Calcium Hydroxide in Dentistry: Applications and Clinical Relevance

Calcium hydroxide (Ca(OH)₂) is a cornerstone material in modern dentistry, particularly in endodontics and restorative procedures. Its unique chemical properties—including high alkalinity (pH ~12.5), antimicrobial action, and ability to stimulate mineralized tissue formation—make it indispensable for various therapeutic applications. This article explores the multifaceted uses of calcium hydroxide in dentistry, detailing its mechanisms, clinical applications, advantages, limitations, and future directions.​

Introduction to Calcium Hydroxide

Calcium hydroxide, chemically represented as Ca(OH)₂, is a widely utilized compound in both industrial and medical settings. In dentistry, it has gained a prominent role due to its distinctive chemical and biological properties that support healing, antimicrobial activity, and mineralized tissue formation. It is commonly referred to as “slaked lime” or “hydrated lime” in industrial contexts, but its purified form is specially formulated for dental applications.

Chemical Composition and Properties

Calcium hydroxide is a white, odorless powder with a slightly bitter taste and a low solubility in water (about 1.73 g/L at 20°C). When dissolved in water, it dissociates into calcium (Ca²⁺) and hydroxyl (OH⁻) ions, producing an alkaline pH of approximately 12.5. This high pH is one of its most critical properties in clinical dentistry, especially for its antimicrobial effects and its role in tissue repair and regeneration.

• Molecular formula: Ca(OH)₂
• Molecular weight: 74.09 g/mol
• Appearance: White, odorless powder
• Solubility in water: Low, but sufficient to achieve desired therapeutic effects

Forms Used in Dentistry

In clinical dentistry, calcium hydroxide is used in various forms, including:

• Powder form: Mixed with distilled water or saline to form a paste.
• Pre-mixed paste: Supplied in syringes or tubes, ready for application.
• Incorporated in sealers and liners: Combined with other components for use in root canal obturation and as pulp-capping agents.

These forms allow for versatile application across multiple dental procedures, ranging from pulp therapy to root canal treatments.

Importance in Dental Treatments

The effectiveness of calcium hydroxide in dentistry stems from three fundamental actions:

• Antibacterial Effect:
  The high pH disrupts bacterial cell walls and enzymatic activity, making it effective against a broad range of microorganisms, including Enterococcus faecalis, a pathogen often implicated in persistent root canal infections.
• Induction of Reparative Dentin:
  Calcium ions stimulate the activity of odontoblast-like cells, which contribute to the formation of reparative or tertiary dentin, especially important in pulp capping and pulpotomy procedures.
• Control of Inflammation and Healing Promotion:
  By creating an environment that suppresses bacterial activity and supports mineral deposition, calcium hydroxide promotes tissue healing and helps prevent periapical pathology.

Historical Context and Evolution

The introduction of calcium hydroxide into dentistry can be traced back to 1920, when it was first used by Hermann for direct pulp capping. Since then, it has become a foundational material in endodontics, trauma management, and restorative dentistry. While newer materials such as mineral trioxide aggregate (MTA) and bioceramics have emerged, calcium hydroxide remains a trusted and cost-effective option in many clinical scenarios.

Mechanism of Action

The efficacy of calcium hydroxide in dental procedures stems from its multifaceted biological and chemical actions. These mechanisms collectively promote disinfection, reduce inflammation, and stimulate tissue regeneration. Below, we explore each core mechanism in detail:

Antimicrobial Properties

One of the most critical features of calcium hydroxide is its strong antibacterial activity, which is primarily due to its high pH (~12.5).

a. Disruption of Bacterial Cell Membranes

The hydroxyl ions (OH⁻) released from calcium hydroxide have a highly reactive and destructive effect on bacterial cytoplasmic membranes. They lead to:

• Denaturation of proteins and enzymes
• Disruption of DNA replication
• Destruction of the lipid bilayer in bacterial cell walls

This action renders the environment hostile to most microorganisms, including common endodontic pathogens such as:

• Enterococcus faecalis
• Candida albicans
• Porphyromonas gingivalis

b. pH-Dependent Bacterial Killing

The antibacterial effect is strongest in an environment where the pH exceeds 9.5. Most oral bacteria cannot survive at a pH above 11, making calcium hydroxide an ideal medicament to sterilize root canals and infected pulp tissue.

c. Sustained Activity

Calcium hydroxide exhibits a long-lasting antimicrobial effect, especially when used as an intracanal dressing. The gradual release of OH⁻ ions ensures continued disinfection between endodontic appointments.

