ENHANCED WITH ADDITION OF LOW CONCENTRATION OF IPBC

TECHNICAL FIELD

The present disclosure relates to the mixture of antimicrobial into a dental gypsum composition to reduce the risk of patient cross-contamination from dental gypsum models. More particularly, the present disclosure relates to the enhancement of the antimicrobial properties of benzoic acid and/or benzoic derivatives with the addition of low concentrations of IPBC into the dental gypsum composition.

BACKGROUND

There are various types of dental gypsum, as represented in the first block diagram lA-00 of FIG. 1A and second block diagram IB-GO of FIG. IB. As shown in FIG. 1A, dental gypsum product lA-01 has at least two types: soft gypsum lA-02a; and hard gypsum lA-02b. Soft gypsum lA-02a has at least two types: type 1 for impressions lA-03a; and type 2 for models and used in orthodontics lA-03b. Hard gypsum lA-02b has at least two types: dental stone lA-04a; and special gypsum lA-04b. As show in the second block diagram lB-00 of FIG. IB, dental stone 1 A-04a has at least four types: type 3 used for impressions and models which has a medium strength lA-05a; type 3 used for models in orthodontics lA-05b; type 4 used for impressions which has high strength and low expansion lA-05c; and type 5 used for impressions which has high strength and high expansion lA-05d. These dental gypsum types are generally sold as calcined gypsum and made into models per the below method.

The general method for making a dental gypsum model is pictured in FIGs. 2A-2D. As pictured in FIG. 2A, a first pictured step 2A-00 is pouring a slurry 2A-01 (prepared in a separate step from a mixture of dental gypsum and water) into an impression 2A-02 (prepared in separate step from the teeth of a patient). As pictured in FIG. 2B, a second pictured step 2B- 00 is setting the slurry 2A-01 in the impression 2A-02 to form the model 2B-01. As pictured in FIG. 2C. a third pictured step 2C-00 is removing the model 2B-01 (once the model 2B-01 has set) from the impression 2A-02. As pictured in FIG. 2D, for a pair of models for the lower and upper teeth (modeled separately), a fourth pictured step 2D-00is pictures the pairing of the model 2B-01 (the lower teeth) with its separately prepared associated model 2D-01 (upper teeth). There is a risk of cross-contamination from dental gypsum models created in dental clinics, hospitals and laboratories. To reduce cross-contamination, the models can be dipped in an antimicrobial or alternatively the dental models can incorporate an antimicrobial mixed into the dental gypsum composition, where the antimicrobial is mixed with the calcined gypsum prior to or during the preparation of the gypsum slurry. Benzoic acid and/or a benzoic derivative can be used as the antimicrobial in the dental gypsum composition. In the alternative the antimicrobial can include IPBC.

Benzoic acid is a colorless crystalline solid and a simple aromatic carboxylic acid. Benzoic acid occurs naturally in many plants. Salts of benzoic acid and benzoic acid are used as food preservatives and/or as a general antimicrobial. Derivatives of benzoic acid can include salts and esters of benzoic acid and are known as benzoates. Example benzoic derivatives include sodium benzoate, potassium benzoate, calcium benzoate and/or other benzoate salts or esters.

An example patent application using sodium benzoate as an antimicrobial mixed into the dental gypsum composition is Thailand patent application number 1601001009, "Antimicrobial Dental Plaster Formulation with Benzoic Acid or Compound as Antimicrobial Agent and Dental Cast Thereof," filed 25 February 2016. As shown in table 4 of this patent application, the efficacy of sodium benzoate increases as the percentage of sodium benzoate increases from 0.001% to 0.01% by weight of the composition.

IPBC is a water-soluble preservative used globally in the paints, coatings, wood preservatives, personal care, and cosmetics industries. IPBC is a powerful antimicrobial. As used in this disclosure, IPBC is meant to include: (a) the IUPAC named IPBC of 3-Iodoprop-2-yn-l-yl butylcarbamate; (b) 3-Iodo-2-propynyl N-butylcarbamate; (c) 3-Iodo-2-propynyl butylcarbamate; (d) the antimicrobial sold under the trademark Iodocarb®; and/or (e) iodopropynyl butyl carbamate. While IPBC is a cosmetic grade chemical and thus mostly non- toxic, IPBC is not a food grade chemical.

