WATER-HARDENING DENTAL CEMENT, METHOD AND KIT FOR PRODUCING THE SAME AND USE THEREOF

Abstract

The invention provides a water-hardening dental cement comprising an acid-reactive powder, a polyprotic acid, water and dispersed polymer particles.

The invention further provides a method for producing a water-hardening dental cement, a kit for producing a water-hardening dental cement and a use of the water-hardening dental cement.

Claims

1. A water-hardening dental cement comprising an acid-reactive powder, a polyprotic acid, water and dispersed polymer particles.

2. The water-hardening dental cement as claimed in claim 1, characterized in that the water-hardening dental cement is a glass ionomer cement, more preferably a conventional glass ionomer cement.

3. The water-hardening dental cement as claimed in claim 1, characterized in that a mean particle size of the polymer particles is less than about 1 μm, more preferably between 5 to 500 nm, yet more preferably between 5 to 100 nm, determined by dynamic light scattering in aqueous dispersion (in water).

4. The water-hardening dental cement as claimed in claim 1, characterized in that the polymer particles have been dispersed in aqueous solution prior to the hardening of the water-hardening cement.

5. The water-hardening dental cement as claimed in claim 1, characterized in that a proportion of dispersed polymer particles in the cement is 0.005% to 10% by weight, more preferably 0.005% to 3% by weight, yet more preferably 0.01% to 1% by weight, further preferably 0.01% to 0.5% by weight, most preferably 0.01% to 0.3% by weight, based on the overall composition of the cement prior to hardening.

6. The water-hardening dental cement as claimed in claim 1, in that it comprises, based on the overall composition of the cement prior to hardening, one or more of the constituents mentioned hereinbelow in the quantitative proportions mentioned hereinbelow: 20% to 90% by weight, preferably 40% to 85% by weight of acid-reactive powder, 4.9% to 40% by weight, preferably 7.4% to 25% by weight of polyprotic acid, and/or 4.9% to 40% by weight, preferably 7.4% to 25% by weight of water.

7. The water-hardening dental cement as claimed in claim 1, characterized in that the acid-reactive powder is selected from metal oxides, metal hydroxides, mineral trioxide aggregate, hydroxyapatite, bioactive glasses, especially acid-reactive glasses and mixtures thereof.

8. The water-hardening dental cement as claimed in claim 1, characterized in that the acid-reactive powder is selected from a first quantity of glass particles having a mean particle size of from 5 to 20 μm, more preferably 5 to 15 μm, and a second quantity of glass particles having a mean particle size of from 1 to 5 μm, more preferably 2 to 3 μm.

9. The water-hardening dental cement as claimed in claim 1, characterized in that the polyprotic acid is selected from polyacids and phosphoric acid.

10. The water-hardening dental cement as claimed in claim 1, characterized in that the water-hardening dental cement includes further additional constituents selected from the group consisting of complexing agents, inorganic and organic fillers, inorganic and organic colorants and mixtures of these.

11. A method for producing a water-hardening dental cement, characterized in that at least an acid-reactive powder, a polyprotic acid, water and dispersed polymer particles are mixed.

12. A kit for producing a water-hardening dental cement comprising the constituents: a) dispersed polymer particles, b) an acid-reactive powder, c) a polyprotic acid, and d) water.

13. The kit as claimed in claim 12, characterized in that it comprises, based on the overall composition of the kit prior to hardening of the dental cement, one or more of the constituents mentioned hereinbelow in the quantitative proportions mentioned hereinbelow: 0.005% to 5% by weight, preferably 0.005% to 3% by weight, more preferably 0.01% to 1% by weight, yet more preferably 0.01% to 0.5% by weight, most preferably 0.01% to 0.3% by weight of dispersed polymer particles, 20% to 90% by weight, preferably 40% to 85% by weight of acid-reactive powder, 4.9% to 40% by weight, preferably 7.4% to 25% by weight of polyprotic acid, and/or 4.9% to 40% by weight, preferably 7.4% to 25% by weight of water.

14. The kit as claimed in either of claim 11, characterized in that the kit is composed of at least two components and the constituents of the kit are divided between these components.