Induction of Hard Tissue Formation

Calcium hydroxide is well known for its ability to stimulate the formation of mineralized (hard) tissue, a property crucial for pulp therapy and apexification.

a. Calcium Ion Release and Cellular Activation

Calcium ions (Ca²⁺) play a vital role in signaling pathways that regulate:

• Odontoblast activity
• Differentiation of pulp progenitor cells
• Stimulation of alkaline phosphatase, an enzyme critical for mineralization

This activity results in the formation of reparative dentin or a calcific barrier, depending on the location and context of use.

b. Stimulation of Reparative Dentinogenesis

When used for direct pulp capping, calcium hydroxide induces a mild, controlled inflammatory response, which leads to the recruitment of undifferentiated mesenchymal cells. These cells then differentiate into odontoblast-like cells, producing tertiary (reparative) dentin beneath the site of injury.

c. Apexification and Barrier Formation

In immature permanent teeth with open apices, calcium hydroxide facilitates the formation of a hard tissue barrier at the root tip (apical closure). The mechanism involves:

• Chemical irritation that stimulates periapical tissues
• Activation of cementoblasts and osteoblasts
• Formation of a mineralized apical plug that allows root canal obturation

Anti-Inflammatory Effects

Though not as pronounced as its antibacterial or mineralizing effects, calcium hydroxide also contributes to modulating the inflammatory process within the pulp and periapical tissues.

a. Neutralization of Acidic Byproducts

Bacterial metabolism in infected root canals produces acidic byproducts. Calcium hydroxide neutralizes these substances, creating a more favorable environment for healing.

b. Suppression of Inflammatory Mediators

By stabilizing the pH and reducing bacterial load, calcium hydroxide indirectly reduces the release of inflammatory cytokines and chemokines, which can otherwise lead to pulp necrosis and periapical bone resorption.

Tissue Dissolution Capability

Calcium hydroxide can dissolve necrotic tissue remnants in the root canal system—a valuable trait for root canal debridement. Hydroxyl ions break down proteins through:

• Hydrolysis of peptide bonds
• Saponification of lipids This helps in removing organic debris that may serve as a nidus for bacterial regrowth.

High Alkalinity and Denaturation of Endotoxins

Bacterial endotoxins (such as lipopolysaccharides from Gram-negative bacteria) are potent stimulators of inflammation in the periapical tissues. Calcium hydroxide’s high pH:

• Denatures lipopolysaccharides (LPS)
• Reduces their inflammatory potential

This property is crucial in endodontic cases involving persistent periapical lesions or resorption.

Promotion of Healing and Biocompatibility

Calcium hydroxide is biocompatible with dental tissues, meaning it generally causes minimal irritation when placed near vital or healing tissues.

a. Hemostasis and Matrix Formation

In cases of pulp exposure, calcium hydroxide facilitates clot formation and the establishment of a fibrin matrix, which is essential for cellular migration and subsequent tissue regeneration.

b. Sealing Ability (with adjunct materials)

Though calcium hydroxide is not an ideal sealing material by itself, it is often used in combination with liners, bases, or sealers to create a protective barrier. Its presence beneath a restoration can shield the pulp from thermal, chemical, and microbial insult.

Summary of Mechanism of Action

Clinical Applications of Calcium Hydroxide in Dentistry

Calcium hydroxide has a wide range of clinical applications in both restorative and endodontic dentistry, owing to its unique combination of antibacterial activity, tissue compatibility, and ability to stimulate hard tissue formation. This section explores the major therapeutic roles of calcium hydroxide in detail:

1. Direct and Indirect Pulp Capping

Pulp capping is a vital pulp therapy technique aimed at preserving the health of the dental pulp following exposure or near exposure due to caries, trauma, or operative procedures.

Direct Pulp Capping

• Applied directly over exposed pulp tissue.
• Aims to stimulate the formation of reparative dentin and maintain pulp vitality.
• Typically used in small mechanical or traumatic exposures with no signs of irreversible pulpitis.
• Calcium hydroxide forms a dentin bridge within a few weeks, sealing off the pulp from the oral environment.

Indirect Pulp Capping

Used in deep caries cases where a thin layer of softened dentin remains over the pulp.

Calcium hydroxide is placed over the affected dentin to:

• Arrest caries progression
• Encourage remineralization
• Preserve pulp vitality

Both techniques benefit from calcium hydroxide’s antimicrobial properties and ability to stimulate dentinogenesis.

