THERMOPLASTIC CUSTOM DENTAL TRAY HAVING HIGH MODULUS WARM STATE

Abstract: A custom dental tray (5a) is made from a homogeneous blend (1a) of a thermoplastic material and thixotropic filler. The blend is a solid with a storage modulus of at least 10<9> dyne/cm<2> at 38 DEG C and a manually-deformable semi-solid with a storage modulus less than 10<12> dyne/cm<2> at a temperature that comfortably can be withstood by oral tissues. The type and amount of filler are sufficient so that the blend has a storage modulus greater than 10<6> dyne/cm<2> at 75 DEG C and an equilibrium relaxation stress greater than 500 dyne/cm<2> at 60 DEG C. The tray can readily be molded into a custom shape while warm, facilitating the taking of an impression with a minimum volume of expensive impression material (7).

Description: THERMOPLASTIC CUSTOM DENTAL TRAY HAVING HIGH MODULUS WARM STATE CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of U.S. Patent Application Serial No. 07/484,106 filed February 23, 1990. FIELD OF THE INVENTION This invention relates to dental impression- making using a customizable thermoplastic tray. BACKGROUND OF THE INVENTION High molecular weight poly (epsilon- caprolactone) (also known as "polycaprolactone") has been used as a thermoplastic molding compound for general- purpose modelmaking and dentistry. References describing polycaprolactone molding compositions include U.S. Pat. No. 4,835,203, Kokai (Japanese Published Pat. Appl.) Nos. 63-171554 and 63-270759, and TONE- POLYMERS P-300 AND P-700 High Molecular Weight Caprolactone Polymers (1988 product literature of Union Carbide Corp. ) . Commercially available thermoplastic dental custom trays include the "EASY TRAY" from Oral Dynamics Inc. Division of Anson International, the "HEAT FORM" tray from Shofu, Inc., and the "AQUERON" custom tray from Erkodent Company. These three products are sold in the form of thin, stiff wafers that are immersed in hot (for example, 77°C) water to soften the wafer, then inserted in a patient's mouth and conformed by hand to the shape of the patient's dental tissue. The shaped wafer is then cooled (for example, using a stream of cold water) and removed from the mouth. The resulting custom impression tray can be filled with elastomeric impression material (for example, a polyvinyl siloxane) and reinserted in the mouth to take an impression of the dental tissue. U.S. Pat. Nos. 4,227,877, 4,361,528, 4,413,979 and 4,768,951 describe thermoplastic impression trays. The trays of the '877 patent are said to be made of acrylic, and when warmed to change from a glassy, brittle state to a leathery state characterized by a "change in stiffness of several orders of magnitude". Japanese Published Application No. Sho [1988] - 47706 describes a fiber-reinforced acrylic plastic impression tray. Although not intended to be heat-softened during use, the tray is said to be reinforced with several materials including fibers and cloth. U.S. Pat. Nos. 4,240,415 and 4,483,333 describe the use of polyethylene and certain other fillers in polycaprolactone orthopedic casts. The patentee cautions against the use of fillers such as fumed silica, mica and clay, on grounds that they are unsuitable for reasons suc as cost, weight, opacification and the need to use expensive equipment to mix the filler with the polycaprolactone. U.S. Pat No. 4,595,713 describes medical implants made from a copolymer of epsilon-caprolactone an a lactide. The implants are said optionally to contain osteogenic fillers or chopped carbon fiber for the purpos of encouraging tissue regeneration. SUMMARY OF THE INVENTION The above-described commercial thermoplastic custom trays are relatively stiff when cold but very flexible when heated to the intended use temperature. Although the AQUERON tray is somewhat less flexible when warm than the EASY TRAY or HEAT FORM products, all three custom tray wafers might best be described as "floppy" when heated. It is very difficult to maintain such a wafer in a desired shape until it cools, especially when working inside the mouth. These difficulties are exacerbated when shaping the wafer to conform to the maxillary arch, or to the mandibular arch of an inclined patient. The dentist must constantly fight the gravitational tendency of the wafer to droop or sag. These problems have discouraged some dentists from using thermoplastic custom tray materials, or led dentists to restrict their use to applications involving less than a full arch. The tray of our invention has substantially improved warm state