15. The use of a water-hardening dental cement as claimed in claim 1 as a filling or as a luting cement.

Description

[0139] The invention will now be explained using advantageous embodiments with reference to the attached drawings. In the figures:

[0140] FIG. 1: Average values and standard deviations for the fracture toughness (stress intensity factor K.sub.Ic (in MPa.Math.√{square root over (m)})) of the cements 1-3 shown in table 4.

[0141] FIG. 2: Average values and standard deviations for the compressive strength (in MPa) of the cements 1-2 shown in table 4.

[0142] FIG. 3: Average values and standard deviations for the flexural strength (in MPa) of the cements 1-3 shown in table 4.

CHEMICALS AND THE PRETREATMENT/USE THEREOF

[0143]

TABLE-US-00001 Polytetrahydrofuran 1000 Merck KGaA 4,4′- Sigma Aldrich Diisocyanatodicyclohexylmethane (H12MDI) Hydroquinone monosulfonic acid Sigma Aldrich potassium salt N-Methyldiethanolamine Sigma Aldrich n-Butyl methacrylate Sigma Aldrich Potassium peroxodisulfate Sigma Aldrich Methyl methacrylate Evonik Performance Materials GmbH Polyacrylic acid, M.sub.N = 14 000 g/mol, M.sub.W = 49 000 g/mol, ground, d50 less than 50 μm Hyperpure water (GPR Rectapur) VWR International

[0144] The polytetrahydrofuran 1000 was heated to 60° C. for 4 hours at 0.03 mbar so that a dried polytetrahydrofuran (PTHF) was obtained. The powder was stored under nitrogen.

Fluoroaluminosilicate Glass A (FAS A):

[0145]

TABLE-US-00002 Composition Si as SiO.sub.2 32.2% by weight Al as Al.sub.2O.sub.3 31.6% by weight Sr as SrO 24.9% by weight P as P.sub.2O.sub.5  5.2% by weight Na as Na.sub.2O  1.7% by weight F as F.sup.−  7.2% by weight

[0146] The glass powder was ground in a ball mill to a mean particle diameter d.sub.50=2.6 μm. The powder was heat treated for 8 hours at 500° C.

Fluoroaluminosilicate Glass B (FAS B):

[0147]

TABLE-US-00003 Composition SiO.sub.2 36.00% by weight Al.sub.2O.sub.3 22.50% by weight CaF.sub.2 21.00% by weight Na.sub.3AlF.sub.6  9.00% by weight AlF.sub.3  6.60% by weight AlPO.sub.4  5.00% by weight

[0148] The glass powder was ground in a ball mill to a mean particle diameter d.sub.50=7.7 μm. 1 kg of the powder was subsequently suspended in a solution of 30 g of KH.sub.2PO.sub.4 in 3 l of distilled water and stirred for 24 hours at room temperature (RT). The suspension was then filtered, washed with distilled water and dried for 6 hours at 100° C.

Methods

[0149] Mean particle diameter and average zeta potential of the ionic polyurethane particles (PU particles):

[0150] The parameters were determined by means of dynamic light scattering using a ‘Zetasizer Nano-ZS’ from Malvern. The mean particle diameter was measured as the average hydrodynamic equivalent radius in the form of the Z-average. The particles were in the form of aqueous dispersions. Dispersions after production were 1:10 diluted with hyperpure water. For the measurements, water was used as dispersing medium with the following parameters:

refractive index 1.33,
dielectric constant 78.5, and
viscosity 0.8873 cP.

[0151] The measurements were conducted at 25° C.

[0152] Particle size of the fluoroaluminosilicate glasses:

[0153] The particle size distribution and the mean particle diameter (d.sub.50) were determined with a Beckman Coulter Laser Particle Sizer LS130 and a Beckman Coulter Laser Particle Sizer LS13320.

