| Objective: Through comparing the compressive strength between nano-ceramic and ordinary ceramic crown standard test specimens with different thickness metal-basal crown , to discuss the relationship between the thickness of metal-basal crown and the compressive strength of metal-ceramic crown, and the difference of nano-ceramic and ordinary ceramic to the compressive strength. The purpose is to provide the theoretical basis for the clinical application of nano-ceramic restoration.Methods:1 Models preparation: A metal model of simulating crown core of the ideal premolar, was processed by precision instrument. The height of the crown core was 5 mm, and the diameter 5 mm, and there were no sharp edges. The base of metal model was 50 mm, the hight 20 mm. Computer Numerical Control lathe was used to process the cobalt chromium alloy into the metal-basal crowns with different thickness. And then, random selection included 50 metal-basal crowns, which met the requirements of experiments. Metal-basal crowns had uniform thickness, respectively 0.2mm, 0.4mm, 0.6mm, 0.8mm,1.0mm. The same thickness of metal-basal crowns were randomed into two groups, 5 in a group, all together 10 groups. Using A, B, C, D and E nano–ceramic groups, and A′, B′, C′, D′, E′respectively ordinary ceramic groups. Ultrasonic oscillator with anhydrous ethanol absolute was adopted to wash the metal-basal crown in choice, oscillation cleaning 5 times, 5 mins a time, in order to remove the dirties on the metal-basal surface, and then dry, to deal the surface with alumina drill to make them obtuse. In 0.5 Mpa pressure, 100 meshed aluminum oxide was put to use in sandblasting processing on the surface specimens, until the surface of metal-basal specimen become homogeneously rough. The metal-basal crowns were washed with flushing water. Then, again the crowns were washed with oscillation cleaning by distilled water, 5 mins a time, all together for three times dried for use. All opaques were fired by twice-fire technique. Coating dentine porcelain and controlling the thickness of the porcelain, sintered in the same porcelain furnace following the respective manufacturers'recommendations. All metal-ceramic crowns were burnished at the same speed by the same dental lathe. The total thickness of opaques and body ceramic were controlled by metal thickness measurement. The thickness of all porcelains was ensured at 1.0 mm. All the specimens were prepared after self-glazing and ultrasonic cleaning,2 Located these specimens in mental model within Instron testing machine. loaded on occlusal surface of each model vertically by a 6 mm pressure head, at the speed of 1 mm per min, and then performed destructive test to determine the compressive strength, to test the most strongly fracture force values ( unit: KN), and record.3 Statistical analysis was conducted on all values of the compressive strength by SPSS13.0 software.Results:1 The destructive values in all crowns of different groups were as follows: Group A ( 1.56±0.16 ) KN, Group B ( 2.76±0.09 ) KN, Group C ( 3.01±0.38 ) KN, Group D ( 3.18±0.18 ) KN, Group E ( 3.55±0.13 ) KN, Group A′( 1.45±0.18 ) KN, Group B′( 2.19±0.06 ) KN, Group C′( 2.20±0.15 ) KN, Group D′( 2.37±0.16 ) KN, Group E′( 2.72±0.25 ) KN.2 Multiple mean differences of variance analysis was performed for nano-ceramics and ordinary ceramic groups to SNK-q inspection individually.In nano-ceramic groups: there were significant differences in the compressive strength among the different thickness of metal-basal crowns, 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm and 1.0 mm groups (P<0.01). In ordinary ceramic groups: there were significant differences in the compressive strength among the different thickness of metal-basal crowns, 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm and 1.0 mm groups (P<0.01).3 Comparison between ordinary ceramic and nano-ceramic groups, showed the results as between nano-ceramic and ordinary ceramic groups: when the thickness of the metal-basal crowns was at 0.2 mm, there was no significant difference in the compressive strength (P>0.05), But there were significant differences in the thickness 0.4 mm, 0.6 mm, 0.8 mm and 1.0 mm, respectively (P<0.01).Conclusion:1 When the porcelain is in certain thickness, a close connection exists between the compressive strength and the thickness of the metal-basal crowns with two porcelain systems.2 During the groups of 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, the compressive strengths of the two porcelain groups increase with the thickness of metal-basal crowns. The compressive strength of metal-basal crown at 0.2 mm is the minimum. And the compressive strength of metal-basal crown at 1.0 mm is maximum.3 From 0.2 mm to 1.0 mm, the compressive strengths of nano-ceramic groups are higher than those of ordinary ceramic groups, at the thickness of metal-basal crowns are the same. But there are no significant differences between the groups, At the thickness 0.2 mm. 0.4 mm, 0.6 mm, 0.8 mm and 1.0 mm interblock comparision, the nano-ceramic groups are higher than ordinary ceramic groups in compressive strength. |
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