Histological evaluation of the regenerative potential of injectable hyaluronic acid hydrogel or collagen with blood clot as scaffolds during revascularization of immature necrotic dog's teeth

Abstract

Background: Regenerative endodontics' primary objective is to establish a favorable environment in the root canal by removing infection, providing a sturdy scaffold, and sealing the apical end of the tooth tightly. These actions should promote pulp regeneration and root development.

Aim: This study evaluated histologically the regenerative potential of injectable hyaluronic acid (HA) hydrogel or collagen with blood clot as scaffolds during revascularization of immature necrotic dog's teeth.

Methods: Sixteen permanent immature necrotic premolars with 32 roots were chosen from two 4-5-month-old mongrel dogs. Out of the 32 roots, 24 roots were sealed for 2 weeks after being cleaned with CaOH₂. According to the treatment protocol, the 24 cleaned roots were randomly assigned to one of three treatment groups (each with 8 roots): blood clot + HA group, blood clot + collagen group, and blood clot group. The control group consisted of the eight infected roots that remained untreated. Three months after the surgery, the assessment of tissue ingrowth in the pulp cavity took into account the kind of cellular components, the intercellular matrix, angiogenesis, and the occurrence of any hard tissue formation. The pulp's capacity for regeneration was described descriptively, taking into account the type of regenerated tissue, the root's apical closure, and any potential periodontal and periapical histological alterations. Semi-quantitative analysis was used to assess the degree of pulp tissue regeneration. Tukey's post hoc test was used after a two-way ANOVA for statistical analysis of all the data.

Results: When comparing the treated groups to the control group, a significant increase in tissue ingrowth and a significant decrease in the periapical inflammatory reaction were noted (p < 0.05). It's interesting to note that blood clot + HA group's inflammatory cell count was significantly greater (p < 0.05) than that of the other treatment groups. Furthermore, blood clot + collagen group and blood clot group did not differ significantly in inflammatory cell count from one another. Tissue ingrowth did not differ significantly (p > 0.05) amongst treated groups.

Conclusion: The tissue regeneration of the immature necrotic teeth is improved by revascularization, whether or not it is combined with HA or collagen scaffolds. After revascularization, using HA as a scaffold is less efficient in reducing the inflammation than collagen.

Keywords: Dental pulps; Periapical pathosis; Regenerative endodontic; Revascularization; Scaffolds.

Fig. 1.. Flowchart showing the main experimental procedures in the present study.

Fig. 2.. A&B: Representative photomicrographs of blood clot + HA group showing more extended pulpal tissue regeneration with calcified mass (black arrow, A), blood vessels (black arrow, B) and dense collagenous fibrous tissues (green arrow, B). C: Representative photomicrograph of blood clot + collagen group showing well-defined connective tissue with developed blood vessels (black arrow) and calcified structures with entrapped cells (green arrow). D: Representative photomicrograph of blood clot + collagen group showing distinct cellular elements and new dentin formation at the pulpal side of root dentin (black arrow) and scattered blood vessels (green arrows) (H&E. A: ×40, B: 200×, C: ×100, D: ×200).

Fig. 3.. A: Representative photomicrograph of blood clot group showing strands of soft tissue (black arrow). B: Representative photomicrograph of the control group (no treatment) showing empty intracanal space (black arrow). C: Representative photomicrograph of the control group showing heterogeneous connective tissue with fibrous areas (black arrow) and hyalinized regions (green arrow) with scattered calcified masses (yellow arrows). D: Representative photomicrograph of the control group showing aggregations of congested red blood corpuscles (black arrow). (H&E. A: ×100, B: ×40, C and D: ×100).

Fig. 4.. A: Representative photomicrographs of blood clot + HA group showing apical closure with cementum like tissue, evidence of cementocytes inside the apical openings (arrows) and dense basophilic condensations (blue arrow, B). C: Representative photomicrograph of blood clot + collagen group showing cemntum like tissue inside the root canal (arrow). D: Photomicrograph of blood clot + collagen group dense basophilic condensations (arrow). (H&E. A: 200, B, C and D: ×100).

Fig. 5.. A: Representative photomicrograph of blood clot group showing regions of minor degenerative changes (arrow). B: Representative photomicrograph of the control group (no treatment) showing periapical tissues with dense aggregation of inflammatory cells (yellow arrow), apical closure with cementum like tissue without cementocytes in their lacunae (black arrow). C: Representative photomicrograph of the control group showing bone resorption sites indicated by Howships lacunae and osteoclasts (arrows). D: Representative photomicrograph of the control group showing regions of densely stained basophilic condensation (arrow) (H&E. A and B: ×100, C and D: ×200).