My former research interests were centered mainly about Mechanical Engineering and Physics. I've now switched gears, so to say, and now am more interested in sustainable design, life-cycle analysis and design methodologies. That being said, I still keep in touch with what's happening in the engineering and physics worlds, as they're always blooming with interesting ideas and concepts.

Please e-mail me if you have any comments, queries, criticism, etc. about my work.

My past research projects:

1. Air Abrasion in Dentistry and Orthopaedics
2. Maple MCML

Air Abrasion in Dentistry and Orthopaedics

The goal of this project was to find the mass erosion rate of teeth via erosion from 50μm Aluminum Oxide (Al₂O₃) particles.

The official description of the project was:
Air Abrasion for Implant Removal in Revision Arthroplasty, establishing air abrasion as a technique that can be used effectively in both dentistry and orthopaedics.

As such, alot of work dealing with dentistry and air abrasion is being researched at the moment, and the first thing we want to do is the eroded depth as a function of angle with respect to the lingual or buccal surface and the abrasive stream. We want to find the optimal angle, and see if it behaves as a brittle material, i.e. follows the function:

e = C [v cos(θ)]^k where

• e ≡ erosion rate [grams enamel / grams Al₂O₃]
• v ≡ velocity of Al₂O₃
• &theta ≡ angle between stream and buccal or lingual surface
• C & k are experimental constants

By following this relationship, it would imply that enamel is a brittle material, which is our theory at the moment.
Preliminary results show that maximum erosion is achieved when the nozzle is orthogonal to the enamel surface, though I wasn't able to do enough tests such that the statistics are in our favour.

My term for this project has ended, and a new Graduate Student, Adedamola (Toby) Oladeinde, is starting where I left off, and furthering it into the orthopaedics field.

I have written a final report summarizing this project, and you can e-mail me (yip.dennis \at gmail.com) or my supervisor (mpapini \at ryerson.ca) if you would like to see it. I don't want to post it freely on the Internet because there is potentially confidential information contained within; however, listed below are articles and sites that I found very useful while doing this research project:

[1] White, Joel M (1998) Ablation rate, caries removal and restoration using Nd:YAG and Er:YAG lasers and air abrasion. Proceedings of SPIE. Volume 3248. 98 – 112.
[2] Horiguchi et. al. (1998) Selective Caries Removal with Air Abrasion. Operative Dentistry. Volume 23. 236 – 243.
[3] Kuriyagawa et. al. (2003) Selective Removal of Carious Dentine with the Micro Abrasive Jet Technology. Key Engineering Materials. Volumes 238 – 239. 405 – 415.
[4] Burke, L. and Greenland, J. (2006) Interim Report. Ryerson University. 16 – 17.
[5] Peruchi, C. et. al. (2002) Evaluation of cutting patterns produced in primary teeth by an air-abrasion system. Quintessence International. Volume 33. 279 – 283.
[6] Santos-Pinto, L. et. al. (2001) Effect of handpiece tip design on the cutting efficiency of an air abrasion system. American Journal of Dentistry. Volume 14, Number 6. 397 – 401.
[7] Chutimanutskul, W. et. al. (2005) Physical properties of human premolar cementum: hardness and elasticity. Australian Orthodontic Journal. Volume 21, Number 2. 117 – 221.
[8] Xu, H.H.K. et. al. (1997) Indentation Damage and Mechanical Properties of Human Enamel and Dentin. Journal of Dental Research. Volume 77, Number 3. 472 – 480.
[9] Boyde, A. (1984) Dependence of rate of physical erosion on orientation and density in mineralized tissues. Anatomy and Embryology. Volume 170. 57 – 62.
[10] Meredith, N. et. al. (1996) Measurement of the Microhardness and Young’s Modulus of Human Enamel and Dentine Using an Indentation Technique. Archives of Oral Biology. Volume 41, Number 6.
[11] Fuentes, V. et. al. (2003) Microhardness of superficial and deep sound human dentin. Journal of Biomedical Materials Research Part A. Volume 66A, Issue 4. 850 – 853.
[12] Marshall, G.W. et. al. (1997) The dentin substrate: structure and properties related to bonding. Journal of Dentistry. Volume 25, Number 6. 441 – 458.
[13] England, Gordon. “Calculator for Conversion between Vickers Hardness Number and SI Units MPa and GPa.” Independent Metallurgist & Consultant to the Thermal Spray Coating Industry.
[14] Poolthong S. Determination of the mechanical properties of enamel, dentine and cementum by the Ultra Micro-Indentation System. Thesis/dissertation, Faculty of Dentistry, University of Sydney, Australia, 1998.
[15] Braden, M. Physics in Dentistry. (1985) Phys. Technol. Volume 16. 58 – 62.
[16] Shillingburg, H.T. Jr and Grace, C.S. (1973) Thickness of Enamel and Dentin. Journal – Southern California Dental Association. Volume 41, Number 1. 33 – 52.
[17] Cuy, J.L. et. al. (2002) Nanoindetation mapping of the mechanical properties of human molar tooth enamel. Archives of Oral Biology. Volume 47. 281 – 291.
[18] Mahoney, E. et. al. (2000) The hardness and modulus of elasticity of primary molar teeth: an ultramicro-indentation study. Journal of Dentistry. Volume 28. 589 – 594.
[19] Weidmann, S.M. et. al. (1967) Variations of Enamel Density in Sections of Human Teeth. Archives of Oral Biology. Volume 12. 85 – 1967.

This work was supported by the Ryerson One Time Opportunity.

Maple MCML

I used the MCML technique to model light propagation with Maple 10.
The current version of my program, mcml2.71mw, is able to simulate light propagation through a multi-layered, finite or infinitely wide prism or cylinder shaped, turbid, isotropic or anisotropic layer of tissue as a function of different launch angles.
The total diffuse reflectance, transmittance, and absorbance values agree with L. Wang's and D. Côté's.
This work was supported by the NSERC USRA. Here are some results:
Results for n_relative = 1.5, thickness = 0.2 cm, μ_a=10 cm^-1, μ_s=90 cm^-1, g = 0

	Rsp	Rd	A	Td	Photons used
Maple	0.04	0.2052802768	0.4727351762	0.2819818992	5000
mcml	0.04	0.213914	0.459152	0.286935	50000

Results for n_relative = 1.33, thickness = 1 cm, μ_a=0.1 cm^-1, μ_s=10 cm^-1, g = 0.93

	Rsp	Rd	A	Td	Photons used
Maple	0.02005931018	0.1875868530	0.2500999096	0.5422517618	5000
Pol-MC (HG)		0.185	0.243	0.551	1000000
Pol-MC (Mie)		0.190	0.247	0.542	1000000
mcml	0.0200593	0.187742	0.2397	0.552499	100000

Picture of n_relative = 1.33, thickness = 1 cm, μ_a=0.1 cm^-1, μ_s=10 cm^-1, g = 0.93, with 100 photons

My supervisor & I have written a paper to publish our work: http://dx.doi.org/10.1016/j.cpc.2007.08.003

Here are some essential Monte Carlo Simulation of Light Propagation links:
→ D. Côté's Pol-MC [site]
→ L. Wang's Publications and main Monte Carlo program [site]
→ S. Prahl's paper -- A Monte Carlo Model of Light Propagation in Tissue [pdf]
→ S. Prahl's Monte Carlo Simulations and notes [site]