Powered Instrumentation & Preventive Agents

6.2 Powered Instrumentation & Preventive Agents

Ultrasonic Scalers: Types and Mechanisms

Ultrasonic scaling uses high-frequency sound waves to remove calculus, plaque, and stain. There are two primary types of ultrasonic scalers: magnetostrictive and piezoelectric.

Magnetostrictive vs. Piezoelectric Units

• Magnetostrictive Scalers (e.g., Cavitron):
  • Frequency: Operates at 25,000 Hz (25K) or 30,000 Hz (30K) cycles per second.
  • Transducer: Uses a stack of metal strips (nickel-alloy) that expands and contracts in an electromagnetic field.
  • Tip Motion: Moves in an elliptical (circular or oval) pattern.
  • Active Surfaces: All surfaces of the tip are active: the point (most powerful), the concave face, the convex back, and the lateral sides. The point must never be directed against the tooth surface to prevent damage.
• Piezoelectric Scalers:
  • Frequency: Operates at 28,000 Hz to 50,000 Hz.
  • Transducer: Uses ceramic crystals that expand and contract when electrical current is applied.
  • Tip Motion: Moves in a linear (back-and-forth) pattern.
  • Active Surfaces: Only the lateral sides of the tip are active. Placing the point or the back/face against the tooth will not remove calculus and can cause heat build-up or gouging.

Mechanisms of Action

Ultrasonic scalers rely on three mechanical and biophysical effects for debridement:

1. Cavitation: The rapid vibration of the tip creates tiny bubbles in the water stream. As these bubbles collapse (implode), they release shockwaves that rupture bacterial cell walls (lysis).
2. Acoustic Turbulence (Microstreaming): The swirling motion of fluid generated around the vibrating tip disrupts subgingival biofilm and washes away debris.
3. Fluid Lavage: A continuous stream of water cools the handpiece and flushes the periodontal pocket of blood, calculus, and loose plaque, enhancing clinical visibility.

Note: Power settings on ultrasonic units adjust the amplitude (stroke length or how far the tip moves), not the frequency (how fast the tip vibrates).

---

Indications and Contraindications

While highly efficient, powered instrumentation is not suitable for all patients.

Indications

• Removal of moderate to heavy calculus deposits.
• Disruption of subgingival biofilm in deep pockets.
• Debridement of necrotizing ulcerative gingivitis (NUG) lesions.
• Irrigation of pockets with chemotherapeutic agents.

Contraindications and Precautions

• Cardiac Pacemakers: Older, unshielded pacemakers can experience electromagnetic interference from magnetostrictive units. Piezoelectric units do not generate a magnetic field and are generally safe. However, manual scaling or consulting the patient's cardiologist is the safest approach.
• Aerosol-Transmitted Diseases: Active tuberculosis, respiratory infections, severe asthma, or COPD. The high aerosol production can transmit pathogens or compromise the patient's breathing.
• Dysphagia: Swallowing disorders or a history of aspiration increase the risk of inhaling lavage fluid.
• Demineralized Enamel: Ultrasonic tips can easily remove thin, demineralized enamel.
• Dental Implants: Metal tips scratch titanium implant abutments, promoting plaque accumulation. Clinicians must use plastic, carbon, or Teflon-coated tips.
• Newly Erupting Teeth: Large pulp chambers are highly sensitive to the heat and vibrations of ultrasonic tips.

---

Selective Polishing

Polishing should be performed selectively, meaning only on teeth with extrinsic stains that cannot be removed by scaling.

• Contraindications: Areas of demineralization, newly erupted teeth (enamel is not fully mineralized), exposed cementum or dentin, inflamed gingival tissues, and restorative materials (porcelain, composite) unless using a highly specialized, low-abrasive paste.
• Technique: Use light pressure, a slow-speed handpiece, and a wet, low-abrasive paste.

---

Fluoride Agents and Toxicology

Topical fluorides prevent dental caries by promoting remineralization, inhibiting demineralization, and reducing bacterial acid production.

Professional Fluoride Applications

1. 5.0% Sodium Fluoride (NaF) Varnish: Contains 22,600 ppm fluoride. It is the gold standard for pediatric and adult patients due to its ease of application, high compliance, and slow release of fluoride, which minimizes the risk of ingestion.
2. 1.23% Acidulated Phosphate Fluoride (APF) Gel/Foam: Contains 12,300 ppm fluoride. The acidic pH (~3.5) enhances fluoride uptake. Contraindication: The acid etches the glass filler in porcelain, composite, and titanium restorations, making NaF a safer option for these patients.
3. 2.0% Sodium Fluoride (NaF) Gel/Foam: Contains 9,040 ppm fluoride. It has a neutral pH (7.0) and is safe for all restorations.

Fluoride Toxicology

• Toxic Dose (TD): 5 mg F/kg body weight. This is the minimum threshold that can cause acute toxicity.
• Safely Tolerated Dose (STD): One-fourth of the CLD (approximately 8 to 16 mg F/kg).
• Certainly Lethal Dose (CLD): 32 to 64 mg F/kg for adults; 15 mg F/kg for children.
• Symptoms of Acute Toxicity: Nausea, vomiting, abdominal pain, diarrhea, hypersalivation, and hypocalcemia (fluoride binds to calcium). Severe hypocalcemia leads to muscle spasms, convulsions, cardiac arrhythmias, and cardiac arrest.
• Emergency Management:
  • Ingestion < 5 mg/kg: Administer calcium-binding agents (milk, calcium carbonate, lime water) and monitor.
  • Ingestion 5 to 15 mg/kg: Induce vomiting (using ipecac syrup), administer calcium/milk, and transport to the hospital.
  • Ingestion > 15 mg/kg: Immediate transport to the emergency room, cardiac monitoring, gastric lavage, and IV calcium gluconate.

---

Pit and Fissure Sealants

Sealants act as a physical barrier to prevent caries in the deep pits and fissures of occlusal surfaces.

1. Acid Etching: The tooth is cleaned and dried, then etched with 35% to 37% phosphoric acid for 15 to 20 seconds.
2. Rinsing and Drying: Rinse the etchant for 10-15 seconds. Dry the tooth completely. The etched enamel must appear chalky and frosted-white. If it is contaminated by saliva, it must be re-etched for 10 seconds.
3. Application and Curing: Paint the sealant material into the pits and fissures, avoiding overfilling. Light cure the material for 20 to 40 seconds.
4. Occlusal Assessment: Check retention with an explorer. Check the occlusion with articulating paper. High spots must be adjusted to prevent temporomandibular discomfort or sealant fracture.