ABSTRACT
<p><b>OBJECTIVE</b>The purpose of this study was to observe the morphological changes of toothmarks in pocket limbs and to explore the durative development of bitemarks.</p><p><b>METHODS</b>Firstly a toothmark model was established by using a universal testing machine and a self-made incisor nod which was pressed particularly on pocket limbs. The changes of toothmarks were observed on alive and dead animals with time elapsing. The scopes of bruise and inden were analyzed by soft on digital photos. The depth data of inden were collected by three dimensional laser measurement.</p><p><b>RESULTS</b>The changes in the alive group were faster than that in dead group. There was no obvious fadeaway of bruise during 24 h. The scopes of inden were decreased remarkably in 1 h, while the decrease slowed down in the following hours.</p><p><b>CONCLUSION</b>The changes of indent are fast in pocket limb. It implies that bitemark evidence should be collected as fast as possible in cases.</p>
Subject(s)
Animals , Humans , Bites, Human , Forensic Dentistry , LasersABSTRACT
<p><b>OBJECTIVE</b>To investigate the cyclic fatigue modes of Vita mark II machinable ceramics under Hertzian's contact.</p><p><b>METHODS</b>Hertzian's contact technique (WC spheres r = 3.18 mm) was used to investigate the cyclic fatigue of Vita mark II machinable ceramic. All specimens were fatigued by cyclic loading in moist environment, furthermore, surviving strength was examined by three point test and morphology damage observation.</p><p><b>RESULTS</b>In homogeneous Vita mark II machinable ceramics, two fatigue damage modes existed after cyclic loading with spheres under moist environment, including conventional tensile-driven cone cracking (brittle mode) and shear-driven microdamage accumulation (quasi-plastic mode). The latter generated radial cracks and deeply penetrating secondary cone crack. Initial strength degradation were caused by the cone cracks, subsequent and much more deleterious loss was caused by radial cracks.</p><p><b>CONCLUSION</b>Cyclic fatigue modes of Vita mark II machinable ceramics includes brittle and quasi-plastic mode.</p>
Subject(s)
Humans , Ceramics , Dental Porcelain , Materials Testing , Surface PropertiesABSTRACT
<p><b>OBJECTIVE</b>To compare the difference in strength degradation and morphology damage of brittle dental ceramic after static load and cyclic fatigue.</p><p><b>METHODS</b>Hertzian's contact technique with a tungsten carbide sphere was used to investigate the response of feldspathic dental porcelain to static load and cyclic fatigue. All specimens were subjected to static or cyclic loading in moist environment. Furthermore the surviving strength of specimens was examined by the three-point test and the morphology damage was observed. Statistical analyses were performed with ANOVA and a P-value less than 0.05 was considered to be significant.</p><p><b>RESULTS</b>Outer cone crack and associated strength degradation simultaneously occurred both after the first cyclic loading and static loading. Up to 1,000 cycles, the specimens showed inner cone cracks and strength degradation was aggravated. No significant difference in the strength degradation among all static loading specimens and no inner cone cracks occurred in static loading specimens.</p><p><b>CONCLUSIONS</b>Both static and cyclic fatigue influence dental ceramic strength, but cyclic fatigue is more deleterious.</p>
Subject(s)
Compressive Strength , Dental Porcelain , Materials TestingABSTRACT
Objective To study soil environment characteristics of high_mortality areas of esophageal cancer in Three Gorge dam region. Methods To contrast the disparity of soil type,soil use,and basic characteristics,in particular microelement contents in high_mortality area and low_mortality area of esophageal cancer. Results Calcareous purple soils distributed dominantly in high_mortality area,and soil pH and CaCO3 content was high,and soil fertility low. While paddy soils occupyed mainly in low_mortality area,and pH and CaCO3 content was low however soil fertility high.Moreover,the microelement contents in soils in high_mortality area were lower than those in low_mortality area apparently. Conclusion Mortality of esophageal cancer was closely relative to the contents of some microelements in the soil environment.