2 Grams of the adhesive composition, 100 g of water and  10 g of diethyl ether were vigorously mixed together, left to  stand still, the aqueous phase thereof was filtered through the  syringe filter, and the obtained filtrate was measured by using  an ion chromatography to measure the concentration of fluo› rine ions (mmols/g) contained in 100 parts by mass of the  polymerizable monomer. The concentration of the fluorine  ions was calculated by using a calibration curve found from  the standard samples of fluorine ions (10 ppm, 25 ppm, 50  ppm).  Within 24 hours after the slaughter, a bovine foretooth was  pulled out, and the enamel surface and the dentin surface were  ground by using a #600 emery paper while pouring water so  as to be in parallel with the labial face to thereby prepare a  tooth for testing the strength.  Next, the compressed air was blown onto the above surface  of the tooth for testing the strength for about 10 seconds to dry  the surface and, thereafter, a double-sided adhesive tape hav› ing a hole of3 mm in diameter perforated therein was fixed to  either the enamel surface or the dentin surface. Next, a par› affin wax of a thickness of 0.5 mm having a hole of 8 mm in  diameter perforated therein was fixed onto the above hole in 25  concentric therewith to form a mimic cavity.  A sample adhesive composition was applied into the mimic  cavity, left to stand for 20 seconds and, thereafter, the com› pressed air was blown thereto for about 10 seconds to dry the  composition followed by the irradiation with light from a  dental visible ray irradiator (Tokuso Powerlight, manufac› tured by Tokuyama Co.) for 10 seconds. Further, a dental  composite resin (Estelite ~, manufactured by Tokuyama Den- tal Co.) was applied thereon, and was irradiated with light  from the visible ray irradiator for 30 seconds to prepare an  adhesion test piece.  The above adhesion test piece was dipped in water of37°  C. for 24 hours and was, thereafter, pulled by using a tension  tester (Autograph manufactured by Shimazu Seisakusho Co.)  at a crosshead speed of 2 mm/min. to measure the tensile  adhering strength between the dentin and the composite resin.  Four test pieces were measured for their adhering strength per  a test relying upon the above method, and an average value  thereof was regarded as an adhering strength to the enamel or 45  to the dentin to evaluate the adhesion to the tooth.  After the adhesive composition was prepared, 1 0 g of the  adhesive composition was introduced into a 20-ml glass  bottle and was stored in an incubator maintained at 37°  C.  Precipitation of a white solid matter from the adhesive com› position was observed by the eye with the passage of time,  and the timings of the salt precipitation were evaluated on the  basis of the following three steps.  The obtained adhesives were measured for their amounts  of polyvalent metal ions and amounts of fluorine ions, and  were tested for their adhesion and storage stability in the same  manner as in Example 1 to obtain results as shown in Tables  5 and 6.  Adhesives of compositions shown in Table 4 were prepared  according to the method of Example 1.  Dental adhesives of compositions shown in Table 1 were  prepared according to the method of Example 1.  The obtained adhesives were measured for their amounts  of polyvalent metal ions and amounts of fluorine ions, and  were tested for their adhesion and storage stability in the same  manner as in Example 1 to obtain results as shown in Tables  2 and 3.  The adhesive was measured for its amount of polyvalent  metal ions and amount of fluorine ions. Thereafter, the adhe› sive was tested for its adhesion and was evaluated for its  adhesion to the enamel and to the dentin. The adhesive was,  further, tested for its storage stability and was evaluated for its  salt precipitation and gelling property. The composition of the  adhesive was as shown in Table 1 and the measured results  were as shown in Tables 2 and 3.  Grams of PM2/hydrogenphosphoric diester monomer  (A-1),  The components were weight out according to the follow› ing recipe, and were stirred and mixed together at room tem› perature (23°  C.) for 24 hours to prepare a dental adhesive.  2 Grams of Al(O-1-pr)/polyvalent metal ion source (B’),  0.4 Gram ofFNa/fluoride ion source (E’),  34 Grams ofIPA/water-soluble organic solvent (D),  7.6 Grams of water, and  0.4 Grams ofCQ and 0.4 g ofDMBE/photopolymerization  initiator (G).  @: The solution was not gelled even after two months have  passed.  10 Grams of the sample adhesive composition was intro› duced into the 20-ml glass bottle and was stored in the incu- bator maintained at 37°  C. Gellation of the adhesive compo› sition was observed by the eye with the passage of time, and  the gellation timings were evaluated on the basis of the fol› lowing three steps.  X: The liquid gelled within 3 days.  0:  The solution was not gelled for more than one month.  The number of days until gelled was recorded.  0:  Slightly precipitated (precipitated on the bottom of the  glass bottle). Number of days until precipitated was  recorded.  @: No salt prec1p1tation was observed even after two  months have passed.  X: White solid matter precipitated in large amounts within  3 days (the liquid was cloudy).  ( 4) Testing the Storage Stability.  (a) Evaluating the Salt Precipitation.  (b) Method of Testing the Adhesion.  (b) Evaluating the Gelling Property.  US 8,815,974 B2  28  27  Example 1  Examples 2 to 22  Comparative Examples 1 to 12  TABLE 1  Ex.1  Ex.2  Ex. 3  Ex.4  Acidic monomer (A)  (A-1)  (A-2)  (C)  PM2  6PPH  PM!  MAC-10 (B’)*  (E’)*  Water  100  Al(O-i-pr)3 (20)  FNa(4)  76  100  Al(O-i-pr)3 (20)  FNa(4)  76  60  40  Al(O-i-pr)3 (20)  FNa(4)  76  60  40  Al(O-i-pr)3 (6)  FNa(l.2)  76  ( a) Preparation of an Adhesion Test Piece:  (3) Evaluating the Adhesion to the Tooth.  (2) Measurement of Fluorine Ions: 