Dental impression tray and dental impression kit

The present invention pertains to a dental impression tray and a dental impression kit comprising the dental impression tray.

Dental impression trays made from metal or polymeric materials are known in the art. Prior art trays have various shapes, comprising an outer side wall and a bottom part or bottom wall. In addition prior art trays may also comprise an inner side wall and/or a handle. A concave portion of known dental impression trays is bounded by at least the outer side wall and the bottom part and forms a repository for a dental impression material. Common materials used for dental impressions are sodium alginate, polyether and silicones - both condensation-cured silicones and addition-cured silicones, such as polyvinyl siloxane.

US 2005/0100853 Al discloses an appliance for use in an oral cavity comprising a polymeric shell containing a polymeric mixture, wherein the shell has cavities that are designed to receive teeth and the polymeric mixture preferably comprises a thermoplastic polymer.

The currently used methods and appliances for preparation of dental impressions suffer from various disadvantages such as high fault rate and patient discomfort. Patient discomfort is caused by impression materials, such as sodium alginate having a Shore hardness of > 40 Shore A after curing. Further, repeat impression preparation necessitated by faulty impressions are a main reason for patient discomfort and irritation.

Thus, there exists a need for a dental impression tray that alleviates patient discomfort and enables a dentist or his assistant to efficiently prepare accurate dental impressions with reduced fault probability.

Accordingly, the present invention has the objective to provide a dental impression tray which enables visual inspection of the conformation of a dental impression material to a patients teeth (and gums). The invention has the further objective to provide a dental impression tray that is suitable for elastomeric impression materials, exhibits increased adhesion and retention and mechanically stabilizes the elastomeric impression material after curing, respectively after crosslinking or vulcanization.

The first objective is achieved through a dental impression tray that is made from a transparent polymeric material. Advantageous implementations of the inventive dental impression tray are characterized in that:

- the dental impression tray has an optical transmission of > 60 % , > 70 % , > 80 % or

> 90 % for wavelengths in the range of 380 to 780 nm ;

- the dental impression tray is colored and has an optical transmission of > 60 % , > 70 % ,

> 80 % or > 90 % for wavelengths in the range of 380 to 780 nm ;

- 30 to 100 % of an inner surface of the dental impression tray has an average surface

roughness Rz of 2 to 500 qm ;

- 30 to 100 % of an inner surface of the dental impression tray has an average surface

roughness Rz of 2 to 10 μτ α , 2 to 20 μιη , 5 to 20 μιη , 10 to 20 μηι , 5 to 30 μηι , 10 to

30 μηι , 10 to 50 μηι , 20 to 100 μπι , 50 to 200 μηι , 50 to 300 μπι , 100 to 400 μι ^η or 200 to 500 μηι ;

- an outer surface of the dental impression tray has an average surface roughness Rz of

≤ 2 μιη ;

- an outer surface of the dental impression tray has an average surface roughness Rz of

< 1 μιη , < 500 nm , < 400 nm , < 300 nm , < 200 nm or < 100 nm ; the dental impression tray is made from a polymeric material consisting of 80 to 99.9 % by weight of one or more polymers and 0.1 to 20 % by weight of additives, based on the total weight of the polymeric material; the dental impression tray is made from a polymeric material consisting of 80 to 99 % by weight of one or more polymers and 1 to 20 % by weight of additives, based on the total weight of the polymeric material; the dental impression tray is made from a polymeric material consisting of 80 to 99.9 % by weight of one or more polymers and 0.1 to 20 % by weight of additives, based on the total weight of the polymeric material, wherein the at least one polymer is selected from

polycarbonates, polyesters, polyamides, polyethylenes, polypropylenes, polyurethanes, polyepoxides or mixtures thereof; the dental impression tray is made from a polymeric material consisting of 80 to 99 % by weight of one or more polymers and 1 to 20 % by weight of additives, based on the total weight of the polymeric material, wherein the at least one polymer is selected from

