BIOACTIVE COATED GUTTA-PERCHA AS ROOT CANAL FILLING MATTER

Abstract

The present invention relates to the deposition of a micro-crystalline hydroxyapatite and tricalcium phosphate coating onto gutta-percha cones, to be used as dental composite for root canal filling. The method proposed for coating involves the surface pretreatment of gutta-percha cones with sodium hydroxide; immersion of gutta-percha cones in simulated body fluid, which contains calcium and phosphate ions; and replacing consumed simulated body fluid after an interval of time, at physiological pH and temperature. The nucleation process results in the biomimetic deposition of a thin and uniform layer of calcium phosphates and hydroxyapatite. Improved characteristics such as in sealing ability, bonding strength, and ability to form hermetic seal, therefore allows the dental composite produced, to be used appropriately as filling matter in root canal treatments.

Claims

1. A dental composite for root canal filling matter, comprising: a gutta-percha substrate, characterized in that, a micro-crystalline hydroxyapatite and tricalcium phosphate coating is adhered onto the gutta-percha substrate.

2. The composite of claim 1, wherein the substrate is cone shaped.

3. The composite of claim 1, wherein the coating has a preferred thickness between 14 and 19 μm.

4. A method of preparing dental composite, comprising: immersing gutta-percha cones in simulated body fluid, said fluid contains calcium and phosphate ions, for a predetermined period of time under physiological conditions; and replacing the consumed ions of simulated body fluid with simulated body fluid having calcium and phosphate ions, at an interval of time.

5. The method of claim 4, wherein the immersing of gutta-percha cones in simulated body fluid is performed for duration of 10 days, at pH 7.4 and temperature 37° C., and replacing the simulated body fluid is performed every 48 hours within 10 days.

6. The method of claim 4, wherein the step of immersing the gutta-percha cones in simulated body fluid involves using simulated body fluid comprising: calcium, phosphate, carbonate, sodium, chloride, potassium, magnesium, and sulphate ions, with TRIS buffer and hydrochloric acid acting as buffering agents.

7. The method of claim 4, further comprising pretreatment step of: exposing the gutta-percha cones surface to sodium hydroxide, for the production of hydroxyl functional groups on the surface of gutta-percha cones, prior to immersing substrate in simulated body fluid.

8. The method of claim 7, wherein the pretreatment is performed at preferred concentration of sodium hydroxide is 5 M.

9. The method of claim 7, wherein the pretreatment is performed at preferred condition which include: immersing gutta-percha cones in sodium hydroxide for a period of 24 hours and at temperature of 60° C.

Description

DESCRIPTION OF THE EMBODIMENTS

[0011] The biomimetic method for coating of hydroxyapatite and tricalcium phosphate onto gutta-percha substrate is introduced in the present invention, in view of other current methods for coating such as plasma-spraying, sputtering, sintering, sol-gel, and electrophoretic methods. The application of hydroxyapatite as coating through the biomimetic route is prevalent in the medical industry, and is considered an attractive approach for bone and tissue engineering. Thus, in the present invention, said coating is developed by a biomimetic approach for the production of a root canal filling matter.

EXAMPLE 1

[0012] In one embodiment of the present invention, the GP cones (ISO colour coded, Dentsply, Malliefier, USA) are pretreated with 5 M sodium hydroxide at temperature of 60° C., for 24 hours. Prior to the pretreatment process, the cones are abraded with #1000 SiC paper (FEPA P#1000, Struers, USA), and washed three times, with acetone, ethanol, and deionized water, respectively, in an ultrasonic bath (WiseClean, Korea). Following pretreatment, the cones are washed with deionized water and dried at 40° C. The pretreatment step is introduced to generate hydroxyl (OH) groups on the surface of GP cones. It is observed that the concentration of carboxyl and hydroxyl groups onpolymer surface most likely have a significant effect on speed and mechanism of calcium phosphate nucleation (Colovic et al, 2011). With high density of carboxyl and hydroxyl groups, there is a high density of nucleation sites. Hence the presence of OH groups is a factor which can influence the growth behavior of apatite crystals. In addition, Takeuchi et al (2005) reported that the arrangement of functional groups is important for the nucleation of hydroxyapatite in SBF, therefore the nucleation of HA on a substrate in a solution mimicking a body fluid is dependent on such structural functional group arrangements.