[0154] 250 mg of the ground glass was mixed with 4 drops of glycerol on a roughened watch glass to give a creamy paste. This paste was predispersed with 1 drop of water using a pestle. The paste was subsequently mixed into 5 ml of water and dispersed in an ultrasonic bath (Bandelin Sonorex RK102H) for 5 minutes with ice-water cooling. The dispersion was introduced into the measurement chamber of the particle sizer (Coulter LS130 or Beckman-Coulter LS13320) and measured while circulating the aqueous dispersion to be measured.

[0155] The measurement was effected in tap water. The evaluation was effected according to the Fraunhofer diffraction optical model.

Freeze Drying:

[0156] Diluted solutions were freeze-dried using the ‘Sublimator VaCo 5’ freeze drier from ZIRBUS technology GmbH.

Flexural Strength (FS):

[0157] The flexural strength was measured in accordance with ISO 9917-2:2010 at an advance rate of 0.8 mm/min.

[0158] Compressive Strength (CS):

[0159] The compressive strength was measured in accordance with ISO 9917-1:2010 at an advance rate of 1 mm/min.

Fracture Toughness (K.SUB.IC.):

[0160] Powder and liquid were mixed in the respectively specified mixing ratio within 1 minute using a spatula on a pad and filled into a mold having the dimensions length L=50 mm, height H=4 mm and width W=3 mm. After 1 hour at 37° C. and >95 relative humidity, the test specimen was demolded and stored for a further 23 hours±1 hour in distilled water at 37° C. The test specimens were notched on one of the 3 mm-wide sides with a low-speed saw (Isomet from Buehler; diamond cutting disk D46/54, thickness 0.20 mm, from Boma). The notch depth was approx. 0.7 mm.

[0161] The width and the height of a test specimen were measured using a caliper. The test specimen was placed with the notch facing downwards on the 3-point bending fracture bending apparatus (spacing between the supports S=20 mm) of a universal testing machine (Zwick Z2.5, from Zwick Roell), so that the notch was located exactly underneath the force-transmitting wedge. The measurement of the maximum force (F.sub.max) until fracture of the test specimens was conducted at an advance rate of 0.8 mm/min.

[0162] An image of the cross-sectional area of the broken test specimen was recorded under a microscope (Leica Leitz DMRX) using a digital camera (Leica DFC295). The notch depths a1, a2 and a3 of the notch were ascertained at three locations using evaluation software (Leica Application Suite V3). The mean value a was formed from the three values in accordance with the formula. The measured values were used to calculate the fracture toughness (stress intensity factor K.sub.IC) according to the formula specified.

[00001]$a=\frac{a.Math..Math.1+a.Math..Math.2+a.Math..Math.3}{3}$$f\left(\frac{a}{H}\right)=\frac{3.Math.{\left(\frac{a}{H}\right)}^{1/2}\left[1.99-\left(\frac{a}{H}\right).Math.\left(1-\left(\frac{a}{H}\right)\right).Math.\left\{2.15-3.93.Math.\left(\frac{a}{H}\right)+2.7.Math.{\left(\frac{a}{H}\right)}^2\right\}\right]}{2.Math.\left(1+2.Math.\left(\frac{a}{H}\right)\right).Math.{\left(1-\left(\frac{a}{H}\right)\right)}^{3/2}}$$K_{\mathrm{IC}}=\frac{F_{\max }.Math.S.Math.{10}^{-6}}{B.Math.H^{3/2}}.Math.f\left(\frac{a}{H}\right)$

Example 1

[0163] Synthesis of the PU Particles with Anionic Groups:

[0164] 10 g of PTHF, 13.9 ml of acetone, 5.25 g of H12MDI and 0.02 ml of catalyst solution (dimethyltin dineodecanoate in toluene, proportion by mass 50%) were heated to 60° C. for 4 hours (reflux condenser, drying tube) and then cooled down to room temperature (RT). The isocyanate group content was determined by means of titration. It was 2.96% by weight.

[0165] At room temperature (approx. 23° C.), 1.65 g of hydroquinone monosulfonic acid potassium salt (DMSO solution, proportion by mass 10%) were then added, and the mixture was heated to 60° C. for 4 hours and subsequently heated to 70° C. for 1.5 hours, and then cooled down to RT. The isocyanate group content was 0.43% by weight.