polycarbonates, polyesters, polyamides, polyethylenes, polypropylenes, polyurethanes, polyepoxides or mixtures thereof; the dental impression tray is prepared by injection molding; the dental impression tray is prepared by injection molding using a mold with an inner mold surface, wherein one or more select areas of the inner mold surface have an average surface roughness Rz of 2 to 500 μηι ; the dental impression tray is prepared by injection molding using a mold with an inner mold surface, wherein one or more select areas of the inner mold surface have an average surface roughness Rz of 2 to 10 μηι , 2 to 20 μηι , 5 to 20 μηι , 10 to 20 μηι , 5 to 30 μιη , 10 to 30 μηι , 10 to 50 μηι , 20 to 100 μηι , 50 to 200 μπι , 50 to 300 μηι , 100 to 400 μηι or 200 to 500 μιη ; the dental impression tray is formed as a U-shaped chute; the dental impression tray is formed as a U-shaped trough; the dental impression tray has a central portion that is dome-shaped; the dental impression tray consists of a contoured sheet of transparent polymer and the contoured sheet has a thickness, i.e. shortest distance between opposite surfaces of 1 to 4 mm , 1 to 3 mm or 1 to 2 mm; the dental impression tray consists of a contoured sheet of transparent polymer and the sheet has holes; the dental impression tray consists of a contoured sheet of transparent polymer and the sheet has notches; the dental impression tray comprises a handle; the dental impression tray comprises a latch-shaped handle; the dental impression tray has an outer side wall that is partly or over its entire extent inwardly inclined; the dental impression tray has an inner side wall that is partly or over its entire extent outwardly inclined; the dental impression tray has an outer side wall that is partly or over its entire extent inwardly inclined and an inclination angle between the outer side wall and a horizontal earner or reference plane of the dental impression tray is in the range of 65 to 85 degree, 65 to 75 degree, 70 to 80 degree or 75 to 85 degree; the dental impression tray has an inner side wall that is partly or over its entire extent outwardly inclined and an inclination angle between the inner side wall and a horizontal carrier or reference plane of the dental impression tray is in the range of 65 to 85 degree, 65 to 75 degree, 70 to 80 degree or 75 to 85 degree; the dental impression tray has an outer side wall that is partly or over its entire extent inwardly curved; the dental impression tray has an outer side wall that is partly or over its entire extent inwardly curved and a curvature of the outer side wall is in the range of 1/160 mm ^"1 to 1/20 mm ^"1 ; the dental impression tray has an inner side wall that is partly or over its entire extent outwardly curved; the dental impression tray has an inner side wall that is partly or over its entire extent outwardly curved and a curvature of the inner side wall is in the range of 1/160 mm ^"1 to 1/20 mm ^"1 ; an outer edge of the dental impression tray is provided with an inwardly protruding bulge extending over select portions or the entire length of the outer edge; an outer edge of the dental impression tray is provided with an inwardly protruding bulge extending over select portions or the entire length of the outer edge and having a height of 1.0 to 5.0 mm relative to an inner surface of the outer side wall; an inner edge of the dental impression tray is provided with an outwardly protruding bulge extending over select portions or the entire length of the inner edge; an inner edge of the dental impression tray is provided with an outwardly protruding bulge extending over select portions or the entire length of the inner edge and having a height of 1.0 to 5.0 mm relative to an inner surface of an inner side wall; an inner surface of the dental impression tray has protrusions; the protrusions are dome-shaped; the protrusions are bead-shaped; the protrusions are dome-shaped or bead-shaped; the protrusions have a height of 0.2 to 3.0 mm ; - the protrusions have a height of 0.2 to 0.6 mm , 0.4 to 0.8 mm , 0.6 to 1.0 mm , 0.5 to 2.0 mm , 0.5 to 3.0 mm , 1.0 to 2.0 mm , 1.0 to 3.0 mm , 1.5 to 2.5 mm or 1.5 to 3.0 mm ;

- the dental impression tray is made from a transparent polymer having a refractive index n _t with 1.3 < n _t < 1.6 for wavelengths in the range of 380 to 780 nm ;

- the dental impression tray is made from a transparent polymer having a refractive index n _t with 1.30 < n _t < 1.40 , 1.35 < n _t < 1.45 , 1.40 < n _t < 1.50 , 1.45≤n _t < 1.55 or

1.50 < n _t < 1.60 for wavelengths in the range of 380 to 780 nm ;

- the surface of the dental impression tray comprises one or more planar regions for optical coupling of light into the walls of the dental impression tray, such as a light from a light emitting diode (LED);

- the surface of the dental impression tray comprises one or more planar regions for optical coupling of light into the walls of the dental impression tray, such as a light from a light emitting diode (LED), the at least one planar surface area having an average surface roughness Rz of < 100 nm, < 50 nm or < 10 nm ;

- the surface of the dental impression tray comprises one or more planar regions for optical coupling of light into the walls of the dental impression tray, such as a light from a light emitting diode (LED), the at least one planar surface area having an average surface roughness Rz of < 100 nm, < 50 nm or < 10 nm and a size of 10 to 100 mm ;

- the dental impression tray comprises at least one recess, seating or socket as receptacle for a light source, such as a light emitting diode (LED); and/or

- the dental impression tray comprises at least one blind hole as recptacle for a light source, such as a light emitting diode (LED), the blind hole having an inner diameter of 1 to 10 mm or 1 to 6 mm.

