CA1103388A - Dental restorative composite - Google Patents
Dental restorative compositeInfo
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- CA1103388A CA1103388A CA269,697A CA269697A CA1103388A CA 1103388 A CA1103388 A CA 1103388A CA 269697 A CA269697 A CA 269697A CA 1103388 A CA1103388 A CA 1103388A
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- dental restorative
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
- A61K6/00—Preparations for dentistry
- A61K6/80—Preparations for artificial teeth, for filling teeth or for capping teeth
- A61K6/884—Preparations for artificial teeth, for filling teeth or for capping teeth comprising natural or synthetic resins
- A61K6/887—Compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
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- Oral & Maxillofacial Surgery (AREA)
- Plastic & Reconstructive Surgery (AREA)
- Epidemiology (AREA)
- Life Sciences & Earth Sciences (AREA)
- Animal Behavior & Ethology (AREA)
- General Health & Medical Sciences (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Dental Preparations (AREA)
Abstract
ABSTRACT
A unique dental restorative material is described comprising a blend of liquid, polymerizable organic binder and a finely divided particulate filler wherein the improvement comprises the utilization of a particulate filler having a size distribution such that 70 to 95% by weight of said particles are in the range of 0.7 to 25 microns in diameter and, correspondingly, 5 to 30% by weight of said particles are in the range of 0.2 to 0.7 micron. The unique composite material provides excellent compressive strength and good translucency.
A unique dental restorative material is described comprising a blend of liquid, polymerizable organic binder and a finely divided particulate filler wherein the improvement comprises the utilization of a particulate filler having a size distribution such that 70 to 95% by weight of said particles are in the range of 0.7 to 25 microns in diameter and, correspondingly, 5 to 30% by weight of said particles are in the range of 0.2 to 0.7 micron. The unique composite material provides excellent compressive strength and good translucency.
Description
F.N. 912,680 110~3~8 DENTAL RESTORATIVE COMPOSITE
This invention relates to dental restorative materials and, more particularly, to dental restorative compositions comprising a blend of polymerizable binder and particulate filler.
Composites useful as dental restorative materials comprising liquid organic polymerizable binder and finely divided lnorganic solid filler are well known. See, for example, the compositions as described in U.S. Patent NoO
3~066,112 (Bowen). As disclosed by Bowen, dental restoratlve composites comprising 17 to 34% by weight Or a thermosetting resin such as the glycidyl methacrylate deriva-tive of Bisphenol A, commonly referred to as BisGMA, and 66 to 83% by weight of a filler (such as clear, colorless, fused sillca having a particle size fine enough to pass through a number 325 sieve of the U.S. Standard Sieve Series ~44 microns)) are acceptable as filling materials for restorative dentistry (having compressive strengths up to 23,000 p~Soi~)~
These dental restorative composites by definltlon should restore both the function and appearance of a defective tooth and, consequently, a number of practical restrictions are placed upon a suitable material. The o~ganlc polymerl-zable binder employed in such composites mu~t possess the property of rapid and complete polymerization under the conditions of the oral env~ronment. The restoratiYe material must exhibit low polymerization shrinkage, low water ~k ~ ~103388 absorption, low solubility in the aqueous fluids of the mouth, low toxicity and satisfactory strength characteristics.
Since these requirements cannot be met in entirety by the resin itself, restorative materials are normally composites, that is, reinforcing filler materials are added to the resin to produce a composite having the deslrable proper-ties.
Addition of fillers to the liquld organlc blnder produces a restorative composlte which, upon polymerlzation, hopefully compares favorably with the natural tooth crown in dimensional stabillty, abraslon~resistance, color, trans-lucency and in strength so that the material will maintain its integrity and support the remaining tooth structure during mastication. The translucency of a polymerized dental restorative composite must compare to the natural translucency of the tooth. This requirement o~ a restorative composite is essential for aesthetically pleasing restoratives, particularly in the anterior portion of the mouth where - composites are principally used. A polymerized composite restorative that is too translucent will appear as a glassy window-like portion within the tooth and, conversely, a composite restorative that does not have adequate trans-lucency or is too opaque will appear as an opaque white spot on the tooth. Consequently, if the restorative material
This invention relates to dental restorative materials and, more particularly, to dental restorative compositions comprising a blend of polymerizable binder and particulate filler.
Composites useful as dental restorative materials comprising liquid organic polymerizable binder and finely divided lnorganic solid filler are well known. See, for example, the compositions as described in U.S. Patent NoO
3~066,112 (Bowen). As disclosed by Bowen, dental restoratlve composites comprising 17 to 34% by weight Or a thermosetting resin such as the glycidyl methacrylate deriva-tive of Bisphenol A, commonly referred to as BisGMA, and 66 to 83% by weight of a filler (such as clear, colorless, fused sillca having a particle size fine enough to pass through a number 325 sieve of the U.S. Standard Sieve Series ~44 microns)) are acceptable as filling materials for restorative dentistry (having compressive strengths up to 23,000 p~Soi~)~
These dental restorative composites by definltlon should restore both the function and appearance of a defective tooth and, consequently, a number of practical restrictions are placed upon a suitable material. The o~ganlc polymerl-zable binder employed in such composites mu~t possess the property of rapid and complete polymerization under the conditions of the oral env~ronment. The restoratiYe material must exhibit low polymerization shrinkage, low water ~k ~ ~103388 absorption, low solubility in the aqueous fluids of the mouth, low toxicity and satisfactory strength characteristics.
Since these requirements cannot be met in entirety by the resin itself, restorative materials are normally composites, that is, reinforcing filler materials are added to the resin to produce a composite having the deslrable proper-ties.
Addition of fillers to the liquld organlc blnder produces a restorative composlte which, upon polymerlzation, hopefully compares favorably with the natural tooth crown in dimensional stabillty, abraslon~resistance, color, trans-lucency and in strength so that the material will maintain its integrity and support the remaining tooth structure during mastication. The translucency of a polymerized dental restorative composite must compare to the natural translucency of the tooth. This requirement o~ a restorative composite is essential for aesthetically pleasing restoratives, particularly in the anterior portion of the mouth where - composites are principally used. A polymerized composite restorative that is too translucent will appear as a glassy window-like portion within the tooth and, conversely, a composite restorative that does not have adequate trans-lucency or is too opaque will appear as an opaque white spot on the tooth. Consequently, if the restorative material
2~ fails to meet these basic requirements it is not acceptable because it fails to restore or simulate the natural appearance of the tooth.
