The present invention is directed to materials for filling dental root canals, and in particular dental root canal filling cones.
Dental root canal treatment generally involves three stages: shaping, cleaning and obturation (generally involving filling and sealing). The purpose of performing dental root canal treatment is to remove infected dental pulp tissue inside the pulp chamber and root canals, and to fill/seal the vacant space with a biocompatible material. More specifically, the ultimate objective of root canal treatment is to eliminate the infection inside the dental root system and to tightly seal or obturate, in three dimensions (3-D), the tiny openings at the end of the root canal, (referred in the profession as an apex). Failure to completely seal the apex or the root canal in 3-D leads to micro-leakage, which will lead to future bacteria colonization inside the root canal system, and re-infection and possible loss of the tooth. Micro-leakage is the most common cause of tooth failure.
Heretofore, root canal treatment processes involve placement of a root canal filling and/or sealing point or cone in a prepared root canal to plug the root canal, ideally in a manner to eliminate micro-leakage. Hereinafter, the term “point” and “cone” will be used interchangeably to refer to dental root canal filler/sealer. In the past twenty-plus years, leading dentists and scientists have improved and revolutionized the shaping and cleaning part of the root canal treatment process. But the basic filling technique still lags behind due to antiquated manufacturing process dated more than 50 years ago. The existing filling points and the process of application thereof do not lend themselves well to providing a good seal of the root canal apex.
More specifically, traditional root canal shaping and cleaning files are round shaped in cross section with single continuous taper across the entire file cutting section, from front tip end to rear end meeting the handle shaft. Different file systems carry different taper pitches. They typically range from 2% taper to 8% taper (the extent of taper can be express as a taper angle in degrees, or as a taper pitch in % of unit axial length). Referring to the schematic depiction in
Years ago, Dr. Herbert Schilder developed new root canal shaping and cleaning concept known as deep shaping. Dr. Schilder believes (and proven to be correct) that most of the infectious pathogens are harbored inside root canal space near the apex area. In order to effectively clean out these pathogens, a more effective cleaning file is needed; i.e., a file that has more than the traditional 2% taper. After this new concept took root, a new generation of endodontic files was developed. They are called greater taper (GT) files. The tapers of these files range from 4% to 8%. Dental root canal cones with matching tapers were also developed. After several years of clinical trial of these new files, clinician realized that greater taper files did clean root canal apex portion better, but its continuous single greater taper design makes the file diameter too big at the orifice portion of the root canal. As a result, the orifice opening 504 of the root canal gets over shaped, loses too much healthy root structure, and results in root fracture or even lateral perforation.
About ten years ago, a team led by Dr. John West further improved on the Dr. Schilder file system to resolve the problem of over-shaping of the root canal at the orifice opening portion. What this team did was to have multiple tapers built into single file, in a reduction sequence from root canal apex to the orifice opening. This new file system is called Progressive Tapering Files. Each file has progressively reducing tapers, which shapes a root canal having a 6% to 8% taper at the apical 5 mm portion of a root canal, and from there, the taper gets reduced every few millimeter moving towards the orifice portion of the root canal. Referring to the schematic depiction of
The most commonly used root canal filling material for many years is a biocompatible latex compound commonly called Gutta Percha, which comprises trans-polyisoprene, with a chemical composition of 1,4-trans-polyisoprene (TPI). Gutta Percha can be softened by heat to increase its plasticity comparing to other rubber based material. It is chemically inert therefore it is more biocompatible. Gutta Percha also hold its dimension quite well when change from heated liquid alpha phase to cooled solid beta stage.
The way to use Gutta Percha to fill/seal the root canal is to make it into a tapered cone shape “cone” or “point”, commonly called Gutta Percha point or cone. Heretofore, root canal filling points are formed of a filling material that is shaped into slender cones each having a small taper angle (e.g., 5-10 degrees). Each point is made into a particular taper shape that matches the shaping instrument (file) used by dentists to shape a root canal cavity for subsequent filling. The traditional way of making these points is by manual labor, specifically hand rolling Gutta Percha material into points to match shaping files. The Gutta Percha material needs to be softened first with higher temperature. Then being rolled into the point while being cooled to hold the final shape. This method of making the points has been in existence for over 50 years without much change. It is grossly inaccurate and risks material contamination since it is mostly handled by human hands.
