A Method of Making Dental Articles

Abstract

A method of making an article having a desired color, the method comprising the steps of: (a) providing a color array, said array comprising a plurality of distinct color points, each color point being independently composed of a resin mixture comprising one or more masterbatch resins; (b) comparing the desired color with the color points on the color array and selecting a color point that substantially corresponds to the desired color of the article; (c) identifying the resin mixture corresponding to said selected color point; and (d) making the article using said identified resin mixture.

Claims

1. A method of making an article having a desired color, the method comprising the steps of: (a) providing a color array, said array comprising at least 36 color points, each color point having a color value, determined in accordance with the CIE (International Commission of l'Eclairage) system, each color point being independently composed of a resin mixture comprising at least one masterbatch resin; (b) comparing the desired color with the color points on the color array and selecting a color point that substantially corresponds to the desired color of the article; (c) identifying the resin mixture corresponding to said selected color point; and (d) making the article using said identified resin mixture, wherein the desired color has a CIE color value, as determined by spectral reflectance or transmittance, and wherein said comparing step comprises selecting a color point from said color array, wherein a color difference value (ΔE) between said color point and the desired color is less than 6.

2. The method of claim 1, wherein the color array comprises at least 144 color points, each color point having a color value, determined in accordance with the CIE system.

3. The method of claim 1, wherein each resin mixture comprises at least two masterbatch resins.

4. The method of claim 3, wherein each resin mixture comprises three to five masterbatch resins.

5. The method of claim 3, wherein a ratio of masterbatch resins in the resin mixture is adjusted to achieve at least 36 color points.

6. The method of claim 1, wherein the desired color is determined based on a color of a reference object, wherein the reference object comprises a human tooth.

7. The method of claim 1, wherein the comparing step further comprises determining the CIE color values of the color points on the color array by measuring the spectral reflectance or transmittance of the color point.

8. The method of claim 7, comprising using a UV-VIS spectrophotometer in the measuring step.

9. The method of claim 1, wherein the comparing step comprises selecting a color point wherein the color difference value (ΔE) between said color point and the desired color is less than 4, or less than 2.

10. The method of claim 1, wherein the making step comprises using said identified resin mixture in a 3D printing process.

11. The method of claim 10, wherein the 3D printing process is selected from the group consisting of: stereolithography (SLA), Digital Light Processing (DLP), and Continuous Liquid Interface Production (CLIP).

12. The method of claim 1, wherein said article is a dental article.

13.-16. (canceled)

Description

BRIEF DESCRIPTION OF DRAWINGS

[0068] The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0069] FIG. 1

[0070] FIG. 1(a) shows a color matching tab being compared with a subject's teeth to assess the target shade and/or color of the tooth.

[0071] FIG. 1(b) shows a visual shade guide that is presently used in dentistry.

[0072] FIG. 2

[0073] FIG. 2 shows a diagram illustrating that the preparation of a resin color array for 3D printing may be carried out using master batch resins A, B, C and D.

[0074] FIG. 3

[0075] FIG. 3 shows a schematic diagram illustrating how all measurements and denture/crown preparation can be carried out. In particular, after digital scanning of a patient's tooth, the computer immediately analyzes the information on the tooth such as 3D dimensions and the color matching. The results will optimize the stereolithography (STL) file of the tooth and send a command to the printer for printing and determine the optimal materials required for color matching. For instance, the composition of the printing resin will be sent to the printer. In particular, based on the spectrophotometric measurement of the patient's tooth, the lab technologist would be aware of the ratio of each master batch to be used. The lab technologist only needs to do a simple blending of the master batch resins and input the information into the printer for 3D printing. After 3D printing and post treatment, real product comparison of the printed tooth/crown with patient's tooth can be achieved immediately. Any flaw or mismatch can be rectified immediately.

[0076] FIG. 4

[0077] FIG. 4 shows a diagram illustrating the uniform color space, CIEL*a*b*. Color space is a numerical area that expresses and references the object's color. Here, L* indicates the lightness coordinate of the object, with values from 0 (absolute black) to 100 (absolute white). The values a* and b* indicate the chromaticity coordinates, showing the three-dimensional position of the object in the color space and its direction.

[0078] FIG. 5

[0079] FIG. 5 shows a 36 color array of resins for dental 3D printing. This color array may be prepared by blending a different ratio of each of the master batches A, B and C (obtained from Example 1).