An example patent application using IPBC as an antimicrobial mixed into the dental gypsum composition is Thailand patent application number 1401001430, "Antimicrobial Dental Plaster Formulation and Dental Cast Thereof," filed 18 March 2014. As shown in table 4 of this patent application, the efficacy of IPBC increases as the percentage of IPBC increases from 0.001% to 0.01 % by weight of the composition. SUMMARY

A primary embodiment of the invention is a composition for an antimicrobial dental gypsum comprising: (a) a calcined gypsum; (b) an additive; (c) an antimicrobial agent comprising a benzoic acid and/or a benzoic derivative; and (d) an antimicrobial enhancing substance comprising IPBC. The antimicrobial agent is in the range of 0.001 to 0.02% by weight of the composition. The antimicrobial enhancing substance is in the range of 0.0001 to 0.01% by weight of the composition.

In alternative embodiments of the first embodiment, the composition, the benzoic derivative can be sodium benzoate, potassium benzoate and/or calcium benzoate. The additive can be a thickener, a retardant, an accelerator, a defoamer, a pigment, a stabilizer and/or a dye, wherein the additive is in the range of 2.5 to 3.5 percent by weight of the composition. The antimicrobial enhancing substance can further comprise citric acid, propionic acid, tartaric acid, acetic acid, oxalic acid, malic acid, salicylic acid, lactic acid, gluconic acid, hydroxyacetic acid and/or methylisothiazolinone. The calcined gypsum can be natural gypsum and/or synthetic gypsum.

A second embodiment of the invention is an antimicrobial dental gypsum model comprising: (a) gypsum; (b) an additive; (c) an antimicrobial agent comprising a benzoic acid and/or a benzoic derivative; and (d) an antimicrobial enhancing substance comprising iodopropynyl butyl carbamate (IPBC). The antimicrobial agent is in the range of 0.001 to 0.02% by weight of the composition. The antimicrobial enhancing substance is in the range of 0.0001 to 0.01% by weight of the composition.

In alternative embodiments of the second embodiment, the benzoic derivative can be sodium benzoate, potassium benzoate and/or calcium benzoate. The additive can be a thickener, a retardant, an accelerator, a defoamer, a pigment, a stabilizer and/or a dye, wherein the additive is in the range of 2.5 to 3.5 percent by weight of the composition. The antimicrobial enhancing substance can further comprise citric acid, propionic acid, tartaric acid, acetic acid, oxalic acid, malic acid, salicylic acid, lactic acid, gluconic acid, hydroxyacetic acid and/or methylisothiazolinone. The gypsum can be natural gypsum and/or synthetic gypsum.

A third embodiment of the invention is a method for preparing an antimicrobial dental gypsum model, the steps comprising: (a) preparing a dental impression from the teeth of a patient; (b) preparing a composition for an antimicrobial dental gypsum to create a slurry; (c) mixing the composition and water to create a slurry; (d) pouring the slurry into the dental impression; (e) setting the slurry to form the model; and (f) removing the model from the dental impression. The composition in this third embodiment comprises: (1) a calcined gypsum; (2) an additive; (3) an antimicrobial agent comprising a benzoic acid and/or a benzoic derivative; and (4) an antimicrobial enhancing substance comprising iodopropynyl butyl carbamate (IPBC). The antimicrobial agent in this third embodiment is in the range of 0.001 to 0.02% by weight of the composition. The antimicrobial enhancing substance in this third embodiment is in the range of 0.0001 to 0.01% by weight of the composition. In alternative embodiments of the third embodiment, the ratio of the water to the composition is in the range of 30:70 to 20:80 by weight. The step of mixing can be performed for 1 to 3 minutes. The step of preparing the composition can include agitating the composition for at least 50 minutes. The benzoic derivative can be sodium benzoate, potassium benzoate and/or calcium benzoate. The additive can be a thickener, a retardant, an accelerator, a defoamer, a pigment, a stabilizer and/or a dye, wherein the additive is in the range of 2.5 to 3.5 percent by weight of the composition. The antimicrobial enhancing substance can further comprise citric acid, propionic acid, tartaric acid, acetic acid, oxalic acid, malic acid, salicylic acid, lactic acid, gluconic acid, hydroxyacetic acid and/or methylisothiazolinone. The calcined gypsum can be natural gypsum and/or synthetic gypsum. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure are described herein with reference to the drawings in which:

FIGs. 1A-1B are block diagrams of the types of dental gypsum product of the prior art.

FIG. 2A-2D are a pictoral representation of steps taken to prepare a model of the prior art. FIG. 3 is a flowchart of the steps to prepare a dental gypsum model of an embodiment of the invention. DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. The illustrative embodiments described in the detailed description, drawings and claims are not meant to be limiting. Other embodiments can be utilized, and other changes can be made, without departing from the spirit or scope of the subject matter presented herein. Unless specified otherwise, the terms "comprising," "comprise," "including" and "include" used herein, and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, un- recited elements. IPBC is a cosmetic grade chemical and thus mostly non-toxic, IPBC is not a food grade chemical. IPBC is safe to include in cosmetics on the outside skin of a person but IPBC is not as safe for eating. The model does not directly contact mucous membranes in the mouth such as the gum line, tonsils, palate and tongue. However, the models are used for fabrication of custom trays, fabrication of dentures, crowns, prosthesis and orthodontics, and these items can be contaminated with trace amounts of IPBC from the dental gypsum of models. A lowered concentration of IPBC in the models can reduce potential risks for oral toxicity. Another reason to reduce the concentration of IPBC is its relatively high cost per kilogram in comparison to other antimicrobials and calcined gypsum. However, as demonstrated in Thailand patent application number 1401001430, the efficacy of IPBC increases as the percentage of IPBC increases. Thus what is needed is a dental gypsum composition with enhanced antimicrobial efficacy despite a low concentration of IPBC.

FIG. 3 is a flowchart 3-00 of the steps to prepare a dental gypsum model of an embodiment of the invention. The flowchart 3-00 includes the steps to:

3-01 Prepare a dental impression from the teeth of a patient.

3-02 Prepare a composition for an antimicrobial dental gypsum to

slurry.

3-03 Mix the composition and water to create a slurry.

3-04 Pour the slurry into the dental impression.

3-05 Set the slurry to form the model.

3-06 Remove the model from the dental impression. The inventive step in this flowchart 3-00 of the steps to prepare a dental gypsum model is the preparation of the composition for the antimicrobial dental gypsum 3-02. Other steps of the flowchart are well known steps in the preparation of a model using dental gypsum. The below text includes a description of the composition for the antimicrobial dental gypsum and the supporting experimental results demonstrating enhanced antimicrobial properties in the usage of the invention.

The primary embodiment of the invention is the composition for an antimicrobial dental gypsum comprising: (a) a calcined gypsum; (b) an additive; (c) an antimicrobial agent comprising a benzoic acid and/or a benzoic derivative; and (d) an antimicrobial enhancing substance comprising iodopropynyl butyl carbamate (IPBC). The antimicrobial agent is in the range of 0.001 to 0.02% by weight of the composition. The antimicrobial enhancing substance is in the range of 0.0001 to 0.01% by weight of the composition.

In alternative embodiments of the first embodiment, the composition, the benzoic derivative can be sodium benzoate, potassium benzoate and/or calcium benzoate. The additive can be a thickener, a retardant, an accelerator, a defoamer, a pigment, a stabilizer and/or a dye, wherein the additive is in the range of 2.5 to 3.5 percent by weight of the composition. The antimicrobial enhancing substance can further comprise citric acid, propionic acid, tartaric acid, acetic acid, oxalic acid, malic acid, salicylic acid, lactic acid, gluconic acid, hydroxyacetic acid and/or methylisothiazolinone. The calcined gypsum can be natural gypsum and/or synthetic gypsum.