The dental impression tray of the present invention in its various embodiments is advantageous in that it enables visual inspection of the filling degree and conformation of the dental impression material in the intermediate space between the dental impression tray and the patients teeth and/or gums. This advantageous effect can be harnessed with opaque and transparent dental impression materials. During an impression procedure performed by a dentist or his assistant air may be accidentally trapped inside the uncured dental impression material and cause formation of cavities or voids. The size of such cavities ranges from 0.2 to 3 mm. In the area proximal to a cavity the pressure, i.e. force per unit area, between the dental impression material and the patients teeth as well as the corresponding pressure between the dental impression material and an inner surface of the dental impression tray is markedly reduced compared to intact areas with maximal filling degree. Due to minor involuntary locomotion of the patients oral musculature and to a lesser extent due to shrinkage of the dental impression material upon curing the dental impression material detaches from the inner surface of the dental impression tray. In case of such detachment one or more visually perceivable detachment spots with a diameter of typically 0.5 to 8 mm occur. The optical contrast of these detachment spots is attributable to light diffraction and/or light interference. Light from a conventional light source or a medical lighting device traverses the wall of the dental impression tray, is partly or to a larger degree reflected by the transparent or opaque dental impression material contained in the space between the patients teeth and the dental impression tray, passes the wall of the dental impression tray a second time and reaches the eye of an observer. Typically the incident light from the light source is not collimated and to a certain extent diffuse i.e. the angle of incidence of the light rays varies within a certain solid angle. Thus, part of the diffusely incident and reflected light rays reach the observer's eye.

On its path from the light source to the observer's eye a light ray traverses the interface between the wall of the transparent dental impression tray and the dental impression material two times. If the refractive index of the medium adj cent to the inner surface of the dental impression tray varies in a discontinuous manner visually perceivable diffraction and/or interference fringes occur. This is the case when the dental impression material detaches from the inner surface of the dental impression tray in a spot pattern. The refractive index of customary polymeric materials suitably used for the manufacture of the dental impression tray ranges from 1.3 to 1.6 in the visible part of the electromagnetic spectrum (i.e. for wavelengths between 380 and 780 nm). Thereto similar, the refractive index of customary dental impression materials is in the range of about 1.4 to 1.6 for wavelengths between 380 and 780 nm. However, the refractive index of air or vacuum is 1 and differs distinctly from that of a dental impression material. Due to the sharp drop in refractive index the boundary of a detachment spot is marked by one or more visually perceivable diffraction and/or interference fringes. In an advantageous embodiment of the invention the optical contrast of detachment spots is augmented through a dental impression tray with an inner surface of which 30 to 100 % has an average surface roughness Rz of 2 to 500 μιη. The inner surface with an average surface roughness Rz of 2 to 500 μηι may be comprised of one contiguous surface area or a multitude of unconnected surface areas. In the presence of air or vacuum as adjacent medium, respectively absence thereof, an inner surface area with an average surface roughness Rz of 2 to 500 μιη causes strong light scattering that is visually perceived as turbidity or haze. Contrary thereto, if such rough surface area is covered by a highly conformal medium such as an elastomeric impression material having a refractive index in the range of 1.4 to 1.6 light scattering at surface irregularities is strongly reduced and visually not perceivable. This is due to the fact that for visible wavelengths the interface between the rough inner surface of the dental impression tray and the conformal elastomeric impression material constitutes a practically homogeneous and isotropic optical medium.

In addition to augmented optical contrast of detachment spots the inventors have found that an inner surface with average surface roughness Rz of 2 to 500 μηα helps to retain and

mechanically stabilize an elastomeric impression material in the dental impression tray after curing. Mechanical retention of the cured elastomeric impression material in the dental impression tray helps avoiding potentially destructive tear caused by adhesion to and incomplete detachment of the finished impression from a patients teeth and gums. Furthermore, the mechanical stabilization imparted to the cured elastomeric impression material is also beneficial for multiple casting and extraction of gypsum molds.

In further embodiments of the invention the dental impression tray is shaped in a specific manner that increases mechanical retention and stability of a cured elastomeric impression material contained therein. This is achieved through various means that may be employed separately or in combination, comprising inwardly inclined or curved inner side walls, outwardly inclined or curved inner side walls and edge protrusions and/or surface protrusions.

Preferably, the dental impression tray of the present invention is made from a polymeric material consisting of 80 to 99 % by weight of one or more polymers and 0.1 to 20 % by weight of additives, based on the total weight of the polymeric material, wherein the at least one polymer is selected from polycarbonates, polyesters, polyamides, polyethylenes, polypropylenes, polyurethanes, polyepoxides or mixtures thereof. Preferably, the dental impression tray of the present invention is prepared by injection molding. Injection molding is the most commonly used manufacturing process for the fabrication of plastic parts. A wide variety of products are manufactured using injection molding, which vary greatly in their size, complexity, and application. The injection molding process requires the use of an injection molding machine, raw plastic material and a mold. The plastic is melted in the injection molding machine and then injected into the mold, where it cools and solidifies into the final part. The two main components of the injection mold are the mold core and the mold cavity. When the mold is closed, the space between the mold core and the mold cavity forms the part cavity, that is filled with molten plastic to create the dental impression tray. The mold core and the mold cavity are customarily made from metallic materials such as carbon steel, stainless steel, aluminums, coppers or bronzes.

