Morphometric analysis of digital radiographic bone images for trabecular bone structure

A morphometric analysis system of digital radiographic images was constructed for the clinical evaluation of bone trabecular structural change. This system consisted of computed radiography, a mathematical morphological filter, skeletal morphometric measurements, star volume analysis, and node-strut analysis. The computed radiographic data were morphologically processed, and the trabecular structure was extracted as binary skeletal images. Analyses were made with regard to the skeletal number, separation, perimeter, complexity, continuity, and connectivity. A trial study of this system was used to evaluate the therapeutic efficacy of vitamin K₂ in the osteoporotic patients. The system enabled the quantitative evaluation of bone trabecular structural change. Significant differences were observed in the parameters of the skeletal perimeter, skeletal number, and skeletal connectivity in the femur, and improvements in the trabecular structure were indicated. In the lumbar vertebra, significant differences were observed in nearly the same parameters as the femur, although the trabecular structure had deteriorated. These results suggest that the system for bone morphometric analysis of digital radiographic images is useful for the evaluation of structural change in bone trabeculation. Source of support This work was performed at Kanagawa Dental College, Research Center of Advanced Technology for Craniomandibular Function and was supported by a grant-in-aid for Bioventure Research from the Japanese Ministry of Education, Culture, Sports, Science, and Technology.     

Measurement of stain on extracted teeth using spectrophotometry and digital image analysis

Abstract: Aim: The aim of this study was to assess the reliability and validate a customized image analysis system, designed for use within clinical trials of general dental hygiene and whitening products, for the measurement of stain levels on extracted teeth and to compare it with reflectance spectrophotometry. Method: Twenty non‐carious extracted teeth were soaked in an artificial saliva, brushed for 1 min using an electric toothbrush and a standard toothpaste, bleached using a 5.3% hydrogen peroxide solution and cycled for 6 h daily through a tea solution. CIE L* values were obtained after each treatment step using the customized image analysis system and a reflectance spectrophotometer. A statistical analysis was carried out in SPSS. Results: Fleiss’ coefficient of reliability for intra‐operator repeatability of the image analysis system and spectrophotometry was 0.996 and 0.946 respectively. CIE L* values were consistently higher using the image analysis compared with spectrophotometry, and t‐tests for each treatment step showed significant differences (P < 0.05) for the two methods. Limits of agreement between the methods were ?27.95 to +2.07, with a 95% confidence of the difference calculated as ?14.26 to ?11.84. The combined results for all treatment steps showed a significant difference between the methods for the CIE L* values (P < 0.05). Conclusion: The image analysis system has proven to be a reliable method for assessment of changes in stain level on extracted teeth. The method has been validated against reflectance spectrophotometry. This method may be used for pilot in vitro studies/trials of oral hygiene and whitening products, before expensive in vivo tests are carried out.     

The influence of simulated masticatory loading regimes on the bi-axial flexure strength and reliability of a Y-TZP dental ceramic

OBJECTIVES: The purpose of the current study was to examine the influence of simulated masticatory loading regimes, to which all-ceramic crown or bridge restorations will routinely be subjected during their service-life, on the performance of a yttria-stabilised tetragonal zirconia polycrystalline (Y-TZP) dental ceramic. METHODS: Ten sets of 30 Y-TZP ceramic discs (13 mm diameter, 1.48-1.54 mm thickness) supplied by the manufacturer were randomly selected. Six groups were loaded for 2000 cycles at 500 N (383-420 MPa), 700N (536-588 MPa) and 800 N (613-672 MPa) with three groups maintained dry and the remaining three groups loaded while immersed in water at 37+/-1 degrees C. A further two groups underwent extended simulated masticatory loading regimes at 80 N (61-67 MPa) for 10(4) and 10(5)cycles under dry conditions. The mean bi-axial flexure strengths, standard deviations and associated Weibull moduli (m) were determined. The surface hardness was also determined using the Vickers hardness indentation technique. RESULTS: No significant difference (P>0.05) was identified in the bi-axial flexure strength of the simulated masticatory loading regimes and the control specimens loaded dry or wet. A significant increase in m was identified for the Y-TZP specimens following loading while immersed in water (8.6+/-1.6, 8.5+/-1.6 and 10.3+/-1.9) compared with the control (7.1+/-1.3). However, the extended loading regime to 10(5)cycles resulted in a significant reduction in the m of the Y-TZP specimens (5.3+/-1.0) compared with the control. Localised areas of increased surface hardness were identified to occur directly beneath the spherical indenter. CONCLUSIONS: The occurrence of localised areas of increased surface hardness could be the result of either a transformation toughening mechanism or crushing and densification of the material beneath the indentor manifested as the formation of a surface layer of compressive stresses that counteracted the tensile field generated at the tip of a propagating crack which increased the Weibull modulus of the Y-TZP specimens. The reduced reliability of the Y-TZP specimens loaded to 80 N for 10(5)cycles was associated with the accumulation of subcritical damage as a result of the extended nature of loading.     

