METHOD FOR KNEADING DENTAL GYPSUM POWDER

Abstract

A method for kneading a dental gypsum powder is provided that includes putting the dental gypsum powder and water in a bottle, the dental gypsum powder containing gypsum hemihydrate and a polycarboxylate-based water reducing agent, contained at 0.05 parts by mass to 0.8 parts by mass with respect to 100 parts by mass of the gypsum hemihydrate, sealing the bottle, and shaking the bottle.

Claims

1. A method for kneading a dental gypsum powder, the method comprising: putting the dental gypsum powder and water in a bottle, the dental gypsum powder containing gypsum hemihydrate and a polycarboxylate-based water reducing agent, contained at 0.05 parts by mass to 0.8 parts by mass with respect to 100 parts by mass of the gypsum hemihydrate, sealing the bottle, and shaking the bottle.

2. The method for kneading a dental gypsum powder according to claim 1, wherein a mass ratio of the water to the dental gypsum powder is greater than or equal to 0.18 and less than or equal to 0.6.

Description

EXAMPLES

[0037] In the following, the method for kneading a dental gypsum powder according to the present invention will be described in detail with reference to specific examples. Note, however, that the present invention is not limited to these specific examples.

[0038] <Preparation of Dental Gypsum Powder>

[0039] Raw materials shown in Table 1 below were put in a pot mill, and the raw materials were mixed for 60 minutes to prepare a dental gypsum powder according to the examples described below.

[0040] Water reducing agents (see Table 1) used in the examples are described below.

[0041] Melflux 2651F, Melflux 5581F, Melflux 4930F, and Melflux 6681F are all polycarboxylate-based water reducing agents manufactured by SKW East Asia Co., Ltd.

[0042] Mighty 100, manufactured by Kao Corporation, is a water reducing agent composed mainly of sodium salt of naphthalenesulfonic acid formaldehyde condensate.

[0043] Melment F10M, manufactured by SKW East Asia Co., Ltd., is a melamine sulfonic acid-based water reducing agent composed mainly of melamine resin sulfonic acid formalin condensate.

[0044] Six different kneading examples (Examples 1 to 6) for kneading a dental gypsum powder were prepared. In these six kneading examples, the dental gypsum powder contained gypsum hemihydrate and 0.05 to 0.8 parts by mass of a polycarboxylate-based water reducing agent with respect to 100 parts by mass of the gypsum hemihydrate, and a mass ratio of water to dental gypsum powder was set to be greater than or equal to 0.18 and less than or equal to 0.6. For purposes of comparison, kneading examples containing no polycarboxylate-based water reducing agent (Comparative Examples 1, 6 and 7), kneading examples containing a polycarboxylate-based water reducing agent at a lower content than the above content range (Comparative Examples 2 and 4), a kneading example containing a polycarboxylate-based water reducing agent at a higher content than the above content range (Comparative Example 3), and a kneading example in which the mass ratio of water to dental gypsum powder was set to be greater than the above mass ratio range (Comparative Example 5) were prepared.

[0045] <Kneading Dental Gypsum Powder>

[0046] 100 g of the prepared dental gypsum powder and water at the corresponding mass ratio shown in Table 1 were put in a cylindrical bottle made of polystyrene resin (opening inner diameter: about 4 cm; height: about 7 cm; capacity: about 90 mL; weight: about 25 g; wall thickness: about 1.5 mm) after which the bottle was sealed, and the bottle was shaken manually for 30 seconds to obtain a gypsum slurry.

[0047] <Presence/Absence of Air Bubbles>

[0048] The obtained gypsum slurry was poured into an impression material, and after 5 minutes had elapsed, the resulting gypsum model (gypsum body) was removed from the impression material. The obtained gypsum model was visually evaluated for the presence/absence of air bubbles. The results of the evaluation are shown in Table 1.