There are a few automated and/or semi-automatic systems designed to make Gutta Percha points. They share same basic design approach, which mimic human hands rolling motion. These machines either use two rollers or one roller against one moving belt to roll points. There are several short comings with these machines. They are rather unstable and not efficient enough. They need constant adjustments for accuracy. Further, they are limited to rolling cones using only Gutta Percha based materials but not materials that have a different consistency compared to Gutta Percha materials.
All Gutta Percha cones fitting for Greater Taper (GT) files have been hand rolled. Hand rolling can only produce single taper cones. For obvious reason, these single taper Gutta Percha cones would not fit well in root canals prepared by Progressive Tapering Files. Referring to
U.S. Pat. No. 5,089,183 discloses a method of manufacturing appliances for use in filling endodontically prepared root canals with filler material, which involves inserting a shaft of a carrier into an uncured Gutta Percha material provided in a cavity of a block, heating and allowing the material to adhere to the carrier shaft. This process is low throughput, as it adds further complication to the making of a filler point for root canal.
It can be seen that the current root canal treatment procedures involve complex and challenging steps, which use cones that may be improperly shaped, which results in poor obturation leading to micro-leakage. An improved cone structure is desired to complement the Progressive Tapering Files. Further, It would be desirable to develop an improved root canal filling cone that lend itself to mass production, and a manufacturing process for high throughput production of root canal filling cones.
The present invention provides an improved root canal filling point/cone having a structure that can be manufactured precisely to result in better obturation with less micro-leakage.
One aspect of the present invention is directed to a molded root canal filling point having progressively decreasing tapers from the smaller tip end to the larger end. Another aspect of the present invention is directed to a thermo-pressure molding process for manufacturing root canal filling appliances (e.g., Gutta Percha points). A further aspect of the present invention is directed to the structure of the mold for undertaking thermo-injection molding.
In one embodiment, the multi-taper cones each has a generally axisymmetric conical structure, wherein at least a section along the length of the cone has a tapered structure, wherein the taper angle varies progressively in the axial direction to result in a multi-taper or variable taper conical structure. In one embodiment, the taper angle varies in small, discrete incremental steps along the length of the point, thus forming a structure having adjoining conical sections having different and discretely varying tapers at different axial sections along the length. The axial length of the conical sections may be similar or different. In another embodiment, the taper angle varies continuously, gradually and smoothly along the length of the point to form a gradual arcuate or curved surface profile in the axial direction representing continuously varying taper angles (represented by the varying angles of the tangents to the curved surface). In a further embodiment, there may be a combination of continuously varying tapers and discretely varying tapers along the length of the cone.
The present invention will be described herein-below in reference to root canal filling points made of endodontic filler material including what is known as Gutta Percha, for example. However it is understood that the present invention could be applied to manufacturing root canal filling points based on other types of endodontic filler materials, currently known or future discovered, without departing from the scope and spirit of the present invention.
For a fuller understanding of the nature and advantages of the invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings. In the following drawings, like reference numerals designate like or similar parts throughout the drawings.
This invention is described below in reference to various embodiments with reference to the figures. While this invention is described in terms of the best mode for achieving this invention's objectives, it will be appreciated by those skilled in the art that variations may be accomplished in view of these teachings without deviating from the spirit or scope of the invention.
The present invention provides an improved root canal filling point/cone having a structure that can be manufactured precisely to result in better obturation with less micro-leakage.