[0013] The concept of the biomimetic method is based on the finding that calcium phosphates are more soluble in mildly acidic medium than at neutral and basic pH, hence the precipitation of calcium phosphates occurs at neutral or basic pH; between solutions having the same concentrations of salts. An increase in pH value of solution can induce the following stages: under-saturation, super-saturation or the formation of metastable state, nucleation, and subsequent crystal growth. In the mechanism of heterogeneous nucleation, calcium phosphate nuclei can deposit onto a substrate when a solution has reached the super-saturation limit or the metastable condition. The predominant molecular form at the metastable phase is the intermediate product, amorphous calcium phosphate (ACP). It is proposed that the process of ACP formation in solution first involves the formation of Ca.sub.9(PO.sub.4).sub.6, also known as Posner's clusters, or CaP clusters, which then aggregates randomly to produce larger spherical particles or globules. These nano-clusters are found to be always present in simulated body fluid (SBF) solutions, and the insertion of suitable alkali-treated substrate surface into the solutions will stimulate the hexagonal packing of the nano-clusters to form apatitic CaP precipitates. At the metastable state, heterogeneous nucleation is favoured by the energy stabilization of nucleus on the substrate. Subsequently, the growth of the nucleated hydroxyapatite film will occur by simultaneous attraction of calcium and phosphate ions from the SBF solution. Finally, the high density of nucleation then ensures a uniform deposition of carbonated calcium phosphate crystals onto the surface of GP cones.

EXAMPLE 2

[0014] In the present invention, the pretreated GP cones are immersed in SBF for duration of 10 days with replacement of the solution every 48 hours. The consumed ions of SBF are replaced with SBF having calcium and phosphate ions. SBF is a solution with inorganic ion concentrations almost equal to those in human blood plasma. The specific concentrations of ions present in the SBF solution prepared in this invention are the following: 27 mM HCO.sub.3.sup.−, 2.5 mM Ca.sup.2+, 1.0 mM HPO.sub.4.sup.2−, 142 mM Na.sup.+, 125 mM Cl.sup.−, 5 mM K.sup.+, 1.5 mM Mg.sup.2+, and 0.5 mM SO.sub.4.sup.2−. This formulation has a Ca/P molar ratio of 2.5, and an ionic strength of 160.5 mM. Preferably, the physiological environment for formation of coating is kept at pH 7.4 and temperature of 37° C. The maintenance of ambient pH from the time of preparation through to the completion of the hydroxyapatite film formation is achieved by replacement of SBF solution in incubators, every 48 hours within 10 days. The buffering agent present in the SBF solution is tris-hydroxymethyl-aminomethane, with chemical formula (CH.sub.2OH).sub.3CNH.sub.2. The buffering agent TRIS is reported to form soluble complexes with several cations, including Ca.sup.2+, which results in the reduced concentration of free Ca.sup.2+ ions available for the real time calcium phosphate coating (Jalota et al, 2006). More importantly, the buffering action of TRIS and added hydrochloric acid (HCl) in SBF allows the maintenance of pH of the system over the range of pH 7.2 to pH 7.4. With respect to the function of TRIS in formation of coating, the buffer system has a proton buffering capacity in which HCO.sub.3.sup.− ions are incorporated into the structures of apatitic calcium phosphates in the form of CO.sub.3.sup.2− ions. In addition, the working pH of 7.4 is near the lower end of the buffering capacity of TRIS, and this facilitates the formation of carbonated apatitic CaP clusters in SBF solutions.

