Hedp- Controlled Invasion to Effective Irrigation

INTRODUCTION

Irrigation plays a significant role in effective root canal therapy. It has different significant goals, which vary with the type of irrigant being used. The process of irrigation involves flushing out a root cannal with solutions. The two aims of an irrigation system are mechanical and biological functions. The present procedures to disinfect the root canal system are primarily by means of chemo-mechanical preparation. However, only 60 to 80% or less of canal outlines can be prepared circumferentially by instrumentation. Thus, the disinfection of the remaining untouched area has to rely on chemical irrigation or intracanal medications. More importantly, mechanical preparation leads to the formation of the smear layer (SL) which can only be efficiently removed by alternating the use of EDTA and NaOCl.¹

SMEAR LAYER REMOVAL

It has been shown that irrigation with 17% EDTA has an effect on cleaning canal walls. Moreover, both the cleaning and antimicrobial actions are more appreciable when EDTA and NaOCl are used in combination rather than being used alone. It is mostly recommended that 17% EDTA should be applied after cleaning and shaping procedure (CSP) in order to remove the SL before root canal obturation.¹

Consequently, irrigation protocols using sodium hypochlorite in an alternating mode with an aqueous solution containing a decalcifying agent such as EDTA or citric acid have been proposed. However, these protocols are not necessarily user-friendly. Because of the chemical reactivity of OCl- (hypochlorite) with most decalcifying agents, especially those in acidic form, combined use is not possible. The search for hypochlorite-compatible decalcifying agents or chelators in endodontic research has yielded two candidates thus far: tetrasodium HEDP (Na4HEDP) and tetrasodium EDTA (Na4EDTA). Both, 1-hydroxyethane 1,1-diphosphonic acid (HEDP or etidronate) and ethylenediaminetetraacetic acid (EDTA) are available as disodium and tetrasodium salts, depending on the desired pH.²

HEDP has a higher calcium binding capacity per gram chelator, while EDTA has a stronger affinity to calcium, i.e. a higher dissociation constant of the complex. Consequently, EDTA has a higher demineralizing effect than HEDP, and can erode dentin. It would appear that the reduction of the available chlorine that occurs in direct mixtures with Na4HEDP is less than that in counterparts containing Na4EDTA.²

HEDP- 1 -HYDROXYETHANE 1,1 -DIPHOSPHONIC ACID

Etidronic acid or 1 -hydroxyethane 1,1 -diphosphonic acid (HEDP or, less commonly, HEBP) is a nitrogen -free bisphosphonate used in water treatment, as a bar soap preservative, and in food disinfection. An etidronate is a salt of etidronic acid , in which cations are bound to the anion of HEDP (usually Na2HEDP or Na4HEDP). Based on the unique short-term compatibility of HEDP with sodium hypochlorite (NaOCl), it is theoretically possible to use a combined NaOCl/HEDP irrigant during chemomechanical root canal preparation and for final irrigation.³

COMPATIBILITY OF HEDP WITH NAOCL

Etidronic acid (HEDP) in a freshly prepared combination with NaOCl which does not interfere with the antimicrobial and tissue-dissolving properties of the resulting solution. The HEBP solution caused some reduction in free available chlorine content after 1 h. This loss is dose-dependent and continued over time. Fresh mixtures, however, retained 100% of free chlorine. In contrast, EDTA solution caused an almost complete loss of OCl-/HOCl immediately upon mixing with NaOCl. This phenomenon was even more pronounced for Citric Acid + NaOCl mixtures, in which the free available chlorine content decreased to zero in less than one minute.² The proteolytic/antibacterial effects of the NaOCl, which are based on the free available chlorine in the system, are maintained. At the same time the HEDP, which is a calcium sequestering agent (chelator), prevents the accumulation of smear layer and hard tissue debris.^3,4

The main difference of HEDP with respect to disodium EDTA is that it is a weak alkaline chelator acting in the pH range of 10.8–12.2, while disodium EDTA operates at lower pH. These alkaline conditions of the ethydronic acid favors its use with NaOCl solutions, not affecting the pH of the NaOCl solution.⁵

Cytotoxicity and genotoxicity of mixed solutions is dictated by the presence of free available chlorine therein.⁶

PREPARATION OF SOLUTION

HEDP AS A CHELATING AGENT

Irrigating solutions used in endodontics should be in close contact with the dentinal walls for effective debris removal and penetration into the root canal system. The latter feature is dependent on their surface tension. Wettability is the tendency of a fluid to spread over or adhere to a solid surface, and this property has been shown to play an essential role for irrigating solutions to penetrate the main and lateral canals, as well as the dentinal tubules. Despite a higher surface tension, the NaOCl + HEDP mixture exerted a better antibacterial action than NaOCl + EDTA. The increased surface tension value, observed in NaOCl + HEDP solution, could depend on the addition of solute (HEDP) into a solvent (NaOCl), that changes the features of the solution, leading to a rise of the surface tension. NaOCl + HEDP could be considered a valid alternative to NaOCl + EDTA, considering its greater antibacterial action.⁷

The irrigation regimes that employed HEBP as a chelating agent resulted in significant decreases in hardness, but these values were lower than those resulting from protocols that employed CA or EDTA. It shows that the decrease in hardness is directly proportional to the chelating power of the substance. These findings confirm that HEBP is a weak calcium-complexing agent that causes less change in dentin than other chelating agents.⁸

HEDP showed high effectiveness in completely removing the smear layer. Its action is enhanced when a low concentration of NaOCl (1.3%) is used. Forthis irrigant, several beneficial effects have been reported:

1. Prevention of smear layer
2. Reduction of hard tissue debris accumulation
3. Possible reduction of torsional load on rotary instrumentation
4. Time-saving application and
5. Not reduction of NaOCl antibacterial effect.⁹

In a study conducted by Alejandro Álvarez-Sagües et al HEDP showed the best results and is the most appropriate chelator to combine with sodium hypochlorite in different irrigation protocols.⁵

Gawdat et al conducted a study on dentinal tubule penetration of bioceramic sealer after different irrigating solutions in which NaOCl + HEDP displayed better sealer penetration inside the dentinal tubules than Groups.¹⁰

In addition, Irrigation with 2.5% NaOCl/9% HEDP significantly improved the pushout bond strength of Biodentine to the root canal dentin.¹¹

AS ALTERNATIVE TO EDTA IN REGENERATIVE ENDODONTICS

HEDP released more VEGF from both disks and cylinders. In cylinders, VEGF release by HEDP was significantly greater than the other conditioners, whereas in disks the release of VEGF was similar with all conditioners.¹²

CONCLUSION

HEDP as a final rinse appears to be a promising irrigation protocol with less impact on the mineral content of the root dentin, it has low cytotoxicity and high pH. This irrigant remains stable and does not affect the tissue dissolving property of NaOCl. Adding etidronate to NaOCl increases its antimicrobial effect in dentinal tubules even though increases its surface tension. Hence it is a promising irrigating solution to obtain a combined effect of antibacterial activity and smear layer removal in the root canal.

REFERENCES