FIELD OF THE INVENTION
The fields of art to which the invention pertains include the field of dentures and the field of silicone rubber and utilization thereof.
BACKGROUND AND SUMMARY OF THE INVENTION
Ordinarily, the lower denture is by far the hardest to make comfortable for the patient, especially where the patient's lower gum ridge has resorbed. Therefore, instead of a firm, hard ridge to support a denture, the patient often times has a knife-edge ridge on which to support a denture. With a knife-edge ridge of this nature, considerable pain occurs when pressure is applied to the ridge. This problem is further amplified by the fact that the force necessarily exerted in biting or chewing is of a very high order, and accordingly, so is the impact and shock to the gum. This is particularly true when the pressure exerted upon the gum ridge is localized over a relatively small area.
In the fabrication of artificial dentures, the denture base is generally formed from an acrylic resin such as methylmethacrylate resin. These resins are well suited for this purpose because they are hard, holding the artificial teeth in their desired positions, and are also quite inert to the saliva and food encountered in the human mouth. However, since dentures made from acrylic resin are relatively hard, they often cause discomfort to the patient when pressure is applied. As a result of this discomfort or pain, it is extremely uncomfortable for the denture wearer to bite down, as he normally would to masticate food. To alleviate some of this discomfort and pain, the prior art has applied a soft lining material to the denture base and methods of applying a soft lining material to a new denture while in the process of fabrication, or relining a denture that has been processed previously, are well known to the prior art.
In my previous U.S. Pat. Nos. 3,339,283 and 3,391,231, I have described an hydraulic cushion which is secured and sealed in the gum engaging groove portions of a denture. Such a cushion results in the distribution of pressure exerted upon any portion of the gum ridge over substantially the entire gum ridge thereby greatly minimizing discomfort associated with the impact and pressure exerted upon the wearer's gums during mastication. The hydraulic cushion is sealed to the denture base utilizing a soft lining material of the type generally used as a denture liner and which is adapted to overlie and conform to the gum ridge of the denture wearer. Some difficulties have been encountered with several soft lining materials which are commercially available and these difficulties have occurred both with utilization of an hydraulic cushion and utilization of the soft lining as the sole cushioning mechanism. Depending upon the type of material utilized, after a short period of time it would lose its resiliency and/or would absorb saliva resulting in shape distortion. Other materials generally have a poor bond to the acrylic base material and the materials lack rigidity and body so that a grinding stone or sand-paper bands or disks cannot readily be used to dress down or remove excess soft lining, and the lining cannot readily be polished smooth with wet pumice and a rag-wheel, typical procedures in the finishing of artificial dentures.
The present invention provides a denture constructed with a resilient liner which does not suffer the foregoing drawbacks. The liner can be directly applied to the acrylic material of the denture base, or applied overlying an hydraulic cushion, as above described, and very effectively bonded thereto without the requirement (although not precluded) of a securing primer. The liner has a very low saliva absorbtion rate, retains its resiliency for extended periods of time, and does not support the growth of fungus. The liner is sufficiently soft as to be comfortable to wear and yet it is sufficiently rigid so that after it is processed it can be dressed down easily with a stone or a sandpaper disk and smoothed with wet pumice and a rag-wheel.
In particular, there is provided a combination of rigid denture carrier formed with a gum line groove and secured in the groove a realtively soft, non-absorbent resilient liner material comprising a silicone rubber denture base material containing more than 2 percent and less than 10 percent by weight, based on the silicone rubber, of methylmethacrylate polymer. The methylmethacrylate polymer in the above amounts produces a proper Shore hardness for processing and wearing of the denture and aids in securing the liner to the denture carrier. In a further embodiment of the invention there is added with the methylmethacrylate polymer a vinylsilane or an acryloxyalkylsilane in an amount sufficient to increase the bonding of the silicone rubber to the carrier. The silane cooperates in this function with the methylmethacrylate polymer contained in the silicone rubber and the acrylic or other plastic material constituting the denture carrier. In a preferred formulation method, the silane is added to the methylmethacrylate for introduction to the silicone rubber so as to coat each particle of the methylmethacrylate therewith. In still a further embodiment a coloring pigment is added to the silicone rubber so that the lining and the denture material are harmonius in color.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of a portion of a dental flask with a portion of a lower denture incorporating an hydraulic cushion and embodying the present invention in a stage of fabrication;
FIG. 2 is a perspective, in partial cross section, of a portion of the denture of FIG. 1 after construction; and
FIG. 3 is a perspective, in partial cross section, of a portion of a denture incorporating a resilient liner only.