One aspect of the present invention is directed to a molded root canal filling point having progressively decreasing tapers from the smaller tip end to the larger end. Another aspect of the present invention is directed to a thermo-pressure molding process for manufacturing root canal filling appliances (e.g., Gutta Percha points). A further aspect of the present invention is directed to the structure of the mold for undertaking thermo-injection molding.
The present invention will be described herein-below in reference to root canal filling points made of endodontic filler material including what is known as Gutta Percha, for example. However it is understood that the present invention could be applied to manufacturing root canal filling points based on other types of endodontic filler materials, currently known or future discovered, without departing from the scope and spirit of the present invention.
The general dimensions of the body of the cone 10 may be within the following ranges, for example:
Concerning the taper of the cone 10, the cone 10 may have a single taper angle for substantially its entire length (i.e., a single-taper cone as shown in
In one embodiment, the multi-taper Gutta Percha cones each has a generally axisymmetric conical structure, wherein at least a section along the length of the Gutta Percha cone has a tapered structure, wherein the taper angle varies progressively in the axial direction to result in a multi-taper or variable taper conical structure. In one embodiment, the taper angles vary in small, discrete incremental steps along the length of the point, thus forming a structure having adjoining conical sections having different and discretely varying tapers at different axial sections along the length.
Generally:
Based on the illustrated dimensions, one can easily determine the taper angle or taper pitch at each section of the cones. As an example, referring to
As shown in
In the above described embodiments, the taper angles vary in small, discrete incremental steps along the length of the point, thus forming a structure having adjoining conical sections having different and discretely varying tapers at different axial sections along the length. While the conical sections (12-1, 12-2, etc) have different axial lengths, the axial length of the conical sections may be similar or different. In another embodiment, the taper angle varies continuously, gradually and smoothly along the length of the point to form a gradual arcuate or curved surface profile in the axial direction representing continuously varying taper angles (represented by the varying angles of the tangents to the curved surface). In a further embodiment, there may be a combination of continuously varying tapers and discretely varying tapers along the length of the cone.
The multi-taper cones in accordance with the present invention achieve several advantages. The progressively decreasing tapers from the tip end to the large end of the cone would result in a relatively smaller diameter at the large end of the cone. Referring to the schematic depiction shown in
The inventive multi-taper cone also provides a good “tuck back” for clinicians. In order to have good sealing at the apex region of the root canal, a Gutta Percha cone must be placed up to the apex opening with a tight fit. Dentists use X-ray imaging to confirm the Gutta Percha cone placement at the apex opening. But under current practice, they still rely on the Gutta Percha cone “tug back” resistance feeling to ensure the tight seal of the apex opening. If there is insufficient “tug back” resistance sensation, it means the tip of the Gutta Percha cone is not sealing the apex opening tight enough. With single taper Gutta Percha cones, it is easy to encounter false “tug back” sensation produced by the falsely from area inside root canal other than apex opening due to Gutta Percha cone getting caught or bent in different areas in the root canal.
In accordance with the present invention, the multi-taper cone 10 is provided with a substantially blunt flat tip 16, having a substantially flat surface orthogonal to the longitudinal axis of the body (which is not achievable with hand-rolled cones in the prior art), instead of a bullet head shaped tip found in hand-rolled cones, for a tight apex fit. Further, the taper of the tip portion (e.g., 3 mm from the tip end) very closely matching the taper of the corresponding file. After the tip portion, the taper of the cone is decreased. Wth respect to the Progressive Tapering File system, the taper of the inventive multi-taper cone after the tip portion is decreased more aggressively than the decrease in taper of the corresponding Progressive Tapering File. This will ensure that the Gutta Percha cone only “bind” at the apical region to produce a true apical “tug back” sensation, while a slight clearance is provided along the length of the Gutta Percha cone. This new multi-taper Gutta Percha cone design benefits not only Progressive Tapering file system, it also benefits Greater Taper file system for the same reasons. The inventive multi-taper cone may be used in a root canal prepared with a single-taper file system (e.g., a Greater Taper file system) or a Progressive Tapering File system.
