Impact of dose reduction and the use of an advanced model-based iterative reconstruction algorithm on spectral performance of a dual-source CT system: A task-based image quality assessment

PurposeTo assess the impact of dose reduction and the use of an advanced modeled iterative reconstruction algorithm (ADMIRE) on image quality in low-energy monochromatic images from a dual-source dual energy computed tomography CT (DSCT) platform.Materials and methodsAcquisitions on an image-quality phantom were performed using DSCT equipment with 100/Sn150 kVp for four dose levels (CTDI_vol: 20/11/8/5mGy). Raw data were reconstructed for six energy levels (40/50/60/70/80/100 keV) using filtered back projection and two levels of ADMIRE (A3/A5). Noise power spectrum (NPS) and task-based transfer function (TTF) were calculated on virtual monoenergetic images (VMIs). Detectability index (d′) was computed to model the detection task of two enhanced iodine lesions as function of keV.ResultsNoise-magnitude was significantly reduced between 40 to 70 keV by ?56 ± 0% (SD) (range: ?56%–?55%) with FBP; ?56 ± 0% (SD) (?56%–?56%) with A3; and ?57 ± 1% (SD) (range: ?57%–?56%) with A5. The average spatial frequency of the NPS peaked at 70 keV and decreased as ADMIRE level increased. TTF values at 50% were greatest at 40 keV and shifted towards lower frequencies as the keV increased. The detectability of both lesions increased with increasing dose level and ADMIRE level. For the simulated lesion with iodine at 2 mg/mL, d’ values peaked at 70 keV for all reconstruction types, except for A3 at 20 mGy and A5 at 11 and 20 mGy, where d’ peaked at 60 keV. For the other simulated lesion, d’ values were highest at 40 keV and decreased beyond.ConclusionAt low keV on VMIs, this study confirms that iterative reconstruction reduces the noise magnitude, improves the spatial resolution and increases the detectability of enhanced iodine lesions.     

The Effect of Water Absorption on Acrylic Surface Properties

PURPOSE: The aim of the present study was to determine whether an increased water content during thermal cycling of hot water-treated acrylic was associated with a reduction in surface hardness and an increased opacity or whitening of the surface. MATERIALS AND METHODS: Ten acrylic samples were treated with 30 soak cycles (cycle duration, 24 hours), using warm water (40 degrees C) and an alkaline peroxide tablet (Efferdent control group); a further ten samples were treated with boiling water (100 degrees C) and one Efferdent tablet (experimental group). Indentation hardness of the acrylic specimens was measured prior to and immediately following the completion of the warm and hot water treatments, using an automated micro-indentation system. The hydrated acrylic specimens were then allowed to air dry at room temperature (20 degrees C) and were weighed weekly until they had obtained a constant dry weight. The loss in weight of the acrylic specimens represented the maximum water absorption. RESULTS: The hot water-treated specimens were much whiter than the warm water-treated specimens. The mean reduction in hardness (H(IT)) of the acrylic specimens following the treatment with hot water and alkaline peroxide tablet was 12.9%. Treatment with warm water and alkaline peroxide resulted in a slight increase in mean hardness (2.63%). There was a significant correlation between the water content of the acrylic specimens after treatment and the percentage of change in indentation hardness (r= 0.495, p= 0.026). CONCLUSIONS: The hot water treatment of the acrylic was associated with a significant reduction in hardness. We attribute the whitening and reduction in the hardness of the hot water-treated specimens to absorption of water and a disruption of the acrylic surface structure.     

两种漂白剂去除牙面色斑效果的分析

目的研究两种漂白剂去除牙面色斑的效果。方法使用洛贝指数和数码照像计算机色度分析,系统分析并比较实验前、后牙面洛贝指数和色斑占牙面百分比的变化。结果两种漂白剂使用2周后与空白对照组比较洛贝指数的3个指标相差显著(P<0.01);色斑占牙面百分比减小。结论两种漂白剂都能去除牙面色斑。     

A comparison of two chlorhexidine gel brushing regimens and a conventional toothpaste brushing regimen for the development of tooth staining over a 6-week period