properties compared to the above-mentioned commercial trays. Our tray retains substantial stiffness when heated, thus avoiding the undesirably floppy character of the commercial trays mentioned above. The customizable dental tray of the invention comprises a homogeneous blend of a thermoplastic material (for example, polycaprolactone) and thixotropic filler (for example, submicron silica), the tray being shaped and sized for use in the mouth, and the blend being a solid with a storage modulus (G') of at least about 10 9 dyne/cm 2 at 38°C and a manually-deformable semi-solid with a storage modulus less than 10 12 dyne/cm 2 at a temperature that comfortably can be withstood by oral tissues, the type and amount of filler being sufficient so that the blend has a storage modulus greater than 10 6 dyne/cm 2 at 75°C and an equilibrium relaxation stress (τ β ) greater than 500 dyne/cm 2 at 60°C. The invention also provides a method for making an impression of dental tissue, comprising the step of enveloping the tissue with a softened tray comprising the above-mentioned homogeneous blend. BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plot of storage modulus vs. temperature for three commercial trays and several trays of the invention; FIG. 2 is a plot of relaxation stress vs. time for three current commercial trays and a tray of the invention; FIG. 3 is a plot of relaxation stress vs. time for a tray of the invention at three different temperatures; FIG. 4 is a perspective view of a tray of the invention; and FIG. 5 is a section through line 5-5 of FIG. 4. DETAILED DESCRIPTION A variety of thermoplastic materials can be use in the custom trays of the invention. Selection of the thermoplastic material should be based in part on the desired tray properties in the softened ("warm") and soli ("cool") states. The warm state is characterized by appreciable mass flow under moderate (hand) pressure at some temperature between body temperature (about 38 β C) an the maximum temperature that comfortably can be withstood by oral tissues. This maximum temperature is generally thought to be about 75°C, although a maximum of about 65° is preferred. The cool state is characterized by sufficient strength and stiffness to permit an acceptably accurate dental impression to be made in the tray, and by minimal apparent mass flow under moderate pressure at temperatures below 38°C. The warm and cool state properties permit the tray to be heated to a moderate temperature, manually shaped inside or outside the mouth ("customized") while warm to conform to the shape of hard and soft oral tissue, and cooled (usually inside) the mouth to form a substantially rigid custom tray. Representative thermoplastic materials include polyesters and polyurethanes such as those described in U.S. Pat. Nos. 3,382,202, 4,059,715, 4,182,829, 4,327,013, 4,361,538, 4,552,906 and 4,569,342, and copolymers such as those described in U.S. Pat. Nos. 4,659,786, 4,740,245 an 4,768,951. The thermoplastic material preferably is a homopolymer or copolymer of epsilon-caprolactone. The polycaprolactone optionally can contain property-modifying or cross-linkable functional groups (for example hydroxyl, acrylate, methacrylate, epoxy, isocyanato or vinyl groups) if desired. Blends of polycaprolactones can also be employed. Preferred polycaprolactones have the formula: 0 0 0 V II » i I. (H0(CH 2 ).C0((CH 2 ).C0) χ (CH 2 ^CM-^ 1 where R 1 is hydrogen or an aromatic or a straight chain or branched aliphatic backbone, which can optionally contain one or more non-interfering substituents such as hydroxyl or amine groups, w is 1 if R 1 is hydrogen, and w otherwise has an average value of about 1 to about 4, M is oxygen or -NR 2 - where R 2 is hydrogen or a non-interfering aromatic or aliphatic group, and the product of w times x is greater than about 35. Preferred commercially available polycaprolac¬ tone polymers include "TONE P-700" and "TONE P-767" (40,000 molecular weight) and "TONE P-300" (10,000 molecular weight) polycaprolactones from Union Carbide Corp., and the "CAPA" polycaprolactones "630" (30,000 molecular weight) , "640" (40,000 molecular weight) , "650" (50,000 molecular weight), and "656" (56,000 molecular weight) from Interox. The thixotropic filler preferably has a fibrous, platy or finely-divided particulate form. Suitable fillers include glass fibers, clay, mica, alumina, submicron silica (for example, fumed, precipitated or colloidal silica) and finely-divided calcium carbonate. The fillers can be untreated or treated with