In an advantageous embodiment of the invention select areas or the total area of the inner surface of the injection mold cavity and/or core are provided with an average surface roughness Rz of 2 to 500 μιη. This is accomplished through established surface texturing processes, such as chemical etching, hard milling, electro discharge machining (EDM), micro-abrasive blasting and/or laser etching. As chemical texturing etchants ferric chloride (FeCl ₃ ) or nitric acid (HN0 ₃ ) are commonly used. In order to texture select areas, the inner surface of the injection mold is coated with protective wax or varnish in a desired pattern, respectively a negative thereof before the texturing operation.

Furthermore, the present invention has the objective to provide a dental impression kit, that improves patient comfort and enables efficient preparation of accurate dental impressions.

This objective is achieved through a dental impression kit comprising a dental impression tray according to any one of the above described embodiments and an elastomeric impression material.

Advantageous embodiments of the inventive dental impression kit are characterized in that:

- the elastomeric impression material is selected from alginates, polyethers, polyurethanes, silicones and mixtures thereof;

- the elastomeric impression material is a silicone polymer;

- the elastomeric impression material is an RTV silicone based material; the elastomeric impression material is a one component vulcanizable silicone based material; the elastomeric impression material is a two component vulcanizable silicone based material; the elastomeric impression material is a one-component or a two-component RTV silicone, wherein at least one component comprises a non-cleaving cross-linking agent; the elastomeric impression material is a one-component or a two-component RTV silicone wherein cross-linking does not release cleaving moieties; the elastomeric impression material is a one-component or a two-component RTV silicone wherein cross-linking causes volume shrinkage of 0 to 3 vol-%, 0 to 2 vol-% or 0 to 1 vol-%, based on the volume of the RTV silicone in its uncured state; the elastomeric impression material is a one-component or a two-component RTV silicone wherein the volume of the RTV silicone after cross-linking is 0 to 3 vol-%, 0 to 2 vol-% or 0 to 1 vol-% smaller than the volume of the RTV silicone in its uncured state; the elastomeric impression material is a one-component or a two-component RTV silicone, wherein at least one component comprises a platin catalyst; the elastomeric impression material is a one-component or a two-component RTV silicone, wherein at least one component comprises one or more SiH-based cross-linking agents; the elastomeric impression material is a one-component or a two-component RTV silicone of type A, wherein at least one component comprises one or more addition-cross-linking agents; the elastomeric impression material is a one-component or a two-component RTV silicone, wherein at least one component comprises one or more cross-linking inhibitors; the elastomeric impression material is a one-component or a two-component RTV silicone and has a cross-linking (curing) time of 150 to 300 s, 150 to 250 s, 200 to 300 s or 180 to 240 s at a temperature of 37 °C; the elastomeric impression material is a one-component or a two-component RTV silicone having a viscosity of 150 to 250 Pa s in its uncured state at 25 °C; the elastomeric impression material is a one-component or a two-component RTV silicone having an elongation-at-break of 150 to 300 % in its cured state at 25 °C; the elastomeric impression material is a one-component or a two-component RTV silicone having a tensile strength of 0.5 to 3.0 N/mm ² in its cured state at 25 °C; the elastomeric impression material is a one-component or a two-component RTV silicone having a tear strength of 0.6 to 3.0 kN/m in its cured state at 25 °C; the elastomeric impression material is a one-component or a two-component RTV silicone having a density of 0.96 to 1.02 g em ^" in its cured state; the elastomeric impression material is transparent and has an optical transmission of > 60 %, > 70 %, > 80 % or > 90 % for wavelengths in the range of 380 to 780 nm at an optical path length of 3 mm ; the elastomeric impression material has a refractive index n _s with 1.38 < n _s < 1.58 for wavelengths in the range of 380 to 780 nm ; the elastomeric impression material has a refractive index n _s with 1.38 < n _s < 1.45 , 1.45 < n _s < 1.55 , 1.50 < n _s < 1.58 for wavelengths in the range of 380 to 780 nm ; the refractive index n _s of the elastomeric impression material and the refractive index n _t of the dental impression tray are matched, such that -0.2 < n _s - n _t < 0.2 or that

-0.15 < n _s - n _t < 0.15 for wavelengths in the range of 380 to 780 nm ; the refractive index n _s of the elastomeric impression material and the refractive index n _t of the dental impression tray are matched, such that -0.1 < n _s - n _t < 0.1 or that