[0015] The biomimetic method applied on gutta-percha cones lead to the deposition of a micro-crystalline, bone-like apatite layer of 16 μm in thickness. The preferred range of thickness of the coating is between 14 to 19 μm; coating of this thickness may reduce the stress imposed on the coating and may enhance the bonding of coating to substrate. The present inventors have demonstrated that the biomimetic method generated a strong adhesion between the bioactive coating and gutta-percha substrate, measured in the critical load range of 431.61-1002.15 mN. A coating that has greater adhesive strength to the substrate is more difficult to delaminate, and results in higher critical load. Analyses using Fourier transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), and scanning electron microscope (SEM) are performed to characterize the chemical composition, morphology and structure of the coatings, and experimental data has confirmed that the coatings produced consist of carbonated calcium phosphates and hydroxyapatite.

[0016] The obturation technique implemented for the present invention is the matching single cone technique, and coated GP cones are obturated with the Endosequence BC sealer (Endosequence®, Brasseler, USA). An in vitro evaluation of sealing ability and bonding strength of the hydroxyapatite and tricalcium phosphate coated GP showed significant improvements in both characteristics when compared to uncoated GP and the resin-coated GP system, EndoReZ™. It is known that biomimetic processes often take place at ambient temperature and results in deposition of calcium phosphate that resembles one, or a combination of the numerous naturally occurring calcium phosphate compositions, therefore, mineralized hydroxyapatite on the gutta-percha cones is able to enhance bone-bonding effects and promote the growth of new bone and tissue surrounding the root canal. Improved sealing ability and bonding strength are significant in the formation of a hermetic seal. This is so that microleakage and adverse bacterial migration in the treated teeth can be prevented, which otherwise may be a cause for reinfection. In addition to the biological functions described above, heat treatment is not required for the biomimetic approach, and no intricate and expensive equipment are necessary. Hence, these aspects of the coated GP provide the solutions, leading to improved integrity as root canal filling matter. The present invention, involving a biomimetic method for coating of bioactive hydroxyapatite and tricalcium phosphate onto pre-treated gutta-percha substrate in SBF solution, is hence, a promising pathway in the fabrication of a root canal filling matter to be further applied in endodontic treatments and restorations.

LIST OF NON-PATENT CITATIONS

[0017] Cheang, P. & Khor, K. A. (1996), ‘Addressing processing problems associated with plasma spraying of hydroxyapatite coatings’, Biomaterials, Vol. 17, No. 5, pp. 537-544. [0018] Colovic, B., Markovic, D. & Jokanovic, V. (2011), ‘Nucleation of biomimetic hydroxyapatite’, Serbian Dental Journal, Vol. 58, No. 1, pp. 7-15. [0019] Jalota, S., Bhaduri, S. B. & Tas, A. C. (2006), ‘Effect of carbonate content and buffer type on calcium phosphate formation in SBF solutions’, Journal of Materials Science: Materials in Medicine, Vol. 17, pp. 697-707. [0020] Mutsuzaki, H., Yokoyama, Y., Ito, A. & Oyane, A. (2013), ‘Formation of apatite coatings on an artificial ligament using a plasma- and precursor-assisted biomimetic process’, International Journal of Molecular Sciences, Vol. 14, pp. 19155-19168. [0021] Ong, J. L. & Chan, D. C. N. (1999), ‘Hydroxyapatite and their use as coatings in dental implants: a review’, Critical Reviews in Biomedical Engineering, Vol. 28, No. 5 & 6, pp. 1-41. [0022] Takeuchi, A., Ohtsuki, C., Miyazaki, T., Kamitakahara, M., Ogata, S., Yamazaki, M., Furutani, Y., Kinoshita, H. & Tanihara, M. (2005), ‘Heterogeneous nucleation of hydroxyapatite on protein: structural effect of silk sericin’, Journal of the Royal Society Interface, Vol. 2, pp. 373-378.