口腔金属材料磁共振成像伪影的初步探讨

目的 探讨1.5 T、3.0 T场强下口腔内常用3种金属材料在磁共振检查时是否产生伪影和伪影的严重程度,并比较不同成像序列对伪影的影响.方法 将3种口腔内常用金属材料组成的烤瓷冠及对照组树脂冠制备成琼脂模型,分别使用1.5 T、3.0 T的磁共振扫描仪进行扫描,测量伪影直径.统计采用4×4×2三因素析因设计,分析不同材料、不同成像序列以及不同磁场强度对MRI成像伪影大小的影响.结果 析因设计方差分析发现,不同材料、成像序列以及磁场强度对成像伪影大小的影响差异均有统计学意义(材料:F=124.796,df=3,P=0.000;成像序列:F=3.020,df=3,P=0.036;磁场强度:F=9.367,df=1,P=0.003).金属材料中,金合金产生的伪影最小;与其他成像序列相比,FSE序列的伪影直径最小;磁场强度为1.5 T的伪影直径<3.0 T.而各因素间的交互作用对伪影的影响差异无统计学意义(P>0.05).结论 合理选择金属材料和扫描序列可以减轻伪影;量化指标显示3.0T场强下伪影增幅只在10%左右,因此,为了临床需要选择高场机器是可行的.     

磨牙残根残冠多根管不平衡桩钉修复的观察

目的采用不平行就位道桩核烤瓷冠修复磨牙残根残冠多根管。方法利用铸造法制做不平行就位道桩核,完成对磨牙残根残冠的保存修复。结果总体修复效果理想。结论不平行就位道增加了核的固位强度,为烤瓷冠修复提供了良好的根基,临床疗效确切,实为一种理想的修复方法。     

金瓷联冠修复因牙周病松动伴深覆盖上前牙临床评价

目的探讨金瓷联冠修复因牙周病松动伴深覆盖的上前牙临床应用价值.方法患牙截冠、核桩改向,将患牙和相邻1～2颗健康牙构成一个联合式修复体.结果松动伴深覆盖的上前牙得以稳固,改向、延长患牙使用时间,并有利于美观.结论利用金瓷联冠治疗因牙周病导致松动伴深覆盖的上前牙有明显的疗效和临床实用价值.     

烤瓷熔附金属修复体的临床研究

目的 对烤瓷熔附金属修复体的临床效果进行观察，总结成功及失败的经验教训，提高口腔修复水平。方法 对597例患者的719件烤瓷熔附金属修复进行5-8年的临床观察。按统一的疗效标准，分为优秀、良好、失败3级，结果 优秀617件，占85.8%，良好94件，占13.1%，失败8件，占1.1%，结论 烤瓷熔附金属修复仍是目前最理想的固定修复方法，但在病例选择，修复体设计与制作，基牙的处理以及修复体的选色与配色方面，必须遵循相应的原则与方法，才能保证其临床效果。     

Pain and discomfort experienced after placement of a conventional or a superelastic NiTi aligning archwire

Two nickel-titanium archwire types commonly used for initial tooth alignment were compared with regard to the pain/discomfort patients experience during the initial phase of tooth movement. The two archwires used were a superelastic nickel-titanium alloy, 0.014 inch Sentalloy, Light (GAC International Inc. Central Islip, NY, USA) and a 0.014 inch Nitinol (unitek, Monrovia, CA, USA), a conventional nickel-titanium aligning archwire.One hundred and twenty-eight consecutive patients attending an orthodontic university clinic and 2 private practices for routine placement of a fixed appliance were randomly assigned one of these 2 initial archwires. Assessments of pain/discomfort were made daily by means of a 100 mm visual analog scale (VAS) over the first 7-day period after bonding. On the first day, recordings were made every hour for the first 11 hours.The results showed that the level of discomfort increased continuously every hour after the insertion of either a Sentalloy or a Nitinol as first archwires, with a peak in the first night, remaining high on the second day and decreasing thereafter to baseline level after 7 days. During the first 10 hours it was apparent that the pain/discomfort experienced after placement of a Sentalloy was less than that found with the Nitinol archwire, although a significant difference could be found at 4 hours only. No significant gender-specific differences were found in either archwire group. A significant difference between the upper and lower dental arches was observed during the first 11 hours after placement of either a Sentalloy or a Nitinol archwire, with the lower arch having the higher pain experience.     

