23.8 Medicaments, Obturation Materials and Techniques

Intracanal Medicaments

When endodontic treatment cannot be completed in a single visit, an intracanal medicament is placed to maintain disinfection and suppress microbial regrowth.

Calcium Hydroxide ($\text{Ca(OH)}_2$)

• Properties: White, odourless powder mixed into a non-setting aqueous paste (e.g., Hypocal, Ultracal).
• Mechanism: Sustained dissociation into calcium ($\text{Ca}^{2+}$) and hydroxyl ($\text{OH}^-$) ions generates an intensely alkaline environment (pH ~12.5). Hydroxyl ions:
  1. Damage bacterial cytoplasmic membranes through lipid peroxidation;
  2. Denature structural proteins and metabolic enzymes;
  3. Inactivate and hydrolyze bacterial lipopolysaccharide (LPS / endotoxin), neutralizing its periapical osteoclast-stimulating toxicity;
  4. Aid in the dissolution of residual necrotic tissue remnants.
• Duration: Requires a minimum of 7 to 14 days inside the canal to penetrate the full thickness of dentinal tubules and overcome dentine's natural buffering capacity.
• Contraindication: Never seal calcium hydroxide into an actively exuding canal or acute apical abscess without first achieving dry canal drainage.

Ledermix & Odontopaste

• Formulation:
  • Ledermix: Corticosteroid (triamcinolone acetonide 1%) + Tetracycline antibiotic (demeclocycline calcium 3.21%). Demeclocycline can cause severe gray-brown tooth discolouration if exposed to sunlight; must be kept below the amelocemental junction (ACJ).
  • Odontopaste: Corticosteroid (triamcinolone acetonide 1%) + Lincosamide antibiotic (clindamycin hydrochloride 5%) + calcium hydroxide; does not cause cosmetic crown staining.
• Indication: Specifically indicated as an emergency dressing in cases of acute symptomatic irreversible pulpitis when time constraints prevent complete chemomechanical instrumentation. The corticosteroid rapidly diffuses across dentinal tubules and apical tissues, downregulating phospholipase A2 and cyclooxygenase enzymes, curbing prostaglandin synthesis and providing dramatic pain relief.

Criteria for Obturation

Obturation seals the shaped and disinfected root canal space, preventing coronal microleakage, entombing residual microorganisms, and eliminating dead spaces that could harbour periapical exudate.

Obturation must only proceed when the following clinical criteria are met:

• Asymptomatic Tooth: The patient must be free of spontaneous pain, with no significant tenderness to mechanical percussion or apical palpation.
• Dry Canal: The canal must be completely dry upon paper point insertion. Persistent weeping of clear inflammatory serous exudate, purulent discharge, or persistent apical haemorrhage indicates active periapical inflammation, precluding obturation.
• Absence of Swelling or Active Sinus Tract: Soft tissues must be completely non-swollen, and any pre-existing sinus tract should show evidence of healing or closure.
• Intact Coronal Seal & Isolation: The treatment field must remain strictly isolated with rubber dam, with no saliva contamination.

Core Obturation Materials: Gutta-Percha

Gutta-percha (GP) is the standard core filling material. Chemically, it is the trans-isomer of polyisoprene ($1,4\text{-polyisoprene}$), contrasting with natural rubber (which is the cis-isomer).

Crystalline Phases of Gutta-Percha

Gutta-percha exhibits two distinct crystalline forms depending on temperature:

1. Beta (β) Phase:
   • The unheated, solid crystalline state present at room temperature (below 42°C).
   • In this phase, GP is firm, compactable, and possesses dimensional stability.
   • Master cones used in cold lateral compaction are manufactured in the β-phase.
2. Alpha (α) Phase:
   • When heated between 42°C and 49°C, GP undergoes an endothermic phase transition into the α-phase.
   • In this phase, GP becomes soft, pliable, amorphous, tacky, and flows under light hydraulic pressure.
   • Utilized in thermoplasticized warm vertical compaction and injectable backfill systems.
   • Physical Property: Upon cooling, α-phase GP shrinks by 1% to 2% as it recrystallizes into the β-phase; warm compaction techniques require continuous vertical pressure during cooling to compensate for this thermal contraction.

Composition of Clinical Gutta-Percha Cones

Standard commercial gutta-percha cones contain:

• Zinc Oxide (Filler): ~60% – 65% (provides stiffness and antibacterial activity).
• Gutta-Percha (Organic Matrix): ~19% – 22% (provides plasticity and core substance).
• Heavy Metal Sulfates (Barium sulfate, Bismuth subcarbonate): ~10% – 15% (radiopacifiers).
• Waxes and Resins (Plasticizers): ~1% – 4% (impart pliability and flow properties).

Endodontic Sealers

Gutta-percha does not adhere to dentine walls. An endodontic sealer is mandatory to fill the microscopic interface, seal dentinal tubule apertures, fill lateral canals, and act as a fluid-tight adhesive barrier.

[!NOTE] Bioceramic Sealer Setting Reaction: Tricalcium silicate ($\text{C}_3\text{S}$) reacts with dentinal moisture to produce a calcium silicate hydrate ($\text{C-S-H}$) gel and calcium hydroxide ($\text{Ca(OH)}_2$). The released $\text{Ca(OH)}_2$ precipitates with tissue phosphate ions to form hydroxyapatite crystals along the dentine-sealer interface, creating a chemical "mineral infiltration zone" with micromechanical tag formation.

Obturation Techniques

1. Cold Lateral Compaction:
   • Technique: A master gutta-percha cone matching the Master Apical File (MAF) size and taper is fitted to full working length, confirming tactile resistance to displacement (tug-back). Sealer is introduced into the canal. The master cone is inserted. A hand or finger spreader is inserted alongside the master cone to within 1.0–2.0 mm of WL, compressing the cone laterally against the wall. The spreader is rotated and removed, and accessory gutta-percha cones are sequentially placed into the void created until the spreader cannot penetrate beyond the coronal third.
   • Evaluation: Simple, predictable length control. However, it produces a non-homogeneous mass of cones held by sealer lakes, does not replicate complex canal irregularities or C-shaped fins, and hand spreaders generate high wedge-like lateral stresses predisposing to vertical root fracture (VRF). Finger spreaders reduce this risk.
2. Warm Vertical Compaction (Continuous Wave of Condensation, e.g., System B):
   • Technique: A non-standardized tapered master cone is trimmed 0.5 mm short of WL to achieve apical tug-back. Coated with sealer. An electric heat plugger activated to 200°C is advanced rapidly through the master cone to a binding point 3.0 to 5.0 mm short of WL, searing off coronal GP (downpack). Firm vertical pressure is maintained on the apical plug with a hand plugger as it cools to compensate for thermal shrinkage. The remaining canal space is then backfilled with thermoplasticized α-phase GP from an extruder gun (backfill) in increments.
   • Evaluation: Produces a dense, homogeneous 3D obturation replicating lateral canals, isthmuses, and apical deltas. Requires careful temperature control to avoid PDL overheating (>10°C rise damages bone).
3. Carrier-Based Obturation (Thermafil / GuttaCore):
   • Utilizes a plastic or cross-linked gutta-percha core carrier coated with α-phase gutta-percha, heated in a dedicated oven and inserted in a single movement to WL. Excellent flow into lateral anatomy, but prone to stripping of GP at the apex during placement, extrusion beyond foramen, and difficulty during post-space preparation or retreatment.