Influence of powder/liquid mixing ratio on porosity and translucency of dental porcelains

STATEMENT OF PROBLEM: Dental technicians use a variety of techniques when condensing dental porcelains. It is unclear whether these techniques affect the total porosity and translucency of dental porcelains. PURPOSE: The objective of this study was to determine whether varying the powder/liquid ratio during condensation affects porosity and translucency of porcelains.Material and methods Duceram LFC dentin, Duceram LFC incisal, IPS Eris dentin, and IPS Eris incisal porcelains were studied. For each specimen, 1.0 g of porcelain powder was mixed with 1 of 3 different volumes of deionized water to form a slurry with a thin, medium, or thick consistency. The slurries were condensed in a plastic syringe mold, fired, and polished to a 3-microm finish to form 12 groups of 4 specimens each (14-mm diameter, 1.10-mm thickness). The apparent density (g/mL) of each specimen was measured using Archimedes method, and the porosity (%) calculated. Each specimen was coupled to standard ceramic tiles using an immersion liquid, and the color shade was measured in CIE Yxy coordinates using a tristimulus colorimeter. Translucency was assessed by calculating the contrast ratio of shade value (Y) in front of black versus white backgrounds. Two-way analysis of variance and Tukey's multiple comparison tests (alpha = .05) were used to test for significant effects of factors. RESULTS: Porcelain type and powder/liquid ratio had a significant interactive effect on the apparent density (P < .001) and on total porosity (P = .003); however, there was no consistent trend. The powder/liquid ratio did not significantly affect translucency (P = .28), but porcelain type had a significant effect on translucency (P < .001). CONCLUSION: In this in vitro study, total porosity of specimens prepared using 4 porcelains was found to be sensitive to powder/liquid ratio; whereas translucency was found to be insensitive to powder/liquid ratio.     

正畸儿童龋病的口腔综合防治

目的：观察口腔综合防治措施对正畸儿童龋病的作用。方法：以56名12-16岁的正畸患者为观察对象，观察矫治前、矫治后半年及1年的龋指数、变形链球菌计数、乳酸杆菌计数的改变。实验组采用口腔综合保健措施。结果：实验组的变形链球菌计数、乳酸杆菌计数明显低于对照组，差异有显著性；实验组无新龋发生，对照组龋均比实验组有所上升，但两组之间无统计学上的差异。结论：正畸治疗患者龋病通过口腔综合防治措施是可以治疗和预防的。     

Sliding contact fatigue of graded zirconia with external esthetic glass

Veneer chipping and fracture are common failure modes for porcelain-veneered zirconia dental restorations. We hypothesized that the graded glass/zirconia/glass with external esthetic glass (e-GZG) can increase the lifetime and improve resistance to veneer chipping and fracture relative to porcelain-veneered zirconia, while providing necessary esthetics. Previously, we have demonstrated that a graded glass-zirconia surface possesses excellent resistance to occlusal-like sliding contact fatigue. Here, we investigated the sliding contact fatigue response of this graded glass-zirconia surface with external esthetic glass. This external glass is essential for shade options, for preventing excessive wear of opposing dentition, and for protecting Y-TZP from hydrothermal degradation. e-GZG plates were bonded to composite blocks and subjected to prolonged sliding contact up to 10 million cycles at 200 N in water. The resistance to sliding contact fatigue of e-GZG matches that of monolithic Y-TZP, and both of these materials demonstrated lifetimes that were orders of magnitude longer than that of porcelain-veneered zirconia. Graded e-GZG is a promising restorative material.     

Digital subtraction arthrography and arthrofluoroscopic dynamic observations on TMJ dysfunction syndrome

Digital subtraction arthrography and arthrofluoroscopic dynamic observation were performed for seventy cases with TMJ dysfunction syndrome. A comparative study between the findings of digital subtraction arthrography and the operative findings was carried out for eleven cases who underwent surgery. It has been found that digital subtraction arthrography can overcome the disadvantages of conventional arthrography and has important diagnostic value for TMJ dysfunction syndrome, especially for disc perforation. In addition. The procedure of digital subtraction arthrography, the normal and abnormal manifestations of digital subtraction arthrograms were described in the present study.     

