Biomedical subjects

Eugene Chan

Publications and source records attributed to Eugene Chan.

3 recordsLinked to original sources

PubMed2006

Physical properties of root cementum: part 7. Extent of root resorption under areas of compression and tension.

INTRODUCTION: The aim of this article was to quantify the extent of root resorption in areas of compression or tension under light and heavy buccal tipping orthodontic forces. METHODS: The sample consisted of 36 premolars in 16 patients. On 1 side, light (25 g) or heavy (225 g) buccal tipping orthodontic forces were activated for 28 days. The contralateral side in each patient served as the control (0 g). The teeth were extracted, disinfected, imaged under a scanning electron microscope, and analyzed with commercial stereo imaging computer software modified for this study. Buccal and lingual surfaces were divided into 3 equal regions: cervical, middle, and apical. The root surface areas of these regions were documented with straight-on images. Quantification of resorption craters by using volumetric analysis was performed from stereo images taken at +/-3 degrees. The degree of resorption was correlated to the amount of surface area under compression or tension. RESULTS AND CONCLUSIONS: The buccal cervical region had 8.16-fold more root resorption in the heavy-force group compared with the light-force group (P <.01). The other regions did not seem to have significant differences in the force levels. In the experimental teeth, there was more root resorption in the high-compression regions than in the other regions (P <.01). There were similar amounts of resorption per unit area on the lingual apical and buccal cervical regions. Regions under compression had more root resorption than regions under tension. There was more resorption in regions under heavy compression than in regions under light compression (P <.01). There was also more root resorption in regions under heavy tension than in regions under light tension (P <.01).

Adolescent↗

PubMed2005

Physical properties of root cementum: Part 5. Volumetric analysis of root resorption craters after application of light and heavy orthodontic forces.

BACKGROUND: In previous studies on root resorption, resorption was quantified by making histologic cuts or by surface area measurements of resorption craters. The aims of this study were to evaluate the effects of orthodontic force magnitude on root resorption craters with volumetric measurements and also to identify the sites that might be predisposed to resorption. METHODS: After an experimental time of 28 days, 36 human premolars previously divided into light-force (25 g) and heavy-force (225 g) groups were extracted and prepared for scanning electron microscope imaging. Pairs of stereo images were taken, and 3-dimensional quantitative volumetric analysis was performed with commercial software. RESULTS AND CONCLUSIONS: The mean volume of the resorption crater in the light-force group was 3.49-fold greater than in the control group; the mean volume of the resorption crater in the heavy-force group was 11.59-fold greater than in the control group ( P < .001). The heavy-force group had 3.31-fold greater total resorption volume than the light-force group ( P < .001). Buccal cervical and lingual apical regions had significantly more resorption craters than the other regions ( P < .001). There was more resorption by volume in the heavy-force group compared with the light-force group and controls. Although more resorption was recorded in the light-force group, the difference in the amount of resorption between the light-force and control groups was not statistically significant. There was significantly more resorption on the buccal cervical and lingual apical regions of the root surfaces than on the other regions, suggesting that high-pressure zones might be more susceptible to resorption after 28 days of force application.

Adolescent↗

PubMed2005

A life-like virtual cell membrane using discrete automata.

A framework is presented that captures the discrete and probabilistic nature of molecular transport and reaction kinetics found in a living cell as well as formally representing the spatial distribution of these phenomena. This particle or agent-based approach is computationally robust and complements established methods. Namely it provides a higher level of spatial resolution than formulations based on ordinary differential equations (ODE) while offering significant advantages in computational efficiency over molecular dynamics (MD). Using this framework, a model cell membrane has been constructed with discrete particle agents that respond to local component interactions that resemble flocking or herding behavioural cues in animals. Results from simulation experiments are presented where this model cell exhibits many of the characteristic behaviours associated with its biological counterpart such as lateral diffusion, response to osmotic pressure gradients, membrane growth and cell division. Lateral diffusion rates and estimates for the membrane modulus of elasticity derived from these simple experiments fall well within a biologically relevant range of values. More importantly, these estimates were obtained by applying a simple qualitative tuning of the model membrane. Membrane growth was simulated by injecting precursor molecules into the proto-cell at different rates and produced a variety of morphologies ranging from a single large cell to a cluster of cells. The computational scalability of this methodology has been tested and results from benchmarking experiments indicate that real-time simulation of a complete bacterial cell will be possible within 10 years.

Cell Membrane↗