Dissolution of porcine incisor pulps in sodium hypochlorite solutions of varying compositions and concentrations

BACKGROUND

The solubility of dental pulp tissue in sodium hypochlorite has been extensively investigated but results have been inconsistent; due most likely to variations in experimental design, the volume and/or rate of replenishment of the solutions used and the nature of the tissues assessed. Traditionally, the sodium hypochlorite solutions used for endodontic irrigation in Australia have been either Milton or commercial bleach, with Milton being the most common. Recently, a range of Therapeutic Goods Administration (TGA) approved proprietary sodium hypochlorite solutions, which contain surfactant, has become available. Some domestic chlorine bleaches now also contain surfactants. The purpose of this study was to perform new solubility assessments, comparing Milton with new TGA approved products, Hypochlor 1% and Hypochlor 4% forte, and with a domestic bleach containing surfactant (White King).

METHODS

Ten randomly assigned pulp samples of porcine dental pulp of approximately equal dimensions were immersed in the above solutions, as well as representative concentrations of sodium hydroxide. Time to complete dissolution was measured and assessed statistically.

RESULTS

White King 4% showed the shortest dissolution time, closely followed by Hypochlor 4% forte. White King 1% and Hypochlor 1% each took around three times as long to completely dissolve the samples of pulp as their respective 4% concentrations, while Milton took nearly 10 times as long. The sodium hydroxide solutions showed no noticeable dissolution of the pulp samples.

CONCLUSIONS

The composition and content of sodium hypochlorite solutions had a profound effect on the ability of these solutions to dissolve pulp tissue in vitro. Greater concentrations provided more rapid dissolution of tissue. One per cent solutions with added surfactant and which contained higher concentrations of sodium hydroxide were significantly more effective in dissolution of pulp tissue than Milton.

A survey of sodium hypochlorite use by general dental practitioners and endodontists in Australia

BACKGROUND

Sodium hypochlorite is used commonly as an endodontic irrigant, but there are no published reports that provide details of its use. This survey sought to determine the percentage of Australian dentists who practiced endodontics, whether they used sodium hypochlorite for irrigation, and the manner of dilution, storage and dispensing sodium hypochlorite used by both dentists and endodontists.

METHODS

All Australian endodontists and a stratified random sample of 200 general dentists in Australia were surveyed to address the issues identified above.

RESULTS

Almost 98 per cent of dentists surveyed performed endodontic treatment. Among endodontists, nearly 94 per cent used sodium hypochlorite for irrigation compared with just under 75 per cent of general dentists. Sodium hypochlorite use by general dentists was more common in Victoria and South Australia than in other States. An infant sanitizer (Milton or Johnson's Antibacterial Solution) was used by just over 92 per cent of general practitioners and by more than 67 per cent of endodontists. All other respondents used domestic bleach. One hundred and sixty four of the respondents (80 per cent of endodontists and over 90 per cent of general dentists) used a 1 per cent w/v solution. Ten practitioners used a 4 per cent w/v solution, five used a 2 per cent w/v solution and four used a 1.5 per cent w/v solution. Eighty per cent of the practitioners who diluted their sodium hypochlorite before use, used demineralized water for this purpose. The remainder used tap water. Only four practitioners stored sodium hypochlorite in a manner which risked light exposure and loss of available chlorine content.

CONCLUSIONS

Sodium hypochlorite is commonly used as an endodontic irrigant and Australian dentists generally stored the material correctly.

The shelf-life of sodium hypochlorite irrigating solutions

BACKGROUND

Sodium hypochlorite (bleach) solutions are widely used as irrigants in endodontics. Their tendency to deteriorate is worsened by environmental influences which could cause loss of available chlorine content.

METHODS

This study measured the loss of available chlorine concentration in a range of sodium hypochlorite solutions under conditions which mimic clinical usage and storage. Domestic bleach, both undiluted and diluted with demineralised water or hard water, was tested, along with Milton, for initial concentration of available chlorine, and then retested after varying periods and modes of storage to measure loss of chlorine concentration. The types of storage were: (1) in closed plastic bottles which were opened daily and agitated; (2) in open plastic bottles; (3) in syringes exposed to sunlight; (4) in syringes kept in the dark; (5) in open stainless steel bowls; (6) in closed stainless steel bowls; and (7) when heated to 50 degrees C. Not all solutions were tested under all storage conditions.

RESULTS

Of the solutions opened daily, undiluted domestic bleach was the most stable and Milton was the least stable. Initially, diluted bleach left open deteriorated rapidly but deterioration slowed with time. Solutions in syringes exposed to sunlight showed the most rapid loss of chlorine content. Heated bleach lost nearly 5 per cent of its strength in six hours. Diluted bleach surprisingly, increased its chlorine concentration in open bowls probably due to evaporation of water. Dilution of bleach with hard tap water did not significantly affect shelf-life. Preloading of diluted bleach into syringes appears to be a sound technique if the syringes are stored away from light.

CONCLUSIONS

This study reinforces the need for sodium hypochlorite to be stored in closed opaque containers. Constant opening of containers appears to cause greater loss in chlorine concentration of diluted bleach solutions, perhaps because a lower concentration of sodium hydroxide allows the pH to drop more rapidly.

Changes in root canal morphology in simulated curved canals over-instrumented with a variety of stainless steel and nickel titanium files

The purpose of this project was to observe the amount of apical and mid-curve transportation produced by a range of nickel titanium (NiTi), titanium alloy and stainless steel (SS) files. Tests were carried out in simulated curved root canals produced in epoxy resin blocks. Seven commercially available file types were tested using sizes 15 to 40. Instrumentation was carried out to 1 mm beyond the apex. Changes in canal dimensions were measured at 10x magnification under a shadowgraph. There were substantial differences in the amount and the pattern of apical and mid-curve transportation produced. The amount of transportation increased with each subsequent size of file. Under the same conditions, nickel titanium files produced significantly less transportation than stainless steel files. The least apical transportation was obtained with the NiTi Mity Turbo and the most by the SS K file and SS Hedstrom file. The least mid-curve transportation was produced by the NiTi Mity Turbo and the most by the SS Hedstrom file.

Sodium hypochlorite and its use as an endodontic irrigant

Sodium hypochlorite has been used as an endodontic irrigant for more than 70 years, and is now one of the most common solutions for this purpose. The chemical properties and production of commercial sodium hypochlorite are reviewed. Domestic bleaches and an infant sanitizer are compared from the point of view of cost and ease of use--Milton being recommended where a 1% solution is required. The cost of syringes and needles for endodontic irrigation is many times greater than the hypochlorite they contain, and total annual practice costs for hypochlorite are low. Brief guidelines for clinical use, storage, handling and disposal are included.