Pixel value modification using RVG-4 automatic exposure compensation for instant high-contrast images

The RVG-4 permits automatic exposure compensation (AEC). The purpose of this investigation was to determine the effects of AEC on image contrast. Images were made either with or without a dental QA jaw phantom using a fixed image projection geometry. Exposures were 6.3 through 27.3 μC/kg using an X-ray generator operated at 70 kVp. Region of interest pixel value distributions were measured at tissue thicknesses in this phantom, and the average pixel values and signal-to-noise ratios (SNR) were calculated. The use of AEC without an object in place resulted in a disproportionate relationship between pixel value and exposure with a marked reduction in SNR. The use of AEC on under- and over-exposed images of the phantom simultaneously enhanced image contrast and reduced SNR. Thus, AEC provides a convenient and quick method for achieving high-contrast images with sub-optimal exposures, however, this could lead to inappropriate patient dosages if the function is used for over-exposed images. AEC reduces the SNR and produces disproportionate pixel values relative to exposure.     

Cavernous sinus thrombosis following odontogenic and cervicofacial infection

Summary Cavernous sinus thrombosis (CST) is rarely seen clinically as a complication of infectious processes since the discovery of penicillin. At the present time, dental abscess is an uncommon cause of CST. We now report our experiences with a 60-year-old diabetic male, who developed CST 38 days after extraction of an infected upper third molar tooth. The importance of eradicating regional cervicofacial foci of infection is stressed.     

口腔修复临床电刀龈成形术的效果观察

现察口腔修复临床电刀龈成形术的效果。方法：对81例口腔修复门诊牙体缺损患者用电刀进行牙龈成形术并定期复诊观察。结果：81例术后牙龈全部达到修复要求而立即修复，其中70例术后牙龈稳定，占总数的86．4％。结论：电刀龈成形术是口腔修复临床上一种可行的治疗手段。     

ART技术封闭恒牙的3年临床效果观察

目的 :评价非创伤性充填 (ART)技术对恒牙窝沟封闭后 ,封闭剂保留及新生龋病发生情况。方法 :1996年在四川省德阳市 4所中学选取 12～ 13岁儿童 14 0名作 191个ART封闭。采用WHO的ART标准器械 ,德国ESPE公司生产的高强度玻璃离子材料 ,对选择的牙面窝沟进行封闭 ;操作者为经中等口腔专业训练的医生。试验 3年后对ART封闭及牙龋病情况进行评价。结果 :封闭后 1、2、3年的封闭成功率分别为 89.6% ,78.8% ,71.9%。试验后 1年没有新生龋齿的发生 ,试验后 2、3年 ,龋患率较低 ,分别为 1.6% ,2 .8%。结论 :ART封闭试验 3年的保存率较高 ,新生龋发生率低 ;作为恒牙龋病防治的措施是适合和可接受的 ;是一种适合于在学校、社区开展的有效、实用的龋病预防方法。     

Treatment time analysis for extensive amalgam restorations

The treatment times for the fabrication of Extensive Amalgam Restorations (EAR) as recorded in a longitudinal clinical trial at the Dental School in Nijmegen were analyzed. 269 EAR's with different retention methods were made on molars by three operators. A mean total treatment time of 60 min was found. The factor operator had a significant influence on all treatment phases resulting in a 26% difference in total treatment time between operators. Also significant influences were found in some treatment phases for the factor retention, side location of the tooth and extension of the restoration. The results of this study with regard to treatment times must be considered from the perspective of the quality of the care provided.     

釉质发育不全乳牙的超微形态研究

目的：观察不同类型乳牙釉质发育不全的超微表面形态，分析其在分类、致病机制、龋齿易感性中的意义。方法：将发育不全的乳牙固定脱水，临界点干燥，喷金镀膜，日立S－450扫描电子显微镜观察，加速电压20kV。结果：发育不全釉质中存在不同程度形态缺损，病报部位还存在矿化不良。结论：釉质发育不全不仅有釉质量的减少，而且有质的改变，因而可能提高了发育不全釉质对龋齿的易感性。     

局麻下深龋充填对成人牙科畏惧症的影响

目的　探讨局麻下深龋充填对成人牙科畏惧症的影响。方法　采用Corah’s牙科畏惧症评分法 ,筛选出 10 0例需深龋充填的DF成人患者 ,分为实验组与对照组。实验组在局麻下行深龋充填术 ,对照组则为常规的牙科治疗。结果　实验组DF程度明显降低 ,与治疗前以及对照组比较都有显著性差异 (P <0 .0 1)。牙科治疗过程中两组脉搏的变化有显著性差异 (P <0 .0 1)。结论　局麻下行深龋充填术 ,对成人牙科畏惧症有治疗作用     

The orthopan tomoscintigram — a new application of emission computed tomography for facial bone scanning

The exact regional correlation of findings of facial bone scans, planar or SPECT, to dental orthopan X-ray films (OPT) is difficult because of the very different projection techniques. To improve correlative imaging in this regard a projection algorithm was developed that uses SPECT data of the skull for reconstructing an orthopan tomoscintigraphic projection. Fourteen conventional SPECT slices of the upper and lower jaws were obtained during bone scanning. All mandibular slices were superimposed resulting in a horseshoe shaped structure, which was marked by an ROI which was divided into segments. All 14 SPECT slices were then masked by this segmental ROI, thereby marking the teeth-carrying bone in all slices. The information from this horseshoe like ROI is then transformed into lines. Line by line arrangement results in an orthopan projection, the orthopan tomoscintigram. This new display allows 1:1 true scale superimposition with the X-ray OPT and markedly facilitates correlative imaging.     

变形链球菌F-ATP酶亚基基因uncA遗传多态性的研究

目的研究变形链球菌临床分离株耐酸因子F—ATP酶亚基α的结构基因uncA的遗传多态性，并探讨基因多态性与细菌耐酸力及龋病发生的关系。方法分别从高龋、无龋个体中分离变形链球菌34和30株，其中包括18株高耐酸株、20株低耐酸株。从细菌组DNA扩增uncA，行限制性内切酶长度多态性分析（RFLP）及核酸测序比较。结果不同限制性内切酶RFLP产生不同的基因型，测序证实了导致多态出现的基因变异；内切酶Hph Ⅰ产生的A、B基因型在不同患龋个体分离菌株的分布不同（P〈0．05），A型uncA在高龋分离株的检出率高于无龋分离株；内切酶MboⅡ产生的C、D基因型在不同耐酸力菌株中的分布不同（P〈0．05），C型uncA在高耐酸力菌株的检出率高于低耐酸力菌株。结论变形链球菌F—ATP酶的α亚基基因uncA具有明显遗传多态性，酸性环境下生存力强的菌株可能出现基因的适应性变异，不同基因型uncA分布与菌株的耐酸力及致龋力相关。     

The bactericidal activity of pulsed Nd-YAG laser radiation in vitro

Pulsed Nd-YAG laser irradiation of bacteria has been suggested as a possible means of treating contaminated intra-oral sites although relatively few studies have been conducted. In this investigation, the antimicrobial activity of a pulsed Nd-YAG laser was assessed in vitro for a range of oral bacteria using several pulse energies and exposure durations. Pure cultures of each organism were lased in saline suspensions followed by standard colony counting techniques for test and control samples. Microbial inhibition was found to be organism-dependent and varied with energy dose and pulse energy. For all nine test species 120-mJ laser pulses proved more efficient than 80-mJ pulses, with 99.9% kills compared with around 90% kills after exposure to 1800 pulses. These killing activity levels compare favourably with those achieved with other lasers in vitro.