Do direct pulp caps and indirect pulp caps induce reactionary or reparative dentine, and are there visible clinical differences between the two types of tertiary dentine?

Tertiary Dentine Formation in Pulp Capping Procedures

Indirect pulp capping induces reactionary dentine formation by stimulating existing odontoblasts, while direct pulp capping typically produces reparative dentine (or more accurately, calcified scar tissue) through fibroblast activity rather than true odontoblast differentiation. 1

Types of Tertiary Dentine and Their Formation Mechanisms

Reactionary Dentine (Indirect Pulp Capping)

• Reactionary dentine is secreted by surviving primary odontoblasts in response to irritation when the pulp remains unexposed 1
• This occurs in indirect pulp capping procedures where dentin exposure exists but pulp tissue remains covered 2
• The newly formed dentine contains sparsely distributed, irregularly arranged dentinal tubules that are continuous with secondary dentine tubules 1
• Indirect pulp capping demonstrates a 93.8% success rate in maintaining pulp vitality over 10 years 3

Reparative Dentine (Direct Pulp Capping)

• Reparative dentine forms after primary odontoblast death through proliferation of progenitor cells into odontoblast-like cells 1
• However, histological evidence reveals this is not true dentine regeneration but rather a repair response producing calcified scar tissue 1
• Direct pulp capping procedures show only a 23.8% success rate compared to indirect capping 3
• The tissue formed is amorphous, dystrophic, and atubular—resembling pulp stones more than genuine dentine 1
• This calcified tissue is lined by fibroblasts and collagen fibrils, not odontoblasts, and sometimes entraps pulpal remnants 1

Clinical Differences Between Reactionary and Reparative Dentine

Histological Features

• Reactionary dentine maintains tubular structure (though irregular and sparse) with continuity to existing dentine 1, 2
• Reparative dentine lacks tubular features characteristic of genuine dentine and appears as dystrophic calcification 1
• In reactionary dentine formation, dentinal tubules beneath original dentin become occluded by peritubular dentin deposition, which helps reduce hypersensitivity 2

Cellular Architecture

• Reactionary dentine shows a reduced but present odontoblast layer (flattened to single cell layer) 1
• Reparative dentine demonstrates fibroblast lining rather than odontoblast palisading 1

Clinical Visibility and Detection

• No reliable clinical method exists to distinguish between reactionary and reparative dentine without histological examination 1
• Radiographically, both appear as increased radiopacity beneath restorations, but histology is required for definitive differentiation 1
• The absence of tubular features in reparative dentine cannot be determined clinically—only through microscopic examination 1

Factors Affecting Tertiary Dentine Formation Success

For Direct Pulp Capping

• Area of pulp exposure significantly correlates with pulp necrosis (p = 0.035)—larger exposures have worse outcomes 3
• Patient age significantly affects pulp vitality maintenance (p = 0.013)—younger patients fare better 3
• Choice of pulp-capping material matters (p = 0.017), with MTA showing better outcomes than resin-based materials 3
• Bleeding after exposure appears independent of outcome (p = 0.053) 3

For Indirect Pulp Capping

• Patient age correlates with success (p = 0.021) 3
• Etch-and-rinse adhesive systems outperform self-etch systems (p = 0.019) 3
• The procedure preserves existing odontoblasts, allowing physiologic reactionary dentine formation 2

Clinical Implications and Pitfalls

Key Clinical Considerations

• Indirect pulp capping should be strongly preferred over direct pulp capping when clinically feasible, given the 93.8% vs 23.8% success rates 3
• The term "reparative dentinogenesis" is clinically misleading—it represents scar tissue formation, not true dentine regeneration 1
• Clinical success (reduced sensitivity, healing) does not equal histological regeneration of physiological dentine 1

Common Pitfalls

• Assuming that hard tissue formation after direct pulp capping represents true dentine regeneration—it does not 1
• Performing direct pulp capping on large exposures—exposure size directly correlates with failure 3
• Using self-etch adhesives for indirect pulp capping—etch-and-rinse systems perform significantly better 3
• Expecting tubular dentine formation after direct pulp capping—histologic evidence for this in human teeth is lacking 1