Influence of the restorative procedure factors on stress values in premolar with MOD cavity: a finite element study

In order to investigate the influence of cusp reduction, cavity isthmus width, and restorative material on stress values in premolar with mesio-occlusal-distal (MOD) cavity, numerical simulations were done on three-dimensional (3D) models of a maxillary second premolar designed using computerized tomography (CT) scan images. The use of four restorative materials (direct resin composite, direct resin composite with resin-modified glass-ionomer cement as the base, indirect resin composite, ceramic), three cavity preparation designs (without cusp coverage, 2-mm palatal cusp coverage, 2-mm palatal and buccal cusp coverage), and two cavity isthmus widths (1/2 and 2/3 intercuspal width) were simulated. After applying a static load of 200 N on the occlusal surface of the tooth, von Mises stresses in the enamel, dentin, and restoration were calculated using finite element analysis (FEA). Stress values in the enamel were primarily influenced by cavity preparation design, while restorative material showed higher contribution in dentin. The lowest stress values were obtained in models with cusp coverage and indirect restorations. Cavity isthmus width had minimal influence on stress values in tooth structures. None of the investigated factors determined stress values in the restoration. In conclusion, the use of ceramic restoration covering both palatal and buccal cusp provided the most favourable stress distribution of premolars with MOD cavity.

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不同厚度垫底材料对龋齿充填后应力分布的影响

目的采用有限元方法对比分析不同厚度垫底材料对充填后牙体应力分布的影响。方法选用正常形态下颌第1磨牙,基于MicroCT扫描建立Ⅰ类洞充填的三维有限元模型,选择Vitrebond和Dycal作为垫底材料,分别考虑4种不同的厚度(0.5、1.0、1.5和2.0mm),施加250N的咬合力,对各模型中牙体、充填体和垫底材料的最大/最小主应力进行比较。结果 Dycal垫底,厚度为2.0mm,牙体的最大主应力峰值超过其抗拉强度,垫底材料的最大/最小主应力峰值分别超过其抗拉和抗压强度;垫底厚度为1.5mm和2.0mm,充填体的最大主应力峰值接近其抗拉强度的90%。Vitrebond垫底时,各材料的最大主应力峰值也都在1.5mm或2.0mm时达到极值。结论从防止充填后牙体折裂的角度,建议临床上采用较薄的垫底层厚度,取0.5～1.0mm。     

A computational and experimental study inside microfluidic systems: the role of shear stress and flow recirculation in cell docking

In this paper, microfluidic devices containing microwells that enabled cell docking were investigated. We theoretically assessed the effect of geometry on recirculation areas and wall shear stress patterns within microwells and studied the relationship between the computational predictions and experimental cell docking. We used microchannels with 150 μm diameter microwells that had either 20 or 80 μm thickness. Flow within 80 μm deep microwells was subject to extensive recirculation areas and low shear stresses (<0.5 mPa) near the well base; whilst these were only presented within a 10 μm peripheral ring in 20 μm thick microwells. We also experimentally demonstrated that cell docking was significantly higher (p < 0.01) in 80 μm thick microwells as compared to 20 μm thick microwells. Finally, a computational tool which correlated physical and geometrical parameters of microwells with their fluid dynamic environment was developed and was also experimentally confirmed.     

Automated Method for Computing the Morphological and Clinical Parameters of the Proximal Femur Using Heuristic Modeling Techniques

Bone morphology and morphometric measurements of the lower limb provide significant and useful information for computer-assisted orthopedic surgery planning and intervention, surgical follow-up evaluation, and personalized prosthesis design. Femoral head radius and center, neck axis and size, femoral offset and shaft axis are morphological and functional parameters of the proximal femur utilized both in diagnosis and therapy. Obtaining this information from image data without any operator supervision or manual editing remains a practical objective to avoid variability intrinsic in the manual analysis. In this article, we propose a heuristic method that automatically computes the proximal femur morphological parameters by processing the mesh surface of the femur. The surface data are sequentially processed using geometrical properties such as symmetries, asymmetries, and principal elongation directions. Numerical methods identify the axis of the shaft of femur (least squares cylinder fitting), the head surface and center (least squares sphere fitting), and the femur neck axis and radius (minimal area of the cross section by evolutionary optimization). The repeatability of the method was tested upon 20 femur (10 left + 10 right) surfaces reconstructed from CT scans taken on cadavers. The repeatability error of the automated computation of anatomical landmarks, angles, sizes, and axes was less than 1.5 mm, 2.5°, 1.0 mm, and 3.5 mm, respectively. The computed parameters were in good agreement (landmark difference: <2.0 mm; angle difference: <2.0°; axes difference: <2.5°; size difference: <1.5 mm) with the corresponding reference parameters manually identified in the original CT images by medical experts. In conclusion, the proposed method can improve the degree of automation of model-based hip replacement surgical systems.     

