19.4 Dentin Hypersensitivity & Desensitizing Agents

19.4 Dentin Hypersensitivity & Desensitizing Agents

Quick Answer: Dentin hypersensitivity is short, sharp pain from exposed dentin in response to stimuli such as cold, air, touch or sweet or acidic foods. It is diagnosed only after the dentist rules out other causes such as caries, a cracked tooth or a leaking restoration. The accepted explanation is the hydrodynamic theory: a stimulus moves fluid in open dentinal tubules, and this movement activates nerve endings at the pulp. Desensitizing agents work in two ways:

• Nerve desensitization: potassium nitrate reduces the excitability of the nerve.
• Tubule occlusion: fluoride varnish, stannous fluoride, oxalates, arginine-calcium carbonate, calcium phosphate products, glutaraldehyde-based agents, and resin sealers or bonding agents block the tubules.

The assistant records a baseline sensitivity score, applies the prescribed agent according to the manufacturer's directions, re-tests with the same stimulus, records the result and gives home-care instructions (7.6.1–7.6.6).

1. Why Dentin Becomes Sensitive

Dentin is exposed when:

• Gingival recession exposes the root. Causes include vigorous horizontal brushing with a hard brush, periodontal disease and its treatment, orthodontic movement, a thin gingival biotype and frenum pull. Cementum on the exposed root is thin and is easily removed.
• Enamel is lost:
  • erosion from acidic drinks and foods, gastric reflux or vomiting
  • abrasion from brushing with abrasive toothpaste
  • attrition from grinding
  • abfraction (cervical lesions related to biting forces).

The hydrodynamic theory (Brännström): hypersensitive dentin has many open, wide tubules. Cold, air, sweet or acidic stimuli and touch move the fluid in the tubules. The movement stimulates A-delta nerve fibres near the pulp and produces brief, sharp, well-localized pain that stops when the stimulus is removed. Heat and lingering pain point to pulpal disease instead, and must be reported to the dentist.

Other times sensitivity occurs: after scaling and root planing, after periodontal surgery, and during or after tooth whitening (section 10.5).

2. Desensitizing Agents and How They Work (7.6.2)

Treatment usually starts with the simplest measures (home-care changes and a desensitizing toothpaste). In-office agents follow if needed. Severe or persistent cases may need restorations or a gingival graft (section 13.3).

3. Indications and Contraindications (7.6.1)

Indications: sensitivity diagnosed as dentin hypersensitivity, sensitivity after periodontal therapy, and sensitivity related to whitening.

Contraindications and cautions:

• Pain from another cause: caries, a cracked tooth, a fractured or leaking restoration, or pulpitis. These need dental treatment, not desensitizer.
• Allergy to an ingredient, for example colophony (rosin) in some fluoride varnishes, glutaraldehyde, methacrylates (HEMA), or milk protein (CPP-ACP).
• Ulcerated or inflamed tissue in the application area, for products whose instructions list this as a contraindication.

4. Procedure (7.6.3–7.6.5)

1. Confirm the prescription, the teeth and surfaces to be treated, and the product. Review the health history for allergies.
2. Baseline assessment:
   • Shield the adjacent teeth with your fingers or cotton rolls.
   • Direct a short blast of air (about 1 second) from the air-water syringe at the exposed surface, or use a gentle tactile stroke with an explorer.
   • Ask the patient to rate the discomfort, for example on a 0 to 10 scale, and record it.
3. Prepare the surface: remove biofilm and debris as the product instructions direct (for example, brushing or a non-fluoride, non-abrasive cleaning). Rinse. Isolate with cotton rolls and an evacuator.
4. Dry the surface as the product directs (some products need a dry surface; some tolerate moisture).
5. Apply a thin layer with a microbrush or applicator to the prescribed surfaces only. Leave it for the time stated by the manufacturer, then rinse, air-dry or leave it in place, as directed.
6. Re-evaluate with the same stimulus used at baseline. Record the new score.
7. Evaluate against criteria:
   • all prescribed surfaces were covered
   • excess material and soft-tissue contact were avoided or removed
   • the sensitivity score was reduced. If the response is poor, re-apply only if the instructions allow it, or inform the dentist.
8. Record:
   • the agent and its lot or batch number if office policy requires it
   • the teeth and surfaces
   • the baseline and post-treatment scores
   • any reaction
   • the instructions given.

5. Patient Instructions (7.6.6)

• After fluoride varnish:
  • Avoid hot drinks, sticky or hard foods and alcohol-containing rinses for the time the product specifies.
  • Do not brush or floss until the next day or after the stated number of hours.
• Desensitizing toothpaste:
  • Use it twice a day and do not rinse heavily afterward, so the active ingredients stay on the teeth.
  • Improvement builds over several weeks.
  • Some patients smear a little on sensitive areas at bedtime.
• Prevent further loss of tooth structure:
  • Use a soft toothbrush with gentle pressure.
  • Avoid very abrasive (some whitening) toothpastes.
  • Limit acidic foods and drinks, and drink acidic beverages with meals or through a straw.
  • Wait before brushing after acid exposure or vomiting; rinse with water first.
  • Ask the dentist about treating grinding or reflux.
• Report sensitivity that lingers, wakes the patient at night, or is triggered by heat or biting. These may point to pulpal disease or a cracked tooth.