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Biomechanical Comparison of Reptilian and Mammalian Prismatic Enamel Microstructures

Biomechanical Comparison of Reptilian and Mammalian Prismatic Enamel Microstructures. By Ms. Vanousheh Ghandhari Ms. Reeshemah Burrell Dr. Hamid Garmestani Dr. Greggory Erickson. OBJECTIVES.

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Biomechanical Comparison of Reptilian and Mammalian Prismatic Enamel Microstructures

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  1. Biomechanical Comparison of Reptilian and Mammalian Prismatic Enamel Microstructures By Ms. Vanousheh Ghandhari Ms. Reeshemah Burrell Dr. Hamid Garmestani Dr. Greggory Erickson

  2. OBJECTIVES • Develop standardized methodology that can be used in the study of dental tissues in any animal, regardless of size. • Provide some of the first material property and performance data for iguanian lizard dentitions that can be used in future comparative analyses of dental biomechanics.

  3. OBJECTIVES • Compare the reptilian type-one enamel with mammalian enamel, to recognize similarities and dissimilarities. • i.e. determine if type-one enamel of Uromastyx iguana possesses similar material properties to the mammal Didelphis Opossum.

  4. PRISMATIC ENAMEL STRUCTURE Enamel Prisms (EP) Protein Sheath (PS) Hydroxy Apatite (HA) Crystallites

  5. PRISMATIC STRUCTURE Enamel prisms (EP): • Bundled hydroxy apatite crystallites bounded by a proteineous sheath (PS). • Set within a matrix of more loosely packed semi-parallel apatite crystallites • The first enamel prisms (Type I) are characterized by their round cross-sectional shape, equidistant spacing from one another within a crystalline matrix

  6. IGUANIAN TOOTH 10x Resin Dentin DEJ Bone Enamel Resin 120 m

  7. ENAMEL THICKNESS • Thickness of enamel on Didelphis (opossum) teeth was 164m  3.20 m • Thickness of enamel on Uromastyx (iguana) teeth were 120 m  1.38 m

  8. SAMPLE DONORS Uromastyx (Iguana) Didelphis (Opossum)

  9. SAMPLE PREPARATION • Samples were cold mounted into Epoxide compound (Buehler Ltd., Lake Bluff, IL) • Sample guides used to maintain correct tooth orientation while resin sets. • Samples were ground and polished with: • the RotoPol-21 at 150 rev/min with interchangeable water proof silicon carbide paper ranging from 1200 grains per inch (9m grit size) to 4000 grains per inch (3 m grit size) • 3 m diamond paste at 200 rev/min using the DP-Mol-wool woven polishing cloth, • Vibromet-2 vibrating polisher, consisting of 0.05 m colloidal silica solution with the PH of 9.0

  10. NANO-SCRATCH INSTRUMENT SETUP

  11. NANO-SCRATCH INSTRUMENT

  12. NANO-SCRATCH • A pre-scan and post-scan were performed in the same direction as the actual scratch so as to minimize material pile-up. • Pre-scan  a topological scan along the path of the proposed scratch that records the surface roughness and discontinuity of the sample. i.e. the initial profile of the sample is recorded. • Post-scan  allows the elastic recovery of the material to be investigated by providing a profile of the residual scratch path.

  13. NANO-SCRATCH • Purpose: Determine the influence of prisms in the wear process of iguanian tooth enamel • Method: Using a nano-scratch tester: • Apply a very small normal load 5 mN with a 2 mm radius conical diamond tip (Rockwell) • Move Rockwell tip across finely polished longitudinally and transversely cut specimens at 0.5 mm/min. • Scratches made parallel, perpendicular and oblique to the dentine enamel junction (DEJ). • ESEM micrographs to yield a pictorial representation of the scratches.

  14. NANO-SCRATCH TEST PARAMETERS

  15. Iguana Scratch Test Graph

  16. IGUANIAN TOOTH 20X20 Dentine Enamel Junction (DEJ) Scratches 120 m

  17. Didelphis Scratch Graph

  18. DIDELPHIS (Opossum) SCRATCHES Horizontal Scratches Vertical Scratches

  19. NANO-INDENTATIONINSTRUMENT SETUP

  20. NANO-INDENTER

  21. NANO-INDENTATIONS • Purpose: To show how stiffness and hardness of enamel are affected by different loads and proximity to the DEJ for the iguana and opossum • Methods: • Vary cyclic parameters to dissipate visco-elastic effects • Vary proximity of indentions to DEJ

  22. NANO-INDENTATION PARAMETERS

  23. IGUANA TOOTH INDENTIONSDEJ and RESIN

  24. DIDELPHIS (OPOSSUM) INDENTATIONS

  25. FRACTURE TOUGHNESS (In Progress) • Purpose: To show prismatic enamel evolved as a mechanism to attenuate cracks to counter fatigue or damage and/or catastrophic rapture associated acquisition of dental occlusion. • To assess fracture toughness in enamel using miniaturized hardness tests, the mean length of cracks are measured and inputed into the equation Kc = XP/(1.5c) [where c = crack length, P = load, X is a constant based on the ratio of Young’s Modulus (material stiffness) and hardness (force applied/plastically deformed area)].

  26. NANO-INDENTOR RESULTS Fracture Toughness Hardness Propagating Cracks

  27. THANK YOU • Dr. Hamid Garmestani • Dr. Greg Erickson • Ms. Reeshemah Burrell • Mr. Bob Goddard • Ms. Gail Jefferson • Mr. Dwayne Clarke

  28. Special Thank You • Dr. Jack Crow • Dr. Pat Dixon • Ms. Gina Hickey • Mr. Karl Hook • Ms. Paula

  29. QUESTIONS?

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