A second embodiment of the invention is an antimicrobial dental gypsum model comprising: (a) gypsum; (b) an additive; (c) an antimicrobial agent comprising a benzoic acid and/or a benzoic derivative; and (d) an antimicrobial enhancing substance comprising IPBC. The antimicrobial agent is in the range of 0.001 to 0.02% by weight of the composition. The antimicrobial enhancing substance is in the range of 0.0001 to 0.01% by weight of the composition.

In alternative embodiments of the second embodiment, the benzoic derivative can be sodium benzoate, potassium benzoate and/or calcium benzoate. The additive can be a thickener, a retardant, an accelerator, a defoamer, a pigment, a stabilizer and/or a dye, wherein the additive is in the range of 2.5 to 3.5 percent by weight of the composition. The antimicrobial enhancing substance can further comprise citric acid, propionic acid, tartaric acid, acetic acid, oxalic acid, malic acid, salicylic acid, lactic acid, gluconic acid, hydroxyacetic acid and/or methylisothiazolinone. The gypsum can be natural gypsum and/or synthetic gypsum.

A third embodiment of the invention is a method for preparing an antimicrobial dental gypsum model, the steps comprising: (a) preparing a dental impression from the teeth of a patient; (b) preparing a composition for an antimicrobial dental gypsum to create a slurry; (c) mixing the composition and water to create a slurry; (d) pouring the slurry into the dental impression; (e) setting the slurry to form the model; and (f) removing the model from the dental impression. The composition in this third embodiment comprises: (1) a calcined gypsum; (2) an additive; (3) an antimicrobial agent comprising a benzoic acid and/or a benzoic derivative; and (4) an antimicrobial enhancing substance comprising IPBC. The antimicrobial agent in this third embodiment is in the range of 0.001 to 0.02% by weight of the composition. The antimicrobial enhancing substance in this third embodiment is in the range of 0.0001 to 0.01 % by weight of the composition.

In alternative embodiments of the third embodiment, the ratio of the water to the composition is in the range of 30:70 to 20:80 by weight. The step of mixing can be performed for 1 to 3 minutes. The step of preparing the composition can include agitating the composition for at least 50 minutes. The benzoic derivative can be sodium benzoate, potassium benzoate and/or calcium benzoate. The additive can be a thickener, a retardant, an accelerator, a defoamer, a pigment, a stabilizer and/or a dye, wherein the additive is in the range of 2.5 to 3.5 percent by weight of the composition. The antimicrobial enhancing substance can further comprise citric acid, propionic acid, tartaric acid, acetic acid, oxalic acid, malic acid, salicylic acid, lactic acid, gluconic acid, hydroxyacetic acid and/or methylisothiazolinone. The calcined gypsum can be natural gypsum and/or synthetic gypsum. The efficacy of the enhanced antimicrobial dental gypsum is demonstrated in the below example preparations of dental gypsum models. The embodiments described in this specification and claims can be used to limit cross-contamination in dental clinics, hospitals and laboratories of streptococcus aureus, Candida albican and pseudomonas aeruginosa. For the Example 1 to Example 13 below, the powder to water ratios of dental gypsum type 3 and type 4 used in the physical and antimicrobial tests listed below are 70:30 and 80:20 by weight, respectively. Example 1— Composition for Dental Gypsum (Ex-1)

An example composition of dental gypsum without antimicrobial agent is produced as follows. The composition is produced from 97% of natural gypsum by weight of the composition mixed with 3% by weight of additives in the mixer. The mixture is stirred for 60 minutes until all the components are well dispersed and homogeneous to obtain dental gypsum Type 4. Before forming the model and testing a sample, the composition is mixed with water (approximately 80:20 by weight) then the slurry is stirred for 1 to 3 minutes.