-0.08 < n _s - n _t < 0.08 for wavelengths in the range of 380 to 780 nm ; the elastomeric impression material comprises color pigments; the elastomeric impression material comprises a dye; the elastomeric impression material comprises 0.1 to 10 % by weight of an inorganic particulate additive, based on the total weight of the elastomeric impression material; the elastomeric impression material comprises 0.1 to 10 % by weight of an inorganic particulate additive selected from silica (Si0 ₂ ), chalk (CaC0 ₃ ) or titanium oxide (Ti0 ₂ ), based on the total weight of the elastomeric impression material; the elastomeric impression material comprises 0.1 to 10 % by weight of an inorganic particulate additive having an average particle size of 30 to 800 nm; the elastomeric impression material comprises 0.1 to 10 % by weight of an inorganic particulate additive having an average particle size of 0.1 to 5.0 μηι; the elastomeric impression material has a Shore hardness of 15 to 60 Shore A, 15 to

40 Shore A , 20 to 40 Shore A, 25 to 45 Shore A, 30 to 50 Shore A, 35 to 55 Shore A or 40 to

60 Shore A after curing or vulcanization; - the elastomeric impression material comprises a flavor compound;

- the dental impression kit comprises a cartridge containing the elastomeric impression

material;

- the dental impression kit comprises a plastic pouch containing the elastomeric impression material;

- the plastic pouch comprises one reservoir chamber or two reservoir chambers;

- the plastic pouch comprises two reservoir chambers and an outlet duct;

- the plastic pouch comprises two reservoir chambers and an outlet duct having a length of 5 to 50 mm;

- the plastic pouch comprises two reservoir chambers and an outlet duct configured as static mixer;

- the dental impression kit comprises an electronic light source, such as a light emitting diode (LED); and/or

- the dental impression kit comprises an electronic light source, such as a light emitting diode (LED) and a battery for powering the light source.

The elastic impression material may be suitably selected from alginates, polyethers, poly- urethanes, silicones and mixtures thereof.

In a particularly preferred embodiment of the invention, the elastic impression material consist of 80 to 100 % by weight of a silicone and 0 to 20 % by weight of additives, based on the total weight of the elastic impression material.

In the present invention the term "silicone" pertains to polymerized siloxanes or polysiloxanes. Polysiloxanes comprise a silicon-oxygen backbone (... -Si-O-Si-O-Si-O- ...) with organic side groups R attached to the silicon atoms and generally have chemical structure I wherein the silicon atoms in the silicon-oxygen backbone are tetravalent.

In an advantageous embodiment of the invention the elastic impression material comprises a condensation cure one-part or two-part room temperature vulcanizable (RTV) silicone with a molecular weight in the range of 15,000 to 150,000.

One-part RTV silicones are crosslinked with moisture-sensitive multi-functional silanes. A one- part moisture cure system may be based on e.g. acetoxy, enoxy, oxime, alkoxy, amine, benz- amido or mixed alkyloxyamino.

A two-part condensation cure silicone may employ e.g. ethylsilicates (polydiethylsiloxanes).

The organic substituents on the crosslinkers may be selected from e.g. vinyl, methyl, ethyl or phenyl.

BRIEF DESCRIPTION OF THE DRAWINGS

The dental impression tray of the present invention is further illustrated in Figures 1 to 15, showing

Fig. 1-4 perspective views of dental impression trays;

Fig. 5 a coordinate system for a dental impression tray;

Fig. 6 a dental impression tray having a handle;

Fig. 7-14 schematic cross sections of dental impression trays; and

Fig. 15 schematic surface roughness profiles.

DETAILED DESCRIPTION

Fig. 1 shows a dental impression tray 1 according to the present invention having an outer side wall 6 and an inner side wall 7 that are connected by a bottom wall 9. Dental impression tray 1 is formed as a U-shaped open-ended chute with rectangular cross. The space confined by sidewalls 6, 7 and bottom wall 9 serves as repository for a dental impression material (not shown in Fig. 1). The inner, respectively opposite surfaces of side walls 6 and 7 and the thereto adjacent upper surface of bottom wall 9 are jointly designated as inner surface 8.

Fig. 2 shows a dental impression tray 2 formed as U-shaped trough with rectangular cross section, side walls 6, 7 and inner surface 8. The shape of dental impression tray 2 differs from impression tray 1 merely by front walls.

Fig. 3 shows a dental impression tray 3 formed as U-shaped chute with semi-elliptic or semi-circular cross section, side walls 6, 7 and inner surface 8.

Fig. 4 shows a dental impression tray 4 comprised of a bottom wall 9 and an outer side wall 6. The upper surface of bottom wall 9 and the thereto adjacent inner surface of outer side wall 6 are jointly designated as inner surface 8. Fig. 4 depicts bottom wall 9 having a central dome-shaped portion and perforations 10.