a suitable coupling agent (for example, a silane). For fibrous or platy fillers, the filler preferably has an aspect ratio greater than about 3:1, more preferably greater than about 5:1, and most preferably greater than about 10:1. For particulate fillerε, the particles preferably have an average partic diameter less than about 100 micrometers, more preferabl less than about 10 micrometers, and most preferably less than about 1 micrometer. The blend from which the tray is formed can if desired contain adjuvants to modify or improve the physical properties of the tray. Suitable adjuvants include solvents, diluents, plasticizers, pigments, dyes indicators, inhibitors, stabilizers, UV absorbers, medicaments (e.g., leachable fluorides), biocides and th like. The blend preferably contains a free-radically polymerizable resin and an initiator. The free-radicall polymerizable resin contains at least one ethylenically unsaturated monomer, oligomer, or polymer capable of undergoing addition polymerization. Suitable monomers include mono-, di- or polyfunctional acrylates and methacrylates such as methyl acrylate, methyl methacrylate, ethyl acrylate, isopropyl methacrylate, n-hexyl acrylate, styryl acrylate, allyl acrylate, glycerol diacrylate, glycerol triacrylate, ethyleneglyco diacrylate, diethyleneglycol diacrylate, triethyleneglyc dimethacrylate, 1,3-propanediol diacrylate, 1,3-propanediol dimethacrylate, tri ethylolpropane triacrylate, 1,2,3-butanetriol trimethacrylate, 1,4-cyclohexanediol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, sorbitol hexacrylate, bis[l-(2-acryloxy) ]-p-ethoxyphenyldimethylmethane, bis[l-(3-acryloxy-2-hydroxy) ]-p-propoxyphenyldi- methylmethane, tris-hydroxyethylisocyanurate triacrylate, beta-methacrylaminoethyl methacrylate, and mixtures thereof. Other suitable monomers include unsaturated amides such as methylene bis-acrylamide, methylene bis-methacrylamide, 1,6-hexamethylene bis-acrylamide and diethylenetriamine tris-acrylamide. Suitable oligomeric or polymeric resins include 200 to 500 molecular weight polyalkylene glycols, acrylated or methacrylated oligomers such as those of U.S. Pat. No. 4,642,126, acrylated urethanes such as "SARTOMER" 9503, 9504 and 9505 (Sartomer Corp.), "INTEREZ" CMD 8803, 8804 and 8805 (Radcure Specialties, Inc.), and "PHOTOMER" 6060, 6110 and 6160 (Henkel Corp.), as well as acrylated polyester oligomers such as "EBERCRYL" 830 (Radcure Specialties, Inc.). Mixtures of free-radically polymerizable monomers, oligomers or polymers can be used if desired. The free-radically polymerizable resin can if desired be cured using a conventional chemical initiator system, such as a combination of a peroxide and an amine. However, chemical cure systems typically require at least partial ingredient separation before use. The resin is preferably cured using a photoinitiato , optionally combined with a suitable photosensitizer or accelerator. The photoinitiator should be capable of generating free radicals for addition polymerization at some wavelength between 200 and 800 nm. Suitable photoinitiators include alpha-diketones, monoketals of alpha-diketones or ketoaldehydes, acyloins and their corresponding ethers, chromophore-substituted halomethyl-s-triazineε, chromophore-subεtituted halomethyl-oxadiazoleε, aryliodonium salts, and other commercially available ultraviolet ("UV") and visible light photoinitiators. Preferred photoinitiator systems include a mono or diketone photoinitiator together with a suitable donor compound or accelerator, such as the systems described in u.S. Pat. Nos. 3,427,161, 3,756,827, 3,759,807, 4,071,424, 4,828,583, U.K. Pat. Specification No. 1,304,112, European Published Pat. Appl. No. 150,952 and Chem. Abε. 95:225704U. The blend should remain substantially homogeneous (that is, it should not undergo macroscopic phase separation or filler sedimentation). The composition preferably should retain its desired physical properties even if repeatedly cycled between the warm and cool states. Thus the selection of ingredients can be guided in part by the desire to preserve homogeneity and thermal reversibility. The types and amounts of ingredients in the blend usually will be empirically selected based on certain desired physical properties of the blend. The blend εhould be a solid at 38°C, and at that temperature should have a storage modulus of at least about 10 9 dyne/cm 2 . At 45°C (a temperature slightly above body temperature, and a temperature at which the blend preferably remains a solid) the blend preferably