INTRA-ORAL SURFACE NON-AQUEOUS HYDROPHOBIC COATING COMPOSITION AND METHOD

CROSS REFERENCE TQ RELATED APPLICATIONS This application claims the benefit of priority to U.S. Patent Application Serial

No. 61/131,163 filed on June 9, 2008, entitled "intra-oral surface non-aqueous hydrophobic coating composition and method", and incorporated herein in its entirety by reference.

FIELD OF THE INVENTION The present invention relates generally to compositions and methods for coating teeth, and more specifically to intra-oral compositions and methods used in conjunction with three-dimensional intra-oral scanning.

BACKGROUND OF THE INVENTION

In order to meet the increasing demand for both dental and orthodontic treatment, many three-dimensional intra-oral scanning methods have been developed.

For example, US 6,592,371 discloses systems and methods for generating a three-dimensional (3D) model of a structure include coating the structure with a luminescent substance to enhance the image quality, the luminescent substance having an excitation range; and capturing one or more images of the structure through at least one image aperture each having a frequency sensitivity, wherein the frequency sensitivity of each image aperture is maximized for the luminescent material emission range.

It was pointed out in '371 that the crystalline nature of the enamel surface of teeth results in an optically anisotropic medium that results in double refraction or birefringence of the incident light pattern. Further, the translucent nature of the enamel results in a spreading or blooming of the incident structured light pattern as observed at the image sensor.

Similar to the enamel, dentin also exhibits birefringence as well as having the dentinal tubes act as light pipes— further contributing to blooming. The observed color of a person's tooth is primarily the result of the frequency selective absorption and reflection of the dentin material.

To minimize the effects of the optical properties of teeth during imaging, several commercial systems (Sirona Inc. Cerec System and Orametrix Inc. Suresmile

System) have the user apply a coating to the area that is to be imaged to create an opaque surface. Typically, titanium dioxide is used because of its' high index of refraction.

Titanium dioxide is a white pigment that is commercially available in one of two crystalline forms: anatase or rutile and is widely used for providing brightness, whiteness, and opacity to such products as paints and coatings, plastics, paper, inks, fibers and food and cosmetics.

According to '371, to achieve its' optical properties, titanium dioxide particles must be created with an ideal particle size of 0.3-1 μm. It is further suggested in '371 that in powder form, titanium dioxide must be applied to a thickness of between 40 to

60 particles to achieve opacity on the tooth surface. This introduces an error into the true surface contour of the tooth that can vary from 12 μm to 60 μm. Since many dental procedures require surface accuracies of 25-50 μm, the use of titanium dioxide imposes severe and unrealistic constraints on the error budgets of the remaining parameters involved with making an accurate measurement of the teeth surface contours.

Further, because titanium dioxide is a crystalline material, it exhibits optical anisotropy so it is important that the applied thickness be sufficient to create a truly opaque surface to eliminate birefringence effects. In addition, because titanium dioxide is an optically rough surface, it provides no reduction in speckle noise if coherent light is used for the illumination source.

Thus, titanium dioxide, or any other equivalent or mixture, must be applied in a sufficiently thick coating to cover all outer surfaces of a tooth.

There are inherent problems with the current coating methodologies. First of all, if the titanium dioxide is not evenly spread, the image created therefrom will be patchy.

Secondly, the titanium dioxide powder sometimes aggregates and forms lumps. It is therefore important to control the aggregate size by sieving or other size- reduction methods. The greatest problem of the current coating methods is that most aqueous imaging solutions/liquid are very difficult to completely dry. This feature also introduces necessary drying times of several seconds to tens of seconds. This requires the patient to sit still with his mouth open and increases the patient time in the dental chair. Additionally, since these coating liquids are aqueous, they are subject to quick dissolution in saliva, removal by the tongue and other intra-oral tissue. Sometimes, a part of the scanner system placed in the mouth will dislodge the coating on part of the tooth's surface.