Though not shown in Fig. 4, the present invention also encompasses dental impression trays comprising a contoured or flat bottom wall with or without perforations. Further, the present invention encompasses dental impression trays with an outer and/or inner side wall having perforations.

Fig. 5 shows a perspective view of a dental impression tray 1 positioned on a flat surface that defines a horizontal carrier or, respectively reference plane 30. In Fig. 5 dental impression tray 1 is enclosed in a virtual bounding box 40 having width W, depth D and height H. A central axis 31 is located at the center of bounding box 40 and aligned in a direction perpendicular to reference plane 30.

In the present invention the terms "inwardly inclined" and "outwardly inclined" refer to an inclination towards central axis 31 and, respectively away from central axis 31.

Furthermore, the term "inner surface" refers to a surface situated oppositely from reference plane 30. Correspondingly, the term "outer surface" refers to a surface situated adjacent to reference plane 30. When viewed in a top-down direction opposite to central axis 31, the "inner surface" or parts thereof are generally located on an upper side of the dental impression tray. The "inner surface" of the dental impression tray partly bounds a generally convex space which serves as repository for the elastomeric impression material. In embodiments where the dental impression tray comprises a dome-shaped central portion as depicted in Fig. 4 and 6 the space serving as repository for the elastomeric impression material is partly concave.

Fig. 6 shows a perspective view of dental impression tray 4' with a handle 5. Dental impression tray 4' is similar to dental impression tray 4 depicted in Fig. 4 but does not have perforations.

The dental impression tray of the present invention comprises at least an outer side wall 6 and a bottom wall or bottom portion. The outer side wall and the bottom wall or bottom portion may have a shape that deviates from the embodiments shown in Fig. 1-6. In addition, the dental impression tray of the present invention may have an inner side wall as depicted in Fig. 1-3. Furthermore, the dental impression tray of the present invention may be equipped with a handle. Preferably, the handle is shaped as flat outwardly protruding bar as shown in Fig. 6.

Fig. 7 shows a cross section of a dental impression tray 1A having a shape that is similar to dental impression tray 1 depicted in Fig. 1 and differs therefrom in that outer side wall 6 is inwardly inclined and inner side wall 7 is outwardly inclined relative to central axis 31. The inclination angle of outer side wall 6 and inner side wall 7 are designated by a and, respectively β and correspond to angles enclosed between the inner surface of side walls 6, 7 and reference plane 30. Side walls 6, 7 are inclined such that angles a and β, independently from each other are in the range of 65 to 85 degree, i.e. 65° < a < 85° and 65° < β < 85° .

Fig. 8 shows a cross section of a dental impression tray 3A having a shape that is similar to dental impression tray 3 depicted in Fig. 3 and differs therefrom in that outer side wall 6 is inwardly inclined and inner side wall 7 is outwardly inclined relative to central axis 31. The inclination angle of outer side wall 6 and inner side wall 7 are designated by a and, respectively β and correspond to the angles enclosed between the inner surface of side walls 6, 7 and reference plane 30. Side walls 6, 7 are inclined such that angles a and β, independently from each other are in the range of 65 to 85 degree, i.e. 65° < a < 85° and 65° < β < 85° .

Fig. 9 shows a cross section of a dental impression tray 4A having a shape that is similar to dental impression tray 4 depicted in Fig. 4 and differs therefrom in that outer side wall 6 is inwardly inclined relative to central axis 31. The inclination angle of outer side wall 6 is designated by a and correspond to the angle enclosed between the inner surface of side wall 6 and reference plane 30. Side wall 6 is inclined such that angle a is in the range of 65 to 85 degree, i.e. 65° < a < 85° . Fig. 7-9 pertain to specific embodiments of dental impression trays according to the present invention. Though not shown in Fig. 7-9, the present invention encompasses embodiments, wherein merely an inner surface of side wall 6 and/or 7 is inclined relative to central axis 31. An outer surface of side wall 6 and/or 7 may or may not be inclined relative to central axis 31.

Fig. 10 shows a cross section of a dental impression tray IB having a shape that is similar to dental impression tray 1 depicted in Fig. 1 and differs therefrom in that outer side wall 6 is inwardly curved and inner side wall 7 is outwardly curved relative to central axis 31. The radius of curvature of outer side wall 6 is indicated by arrow 61 and the radius of curvature of inner side wall 7 is indicated by arrow 71. Side walls 6 and 7 are curved independently from each other such that the radius of curvature 61 and, respectively the radius of curvature 71 are in the range of 20 to 160 mm. Accordingly, the curvature of side walls 6 and 7, which is defined as K = 1 / (radius of curvature) is in the range of 1/160 mm ^"1 to 1/20 mm ^"1 , independently from each other.