The inventive multi-taper cones 10 also provide identifying indicia, which hand-rolled cones would not be able to provide.
In accordance with one embodiment of the present invention, the cone 10 (single taper or multi-taper cone) is made by molding, and in particular a thermo-pressure molding process, such as a thermo-injection molding process. The molding process of the present invention produces cones having good dimension control, within tight/small tolerances, such as ±0.01 mm.
In accordance with the present, the thermo-injection molding system for mold the cones discussed above and hereinbelow can be based on the mold and injection molding systems disclosed in copending U.S. patent application Ser. No. 14/181,621 filed on Feb. 14, 2014, which is fully incorporated by reference herein. For the sake of completeness, examples of injection molding systems are discussed below.
In one embodiment, a split mold is used for injection molding the cones 10 (single taper or multi-taper cones). Once again, the present invention will be described herein-below in reference to root canal filling points made with endodontic filler material including what is commonly known as dental Gutta Percha. However it is understood that the present invention could be applied to manufacturing root canal filling points based on other types of endodontic filler material, currently know or future discovered such as metallic, organic, inorganic based thermo-conducting material, without departing from the scope and spirit of the present invention. The split mold design is directed to molding using two complementary mold halves that together define mold cavities for dental root canal filler points/cones (i.e., using split mold). After the two mold halves of the above described split mold is pressed together, Gutta Percha material is injected into the mold cavities, cooled to set the material, the mold halves are separated, and the molded piece is released from the retaining mold halve by pushing the piece out of the mold cavity (e.g., using push rod 61 shown in
Heretofore, inventors are not aware of any Gutta Percha cones made by injection molding. In developing molded Gutta Percha points, the inventors explored conventional split mold designs and plastic injection molding processes. Referring to
The inventors realized that conventional split mold designs and plastic injection processes are not compatible with making Gutta Percha cones. The inventors found that conventional plastic injection molding machines, without modification in accordance with the present invention, would not be able to mold dental Gutta Percha cones due to the inherent nature of dental Gutta Percha material and the characteristics of conventional molding process not being compatible for Gutta Percha material. Split mold injection manufacturing process that were developed and used in plastic industry were designed to handle plastic materials that general have very high flow characteristic and melts at relatively low temperature. Because of the high stickiness/low flow character of dental Gutta Percha, extreme small dimension (can be as small as 0.10 mm tip diameter) of the desired products and very tight tolerance of the dimension are required. For example, for root canal filling, the Gutta Percha cones should not have significant residual mold lines (excessive material creeping from the mold cavity into the interface between a two-part mold, which remains on the cone after molding). In accordance with the present invention, conventional injection molding machine is adapted but must be modified with the inventive mold design and injection molding process in order to be able to conduct injection molding to obtain useful Gutta Percha cones of acceptable quality.
In summary, the inventors created a novel mold design and injection molding process by considering and overcoming the following issues particular to Gutta Percha material, so as to overcome the challenges of injection molding Gutta Percha cones:
1. Dental Gutta Percha material has low melting temperature and poor flow ability, which makes it difficult to fill entire mold cavity to form an ideal shaped product.
2. Because of low melting temperature of dental Gutta Percha, the residual elevated temperature inside metal mold chamber prevents Gutta Percha from hardening fast enough for a successful mold separation without Gutta Percha cone distortion.
3. Dental Gutta Percha has some stickiness when softened up, which makes it not being a very desirable material for plastic mold injection machine.
4. Dental Gutta Percha cone requires precision dimension for clinical use. The conventional plastic mold injection machine and mold design often leaves a rather large mold line which would not meet the precision required for dental Gutta Percha cone.
5. Because of dental Gutta Percha's low melting point and lack of flowability, higher temperature and higher pressure are required to extrude and inject Gutta Percha into a mold cavity. This often results in the permanent molecular changes inside dental Gutta Percha compound.
