Objective: To measure the convergence angles of teeth in different teeth positions and different denture designs.Methods:Mesio-distal widths and labio-lingual widths were measured on 226 teeth according to three points in a line on three surfaces (gingival, middle and incise) of each tooth.The distance between every point and the counterpart point in the adjacent surface was measured.Then convergence angles were calculated. Results:The means of the angles were 4.13°±0.77°,4.14°±0.76°, 4.46°±0.95°, 4.76°±0.84° on the first and second premolar, the first and second molar,respectively . There were significant differences between the premolars and molars(P<0.05).On the dentures with the designs of monocrown, triunit-bridge and long bridge the means of the angles were 3.78°±0.74°,4.69°±0.75° and 5.08°±0.85° respectively,the angle on the denture with the design of monocrown was smaller than that of bridge (P<0.05).Conclusion:The convergence angles are different according to different teeth positions and different denture designs, so they should be adjusted according to the clinical requirements.

0.01). There was a significant difference in TIMP-1,-2 expressions between saccule injury group and control group (P

0.05,group 1 or group 2 vs group 3 P

s〕 Objective:To investigate the influence of repeated firings on the color of porcelain fused to metal crown(PFM) . Methods: 5 PFM samples were prepared and fired for 9 times.The color of the samples was measured following firing with CIE1976 L*a*b* color system . The color difference ?E ab *,hue angle h ab * and chroma C ab * were calculated according to the following calculations:?E ab * ={(?L*) 2 +(?a*) 2 +(?b*) 2} 1/2 , C ab * ={(a*) 2+(b*) 2} 1/2 , h ab *=tg 1 b*/ a*, L* presented brightness. Results: After repeated firing, L* value of PFM , C ab * and L* value of dentin layer and h ab * value of opaque layer increased. Conclusion: The color of PFM after repeated firing may become brighter. The color change is resulted from the increase of L* and C ab * of dentin layer.

Objective: To study the influence of repeated firings on the PFM bond strength. Methods: 25 specimens of PFM in the diameter of 13.0 mm and thickness of (1.0?0.02) mm were prepared and fired at 920 ℃ for 1, 3, 5, 7 or 9 times(5 samples for each time). The remained porcelain rate(RPR) was measured by Mackert method and used to evaluate the bond strength.Results: After 3 firings, the RPR of PFM decreased obviously, and additional firings had no obvious effect on the RPR. Conclusion: 3 times firing or more may decrease the bond strength of PFM.

Objective: To study the ionic diffusion and the distri bu tion character in the interfacial area of aurogalvano form ceramic crown, and t o discuss the bond mechanism of porcelain fused to 99.9% gold. Method s: The ionic diffusion and the distribution character in the interfac ial area of aurogalvano form ceramic crown were observed by electron probe and scanning electron microscope. Results: The examination wit h electron microprobe showed that from gold to porcelain aluminum ascended from zero to peak value, aurum dropped from the peak value to zero, and the bandwidt h was about 3～4 ?m.There were obvious mechanical table and tuber. C onclusion: There is ionic diffusion and no crack in the interfacial a rea;there are physical and chemical combinations between porcelain and 99.9% gol d.

Objective: To study the effect of B 2O 3 and P 2O 5 on fluorosilicic mica glass-ceramic sintering process.Methods: Six sets of K 2O-MgO-SiO 2-MgF glass were prepared by using B 2O 3 and P 2O 5as sintering aid respectively. Green bodies of the glass powder were formed by gelcasting and sintered at 800,850,900,950 and 1 000 ℃ for 6 h respectively. The sintering and crystallization behavior were studied by thermal shrinkage , X-ray diffraction (XRD) and SEM.Results:The shrinkage rate of the glass with 2% B 2O 3 and P 2O 5 was the highest ,while that of the glass with 5% P 2O 5 the lowest. The size of the precipitated crystal from the glass ceramics containing 2% B 2O 3 and 2% P 2O 5 was bigger.Conclusion:The density and shrinkage measurements of the sintered bodies show that the glass powder of pure K 2O-MgO-SiO 2-MgF system has poor sinterability, while minor addition (

Objective:To investigate the effect of sintering temperature on the shrinkage and microstructure of dental fluorosilicic mica glass-ceramic with two different particle size. Methods:Fluorosilicic mica glass powder with average particle diameter of 72.8 ?m was named PO and that with average diameter of 4.5 ?m was named Pm. PO and Pm were molded by cool isostatic pressing technique and then sintered at different temperatures between 600-1 000 ℃. The shrinkage and microstructure of the sintered blocks of PO and Pm were systematically compared with each other. Results:The shrinkage of PO and Pm blocks were all increased as the temperature ascended. However, the shrinkage curves were distinctly different. At the same sintering temperature the shringkage of Pm was larger than that of PO. Moreover, the turning points of temperature (reflecting transition of the sintering mechanisms) of Pm was higher than that of PO. The microstructure observation showed that sintering at 950 ℃ resulted in mica crystal in glass-ceramics and the best compactness of the sintered blocks of both PO and Pm. Conclusion:Sintering glass powder of smaller particle size at 700-850 ℃ may achieve better sintering compactness.

Objective: To measure the color of dental CAD/CAM alumina-glass-composites(AGC). Methods: Dental CAD/CAM alumina block were infiltrated at 1 120 ℃ by laboratory made AG1,AG2,AG3 and AG4 color serials of infiltration glass powder and Vita In-Ceram Alumina AL1,AL2,AL3 and AL4 infiltration glass respectively. Specimens were made with the area of 10 mm?10 mm,thickness of 0.5,1 and 1.5 mm respectively. Color parameters were measured by Minolta CM-2600d spectrophotometer. Results:The specimen with the thickness of 1 mm was used as the standard for color measurement.After infiltration with AL1-AL4 glass powder,the color parameters of Vita alumina core ceramic were L*: 69.39-78.41,a*:1.82- 4.02,b*:18.35-24.42,when infiltrated with AG1-AG4 glass powder, the color parameters of CAD/CAM AGC were L*:68.80-78.44,a*:1.32- 4.75,b*:16.85- 21.86. b*value and chroma of the AG3 core ceramic were lower than that of AL3 core ceramic,while a* value was higher.b* value and chroma of the AG1 and AG2 core ceramic were lower than that of AL1 and AL2 core ceramic. The reflectance curve of CAD/CAM AGC infiltrated by AG1-AG4 glass powder demonstrated the similar trend as that of the core ceramic infiltrated by Vita In-Ceram glass powder. Conclusion: The color range and surface reflection rate of laboratory made AG1-AG4 AGC are similar with those of Vita AL1-AL4 In-Ceram Alumina core and may meet the need of color match with veneer ceramics.