3-D Finite element analysis of all-ceramic posterior crowns

The purpose of this study was to evaluate the stress distribution under various loading conditions within posterior all-ceramic crowns. A three-dimensional finite element model representing a lower first molar was constructed. Variations of the model had two types of single layer all-ceramic crowns (Dicor and Empress) and two types of double layer all-ceramic crowns (In-Ceram and Empress2) cemented. A load of 600 N, simulating the maximum bite force, was applied vertically to the crowns. Loads of 225 N, simulating masticatory force, were applied from three directions (vertically, at a 45 degrees angle, and horizontally). In the test simulating maximum bite force, the maximum tensile stresses on all crowns (17.4-19.4 MPa) concentrated around the loading points. In the masticatory force simulation test, the specimens experienced maximum tensile stresses of 19.7-27.0 MPa under a horizontal load and 10.8-10.9 MPa under a vertical load. When the load was applied horizontally, the maximum tensile stress was observed around the loading points on the surface in the case of the single layer crowns, and of the cervical area of the inner core of the double layer crowns. Within the limitation of this study, it was found that the strength of occlusal contact points is important to the integrity of posterior all-ceramic crowns and that bite forces applied from the horizontal direction are a critical factor.     

梯度旋转下降法修复单侧完全性唇裂的初步研究

目的探讨梯度旋转下降法修复单侧完全性唇裂的术后效果。方法分析85例单侧完全性唇腭裂患儿的术前，术后即刻以及术后一年的面部石膏模型唇部指标，同时比较这85例单侧完全性唇腭裂患儿术后一年的唇部指标与相似年龄的45例单纯不完全性腭裂患儿的唇部指标。结果在术后即刻虽然健患侧唇高、健患侧唇宽的差值减小，但其健患侧仍不协调。术后一年，健患侧唇高和健患侧唇宽都达到协调。与对照组进行比较，唇高在术后一年恢复到正常值，而唇宽在一年后无论是健侧还是患侧，仍然低于正常值。结论采用梯度旋转下降法修复单侧完全性唇裂可以达到一个很好的唇部美观效果。     

Fracture strength of teeth with flared root canals restored with glass fibre posts

OBJECTIVE: To investigate the fracture strength and pattern of failure of teeth with weakened roots reconstructed by different procedures. METHODS: In an in vitro study root posts were placed in 50 endodontically treated canines, divided into 5 groups (n=10) as follows: cast metallic post; glass fibre post with smaller diameter than the root canal; glass fibre post with smaller diameter than the root canal + glass fibre strips; glass fibre post with smaller diameter than the root canal + accessory glass fibre posts; anatomical post (glass fibre post with smaller diameter than the root canal, relined with low viscosity composite resin). Posts were luted with resin cement and the coronal portion of posts was constructed with composite resin. Metallic crowns were cemented on the posts. Specimens were submitted to compressive load in a universal testing machine. Fracture strength values of each group were compared. RESULTS: Fracture strength values were for Groups 1-5 respectively: 1087.06; 745.69; 775.41; 920.64; 876.12kgf, with significant differences between Groups 1 and 2 and between Groups 1 and 3 (p<0.05). Observed patterns of fracture were: Group 1 - 100% of roots fractured; Groups 2 and 4 - variable fracture modes; Group 3 - 60% of fractures occurred in the cervical root third; Group 5 - 50% of failures occurred in the coronal portion of the post. CONCLUSIONS: The fracture strength of teeth with cast metallic posts, teeth with anatomical posts or teeth with glass fibre posts combined with accessory posts was similar. All teeth restored with cast metallic posts presented fractures and were unfavourable to maintenance of the remaining tooth structure. Teeth with fibre posts (Groups 2 to 5) presented variable fracture modes; however, the maximum percentage of unfavourable fractures was 30%.     