Galvanic currents between dental alloys in vitro

The galvanic current densities between gold, amalgam and cobalt-chromium, three different classes of dental alloys, were determined in vitro in artificial saliva kept at 35°C. The maximum current density of 200 μA/drn²was obtained between the conventional amalgam and a type III gold alloy. Galvanic currents of lesser magnitude could also be measured between amalgams high in copper and the other alloys. No measurable current densities were obtained between gold alloys and between gold and cobalt-chromium alloy with the exception of a casting and a solder gold alloy commonly used in combination.     

假体磨屑所致关节滑膜反应的实验研究

为了研究假体磨屑动物体内引起的组织学反应，不同磨屑所致反应的差别。方法将６４只家兔按注射磨屑和观察时间不同，随机分成８组，分别将聚乙烯，钛合金，两种混磨屑和盐水注入膝关节内，２周注射一次，封续３－６月。通过光镜，偏振光显微镜，电镜观察滑膜变化。     

Patch test reactivity to nickel alloys

11 widely used nickel alloys were investigated with respect to corrosion stability and reactivity in nickel-sensitive individuals. Alloys with a nickel release in synthetic sweat exceeding 1 microgram/cm2/week gave a strong patch test reaction in nickel-sensitive persons; those with a release below 0.5 microgram/cm2/week showed weak reactivity with one exception. Nickel allergy is a health problem. It may be minimized by using nickel alloys with a corrosion level below 0.5 microgram/cm2/week. Action should be taken by dermatologists, industry and authorities to solve this neglected problem.     

Resistance to mercury embrittlement of some alloys for amalgam

Dental amalgam is a composite material in which dispersed unconsumed alloy particles reinforce the system. The strength of amalgam is governed by the fracture resistance of the particles and the bond between the particles and the matrix. The purpose of the present experiment is to examine the resistance to mercury embrittlement of some alloys used to make powder for dental amalgam. Tensile specimens of pure silver, pure tin, and six different alloys were prepared: Eut (71.9 w/o Ag-28.9 w/o Cu), ACS (Eut+10 w/o Sn), AgCu (49 w/o Ag-51 w/o Cu), Op (70 w/o Ag-26 w/o Sn-4 w/o Cu), Ty (60 w/o Ag-27 w/o Sn-13 w/o Cu) and Sy (40 w/o Ag-30 w/o Sn-30 w/o Cu). Mercury was electroplated onto the middle portion of the specimens. Four specimens of each pure metal and alloy were tested at 5 min, 30 min, 1 hour and 24 h after the plating with a loading rate of 0.25 mm/min. As-cast specimens were also tested. The present study revealed that: 1) 5 min after plating, all the alloys, except Op, Sy, and Eut, are significantly weaker than the unplated alloys; 2) the alloys with the lowest percentage of their unplated strength 5 min after plating are ACS (41.4 w/o) and Ty (41.8 w/o); 3) after 30 min, the effect of plating diminishes so that significant decreases in strength are consistently found only in ACS and Sn; 4) the silver-copper alloys were the least affected by plating. The results suggested that mercury released during aging or corrosion of amalgams in vivo might embrittle unconsumed alloy particles, weakening the amalgam restoration.     

Oxide adherence to a Ni-Cr-Mo ternary alloy

The success of a porcelain-fused-to-metal (PFM) restoration depends upon the quality of the porcelain-metal bond. Oxide adherence to commercial PFM alloys has been previously shown to vary widely and to correspond to porcelain-bonding behavior. Most non-precious PFM alloys are based upon a Ni?Cr?Mo ternary alloy and contain small amounts of other elements. The purpose of the present study was to evaluate the oxide adherence of a 76Ni?19Cr?5Mo ternary alloy similar to dental PFM alloys, yet without the additional elements found in these alloys. The outer oxide (NiO) on both polished and cold-worked specimens was found to delaminate at a stress of about 1 MPa. The darkened underlayer thus revealed was found to be enriched in Cr and Mo and appeared to be an internal oxide layer. The oxide adherence to this unmodified Ni?Cr?Mo ternary was substantially lower than any of the commercial alloys tested previously. Cold work was not found to improve the oxide adherence. These results indicate that the alloying elements present in commercial Ni?Cr?Mo alloys exert a pronounced influence on their oxide adherence. Measurement of the effects of various alloying additions on oxide adherence is planned for future work.