The ~asic physical and o~tical properties of the organic binder referred to in U.S~ Patent NoO 3,066,112 are ~03388 adequate to produce a composite which possesses proper trans-lucency for a natural-appearlng restorative. The filler used must have an lndex of refraction which matches the index of refraction of the polymerized blnder such that the translucency of the restorative composite matches that of the natural tooth structure. m is property o~ translucency is tested by A.D.A. Spec. No. 9 for Dental Silicate Cement and should provide for an opacity by this test of about 35%
(Co. 70).
Thus, most of the commercially available dental restorative composites are based upon the organic binder system referred to in the above-mentioned Bowen patent and most of these typically use quartz particulate fillers. The polymers have a refractlve index of 1.50 to 1.55, and the quartz fillers also have refra~tive indices of about 1.50 to 1.55. According to some literature there should be a slight difference between the refractive indices of the resin and the filler for best appearance ~i.e. a difference o~ about 0.005, but preferably not greater than 0O025~
However, recently there has been much desire for dental restorative materials having much improved compresslve strength. Generally speaking, it is possible to increase the compressive strength by increasing the amount o~ parti-culate ~iller present in the ~ompositions. And, conse~uently, in order to obtain high load~ngs of filler lt is necessary ~or the filler to be in finely reduced state.
There are a number of patents which teach the use of a finely dlv~ded parti~ulate filler in these restGratl~e compos~t~on~O See, for e~ample, U.S. Patents 3,70g,86~;
The ~asic physical and o~tical properties of the organic binder referred to in U.S~ Patent NoO 3,066,112 are ~03388 adequate to produce a composite which possesses proper trans-lucency for a natural-appearlng restorative. The filler used must have an lndex of refraction which matches the index of refraction of the polymerized blnder such that the translucency of the restorative composite matches that of the natural tooth structure. m is property o~ translucency is tested by A.D.A. Spec. No. 9 for Dental Silicate Cement and should provide for an opacity by this test of about 35%
(Co. 70).
Thus, most of the commercially available dental restorative composites are based upon the organic binder system referred to in the above-mentioned Bowen patent and most of these typically use quartz particulate fillers. The polymers have a refractlve index of 1.50 to 1.55, and the quartz fillers also have refra~tive indices of about 1.50 to 1.55. According to some literature there should be a slight difference between the refractive indices of the resin and the filler for best appearance ~i.e. a difference o~ about 0.005, but preferably not greater than 0O025~
However, recently there has been much desire for dental restorative materials having much improved compresslve strength. Generally speaking, it is possible to increase the compressive strength by increasing the amount o~ parti-culate ~iller present in the ~ompositions. And, conse~uently, in order to obtain high load~ngs of filler lt is necessary ~or the filler to be in finely reduced state.
There are a number of patents which teach the use of a finely dlv~ded parti~ulate filler in these restGratl~e compos~t~on~O See, for e~ample, U.S. Patents 3,70g,86~;
3 ~ 8 3,452,437; 3,629~187; 3,539,533; and 3,751,399. UOS~
Patent 3,792,531 (Rossi~ teaches a restcrative compcsltion in which finely divided particulate filler has a particle size of 0.7 to 30 microns, with care being taken tG
eliminate the presence of any appreciable amount of particles having a diameter less than 0.7 micron (since such particles are said to adversely affect the translucency of the restorative). German Offenlegungsschrift 2,403,211 describes a dental composition in which all of the finely divided filler is less than 0.7 micron in diameter ~and preferably is much smaller). German Of~enlegungsschri~t 2,405,578 describes a dental composition in which the ~iller has a maximum particle size of 0.07 micron. Although men-tion is made that finely particulate glass (particle size less than 5 microns) may be present, it i5 present ln amounts only up to 25% by weight of the total fillerO
Contrary to the prior art, it has been found in the present invention that a significant increase ln com-pressive strength ls obtained, without sacrifice of desir-able translucency, by using as the finely divided partil~ulate ~iller a material havlng a particle size distribution such that a signi~icant portion of the I~iller is ln the range of 0.2 to 0.7 micron while the balanc.e of the ~1ller is in the range of 0.7 tc 25 microns in sizeO
In accordance w~th the invention there is pro-~ided an improved dental restorative material prepared by mixing and polymerizing a liquid organlc polymerizable binder and a ~inely divided particulate ~lller wherein the improvement comprises sald fil.ler having a partlcie size ~;~388 distribution such that 70 to 95% by weight of sald particles are in the range of 0.7 to 25 microns and correspondlngly 5 to 30~ by weight of said particles are in the range of 0.2 to 0 G 7 micron in diameter.
The dental restorative materials o~ the in~ention exhibit excellent compressive strength and desirable trans-lucency as compared to dental restorati~e mater~als haYing particulate filler of different particle size distributionsO
Since the advantages obtained by the present ln-vention are attrlbutable to the particle size distributlon of the partlculate filler used herein, any liquid organic polymerizable blnder may be used in this invention~ There are a variety of known useful polymerizable binders. For example, the BlsGMA type described in U.S. 3,066,112 are quite useful and are presently preferred in this invention Such polymerizable binders preferably Contaln an amount of a reactive diluent ~such as triethyleneglycol dimeth-acrylate or tetraethyleneglycol dimethacrylate) for purposes o~ reducing the viscosity thereof. The amount of diluent typically used for viscosity control is in the range o~
about 25 to 50% by weight of the polymerizable binder, Liquld polymerizable binders are also described in U~S, 3,539,533. Still another type of useful polymerizable binder is the photopolymerizable type descrlbed in ~.S~
3,709,866. Other useful polymerizable binders are well known in the art.