To overcome all of the above mentioned challenges, various modifications have been implemented to improve a conventional plastic injection molding system to become suitable for injection molding dental Gutta Percha material. The improvements and features incorporated into the novel dental Gutta Percha injection mold structure and injection molding process are discussed below.
A. Features to improve Gutta Percha material flowability by designing a new mold injection pathway and temperature control system:
1. Using specially designed material heating/compaction chamber (injection cylinder 57) with high strength material and smaller diameter extrusion screw to increase extrusion pressure.
2. Removing injection opening pathway and shortened injection nozzle 56 to reduce injection resistance. It also helps in eventual mold separation process.
3. Adding heating ring around injection nozzle 55 to facilitate Gutta Percha flow into mold cavities 32.
4. Adding venting channels 77 at far (tip) end of mold cavities to vent air to reduce air resistance, therefore to improve Gutta Percha flowability into the mold cavities. The air vent channels are drilled a couple of microns deep groove in the surface and at an optimal angle so only air, not the dental Gutta Percha material, is escaping.
5. Incorporating hot/cold water circulating system 78 as part of the mold structure to preheat entire mold block for improved Gutta Percha flowability.
6. Changing mold internal injection secondary channels 46 angulation from main channel 47 (initial passage in mold receiving material from injection) to the final mold cavities 32 to reduce flow resistance.
B. Features to improve mold thermo conductivity to make Gutta Percha cool and harden faster to assist mold separation process:
1. Mold core halves (41, 43) are made of material with higher thermo conductivity to distribute heat faster in the internal region of the mold halves.
2. Redesigned mold internal hot/cold water circulating system. When running ice cold water through the mold block, Gutta Percha points get cold and harden faster for easier mold automatic separation.
C. Features to control Gutta Percha stickiness by reducing its surface tension to facilitate mold separation step:
1. Other than providing water circulating cooling, spray openings 79 are provided in the mold to spray separation lubricating agent into mold cavities to keep cavities clean and surface tension low. Therefore it will be easier to separate the cold without Gutta Percha points sticking to the mold cavity surface.
2. Removed traditional injection opening pathway to reduce contact surface area of residual molded material. The short main injection channel 47 minimizes the resistance when separating the mold.
D. Features to improve molded product precision, to avoid mold mismatching when closing, and to reduce/eliminate mold line:
1. To improve lateral alignment of the mold halves 40 and 42, other than locking/alignment pins (similar to the alignment pins 116 in
2. Increased thickness of the mold frames 70 and 72, and subject the mold frames to high temperature treatment. This increases its strength and reduce deformation when pressure is applied to lock the mold halves together.
3. Internal surfaces of mold cavities 32 are treated with Nitrogen to increase surface hardness and/or strength, thus reducing wear. This ensures the integrity of the mold cavities to allow for precision closing of the mold cavities using the mold halves, to minimize and substantially eliminate residual mold line on the molded pieces.
4. Providing a cold water circulating system to cooling channels 78 to quickly reduce mold body temperature to minimize thermo expansion from repeated mold injection operation.
E. Features and process protocols implemented in injection molding machine to provide correct technical references specific for dental Gutta Percha material to protect its molecular stability and its properties for clinical applications:
1. Reducing the holding volume of the heating/compacting chamber or injection cylinder 57 for preparing the final Gutta Percha material ready before injection. This minimizes the length of time for Gutta Percha material to remain inside a high temperature and high pressure chamber to avoid possible changes to its molecular structure.
2. The holding/compacting chamber or injection cylinder 57 has several heating zones (e.g., three to five zones) to gradually increase the temperature of Gutta Percha material to its melting point as it is moved towards the injector 56. This further prevents breakdown of Gutta Percha molecular structure.
In accordance with the present invention, the Gutta Percha points made by the novel Gutta Percha injection molding system has improved tolerance and quality that meet the requirements for clinical use. Manufacturing efficiency is improved, reducing production costs. The molded pieces and associated injection molding process can also mark ISO size codes onto each individual Gutta Percha point to reduce the chance of dentist error in picking a wrong size/shape Gutta Percha point. Manual hand-rolled Gutta Percha points cannot include this safety feature. The novel Gutta Percha injection molding system can produce single taper Gutta Percha points or points having multi-tapers on a single point. This will satisfy clinicians' needs to have multi-tapered Gutta Percha points to match the new generation of multi-tapered root canal cleaning instruments/files.