Various attempts have been made to improve the adhesion of the aqueous solutions, such as adding SPRITE, flat root beer and the like. However, the underlying problem of these aqueous solutions remains that they are easily dissolved in saliva and easily removed by the tongue.

US2003232302A describes a dental instrument and method for imaging the three-dimensional topography of one or more teeth in the oral cavity of an individual is provided. The instrument includes a probe insertable into the oral cavity to receive the image of these surfaces which can then be processed. Combined with the probe is an auxiliary which projects an air stream toward the surface to be imaged by the probe and acts to evaporate and remove from these surfaces a liquid film coating formed by saliva and other fluids present in the oral cavity, to render these surfaces dry and enhance their reflectivity and in doing so, provide clearer images.

US2005153257A discloses systems and methods for imaging a dental occlusal registration impression; developing a digital 3D surface contour model of the occlusal registration impression from the image data; electronically transferring the data representing the digital 3D surface contour model of the occlusal registration impression; fabricating a physical replicate of the occlusal registration impression; correlating features on upper and lower jaw dental models with features on the

replicate occlusal registration impression model; and determining occlusal alignment of the upper and lower jaw dental models using the replicate occlusal registration impression model.

US2003175658A provides a method for scanning the surface of an object in which moisture such as saliva or water is present on the surface. The method includes the step of applying a saliva and water-resistant composition to the surface, wherein the composition is characterized in that it does not readily wash off the surface after application of the composition to the surface in the presence of saliva or water. The composition forms an opaque film on the surface. The method further includes the step of scanning the surface having the film with a scanner. Several formulations for the composition are disclosed. One includes a liquid alcohol base, such as dehydrated ethyl alcohol, a reflective pigment, and a binder for promoting good adhesion of the formulation to the surface of the object being scanned. A suitable binder for scanning teeth and other oral structures is a denture adhesive such as an off-the-shelf denture adhesive, in powder form, that is mixed with the pigment and the alcohol base. Other suitable compositions can be derived by persons skilled in the art from the teachings disclosed herein.

US 5897696 discloses a process for preparing a water-soluble, radio-opaque paint for marking acrylic resin dental stents includes the steps of preparing a solution comprising 50 ml of ethanol, 6.4 grams of glycerol; 4.0 ml of benzaldehyde; 1.0 ml of glacial acetic acid, and 0.15 grams of hydroxy propyl cellulose. A radio-opaque powder, such as 50 grams of barium sulfate powder having a mean particle diameter of about 10 μm, is then added to the solution. The solution is then mixed to obtain the paint, wherein the paint has a uniform dispersion of the radio-opaque powder. This paint may be used on dental stents to locate and guide placement of dental implants. The method may include the steps of preparing a water-soluble, radio-opaque paint for marking dental stents comprising the steps of preparing a solution described above; adding a radio-opaque powder, such as 50 grams of barium sulfate powder; and mixing the solution to obtain the paint, wherein the paint has a uniform dispersion of the radio-opaque powder. The uniform dispersion may be obtained by using ultrasound. Further, the method comprises applying the paint to a dental stent; placing the stent in contact with a patient's teeth; taking a radiographic image of the stent and the patient's teeth. The stent then is removed from the patient's teeth, and the paint is removed from the stent. The publications hereinabove teach methods for coating teeth prior to 3D- scanning, in which the quality of the coatings, and/or partial inadvertent removal thereof, introduces significant measurement errors in the scanning process. Therefore, there remains a need to provide a method and composition for coating teeth, which enables performance of accurate and precise intra-oral 3D-scanning, without introducing major surface contour errors of the compositions, as described in the publications hereinabove.

SUMMARY OF THE INVENTION

It is an object of some aspects of the present invention to provide a method for coating a surface and compositions therefor, the method of which enables performance of accurate and precise 3D-scanning.

In preferred embodiments of the present invention, improved intra-oral surface coating compositions and methods are provided for preparing an intra-oral structure, such as a tooth, for three-dimensional (3D) scanning.

In other embodiments of the present invention, a method is described for providing a sticky coating to an intra-oral surface, such as a tooth, wherein the coating dries into a layer which is of less than 50 micron thickness, more preferably, less than 30 micron thickness and yet more preferably less than 10 micron thickness.

