Correlative Micro-CT and Histologic Analysis of Newly Formed Reparative Dentin

Objectives: Successful pulp capping results in the formation of a homogenous, thick and continuous mineralized dentin bridge. Due to its potential to detect radiodensity changes non-destructively in 3D, micro-CT has widely been used to calculate the thickness/volume of newly formed mineralized tissue in animal models. We aimed to evaluate the applicability of micro-CT to assess the maturing stages of dentin-bridge formation as compared with standard histologic assessment.

Methods: Forty-six teeth from three minipigs were mechanically exposed and capped with five different pulp-capping materials: Exp. PPL (GC), Exp. TCS 50 (BIOMAT), Biodentine (Septodont), ProRoot MTA (Dentsply Sirona) and TheraCal LC (Bisco). Half of the teeth were scheduled for 7-day and the other half for 70-day evaluation. After sacrifice, the teeth were scanned using micro-CT and assessed histologically. The mineralization of the hyperdense zone beneath the exposure site was evaluated in 3D by micro-CT and compared to the corresponding histological sections.

Results: Hard-tissue barriers, varying in thickness between 200 and 750 µm, were formed beneath the exposure sites in the micro-CT scans and were confirmed as mineralized tissue upon evaluating the corresponding histologic sections for all 70-day specimens. Initial dentin-bridge formation was recorded by micro-CT for only 63.0% of the teeth at 7 days after pulp-capping. All the hyperdense layers beneath the exposure sites, which appeared indicative of reparative dentin formation at 7 days, were not confirmed by the corresponding histology; these zones presented with pulp tissue rich in cells, collagen fibers, and capillaries. The teeth that exhibited no obvious change in radiodensity at 7 days histologically disclosed a normal pulp-tissue morphology.

Conclusions: These results prove that micro-CT is applicable to evaluate dentin-bridge formation at the later stage of 70 days after pulp-capping, but not for the early stages of pulpal repair at 7 days, when histology remains the standard evaluation methodology.