Discussion - References.
Microorganisms in dentinal tubules may constitute a reservoir from which root canal and surrounding tissue infection and reinfection may occur. Treatment strategies designed to eliminate this reservoir should include agents that can penetrate the dentinal tubules and destroy these microorganisms, since they are located beyond the host defense mechanism, and out of reach of systemically administered antimicrobial agents. The present study evaluated the ability of intracanal medicaments to disinfect dentinal tubules leading from the root-canal space. For this purpose, cylindrical root specimens prepared from bovine teeth were used in anin vitro model of dentinal tubule infection (Haapasalo & Grstavik 1987). We modified this experimental model slightly to obtain additional quantitative information.
Calcium hydroxide (CH) has a lasting antibacterial activity in the root-canal space due to its high pH (Fuss et al.1989,1996). However, CH has poor solubility and its bactericidal effect on penetration into the dentinal tubules is unsatis factory (Haapasalo & Grstavik 1987).
Safavi et al. (1990) have shown that IKI penetrates into the dentinal tubules from a distance and kills bacteria in vitro. However, the duration of its antimicrobial efficiency is short (Engstrom1958); it is expected to remain active from 1 to 3 days depending on the rate of fluid exchange through the apical foramen (Moller 1966). In the present study, the use of IKI combined with CH proved to be more effective in dentinal tubules than pure CH. The use of this combination is especially important in root canals with complex anatomy where packing CH is complicated or impossible.
Molander et al. (1999) tested the activity of CH in the root canal following pretreatment with 5% IKI for 3-7 days; CH had no increased antimicrobial effect following such pretreatment. They suggested that the smear layer should be removed and the IKI mixed with a vehicle. This could enhance its antibacterial effect in the dentinal tubules and increase its duration of activity. In the present study, CH was used as a vehicle for the IKI and the smear layer was removed. This may explain the significantly better effect in the dentinal tubules compared to the former study. In a pilot test, there were no significant changes in pH values of CH paste following the addition of iodine (pH >12.5).
In this in vitro model, the best results were obtained with the addition of copper to CH and with the use of an electric current, according to the method described by Knappwost (1993). The depth of complete disinfection was at least 500 mm, which is superior to other medicaments. It is generally accepted that the choice of an intracanal medicament should balance antibacterial potency with tissue toxicity, a balance that is often difficult to achieve because medicaments that are bactericidal, usually exhibit some toxicity to mammalian cells (Spangberg1990). Coppermay be toxic to the periradicular tissues, therefore, its clinical use should be questioned and limited. In addition, electrodes which do not penetrate to the root-end (apex) as described by Knappwost (1993), are limited in their effectiveness at the most important site, the apical delta.
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