Abstract:  Aims:  A single-centre, randomized single-blind parallel study was undertaken to compare staining seen with three brushing regimens and to determine subject perception of side effects such as staining and effects on taste. Methods:  This 6-week parallel study used 157 volunteers who were randomized into one of three treatment groups: (i) brushing in the morning and evening with a normal dose of a 1% chlorhexidine gel, (ii) brushing with a low dose of chlorhexidine gel in the evening and a whitening dentifrice in the morning, and (iii) brushing with a standard fluoride paste in the morning and evening. Following home usage of their allocated products, the study volunteers returned after 3 and 6 weeks to record the amount of stain present. After the 6-week period, subject perception of taste and stain acceptability was determined using a questionnaire. Results:  After 6 weeks of use of the low-dose chlorhexidine gel and whitening dentifrice, significantly more stain was seen compared with the use of a standard dentifrice ( P  < 0.0001). Similarly, significantly more stain was seen with use of the normal-dose chlorhexidine gel compared with the low-dose gel and whitening dentifrice ( P  = 0.0007). Approximately 30% of individuals on the low-dose chlorhexidine gel regimen found the amount of stain unacceptable and 10% noted an effect on their taste perception. Conclusions:  The use of low dose of chlorhexidine gel at night and a whitening paste in the morning produced a significant amount of stain that 30% of subjects considered unacceptable.     

In vitro efficacy of a whitening toothpastecontaining calcium carbonate and perlite

Objectives : The studies described in this paper aimed to assess the stain removal efficacy, fluoride efficacy and abrasivity to enamel and dentine of a new whitening toothpaste containing calcium carbonate and perlite, using appropriate in vitro models. Methods : Stain removal efficacy was assessed using the pellicle cleaning ratio (PCR) method. Fluoride efficacy was assessed using remineralisation, demineralisation and fluoride‐uptake methods. Abrasivity was assessed using an enamel and dentine wear method. Results : The results showed that the new whitening toothpaste was able to remove extrinsic tooth stain more effectively than three commercially available toothpaste formulations. The fluoride efficacy was superior to a non‐fluoridated control and was not significantly different to a clinically tested fluoride‐containing toothpaste. The abrasivity data showed that the calcium carbonate/perlite toothpaste is no more abrasive to enamel or dentine than two other commercially available whitening toothpastes. Conclusions : The studies show that the new whitening toothpaste is effective in extrinsic stain removal, has an efficacious fluoride source and does not have an undue degree of abrasivity to enamel or dentine compared to other relevant commercially available products.     

Review of the extrinsic stain removal and enamel/dentine abrasion by a calcium carbonate and perlite containing whitening toothpaste

There has been an increase in the demand from consumers and patients for products that whiten teeth. To meet this demand, a whitening toothpaste containing calcium carbonate and perlite as the abrasive system and an efficacious fluoride source has recently been launched. The aim of the current paper is to review the toothpaste's stain removal efficacy and its effects on enamel and dentine wear. It has been shown to be effective at removing model extrinsic stain in vitro. Further, it has been shown to be more effective in removing naturally occurring extrinsic tooth stain than a silica non-whitening control toothpaste after two weeks of twice daily brushing in a parallel group, double-blind clinical study using 152 adult volunteers. In addition, the enhanced whitening effect did not give a clinically relevant level of wear to enamel or a significant increase in dentine wear compared to marketed non-whitening toothpaste formulations, as shown by using an in situ type model with ex vivo brushing.     

基于中医药美白理论的白及研发思考

白及是传统美白方中的主要药物。从中医药美白理论、中医美白历史沿革、美白药理作用机制,以及白及"以白治黑"相关的化学成分、白及美白研究现状等多个角度,系统阐述了白及美白的传统理论基础和现代药理研究概况,并初步提出白及美白产业化研发思路。为中药白及美白产品开发和产业化提供思路和参考。     

Beyond冷光美白诊室法与家庭法治疗着色牙的效果比较

目的比较Beyond冷光美白诊室法与家庭法治疗着色牙的效果。方法实验组20例病人以Beyond冷光美白仪进行诊室内漂白,对照组20例病人以Beyond冷光美白套装进行家庭漂白治疗。用VITA比色板进行美白治疗前后颜色的对比并进行组间比较。结果实验组的脱色显效率为85%,对照组的脱色显效率为50%,两组比较差异有显著性（χ^2=4.00,P〈0.05）。两组有效率分别为95%、90%,两组比较差异无显著性（χ^2=0.00,P〉0.05）。结论Beyond冷光美白诊室法与家庭冷光美白法治疗着色牙均是有效的,并且无明显副作用,但诊室法脱色效果优于家庭法。