[0049] <Strength of Gypsum Body>

[0050] With respect to the gypsum model (gypsum body) obtained by the above method, after 60 minutes had elapsed from the time kneading of the dental gypsum powder was started, the physical property (strength) of the resulting gypsum body was evaluated using the test method specified in JIS T6605 Dental Stone. The results of the evaluation are shown in Table 1. The rating scale categories used for the strength evaluation in Table 1 are described below. [0051] Excellent strength is greater than 10 MPa [0052] Good strength is greater than or equal to 3 MPa and less than or equal to 10 MPa [0053] Fair strength is less than 3 MPa

TABLE-US-00001 TABLE 1 (Composition: Parts by weight) Com Com Com Com Com- Com- Com- par- par- par- par- per- par- par- ative ative ative ative ative ative ative Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 ple1 ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 Gyp- - 100 100 100 100 100 100 100 100 100 100 100 100 100 sum Gyp- hemi sum hy- hemi- drate hy- drate Poly- Poly- Melflux 0.3 0.6 0.3 0.01 0.9 carboxy car- 2651F late- boxy- Melflux 0.2 0.1 based late 5581F water ether Melflux 0.1 0.05 reducing 4930F agent Melflux 0.5 6681F Miscel- Gypsum 3 3 4 2.5 3.4 3 1 3 3 laneous dihydrate Potassium 2 0.6 0.1 0.5 sulfate Sodium 0.6 1 0.6 0.6 0.6 0.6 sulfate Water reducing Mighty 0.1 agent other than 100 polycarboxy Mel- 0.1 late-based water ment reducing agent F10M Mass ratio of water to 0.24 0.3 0.4 0.42 0.2 0.45 0.3 0.24 0.24 0.16 0.7 0.3 0.3 dental gypsum powder Presence/ NO NO NO NO NO NO YES YES NO YES NO YES YES absence of air bubbles Strength of gypsum body excel- excel- good good excel- good excel- excel- fair excel- fair excel- excel- (after 60 min) lent lent lent lent lent lent lent lent

[0054] Referring to the evaluation results shown in Table 1, it can be appreciated that when the content of the polycarboxylate-based water reducing agent was greater than or equal to 0.05 parts by mass and less than or equal to 0.8 parts by mass with respect to 100 parts by mass of the gypsum hemihydrate, air bubbles were absent in the gypsum slurry that had set, and a gypsum body having sufficient strength was obtained.

[0055] On the other hand, when no polycarboxylate-based water reducing agent was included (Comparative Examples 1, 6, and 7), or when the content of the polycarboxylate-based water reducing agent was lower than the above content range (Comparative Examples 2 and 4), air bubbles were observed in the gypsum slurry that had set. Further, when the content of the polycarboxylate-based water reducing agent was higher than the above content range (Comparative Example 3), no air bubbles were observed in the gypsum slurry that had set, but the strength of the resulting gypsum body was insufficient.

[0056] Also, even when the content of the polycarboxylate-based water reducing agent was within the above content range, when the mass ratio of water to dental gypsum powder was greater than the above mass ratio range (Comparative Example 5), the strength of the resulting gypsum body was insufficient.

[0057] As described above, the content of the polycarboxylate-based water reducing agent and the mass ratio of water to dental gypsum powder were altered, and the presence/absence of air bubbles in the resulting gypsum slurry and the strength of the gypsum body resulting from letting the gypsum slurry set were evaluated. As a result, it was found that a gypsum slurry without air bubbles can be obtained when the content of the polycarboxylate-based water reducing agent is greater than or equal to 0.05 parts by mass and less than or equal to 0.8 parts by mass with respect to 100 parts by mass of the gypsum hemihydrate, and the mass ratio of water to dental gypsum powder is less than or equal to 0.6.

INDUSTRIAL APPLICABILITY

[0058] The present invention relates to a method for kneading a dental gypsum powder and may be suitably implemented as a method for kneading a dental gypsum powder in a home visit setting or some environment not requiring a dedicated mechanical device or tool, for example.

[0059] The present application is based on and claims priority to Japanese Patent Application No. 2016-107022 filed on May 30, 2016, the entire contents of which are hereby incorporated by reference.