Microsporidian parasites: a danger facing marine fishes of the Red Sea

Out of 600 marine fish from the Red Sea belonging to three different species that were collected and examined for microsporidian parasites, 87 (14.5%) fish were found to be infected. The infection was recorded as cysts or xenomas embedded in the gut epithelium and the peritoneal cavity of the three fish species. The highest percent of infection with microsporidian parasites was recorded in Saurida tumbil 19.5% (39/200) followed by Pagrus pagrus 15% (45/300) and the lowest percent of infection was recorded in Epinephelus chlorostigma 3% (three out of 100). After rupture of the cysts, the spores were released and examined by light microscopy. Each spore was elongated to ellipsoidal in shape and possessed a posterior vacuole which is characteristic to phylum Microspora. They measure 1.6 ± 0.5 μm (1.5–2.4 μm) × 1.3 ± 0.1 μm (1.3–2.0 μm) in Saurida tumbil and Pagrus pagrus, respectively. The spores of Pleistophora sp recorded from E. chlorostigma were ovoid to pyriform in shape and measure 1.9 ± 0.5 μm (1.8–2.7 μm) × 1.6 ± 0.4 μm (1.5–2.4 μm).     

Ultrastructure of a Sarcocystis sp. infecting skinks of the genus Agama

Macroscopically visible sarcocysts were observed in the skeletal muscles of naturally infected skinks of the genus Agama (infection rate 11.3%). Sarcocysts were described by means of transmission electron microscopy. These cysts measured 0.03–0.25 × 0.38–1.7 mm (mean 0.12 × 1.1 mm). Typical mature cysts were bordered by a primary cyst wall that measured 2.4–5.3 μm (mean 3.9 μm) and was folded into a few nonbranched finger-like protrusions measuring 0.7–1.5 × 1.0–2.5 μm (mean 1.2 × 1.5 μm). These protrusions contained granular elements, but filaments and tubular elements were not observed. A relatively thick, homogeneous tape was observed just underneath the primary cyst wall, measuring 0.5–1.0 μm (mean 0.8 μm) and containing a granulated ground substance in which filaments and tubular elements were not observed. Metrocytes measured 3.1–5.5 × 4.2–7.2 μm (mean 4.0 × 5.8 μm) and merozoites measured 1.2–3.3 × 4.4–8.6 μm (mean 2.6 × 7.5 μm). The fine ultrastructural characteristics of both metrocytes and merozoites were similar to those described for many Sarcocystis species and were generally nonspecific. Received: 21 February 2000 / Accepted: 1 March 2000     

Computational Stress Analysis of Atherosclerotic Plaques in ApoE Knockout Mice

The aortic sinus lesions of apolipoprotein E knockout (ApoE KO) mice seldom show any signs of fibrous cap disruption, whereas cap ruptures have been recently reported in the proximal part of their brachiocephalic arteries (BCA). We use histology based finite element analysis to evaluate peak circumferential stresses in aortic and BCA lesions from six 42–56 week-old fat-fed ApoE KO mice. This analysis is able to both explain the greater stability of aortic lesions in mice and provide new insight into the BCA lesion as a model for the stability of human lesions with and without microcalcifications in their fibrous caps. The predicted average peak stress in fibrous caps of aortic lesions of 205.8 kPa is significantly lower than the average value of maximum stresses of 568.8 kPa in BCA caps. The aortic plaque stresses only slightly depend on the cap thickness, while BCA lesions demonstrate an exponential growth of peak cap stresses with decreasing cap thickness similar to human vulnerable plaques. Murine BCA ruptured lesions with mean cap thickness of 2 μm show stresses ≈1400 kPa, three times higher than human ruptured plaques with a mean cap thickness of 23 μm without microcalcifications in the cap, but nearly identical to the peak stress around an elongated microcalcification with aspect ratio 2 in a human thin cap ≈50 μm thick. We predict biomechanical stress patterns in mouse BCA close to human vulnerable plaques without microcalcification in the cap, while aortic lesions show stress tendency similar to stable lesions in human.     

