Patent Application
20190021958
The present invention relates to the process of creating an improved biological Mineral Trioxide Aggregate (MTA) in a dense tile, or Target. The Target enables a process of coating the improved MTA on implantable medical devices or can be micronized into a MTA material for traditional use.
Mineral trioxide aggregate (MTA) (sold under the trade names gray or white ProRoot MTA (Dentsply Sirona Inc., York, Pa., US) is a substance currently used in general dentistry and in endodontics to replace natural tooth material in apexification, pulp capping, pulpotomy, regenerative endodontics, root canal filling, root-end filling, root perforation repair, tooth restorations and the like. An example of MTA used in endodontic applications is disclosed in U.S. Pat. No. 8,979,991 which is hereby incorporated by reference for such disclosure.
It would be desirable to provide an MTA material for dental applications including for endodontic, restorative or other uses that has improved biological effect. More particularly, it would be beneficial to the dental arts to provide such a material that is demonstrated to improve the production of hydroxyl apatite (HA) in the presence of body fluids (or simulated body fluids such as phosphate buffered saline) to produce a material having cementum qualities.
For example, in endodontic applications, the material or composition should provide a stable barrier to bacteria and fluid leakage in the root canal system of a tooth. In addition, the composition should help promote the growth of the new bone and tissue surrounding the root tip area.
The patent or application file contains at least one drawing executed in color. Copies of the patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
A dense Mineral trioxide aggregate (MTA) tile is produced through a series of process steps which creates a Target suitable for physical vapor deposition (PVD) methods. The resulting MTA material (Target) has improved biological effects and produces hydroxyapatite (HA) at an accelerated rate when immersed into simulated body fluid. The resulting Target can be used to deposit a thin layer as desired, such as upon an obturation point, or can be micronized to use as powder in sealer mixture or as additive to gutta-percha resin during compression molding and/or injection molding process. Conventional obturation points such as those made of gutta percha materials are useful in the application of the present invention.
According to one embodiment of the invention, a thin layer of a processed MTA was deposited using PVD method on the surface of otherwise conventional gutta-percha points. Both processed MTA (Target) and thin layer deposited from Target produces hydroxy apatite mineral in the presence of Phosphate Buffered Saline which is beneficial in the formation of cementum like material for natural sealing of dental root canals.
Another embodiment comprises the use of micronized Target molded onto the surface of a gutta-percha point using a compression molding technique.
A further embodiment of the invention includes the use of micronized Target molded onto the surface of the gutta-percha using an injection molding technique.
Another preferred embodiment is deposition of processed MTA (Target) in a form of thin film onto implantable and prosthetic devices using PVD methods.
A dense MTA with improved biological effects is produced through special processing techniques including: setting which includes steps of: (i) mixing distilled water and cement, weight ratio 1/3; (ii) placing mixture in a mold and vacuum; (iii) Humidity chamber [CO2 6000] Humidity 90%, Temperature 36° C. for 48 hours; (iv) Baking in oven (temperature 160° C. for 6, hours) micronization which includes steps of (i) Grinding [COL-INT-Tech] and/or (ii) Ball milling [SPEX Sample Prep Mixer/Mill 8000M: Zirconia or alumina ball, alcohol can be used as liquid media, Milling for 15-30 minutes, particles size below 53 micron,
Target/powder pressing, which include Green compacts pressing {carver hydraulic press #3925: Circular dies for compact pressing, diameters 13 mm, 31 mm and 50 mm.; applied pressure up to 90 Psi and
Sintering (a) Conventional [Conventional furnace [Carbolite BLF-1700}: Ramp 2.5° C./min to 180° C.; Dwell @180° C. for 15-30 min; Ramp 2.5° C./min to 450° C., Dwell@450° C. for 30 min-1 hr, Ramp 2.5° C./min to 850° C., Dwell@850° C. for 8-24 hrs] (b) HIP (Hot Isostatic Press (AIP6-30H]: Ramp 10° C./min to 180° C., vacuum; Dwell @180° C. for 15 min, vacuum; Ramp 10° C./min to 450° C., vacuum; Dwell@450° C. for 30 min, up to 5 ksi; Ramp 5° C./min to 750° C., up to 10 ksi ; Dwell @750° C. for 1-4 hrs, 10-20 ksi. (
Dense MTA targets can be created for use in physical vapor deposition (PVD) methods to create a thin layer of MTA material on the surface of implantable devices such as dental implants, endodontic obturation materials and the like. PVD techniques include:
Cathodic Arc Deposition: In which a high-power electric arc discharged at the target (source) material blasts away some into highly ionized vapor to be deposited onto the work piece.
Electron beam physical vapor deposition: In which the material to be deposited is heated to a high vapor pressure by electron bombardment in “high” vacuum and is transported by diffusion to be deposited by condensation on the (cooler) work piece.