The finely di~ided partlculate ~ er whlch is useful. in the practice o~ this invention must have a particle size distribution such that 70 to 95% by weight c~
~03388 the particles are in the range of 0.7 to 25 microns in diameter and correspondingly 5 to 30~ by weight of the particles are in the range of 0.2 to 0.7 micron. Particles greater than 25 microns in diameter are not desired because when they are present in more than trace amounts they impart a greater surface roughness than deslred, and they also tend to decrease the compressive strength of the restorative material. Although partlcles less than 0.2 micron in diameter may be used in the dental restorative as a conventional thickener, such particles should not be used in amounts exceeding about five percent by weight of the filler because, in addition to greatly increasing the viscosity of the binder prior to cure, they cause a decrease in the amount of filler which may be present with attendant decrease in compressive strength obtained after curing of the binder.
With the particle size distribution used in this invention the medlan particle size is in the range of 1 to 5 microns and is accordingly smaller than that used in commercially available dental restoratives. Although others have heretofore suggested that large amounts of ultraflne particles (e.g. silica particles such as "Cab-0-Sil"~ may be included in dental restoratives in addition to relatively large particles (e.g. 1 to 30 microns~, the presence of a sign~ficant amount of ultrafine particles also significantly increases the viscosity of the liquid polymerizable binder.
Conse~uently, it is not possible to incorporate a very h~gh loading of filler into such restorative materials~ As a result, such restorative ma~erials do not exhibit hlgh ~033~s compressive strengths.
Surprisingly, however, it has been found that with the broad particle size distribution used in the present invention, and resulting small median particle size, it is possible to incorporate large amounts Or particulate filler into dental restorative materials of the invention with correspondingly high compressive strength being obtained.
Thus, in accordance with the present invention particulate filler may comprise 75 to 90% by weight of the restorative material. This is surprising in view of the fact that fine partlcles are expected to greatly thicken the liquid poly-merizable binder and accordingly limit the amount Or par-ticulate filler which may be incorporated into the restora-tive. It is also surprislng that the dental restorative materials Or the invention exhiblt desirable translucency since it would be expected that the presence of a signifi-cant amount of particulate filler having a diameter corres-ponding to the wavelength of visible light (about 0.7 micron~
would impart significant opacity.
The types of ~inely divided particulate filler which may be used herein encompass those which are conven-tionally a~ailable and preferably have a Moh's hardness of about 3 to 8, more preferably 5 to 7. Thus, useful materials include crystalline quartz (so-called alpha quartz) whlch is presently preferred, rused silica, ground glass, synthetic siliceous materials, aluminum oxide, and other ~illers which are well known in ~he art.
In order to achieve a dental restorative material having the proper translucency (i.e. 0.2 to 0O5 optlcal density un~ts as measured by transmission densitometer~, 11~)3388 lt is necessary for the refractive index of the particulate filler to closely match the refractive lndex of the cured binder resin, as is known ln the art.
Although the conventional technique for preparing finely divided particulate filler is to grind relatively large particles in a mill ~ar until the desired particle size is obtained, it has been found that such technlque ls not totally satisfactory when using conventional grindlng apparatus to prepare small particles such as those made of quartz. A conventional mill ~ar is made of ceramic and accordingly has a hlgh alumina content (e.g. 70-80% alumina).
Conventional grinding media, used in the mill ~ar, such as porcelain balls and borundum also have a high alumina con-tent. Flint pebbles, which are commonly used as grinding media, are made of silicon diox~de and further contain trace contamlnants. Consequently, during normal milling the particles being prepared are unavoidably contaminated with alumina, or other contaminant, having a relatively hlgh index of refraction.
Although this contamination does not significantly modify the refractive index of those particles which are about one mlcron or larger in diameter, the refractive index of particles which are about 0.7 micron ln diameter (approximately the same as the wavelength of ~isible light) is drastically modified. Consequently, small particles which are prepared by conventional ball milling will be very undesirable ~or use in dental restoratives since their refractive index will differ from that of the larger particles (i.e. particles greater than about one micron in diameter) of the same materlal.
11~)3388 To overcome this inherent drawback associated with conventional ball milling techniques, the present invention provides an improved technique whereby very small particles Or materials such as quartz may be prepared whlch are not undesirably altered in their refractive index. The im-proved technique may be referred to as autogenous milling, i.e. the grinding media has the same chemical makeup as the material to be ground into small partlclesD Further, the interior of the mill ~ar is lined with a tough, durable organic coating (e.g. polyurethane) which is pre-ferably free of pigments and other inorganic contaminants.
The grinding is done in the dry state because wet grind-ing of the particles results in a particle size distribu-tion which is narrower than required in this lnvention.
After the grinding ls completed the particles are heated to a high temperature to remove any possible organlc con-tamination thereof.
Thus, for example, in order to prepare quartz particles having the desired partlcle size distribution, quartz crystals (approximately 0.5 to 5 cm.~ are used as the grinding media, and fractured quartz frit is used as the feed materlal. These materials are placed in the mill (preferably a vibratory mlll having its interlor llned as described above) and milling is continued in the dry state for several hours, after which the finely divided particulate quartz is recovered and heated to a hlgh temperature (e.g. 900C.).
The flnely d~lded particulate filler to be used in the restorative should preferably be treated with a keying agent to impro~e the bondlng between the I~iller 1~)3388 and the bonding resin and also to reduce the moisture sus-ceptibility of the filler-resin interface. There are a variety of well known keying agents which are useful for this purpose. Preferred keying agents are the ethylenically unsaturated organosilanes. See, for example, the keying agents and technique described in U.S. 3,066,112 (Bowen).
Other suitable keying agents are described ln U.S.
3,539,533. Particularly preferred keying agents for use in this invention include gamma-methacryloxypropyltrimethoxy silane and vinyltrimethoxy sllane. Other l~seful keying agents are well known ln the art.
One manner for treating the finely divided par-ticulate filler with a keying agent is described in UOS.
3,862,920 wherein gamma-methacryloxyproQyltrimethoxy silane is dissolved in a water/acetone blend. The particulate filler is then mixed with the silane solutlon to form a slurry. The water and acetone are then removed at 100Co after which the treated filler is heated at 125C. for two hours. Another technique for treating the partlculate filler with a keying agent involves dissolving the silane in toluene (e.g. to form a 50% solution~ and then mixing the solutio~ with the particulate ~iller, followed by drying the damp cake at 115C.