2. Pulpotomy

Pulpotomy is a vital pulp therapy procedure in which the coronal portion of the dental pulp is removed, and the remaining radicular pulp is treated to preserve vitality.

• Common in primary teeth and young permanent teeth with open apices.

• Calcium hydroxide is applied to the radicular pulp stumps to:

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  • Promote healing

  • Stimulate continued root development (in immature teeth)

  • Avoid premature loss of the tooth

Although newer materials like mineral trioxide aggregate (MTA) are now favored, calcium hydroxide is still widely used, especially in resource-limited settings due to its affordability and efficacy.

3. Apexogenesis

Apexogenesis refers to the encouragement of continued physiological root development in a vital, immature permanent tooth.

• When a young permanent tooth with an open apex suffers trauma or deep caries, it’s essential to preserve pulp vitality to allow root elongation and apical closure.
• Calcium hydroxide, when placed over healthy pulp after partial removal (pulpotomy), maintains pulp vitality and allows normal root development.

Its ability to stimulate the formation of dentin bridges plays a central role in successful apexogenesis.

4. Apexification

Apexification is the induction of a calcified barrier at the apex of a non-vital tooth with an incompletely formed root.

• These teeth are often the result of trauma or infection that has led to pulp necrosis before root formation is complete.
• Calcium hydroxide is introduced into the root canal system as a long-term dressing (for 6–24 months), encouraging the formation of a hard tissue barrier at the apex.
• This allows for proper obturation of the root canal system.

Although newer materials like MTA and biodentine are increasingly used for single-visit apexification, calcium hydroxide remains effective and economical.

5. Intracanal Medicament

Calcium hydroxide is one of the most common interappointment intracanal medicaments used during root canal treatment.

• Placed between appointments to disinfect the canal system.
• It helps eliminate residual bacteria that may persist after instrumentation.
• Particularly effective against Enterococcus faecalis, Candida albicans, and obligate anaerobes.

It also serves to dry up exudate, reduce inflammation, and prevent reinfection, especially in cases with persistent periapical pathology.

6. Root Canal Sealers

Some root canal sealers are based on calcium hydroxide or contain it as a component.

• These sealers provide a high pH environment that helps neutralize any remaining microbes.
• They contribute to the biological sealing of the canal system and can stimulate periapical healing.
• However, their solubility is higher than ideal, so they are often used in combination with other more durable materials.

7. Treatment of Internal and External Root Resorption

Resorption of dental hard tissues can be pathological (e.g., trauma, orthodontic movement, inflammation).

• Internal root resorption: Calcium hydroxide can help inactivate resorptive cells and promote hard tissue repair.

• External inflammatory root resorption: Often seen in traumatized teeth, especially those that have been luxated or avulsed.

  • Calcium hydroxide helps neutralize the acidic microenvironment caused by inflammation.

  • It prevents further resorption and promotes periapical healing.

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Repeated dressings over weeks or months may be necessary depending on the severity.

8. Management of Dental Trauma

Following traumatic dental injuries, calcium hydroxide plays a crucial role in preventing or managing complications.

a. Avulsed Teeth (Tooth Knocked Out)

When a tooth is replanted, especially after a delayed period, the root canal is often treated with calcium hydroxide to prevent external inflammatory root resorption.

b. Intrusive or Lateral Luxation Injuries

In these cases, the risk of pulpal necrosis and resorption is high.

Calcium hydroxide can be used to:

• Treat necrotic pulps
• Arrest or prevent root resorption
• Promote periapical healing

9. Use as a Cavity Liner/Base

In restorative dentistry, calcium hydroxide is frequently used as a liner or base beneath restorations to:

• Protect the pulp from chemical and thermal irritation
• Stimulate secondary dentin formation

It is commonly placed under amalgam, composite, or indirect restorations, especially in deep cavities where remaining dentin is thin.

However, it should always be covered with a stronger base or bonding agent, as it has poor compressive strength and can degrade over time.

10. Perforation Repair (Historically)

Although newer materials such as MTA are now preferred, calcium hydroxide was previously used for repairing root perforations due to its ability to stimulate hard tissue formation.

• Used in non-surgical endodontics to seal small perforations temporarily
• Encouraged the growth of hard tissue over the defect

11. Periodontal and Surgical Applications

In some periodontal procedures and oral surgeries, calcium hydroxide has been used to:

• Promote bone regeneration
• Reduce microbial load in surgical sites
• Encourage healing in bone defects

Its antibacterial and osteoinductive properties have been investigated in bone grafts and guided tissue regeneration, although it’s now less common in these fields.