Evaporative deposition: In which the material to be deposited is heated to a high vapor pressure by electrically resistive heating in “low” vacuum.
Pulsed laser deposition: In which a high-power laser ablates material from the target into a vapor.
Sputter deposition: In which a glow plasma discharge (usually localized around the “target” by a magnet) bombards the material sputtering some away as a vapor for subsequent deposition.
A thin layer of MTA (Mineral Trioxide Aggregate) was deposited from sintered targets on the surface of gutta percha points and titanium implantable device. The processed MTA material may also be ground into small particles for use in Dental products or as a MTA powder with improved biologicals effects.
The improved MTA is particularly suitable for obturating and sealing dental root canals. The improved MTA provides a stable barrier to bacterial and fluid leakage in the root canal. The accelerated generation of HA will also help promote the growth of new bone and tissue surrounding the root tip area. The improved MTA should also provide a stable barrier to bacteria and fluid leakage in the root canal system of the tooth.
A method for forming the dense MTA material (Target) may include one or more of the steps/processes described below and further shown in
Mixing (white) Portland Cement (WPC or PC) to Deionized water having a ratio in the range of about 10:1 to about 1:10, preferably about 5:1 to about 1:5, and more preferably about 5:1 to about 1:1 (e.g., about 3:1 such as about 3 parts PC (WPC) to about 1 part deionized water). The mixture is thoroughly blended and vacuum is drawn out to create a harmonized cake mix and then placed in molds.
Once the mixed cement is put in molds, the molds are placed in a humidity chamber to cure. The humidity chamber is set at 36° C. with 90% Relative Humidity (RH) from about 5 hours to about 10 days, and preferably from about 12 hours to about 5 days (e.g., about 2 days).
Once the cement is cured, the set cement is placed in a Post cure bake oven set at a temperature from about 50° C. to about 500° C., and preferably from about 100° C. to about 250° C. (e.g., about 160° C.) for a time ranging from about 15 mins to about 2 days, and preferably from about 1 hour to about 12 hours (e.g., about 6 hours).
The target creation process may include a micronizing step. Once the cement is post baked, it is then pulverized, micronized and sieved to a particle size ranging from about 1 micron to about 200 microns, and preferably from about 10 microns to about 100 microns (e.g., about 53 microns (μ53)).
The target creation process may include a Sintering Step. The Powder Micronized MTA is pressed into a green compacts using a hydraulic press with the applied pressure range from 60 Psi to 120 Psi. The green compacts are placed into a sintering chamber for a heat treatment that consists of several heating steps/stages. The first stage is heating up to the temperature range from about 25° C. to about 200° C., preferably from about 100° C. to about 150° C. (e.g., about 125° C.) and dwell at this temperature for a time period of 5 mins to about 5 hours, preferably from 15 mins to about 2 hours (e.g., about 30 to about 40 mins). The second stage of heat treatment, includes the temperature to range from about 275° C. to about 650° C., and preferably from about 350° C. to about 525° C. (e.g., about 450° C.) for a time period ranging from about 5 minutes to about 5 hours, and preferably from about 15 mins to about 3 hours (e.g., about 1 to 2 hours). At the final step of the sintering process, the temperature ranging from about 550° C. to about 1100° C., and preferably from about 650° C. to about 975° C. (e.g., about 750° C. to 850° C.) for a period of time ranging from about 30 mins to about 2 days, and preferably from about 2 hours to about 1 day (e.g., about 4 hours to about 12 hours).The overall sintering process can be completed in one step at the temperature range about 750° C.- 850° C. with the slow heating ramp and longer dwell time. The effect of sintering parameters on density of sintered MTA (Target) is shown in table and graph presented on
The target creation process may include a hot isostatic pressing (HIP) step/process. The set sintered targets may be placed into a HIP chamber at a temperature ranging from about 250° C. to about 1500° C., and preferably from about 500° C. to about 1000° C. (e.g., about 750° C. to about 850° C.) for a period of time ranging from about 30 mins to about 2 days, and preferably from about 2 hours to about 1 day (e.g., about 4 hours to about 12 hours) at a pressure ranging from about 1,000 psi to about 50,000 psi, and preferably from about 7,500 psi to about 35,000 psi (e.g., about 15,000 psi to 20,000 psi). The effect of HIP sintering parameters on density of sintered MTA (Target) is shown in
The pre-calcination process that reported to be an improvement for density and mechanicals properties of sintering ceramics doesn't have a significant effect on properties of MTA as can be seen from graphs presented on
The changes in chemical composition in MTA material during sintering processes described above were monitored using Raman spectroscopy and X-Ray Florescence spectroscopy (XRF). The Raman analysis indicates that pre-calcination heat treatment affect the degree of hydration and with the high calcination temperature (lines m1350 and m1450 on
The sintered MTA targets may also be further micronized to a particle size ranging from about 1 micron to about 200 microns, and preferably from about 10 microns to about 100 microns (e.g., about 53 microns). The resultant powder MTA has improved biological effects and produces HA at an accelerated rate, so it can be used as additive to existing dental sealers to improve biocompatibility and osteointegration process.
