Critical appraisal of studies on dentinal radicular microcracks in endodontics: methodological issues,contemporary concepts,and future perspectives

The dentinal radicular microcrack is a difficult clinical problem to diagnose and treat, and it is one of the most common reasons for tooth extraction. These microcracks start in the radicular dentin, and laboratory studies have linked crack formation to some routine endodontic procedures, namely root canal preparation, obturation, and retreatment. Most of these studies were performed using destructive methods, such as the sectioning technique, previously developed for the study of the internal anatomy of teeth. Nowadays, technological advances in the field of imaging may lead to a more thorough understanding of dentinal microcracks. This article seeks to critically appraise the methodological aspects involved in the study of dentinal radicular microcrack formation after root canal preparation, obturation, and retreatment.     

Similar Influence of Stabilized Alkaline and Neutral Sodium Hypochlorite Solutions on the Fracture Resistance of Root Canal–treated Bovine Teeth

Introduction

Stabilizing sodium hypochlorite (NaOCl) at an alkaline pH is proposed to increase solution stability and tissue dissolution ability; however, a reduction on the flexural strength of dentin discs has been found to be a side effect. This study sought to determine whether a stabilized alkaline NaOCl reduces the fracture resistance of root canal–treated bovine teeth after root canal preparation compared with a neutral solution counterpart.

Methods

The 4 anterior incisors were removed from 20 mandibular bovine jaws, and each 1 was randomly assigned to 1 of 4 groups (20 teeth each). Teeth were prepared with a sequence of 6 K-type files. The following experimental groups received a different irrigation regimen: G1: distilled water (negative control), G2: 5% NaOCl at a pH of 7.2, and G3: 5% NaOCl at a pH of 12.8; in the positive control group (G4), teeth remained untreated. The time of contact and volume of solution were carefully standardized. After bone and periodontal ligament simulation, teeth were subjected to a fracture resistance test.

Results

A significant difference was observed among the 4 groups tested (analysis of variance, P < .05). The 5% NaOCl groups (G2 and G3) presented significantly lower resistance to fracture than the control (G1 and G4) (Tukey test, P < .05). Both NaOCl solutions similarly reduced the fracture resistance at approximately 30% (Tukey test, P > .05). No differences were observed between positive and negative control groups (Tukey test, P > .05).

Conclusions

Stabilized alkaline and neutral NaOCl solutions similarly reduced the fracture resistance of root canal–treated bovine teeth by about 30%.     

Reciprocating Versus Rotary Systems for Root Filling Removal: Assessment of the Apically Extruded Material

Introduction

This study was designed to quantitatively evaluate the amount of apically extruded debris by comparing the ProTaper Universal Retreatment system (Dentsply Maillefer, Ballaigues, Switzerland) with 2 reciprocating single-file systems (Reciproc [VDW, Munich, Germany] and WaveOne [Dentsply Maillefer]) during endodontic retreatment.

Methods

Forty-five mandibular premolars with a single canal were prepared with the ProTaper Universal system and then obturated. The specimens were divided into 3 groups (n = 15) according to the system used for filling removal: ProTaper Universal Retreatment system associated with the ProTaper Universal system (until file F4 40/0.06]), Reciproc system (Reciproc R40 [40/0.06]), and WaveOne system (WaveOne Large [40/0.08]). Sodium hypochlorite was used as an irrigant, and the apically extruded debris was collected in glass vials and then dried. The mean weight of debris was assessed with a microbalance and statistically analyzed using 1-way analysis of variance and post hoc Tukey multiple comparison tests (P < .05).

Results

The ProTaper Universal Retreatment system produced significantly more debris compared with the Reciproc and WaveOne systems (P < .01). The reciprocating systems showed no significant difference between them (P > .05).

Conclusions

Under the conditions of the present study, all systems caused apical debris extrusion. Reciprocating systems were associated with less debris extrusion when compared with a conventional rotary retreatment system.     

Torsional Fatigue Resistance of Blue-treated Reciprocating Instruments

Introduction

The aim of the present study was to evaluate the influence of blue thermal treatment on the torsional resistance behavior of M-Wire Reciproc files (VDW, Munich, Germany).

Real-time atomic force microscopy of root dentine during demineralization when subjected to chelating agents

AIM: To explore the potential of atomic force microscopy (AFM) for the examination of changes to dentine surfaces during demineralization and evaluate qualitatively the effect of EDTA, EDTAC and citric acid. METHODOLOGY: Nine canine teeth were sectioned transversely at the cemento-enamel junction, and the crowns discarded. Subsequently, each root was embedded in an epoxy cylinder and discs approximately 5 mm thick were cut. A standard metallographic procedure was then used to prepare the surfaces for observation. From the central portion of these samples, two specimens were symmetrically prepared per tooth so that a total number of 18 samples was produced. To allow the use of a liquid cell during AFM, the samples were embedded in silicone rubber and were then randomly divided into three groups, as follows: group 1: 17% EDTA (pH 7.7), group 2: 17% EDTAC (pH 7.7) and group 3: 10% citric acid (pH 1.4). Topographical images were acquired during the demineralization process, allowing real-time observation of the dentine surface. Two operators assigned scores to the AFM images using a double-blind method. anova analysis with random effects (P < 0.05) was used to compare the results. RESULTS: The average scores were 6.13 +/- 0.35 for EDTAC, 7.36 +/- 0.23 for EDTA and 14.55 +/- 1.21 for citric acid. Citric acid was statistically different from EDTA and EDTAC while EDTA and EDTAC were not statistically different. CONCLUSIONS: The most effective demineralizing substance was citric acid. The methodology developed for real-time observation of dentine surfaces is a valuable method to evaluate demineralization.