Summary of Clinical Uses

Advantages of Calcium Hydroxide in Dentistry

Calcium hydroxide has remained a mainstay in dental practice for nearly a century due to its unique biological effects, therapeutic versatility, and clinical practicality. Despite the emergence of newer biomaterials, it continues to be widely used because of the following key advantages:

1. Broad-Spectrum Antimicrobial Activity

One of the most valuable properties of calcium hydroxide is its potent antibacterial effect:

• The high pH (~12.5) creates an environment that is inhospitable to most oral bacteria, including Enterococcus faecalis, a common and persistent endodontic pathogen.
• Hydroxyl ions are highly reactive, causing oxidative damage to bacterial cell walls, proteins, and DNA.
• Its antifungal properties also make it effective against organisms like Candida albicans.

This makes calcium hydroxide an essential medicament in root canal therapy, especially in teeth with chronic periapical infections or re-treatment cases.

2. Biocompatibility

Calcium hydroxide demonstrates excellent biocompatibility with dental tissues, meaning it is:

• Non-toxic when applied properly
• Well tolerated by the pulp and periapical tissues
• Safe for use in vital pulp therapies like pulp capping and pulpotomy

Its ability to promote tissue healing without eliciting a strong inflammatory reaction makes it ideal for procedures that involve direct contact with pulpal or periapical tissues.

3. Promotion of Hard Tissue Formation

Calcium hydroxide is one of the few dental materials that can actively stimulate the formation of mineralized tissue:

• It facilitates reparative dentinogenesis in the pulp.
• It promotes apical barrier formation in immature teeth undergoing apexification.
• It helps form a calcified bridge in pulp capping procedures.

The release of calcium ions activates alkaline phosphatase and other mineralizing enzymes, leading to the deposition of hydroxyapatite crystals—the primary component of dentin and bone.

4. Versatility in Clinical Use

Calcium hydroxide is among the most versatile materials in dentistry, with applications in:

• Vital pulp therapy (e.g., direct/indirect pulp capping, pulpotomy, apexogenesis)
• Non-vital therapy (e.g., apexification, intracanal medicament)
• Root resorption treatment
• Root canal sealer
• Restorative dentistry (as a cavity liner)
• Trauma management

Its broad range of applications makes it cost-effective and logistically convenient, especially in general practice or resource-limited environments.

5. Ease of Application

Calcium hydroxide is available in multiple convenient forms:

• Powder (to be mixed with sterile water or saline)
• Pre-mixed paste (in syringe or tube form)
• Ready-to-use liners and cements
• Components in some root canal sealers

These formulations make application quick, easy, and precise, requiring minimal equipment or training. The material is also radiopaque, allowing clinicians to verify placement on radiographs.

6. Cost-Effectiveness

Compared to newer materials like MTA, biodentine, and bioceramics, calcium hydroxide is:

• Inexpensive
• Widely available
• Long shelf life in dry form

This makes it particularly valuable in public health dentistry, school-based programs, and in clinics with limited financial or material resources.

7. Anti-inflammatory and Detoxifying Effects

• Calcium hydroxide neutralizes acidic byproducts from bacterial metabolism in infected pulp or periapical tissues.
• It also inactivates bacterial endotoxins (e.g., lipopolysaccharides), which are major contributors to inflammation and bone resorption.
• These properties help reduce periapical inflammation and promote healing of periradicular tissues.

8. Encouragement of Healing and Regeneration

When used appropriately, calcium hydroxide supports the body’s natural healing mechanisms. It:

• Creates a favorable environment for cell proliferation and tissue repair.
• Helps form a fibrin matrix in exposed pulp or damaged tissue, facilitating migration of progenitor cells.
• Encourages the regeneration of cementum and bone in root resorption or apexification cases.

9. Minimal Systemic Toxicity

When used topically or intracanal, calcium hydroxide has virtually no systemic side effects:

• It is not absorbed in significant amounts into the bloodstream.
• It poses no known allergic risks or toxicity when confined to dental tissues.

This makes it safe for use in pediatric dentistry, pregnant patients, and compromised individuals.

10. Long History of Clinical Success

• Calcium hydroxide has been used in dentistry for over 100 years, with a substantial body of clinical evidence supporting its efficacy.
• Its mechanism of action is well understood, and its clinical behavior is predictable.
• Dentists and specialists across the world trust it for routine and advanced procedures, ensuring high reliability and acceptance.