Compression molding process which entails sprinkling MTA powder on the substrate during compression molding process; and powder spraying process which, entails blasting the substrate with high velocity spray of MTA powder.
The preferred method of coating medical devices with MTA target is physical vapor deposition such as Pulsed Laser Deposition (PLD) or RF Magnetron Sputtering. Alternative methods of creating coating from dense MTA target may also include E-beam and thermal evaporations like is discussed above.
This is a thin film deposition technique where a high-power pulsed laser beam is focused inside a vacuum chamber to strike a target of the material that is to be deposited. This material is vaporized from the target (in a plasma plume) which deposits it as a thin film on the substrate (in this case the GP points); this process occurs in ultra-high vacuum.
While the basic-setup is simple relative to many other deposition techniques, the physical phenomena of laser-target interaction and film growth are quite complex. When the laser pulse is absorbed by the target, energy is first converted to electronic excitation and then into thermal, chemical and mechanical energy resulting in evaporation, ablation, plasma formation and even exfoliation. The ejected species expand into the surrounding vacuum in the form of a plume containing many energetic species including atoms, molecules, electrons, ions, clusters, particulates and molten globules, before depositing on the substrate. The general workflow of manufacturing MTA thin film with the PLD process presented on
RF (Radio-Frequency) Magnetron Sputtering is a plasma-assisted method for physical vapor deposition of thin films. RF source utilizes high power voltage pulses (impulses) of with the fixed frequency of 13.6 MHz.
The RF-sputtering technique offer an advantage of depositing nonconductive materials onto substrate at low deposition temperatures.
The general workflow of manufacturing MTA thin film with the magnetron sputtering process is depicted in
MTA films were deposited on Silicone (
PVD can also be used to deposit a thin layer of MTA on a variety of surfaces. Feasibility has been established for PVD of MTA on polyisoprene and ceramic surfaces. Other potential applications include deposition of a MTA film on variety of metal or ceramic surfaces such as titanium, NiTi alloys, stainless steel, and porcelain.
In order to confirm bio-activity of sintered MTA and MTA coating produced by PVD the HA-forming ability was tested on sintered targets and films deposited on gutta-percha and titanium. The bioactivity of bone-bonding material is commonly evaluated in vitro by immersion of the test material into simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma, and examining the formation of hydroxyapatite (HA) on its surface.
Set of films, deposited on Gutta Percha and Titanium samples, were immersed in 2 ml of SBF (Dulbecco PBS lx) at 37° C. for 1, 3, 7, 14 and 21 days. After immersion, the surface morphology of the samples and theirs composition were investigated by SEM, XRD, and EDS techniques. Based on reported studies, we expected the formation of HA after 3-7 days of immersion, the crystallized fraction HA commonly reported after 14-21 days. The typical sign of apatite formation is flower-like HA crystals observed by SEM. In addition to imaging the XRD and Raman analysis employed to determine the type of apatite forming. The major characteristic of appetites is Ca/P ratio that was determined by EDS analysis, the ratio 1.67 indicates the bone-like apatite formation.
The SEM images shown formation of HA-like crystals after 1 day immersion on films deposited on Gutta-percha (
The similar bioactivity evaluation was conducted on sintered MTA-targets. The pressed and sintered samples were immersed in 10 ml of SBF (Dulbecco PBS 1×) at 37° C. for 1, 3, 7 and 14 days. The HA forming ability was evaluated by weight method—comparing initial weights of samples and weight after immersion. The samples after immersion were air-dried at least for 24 hours before weighting. The graphical results of weight analysis are presented on
Thus, it should be evident that the invention as disclosed herein carries out one or more of the objects of the present invention set forth above and otherwise constitutes an advantageous contribution to the art. As will be apparent to persons skilled in the art, modifications can be made to the preferred embodiments disclosed herein without departing from the spirit of the invention, the scope of the invention herein being limited solely by the scope of the attached claims.
This application is a continuation of pending U.S. non-provisional patent application Ser. No. 15/140,586, filed on Apr. 24, 2016, which claims priority to provisional U.S. patent application Ser. No. 62/154,282 filed on Apr. 29, 2015, where are herein incorporate for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 62154282 | Apr 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15140586 | Apr 2016 | US |
| Child | 15972360 | US |
