the technical feature of the present invention will be described in more detail , accompanied with the following examples . oyster shells were cleaned completely , and the black parts were removed . after the oyster shells were pulverized , the powder was sintered under 1100 ° c . for 2 hours to obtain calcium - containing powders , and the main component of the calcium - containing powders was calcium oxide . then 5 g of the calcium - containing powder was added into 1 l deionized water , followed by stirring , filtering , and collecting the basic filtrate to obtain a basic calcium - containing solution with high concentration . the 1m aqueous na 2 hpo 4 solution and aforementioned basic calcium - containing solution were mixed by stirring to precipitate a white product , i . e . amorphous calcium phosphate . finally , the solid product was separated from liquid through filtration , followed by drying the solid product directly to obtain amorphous calcium phosphate powders . the amorphous calcium phosphate powders prepared in the present example were analyzed by using an x - ray diffraction meter , and the test conditions are described as following : fig1 shows the x - ray diffraction data , which indicates that the product prepared in the present example is amorphous calcium phosphate . in the present comparative example , amorphous calcium phosphate was prepared by using the conventional process , which uses calcium chloride as a starting material . 1m na 2 hpo 4 solution and 1 . 67m calcium chloride solution were mixed by stirring to obtain amorphous calcium phosphate powders . during the process of mixing two solutions , a sodium hydroxide solution was used to adjust the ph of the reaction solution and control the ph between 8 . 5 ˜ 12 . the reaction time was about 24 hours to stabilize the ph value of the reaction solution . then , the solid product was separated from the reaction solution by filtration and washed using a suitable amount of deionized water to remove the nacl generated from neutralization . finally , the solid product was filtered again , followed by drying to obtain amorphous calcium phosphate powders . the method for preparing the amorphous calcium phosphate powder in comparative example 2 is the same as the method used in comparative example 1 , except that the ph value of the reaction solution is 4 . 0 . the method for preparing the amorphous calcium phosphate powder in comparative example 3 is the same as the method used in comparative example 1 , except that the ph of the reaction solution is 7 . 0 . the method for preparing the amorphous calcium phosphate powder in comparative example 4 is the same as the method used in comparative example 1 , except that the solid product was not washed completely . hence , some nacl still remained in the amorphous calcium phosphate powders . 5 g of cao powder was added into 1 l deionized water , followed by stirring , filtering , and collecting the basic filtrate to obtain a basic calcium - containing solution with high concentration . then , the method used for preparing calcium phosphate powder was performed . the method used for preparing calcium phosphate powder was the same as the method described in example 1 to obtain amorphous calcium phosphate powders of the present comparative example . comparison of the process of example 1 with those of comparative examples 2 - 4 the powder products prepared in example 1 and comparative examples 2 - 4 were analyzed with an x - ray diffraction meter . the test condition was the same as that described above , and the test result is shown in fig2 . after performing x - ray diffraction analysis , different forms of calcium phosphate were found in the powder product prepared by using comparative example 2 . hence , the product of comparative example 2 was not the amorphous calcium phosphate powders as expected . furthermore , the x - ray diffraction analysis showed that the powder product prepared in comparative example 3 was crystalline calcium phosphate . the solubility of crystallized calcium phosphate is so low that diminishes the releasing rate of ca 2 + and po 4 3 − . the crystalline calcium phosphate cannot be applied effectively to oral care compositions . on the other hand , although the ph of the reaction solution was controlled properly in comparative example 4 , the solid product was not washed appropriately , so salts still remained in the powder product . when the conventional method was used to prepare amorphous calcium phosphate , a suitable amount of water was needed to remove the salt generated from neutralization . if the amount of the washing water is too much , the form of calcium phosphate will be changed , as shown in comparative example 3 . if the amount of the washing water is inadequate , metal salt will be detected in the product , as shown in comparative example 4 . hence , the water amount for cleaning will influence the quality of the products . the x - ray diffraction data shows that the powder product prepared in example 1 is amorphous calcium phosphate powder with high purity , and there are no contaminants in the amorphous calcium phosphate powders . when the method of example 1 is used for preparing amorphous calcium phosphate , the problems of ph value and salt residues do not arise . hence , amorphous calcium phosphate with high purity can be steadily generated in a simple and rapid way by use of the method described in example 1 . element analysis of amorphous calcium phosphate powders by inductively coupled plasma mass spectroscopy ( icp - ms ) the amorphous calcium phosphate powders prepared in example 1 and comparative example 5 were analyzed by icp - ms , and the analysis results were shown in table 1 . the amorphous calcium phosphate powders prepared in example 1 contains fluoride of 535 . 97 ppm and strontium of 168 . 10 ppm , but these two trace elements were not detected in the amorphous calcium phosphate powder prepared in comparative example 5 . as shown in table 1 , the method of the present invention can synthesize amorphous calcium phosphate from oyster shells , and the trace elements contained in the oyster shells can be still kept in the product . in addition , trace elements of fluoride and strontium are not included in other amorphous calcium phosphate products prepared by general material and process . the powders prepared by using example 1 and comparative example 1 were individually dissolved in deionized water to obtain 1 wt % amorphous calcium phosphate solution . at the same time , deionized water was used as a control group to compare with the aforementioned amorphous calcium phosphate solution . then , 1 n hydrogen chloride solution was discharged into deionized water and amorphous calcium phosphate solution drop - by - drop , respectively . a ph meter was used to detect the ph change in each solution system . the ph changing cure represents the buffering capacity of each solution and the test results are summarized in fig3 . the slope of the ph changing rate represents the buffer slope of each solution and the results are listed in table 2 . when hydrogen chloride solution was gradually dropped into deionized water , the ph of deionized water decreased from 6 . 