According to some embodiments, the coating is of between 0-8 micron thickness. Thereafter, a hydrophobic powder is sprayed onto the dried coating layer.

According to some embodiments, the hydrophobic powder comprises titanium dioxide. Typically, the coated powder has a low or no wettability.

According to some embodiments, the powder layer is less than 10 microns thick. More preferably it is 0-5 microns thick. Thus, the bilayer of sticky coating and powder formed on an intra-oral surface, such as a tooth, is preferably less than 30 microns thick, more preferably, less than 20 microns thick and yet more preferably, less than 10 microns thick. This bilayer allows for small to minimal distortions and error in scanning measurements, relative to prior art coatings and paints disclosed hereinabove. Additionally, in other preferred embodiments of the present invention, the method of providing this bilayer coating is quicker than that of prior art coating methods, thus the dentist does not wait for the application to dry as in the prior art application of coating solutions and paints.

The prior art coating methods allow for long drying times during which the oral soft tissues can abrade and mechanically remove coating by physical contact therewith. In sharp contrast, the present invention methods allows for the application of the powder separately, which creates a fairly hard optically-good surface almost instantaneously, and thus the prior art problem of mechanical removal by the tongue or other soft tissue, or by the scanner, is overcome. In other embodiments of the present invention, the bilayer non-wettable or poorly-wettable coatings of the present invention are more resilient than the prior art coatings, and are sustainable for the duration of the scan.

Additionally, the coating compositions of the present invention are more easily removed that the adhesive-containing prior art compositions. In further embodiments of the present invention, the bilayer coating may be easily removed after performing the scan by toothbrushing.

In order to identify the finishing line of a dental prosthetics preparation which is at the gingival margin, a gingival retraction cord is often placed in a gingival sulcus

(gap between the tooth and the gum). In classical impressions, impression material is forced into the space left when the retraction cord is removed, the retraction cord making this space more obvious and wider.

In scanning impressions, it is also necessary to identify the margin of prosthetic tooth preparations. After placing the powder, which covers the cord, removal of the cord together with the powder results in the subsequent scan receiving little or no signal for subsequent 3D reconstruction, from the area from which the powder was removed. In prior art systems, when the cord is removed, it often removes powder from the tooth itself, thus giving a false inaccurate margin and a subsequent poorly fitting prosthetic restoration.

The coating compositions of the present invention allow for good retention of the hydrophobic powder during and after removal of a gingival retraction cord for the

preparation of an impression, thus allowing for accurate and well-fitting dental prosthetics.

There is thus provided, according to an embodiment of the present invention, an intra-oral surface coating composition for forming at least one layer on a surface of an intra-oral object for scanning, the composition including; at least one non-toxic volatile organic solvent; at least one GRAS polymer; and at least one hydrophobic metallic oxide powder, wherein the at least one hydrophobic metallic oxide powder is adapted to provide non-wettability to the intra-oral surface.

According to some embodiments of the present invention, the scanning is three-dimensional scanning.

In some cases, the at least one non-toxic volatile organic solvent includes ethanol. According to some further embodiments, the at least one GRAS polymer includes a polymer selected from the group consisting of a naturally-occurring polymeric material and a semi-synthetic polymeric material.

Yet further, according to some embodiments of the present invention, the semi-synthetic polymeric material includes ethyl cellulose. In some cases, the ethyl cellulose includes at least one Dow Ethocel. In further cases, the ethyl cellulose includes Dow Ethocel 45.

Additionally, according to some further embodiments of the present invention, the at least one hydrophobic metallic oxide powder includes hydrophobic titanium dioxide powder. In some cases, the hydrophobic titanium dioxide powder includes nanoparticles. The nanoparticles may, according to some embodiments of the present invention, have a mean particle size of 10-30 nm.

Furthermore, according to some embodiments of the present invention, the at least one layer includes a monolayer.

According to some further embodiments, the at least one layer includes a bilayer.