[0080] FIG. 6

[0081] FIG. 6(a) shows the reflective spectra of the 36 color array resins as shown in FIG. 5.

[0082] FIG. 6(b) is a graph showing the corresponding color coordination of the 36 color array resins as shown in FIG. 5. Each color resin is defined by its calculated y-value and its x-value.

[0083] FIG. 7

[0084] FIG. 7(a) shows a spectral reflectance of each of the x.sup.−, y.sup.− and z.sup.− color coordinate value for a sample color.

[0085] FIG. 7(b) shows a spectral power distribution of a reference illuminant, D65.

[0086] FIG. 8

[0087] FIG. 8 demonstrates two (2) examples of dental printing by using resin of different colors.

EXAMPLES

[0088] Non-limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1—Masterbatch Resin Preparation

[0089] The formulations of Masterbatch resins A, B, C and D are shown in Tables 1-4. To prepare Masterbatch resin A, all the components listed in Table 1 were weighed into a flask and were stirred in the absence of light for 8-24 hours until all solid contents were dissolved and homogeneous. Masterbatch resins B, C and D were prepared similarly based on the compositions as shown in Tables 2-4 respectively.

TABLE-US-00001 TABLE 1 The integration of master batch resin A. Ingredient Percentages (wt %) bisphenol A dimethacrylate 50 poly(ethylene glycol) diacrylate 30 tetrahydrofurfuryl methacrylate 4 Silicon dioxide (200 nm particles size) 15 Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide 0.8 2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene 0.2

TABLE-US-00002 TABLE 2 The integration of master batch resin B. Ingredient Percentages (wt %) bisphenol A dimethacrylate 50 poly(ethylene glycol) diacrylate 30 tetrahydrofurfuryl methacrylate 4 Kaolin (powder, 300 mesh) 15 Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide 0.8 2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene 0.2

TABLE-US-00003 TABLE 3 The integration of master batch resin C. Ingredient Percentages (wt %) bisphenol A dimethacrylate 50 poly(ethylene glycol) diacrylate 30 tetrahydrofurfuryl methacrylate 4 Titanium dioxide (powder, 325 mesh) 15 Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide 0.8 2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene 0.2

TABLE-US-00004 TABLE 4 The integration of master batch resin D. Ingredient Percentages (wt %) bisphenol A dimethacrylate 50 poly(ethylene glycol) diacrylate 40 tetrahydrofurfuryl methacrylate 4 Iron(III) oxide (powder, <5 μm) 5 Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide 0.8 2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene 0.2

Example 2—36-Color Array Preparation

[0090] The masterbatch resins A, B and C from Example 1 were blended in accordance with the ratio as shown in Table 5 to build the 36-color array as shown in FIG. 5. For instance, the trial 001 was prepared by mixing 20 g resin A and 20 g of resin C in a bottle and stirring at room temperature for 2 hours until a homogeneous mixture was obtained. Other trials from 002 to 036 were prepared similarly based on the compositions as shown in Tables 5 respectively.

TABLE-US-00005 TABLE 5 Composition (mixing ratio) of the color points on the 36-color array Number Resin A Resin B Resin C 001 5 0 5 002 10 0 0 003 9.7 0.3 0 004 9.4 0.6 0 005 9.1 0.9 0 006 8.8 1.2 0 007 8.5 1.5 0 008 8.2 1.8 0 009 7.9 2.1 0 010 7.6 2.4 0 011 7.3 2.7 0 012 7 3 0 013 6.7 3.3 0 014 6.4 3.6 0 015 6.1 3.9 0 016 5.8 4.2 0 017 5.5 4.5 0 018 5.2 4.8 0 019 4.9 5.1 0 020 4.6 5.4 0 021 4.3 5.7 0 022 4 6 0 023 3.7 6.3 0 024 3.4 6.6 0 025 3.1 6.9 0 026 2.8 7.2 0 027 2.5 7.5 0 028 2.2 7.8 0 029 1.9 8.1 0 030 1.6 8.4 0 031 1.3 8.7 0 032 1 9 0 033 0.7 9.3 0 034 0.4 9.6 0 035 0.1 9.9 0 036 0 9 1

Example 3—Color Calculation

[0091] Step 1: Measuring spectral reflectance S(λ) or transmittance of the target sample with a UV-Vis spectrometer and calculating the X, Y, and Z color coordinates values.