[0166] Next, the mixture was heated to 50° C. and 38.3 ml of deionized water were added dropwise over approx. 35 min. A milky-white cloudiness developed. The acetone was removed on a rotary evaporator. The mean particle diameter of the remaining dispersion was Z-average=77 nm and the average zeta potential=−31 mV.

[0167] The dispersion was purified by means of dialysis. To this end, the dispersion containing approx. 20% by weight of polyurethane particles was diluted with deionized water. 100 ml of the diluted dispersion were dialyzed over 5 days against 8 liters of deionized water (dialysis tube made from regenerated cellulose (‘Zellutrans’, Carl Roth GmbH, MWCO=6000-8000)). The water was changed four times during this time. The solids content of the dispersion was ascertained by freeze drying and was 0.97% by weight.

Example 2

[0168] Synthesis of the PU Particles with Cationic Groups:

[0169] 10 g of PTHF, 13.9 ml of acetone, 5.25 g of H12MDI and 0.02 ml of catalyst solution were heated to 60° C. for 4 hours and then cooled down to RT. The isocyanate group content was 3.25% by weight.

[0170] 0.956 ml of N-methyldiethanolamine were added, and the mixture was heated to 60° C. for a further 4 hours and cooled down again.

[0171] Next, 1.94 ml of glacial acetic acid and 47 ml of acetone were added, the mixture was heated to 40° C. and then 35 ml of deionized water were added dropwise over approx. 35 min. A milky-white cloudiness developed.

[0172] The acetone was removed on a rotary evaporator. The mean particle diameter of the remaining transparent dispersion was Z-average=35 nm and the average zeta potential was 69 mV. The solids content was 22.2% by weight.

Example 3

[0173] Synthesis of the PU particles without ionic groups:

Batch 1:

[0174]

TABLE-US-00004 H12MDI 0.04 mol Butane-1,4-diol 0.005 mol Terathane 650 0.005 mol PEG600 0.01 mol DABCO 1 spatula tip DBTDL 3 drops S acetone

Batch 2:

[0175]

TABLE-US-00005 H12MDI 0.2 mol PolyTHF250 0.1 mol PEG350 0.1 mol DABCO 1 spatula tip DBTDL 3 drops S THF

[0176] Diisocyanate and 2 diol components were each dissolved in the specified solvent (S). In addition, 1,4-diazabicyclo[2.2.2]octane (DABCO) and dibutyltin dilaurate (DBTDL) as catalyst were added to the reaction solution. The solution was stirred for 24 hours, so that a complete reaction was achieved. The prepolymers obtained were added dropwise to an excess of water with vigorous stirring. Particles formed instantaneously in the process. The aqueous particle suspensions obtained were purified three times with water by means of ultrafiltration. The residue from the ultrafiltration was in each case redispersed with a few milliliters of water. The resulting dispersions were analyzed gravimetrically for their solids content and subsequently used to produce the liquids for the glass ionomer cements. The size of the particles obtained was determined using the particle sizer:

Batch 1

[0177] Solids content of the dispersion: 18.6% by weight

[0178] Size of the particles: 300 nm

Batch 2

[0179] Solids content of the dispersion: 16.3% by weight

[0180] Size of the particles: 165 nm

Example 4

Production of the Kit Constituents:

Powder:

[0181] 18.2 parts of polyacrylic acid (PAA) and 81.8 parts of FAS B were mixed together.

Liquid:

[0182] The liquids of the invention were prepared by mixing deionized water and the dispersions obtained in example 3.

Production of Water-Hardening Dental Cements:

[0183] Powder and liquid were mixed in the weight ratios given in tables 1 and 2, test specimens were formed and the fracture toughness was determined. The fracture toughness K.sub.1c and the standard deviation (SD) are given.