Example 2— Composition for Dental Gypsum (Ex-2)

An example composition of dental gypsum without antimicrobial agent is produced as follows. The composition is produced from 97% of natural gypsum by weight of the composition mixed with 3% by weight of additives in the mixer. The mixture is stirred for 60 minutes until all components are well dispersed and homogeneous to obtain dental gypsum Type 3. Before forming the model and testing a sample, the composition is mixed with water (approximately 70:30 by weight) then the slurry is stirred for 1 to 3 minutes.

Example 3 -- Composition for Dental Gypsum (Ex-3)

An example composition of dental gypsum with 0.001% of antimicrobial agent is produced as follows. The composition is produced from 97% of natural gypsum by weight of the composition mixed with 3% by weight of additives and 0.001% of sodium benzoate in the mixer. The mixture is stirred for 60 minutes until all the components are well dispersed and homogeneous to obtain dental gypsum Type 4. Before forming the model and testing a sample, the composition is mixed with water (approximately 80:20 by weight) then the slurry is stirred for 1 to 3 minutes.

Example 4— Composition for Dental Gypsum (Ex-4)

An example composition of dental gypsum with 0.005% of antimicrobial agent is produced as follows. The composition is produced from 97% of natural gypsum by weight of the composition mixed with 3% by weight of additives and 0.005% of sodium benzoate in the mixer. The mixture is stirred for 60 minutes until all the components are well dispersed and homogeneous to obtain dental gypsum Type 4. Before forming the model and testing a sample, the composition is mixed with water (approximately 80:20 by weight) then the slurry is stirred for 1 to 3 minutes. Example 5— Composition for Dental Gypsum (Ex-5)

An example composition of dental gypsum with 0.01% of antimicrobial agent is produced as follows. The composition is produced from 97% of natural gypsum by weight of the composition mixed with 3% by weight of additives and 0.01% of sodium benzoate in the mixer. The mixture is stirred for 60 minutes until all the components are well dispersed and homogeneous to obtain dental gypsum Type 4. Before forming the model and testing a sample, the composition is mixed with water (approximately 80:20 by weight) then the slurry is stirred for 1 to 3 minutes.

Example 6— Composition for Dental Gypsum (Ex-6)

An example composition of dental gypsum with 0.01% of antimicrobial agent is produced as follows. The composition is produced from 97% of natural gypsum by weight of the composition mixed with 3% by weight of additives and 0.01% of IPBC in the mixer. The mixture is stirred for 60 minutes until all the components are well dispersed and homogeneous to obtain dental gypsum Type 4. Before forming the model and testing a sample, the composition is mixed with water (approximately 80:20 by weight) then the slurry is stirred for 1 to 3 minutes.

Example 7— Composition for Dental Gypsum (Ex-7)

An example composition of dental gypsum with 0.001% of antimicrobial agent is produced as follows. The composition is produced from 97% of natural gypsum by weight of the composition mixed with 3% by weight of additives and 0.001% of sodium benzoate in the mixer. The mixture is stirred for 60 minutes until all the components are well dispersed and homogeneous to obtain dental gypsum Type 3. Before forming the model and testing a sample, the composition is mixed with water (approximately 70:30 by weight) then the slurry is stirred for 1 to 3 minutes. Example 8— Composition for Dental Gypsum (Ex-8)

An example composition of dental gypsum with 0.005% of antimicrobial agent is produced as follows. The composition is produced from 97% of natural gypsum by weight of the composition mixed with 3% by weight of additives and 0.005% of sodium benzoate in the mixer. The mixture is stirred for 60 minutes until all the components are well dispersed and homogeneous to obtain dental gypsum Type 3. Before forming the model and testing a sample, the composition is mixed with water (approximately 70:30 by weight) then the slurry is stirred for 1 to 3 minutes.

