Larger apical sizes result in cleaner root canals

Abstract

Objectives: Chemomechanical preparation of the root canal system is the cornerstone of successful outcome of root canal treatment. Long-term outcome studies have demonstrated a failure rate of 20-35%, despite technological advances. These failures could be biological or structural. While teeth with biological failures may be retreated, teeth that fail structurally need to be extracted, resulting in deteriorated quality of life. One reason for structural failures is overzealous root canal shaping with an assumption that larger canals imply cleaner canals. This is attributed to the lack of robust recommendations on the optimal apical size and taper of root canal preparation. Consequently, it is imperative to identify preparation sizes that offer clean canals yet can conserve dentin. The objective of this study was to investigate the root canal cleanliness when canals were prepared to two apical sizes using a highly sensitive histological approach. Methods: Freshly extracted, formalin-stored premolars (n=16) were prepared using nickel-titanium instruments (0.04 taper) to an apical size of 0.20 or 0.40. A standardized volume (10 mL) of 5.25% sodium hypochlorite was used during shaping. After shaping, root canals were irrigated with 2 mL of 17% EDTA for 2 minutes, followed by 2 mL of 5.25% sodium hypochlorite and 2mL of saline. The specimens were then processed for histology. Staining was performed using Masson’s trichrome stain to demonstrate the amount of remaining pulp tissue (RPT) and remnant predentin layer at all root-thirds. Statistical analysis of the data was performed using one-way ANOVA and post hoc tests (P=0.05). Results: Root canal preparation to a larger size resulted in clear canals (significantly less RPT) in the middle and apical third (P<0.05), but not in the coronal third (P>0.05), when compared to the smaller preparation size. Conclusions: When syringe irrigation is used, preparation of root canals to larger apical sizes produces cleaner canals.