| Introductionporcelain - fused - to - metal restoration is now widely used in clinic. The margin of common porcelain - fused - to - metal crown contact to base teeth with metal. , while the color of metal will form " gingival stained" , which effect the outlook of the patient. If gingival recede, the metal margin will be exposed, resulting in severe problem of effecting aesthetic. The design of shoulder margin of PFM crown combine aesthetics of the porcelain of labial margin with intensity, which especially suit for patients with thin gingival and high laugh line. After enameling, the smooth surface reduce the aggregation of bacterial, furthermore, with a concealing margin, It improve the health level of periodontal of teeth. Tightness of the margin with the teeth directly affect the quality of the restoration. There are many aspects that affect the compatibility, and involve in every manufactory procedure. Therefore, reducing factors that affect compatibility and improve compatibility of the restoration may play a important role in clinic.ObjectivesThe aim of this study is to measure the length of margin gap after cementation between common PFM and PFM with shoulder porcelain. Analysis and compare the compatibility between the two margins, in order to provide evidence for clinic.Materials and EquipmentsMaterials: Carborundum pin, retraction cord, cord presser, silastic, im-pression injector(1:1), nickel - chromium alloy, inc phosphate cementation, shoulder porcelain Modellierciquid N build - up liquid N, epoxy resinEquipment: Sandblasting machine ( PHIK PSJ - II) , vacuum blender (WHIP MIX ) , porcelain oven ( Programat XI ) , microscopy ( OLYMPUS DP 10) , microscopy image analysis systemMethods1 Selecting cases;20 cases aged 20 -50 who wanted to restore their tooth between year 2003 and 2004 were selected,7 male and 13 female, and there were 23 tooth selected, not moveable , health periodontal residual root of labial teeth, no dental caries of the residual crown, or 2mm above the gingival after gingivaltocmy were required. The 20 cases randomized into 2 groups, cases in 1 group use shoulder porcelain to restore, while cases in 2 group use common PFM to restore.2 prepare labial and lingual of the teeth, prepare shoulder of the teeth, the width of the finished shoulder is lmm,and intr - angle of the shoulder should be round and blunt, the shoulder of the labial of the teeth is right angle, fovea form should be prepared in lingual, press, make impression with secondary impression method with silastic. Prepare die in common method, embbed, pre -heated , smelt, for nickel - chromium alloy, casting with high frequency centrifugal casting machine, milling intracrown with 80mm aluminium chloride, control the wall to 0. 3mm with ruler, and make the labial margin stop at gingival axis, clear the air and pre - chlorinated in vacuum Progrmat XI, stain opacity porcelain at tow time . shoulder porcelain was made two time, body porcelain, clearing, incisal porcelain, enemaling, and the go back to the clinic.Make the finished restoration take place, examine the integrity with explorer, that is the explorer cant be blocked, or blocked but cant observe visible gap when move to the tooth from surface of the restoration, polish, sterilization, dry, then cenmented, and press for 5min, gingival retraction, make impression with secondary impression method with silastic.3Micro - image analysis;samples were fixed vertical to long axis view,take photos with OLYMPUS DP10 microscope, then analysis with Aelamoph/ DplO/BX4 analysis system, measure the exceeding margin, and 3 points was selected. Average of the value reflect the tightness of the neck porcelain.ResultsResults show that there was significant difference between the margin of common PFM and shoulder porcelain (P <0. 05). the compatibility of shoulder porcelain has advantage over common PFM porcelain.DiscussionThe results showed that PFM with shoulder porcelain has good compatibility, the probable reasons are(l) labial surface of metal crown stop at the gingi-val - axis angle, which enhance the intensity of neck porcelain margin supported by metal, and the thin neck make the porcelain contract less. ( 2 ) application of shoulder porcelain, shoulder porcelain mach body porcelain in color, conducting a more aesthetic effect, when heat temperature is above 50t that of body porcelain , shoulder porcelain can not be destructed, which can improve compatibility. (3)technology of porcelain -liquid extraction. Chnarts technology is divided into platinum foil medium technology, fire - bear die technology, and direct extraction technology, direct extraction technology is easy to control, and can be adjusted for many times, and which is a popular trend, direct extraction method is divided into porcelain - liquid method, porcelain — wax method and porcelain -resin method, ROBIN is a good porcelain. There is no difference between shoulder porcelain and body porcelain, while porcelain -wax combining porcelain and porcelain - resin method has a low intensity and density;porcelain -wax method do not suitable for use in clinic. Findings also can be found that margin fabricated by porcelain - liquid contract large, but has a high density, small hole, indicating a good intensity, which in favor of forming a smooth surface, and can reduce aggregation of bacterial. (4) during fabrication, a wood model and one control model were used, which can make up the wearing of themodel, so it can contact perfect with the teeth, improving the compatibility of the margin.According to the view of most of the authors, the maximum acceptable value in clinic of margin width between teeth and the crown is 120um. Results of this study showed that compatibility labial margin of common PFM and shoulder porcelain is within the acceptable range in clinic.Conclusion1 In this study, compatibility of margin of shoulder porcelain has advantage over that of common porcelain - fused - to - metal .2 The compatibility of common porcelain - fused - to - metal is within the acceptable range in clinic.
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