has a storage modulus greater than about 2 X 10 9 dyne/cm 2 , and more preferably greater than about 3 X 10 9 dyne/cm 2 . Storage modulus measurements are conveniently made using rheoraetric dynamic analyzer (Rheometrics, Inc.) operated at 1.4% maximum εtrain and a 10 radian/second strain rate When heated above body temperature to an elevated temperature that comfortably can be withstood by oral tissues, the blend should form a manually-deformable semi-εolid. By thiε we mean that a thin (for example, 3m thick) sheet of the blend should not flow under its own weight, but should be bendable and stretchable using hand pressure. When heated to this elevated temperature, the blend should have a storage modulus between about 10 6 dyne/cm 2 and about 10 10 dyne/cm 2 . Preferably throughout the range of temperatures between 45 β C and 75°C the storage modulus is lesε than about 10 12 dyne/cm 2 but greater than about 10 6 dyne/cm 2 . More preferably, throughout the range of tempertures between 50°C and 70°C the storage modulus is lesε than 10 11 dyne/cm 2 but greate than 3 X 10 6 dyne/cm 2 . Most preferably, throughout the range of temperatures between 50°C and 65°C the storage modulus is lesε than 10 dyne/cm but greater than 5 X ιo 6 dyne/cm 2 . These latter three limiting ranges correspond to the boxes depicted in FIG. 1. At 60°C (a temperature at which the blend comfortably and efficiently can be used intraorally) , the blend should have an equilibrium relaxation stress (τ ) greater than about 5 X 10 2 dyne/cm 2 . Preferably the 60°C equilibrium relaxation stress is greater than about 10 3 dyne/cm 2 , more preferably it is greater than 3 X 10 3 dyne/cm 2 , and most preferably it is greater than 10 4 dyne/cm 2 . A 600 second (10 minute) time limit, or a relaxation streεε leεs than 500 dyne/cm 2 (the lower detection limit of the rheometric dynamic analyzer), is a convenient cut-off period for measurement of the equilibrium relaxation εtreεε. Relaxation εtress meaεurementε are conveniently made by operating the rheometric dynamic analyzer at 50% step strain, using a 12.5mm radius circular platen. in rheological terms, the blends used in the trays of our invention behave aε a viεcoelaεtic solid, whereas the commercial trays mentioned above behave more like Newtonian liquids. As a further guide, the preferred amounts of thermoplastic material and filler in the tray are aε follows: Preferred Most Preferred Ingredient Weight % Weight % Thermoplastic material up to 90 80 - 40 Filler 0-70 20 - 60 The tray ingredients can be combined by hand or by mechanical mixing. The ingredients preferably are warmed sufficiently to melt the thermoplastic material, but if desired can be mixed at lower temperatures. Any suitable mixing device can be used, including kettles equipped with a mechanical stirrer, extruders, rubber millε, and the like. The tray can be εhaped uεing methods such aε extrusion, injection molding and web proceεεing using a coating knife or rollers. The tray can be sold to the dentist in a variety of forms including flat or curved waferε, conventional molded tray configurations, preforme sheets, ropes, buttons, woven or non-woven webs and the like. The tray can be sold unwrapped, loosely wrapped in a package, or packaged in a flexible outer plastic skin. The tray can be extruded or cast in mono-, bi-, or poly-layers (for example, coplanar layerε or layers arranged in core-shell fashion) in which each layer has a selected melting temperature, viscosity, modulus, stickiness, or other desired physical properties. A preferred form of the invention is shown in FIGS. 4 and 5. Arch-shaped tray 5a has outer thermoplastic shell la made from a blend according to the invention. The interior of the tray is lined with scrim 3a, which promotes adhesion between material la and curable impression material 7. By warming tray 5a and shaping it to conform closely to the teeth to be modeled, the required amount of impression material 7 (typically an expensive εubstance) can be minimized. The required amount will typically be much lesε than depicted in FIG. 5 (in which the tray iε εhown in an uncuεtomized state and full of impression material), and ordinarily need be only enough to coat the walls of tray 5a. The tray can be converted from the cool state to the warm εtate by using a variety of energy sourceε. The tray can be immerεed in a heated bath containing a suitable inert liquid (for example, water or a fluorochemical fluid) that will not disεolve or εwell the tray in either itε cool or warm states. The tray can also be softened using heat sources such as a hot air gun, hot plate, conventional oven, infrared heater or microwave oven. Transforming the tray from a warm state to a cool state requires loss of thermal energy and can be carried out using a variety of cooling techniques. Cooling can take place under ambient conditions in the presence of air only.