In accordance with the present invention, given the design of the mold and molding process, the mold remains in the injection molding machine without moving between stations, as was in the earlier embodiment. Mold cleaning and preparation are easier to undertake more frequently.
The clinical aspect of root canal treatment techniques and material are evolving rapidly. Using the novel mold design and injection molding technology, challenges encountered by dental clinicians have been meet. The novel injection molding system can be adapted to evolve with new clinical challenges in dentistry.
While the above embodiment illustrated in the drawings refers to mold halves supported for horizontal movements in an injection molding machine, it is contemplated that the mold halves can be supported for vertical movements in another injection molding machine, without departing from the scope and spirit of the present invention.
Below are further elaborations of further improvements to the injection molding system.
Dental Gutta Percha material requires much higher pressure to inject into the mold than plastic material. This requires even tighter closing of the split mold, to ensure tight mating of the mold core halves to tightly define a mold cavity. Instead of just increasing split mold locking pressure, the mold is designed such that instead of having each mold core halve supported in its respective frame with the surface of the mold core halve flush with the surface of the frame, the mold core halve is raised a few microns with respect to the surround surface of the frame, so that the mating surface of the mold core halve protrudes above the adjacent surface of the frame. When two halves of the mold close and lock together, the mold core halves will close much tighter to ensure a complete injection of the dental Gutta Percha material with better tolerance.
To increase the injection pressure inside the cavity chamber, the diameters of the network of secondary injection channels 46 (the channels in the plane of the mold cavities) leading to the mold cavities 32 are reduced. This will allow Gutta Percha material to build up extra pressure before bursting into the cavity chamber through those reduced diameter secondary channels 46. The main injection channel in line with the injection nozzle is shortened to reduce resistance and to save expensive dental Gutta Percha material. The injection speed of the Gutta Percha material, which dictates the travel speed of the material into the mold cavities, is important to a perfect Gutta Percha cone finish.
To increase the dental Gutta Percha material flow rate, an electrical heating element is provided in the form of a ring inside the mold supporting frame where the injection nozzle meet the mold core at the main injection channel opening. This will ensure the Gutta Percha material stays hot and liquid stage when entering into the cavity chamber. The cooling channels provided in the supporting mold frame help cooling off the mold quickly after a successful injection. The length of the injection nozzle is kept to a minimum and made “fatter” to better retain heat from the heating ring.
Referring to
If Gutta Percha compound is kept inside pre-heating and injection compartment for too long, the Gutta Percha material will degrade. The size of pre-heating and injection cylinder is reduced in length and in diameter to hold less amount of Gutta Percha material and to increase injection pressure and speed. Heating stations in this cylinder is reduced from 5 to 3. The temperature setting for heating stations are set in a progressively decreasing manner, from injection nozzle to back end of the cylinder, e.g., at 140, 120, 90 Celsius degree, at the respective station.
Because it uses very small amount of Gutta Percha material for each injection batch, the drive screw in the injection cylinder 57 (the cylinder behind the injection nozzle 56, which holds the material ready to be injected) in the molding machine barely starts rotating to push the material to be injected, and hydraulic pressure barely builds up to the optimum level for injection, yet Gutta Percha material is already injected from cylinder into mold chamber. This results in incomplete mold injection and results in not fully filled mold cavities. To correct these problems, the “driving screw” inside the injection cylinder 57 is redesigned so it moves less amount of Gutta Percha material to the front (nozzle end) with more rotations of the screw. At same time, forward plunging motion is provided to axially push the screw to achieve very fast high pressure injection.