[0092] The XYZ color coordinates are calculated based on the following equations:

[00003]$X=\frac{1}{N}{\int }_{\lambda =390}^{\lambda =830}{x}^{-}\left(\lambda \right)S\left(\lambda \right)I\left(\lambda \right)d\lambda$$Y=\frac{1}{N}{\int }_{\lambda =390}^{\lambda =830}{y}^{-}\left(\lambda \right)S\left(\lambda \right)I\left(\lambda \right)d\lambda$$Z=\frac{1}{N}{\int }_{\lambda =390}^{\lambda =830}{z}^{-}\left(\lambda \right)S\left(\lambda \right)I\left(\lambda \right)d\lambda$$N={\int }_{\lambda =390}^{\lambda =830}{y}^{-}\left(\lambda \right)I\left(\lambda \right)d\lambda$

[0093] where x.sup.−, y.sup.− and z.sup.− are the CIE standard observer functions with functions as shown in FIG. 7(a);

[0094] where I(λ) is the spectral power distribution of a CIE standard reference illuminant (D65 in this case) with function as shown in FIG. 7(b). The integrals are computed over the visible spectrum (390 nm to 830 nm).

[0095] Step 2: Converting the calculated X, Y and Z values may be converted to L*1, a*1 and b*1 values in accordance with the following equations:

[00004]$L_1^{z*}=116f\left(\frac{Y}{Y_n}\right)-16$$a_1^{*}=500\left(f\left(\frac{X}{X_n}\right)-f\left(\frac{Y}{Y_n}\right)\right)$$b_1^{*}=200\left(f\left(\frac{Y}{Y_n}\right)-f\left(\frac{Z}{Z_n}\right)\right)$$\mathrm{where}$$f\left(t\right)=\{\begin{array}{cc}\sqrt[3]{t},& t>{\delta }^3\\ \frac{t}{3{\delta }^2}+\frac{4}{29},& \mathrm{otherwise}\end{array}$$\delta =\frac{6}{29}$

[0096] Here, Xn, Y.sub.n and Z.sub.n are the CIE XYZ tristimulus values of the reference white point (the subscript n suggests “normalized”). Under Illuminant D65 with normalization Y=100, the values are: X.sub.n=95.047, Y.sub.n=100 and Z.sub.n=108.883.

Example 4—Calculating the Color Difference Value (ΔE)

[0097] The color difference value (ΔE) was determined by the CIE color values of the color point on the color array (L*2, a*2 and b*2) with that of the target object (L*1, a*1 and b*1) in accordance with the following equations:

ΔE=√{square root over ((L*.sub.2−L*.sub.1).sup.2+(a*.sub.2−a*.sub.1).sup.2+(b*.sub.2−b*.sub.1).sup.2)}.

[0098] The color point to be selected for 3D printing corresponds to the one which provided the lowest E. An average difference of up to 3.7 ΔE was considered acceptable in the dental industry according to the Extended Visual Rating Scale for Appearance Match as shown in Table 6. The resin mixture corresponding to the selected color point will be used for 3D printing.

TABLE-US-00006 TABLE 6 Extended Visual Rating Scale for Appearance Match (EVRSAM) ΔE Clinical significance 0 Excellent esthetics with accurate color choice, not being clinically percieved, or only with great difficulty. 2 Very slight difference in color, with very good aesthetics. 4 Obvious difference, but with an average acceptable to most patients. 6 Poor aesthetics, but within the limits of acceptability. 8 Aesthetics are very poor and unacceptable to most patients. 10 Aesthetics are totally unacceptable.

Example 5—Dental Printing by Using Different Color Resins

[0099] Dentures were printed on a DLP printer (LittleRP with build volume 60 mm (λ) 40 mm (Y) 100 mm (Z) using the resin mixture for preparing the selected color point, which uses DLP projector with a resolution of 1024×768 (Brand & Model: Acer P128) as light source and Creation Workshop as controlling software). Printing was carried out with slice thickness of 50 μm. Exposure time per layer was 30 seconds. After printing, the printed part was washed thoroughly with isopropanol, air dried and placed inside a UV oven for further curing. The printed dentures with different colors are shown in FIG. 8.

INDUSTRIAL APPLICABILITY

[0100] The method may be useful for making a polymeric replicate of a target object with excellent color match with the object. For instance, the method of the present disclosure may be used by dentists to prepare dental prosthetic which matches the color of original patients' teeth. Advantageously, the method of the present disclosure may result in dental prosthetic which very accurately matches the color of the patient's teeth and offers excellent aesthetics.

[0101] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.