* Cooling can be expedited using forced air, cold water, ice, or heat sinks such aε chilled "cold packs" or flexible pouches containing low boiling inert liquids. Of particular interest for dental applications are chilled cold packs in flexible pouches that have been preshaped to match the contourε of the tray being cooled. For example, flexible pouches containing a chilled coolant can be fabricated in the shape of a full arch or quadrant and placed intraorally in contact with the warm tray. A simplified dental impression system can be prepared from the tray. Traditional impresεioning εystems employ one or more low viscoεity, flowable elastomeric materials such as an alginate, hydrocolloid, polyvinylsiloxane, polyether, or polyεulfide contained in a fairly rigid adheεive-coated plastic or metal arch-shaped standard tray. The elastomeric material often iε applied both to the dental tiεεue to be modeled and to the εtandard tray. The elastomeric material and surrounding standard tray are subsequently pressed against the dental tissue, and left in place until the elastomeric material has hardened. This traditional process involves several materials and steps, material waste and fairly lengthy set times. The present invention permits impressioning uεing a monolayer or a bilayer thermoplaεtic tray. In a preferred embodiment, a flat εheet or a preformed arch-εhaped tray iε made from two coextruded thermoplaεtic layers. The phyεical properties of each layer emulate in part the properties of a conventional rigid tray and the elaεtomeric material respectively. The "tray" layer preferably is a tray of the invention. At a suitable elevated temperature the tray layer becomes a conformable, non-sticky, non-floppy shell (thereby permitting the warm tray layer to be hand-shaped into a cuεtom tray configuration) and the "elaεto er" layer exhibits good flow and low viεcoεity (thereby permitting the warm elaεtomer layer to flow .around tooth εtructure and provide an accurate model). The warm bilayer conεtruction provides easy placement, accurate impreεsioning, and efficient use of materials. Cooling can take place rapidly, and in lesε time than is required to harden a conventional impresεion. While cooling, the tray layer exhibitε sufficient rigidity to discourage distortion of the impreεεion during cooling, removal from the mouth and εubεequent handling. If deεired, a tray of the invention can be filled with a conventional elaεtomeric impreεεion materia (for example, a εilicone elastomer). By shaping the tray in the mouth before (or if desired, after) it is filled with elastomer, the tray volume and required amount of elastomer will be minimized. The following examples are offered to aid in understanding the invention and are not to be conεtrued a limiting itε εcope. Unleεs otherwise indicated, all part and percentages are by weight. EXAMPLE 1 A thermoplaεtic cuεtom tray waε prepared by combining 22.5 partε "TONE P-767" (40,000 molecular weight) polycaprolactone, 7.5 parts "SR-9505" urethane diacrylate oligomer, ,1.2 parts "EBERCRYL 830" polyester hexacrylate, 45 parts "VICRON" calcium carbonate (Pfizer Corp.), 10 parts "SIPERNAT D-ll" treated precipitated silica (North American Silica Co.), 5 parts "ULTRASIL VN 3 SP" untreated precipitated silica (North American Silica Co.), 4 partε "1156" chopped glaεs fibers (PPG), and 0.75 parts each camphorquinone ("CPQ") and p-dimethylaminobenzoate ("EDMAB"). The ingredients were stirred in a warm vessel at 100°C until homogeneous. The resulting blend formed a castable thermoplastic that was solid and εtiff at 38°C, but which softened readily in a 60°C water bath to form a manually-deformable but usefull stiff semi-solid with excellent warm handling properties. EXAMPLE 2 Using the method of EXAMPLE 1, but using "QUSO WR55" hydrophobic silica (North American Silica Co.) in place of "SIPERNAT D-ll" silica, 33 tray compositions were prepared, containing ingredients in the amounts set out below in TABLE I: TABLE I Ingredients Urethane Polyester Calcium Treated Untreated Glass.. Run PCL 1 diacrylate 2 hexacrylate 3 carbonate 4 silica silica Fibers CPQ EDMAB 1 498.5 166.2 22.18 960 218 20 82 16.63 16.63 