Advancing Adhesive Strategies for Endodontically Treated Teeth-Part I: Impact of Endodontic Irrigation Protocols on the Chemical Composition and Structural Integrity of Coronal Dentin.

Objective: To evaluate the effects of four endodontic irrigation protocols on the chemical composition and ultrastructure of coronal dentin.

Materials and methods: Coronal dentin fragments were assigned to five study groups: NaOCl (3% sodium hypochlorite), NaOCl/EDTA (3% NaOCl and 17% ethylenediaminetetraacetic acid), NaOCl/EDTA/CHX (3% NaOCl, 17% EDTA and 2% chlorhexidine), NaOCl/HEDP (mixture of 3% NaOCl and 9% etidronic acid), and control (distilled water). Confocal Raman microscopy was employed to analyze the spatial distribution of organic and inorganic components, while attenuated total reflection Fourier transform infrared spectroscopy and energy-dispersive spectroscopy were used to assess the surface composition of dentin. Ultrastructural evaluation was conducted using scanning electron microscopy (SEM). Statistical analysis was performed using a mixed linear model with a significance level of 0.05.

Results: All NaOCl-treated groups showed reduced amide II (p < 0.001), indicating protein degradation. Exclusive NaOCl irrigation yielded the lowest amide II, highest mineral content, and increased phosphate/amide II and carbonate/phosphate ratios (p < 0.05). Chelators reduced mineral content (p < 0.001), with NaOCl/HEDP and NaOCl/EDTA/CHX producing more mineralized surfaces than NaOCl/EDTA and control groups (p < 0.05). A general decrease in organic (C and N) and an increase in inorganic (O, P, and Ca) components occurred across treatments, particularly in NaOCl and NaOCl/HEDP groups. EDTA disturbed the Ca/P equilibrium (p < 0.05). SEM showed a dense smear layer and mostly obliterated tubules in NaOCl and control samples, while chelators reduced the smear layer, partially opened tubules, and caused erosion.

Conclusions: Exclusive use of 3% NaOCl produces hypermineralized, collagen-depleted coronal dentinal surfaces, with a dense smear layer. Sequential irrigation with 17% EDTA induces stronger demineralization compared to a continuous chelation protocol with 9% HEDP. Both EDTA- and HEDP-treated coronal dentin display partially opened dentinal tubules, signs of erosion, and substantial smear layer reduction.

Clinical significance: Clinically recommended endodontic irrigation protocols significantly alter the chemical composition and ultrastructural integrity of coronal dentin, the primary substrate for adhesive restorations. These findings enhance the understanding of post-irrigation coronal dentin conditions and their potential implications on the interaction with adhesive restorative materials.