Fig. 14 shows a cross section of a dental impression tray 4B having a shape that is similar to dental impression tray 4 depicted in Fig. 4 and differs therefrom in that outer side wall 6 is inwardly curved relative to central axis 31. The radius of curvature of outer side wall 6 is indicated by arrow 61. Side wall 6 is curved such that the radius of curvature 61 is in the range of 20 to 160 mm. Accordingly, the curvature κ of side wall 6, which is defined as K = 1 / (radius of curvature) is in the range of 1/160 mm ^"1 to 1/20 mm .

Fig. 10 and 11 pertain to specific embodiments of dental impression trays according to the present invention. Though not shown in Fig. 10 and 11, the present invention encompasses embodiments, wherein merely an inner surface of side wall 6 and/or 7 is curved relative to central axis 31. An outer surface of side wall 6 and/or 7 may or may not be curved relative to central axis 31.

Fig. 12 shows a cross section of a dental impression tray 1C having a shape that is similar to dental impression tray 1 depicted in Fig. 1 and differs therefrom in that the edge of outer side wall 6 has an inwardly protruding bulge 63, extending over select portions or the full extent of the edge; and the edge of inner side wall 7 has an outwardly protruding bulge 73, extending over select portions or the full extent of the edge. Protrusions 63 and 73, indpendently from each other have a height of 1.0 to 5.0 mm relative to an inner surface of side wall 6 and, respectively side wall 7. Fig. 13 shows a cross section of a dental impression tray 3 C having a shape that is similar to dental impression tray 3 depicted in Fig. 3 and differs therefrom in that the edge of outer side wall 6 has an inwardly protruding bulge 63, extending over select portions or the full extent of the edge; and the edge of inner side wall 7 has an outwardly protruding bulge 73, extending over select portions or the full extent of the edge. Protrusions 63 and 73, indpendently from each other have a height of 1.0 to 5.0 mm relative to an inner surface of side wall 6 and, respectively side wall 7.

Fig. 14 shows a cross section of a dental impression tray 4C having a shape that is similar to dental impression tray 4 depicted in Fig. 4 and differs therefrom in that the edge of outer side wall 6 has an inwardly protruding bulge 63, extending over select portions or the full extent of the edge. Protrusions 63 has a height of 1.0 to 5.0 mm relative to an inner surface of side wall 6 and, respectively side wall 7.

Fig. 15 schematically shows a primary height profile 100 recorded from an inner surface of a dental impression tray of the present invention and thereof derived secondary height profiles 110, 120 and 130. Primary height profile 100 may be recorded from a flat or contoured surface portion using a profilometer such as a "Hommel-Etamic W20" instrument from Jenoptik. Through software-based low-pass filtering as specified in DIN EN ISO 16610:2013 with a suitable filter wavelength Xs in the range of 8 to 50 μηι primary height profile 100 is separated into contour profile 110 and roughness profile 120. The average roughness Rz as used in the present invention is determined from roughness profile 120.

Contour profile 110 comprises peaks 130 which correspond to functionally designed dome- shaped or bulge-shaped protrusions. A height H _P of a protrusion relative to a surface base level 130 may be determined directly from contour profile 110 with good accuracy. Alternatively, in order to determine surface base level or profile 130 and the height of designed protrusions in an objective manner, contour profile 110 is also subjected to software-based low- pass filtering according to DIN EN ISO 16610:2013 with a suitable filter wavelength Xs in the range of 0.5 to 3 mm.

MEASUREMENT METHODS

The physical properties of the inventive dental impression tray and the elastomeric impression material are measured as described hereafter. The average roughness Rz of a surface portion of the inventive dental impression tray is determined according to DIN EN ISO 4287:2010. In cases where the surface portion to be measured is not freely accessible, an impression is taken by means of a molding compound. As impression compound, respectively molding compound a material such as cast (gypsum) or a silicone-based precision impression material, e.g. high-viscosity condensation crosslinked polysiloxane as specified in DIN 13 913 A2, ISO 4823 is used. A primaiy height profile of a surface portion of the dental impression tray or alternatively of a high precision impression thereof is recorded by means of a tactile profilometer conforming to DIN EN ISO 3274: 1998, for example a "Hommel-Etamic W20" instrument from Jenoptik. The radius of the sensor tip of the profilometer is between 2 and 5 μιη.

Generally, the surface of the dental impression tray is not planar and has a functionally designed topography or contour. Furthermore, the surface of the dental impression tray may have designed protrusions. In order to determine the surface roughness, contributions to the primary height profile that are attributable to the functionally designed surface contour are removed by software-based low-pass filtering as specified in DIN EN ISO 16610:2013. By way of this low-pass filtering the primary height profile is split into a roughness profile and a contour profile.

