| Objective: To develop nano composite zinc phosphate cement. Observation was made on the influence of nano particle on adhesive property of zinc phosphate cement and mechanism was discussed. Methods: 1. Preparation of nano composite zinc phosphate cement: the nanophase zinc oxide powder and zinc phosphate cement powder were measured by the ratios of 0wt%,0.5wt%,1 wt%,1.5 wt%,2 wt%,2.5 wt%,3 wt%,5 wt%, respectively by analytic balance. After measurement, the corresponding powders were put into the clean container and triturated for five minutes. Then a layer of thin plastic film with a hole covered the container, and air sprayer was inserted through the hole and blew in three times. The developed cements with percentages of nanopowder, which were divided into 8 groups correspondingly, or Aï¼H, and stored in refrigerator for future use. 2. Making of specimens and measurement of shear bonding strength(SBS): Each specimen was composed of two kinds of casting. Forty piece-shaped wax patterns with the dimension of 15mm×12 mm×1mm were made. Sprue was put on the side of 15mm×12 mm, and the other side was the adhesive surface. Forty bar-shaped wax patterns were also made with the dimension of 7mm×3.5mm. Sprue was put on one end of the bar. The side of 7mm×3.5mm was used as the adhesive surface. All wax patterns were invested and cast by wax-lost method. Eighty castings were ground flat by stone first, and then ground twice by the same type diamond bur in the same direction. The piece-shaped castings were invested with self-cured resin into the blocks with the volume of 50mm×15mm×10mm, and a 25mm×10mm, round seat was made for each block. Forty resin blocks and forty bar-shaped castings were divided into eight groups, respectively and randomly, and were paired randomly, for the preparation of adhesion. The two adherends were bonding, and was pressed with the stable load of 5kg for five minutes. Specimens were immersed into distilled water for twenty four hours with the temperature of 37℃. Specimens were mounted on the test machine and were tested with the shear force at a crosshead speed of 0.5 mm/min. The result of SBS and the type of failure were recorded. 3. Making and observation of SEM specimen: Alloy piece specimens, which were dimensioned 5 mm×3mm×1mm, were made with the same steps above, and were bonded with three cements, or zinc phosphate cement, 1 wt% and 3 wt% nano composite zinc phosphate cement, which were marked by specimen I,II and III. After adhesion, the fresh cross-section of specimens were ground out by high-speed bur. specimens were dried and observed by SEM. 4. All statistics of SBS was analyzed with one-way ANOVA and q-test by using SPSS software package. Results: 1. SBS: The change of the results of eight groups was seemingly with regularity, with the percentage of nanopowder from low to high. Via analysis of ANOVA and q-test, the SBS of group A was higher statistically than those of other seven groups(P<0.05), and SBS of group H was lower than those of other seven groups statistically. SBS of group B was not different with that of group C significantly(P>0.05). Group B and group A,E,F and G had not significant difference(P>0.05). However, SBS of group D was higher than group A,E,F and G significantly(P<0.05). 2. Type of failure: Almost all adhesive failure was happened in group E,F,G and H, and adhesive failure and cohesive failure, or mixture failure, were both happened in group C and D. Group A and B, however, demonstrated indefinite type failure. Generally, amount of mixture failure was increasing with the increase of SBS, and amount of adhesive failure was increasing with the decrease of SBS. 3. Observation of SEM: Specimen I : A deep fissure was seen along the adhesive interface, with the width of 2μm.Many microdefects in luting agent and microcracks through the cement layer can also be observed. The structure of the cement was loose, and there were much amorphous substance, with the different sizes. It was demonstrated by high magnification th...
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