类风湿性关节炎患者牙周骨丧失程度的临床研究

目的:揭示类风湿性关节炎患者关节炎严重程度与牙周骨丧失程度的相关性。方法: 70例类风湿关节炎患者根据牙周附着丧失与牙槽骨吸收程度分为2组:无、轻度骨丧失组和中、重度骨丧失组。分别检查患者晨僵持续时间、红细胞沉降率以及血清C反应蛋白,并进行分析。结果:经统计学分析, 2组在晨僵时间、红细胞沉降率及C反应蛋白水平均有显著性差异,中、重度组均高于无、轻度组。结论:类风湿关节炎患者牙周骨丧失的程度与其类风湿临床症状严重程度密切相关。     

倾斜种植体在上颌后牙区骨量不足患者中的应用

目的:探讨倾斜种植体作为一种避免上颌窦植骨的方法,应用于上颌骨后牙区骨量不足患者种植修复的可靠性。方法:2005年1月—2007年12月间,21例患者共27个固定桥修复上颌后牙缺失,分别使用ITI和Br覽nemark 2种种植系统共植入78颗种植体,其中34颗种植体采用倾斜植入,44颗轴向植入。所有患者均为上颌后牙区骨量不足无法直接接受常规种植体植入。种植体植入后常规愈合3个月,除1颗种植体失败外,其余种植体均功能性负载支持固定义齿修复,修复方式为黏结固位和螺丝固位。每例患者均于负载后12、24和36个月接受临床和放射学随访检查。采用SPSS11.0软件包对数据进行统计学处理。结果:上颌有1颗轴向种植体在术后2个月时失败,倾斜种植体无失败。随访时间为36个月。上颌轴向种植体的累积存活率为97.72%,倾斜种植体的累积存活率为100%,修复成功率为100%。随访期间,种植体周围软组织保持稳定,平均探诊深度和附着水平无明显变化。结论:倾斜种植体作为一种上颌骨后牙区骨量不足患者的治疗方法是可靠的,能有效避免植骨手术,并节约治疗时间。     

创伤致家兔颞下颌关节滑膜和软骨超微结构的改变

目的研究创伤对家兔颞下颌关节滑膜和软骨的影响。方法采用实验性创伤动物模型，透射电镜下观察创伤后颞下颌关节滑膜和软骨的超微结构特征。结果髁突软骨表层结构破损，软骨层不同程度的软骨细胞变性、坏死。滑膜内膜层滑膜细胞变性，胞质内可见大量的空泡和近胞膜处的小泡，微丝增多、密集；细胞膜上可见微绒毛突起；内膜下层出现类“蚓状小体”结构；并首次描述了滑膜内膜层滑膜细胞之间的点粘连连接方式。结论创伤确实可以导致颞下颌关节的退行性改变。     

Double-layer porcelain veneers: effect of layering on resulting veneer color

STATEMENT OF PROBLEM: Densely sintered aluminum oxide veneered with feldspathic porcelain seems to be a promising technology for the fabrication of porcelain laminate veneers, which provide both strength and esthetics. To effectively use this approach for porcelain veneers, practitioners should know how the resulting color is affected by adding a layer of veneering porcelain onto the aluminum oxide. PURPOSE: This study compared changes in CIE L*a*b* color coordinates of simulated stained teeth when covered with the aluminum oxide core disks alone and after the disks had been veneered with 3 different shades of porcelain. MATERIAL AND METHODS: Fifteen aluminum oxide disks were divided into 3 groups. Each of 5 disks was veneered with porcelain of the Vita shades A1, A2, and B4, respectively. The colors of the substrate covered with the nonveneered disks and the veneered disks were measured separately, and the color differences were calculated. Measurements of the disks on a white background were also performed and used as controls. The extracted data were compared with Vita shade values available from the literature. RESULTS: Statistically significant differences in color coordinates of dark substrates were recorded between the substrate covered by an aluminum oxide disk and the addition of veneering porcelain to the aluminum oxide disks. Veneering the aluminum oxide disks with A1, A2, and B4 porcelain produced significant differences in the resulting color when placed on a dark substrate. The direction of the color modifications correlated with values obtained from the literature. The resulting color was also affected by the color of the underlying structures. CONCLUSION: Although aluminum oxide alone does have a degree of masking capability, the resulting color of porcelain veneers with the use of this material can successfully be modified with the veneering porcelain.     

Oral health care system in Chinese Mainland

The purpose of this review is to describe the training of dental professionals and to give an overview of the oral health care system in Mainland China. It may be of interest and importance for American readers to become aware that there are alternative practice structures and the world is getting smaller.