Characterization of heat resistant hydraulic sealer for warm vertical obturation

Abstract

Objective

Warm vertical compaction of gutta-percha is a technique that is used by most specialists for root canal obturation. The sealers currently available exhibit irriversible chemical changes when heated. New biologically active sealers that do not sustain irreversible changes when heated are an attractive alternative to be used with warm vertical compaction obturation technique. The aim of this study was to measure the heat generated by warm vertical compactors inside the root canal, characterize a newly developed root canal sealer at different temperatures and verify its suitability at the actual temperature window used clinically.

Methods

The typical temperatures generated by two heat carriers in a root canal were assessed by thermocouples. Two premixed root canal sealers TotalFill BC and HiFlow BC (FKG, Switzerland) were allowed to set and they were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD) immediately after setting and by XRD after 28 days in physiological solution. The ion leaching in solution was assessed by inductively coupled plasma (ICP). The organic component was extracted in acetone and assessed by Fourier transform infrared spectroscopy (FT-IR) for both the unset sealer and sealer subjected to different temperatures. The heat profiles of both sealers were investigated by FT-IR and thermographic analysis.

Results

None of the devices tested achieved the temperatures set on the dial. The highest temperatures were coronal followed by apical for both devices. The sealers were identical except for the vehicle. The inorganic components included tricalcium silicate, dicalcium silicate and zirconium oxide. No calcium hydroxide was produced by any of the sealers after immersion in physiological solution but calcium was released in solution. The chemistry of both sealers was modified when heated but both recovered when cooled.

Significance

The heat carriers were unreliable and the heat generated inside the canal was not the same as the temperature set on the dial. Since both sealers had identical chemistry save for minimal modifications to the organic component and were both resistant to heat, TotalFill BC sealer is recommended for use with warm vertical compaction technique as it is cheaper and as effective as the HiFlow.

Introduction

The warm vertical compaction of gutta-percha is a very popular obturation technique where the gutta-percha is heated until it changes phase and softens, then it is compacted vertically to take the shape of the prepared root canal [1]. With this technique the obturation is composed mostly of gutta-percha with minimal amounts of sealer. There is no specific sealer that is suggested for use with this technique so all sealer types are believed to be suitable.

The temperature of phase changes to gutta-percha have been reported to be 60 °C to convert from the β form to completely amorphous [2], [3]. Regardless of this, all the heat carriers indicate the use of temperature settings ranging from 180 to 230 °C. There seems to be no scientific reason for the use of such temperatures which are unsafe. Increases in temperature of bone has been shown to lead to necrosis as the bone can only tolerate an increase by few degrees [4]. Regardless of the reading on the dial, the temperature of the heat carriers is less [5], [6] and the temperature is further dissipated when the heat carrier is placed in a tooth [6], [7] and sealer is used in the root canal [6]. As a result of this, the temperature rise on the external surface of the root is minimal [5], [6], [8].

A rise in temperature in the root canal has deleterious effects on the root canal sealers particularly the epoxy resin-based sealers such as AH Plus (Dentsply). At higher temperatures the AH Plus showed irreversible changes in chemistry [5], [6], [9], [10] and its physical properties were modified with a reduction in the setting time and flow and increase in film thickness [5], [6], [10], [11], [12]. Zinc oxide eugenol-based sealers sustained an increase in setting time when exposed to heat but the flow was unaffected [11] while BioRoot RCS showed changes in its chemistry due to the water evaporation at high temperature [8], [10] and iRoot SP had reduced flow [11]. Heating of AH Plus also resulted in an increase in void volume while BioRoot RCS and Gutta-flow were unaffected [12].

Recently a new hydraulic calcium silicate-based sealer which can be used with warm vertical compaction of gutta-percha has been developed. This sealer is claimed to have a similar chemistry to the premixed hydraulic sealers (BC sealers) manufactured by Brasseler/FKG Dentaire but is resistant to heat thus is recommended for use with warm vertical compaction obturation technique. The aim of this research was to determine the temperature generated by two heat carriers inside the root canal in a simulated clinical environment and to characterize both the classical BC sealer and the HiFlow and assess their heat profiles and chemical changes when subjected to high temperatures.