Example 9 -- Composition for Dental Gypsum (Ex-9)

An example composition of dental gypsum with 0.01% of antimicrobial agent is produced as follows. The composition is produced from 97% of natural gypsum by weight of the composition mixed with 3% by weight of additives and 0.01% of sodium benzoate in the mixer. The mixture is stirred for 60 minutes until all the components are well dispersed and homogeneous to obtain dental gypsum Type 3. Before forming the model and testing a sample, the composition is mixed with water (approximately 70:30 by weight) then the slurry is stirred for 1 to 3 minutes.

Example 10— Composition for Dental Gypsum (Ex-10)

An example composition of dental gypsum with 0.01% of antimicrobial agent is produced as follows. The composition is produced from 97% of natural gypsum by weight of the composition mixed with 3% by weight of additives and 0.01% of IPBC in the mixer. The mixture is stirred for 60 minutes until all the components are well dispersed and homogeneous to obtain dental gypsum Type 3. Before forming the model and testing a sample, the composition is mixed with water (approximately 70:30 by weight) then the slurry is stirred for 1 to 3 minutes.

Example 11 -- Composition for Dental Gypsum (Ex-lf)

An example composition of dental gypsum with 0.51% of antimicrobial agent is produced as follows. The composition is produced from 97% of natural gypsum by weight of the composition mixed with 3% by weight of additives and 0.51% of sodium benzoate in the mixer. The mixture is stirred for 60 minutes until all the components are well dispersed and homogeneous to obtain dental gypsum Type 3. Before forming the model and testing a sample, the composition is mixed with water (approximately 70:30 by weight) then the slurry is stirred for 1 to 3 minutes.

Example 12— Composition for Dental Gypsum (Ex-12)

An example composition of dental gypsum with 0.51% of antimicrobial agent is produced as follows. The composition is produced from 97% of natural gypsum by weight of the composition mixed with 3% by weight of additives and 0.51 % of IPBC in the mixer. The mixture is stirred for 60 minutes until all the components are well dispersed and homogeneous to obtain dental gypsum Type 3. Before forming the model and testing a sample, the composition is mixed with water (approximately 70:30 by weight) then the slurry is stirred for 1 to 3 minutes. Example 13— Composition for Dental Gypsum (Ex-13)

An example composition of dental gypsum with 0.01% of antimicrobial agents is produced as follows. The composition is produced from 97% of natural gypsum by weight of the composition mixed with 3% by weight of additives and 0.0091% of sodium benzoate and 0.0009% of IPBC in the mixer. The mixture is stirred for 60 minutes until all the components are well dispersed and homogeneous to obtain dental gypsum Type 3. Before forming the model and testing a sample, the composition is mixed with water (approximately 70:30 by weight) then the slurry is stirred for 1 to 3 minutes.

Example 14— Antimicrobial Test (Ex-14)

Seven samples are tested. Three types of microorganisms {staphylococcus aureus ATCC 6538, pseudomonas aeruginosa ATCC 27853 and Candida albicans ATCC 10231) were used. The microorganisms are grown on Brain Heart Infusion (BHI) agar (BBL, USA). Colonies are subcultured in BHI broth and incubated at 37 °C for 24 h. Microbial suspensions are prepared at the concentration of 108 CFU/mL using 0.5 MacFarland Standard. The testing process is done as follows. One hundred i of each microbial suspension is dropped on irreversible hydrocolloid impression (such as with caulk sold under the trademark Jeltrate®) and left dry for 10 min. Gypsum mix with different concentrations of IPBC are prepared and poured onto the impressions and allowed to set for 60 minutes. Then the gypsum mass samples are removed and the microbial contact surfaces are imprinted on BHI agar plates. The plates are incubated at 37 °C for 24 to48 hours. Colonies appearing on the agar are gram-stained and counted. Dental gypsum without antimicrobial is used as the control. All experiments are done in triplicate on three separate occasions.

CFU average = (Xi+X ₂ + X ₃ )/3

When Xi is Microbial Number (CFU) of model of Ex-2.

When X ₂ is Microbial Number (CFU) of model of Ex-3.

