide is cytotoxic on cell cultures. Its basic pH is the main reason for its toxicity.
Similarly, calcium hydroxide has the ability to dissolve pulp tissues. It denatures proteins and lyses organic matter.
When placed in contact with healthy pulp, it causes coagulation necrosis on the surface of the pulp tissue.
However, given its low diffusion rate, this alteration of the pulp remains superficial. In fact, calcium hydroxide is only toxic to what it comes into contact with.
Due to its low solubility in tissue fluids, it is considered a biocompatible material.
3.2.2. Anti-inflammatory action:
Calcium hydroxide reduces inflammatory reactions in the dental pulp and periapical tissue. By alkalizing the environment, it acts as a buffer to inflammatory acidosis. It reduces macrophage cohesion and inhibits their function.
The action of osteoclasts and dentinoblasts is also reduced by it, leading to the predominance of dentinogenic mechanisms.
This phenomenon explains, in part, the mineralizing property of calcium hydroxide.
In addition, calcium hydroxide promotes the activation of complement, involved in immunological reactions. It also decreases the expression of inflammatory mediators.
3.2.3. Anti-hemorrhagic action:
The hemostatic properties of calcium hydroxide are due to the presence of calcium which is one of the factors of blood coagulation. Calcium ions will induce a contraction of the capillaries, which reduces their permeability.
In addition, the coagulation necrosis caused by the application of calcium hydroxide during pulp capping limits the appearance of a possible blood clot between the pulp and the material.
3.2.4. Antimicrobial activity:
Calcium hydroxide has bactericidal properties and disinfects the superficial pulp.
Its antimicrobial activity is linked to its high pH and the release of hydroxyl ions. The highly alkaline nature of this product makes the environment unsuitable for bacterial life. In fact, the majority of bacteria cannot survive at a pH higher than 9. In addition, the released Ca² + ions will maintain an environment unfavorable to bacterial proliferation over time.
4. Different indications in OCE:
– direct and indirect pulp capping,
– pulpotomy,
– apexogenesis,
– apexification,
– treatment of root resorption,
– treatment of iatrogenic root perforations,
– root fractures,
– intracanal medication between two endodontic treatment sessions,
CONCLUSION
Calcium hydroxide is used in Conservative Dentistry/Endodontics for its many properties. Due to its high pH, it stimulates the development of calcified tissue, it degrades necrotic tissue and denatures proteins, it reduces inflammatory acidosis and osteoclastic activity;
Calcium Hydroxide Cements
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