TABLE-US-00006 TABLE 1 Production of the water-hardening cements using the dispersion (Disp) from batch 1, example 3 (300 nm). PU particles Liquid in the composition mixture K.sub.1c Powder Liquid m(H.sub.2O):m(Disp) [% by [MPa/ Increase [g] [g] [g/g] weight] m.sup.1/2] SD [%] 5.40 1.00 1.00:0    0 0.365 0.038 — 1.40 0.268 1.44:0.276 0.48 0.430 0.075 18 5.40 1.19 .sup. 0:1.00 3.35 0.461 0.039 26

TABLE-US-00007 TABLE 2 Production of the water-hardening dental cements using the dispersion from batch 2, example 3 (165 nm). PU Liquid particle composition mixture K.sub.1c Powder Liquid m(H.sub.2O):m(Disp) [% by [MPa/ Increase [g] [g] [g/g] weight] m.sup.1/2] SD [%] 5.40 1.00 1.00:0   0 0.365 0.038 — 5.40 1.03 3.78:3.78 1.31 0.465 0.037 27

Example 5

Production of the Kit Constituents (Powder and Liquid)

Powder:

[0184] 47.5 parts of FAS A, 31.7 parts of FAS B and 20.8 parts of PAA were mixed together.

Liquid:

[0185] The liquids were prepared by mixing deionized water, tartaric acid and the dispersions obtained in examples 1 and 2. The composition of the liquids is given in table 3.

TABLE-US-00008 TABLE 3 Composition of the liquids. Liquid 1 (L1) Liquid 2 (L2) Liquid 3 (L3) [g] [%] [g] [%] [g] [%] Water 23.78 94.97 5.366 50.95 18.435 92.11 Dispersion — — 4.640 44.06 — — from example 1 Dispersion — — — — 0.575 2.87 from example 2 Tartaric acid  1.26  5.03 0.526 4.99 1.004 5.02 Sum total 25.04 100.00  10.532  100.00 20.014 100.00 PU content — — 0.045 0.427 0.128 0.640

Example 6

Production of Water-Hardening Dental Cements:

[0186] 2.4 g of powder and 0.38 g of liquid were in each case mixed on a pad within a minute using a spatula and test specimens were formed. The compressive strength (CS), flexural strength (FS) and fracture toughness (K.sub.IC) of the set test specimens were determined as described.

TABLE-US-00009 TABLE 4 Properties of the water-hardening dental cements. Cement 1 Cement 2 Cement 3 Powder [g] 2.4  2.4  2.4  L1 [g] 0.38 — — L2 [g] — 0.38 — L3 [g] — — 0.38 CS (MPa, 24 h) 255 ± 6  245 ± 17 — FS (MPa, 24 h) 39.8 ± 7.1  44.8 ± 4.8 41.0 ± 7.7  K.sub.IC (MPa√{square root over (m)}, 24 h) 0.75 ± 0.03  0.82 ± 0.05 0.84 ± 0.07

[0187] The proportions by mass of ionic PU particles in the water-hardening dental cements were 0.06% and 0.09% by weight. It can be seen that the addition of small amounts of these polyurethane particles brought about a marked increase in the fracture toughness (stress intensity factor K.sub.IC of the cements (cf. FIG. 1), while the addition had no effect on compressive strength and flexural strength (cf. FIGS. 2 and 3).

Example 7—Synthesis of PMMA Particles

[0188] A 250 ml three-neck flask equipped with a precision glass stirrer and two septa was initially charged with 150 ml of ultrapure water. The contents were heated to 90° C. under a stream of nitrogen. After 45 min, the nitrogen stream was switched off and 15 ml (141 mmol) of methyl methacrylate were added through the septum. In order to initiate the polymerization, after a further 30 min at 90° C. 5 ml (1.8 mmol) of a 10% aqueous potassium peroxodisulfate solution were added as initiator. This solution had likewise been flushed beforehand with nitrogen for 10 min at 90° C. The reaction solution was stirred at 400 rpm with the precision glass stirrer. For monitoring the reaction, every 30 min 0.1 ml of reaction solution was withdrawn through the septum and dried in air on a glass substrate. When the reflection color of the dried film no longer changed, the solution was stirred for a further 30 min at 90° C. In order to end the reaction, the septum was removed and the suspension was stirred in air for approximately a further 20 min.