The composite dental restcrative ~aterials of the invention are typically provided as two-part systems. Pre-ferably the polymerizable blnder is separated lnto two equal or approximately equal volume portions and the desired particulate filler ls a~so separated into two por-tions and then admixed with the binder portions to form two pastes. The catalyst for the polymeriæable binder is eon-- 1 10~
tained in one paste portion and an activator is ccntained in the other paste portion. Thus, the two pastes are each quite stable and may be separately packaged. Then, at the time of use, equal volumes of the pastes are mixed together thoroughly and placed in the tooth cavity to be filled. Curing of the binder then occurs in situ to pro-vide a dental restorative having high compressive strength and desirable translucency.
The inventlon is further illustrated by means of the following non-limiting examples wherein the term "parts"
refers to parts by weight unless otherwlse indicatedO
Example 1 Raw alpha-quartz is heated to 1000C. and is then quenched by allowing the heated quartz to fall into water. The resulting fractured frit is dried at 150Co and then cooled. This fractured frit is then charged into a lined vibratory grinding mill with quartz pebbles ( 0 ~ 5 ~ 5 cm. diameter) as the grinding media. The grind-ing mill itself is commercially available from Sweco, Inc.
as Model ~DM-3~o Before use the interior sur~ace of the mill is lined with a tough polyurethane polymer ~"Adiprene L-167", commercially ava~lable from E~ I. DuPont, and cured with MOCA)~
The fractured fr~t is milled for 4~ hours to reduce the parti~le size. m e resultant powdered quartz is then heated to 900C. to remove organic ~ontaminants.
After the finely divided filler is allowed to cool, i~ is passed through a 325 mesh nylon screen ~aterial.
The resulting powdered quartz has the following distrlbu-3Q tion of particle sizes:
~03388 Particle Diameter ~Microns) Percent By Welght F~ner Than .
808 go 5.4 75 2.5 50 1~7 40 0.9 ~5 0.7 20 0.5 15 0.2 2 Example 2 An amount of the quartz particles prepared inaccordance with the procedure of Example 1 are charged to a conventional powder blender along with four percent by weight ~based on the weight cf the quartz partlcles~ of colloidal silica thi~kener (t'Cab-0-Sil M-5", commerclally available from Cabot Corporation~. These materials are thoroughly blended a~ter which eight percent by weight (based on the total weight o~ ~uartz particles and colloidal silica~ of a 50% solution of gamma-methacryloxy-propy1trimethoxy s11ane in toluene is added with further blending~ A~ter thorough blending the resulting damp cake is spread in thin layers, dried at 115Co for one hour and then cooled.
Example 3 A two-part paste dental restorative is prepared as ~ollows:
A resin binder ~containing an act1~atcr thereI~cr, is compounded by addlng 205 grams of N,N-dl-(~-hydro~yethyl~-p~toluidine to 48.8 grams of triethylene glyc~ol dlmethacr~iate~
followed by mlxing until a solution is obtained, The sol~-tion is then thoroughly mixed wlth 4605 grams of BlsGMA
~i.e. the glycidyl methacrylate derivatlve of Bisphenoi A;.
Then 525 grams of the treated particulate filler prepared in Example 2 is added slowly with stirring until a uniform paste is obtalned.
A resin binder ~containing a catalyst3 is ~om-pounded by dissolving 1.1 grams of benæoyl peroxide in 48.7 grams of triethylene glycol dimethacrylateO The re-sulting solution is then thoroughly mixed with 49.3 gramsof BisGMA. A small amount of a polymerization inhlbi~or (such as a substituted phenol) is also added. Then 525 grams of the treated particulate filler prepared in Example 2 is added slowly with stlrring until a uni~orm paste is obtianed.
Example 4 A tooth cavity is restored by first mixing equal volume portions of the two pastes prepared in Example 30 Typically the mixing is effected with a small spatula of wood, plastic or porcelain and requires only about 20 seconds. Then the restorative material is placed in ~he tooth cavity where the binder polymerizes 1n situ ~in about two minutes) to form a dental restorative having high eom-pressive strength.
Another sample of the cured dental restorati~e 1s immersed in water ~37C.~ ~or 24 hours and then tested for compressive strength. A value of 55~000 poscio is obser~ed.
Example 5 A test sample of the dental restcrative is pre-pared as follows:
11~)3388 Equal volume portions of the two pastes o~
Example 3 are thoroughly mixed and immediately placed in a ring mold (20 mm. in diameter) sitting on a polyester film (250 microns thick). The top of the ring mold is then covered with another piece Or polyester film (250 microns thick), after which the entire mold assembly is placed in a press. The assembly is then sub~ected to a pressure greater than 20~000 p.s.i. in one second or less and such pre-ssure is continued for at least five minutes. The pressure is then released and the test disk is removed from the mold. The steps of mixing the pastes, placing the mixture in the mold, and sub~ecting it to a pressure greater than 20,000 p.s.i. must be accomplished in one minute or less.
Example 6 The test disk prepared in Example 5 is placed on the stage of a conventional transmission densitometer (Macbeth Model "TD 501") which has been fitted with a light fllter in the vlsible light region (calibrated to zero reading and also calibrated to the opacity range of dental restorative materials).
A measurement of the opacity of the test disk yields a reading of 0.25 optical density units ~which means that the dental restorativ~ has acceptable translucency).
Example 7 Raw alpha quartz is heated to 1000C. and quenched by allowlng the heated quartz to fall into waterO
The resulting ~ractured frit is charged into a lined vi-bratory grinding mill with quartz crystals as grinding media. An amount of water equal to the weight of the frac-tured frit is also charged into the mill. The fractured frit is then milled for 26.5 hours. The resulting s urry was drained from the mill, dried in a forced air oven, heated to 900C., and then screened through a 325 mesh nylon screen material. The resulting powdered quartz had the following particle size distribution:
Particle Diameter (Micron ) Percent By Welght Finer Than 7.4 90 5.2 75 3.4 50 2.8 40 2.0 25 1.6 20 1.1 10 o.8 5 0.7 2 The ground quartz is blended with colloidal silica and treated with the silane coupling agent, all as described in Example 2. Using the resin formulations of Example 1, it was found that only 317 g of the filler material of this example could be incorporated into the resin (as compared to 525 grams of filler in Example 3). Attempts to incor-porate additional filler resulted in a dry mixture unsuit-able for use as a dental restorative material.