In some cases, the monolayer has a thickness of less than 20 microns.

According to some additional embodiments, the monolayer has a thickness of less than 10 microns.

According to some further embodiments, the solvent to polymer ratio by weight 5:1 to 20:1.

There is thus provided, according to another embodiment of the present invention, a bilayer intra-oral surface coating suitable for preparing an intra-oral surface of an object for scanning, the coating including; an underlayer (termed herein "glue") including at least one non-toxic volatile organic solvent and at least one GRAS polymer in a solvent:polymer ratio in a range of 5; l to 20; 1; and an overlayer, suitable for coating the underlayer, the overlayer including least one hydrophobic metallic oxide powder, wherein the overlayer is adapted to provide non-wettability to the intra-oral surface.

Furthermore, according to some embodiments of the present invention, the underlayer has a thickness of 5-30 microns.

Additionally, according to some embodiments of the present invention, the underlayer has a thickness of 5-10 microns. In some cases, the overlayer has a thickness of 0.1-10 microns.

Yet further, according to some further embodiments, the overlayer has a thickness of 0.1-3 microns.

In some cases, the overlayer has a thickness of 0.1-0.5 microns.

Furthermore, according to some embodiments of the present invention, the scanning is three-dimensional scanning.

Furthermore, according to some embodiments of the present invention, the at least one non-toxic volatile organic solvent, may according to some embodiments of the present invention, include ethanol.

Furthermore, according to some embodiments of the present invention, the at least one GRAS polymer includes a polymer selected from the group consisting of a naturally-occurring polymeric material and a semi-synthetic polymeric material.

In some cases, the bilayer includes the semi-synthetic polymeric material comprising ethyl cellulose. In some cases, the ethyl cellulose includes at least one Dow Ethocel. In some further cases, the ethyl cellulose includes Dow Ethocel 45. According to some embodiments of the present invention, the at least one hydrophobic metallic oxide powder includes hydrophobic titanium dioxide powder.

The bilayer including hydrophobic titanium dioxide powder may include nanoparticles. According to some embodiments of the present invention, the nanoparticles have a mean particle size of 10-30 nm. There is thus provided, according to an additional embodiment of the present invention, a method for preparing an intra-oral object for scanning, the method including; applying an intra-oral surface coating composition as described herein to the object. There is thus provided, according to a further embodiment of the present invention, a method for preparing a surface of an intra-oral object for scanning, the method including; applying a composition including at least one non-toxic volatile organic solvent and at least one GRAS polymer in a solvent to polymer ratio in a range of 5;1 to 20; 1 to the surface to form a first coating layer; and applying at least one hydrophobic metallic oxide powder onto the first coating layer to form a second coating layer; wherein the second coating layer is adapted to provide non-wettability to the surface. According to some further embodiments of the present invention, the method may further include drying the surface prior to applying the first coating layer.

In some cases, the method further includes drying the first coating layer.

According to some embodiments of the present invention, the first coating layer and the second coating layer are sufficiently thin to prevent a significant scanning optical error.

Furthermore, according to some embodiments of the present invention, a ratio of the thickness of the first coating layer to a thickness of the second coating layer is from 2:1 to 10:1.

In some cases, the second coating layer has a thickness of less than 10 microns.

According to some further embodiments of the present invention, the first coating layer and the second coating layer are sufficiently thin to prevent significant scanning optical error.

According to some additional embodiments of the present invention, the scanning is performed employing a commercial scanner selected from a Densys 1

Oral Scanner, a Sirona scanner, a Cerec System scanner, an Orametrix Scanner and a Suresmile System scanner, a3M Brontes 3d scanner, or an E4d scanner

There is thus provided, according to a further embodiment of the present invention, a two-phase intra-oral surface coating composition for forming at least one layer on a surface of an intra-oral object for scanning, the composition comprising: a first phase comprising: at least one non-toxic volatile organic solvent; and at least one GRAS polymer; and a second phase comprising at least one hydrophobic metallic oxide powder, wherein said at least one hydrophobic metallic oxide powder is adapted to provide non-wettability to said intra-oral surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in connection with certain embodiments with reference to the following illustrative figures so that it may be more fully understood. With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings: Fig. 1 is a simplified flowchart of a method for applying a bilayer intra-oral coating composition and performing an intra-oral scan, in accordance with a preferred embodiment of the present invention; and