2 498.5 166.2 22.18 704 166 82 328 16.63 16.63 3 415.4 138.5 18.48 1050 182 34 134 13.86 13.86 4 498.5 166.2 22.18 960 166 123 31 16.63 16.63 5 415.4 138.5 18.48 770 182 358 90 13.86 13.86 6 498.5 166.2 22.18 704 218 287 72 16.63 16.63 7 415.4 138.5 18.48 1050 238 90 22 13.86 13.86 8 415.4 138.5 18.48 770 238 78 314 13.86 13.86 9 456.9 152.3 20.33 871 201 134 134 15.25 15.25 10 456.9 152.3 20.33 871 201 134 134 15.25 15.25 11 456.9 152.3 20.33 871 201 134 134 15.25 15.25 12 498.5 166.2 22.18 960 166 31 123 16.63 16.63 13 498.5 166.2 22.18 704 166 328 82 16.63 16.63 14 415.4 138.5 18.48 1050 238 22 90 13.86 13.86 15 415.4 138.5 18.48 770 182 90 358 13.86 13.86 16 415.4 138.5 18.48 770 238 314 78 13.86 13.86 17 498.5 166.2 22.18 704 218 72 287 16.63 16.63 18 415.4 138 .5 18.48 1050 182 134 34 13.86 13.86 19 498.5 166.2 22.18 960 218 82 20 16.63 16.63 20 456.9 152.3 20.33 871 201 134 134 15.25 15.25 21 456.9 152.3 20.33 871 201 134 134 15.25 15.25 22 456.9 152.3 20.33 871 201 134 134 15.25 15.25 23 373.8 124.6 16.63 949 219 146 146 12.47 12.47 24 540.0 180.0 24.02 793 183 122 122 18.02 18.02 25 456.9 152.3 20.33 603 201 268 268 15.25 15.25 26 456.9 152.3 20.33 1139 201 0 0 15.25 15.25 27 456.9 152.3 20.33 871 201 16 252 15.25 15.25 28 456.9 152.3 20.33 871 201 252 16 15.25 15.25 29 456.9 152.3 20.33 871 147 161 161 15.25 15.25 30 456.9 152.3 20.33 871 255 107 107 15.25 15.25 31 456.9 152.3 20.33 871 201 134 134 15.25 15.25 32 456.9 152.3 20.33 871 201 134 134 15.25 15.25 1 "PCL" = "TONE P-767" 40,000 molecular weight polycaprolactone. 2 "SR-9505" urethane diacrylate. 3 "EBERCRYL 830" polyester hexacrylate. 4 "VICRON" calcium carbonate. 5 "QUSO WR55 treated silica. 6 "ULTRASIL VN 3 SP" untreated silica. 7 "1156" chopped glass fibers. The trays of EXAMPLE 1 and of Runs 1 through 4, 6 through 8, 10 and 26 of EXAMPLE 2 were evaluated to determine storage moduluε. Samples of "EASY TRAY", "HEA FORM", and "AQUERON" tray materials were similarly evaluated. FIG. 1 shows an unsmoothed plot of εtorage moduluε vε. temperature for each tray over the range fro 30°C to 80°C. Curveε A, B, and C εhow the reεultε for "EASY TRAY", "HEAT FORM", and "AQUERON" tray materialε, respectively. Note that once these trays begin to melt (at about 60°C) storage modulus drops precipitously, falling below 10 6 dyne/cm 2 before the temperature reaches 75°C. When warm, these trays are difficult to maintain i a desired shape, especially while working intraorally. Curve F shows the reεultε for the tray of EXAMPLE 1, and curveε D, E and G through M εhow the results for the trays of Runs 6, 8, 10, 2, 7, 4, 3, 1 and 26 of EXAMPLE 2. The tray material of Run 6 (curve D) softened above about 57°C, but was very stiff and would b difficult to form to a desired shape, especially while working intraorally. The trays shown in the remaining curves had very good properties in the warm state. The trays shown in curves E through I were particularly easy to maintain in a desired shape during cooling. EXAMPLE 3 The tray of EXAMPLE 1 was evaluated to determin 60°C equilibrium relaxation stress. Samples of "EASY TRAY", "HEAT FORM", and "AQUERON" tray materials were similarly evaluated. FIG. 2 shows a plot of relaxation stress vs. time for each tray over a ten minute time span Curveε N, 0, and P εhow the reεultε for "EASY TRAY", "HEA FORM", and "AQUERON" tray materials, respectively. Note that once these trays are subjected to an initial step streεs, the relaxation streεε drops steadily, falling below 3 X 10 3 dyne/cm 2 in lesε than ten minuteε. In contraεt, the tray of EXAMPLE 1 (curve Q) aεymptotically approacheε a relaxation stress greater than about 10 4 dyne/cm 2 . The tray of EXAMPLE 1 exhibited rheological behavior characteristic of a viscoelaεtic εolid. Similar measurements were performed for the trays of Runs 1 and 26 of TABLE I. Set out below in TABLE II are the relaxation streεs values and the times at which the measurement was stopped (or at which the relaxation streεε dropped below the 500 dyne/cm 2 detection limit of the rheometric dynamic analyzer) for each tray, at temperatureε of 60°C, 70°C and 80°C. TABLE II Relaxation stress Tray Temp. , °C (τ) , dyne/cm Time, sec "EASY TRAY" 60 <500 103 "EASY TRAY" 70 <500 178 "EASY TRAY" 80 <500 141 "HEAT FORM" 60 <500 253 "HEAT FORM" 70 <500 254 "HEAT FORM" 80 <500 55 "AQUERON" 60 2,081 >600 "AQUERON" 70 2,606 >600 "AQUERON" 80 2,397 >600 EXAMPLE 1 60 16,060 >600 EXAMPLE 1 70 9,790 >600 EXAMPLE 1 80 9,374 >600 Run 1, TABLE I 60 4,148 >600 Run 1, TABLE I 70 1,707 >600 Run 1, TABLE