Test speclmens were made accordin~ to the stan-dards of the American Dental Associatlon Specification No~
9 for compressive strength. After storage for 24 hours at 37C., the test samples are crushed yielding a com-liO33~8 pressive strength of 45,000 p.s.i. This polymerized dentalrestorative composition gave a Barcol Hardness value of 80 after 24 hours storage in distilled water at 37C.
This example demonstrates that a narrow partlcle size distribution for the particulate filler inherently limits the amount of filler which may be incorporated into the dental restorative material (with accordingly lower compressive strength).
Patent 3,792,531 (Rossi~ teaches a restcrative compcsltion in which finely divided particulate filler has a particle size of 0.7 to 30 microns, with care being taken tG
eliminate the presence of any appreciable amount of particles having a diameter less than 0.7 micron (since such particles are said to adversely affect the translucency of the restorative). German Offenlegungsschrift 2,403,211 describes a dental composition in which all of the finely divided filler is less than 0.7 micron in diameter ~and preferably is much smaller). German Of~enlegungsschri~t 2,405,578 describes a dental composition in which the ~iller has a maximum particle size of 0.07 micron. Although men-tion is made that finely particulate glass (particle size less than 5 microns) may be present, it i5 present ln amounts only up to 25% by weight of the total fillerO
Contrary to the prior art, it has been found in the present invention that a significant increase ln com-pressive strength ls obtained, without sacrifice of desir-able translucency, by using as the finely divided partil~ulate ~iller a material havlng a particle size distribution such that a signi~icant portion of the I~iller is ln the range of 0.2 to 0.7 micron while the balanc.e of the ~1ller is in the range of 0.7 tc 25 microns in sizeO
In accordance w~th the invention there is pro-~ided an improved dental restorative material prepared by mixing and polymerizing a liquid organlc polymerizable binder and a ~inely divided particulate ~lller wherein the improvement comprises sald fil.ler having a partlcie size ~;~388 distribution such that 70 to 95% by weight of sald particles are in the range of 0.7 to 25 microns and correspondlngly 5 to 30~ by weight of said particles are in the range of 0.2 to 0 G 7 micron in diameter.
The dental restorative materials o~ the in~ention exhibit excellent compressive strength and desirable trans-lucency as compared to dental restorati~e mater~als haYing particulate filler of different particle size distributionsO
Since the advantages obtained by the present ln-vention are attrlbutable to the particle size distributlon of the partlculate filler used herein, any liquid organic polymerizable blnder may be used in this invention~ There are a variety of known useful polymerizable binders. For example, the BlsGMA type described in U.S. 3,066,112 are quite useful and are presently preferred in this invention Such polymerizable binders preferably Contaln an amount of a reactive diluent ~such as triethyleneglycol dimeth-acrylate or tetraethyleneglycol dimethacrylate) for purposes o~ reducing the viscosity thereof. The amount of diluent typically used for viscosity control is in the range o~
about 25 to 50% by weight of the polymerizable binder, Liquld polymerizable binders are also described in U~S, 3,539,533. Still another type of useful polymerizable binder is the photopolymerizable type descrlbed in ~.S~
3,709,866. Other useful polymerizable binders are well known in the art.
The finely di~ided partlculate ~ er whlch is useful. in the practice o~ this invention must have a particle size distribution such that 70 to 95% by weight c~
~03388 the particles are in the range of 0.7 to 25 microns in diameter and correspondingly 5 to 30~ by weight of the particles are in the range of 0.2 to 0.7 micron. Particles greater than 25 microns in diameter are not desired because when they are present in more than trace amounts they impart a greater surface roughness than deslred, and they also tend to decrease the compressive strength of the restorative material. Although partlcles less than 0.2 micron in diameter may be used in the dental restorative as a conventional thickener, such particles should not be used in amounts exceeding about five percent by weight of the filler because, in addition to greatly increasing the viscosity of the binder prior to cure, they cause a decrease in the amount of filler which may be present with attendant decrease in compressive strength obtained after curing of the binder.
With the particle size distribution used in this invention the medlan particle size is in the range of 1 to 5 microns and is accordingly smaller than that used in commercially available dental restoratives. Although others have heretofore suggested that large amounts of ultraflne particles (e.g. silica particles such as "Cab-0-Sil"~ may be included in dental restoratives in addition to relatively large particles (e.g. 1 to 30 microns~, the presence of a sign~ficant amount of ultrafine particles also significantly increases the viscosity of the liquid polymerizable binder.
Conse~uently, it is not possible to incorporate a very h~gh loading of filler into such restorative materials~ As a result, such restorative ma~erials do not exhibit hlgh ~033~s compressive strengths.
Surprisingly, however, it has been found that with the broad particle size distribution used in the present invention, and resulting small median particle size, it is possible to incorporate large amounts Or particulate filler into dental restorative materials of the invention with correspondingly high compressive strength being obtained.
Thus, in accordance with the present invention particulate filler may comprise 75 to 90% by weight of the restorative material. This is surprising in view of the fact that fine partlcles are expected to greatly thicken the liquid poly-merizable binder and accordingly limit the amount Or par-ticulate filler which may be incorporated into the restora-tive. It is also surprislng that the dental restorative materials Or the invention exhiblt desirable translucency since it would be expected that the presence of a signifi-cant amount of particulate filler having a diameter corres-ponding to the wavelength of visible light (about 0.7 micron~
would impart significant opacity.
The types of ~inely divided particulate filler which may be used herein encompass those which are conven-tionally a~ailable and preferably have a Moh's hardness of about 3 to 8, more preferably 5 to 7. Thus, useful materials include crystalline quartz (so-called alpha quartz) whlch is presently preferred, rused silica, ground glass, synthetic siliceous materials, aluminum oxide, and other ~illers which are well known in ~he art.
In order to achieve a dental restorative material having the proper translucency (i.e. 0.2 to 0O5 optlcal density un~ts as measured by transmission densitometer~, 11~)3388 lt is necessary for the refractive index of the particulate filler to closely match the refractive lndex of the cured binder resin, as is known ln the art.
