22.1 Minimal Intervention and Selective Caries Removal

Principles of Minimally Invasive Dentistry (MID)

Minimally Invasive Dentistry (MID) is a systematic approach to patient care that recognizes caries as a biological disease process rather than a mechanical defect requiring restorative surgery. Its foundational pillars comprise:

                             Pillars of Minimally Invasive Dentistry
                                               │
      ┌──────────────────┬─────────────────────┴─────────────────────┬──────────────────┐
      ▼                  ▼                                           ▼                  ▼
Early Detection      Risk Modification                           Hard Tissue         Repair Over
& Biofilm Control    • Diet advice                               Preservation        Replacement
• ICDAS scoring      • Fluoride varnish                          • Selective carious • Refurbishment
• Remineralisation   • 2800/5000 ppm fluoride                           tissue removal    • Re-sealing
• Saliva testing     • Chlorhexidine                             • Adhesive preps    • Localised repair

1. Early Diagnosis & Lesion Arrest: Identifying lesions at the non-cavitated stage (ICDAS 1 and 2) to permit non-operative remineralisation via fluoride and biofilm disruption.
2. Preservation of Sound Dental Hard Tissue: Operative intervention is reserved strictly for cavitated lesions that cannot be cleaned by the patient. Cavity preparation boundaries are dictated solely by the extent of the pathology, not by geometric rules of mechanical retention.
3. Repair Rather Than Replacement: When an existing restoration develops secondary margin ditching or minor recurrent caries, localized repair, resealing, or refurbishment is preferred over complete restoration removal, preventing the restorative death spiral of progressively larger cavities.

Carious Tissue Removal Concepts: Contemporary Evidence

Historically, complete excavation ("non-selective removal to hard dentine") was mandated under the mistaken belief that leaving any softened or discoloured dentine would allow residual bacteria to propagate caries beneath the restoration. Contemporary microbiological evidence has overturned this: bacteria trapped beneath a hermetically sealed adhesive restoration become dormant or die, halting lesion progression.

                               Carious Tissue Removal Protocols
                                               │
      ┌────────────────────────────────────────┼────────────────────────────────────────┐
      ▼                                        ▼                                        ▼
Non-Selective Removal                 Selective to Firm Dentine                 Selective to Soft Dentine
(Complete Excavation)                 (Shallow / Moderate Lesions)              (Deep Lesions: Inner 1/3)
• Excavated to hard dentine           • Periphery: hard dentine                 • Periphery: hard dentine (360°)
• Severe pulp exposure risk           • Pulpal floor: firm / leathery           • Pulpal floor: soft dentine preserved
• Outdated in deep lesions            • Tactile: scratchy, stiff                • Preserves vital pulp; ↓ exposure 77%

1. Non-Selective Removal to Hard Dentine (Complete Excavation)

• Technique: All soft, demineralised, and discoloured dentine is excavated until only hard dentine remains across the entire cavity floor and axial walls, exhibiting a sharp "scratching" sound when probed with a dental explorer.
• Status: Contraindicated in deep carious lesions. Cochrane systematic reviews confirm that non-selective complete excavation in deep lesions leads to an unacceptable rate of iatrogenic pulpal exposure, dramatically increasing the need for endodontic therapy or extraction.

2. Selective Removal to Firm Dentine (Shallow or Moderate Lesions)

• Indications: Lesions extending radiographically into the outer or middle third of dentine (ICDAS 3–4).
• Technique: The cavity margins and peripheral walls are excavated to hard sound dentine. Over the pulpal floor, excavation ceases when firm dentine is reached—dentine that offers physical resistance to a hand excavator and feels physically leathery or firm upon probing.

3. Selective Removal to Soft Dentine (Deep Lesions / One-Step Indirect Pulp Therapy)

• Indications: Deep carious lesions radiographically extending into the inner third or quarter of dentine, presenting with a vital, asymptomatic pulp or a diagnosis of reversible pulpitis.
• Technique:
  • Peripheral Cavity Preparation: The outer enamel margins and peripheral dentinal walls (at least 1.5–2.0 mm wide circumferential zone) are excavated completely to hard, sound dentine.
  • Pulpal Floor Preservation: Soft, demineralised, carious dentine is deliberately left in place directly over the pulp chamber roof to prevent mechanical pulpal exposure.
  • Hermetic Seal: An adhesive restoration (or biomaterial liner covered by composite/GIC) is placed to establish an immediate, impervious peripheral seal.
• Evidence: Clinical trials (Schwendicke et al., 2016) demonstrate that selective removal to soft dentine reduces the risk of pulpal exposure by ~77% and yields significantly higher pulpal survival rates than non-selective excavation.

4. Stepwise Excavation Technique

• Protocol: A two-stage procedure performed in deep lesions:
  1. First Visit: Selective excavation leaves soft, infected/affected dentine over the pulp floor. A provisional calcium hydroxide or high-viscosity GIC restoration is placed for 6 to 12 months to allow the pulp to form tertiary dentine and promote tubular sclerosis.
  2. Second Visit: The cavity is re-entered, the temporary restoration is removed, and residual dentine is excavated down to firm/hard dentine before final restoration.
• Modern Appraisal: While effective, contemporary European and British endodontic and restorative consensus panels now prefer one-step selective removal to soft dentine over stepwise excavation. Re-entering the cavity at the second visit introduces unnecessary patient discomfort, costs, and a substantial secondary risk of pulpal exposure.

Sealing Rather Than Chasing Caries

The evidence base that underpins selective removal is that caries arrests when it is sealed from the oral environment. Studies of sealed lesions, of the Hall technique and of stepwise excavation consistently show that residual bacteria beneath a well-sealed restoration become non-viable or inactive, and that the pulp lays down reactionary dentine. This is why the quality of the peripheral seal, not the completeness of dentine removal, is the determinant of success, and why the periphery of the cavity is always taken back to hard, sound dentine and enamel even when soft dentine is deliberately left over the pulp.