The total length Lt of the measurement track is greater than 15 mm (Lt > 15 mm) and comprises a lead-in and lead-out distance and 5 consecutive measurement segments each having a length of lr > 2.5 mm . The value used as limiting wavelength c for the low-pass filter for separation of surface roughness and contour in accordance with DIN EN ISO 16610:2013 is Xc = lr .

The height of designed surface protrusions is measured, respectively verified using a contour profile obtained through the above described measurement technique in accordance with DIN EN ISO 4287:2010 and DIN EN ISO 16610:2013.

The refractive index of the dental impression tray of the present invention is determined according to DIN EN ISO 489:1999-08. For the measurement a flat sample is either cut from a dental impression tray or molded from the polymer composition used for the manufacture of the dental impression tray. If required two main opposing surfaces of the flat sample are ground and polished to obtain the surface finish prescribed by DIN EN ISO 489: 1999-08.

The refractive index of the elastomeric impression material of the present invention is also determined according to DIN EN ISO 489: 1999-08. In order to prepare a suitable sample the elastomeric impression material is cast into a flat film with a doctor blade using a glass plate as carrier and subsequently cured or vulcanized to obtain a cured film with final thickness of about 2 mm. The final thickness of the cured film is determined using a low-force digital micrometer (e.g. Digimatic Micrometer 227 from Mitutoyo Corp.). The term "optical transmission" as used in the present invention refers to the average total transmittance T _a . The total transmittance Τ(λ) of the dental impression tray as function of wavelength λ is determined according to DIN EN ISO 13468-2:2006-07 using a spectrophotometer equipped with an integrating sphere for detection of transmitted light (e.g. employing a Shimadzu UV-3600 Plus Spectrometer with ISR-1503 integrating sphere with 150 mm diameter). For the measurement of total transmittance Τ(λ) a collimated beam of incident light with intensity Ι ₀ (λ) is directed in a normal direction onto an outer surface of the dental impression tray. The incident light beam is partly reflected at the outer and inner surfaces of the dental impression tray. The sum of reflected intensities is designated as ¾λ) . As the incident light beam traverses and exits the wall of the dental impression tray further intensities 1A( ) , ¼ _¾ (λ) and I _BS W are diverted from the incident light beam due to absorption, forward scattering and, respectively backscattering. In embodiments where the inner surface of the dental impression tray has an average surface roughness Rz of 2 to 500 μιη the transmitted light is strongly scattered. Due to the use of an integrating sphere for the detection of transmitted light the forward scattered light intensity ¾ _¾ (λ) is recorded by the spectrophotometer. Accordingly, the measured total transmittance Τ(λ) can be described by following equality

Τ(λ) = c - [ Ι ₀ (λ) - ¼λ) - Ι _Β8 (λ) ] / Ι ₀ (λ) wherein c designates a factor that is determined through proper instrument calibration, e.g. by measuring total transmittance without sample. The optical transmission i.e. the average total transmittance T _a is obtained by averaging Τ(λ) over the visible wavelength range of 380 to 780 nm, according to the relation

In instances where the wall of the dental impression tray is strongly contoured (i.e. has a large curvature) a sample with suitable dimensions of about 15 mm length and about 15 mm width is cut out and mounted in the sample holder of the spectrophotometer. The optical transmission i.e. the average total transmittance of a transparent elastomeric impression material of the present invention is also determined according to DIN EN ISO 13468- 2:2006-07 using a spectrophotometer equipped with an integrating sphere for detection of transmitted light. In order to prepare a suitable sample the elastomeric impression material is cast into a flat film with a doctor blade using a glass plate as carrier and subsequently cured or vulcanized to obtain a cured film with final thickness of about 4 mm. The final thickness of the cured film is determined using a low-force digital micrometer (e.g. Digimatic Micrometer 227 from Mitutoyo Corp.). The total transmission for an optical path length or thickness of 3 mm is calculated, respectively converted based on the well known Beer-Lambert law. The Shore hardness of the elastomeric impression material of the present invention after curing or vulcanization is determined according to DIN ISO 7619-1-2013 (e.g. using an HDA 100-1 instrument from ATP Messtechnik GmbH). For measurement of Shore hardness the elastomeric impression material is cast into a film having a thickness of about 5 mm after curing or vulcanization. The elongation at break and the tensile-tear strength of the elastomeric impression material are determined according to DIN 53504:2009-10, SI .

The tear strength of the elastic impression material is measured according to ASTM D624-00 (2012) or DIN ISO 34-1 :2004-07.

The viscosity of the uncured elastomeric impression material is determined according to DIN EN ISO 3219:1994-10 or ASTM D2196-15 using a rotational viscometer (BH rotor no. 7) at 10 rpm.

The density of the cured elastomeric impression material is measured according to DIN EN ISO 1183-1 :2013-04.