Although the conventional technique for preparing finely divided particulate filler is to grind relatively large particles in a mill ~ar until the desired particle size is obtained, it has been found that such technlque ls not totally satisfactory when using conventional grindlng apparatus to prepare small particles such as those made of quartz. A conventional mill ~ar is made of ceramic and accordingly has a hlgh alumina content (e.g. 70-80% alumina).
Conventional grinding media, used in the mill ~ar, such as porcelain balls and borundum also have a high alumina con-tent. Flint pebbles, which are commonly used as grinding media, are made of silicon diox~de and further contain trace contamlnants. Consequently, during normal milling the particles being prepared are unavoidably contaminated with alumina, or other contaminant, having a relatively hlgh index of refraction.
Although this contamination does not significantly modify the refractive index of those particles which are about one mlcron or larger in diameter, the refractive index of particles which are about 0.7 micron ln diameter (approximately the same as the wavelength of ~isible light) is drastically modified. Consequently, small particles which are prepared by conventional ball milling will be very undesirable ~or use in dental restoratives since their refractive index will differ from that of the larger particles (i.e. particles greater than about one micron in diameter) of the same materlal.
11~)3388 To overcome this inherent drawback associated with conventional ball milling techniques, the present invention provides an improved technique whereby very small particles Or materials such as quartz may be prepared whlch are not undesirably altered in their refractive index. The im-proved technique may be referred to as autogenous milling, i.e. the grinding media has the same chemical makeup as the material to be ground into small partlclesD Further, the interior of the mill ~ar is lined with a tough, durable organic coating (e.g. polyurethane) which is pre-ferably free of pigments and other inorganic contaminants.
The grinding is done in the dry state because wet grind-ing of the particles results in a particle size distribu-tion which is narrower than required in this lnvention.
After the grinding ls completed the particles are heated to a high temperature to remove any possible organlc con-tamination thereof.
Thus, for example, in order to prepare quartz particles having the desired partlcle size distribution, quartz crystals (approximately 0.5 to 5 cm.~ are used as the grinding media, and fractured quartz frit is used as the feed materlal. These materials are placed in the mill (preferably a vibratory mlll having its interlor llned as described above) and milling is continued in the dry state for several hours, after which the finely divided particulate quartz is recovered and heated to a hlgh temperature (e.g. 900C.).
The flnely d~lded particulate filler to be used in the restorative should preferably be treated with a keying agent to impro~e the bondlng between the I~iller 1~)3388 and the bonding resin and also to reduce the moisture sus-ceptibility of the filler-resin interface. There are a variety of well known keying agents which are useful for this purpose. Preferred keying agents are the ethylenically unsaturated organosilanes. See, for example, the keying agents and technique described in U.S. 3,066,112 (Bowen).
Other suitable keying agents are described ln U.S.
3,539,533. Particularly preferred keying agents for use in this invention include gamma-methacryloxypropyltrimethoxy silane and vinyltrimethoxy sllane. Other l~seful keying agents are well known ln the art.
One manner for treating the finely divided par-ticulate filler with a keying agent is described in UOS.
3,862,920 wherein gamma-methacryloxyproQyltrimethoxy silane is dissolved in a water/acetone blend. The particulate filler is then mixed with the silane solutlon to form a slurry. The water and acetone are then removed at 100Co after which the treated filler is heated at 125C. for two hours. Another technique for treating the partlculate filler with a keying agent involves dissolving the silane in toluene (e.g. to form a 50% solution~ and then mixing the solutio~ with the particulate ~iller, followed by drying the damp cake at 115C.
The composite dental restcrative ~aterials of the invention are typically provided as two-part systems. Pre-ferably the polymerizable blnder is separated lnto two equal or approximately equal volume portions and the desired particulate filler ls a~so separated into two por-tions and then admixed with the binder portions to form two pastes. The catalyst for the polymeriæable binder is eon-- 1 10~
tained in one paste portion and an activator is ccntained in the other paste portion. Thus, the two pastes are each quite stable and may be separately packaged. Then, at the time of use, equal volumes of the pastes are mixed together thoroughly and placed in the tooth cavity to be filled. Curing of the binder then occurs in situ to pro-vide a dental restorative having high compressive strength and desirable translucency.
The inventlon is further illustrated by means of the following non-limiting examples wherein the term "parts"
refers to parts by weight unless otherwlse indicatedO
Example 1 Raw alpha-quartz is heated to 1000C. and is then quenched by allowing the heated quartz to fall into water. The resulting fractured frit is dried at 150Co and then cooled. This fractured frit is then charged into a lined vibratory grinding mill with quartz pebbles ( 0 ~ 5 ~ 5 cm. diameter) as the grinding media. The grind-ing mill itself is commercially available from Sweco, Inc.
as Model ~DM-3~o Before use the interior sur~ace of the mill is lined with a tough polyurethane polymer ~"Adiprene L-167", commercially ava~lable from E~ I. DuPont, and cured with MOCA)~
The fractured fr~t is milled for 4~ hours to reduce the parti~le size. m e resultant powdered quartz is then heated to 900C. to remove organic ~ontaminants.
After the finely divided filler is allowed to cool, i~ is passed through a 325 mesh nylon screen ~aterial.
The resulting powdered quartz has the following distrlbu-3Q tion of particle sizes:
~03388 Particle Diameter ~Microns) Percent By Welght F~ner Than .
808 go 5.4 75 2.5 50 1~7 40 0.9 ~5 0.7 20 0.5 15 0.2 2 Example 2 An amount of the quartz particles prepared inaccordance with the procedure of Example 1 are charged to a conventional powder blender along with four percent by weight ~based on the weight cf the quartz partlcles~ of colloidal silica thi~kener (t'Cab-0-Sil M-5", commerclally available from Cabot Corporation~. These materials are thoroughly blended a~ter which eight percent by weight (based on the total weight o~ ~uartz particles and colloidal silica~ of a 50% solution of gamma-methacryloxy-propy1trimethoxy s11ane in toluene is added with further blending~ A~ter thorough blending the resulting damp cake is spread in thin layers, dried at 115Co for one hour and then cooled.
Example 3 A two-part paste dental restorative is prepared as ~ollows:
A resin binder ~containing an act1~atcr thereI~cr, is compounded by addlng 205 grams of N,N-dl-(~-hydro~yethyl~-p~toluidine to 48.8 grams of triethylene glyc~ol dlmethacr~iate~
followed by mlxing until a solution is obtained, The sol~-tion is then thoroughly mixed wlth 4605 grams of BlsGMA
~i.e. the glycidyl methacrylate derivatlve of Bisphenoi A;.