When X ₃ is Microbial Number (CFU) of model of Ex-4. The amount of microbes is compared with the percentage of the microbe of dental gypsum model from the formula without antimicrobial agent (Ex-1).

Example 15 -- Physical Property Test (Ex-15)

In this analysis, the gypsum is mixed and poured into mold (20+0.2 mm in diameter and 40+0.4 mm in length) to fabricate dental gypsum model. The dental gypsum models are stored in conditions mentioned above. At 60+5 min after the start of mixing, models were stressed in the compressive mode until fractured using testing machine sold under the trademark Instron® with a cross-head speed of 5+2 kN/min. The maximum stress of each model (S) expressed in megapascal (MPa) using the recorded maximum force (F) was calculated with S = F/314 formula.

Result & Discussion

Remark: All test items follow ISO 6873 standard test Antimicrobial properties

Increasing amount of sodium benzoate (see Ex-3 to Ex-5) and IPBC (see Ex-10 and Ex-12) showed better antimicrobial activity as expected. In both dental gypsum types, IPBC showed more effective antimicrobial action against the all tested bacteria (see Ex-5, Ex-6, Ex-11 and Ex-12). Almost no C. Albican can be observed in dental gypsum type 3 incorporated with >0.01% of IPBC (see Ex-10 and Ex-12). For type 3, mixing antimicrobial with the same amount showed more effective antimicrobial action against the all tested bacteria (see Ex-10 and Ex- 13).

Dental gypsum incorporated with 3-iodo-2-propynylbutylcarbamate (IPBC) and a benzoate salt showed antimicrobial activity against all microorganisms tested within acceptable microbial reduction range.

Physical properties

Remark: All test items follow ISO 6873 standard test In terms of physical properties, addition of more antimicrobial to dental gypsum type 3 significantly affected the dry compressive strength and retardation in the setting time (see Ex-7 to Ex- 13). High concentration of IPBC can significantly alter setting time and setting expansion (see Ex- 10 and Ex- 12) however it is not out of specification and still functioning properly. Increasing amount of sodium benzoate can shorten the setting time (see Ex-7 to Ex-9 and Ex- 1 1). The alteration of compressive strength can be observed in almost cases using sodium benzoate as antimicrobial (see Ex-7 to Ex-9, Ex- 12 and Ex- 13), however mixing both reagents provided longer setting time (see Ex- 13). Stone-containing antimicrobials showed higher compressive strength and mostly lower setting expansion. This could be an advantage of these newly developed stone materials.

As shown in the above data, the antimicrobial efficacy of sodium benzoate can be enhanced with the addition of small concentrations of IPBC. Additional enhancing substances that can be included in the composition with IPBC can include citric acid, propionic acid, tartaric acid, acetic acid, oxalic acid, malic acid, salicylic acid, lactic acid, gluconic acid, hydroxyacetic acid and/or methylisothiazolinone.

While various aspects and embodiments have been disclosed herein, 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. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit of the invention being indicated by the appended claims.

REFERENCES

Thailand patent application number 1401001430, "Antimicrobial Dental Plaster Formulation and Dental Cast Thereof," filed 18 March 2014.

Thailand patent application number 1601001009, "Antimicrobial Dental Plaster Formulation with Benzoic Acid or Compound as Antimicrobial Agent and Dental Cast Thereof," filed 25 February 2016.

European patent application number 05025182.6, published as EP1787627A1, "Anti-microbial dental impression material," filed 17 November 2005, published 23 May 2007.

"Antimicrobial Activity of Type III Dental Gypsum Incorporated with 3- iodo-2-propynyl-butylcarbamate and Its Physical Properties," Sroisiri Thaweboon et al.,

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"An analysis of the persistent presence of opportunistic pathogens on patient-derived dental impressions and gypsum casts," Int J Prosthodont. 2008 Jan-Feb; 21(1): 62-8.

"The effect of repeated immersion of gypsum cast in sodium hypochlorite and glutaraldehyde on its physical properties: An in vitro study," J Pharm Bioallied Sci. 2012; 4: 353-7.