I 80 3,290 >600 Run 26, TABLE I 60 17,610 >600 Run 26, TABLE I 70 5,556 >600 Run 26, TABLE I 80 5,854 >600 The above data illustrates the substantial equilibrium relaxation stress of several trays of the invention. FIG. 3. shows a plot of relaxation streεε vε. time for the tray of EXAMPLE 1 at 60°C (curve R), 70°C (curve S) and 80°C (curve T). Aε εhown by the curves, th desirable rheological properties of the tray were maintained at elevated temperatures. EXAMPLE 4 The blend of EXAMPLE 1 waε heated on a hot plat until softened, then cast atop polyester film into a 2.5m thick sheet into which was pressed a web of "SONTARA 8000" nonwoven material (E.I. DuPont de Nemours & Co.). The warm sheet was cut into generally U-shaped pieces uεing a "cookie cutter" εtyle cutting implement. Each piece waε εqueezed while still warm between two halves of a silicone mold to form an arch-shaped, nonwoven scrim-lined customizable tray. The tray could be reheated and shaped while warm to conform to a patient's dentition. When irradiated for two minutes in a "STAR-CURE" curing chamber (Star X-ray, Inc.), a tray with heat-resistant semi-permanent shape memory was obtained. The tray can alεo be photocured by εetting it under a conventional dental operatory light (for example, a "RITTER STAR LIGHT", Sybron Corp.) for two minuteε per side. EXAMPLE 5 Using the method of EXAMPLE 1, a photosettable thermoplaεtic custom tray waε prepared by mixing the ingredientε εet out below in TABLE III: TABLE I I I Ingredient Parts "TONE P-767" Polycaprolactone 27 . . 0 "CMD 8805" Urethane diacrylate 12 . . 3 CPQ 0 . . 5 EDMAB 0 . . 5 "IMSIL A-25" Filler 10 . . 0 The resulting thermoplastic blend was fabricated into a partially formed tray having a half-moon εhape and a protruding handle at the midline. The tray (excluding itε handle) waε εuεpended in a 70°C water bath until tranεparent, then εhaped to fit around the full arch of a "TYPODONT" model (Columbia Dentoform, Inc.). The tray waε allowed to cool εlightly and then removed from the model. The reεulting cuεtom tray was uniformly irradiated with a "VISILUX 2" curing light for about 2 minutes, yielding a rigid photoset tray. The tray was placed in an 80°C oven for 10 minutes. It retained its shape without slumping. "EXPRESS" tray adhesive (3M) waε applied to the photoεet cuεtom tray with a bruεh and allowed to dry for about 5 minuteε. "IMPRINT" single phase impresεion material (3M) waε εyringed onto the model and into the tray. The tray waε reseated on the model and the impression material allowed- to set for about 5 minuteε. Upon removal of the tray from the model the impression material remained firmly adhered to the tray. EXAMPLE 6 Using the method of EXAMPLE 5, an unirradiated customizable tray was prepared and placed in a resealable polyethylene bag of di enεions slightly greater than the tray. The bag was immersed in 70°C water until the full arch portion of the tray waε tranεparent. The bag was removed from the water, and the bag and tray shaped to fit the full arch of a "TYPODONT" model. After cooling, the custom tray waε eaεily removed from the bag. The bag serveε aε a convenient cuεtom tray encloεure that diεcourageε meεε and contamination, and εerveε aε a εpac between the dental tiεεue and tray. The εpacer allows clearance for adequate amounts of i presεion material wh a final impreεεion iε formed. EXAMPLE 7 20 Partε "IMSIL A-25" ground quartz filler were added with εtirring to an open veεεel containing 24.5 partε "CMD-8805" urethane acrylate oligomer, 0.5 parts C and 1.0 parts EDMAB. The mixture was stirred at 80°C until homogeneous. 54 Partε "TONE P-767" polycaprolacto were added to the veεεel, and the mixture was heated with stirring at 80°C until molten. Uεing a similar procedure, a control compositio containing no filler and eight additional compoεitionε containing various types and amounts of fillers were prepared. Set out below in TABLE IV are the amounts of polycaprolactone ("PCL") and polymerizable resin ("Resin" in each composition, the type and amount of filler in eac composition, and the modulus for compositionε that were not irradiated ("NIR") or irradiated while cold ("IR Cold"). TABLE IV Ingredients Modulus, 30 CC, Run PCL Resin Filler dyne/cm X 10* no. Amount Amount T YP e Amount NIR IR cold 1 74.0 24.5 3.2 8.1 2 54.0 24.5 "IMSIL" 1 20 5.1 7.1 3 39.0 19 n 40 NM 2 2.8 4 54.0 24 "VILRON" 3 20 1.5 8.6 5 39.0 19 It 40 NM 9.1 6 54.0 24 "DUROSIL" 4 20 7.0 8.1 7 54.0 24 "OX-50" 5 20 6.8 6.7 8 54.0 24.5 Treated "OX-10" 6 20 3.9 9.4 9 54.0 24.5 Quartz 7 20 8.4 6.9 1 "IMSIL" Quartz filler (Illinois Minerals). 