[0189] The reaction solution was filtered off warm for purification, in order to remove coarse impurities. The filtrate was subsequently centrifuged. At the start, centrifugation was performed at least twice for 5 to 10 min at 4000 rpm, in order to remove colorless sediment. Thereafter, the solution was centrifuged for 30 to 90 min, until a clear solution had formed above the iridescent sediment. The liquid phase was decanted and the sediment redispersed again in 60 ml of distilled water. This procedure was repeated three to four times in order to fully clear the polymer of low molecular weight reaction residues.

[0190] Storage was effected as a 5% to 20% aqueous suspension. The size of the particles obtained was determined using a particle sizer from Beckmann-Coulter with a mean particle size of 342 nm.

Example 8—Synthesis of PMMA-co-n-butylMA Particles (80:20)

[0191] Synthesis was effected analogously to example 7—Synthesis of the PMMA particles. However, 12 ml (113 mmol) of methyl methacrylate and 4.5 ml (28 mmol) of n-butyl methacrylate were added.

[0192] The size of the particles obtained was determined with a mean particle size of 323 nm.

Example 9—Synthesis of PMMA-co-n-butylMA Particles (60:40)

[0193] Synthesis was effected analogously to example 7—Synthesis of the PMMA particles. However, 9 ml (84.6 mmol) of methyl methacrylate and 9 ml (56 mmol) of n-butyl methacrylate were added.

[0194] The size of the particles obtained was determined with a mean particle size of 345 nm.

Example 10—Synthesis of PMMA-co-n-butylMA Particles (40:60)

[0195] Synthesis was effected analogously to example 7—Synthesis of the PMMA particles. However, 6 ml (56 mmol) of methyl methacrylate and 13.6 ml (85 mmol) of n-butyl methacrylate were added.

[0196] The size of the particles obtained was determined with a mean particle size of 332 nm.

Example 11—Synthesis of Core-Shell Particles (PnbutylMA-PMMA)

[0197] Synthesis was initially effected analogously to example 7—Synthesis of the PMMA particles. However, 13.6 ml (85 mmol) of undistilled n-butyl methyl methacrylate were first added. When the reflection color of the dried film no longer changed, 6 ml (56 mmol) of methyl methacrylate were added through the septum and the reaction was then continued again analogously to example 7.

[0198] The size of the particles obtained was determined with a mean particle size of 380 nm.

Example 12

Kit Constituents

[0199] The powder consisted of a homogeneous mixture of fluoroaluminosilicate glass B (FAS B) and polyacrylic acid in the ratio 4.51:1.

[0200] The liquid consisted of demineralized water for the reference system or an aqueous particle dispersion for a particle-reinforced glass ionomer cement. The particle dispersions were each produced by redispersing an appropriate amount of polymer particles in demineralized water. The individual particle contents of the aqueous particle dispersions are given in table 5.

Example 13

Production of Glass Ionomer Cements

[0201] The glass ionomer cements were mixed from the kit constituents using a spatula on a pad. The individual mixing ratios are given in table 5.

TABLE-US-00010 TABLE 5 Polymer Polymer particles particles in the in the cement Polymer Powder Liquid liquid [% by K1c Increase in particles [g] [g] [g/g] weight] [MPa/m.sup.1/2] SD K1c [%] Reference 1.4 0.26 0 0 0.365 0.037 — Example 7 1.4 0.264 0.015 0.25 0.402 0.026 10.06 1.4 0.268 0.03 0.48 0.412 0.045 12.99 1.4 0.273 0.05 0.75 0.406 0.042 10.06 Example 8 1.4 0.268 0.03 0.48 0.388 0.049 6.29 Example 9 1.4 0.268 0.03 0.48 0.400 0.041 9.64 Example 10 1.4 0.268 0.03 0.5 0.425 0.025 16.35 Example 11 1.4 0.264 0.015 0.25 0.400 0.044 9.64 1.4 0.268 0.03 0.5 0.402 0.033 10.27 1.4 0.277 0.065 1 0.410 0.025 12.37

[0202] As a result of the addition of 0.25% to 0.75% by weight of the polymer particles from examples 7 to 11 in aqueous dispersion, the fracture toughness of the glass ionomer cement (reference) was markedly improved.