As required, detailed illustrative embodiments of the invention are disclosed herein. However, it is to be understood that these embodiments merely exemplify the invention which may take forms that are different from the specific illustrative embodiments disclosed. Therefore, specific structural and functional details are not to be interpreted as limiting, but merely as a basis for the claims which define the scope of the invention. In this regard, while removable full lower dentures are illustrated and described hereinafter, it is understood that these embodiments are shown for illustrative purposes only. The invention is also suitable for use with removable partial dentures and with the relining of a denture that has been processed previously.
Referring to FIG. 1, a step in the fabrication of a denture which incorporates an hydraulic cushion is illustrated. SUch a cushion and the manner of construction of a denture in which it is incorporated is disclosed in detail in my prior U.S. Pat. Nos. 3,339,283 and 3,391,231, which by reference are made part of the disclosure of the present invention. FIG. 1 illustrates a step in the fabrication wherein a denture carrier 10 has been formed by packing of a conventional sectional dental flask, indicated generally at 12, with a plastic such as an acrylic which, upon curing, forms a tough rigid material constituting the carrier 10. In place of acrylic, some dentures utilize lucite or other such material. The dental flask 12 serves as a container for a gum ridge model 14 and teeth 16 invested in stone 18, prepared by methods well known in the art. At a stage in fabrication prior to that illustrated in FIG. 1, a horesshoe shaped strip of relatively low melting point wax was placed on the gum ridge model 14 in the space occupied by the liner indicated at 20, to be described hereinafter. Thereafter, a horseshoe shaped spacer formed of a relatively rigid inert plastic such as neoprene was placed on the wax strip in a position generally occupied by the hydraulic cushion indicated at 22, which will be described hereinafter. The flask 12 was then packed with the acrylic as above described and after the excess of acrylic was expressed, the wax strip and spacer were removed by removal of the lower portion of the flask 12 and gum ridge model 14. At that point, an hydraulic cushion 22 is placed in the space previously occupied by the spacer. The hydraulic cushion includes a sealed bag 24 formed of a suitable resilient plastic such as silastic rubber produced by Dow-Corning for example, which is substantially filled with a viscous fluid 26 such as a liquid uncatalyzed cold cure silicone rubber produced by Dow-Corning and sold under the trademark of Silastic 390. A horseshoe shaped plastic bag filled with such a liquid 26 will have a viscosity comparable to the pressure-bearing ability of the mucous membrane of the mouth. Further details as to the manner of operation of the hydraulic cushion can be obtained with reference to my prior patents referred to above.
In accordance with the present invention, the remainder of the void formed in the carrier 10 by removal of the strip of base wax is packed with an uncured silicone rubber of specific composition and is hereinafter described in more detail. The flask is closed thus expressing any excess silicone rubber and submerged in a water bath at about 60°-100°C for a sufficient time, about 0.5-5 or more minutes to allow for curing of the acrylic and, at the same time, the silicone rubber which forms the resilient liner 20. The flask 12 is then removed and the stone 18 is carefully chipped away from the completed denture.
Both the spacer and strip of wax utilized to form the voids for the hydraulic cushion 22 and resilient liner 20, respectively, can be provided in a number of sizes so as to properly overlie the configuration of the gum ridge. Normally three sizes are sufficient to properly fit persons requiring dentures.
Referring to FIG. 2, the completed denture is illustrated and it is seen that the resilient liner 20 overlies the hydraulic cushion 22 and extends therebeyond to seal with the acrylic material of the carrier 10, as at 28, completely enclosing the hydraulic cushion 22. While prior methods have utilized a primer for the silicone rubber in effecting such a seat, the present invention, while not precluding the use of a primer, can operate successfully and satisfactorily without a primer.
Referring to FIG. 3, an alternative construction is illustrated wherein a resilient liner 20' constitutes the entire cushioning component of the denture and is in direct contact along substantially the entire surface of the gum ridge groove formed in the carrier 10'. In this embodiment, during fabrication of the denture, a strip of low melting point wax defines the shape of the groove, the spacer above referred to not being utilized. After removal of the wax strip, the void in the carrier thereby formed is packed with the uncured silicone rubber referred to above, which after curing as above described, forms the resilient liner 20'.
Further in accordance with the present invention, I have found that the utilization of a silicone rubber having specific composition results in a superior denture product. The uncured silicone rubber contains more than 2 percent and less than 10 percent by weight based on the silicone rubber, of methylmethacrylate polymer and a vinylsilane or an acryloxyalkylsilane in an amount sufficient to increase the bonding of the silicone rubber to the carrier. Silicone rubber is a polysiloxane resin which contains a plurality of organic-substituted, e.g., hydrocarbon-substituted, silicone atoms linked by oxygen atoms, and can be prepared, for example, by hydrolysis and condensation of a mixture of organohalogenosilanes. Reference can be made to Welsh U.S. Pat. No. 2,449,572 and to the Encyclopedia of Polymer Science and Technology, Interscience Publishers, New York (1970), Vol. 12, pages 531-552. Silicone rubber is generally a linear condensation polymer based on dimethylsiloxane, but the methyl groups may be substituted with other groups such as phenyl or vinyl. Room temeprature vulcanizing silicone rubber compounds are particularly preferred as being readily curable, but other products can be utilized. Examples include General Electric's RTV-108 and Dow-Corning's Silastic 390.
