22.2 Pulp Vitality Assessment and Biological Pulp Capping

Diagnostic Assessment of Pulpal Vitality Prior to Excavation

Before undertaking operative intervention on deep carious lesions, accurate assessment of the pulpal-periapical status is mandatory:

                                  Pulpal Diagnostic Spectrum
                                               │
      ┌────────────────────────────────────────┴────────────────────────────────────────┐
      ▼                                                                                 ▼
Reversible Pulpitis                                                             Irreversible Pulpitis
• Sharp, provoked pain (cold/sweet)                                             • Dull, throbbing, spontaneous pain
• Resolves IMMEDIATELY (<10–15s)                                                • Lingers >30 seconds after cold
• No spontaneous nocturnal pain                                                 • Nocturnal awakening
• Normal periapical tissues                                                     • Heat provokes; cold may relieve
• Vital pulp testing: normal response                                           • Endodontic treatment mandatory
• SUITABLE FOR VITAL PULP THERAPY                                               • CONTRAINDICATED FOR PULP CAPPING

1. Diagnostic Testing Modalities:
   • Thermal Cold Testing: Application of refrigerant spray (Endo-Ice: 1,1,1,2-tetrafluoroethane, -26.2°C) on a cotton pellet to the middle third of the buccal tooth surface. Rapid, sharp sensation that dissipates within seconds indicates a healthy, vital pulp.
   • Electric Pulp Testing (EPT): Delivers a high-frequency pulsating electrical current to stimulate A-delta sensory fibres. Confirms neural vitality (positive response) vs pulpal necrosis (negative response), but does not quantify pulpal vascularity.
   • Periapical Radiography: Must show an intact periodontal ligament (PDL) space, intact lamina dura, and complete absence of periapical or furcal radiolucencies.
   • Percussion & Palpation: Gentle vertical and lateral tapping. Marked tenderness indicates inflammation extending into the periapical tissues (symptomatic apical periodontitis).

Biological Pulp Capping: Indications, Protocols & Biomaterials

Vital pulp therapy aims to preserve pulpal vitality and stimulate reparative dentinogenesis following pulpal trauma or exposure.

                                   Biological Pulp Capping
                                              │
            ┌─────────────────────────────────┴─────────────────────────────────┐
            ▼                                                                   ▼
Indirect Pulp Therapy (IPT)                                         Direct Pulp Capping (DPC)
• Deep carious lesion                                               • Pinpoint exposure (<1 mm)
• Dentine barrier preserved (no exposure)                           • Traumatic or mechanical
• Biomaterial placed on soft/affected dentine                       • Asymptomatic vital pulp
• Hermetic adhesive peripheral seal                                 • Haemostasis within 5 min with NaOCl
• Success rate >90%                                                 • MTA / Biodentine superior to Ca(OH)₂

Clinical Criteria for Direct Pulp Capping

Direct pulp capping involves applying a biomaterial directly onto exposed pulpal tissue. It is strictly indicated under specific clinical parameters:

• Strict Indications:
  1. Mechanical or traumatic exposure measuring <1.0 mm in diameter;
  2. Completely asymptomatic tooth or history consistent only with transient reversible pulpitis;
  3. Operative procedure conducted under strict rubber dam isolation (preventing salivary contamination);
  4. Haemostasis achieved within 5 minutes following gentle pressure with a sterile cotton pellet soaked in 2.5% to 5.0% sodium hypochlorite (NaOCl) or sterile saline.
• Absolute Contraindications:
  1. Carious exposure in an area of chronically infected, softened dentine (high bacterial load within pulpal parenchyma);
  2. Spontaneous, unprovoked, or nocturnal throbbing pain (symptomatic irreversible pulpitis);
  3. Lingering pain lasting >30 seconds following cold testing;
  4. Uncontrollable pulpal haemorrhage exceeding 5 minutes (indicates severe, irreversible radicular pulp tissue inflammation);
  5. Clear periapical radiolucency, root resorption, or non-vital response;
  6. Purulent exudate leaking from the exposure site.

