24.9 Periodontal Instrumentation and Healing

2. Periodontal Instrumentation: Ultrasonic vs Hand Debridement

High-quality clinical trials confirm that ultrasonic instrumentation and hand instrumentation achieve equivalent clinical outcomes regarding probing depth reduction, attachment gain, and subgingival microbial reduction. In practice, clinicians frequently combine both modalities.

Ultrasonic Biomechanics: Magnetostrictive vs Piezoelectric

1. Magnetostrictive Units (Cavitron):
   • Frequency: $20,000-42,000\text{ Hz}$ (cycles per second).
   • Transducer: Ferromagnetic metal stack or ferrite rod expanding and contracting within an alternating electromagnetic field.
   • Stroke Motion: Elliptical (figure-of-eight) stroke pattern. Consequently, all surfaces of the tip (point, concave face, convex back, and lateral edges) are active and emit energy.
   • Heat Generation: High; requires continuous internal water flow for cooling.
2. Piezoelectric Units:
   • Frequency: $25,000-50,000\text{ Hz}$.
   • Transducer: Ceramic crystal disks expanding and contracting in response to alternating electric currents.
   • Stroke Motion: Linear (back-and-forth) reciprocating stroke pattern. Consequently, only the two lateral surfaces of the tip are active and safe to apply against the root surface.
   • Heat Generation: Moderate; water coolant is required primarily for flushing and cavitation.
3. Cavitation and Acoustic Microstreaming:
   • Cavitation: High-frequency tip vibrations generate localized areas of intense negative pressure within the water coolant, creating millions of sub-microscopic vapour bubbles. When these microbubbles enter high-pressure zones, they violently implode, releasing localized acoustic shockwaves that rupture bacterial cell walls and lyse endotoxins.
   • Acoustic Microstreaming: Vigorous hydrodynamic fluid currents and shear stresses generated around the vibrating tip strip away subgingival biofilm matrices from root concavities beyond the physical reach of the metal tip.

Hand Instrumentation: Site-Specific Gracey Curettes

Unlike universal curettes (which possess a $90^\circ$ blade angle with two cutting edges per end), Gracey curettes are site-specific and feature an offset blade angle of $70^\circ$ relative to the lower terminal shank. This design means that only one cutting edge—the lower, longer, outer convex edge—is the active working cutting edge.

Gracey Curette Cross-Section (Offset Blade Design)

          Upper Shank
               │
               ▼
         ┌───────────┐
         │           │
         └─────┬─────┘
               │
               ▼ Lower (Terminal) Shank
               │
               ├───┐  70° Offset Face Angle
               │   │
  Non-working  │   └───┐
  Cutting Edge └───┐   │  WORKING CUTTING EDGE
                   │   │  (Lower, longer, outer convex margin)
                   └───┘

Gracey Curette Allocations Across the Dentition
  ├── Gracey 1/2 & 3/4   ──> Anterior Teeth (Incisors and Canines - all surfaces)
  ├── Gracey 5/6         ──> Anterior Teeth and Premolars
  ├── Gracey 7/8 & 9/10  ──> Posterior Teeth: Buccal and Lingual / Palatal surfaces
  ├── Gracey 11/12       ──> Posterior Teeth: MESIAL surfaces only
  ├── Gracey 13/14       ──> Posterior Teeth: DISTAL surfaces only
  ├── Gracey 15/16       ──> Posterior MESIAL surfaces (Acute shank bend modification of 11/12)
  └── Gracey 17/18       ──> Posterior DISTAL surfaces (Exaggerated shank bend modification of 13/14)

• Operator Technique: When the Gracey lower terminal shank is aligned parallel to the long axis of the root surface, the working cutting edge automatically engages the tooth at the ideal working angle of $70^\circ$, eliminating the risk of soft tissue gouging.

---

3. Periodontal Wound Healing and Dentine Hypersensitivity

Histology of Periodontal Healing Following Debridement

A foundational concept in periodontology is that non-surgical mechanical debridement results in repair, not true anatomical regeneration:

1. Long Junctional Epithelium (LJE): Fast-proliferating oral epithelial basal cells migrate down the debrided root surface at a rate of $0.5-1.0\text{ mm/day}$. By 7 to 14 days, they form a thin, elongated Long Junctional Epithelium (LJE) attached to the root surface via hemidesmosomes. True new connective tissue attachment (new cementum with inserting collagen Sharpey's fibres) and new alveolar bone formation do not occur following non-surgical RSD.
2. Mechanisms of Probing Depth Reduction: Pocket reduction occurs via two primary biological mechanisms:
   • Gingival Margin Recession (Soft Tissue Shrinkage): Accounts for approximately $1-2\text{ mm}$ of pocket reduction as oedema, vascular congestion, and inflammatory infiltrate subside.
   • Gain in Clinical Attachment / Probing Resistance: As the dense collagen network matures within the subepithelial connective tissue corium, it increases tissue tone. During post-treatment probing, the probe tip stops coronally at the repaired tissue interface rather than piercing through inflamed connective tissue.

Dentine Hypersensitivity: Brännström's Hydrodynamic Theory

Following successful subgingival instrumentation, soft tissue recession exposes root dentine, often inducing acute, sharp dentine hypersensitivity.

• Hydrodynamic Mechanism (Brännström): Physical, thermal, or evaporative stimuli (cold water, air blast, tactile contact, sweet/sour food) cause rapid displacement and fluid flow within open dentinal tubules. This fluid shift deforms sensory mechanoreceptors on intradental nerve endings (A-beta and A-delta myelinated nerve fibres) situated in the pulpal horn, transmitting sharp, localized pain.
• Management Strategies:
  • Tubule Occlusion (Physical Barriers): Professional application of sodium fluoride varnish (22,600 ppm fluoride), stannous fluoride, silver diamine fluoride (SDF), arginine-calcium carbonate pastes, or bonding resins to seal patent dentinal tubule orifices.
  • Nerve Depolarisation: Potassium salts (potassium nitrate, potassium chloride) contained in desensitizing toothpastes diffuse down tubules to elevate extracellular potassium concentration, depolarizing sensory nerve axolemmas and preventing action potential propagation.

---

Instrumentation and Systemic Considerations

Ultrasonic scalers generate aerosol, which matters for infection control, and they are contraindicated or used with caution in patients with an unshielded pacemaker or implantable cardioverter defibrillator where the manufacturer advises it, in patients at risk of aspiration, and around titanium implant surfaces, where specific tips are required. Air-polishing with glycine or erythritol powder is preferred to sodium bicarbonate for subgingival use, and air-polishing is avoided in patients on a sodium-restricted diet when sodium-containing powders are used.