Generally, those silicone rubbers which are self curing at room temperature are desirable for ease of utilization, however, silicone rubbers requiring a curing agent can also be used, e.g., General Electric RTV-511 or 615 which are supplied with their own curing agents. For other silicone rubbers having the desired Shore A Durometer hardness, such curing agents as tin octoate (e.g., as sold under the trade name Nucure 28 by Tenneco Chemicals, Inc.) and dibutyl tin dilaurate (sold under the trade name Thermolite-12 by M & T Chemicals) can be used at levels ranging from about 0.1 percent to about 0.5 percent by weight. The silicone rubber should be chosen so that when combined with the methylmethacrylate polymer and silane, as described below, the combination has a Shore hardness of about 10-75.
The methylmethacrylate polymer component generally has a molecular weight of about 300,000 to about 3,000,000, a preferred range being about 450,000 to 550,000. The methylmethacrylate polymer acts as a low water absorbing filler to help produce a desirable Shore hardness compatible with the soft tissues of the denture-bearing area of the wearer's gums. The resilient liner will thus be gentle, yet firm enough so that there will be no marked distortion of the liner under the stress of mastication. The methylmethacrylate polymer imparts enough rigidity and body so that a grinding stone or sandpaper bands or disks, which are used in the dressing-down or finishing of a conventional denture, can be used to dress-down or remove excess lining. The lining can then be polished smooth with wet pumice and a rag-wheel. The inclusion of the methylmethacrylate polymer also helps to promote a more secure bond between the silicone rubber and the denture carrier. Greater than 2 percent by weight and less than 10 percent by weight, based on the silicone rubber, of the methylmethacrylate is added to the silicone rubber. Less than this amount is insufficient to effect the additional rigidity required for finishing and less than sufficient for bonding in cooperation with the silane as hereinafter described, to the carrier. More than this amount generally results in too much rigidity for comfort.
Prior to adding methylmethacrylate polymer to the silicone rubber, it is first mixed and blended with a vinylsilane or acryloxyalkylsilane, the silane covering or moistening the methylmethacrylate polymer particles. While this method of formulation is preferred, the invention can also function by separate mixing of each ingredient with the silicone rubber. No solvents are required, but are not precluded. The silane serves in conjunction with the methylmethacrylate polymer to obtain a firm and lasting bond between the silicone rubber and denture carrier. In this regard, it is preferred to utilize acrylic carriers as above described, but other carriers such as lucite are not precluded.
The silanes which are generally useful herein have the formula
CH2 =CR[COO(R')b --R"]a SiX3
wherein R is a methyl radical or a hydrogen atom; R' is a divalent group composed of carbon, hydrogen, and which may contain oxygen (the oxygen being in a configuration selected from ether linkages and hydroxyl groups, the ratio of carbon atoms to oxygen atoms being generally not greater than 3:1, R' being attached to both the COO and the R" groups through CO linkages; R" is an alkylene radical of from one to four carbon atoms, a and b have values independently selected from 0 and 1; and X is a monovalent hydrolyzable group. The term "hydrolyzable group" as employed herein means that the X group reacts with water under the normal conditions for hydrolyzing silanes. Thus, X can be, for example, any halogen such as chlorine, bromine, iodine or fluorine, any group containing a silicon nitrogen bond such as (CH3)2 N-, or (CH3 CH2)2 N-, or any monovalent hydrocarbonoxy group such as methoxy, ethoxy, butoxy, isopropoxy, --CH2 CH2 OH, or radicals of the formula -- (CH2 CH2 O)n Y wherein Y is an aliphatic hydrocarbon radical of one to four carbon atoms, phenoxy, cresyloxy and ##SPC1##
any aceyloxy group such as acetoxy, formyloxy, prioionoxy; groups containing the silicon-oxygen-nitrogen bond such as (CH3)2C= NO- and (CH3 --CH2)2C=NO- and any sulfate group such as ##SPC2##
The hydrocarbon portions of X can be substituted with other radicals to give for example CF3 CF2 O--, CF3 COO--, (CH3)2 NCH2 CH2 O-- ##SPC3##
and NCCH2 CH2 O--.