Fig. 2 is a simplified pictorial illustration of part of a tooth coated in a bilayer intra-oral coating composition, in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention discloses a coating composition and methods for a surface, which enables performance of accurate and precise 3D-scanning. Reference is now made to Fig. 1, which is a simplified flowchart 100 of a method for applying a bilayer intra-oral coating composition and performing an intraoral scan, in accordance with a preferred embodiment of the present invention.

A dentist or other dental professional typically performs the following method to a patient undergoing an intra-oral 3D scan. In an optional drying step 110, the dentist dries the patient's teeth using a standard air dryer used in dental practice for a short period of time (typically two seconds or less), at an air temperature in the range of room temperature to thirty seven degrees Celsius).

In an application step 120, a sticky composition, termed herein "glue", comprising 1-20% by weight of GRAS (generally regarded as safe) polymer or polymers previously mixed with 10-99% by weight non-toxic volatile organic solvent or solvents is applied to a tooth, a part of a tooth or to several teeth inside the mouth.

One example of the polymer serving as a glue is polypropylene glycol (CAS no. 25322-69-4). In some cases, the glue further comprises 0.1 -71 % water.

The application step may include spraying, brushing, coating or any other suitable method known in the art.

The polymer or polymers may be natural, semi-synthetic or synthetic. The polymers should provide a syrup-like solution in a non-aqueous solvent or aqueous solvent.

Exemplary polymeric agents include, in a non-limiting manner, naturally- occurring polymeric materials, such as locust bean gum, sodium alginate, sodium caseinate, egg albumin, gelatin agar, carrageenan gum, sodium alginate, xanthan gum, quince seed extract, tragacanth gum, guar gum, cationic guars, hydroxypropyl guar gum, starch, amine-bearing polymers such as chitosan; acidic polymers obtainable from natural sources, such as alginic acid and hyaluronic acid; chemically modified starches and the like, carboxyvinyl polymers, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylic acid polymers, polymethacrylic acid polymers, polyvinyl acetate polymers, polyvinyl chloride polymers, polyvinylidene chloride polymers and the like.

Additional exemplary polymeric agents include semi-synthetic polymeric materials such as cellulose ethers, such as methylcellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose, hydroxyethyl cellulose, hydroxy propylmethyl cellulose, methylhydroxyethylcellulose, ethylcelllulose polymers, methylhydroxypropylcellulose, hydroxyethylcarboxymethylcellulose, carboxymethyl cellulose, carboxymethylcellulose carboxymethylhydroxyethylcellulose, and cationic celluloses. Polyethylene glycol, having molecular weight of 1000 or more (e.g., PEG 1,000, PEG 4,000, PEG 6,000 and PEG 10,000) are also considered to be polymeric agents.

Mixtures of the above polymeric agents are contemplated.

Non-toxic volatile organic solvents may include one or more of short chain alcohols, having up to 5 carbon atoms in their carbon chain skeleton and one hydroxyl group, such as ethanol. Other short chain alcohols having one or more hydroxyl groups may be used if they meet the standard GRAS non-toxic requirements.

Additionally or alternatively, other volatile non-toxic solvents known in the art may be employed.

Mixtures of the above solvents are also contemplated.

The applied "glue" typically forms a fairly homogeneous layer on the tooth surface. Preferably, the layer is less than 50 microns thick.

In a second optional drying step 130, the glue is dried for a short period of time using a standard air dryer. The dried glue is preferably less than 30 microns thick, and yet more preferably, less than 10 microns thick.