Comparative Analysis of Pulp Capping Biomaterials

  Evolution of Pulp Capping Materials:
  
  Calcium Hydroxide [Ca(OH)₂]  ──►  Mineral Trioxide Aggregate (MTA)  ──►  Biodentine
  • Alkaline pH (~12.5)              • Hydraulic calcium silicate           • Pure tricalcium silicate
  • Caustic liquefaction necrosis    • Forms hydroxyapatite seal            • 12 min rapid setting
  • Soluble over time                • Thick, non-porous dentine bridge     • High compressive strength
  • "Tunnel defects" in bridge       • Slow setting (2–4 h); tooth stain    • Zero tooth discolouration

1. Calcium Hydroxide ($Ca(OH)_2$ - e.g. Dycal, Life):

   • Mechanism: Highly alkaline pH (~12.5). Upon direct contact with pulpal tissue, the hydroxyl ions cause a superficial, chemical liquefaction necrosis (zone of coagulation necrosis ~1–1.5 mm thick). Beneath this necrotic zone, mild irritation stimulates pulpal cells to release bioactive molecules, particularly transforming growth factor-beta 1 (TGF-$\beta1$).
   • Dentine Bridge Formation: TGF-$\beta1$ promotes the differentiation of mesenchymal dental pulp stem cells into odontoblast-like cells, which secrete a reparative dentine bridge (dentinoma).
   • Critical Limitations: Calcium hydroxide is chemically unstable and soluble under restorations. Over time, it washes out, leaving a physical void beneath restorations. Furthermore, histological analysis reveals that dentine bridges formed under $Ca(OH)_2$ contain numerous "tunnel defects" (microscopic vascular inclusions and porosities) through which microleakage and secondary pulpal death can occur.

2. Mineral Trioxide Aggregate (MTA - e.g. ProRoot MTA):

   • Composition: Hydraulic calcium silicate cement consisting of tricalcium silicate, dicalcium silicate, tricalcium aluminate, and bismuth oxide (radiopacifier).
   • Mechanism: In the presence of tissue moisture, MTA hydrates to form calcium silicate hydrate gel and calcium hydroxide. It maintains a sustained alkaline pH (12.5), exhibits excellent biocompatibility, and provides an impermeable marginal seal. It induces thick, continuous dentine bridges entirely free of tunnel defects.
   • Limitations: Prolonged setting time (2 to 4 hours for traditional formulations), difficult handling characteristics, and potential grey-black discoloration of the tooth crown caused by oxidation of the bismuth oxide radiopacifier in the presence of sodium hypochlorite and dentine collagen.

3. Biodentine (Active Biosilicate Technology):

   • Composition: Powder consists of high-purity tricalcium silicate, calcium carbonate (filler), and zirconium oxide (non-staining radiopacifier); liquid contains calcium chloride (setting accelerator) and a water-soluble polymer.
   • Advantages: Solves the primary clinical flaws of MTA. It achieves a rapid initial set in 10 to 12 minutes, allowing one-visit definitive restorative placement. It exhibits compressive strength and elastic modulus matching natural dentine ($220\text{ MPa}$), releases large quantities of calcium and hydroxyl ions, induces rapid TGF-$\beta1$ mediated dentinogenesis, and causes zero tooth discoloration.

When Not to Cap

The examinable limits of pulp capping are as important as the technique. Direct pulp capping is appropriate for a small, traumatic or carious exposure in a tooth with a normal pulp or reversible pulpitis, where haemostasis is achieved within a few minutes under rubber dam. It is inappropriate where there is a history of spontaneous or lingering pain indicating irreversible pulpitis, where bleeding is profuse or cannot be controlled, where the exposure is large, where the tooth cannot be adequately isolated, or where there is radiographic periapical change. Attempting to cap an irreversibly inflamed pulp merely delays definitive treatment and is a reliable wrong answer.