The foregoing silanes can be characterized as vinylsilanes wherein a is 0 and acryloxyalkylsilanes where a is 1. In the latter case, "acryloxyalkylsilanes" are intended to include not only compounds wherein R is hydrogen but also "methacryloxylkyl-silanes." Examples of specific silanes can be found in Plueddeman et al. U.S. Pat. No. 3,398,210, which by reference is made part of the disclosure of the present invention. Specific examples of vinylsilanes are vinyltrichlorosilane, vinyltriethoxysilane and vinyltris(beta-methoxyethoxy)silane.
The acryloxyalkylsilanes are particularly useful in this invention and are preferred compounds. The methacryloxyalkylsilanes, that is where a is 1 and R' is methyl, are most particularly preferred. The specific compound gamma-methacryloxypropyltrimethoxysilane is particularly useful in the present invention. Such a silane is sold by Union Carbide under the designation "A-174."
The silanes are added to the methylmethacrylate polymer to constitute from about 5 percent to about 75 percent of the weight of the mixture thereof, preferably about 30-60 percent, and in the silicone rubber constitutes about 0.175 weight percent, based on the silicone rubber. Preferred ranges in the silicone rubber are 2.5-5.0 percent by weight of methylmethacrylate and 0.125-3.0 weight percent silane, based on the silicone rubber.
In a further embodiment of the invention, a coloring pigment can be added to the silicone rubber so that the lining and the denture base material are harmonius in color, or are one and the same color. In formulating the silicone rubber, the pigment is preferably first mixed and blended with the methylmethacrylate polymer and the silane and the mixture added to the silicone rubber. As pigment, one can use titanium dioxide, or the like, with sufficient Washung Red, Bond Red, or the like, to blend to color desired. About 0.0001-1 percent by weight, based on the silicone rubber, of the pigment can be added.
The following examples illustrate specific applications of the invention.
19.15 Parts of methylmethacrylate polymer, 9.16 parts of gamma-methacryloxypropyltrimethoxysilane (Union Carbide A-174 Silane) and 0.075 parts of titanium dioxide blended to gum color with Washung Red as a coloring pigment were mixed together and then added to 720 parts of silicone rubber (General Electric RTV-108). The resultant mixture was applied to a flask prepared as described with respect to FIG. 1 and immersed for about 3 hours in water at a temperature of about 100°C. Upon removal from the flask, the resultant denture had excellent comfort properties and the silicone rubber adhered well to the denture carrier.
A sample of silicone rubber-methylmethacrylate polymersilane mixture was prepared utilizing the ingredients and procedure of Example 1 except that the rubber was cured without incorporation in a denture, by immersion for 3 hours in water at 100°C. In one run, the rubber was cut into one inch square samples having a thickness of about 4 mil. One of these test specimens was subjected to a Shore A Durometer hardness test in accordance with ASTM-D-2240-64T. Another test specimen was subjected to an immersion test in accordance with ASTM-D-471-66 in which it was conditioned for 7 days in human saliva at 98° ±2°F and then subjected to a Shore A Durometer hardness test and visual examination. Another specimen was subjected to a fungus resistance test in accordance with MIL-E-5272C in which the specimen was exposed for 14 days under 95° ±5 percent relative humidity at 86° ±2°F in a fungus cabinet to Chaetomium globsum, Aspergillus niger, Aspergillus florus and Penicillium citrinum. In another run similar specimens were prepared but were cured bonded to an acrylic base. These specimens were subjected to bond strength tests in which one specimen was conditioned in air at 73° ±2°F for 7 days while another specimen was conditioned in distilled water at 98° ±2°F for 7 days.
Concurrently with the foregoing, test specimens were prepared utilizing Dow-Corning's Silastic 390, without the methylmethacrylate polymer and silane and utilizing a commercial denture liner sold by the National Patent Development Co. under the trade name Sofdent. The following test results were obtained.
Silas- Example tic- Test 2 390 Sofdent Shore A Hardness, as received 35 18 1001 Human Saliva immer- sion Shore A Hardness, change - 3 0 602 Change in weight,% + 0.14 +0.80 +45.90 Visual examination No evidence of any Considerable change in coloring or de- swelling and terioration softness Fungus Resistance Visual examination after 7 day expo- sure No evidence of any fungus growth 14 day exposure No evidence Slight No evidence of fungus any growth of fungus fungus around growth edges growth of spe- cimen Bond Strength,lb/ inch of width As received 16.0 7.1 --3 7 days water immersion 15.8 7.0 --3 1 maximum reading on "A" scale 2 from maximum reading on "A" scale 3 not conducted
An examination of the foregoing data reveal that specimens prepared in accordance with the foregoing invention have a good bond between the liner and acrylic base material without any additional primer before the liner is applied. The lining is durable both in bond strength and in retention of its hardness level and visual and weight characteristics, having a low water and saliva absorbtion rate.