In a powder application step 140, a translucent powder is applied to the teeth in situ. The powder typically comprises one or more translucent metal oxides, such as white nanopowders available commercially, such as from , MKNano (M. K. IMPEX CANADA 6382 Lisgar Drive Mississauga, Ontario L5N 6X1 Canada) or Nanostructured & Amorphous Materials, Inc. (16840 Clay Road, Suite 113 Houston, TX 77084, USA). These nanopowders may comprise one or more metals and oxide or other oxides. According to some embodiments, hydrophobic titanium dioxide is used. See, for example, US Patent 5,565,591, incorporated herein by reference.

According to some embodiments, the metal oxide powders are finely ground to a mean particle size of around 15 nm. According to other embodiments, the mean particle size may be larger.

According to some further embodiments, the translucent powder may be colored for certain scanning applications. Again, such nanopowders are known in the art. They too may be obtained commercially.

The nanopowder may be sprayed using a typical dental spray appliance, such as, but not limited to, an instrument from Powder Meister, Inc. 2909 Buick Cadillac

Blvd. Bloomington, IN 47401, USA., or using other instruments as are known in the art. The powder sticks onto the glue and does not require drying.

The dentist can then proceed to perform a scan in a scanning step 150 using any 3D- system known in the art such as those available from Sirona Inc., Cerec System and Orametrix Inc. Suresmile System).

In a glue removal step 160, the patient removes the glue by standard brushing of his teeth. Alternatively, the dentist may perform this step.

According to some further embodiments, step 140 may be integrated into step

120. In other words, a composition comprising at least one volatile non-toxic solvent, at least one GRAS polymer and at least one hydrophobic nanopowder may be applied to teeth and then optionally dried in step 130. In such a case, step 140 would not be necessary.

In the prior art publication US 6,854,973, the non-wettability of the composition containing the titanium dioxide, as described, arises from the non- wettability of the non-aqueous solution. In '973, FIX-O-DENT denture adhesive is used. According to US 5,073,604, this denture adhesive comprises lower alkyl vinyl ether-maleic acid copolymer. In sharp contrast thereto, in the present invention, the non-wettability arises from the use of hydrophobic titanium dioxide, which may, in some cases, be separately applied as a powder, without the adhesive.

Reference is now made to Fig. 2, which is a simplified pictorial illustration 200 of part of a tooth coated 210 in a bilayer intra-oral coating composition. Typically, a "glue" layer 220 is fairly smooth and homogeneous. The layer is typically of a thickness of less than 20 microns.

A powder layer 235 of at least one hydrophobic metal oxide, such as titanium dioxide is formed on top of the glue layer. The powder layer is preferably less than 10 microns thick.

EXAMPLE 1

A male Caucasian aged 49 volunteered for the following trial. His teeth were brushed and then air dried for a few seconds A sticky composition was prepared as follows: 10 grams of Ethocel™ 45 (Dow, Midland, Michigan, US) were well mixed in

90 grams of food grade ethanol at room temperature overnight.

The resultant composition was a fairly viscous dispersion. A small amount of the dispersion was sparingly applied to the teeth of the male Caucasian using a paintbrush until all surfaces of his teeth were covered. Thereafter, his teeth were each surface air dried for around two seconds.

Hydrophobic titanium dioxide (UV-TITAN M 161 (KEMIRA PIGMENTS OY, TITANITIE Fin-28840 Pori Finland) was placed in a Powder Meister (Powder Meister, Inc. 2909 Buick Cadillac Blvd. Bloomington, IN 47401, USA.). The powder was carefully sprayed on all the surfaces of the teeth. In a scanning step 150, the patient's teeth were scanned using a DENSYS 1

Oral Scanner.

In a glue removal step 160, the patient brushed his teeth using a standard toothbrush. The dentist inspected his teeth thereafter and did not find any traces of the glue or nanopowder. The references cited herein teach many principles that are applicable to the present invention. Therefore the full contents of these publications are incorporated by reference herein where appropriate for teachings of additional or alternative details, features and/or technical background.

It is to be understood that the invention is not limited in its application to the details set forth in the description contained herein or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as

hereinbefore described without departing from its scope, defined in and by the appended claims.