Summary of Advantages

Limitations of Calcium Hydroxide in Dentistry

While calcium hydroxide has numerous advantages and is a widely used material in endodontic and restorative procedures, it is not without its limitations. Understanding its shortcomings is critical for making informed clinical decisions, especially in comparison to newer bioactive materials like MTA, bioceramics, and biodentine.

1. High Solubility and Limited Longevity

One of the most significant drawbacks of calcium hydroxide is its high solubility in oral fluids.

• When used as a liner or base, it may dissolve over time in the presence of saliva or dentinal fluid.
• This solubility compromises the long-term seal and protection of the pulp.
• In apexification or as an intracanal medicament, the material must often be reapplied multiple times over several weeks or months to maintain effectiveness.

Clinical implication: Requires frequent recall visits and has limited durability, especially in high-moisture environments.

2. Weak Mechanical Properties

Calcium hydroxide has poor compressive strength and is brittle when set:

• It cannot withstand occlusal forces, so it is not suitable as a stand-alone base or restorative material.
• In areas under load (e.g., beneath large posterior restorations), it must be covered with a stronger material such as glass ionomer cement or composite resin.

Clinical implication: Its structural weakness restricts its use in situations requiring support or long-term durability.

3. Inferior Sealing Ability

Calcium hydroxide alone does not provide an effective seal against microleakage:

• It shrinks upon setting and may develop gaps or voids at the interface with dentin.
• It does not bond chemically to tooth structures.
• This increases the risk of bacterial reinfiltration and failure of pulp capping or root canal therapy if not adequately sealed by other materials.

Clinical implication: Must always be used in combination with sealing or restorative agents to ensure clinical success.

4. Extended Treatment Time in Apexification

While effective for inducing apical closure, calcium hydroxide-based apexification has significant drawbacks:

• Takes several months (often 6–24 months) to form a calcific barrier at the apex.
• Requires multiple appointments and radiographic evaluations.
• Patient compliance can be an issue.
• There is a risk of tooth fracture during the extended treatment period due to weakened root structure.

Clinical implication: Modern alternatives like MTA and bioceramics allow single-visit apexification and are more time-efficient.

5. Incomplete Bacterial Elimination

Although calcium hydroxide is broadly antimicrobial, it is not effective against all species, particularly:

• Enterococcus faecalis in its biofilm form
• Candida albicans under certain conditions
• Bacteria in inaccessible or non-instrumented areas of the root canal system

Clinical implication: May not fully disinfect complex canals or retreatment cases, where biofilms are established.

6. Potential for Tissue Irritation

In some cases, if extruded beyond the root apex during endodontic treatment, calcium hydroxide can:

• Cause tissue necrosis or damage to the neurovascular bundle
• Lead to inflammatory responses in the periapical tissues
• Prolong the healing process

Although generally biocompatible, excessive exposure or improper application can have adverse effects.

Clinical implication: Must be used with caution in open apices or perforation cases.

7. Limited Use in Permanent Restorations

Due to its poor physical properties, calcium hydroxide is unsuitable as:

• A permanent filling material
• A core build-up material
• A long-term liner without protective overlay

Its resorbable nature means it can degrade over time, compromising the integrity of permanent restorations if not properly sealed.

8. Aesthetic Limitations

• When used in anterior teeth, calcium hydroxide may cause tooth discoloration, particularly if remnants are not completely removed prior to final restoration.
• This can compromise esthetic outcomes, especially under composite restorations.

Clinical implication: Alternative materials should be considered in esthetically sensitive areas.

9. Lack of Adhesion

Calcium hydroxide does not adhere to dentin or enamel:

• It cannot form a hybrid layer or micromechanical bond.
• This makes it vulnerable to microleakage, displacement, and washout if not protected by adhesive liners or bases.

Clinical implication: Must always be used in conjunction with adhesive restorative techniques.

10. Not a Permanent Solution for Severe Cases

In cases involving:

• Large perforations
• Extensive resorption
• Complex endodontic pathologies

Calcium hydroxide may not provide the desired clinical outcome, and bioactive alternatives like MTA, Biodentine, or regenerative endodontic procedures may be required for optimal success.

Summary of Limitations

Conclusion

Calcium hydroxide remains a vital material in dentistry due to its antimicrobial properties and ability to stimulate hard tissue formation. Despite its limitations, its versatility and efficacy in various clinical applications make it an indispensable tool in dental practice.