Effect of water storage time and composite cement thickness on fatigue of a glass-ceramic trilayer system

AIM: Static Hertzian contact tests of monolayer glass-ceramics in trilayer configurations (glass-ceramic/cement/composite) have shown that thick cement layers lower strength. This study sought to test the hypothesis that thick resin cement layers lower mouth motion fatigue reliability for flat glass-ceramic/cement/composite trilayer systems and that aging in water reduces reliability. METHODS: Dicor plates (n > or = 12 per group) (10 x 10 x 0.8 mm(3)) were aluminum-oxide abraded (50 microm), etched (60 s), silanized, and bonded (Rely X ARC) to water aged (30 days) Z100 resin blocks (10 x 10 x 4 mm(3)). Four groups were prepared: (1) thick cement layer (>100 microm) stored in water for 24-48 h, (2) thick cement layer stored for 60 days, (3) thin cement layer (< or =100 microm) stored for 24-48 h, and (4) thin cement layer stored for 60 days. The layered structures were fatigued (2 Hz) utilizing mouth motion loading with a step-stress acceleration method. A master Weibull distribution was calculated and reliability determined (with 90% confidence intervals) at a given number of cycles and load. RESULTS: The aged group (60 d) with thick cement layer had statistically lower reliability for 20,000 cycles at 150 N peak load (0.11) compared with both nonaged groups (24-48 h) (thin layer = 0.90 and thick layer = 0.82) and aged group with thin cement layer (0.89). CONCLUSION: Trilayer specimens with thick cement layers exhibited significantly lower reliability under fatigue testing only when stored for 60 days in water. The hypothesis was accepted. These results suggest that diffusion of water into the resin cement and also to the glass-ceramic interface is delayed in the thick cement specimens at 24-48 h. .     

Alteration of dentin–enamel mechanical properties due to dental whitening treatments

The mechanical properties of dentin and enamel affect the reliability and wear properties of a tooth. This study investigated the influence of clinical dental treatments and procedures, such as whitening treatments or etching prior to restorative procedures. Both autoclaved and non-autoclaved teeth were studied in order to allow for both comparison with published values and improved clinical relevance. Nanoindentation analysis with the Oliver–Pharr model provided elastic modulus and hardness across the dentin–enamel junction (DEJ). Large increases were observed in the elastic modulus of enamel in teeth that had been autoclaved (52.0 GPa versus 113.4 GPa), while smaller increases were observed in the dentin (17.9 GPa versus 27.9 GPa). Likewise, there was an increase in the hardness of enamel (2.0 GPa versus 4.3 GPa) and dentin (0.5 GPa versus 0.7 GPa) with autoclaving. These changes suggested that the range of elastic modulus and hardness values previously reported in the literature may be partially due to the sterilization procedures. Treatment of the exterior of non-autoclaved teeth with Crest Whitestrips?, Opalescence? or UltraEtch? caused changes in the mechanical properties of both the enamel and dentin. Those treated with Crest Whitestrips? showed a reduction in the elastic modulus of enamel (55.3 GPa to 32.7 GPa) and increase in the elastic modulus of dentin (17.2 GPa to 24.3 GPa). Opalescence? treatments did not significantly affect the enamel properties, but did result in a decrease in the modulus of dentin (18.5 GPa to 15.1 GPa). Additionally, as expected, UltraEtch? treatment decreased the modulus and hardness of enamel (48.7 GPa to 38.0 GPa and 1.9 GPa to 1.5 GPa, respectively) and dentin (21.4 GPa to 15.0 GPa and 1.9 GPa to 1.5 GPa, respectively). Changes in the mechanical properties were linked to altered protein concentration within the tooth, as evidenced by fluorescence microscopy and Fourier transform infrared spectroscopy.     

Thickness of Palatal Masticatory Mucosa and Its Relationship with Different Parameters in Turkish Subjects

Background: The aim of the study was to clinically investigate the mucosal variations in different parts of hard palate subject to soft tissue harvesting and its relationship with selected parameters in patients with gingival recessions.Materials & Methods: Fifty periodontally healthy, dentate subjects (13 males) with gingival recessions were enrolled into the study. After initial periodontal therapy they were scheduled for surgical procedures. Palatal masticatory mucosa of five teeth was evaluated at five different points from the gingival margin and two points on the buccal gingival mucosa were evaluated on the day of surgical intervention via bone sounding method. Totally 27 assessments were performed for each patient.Results: The overall mean thickness of palatal masticatory mucosa (PMM) was 2.55±0.49mm. The mean mid-facial gingival thickness was 1.11±0.39mm. The PMM showed an increase towards the posterior and raphe palatina. No difference was observed between genders, and no association of body mass index (BMI) and age with PMM was determined. An association was observed between the thicknesses of mid-facial gingival and palatal masticatory mucosa.Conclusion: The thickness of PMM in this study seems to be less than other reports possibly due to ethnicity or measurement design. Canine and premolar region reveals higher thickness values, and the increase in the tissue thickness towards the midline should also been taken into consideration. Clinicians planning soft tissue harvesting from the palate should take this variation into consideration. In this regard transmucosal probing of the donor site may provide valuable information where considerable variation exists.