X连锁无汗性外胚叶发育不全家系ED1基因的突变检测

目的探讨国内X连锁无汗性外胚叶发育不全家系中ED1基因的突变情况，为该病的遗传咨询、产前诊断、确诊携带者提供依据。方法收集2个X连锁无汗性外胚叶发育不全家系及1个散发患者的外周血样本，盐析法提取基因组DNA，采用聚合酶链反应（polymerase chain reaction，PCR）和直接测序对ED1基因进行突变检测。结果家系一患者ED1基因第9外显子发生错义突变（1045G〉A），家系二和散发患者ED1基因第3外显子发生错义突变，分别为467G〉A和466C〉T。结论ED1基因的错义突变可导致X连锁无汗性外胚叶发育不全。这3个突变与国外学者的报道一致。     

Mechanical behavior of ProTaper universal F2 finishing file under various curvature conditions: a finite element analysis study

Introduction

The purpose of this study was to visualize the stresses and strain distribution patterns in ProTaper Universal F2 files (Dentsply Maillefer, Ballaigues, Switzerland) and to establish the stress- and strain-curvature relationship for this instrument under various conditions by using a dynamic, three-dimensional finite-element model.

Methods

An accurate geometric model of a ProTaper Universal F2 instrument was created. Two short, straight tubes were also modeled to represent the parts of root canal apical and coronal to the curvature. Then, the file was constrained to a curve of varying degree, curve length, and position. The maximum von Mises stress and strain on the tension side of the instrument was measured at 5-degree intervals in a numerical simulation package (LS-DYNA; Livermore Software Technology, Livermore, CA).

Results

The mechanical performance of the ProTaper F2 file under various conditions was simulated. A long curvature length produced lower values of stress and strain under the same angle of curvature. An increase in the curvature angle generally induces higher stress and strain. For the same degree and curve length, the stress and strain increased if the curved portion was situated further up the shaft of the instrument (ie, with a larger diameter).

Conclusions

The dynamic, numerical model may be used to evaluate and compare the effect of various root canal curvatures on the behavior of different designs of root canal instrument. The magnitude of stress and strain imposed on the instrument is influenced by the abruptness and degree of curvature as well as the location of the curved portion.     

瓷层厚度影响金瓷界面抗断裂能力的初步研究

目的：采用云纹干涉法结合界面断裂力学研究瓷厚度对金瓷界面抗断裂能力的影响。方法：比较瓷厚度分别为0．5mm,1.5mm,2.5mm的试件（金属均为0．5mm)界面断裂韧性Jc并观测裂纹扩展。结果：0．5mm组试件的Jc值及承受最大载荷均值（2．813N/m,9.979N)低于1．5mm及2．5mm组（5．395N／m,19.134N与5．429N/m,19.256N).1.5mm与0．5mm组试件，裂纹易沿界面扩展。结论：（1）瓷厚度为1．5mm与2．5mm组的金瓷界面抗断裂能力相当，厚度为0．5mm时减弱，（2）瓷厚度为1．5mm与0．5mm组的界面裂纹易沿界面扩展，厚度为2．5mm组易向瓷层内扩展。     

110例上海地区正常合汉族成人软组织侧貌的X线头影测量分析研究

本文对上海地区正常胎成人作了软组织侧貌的头影测量分析，认为侧貌形态的数值化测量，较目测或照片提供了更为可靠的疗效评价依据，其测量指标，对正颌外科手术设计，有重要的参考价值，甚至具有决定作用。