Then 525 grams of the treated particulate filler prepared in Example 2 is added slowly with stirring until a uniform paste is obtalned.
A resin binder ~containing a catalyst3 is ~om-pounded by dissolving 1.1 grams of benæoyl peroxide in 48.7 grams of triethylene glycol dimethacrylateO The re-sulting solution is then thoroughly mixed with 49.3 gramsof BisGMA. A small amount of a polymerization inhlbi~or (such as a substituted phenol) is also added. Then 525 grams of the treated particulate filler prepared in Example 2 is added slowly with stlrring until a uni~orm paste is obtianed.
Example 4 A tooth cavity is restored by first mixing equal volume portions of the two pastes prepared in Example 30 Typically the mixing is effected with a small spatula of wood, plastic or porcelain and requires only about 20 seconds. Then the restorative material is placed in ~he tooth cavity where the binder polymerizes 1n situ ~in about two minutes) to form a dental restorative having high eom-pressive strength.
Another sample of the cured dental restorati~e 1s immersed in water ~37C.~ ~or 24 hours and then tested for compressive strength. A value of 55~000 poscio is obser~ed.
Example 5 A test sample of the dental restcrative is pre-pared as follows:
11~)3388 Equal volume portions of the two pastes o~
Example 3 are thoroughly mixed and immediately placed in a ring mold (20 mm. in diameter) sitting on a polyester film (250 microns thick). The top of the ring mold is then covered with another piece Or polyester film (250 microns thick), after which the entire mold assembly is placed in a press. The assembly is then sub~ected to a pressure greater than 20~000 p.s.i. in one second or less and such pre-ssure is continued for at least five minutes. The pressure is then released and the test disk is removed from the mold. The steps of mixing the pastes, placing the mixture in the mold, and sub~ecting it to a pressure greater than 20,000 p.s.i. must be accomplished in one minute or less.
Example 6 The test disk prepared in Example 5 is placed on the stage of a conventional transmission densitometer (Macbeth Model "TD 501") which has been fitted with a light fllter in the vlsible light region (calibrated to zero reading and also calibrated to the opacity range of dental restorative materials).
A measurement of the opacity of the test disk yields a reading of 0.25 optical density units ~which means that the dental restorativ~ has acceptable translucency).
Example 7 Raw alpha quartz is heated to 1000C. and quenched by allowlng the heated quartz to fall into waterO
The resulting ~ractured frit is charged into a lined vi-bratory grinding mill with quartz crystals as grinding media. An amount of water equal to the weight of the frac-tured frit is also charged into the mill. The fractured frit is then milled for 26.5 hours. The resulting s urry was drained from the mill, dried in a forced air oven, heated to 900C., and then screened through a 325 mesh nylon screen material. The resulting powdered quartz had the following particle size distribution:
Particle Diameter (Micron ) Percent By Welght Finer Than 7.4 90 5.2 75 3.4 50 2.8 40 2.0 25 1.6 20 1.1 10 o.8 5 0.7 2 The ground quartz is blended with colloidal silica and treated with the silane coupling agent, all as described in Example 2. Using the resin formulations of Example 1, it was found that only 317 g of the filler material of this example could be incorporated into the resin (as compared to 525 grams of filler in Example 3). Attempts to incor-porate additional filler resulted in a dry mixture unsuit-able for use as a dental restorative material.
Test speclmens were made accordin~ to the stan-dards of the American Dental Associatlon Specification No~
9 for compressive strength. After storage for 24 hours at 37C., the test samples are crushed yielding a com-liO33~8 pressive strength of 45,000 p.s.i. This polymerized dentalrestorative composition gave a Barcol Hardness value of 80 after 24 hours storage in distilled water at 37C.
This example demonstrates that a narrow partlcle size distribution for the particulate filler inherently limits the amount of filler which may be incorporated into the dental restorative material (with accordingly lower compressive strength).
Claims (6)
1. A composite dental restorative material prepared by mixing and polymerizing a liquid organic polymerizable binder and a finely-divided particulate filler, wherein the improvement comprises said filler having a particle size distribution such that 70 to 95% by weight of said particles are in the range of 0.7 to 25 microns and correspondingly 5 to 30% by weight of said particles are in the range of 0.2 to 0.7 micron.
2. A composite dental restorative material in accordance with claim 1, wherein 75 to 85% by weight of said particles are in the range of 0.7 to 20 microns and correspondingly 15 to 25% by weight of said particles are in the range of 0.2 to 0.7 micron.
3. A composite dental restorative material in accordance with claim 1, wherein said particles are alpha quartz.
4. A composite dental restorative material in accordance with claim 1, wherein said particulate filler comprises about 75 to 90% by weight of said restorative material.
5. A composite dental restorative material in accordance with claim 1, wherein said polymerizable binder comprises the glycidyl methacrylate derivative of Bisphenol A.