Another change for the injection cylinder is to change the size and the length of the injection nozzle 56. The injection cylinder 57 and nozzle 56 temperature is much higher than the mold temperature. When the nozzle 56 locks into mold injection channel opening, high temperature is needed to ensure the proper flow of Gutta Percha material. Sudden cool off can “freeze” the Gutta Percha material inside the nozzle. A heating element 55 is provided inside the mold around the tip of the nozzle 56 to keep the region around the nozzle opening reasonably warm. The nozzle length and internal diameter are also reduced to reduce Gutta Percha material traveling time from injection cylinder 57 to mold cavity 32. The nozzle's outer diameter is increased so it retains more heat.
Injecting Gutta Percha material requires much higher pressure than injecting plastic. An instant compressed gas chamber system is created to assist hydraulic system to deliver maximum and “instant” pressure needed. A liquid nitrogen gas cylinder is provided to help increase pressure build up speed. Air pressure travels faster than hydraulic pressure. The air pressure system is added at the front of the hydraulic pressure system. When it is ready to inject and pressure system is activated, both air and hydraulic system delivers pressure to give the instant push. This is an important element of obtaining optimum injection time and pressure. Short injection time is preferred, without the negative effect of higher injection pressure. A balance of fast injection (reaction) time and optimum injection pressure is preferred.
Concerning timing of the injection, bigger hydraulic pump with faster reaction time is employed. Since only a very small amount of Gutta Percha material is injected into mold cavities each cycle of injection, and injection time is just a few mile-second, machine needs to build up optimum pressure before injection cylinder screw push out the Gutta Percha material. Further, pressure needs to be activated without delay when screw starts pushing forward, similar to a plunder in a syringe. Computer controlled faster reacting pump further improves injection reaction timing, in addition to gas assisted hydraulic system noted above.
To further secure fast injection time and optimum injection pressure combination, a vacuum line is provided at space just in front of injection nozzle 57, near the main mold channel 47. Before injection starts, vacuum pump will remove most of the air from mold main channel 47 and secondary channels 46. The vacuum pump turned off for injection to take place. This will reduce resistance and increase injection speed. This vacuum feature is preferably used when using a harder type dental Gutta Percha material.
The mold separation process can be further improved by using a mold injection machine having a vertical axis of movement for the mold halve. Wth this vertical configuration, the stationary (fixed) mold halve 40 is at the bottom, with the moveable mold halve 42 movable with respect to the fixed mold halve 40. This stationary fixed mold halve 40 has the locking stub openings 52 behind the cone cavity chamber to retain the Gutta Percha cones in this mold halve as discussed above, when the top mold halve 42 is lifted and separated. After separation, push rods 54 and 61 from underneath the bottom mold halve 40 (see
To further improve production efficiency and throughput, two similar stationary mold halves 40 can be provided side by side, and can move horizontally along precision guide rails or on a precision sliding table, to be place sequentially below the top mold halve 42. The two mold halves 40 therefore take turns to mate with top mold halve 42, so one mold halve 40 would be going through an injection molding cycle while the other mold halve 40 is processed to remove the molded rack of cones and prepared for the next injection cycle.
While the present invention has been described above in connection with the illustrated embodiments, the scope of patent invention covers all possible present and future variations and improvements that is apparent from the disclosure above. While the invention has been particularly shown and described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit, scope, and teaching of the invention. Accordingly, the disclosed invention is to be considered merely as illustrative and limited in scope only as specified in the appended claims.
This application is a continuation of U.S. application Ser. No. 14/187,215, filed on Feb. 21, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 14/181,621 filed on Feb. 14, 2014, which claims the benefit of priority of U.S. Provisional Patent Application No. 61/767,254 filed on Feb. 21, 2013, and U.S. Provisional Patent Application No. 61/940,367 filed on Feb. 14, 2014; which are fully incorporated by reference as if fully set forth herein. All publications noted below are fully incorporated by reference as if fully set forth herein.
Number | Date | Country | |
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61767254 | Feb 2013 | US |