5 to 2 . 1 , and the buffering slope thereof was − 411 ( δph / 0 . 01 ml 1n hcl ). when hydrogen chloride solution was dropped into the amorphous calcium phosphate solution formulated by the amorphous calcium phosphate powder prepared in comparative example 1 , the ph of the amorphous calcium phosphate solution decreased from 7 . 4 to 5 . 5 , and the buffer slope thereof was − 43 ( δph / 0 . 01 ml 1n hcl ). however , when hydrogen chloride solution was titrated into the amorphous calcium phosphate solution formulated by the amorphous calcium phosphate powder prepared in example 1 , the ph value of the amorphous calcium phosphate solution decreased from 7 . 7 to 5 . 9 , and the buffer slope thereof was only − 26 ( δph / 0 . 01 ml 1n hcl ). according to the aforementioned results , the amorphous calcium phosphate powder prepared by using example 1 exhibits excellent buffering effect compared with deionized water as well as amorphous calcium phosphate powder prepared in comparative example 1 . it is feasible to reduce the acidity in mouth fluid and decrease the incidence rate of caries when the amorphous calcium phosphate powders prepared by using example 1 are applied . the oral care composition containing amorphous calcium phosphate powders from example 1 shows effective buffering effect on dental care . in addition , the amorphous calcium phosphate powder from the method of example 1 contains strontium ( sr ) and fluoride ( f ) which is different from the amorphous calcium phosphate powder prepared by the conventional method . the amorphous calcium phosphate powders prepared from example 1 , comparative example 1 , and comparative example 5 were dissolved under a ratio of 2 mg powder / 10 ml deionized water into a solution , respectively . after 10 min , calcium ion electrode was used to detect concentration change to represent calcium ion releasing rate . the test result is shown in fig4 . the ca 2 + concentration was 56 ppm in the amorphous calcium phosphate solution of example 1 , only 24 ppm in the amorphous calcium phosphate solution of comparative example 1 , and 42 ppm in the amorphous calcium phosphate solution of comparative example 5 . comparing the effect of example 1 with that of comparative example 1 , the ca 2 + concentration increased 127 %. also , comparing the effect of example 1 with that of comparative example 5 , the ca 2 + concentration increased 32 %. these results indicate that the amorphous calcium phosphate powders prepared by using example 1 has excellent ca 2 + release rate , so it is possible to supply ca 2 + in mouth to enhance the remineralization on teeth . in conclusion , the method for preparing amorphous calcium phosphate and the oral care composition containing amorphous calcium phosphate prepared by the same of the present invention has the following advantages . ( 1 ) the method of the present invention can fully utilize the abundant calcium content in the oyster shells and reduce the cost of manufacturing amorphous calcium phosphate . the oyster shells can be reused and reduced environment pollution . ( 2 ) the method of the present invention is very simple , and the time for preparing amorphous calcium phosphate can be shorted down to about 5 min . however , the reaction time for conventional method is about 24 hours . ( 3 ) the yield of amorphous calcium phosphate is about 90 % by the method of the present invention . ( 4 ) the amorphous calcium phosphate powder grain prepared by the method of the present invention is smaller and more transparent than that prepared by using the conventional method . hence , the dissolution rate of the amorphous calcium phosphate powder can be increased . ( 5 ) the method of the present invention does not need alkaline solution to maintain the ph of the reaction solution , so the problem of the presence of salt residue can be eliminated . ( 6 ) the oral care composition of the present invention contains trace elements , such as strontium ( sr ) and fluoride ( f ), which can improve the effectiveness of dental care . ( 7 ) the amorphous calcium phosphate powder prepared by the method of the present invention has good buffering capacity . hence , it is possible to neutralize the acidity in mouth fluid and prevent caries . ( 8 ) the amorphous calcium phosphate powder prepared by the method of the present invention has excellent ca 2 + release rate , so it is possible to enhance the remineralization on teeth . according to the method of the present invention , the starting material is oyster shell , so the problem of environment pollution caused by wasted oyster shells can be resolved and the manufacturing process is relatively simple . in addition , the method of the present invention does not need any alkaline solution during the process of synthesizing amorphous calcium phosphate , and the starting materials ( sintered oyster shells and phosphate ) are very cheap . hence , the cost of producing amorphous calcium phosphate can be reduced greatly . furthermore , the method of the present invention does not comprise steps of washing products ; therefore , the wastewater discharge can be reduced , whereby environment pollution is accordingly reduced . hence , when the amorphous calcium phosphate prepared by the method of the present invention is applied to the oral care composition , such as toothpaste and mouthwash , not only the production cost can be reduced , but also the effects of caries prevention and remineralization on teeth can be achieved . in addition , the amorphous calcium phosphate prepared by the present invention can further be added into food products , such as chewing gum , calcium - containing drinks , and calcium - containing food , in order to supply calcium and neutralize the acidity in mouth . although the present invention has been explained in relation to its preferred example , it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed .
a method for preparing amorphous calcium phosphate and oral care composition containing acp prepared by the same are disclosed , wherein the method comprises the following steps : cleaning and pulverizing the oyster shells ; sintering the oyster shells to obtain a calcium - containing powder ; dissolving the calcium - containing powder in water to obtain a calcium - containing solution ; and mixing the calcium - containing solution with a other phosphate - containing solution , to produce amorphous calcium phosphate . the method of the present invention not only can simplify the process and reduce the cost , but also can solve the problem of environment pollution resulting from wasted oyster shells . in addition , the acp prepared in accordance with the method of the present invention further comprises some trace elements , such as strontium and fluoride , which can improve dental health .