Dentinal tubule penetration and root canal cleanliness following ultrasonic activation of intracanal‐heated sodium hypochlorite

This study investigated the effect of ultrasonic activation of intracanal‐heated sodium hypochlorite (NaOCl) on its dentinal tubular penetration and root canal cleanliness in vitro. In experiment 1, mandibular premolars were randomly allocated to three groups (n = 8): group A, ultrasonic activation; group B, ultrasonic activation of intracanal‐heated NaOCl and group C, syringe‐and‐needle irrigation. Penetration of the fluorescent‐labelled NaOCl was investigated using light microscopy. In experiment 2, mandibular premolars were randomly allocated to group B or C (n = 10), for histological analysis of the remaining pulp tissue and debris. Data were statistically analysed using Kruskal–Wallis and Mann–Whitney tests (P = 0.05). The highest penetration of NaOCl was observed in group B, followed by group A (P < 0.05). Group B showed significantly less amount of debris than group C (P < 0.05). Dentinal tubule penetration of NaOCl and root canal cleanliness were significantly improved by ultrasonic activation of intracanal‐heated NaOCl.     

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%.     

Effect of endodontic irrigation on bonding of resin cement to radicular dentin

The influence of endodontic irrigation on shear bond strengths of resin cement to radicular dentin was investigated. Human radicular dentin blocks were divided into four groups and subjected to one of four endodontic irrigations: ethylenediaminetetraacetic acid (EDTA) group, 17% EDTA for 60 s; EDTA/sodium hypochlorite (NaOCl) group, 17% EDTA for 60 s followed by 10 ml of 5% NaOCl for 15 s; NaOCl group, 10 ml of 5% NaOCl for 15 s; and control group, no treatment. Morphological changes of dentin surface after endodontic irrigation were observed by scanning electron microscopy (SEM). A resin block was bonded to the radicular dentin after irrigation using resin cement with either wet-bonding (Uni-Etch/One-Step; Bisco) or self-etching (Tyrian SPE/One-Step Plus; Bisco) adhesives. Shear bond strengths were measured and the penetration of resin tags into dentinal tubules at resin-dentin interface was observed by SEM. With the wet-bonding system, the shear bond strengths for the EDTA/NaOCl group, in which dentinal tubules openings and uniform resin tag penetration into dentinal tubules were observed, were significantly higher than the EDTA and control groups. With the self-etching system, the shear bond strengths were significantly lower in the EDTA group compared with the NaOCl and control groups. The effects of endodontic irrigation on the bonding of resin cement to radicular dentin depended on the dentin bonding system used.     

Clinical evaluation of the cleansing properties of the noninstrumental technique for cleaning root canals

AIM: The purpose of the present study was to evaluate noninstrumentation technology (NIT) for root-canal cleansing in vivo. METHODOLOGY: A total of 22 teeth that were to be extracted in 18 patients were treated with NIT for 30 min with 3.0% NaOCl. After extraction, the remaining organic debris in the root canals was evaluated histologically and categorized as the percentage of the corresponding canal length in the apical middle and coronal regions of the roots. Percentage of residual debris was categorized as follows: D1, 0%; D2, 1-50% and D3, 51-100%. RESULTS: In the coronal region, 55% of the roots were totally clean (Dl), whereas 12% and 33% were scored as D2 and D3, respectively. The middle section was evaluated as D1 in 27%, D2 in 18% and D3 in 55%. In the apical region, only 21% of the roots were totally cleaned: the remaining 79% were scored as D3. CONCLUSION: The results indicate that the noninstrumental technique for cleaning root canals needs further modifications for achieving acceptable results under clinical conditions.     