2 NM = not measured 3 "VICRON" calcium carbonate (Pfizer Corp.). 4 "DUROSIL" silica (North American Silica Co.). 5 "OX-50" pyrogenic silica (Degussa). 6 OX-50 pyrogenic silica treated with gamma-methacryloxypropyl trimethoxysilane 7 quartz treated with gamma-methacryloxypropyl trimethoxyεilane. EXAMPLE 8 A thermoplastic custom tray waε prepared by combining 36.7 parts "TONE P-767" polycaprolactone, 12 parts "SR-9505" urethane diacrylate oligomer, 2 partε "EBERCRYL 830" polyeεter hexacrylate, 20 partε "3075" chopped glaεε fibers (PPG), 11.7 parts "QUSO WR55" hydrophobic silica (North American Silica Co.), 16.6 par "ULTRASIL VN 3 SP" untreated precipitated silica, 0.9 parts EDMAB, and 0.23 partε CPQ. The ingredients were εtirred in a warm veεεel at 100°C until homogeneous. Th resulting blend formed an injection-moldable thermoplast that waε εolid and εtiff at 38°C, but which εoftened readily in a 60°C water bath to form a manually-deformab but uεefully εtiff εemi-solid with excellent warm handli properties. EXAMPLE 9 Using the method of EXAMPLE 8, a thermoplastic tray waε prepared from a blend of 39.3 partε polycaprolactone, 14 partε urethane diacrylate oligomer, parts polyester hexacrylate, 18.6 parts chopped glass fibers, 13.4 parts hydrophobic silica, 9.7 partε precipatated εilica, 0.3 partε EDMAB, and 0.07 partε CPQ. The reεulting compoεition had a εomewhat whiter colorati and good handling properties. Although this invention has been described usi certain illuεtrative examples, it should be understood that the invention is not limited to the specific exemplary embodiments shown in this specification.

Claims: CLAIMS 1. A custom dental tray, comprising a homogenous blend of a thermoplaεtic material and thixotropic filler, the tray being εhaped and εized for use in the mouth, and the blend being a solid with a storage moduluε of at least 10 9 dyne/cm 2 at 38°C and a manually-deformable semi-εolid with a εtorage moduluε less than 10 12 dyne/cm 2 at a temperature that comfortably can be withstood by oral tisεueε, the type and amount of filler being εufficient εo that the blend haε a εtorage moduluε greater than 10 6 dyne/cm 2 at 75 β C and an equilibrium relaxation εtreεs greater than 500 dyne/cm 2 at 60°C. 2. A tray according to claim 1, wherein throughout the range of temperatureε between 45 β C and 75 β C the storage modulus of the blend is less than 10 12 dyne/cm 2 but greater than 10 6 dyne/cm . 3. A tray according to claim 1, wherein throughout the range of temperatures between 50 β C and 70°C the storage modulus of the blend is less than 10 11 dyne/cm 2 but greater than 3 X 10 6 dyne/cm 2 . 4. A tray according to claim 1, wherein throughout the range of temperatures between 50 β C and 65 β C the storage modulus of the blend is lesε than 10 11 dyne/cm 2 but greater than 5 X 10 6 dyne/cm 2 . 5. A tray according to claim 1, wherein the blend has an equilibrium relaxation stress greater than 10 3 dyne/cm 2 at 60°C. 6. A tray according to claim 1, wherein the blend has an equilibrium relaxation stresε greater than 3 X 10 3 dyne/cm 2 at 60°C. 7. A tray according to claim 1, wherein the blend has an equilibrium relaxation streεε greater than 10 4 dyne/cm 2 at 60°C. 8. A tray according to claim 1, wherein the filler compriεes a fibrous, platy or finely-divided particulate material. 9. A tray according to claim 1, wherein the filler is selected from the group consisting of glass fiber, clay, mica, alumina, silica and calcium carbonate. 10. A tray according to claim 1, wherein the thermoplastic material compriseε a polyester, polyurethane, or polycaprolactone. 11. A tray according to claim 10, wherein the material is polycaprolactone having the formula: ___- 0 0 0 ** (HO(CH 2 ) 5 CO((CH 2 ) 5 CO) χ (CH 2 ) 5 CM^R 1 where R 1 is hydrogen or an aromatic or a straight chain or branched aliphatic backbone, w iε 1 if R 1 iε hydrogen, and w otherwiεe haε an average value from 1 to 4, M iε oxygen or -NR 2 - where R 2 is hydrogen or a non-interfering aromatic or aliphatic group, and the product of w times x iε greater than 35. 12. A tray according to claim 1, wherein the blend comprises at least one layer of a multi-layer thermoplastic molding compoεition. 13. Uεe of the softened tray of claim 1 for making an impresεion of dental tiεsue.

Inventors: OXMAN JOEL D, UBEL F ANDREW III, OXMAN, JOEL, D., UBEL, F., ANDREW, III
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1991
Main classification: A61C9
IPC codes: A61C9