6. A composite dental restorative material in accordance with claim 1, wherein said binder further contains a reactive diluent.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US65652276A | 1976-02-09 | 1976-02-09 | |
| US656,522 | 1976-02-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1103388A true CA1103388A (en) | 1981-06-16 |
Family
ID=24633394
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA269,697A Expired CA1103388A (en) | 1976-02-09 | 1977-01-13 | Dental restorative composite |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5298391A (en) |
| AU (1) | AU508664B2 (en) |
| CA (1) | CA1103388A (en) |
| CH (1) | CH630524A5 (en) |
| DE (1) | DE2705220A1 (en) |
| FR (1) | FR2340085A1 (en) |
| GB (1) | GB1544776A (en) |
| SE (1) | SE458906B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4674980A (en) * | 1982-05-03 | 1987-06-23 | Den-Mat, Inc. | Dental composite and porcelain repair |
| US8552087B2 (en) | 2008-09-15 | 2013-10-08 | Ivoclar Vivadent Ag | Dental materials with a high flexural modulus |
Families Citing this family (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS56118009A (en) * | 1980-02-25 | 1981-09-16 | Inoue Japax Res Inc | Filler for dental use |
| JPS5780311U (en) * | 1980-11-06 | 1982-05-18 | ||
| DE3172366D1 (en) * | 1980-12-03 | 1985-10-24 | Ici Plc | Dental compositions |
| ZA817967B (en) * | 1980-12-03 | 1982-09-29 | Ici Plc | Dental compositions |
| US4388069A (en) * | 1982-04-15 | 1983-06-14 | Blendax-Werke R. Schneider Gmbh & Co. | Dental restorative material |
| NZ204975A (en) * | 1982-08-02 | 1985-10-11 | Johnson & Johnson Dental Prod | Polymerisable dental restorative compositions having improved mechanical properties and hydrolytic stability |
| GB2150141B (en) * | 1983-11-24 | 1987-04-29 | Glaverbel | Compositions incorporating glass beads and methods of preparing them |
| DE3403040A1 (en) * | 1984-01-30 | 1985-08-08 | Blendax-Werke R. Schneider Gmbh & Co, 6500 Mainz | DENTAL FILLING MATERIAL |
| JPS61148109A (en) * | 1984-12-24 | 1986-07-05 | Tokuyama Soda Co Ltd | Compound reparative material |
| FR2592789B1 (en) * | 1986-01-14 | 1988-04-15 | Bourrelly Georges | PROCESS FOR THE PREPARATION OF A CERAMIC PASTE FOR DENTAL PROSTHESIS RETAINING THE SAME COLOR AFTER BAKING |
| DE3642212A1 (en) * | 1986-12-10 | 1988-06-23 | Espe Stiftung | POLYMERIZABLE MEASURES, METHOD FOR THEIR PRODUCTION AND THEIR USE AS DENTAL MEASURES |
| US4888489A (en) * | 1988-05-09 | 1989-12-19 | Minnesota Mining And Manufacturing Company | Hand-held device for curing a dental restorative material |
| US4957441A (en) * | 1988-12-20 | 1990-09-18 | Minnesota Mining And Manufacturing Company | Method of enhancing the curing of a photocurable dental restorative material |
| EP1169009B1 (en) * | 1999-04-12 | 2006-04-26 | Dentsply International, Inc. | Dental composite restorative material and method of restoring a tooth |
| US7001932B2 (en) | 1999-04-12 | 2006-02-21 | Dentsply Detrey Gmbh | Dental composite restorative material and method of restoring a tooth |
| DE10108261B4 (en) * | 2001-02-21 | 2006-07-20 | Ivoclar Vivadent Ag | Polymerizable composition with particulate composite based filler |
| DE102009016025B4 (en) | 2009-04-02 | 2014-12-11 | Voco Gmbh | Plastic modified glass ionomer cement, its use and process for its preparation |
| JP4917692B1 (en) | 2011-07-29 | 2012-04-18 | 株式会社松風 | Dental composition for cutting equipment |
| JP5025829B1 (en) | 2012-01-24 | 2012-09-12 | 株式会社松風 | Dental composition suitable for cutting with automatic cutting equipment |
| CN102895125B (en) * | 2011-07-29 | 2017-04-12 | 株式会社松风 | Dental composition suitable for grinding with automatic grinding apparatus |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE870470C (en) * | 1943-04-23 | 1953-03-12 | Degussa | Process for the production of tooth cement powder |
| US3066112A (en) * | 1959-01-30 | 1962-11-27 | Rafael L Bowen | Dental filling material comprising vinyl silane treated fused silica and a binder consisting of the reaction product of bis phenol and glycidyl acrylate |
| CA878004A (en) * | 1968-06-14 | 1971-08-10 | Ii Henry L. Lee | Dental filling package |
| US3792531A (en) * | 1970-12-28 | 1974-02-19 | Lee Pharmaceuticals | Dental restorative material of improved polishability |
| DE2312258C2 (en) * | 1972-03-21 | 1986-04-24 | Dentsply International Inc., York, Pa. | Dental materials for prosthetic purposes |
| ZA744926B (en) * | 1973-08-07 | 1975-08-27 | Lee Pharmaceuticals | Dental glazing compound |
| ZA746187B (en) * | 1973-09-28 | 1975-11-26 | Lee Pharmaceuticals | X-ray opaque filler useful in dental and medical restorative compositions |
| ZA746188B (en) * | 1973-09-28 | 1975-11-26 | Lee Pharmaceuticals | Silica filler useful in dental and medical restorative materials |
| US4115487A (en) * | 1973-11-19 | 1978-09-19 | American Hospital Supply Corporation | Method for dental restoration |
| FR2272638B1 (en) * | 1974-01-23 | 1982-06-25 | Perdent Gmbh |
-
1977
- 1977-01-11 SE SE7700202A patent/SE458906B/en not_active IP Right Cessation
- 1977-01-13 CA CA269,697A patent/CA1103388A/en not_active Expired
- 1977-02-08 CH CH151177A patent/CH630524A5/en not_active IP Right Cessation
- 1977-02-08 DE DE19772705220 patent/DE2705220A1/en active Granted
- 1977-02-08 FR FR7703493A patent/FR2340085A1/en active Granted
- 1977-02-08 JP JP1289277A patent/JPS5298391A/en active Granted
- 1977-02-08 AU AU22049/77A patent/AU508664B2/en not_active Expired
- 1977-02-08 GB GB5168/77A patent/GB1544776A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4674980A (en) * | 1982-05-03 | 1987-06-23 | Den-Mat, Inc. | Dental composite and porcelain repair |
| US8552087B2 (en) | 2008-09-15 | 2013-10-08 | Ivoclar Vivadent Ag | Dental materials with a high flexural modulus |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6347682B2 (en) | 1988-09-26 |
| AU2204977A (en) | 1978-08-17 |
| AU508664B2 (en) | 1980-03-27 |
| SE7700202L (en) | 1977-08-10 |
| JPS5298391A (en) | 1977-08-18 |
| FR2340085B1 (en) | 1982-09-10 |
| GB1544776A (en) | 1979-04-25 |
| DE2705220A1 (en) | 1977-08-11 |
| FR2340085A1 (en) | 1977-09-02 |
| CH630524A5 (en) | 1982-06-30 |
| DE2705220C2 (en) | 1988-06-09 |
| SE458906B (en) | 1989-05-22 |
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