The antioxidant protection of CELLFOOD® against oxidative damage in vitro

CELLFOOD® (CF) is an innovative nutritional supplement containing 78 ionic/colloidal trace elements and minerals combined with 34 enzymes and 17 amino acids, all suspended in a solution of deuterium sulfate. The aim of this study was to investigate, for the first time, the antioxidant properties of CF in vitro in different model systems.Three pathophysiologically relevant oxidants were chosen to evaluate CF protection against oxidative stress: hydrogen peroxide, peroxyl radicals, and hypochlorous acid. Both biomolecules (GSH and plasmid DNA) and circulating cells (erythrocytes and lymphocytes) were used as targets of oxidation.CF protected, in a dose-dependent manner, both GSH and DNA from oxidation by preserving reduced GSH thiol groups and supercoiled DNA integrity, respectively. At the same time, CF protected erythrocytes from oxidative damage by reducing cell lysis and GSH intracellular depletion after exposure to the oxidant agents. In lymphocytes, CF reduced the intracellular oxidative stress induced by the three oxidants in a dose-dependent manner.The overall in vitro protection of biomolecules and cells against free radical attacks suggests that CF might be a valuable coadjuvant in the prevention and treatment of various physiological and pathological conditions related to oxidative stress, from aging to atherosclerosis, from neurodegeneration to cancer.     

Improving the effect of NaOCl pretreatment on bonding to caries-affected dentin using self-etch adhesives

Objective

To evaluate the effect of sodium hypochlorite pretreatment on adhesion to normal and caries-affected dentin using self-etch adhesives.

Methods

Forty extracted human molars with coronal carious lesions were used in this experiment. The occlusal dentin surfaces including the caries-affected dentin in each group were treated as follows: group 1, rinsed with water; group 2, treated with 6% NaOCl for 15 s; group 3, treated with 6% NaOCl for 30 s; group 4, application with Accel for 30 s after NaOCl-30 s pretreatment. After rinsing with water and air-drying, the treated dentin surfaces were applied with self-etch systems (Bond Force and Clearfil Protect Bond) according to the manufacturers’ instructions, and built-up with resin composite. After 37 °C water storage for 24 h, the bonded normal or caries-affected dentin areas were isolated to create an hourglass configuration with a cross-sectional area of approximately 1 mm². The specimens were subjected to tensile stress at a cross-head speed of 1.0 mm/min.

Results

NaOCl-15 s pretreatment significantly improved the μTBS of both self-etch adhesives to caries-affected dentin, while the 30 s pretreatment did not affect them. For normal dentin, NaOCl-30 s pretreatment significantly reduced the μTBS of both self-etch adhesives although the 15 s pretreatment did not alter them. Furthermore, the application of Accel with a reducing effect increased the μTBS to normal and caries-affected dentin treated with NaOCl for 30 s.

Conclusions

The effects of NaOCl pretreatment on bonding of both self-etch adhesives were dependent upon type of dentin (normal and caries-affected dentin) and the treatment time.     

EDTA or H3PO4/NaOCl dentine treatments may increase hybrid layers’ resistance to degradation: A microtensile bond strength and confocal-micropermeability study

Objectives

The aim of this study was to reduce hybrid layer degradation created with simplified dentine adhesives by using two different methods to condition the dentine surface.

Methods

A smear-layer was created on flat dentine surfaces from extracted human third molars with a 180-grit/SiC-paper. Dentine specimens were conditioned before bonding with the following procedures: 37% H₃PO₄; H₃PO₄/0.5% NaOCl; 0.1 M EDTA; 0.1 M EDTA/0.5% NaOCl. Two etch-and-rinse adhesives: (Scotchbond 1XT or Optibond Solo Plus) were applied and light-cured. Composite build-ups were constructed. The bonded teeth were sectioned into beams, stored in distilled water (24 h) or 12% NaOCl solution (90 min) and finally tested for microtensile bond strengths (μTBS). Additional dentine surfaces were conditioned and bonded as previously described. They were prepared for a pulpal-micropermeability confocal microscopy study and finally observed using confocal microscopy.

Results

μTBS results revealed that both adhesives gave high bond strengths to acid-etched dentine before, but not after a 12% NaOCl challenge. Bonds made to acid-etched or EDTA-treated dentine plus dilute NaOCl, gave high μTBS that resisted 12% NaOCl treatment, as did EDTA-treated dentine alone. A confocal micropermeability investigation showed very high micropermeability within interfaces of the H₃PO₄, etched specimens. The lowest micropermeability was observed in H₃PO₄ + 0.5% NaOCl and 0.1 M EDTA groups.

Conclusions

The use of dilute NaOCl (0.5%) after acid-etching, or the conditioning of dentine smear layers with 0.1 M EDTA (pH 7.4) produced less porous resin–dentine interfaces. These dentine-conditioning procedures improve the resistance of the resin–dentine bond sites to chemical degradation (12% NaOCl) and may result in more durable resin–dentine bonds.